Detailed analysis of Balmer lines in cool dwarf stars

Abstract

Abstract. An analysis of Hα and Hβ spectra in a sample of 30 cool dwarf and subgiant stars is presented using MARCS model atmospheres based on the most recent calculations of the line opacities. A detailed quantitative comparison of the solar flux spectra with model spectra shows that Balmer line profile shapes, and therefore the temperature structure in the line formation region, are best represented under the mixing length theory by any combination of a low mixing-length parameter α and a low convective structure parameter y. A slightly lower effective temperature is obtained for the sun than the accepted value, which we attribute to errors in models and line opacities. The programme stars span temperatures from 4800 to 7100 K and include a small number of population II stars. Effective temperatures have been derived using a quantitative fitting method with a detailed error analysis. Our temperatures find good agreement with those from the Infrared Flux Method (IRFM) near solar metallicity but show differences at low metallicity where the two available IRFM determinations themselves are in disagreement. Comparison with recent temperature determinations using Balmer lines by Fuhrmann (1998Fuhrmann ( , 2000, who employed a different description of the wing absorption due to self-broadening, does not show the large differences predicted by Barklem et al. (2000b). In fact, perhaps fortuitously, reasonable agreement is found near solar metallicity, while we find significantly cooler temperatures for low metallicity stars of around solar temperature.

Regular frequency patterns in the youngδScuti star HD 261711 observed by the CoRoT and MOST satellites

“…Because of gaps in the spectral orders in the red, the Hα line is not fully covered. We normalised the Hγ line using the artificial flat-fielding technique described in Barklem et al (2002), which has already proven to be successful with TS data (Fossati et al 2011b). To supplement the Hγ observation acquired at Mc Donald Observatory, we obtained a low resolution (R ∼ 15 000) spectrum, covering Hα (6470-6710 Å), with the 1.8-m telescope of the Dominion Astrophysical Observatory (Canada).…”

The Hamburg/ESO R-process enhanced star survey (HERES)

“…independently determined the effective temperatures of both stars by applying the Stark broadening theory described in Stehlé & Hutcheon (1999) and the self-broadening theory of Barklem et al (2000), using MARCS model atmospheres, and adopting HERES surface gravities and metallicities. Synthetic profiles fits were performed for both Hα and Hβ, using an automated procedure (see Barklem et al 2002). This approach yielded T eff = 5060 K for HE 1219−0312.…”

Model Atmospheres with Individualized Abundances

“…In most cases the v turb damping constants and necessary to compute the C 4 C 6 Lorentzian width are supplied with the line list. For the strongest lines of the most abundant neutral and singly ionized atoms VALD provides van der Waals broadening parameters based on accurate quantum mechanical calculations (Barklem, Piskunov, & OÏMara 2000b …”

“…As for the numerical procedures and approximations used we started with the SYNTHE code of Kurucz (1993b) who in turn adopted the code by Peterson but also added the proper treatment of the Ðne splitting of the a lines in each series. We have also included the broadening of hydrogen lines by collisions with the neutral ground-state hydrogen atoms (Barklem, Piskunov, & OÏMara 2000c ;Barklem et al 2000a) extending the techniques, which were previously successfully applied to metallic lines. This e †ect becomes particularly important at cooler temperatures.…”