New hydrogen-deficient (pre-) white dwarfs in the Sloan Digital Sky Survey Data Release 10

Werner, K.; Rauch, T.; Kepler, S. O.

doi:10.1051/0004-6361/201423441

Cited by 51 publications

(50 citation statements)

References 16 publications

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“…Interestingly, we find that other He-dominated objects (e.g. He-rich subdwarfs; Müller-Ringat 2013; Németh et al 2012;Naslim et al 2010;Hirsch 2009;Ahmad et al 2004;Rauch et al 1998Rauch et al , 1991Husfeld et al 1989;Stroeer et al 2007, DO WDs Werner et al 2014;Mahsereci 2011;Hügelmeyer et al 2006;Dreizler & Werner 1996) also show these differences in the CNO abundances 13 . Some objects are enriched in N but not in C, some C-enriched objects do not show N, but there also are objects which are enriched in both.…”

Section: Resultsmentioning

confidence: 48%

“…Rauch et al (2008) suggested that RCB stars might be possible progenitors of the O(He) stars. This could be true for the two C and N enriched O(He) stars SDSS J 172854.34+361958.62 (Werner et al 2014) and KPD 0005+5106 (Wassermann et al 2010). In between evolutionary objects could be the C-and N-enriched luminous sdO stars LSE 259 (Husfeld et al 1989), GJJC 1 (Rauch et al 1998), and KS 292 (Rauch et al 1991).…”

Section: Single-star Evolutionmentioning

confidence: 97%

“…For more than 15 years, only the two central stars of planetary nebulae (CSPNe) K 1−27 1 (WD 0558−756) and LoTr 4, as well as HS 1522+6615 (WD 1522+662), and HS 2209+8229 (WD 2209−8229) were known (Rauch et al 1994(Rauch et al , 1996(Rauch et al , 1998. Recently, Werner et al (2014) found four more of these objects, namely SDSS J 172854.34+361958.62, SDSS J 171916.97+365326.70, SDSS J 141812.50+024426.92, and SDSS J 075732.18+184329.28. They also pointed out that KPD 0005+5106 is a pre-WD.…”

Section: Introductionmentioning

confidence: 99%

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On helium-dominated stellar evolution: the mysterious role of the O(He)-type stars

Reindl¹,

Rauch²,

Werner³

et al. 2014

A&A

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Context. About a quarter of all post-asymptotic giant branch (AGB) stars are hydrogen-deficient. Stellar evolutionary models explain the carbon-dominated H-deficient stars by a (very) late thermal pulse scenario where the hydrogen-rich envelope is mixed with the helium-rich intershell layer. Depending on the particular time at which the final flash occurs, the entire hydrogen envelope may be burned. In contrast, helium-dominated post-AGB stars and their evolution are not yet understood. Aims. A small group of very hot, helium-dominated stars is formed by O(He)-type stars. A precise analysis of their photospheric abundances will establish constraints to their evolution. Methods. We performed a detailed spectral analysis of ultraviolet and optical spectra of four O(He) stars by means of state-of-the-art non-LTE model-atmosphere techniques. Results. We determined effective temperatures, surface gravities, and the abundances of H, He, C, N, O, F, Ne, Si, P, S, Ar, and Fe. By deriving upper limits for the mass-loss rates of the O(He) stars, we found that they do not exhibit enhanced mass-loss. The comparison with evolutionary models shows that the status of the O(He) stars remains uncertain. Their abundances match predictions of a double helium white dwarf (WD) merger scenario, suggesting that they might be the progeny of the compact and of the luminous helium-rich sdO-type stars. The existence of planetary nebulae that do not show helium enrichment around every other O(He) star precludes a merger origin for these stars. These stars must have formed in a different way, for instance via enhanced mass-loss during their post-AGB evolution or a merger within a common-envelope (CE) of a CO-WD and a red giant or AGB star. Conclusions. A helium-dominated stellar evolutionary sequence exists that may be fed by different types of mergers or CE scenarios. It appears likely that all these pass through the O(He) phase just before they become WDs.

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Section: Resultsmentioning

confidence: 48%

Section: Single-star Evolutionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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On helium-dominated stellar evolution: the mysterious role of the O(He)-type stars

Reindl¹,

Rauch²,

Werner³

et al. 2014

A&A

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“…The element abundances are summarized in Table 4 and displayed in Fig. 7, together with results for RCB and EHe stars (from Jeffery et al 2011, and references Currently, ten objects were assigned to the group of O(He) stars (Reindl et al 2014;Werner et al 2014;De Marco et al 2015). They cover a parameter range of T eff = 80 000−195 000 K and log g = 5.0−6.7.…”

Section: Summary and Discussionmentioning

confidence: 99%

HubbleSpace Telescope ultraviolet spectroscopy of the hottest known helium-rich pre-white dwarf KPD 0005+5106

Werner¹,

Rauch²

2015

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We present a model-atmosphere analysis of the ultraviolet echelle spectra of KPD 0005+5106 taken with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. The star is the hottest known pre-white dwarf (T eff = 200 000 ± 20 000 K, log g = 6.7 ± 0.3 (cm/s 2 )). Its atmosphere is composed of helium with trace amounts of metals. It is of the so-called O(He) spectral type that comprises very hot helium-rich pre-white dwarfs whose origin is debated. From neon and silicon ionisation balances, we derive tighter constraints on the effective temperature (195 000 ± 15 000 K) and improve previous abundance determinations of these elements. We confirm the idea that KPD 0005+5106 is the descendant of an R Coronae Borealis (RCB) star, so is the outcome of a binary-whitedwarf merger. We discuss the relation of KPD 0005+5106 to other O(He) and RCB stars.

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“…For the spectral analysis we used our non-LTE code TMAP 8 (Werner et al 2012) to compute plane-parallel, line-blanketed atmosphere models in radiative and hydrostatic equilibrium (Werner & Dreizler 1999;Werner et al 2003). They include the three most abundant elements in H1504+65, namely, C, O, and Ne.…”

Section: Model Atoms and Model Atmospheresmentioning

confidence: 99%

Analysis of HST/COS spectra of the bare C–O stellar core H1504+65 and a high-velocity twin in the Galactic halo

Werner

Rauch

2015

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H1504+65 is an extremely hot white dwarf (effective temperature T eff = 200 000 K) with a carbon-oxygen dominated atmosphere devoid of hydrogen and helium. This atmospheric composition was hitherto unique among hot white dwarfs (WDs), and it could be related to recently detected cooler WDs with C or O dominated spectra. The origin of the H and He deficiency in H1504+65 is unclear. To further assess this problem, we performed ultraviolet spectroscopy with the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope (HST). In accordance with previous far-ultraviolet spectroscopy performed with the Far Ultraviolet Spectroscopic Explorer, the most prominent lines stem from C iv, O v-vi, and Ne vi-viii. Archival HST/COS spectra are utilized to prove that the supersoft X-ray source RX J0439.8−6809 is, considering the exotic composition, a twin of H1504+65 that is even hotter (T eff = 250 000 K). In contrast to earlier claims, we find that the star is not located in the Large Magellanic Cloud but a foreground object in the Galactic halo at a distance of 9.2 kpc, 5.6 kpc below the Galactic plane, receding with v rad = +220 km s −1 .

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New hydrogen-deficient (pre-) white dwarfs in the Sloan Digital Sky Survey Data Release 10

Cited by 51 publications

References 16 publications

On helium-dominated stellar evolution: the mysterious role of the O(He)-type stars

On helium-dominated stellar evolution: the mysterious role of the O(He)-type stars

HubbleSpace Telescope ultraviolet spectroscopy of the hottest known helium-rich pre-white dwarf KPD 0005+5106

Analysis of HST/COS spectra of the bare C–O stellar core H1504+65 and a high-velocity twin in the Galactic halo

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