NLTE Analysis of Four PG1159 Stars

Werner, K.; Heber, U.; Hunger, K.

doi:10.1007/978-94-011-3230-5_23

Cited by 69 publications

(99 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…PG 1707+427 and PG 1424+535 were among the first stars classified as PG 1159 stars (Liebert & Stockman 1980;Sion et al 1984;Wesemael et al 1985) and constituted two of the four PG 1159 stars that were first analysed with non-LTE model atmospheres (Werner et al 1991). Based on optical spectra, identical values for the basic atmospheric parameters (T eff and surface gravity g) were derived for both objects: T eff = 100 000 K, log g = 7 (g in cm s −2 ).…”

Section: The Program Starsmentioning

confidence: 99%

The far-ultraviolet spectra of “cool” PG 1159 stars

Werner¹,

Rauch²,

Kruk³

2015

A&A

Self Cite

View full text Add to dashboard Cite

We present a comprehensive study of Far Ultraviolet Spectroscopic Explorer (FUSE) spectra (912-1190 Å) of two members of the PG 1159 spectral class, which consists of hydrogen-deficient (pre-) white dwarfs with effective temperatures in the range T eff = 75 000-200 000 K. As two representatives of the cooler objects, we have selected PG 1707+427 (T eff = 85 000 K) and PG 1424+535 (T eff = 110 000 K), complementing a previous study of the hotter prototype PG 1159−035 (T eff = 140 000 K). The helium-dominated atmospheres are strongly enriched in carbon and oxygen, therefore, their spectra are dominated by lines from C iii-iv and O iii-vi, many of which were never observed before in hot stars. In addition, lines of many other metals (N, F, Ne, Si, P, S, Ar, Fe) are detectable, demonstrating that observations in this spectral region are most rewarding when compared to the near-ultraviolet and optical wavelength bands. We perform abundance analyses of these species and derive upper limits for several undetected light and heavy metals including iron-group and trans-iron elements. The results are compared to predictions of stellar evolution models for neutron-capture nucleosynthesis and good agreement is found.

show abstract

Section: The Program Starsmentioning

confidence: 99%

The far-ultraviolet spectra of “cool” PG 1159 stars

Werner¹,

Rauch²,

Kruk³

2015

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…N v λ4605 is in emission for NLTE models with T eff, p ≥ 110 000 K. There are no known sdOs with such high temperatures (S. Dreizler, private communication). There is, however, PG1144+005 (T eff = 150 000 K and log g = 6.5), which is a peculiar PG1159-like star that shows such N v emission lines at λ4603 and 4619 Å (Werner & Heber 1991). Therefore this NLTE effect seems reasonable and suggests a lower T eff, p than 100 000 K, probably even lower than 90 000-95 000 K; therefore our model is contradicting the primary temperature of 120 000 K found by Shimansky et al (2008).…”

Section: Primary Componentmentioning

confidence: 99%

Structure and spectra of irradiated secondaries in close binaries

Wawrzyn¹,

Barman²,

Günther

et al. 2009

A&A

View full text Add to dashboard Cite

Context. The standard stellar model atmosphere ignores the influence of external radiation. This assumption, while sufficient for most stars, fails for many short-period binaries. Aims. In setting up combined model atmospheres for close binaries, we want to constrain the parameters of both components, especially in the case of a hot primary component strongly influencing its cool secondary companion. This situation can be found after common envelope evolution (CEE). The status of both components today allows one to retrace the CEE itself. Methods. We used our stellar atmosphere code PHOENIX, which includes the effect of irradiation in its radiation transport equation, to investigate the close binary star UU Sge. We combined our calculated spectra of both components, weighted by their visible size, and adjusted the input parameters until reasonable agreement with observations is reached. Results. We derive a range of 80 000−85 000 K for the effective temperature of the primary (T eff, p ) and give a rough estimate for the primary's abundances, particularly the nitrogen enrichment. The heated day-side of the secondary has an apparent "effective" or equilibrium temperature of 24 000−26 000 K, nearly independent of its intrinsic luminosity. It shows an enhancement in nitrogen and carbon. Conclusions. The evolution of the primary and secondary stars were strongly influenced by the other's presence. Radiation from the primary on the secondary's day-side is still an important factor in understanding the secondary's atmospheric structure.

show abstract

“…The first analysis of PG 1520+525 (WD 1520+525) based on optical spectra was performed by Werner et al (1991) and gave T eff = 140 000 ± 20 000 K and log g = 7.0 ± 1.0. A first indication that the temperature exceeds 140 000 K was derived from the shape of an EUVE spectrum (Werner et al 1996).…”

Section: Previous Investigationsmentioning

confidence: 99%

Chandragrating spectroscopy of three hot white dwarfs

Adamczak

Werner²,

Rauch³

et al. 2012

A&A

Self Cite

View full text Add to dashboard Cite

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.

show abstract

NLTE Analysis of Four PG1159 Stars

Cited by 69 publications

References 7 publications

The far-ultraviolet spectra of “cool” PG 1159 stars

The far-ultraviolet spectra of “cool” PG 1159 stars

Structure and spectra of irradiated secondaries in close binaries

Chandragrating spectroscopy of three hot white dwarfs

Contact Info

Product

Resources

About