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Published May 10, 2014 | Published + Submitted
Journal Article Open

An Optical Spectroscopic Study of T Tauri Stars. I. Photospheric Properties


Estimates of the mass and age of young stars from their location in the H-R diagram are limited by not only the typical observational uncertainties that apply to field stars, but also by large systematic uncertainties related to circumstellar phenomena. In this paper, we analyze flux-calibrated optical spectra to measure accurate spectral types and extinctions of 281 nearby T Tauri stars (TTSs). The primary advances in this paper are (1) the incorporation of a simplistic accretion continuum in optical spectral type and extinction measurements calculated over the full optical wavelength range and (2) the uniform analysis of a large sample of stars, many of which are well known and can serve as benchmarks. Comparisons between the non-accreting TTS photospheric templates and stellar photosphere models are used to derive conversions from spectral type to temperature. Differences between spectral types can be subtle and difficult to discern, especially when accounting for accretion and extinction. The spectral types measured here are mostly consistent with spectral types measured over the past decade. However, our new spectral types are one to two subclasses later than literature spectral types for the original members of the TW Hya Association (TWA) and are discrepant with literature values for some well-known members of the Taurus Molecular Cloud. Our extinction measurements are consistent with other optical extinction measurements but are typically 1 mag lower than near-IR measurements, likely the result of methodological differences and the presence of near-IR excesses in most CTTSs. As an illustration of the impact of accretion, spectral type, and extinction uncertainties on the H-R diagrams of young clusters, we find that the resulting luminosity spread of stars in the TWA is 15%-30%. The luminosity spread in the TWA and previously measured for binary stars in Taurus suggests that for a majority of stars, protostellar accretion rates are not large enough to significantly alter the subsequent evolution.

Additional Information

© 2014 The American Astronomical Society. Received 2013 August 26; accepted 2014 March 4; published 2014 April 22. We thank the referee for helpful comments that improved the clarity and robustness of the results. We appreciate valuable discussions with Suzan Edwards, Adam Kraus, Sylvie Cabrit, Kevin Covey, and Davide Fedele, and also thank Kraus for help with a Taurus membership database. G.J.H. appreciates financial support for this project provided by the Youth Qianren Program of the National Science Foundation of China and the Observatoire de Paris for hosting him as a visiting astronomer.

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Published - 0004-637X_786_2_97.pdf

Submitted - 1403.1675v1.pdf


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