Adding More Mysteries to the DA White Dwarf GD 394

Dupuis, J.; Chayer, P.; Vennes, S.; Christian, D. J.; Kruk, J. W.

doi:10.1086/309079

Cited by 47 publications

(85 citation statements)

References 65 publications

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“…The origin of the metals has been intensively debated in the past (Shipman et al 1995;Bannister et al 2003;Barstow et al 2003;Dickinson et al 2012a,b), but it is very likely that it is, at least in part, also related to planetary debris (Barstow et al 2014). One particularly promising candidate of a hot white dwarf accreting planetary debris at a high rate is the extremely metal-polluted GD394 (≈40 000 K, Barstow et al 1996;Dupuis et al 2000).…”

Section: Resultsmentioning

confidence: 99%

The frequency of planetary debris around young white dwarfs

Koester

Gänsicke

Farihi

2014

A&A

454

531

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Context. Heavy metals in the atmospheres of white dwarfs are thought in many cases to be accreted from a circumstellar debris disk, which was formed by the tidal disruption of a rocky planetary body within the Roche radius of the star. The abundance analysis of photospheric elements and conclusions about the chemical composition of the accreted matter are a new and promising method of studying the composition of extrasolar planetary systems. However, ground-based searches for metal-polluted white dwarfs that rely primarily on the detection of the Ca ii K line become insensitive at T eff > 15 000 K because this ionization state depopulates.Aims. We present the results of the first unbiased survey for metal pollution among hydrogen-atmosphere (DA type) white dwarfs with cooling ages in the range 20-200 Myr and 17 000 K < T eff < 27 000 K. Methods. The sample was observed with the Cosmic Origins Spectrograph on board the Hubble Space Telescope in the far ultraviolet range between 1130 and 1435 Å. The atmospheric parameters were obtained using these spectra and optical observations from the literature. Element abundances were determined using theoretical models, which include the effects of element stratification due to gravitational settling and radiative levitation. Results. We find 48 of the 85 DA white dwarfs studied, or 56% show traces of heavy elements. In 25 stars (showing only Si and occasionally C), the elements can be explained by radiative levitation alone, although we argue that accretion has very likely occurred recently. The remaining 23 white dwarfs (27%), however, must be currently accreting. Together with previous studies from the ground and adopting bulk Earth abundances for the debris, accretion rates range from a few 10 5 g s −1 to a few 10 8 g s −1 , with no evident trend in cooling age from ≈40 Myr to ≈2 Gyr. Only a single, modest case of metal pollution (Ṁ < 10 6 g s −1 ) is found among ten white dwarfs with T eff > 23 000 K, in excellent agreement with the absence of infrared excess from dust around these warmer stars. The median, main sequence progenitor of our sample corresponds to an A-type star of ≈2 M , and we find 13 of 23 white dwarfs descending from main sequence 2-3 M , late B-and A-type stars to be currently accreting. Only one of 14 targets with M wd > 0.8 M is found to be currently accreting, which suggests a large fraction of these stars result from double-degenerate mergers, and the merger disks do not commonly reform large planetesimals or otherwise pollute the remnant. We reconfirm our previous finding that two 625 Myr Hyades white dwarfs are currently accreting rocky planetary debris. Conclusions. At least 27% of all white dwarfs with cooling ages 20-200 Myr are accreting planetary debris, but that fraction could be as high as ≈50%. At T eff > 23 000 K, the luminosity of white dwarfs is probably sufficient to vaporize circumstellar dust grains, so no stars with strong metal-pollution are found. Planetesimal disruption events should occur in this cooling age and temper...

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Section: Resultsmentioning

confidence: 99%

The frequency of planetary debris around young white dwarfs

Koester

Gänsicke

Farihi

2014

A&A

454

531

View full text Add to dashboard Cite

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“…The Si abundance by number is (Si/H)∼10 −5 . Dupuis et al (2000) suggest that the 1.15 day period variability seen in the EUVE light curve of GD 394 is due to inhomogeneous abundance distribution of metals over the surface of the star. In their model, an almost circular spot with a higher heavy element abundance reduces the EUV emission over the spot region, causing 25% dips in brightness.…”

Section: Not a Disintegrating Planetmentioning

confidence: 89%

“…GD 394 presents an unusual case where Dupuis et al (2000) detect 25% amplitude variations in the extreme ultraviolet with a period of 1.15 days, but there is no evidence of a magnetic field down to a limit of 12 kG. Dupuis et al (2000) interpret the observed photometric variations as evidence of surface abundance inhomogeneities.…”

Section: Introductionmentioning

confidence: 93%

“…Hence, starspots can explain the stability of the photometric dips in our data spanning four months. Figure 4 also shows the Extreme-Ultraviolet Explorer (EUVE) data on GD 394 from Dupuis et al (2000). The similarities between the GD 394 and J1529+2928 light curves are stunning.…”

Section: Not a Disintegrating Planetmentioning

confidence: 99%

“…Gary et al (2013) find 2.7 hr period, low-amplitude (5 mma) optical variations on WD 2359-434, a magnetic white dwarf with a relatively low field strength of B=3.1±0.4 kG (Aznar Cuadrado et al 2004). GD 394 presents an unusual case where Dupuis et al (2000) detect 25% amplitude variations in the extreme ultraviolet with a period of 1.15 days, but there is no evidence of a magnetic field down to a limit of 12 kG. Dupuis et al (2000) interpret the observed photometric variations as evidence of surface abundance inhomogeneities.…”

Section: Introductionmentioning

confidence: 99%

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A Dark Spot on a Massive White Dwarf

Kilic

Gianninas

Bell

et al. 2015

ApJ

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We present the serendipitous discovery of eclipse-like events around the massive white dwarf SDSS J152934.98 +292801.9 (hereafter J1529+2928). We selected J1529+2928 for time-series photometry based on its spectroscopic temperature and surface gravity, which place it near the ZZ Ceti instability strip. Instead of pulsations, we detect photometric dips from this white dwarf every 38 minutes. Follow-up optical spectroscopy observations with Gemini reveal no significant radial velocity variations, ruling out stellar and brown dwarf companions. A disintegrating planet around this white dwarf cannot explain the observed light curves in different filters. Given the short period, the source of the photometric dips must be a dark spot that comes into view every 38 minutes due to the rotation of the white dwarf. Our optical spectroscopy does not show any evidence of Zeeman splitting of the Balmer lines, limiting the magnetic field strength to B<70 kG. Since up to 15% of white dwarfs display kG magnetic fields, such eclipse-like events should be common around white dwarfs. We discuss the potential implications of this discovery on transient surveys targeting white dwarfs, like the K2 mission and the Large Synoptic Survey Telescope.

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