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Applicability of colour index calibrations to T Tauri stars

T. Sch÷ning, M. Ammler-von Eiff

Abstract
We examine the applicability of effective temperature scales of several broad band colours to T Tauri stars(TTS). We take into account different colour systems as well as stellar parameters like metallicity and surface gravity which influence the conversion from colour indices or spectral type to effective temperature. For a large sample of TTS, we derive temperatures from broad band colour indices and check if they are consistent in a statistical sense with temperatures inferred from spectral types. There are some scales(for V-H, V-K, I-J, J-H, and J-K) which indeed predict the same temperatures as the spectral types and therefore can be at least used to confirm effective temperatures. Furthermore, we examine whether TTS with dynamically derived masses can be used for a test of evolutionary models and effective temperature calibrations. We compare the observed parameters of the eclipsing T Tauri binary V1642 Ori A to the predictions of evolutionary models in both the H-R and the Kiel diagram using temperatures derived with several colour index scales. We check whether the evolutionary models and the colour index scales are consistent with coevality and the dynamical masses of the binary components. It turns out that the Kiel diagram offers a stricter test than the H-R diagram. Only the evolutionary models of cite {BCAH98} with mixing length parameter alpha=1.9 and of cite{DM94,DM97} show consistent results in the Kiel diagram in combination with some conversion scales of cite{HBS00} and of cite{KH95}.

Keywords
stars: fundamental: parameters - stars: individual:(V1642 Ori A) - stars: pre-main: sequence

Astronomische Nachrichten
Volume 329, Number 1, Page 26
2008 January

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Instituto de Astrof├şsica e Ci├¬ncias do Espa├žo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Funda├ž├úo para a Ci├¬ncia e a Tecnologia
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