Astron. Astrophys. Suppl. Ser. 140, 261-277

The effective temperature scale of giant stars (F0-K5)

II. Empirical calibration of $T_{{\rm eff}}$ versus colours and [Fe/H]

A. Alonso - S. Arribas - C. Martínez-Roger

Send offprint request: A. Alonso

Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
e-mail: aas@ll.iac.es, sam@ll.iac.es and cmr@ll.iac.es

Received March 19; accepted July 23, 1999

Abstract:

We present calibrations of the effective temperatures of giant stars versus [Fe/H] and colours (U-V), (B-V), (R-I), (V-R), (V-I), (V-K), (J-H), (J-K), (I-K), (V-L'), (b-y) and (u-b). These calibrations are based on a large sample of field and globular cluster stars which roughly cover spectral types from F0 to K5. Their effective temperatures, scaled to direct $T_{{\rm eff}}$ determinations via reliable angular diameter measurements, were derived by applying the infrared flux method. The empirical relations have been fitted to polynomials of the form $\theta_{{\rm eff}} = P({\rm colour,[Fe/H]})$ by using the least squares method. The precision of the fits ranges from 40 K for (V-K)to 170 K for (J-H). We tabulate intrinsic colours of giant stars in the ranges: 3500 K $\leq T_{{\rm eff}} \leq$ 8000 K; -3.0 $\leq [{\rm Fe/H}] \leq +0.5$. We also present the calibration of BC(V) as a function of log $(T_{{\rm eff}})$ and metallicity. Finally, we compare the resulting scale of temperatures with previous works.

Key words: stars: fundamental parameters -- stars: Population II -- stars: giants -- stars: atmospheres -- stars: general