The New Class of Dusty DAZ White Dwarfs

We report the detection of a radial velocity companion to SDSS J091709.55+463821.8, the lowest mass white dwarf currently known, with M $ 0:17 M . The radial velocity of the white dwarf shows variations with a semi-amplitude of 148:8 AE 6:9 km s À1 and a period of 7:5936 AE 0:0024 hr, which implies a companion mass of M ! 0:28 M . The lack of evidence of a companion in the optical photometry forces any main-sequence companion to be smaller than 0.1 M , hence a low-mass main-sequence star companion is ruled out for this system. The companion is most likely another white dwarf, and we present tentative evidence for an evolutionary scenario that could have produced it. However, a neutron star companion cannot be ruled out, and follow-up radio observations are required to search for a pulsar companion.

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“…Several calcium-rich WDs are known to host disks ( Kilic et al 2006;von Hippel et al 2007). These WDs are 0.2-1.0 Gyr old.…”

Section: A Neutron Starmentioning

confidence: 99%

“…These WDs are 0.2-1.0 Gyr old. The presumed origin of these disks is tidal disruption of asteroids or comets; however, a leftover disk from the giant phase of the WD is not completely ruled out (von Hippel et al 2007). Su et al (2007) detected a disk around the central star of the Helix planetary nebula.…”

Section: A Neutron Starmentioning

confidence: 99%

The Discovery of a Companion to the Lowest Mass White Dwarf

Kilic

Brown

Prieto

et al. 2007

ApJ

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“…This dust is thought to originate from the the tidal disruption of some rocky material, left over from a former planetary system (Debes & Sigurdsson 2002;Jura 2003). This idea has gained more and more acceptance in the last decade, mainly through the discovery of infrared excesses due to circumstellar dust in a significant fraction of DAZs and DBZs (Jura 2006;von Hippel et al 2007;Farihi et al 2009Farihi et al , 2010b. In particular the gaseous disks with Ca ii emission lines (Gänsicke et al 2006(Gänsicke et al , 2007(Gänsicke et al , 2008 are the strongest confirmation for the disk geometry and its location inside the Roche lobe of the white dwarfs, a key prediction of the tidal disruption hypothesis.…”

Section: Introductionmentioning

confidence: 99%

Cool DZ white dwarfs in the SDSS

Koester

Girven²,

Gänsicke³

et al. 2011

A&A

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Aims. We report the identification of 26 cool DZ white dwarfs that lie across and below the main sequence in the Sloan Digital Sky Survey (SDSS) (u − g) vs. (g − r) two-color diagram; 21 of these stars are new discoveries. Methods. The sample was identified by visual inspection of all spectra of objects that fall below the main sequence in the two-color diagram, as well as by an automated search for characteristic spectral features over a large area in color space that included the main sequence. The spectra and photometry provided by the SDSS project are interpreted with model atmospheres, including all relevant metals. Effective temperatures and element abundances are determined, while the surface gravity has to be assumed and was fixed at the canonical value of logg = 8. Results. These stars represent the extension of the well-known DZ sequence towards cooler temperatures and fill the gap around T eff = 6500 K present in a previous study. The metal abundances are similar to those in the hotter DZ, but the lowest abundances are missing, probably because of our selection procedures. The interpretation is complicated in terms of the accretion/diffusion scenario, because we do not know if accretion is still occurring or has ended long ago. Independent of that uncertainty, the masses of the metals currently present in the convection zones -and thus an absolute lower limit of the total accreted masses -of these stars are similar to the largest asteroids in our solar system.

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“…This IR excess is interpreted as originating from a small hot disk, which is due to the infall and destruction of single asteroids that come within the star's Roche limit (Gänsicke et al 2006). However, we exclude the presence of a debris disk in the case of J1556, because at such high T eff , solids would be sublimated into gaseous disks (von Hippel et al 2007). In addition the double-peaked Ca ii triplet, which is the hallmark of a gaseous, rotating disk (Young et al 1981;Horne & Marsh 1986), cannot be detected.…”

Section: Search For Nebular Lines and Infrared Excessmentioning

confidence: 99%

Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

Reindl¹,

Geier

Kupfer

et al. 2016

A&A

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In the course of the MUCHFUSS project we recently discovered four radial velocity (RV) variable, hot (T eff ≈ 80 000−110 000 K) post-asymptotic giant branch (AGB) stars. Among them, we found the first known RV variable O(He) star, the only second known RV variable PG 1159 close binary candidate, as well as the first two naked (i.e., without planetary nebula (PN)) H-rich post-AGB stars of spectral type O(H) that show significant RV variations. We present a non-LTE spectral analysis of these stars along with one further O(H)-type star whose RV variations were found to be not significant. We also report the discovery of a far-infrared excess in the case of the PG 1159 star. None of the stars in our sample displays nebular emission lines, which can be explained well in terms of a very late thermal pulse evolution in the case of the PG 1159 star. The "missing" PNe around the O(H)-type stars seems strange, since we find that several central stars of PNe have much longer post-AGB times. Besides the non-ejection of a PN, the occurrence of a late thermal pulse, or the re-accretion of the PN in the previous post-AGB evolution offer possible explanations for those stars not harbouring a PN (anymore). In the case of the O(He) star J0757, we speculate that it might have been previously part of a compact He transferring binary system. In this scenario, the mass transfer must have stopped after a certain time, leaving behind a low-mass close companion that may be responsible for the extreme RV shift of 107.0 ± 22.0 km s −1 that was measured within only 31 min.

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The New Class of Dusty DAZ White Dwarfs

Cited by 151 publications

References 47 publications

The Discovery of a Companion to the Lowest Mass White Dwarf

The Discovery of a Companion to the Lowest Mass White Dwarf

Cool DZ white dwarfs in the SDSS

Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

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