Non-LTE abundances of magnesium, aluminum and sulfur in OB stars near the solar circle

Abstract

Abstract. Non-LTE abundances of magnesium, aluminum and sulfur are derived for a sample of 23 low-v sin i stars belonging to six northern OB associations of the Galactic disk within 1 kpc of the Sun. The abundances are obtained from the fitting of synthetic line profiles to high resolution spectra. A comparison of our results with HII region abundances indicates good agreement for sulfur while the cepheid abundances are higher. The derived abundances of Mg show good overlap with the cepheid results. The aluminum abundances for OB stars are significantly below the cepheid values. But, the OB star results show a dependence with effective temperature and need further investigation. The high Al abundances in the cepheids could be the result of mixing. A discussion of the oxygen abundance in objects near the solar circle suggests that the current mean galactic oxygen abundance in this region is 8.6-8.7 and in agreement with the recently revised oxygen abundance in the solar photosphere. Meaningful comparisons of the absolute S, Al and Mg abundances in OB stars with the Sun must await a reinvestigation of these elements with 3D hydrodynamical model atmospheres for the Sun. No abundance gradients are found within the limited range in galactocentric distances in the present study. Such variations would be expected only if there were large metallicity gradients in the disk.

A Low Solar Oxygen Abundance from the First‐Overtone OH Lines

“…This new determination of the oxygen abundance in the Sun is consistent with the abundance obtained in B and late O stars (Daflon et al 2003), solving the problem of the Sun being more oxygen-rich than the ISM. Nevertheless, the depth of the solar convection zone computed with the new solar abundance lines errors due to blends with Ni i and CN lines are considered.…”

“…2 This value was supported by the impressive agreement between the abundance obtained from the [O i] lines (Lambert 1978; A O ¼ 8:92 dex) and the pure rotation ; A O ¼ 8:91 dex) and fundamental vibration-rotation OH lines ; A O ¼ 8:93 dex). That solar oxygen abundance (A O ¼ 8:9) is high when compared to the abundance of nearby young OB stars (e.g., Daflon et al 2003; A O ¼ 8:6 8:7 dex). Considering that the Sun is about 4.6 Gyr old, its oxygen abundance is supposed to be lower than or equal to that of the present day interstellar medium (ISM).…”

Constrained fitting of disentangled binary star spectra: application to V615 Persei in the open cluster h Persei

“…We find a mean abundance of log (Mg) = 7.21 ± 0.07. This is 0.46 dex lower than the mean value found by Lyubimkov et al (2005) and 0.16 dex lower than that found by Daflon et al (2003) for OB stars in the solar circle. The components of V615 Per have a subsolar Mg abundance and resemble halo B stars more than nearby examples (Daflon et al 2004).…”

Radial velocity measurements of B stars in the Scorpius-Centaurus association

“…Radial-velocity standard stars were not observed. (The adopted linelists can be found in Daflon et al 2001Daflon et al , 2003 We inspected and identified all unblended lines visible in the spectral range between 3798 Å (H i) and 7065 Å (He i) in each target star: the number of measurable lines varied between 10 and 74, depending on the star spectral type, rotation velocity, possible multiplicity, but also on the signal-to-noise of the obtained spectra. (We note, however, that for the double lined binary HD 133242, it was possible to measure positions only for 4 lines in component A and 6 lines in component B.)…”