text:
\section{Introduction}
Supernova Ia (SNIa) light curves are scalable to one prototype light curve due to the consistent production of a certain peak luminosity \citep[e.g.][]{Phi93}. This characteristic makes it relatively easy to estimate distances to observed SNeIa, which is why they can be used as standard candles in cosmology \citep[e.g.][]{LTCC91, Rie98, Per99}. SNeIa also strongly affect the Galactic chemical evolution through the expulsion of iron \cite[e.g.][]{Ber91}. In addition, SNeIa play an important role in astroparticle physics, because the accompanying shocks are prime accelerator sites for galactic cosmic ray particles \citep{BO78}. Although they are part of many research fields, their origin and the details of the underlying physical processes are not fully understood.

It is generally accepted that SNIa events are caused by the thermonuclear explosions of carbon/oxygen (C/O) white dwarfs (WDs) with masses near the Chandrasekhar mass \citep{Nom82}. Of the two classical progenitor scenarios, we look at the single-degenerate (SD) channel \citep{Whe73}, in which a WD accretes from a companion. The double-degenerate (DD) channel describes the merger of two WDs \citep[e.g.][]{IT84, W84, Too12}. Other channels are amongst others accreting WDs from helium-rich, non-degenerate companions \citep[see e.g.][]{Wan09b}, and mergers between a WD and the core of an asymptotic giant branch star \citep{Kas11}.

The progenitor theory should give a reliable description of the evolution of a SNIa progenitor binary. Beyond this, it should be able to explain and reproduce general features of the type Ia supernova class. Both the SD and DD scenarios have problems in matching observed features of the SNeIa events. We briefly mention the most important issues; however, see \citet{Liv00} and \citet{Wan12} for reviews. Regarding the DD scenario, a serious concern is whether the collapse of the remnant would lead to a supernova or to a neutron star through accretion-induced collapse \citep[see][]{Nom85, Sai85, Pie03, Yoo07, Pak10, Pak12, She12}. In the SD channel, a SNIa-like event is more easily reproduced in the simulations of the explosion process, although the explosion process needs to be fine-tuned to reproduce the observed spectra and lightcurves \citep[see e.g.][for a review]{Hil00}.
Another issue is the long phase of supersoft X-ray emission SNIa SD progenitors should go through. It is unclear whether there are enough of these sources to account for the SNIa rate \citep[see][]{DiS10, Gil10, Hac10}. Archival data of known SNeIa have not shown this emission unambiguously, although there is possibly one case \citep[see][]{Vos08, Roe08, Nie10}.
Finally, several predictions for the SD rate have been made by different groups using binary population synthesis (BPS) simulations \citep{YL00, Han04, Rea09, Men09, Mea10,Wan10,Y10,Cea11}, time-integrated rates, as well as the distribution of rates over time, the so-called delay time distribution (DTD). For an overview, see \citet{Nel12}. However, the results show a wide spread and do not agree with each other or with observational data. The exact origin of these differences is so far unclear.

In this paper we try to uncover the reason for these differences, and we focus in particular on the efficiency with which the WD accretes and retains matter from its companion and on the common envelope (CE) phase. There are several prescriptions \citep[][hereafter NSKH07, RBF09 and Y10 respectively]{NSKH07, Rea09, Y10} in the literature for the efficiency of retaining matter by the WD. The retention efficiencies of \citetalias{NSKH07}, \citetalias{Rea09} and \citetalias{Y10} differ strongly. We study how the retention efficiency influences the SNIa rate and the DTD. Furthermore we investigate if the differences in the assumed retention efficiencies can explain the differences in the predicted SNIa rate from different BPS codes.

Differences between the retention efficiencies arise from the uncertainty in the novae phase and the strength of the optically thick WD wind at high mass transfer rates \citep{KH94}.
The optically thick wind stabilises mass transfer such that a CE phase can be avoided. \citep[][hereafter HKN99b]{HKN99} argues that the WD wind can interact with the envelope of the companion and strip some of the envelope mass from the donor, which stabilises the mass transfer further. The wind-stripping effect affects the retention efficiency moderately, but enlarges the parameter space for producing SNeIa effectively. However, for low metallicities the wind attenuates \citep[e.g.][]{Kob98, Kob09}, but a low-metallicity threshold of SNeIa in comparison with SNe type II have not been found in observations \citep{Pri08, Bad09}.
Regarding the novae phase, despite much progress in the understanding of classical novae, they are still poorly understood e.g. the mixing between the accreted envelope and WD \citep[e.g.][]{Den13}. Currently it is unclear if a cycle of novae outbursts removes more mass from the WD than the accreted envelope, effectively reducing the WD in mass \citep[][]{Pri86, PK95, Tow04, Yar05}. In particular, the results from helium novae are different, which affects the chain of nuclear burning in the SD channel for which first hydrogen-rich material is burned into helium-rich material and consequently the helium-rich matter into carbon-rich material. The uncertainty in helium accretion creates the strongest difference between the assumed retention efficiencies.

In Sect.\,\ref{sec_ch2:progs} the general evolution of a progenitor binary will be described. The CE phase and the growth in mass of the WD will be discussed in detail. To predict the distribution of SNIa rates for different assumptions we simulate the evolution for a large population of binaries using the population synthesis code SeBa, which is described in Sect.\,\ref{sec_ch2:methods}. Different methods for selecting those binaries that will evolve into a SNIa are also outlined. This includes a straightforward selection on binary parameters and an implementation in SeBa of the efficiency of mass retention on the WD. The resulting rates are presented in Sect.\,\ref{sec_ch2:results}, and compared with theoretical predictions from different groups in Sect.\,\ref{discussion}.

\section{Evolution of single degenerate SNIa progenitors}
\label{sec_ch2:progs}
\subsection{Global evolution}
The evolution of most binaries starts with two zero-age main sequence (ZAMS) stars in orbit around their common centre of mass. This is shown as the first stage in Fig.\,\ref{fig_ch2:track}, which shows the evolutionary stages a SD progenitor binary goes through. The initially more massive (hereafter primary) star has a mass of about 3-8$M_{\odot}$~and evolves into a C/O WD of about 0.6-1.2$M_{\odot}$. In order to form a compact system, binaries go through one or several mass transfer phases. The mass transfer can be stable or unstable, where the latter is described by the CE phase, the onset of which is shown in the second stage in Fig.\,\ref{fig_ch2:track}. Here the primary has evolved off the main sequence (MS) and overfills its Roche lobe. In the following CE phase the envelope of the primary star engulfs the initially less massive star, hereafter secondary. The core of the primary and secondary spiral inward through the envelope and the envelope itself is expelled.
After the CE phase the binary consists of a degenerate C/O WD and a MS star in a close binary, see the third stage in Fig.\,\ref{fig_ch2:track}. Note that the evolutionary stages following the MS are relatively short, so that even an initially small mass difference can lead to a binary with a WD and a MS star. In spite of the importance of the CE phase for creating short period systems containing compact objects, the phenomenon is not yet well understood. In Sect.\,\ref{sec_ch2:CE} we discuss two prescriptions for the CE phase.

If the orbital separation of the binary after the CE phase is small, the secondary will fill its Roche lobe when it evolves. Depending on the exact orbital distance this may occur when the secondary is a late MS star, a Hertzsprung gap star, or after it has evolved into a red giant.

Mass from the outer layers of the secondary will be transferred through the first Lagrangian point onto the WD. The hydrogen-rich material accumulates in a layer on the surface of the WD. When the pressure and temperature are high enough, the hydrogen layer ignites. As a result (a fraction of the) mass can be expelled from the WD and (a fraction of the) mass can be retained by the WD to form a helium layer on the WD. If the helium layer ignites, carbon and oxygen will be formed. Under the right conditions this mass too can be retained by the WD. A favourable combination of these two stages is needed for the C/O WD to be able to grow significantly in mass. In section \ref{sec_ch2:wd_growth} we will discuss in more detail the possible mechanisms of helium and hydrogen burning layers and expulsion efficiencies. As the mass of the WD approaches the critical mass limit of $M_\mathrm{SNIa}$ = 1.38$M_{\odot}$\footnote{In accordance with most of the cited papers.}, carbon ignites. Due to the degenerate nature of the WD a thermonuclear runaway takes place, leading to a SNIa event.

\begin{figure}[!hbtp]
\centering
\begin{tabular}{c}
\resizebox{0.8\hsize}{!}{\includegraphics[angle = 270]{rochelobes_SD1_final.eps}} \\
CE \\
\resizebox{0.8\hsize}{!}{\includegraphics[angle = 270]{rochelobes_SD2_final.eps}} \\
\end{tabular}
\caption{Binary evolution for a single-degenerate SNIa progenitor. In this case the donor is a MS star. The top and bottom parts of the figure have different scales due to the common envelope phase, denoted as CE in the figure.}
\label{fig_ch2:track}
\end{figure}

\subsection{Common envelope phase}
\label{sec_ch2:CE}
The classical way to parametrise the CE phase is by the $\alpha$-formalism \citep{P76, W84} which is based on conservation of energy:
\begin{equation}
\frac{G M M_\mathrm{e}}{\lambda R} = \alpha ~ \Big{(}\frac{G M_\mathrm{c} m}{2 a_f}-\frac{G M m}{2 a_i}\Big{)} ~,
\label{eq_ch2:alpha}
\end{equation}
where the left hand side represents the binding energy of the CE $\Delta E_\mathrm{bind}$ and the right hand side a fraction $\alpha$ of the orbital energy $\Delta E_\mathrm{orb}$ of the binary. $M$ represents the mass of the donor star and the subscripts e and c refer to the envelope and core of the donor star. The secondary mass is denoted by $m$ and is assumed not to vary during the CE phase. The $a_i$ and $a_f$ are the initial and final separation of the binary. $R$ is the radius of the donor star and $\lambda$ is a structural parameter of the envelope. All the uncertainty can be taken into one parameter, the product $\alpha\lambda$. For higher values of $\alpha\lambda$, the CE is expelled more efficiently and the change in orbital separation will be less dramatic. However, in all cases the orbital separation shrinks as a result of the CE phase. Contradicting this, observed double WD binaries seem to have mass ratios close to one \citep{M&M99}. To form a double WD pair the binary usually goes through two CE phases. One when the primary star evolves into a giant and subsequently a WD and one when the secondary evolves. In order for the mass of the WDs to be roughly equal, the conditions at the start of the first CE cannot differ much from those at the onset of the second CE. Therefore the orbital separation of these systems cannot shrink substantially during the first CE phase.

As a possible solution to this problem the $\gamma$-algorithm was introduced by \citet{Nea00}. Based on the conservation of angular momentum, angular momentum is lost in a linear way with mass according to:
\begin{equation}
\frac{\Delta J}{J} = \gamma \frac{\Delta M_\mathrm{tot}}{M_\mathrm{tot}} = \gamma \frac{M_\mathrm{e}}{M + m},
\label{eq_ch2:gamma}
\end{equation}
where $J$ represents the angular momentum of the binary, $M_{tot}$ is the total mass of the binary and the other parameters have the same meaning as before. Depending on the mass ratio, the orbital separation will be unchanged or decreased due to the description of the CE phase. The physical mechanism behind the $\gamma$-description remains unclear. Interesting to note here is that recently \citet{Woo12} suggested a new evolutionary model to create DWDs. These authors find that mass transfer between a red giant and a MS star can be stable and non-conservative. The effect on the orbit is a modest widening, with a result alike to the $\gamma$-description.

\subsection{Growth of the white dwarf}
\label{sec_ch2:wd_growth}
How efficiently the WD grows in mass as a result of the accretion is described by the total retention efficiency $\eta_\mathrm{tot}$. This represents the fraction of transferred hydrogen-rich matter from the companion that eventually burns into carbon-rich matter and stays on the WD. Therefore $\dot{M}_\mathrm{WD} = \eta_\mathrm{tot} |\dot{M}_\mathrm{comp}|$, where $\dot{M}_\mathrm{WD}$ represents the mass growth rate of the WD and $\dot{M}_\mathrm{comp}$ the mass transfer rate of the companion. Note that $\dot{M}_\mathrm{comp} < 0$, while $\dot{M}_\mathrm{WD} > 0$. Ultimately the retention efficiency of the transferred mass determines in which systems a SNIa event takes place and therefore shapes the SNIa rate and delay time distribution.

\subsubsection{Hydrogen-rich accretion}
When hydrogen-rich material is transferred onto a WD, the evolution of the accreted layer depends on the mass transfer rate of the companion $\dot{M}_\mathrm{comp}$ and the WD mass $M_\mathrm{WD}$. The evolution can be split into three distinct regimes, separated by a so-called steady and critical accretion rate $\dot{M}_\mathrm{st}(M_\mathrm{WD})$ and $\dot{M}_\mathrm{cr}(M_\mathrm{WD})$ \citep{N82, HK01}. These are both functions of the WD mass and are discussed in detail below.

For low mass transfer rates ($|\dot{M}_\mathrm{comp}| < \dot{M}_\mathrm{st}$) the hydrogen-rich matter is transferred to the WD conservatively, so that the mass transfer rate onto the WD is $\dot{M}_\mathrm{H} = |\dot{M}_\mathrm{comp}|$. The temperature in the accumulating hydrogen layer on the WD is too low to ignite the hydrogen immediately. The layer will gradually grow in mass, increasing the pressure and temperature until hydrogen ignition values are reached. Then nuclear burning will quickly spread through the layer, which starts expanding. The strength of these so-called novae \citep{Sta72} depends strongly on the amount of mass involved. This also determines how much of the processed layer is expelled from the binary and how much falls back onto the WD as helium. The accretion rate of the helium-rich matter will be denoted by $\dot M_\mathrm{He}$. We define the hydrogen retention efficiency to be the fraction of transferred mass which is burned and retained by the WD:
\begin{equation}
\eta_\mathrm{H} = \frac{\dot{M}_\mathrm{He}}{\dot{M}_\mathrm{H}}.
\end{equation}
If none of the matter stays on the WD $\eta_\mathrm{H}=0$ and if all of the transferred matter is retained by the WD as helium $\eta_\mathrm{H}=1$. In the nova regime $\eta_\mathrm{H} < 1$. For very strong novae not only the complete layer but also some of the WD itself may be expelled. In these cases $\eta_H < 0$.

Intermediate mass transfer rates are those between the steady and critical value, so that $\dot{M}_\mathrm{st} \leq |\dot{M}_\mathrm{comp}| \leq \dot{M}_\mathrm{cr}$. All of the mass lost by the companion star is transferred to the WD, so that $\dot{M}_\mathrm{H} = |\dot{M}_\mathrm{comp}|$. On the WD the hydrogen accumulates in such a way that the ignition values are reached at the bottom of the layer and the hydrogen stably burns into helium. No material is lost from the layer or the WD, therefore $\eta_\mathrm{H} = 1$ and $\dot{M}_\mathrm{He} = \dot{M}_\mathrm{H}$.

For higher mass transfer rates exceeding the critical value ($|\dot{M}_\mathrm{comp}| > \dot{M}_\mathrm{cr}$) a hydrogen red-giant-like envelope forms around the WD. If the high accretion rate is maintained a CE phase will soon follow. However, hydrogen burning on top of the WD is strong enough for a wind to develop from the WD \citep[][\citetalias{HKN99}]{KH94}. This attenuates the mass transfer rate $\dot{M}_\mathrm{H}$ and hydrogen retention efficiency $\eta_\mathrm{H}$, and ensures that the CE phase is postponed. Part of the hydrogen-rich matter, corresponding to $\dot{M}_\mathrm{cr}$, is burned into helium and stays on the WD. The remainder $\dot{M}_\mathrm{H}-\dot{M}_\mathrm{cr} = \dot{M}_\mathrm{wind}$ is carried away by the wind. In this wind regime, $\dot{M}_\mathrm{He} = \dot{M}_\mathrm{cr} = \eta_\mathrm{H} \dot{M}_\mathrm{H}$ and so $\eta_\mathrm{H} < 1$.

A possible second effect influencing the retention efficiency in this high mass transfer rate regime, results from the wind if it reaches the companion star. There it heats up the envelope of the companion, which expands and can then be stripped off by subsequent wind \citepalias{HKN99}. It is now no longer the case that all of the mass lost by the companion is transferred to the WD. The part that is transferred to the WD is equivalent to the amount lost by the companion minus the amount stripped away by the WD wind: $\dot{M}_\mathrm{H} = |\dot{M}_\mathrm{comp}| - |\dot{M}_\mathrm{strip}|$, where $\dot{M}_\mathrm{strip} < 0$. The strength of this stripping effect is represented by the stripping parameter $c_1$, defined by
\begin{equation}
\dot{M}_\mathrm{strip} = c_1 \dot{M}_\mathrm{wind}.
\label{eq_ch2:stripping}
\end{equation}

Details on how and when this stripping effect is taken into account are described in section\,\ref{sec_ch2:methods} and appendix\,\ref{app_ch2:retentionefficiencies}.

\subsubsection{Helium-rich accretion}
After a fraction of the hydrogen-rich matter is burned into helium-rich material, the helium-rich material accumulates in a layer on the surface of the WD. This layer sits in between the WD and the (still accumulating) hydrogen layer. For the helium-rich accretion similar regimes exist for low and medium helium accretion rates, resulting in helium novae and steady helium burning respectively. No helium wind regime exists because these high helium accretion rates cannot be reached by the hydrogen burning. The fraction of helium that is burned into carbon-rich material is represented by the helium retention efficiency $\eta_\mathrm{He}$. The total retention efficiency is then given by:
\begin{equation}
\eta_\mathrm{tot} = \eta_\mathrm{H}(\dot{M}_\mathrm{comp}) \cdot \eta_\mathrm{He}(\dot{M}_\mathrm{He}).
\label{eq_ch2:eta_tot}
\end{equation}

\section{Method}
\label{sec_ch2:methods}
To test the viability of SD SNIa theory a population of binary stars is simulated and the corresponding theoretical SNIa rate is compared to observational results. We employ the binary population synthesis code SeBa \citep{PZV96, Nea01, Too12} for fast stellar and binary evolution computations. In SeBa stars are evolved from the ZAMS until remnant formation. At every timestep, processes as stellar winds, mass transfer, angular momentum loss, magnetic braking and gravitational radiation are taken into account with appropriate recipes. SeBa is a Monte Carlo based code in which the initial binary parameters are generated randomly according to appropriate distribution functions. The initial mass of the primary stars is drawn from a Kroupa Initial Mass Function \citep{Kroupa} which ranges from 0.1-100$M_{\odot}$~and the initial mass of the secondary from a flat mass ratio distribution with values between 0 and 1. We assume that a complete stellar population consists of 50\% binary stars and 50\% single stars. The semi-major axis of the binary is drawn from a power law distribution with an exponent of -1 \citep{Abt83}, ranging from 0 to $10^6$$R_{\odot}$~and the eccentricity from a thermal distribution, ranging from 0 to 1 \citep{Heggie75}. For the metallicity solar values are assumed.

In this research we differentiate between four ways to determine which binaries will give rise to a SNIa event. For the first method (model NSKH07) we adopt the retention efficiencies given by \citetalias{NSKH07}, including updates from \citet[][hereafter HKN08]{HKN08}. Using SeBa in combination with these retention efficiencies, a population of binaries is simulated and those systems in which a C/O WD reaches the critical mass limit are selected as SNIa progenitors. For the second approach (model RBF09) we utilise the retention efficiencies used in \citetalias{Rea09} and for the third approach (model Y10) the efficiencies based on \citetalias{Y10}. The assumed retention efficiencies differ strongly. For the final method (model Islands) the phase of stable mass transfer onto the WD is not modelled by SeBa. Instead we select those systems that at the formation of the C/O WD lie in specific regions of the parameter space of orbital period, WD mass and companion mass ($P_\mathrm{orb}$ - $M_\mathrm{WD}$ - $M_\mathrm{comp}$). Systems in these specific regions, hereafter islands, are determined to lead to SNeIa \citepalias[][and references therein]{HKN08, HKN99}.

In order to compare our simulated rates to the results of research groups that use the same retention efficiencies, the prescription of the CE is varied to match different BPS codes. We distinguish between two models. The first model is based on the $\alpha$-prescription assuming a value of $\alpha = 1$ and $\lambda = 0.5$ as in accordance with \citetalias{Rea09}. The second model assumes the $\gamma$-formalism with a value of $\gamma = 1.75$ \citep[see][]{Nea01}.\footnote{The $\gamma$-formalism is applied, unless the binary contains a compact object or the CE is triggered by a tidal instability \citep{Dar1879} for which the $\alpha$-formalism is used.}

\subsection{Retention efficiencies}
\label{sec_ch2:retention_efficiencies}
\begin{figure}[!tbhp]
\resizebox{\hsize}{!}{\includegraphics{etaH1H2He1He2.eps}}
\caption{Examples of hydrogen and helium retention efficiencies as a function of the mass transfer rate for a WD of 1$M_{\odot}$. The prescriptions for the hydrogen retention efficiency $\eta_\mathrm{H1}$ \citepalias[solid line - ][]{NSKH07, HKN08} \& $\eta_\mathrm{H2}$ \citepalias[dashed line - ][]{Rea09, Y10} and the helium retention efficiency $\eta_\mathrm{He1}$ \citep[dot-dashed line - ][]{Hea99, KH99} \& $\eta_\mathrm{He2}$ \citep[dotted line - ][]{IT96} are shown in Appendix\,\ref{app_ch2:retentionefficiencies}. Note that the position of the peak of $\eta_\mathrm{H2}$ is dependent on the exact prescription for $\dot{M}_\mathrm{cr}$. The mass transfer rate for hydrogen accretion is given by $|\dot{M}_\mathrm{comp}|$. For helium accretion this is $\dot M_\mathrm{He}$. }
\label{fig_ch2:reteffs_HHe}
\end{figure}

In this section we describe the three prescriptions for the hydrogen and helium retention efficiencies as given by \citetalias{NSKH07} \citetalias{Rea09} and \citetalias{Y10}. The total retention efficiency is a combination of the hydrogen and helium one as described by eq.\,\ref{eq_ch2:eta_tot}.
The retention efficiency used in \citetalias{NSKH07}, including updates from \citetalias{HKN08}, is a combination of the hydrogen retention efficiency $\eta_\mathrm{H1}$ and the helium retention efficiency $\eta_\mathrm{He1}$, see Fig.\,\ref{fig_ch2:reteffs_HHe}. For $\eta_\mathrm{H1}$ the region of steady burning occurs at mass transfer rates between
\begin{equation}
\dot{M}_\mathrm{st} = 3.1 \cdot 10^{-7} (M_\mathrm{WD} - 0.54) ~ \mathrm{M}_{\odot} \mathrm{yr}^{-1} \mathrm{~ and} \\
\label{eq_ch2:MstN}
\end{equation}
\begin{equation}
\dot{M}_\mathrm{cr} = 7.5 \cdot 10^{-7} (M_\mathrm{WD} - 0.40) ~ \mathrm{M}_{\odot} \mathrm{yr}^{-1},
\label{eq_ch2:McritNR}
\end{equation}
which are the updated formulae from \citetalias{HKN08} with $M_\mathrm{WD}$ in units of $M_{\odot}$. This region is visible in Fig.\,\ref{fig_ch2:reteffs_HHe} as the plateau at intermediate mass transfer rates. In the wind regime
$|\dot{M}_\mathrm{comp}| > \dot{M}_\mathrm{cr}$, the wind-stripping effect is included with $c_1=3$ (see eq.\,\ref{eq_ch2:stripping}). For the prescription of $\eta_\mathrm{He1}$ see Appendix\,\ref{app_ch2:retentionefficiencies} \citepalias[\citealp{KH99};][]{HKN99}.

The retention efficiency based on \citetalias{Rea09} combines  $\eta_\mathrm{He1}$ with $\eta_\mathrm{H2}$, see Fig.\,\ref{fig_ch2:reteffs_HHe}. In this model there is no region of steady hydrogen burning. Instead the nova regime immediately borders the wind regime. The critical mass transfer rate $\dot{M}_\mathrm{cr}$ is given by eq.\,\ref{eq_ch2:McritNR}. The stripping effect is not taken into account, hence $c_1=0$ (see eq.\,\ref{eq_ch2:stripping}). The retention efficiency in the nova regime ($|\dot{M}_\mathrm{comp}| < \dot{M}_\mathrm{cr}$) is based on an interpolation of results from \citet{PK95}. Our own fit to these results is included in Appendix\,\ref{app_ch2:retentionefficiencies}. For lower (higher) $M_\mathrm{WD}$ than assumed in Fig.\,\ref{fig_ch2:reteffs_HHe}, the retention efficiency in the nova regime stays the same between $10^{-8} < |\dot{M}_\mathrm{comp}| < 10^{-7}$ and shifts with the peak in the regime $10^{-7} < |\dot{M}_\mathrm{comp}| < \dot{M}_\mathrm{cr}$.

The retention efficiency based on \citetalias{Y10} combines $\eta_\mathrm{H2}$ with $\eta_\mathrm{He2}$, see Fig.\,\ref{fig_ch2:reteffs_HHe}. The critical rate for the hydrogen accretion is given by
\begin{equation}
\dot{M}_\mathrm{cr} = 10^{-9.31+4.12M_\mathrm{WD}-1.42M^2_\mathrm{WD}} ~ \mathrm{M}_{\odot} \mathrm{yr}^{-1},
\label{eq_ch2:McritY}
\end{equation}
with $M_\mathrm{WD}$ in units of $M_{\odot}$. For the retention efficiency in the hydrogen nova regime the same interpolation from \citet{PK95} is used as for the efficiency of \citetalias{Rea09}, see Appendix\,\ref{app_ch2:retentionefficiencies}. Again there is no region of steady hydrogen burning, the wind is taken into account but the stripping effect is not. Due to the different prescription for $\dot{M}_\mathrm{cr}$ the position of the peak is slightly different from the example curve.
Using eq.\,\ref{eq_ch2:McritY} as the border to the wind regime for hydrogen accretion, the peak occurs at smaller values of $|\dot{M}_\mathrm{comp}|$ for a given $M_\mathrm{WD}$, as compared to eq.\,\ref{eq_ch2:McritNR}. This reduces the total retention efficiency $\eta_\mathrm{tot}$ substantially, as we will see in Fig.\,\ref{fig_ch2:reteffs_tot}. Following \citetalias{Y10}, the prescription for $\eta_\mathrm{He2}$ was taken from \citet{IT96}.

The exact prescriptions of the hydrogen and helium retention efficiencies for \citetalias{NSKH07}, \citetalias{Rea09} and \citetalias{Y10} are detailed in Appendix\,\ref{app_ch2:retentionefficiencies}. Fig.\,\ref{fig_ch2:reteffs_tot} shows the large variety in the total retention efficiency for the three prescriptions as a function of mass transfer rate of the companion. The most optimistic retention efficiency is that of \citetalias{NSKH07} and the most pessimistic that of \citetalias{Y10}.
Note that in the regime with strong novae the retention efficiency $\eta_\mathrm{tot} \leq 0$. Here we have set $\eta_\mathrm{tot} = 0$ in this regime for simplicity as these systems are not part of the SD channel.

\begin{figure}[!tbhp]
\resizebox{\hsize}{!}{\includegraphics{etatotNRY.eps}}
\caption{Total retention efficiencies, resulting from different combinations of the hydrogen and helium retention efficiencies. In this figure we have assumed $M_\mathrm{WD} = 1$$M_{\odot}$~as an example. The mass transfer rate $\dot{M} = |\dot{M}_\mathrm{comp}|$. For lower (higher) $M_\mathrm{WD}$ the maximum retention efficiency shift to lower (higher) $|\dot{M}_\mathrm{comp}|$. For a more detailed explanation of the retention efficiencies see Sect.\,\ref{sec_ch2:retention_efficiencies}. }
\label{fig_ch2:reteffs_tot}
\end{figure}

A complication of this method is that the instantaneous mass transfer rates in binary population synthesis codes, such as SeBa, is only an approximation to the one derived from detailed stellar evolution codes. Therefore, we also implemented a hybrid method in which progenitors are selected from binary population synthesis according to results from the literature based on more detailed mass transfer tracks. These tracks can be calculated by an analytical approach e.g. \citetalias{HKN99} or by a detailed binary evolution code e.g. \citet{Li02}, \citet{Han04} and \citetalias{HKN08}.

\subsection{Islands}
In this method, the progenitor binaries are selected on $P_\mathrm{orb}$, $M_\mathrm{WD}$, and $M_\mathrm{comp}$ at the time of WD birth (third stage in Fig.\,\ref{fig_ch2:track}).
The parameter regions used are shown at the right hand side in Fig.\,\ref{fig_ch2:WD+MS} for binaries containing a WD and a MS star or Hertzsprung gap star (WD+MS binaries) and Fig.\,\ref{fig_ch2:WD+RG} for those containing a WD and a red giant star (WD+RG binaries). They are made to match the islands in \citetalias{HKN08} and \citetalias{HKN99} respectively, which are shown on the left hand side in these figures. For the WD+MS channels a moderate wind-stripping parameter of $c_1=3$ is taken (see eq.\,\ref{eq_ch2:stripping}).
\begin{figure}[!hbtp]
\centering
\includegraphics[width=0.24\textwidth]{MSIsland.eps}
\includegraphics[width=0.24\textwidth]{myMSIsland.eps}
\caption{Initial parameter regions for the WD+MS track to SNeIa. The different contours are for different WD masses (increasing in size with increasing mass) and the stripping parameter $c_1 = 3$. Left: from \citetalias{HKN08}. The hatched regions indicate SNIa explosions with short delay times of $t < 100$Myr for M = 0.7$M_{\odot}$~and M = 1.1$M_{\odot}$. Right: initial parameter regions as used in this work.}
\label{fig_ch2:WD+MS}
\end{figure}

\begin{figure}[!hbtp]
\centering
\includegraphics[width=0.24\textwidth]{RGIsland.eps}
\includegraphics[width=0.24\textwidth]{myRGIsland.eps}
\caption{Initial parameter regions for the WD+RG track to SNeIa. The different contours are for different WD masses (increasing in size with increasing mass) and the stripping parameter $c_1 = 1$. Left: from \citetalias{HKN99}. Right: initial parameter regions as used in this work.}
\label{fig_ch2:WD+RG}
\end{figure}

\section{Results: SNIa rates and delay times}
\label{sec_ch2:results}
We have simulated a population of SD SNIa progenitors for the four approaches described in Sect.\,\ref{sec_ch2:methods} assuming our model for the $\gamma$-prescription or the $\alpha$-prescription. The delay time distributions for the $\gamma$-prescription simulations can be seen in Fig.\,\ref{fig_ch2:SDDTDs} and for the $\alpha$-prescription in Fig.\,\ref{fig_ch2:SDDTDs_alpha}. The delay time $t$ is the time at which a SNIa occurs, where $t=0$ is the time when the binary is born as a double ZAMS-star binary. A DTD shows the distribution of delay times after a single starburst involving a large number of binaries.
For model Islands, we assume the phase between the onset of mass transfer and the SNIa explosion is short compared to the lifetime of the binary.

The progenitor islands are based on the work of \citetalias{NSKH07} and \citetalias{HKN08}, as is our model NSKH07 that uses the retention efficiencies directly. If we compare the DTD resulting from model Islands with model NSKH07, there is a noticeable difference at early delay times. The DTD of model Islands peaks earlier and higher. The reason is the extend of the Islands to high donor masses of about 6$M_{\odot}$ for WD+MS progenitors. These massive companions fill their Roche lobes soon and therefore the SNIa explosion occurs at earlier delay times ($t < 1$Gyr). In SeBa, binaries with such high mass ratios undergo unstable mass transfer and a CE phase. They do not develop a SNIa explosion, resulting in less SNeIa at early delay times from the retention efficiencies method.

Our progenitor regions in model Island consist of adjacent slices that increase in size for increasing M$_\mathrm{WD}$, for both WD+MS and WD+RG progenitors. These slices have a thickness of 0.1$M_{\odot}$~around the values M$_\mathrm{WD}$ = 0.7, 0.8, 0.9, 1.0 and 1.1$M_{\odot}$~for WD+MS binaries and M$_\mathrm{WD}$ = 0.8, 0.9, 1.0 and 1.1$M_{\odot}$~for WD+RG binaries. Ideally the volume enclosing the progenitor binaries has smooth edges in all three dimensions. Since this is not the case in our approach we explored the resulting inaccuracy by increasing our resolution. We double the amount of islands covering the same range of WD mass, so the thickness of each island slice is now 0.05$M_{\odot}$. We found that the change in the final integrated SNIa rate is 3-4\% and the DTD is barely affected.

The SNIa DTD and integrated rate are strongly influenced by the prescription of the retention efficiency, as shown in Fig.\,\ref{fig_ch2:SDDTDs} and Fig.\,\ref{fig_ch2:SDDTDs_alpha}, and Table\,\ref{tbl_ch2:rates}. For more pessimistic values of the total retention efficiency the rates and overall height of the DTD decreases. Note that the total retention efficiency of model Y10 is so small that no SNeIa developed and only an upper limit is given in Table\,\ref{tbl_ch2:rates}. Model NSKH07 and RBF09 give rise to DTDs that differ most strongly at short delay times. This is due to high donor masses that transfer mass at a high rates, where the total retention efficiencies differ significantly, see Fig.\,\ref{fig_ch2:reteffs_tot}. This results from the inclusion of the wind stripping effect in \citetalias{NSKH07}.

Changing the prescription used for the CE phase modifies the integrated SNIa rate by a factor of about two.
When the $\gamma$-prescription is applied, less (very) close binaries are created as the binary orbits do not shrink as effectively as for the $\alpha$-prescription. An exception to this is when the mass ratio of the binary is extreme at the moment of Roche lobe overflow.
These systems merge at short delay times t$<$0.1Gyr. Therefore the DTD when the $\gamma$-prescription is assumed declines faster with time than when the $\alpha$-prescription is assumed. The classical evolution path towards a SD binary as depicted in Fig.\,\ref{fig_ch2:track}, is less common in the BPS model using the $\gamma$-prescription. Assuming the $\alpha$-prescription 80\% of the SD binaries evolve through this channel, where as for the  $\gamma$-prescription this has decreased to 30-40\% (depending on the retention efficiency). In the most common evolution path for the model assuming the $\gamma$-prescription, the first phase of mass transfer is stable.

\begin{table*}[t]
\caption{Time-integrated SNIa rates in the SD channel for different combinations of the retention efficiency and the common envelope prescription in units of $10^{-4}$$M_{\odot}$$^{-1}$.}
\centering
\begin{tabular}{l l c c}
\hline\hline
Model & Approach used & $\gamma$-prescription & $\alpha$-prescription \\
\hline
Model NSKH07 & Retention efficiency of \citetalias{NSKH07}$^1$ & 0.59 & 1.3 \\
Model RBF09 & Retention efficiency of \citetalias{Rea09}$^2$ & 0.19 & 0.35 \\
Model Y10 & Retention efficiency of \citetalias{Y10}$^3$ & $<$0.001 & $<$0.001 \\
Model Islands & Islands of \citetalias{HKN08}$^4$, \citetalias{HKN99}$^5$ & 0.73 & 1.5 \\
\hline
\end{tabular}
\begin{flushleft}
\tablefoot{$^{1}$ \citet{NSKH07}; $^{2}$ \citet{Rea09}; $^{3}$ \citet{Y10}; $^{4}$ \citet{HKN08}; $^{5}$ \citet{HKN99}}
\end{flushleft}
\label{tbl_ch2:rates}
\end{table*}

\begin{figure}[]
\resizebox{\hsize}{!}{\includegraphics{delay_time_hist_r80_norm_sd_gamma.ps}}
\caption{Delay time distribution assuming the $\gamma$-algorithm for the CE with $\gamma = 1.75$. Different lines correspond to the delay time distributions that result from four different approaches described in Sect\,\ref{sec_ch2:methods}, all for the $\gamma$-prescription. The dot-dashed line shows the result of the Islands selection method, the three other linestyles correspond to the retention efficiencies as in Fig.\,\ref{fig_ch2:reteffs_tot}. Note that for the retention efficiency of \citetalias{Y10} no SD binaries evolve into a SNeIa.}
\label{fig_ch2:SDDTDs}
\end{figure}

\begin{figure}[]
\resizebox{\hsize}{!}{\includegraphics{delay_time_hist_r80_norm_sd_alpha.ps}}
\caption{Same as in Fig.\,\ref{fig_ch2:SDDTDs} but assuming the $\alpha$-formalism with $\alpha\lambda = 0.5$. Again no SD binaries evolve into a SNeIa for the retention efficiency of \citetalias{Y10}.}
\label{fig_ch2:SDDTDs_alpha}
\end{figure}

\section{Discussion}
\label{discussion}

The theoretical SD SNIa rates that follow from SeBa in this study can be compared to the results of various other BPS research groups \citep[e.g. \citetalias{Rea09}; \citetalias{Y10};][]{Mea10, Wan10, Cea11}. Table\,\ref{tbl_ch2:snrates} shows the time-integrated SNIa rates of these groups taken from \citet{Nel12}. The disagreement in the rates is large up to a factor of about 600, but so far no explanation has been found.
Note that \citet{Nel12} rescaled the results (if needed) to the same initial distribution of parameters as discussed in Sect.\,\ref{sec_ch2:methods}. Assumptions and simplifications vary between the different BPS codes \citetext{See Toonen et al. in prep. for a study on this} causing differences in their predictions. An important assumption for the BPS simulations is the assumed CE-prescription, which is also given in in Table\,\ref{tbl_ch2:snrates}. The effect of different values for $\alpha$ has been studied by several groups, e.g. the effect on the DTD \citep{Wan10, Rea09, Mea10, Cea11}. The effect on the integrated rate of a small change in $\alpha$ is of the order of a factor 0.7-3 \citep[][]{Rea09, Mea10}, however the effect can be up to an order of magnitude for larger changes in $\alpha$ (Claeys et al. in prep.).

The entries in Table\,\ref{tbl_ch2:snrates} are ordered to increase in rate. The smallest rate is from the work of Yungelson \citepalias[]{Y10}. Similarly we find the lowest rate for model Y10, however we find an even lower rate than Yungelson.
The preliminary rate of \citet{Cea11} is significantly lower than our corresponding model. However \citet{Cea11} use a variable lambda prescription, whereas in our best corresponding model we set $\alpha\lambda=0.5$
The integrated rates of \citet{Rea09} is a factor of about two lower than the rates of our best corresponding model. The rates of \citet{Mea10} and \citet{Wan10} are a factor of a about seven and two higher respectively. So although our results do recover the trend in the theoretical predictions from different binary population synthesis codes, they do not fully explain the large disagreement among them.

The integrated rates based on observations are given in Table\,\ref{tbl_ch2:snrates}. The most recent measurements are based on field galaxies and generally show lower rates, while earlier estimates based on galaxy clusters are higher. At this moment it is unclear if the different observed integrated rates are due to systematic effects or if there is a real enhancement of SNeIa in cluster galaxies. See also \citet{Mao12} for a discussion. Even though the different retention efficiency models affect the SNIa rates with a factor $>10^3$, none of the integrated rates comfortably matches the observed rates, especially those from galaxy clusters. In addition, the DTD reconstructed from observations typically show a continuation to longer delay times, which are absent in all our SD DTDs. We conclude from this, that in the current model of SD SNIa theory, the main contribution to the SNIa rate comes from other evolution channels. One possible channel involves semi-detached binaries in which a WD accretes from a hydrogen-poor helium-rich donor, such as sdB stars. \citet{Wan09}, \citet{Rea09} and \citet{Cea11} showed that in this channel the DTD peaks at delay times of about 100Myr, although rates at this delay time vary between $10^{-4}-10^{-2} \mathrm{yr}^{-1} (10^{10}$$M_{\odot}$$)^{-1}$. The contribution from binaries of the DD channel is debated heavily. Explosion models favour accretion-induced collapse to a neutron star over a SNIa event \citep[see e.g.][for a review]{Hil00}. However, BPS codes find more SNIa events from the standard DD channel than the SD channel \citep[\citetalias{Rea09}; \citetalias{Y10};][]{Mea10, Too12}\footnote{Note that the integrated rate from the violent merger model for double WDs \citep{Pak10,Pak11,Pak12,Rop12} can be much lower \citep{Too12, Che12, Rui12}}. \citet{Too12} study the contribution from the double-degenerate channel with SeBa comparing the $\alpha$- and $\gamma$-prescription for the CE. They find that even though the DD DTDs fit the observed DTD beautifully, the normalisation does not by a factor of about 7-12 compared to the cluster rates. Taking into account the new rates from field galaxies, the factor becomes about 1.2-12. Other contributions to the SNIa rate can possibly come from e.g. core-degenerate mergers \citep{Kas11}, double detonating sub-Chandrasekhar accretors \citep[see e.g.][]{Kro10} or Kozai oscillations in triple systems \citep{Sha12, Ham13}.

\begin{table*}[]
\caption{Time-integrated SNIa rates in the SD channel for the assumptions of different research groups in units of $10^{-4}$$M_{\odot}$$^{-1}$}
\label{tbl_ch2:snrates}
\centering
\begin{tabular}{c c c c |c c}
\hline\hline
BPS & WD accretion & SNIa rate  & CE &  SNIa rate &  CE                             \\
  \hline
Yungelson$^{1}$ & \citetalias{Y10}                             & $<$0.001 & $\gamma=1.5 $       & 0.006     & $\gamma=1.5$                    \\
Claeys$^{2}$    & \citetalias{HKN99}                           & 1.3      & $\alpha\lambda=0.5$ & 0.13      & $\alpha=1$, $\lambda=variable$  \\
Ruiter$^{3}$    & \citetalias{Rea09}                           & 0.35     & $\alpha\lambda=0.5$ & 0.17      & $\alpha\lambda=0.5$             \\
Wang/Han$^{4}$  & \citetalias{HKN99}                           & 1.3      & $\alpha\lambda=0.5$ & 2.8       & $\alpha\lambda = 0.5$           \\
Mennekens$^{5}$ & \citetalias{HKN99}, \citetalias{HKN08}       & 0.55     & $\alpha\lambda=1$   & 3.7       & $\alpha\lambda = 1$             \\
\hline
Observed$^{6}$  &  & 4-26 & & & \\
\hline
\end{tabular}
\begin{flushleft}
\tablefoot{Columns~3~and~5 shows the integrated rate predicted by SeBa and the BPS group in question respectively. The assumption of the BPS group for the CE-evolution is shown in column~6 and the best corresponding CE-model in SeBa is shown in column~4. $^{1}$ \citetalias{Y10}; $^{2}$ \citet{Cea11} (preliminary results); $^{3}$ \citetalias{Rea09}; $^{4}$ \citet{Wan10}; $^{5}$ \citet{Mea10}; $^{6}$ \citet{Mao11b, Per12, Mao12, Gra12}}
\end{flushleft}
\end{table*}

\section{Conclusions}
\label{sec_ch2:conclusions}
In this work we have studied the effect of the poorly understood phase of WD accretion in the context of supernova type Ia rates. We employed the binary population synthesis code SeBa \citep{PZV96, Nea01, Too12} to study the SNIa rates and progenitors for different CE prescriptions. We differentiated between four models assuming either one of three retention efficiencies of \citetalias{NSKH07}, \citetalias{Rea09} and \citetalias{Y10} or making a selection of SNIa progenitors based on binary parameters at the time of WD formation \citepalias{HKN08, HKN99}. The three retention efficiencies assumed by different binary population synthesis codes differ strongly. The difference comes from a lack of understanding at low mass transfer rates where novae occur, and mass transfer rates higher than the rate for stable burning. This is true for the accretion of hydrogen that is transferred to the WD by the companion, as well as the accretion of helium that has been burned from hydrogen on the WD. The efficiency with which a C/O WD grows in mass is strongly affected by the combination of the efficiency of hydrogen and helium accretion. For example the hydrogen and helium retention efficiencies of \citetalias{Y10} are maximal at different ranges of the mass transfer rate resulting in a low total retention efficiency.

The total number of SNIa progenitors is significantly influenced by the choice of the model. The integrated SNIa rate vary between $<1\cdot10^{-7}-1.5\cdot10^{-4}$$M_{\odot}$$^{-1}$, where the rates are highest for the model that assume the retention efficiencies of \citetalias{NSKH07} and only an upper limit can be given for \citetalias{Y10}. Our method based on the parameter space of binaries at WD birth of \citetalias{HKN08} and \citetalias{HKN99} consists of a discrete set of islands in ($P_\mathrm{orb}$ - $M_\mathrm{WD}$ - $M_\mathrm{comp}$). The discretisation introduces an error of 3-4\% on the integrated rates. We showed in this paper that independent of the WD accretion model the SNIa rate approximately doubles when the $\alpha$-prescription is assumed with $\alpha\lambda = 0.5$ as compared to the $\gamma$-formalism with $\gamma=1.75$. The effect of different values for $\alpha$ on the SD SNIa rate is a factor of 0.7-3 \citep{Rea09, Mea10} for small changes in the CE-efficiency and up to an order of magnitude for larger changes in the CE-efficiency (Claeys et al. in prep.). Also note that throughout this work we have assumed solar values for the stellar metallicities. Using a broad range of metallicities in the BPS code might influence the SNIa rates and DTDs, both in the Islands and retention efficiency approach. See \citet{KTNHK98} for a study on how the progenitor islands depend on metallicity.

Several predictions for the SD rate have been made by different groups using binary population synthesis simulations. The results show a wide spread and do not agree with each other or with observational data. The integrated rates vary between $6\cdot10^{-7}-3.7\cdot10^{-4}$$M_{\odot}$$^{-1}$. In this study we find that also the model for the WD accretion is a major source of uncertainty on the SNIa rates. The different prescriptions for the retention efficiency introduce a source of uncertainty with an effect on the integrated rates by a factor of about 3-4 (comparing our models that assume the retention efficiencies of \citetalias{NSKH07} with \citetalias{Rea09}) or even larger up to a factor of a few hundred (comparing with the efficiency of \citetalias{Y10}). Although our results do recover the trend in the theoretical predictions from different binary population synthesis codes, they do not fully explain the large disagreement among them. As the exact origin of the differences in the SD rate remains unclear, Toonen et al. in prep. study the results of four different binary population synthesis codes and investigate the importance of the different assumptions and numerical approaches in these codes.

\begin{acknowledgements}
We thank Zhanwen Han for useful comments which helped us to improve the manuscript. This work was supported by the Netherlands Research Council NWO (grant VIDI [\# 639.042.813]) and by the Netherlands Research School for Astronomy (NOVA).
\end{acknowledgements}

\bibliographystyle{aa}

redpajama_set_name: RedPajamaArXiv


Carrie, a future 'Dancing With the Stars' best in show?
My wife was laughing while watching her computer last week and she wasn't listening to my podcast. I inquired as to the source of the mirth and she said she was watching a dancing dog. I immediately dismissed it as some sort of digital computer trick. She offered to send it to me, but I declined. There are so many animal videos going viral these days that I thought I had seen it all.
Turns out, it was almost my unfathomable loss. This video takes the cake, or the dog biscuit if you will. It is the oddest thing that I have ever seen any animal do. You can find it at the end of this column or by searching for "amazing dog dancing merengue" at YouTube.
This video features a merengue-dancing golden retriever. The dog, according to Web reports, is named Carrie, and is dancing in a strip mall parking lot with a Chilean man named Jose Fuentes. Carrie remains on her hind legs for more than three minutes. They dance a full song and perform several intricate merengue moves. The number ends with Fuentes giving Carrie a full dip down onto the asphalt before she springs back up to take a bow. Carrie is wearing some sort of colorful South American dog dress, and Fuentes is dressed like a Chilean cowboy. There's a cheering throng in the lot, and it almost seems like it should be a cartoon.
I love dogs, and I really like dogs that can do cool stuff. My dogs, although both technically "working dogs," do very little work and spend most of their time sleeping. I'm not sure what makes them so tired. The Labrador is rarely required to fetch anything, and the Portuguese water dog barely knows how to swim. Perhaps they're mentally tired from having to decide which room to sleep in and on what piece of furniture. They are very good at sensing when it's time to eat. I'm not sure if that's a trick or a survival skill. At least they can't dance better than I can.
The only hind-leg time my dogs log is when they are taking something off of the counter. How on earth does a guy get his dog to stand on her hind legs and dance a full merengue with him? One might also ask why? Whatever the reason or the inspiration, Carrie and Juan are a full-fledged Internet phenomenon. The YouTube video of their street dancing has more than 3 million views, and Carrie even has her own Facebook page. I wouldn't be surprised if she set it up herself. Just search Facebook for Carrie Perrita Bailarina.
I'm sure that you will be seeing both Carrie and her owner trip the light fantastic on a television near you. She's already been featured on the Spanish language "Don Francisco Presenta" on Univision. There's a link on Ellen DeGeneres' Web page to the video. I wouldn't be surprised to see a little all-girl merengue on her upcoming season. Oprah Winfrey tends to like dogs that have rescued people, are horribly deformed or can be redeemed by her Dog Whisperer, Cesar Millan. My dogs could use a visit or two from him.
Some have posted complaints about Carrie being mistreated. She looks quite happy to me. A male dog might be a little embarrassed about the dress. Carrie, on the other paw, is even wagging her tail. I originally thought there might be some counterweights in her frock to help her stand up. The whole thing just begs for a mechanical explanation. I wouldn't mind seeing the dance performed without the dress just to be sure. Carrie, the golden retriever, is cuter and dances better than some of the contestants on "Dancing With the Stars."
Steve Dahl is a Tribune special contributor. To read and hear more Steve Dahl, go to dahl.com.


The Taco Truck Birdhouse looks like a Orange Taco Truck. This birdhouse will add a splash of fun color to your room or yard. Wool is naturally water repellent and mold resistant providing a safe and comfortable environment for the nesting birds.


DSIM's Guide- What Instagram's IGTV has brought for you?
Home > Blog > Blog > DSIM's Guide- What Instagram's IGTV has brought for you?
The best feature about Instagram is its approach towards serving newest things to the audience.
This time, Instagram has facilitated its users with IGTV, a new tool for video watching.
Before this, Instagram videos tend to consume 1 minute or lesser, but the new tool will allow uploading 1 hour long videos and that is, in high definition quality.
Instagram's new app for watching long-form and vertical video.
Like TV, Instagram also has channels and they are called creators. When you follow these creators, their IGTV channel will notify you what to watch or about the latest videos.
Anyone can become creator by starting his or her channel on IGTV.
You would have seen a number of video playing apps, but the IGTV acclaims itself different from the rest.
The first unique feature of the app is that it focuses on the actual use of your phone.
This means videos are full screen and vertical. Previously, the Instagram videos used to be of 1-minute length but IGTV videos will run up to 1 hours max.
The next feature is again similar to the TV. Like TV, as soon you open the app the IGTV starts playing. Another advantage is that you won't have to search content from people you're following on Instagram.
The third advantage feature is that "Swipe Up to Discover More".
IGTV provides Direct that allows you to like, comment and send videos to friends.
How Can You Set Up Your IGTV Channel?
IGTV channel can be set up through mobile or desktop or both.
Download the free IGTV app available in iOS and Android.
After installation, open the app and connect your Insta account.
Next, click on your photo.
Then choose, "Create Channel Option" from the pop-up menu.
Proceed further with step-wise guidance provided by your channel.
Once created and connected, Insta account info will be fetched into your channel and you'll be able to upload a video.
Log in to your Instagram account using your username and password.
Below your bio, you'll find tabs for Posts, IGTV and Saved.
Open the IGTV tab and click on Get Started.
IGTV allows only video uploading not the video recording within the app.
Videos should be uploaded in vertical or portrait mode. Size ration remains 9:16 for vertical videos, but for square, the ration becomes 4:5. Only 9:16 videos will fill the screen.
Tap on "+" icon available above the "Bio" information to upload a video in IGTV.
Then choose the video from your gallery section to select the video to upload.
Instagram Live videos can't be uploaded. Save the live video to another folder on your device.
After selecting the video, edit "title, description, and cover image".
Videos titles can't be edited in mobile so be cautious of all typos and avail right information. Titles and descriptions can be edited in the desktop.
Now go for editing your cover photo, choose Edit Cover.
Upload a separate image for the cover photo or choose from the options given.
When you've completed all the steps, tap Post and thus video will be uploaded to your channel.
Till your video gets uploaded, complete the title and description details.
After the video is uploaded, go for editing your cover photo as per the instructions.
When your video is all set to upload, click on Post to upload it to your channel. You can also save it in the draft for uploading it later.
Now, desktop version allows you to edit your video after upload.
If you want to edit your title or description, "view your video from your IGTV channel, tap on the 3-dot button, and select Edit Video".
Instagram always likes to bring new features and apps to provide more utilities to users.
This time Instagram has come up with a superb app called IGTV that is completely different from the rest of features you've seen on the platform.
This a complete guide for creating IGTV channel and uploading videos.


We are thrilled to hear that London Over the Border fund is awarding us £10,000 to buy fresh fruit and vegetables for a year for our Migrant and Refugee Project food bank.
This will make a huge difference to the destitute families who rely on our support, such as one mum who told us the only way she can provide her daughter with packed lunch for school is with items from our food bank.
The grant will enable The Renewal Programme to run a new project aimed at helping local people in Manor Park learn how to eat and cook healthily.
Do you have the ability to inspire and engage people who may be facing challenges? Are you interested in supporting people to achieve their full potential? We are looking for a vibrant and enthusiastic person to join our Supported Housing Team!
Could you be a delivery partner for Renewal Programme Training?
Poor skills have been blamed for the UK's relatively low productivity compared to other EU countries" (ref Dept for Bus Info & Skills Feb 2016). We are actively seeking a professional training partner to provide a commercial outlet for our range of training courses.
University College of London PhD students undertakes an evaluation of The Renewal Programme's ESOL for women over 60 group funded by the City Bridge Trust.
Yesterday we launched our Health & Lifestyle project.
Over 25 young people got together to celebrate an amazing year; the evening included games, prizes, food and a presentation of awards.
The Renewal Programme's Youth Service help to deliver Christmas Hampers to the elderly in East Ham, Newham; with the help of Cllr Julianne Marriott and other Newham organisations.
The Renewal Programme, thanks to the East London Business Alliance Newham community, help spread Christmas spirit to the children of local destitute refugee and migrant families.
Congratulations to Tomi Akintude, Newham's newly elected eleventh mayor.


Mobile app stores — the iOS App Store and Google Play — saw a record-breaking quarter, according to App Annie. Downloads grew 15% YoY during Q1 2017, reaching 25 billion downloads globally, and consumer spending was up 45% YoY to $15 billion in Q1 2017.
Although Google continues to dominate global app downloads, Apple is growing its lead over Google in terms of revenue generation. Global downloads for Google Play increased 20% YoY compared with the iOS App Store, which grew just 5% YoY, lengthening its lead over Apple to 135%. Nevertheless, the App Store saw a 45% YoY increase in consumer spending, compared with Google Play's 40% YoY growth. The App Store now leads Google Play in consumer spending by 100%, up from 90% in Q1 2016.
Android has more of a global presence. According to recent figures reported by Gartner, 81% of smartphones shipped in Q4 2016 ran Android, compared with 17.9% for Apple.
Android is generally more accessible. Last year, the average selling price for phones running Apple iOS was $691, while phones running Android averaged $215, Fortune reported.
Android is projected to top iOS in revenue for 2017. Another recent report from App Annie predicted that 2017 would be the first time Android app revenues top iOS. However, this projection also includes Android third-party app stores from vendors such as Tencent, Baidu, and Xiaomi.
Because of this, brands looking to capitalize on increasing app usage in emerging markets may be wise to develop an Android experience. As consumers in emerging markets become more comfortable making in-app purchases, Android developers could be well positioned to reap the benefits.


A beautiful quality classic round wastepaper basket finely woven from rattan in Myanmar.
This would look lovely alongside our other matching items in the Myanmar Range such as the Shaped Storage Basket.
Great as a gift for a home office.


More than 1000 mourners, including some South Africans attended the burial in Sanyati Zimbabwe of the four of the slain Zimbabweans.
Each mourner had his-or her own profound reasons for being at the funeral in Sanyathi and Glenview to witness the burial of Four members of the same family who died in the inferno believed to be linked to the Xenophobic attacks which were called upon and encouraged by President Ramaphosa of South Africa last week.
Scores of people came and many of whom escorted the four coffins containing the bones and ashes of two adults and two children to their final resting place, this was a moment – a chance to finally, symbolically, grant their mothers and fathers, brothers and sisters Zimbabweans at large an opportunity to see the cruelty of staying abroad.
Others among more than 1000 mourners were there to bear witness to a momentous moment in Xenophobic aftermath history Zimbabwe's first funeral for Citizens who died in the time when Xenophobia was in progress.
The son of the land Lord who was heard earlier on shouting hate words towards the deceased telling her mom that the Kwerekweres will be burnt alive and let us see if you will get the money you are refusing to give me has not yet been arrested. The police have not yet apprehended any suspect. In most cases where foreigners are victims, the case is never taken seriously.
In more than six hundred Xenophobic deaths in South Africa despite some offences committed on camera no. Arrests have been made. Not even one person was questioned. Despite the South African government dismissing the attacks as criminal activities no criminal has been convicted let alone arrested. This clearly shows where the order is coming from.
The remains were transported to Zimbabwe for burial. One could not hold tears back as the innocent children and their parents were lowered down to be covered in the cold dust to wait for the Lord to come again if he will indeed come. There was nothing heartbreaking to see the parents relatives and friends all overtaken by grief and plunged into the pool of tears. Nothing could be done to comfort them but to put their hope in the hands of God. Some could be heard asking where was God when this South African set fire on the house killing seven family members injuring four.
One asked: "Whose ashes are you? From where have you come? How is it possible to articulate our pain? For the ashes of our families, for the dust of our communities. For the broken tables of our people. The remnants of our youths and elders, our brides and grooms, our sons and daughters, our pastors and our leaders, our schoolmasters and school mistresses, our parents and infants. After a painful death, you have come to rest – perhaps your place can begin to comfort us."
In a deeply poignant address which moved many to tears, a man identified only as mufundisi spoke personally to the infant among the four saying: "Your young life was robbed. You experienced such fear and dread, then the ultimate wickedness saw your life taken in cruel fire. We don't know who was it we only know why was it done, But we do know you were an innocent Zimbabwean All of us here feel a strong connection to you. God will one day help us to forgive the South Africans. God will help the South Africans to remember this cruelty. By fire they extinguished your life now you will sleep in the cold earth. You are the child of the soil you will go back to the soil. Someone will seek justice for your life. We will not be barbaric like our brothers in the South. We will out these lives before God and God in His wisdom will find peace in our hearts. But for now we will have to find a doctor to heal our broken hearts. They bleed but it will be well. For it is well in my soul "
"A tiny coffin has enough space for you all. You were stripped of all dignity in life and in death," said One preacher quoting the UK Chief Rabbi Ephraim Mirvis in eulogy.
"We don't know your pains but God knows your comfort For so many Xenophobic victims, no Prayer has ever been said for them. But there is a God and he hears your pain and suffering.
The Zimbabwean family had fled to Cape town to escape the hunger and poverty All 7 of them including four children died in a house fire.
The sight of four coffins Unimaginable.
But that's the grim reality the Mazungunye and Vare family faces after all seven of the family's children died in a house fire in Cape town South Africa. The family from Zimbabwe sought refuge in South Africa to escape the economic melt down in Zimbabwe that's decimated their home country. They got more than they expected. They paid for their hard work with their own lives.
The family was staying at number 2219 Sanqoba Street Chris Hani Mbekweni. Cape Town. They were all buried in Sanyati Zimbabwe. A very dark cloud was cast upon the lives of the family and friends. It was not a dream. It is real they perished in the inferno and their killer is free and boasting.
The deceased are named as Maxwell Mazungunye born 13 December 1978 his wife Margaret Vare born on 13November 1992 . Children Mirriam Mazungunye born on 8 May 2002 .Tadiwanashe Mazungunye born on the 21 December 2012. Three of the family members survived the inferno with life threatening burns. They are at Paarl Hospital intensive care unit. They are Vanessa Mazungunye born on the 20th February 2002 Tatenda Mazungunye born on 21December2012 Mikeiler Mazungunye 9Months 2018 Mikleiler is admitted at Red cross Hospital burns unit Cape town.
The survivors of the blaze in the were taken to hospital after neighbours reported hearing "popping" and "explosions" coming from the house in the early hours.
Pictures from the scene show the roof of the house destroyed by the blaze and emergency workers continued to work on the house mid-morning. Witnesses could hear small pops and explosions coming from the house".
They were 10 people in the inferno but seven others were tragically pronounced dead at the scene.
The shocking deaths comes after president Ramaphosa rallied his killing machines to deal with foreigners. The Xenophobic attacks on all foreigners has increased and political parties are using the foreigners as their campaign collateral damage.
ANC is determined to win at all costs. They will paint their victory with the blood of the foreigners.
Last week president Ramaphosa was forced to clarify his position on Xenophobia. He called those attacking foreigners as criminal elements. Surprisingly his U turn speech was just loud sounding nothing it came too late as relatives wet their cheeks with tears and victims with no limbs lick their wounds.
The shocking thing is that only black foreigners are targeted. This is a black on black violence supported by Ramaphosa and his cabinet.
African governments had voiced their concerns and they have pleaded with their nationals not to revenge in any way. Eye for an eye makes the world blind.
The leader of the opposition party comrade Julius Malema has come out denouncing this black on black violence. Malema leads the EEF which is an upcoming and strong force to recon in South Africa. Malema described these killings as barbaric inhuman and indeed un African.
Meanwhile the family has thanked all good people who assisted in ferrying the bodies home for burial.


text:
How Undisclosed SEC Investigations Lead to Insider Trading
Wharton's Daniel Taylor discusses his research on the effects of undisclosed SEC investigations.
http://media.blubrry.com/kw/p/d1c25a6gwz7q5e.cloudfront.net/audio/20200214-KW-Taylor-01.mp3
In November 2019, The Wall Street Journal reported that the Securities and Exchange Commission was investigating Under Armour, a Baltimore-based maker of footwear, sports and casual apparel. Though the investigation had begun more than two years earlier, the company had not disclosed the fact that regulators were looking into its accounting practices. On the day the story broke, Under Armour's shares fell by 19%. Clearly, the market's reaction showed that investors believed this was relevant information and material to their perception of the shares' — and the company's — value.
Should companies like Under Armour go public sooner about the fact that the SEC is investigating them? If so, when is the right time to disclose such potentially damaging information? And before the company makes the disclosure, do insiders — who may or may not be direct targets of the probe — gain an unfair advantage in being able to sell shares before the information hits the market?
Daniel Taylor, a professor of accounting at Wharton, and his co-authors — Terrence Blackburne of Oregon State University; John D. Kepler of Stanford University; and Phillip J. Quinn of the University of Washington — investigated these questions and more in their research paper titled, "Undisclosed SEC Investigations." The researchers reviewed data obtained from the SEC on every formal investigation between 2000 and 2017, which was previously not public, to come up with their findings.
Taylor spoke with Knowledge@Wharton about this research and the implications for SEC investigations, share prices and insider trading. An edited transcript of the conversation appears below. (Listen to the podcast at the top of this page.)
Knowledge@Wharton: What prompted your study on undisclosed investigations by the SEC?
Daniel Taylor: Two events prompted the research. Back in January 2016, the Southern District of New York had a case in front of it, Lionsgate Entertainment, which went all the way through the court system. The ruling was that corporations are not under any obligation to disclose SEC investigations or receipt of a Wells Notice. (A Wells Notice tells the corporation that the SEC is likely to enforce against them.) The court held that "the defendants did not have a duty to disclose the SEC investigation and Wells Notices because the security laws do not impose an obligation on a company to predict the outcome of investigations. There is no duty to disclose litigation that is not 'substantially likely to occur.'"
That was surprising to me. I work at the intersection of accounting and finance and economics. We teach students that materiality is about whether a reasonable person would alter their valuation of the firm or their investing decision based on the information. In accounting we regularly recognize and account for uncertain negative events. For example, banks typically make an allowance for loan losses or for doubtful accounts, even though the loans haven't actually defaulted; they provide an accounting contingency. We have loss contingencies related to litigation and environmental issues. That is why I was surprised that in this case, the Southern District of New York seemed to set the bar to disclosure only when there is enforcement. That is at odds with how we typically think in economics about materiality. That got me thinking, "This is an interesting case where the bar for disclosure is different than what we see in other accounting and finance settings."
Less than 50% of firms disclose SEC investigations eventually.
Then, last November, The Wall Street Journal broke the news that the SEC was investigating Under Armour's accounting practices. Under Armour had, in fact, been cooperating for two and a half years but had not disclosed that investigation or that cooperation to shareholders. On the day that story broke, Under Armour's [stock] price fell 19%. Clearly, the market thought the investigation was sufficiently material to alter valuation by a substantial amount.
This got me thinking – along with my coauthors — about the frequency with which firms are not disclosing material SEC investigations. If The Wall Street Journal had not broken that story, would Under Armour have eventually disclosed it, or would shareholders never have learned about the investigation unless it actually led to an enforcement action?
The next question is, if the company has an ongoing SEC investigation and chooses not to disclose it – which they may not be obligated to — do they also not trade on that information? If the firm chooses not to disclose the investigation, and the investigation is material, that potentially means that insiders have an information advantage over normal shareholders. We typically think that fiduciary duty compels managers to either disclose the information or abstain from trading. So, they're not required to disclose, [but] do they abstain from trading?
When we started our research, we didn't quite appreciate how topical, relevant and far-reaching it was. Let me illustrate with a simple example; on February 13, Tesla disclosed it received an SEC subpoena on December 4 and it was cooperating with the SEC in their investigation. That puts about a two-month gap between when Tesla was hit with a subpoena and when it disclosed the subpoena. The natural question is whether the investigation is material. We don't necessarily know yet. Insiders at Tesla might, but outsiders don't. Given the disclosure occurred on February 13 and the subpoena was back in December, did any insiders in Tesla trade in the intervening period between when they learned of the subpoena and when they disclosed it? This is very, very topical and touches a lot of different companies out there right now.
K@W: Considering that the SEC is highly secretive when a company is being investigated, how challenging was it to gather the information you needed? How did you go about gathering the data?
Taylor: This paper relies on data that the SEC provided to us. SEC investigations are shrouded in secrecy. The SEC doesn't comment on ongoing investigations. Only the firm being investigated, the firm's counsel and the SEC and investigators are typically aware of the investigation. And, as we just discussed, the firm doesn't have any obligation to disclose that investigation. So prior work typically only observed investigations when the firm disclosed the investigation or when enforcement was brought. You couldn't observe instances of SEC investigations that were undisclosed.
We wanted to figure out what fraction of firms had undisclosed investigations. This presents a challenge, because the firm isn't disclosing it, and the SEC may not have an enforcement action on it. So how do we uncover these undisclosed investigations?
We found that one year after the investigation is opened, the median investigated firm underperforms the market by about 6%. Two years later, it underperforms the market by about 10%.
Over the course of six months, one of my coauthors went back and forth with the SEC, requesting information under the Freedom of Information Act on closed investigations — not open investigations but those that had closed. As part of the process of that back-and-forth with the SEC, we negotiated with them to release data on all closed, formal SEC investigations between 2000 and 2017. It's about 17 or 18 years of data on whom the SEC has been formally investigating.
The data includes everyone that is investigated regardless of the outcome. In some sense, we observe the master list of those individuals and entities that were formally investigated by the SEC. The key adjective is "formally." The SEC has many different scopes of investigation, "matter under inquiry" being one that's not formal. A formal investigation implies subpoena power by the SEC. We wanted to focus on instances in which things are serious enough to warrant subpoenas. The data entailed 299 pages of records of those individuals and entities, more than 12,000 investigations that the SEC undertook over that period. So now we know whom the SEC was investigating over the period, independent of the outcome of the investigation and independent of whether the firm disclosed it.
K@W: What are the main takeaways from your research?
Taylor: As I mentioned, the SEC turned over records to us of more than 12,000 investigations. Most of those investigations are not against publicly traded entities. They're against individuals, broker dealers, they're investigations for Ponzi schemes for non-publicly traded entities … [there are] all sorts of investigations out there.
One of the fun aspects of working on this paper is that almost every one of the observations is a story; each investigation has a back-story about what is being investigated, who is being investigated and why they are being investigated. We took the 12,000-plus investigations and focused on investigations of entities that are traded on the three major exchanges – the New York Stock Exchange, the NASDAQ and the American Stock Exchange (AMEX). That got us down to fewer than 4,000 investigations from 2000 to 2017.
The first thing we did once we had the set of investigations is look at what fraction of those firms that were under a formal investigation actually disclosed it and the timing of that disclosure. What we found is that about 19% to 20% of firms disclose some sort of SEC investigation within ten days of the investigation opening. By day-plus-ten after the investigation opened, 20% of firms have been forthcoming and have said look, the SEC is looking into something. The disclosures are not necessarily detailed but at least we have some evidence the company was forthcoming. Interestingly, less than 50% of firms disclose the investigations eventually. So, a large chunk of investigations appear to go undisclosed by the firm. We can disagree whether it should be allowed or not, but it seems to be allowed under the law.
If you knew that the firm was under investigation, and you sold your shares immediately upon learning that, you would have avoided significant losses across the entire sample.
The next question is, let's look at who's under investigation. The first thing we looked at was industry distribution. It looks like the distribution of industries that the SEC tends to investigate lines up well with the distribution of industries across the three major exchanges. You don't see the SEC investigating disproportionately into any one industry.
After that, we looked at the distribution of size, the company size. There we found something pretty interesting. Some 20% of the SEC's investigations tend to target the largest 10% of firms. I found that very surprising, because my belief coming into this was that potentially the largest 10% of firms are going to have the most well-resourced defense teams and going to be the most experienced. Our research suggests that the SEC doesn't shy away from taking on those firms that can mount, potentially, the best defenses. It also is consistent with the notion that the SEC targets those firms that have the largest scope of malfeasance. If you're a large firm and you have a potential fraud, there's likely going to be more harm done, and so potentially that's something that goes into the SEC's decision to investigate larger firms. Conversely, very few investigations occur in the smallest firms.
And then we looked at future performance. We have this investigation data. The investigations are undisclosed. Well, are the investigations in fact material? We decided to get at that by looking at what happens to the firm over the course of the investigation. We found that a year after the investigation is opened, the median investigated firm underperforms the market by about 6%. And two years later, it underperforms the market by about 10%. That's the median. What this means is that more than 50% of investigated firms have declines in their stock price even larger than 10% market-adjusted after two years. We found also that the investigations tend to foreshadow drops in the firm's earnings and increases in stock price volatility.
The results of the stock price performance and operating performance suggest that the investigations are economically material. If you knew that the firm was under investigation, and you sold your shares immediately upon learning that, you would have avoided significant losses across the entire sample.
Now, this doesn't mean that every investigation is material. There could certainly be immaterial investigations. But most of the investigations in the sample, the majority of those 4,000 or so investigations, do appear to be clearly economically material events.
It's important to point out that it's not necessarily the individual being investigated who is doing the trading.
K@W: Let's drill a little deeper. As your paper says, senior managers or insiders of a company that is being investigated learn about the investigation sooner than the outside investors. How does this insider knowledge influence their behavior? Do insiders exploit this advance knowledge and trade based on their access to this confidential information?
Taylor: One can view this research as having four effective steps. Step one is acquire data from the SEC on whom they have investigated regardless of whether the firm discloses it or the SEC discloses it. So, we acquire data on all investigations. Step two is [to determine] what percentage of firms actually disclosed the investigation, so we looked at the rate of disclosure of all the investigations. Step three is then to establish whether the investigations are in fact material. We know for a large number, they're undisclosed. The natural question is of these undisclosed investigations, are they economically material? All right, so we've established the vast majority [of investigations are] undisclosed, we've established that the vast majority are economically material.
The fourth step is [to ask], if an investigation is undisclosed and it is material, do insiders abstain from trading? Fiduciary duty compels insiders to either disclose material information or abstain from trading. We've established that disclosure isn't necessarily required in this setting. Among those firms that do not disclose, we then look at whether the insiders in fact trade. And the answer to that is yes, they do appear to be trading during the investigation. Now we know not only that the investigation is undisclosed, that the investigation is material, but that insiders don't seem to be abstaining from trading during the period of the investigation. That's really interesting because what it suggests is that there is some gray area as to legality here, and a gray area as to whether we should even be allowing that to occur.
It doesn't appear that companies are locking down and preventing their insiders from trading during the investigation. Now, it's important to point out that it's not necessarily the individual being investigated who is doing the trading. You can imagine certain individuals at the firm learning that the SEC is investigating one of their colleagues for, say, accounting fraud or foreign corrupt practices or some bad behavior. It's those other individuals — who aren't actually the subject of the investigation — that appear to be trading once they learn that one of their colleagues or some division of the firm is being investigated.
The SEC should be examining insider trading during the course of investigations, even if the investigation itself is unrelated to insider trading.
K@W: Were these individuals penalized for insider trading?
Taylor: There are cases, obviously, in which executives who are engaging in fraud start cashing out. The SEC is good at catching those — because if they're investigating for accounting fraud, they're looking at incentives to do so, and one of the incentives is to inflate the stock price to cash out the shares. The next question is, what about the lower-level employees, what about some of the other insiders whom the SEC isn't necessarily investigating for the fraud, but once they learn that the CEO or the CFO is being charged, they start selling their shares? That's what our research is diving into. It suggests that both firms and the SEC need to do a better job of monitoring incidental trading in firms that are being investigated by the SEC.
K@W: What are the implications of your research for regulators, for managers and for investors?
Taylor: The first thing is that the SEC should be examining insider trading during the course of investigations, even if the investigation itself is unrelated to insider trading. For example, the SEC might serve a subpoena for bribing a foreign official, a Foreign Corrupt Practices Act violation. Individuals privy to the subpoena at the firm may take that opportunity to liquidate some of their shares, even though those individuals had nothing to do with the original offense, with the original bribe. Our findings suggest that the SEC should be monitoring for insider trading even when the investigation doesn't necessarily relate to insider trading or doesn't necessarily relate to accounting fraud.
We have not examined trading in, say, the options market or hedge funds or trading by outside parties. We don't seem to find any evidence of abnormal trading in the market on the firms' shares in the NYSE, the NASDAQ or the AMEX. One thing that the SEC should be doing is looking at trading during periods of investigation. This is because that provides an opportunity — if the investigation is material — for insiders, either corporate insiders or insiders at the law firm that's helping the firm. It provides them with the opportunity to potentially trade profitably.
With respect to managers and the firm itself, the implication here is clear. Boards and general counsels need to lock down the trading of anyone involved with ongoing regulatory investigations and comport with best practices. This isn't a question of legality. This is a question of corporate governance, of best practices. If executives at the firm that know their division is under investigation by the SEC, and that has the potential to turn bad, then good corporate governance would be to prevent those individuals from trading. As the general counsel or the board, [they need to say] if we're not going to disclose this information to shareholders then we need to stop these corporate insiders from trading.
…We seem to be seeing notable exceptions to this. When Boeing was under investigation for issues related to its 737 Max, did it clamp down on the trading of its insiders? I have written a case study that would suggest otherwise. There are other examples out there. I have done related research on product recalls. Does the firm clamp down on the trading of insiders while it is investigating for product defects and product recalls? There needs to be a recognition that there are things other than accounting information that can be material information that would warrant the general counsel locking down the trading of corporate insiders.
There are many, many examples of this. One of the popular examples now making its way through the court is CBS. [Former chairman and CEO] Les Moonves was investigated as part of the Me Too movement, and the board seemed to be aware of this before the public knew about it. Litigants have alleged that the board knew about this and traded in the intervening period before the disclosure. That would be another case where the board knows about an investigation, even if not from the SEC — [it could be] from the Department of Justice, from the FBI, from the police, or from other regulators. In such cases, the board and the general counsel need to up their game and clamp down on trading.
Insiders — if the investigation is not disclosed — should be abstaining from trading. That evidence is an open-and-shut case.
K@W: Based on your research, do you think the rules of disclosure should be modified?
Taylor: Well, one can think about whether it should be mandatory for firms to disclose any investigations. That is one path to go down. Here, I don't think the evidence is necessarily clear that we should require all investigations to be disclosed. The evidence suggests that many investigations are immaterial. They end relatively quickly. You don't want to require disclosure in such cases because investors may overreact to the disclosure of what might turn out to be an immaterial investigation. For me, I don't think there are necessarily implications for whether we should require disclosure of these investigations.
But I absolutely think that insiders — if the investigation is not disclosed — should be abstaining from trading. That evidence is an open-and-shut case for me. This is especially [true] in the investigations we found that are material. I think the most surprising aspect of the paper was that there is a substantial fraction of firms that aren't disclosing the investigation, where the investigation is material, and where managers are not abstaining from trading in the intervening period between when they receive the subpoena and when the subpoena or the investigation is disclosed. The evidence suggests that in the absence of disclosure, managers aren't abstaining from trading, and instead seem to be potentially profiting handsomely from their trades.
The general counsels and the boards need to step up their game in terms of clamping down on trading by those who are aware of investigations into their firms.
Imagine a scenario in which your firm has been served a subpoena. The firm doesn't disclose it for another six months. If it's a material investigation, that gives you potentially six months' window to begin liquidating your shares before that information hits the market. You may have incentives to liquidate even if you are not the person who engaged in the fraud or the underlying bad activity in the first place. In the paper, we calculate some statistics for how large the losses are that insiders can avoid. What we find is that by selling at the outset of the investigation when they first learn of it, they're able to avoid losses in excess of 15% over a six-month period. And that's only six months after the investigation starts.
That to us suggests that the general counsels and the boards need to step up their game in terms of clamping down on trading by those who are aware of investigations into their firms. The issue of large losses is substantial and kind of eye opening. But it is intuitive when you walk through it. The SEC is investigating you for something very bad. You now have a six-month window to sell your shares before that hits the news. Right? So when it hits the news — in the case of Under Armour [the stock price] went down 19%. This was also the case with CBS and Les Moonves; the stock price went down a substantial amount and generated lawsuits. When one recognizes that the average investigation that is material has a stock price drop of 10%, loss avoidance of 15% seems to be in line with the notion that these investigations are in fact material.
K@W: What policy recommendations follow from what you have just been saying?
Taylor: Here the recommendation is for the SEC. I don't really think it's necessarily a disclosure route. The SEC provided us with the data. They have even richer data: key dates of the investigations; they know when the subpoenas are served; whom they're served to; various points in time of the investigation of when they make their discoveries, when they alert the board, when they alert certain managers. For each of those dates, I think our research would say the SEC has sufficient grounds to investigate trading of officers and directors at the firm — and even potentially outsiders, such as outside legal counsel, for example — around those dates.
Our recommendation would be for the SEC to drill down during each investigation — even if it's not an insider trading investigation — to drill down, to look, to investigate insider trading in conjunction with the actual investigation. Look to see whether the outside law firm was involved, if there was trading there. Look to see whether there's trading by lower-level employees, by officers and directors and potentially come up with additional charges based on what they find. Maybe they will find that one of the employees who was in charge of delivering the subpoena actually was one of the individuals who traded. With every investigation, the research suggests, comes the opportunity for opportunistic trading. So consequently, the SEC has justification for investigating trading with every investigation that they open.
With every investigation, the research suggests, comes the opportunity for opportunistic trading. The SEC has justification for investigating trading with every investigation that they open.
K@W: What future research do you plan to pursue based on what you've learned?
Taylor: Getting unique data from the SEC in terms of the total set of formal investigations over a decade and a half has opened some opportunities for future research, even moving beyond insider trading. One can start to map out what are the SEC's enforcement preferences. Whom does the SEC tend to go after earlier? Does the SEC seem to respond to media articles, so if there are media articles that allege bad behavior, does that trigger an investigation? What are the triggers of formal investigations that we could potentially map out from observable firm characteristics? What are the characteristics of firms that lead to a higher probability of an SEC investigation?
We've also recently received data from the SEC on Wells notices. These notices are an even stronger indicator of something coming down the pipeline than an undisclosed investigation. Wells notices are served to individuals and entities against whom the SEC has a high likelihood of pursuing an enforcement action; they provide the recipient with an opportunity to respond to the allegations before the case is brought.
That speaks to the Lionsgate ruling that motivated our research. We're finding some evidence that Wells notices served against entities have a very high rate of enforcement. More than 85% of Wells notices served to companies get enforced. These are the egregious cases. And so here again, because of that court ruling, are firms disclosing the Wells notices? Do we see trading in the intervening period between when they received the Wells notice and when they disclosed the Wells notice? Again, we can ask, now that we have the full set of Wells notices, what types of firms receive or tend to receive Wells notices? We can try and get a sense of the types of firms that may be heavily scrutinized by the SEC.
So, there are lots of questions that are going to be coming down the pipeline. Readers and listeners [of K@W] should stay tuned for more.
"How Undisclosed SEC Investigations Lead to Insider Trading." Knowledge@Wharton. The Wharton School, University of Pennsylvania, 02 March, 2020. Web. 21 January, 2021	<https://knowledge.wharton.upenn.edu/article/undisclosed-sec-investigations-lead-insider-trading/>
How Undisclosed SEC Investigations Lead to Insider Trading. Knowledge@Wharton (2020, March 02). Retrieved from https://knowledge.wharton.upenn.edu/article/undisclosed-sec-investigations-lead-insider-trading/
"How Undisclosed SEC Investigations Lead to Insider Trading" Knowledge@Wharton, March 02, 2020,
accessed January 21, 2021. https://knowledge.wharton.upenn.edu/article/undisclosed-sec-investigations-lead-insider-trading/
Do Corporate Audits Lead to Insider Trading?
Wharton research looks at whether corporate insiders trade more around the audit report date -- and what it means.
How Big Data Connects Bankers, Politics and Insider Trading
Insider trading by politically connected bankers spiked just before the massive bailouts of October 2008, research by Wharton professor Daniel Taylor shows.

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