<p>I have the values from B, V and R filters. How do I obtain the total luminescence of a star?
My ultimate aim is to find the relative masses and luminescence of various stars/galaxies in a galactic cluster from the B, V and R values.</p>

CC BY-SA 4.0
2024-05-22T22:44:56.553Z
How do you define luminescence?
pela
CC BY-SA 4.0
2024-05-23T03:48:32.683Z
I believe Luminescence = B + V + R. But not sure.
Angela
CC BY-SA 4.0
2024-05-24T13:47:58.800Z
I don't know this definition, and it doesn't really make sense to me, since those are magnitudes and magnitudes can't be added. You should probably make sure to define in the question what you actually want to know; otherwise it's difficult to answer.
pela
CC BY-SA 4.0
2024-05-25T15:12:47.897Z
Is it $Luminescence \propto (4\pi d^2) (10^{-0.4*R} + 10^{-0.4*V} + 10^{-0.4*B} )$ ?
Angela
CC BY-SA 4.0
2024-05-25T20:20:43.303Z
Luminescence typically means some sort of emission that doesn't involve heat, and is rarely used in astronomy. Do you mean _luminosity_?  The $10^{-0.4m}$ terms that you write give you some sort of flux _density_, but you cannot convert that to luminosity (by multiplying with 4πd²) before integrating over the filter to get a flux. If you really want to add magnitudes, you can convert, like you do, to flux densities, and then take the log and multiply by -2.5 to go back: $-2.5\log(10^{-0.4B} + 10^{-0.4V} + 10^{-0.4R})$. That will give you something that you may call "The total B+V+R magnitude".
pela
CC BY-SA 4.0
2024-05-26T09:12:07.423Z
From the second part of your question, I'm wondering if what you want to do is an SED fitting, where you fit the spectrum of a synthetic stellar population to the magnitudes in a range of filters, to get the mass, age, metallicity and redshift of a galaxy. That would typically require more bands than just B, V, and R, though, but could in principle be done. Can you provide some more details on what you have, what you want to obtain, why, etc.?
pela
CC BY-SA 4.0
2024-05-26T09:54:44.250Z
I am trying to get the luminosity from clustergal.dat in https://flamingos.astro.ufl.edu/1e0657/data/ So, should I multiply $10^{-0.4B}, 10^{-0.4R} and 10^{-0.4V}$ with $\Delta \lambda = fwhm \times \lambda$  before adding?
Angela
CC BY-SA 4.0
2024-05-26T11:15:24.373Z
I think you should ask your teacher for some more information, because there are things that don't really make sense (to me, at least). The `fwhm` values listed there cannot be filter widths unless they're narrowbands, which B, V, and R aren't. But remember that $10^{-0.4M}$ gives you flux density _per unit frequency_, so you'll need to convert to flux density per unit _wavelength_ (through $f_\lambda = f_\nu c / \lambda^2$) before multiplying by a filter width (or more accurately integrate over the filter shape), if you're interested in the total luminosity in a given filter.
pela
CC BY-SA 4.0
2024-05-26T12:21:20.650Z
Can you point me to any book or online link which can provide the introductory material on the calculations?
Angela
CC BY-SA 4.0
2024-05-27T05:57:53.187Z
Since I still don't really know exactly what you want, I'd just point you to texts on the connection between magnitudes, fluxes, and filters, e.g. [here](https://www.sdss4.org/dr17/algorithms/magnitudes/), [here](https://astro.ucla.edu/~wright/magcolor.htm), [here](https://phys.libretexts.org/Bookshelves/Astronomy__Cosmology/Supplemental_Modules_(Astronomy_and_Cosmology)/Cosmology/Astrophysics_(Richmond)/07%3A_Astronomical_Spectra%2C_Filters_and_Magnitudes), and [here](https://sites.astro.caltech.edu/~george/ay21/Fluxes%20and%20Magnitudes.pdf). It would probably be better to ask your teacher…
pela
CC BY-SA 4.0
2024-05-29T02:15:38.917Z
Thank you for the pointers
Angela
<photography><photometry><luminosity><galaxy-cluster>
BVR photometry and Luminiscense
Angela
# BVR photometry and Luminiscense

(Asked by: username_0 on 2024-05-22)

I have the values from B, V and R filters. How do I obtain the total luminescence of a star?
My ultimate aim is to find the relative masses and luminescence of various stars/galaxies in a galactic cluster from the B, V and R values.

**Tags:** photography, photometry, luminosity, galaxy-cluster
> **Comments:**
> **username_1**: How do you define luminescence?  
> **username_0**: I believe Luminescence = B + V + R. But not sure.  
> **username_1**: I don't know this definition, and it doesn't really make sense to me, since those are magnitudes and magnitudes can't be added. You should probably make sure to define in the question what you actually want to know; otherwise it's difficult to answer.  
> **username_0**: Is it $Luminescence \propto (4\pi d^2) (10^{-0.4*R} + 10^{-0.4*V} + 10^{-0.4*B} )$ ?  
> **username_1**: Luminescence typically means some sort of emission that doesn't involve heat, and is rarely used in astronomy. Do you mean _luminosity_?  The $10^{-0.4m}$ terms that you write give you some sort of flux _density_, but you cannot convert that to luminosity (by multiplying with 4πd²) before integrating over the filter to get a flux. If you really want to add magnitudes, you can convert, like you do, to flux densities, and then take the log and multiply by -2.5 to go back: $-2.5\log(10^{-0.4B} + 10^{-0.4V} + 10^{-0.4R})$. That will give you something that you may call "The total B+V+R magnitude".  
> **username_1**: From the second part of your question, I'm wondering if what you want to do is an SED fitting, where you fit the spectrum of a synthetic stellar population to the magnitudes in a range of filters, to get the mass, age, metallicity and redshift of a galaxy. That would typically require more bands than just B, V, and R, though, but could in principle be done. Can you provide some more details on what you have, what you want to obtain, why, etc.?  
> **username_0**: I am trying to get the luminosity from clustergal.dat in https://flamingos.astro.ufl.edu/1e0657/data/ So, should I multiply $10^{-0.4B}, 10^{-0.4R} and 10^{-0.4V}$ with $\Delta \lambda = fwhm \times \lambda$  before adding?  
> **username_1**: I think you should ask your teacher for some more information, because there are things that don't really make sense (to me, at least). The `fwhm` values listed there cannot be filter widths unless they're narrowbands, which B, V, and R aren't. But remember that $10^{-0.4M}$ gives you flux density _per unit frequency_, so you'll need to convert to flux density per unit _wavelength_ (through $f_\lambda = f_\nu c / \lambda^2$) before multiplying by a filter width (or more accurately integrate over the filter shape), if you're interested in the total luminosity in a given filter.  
> **username_0**: Can you point me to any book or online link which can provide the introductory material on the calculations?  
> **username_1**: Since I still don't really know exactly what you want, I'd just point you to texts on the connection between magnitudes, fluxes, and filters, e.g. [here](https://www.sdss4.org/dr17/algorithms/magnitudes/), [here](https://astro.ucla.edu/~wright/magcolor.htm), [here](https://phys.libretexts.org/Bookshelves/Astronomy__Cosmology/Supplemental_Modules_(Astronomy_and_Cosmology)/Cosmology/Astrophysics_(Richmond)/07%3A_Astronomical_Spectra%2C_Filters_and_Magnitudes), and [here](https://sites.astro.caltech.edu/~george/ay21/Fluxes%20and%20Magnitudes.pdf). It would probably be better to ask your teacher…  
> **username_0**: Thank you for the pointers  

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## 0 answers

