EDP Sciences
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Volume 391, Number 3, September I 2002
Page(s) 1039 - 1052
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20020806

A&A 391, 1039-1052 (2002)
DOI: 10.1051/0004-6361:20020806

The determination of ${{\vec T}_{\sf eff}}$ for metal-poor A-type stars using ${\vec V}$ and 2MASS ${\vec J}$, ${\vec H}$ and ${\vec K}$ magnitudes

T. Kinman1 and F. Castelli2, 3

1  Kitt Peak National Observatory, National Optical Astronomy Observatories, Box 26732, Tucson, AZ 85726-6732, USA
2  Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, via del Fosso del Cavaliere, 00133 Roma, Italy
3  Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy
    e-mail: castelli@ts.astro.it

(Received 5 April 2002 / Accepted 27 May 2002)

Effective temperatures ( $T_{\rm eff}$) can be determined from $(V-J)_{\rm0}$, $(V-H)_{\rm0}$  and $(V-K)_{\rm0}$ colours that are derived from 2MASS magnitudes. This gives another way to estimate the $T_{\rm eff}$ of faint blue halo stars ( V $\la$ 15) whose temperatures are now usually deduced from $(B-V)_{\rm0}$. Transformations (adapted from Carpenter 2001b) are used to change colours derived from the 2MASS data to the Johnson system. $T_{\rm eff}$  is then derived from these colours using an updated Kurucz model. Tables are given to derive $T_{\rm eff}$ as a function of $(V-J)_{\rm0}$, $(V-H)_{\rm0}$ and $(V-K)_{\rm0}$ for a variety of metallicities and $\log g$ suitable for blue horizontal branch and main sequence stars. The temperatures obtained in this way are compared with those in the recent literature for various stars with 5 $\leq$ V $\leq$ 15 and $T_{\rm eff}$  in the range 6500 to 9500 K; systematic differences are ~100 K. An exception is the sample of BHB stars observed by Wilhelm et al. (1999) whose $T_{\rm eff}$  are significantly cooler than those we derive by an amount that increases with increasing temperature.

Key words: stars: fundamental parameters (temperatures) -- stars: horizontal-branch

Offprint request: T. Kinman, kinman@noao.edu

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