Astronomy and Astrophysics, volume 285, 585-594 (1994/5-2)
Balmer lines in cool dwarf stars II. Effective temperatures and calibration of colour indices.
FUHRMANN K., AXER M. and GEHREN T.
Abstract (from CDS):
Effective temperatures obtained from synthesis of the extended profile wings of the first four Balmer lines are presented for more than 100 dwarfs and subgiants of different metal abundances and surface gravities in the temperature range from 5000 to 6500 K. Line formation is based on homogeneous ODF blanketed model atmospheres in LTE. The resulting temperatures of the more metal-rich stars differ systematically from those determined by reference to synthetic broad- or intermediate-band colours such as B-V , b-y , R-I or V-K . While the Balmer line temperatures give room to only very small individual errors and result in a convincingly small mean error for all four lines, the scatter against temperatures determined from broad-band colours is by far outside the internal errors claimed in recent applications. This may be attributed to either (a) observational errors, (b) dependence on the relative mixture of metal abundances, (c) unknown line blocking in most of the visible and near-infrared spectrum or (d) the inhomogeneity found in the granular patterns of stellar surfaces. Our results suggest that broad-band colours are insufficient individual temperature indicators, reliable only in a statistical sense.