Journal Article

Spectrophotometric properties of pre-main-sequence stars: the ε Chamaeleontis cluster

A.-Ran Lyo, Warrick A. Lawson and M. S. Bessell

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 389, issue 3, pages 1461-1469
Published in print September 2008 | ISSN: 0035-8711
Published online September 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13688.x
Spectrophotometric properties of pre-main-sequence stars: the ε Chamaeleontis cluster

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We present a study of flux-calibrated low-resolution optical spectroscopy of 10 stars belonging to eight systems in the ∼5-Myr-old ε Chamaeleontis (ε Cha) pre-main-sequence (PMS) star cluster. Using synthetic broad-band colours, narrow-band continuum, atomic and molecular lines derived from the spectra, we compare the ε Cha stars to a slightly older PMS cluster, the ≈8-Myr-old η Cha cluster and to main-sequence dwarfs. Using synthetic VRI colours and other indices, we find that the relationship between broad-band colours and spectroscopic temperature indicators for ε Cha cluster members is indistinguishable from that of Gyr-old dwarfs. This result is identical to that found earlier in η Cha. Gravity-sensitive line indices place the cluster between the giant and dwarf sequences, and there is clear evidence that ε Cha stars have lower surface gravity than η Cha stars. This result is consistent with ε Cha being the slightly younger PMS association, a few Myr younger according to the Hertzsprung–Russell (HR) diagram placement of these two clusters and comparison with PMS evolutionary grids. Late M-type ε Cha cluster members show a B-band flux excess of ≈0.2 mag compared to observations of standard dwarfs, which might be related to enhanced magnetic activity. A similar level of excess B-band emission appears to be a ubiquitous feature of low-mass members of young stellar populations with ages less than a few hundred Myr, a very similar time-scale to the PMS phase of elevated relative X-ray luminosity.

Keywords: stars: fundamental parameters; stars: pre-main-sequence; open clusters and associations: individual: ε Chamaeleontis

Journal Article.  5552 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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