scholarly journals Asteroseismological analysis of the ultra-massive ZZ Ceti stars BPM 37093, GD 518, and SDSS J0840+5222

2019 ◽  
Vol 632 ◽  
pp. A119
Author(s):  
Alejandro H. Córsico ◽  
Francisco C. De Gerónimo ◽  
María E. Camisassa ◽  
Leandro G. Althaus
Keyword(s):  
Chemical Composition ◽  
White Dwarf ◽  
White Dwarfs ◽  
Intrinsic Property ◽  
Stellar Mass ◽  
Evolutionary Origin ◽  
Instability Strip ◽  
Single Star ◽  
The Core ◽  
Effective Temperatures

Context. Ultra-massive (≳1 M⊙) hydrogen-rich (DA) white dwarfs are expected to have a substantial portion of their cores in a crystalline state at the effective temperatures characterising the ZZ Ceti instability strip (Teff ∼ 12 500 K) as a result of Coulomb interactions in very dense plasmas. Asteroseismological analyses of these white dwarfs can provide valuable information related to the crystallisation process, the core chemical composition, and the evolutionary origin of these stars. Aims. We present a thorough asteroseismological analysis of the ultra-massive ZZ Ceti star BPM 37093, which exhibits a rich period spectrum, on the basis of a complete set of fully evolutionary models that represent ultra-massive oxygen/neon (ONe) core DA white dwarf stars harbouring a range of hydrogen (H) envelope thicknesses. We also carry out preliminary asteroseismological inferences on two other ultra-massive ZZ Ceti stars that exhibit fewer periods, GD 518, and SDSS J0840+5222. Methods. We considered g-mode adiabatic pulsation periods for ultra-massive ONe-core DA white dwarf models with stellar masses in the range 1.10 ≲ M⋆/M⊙ ≲ 1.29, effective temperatures in the range 10 000 ≲ Teff ≲ 15 000 K, and H-envelope thicknesses in the interval −10 ≲ log(MH/M⋆)≲ − 6. We explored the effects of employing different H-envelope thicknesses on the mode-trapping properties of our ultra-massive ONe-core DA white dwarf models and performed period-to-period fits to ultra-massive ZZ Ceti stars with the aim of finding an asteroseismological model for each target star. Results. We find that the trapping cycle and trapping amplitude are larger for thinner H envelopes, and that the asymptotic period spacing is longer for thinner H envelopes. We find a mean period spacing of ΔΠ ∼ 17 s in the data of BPM 37093, which is likely to be associated with ℓ = 2 modes. However, we are not able to put constraints on the stellar mass of BPM 37093 using this mean period spacing due to the simultaneous sensitivity of ΔΠ with M⋆, Teff, and MH, which is an intrinsic property of DAV stars. We find asteroseismological models for the three objects under analysis, two of them (BPM 37093 and GD 518) characterised by canonical (thick) H envelopes, and the third one (SDSS J0840+5222) with a thinner H envelope. The effective temperature and stellar mass of these models are in agreement with the spectroscopic determinations. The percentage of crystallised mass for these asteroseismological models is 92%, 97%, and 81% for BPM 37093, GD 518, and SDSS J0840+5222, respectively. We also derive asteroseismological distances which differ somewhat from the astrometric measurements of Gaia for these stars. Conclusions. Asteroseismological analyses like the one presented in this paper could lead to a more complete understanding of the processes occurring during crystallisation inside white dwarfs. Also, such analyses could make it possible to deduce the core chemical composition of ultra-massive white dwarfs and, in this way, to infer their evolutionary origin, such as the correlation between a star’s ONe core and its having originated through single-star evolution or a carbon/oxygen (CO) core indicating the star is the product of a merger of the two components of a binary system. However, in order to achieve these objectives, it is necessary to find a greater number of pulsating ultra-massive WDs and to carry out additional observations of known pulsating stars to detect more pulsation periods. Space missions such as TESS can provide a great boost towards achieving these aims.

scholarly journals 11. Effective Temperatures of White Dwarfs

1971 ◽  
Vol 42 ◽  
pp. 67-76 ◽  
Author(s):  
J. B. Oke ◽  
H. L. Shipman
Keyword(s):  
Chemical Composition ◽  
White Dwarf ◽  
White Dwarfs ◽  
Dwarf Stars ◽  
Evolved Stars ◽  
White Dwarf Stars ◽  
Effective Temperatures ◽  
Highly Evolved

White dwarf stars are among the most challenging and interesting objects which can be studied. Because they represent the interiors of highly-evolved stars, the chemical composition can be enormously variable from object to object. Furthermore, because of the very large gravities, the composition of the atmosphere may be very different from that in the interior. The theory of the degenerate interior provides a relation among mass, radius and chemical composition. Since temperatures, effective gravities, and redshifts can, for certain stars, provide further relations between mass and radius, one can hope to make checks on the theory which are not possible with ordinary stars.

scholarly journals Searching for ZZ Ceti white dwarfs in the Gaia survey

2019 ◽  
Vol 15 (S357) ◽  
pp. 123-126
Author(s):  
Olivier Vincent ◽  
Pierre Bergeron ◽  
David Lafrenière
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Physical Parameters ◽  
Hydrogen Line ◽  
Instability Strip ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Effective Temperatures

AbstractThe Gaia satellite recently released parallax measurements for nearly 400,000 white dwarf stars, allowing for precise measurements of their physical parameters. By combining these parallaxes with Pan-STARRS and CFIS-u photometry, we measured the effective temperatures and surface gravities for all white dwarfs within 100 pc and identified a sample of ZZ Ceti white dwarf candidates within the instability strip. We report the results of a photometric follow-up, currently under way, aimed at identifying new ZZ Ceti stars among this sample using the PESTO camera attached to the 1.6-m telescope at the Mont Mégantic Observatory. Our goal is to verify that ZZ Ceti stars occupy a region in the logg-Teff plane where no nonvariable stars are found, supporting the idea that ZZ Ceti pulsators represent a phase through which all hydrogen-line (DA) white dwarfs must evolve.

scholarly journals White Dwarf Seismology at the Université de Montréal

1993 ◽  
Vol 139 ◽  
pp. 120-120
Author(s):  
G. Fontaine ◽  
P. Brassard ◽  
P. Bergeron ◽  
F. Wesemael
Keyword(s):  
Specific Heat ◽  
Cooling Rate ◽  
Internal Structure ◽  
White Dwarf ◽  
White Dwarfs ◽  
Period Change ◽  
Core Material ◽  
The Core ◽  
Core Composition ◽  
Chemical Stratification

Over the last several years, we have developed a comprehensive program aimed at better understanding the properties of pulsating DA white dwarfs (or ZZ Ceti stars). These stars are nonradial pulsators of the g-type, and their study can lead to inferences about their internal structure. For instance, the period spectrum of a white dwarf is most sensitive to its vertical chemical stratification, and one of the major goals of white dwarf seismology is to determine the thickness of the hydrogen layer that sits on top of a star. This can be done, in principle, by comparing in detail theoretical period spectra with the periods of the observed excited modes. Likewise, because the cooling rate of a white dwarf is very sensitive to the specific heat of its core material (and hence to its composition), it is possible to infer the core composition through measurements and interpretations of rates of period change in a pulsator.

scholarly journals 19. Convection Zones and Coronae of White Dwarfs

1971 ◽  
Vol 42 ◽  
pp. 130-135 ◽  
Author(s):  
K. H. Böhm ◽  
J. Cassinelli
Keyword(s):  
Chemical Composition ◽  
Temperature Gradient ◽  
White Dwarf ◽  
White Dwarfs ◽  
Convection Zone ◽  
Adiabatic Temperature ◽  
Turbulent Convection ◽  
Cool White Dwarfs ◽  
Adiabatic Temperature Gradient

Outer convection zones of white dwarfs in the range 5800 K ≤ Teff ≤ 30000 K have been studied assuming that they have the same chemical composition as determined by Weidemann (1960) for van Maanen 2. Convection is important in all these stars. In white dwarfs Teff < 8000 K the adiabatic temperature gradient is strongly influenced by the pressure ionization of H, HeI and HeII which occurs within the convection zone. Partial degeneracy is also important.Convective velocities are very small for cool white dwarfs but they reach considerable values for hotter objects. For a white dwarf of Teff = 30000 K a velocity of 6.05 km/sec and an acoustic flux (generated by the turbulent convection) of 1.5 × 1011 erg cm−2 sec−1 is reached. The formation of white dwarf coronae is briefly discussed.

scholarly journals The internal structure of ZZ Cet stars using quantitative asteroseismology: The case of R548

2013 ◽  
Vol 9 (S301) ◽  
pp. 285-288
Author(s):  
N. Giammichele ◽  
G. Fontaine ◽  
P. Brassard ◽  
S. Charpinet
Keyword(s):  
Internal Structure ◽  
White Dwarf ◽  
White Dwarfs ◽  
Optimization Technique ◽  
Seismic Model ◽  
The Core ◽  
Spectroscopic Analyses ◽  
Core Composition ◽  
Oscillation Modes ◽  
Chemical Stratification

AbstractWe explore quantitatively the low but sufficient sensitivity of oscillation modes to probe both the core composition and the details of the chemical stratification of pulsating white dwarfs. Until recently, applications of asteroseismic methods to pulsating white dwarfs have been far and few, and have generally suffered from an insufficient exploration of parameter space. To remedy this situation, we apply to white dwarfs the same double-optimization technique that has been used quite successfully in the context of pulsating hot B subdwarfs. Based on the frequency spectrum of the pulsating white dwarf R548, we are able to unravel in a robust way the unique onion-like stratification and the chemical composition of the star. Independent confirmations from both spectroscopic analyses and detailed evolutionary calculations including diffusion provide crucial consistency checks and add to the credibility of the inferred seismic model. More importantly, these results boost our confidence in the reliability of the forward method for sounding white dwarf internal structure with asteroseismology.

scholarly journals Hot DQ white dwarfs: a pulsational test of the mixing scenario for their formation

2009 ◽  
Vol 5 (H15) ◽  
pp. 370-370
Author(s):  
A. Romero ◽  
A. H. Córsico ◽  
L. G. Althaus ◽  
E. García-Berro
Keyword(s):  
Stability Analysis ◽  
White Dwarf ◽  
White Dwarfs ◽  
Evolutionary Models ◽  
Instability Strip ◽  
Dwarf Stars ◽  
Photometric Variability ◽  
New Class ◽  
White Dwarf Stars ◽  
Born Again

Hot DQ white dwarfs constitute a new class of white dwarf stars, uncovered recently within the framework of SDSS project. There exist nine of them, out of a total of several thousands white dwarfs spectroscopically identified. Recently, three hot DQ white dwarfs have been reported to exhibit photometric variability with periods compatible with pulsation g-modes. In this contribution, we presented the results of a non-adiabatic pulsation analysis of the recently discovered carbon-rich hot DQ white dwarf stars. Our study relies on the full evolutionary models of hot DQ white dwarfs recently developed by Althaus et al. (2009), that consistently cover the whole evolution from the born-again stage to the white dwarf cooling track. Specifically, we performed a stability analysis on white dwarf models from stages before the blue edge of the DBV instability strip (Teff ≈ 30000 K) until the domain of the hot DQ white dwarfs (18000-24000 K), including the transition DB→hot DQ white dwarf. We explore evolutionary models with M*= 0.585M⊙ and M* = 0.87M⊙, and two values of thickness of the He-rich envelope (MHe = 2 × 10−7M* and MHe = 10−8M*).

A catalog of 159,238 white dwarf ages

2019 ◽  
Vol 15 (S357) ◽  
pp. 188-191
Author(s):  
Ted von Hippel ◽  
Adam Moss ◽  
Isabelle Kloc ◽  
Natalie Moticska ◽  
Jimmy Sargent ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Stellar Mass ◽  
Posterior Distributions ◽  
Trigonometric Parallaxes ◽  
On Line ◽  
Better Than

AbstractWe employ Pan-STARRS photometry, Gaia trigonometric parallaxes, modern stellar evolution and atmosphere models, and our Bayesian fitting approach to determine cooling and total ages for 159,238 white dwarfs. In many cases we are able to derive precise ages (better than 5%) for individual white dwarfs. These results are meant for broad use within the white dwarf and stellar astrophysics communities and we plan to make available on-line the posterior distributions for cooling age, total age, initial stellar mass, and other parameters.

scholarly journals The chemical structure of the hot pulsating DB white dwarf KIC 08626021 from asteroseismology

2019 ◽  
Vol 15 (S357) ◽  
pp. 119-122
Author(s):  
S. Charpinet ◽  
P. Brassard ◽  
N. Giammichele ◽  
Gilles Fontaine
Keyword(s):  
Chemical Composition ◽  
White Dwarf ◽  
White Dwarfs ◽  
Chemical Structure ◽  
Neutrino Emission ◽  
Energy Losses ◽  
Seismic Model ◽  
Limited Impact ◽  
Static Models

AbstractGiammichele et al. (2018) proposed a full determination, largely independent of evolution calculations, of the chemical composition and stratification inside the hot pulsating DB white dwarf KIC 08626021. However, Timmes et al. (2018) pointed out that neglecting the effects of neutrino cooling, such as in the static models used in Giammichele et al. study, could impact significantly the derived seismic solution and compromise conclusions drawn upon it. Here we present a reanalysis of KIC 08626021, using improved static models which now incorporate more realistic luminosity profiles that reflect the still significant energy losses induced by neutrino emission mechanisms in hot DB white dwarfs. We show that this effect has only a limited impact on the derived seismic model properties and, more importantly, that all the conclusions brought by Giammichele et al. (2018) remain entirely valid.

scholarly journals Electromagnetic transients and gravitational waves from white dwarf disruptions by stellar black holes in triple systems

2020 ◽  
Vol 495 (1) ◽  
pp. 1061-1072
Author(s):  
Giacomo Fragione ◽  
Brian D Metzger ◽  
Rosalba Perna ◽  
Nathan W C Leigh ◽  
Bence Kocsis
Keyword(s):  
White Dwarf ◽  
Gamma Ray ◽  
High Energy ◽  
Stellar Mass ◽  
Compact Objects ◽  
Electromagnetic Transients ◽  
Tidal Disruption ◽  
Single Star ◽  
Triple Systems ◽  
Nearby Galaxies

ABSTRACT Mergers of binaries comprising compact objects can give rise to explosive transient events, heralding the birth of exotic objects that cannot be formed through single-star evolution. Using a large number of direct N-body simulations, we explore the possibility that a white dwarf (WD) is dynamically driven to tidal disruption by a stellar-mass black hole (BH) as a consequence of the joint effects of gravitational wave (GW) emission and Lidov–Kozai oscillations imposed by the tidal field of an outer tertiary companion orbiting the inner BH–WD binary. We explore the sensitivity of our results to the distributions of natal kick velocities imparted to the BH and WD upon formation, adiabatic mass loss, semimajor axes and eccentricities of the triples, and stellar-mass ratios. We find rates of WD–tidal disruption events (TDEs) in the range 1.2 × 10−3 − 1.4 Gpc−3 yr−1 for z ≤ 0.1, rarer than stellar TDEs in triples by a factor of ∼3–30. The uncertainty in the TDE rates may be greatly reduced in the future using GW observations of Galactic binaries and triples with LISA. WD–TDEs may give rise to high-energy X-ray or gamma-ray transients of duration similar to long gamma-ray bursts but lacking the signatures of a core-collapse supernova, while being accompanied by a supernova-like optical transient that lasts for only days. WD–BH and WD–NS binaries will also emit GWs in the LISA band before the TDE. The discovery and identification of triple-induced WD–TDE events by future time domain surveys and/or GWs could enable the study of the demographics of BHs in nearby galaxies.

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.

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