Search for vertical stratification of metals in atmospheres of blue horizontal-branch stars

Abstract

The observed abundance peculiarities of many chemical species relative to the expected cluster metallicity in blue horizontal-branch (BHB) stars presumably appear as a result of atomic diffusion in the photosphere. The slow rotation (typically $v\sin i<$ 10 km s${}^{-1}$) of BHB stars with effective temperatures $T_{\mathrm{eff}}>$ 11,500 K supports this idea since the diffusion mechanism is only effective in a stable stellar atmosphere. In this work we search for observational evidence of vertical chemical stratification in the atmospheres of six hot BHB stars: B84, B267 and B279 in M15 and WF2-2541, WF4-3085 and WF4-3485 in M13. We undertake an abundance stratification analysis of the stellar atmospheres of the aforementioned stars, based on acquired Keck HIRES spectra. We have found from our numerical simulations that three stars (B267, B279 and WF2-2541) show clear signatures of the vertical stratification of iron whose abundance increases toward the lower atmosphere, while the other two stars (B84 and WF4-3485) do not. For WF4-3085 the iron stratification results are inconclusive. B267 also shows a signature of titanium stratification. Our estimates for radial velocity, $v\sin i$ and overall iron, titanium and phosphorus abundances agree with previously published data for these stars after taking the measurement errors into account. The results support the hypothesis regarding the efficiency of atomic diffusion in the stellar atmospheres of BHB stars with $T_{\mathrm{eff}}>$ 11,500 K.

arXiv comment8 pages, 12 figures, accepted for publication in Astronomy and Astrophysics

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Cited by in corpus (12)

• The Chemical Compositions of Non-Variable Red and Blue Field Horizontal Branch Stars
• Stratification of the elements in the atmospheres of blue horizontal-branch stars
• Vertical stratification of iron in atmospheres of blue horizontal-branch stars
• Project VeSElkA: Analysis of Balmer line profiles in slowly rotating chemically peculiar stars
• Abundances and search for vertical stratification in the atmospheres of four HgMn stars
• Hot horizontal branch stars in NGC 288 - effects of diffusion and stratification on their atmospheric parameters
• An abundance analysis from the STIS-HST UV spectrum of the non-magnetic Bp star HR 6000
• Project VeSElkA: results of abundance analysis for HD53929 and HD63975
• NLTE spectroscopic analysis of the ${}^3$He anomaly in subluminous B-type stars
• Project VeSElkA: Abundance analysis of chemical species in HD41076 and HD148330
• Spectral analysis and abundances of the post-HB star HD 76431
• Project VeSElkA: Search for vertical stratification of element abundances in HD157087