scholarly journals GD 424 – a helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal

2020 ◽  
Author(s):  
Paula Izquierdo ◽  
Odette Toloza ◽  
Boris T Gänsicke ◽  
Pablo Rodríguez-Gil ◽  
Jay Farihi ◽  
...  
Keyword(s):  
Steady State ◽  
Effective Temperature ◽  
White Dwarf ◽  
Metal Pollution ◽  
White Dwarfs ◽  
Surface Gravity ◽  
Atmospheric Composition ◽  
Atmospheric Parameters ◽  
Hybrid Analysis ◽  
Helium Atmosphere

Abstract The photospheric metal pollution of white dwarfs is now well-established as the signature of the accretion of planetary debris. However, the origin of the trace hydrogen detected in many white dwarfs with helium atmospheres is still debated. Here, we report the analysis of GD 424: a metal-polluted, helium-atmosphere white dwarf with a large amount of trace hydrogen. We determined the atmospheric parameters using a hybrid analysis that combines the sensitivity of spectroscopy to the atmospheric composition, log (H/He), with that of photometry and astrometry to the effective temperature, Teff, and surface gravity, log g. The resulting white dwarf mass, radius, and cooling age are ${M_{\rm{WD}}}=0.77\pm 0.01\, {\rm{M}_{\odot}}$, ${R_{\rm{WD}}}=0.0109\pm 0.0001\, {\rm{R}_{\odot}}$, and τcool = 215 ± 10 Myr, respectively. We identified and measured the abundances of 11 photospheric metals and argue that the accretion event is most likely either in the increasing or steady state, and that the disrupted planetesimal resembles either CI chondrites or the bulk Earth in terms of its composition. We suggest that the observed 1.33 × 1022 g of trace hydrogen in GD 424 were at least partly acquired through accretion of water-rich planetary debris in an earlier accretion episode.

scholarly journals Some Properties of Hot, High-Gravity, Pure Helium Atmospheres

1979 ◽  
Vol 53 ◽  
pp. 125-129
Author(s):  
F. Wesemael ◽  
H.M. Van Horn
Keyword(s):  
Effective Temperature ◽  
White Dwarf ◽  
White Dwarfs ◽  
Model Atmosphere ◽  
Surface Gravity ◽  
High Gravity ◽  
Pure Helium

Model atmosphere analyses of white dwarf spectra have contributed significantly to our understanding of the properties of degenerate stars.: In particular, the pioneering investigations of Bues (1970), Strittmatter and Wickramasinghe (1971) and Shipman (1972) have provided the first reliable determinations of the effective temperature and surface gravity of these objects (see Shipman 1979 and Weidemann 1978 for recent results). We now know with certainty that the hydrogen-rich white dwarf sequence extends at least over the range Te ∽ 6000 – 60.000K. In contrast, the hottest identified helium-rich white dwarfs seem to reach Te ~ 25.000K only, a puzzling result since the progenitors of DB white dwarfs should presumably also be helium-rich.

scholarly journals An Isolated White Dwarf with a 70 s Spin Period

2021 ◽  
Vol 923 (1) ◽  
pp. L6
Author(s):  
Mukremin Kilic ◽  
Alekzander Kosakowski ◽  
Adam G. Moss ◽  
P. Bergeron ◽  
Annamarie A. Conly
Keyword(s):  
White Dwarf ◽  
High Speed ◽  
White Dwarfs ◽  
Tangential Velocity ◽  
Large Mass ◽  
Atmospheric Composition ◽  
Instability Strip ◽  
Detailed Model ◽  
Helium Atmosphere ◽  
Spin Period

Abstract We report the discovery of an isolated white dwarf with a spin period of 70 s. We obtained high-speed photometry of three ultramassive white dwarfs within 100 pc and discovered significant variability in one. SDSS J221141.80+113604.4 is a 1.27 M ⊙ (assuming a CO core) magnetic white dwarf that shows 2.9% brightness variations in the BG40 filter with a 70.32 ± 0.04 s period, becoming the fastest spinning isolated white dwarf currently known. A detailed model atmosphere analysis shows that it has a mixed hydrogen and helium atmosphere with a dipole field strength of B d = 15 MG. Given its large mass, fast rotation, strong magnetic field, unusual atmospheric composition, and relatively large tangential velocity for its cooling age, J2211+1136 displays all of the signatures of a double white dwarf merger remnant. Long-term monitoring of the spin evolution of J2211+1136 and other fast-spinning isolated white dwarfs opens a new discovery space for substellar and planetary mass companions around white dwarfs. In addition, the discovery of such fast rotators outside of the ZZ Ceti instability strip suggests that some should also exist within the strip. Hence, some of the monoperiodic variables found within the instability strip may be fast-spinning white dwarfs impersonating ZZ Ceti pulsators.

scholarly journals 14. White Dwarf Atmospheres

1971 ◽  
Vol 42 ◽  
pp. 81-96 ◽  
Author(s):  
V. Weidemann
Keyword(s):  
Chemical Composition ◽  
Observational Data ◽  
Effective Temperature ◽  
White Dwarf ◽  
General Information ◽  
Stellar Atmospheres ◽  
Surface Gravity ◽  
Atmospheric Parameters

We first consider the general information scheme for the interpretation of observational data (Figure 1). From the relations plotted it is evident that (in going from left to right) this scheme can only be solved if distances are known and if we are able to determine the atmospheric parameters: effective temperature, Teff, surface gravity, g, and chemical composition from observations of colors and spectra – which is the genuine task of the theory of stellar atmospheres.

scholarly journals 3D spectroscopic analysis of helium-line white dwarfs

2020 ◽  
Author(s):  
Elena Cukanovaite ◽  
Pier-Emmanuel Tremblay ◽  
Pierre Bergeron ◽  
Bernd Freytag ◽  
Hans-Günter Ludwig ◽  
...  
Keyword(s):  
Effective Temperature ◽  
White Dwarfs ◽  
Energy Transport ◽  
3D Models ◽  
Spectroscopic Technique ◽  
Surface Gravity ◽  
Atmospheric Models ◽  
Physical Treatment ◽  
Spectroscopic Parameters ◽  
1D Model

Abstract In this paper, we present corrections to the spectroscopic parameters of DB and DBA white dwarfs with −10.0 ≤ log (H/He) ≤−2.0, 7.5 ≤ log g ≤9.0 and 12 000 K ≲ Teff ≲ 34 000 K, based on 282 3D atmospheric models calculated with the CO5BOLD radiation-hydrodynamics code. These corrections arise due to a better physical treatment of convective energy transport in 3D models when compared to the previously available 1D model atmospheres. By applying the corrections to an existing SDSS sample of DB and DBA white dwarfs, we find significant corrections both for effective temperature and surface gravity. The 3D log g corrections are most significant for Teff ≲ 18, 000 K, reaching up to −0.20 dex at log g = 8.0. However, in this low effective temperature range, the surface gravity determined from the spectroscopic technique, can also be significantly affected by the treatment of the neutral van der Waals line broadening of helium and by non-ideal effects due to the perturbation of helium by neutral atoms. Thus, by removing uncertainties due to 1D convection, our work showcases the need for improved description of microphysics for DB and DBA model atmospheres. Overall, we find that our 3D spectroscopic parameters for the SDSS sample are generally in agreement with Gaia DR2 absolute fluxes within 1-3σ for individual white dwarfs. By comparing our results to DA white dwarfs, we determine that the precision and accuracy of DB/DBA atmospheric models are similar. For ease of user application of the correction functions, we provide an example Python code.

scholarly journals Tidal circularization of gaseous planets orbiting white dwarfs

2019 ◽  
Vol 489 (2) ◽  
pp. 2941-2953 ◽  
Author(s):  
Dimitri Veras ◽  
Jim Fuller
Keyword(s):  
Phase Space ◽  
White Dwarf ◽  
Metal Pollution ◽  
White Dwarfs ◽  
Thermal Destruction ◽  
Giant Planet ◽  
Giant Planets ◽  
Potential Source ◽  
Mode Excitation ◽  
Coupled Constraints

ABSTRACT A gas giant planet which survives the giant branch stages of evolution at a distance of many au and then is subsequently perturbed sufficiently close to a white dwarf will experience orbital shrinkage and circularization due to star–planet tides. The circularization time-scale, when combined with a known white dwarf cooling age, can place coupled constraints on the scattering epoch as well as the active tidal mechanisms. Here, we explore this coupling across the entire plausible parameter phase space by computing orbit shrinkage and potential self-disruption due to chaotic f-mode excitation and heating in planets on orbits with eccentricities near unity, followed by weakly dissipative equilibrium tides. We find that chaotic f-mode evolution activates only for orbital pericentres which are within twice the white dwarf Roche radius, and easily restructures or destroys ice giants but not gas giants. This type of internal thermal destruction provides an additional potential source of white dwarf metal pollution. Subsequent tidal evolution for the surviving planets is dominated by non-chaotic equilibrium and dynamical tides which may be well-constrained by observations of giant planets around white dwarfs at early cooling ages.

scholarly journals Constraints on the Atmospheric Parameters of the Binary DA White Dwarf L870-2 (EG11)

1989 ◽  
Vol 114 ◽  
pp. 435-439
Author(s):  
P. Bergeron ◽  
F. Wesemael ◽  
J. Liebert ◽  
G. Fontaine ◽  
P. Lacombe
Keyword(s):  
Observational Data ◽  
Stellar Evolution ◽  
Effective Temperature ◽  
White Dwarf ◽  
Binary Systems ◽  
Absolute Magnitude ◽  
Atmospheric Parameters ◽  
Spectroscopic Binary ◽  
Short Period ◽  
Period System

The recent discovery that the cool DA white dwarf L870-2 (EG11, WD0135-052) is a double-lined spectroscopic binary composed of a detached pair of DA white dwarfs (Saffer, Liebert, and Olszewski 1988, SLO hereafter) has raised some challenging problems for stellar evolution theories of such binary systems. One first important step in the understanding of this short-period system is to establish the atmospheric parameters of each component. SLO have argued from previous determinations of the effective temperature and absolute magnitude of the system, and also from their own study of the composite Hα profile, that the two components should be similar. We wish here to reexamine this assertion by taking a new look at the constraints on the two components brought about by the available observational data.

Observation of a Variable, ZZ Ceti White Dwarf: GD154

1993 ◽  
Vol 134 ◽  
pp. 201-204
Author(s):  
B. Pfeiffer ◽  
G. Vauclair ◽  
N. Dolez ◽  
M. Chevreton ◽  
J. R. Fremy ◽  
...  
Keyword(s):  
Time Scales ◽  
Effective Temperature ◽  
White Dwarf ◽  
White Dwarfs ◽  
Nonlinear Phenomena ◽  
Instability Strip ◽  
Temperature Range

The ZZ Ceti stars form a class of variable white dwarfs: the hydrogen dominated atmosphere ones, which do pulsate in an instability strip in the effective temperature range 13000K-11500K. We know 22 such ZZ Ceti white dwarfs. Their variations are caused by nonradial g-mode pulsations with periods are in the range 100-1000 seconds.A subsample of the ZZ Ceti stars shows amplitude variations on time scales of the order of one month. These variations could be driven by nonlinear phenomena.

scholarly journals The lifetimes of planetary debris discs around white dwarfs

2020 ◽  
Vol 496 (2) ◽  
pp. 2292-2308 ◽  
Author(s):  
Dimitri Veras ◽  
Kevin Heng
Keyword(s):  
Steady State ◽  
White Dwarf ◽  
White Dwarfs ◽  
Input Parameter ◽  
Evolutionary Constraints ◽  
Minor Planets ◽  
Evolutionary Models ◽  
Tidal Disruption ◽  
Different Types ◽  
Break Up

ABSTRACT The lifetime of a planetary disc that orbits a white dwarf represents a crucial input parameter into evolutionary models of that system. Here we apply a purely analytical formalism to estimate lifetimes of the debris phase of these discs, before they are ground down into dust or are subject to sublimation from the white dwarf. We compute maximum lifetimes for three different types of white dwarf discs, formed from (i) radiative YORP break-up of exo-asteroids along the giant branch phases at 2–100 au, (ii) radiation-less spin-up disruption of these minor planets at ${\sim} 1.5\!-\!4.5\, \mathrm{R}_{\odot }$, and (iii) tidal disruption of minor or major planets within about $1.3\, \mathrm{R}_{\odot }$. We display these maximum lifetimes as a function of disc mass and extent, constituent planetesimal properties, and representative orbital excitations of eccentricity and inclination. We find that YORP discs with masses of up to 1024 kg live long enough to provide a reservoir of surviving cm-sized pebbles and m- to km-sized boulders that can be perturbed intact to white dwarfs with cooling ages of up to 10 Gyr. Debris discs formed from the spin or tidal disruption of these minor planets or major planets can survive in a steady state for up to, respectively, 1 or 0.01 Myr, although most tidal discs would leave a steady state within about 1 yr. Our results illustrate that dust-less planetesimal transit detections are plausible, and would provide particularly robust evolutionary constraints. Our formalism can easily be adapted to individual systems and future discoveries.

scholarly journals 18. Model Atmospheres for Hydrogen-Deficient White Dwarfs

1971 ◽  
Vol 42 ◽  
pp. 125-129
Author(s):  
I. Bues
Keyword(s):  
Effective Temperature ◽  
White Dwarfs ◽  
Atmospheric Parameters ◽  
Metal Abundances ◽  
Different Parts

The determination of atmospheric parameters for non-DA white dwarfs is investigated with the computed helium-rich model atmospheres by Bues (1970). Only poor predictions are possible from UBV colors alone for DB and DC stars. From uvby colors a determination of effective temperature is possible within 1000 K. Profiles of lines in different parts of the spectrum are necessary for better results.A deficiency of metal abundances for the cooler non-DA stars is obtained.

scholarly journals The High Resolution Spectrum of the Pulsating, Pre-White Dwarf Star PG 1159-035 (GW VIR)

1989 ◽  
Vol 114 ◽  
pp. 384-387
Author(s):  
James Liebert ◽  
F. Wesemael ◽  
D. Husfeld ◽  
R. Wehrse ◽  
S. G. Starrfield ◽  
...  
Keyword(s):  
High Resolution ◽  
Effective Temperature ◽  
White Dwarf ◽  
White Dwarfs ◽  
High Resolution Spectrum ◽  
Dwarf Star ◽  
Dwarf Stars ◽  
New Class ◽  
White Dwarf Stars ◽  
Nonradial Pulsation

First reported at the IAU Colloquium No. 53 on White Dwarfs (McGraw et al. 1979), PG 1159-035 (GW Vir) is the prototype of a new class of very hot, pulsating, pre-white dwarf stars. It shows complicated, nonradial pulsation modes which have been studied exhaustively, both observationally and theoretically. The effective temperature has been crudely estimated as 100,000 K with log g ~ 7 (Wesemael, Green and Liebert 1985, hereafter WGL).

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