Four new massive pulsating white dwarfs including an ultramassive DAV

Curd, Brandon; Gianninas, A.; Bell, Keaton J.; Kilic, Mukremin; Romero, A. D.; Prieto, C. Allende; Winget, D. E.; Winget, K. I.

doi:10.1093/mnras/stx320

Cited by 35 publications

(50 citation statements)

References 59 publications

(81 reference statements)

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“…4, top) obtained with the Thai National Telescope (TNT) -two nights in January and two in February 2019 -unambiguously confirmed the variability as a single pulsation mode. The 840 s period is found to be typical for hydrogen-atmosphere white dwarfs with these stellar parameters 24 . While a single peak in the Fourier transform ( Fig.…”

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confidence: 84%

An ultra-massive white dwarf with a mixed hydrogen–carbon atmosphere as a likely merger remnant

et al. 2020

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White dwarfs are dense, cooling stellar embers consisting mostly of carbon and oxygen 1 , or oxygen and neon (with a few percent carbon) at higher initial stellar masses 2 . These stellar cores are enveloped by a shell of helium which in turn is usually surrounded by a layer of hydrogen, generally prohibiting direct observation of the interior composition. However, 1 arXiv:2003.00028v1 [astro-ph.SR] 28 Feb 2020 carbon is observed at the surface of a sizeable fraction of white dwarfs 3, 4 , sometimes with traces of oxygen, and it is thought to be dredged-up from the core by a deep helium convection zone 5, 6 . In these objects only traces of hydrogen are found 7, 8 as large masses of hydrogen are predicted to inhibit hydrogen/helium convective mixing within the envelope 9 . We report the identification of WD J055134.612+413531.09, an ultra-massive (1.14 M ) white dwarf with a unique hydrogen/carbon mixed atmosphere (C/H = 0.15 in number ratio). Our analysis of the envelope and interior indicates that the total hydrogen and helium mass fractions must be several orders of magnitude lower than predictions of single star evolution 10 : less than 10 −9.5 and 10 −7.0 , respectively. Due to the fast kinematics (129 ± 5 km s −1 relative to the local standard of rest), large mass, and peculiar envelope composition, we argue that WD J0551+4135 is consistent with formation from the merger of two white dwarfs in a tight binary system [11][12][13][14] .WD J0551+4135 was identified as a candidate high-mass white dwarf 15 from its location in the Gaia Hertzsprung-Russell diagram 16 (Fig. 1). The Gaia parallax places WD J0551+4135 at 46.45 ± 0.15 pc away from the Sun. Compared to most other white dwarfs of the same G BP − G RP colour, WD J0551+4135 is fainter in absolute magnitude, signifying a relatively small radius, and thus a large mass given the mass-radius relation of white dwarfs whose structure is dominated by electron degeneracy 17 .− log(1 − m r /M wd ) = 4 (where m r is the mass enclosed within a sphere of radius r), the models are almost indistinguishable. Therefore the degree of oxygen dredge-up is not found to depend upon the core-composition, and so the atmospheric non-detection of oxygen cannot be used to test the evolutionary history. 6

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confidence: 84%

An ultra-massive white dwarf with a mixed hydrogen–carbon atmosphere as a likely merger remnant

et al. 2020

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“…Besides their high magnetic fields, most of them have been shown to be massive, and responsible for the high-mass peak at 1 M of the WD mass distribution; for instance: REJ 0317-853 has M ≈ 1.35 M and B ≈ (1.7-6.6) × 10 8 G ( Barstow et al 1995;Külebi et al 2010); PG 1658+441 has M ≈ 1.31 M and B ≈ 2.3 × 10 6 G (Liebert et al 1983;Schmidt et al 1992); and PG 1031+234 has the highest magnetic field B ≈ 10 9 G (Schmidt et al 1986;Külebi et al 2009). The existence of ultra-massive WDs has been revealed in several studies (see e.g., Castanheira et al 2013;Hermes et al 2013;Curd et al 2017;Camisassa et al 2019;Gentile Fusillo et al 2018;Jiménez-Esteban et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Gravitational waves from fast-spinning white dwarfs

Sousa

Coelho

2020

Monthly Notices of the Royal Astronomical Society

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Two mechanisms of gravitational waves (GWs) emission in fast-spinning white dwarfs (WDs) are investigated: accretion of matter and magnetic deformation. In both cases, the GW emission is generated by an asymmetry around the rotation axis of the star. However, in the first case, the asymmetry is due to the amount of accreted matter on the magnetic poles, while in the second case it is due to the intense magnetic field. We have estimated the GW amplitude and luminosity for three binary systems that have a fast-spinning magnetized WD, namely, AE Aquarii, AR Scorpii and RX J0648.0-4418. We find that, for the first mechanism, the systems AE Aquarii and RX J0648.0-4418 can be observed by the space detectors BBO and DECIGO if they have an amount of accreted mass of δm ≥ 10 −5 M . For the second mechanism, the three systems studied require that the WD have a magnetic field above ∼ 10 9 G to emit GWs that can be detected by BBO. We also verified that, in both mechanisms, the gravitational luminosity has an irrelevant contribution to the spindown luminosity of these three systems. Therefore, other mechanisms of energy emission are needed to explain the spindown of these objects.

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“…This ultra-massive ZZ Ceti star was discovered by Curd et al (2017) Our best fit model is characterized by χ 2 = 0.14, δ = 0.37 s, σ = 0.38 s, and BIC= −0.37 with one period (797.4 s) identified as a ℓ = 2 mode, and the remaining periods identified as ℓ = 1 modes. The derivation of the stellar parameters gives T eff = 12 550 K, M ⋆ = 1.10M ⊙ , M H /M ⋆ = 1.02 × 10 −7 , M He /M ⋆ = 3.0 × 10 −4 , M cr /M ⋆ = 0.81, with a central 20 Ne abundance of 0.52.…”

Section: Sdss J08402123+5222174mentioning

confidence: 85%

“…The location of ultra-massive DA WD stars (Kleinman et al 2013;Kepler et al 2016;Curd et al 2017) are indicated with black star symbols. The black circles indicate the location of the known ultra-massive ZZ Ceti stars: BPM 37093 (Nitta et al 2016), SDSS J084021 (Curd et al 2017), GD 518 (Hermes et al 2013), and WD J212402 (Rowan et al 2019). up to date on the basis of the new grid of ONe-core WD models presented in Camisassa et al (2019) Rowan et al 2019). The location of these stars in the spectroscopic Hertzsprung-Russell (HR) diagram is shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

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

Córsico

Gerónimo

Camisassa

et al. 2019

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Context. Ultra-massive ( 1M ⊙ ) hydrogen-rich (DA) white dwarfs are expected to have a substantial portion of their cores in a crystalline state at the effective temperatures characterizing the ZZ Ceti instability strip (T eff ∼ 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 crystallization 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 T eff 15 000 K, and H envelope thicknesses in the interval −10 log(M H /M ⋆ ) −6. We explore the effects of employing different H-envelope thicknesses on the mode-trapping properties of our ultra-massive ONe-core DA white dwarf models, and perform period-to-period fits to ultra-massive ZZ Ceti stars with the aim of finding an asteroseismological model for each target star. Results. We found 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 found a mean period spacing of ∆Π ∼ 17 s in the data of BPM 37093, which is likely to be associated to 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 ∆Π with M ⋆ , T eff , and M H , an intrinsic property of DAV stars. We found asteroseismological models for the three objects under analysis, two of them (BPM 37093 and GD 518) characterized 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 crystallized mass of these asteroseismological models is 92 %, 97 %, and 81 % for BPM 37093, GD 518, and SDSS J0840+5222, respectively. We also derive asteroseismological distances which are in agreement with the astrometric measurements of Gaia for these stars. Conclusions. Asteroseismological analyses like the one presented in this paper could lead to a more complete knowledge of the processes occurring during crystallization inside white dwarfs. Also, they could make it possible to deduce the core chemical composition of ultra-massive white dwarfs, and in this way, to infer their evolutionary origin, i.e., if the star has a ONe co...

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Four new massive pulsating white dwarfs including an ultramassive DAV

Cited by 35 publications

References 59 publications

An ultra-massive white dwarf with a mixed hydrogen–carbon atmosphere as a likely merger remnant

An ultra-massive white dwarf with a mixed hydrogen–carbon atmosphere as a likely merger remnant

Gravitational waves from fast-spinning white dwarfs

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

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