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

TL;DR

This study analyzes the spectrophotometric properties of pre-main sequence stars in the Epsilon Chamaeleontis cluster, comparing their spectral and photometric features to other clusters and main-sequence stars to understand their physical characteristics.

Contribution

It provides new insights into the spectral properties, surface gravity, and magnetic activity of young PMS stars in the Epsilon Chamaeleontis cluster, highlighting differences from older clusters and main-sequence stars.

Findings

Eps Cha stars have similar colour-temperature relations as Gyr-old dwarfs.

Surface gravity of Eps Cha stars is lower than Eta Cha stars, consistent with younger age.

Late M-type members show B-band excess likely due to magnetic activity.

Abstract

We present a study of flux-calibrated low-resolution optical spectroscopy of ten stars belonging to eight systems in the ~ 5 Myr-old Epsilon Chamaeleontis (Eps Cha) pre-main-sequence (PMS) star cluster. Using synthetic broadband colours, narrow-band continuum, atomic and molecular lines derived from the spectra, we compare the Eps Cha stars to a slightly older PMS cluster, the ~ 8 Myr-old Eta Cha cluster, and to main-sequence dwarfs. Using synthetic VRI colours and other indices, we find that the relationship between broadband colours and spectroscopic temperature indicators for Eps Cha cluster members is indistinguishable from that of Gyr-old dwarfs. This result is identical to that found earlier in Eta Cha. Gravity-sensitive line indices place the cluster between the giant and dwarf sequences, and there is clear evidence that Eps Cha stars have lower surface gravity than Eta Cha stars. This result is consistent with Eps 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 Eps 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 timescale to the PMS phase of elevated relative X-ray luminosity.