9/14/2023 0 Comments O type main sequence star![]() ![]() (2004) showed that the relationship between colours and spectroscopic temperature indicators for the ≈8-Myr-old η Chamaeleontis (η Cha) cluster was indistinguishable from that for Gyr-old disc dwarfs, although the spectra showed some evidence for higher metallicity and clear evidence for lower gravity. Using synthetic broad-band colours, narrow-band continuum, atomic and molecular line indices derived from calibrated spectra, we can study temperature, surface gravity and metallicity effects, e.g. Bessell 1991 Lyo, Lawson & Bessell 2004). For nearby stars and stellar associations, such observations are readily obtained even with telescopes of modest aperture (e.g. Stars: fundamental parameters, stars: pre-main-sequence, open clusters and associations: individual: ε Chamaeleontis 1 INTRODUCTIONĪnalysis of flux-calibrated low-resolution optical spectra is a useful method for investigating the physical properties of stars in comparison with spectra of standard stars with well-defined properties. 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. 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. 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. 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 identical to that found earlier in η Cha. 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. 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. 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. ![]()
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