Applicability of colour index calibrations to T Tauri stars

TL;DR

This study evaluates the effectiveness of various broad band colour indices in determining the effective temperatures of T Tauri stars, comparing them with spectral types and evolutionary models to identify reliable calibration scales.

Contribution

It identifies specific colour index scales that accurately predict T Tauri star temperatures and tests their consistency with dynamical mass measurements and evolutionary models.

Findings

V-H, V-K, I-J, J-H, J-K scales match spectral type temperatures

Certain evolutionary models are consistent with dynamical masses in the Kiel diagram

Kiel diagram provides a stricter test than the H-R diagram

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 Baraffe et al. (1998) with mixing length parameter 1.9 and of D'Antona & Mazzitelli (1994, 1997) show consistent results in the Kiel diagram in combination with some conversion scales of Houdashelt et al. (2000) and of Kenyon & Hartmann (1995).