A new method for an objective,χ²-based spectroscopic analysis of early-type stars

Abstract

Astrophysics ABSTRACTContext. A precise quantitative spectral analysis, encompassing atmospheric parameter and chemical elemental abundance determination, is time-consuming due to its iterative nature and the multi-parameter space to be explored, especially when done by the naked eye. Aims. A robust automated fitting technique that is as trustworthy as traditional methods would allow for large samples of stars to be analyzed in a consistent manner in reasonable time.Methods. We present a semi-automated quantitative spectral analysis technique for early-type stars based on the concept of χ 2 minimization. The method's main features are as follows: far less subjectivity than the naked eye, correction for inaccurate continuum normalization, consideration of the whole useful spectral range, and simultaneous sampling of the entire multi-parameter space (effective temperature, surface gravity, microturbulence, macroturbulence, projected rotational velocity, radial velocity, and elemental abundances) to find the global best solution, which is also applicable to composite spectra. Results. The method is fast, robust, and reliable as seen from formal tests and from a comparison with previous analyses. Conclusions. Consistent quantitative spectral analyses of large samples of early-type stars can be performed quickly with very high accuracy.

New and revised parameters for several southern OB binaries

“…We applied a new method developed by Irrgang et al (2014) for an objective spectroscopic analysis of early-type single and binary stars. The approach is based on a grid of synthetic spectra calculated under the assumption of line-blanketed, plane-parallel model atmospheres with appropriate non-LTE modifications.…”

On the 3He anomaly in hot subdwarf B stars

“…All model atoms were used to calculate non-LTE occupation number densities in statistical equilibrium within DETAIL and the emergent flux spectrum with SURFACE. We computed synthetic spectra, including spectral lines of H , He / , C / , N / , O , Ne , Mg , Al , Si / / , S / , Ar , and Fe , and employed updated model atoms of the ones listed in Irrgang et al (2014). Here, we restrict ourselves to the results on atmospheric parameters.…”

“…Arbitrary parameter combinations within this mesh could be approximated by linear interpolation between the calculated synthetic spectra. A detailed description on how we calculated individual model spectra is given in Irrgang et al (2014). Since it is extremely important to know the exact radial velocity v rad of the individual stellar spectrum in order to determine a meaningful abundance ratio 4 He/ 3 He, we implemented a precise radial velocity determination by including metal absorption lines in our fit routine.…”

“…We carried out the whole analysis in ISIS (Interactive Spectral Interpretation System; Houck & Denicola 2000) in analogy to the analysis of Irrgang et al (2014). ISIS made use of the whole spectrum at once, including all synthesized metal lines.…”

Links between surface magnetic fields, abundances, and surface rotation in clusters and in the field

“…Pavlovski & Southworth 2013) or spectrum synthesis accounting for both sources (e.g. Irrgang et al 2014).…”