The superimposed photospheric and stellar wind variability of the O-type supergiant Camelopardalis
Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK e-mail: email@example.com
2 Institute of Astronomy, Bulgarian National Astronomical Observatory, PO Box 136, 4700 Smoljan, Bulgaria e-mail: [nmarkova;hmarkov]@astro.bas.bg
3 INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy e-mail: firstname.lastname@example.org
Accepted: 14 June 2006
Aims.This study seeks to provide empirical constraints on the different physical components that can yield temporal variability in predominantly or partially wind-formed optical lines of luminous OB stars, and thus potentially affect the reliable determination of fundamental parameters, including mass-loss rates via clumped winds.
Methods.Using time-series spectroscopy from epochs spread over ~4 years, we present a case study of the O9.5 supergiant α Cam. We demonstrate that the HeI λ5876 (23P0–33D) line is an important diagnostic for photospheric and wind variability in this star. The actions of large radial velocity shifts (up to ~30 km s-1) in the photospheric absorption lines can also affect the morphology of the H\alpha line profile, which is commonly used for measuring mass-loss rates in massive stars.
Results.We identify a 0.36-day period in subtle absorption profile changes in HeI λ5876, which likely reveals the photospheric structure, perhaps due to low-order non-radial pulsations. This signal persists over ~2 months, but it is not present 2 years later (November 2004); it is also not seen in the stellar wind components of the line profiles. Using a pure H\alpha line-synthesis code we interpret maximum changes in the redward and peak emission of α Cam in terms of mass-loss rate differences in the range ~5.1 10-6 to 6.5 10 yr-1. However, the models generally fail to reproduce the morphology of blueward (possibly absorptive) regions of the profiles.
Conclusions.The optical line profiles of α Cam are affected by (i) deep-seated fluctuations close to, or at, the photosphere, (ii) atmospheric velocity gradients, and (iii) large-scale stellar wind structure. This study provides new empirical perspectives on accurate line-synthesis modelling of stellar wind signatures in massive luminous stars.
Key words: stars: early-type / stars: mass-loss / stars: individual: α Camelopardalis
© ESO, 2006