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  • richardmitnick 12:43 pm on December 19, 2018 Permalink | Reply
    Tags: , , , , , White dwarfs   

    From astrobites: “Hunting for Variable White Dwarfs in the GALEX Archives” 

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    From astrobites

    Title: Detections and Constraints on White Dwarf Variability from Time-Series GALEX Observations
    Authors: Dominick M. Rowan, Michael A. Tucker, Benjamin J. Shappee, and J.J. Hermes
    First Author’s Institution: Institute for Astronomy, University of Hawaii, Honolulu, USA

    U Hawaii Institute for Astronomy


    Status: Submitted to MNRAS, open access

    1
    Figure 1: A plot of brightness against colour for stars that were observed by the Gaia satellite. White dwarf candidates that were selected for today’s paper are shown by the coloured points. Source: Figure 1 in today’s paper.

    White dwarfs are stars in their silver years. 97% of all stars will end their lives as white dwarfs. These stars have stopped all fusion in their cores and are powered by left-over heat from their younger lives. It’s easy to think of white dwarfs as ‘dead stars’, doing nothing but hanging in space while they slowly cool. However, these stars have plenty of activity left in them. Some white dwarfs pulsate: instabilities in their atmospheres cause them to shrink and stretch in size. Studying these pulsations can tell us about the internal structure of a white dwarf. Other white dwarfs are in binary systems and undergo eclipses when their companion star blocks their light from reaching us. Studying these eclipses can help us accurately measure the masses and radii of the two stars. And some white dwarfs have their own planetary systems, which collide, rip themselves apart and shower the white dwarf with debris. These can help us study the composition of planets and give us an insight into planetary systems in the late stages of their lives.

    See the full article here .


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    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 5:40 am on August 30, 2018 Permalink | Reply
    Tags: Astronomers use Hubble to 'weigh' Dog Star's companion, , , , , , , Red shift, White dwarfs   

    From Hubble via Manu: “Astronomers use Hubble to ‘weigh’ Dog Star’s companion” 


    From Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.

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    From NASA/ESA Hubble Telescope

    13 December 2005
    Martin Barstow
    University of Leicester, United Kingdom
    Tel: +44-11-44-116-252-3492
    Cell: +44-776-62-333-62
    E-mail: mab@star.le.ac.uk or

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    Space Telescope Science Institute, Baltimore, USA
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    Jay Holberg, Lunar Planetary Lab, Tucson, USA
    Tel: +1-520-621-4571
    E-mail: holberg@argus.lpl.arizona.edu

    1
    White dwarfs are important to theories of both stellar and cosmological evolution. New results published in the Monthly Notices of the Royal Astronomical Society provide for the first time an accurate measurement of the weight of the nearest white dwarf, Sirius B, companion of the brightest star in the sky. It turns out that Sirius’s companion, despite being smaller than the Earth, has a mass that is 98% that of our own Sun.

    2
    This picture is an artist’s impression showing how the binary star system of Sirius A and its diminutive blue companion, Sirius B, might appear to an interstellar visitor. The large, bluish-white star Sirius A dominates the scene, while Sirius B is the small but very hot and blue white-dwarf star on the right. The two stars revolve around each other every 50 years. White dwarfs are the leftover remnants of stars similar to our Sun. The Sirius system, only 8.6 light-years from Earth, is the fifth closest stellar system known. Sirius B is faint because of its tiny size. Its diameter is only 7,500 miles (about 12 thousand kilometres), slightly smaller than the size of our Earth. The Sirius system is so close to Earth that most of the familiar constellations would have nearly the same appearance as in our own sky. In this rendition, we see in the background the three bright stars that make up the Summer Triangle: Altair, Deneb, and Vega. Altair is the white dot above Sirius A; Deneb is the dot to the upper right; and Vega lies below Sirius B. But there is one unfamiliar addition to the constellations: our own Sun is the second-magnitude star, shown as a small dot just below and to the right of Sirius A. Credit: NASA, ESA and G. Bacon (STScI)

    3
    Based on the Hubble measurements made with the Space Telescope Imaging Spectrograph, an international team found that Sirius B has a mass that is 98 percent that of our own Sun. Despite this large mass Sirius B is only 12,000 kilometers in diameter, making it smaller than even the Earth and much denser. Sirius B’s powerful gravitational field is 350,000 times greater than Earth’s, meaning that a 68 kilogram person would weigh 25 million kilograms standing on its surface. Credit: NASA/ESA Hubble

    4
    This picture is an artist’s impression showing how the binary star system of Sirius A and its diminutive blue companion, Sirius B, might appear to an interstellar visitor. The large, bluish-white star Sirius A dominates the scene, while Sirius B is the small but very hot and blue white-dwarf star on the right. The two stars revolve around each other every 50 years. White dwarfs are the leftover remnants of stars similar to our Sun. The Sirius system, only 8.6 light-years from Earth, is the fifth closest stellar system known. Sirius B is faint because of its tiny size. Its diameter is only 7,500 miles (about 12 thousand kilometres), slightly smaller than the size of our Earth. The Sirius system is so close to Earth that most of the familiar constellations would have nearly the same appearance as in our own sky. In this rendition, we see in the background the three bright stars that make up the Summer Triangle: Altair, Deneb, and Vega. Altair is the white dot above Sirius A; Deneb is the dot to the upper right; and Vega lies below Sirius B. But there is one unfamiliar addition to the constellations: our own Sun is the second-magnitude star, shown as a small dot just below and to the right of Sirius A. Credit: NASA, ESA and G. Bacon (STScI)

    For astronomers, it’s always been a source of frustration that the nearest white-dwarf star is buried in the glow of the brightest star in the nighttime sky. This burned-out stellar remnant is a faint companion of the brilliant blue-white Dog Star, Sirius, located in the winter constellation Canis Major.

    Now, an international team of astronomers has used the keen eye of the NASA/ESA Hubble Space Telescope to isolate the light from the white dwarf, called Sirius B. The new results allow them to measure precisely the white dwarf’s mass based on how its intense gravitational field alters the wavelengths of light emitted by the star.

    “Studying Sirius B has challenged astronomers for more than 140 years,” said Martin Barstow of the University of Leicester, U.K., who is the leader of the observing team. “Only with Hubble have we at last been able to obtain the observations we need, uncontaminated by the light from Sirius, in order to measure its change in wavelengths.”

    “Accurately determining the masses of white dwarfs is fundamentally important to understanding stellar evolution. Our Sun will eventually become a white dwarf. White dwarfs are also the source of Type Ia supernova explosions that are used to measure cosmological distances and the expansion rate of the universe.

    A white dwarf fed by a normal star reaches the critical mass and explodes as a type Ia supernova. Credit: NASA/CXC/M Weiss

    Measurements based on Type Ia supernovae are fundamental to understanding ‘dark energy,’ a dominant repulsive force stretching the universe apart.

    Dark energy depiction. Image: Volker Springle/Max Planck Institute for Astrophysics/SP)

    MPG Institute for Astrophysics

    Standard Candles to measure age and distance of the universe NASA

    Also, the method used to determine the white dwarf’s mass relies on one of the key predictions of Einstein’s theory of General Relativity; that light loses energy when it attempts to escape the gravity of a compact star.”

    Sirius B has a diameter of 12,000 kilometres, less than the size of Earth, but is much denser. Its powerful gravitational field is 350,000 times greater than Earth’s, meaning that a 68 kilogram person would weigh 25 million kilograms standing on its surface. Light from the surface of the hot white dwarf has to climb out of this gravitational field and is stretched to longer, redder wavelengths of light in the process. This effect, predicted by Einstein’s theory of General Relativity in 1916, is called gravitational redshift, and is most easily seen in dense, massive, and hence compact objects whose intense gravitational fields warp space near their surfaces.

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Red shift and evidence for an expanding universe spiff.rit.edu

    Astronomical Red shift Imaging the Universe University of Iowa

    Red shift and wave length shift-The Earliest Stars And Galaxies In The Universe Science at ESA

    Based on the Hubble measurements of the redshift, made with the Space Telescope Imaging Spectrograph, the team found that Sirius B has a mass that is 98 percent that of our own Sun. Sirius itself has a mass of two times that of the Sun and a diameter of 2.4 million kilometres.

    NASA/ESA Hubble Space Telescope Imaging Spectrograph

    White dwarfs are the leftover remnants of stars similar to our Sun. They have exhausted their nuclear fuel sources and have collapsed down to a very small size. Despite being the brightest white dwarf known, Sirius B is about 10,000 times fainter than Sirius itself, making it difficult to study with telescopes on the Earth’s surface because its light is swamped in the glare of its brighter companion. Astronomers have long relied on a fundamental theoretical relationship between the mass of a white dwarf and its diameter. The theory predicts that the more massive a white dwarf, the smaller its diameter. The precise measurement of Sirius B’s gravitational redshift allows an important observational test of this key relationship.

    The Hubble observations have also refined the measurement of Sirius B’s surface temperature to be 25,000 degrees C. Sirius itself has a surface temperature of 10,000 degrees C.

    At 8.6 light-years away, Sirius is one of the nearest known stars to Earth. Stargazers have watched Sirius since antiquity. Its diminutive companion, however, was not discovered until 1862, when it was first glimpsed by astronomers examining Sirius through one of the most powerful telescopes of that time.

    See the full article here .


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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 1:28 pm on January 9, 2018 Permalink | Reply
    Tags: , , , , , White dwarf’s inner makeup is mapped for the first time, White dwarfs   

    From ScienceNews: “White dwarf’s inner makeup is mapped for the first time” 

    ScienceNews

    January 8, 2018
    Lisa Grossman

    The stellar corpse is richer in oxygen than expected, challenging long-standing theories about stellar evolution.

    1
    WHAT LIES WITHIN The inner structure of a white dwarf star (shown in this artist’s impression) has been mapped for the first time — and it’s more oxygen-rich than expected. Stéphane Charpinet.

    Astronomers have probed the inner life of a dead star. Tiny changes in a white dwarf’s brightness reveal that the stellar corpse has more oxygen in its core than expected, researchers report online January 8 in Nature. The finding could challenge theories of how stars live and die, and may have implications for measuring the expansion of the universe.

    As a star ages, it sheds most of its gas into space until all that remains is a dense core of carbon and oxygen, the ashes of a lifetime of burning helium (SN: 4/30/16, p. 12). That core, plus a thin shellacking of helium, is called a white dwarf.

    But the proportion of those elements relative to one another was uncertain. “From theory, we have a rough idea of how it’s supposed to be, but we have no way to measure it directly,” says astrophysicist Noemi Giammichele, now at the Institute of Research in Astrophysics and Planetology in Toulouse, France.

    Luckily, some white dwarfs encode their inner nature on their surface. These stars change their brightness in response to internal vibrations. Astrophysicists can infer a star’s internal structure from the vibrations, similar to how geologists learn about Earth’s interior by measuring seismic waves during an earthquake.

    Giammichele and her colleagues used data from NASA’s Kepler space telescope, which watched stars unblinkingly to track periodic changes in their brightness. Kepler’s chief aim was to find exoplanets, the worlds orbiting distant stars (SN Online: 10/31/17). But it also monitored white dwarf KIC 08626021, located 1,375 light-years away in the constellation Cygnus, for 23 months. The observations provided the highest-precision data ever on tiny changes in a white dwarf’s brightness and, indirectly, its vibrations.

    Next, Giammichele borrowed a computer simulation technique from her former life as an aeronautical engineer to figure out how the changes in vibrations related to the makeup of the core. The team ran millions of simulations, looking for one that reproduced the exact light changes that Kepler observed. One simulation fit the data perfectly, showing that the white dwarf had the expected carbon and oxygen core with a thin shell of helium.

    But the details were surprising. The core was about 86 percent oxygen, 15 percent greater than physicists had previously calculated. That suggests that something about the processes that convert helium to carbon and oxygen or mix elements in the star’s core during its active lifetime must boost the amount of oxygen.

    Four other white dwarfs show a similar trend, says study coauthor Gilles Fontaine, an astrophysicist at the University of Montreal. “We certainly will go ahead and analyze many more.” If other white dwarfs turn out to be similar, the results will send theorists who study stellar evolution back to the drawing board, he says.

    White dwarfs are also thought to be the precursors of type 1a supernovas. These catastrophic stellar explosions were once thought to have the same intrinsic brightness, meaning they appeared brighter or dimmer depending only on their distance from Earth. Measuring their actual distances led to the discovery that the universe is expanding at an accelerating rate (SN: 8/6/16, p. 10), which physicists explain by invoking a mysterious substance called dark energy.

    More recent observations suggest that these so-called standard candles may not be so standard after all. If the white dwarfs that help create supernovas have varying oxygen contents, that may help explain some of the differences, Fontaine says.

    Accounting for that difference may someday help reveal details of what dark energy is made of, says astrophysicist Alexei Filippenko of the University of California, Berkeley. But those implications are a long way off. “Just how much bearing it will have on cosmology remains to be seen,” he says.

    See the full article here .

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  • richardmitnick 3:26 pm on October 5, 2017 Permalink | Reply
    Tags: , , , , NAOJ Cray XC30 ATERUI, , , , White dwarfs   

    From NOAJ Subaru: “Surface Helium Detonation Spells End for White Dwarf” 

    NAOJ

    NAOJ

    October 4, 2017
    No writer credit

    An international team of researchers has found evidence that the brightest stellar explosions in our Universe could be triggered by helium nuclear detonation near the surface of a white dwarf star. Using Hyper Suprime-Cam mounted on the Subaru Telescope, the team detected a type Ia supernova within a day after the explosion, and explained its behavior through a model calculated using the supercomputer ATERUI.

    NAOJ Cray XC30 ATERUI, installed in the NAOJ Mizusawa campus

    1
    Figure 1: A type Ia supernova detected within a day after exploding. Taken with Hyper Suprime-Cam mounted on the Subaru Telescope. Figure without the labels is linked here. (Credit: University of Tokyo/NAOJ)

    NAOJ Subaru Hyper Suprime-Cam

    Some stars end their lives with a huge explosion called a supernova. The most famous supernovae are the result of a massive star exploding, but a white dwarf, the remnant of an intermediate mass star like our Sun, can also explode. This can occur if the white dwarf is part of a binary star system. The white dwarf accretes material from the companion star, then at some point, it might explode as a type Ia supernova.

    Because of the uniform and extremely high brightness (about 5 billion times brighter than the Sun) of type Ia supernovae, they are often used for distance measurements in astronomy. However, astronomers are still puzzled by how these explosions are ignited. Moreover, these explosions only occur about once every 100 years in any given galaxy, making them difficult to catch.

    An international team of researchers led by Ji-an Jiang, a graduate student of the University of Tokyo, and including researchers from the University of Tokyo, the Kavli Institute for the Physics and Mathematics of the Universe (IPMU), Kyoto University, and the National Astronomical Observatory of Japan (NAOJ), tried to solve this problem. To maximize the chances of finding a type Ia supernova in the very early stages, the team used Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope, a combination which can capture an ultra-wide area of the sky at once. Also they developed a system to detect supernovae automatically in the heavy flood of data during the survey, which enabled real-time discoveries and timely follow-up observations.

    They discovered over 100 supernova candidates in one night with Subaru/Hyper Suprime-Cam, including several supernovae that had only exploded a few days earlier. In particular, they captured a peculiar type Ia supernova within a day of it exploding. Its brightness and color variation over time are different from any previously-discovered type Ia supernova. They hypothesized this object could be the result of a white dwarf with a helium layer on its surface. Igniting the helium layer would lead to a violent chain reaction and cause the entire star to explode. This peculiar behavior can be totally explained with numerical simulations calculated using the supercomputer ATERUI. “This is the first evidence that robustly supports a theoretically predicted stellar explosion mechanism!” said Jiang.

    This result is a step towards understand the beginning of type Ia supernovae. The team will continue to test their theory against other supernovae, by detecting more and more supernovae just after the explosion. The details of their study are to be published in Nature on October 5, 2017 (Jiang et al. 2017, A hybrid type la supernova with an early flash triggered by helium-shell detonation, Nature).

    See the full article here .

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    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

    NAOJ Subaru Telescope

    NAOJ Subaru Telescope interior
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    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

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    Solar Flare Telescope

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    Nobeyama Solar Radio Telescope Array
    Nobeyama Radio Observatory: Solar

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    Okayama Astrophysical Observatory

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

     
  • richardmitnick 2:20 pm on July 17, 2017 Permalink | Reply
    Tags: , , , , , White dwarfs   

    From astrobotes: “How well do we measure the radii of white dwarfs?” 

    Astrobites bloc

    Astrobites

    Jul 17, 2017
    Ingrid Pelisoli

    Title: Testing the white dwarf mass-radius relationship with eclipsing binaries
    Authors: S. G. Parsons, B. T. Gänsicke, T. R. Marsh et al.
    First Author’s Institution: Department of Physics and Astronomy, University of Sheffield, UK

    Status: Accepted to MNRAS [open access]

    Look outside your window. Can you see the Sun? If it’s night-time, just pick a random star instead. Our Sun one day will become a white dwarf star, and the chance that the random star you’ve picked will follow the same path is over 95%. White dwarfs are by far the most common final evolutionary state for a star. The famous supernovas actually only occur when a star is massive enough to burn elements heavier than helium in its core, and that is usually not the case. What happens instead is that the star can only produce elements up to carbon and oxygen, and then nuclear reactions in the core cease to occur. With no release of energy to counteract the gravitational force, the carbon-oxygen core will contract more and more until it becomes degenerate. This degenerate core is essentially the white dwarf, which becomes visible when the outer layers of the star are ejected on its final breadth of hydrogen burning in outer shells.

    What does it mean to be degenerate?

    Degenerate matter occurs in stars when the density is so high that all the electrons are cramped in lower energy states. But there’s a catch: due to the Pauli exclusion principle, only two fermions, e.g. electrons, can occupy the same energy level. So other electrons end up in higher energy states and cannot move to already filled lower energy levels. This makes degenerate matter very resistible to compression, and is in fact what keeps white dwarfs from collapsing.

    Degenerate matter has a really cool property: the pressure does not depend on temperature. This is because the kinetic energies of these electrons that cannot move to lower states of energy are quite high, and the rate of collisions between electrons and other particles is quite low, so the electrons essentially travel at the speed of light. The pressure on the gas depends on this speed. As the speed of light is the fastest the electrons can travel, adding heat will not change the pressure at all. This has an effect somewhat counter-intuitive. As the only way to increase pressure is by adding mass, when you increase pressure you also increase gravity and make the particles become spaced closer together, so the object becomes smaller. In other words, the more massive the white dwarf, the smaller its radius. As a consequence of this weird property of degenerate matter, there’s a relationship between a white dwarf’s mass and its radius, so that if you know one you can estimate the other and the other way around. But how accurate is this mass-radius relationship? Today’s paper authors decided to test!

    Obtaining mass and radius independently

    Despite being widely used, the mass-radius relationship remained untested observationally until this paper. That is because there aren’t many ways to estimate the mass of a white dwarf without relying on this relationship at some point. What the authors realised is that we can use eclipsing binary stars for that. Eclipsing binaries orbit in a plane which intersects our line of sight, allowing us to detect dips in light when the stars transit in front of each other. For these objects, we can combine photometric and spectroscopic measurements to estimate the mass and the radius independently.

    The shape of the eclipses of the white dwarfs by their companions, which in this paper are all main-sequence stars, gives us two pieces of information: the width and the duration of the eclipses. However, there’s an issue: we have three unknown quantities, namely the orbital inclination and the radius of each star. So we need one more piece of information to be able to determine all the unknowns.

    The authors suggest different methods, but what works best in their sample is to use the gravitational redshift estimated from spectroscopy. As the gravity in white dwarfs is really high (about 350,000 times the gravity of Earth!), light gets shifted a measurable amount towards the red when it exits the white dwarf, as it was delayed. The amount of redshift depends on the mass and radius of the white dwarf. Combining that with Kepler’s third law, we obtain a relationship between the white dwarf’s radius and the binary inclination. All we need is to estimate the radial velocity semi-amplitudes for both stars, hence the necessity of spectroscopy, which was also used to constrain the effective temperature of the white dwarf. Going back to Kepler’s third law with the estimated inclination, we can also estimate the mass of the white dwarf.

    So the combined fit of the light curve and the radial velocities of both stars, together with Kepler’s law and the known relation for gravitational shift, give us the mass and the radius without having to recur to the mass-radius relationship. Just the independent measure we needed!

    The results

    Figure 1 shows the comparison between the values the authors obtained with the theoretical models for different temperatures. Black lines are for the more common C/O core white dwarfs, while green lines are for white dwarfs with a He core. He-core white dwarfs are less massive and are formed when the outer envelope is lost by the progenitor star before helium is even ignited. They would be formed by lower mass stars that do not achieve conditions to burn helium, but the Universe is not old enough for them to have evolved off the main sequence just yet, so this objects are explained by some form of enhanced mass loss (such as binary evolution). As the analysed white dwarfs have different temperatures and core compositions, is difficult to define how the results agree with the theory based on this figure.

    1
    Figure 1: Comparison between mass and radius obtained from observations, represented by the red data points, and theoretical mass-radius relationships for different effective temperatures. Black lines assume a C/O core and green lines assume a He core. [Adapted from figure 9 in the paper.]

    Instead, the authors analyse what we see in Figure 2, which is the ratio between the radii estimated observationally and using the mass-radius relationship as a function of mass. Below 0.5 solar masses, the authors assume both a relationship assuming a He core and a C/O core. The first result is that white dwarfs with masses below 0.5 solar masses are more consistent with a He core, which agrees with our theories of stellar evolution. However, this is the first time we have direct observational evidence for that.

    2
    Figure 2: Ratio of the estimated white dwarf radii to theoretical predictions as a function of mass. Below 0.5 solar masses, black points assume a C/O core white dwarf and red points assume a He core white dwarf. Almost all radius measurement at this range are more consistent with He core. [Figure 10 in the paper.]

    Another interesting test the authors made was to compare surface gravities obtained from their fit to the spectra and derived from the mass and radius obtained from the light curves. Fitting spectra is the most widely used method to obtain the physical parameters of a white dwarf, so testing this independently is important to check we are basing our science in correct estimates. As Figure 3 shows, in most cases there’s excellent agreement between the results, but there are a few outliers where the spectral fit overestimates the gravity. In most of these cases, this disagreement can easily be explained by contamination from the companion. There’s one exception where the white dwarf dominates the spectrum so contamination from the companion is not enough to cause the discrepancy, but for this one the discrepancy is only at a 2-sigma level. Additional broadening mechanisms, such as magnetic fields, might be the cause for that.

    3
    Figure 3: Comparison between surface gravities estimated from spectral fits, and those computed from the mass and radius values obtained from the light curves. [Figure 13 in the paper.]

    Why does it matter?

    The authors came to conclude that both our mass-radius relationship and spectral modelling are quite good at estimating the properties of white dwarfs. This result is important not only for those directly interested in white dwarfs, but has also implications for cosmology. The radius of a white dwarf is related to its cooling rate, which depends on its surface area. As you can read on this bite, the cooling times of white dwarfs can be used to estimate the ages of different stellar populations. The mass-radius relationship also sets an upper limit to the mass of a white dwarf, which is an important result to the study of type Ia supernovae, which in turn are used to measure the expansion of the Universe.

    Now that we know that our theoretical models are doing a good job, we can keep doing cool science with them!

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
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