<i>Gaia</i> white dwarfs within 40 pc – I. Spectroscopic observations of new candidates

Tremblay, Pier-Emmanuel; Hollands, Mark; Fusillo, N. P. Gentile; McCleery, J.; Izquierdo, Paula; Gänsicke, B. T.; Cukanovaite, E.; Koester, D.; Brown, Warren R.; Charpinet, S.; Cunningham, Tim; Farihi, Jay; Giammichele, N.; Grootel, Valérie Van; Hermes, J. J.; Hoskin, Matthew J.; Jordan, S.; Kepler, S. O.; Kleinman, S. J.; Manser, Christopher J.; Marsh, T. R.; Martino, D. de; Nitta, A.; Parsons, S. G.; Pelisoli, Ingrid; Raddi, R.; Rebassa‐Mansergas, A.; Ren, Juanjuan; Schreiber, M. R.; Silvotti, R.; Toloza, Odette; Toonen, Silvia; Torres, Santiago

doi:10.1093/mnras/staa1892

Cited by 72 publications

(62 citation statements)

References 88 publications

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“…Also reported within the past year, there is a fourth DA star with Balmer emission lines, WD J041246. 85 + 754942.3 (hereafter J0412;Tremblay et al 2020). It is remarkably similar to the three known DAHe stars; it lies in precisely the same and compact region of the HR diagram, and it has rapid rotation.…”

Section: Intrinsic Chromospheric Activity In White Dwarfsmentioning

confidence: 74%

“…The exact physical nature of such a spot and its origin remain unclear, despite extensive and multiwavelength efforts to detect a companion, a corona or accretion (Ferrario et al 1997;Weisskopf et al 2007;Wickramasinghe et al 2010). Interestingly, at least two, and possibly three further examples of DAHe stars have been reported within the past year (Gänsicke et al 2020;Reding et al 2020;Tremblay et al 2020); all are isolated (i.e. not cataclysmic variables, no circumstellar discs), relatively fast rotators, and have cool atmospheres where T eff < 10 000 K. Thus, GD 356 is now the prototype of a small class of DAHe stars, but the new discoveries only deepen the mystery.…”

Section: Introductionmentioning

confidence: 99%

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A test of the planet–star unipolar inductor for magnetic white dwarfs

Walters

Farihi

Marsh

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Despite thousands of spectroscopic detections, only four isolated white dwarfs exhibit Balmer emission lines. The temperature inversion mechanism is a puzzle over 30 years old that has defied conventional explanations. One hypothesis is a unipolar inductor that achieves surface heating via ohmic dissipation of a current loop between a conducting planet and a magnetic white dwarf. To investigate this model, new time-resolved spectroscopy, spectropolarimetry, and photometry of the prototype GD 356 are studied. The emission features vary in strength on the rotational period, but in anti-phase with the light curve, consistent with a cool surface spot beneath an optically thin chromosphere. Possible changes in the line profiles are observed at the same photometric phase, potentially suggesting modest evolution of the emission region, while the magnetic field varies by 10 per cent over a full rotation. These comprehensive data reveal neither changes to the photometric period, nor additional signals such as might be expected from an orbiting body. A closer examination of the unipolar inductor model finds points of potential failure: the observed rapid stellar rotation will inhibit current carriers due to the centrifugal force, there may be no supply of magnetospheric ions, and no anti-phase flux changes are expected from ohmic surface heating. Together with the highly similar properties of the four cool, emission-line white dwarfs, these facts indicate that the chromospheric emission is intrinsic. A tantalizing possibility is that intrinsic chromospheres may manifest in (magnetic) white dwarfs, and in distinct parts of the HR diagram based on structure and composition.

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Section: Intrinsic Chromospheric Activity In White Dwarfsmentioning

confidence: 74%

Section: Introductionmentioning

confidence: 99%

A test of the planet–star unipolar inductor for magnetic white dwarfs

Walters

Farihi

Marsh

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…This highlights the fact that the treatment of the microphysics for cool DB and DBA white dwarfs needs to be revisited. For example, after making a major improvement in the treatment of Stark broadening of neutral helium atoms using computer simulations, Tremblay et al (2020b) also plan to extend their simulations to improve van der Waals broadening.…”

Section: Discussionmentioning

confidence: 99%

“…An issue with the approximate treatment of dereddening in Gentile Fusillo et al (2019a) is unlikely because there is no obvious correlation between the observed offset and distance (Tremblay et al 2019), e.g. the offset is similar even for bright DA white dwarfs within 40 pc (Tremblay et al 2020a) for which reddening is expected to be negligible. It cannot be due to 3D spectroscopic effects, as 1D DB/DBA models predict a similar offset (see Fig.…”

Section: Comparison Between He-and H-atmosphere White Dwarfsmentioning

confidence: 98%

3D spectroscopic analysis of helium-line white dwarfs

Cukanovaite

Tremblay

Bergeron

et al. 2020

Monthly Notices of the Royal Astronomical Society

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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.

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“…Finally, we carry out an additional verification comparing the photometric luminosity of our work with other values published in the literature and also derived photometrically (Kilic et al 2018;Tremblay et al 2020). The results are shown in the bottom right panel of Fig.…”

Section: Methodology and Testingmentioning

confidence: 52%

The Gaia DR2 halo white dwarf population: the luminosity function, mass distribution, and its star formation history

Torres

Rebassa‐Mansergas

Camisassa

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We analyse the volume-limited nearly complete 100 pc sample of 95 halo white dwarf candidates identified by the second data release of Gaia. Based on a detailed population synthesis model, we apply a method that relies on Gaia astrometry and photometry to accurately derive the individual white dwarf parameters. This method is tested with 25 white dwarfs of our sample for which we took optical spectra and performed spectroscopic analysis. We build and analyse the halo white dwarf luminosity function, for which we find for the first time possible evidences of the cut-off, leading to an age estimate of ${\simeq}12\pm 0.5$ Gyr. The mass distribution of the sample peaks at $0.589\, \mathrm{ M}_{\odot }$, with $71{{\ \rm per\ cent}}$ of the white dwarf masses below $0.6\, \mathrm{ M}_{\odot }$ and just two massive white dwarfs of more than $0.8\, \mathrm{ M}_{\odot }$. From the age distribution, we find three white dwarfs with total ages above 12 Gyr, of which J1312−4728 is the oldest white dwarf known with an age of $12.41\pm 0.22\,$ Gyr. We prove that the star formation history is mainly characterized by a burst of star formation that occurred from 10 to 12 Gyr in the past, but extended up to 8 Gyr. We also find that the peak of the star formation history is centred at around 11 Gyr, which is compatible with the current age of the Gaia-Enceladus encounter. Finally, $13{{\ \rm per\ cent}}$ of our halo sample is contaminated by high-speed young objects (total age <7 Gyr). The origin of these white dwarfs is unclear but their age distribution may be compatible with the encounter with the Sagittarius galaxy.

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Gaia white dwarfs within 40 pc – I. Spectroscopic observations of new candidates

Cited by 72 publications

References 88 publications

A test of the planet–star unipolar inductor for magnetic white dwarfs

A test of the planet–star unipolar inductor for magnetic white dwarfs

3D spectroscopic analysis of helium-line white dwarfs

The Gaia DR2 halo white dwarf population: the luminosity function, mass distribution, and its star formation history

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