NLTE-Analysis of Three Extremely Helium-Rich O-Type Subdwarfs

Husfeld, D.; Heber, U.; Drilling, J. S.

doi:10.1007/978-94-009-4744-3_39

Cited by 19 publications

(30 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…LB 1630 (sdOC5VI:He38) (53.4, 4.4, 0.9) has markedly narrower He lines than the remainder of this group, hence its lower luminosity class and, indeed, surface gravity. It is possibly similar to the helium-rich subdwarfs LSE 153, 259 and 263 (Husfeld et al 1989) or BD+37 442 and BD+37 1977(Jeffery & Hamann 2010 and hence the descendant of a helium-shell-burning giant rather than a helium-core-burning subdwarf. Detailed fine analysis of this and the higher-gravity subdwarfs in this group would address important questions about their origin and fate.…”

Section: Sp Sdo6mentioning

confidence: 87%

The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis

Jeffery

Miszalski

Snowdon

2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

A medium- and high-resolution spectroscopic survey of helium-rich hot subdwarfs is being carried out using the Southern African Large Telescope (SALT). Objectives include the discovery of exotic hot subdwarfs and of sequences connecting chemically-peculiar subdwarfs of different types. The first phase consists of medium-resolution spectroscopy of over 100 stars selected from low-resolution surveys. This paper describes the selection criteria, and the observing, classification and analysis methods. It presents 107 spectral classifications on the MK-like Drilling system and 106 coarse analyses (${\,T_{\rm eff}}, \log g, \log y$) based on a hybrid grid of zero-metal non-LTE and line-blanketed LTE model atmospheres. For 75 stars, atmospheric parameters have been derived for the first time. The sample may be divided into 6 distinct groups including the classical ‘helium-rich’ sdO stars with spectral types (Sp) sdO6.5 - sdB1 (74) comprising carbon-rich (35) and carbon-weak (39) stars, very hot He-sdO’s with Sp ≲ sdO6 (13), extreme helium stars with luminosity class ≲ 5 (5), intermediate helium-rich subdwarfs with helium class 25 – 35 (8), and intermediate helium-rich subdwarfs with helium class 10 − 25 (6). The last covers a narrow spectral range (sdB0 – sdB1) including two known and four candidate heavy-metal subdwarfs. Within other groups are several stars of individual interest, including an extremely metal-poor helium star, candidate double-helium subdwarf binaries, and a candidate low-gravity He-sdO star.

show abstract

Section: Sp Sdo6mentioning

confidence: 87%

The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis

Jeffery

Miszalski

Snowdon

2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…J1902−5130 (CD‐51 11879, LSE 263) was analysed by Husfeld et al (). They found T eff = 70 000 ± 2500 K, log g = 4.9 ± 0.25, [H/He] • < −1.0, [C/He] • = −4.0 ± 0.5 and [N/He] • = −2.4 ± 0.3.…”

Section: Catalogue Of Subluminous Starsmentioning

confidence: 99%

A selection of hot subluminous stars in theGALEXsurvey – II. Subdwarf atmospheric parameters

Németh

Kawka

Vennes

2012

Monthly Notices of the Royal Astronomical Society

152

298

View full text Add to dashboard Cite

We present an update of our low-resolution spectroscopic follow-up and model atmosphere analysis of hot subdwarf stars from the Galaxy Evolution Explorer (GALEX) survey. Targets were selected on the basis of colour indices calculated from the GALEX GR6 N UV , Guide Star Catalogue (GSC2.3.2) V and the Two Micron All Sky Survey (2MASS) J and H photometry. High signal-to-noise ratio spectra were obtained at the European Southern Observatory (ESO) and the Kitt Peak National Observatory (KPNO) over the course of three years. Detailed H, He and CNO abundance analysis helped us improve our T eff , log g and He abundance determination and to constrain CNO abundances. We processed 191 observations of 180 targets and found 124 sdB and 42 sdO stars in this sample while some blue horizontal branch stars were also found in this programme. With quantitative binary decomposition of 29 composite spectra we investigated the incidence of A, F and G type companions. The incidence of late G and K type companions and their effects on subdwarf atmospheric parameters were also examined.

show abstract

“…The same general approach was used in a number of published works, where non‐LTE computations of He i lines have been implemented with detail and surface . The model atom described by Husfeld et al (1989) can be mentioned as an example. The latest calculations of He i lines performed with { detail and surface are still based on a model atom, where only the transitions up to n = 4 are considered explicitly (McErlean, Lennon & Dufton 1998; Przybilla & Butler 2001; Przybilla, private communication).…”

Section: Selection Of He I Lines For Analysismentioning

confidence: 99%

Surface abundances of light elements for a large sample of early B-type stars – III. An analysis of helium lines in spectra of 102 stars

Lyubimkov

Rostopchin

Lambert

2004

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Non-local thermodynamic equilibrium analysis of He I lines in spectra of 102 B stars is implemented in order to derive the helium abundance He/H, the microturbulent parameter V t and the projected rotation velocity v sin i. A simultaneous determination of He/H and V t for the stars is effected by analysing equivalent widths of the 4471-and 4922-Å lines primarily as indicators of He/H and the 4713-, 5016-, 5876-and 6678-Å lines primarily as indicators of V t . The rotation velocities v sin i are found from profiles of the same lines. It is shown that, when V t > 7 km s −1 , the V t (He I) values determined from He I lines are systematically overestimated as compared with the V t (O II, N II) values derived from O II and N II lines. This discrepancy is especially appreciable for hot evolved B giants with V t (He I) = 16-23 km s −1 and may indicate a failure of classical model atmospheres to represent the strong He I lines for these stars.Two programme stars, HR 1512 and 7651, are found to be helium-weak stars. The remaining 100 stars are divided into three groups according to their masses M. The microturbulent parameter V t (He I) is low for all stars of group A (M = 4.1-6.9 M ) and for all stars with the relative ages t/t MS < 0.8 of group B (M = 7.0-11.2 M ). Their V t (He I) values are within the 0 to 5 km s −1 range, as a rule; the mean value is V t = 1.7 km s −1 . Only evolved giants of group B, which are close to the termination of the main-sequence (MS) evolutionary phase (t/t MS > 0.8), show V t (He I) up to 11 km s −1 . The helium abundance He/H is correlated with the relative age t/t MS in both groups; the averaged He/H enhancement during the MS phase is 26 per cent. For group C, containing the most massive stars (M = 12.4-18.8 M ), the V t (He I) values display a correlation with t/t MS , varying from 4 to 23 km s −1 . The He/H determination for hot evolved B giants of the group with V t (He I) > 15 km s −1 depends on a choice between the V t (He I) and V t (O II, N II) scales. The mean He/H enrichment by 67 per cent during the MS phase is found, if the abundances He/H are based on the V t (O II, N II) scale; however, two evolved giants with especially high v sin i, HR 7446 and 7993, show the He/H enhancement by about a factor of 2.5. When using the same V t scale, we found a trend of He/H with projected rotational velocities v sin i; a large dispersion for v sin i > 150 km s −1 can result from differences in masses M.A comparison with the stellar model computations with rotationally induced mixing shows that the observed helium enrichment during the MS phase can be explained by rotation with initial velocities 250-400 km s −1 . The He/H distribution on M and v sin i based on the V t (O II, N II) scale seems to be in better agreement with the theory than one based on the V t (He I) scale. The mean value He/H = 0.10 derived for stars in the zero age main sequence (ZAMS) vicinity can be adopted as the typical initial helium abundance for early B stars in the solar neighbourhood. Non-LTE computations of He ...

show abstract

NLTE-Analysis of Three Extremely Helium-Rich O-Type Subdwarfs

Cited by 19 publications

References 0 publications

The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis

The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis

A selection of hot subluminous stars in theGALEXsurvey – II. Subdwarf atmospheric parameters

Surface abundances of light elements for a large sample of early B-type stars – III. An analysis of helium lines in spectra of 102 stars

Contact Info

Product

Resources

About