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One of the most massive stars known is Eta Carinae , which , with 100 – 150 times as much mass as the Sun , will have a lifespan of only several million years . Studies of the most massive open clusters suggests 150 M ☉ as an upper limit for stars in the current era of the universe . This represents an empirical value for the theoretical limit on the mass of forming stars due to increasing radiation pressure on the accreting gas cloud . Several stars in the R136 cluster in the Large Magellanic Cloud have been measured with larger masses , but it has been determined that they could have been created through the collision and merger of massive stars in close binary systems , sidestepping the 150 M ☉ limit on massive star formation .
The first stars to form after the Big Bang may have been larger , up to 300 M ☉ , due to the complete absence of elements heavier than lithium in their composition . This generation of supermassive population III stars is likely to have existed in the very early universe ( i.e. , they are observed to have a high redshift ) , and may have started the production of chemical elements heavier than hydrogen that are needed for the later formation of planets and life . In June 2015 , astronomers reported evidence for Population III stars in the Cosmos Redshift 7 galaxy at z = 6 @.@ 60 .
With a mass only 80 times that of Jupiter ( MJ ) , 2MASS J0523 @-@ 1403 is the smallest known star undergoing nuclear fusion in its core . For stars with metallicity similar to the Sun , the theoretical minimum mass the star can have and still undergo fusion at the core , is estimated to be about 75 MJ . When the metallicity is very low , however , the minimum star size seems to be about 8 @.@ 3 % of the solar mass , or about 87 MJ . Smaller bodies called brown dwarfs , occupy a poorly defined grey area between stars and gas giants .
The combination of the radius and the mass of a star determines its surface gravity . Giant stars have a much lower surface gravity than do main sequence stars , while the opposite is the case for degenerate , compact stars such as white dwarfs . The surface gravity can influence the appearance of a star 's spectrum , with higher gravity causing a broadening of the absorption lines .
The rotation rate of stars can be determined through spectroscopic measurement , or more exactly determined by tracking their starspots . Young stars can have a rotation greater than 100 km / s at the equator . The B @-@ class star Achernar , for example , has an equatorial velocity of about 225 km / s or greater , causing its equator to be slung outward and giving it an equatorial diameter that is more than 50 % greater than between the poles . This rate of rotation is just below the critical velocity of 300 km / s at which speed the star would break apart . By contrast , the Sun rotates once every 25 – 35 days , with an equatorial velocity of 1 @.@ 994 km / s . A main sequence star 's magnetic field and the stellar wind serve to slow its rotation by a significant amount as it evolves on the main sequence .
Degenerate stars have contracted into a compact mass , resulting in a rapid rate of rotation . However they have relatively low rates of rotation compared to what would be expected by conservation of angular momentum — the tendency of a rotating body to compensate for a contraction in size by increasing its rate of spin . A large portion of the star 's angular momentum is dissipated as a result of mass loss through the stellar wind . In spite of this , the rate of rotation for a pulsar can be very rapid . The pulsar at the heart of the Crab nebula , for example , rotates 30 times per second . The rotation rate of the pulsar will gradually slow due to the emission of radiation .
The surface temperature of a main sequence star is determined by the rate of energy production of its core and by its radius , and is often estimated from the star 's color index . The temperature is normally given in terms of an effective temperature , which is the temperature of an idealized black body that radiates its energy at the same luminosity per surface area as the star . Note that the effective temperature is only a representative of the surface , as the temperature increases toward the core . The temperature in the core region of a star is several million kelvins .
The stellar temperature will determine the rate of ionization of various elements , resulting in characteristic absorption lines in the spectrum . The surface temperature of a star , along with its visual absolute magnitude and absorption features , is used to classify a star ( see classification below ) .
Massive main sequence stars can have surface temperatures of 50 @,@ 000 K. Smaller stars such as the Sun have surface temperatures of a few thousand K. Red giants have relatively low surface temperatures of about 3 @,@ 600 K ; but they also have a high luminosity due to their large exterior surface area .
The energy produced by stars , a product of nuclear fusion , radiates to space as both electromagnetic radiation and particle radiation . The particle radiation emitted by a star is manifested as the stellar wind , which streams from the outer layers as electrically charged protons and alpha and beta particles . Although almost massless , there also exists a steady stream of neutrinos emanating from the star 's core .
The production of energy at the core is the reason stars shine so brightly : every time two or more atomic nuclei fuse together to form a single atomic nucleus of a new heavier element , gamma ray photons are released from the nuclear fusion product . This energy is converted to other forms of electromagnetic energy of lower frequency , such as visible light , by the time it reaches the star 's outer layers .
The color of a star , as determined by the most intense frequency of the visible light , depends on the temperature of the star 's outer layers , including its photosphere . Besides visible light , stars also emit forms of electromagnetic radiation that are invisible to the human eye . In fact , stellar electromagnetic radiation spans the entire electromagnetic spectrum , from the longest wavelengths of radio waves through infrared , visible light , ultraviolet , to the shortest of X @-@ rays , and gamma rays . From the standpoint of total energy emitted by a star , not all components of stellar electromagnetic radiation are significant , but all frequencies provide insight into the star 's physics .
Using the stellar spectrum , astronomers can also determine the surface temperature , surface gravity , metallicity and rotational velocity of a star . If the distance of the star is found , such as by measuring the parallax , then the luminosity of the star can be derived . The mass , radius , surface gravity , and rotation period can then be estimated based on stellar models . ( Mass can be calculated for stars in binary systems by measuring their orbital velocities and distances . Gravitational microlensing has been used to measure the mass of a single star . ) With these parameters , astronomers can also estimate the age of the star .
The luminosity of a star is the amount of light and other forms of radiant energy it radiates per unit of time . It has units of power . The luminosity of a star is determined by its radius and surface temperature . Many stars do not radiate uniformly across their entire surface . The rapidly rotating star Vega , for example , has a higher energy flux ( power per unit area ) at its poles than along its equator .
Patches of the star 's surface with a lower temperature and luminosity than average are known as starspots . Small , dwarf stars such as our Sun generally have essentially featureless disks with only small starspots . Giant stars have much larger , more obvious starspots , and they also exhibit strong stellar limb darkening . That is , the brightness decreases towards the edge of the stellar disk . Red dwarf flare stars such as UV Ceti may also possess prominent starspot features .
The apparent brightness of a star is expressed in terms of its apparent magnitude . It is a function of the star 's luminosity , its distance from Earth , and the altering of the star 's light as it passes through Earth 's atmosphere . Intrinsic or absolute magnitude is directly related to a star 's luminosity , and is what the apparent magnitude a star would be if the distance between the Earth and the star were 10 parsecs ( 32 @.@ 6 light @-@ years ) .
Both the apparent and absolute magnitude scales are logarithmic units : one whole number difference in magnitude is equal to a brightness variation of about 2 @.@ 5 times ( the 5th root of 100 or approximately 2 @.@ 512 ) . This means that a first magnitude star ( + 1 @.@ 00 ) is about 2 @.@ 5 times brighter than a second magnitude ( + 2 @.@ 00 ) star , and about 100 times brighter than a sixth magnitude star ( + 6 @.@ 00 ) . The faintest stars visible to the naked eye under good seeing conditions are about magnitude + 6 .
On both apparent and absolute magnitude scales , the smaller the magnitude number , the brighter the star ; the larger the magnitude number , the fainter the star . The brightest stars , on either scale , have negative magnitude numbers . The variation in brightness ( ΔL ) between two stars is calculated by subtracting the magnitude number of the brighter star ( mb ) from the magnitude number of the fainter star ( mf ) , then using the difference as an exponent for the base number 2 @.@ 512 ; that is to say :
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Relative to both luminosity and distance from Earth , a star 's absolute magnitude ( M ) and apparent magnitude ( m ) are not equivalent ; for example , the bright star Sirius has an apparent magnitude of − 1 @.@ 44 , but it has an absolute magnitude of + 1 @.@ 41 .
The Sun has an apparent magnitude of − 26 @.@ 7 , but its absolute magnitude is only + 4 @.@ 83 . Sirius , the brightest star in the night sky as seen from Earth , is approximately 23 times more luminous than the Sun , while Canopus , the second brightest star in the night sky with an absolute magnitude of − 5 @.@ 53 , is approximately 14 @,@ 000 times more luminous than the Sun . Despite Canopus being vastly more luminous than Sirius , however , Sirius appears brighter than Canopus . This is because Sirius is merely 8 @.@ 6 light @-@ years from the Earth , while Canopus is much farther away at a distance of 310 light @-@ years .
As of 2006 , the star with the highest known absolute magnitude is LBV 1806 @-@ 20 , with a magnitude of − 14 @.@ 2 . This star is at least 5 @,@ 000 @,@ 000 times more luminous than the Sun . The least luminous stars that are currently known are located in the NGC 6397 cluster . The faintest red dwarfs in the cluster were magnitude 26 , while a 28th magnitude white dwarf was also discovered . These faint stars are so dim that their light is as bright as a birthday candle on the Moon when viewed from the Earth .
The current stellar classification system originated in the early 20th century , when stars were classified from A to Q based on the strength of the hydrogen line . It thought that the hydrogen line strength was a simple linear function of temperature . Rather , it was more complicated ; it strengthened with increasing temperature , it peaked near 9000 K , and then declined at greater temperatures . When the classifications were reordered by temperature , it more closely resembled the modern scheme .
Stars are given a single @-@ letter classification according to their spectra , ranging from type O , which are very hot , to M , which are so cool that molecules may form in their atmospheres . The main classifications in order of decreasing surface temperature are : O , B , A , F , G , K , and M. A variety of rare spectral types are given special classifications . The most common of these are types L and T , which classify the coldest low @-@ mass stars and brown dwarfs . Each letter has 10 sub @-@ divisions , numbered from 0 to 9 , in order of decreasing temperature . However , this system breaks down at extreme high temperatures as classes O0 and O1 may not exist .
In addition , stars may be classified by the luminosity effects found in their spectral lines , which correspond to their spatial size and is determined by their surface gravity . These range from 0 ( hypergiants ) through III ( giants ) to V ( main sequence dwarfs ) ; some authors add VII ( white dwarfs ) . Most stars belong to the main sequence , which consists of ordinary hydrogen @-@ burning stars . These fall along a narrow , diagonal band when graphed according to their absolute magnitude and spectral type . The Sun is a main sequence G2V yellow dwarf of intermediate temperature and ordinary size .
Additional nomenclature , in the form of lower @-@ case letters added to the end of the spectral type to indicate peculiar features of the spectrum . For example , an " e " can indicate the presence of emission lines ; " m " represents unusually strong levels of metals , and " var " can mean variations in the spectral type .
White dwarf stars have their own class that begins with the letter D. This is further sub @-@ divided into the classes DA , DB , DC , DO , DZ , and DQ , depending on the types of prominent lines found in the spectrum . This is followed by a numerical value that indicates the temperature .
Variable stars have periodic or random changes in luminosity because of intrinsic or extrinsic properties . Of the intrinsically variable stars , the primary types can be subdivided into three principal groups .
During their stellar evolution , some stars pass through phases where they can become pulsating variables . Pulsating variable stars vary in radius and luminosity over time , expanding and contracting with periods ranging from minutes to years , depending on the size of the star . This category includes Cepheid and Cepheid @-@ like stars , and long @-@ period variables such as Mira .
Eruptive variables are stars that experience sudden increases in luminosity because of flares or mass ejection events . This group includes protostars , Wolf @-@ Rayet stars , and flare stars , as well as giant and supergiant stars .
Cataclysmic or explosive variable stars are those that undergo a dramatic change in their properties . This group includes novae and supernovae . A binary star system that includes a nearby white dwarf can produce certain types of these spectacular stellar explosions , including the nova and a Type 1a supernova . The explosion is created when the white dwarf accretes hydrogen from the companion star , building up mass until the hydrogen undergoes fusion . Some novae are also recurrent , having periodic outbursts of moderate amplitude .
Stars can also vary in luminosity because of extrinsic factors , such as eclipsing binaries , as well as rotating stars that produce extreme starspots . A notable example of an eclipsing binary is Algol , which regularly varies in magnitude from 2 @.@ 3 to 3 @.@ 5 over a period of 2 @.@ 87 days .
The interior of a stable star is in a state of hydrostatic equilibrium : the forces on any small volume almost exactly counterbalance each other . The balanced forces are inward gravitational force and an outward force due to the pressure gradient within the star . The pressure gradient is established by the temperature gradient of the plasma ; the outer part of the star is cooler than the core . The temperature at the core of a main sequence or giant star is at least on the order of 107 K. The resulting temperature and pressure at the hydrogen @-@ burning core of a main sequence star are sufficient for nuclear fusion to occur and for sufficient energy to be produced to prevent further collapse of the star .
As atomic nuclei are fused in the core , they emit energy in the form of gamma rays . These photons interact with the surrounding plasma , adding to the thermal energy at the core . Stars on the main sequence convert hydrogen into helium , creating a slowly but steadily increasing proportion of helium in the core . Eventually the helium content becomes predominant , and energy production ceases at the core . Instead , for stars of more than 0 @.@ 4 M ☉ , fusion occurs in a slowly expanding shell around the degenerate helium core .
In addition to hydrostatic equilibrium , the interior of a stable star will also maintain an energy balance of thermal equilibrium . There is a radial temperature gradient throughout the interior that results in a flux of energy flowing toward the exterior . The outgoing flux of energy leaving any layer within the star will exactly match the incoming flux from below .
The radiation zone is the region of the stellar interior where the flux of energy outward is dependent on radiative heat transfer , since convective heat transfer is inefficient in that zone . In this region the plasma will not be perturbed , and any mass motions will die out . If this is not the case , however , then the plasma becomes unstable and convection will occur , forming a convection zone . This can occur , for example , in regions where very high energy fluxes occur , such as near the core or in areas with high opacity ( making radiatative heat transfer inefficient ) as in the outer envelope .
The occurrence of convection in the outer envelope of a main sequence star depends on the star 's mass . Stars with several times the mass of the Sun have a convection zone deep within the interior and a radiative zone in the outer layers . Smaller stars such as the Sun are just the opposite , with the convective zone located in the outer layers . Red dwarf stars with less than 0 @.@ 4 M ☉ are convective throughout , which prevents the accumulation of a helium core . For most stars the convective zones will also vary over time as the star ages and the constitution of the interior is modified .
The photosphere is that portion of a star that is visible to an observer . This is the layer at which the plasma of the star becomes transparent to photons of light . From here , the energy generated at the core becomes free to propagate into space . It is within the photosphere that sun spots , regions of lower than average temperature , appear .
Above the level of the photosphere is the stellar atmosphere . In a main sequence star such as the Sun , the lowest level of the atmosphere , just above the photosphere , is the thin chromosphere region , where spicules appear and stellar flares begin . Above this is the transition region , where the temperature rapidly increases within a distance of only 100 km ( 62 mi ) . Beyond this is the corona , a volume of super @-@ heated plasma that can extend outward to several million kilometres . The existence of a corona appears to be dependent on a convective zone in the outer layers of the star . Despite its high temperature , and the corona emits very little light , due to its low gas density . The corona region of the Sun is normally only visible during a solar eclipse .
From the corona , a stellar wind of plasma particles expands outward from the star , until it interacts with the interstellar medium . For the Sun , the influence of its solar wind extends throughout a bubble @-@ shaped region called the heliosphere .
A variety of nuclear fusion reactions take place in the cores of stars , that depend upon their mass and composition . When nuclei fuse , the mass of the fused product is less than the mass of the original parts . This lost mass is converted to electromagnetic energy , according to the mass @-@ energy equivalence relationship E = mc2 .
The hydrogen fusion process is temperature @-@ sensitive , so a moderate increase in the core temperature will result in a significant increase in the fusion rate . As a result , the core temperature of main sequence stars only varies from 4 million kelvin for a small M @-@ class star to 40 million kelvin for a massive O @-@ class star .
In the Sun , with a 10 @-@ million @-@ kelvin core , hydrogen fuses to form helium in the proton @-@ proton chain reaction :
41H → 22H + 2e + + 2νe ( 2 x 0 @.@ 4 MeV )
2e + + 2e- → 2γ ( 2 x 1 @.@ 0 MeV )
21H + 22H → 23He + 2γ ( 2 x 5 @.@ 5 MeV )
23He → 4He + 21H ( 12 @.@ 9 MeV )
These reactions result in the overall reaction :
41H → 4He + 2e + + 2γ + 2νe ( 26 @.@ 7 MeV )
where e + is a positron , γ is a gamma ray photon , νe is a neutrino , and H and He are isotopes of hydrogen and helium , respectively . The energy released by this reaction is in millions of electron volts , which is actually only a tiny amount of energy . However enormous numbers of these reactions occur constantly , producing all the energy necessary to sustain the star 's radiation output . In comparison , the combustion of two hydrogen gas molecules with one oxygen gas molecule releases only 5 @.@ 7 eV .
In more massive stars , helium is produced in a cycle of reactions catalyzed by carbon called the carbon @-@ nitrogen @-@ oxygen cycle .
In evolved stars with cores at 100 million kelvin and masses between 0 @.@ 5 and 10 M ☉ , helium can be transformed into carbon in the triple @-@ alpha process that uses the intermediate element beryllium :
4He + 4He + 92 keV → 8 * Be
4He + 8 * Be + 67 keV → 12 * C
12 * C → 12C + γ + 7 @.@ 4 MeV
For an overall reaction of :
34He → 12C + γ + 7 @.@ 2 MeV
In massive stars , heavier elements can also be burned in a contracting core through the neon burning process and oxygen burning process . The final stage in the stellar nucleosynthesis process is the silicon burning process that results in the production of the stable isotope iron @-@ 56 , an endothermic process that consumes energy , and so further energy can only be produced through gravitational collapse .
The example below shows the amount of time required for a star of 20 M ☉ to consume all of its nuclear fuel . As an O @-@ class main sequence star , it would be 8 times the solar radius and 62 @,@ 000 times the Sun 's luminosity .
Perry the Platypus , also known as Agent P or simply Perry , is an anthropomorphic platypus from the animated series Phineas and Ferb . Perry was created by the series ' co @-@ founders , Dan Povenmire and Jeff " Swampy " Marsh . He first appeared along with the majority of the main cast in the pilot episode " Rollercoaster . " Perry is featured as the star of the B @-@ plot for every episode of the series , alongside his nemesis Dr. Heinz Doofenshmirtz . A mostly silent character , his lone vocal characteristic ( a rattling of Perry 's beak ) was provided by Dee Bradley Baker .
Perry is the pet platypus of the Flynn @-@ Fletcher family , and is perceived as mindless and domesticated . In secret , however , he lives a double life as a member of an all @-@ animal espionage organization referred to as O.W.C.A. ( The Organization Without a Cool Acronym ) . Many secret entrances to his underground lair exist all around the house ; such as the side of the house , most notably the tree that his owners sit under in the backyard , and several other everyday objects that seem to elude the family 's attention . He engages in daily battles with Dr. Heinz Doofenshmirtz , an evil scientist who desires to take over the Tri @-@ state area with obscure contraptions that work perfectly according to his intended function but fail in his application of them every time .
Perry was made a platypus because of the animal 's striking appearance and the lack of public knowledge of the animal , which allowed the writers to make things up about the species . Critical reception for the character from both professionals and fans have been considerably positive . Merchandising of the character include plush toys , t @-@ shirts , wooden toys , glasses , and coloring books , along with appearances in literature and a 2009 video game for the Nintendo DS .
Perry is the docile pet platypus of the blended Flynn @-@ Fletcher family , who adopted him because his unfocused gaze made it seem as if he were looking at both Phineas and Ferb at the same time , as shown in the 2011 movie , Phineas and Ferb the Movie : Across the 2nd Dimension . Unbeknownst to them , Perry lives a double life as a crime @-@ fighting spy working for the " Organization Without a Cool Acronym " / The OWCA , going by the codename " Agent P. " He reports to his superior , Major Monogram , via telecast in his large , high @-@ tech , underground hideout . Every day , he engages in battles with the evil scientist Dr. Heinz Doofenshmirtz , who tries using inventions to take over the tri @-@ state area . Perry is always able to foil Doofenshmirtz 's plans and in doing so accidentally leads to the destruction of whatever form of contraption his owners , Phineas Flynn and Ferb Fletcher , are building in order to make summer better . Phineas and Ferb are aware that something happens to get rid of their scheme for the day , but do not know that Perry is the cause behind it and are largely dismissive of it . Their sister , Candace , also does not know that Perry is behind the destruction and is driven to near insanity trying to figure it out . Throughout the series , Perry is aware of Phineas and Ferb 's inventions , but is largely uninterested in them , save whenever he notices that their latest invention may help him thwart Doofenshmirtz .
Perry and Doofenshmirtz at first seem to loathe each other in the beginning of the series , and have been arch @-@ nemeses since the day they met . However , they are often cordial and friendly towards one another and it is said by Doofenshmirtz that Perry is his best friend , and Perry will often act to save Doofenshmirtz 's life when his plot inevitably blows up in his face . Habitually , their daily brawls involve Doofenshmirtz devising a scheme , which Perry goes to stop after being briefed by Major Monogram . He is trapped by Doofenshmirtz while trying to do so and is told of the doctor 's scheme , usually pertaining to some backstory or pet peeve . He then escapes and the two fight , Perry coming out victorious . The two rely on this daily structure , Doofenshmirtz even specifically mentioning it in " Journey to the Center of Candace " and in episodes such as " It 's About Time ! " in which Doofenshmirtz temporarily replaces Perry with secret agent Peter The Panda and they become depressed about not having each other to fight . Perry realizes he misses Doof too . When Perry does not arrive on the scene of Doofenshmirtz 's evil plan , the doctor hesitates to execute his plans and fears for where Perry has gone , though he notes that he " hopes something terrible has happened to him . " . Sometimes , they decided not to fight and have fun , as shown in " Happy New Year ! " and " Candace Disconnected " . On other occasions , depending on whatever situation Doofenshmirtz is facing , Perry would often help Doofenshmirtz with his non @-@ evil plans , such as helping him overcome evil scientist 's block , helping him put on a birthday party for his 16 @-@ year @-@ old daughter Vanessa , impressing a square dancing girl with programmable square dancing boots that Doofenshmritz created , working together to stop a raging platypus hunter from hunting them down , or helping him convince his rich ex @-@ wife to help pay off his mortgage debt . Also , Perry tends to use Doofenshmirtz 's inventions to erase evidence of whatever contraptions Phineas and Ferb had made , leaving Candace unable to bust them . Examples include when Perry asked to borrow Doofenshmirtz 's robot Norm to pick up footage from the city surveillance cameras in order to preserve his job as an agent , as well as using Doofenshmirtz 's Pick @-@ Him @-@ Up @-@ inator to rescue a lost Candace and bring her home .
In Phineas and Ferb the Movie : Across the 2nd Dimension , an alternate reality ( yet more evil and ruthless ) version of Perry ( known as Platyborg ) appears as the secondary antagonist , with the regular Perry serving as a supporting protagonist . Platyborg would later return in the episode sequel , Tales from the Resistance : Back to the 2nd Dimension , this time , as a supporting protagonist .
While working on the animated television series Rocko 's Modern Life , Phineas and Ferb co @-@ founders Dan Povenmire and Jeff " Swampy " Marsh utilized several recurring elements in the episodes that they wrote . Among these were actions sequences and chase scenes . Povenmire and Marsh wanted to reuse these elements in their series and chose Perry to execute it . The pair gave him a consistent and continuous nemesis in the form of Doofenshmirtz as a means of allowing viewers to get to know him .
While choosing a species for Perry , Povenmire and Marsh wanted to keep in mind selecting one that was uncommon , an animal that kids could not " pick out at a pet store and beg [ their parents ] for . " They chose a platypus because of the animal 's obscure and striking appearance . The animal was scarcely used in American animated programs , so the pair opined that Perry " would not have to compete with preconceived notions that viewers might bring to a more conventional critter . " The blank storyboard they were given allowed them to " make stuff up " since " no one knows very much about [ them ] . "
Perry has a theme song tentatively entitled " Perry , " performed by Randy Crenshaw and Laura Dickinson , and written by Povenmire and Marsh , who write the majority of songs in the series . The song , along with the number " Gitchee Gitchee Goo " from the episode " Flop Starz , " was the first musical composition Povenmire and Marsh pitched to The Walt Disney Company . They were nervous doing so , because , as Povenmire explained , " Disney has a big history of music -- what if they hate it ? " Their reaction , however , was considerably positive and the pair was asked to write a song for each episode , which they vehemently agreed to . The opening lyrics for the song describe Perry as a standard textbook definition of a platypus : " He 's a semi @-@ aquatic egg @-@ laying mammal of action . "
Like the other characters of the series , Perry was structured in a simple style to allow young viewers to easily draw him . In keeping with the show 's general design scheme , Perry is constructed of geometric shapes in a style reminiscent of deceased Looney Tunes animator Tex Avery . Povenmire uses different design styles for drawing Perry depending on how he is portrayed . When Perry is portrayed as a domesticated and mindless pet , Povenmire begins with a square shaped like a loaf of bread . He then draws his front legs and feet before drawing his bill , which is set at a certain angle . Povenmire then draws his eyeballs , which are never focused and look in opposing directions in a daze . He concludes the figure by adding his hind legs , tail , hair , and finally color .
When portrayed as a secret agent , Povenmire starts with a similar bread loaf square design , but draws it standing up vertically and places a fedora on the top of his head , which is combined with the square torso . In contrast to his mindless and wild @-@ eyed expression as a pet , the secret agent version of Perry is detailed with eyes " full of steely blue resolve . " Povenmire proceeds by drawing his arms , which bear hands that are open and prepared for fighting or any danger . His legs are bent , as well prepared for an act of danger or action needed . Povenmire finishes the design by adding his beaver tail and color .
Perry 's undercover identity as a pet leads to characters throughout the series to deem him as a " mindless domestic pet " that " doesn 't do much " . This definition of the character led to Phineas and Ferb spearheading production of a new toyline based on Perry called " Perry the Inaction Figure , " whose tagline revolved around it not doing anything but allowing the customer to make it whatever they desire it to be . In all actuality , Perry is a skilled fighter who is able to perform several implausible judo fighting moves and escapes . He has access to several different types of technology and inventions provided to him by The O.W.C.A. , including a hover craft dubbed the " Platypusmobile , " a jet ski , and a whistle set that allows him to summon different types of animals .
Although his appearance as a domestic pet is mostly a cover , Perry has nonetheless expressed care and devotion for the Flynn @-@ Fletcher family . In the episode " The Ballad of Bad Beard " , Perry managed to drag Candace out of the Dark Cave before it caved in because of Dr. Doofenshmirthz 's " self destruction button " that which Candace had accidentally pressed while under the orange moss hallucination , thinking it was a vending machine . He did this even though he knew that Candace saw that Perry was a secret agent talking to Agent E ( Eagle ) and to Major Monogram in a cracked egg . Candace thought she was just hallucinating because of the orange moss she accidentally touched earlier in the episode . Also , when an invention of Doofenshmirtz 's in the episode " Journey to the Center of Candace " might cause severe harm to Phineas and Ferb , Perry thoroughly beats up Doofenshmirtz and quickly handcuffs him . He then ties him to a pipe and , instead of just leaving him like he usually does in the series , calls for special forces from the O.W.C.A. to come and arrest the doctor , though they never show up . In " Oh , There You Are , Perry , " Doofenshmirtz is downgraded to a low threat level and Perry is reassigned to a new nemesis . This causes him to have to leave his home with the Flynn @-@ Fletchers , which makes him sad and he does not enjoy his new villain . Phineas and Ferb are fearful about where Perry could have gone to and put up several flyers around town for people to find him . They decide to throw a concert on the roof of a building , singing a song about how much they love Perry and want him to come home . Concurrently , Perry is reassigned to Doofenshmirtz again and returns to the brothers once more .
Though Perry is anthropomorphic , he does not speak , only communicating through an " aggravated purr " type of noise made by flapping his bill . This noise is provided by actor Dee Bradley Baker ; to this day , Povenmire and Marsh do not understand how Baker produces the noise . Thomas Sangster , who plays Ferb , is notoriously good at making the noise and is considered second only to Baker himself . When in his " Agent P " persona , Perry is almost completely silent .
As a character , Perry has been well received by both fans and critics . As Cynthia Littleton of Variety magazine wrote , " Perry the platypus is a breakout star from the Disney Channel toon ' Phineas and Ferb . ' " The New York Times writer Susan Stewart called him " intrepid . " Jean Yoo , a press member for Disney Channel , said that Perry is " suave " and " makes James Bond look like a rank amateur . " Aaron H. Bynum of Animator Insider opined that he is " indubitably confident . " Carly H. of Scholastic , Inc. declared Perry " pretty darn awesome . " Josh Jackson , editor of Paste , described Perry and Doofenshmirtz 's relationship as " pitch @-@ perfect . "
Certain reviewers have also commented negatively about Perry and his subplot , which Sherry Robinson of the St. Petersburg Times considers " pretty trippy . " Kevin McDonough of Sun Coast Today described it as " complicated " and " loosely connected " to the rest of the series , writing that he is " not sure what this accomplishes except to add the noise of explosions to the already constant din of singing and screaming . " Ed Liu of Toon Zone feels it is " truly puzzling what Perry the secret agent is doing in this show in the first place . " Liu considers his subplot to be a type of " throw everything against the wall and see what sticks " element and writes that " many of the earlier episodes of the show don 't manage to do a very good job of balancing the subplot and the main one . "
Perry was nominated for a Nickelodeon Kids ' Choice Award in 2014 under the category of Favorite Animated Animal Sidekick .
In addition to the main television series , Perry has appeared in several pieces of Phineas and Ferb merchandise . To date , he has appeared in all Phineas and Ferb novelizations , published by Disney Press . The character has been adapted into a 20 inch plush toy , released by The Walt Disney Company . The plush has a button on its hand that allows it to emit Perry 's signature chattering noise . Certain t @-@ shirts based on the series released by both Disney and the online retail website Zazzle also display Perry and the phrase " Hey , where 's Perry ? " which most characters like Phineas , Isabella , Stacy , Irving , Ferb , and Lawrence utter when Perry goes to Major Monogram in his secret lair in almost every episode . There also is a T @-@ Shirt with Perry 's face . Perry appears in the Nintendo DS video game based on the series , simply titled Phineas and Ferb , where a mini @-@ game involves Perry stopping Doofenshmirtz 's latest evil scheme . As of 1 April 2014 , Perry is also a playable character in the video game Disney Infinity .
Amylostereum is the single genus in the fungal family Amylostereaceae . The genus currently comprises four saprotrophic and parasitic species , which live off living or dead wood . The Amylostereaceae cause white rot in the wood by disintegrating the tissue component lignin . They produce crust @-@ like , partially wavy fruit bodies on the surface of infested trees , which are similar to those produced by Stereum species .
There are four described species in the Amylostereaceae : A. chailletii ( the type ) , A. areolatum , A. ferreum and A. laevigatum . The species were initially considered part of Stereum until mycologist Jacques Boidin found atypical microscopic differences between them . Forty years after his extensive researches from 1958 , Boidin reclassified Amylostereum into its own family .
Three Amylostereum species are symbionts of wood wasps in the genera Sirex , Urocerus , and Xoanon , which infest conifers . The female wood wasps deposit their eggs together with fungal spores and mucus in trees , and the fungus is eaten by the wasp 's larva as food . The fungus propagates vegetatively through the formation of asexual spores in newly emerged females that are stored in special structures adapted for the transport of symbiotic fungi . The A. areolatum – Sirex woodwasp ( S. noctilio ) symbiont complex has been studied extensively because of its potential to cause substantial economic losses in the forestry industry , particularly in non @-@ native regions .
Amylostereaceae species were for a long time classified in the genus Stereum , based primary on the layered structure of the fruit body and the similar physiological activity . Mycologist Jacques Boidin separated Amylosterum from Stereum in 1958 , justifying this decision by explaining that microscopic differences such as amyloid spores and encrusted cystidia were sufficiently distinct to warrant recognition as a new genus . Although the type species of the genus ( today called A. chailletii ) was initially named Trichocarpus ambiguus , the name Trichocarpus had already been used for a genus in the flowering plant family Malvaceae . Boidin thus chose the genus name Amylostereum , referring to the amyloid spores .
Based on DNA analysis , Boidin in 1998 moved Amylostereum into a new , monotypic family , the Amylostereaceae , which he attributed to the Hericiales order . Later studies , however , supported the initial classification in the Russulales .
The classification of the Amylostereaceae is not completely resolved . The next closest relatives might be – depending on the research – either Echinodontium tinctorium and most other species of the genus Echinodontium , or Artomyces pyxidatus . Most of the previous DNA analysis results suggest a narrow relation to Echinodontium , but several results of studies partially contradict this conclusion . Only the classification to the Russulales is regarded as correct . Some authors have suggested that Amylostereum should be placed in the family Echinodontiaceae .
The similarities between A. chailletii and A. areolatum have caused some confusion regarding their placement in the genus . As only the size of their fruit bodies differ from each other in appearance , researcher German Josef Krieglsteiner assumed that both are the same species in different age stages . Experiments with pure cultures of the fungi , however , showed that the mycelia of A. chailletii , A. laevigatum and A. ferreum were partially compatible to each other , but the mycelium of A. areolatum was incompatible to other species . Boidin believes that the common ancestor of all Amylostereum fungi used yellowwoods as a host . This genus of conifers was native in Europe until the Paleogene and Neogene Periods ( 66 million to 2 @.@ 6 million years ago ) , but became extinct there , so the Amylostereum fungi specialized on other conifers and differentiated into several species . Only A. ferreum specialized on yellowwoods in South America .
Compatibility tests as well as molecular analysis indicated that A. areolatum separated very early from other Amylostereum fungi . The other three species separated later from each other and are thus partially compatible to each other . A. ferreum and A. laevigatum produced in 59 % of all cases a common mycelium , A. ferreum and A. chailletii only in 44 % . There is an undescribed species in Amylostereum ; according to DNA analysis , it stands between A. laevigatum and A. ferreum . This is remarkable , as these fungi originated from Mycetangae ( storing organs of Platypodinae ) of a North American wood wasp , while A. laevigatum has never been seen as symbiont of wood wasps , neither in North American nor in Europe . The fungus possibly represents a separated species or a subtaxon of A. laevigatum . As A. areolatum and A. chailletii mainly reproduce asexually through the symbiosis of wood wasps , the genetic variability within these species is relatively low .
The Amylostereaceae produce crust @-@ like , dry and leathery @-@ corky fruit bodies on the bark of infested trees . The fruit bodies are 0 @.@ 5 – 1 @.@ 5 mm ( 0 @.@ 02 – 0 @.@ 06 in ) thick , irregularly shaped and are able to cover a large surface on the bark or otherwise can appear as small spots . They lie directly on the bark . The ochrous , grey or brownish fruit body ( hymenium ) has a smooth to warty surface texture and is turned outwards . It is bordered by a highly bent and wavy ( effuso @-@ reflex ) edge on all species except A. laevigatum , which has a churlish surface ( a tomentum ) and is usually dirty @-@ brown coloured . In some species , the tomentum stands clearly above and forms a kind of roof above the fruit body ; if it completely surrounds this roof , there might appear cuplike shapes .
The Amylostereaceae possess a dimitic trama , meaning that there are in its mycelia two kinds of hyphae . The first type is brownish skeletal hyphae , which provide stability to the fruit body . These hyphae run parallel to the bark and often have hairpin @-@ like turns , so that the loops form thick @-@ walled , cystidium @-@ like structures , the so @-@ called pseudocystidia . The second type is generative hyphae . They are translucent ( hyaline ) and serve to promote the growth of the fungus . Genuine cystidia arise in the hymenium and the layer directly below , the subhymenium . Both pseudocystidia and cystidia are encrusted , meaning that they feature crystal @-@ like structures on the top .
With the exception of A. laevigatum , all species have a thin separating layer , the cortex , between the hymenium and the tomentum . A cortex is also present on many Stereum fungi ( on a broader front ) and serves to bend up the fruit body . As this cortex is missing on A. laevigatum , its fruit body lies flat on the bark .
The basidia are 15 – 25 × 3 @.@ 5 – 5 @.@ 5 µm and have a slim , club @-@ like shape . Each basidium features four sterigmata , each of which bear one spore . The spores ' shape is slimly ellipsoidal or cylindrical . Their surface is smooth and their walls are thin . Although they are colourless and hyaline , the spores are amyloid , meaning they will turn bluish or purple when stained with Melzer 's reagent . This characteristic differs from other very similar species , and this gave the genus its name .
The range of the Amylostereaceae originally comprised only Holarctic regions , including North America and Eurasia , and the Neotropics , with Central and South America . The introduction of A. areolatum and its symbionts , the Sirex woodwasps , saw the spread of the genus to all continents except Antarctica .
Amylostereum chailletiiz is common in the temperate regions of North America and Eurasia . A. laevigatum can be also found in temperate Eurasia , but it is unclear how broadly this species is distributed in North America . A. areolatum is originally native in North Africa and Eurasia ; it was however distributed through the 20th century in Australia , New Zealand , Southern Africa as well as in South and North America . Only A. ferreum is originally native in the tropics and is common in Brazil and the Caribbean .
Amylostereaceae usually infest only dead or cut down conifer wood . Three species – A. areolatum , A. laevigatum and A. chailletii – may also establish a symbiosis with wood wasps ( Siricidae ) , which beside freshly logged trees also infest living trees and infect them with fungi . Symbioses have been recorded with several species : Sirex noctilio , S. juvencus , S. nitobei , S. cyaneus , S. edwarsii , S. nitidus , and , in Japan , Urocerus antennatus and Xoanon matsumurae . Wasps of the genera Sirex and Urocerus store oidia ( the hypha of fungi split up to spores ) in special abdominal organs . The wood wasps infect trees by splashing a phytotoxic secretion below the bark and at the same time injecting fungal spores into the hole . The secretion weakens the tree and temporarily diminishes its immune system , whereby the fungus can spread along the xylem . The infection with Amylostereaceae fulfill two functions for the wasps : it provides the larvae food , because the white rot softens the wood ; at the same time , the mycelia of the fungi serves as food for the larvae . After the larvae pupate , it absorbs the mycelia of the Amylostereaceae into its body to oviposit together with its eggs . The fungus benefits from the symbiosis as it spreads faster and more effectively than through airborne spores and furthermore does not need to develop fruit bodies . A. ferreum is the only Amylosterum species that has not been associated with any woodwasps .
The host spectrum of the Amylostereaceae comprises several , partially very different genera of Coniferae . A. chailletii usually infests Pinaceae such as firs ( Abies ) and spruces ( Picea ) , but also cedars ( Cedrus ) and Douglas firs ( Pseudotsuga ) . A. areolatum has a similar host spectrum , which uses mainly firs , Japanese cedars ( Cryptomeria ) , larches ( Larix ) , spruces , pines ( Pinus ) and Douglas firs as hosts . While spruces dominate as hosts in the native habitat , this species is more common in pines on other locations . The host spectrum of A. laevigatum comprises Cupressaceae such as junipers ( Juniperus ) or cypresses ( Cupressus ) and the English yew ( Taxus baccata ) . A. ferreum is , however , only common on neotropic yellowwoods ( Podocarpus ) .
The Amylostereaceae are white rot pathogens . They disintegrate the lignin of the host wood , whereby the infested wood parts become less stable and take a fibrous structure . The wood bleaches as fungal enzymes break down and remove the brown @-@ pigmented lignin . The distribution in wood takes place mainly along the transport channels in the xylem . If the wood is crosscut , the red rot is vertically positioned , on which bleached , infested areas contrast with intact wood . Symptoms of infestion by the symbiotic partner — wood wasps — include circular exit holes in the crust and acute stress through dryness , common in hanging , falling or tanning needles .
In their native habitat , all Amylostereum species have a minor importance as forest pests . The infestation through wood wasps does not assume greater dimensions and is , compared with other pests , almost insignificant . The infection rates are even lower during sexual reproduction via fruit bodies , as the wasps do not play a part in the process . Furthermore , the Amylostereum fungi are alone often incapable of infesting healthy trees . They thus mostly act as saprobiontics . Pine monocultures in Australia , New Zealand , Africa and South America were shown to be susceptible to the Sirex woodwasp ( Sirex noctilio ) , which was introduced there and which is associated with A. areolatum . The wasp 's phytotoxic secretion , its larvae and the fungus combine very effectively with each other and contribute to forest decline rates of up to 80 % . This is mainly owing to the poor water and nutrient supply of the trees , which can poorly reconcile the drought stress caused by infestation . S. noctilio was detected in North America in the 2000s ( decade ) ; in Canada alone , the total economic loss to the forestry industry caused by the Sirex – Amylostereum symbiosis could be as high as $ 254 million per year for the next 20 years .
As a countermeasure , cultures of the nematode Deladenus siricidicola have been used as biological control to protect trees since the 1980s . This parasite feeds on the mycelia of A. areolatum and is therefore a food competitor of wood wasp larvae . Where S. noctilio larvae are present , the parasite infects and sterilizes the eggs of female wasps , causing them to be infertile . These infertile females lay infected eggs into new trees and thus spread the nematode . This control method has proven to be relatively successful to combat the Sirex – Amylostereum complex . In the Southern Hemisphere , where the technique has been widely employed , reductions of parasitism levels of 70 % – 100 % have been achieved .
Charles @-@ Valentin Alkan ( French : [ ʃaʁl valɑ ̃ tɛ ̃ alkɑ ̃ ] ; 30 November 1813 – 29 March 1888 ) was a French @-@ Jewish composer and virtuoso pianist . At the height of his fame in the 1830s and 1840s he was , alongside his friends and colleagues Frédéric Chopin and Franz Liszt , among the leading pianists in Paris , a city in which he spent virtually his entire life .
Alkan earned many awards at the Conservatoire de Paris , which he entered before he was six . His career in the salons and concert halls of Paris was marked by his occasional long withdrawals from public performance , for personal reasons . Although he had a wide circle of friends and acquaintances in the Parisian artistic world , including Eugène Delacroix and George Sand , from 1848 he began to adopt a reclusive life style , while continuing with his compositions – virtually all of which are for the keyboard . During this period he published , among other works , his collections of large @-@ scale studies in all the major keys ( Op. 35 ) and all the minor keys ( Op. 39 ) . The latter includes his Symphony for Solo Piano ( Op. 39 , nos . 4 – 7 ) and Concerto for Solo Piano ( Op. 39 , nos . 8 – 10 ) , which are often considered among his masterpieces and are of great musical and technical complexity . Alkan emerged from self @-@ imposed retirement in the 1870s to give a series of recitals that were attended by a new generation of French musicians .
Alkan 's attachment to his Jewish origins is displayed both in his life and his work . He was the first composer to incorporate Jewish melodies in art music . Fluent in Hebrew and Greek , he devoted much time to a complete new translation of the Bible into French . This work , like many of his musical compositions , is now lost . Alkan never married , but his presumed son Élie @-@ Miriam Delaborde was , like Alkan , a virtuoso performer on both the piano and the pedal piano , and edited a number of the elder composer 's works .