Download or read book The Luminosity Function for White Dwarfs in the SuperCOSMOS Sky Survey written by Nicholas Rowell and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Luminosity Function for White Dwarfs in the SuperCOSMOS Sky Survey written by Nicholas Robertson Rowell and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Hot White Dwarf Luminosity Function from the Sloan Digital Sky Survey written by Jurek Krzesiński and published by . This book was released on 2009 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aims. We present a hot white dwarf (WD) luminosity function (LF) using data taken from the Sloan Digital Sky Survey (SDSS) Data Release 4. We present and discuss a combined LF, along with separate DA and non-DA as LFs. We explore the completeness of our LFs and interpret a sudden drop in the non-DA LF near 2 M-bol as a transition of the non-DA WD atmosphere into the DA one during WD evolution. Our LF extends roughly between -0.5 M-bol 7 or equivalently, [around] 120 000 K T-eff '25 000 K. Our LF should now be useful for estimates of recent star formation and for studies of neutrino and other potential particle emission losses in hot WDs. Methods: To create a sample whose completeness can be characterized fully, we used stars whose spectra were obtained via the SDSS's 'hot standard' target selection criteria. The hot standard stars were purposefully targeted to a high level of completeness by the SDSS for calibration purposes. We are fortunate that many of them are hot white dwarfs stars. We further limited the sample to stars with fitted temperatures exceeding 23 500 K and log(g)> 7.0. We determined stellar distances for our sample based on their absolute SDSS g filter magnitudes, derived from WD stellar atmosphere model fits to the SDSS stellar spectra. Results: We compared our LF with those of other researchers where overlap occurs; however, our LFs are unique in their extension to the most luminous/hottest WDs. The cool end of our LF connects with the hot end of previously determined SDSS WD LFs and agreement here is quite good. It is also good with previous non-SDSS WD LFs. We note distinct differences between the DA and non-DA LFs and discuss the reliability of the DA LF at its hot end. We have extended the range of luminosities covered in the most recent WD LFs. The SDSS sample is understood quite well and its exploration should contribute to a number of new insights into early white dwarf evolution.
Download or read book Lettre l diteur de l Almanach des Muses written by and published by . This book was released on 1770 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book White Dwarf Luminosity Functions from Sloan Digital Sky Survey Spectra written by and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book White Dwarfs From the SDSS 90 Prime Goin Deep in the White Dwarf Luminosity Function written by and published by . This book was released on 2006 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: A large sample of cool white dwarfs from the Sloan Digital Sky Survey has been used to construct a luminosity function (LF), with the selection based on the method of reduced proper motion. While the sample is 60 times larger than that from our Luyten Half Second proper motion survey, its sensitivity to the region past the peak of the LF is severely limited by the necessity to match positions with detections from Palomar plates. A new survey to realize the full limiting magnitudes of the SDSS is described.
Download or read book Population Synthesis Studies of the White Dwarfs of the Galactic Disk and Halo written by Elena-Ruxandra Cojocaru and published by . This book was released on 2017 with total page 157 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the evolutionary end-point of most main-sequence stars, white dwarfs can be used to infer important properties concerning the formation and evolution of the different Galactic stellar populations. Population synthesis methods, when correlated with the excellent quality of modern white dwarf cooling tracks, can prove to be a powerful tool for further exploring the information offered by observed samples of white dwarfs. Possible applications may include estimating the age and history of stellar populations, measuring the local stellar formation rate and stellar density, constraining the local content of baryonic matter, examining intrinsic aspects of single and binary stellar evolution and exploring different progenitor scenarios for type Ia supernovae. In this thesis we studied the white dwarf populations of the Galactic disk and halo and our work was focused on four main objectives. The first was to analyze the effects of stellar metallicity on the white dwarf luminosity function of the Galactic disk. We use our Monte Carlo population synthesis code to produce synthetic samples of white dwarfs which we later compare to two relatively large observational samples, from the Sloan Digital Sky Survey (SDSS) and SuperCosmos Sky Survey (SSS). For each of the two cases, we implement the corresponding observational selection criteria. We first explore the impact of varying the fraction of white dwarfs with hydrogen-deficient atmospheres and of using alternative sets of cooling tracks. We then test different age-metallicity relations, considering the impact of progenitor metallicity throughout the entire evolution of the star. Our second objective was to determine the luminosity, mass and cumulative age functions derived from a sample of disk white dwarfs identified by the LAMOST Sky Survey of the Galactic Anti-Center. We initially compute the observed functions and then the theoretical ones, according to series of initial assumptions, using our population synthesis code. We derive values for the local space density and formation rate of hydrogen-rich white dwarfs and analyze the possible causes behind the apparent excess of massive white dwarfs identified in the observed mass function. The next objective of this thesis was to revisit the halo white dwarf luminosity function, modeling the halo white dwarf population using a self-consistent prescription for very low metallicity progenitors. We pass the synthetic sample through a series of filters that reproduce the selection criteria employed in culling the observed sample of halo white dwarfs from the SSS. Given that for very low-metallicity progenitors residual hydrogen burning can become a significant source of energy, we test two different sets of cooling tracks, one that incorporates residual hydrogen burning and another where this phenomenon is artificially ignored. Finally, our last study consisted in modeling the sample of white dwarf-main sequence binaries in the Galactic disk. We compare our simulations to the largest and most recent catalog of white dwarf-main sequence binaries from the SDSS and we provide a detailed account of observational biases and errors. We use this sample to constrain several important inputs for binary formation and evolution, namely the initial mass ratio distribution and the common envelope efficiency parameter. To conclude, the work presented in this thesis testifies to the versatility of using white dwarf populations for constraining different properties of the Galactic disk and halo. The methodology described here can be used in future studies of this kind, with a myriad of new applications, especially given than in the near future a noticeable improvement in terms of the size and quality of observed white dwarf catalogs is expected.
Download or read book White Dwarfs Advances in Observation and Theory written by M.A. Barstow and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 555 pages. Available in PDF, EPUB and Kindle. Book excerpt: The European Workshop on White Dwarfs was initiated by Prof. V. Weidemann, with the first meeting held in Kiel (FRG) in 1974. Since then a similar workshop has been held almost every two years: Frascati (1976), Tel Aviv (1978), Paris (1981), Kiel (1984), Frascati (1986) and Toulouse (1990). Two major IAU colloquia have also been devoted to the study of white dwarfs (No. 53, Rochester NY, 1979; No. 114, Hanover, NH, 1988). Our most recent meeting, the 8th Workshop, marks a number of important advances in both observational and theoretical studies of white dwarfs. This coincides with a significant expansion in the size of the community active in the field, as was clear from an increase in the number of participants between this workshop (77) and that in Toulouse (46), just two years ago. Key parts of any workshop are the discussion sessions following the pa pers. However, these are difficult to record and, very often, the 'live' flavour of the debates is lost. During this workshop we carried out an experiment, recording the discussion sessions on video tape and then transcribing these later for the proceedings. Although the recordings were made in non-studio conditions with regard to lighting and noise, only a very small part was unin telligible. All participants were given an opportunity to check their questions and answers for scientific accuracy and to correct any errors arising in the transcription process.
Download or read book White Dwarfs written by Domitilla de Martino and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 443 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of the NATO Advanced Research Workshop, held in Naples, Italy, 24-28 June 2002
Download or read book White Dwarfs Cosmological and Galactic Probes written by E. Sion and published by Springer Science & Business Media. This book was released on 2005-12-08 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: The emphasis on white dwarf stars and cosmology arises from the most recent advances in cosmological and galactic structure research in which white dwarf stars are playing a very prominent role. Examples are Type Ia supernovae (i.e. white dwarf supernovae), the origin and evolution of the universe, the age of the galactic disk, cosmochronology using white dwarfs in globular clusters and galactic clusters, and the physics of accretion onto compact (very dense) stars. As an assisting guide to the reader, we have included, by invitation, comprehensive review articles in each of the four major areas of the book, white dwarf supernovae, cosmology, accretion physics and galactic structure. The reviews include introductory material that they build upon. The book is suitable and most useful to advanced undergraduates, graduate students and scientific professionals (e.g. astronomers, astrophysicists, cosmologists, physicists).
Download or read book 14th European Workshop on White Dwarfs written by Detlev Koester and published by . This book was released on 2005 with total page 722 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book White Dwarfs written by Evry L. Schatzman and published by Springer Science & Business Media. This book was released on 1991 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: 1-Pre-White Dwarf Evolution and White Dwarf Cooling.- New pre-white dwarf evolutionary tracks.- Influence of the phase diagram in the cooling of white dwarfs.- PG1159 stars and the PNN-white dwarf connection.- Analysis of the soft X-ray data from the central star of NGC 7293.- Planetary Nebulae Nuclei with white dwarf spectra.- Atmospheric parameters of subluminous B stars.- White dwarf space densities and birth rates reconsidered.- A spectroscopic determination of the mass distribution of DA white dwarfs.- The age and formation of the Galaxy: clues from the white dwarf luminosity function.- Early results from the ROSAT Wide Field Camera.- The stellar component of the Hamburg Schmidt Survey.- White dwarfs in the Hamburg Schmidt Survey.- 2-Asteroseismology of White Dwarfs.- Asteroseismology of white dwarf stars with the Whole Earth Telescope.- A measurement of the evolutionary timescale of the cool white dwarf G117-B15A with WET.- On the interpretation of the dP/dt measurement in G117-B15A.- The boundaries of the ZZ Ceti instability strip.- Long term variations in ZZ Cetis: G191-16 and HL Tau 76.- Predicting the white dwarf light curves.- A wavelet analysis of the ZZ Ceti star G191 16.- An adiabatic survey for ZZ Ceti stars based on a finite element code.- A study of period change rates in post-AGB stars I. PG 1159-035.- Nonadiabatic nonradial pulsations for DAV white dwarf stars.- 3-Atmospheres and Envelopes.- NLTE Analysis of four PG1159 stars.- A search for trace amounts of hydrogen in DB stars.- Abundances of trace heavy elements in hot DA white dwarfs.- New results on radiative forces on iron in hot white dwarfs.- The effective temperature of the DBV's, and the sensitivity of DB model atmospheres to input physics.- The modified hydrostatic equilibrium equations for stratified high gravity stellar atmospheres.- The DBAQ G35-26.- LP 790-29: preliminary model atmospheres for this strongly polarized carbon white dwarf.- Some effect of the UV radiation from white dwarfs on the accretion of interstellar hydrogen.- Convection in white dwarfs: application of CM theory to helium envelope WDs.- Abundances in cool DZA and DAZ white dwarfs: new results using laboratory damping constants.- Evidence for fractionated accretion of metals on cool white dwarfs.- A new look at old friends: 40 Eri B and GD 323.- The Lyman Alpha line wing in hydrogen-rich white dwarf atmospheres.- Atmospheric parameters for DA white dwarfs in the vicinity of the ZZ Ceti instability strip.- Space Telescope observations of white dwarf stars.- 4-White Dwarfs in Binaries.- A deep spectroscopic survey of white dwarfs in common proper motion binaries.- Double degenerate common proper motion binaries.- Close binary white dwarfs.- New results on cataclysmic variable white dwarfs.- Whole Earth Telescope observations of the interacting white dwarf binary system AM CVn: first results.- IUE observations of V803 Cen in high and low states.- Whole Earth Telescope observations of PG1346+082.- On the origin of LMXRBS: the ONEMG case.
Download or read book TASPO Wissen written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book White Dwarfs written by International Astronomical Union and published by Springer Science & Business Media. This book was released on 1971-06-30 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of IAU Symposium 42, held at St. Andrews, Fife, Scotland, August 11-13, 1970
Download or read book A Photometric Search for White Dwarfs in Intermediate age Open Clusters written by Barbara Jean Anthony Twarog and published by . This book was released on 1983 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book White Dwarfs and the Ages of Stellar Populations written by Steven Andrew De Gennaro and published by . This book was released on 2009 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: Our group has developed a Bayesian modeling technique to determine the ages of stellar populations (in particular, open and globular clusters) using white dwarf (WD) cooling physics. As the theory of WD cooling is both simpler than, and essentially independent of, main sequence evolutionary theory, white dwarfs provide an independent measure of the ages of Galactic populations. We have developed a Bayesian technique that objectively incorporates our prior knowledge of stellar evolution, star cluster properties, and data quality estimates to derive posterior probability distributions for a cluster's age, metallicity, distance, and line-of-sight absorption, as well as the individual stellar parameters of mass, mass ratio (for unresolved binaries) and cluster membership probability. The key advantage of our Bayesian method is that we can calculate probability distributions for cluster and stellar parameters with reference only to known, quantifiable, objective, and repeatable quantities. In doing so, we also have more sensitivity to subtle changes in cluster isochrones than traditional "chi-by-eye'" cluster fitting methods. As a critical test of our Bayesian modeling technique, we apply it to Hyades UBV photometry, with membership priors based on proper motions and radial velocities, where available. We use secular parallaxes derived from Hipparcos proper motions via the moving cluster method to put all members of the Hyades at a common distance. Under the assumption of a particular set of WD cooling and atmosphere models, we estimate the age of the Hyades based on cooling white dwarfs to be 610 ± 110 Myr, consistent with the best prior analysis of the cluster main-sequence turn-off age (Perryman, et al. 1998). Since the faintest white dwarfs have most likely evaporated from the Hyades, prior work provided only a lower limit to the cluster's white dwarf age. Our result demonstrates the power of the bright white dwarf technique for deriving ages (Jeffery, et al. 2007) and further demonstrates complete age consistency between white dwarf cooling and main-sequence turn-off ages for seven out of seven clusters analyzed to date, ranging from 150 Myr to 4 Gyr. We then turn our attention to the white dwarf luminosity function. We use Sloan Digital Sky Survey (SDSS) data to create a white dwarf luminosity function with nearly an order of magnitude (3,358) more spectroscopically confirmed white dwarfs than any previous work. We determine the completeness of the SDSS spectroscopic white dwarf sample by comparing a proper-motion selected sample of WDs from SDSS imaging data with a large catalog of spectroscopically determined WDs. We derive a selection probability as a function of a single color (g-i) and apparent magnitude (g) that covers the range -1.0
Download or read book White Dwarf Luminosity Functions from the Pan STARRS1 3 Survey written by Marco Cheuk-Yin Lam and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
