Chandra and FUSE spectroscopy of the hot bare stellar core H 1504+65

Werner, K.; Rauch, T.; Barstow, M. A.; Kruk, J. W.

doi:10.1051/0004-6361:20047154

Cited by 41 publications

(43 citation statements)

References 24 publications

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“…Estimated errors for the abundances are ±20% for C and O and a factor of 3 for the other elements (see also Werner et al 2004a). …”

Section: Ironmentioning

confidence: 96%

“…Non-local thermodynamic equilibrium (non-LTE) modeling of ultraviolet (UV) and optical spectra proved the high temperature and showed that the atmosphere is mainly composed by carbon and oxygen in equal amounts (Werner 1991). Over the years, substantial efforts were made with subsequent spectroscopy in the soft X-ray range (with EUVE 2 and Chandra observatories), in the UV (HUT 3 , FUSE 4 , HST 5 ), and in the optical with large ground-based telescopes (Werner & Wolff 1999;Werner et al 2004aWerner et al ,b, 2007Werner et al , 2010, leading to tight constraints on effective temperature and gravity (T eff = 200 000 ± 20 000 K, log g = 8.0 ± 0.5) and the detection of high amounts of neon (2-5%, by mass) and magnesium (2%) as well as iron at solar abundance level. Highresolution UV spectroscopy presented in the paper at hand was performed with the aim to further constrain the trace element abundances and to shed more light on the origin of the exotic composition of H1504+65.…”

Section: Introductionmentioning

confidence: 99%

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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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“…Estimated errors for the abundances are ±20% for C and O and a factor of 3 for the other elements (see also Werner et al 2004a). …”

Section: Ironmentioning

confidence: 96%

Section: Introductionmentioning

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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“…These stars do not fit satisfactorily in any of the currently known theories of post-AGB evolution. They are considered to be the cooler counterpart of the unique and extensively studied PG1159 star H1504+65 (Nousek et al 1986;Werner 1991;Werner et al 2004a) and might form a new evolutionary sequence that follows the AGB. Another case of H-deficient WDs that need to fit into the evolutionary picture are the oxygen-dominated WDs discovered by Gänsicke et al (2010).…”

Section: Introductionmentioning

confidence: 99%

Analysis of cool DO-type white dwarfs from the Sloan Digital Sky Survey data release 10

Reindl¹,

Rauch²,

Werner³

et al. 2014

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We report on the identification of 22 new cool DO-type white dwarfs (WDs) detected in data release 10 (DR10) of the Sloan Digital Sky Survey (SDSS). Among them, we found one more member of the so-called hot-wind DO WDs, which show ultrahigh excitation absorption lines. Our non-LTE model atmosphere analyses of these objects and two not previously analyzed hot-wind DO WDs, revealed effective temperatures and gravities in the ranges T eff = 45−80 kK and log g = 7.50−8.75. In eight of the spectra we found traces of C (0.001−0.01, by mass). Two of these are the coolest DO WDs ever discovered that still show a considerable amount of C in their atmospheres. This is in strong contradiction with diffusion calculations, and probably, similar to what is proposed for DB WDs, a weak mass-loss is present in DO WDs. One object is the most massive DO WD discovered so far with a mass of 1.07 M if it is an ONe-WD or 1.09 M if it is a CO-WD. We furthermore present the mass distribution of all known hot non-DA (pre-) WDs and derive the hot DA to non-DA ratio for the SDSS DR7 spectroscopic sample. The mass distribution of DO WDs beyond the wind limit strongly deviates from the mass distribution of the objects before the wind limit. We address this phenomenon by applying different evolutionary input channels. We argue that the DO WD channel may be fed by about 13% by post-extreme-horizontal branch stars and that PG 1159 stars and O(He) stars may contribute in a similar extent to the non-DA WD channel.

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“…The first set is identical to that described in detail by Werner et al (2004a) and Ni which are treated in a statistical way using superlevels and superlines (Rauch & Deetjen 2003). Table 1 summarizes the set of data used for the DA analyses.…”

Section: Model Atomsmentioning

confidence: 99%

“…The identification of Mg lines is ambiguous. For a detailed list of possible lines in this wavelength range we refer to the analysis of H 1504+65 (Werner et al 2004a). We have calculated a small grid of models for T eff = 140 000 K, 150 000 K, 160 000 K, and log g = 6.4, 7.0, 7.5.…”

Section: Chandra Analysismentioning

confidence: 99%

Chandragrating spectroscopy of three hot white dwarfs

Adamczak

Werner²,

Rauch³

et al. 2012

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Context. High-resolution soft X-ray spectroscopic observations of single hot white dwarfs are scarce. With the Chandra Low-Energy Transmission Grating, we have observed two white dwarfs, one is of spectral type DA (LB 1919) and the other is a non-DA of spectral type PG 1159 (PG 1520+525). The spectra of both stars are analyzed, together with an archival Chandra spectrum of another DA white dwarf (GD 246). Aims. The soft X-ray spectra of the two DA white dwarfs are investigated in order to study the effect of gravitational settling and radiative levitation of metals in their photospheres. LB 1919 is of interest because it has a significantly lower metallicity than DAs with otherwise similar atmospheric parameters. GD 246 is the only white dwarf known that shows identifiable individual iron lines in the soft X-ray range. For the PG 1159 star, a precise effective temperature determination is performed in order to confine the position of the blue edge of the GW Vir instability region in the HRD. Methods. The Chandra spectra are analyzed with chemically homogeneous as well as stratified NLTE model atmospheres that assume equilibrium between gravitational settling and radiative acceleration of chemical elements. Archival EUV and UV spectra obtained with EUVE, FUSE, and HST are utilized to support the analysis. Results. No metals could be identified in LB 1919. All observations are compatible with a pure hydrogen atmosphere. This is in stark contrast to the vast majority of hot DA white dwarfs that exhibit light and heavy metals and to the stratified models that predict significant metal abundances in the atmosphere. For GD 246 we find that neither stratified nor homogeneous models can fit the Chandra spectrum. The Chandra spectrum of PG 1520+525 constrains the effective temperature to T eff = 150 000 ± 10 000 K. Therefore, this nonpulsating star together with the pulsating prototype of the GW Vir class (PG 1159−035) defines the location of the blue edge of the GW Vir instability region. The result is in accordance with predictions from nonadiabatic stellar pulsation models. Such models are therefore reliable tools to investigate the interior structure of GW Vir variables. Conclusions. Our soft X-ray study reveals that the understanding of metal abundances in hot DA white dwarf atmospheres is still incomplete. On the other hand, model atmospheres of hydrogen-deficient PG 1159-type stars are reliable and reproduce well the observed spectra from soft X-ray to optical wavelengths.

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Chandra and FUSE spectroscopy of the hot bare stellar core H 1504+65

Cited by 41 publications

References 24 publications

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

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

Analysis of cool DO-type white dwarfs from the Sloan Digital Sky Survey data release 10

Chandragrating spectroscopy of three hot white dwarfs

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