scholarly journals The Low State Temperature Distribution and First Chemical Abundances of White Dwarfs in Polars

2004 ◽  
Vol 190 ◽  
pp. 2-7
Author(s):  
Edward M. Sion
Keyword(s):  
Temperature Distribution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Heating And Cooling ◽  
Cyclotron Emission ◽  
Far Ultraviolet ◽  
Optical Brightness

AbstractDuring the low optical brightness states of AM Her systems (polars) when accretion has declined to a very low value, the underlying magnetic white dwarf photosphere can be modelled without the complication of thermal bremstrahlung and cyclotron emission from the luminous accretion column. The far ultraviolet spectra can be modelled with high gravity Solar composition photospheres. In this way, I present new temperatures and the first chemical abundance estimates for the white dwarfs in three selected polars from the IUE NEWSIPS archive. For the white dwarf in V834 Cen with Teff = 16,000K, Si/H = 0.1 Solar, C/H = 0.5 Solar, for BY Cam, Teff = 17,000K, Si/H = 0.1, C/H = 5 Solar and for RX J1313-32, Teff = 22,000K, Si/H = 0.1 Solar, C/H = 0.1 Solar. The temperature distribution of 24 white dwarfs in polars with known temperatures above and below the period gap is compared with the distribution of the white dwarf temperatures in dwarf novae during quiescence. In both cases, the magnetic white dwarfs in polars are significantly cooler than the non-magnetics. For all CV white dwarfs, magnetic and non-magnetic with Teff < 12,500K, 91% of the objects (10 out of 11) are magnetics in polars. This suggests that long term accretion heating and cooling of white dwarfs in polars differs from the effects of long term accretion in non-magnetic disk accretors.

scholarly journals The Effective Temperature Distribution Function of Cataclysmic Variable White Dwarfs

1987 ◽  
Vol 93 ◽  
pp. 47-51
Author(s):  
E.M. Sion
Keyword(s):  
Distribution Function ◽  
Temperature Distribution ◽  
Orbital Period ◽  
White Dwarf ◽  
White Dwarfs ◽  
Cataclysmic Variables ◽  
Cataclysmic Variable ◽  
Term Evolution ◽  
Effective Temperatures

AbstractWith the recent detection of direct white dwarf photospheric radiation from certain cataclysmic variables in quiescent (low accretion) states, important implications and clues about the nature and long-term evolution of cataclysmic variables can emerge from an analysis of their physical properties. Detection of the underlying white dwarfs has led to a preliminary empirical CV white dwarf temperature distribution function and, in a few cases, the first detailed look at a freshly accreted while dwarf photosphere. The effective temperatures of CV white dwarfs plotted versus orbital period for each type of CV appears to reveal a tendency for the cooler white dwarf primaries to reside in the shorter period systems. Possible implications are briefly discussed.

scholarly journals White Dwarfs in Cataclysmic Variables: An Update

2015 ◽  
Vol 2 (1) ◽  
pp. 35-40
Author(s):  
E. M. Sion ◽  
P. Godon
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Cataclysmic Variables ◽  
Chemical Abundances ◽  
Rotation Rates ◽  
Surface Temperatures ◽  
Accretion Rates ◽  
Magnetic Cataclysmic Variables ◽  
Far Ultraviolet ◽  
Nova Outburst

In this review, we summarize what is currently known about the surface temperatures of accreting white dwarfs in nonmagnetic and magnetic cataclysmic variables (CVs) based upon synthetic spectral analyses of far ultraviolet data. We focus only on white dwarf surface temperatures, since in the area of chemical abundances, rotation rates, WD masses and accretion rates, relatively little has changed since our last review, pending the results of a large HST GO program<br />involving 48 CVs of different CV types. The surface temperature of the white dwarf in SS Cygni is re-examined in the light of its revised distance. We also discuss new HST spectra of the recurrent nova T Pyxidis as it transitioned into quiescence following its April 2011 nova outburst.

scholarly journals Nova Explosion of Mass Accreting White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 529-529 ◽  
Author(s):  
Ken’ichi Nomoto ◽  
Kyoji Nariai ◽  
Daiichiro Sugimoto
Keyword(s):  
Temperature Distribution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Accretion Rate ◽  
Thermal Structure ◽  
Stellar Surface

Evolution of a mass accreting white dwarf has been computed from the onset of accretion through nova explosion. We have considered a white dwarf of 1.3M⊙ with the accretion rate of 1×10-10M⊙ yr-1. Because the thermal structure during the accretion phase has been fully taken into computation, the mass of the accreted hydrogen-rich envelope and the corresponding temperature distribution in the envelope have been determined. When the hydrogen-rich envelope of mass ΔMH = 1.63 × 10-4M⊙ has been formed, a hydrogen-shell flashes commences. The flashing shell lies midway between the bottom of the envelope and the stellar surface; the mass lying above this shell is 5.7 × 10-5M⊙

scholarly journals A far-UV survey of three hot, metal-polluted white dwarf stars: WD0455−282, WD0621−376, and WD2211−495

2019 ◽  
Vol 487 (3) ◽  
pp. 3470-3487 ◽  
Author(s):  
Simon P Preval ◽  
Martin A Barstow ◽  
Matthew Bainbridge ◽  
Nicole Reindl ◽  
Thomas Ayres ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Hubble Space Telescope ◽  
Line Of Sight ◽  
Hot Metal ◽  
Dwarf Stars ◽  
High Resolution Data ◽  
White Dwarf Stars ◽  
Order Of Magnitude ◽  
Far Ultraviolet

ABSTRACT Using newly obtained high-resolution data (R ∼ 1 × 105) from the Hubble Space Telescope, and archival UV data from the Far Ultraviolet Spectroscopic Explorer, we have conducted a detailed UV survey of the three hot, metal-polluted white dwarfs WD0455−282, WD0621−376, and WD2211−495. Using bespoke model atmospheres, we measured Teff, log g, and photospheric abundances for these stars. In conjunction with data from Gaia, we measured masses, radii, and gravitational redshift velocities for our sample of objects. We compared the measured photospheric abundances with those predicted by radiative levitation theory, and found that the observed Si abundances in all three white dwarfs, and the observed Fe abundances in WD0621−376 and WD2211−495, were larger than those predicted by an order of magnitude. These findings imply not only an external origin for the metals, but also ongoing accretion, as the metals not supported by radiative levitation would sink on extremely short time-scales. We measured the radial velocities of several absorption features along the line of sight to the three objects in our sample, allowing us to determine the velocities of the photospheric and interstellar components along the line of sight for each star. Interestingly, we made detections of circumstellar absorption along the line of sight to WD0455−282 with three velocity components. To our knowledge, this is the first such detection of multicomponent circumstellar absorption along the line of sight to a white dwarf.

Variable white dwarfs

2019 ◽  
Vol 15 (S357) ◽  
pp. 107-109
Author(s):  
H. L. Shipman
Keyword(s):  
Present State ◽  
White Dwarf ◽  
White Dwarfs ◽  
Long Term Evolution ◽  
Surface Layers ◽  
Dwarf Stars ◽  
Comprehensive View ◽  
White Dwarf Stars ◽  
Term Evolution

AbstractAsteroseismology of white dwarf stars has led to a number of interesting results pertaining to the long term evolution and present state of white dwarf interiors. I will review recent results and will give a not necessarily comprehensive view of the prospects for further progress in this area. Two – but only two white dwarf stars - have shown the expected cooling as they age. Careful observations of a few white dwarfs with rich pulsational properties reveal interior compositions as well as the thickness of their surface layers. A few very well observed stars have revealed changes in their pulsational spectra which we don’t understand yet.

scholarly journals Middle- and Far-Ultraviolet Observations of Hot White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 109-113
Author(s):  
S. B. Parsons ◽  
J. D. Wray ◽  
K. G. Henize
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Dwarf Star ◽  
Low Resolution ◽  
Objective Prism ◽  
Far Ultraviolet ◽  
Ultraviolet Observations

Several hot subluminous stars were first recognized as such from low-resolution spectra obtained with the ultraviolet objective-prism survey from Skylab, Experiment S-019. About 9 percent of the sky was photographed, 3 percent with unwidened spectra. Two hot subdwarf stars have been reported previously, HDE 283048 (Laget et al. 1978) and the companion to HR 3080 (Parsons et al. 1976a). Papers on two other subdwarfs are in preparation. One previously unrecognized white dwarf star was found, HD 149499 B, and new observations (Wray, Parsons and Henize 1979) show it to be probably the hottest white dwarf known.

scholarly journals Bayesian constraints on the origin and geology of exo-planetary material using a population of externally polluted white dwarfs

2021 ◽  
Author(s):  
John H D Harrison ◽  
Amy Bonsor ◽  
Mihkel Kama ◽  
Andrew M Buchan ◽  
Simon Blouin ◽  
...  
Keyword(s):  
Solar System ◽  
White Dwarf ◽  
Bayesian Model ◽  
Total Mass ◽  
White Dwarfs ◽  
Bulk Composition ◽  
Planetary Systems ◽  
The Moon ◽  
Planetary Bodies ◽  
Nearby Stars

Abstract White dwarfs that have accreted planetary bodies are a powerful probe of the bulk composition of exoplanetary material. In this paper, we present a Bayesian model to explain the abundances observed in the atmospheres of 202 DZ white dwarfs by considering the heating, geochemical differentiation, and collisional processes experienced by the planetary bodies accreted, as well as gravitational sinking. The majority (&gt;60%) of systems are consistent with the accretion of primitive material. We attribute the small spread in refractory abundances observed to a similar spread in the initial planet-forming material, as seen in the compositions of nearby stars. A range in Na abundances in the pollutant material is attributed to a range in formation temperatures from below 1,000 K to higher than 1,400 K, suggesting that pollutant material arrives in white dwarf atmospheres from a variety of radial locations. We also find that Solar System-like differentiation is common place in exo-planetary systems. Extreme siderophile (Fe, Ni or Cr) abundances in 8 systems require the accretion of a core-rich fragment of a larger differentiated body to at least a 3σ significance, whilst one system shows evidence that it accreted a crust-rich fragment. In systems where the abundances suggest that accretion has finished (13/202), the total mass accreted can be calculated. The 13 systems are estimated to have accreted masses ranging from the mass of the Moon to half that of Vesta. Our analysis suggests that accretion continues for 11Myrs on average.

scholarly journals Direct detection of atomic dark matter in white dwarfs

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
David Curtin ◽  
Jack Setford
Keyword(s):  
Dark Matter ◽  
Energy Loss ◽  
Cooling Rate ◽  
White Dwarf ◽  
White Dwarfs ◽  
Luminosity Function ◽  
Direct Detection ◽  
Matter Density ◽  
Mixing Parameter ◽  
First Time

Abstract Dark matter could have a dissipative asymmetric subcomponent in the form of atomic dark matter (aDM). This arises in many scenarios of dark complexity, and is a prediction of neutral naturalness, such as the Mirror Twin Higgs model. We show for the first time how White Dwarf cooling provides strong bounds on aDM. In the presence of a small kinetic mixing between the dark and SM photon, stars are expected to accumulate atomic dark matter in their cores, which then radiates away energy in the form of dark photons. In the case of white dwarfs, this energy loss can have a detectable impact on their cooling rate. We use measurements of the white dwarf luminosity function to tightly constrain the kinetic mixing parameter between the dark and visible photons, for DM masses in the range 10−5–105 GeV, down to values of ϵ ∼ 10−12. Using this method we can constrain scenarios in which aDM constitutes fractions as small as 10−3 of the total dark matter density. Our methods are highly complementary to other methods of probing aDM, especially in scenarios where the aDM is arranged in a dark disk, which can make direct detection extremely difficult but actually slightly enhances our cooling constraints.

scholarly journals Absorption by Cyclotron Harmonics in the Optical Spectrum of VV Puppis

1979 ◽  
Vol 53 ◽  
pp. 334-340 ◽  
Author(s):  
H.S. Stockman ◽  
James Liebert ◽  
Howard E. Bond
Keyword(s):  
White Dwarf ◽  
Optical Spectrum ◽  
Cyclotron Frequency ◽  
Theoretical Models ◽  
Doppler Broadening ◽  
Cyclotron Emission ◽  
Optical Continuum ◽  
Cyclotron Harmonics ◽  
Accretion Shock ◽  
Depth Effects

Most theoretical models of the AM Her variables (AM Her, AN UMa, W Pup and 2A0311-22) rely on strong cyclotron emission at the fundamental cyclotron frequency and higher harmonics to produce the observed, strongly-polarized optical continuum (e.g. Lamb and Masters 1979). The cyclotron lines, which presumably originate in the hot, isothermal accretion shock at the surface of the white dwarf (kT ≳ 10 keV, h/R* ≲ 0.1), should be blurred into a continuous spectrum by both optical depth effects and electron Doppler broadening. Thus the lack of even weak cyclotron features in the optical spectra of these objects is still compatible with a cyclotron origin.

scholarly journals The most massive white dwarfs in the solar neighbourhood

2021 ◽  
Vol 503 (4) ◽  
pp. 5397-5408
Author(s):  
Mukremin Kilic ◽  
P Bergeron ◽  
Simon Blouin ◽  
A Bédard
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Transverse Velocity ◽  
Maximum Mass ◽  
Model Calculations ◽  
Rapid Rotation ◽  
Rotation Rates ◽  
Binary Mergers ◽  
Chandrasekhar Limit

ABSTRACT We present an analysis of the most massive white dwarf candidates in the Montreal White Dwarf Database 100 pc sample. We identify 25 objects that would be more massive than $1.3\, {\rm M}_{\odot }$ if they had pure H atmospheres and CO cores, including two outliers with unusually high photometric mass estimates near the Chandrasekhar limit. We provide follow-up spectroscopy of these two white dwarfs and show that they are indeed significantly below this limit. We expand our model calculations for CO core white dwarfs up to M = 1.334 M⊙, which corresponds to the high-density limit of our equation-of-state tables, ρ = 109 g cm−3. We find many objects close to this maximum mass of our CO core models. A significant fraction of ultramassive white dwarfs are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. We identify four outliers in transverse velocity, four likely magnetic white dwarfs (one of which is also an outlier in transverse velocity), and one with rapid rotation, indicating that at least 8 of the 25 ultramassive white dwarfs in our sample are likely merger products.

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