The white dwarf mass-radius relation with Gaia, Hubble and FUSE

2017 ◽  
Vol 12 (S330) ◽  
pp. 301-304
Author(s):  
Simon R. G. Joyce ◽  
Martin A. Barstow ◽  
Sarah L. Casewell ◽  
Jay B. Holberg ◽  
Howard E. Bond
Keyword(s):  
Star Formation ◽  
High Precision ◽  
White Dwarf ◽  
White Dwarfs ◽  
Distance Measurements ◽  
Theoretical Mass ◽  
History Of

AbstractWhite dwarfs are becoming useful tools for many areas of astronomy. They can be used as accurate chronometers over Gyr timescales. They are also clues to the history of star formation in our galaxy. Many of these studies require accurate estimates of the mass of the white dwarf. The theoretical mass-radius relation is often invoked to provide these mass estimates. While the theoretical mass-radius relation is well developed, observational tests of this relation show a much larger scatter in the results than expected. High precision observational tests to confirm this relation are required. Gaia is providing distance measurements which will remove one of the main source of uncertainty affecting most previous observations. We combine Gaia distances with spectra from the Hubble and FUSE satelites to make precise tests of the white dwarf mass-radius relation.

scholarly journals The Luminosity Function and Evolution of Cool White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 146-164 ◽  
Author(s):  
James Liebert
Keyword(s):  
Star Formation ◽  
White Dwarf ◽  
White Dwarfs ◽  
Luminosity Function ◽  
List Type ◽  
Type Number ◽  
Atmospheric Parameters ◽  
Theoretical Interest ◽  
History Of ◽  
Cool White Dwarfs

In the review, I attempt to focus on what we have recently learned from the observations about three general topics of great theoretical interest: 1. evidence for evolution of white dwarf surface abundances,2. the special problems of determining atmospheric parameters and abundances at the cool end of the sequence, and3. evidence for a peaking of the white dwarf luminosity function at Mbol = + 15 ± 1, with possible implications for cooling theory and the history of galactic star formation.

scholarly journals An Example Demonstrating the Potential for Asteroseismology of DB White Dwarf Stars

1993 ◽  
Vol 139 ◽  
pp. 116-116
Author(s):  
P.A. Bradley ◽  
M.A. Wood
Keyword(s):  
Internal Structure ◽  
Stellar Evolution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Galactic Disk ◽  
Helium Surface ◽  
Dwarf Stars ◽  
University Of Texas ◽  
White Dwarf Stars ◽  
History Of

AbstractWe present the results of a parametric survey of evolutionary models of compositionally stratified white dwarfs with helium surface layers (DB white dwarfs). Because white dwarfs are the most common final end state of stellar evolution, determining their internal structure will offer us many clues about stellar evolution, the physics of matter under extreme conditions, plus the history of star formation and age of the local Galactic disk. As a first step towards determining the internal structure of DB white dwarf stars, we provide a comprehensive set of theoretical g-mode pulsation periods for comparison to observations.Because DB white dwarfs have a layered structure consisting of a helium layer overlying the carbon/oxygen core, some modes will have the same wavelength as the thickness of the helium layer, allowing a resonance to form. This resonance is called mode trapping (see Brassard et al. 1992 and references therein) and has directly observable consequences, because modes at or near the resonance have eigenfunctions and pulsation periods that are similar to each other. This results in much smaller period spacings between consecutive overtone modes of the same spherical harmonic index than the uniform period spacings seen between non-trapped modes. We demonstrate with an example how one can use the distribution of pulsation periods to determine the total stellar mass, the mass of the helium surface layer, and the extent of the helium/carbon and carbon/oxygen transition zones. With these tools, we have the prospect of being able to determine the structure of the observed DBV white dwarfs, once the requisite observations become available.We are grateful to C.J. Hansen, S.D. Kawaler, R.E. Nather, and D.E. Winget for their encouragement and many discussions. This research was supported by the National Science Foundation under grants 85-52457 and 90-14655 through the University of Texas and McDonald Observatory.

scholarly journals Optical detection of the rapidly spinning white dwarf in V1460 Her

2021 ◽  
Author(s):  
Ingrid Pelisoli ◽  
R T Marsh ◽  
R P Ashley ◽  
Pasi Hakala ◽  
A Aungwerojwit ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Binary Systems ◽  
Hubble Space Telescope ◽  
Cataclysmic Variable ◽  
Optical Photometry ◽  
Arrival Times ◽  
Precise Ephemeris ◽  
History Of

Abstract Accreting magnetic white dwarfs offer an opportunity to understand the interplay between spin-up and spin-down torques in binary systems. Monitoring of the white dwarf spin may reveal whether the white dwarf spin is currently in a state of near-equilibrium, or of uni-directional evolution towards longer or shorter periods, reflecting the recent history of the system and providing constraints for evolutionary models. This makes the monitoring of the spin history of magnetic white dwarfs of high interest. In this paper we report the results of a campaign of follow-up optical photometry to detect and track the 39 sec white dwarf spin pulses recently discovered in Hubble Space Telescope data of the cataclysmic variable V1460 Her. We find the spin pulsations to be present in g-band photometry at a typical amplitude of 0.4 per cent. Under favourable observing conditions, the spin signal is detectable using 2-meter class telescopes. We measured pulse-arrival times for all our observations, which allowed us to derive a precise ephemeris for the white dwarf spin. We have also derived an orbital modulation correction that can be applied to the measurements. With our limited baseline of just over four years, we detect no evidence yet for spin-up or spin-down of the white dwarf, obtaining a lower limit of $|P/\dot{P}| > 4\times 10^{7}$ years, which is already 4 to 8 times longer than the timescales measured in two other cataclysmic variable systems containing rapidly rotating white dwarfs, AE Aqr and AR Sco.

New Developments in Hot White Dwarf Models

1996 ◽  
Vol 152 ◽  
pp. 185-192
Author(s):  
Detlev Koester
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Theoretical Models ◽  
Short History ◽  
New Developments ◽  
Present Generation ◽  
History Of ◽  
Atomic Lines

A short history of EUV observations of white dwarfs is presented, and how they have forced us to use increasingly sophisticated theoretical models—starting from blackbody spectra up to the present generation of NLTE models which include the blanketing effect of millions of atomic lines.

Ultra-high precision white dwarf asteroseismology

2015 ◽  
Vol 11 (A29B) ◽  
pp. 596-599
Author(s):  
Noemi Giammichele ◽  
Stéphane Charpinet ◽  
Gilles Fontaine ◽  
Pierre Brassard ◽  
Weikai Zong
Keyword(s):  
High Precision ◽  
Parameter Space ◽  
White Dwarf ◽  
White Dwarfs ◽  
Optimization Procedure ◽  
Progress Report ◽  
Point Of View ◽  
Evolutionary Models ◽  
Period Data ◽  
Seismic Models

AbstractWe present a brief progress report in our quest for deriving seismic models of pulsating white dwarfs that can account simultaneously for all the observed periods at the precision of the observations. We point out that this is possible from a pratical point of view only if parametrized models are used to complement evolutionary models. We adopt a double optimization procedure that insures that the best possible model in parameter space is found objectively and automatically. Our ultimate goal is to be able to account for the exquisite period data gathered withKeplerandKepler-2on key pulsating white dwarfs of both the DA (ZZ Ceti) and DB (V777 Her) type.

scholarly journals The Whole Earth Telescope

1989 ◽  
Vol 114 ◽  
pp. 109-114 ◽  
Author(s):  
R. Edward Nather
Keyword(s):  
Star Formation ◽  
Light Curve ◽  
Early Universe ◽  
White Dwarf ◽  
Dwarf Stars ◽  
Detailed History ◽  
White Dwarf Stars ◽  
Observational Technique ◽  
History Of ◽  
Whole Earth

AbstractThe history of our galaxy and the detailed history of star formation in the early universe is written in the white dwarf stars. Recently we have learned how to reach beneath their exposed surfaces by observing white dwarfs that are intrinsic variables. We use the stellar equivalent of seismology to probe their interiors, and thus to unravel the history they hold inside. We have designed and placed into operation an observational technique that uses the whole earth as a telescope platform, defeating the effects of daylight which, until now, had seriously limited the length of a single light curve, and therefore the amount of information we could hope to extract from it. This paper describes our new telescope and presents preliminary results from our first observing run in March, 1988.

scholarly journals The Internal Structure of White Dwarf Stars Using the Whole Earth Telescope

1993 ◽  
Vol 139 ◽  
pp. 117-119
Author(s):  
P.A. Bradley
Keyword(s):  
Internal Structure ◽  
Stellar Evolution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
History Of ◽  
The Way ◽  
Whole Earth

AbstractWhite dwarfs are the final end state for the majority of stars, and hold clues to help solve many current pressing astrophysical problems. We can perform asteroseismology on the pulsating white dwarfs to better understand their internal structure and input physics, paving the way to a better understanding of astrophysics, stellar evolution, and the history of our Galaxy. I describe briefly the potential of asteroseismology by using it to infer the internal structure of PG1159-035.

scholarly journals Identification of Cool White Dwarfs in the Sloan Digital Sky Survey

2000 ◽  
Vol 176 ◽  
pp. 514-514 ◽  
Author(s):  
T. S. Metcalfe ◽  
A. Mukadam ◽  
D. E. Winget ◽  
X. Fan ◽  
M. A. Strauss ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Luminosity Function ◽  
Galactic Disk ◽  
Sloan Digital Sky Survey ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
The Galaxy ◽  
History Of ◽  
Cool White Dwarfs

AbstractWe are searching for the coolest white dwarf stars in the galactic disk and halo. The Sloan survey, in due course, will identify an enormous number of new white dwarf stars which will better define the white dwarf luminosity function—an important tool for understanding the age and history of the stellar population of the galaxy. The broadband filter data obtained in the digital photometry phase of the survey will not permit identification of the most interesting of these, the coolest white dwarf stars. This is because the cool main sequence and subdwarf stars become indistinguishable from the white dwarfs in the various colorcolor diagrams. We have interference filters designed to separate out these classes of objects. We have obtained photometry of test fields to complement the Sloan data and identify the population of cool white dwarf stars. These data will ultimately resolve the controversies, based for the most part on small-number statistics, of the location of the turndown in the white dwarf luminosity function for the disk. If the halo is significantly older than the disk, we will find a second peak in the white dwarf luminosity function, at lower luminosities than the disk turndown. Our data will provide the first meaningful constraints on the location of the turndown in the halo white dwarf luminosity function.

The Space Density of Hot White Dwarfs

1983 ◽  
Vol 5 (2) ◽  
pp. 230-232
Author(s):  
Neill Reid ◽  
D.T. Wickramasinghe ◽  
M.S. Bessell
Keyword(s):  
Star Formation ◽  
Observational Studies ◽  
White Dwarfs ◽  
Luminosity Function ◽  
Birth Rate ◽  
Main Sequence ◽  
Mass Density ◽  
Statistical Significance ◽  
Space Density ◽  
History Of

The space density of degenerate stars is an important parameter in Galactic Structure studies, not only because white dwarfs represent a significant fraction of the local mass density, but also because they act as tracers of the history of star formation (see e.g., Bessell 1978). Combining the present day luminosity function with theoretical cooling tracks allows constraints to be set on the birth rate of main sequence progenitors. However, since white dwarfs are intrinsically low luminosity objects, observational studies are hampered by difficulties in defining complete samples large enough to have statistical significance. This paper discusses preliminary results from one method of tackling this problem.

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