Open AccessThe spectroscopic characteristics of intermediate‐aged pre‐main‐sequence stars: the η Chamaeleontis cluster
Author(s) -
Lyo ARan,
Lawson Warrick A.,
Bessell M. S.
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.08318.x
Subject(s) - physics , stars , astrophysics , metallicity , surface gravity , spectral line , open cluster , stellar classification , cluster (spacecraft) , hertzsprung–russell diagram , star cluster , effective temperature , blue straggler , main sequence , k type main sequence star , astronomy , stellar evolution , t tauri star , computer science , programming language
We present a study of calibrated low‐resolution spectra of the 18 known primaries of the ≈9‐Myr‐old η Chamaeleontis (η Cha) pre‐main‐sequence (PMS) star cluster. Using synthetic broad‐band colours and narrow‐band continuum‐sensitive, temperature‐sensitive and gravity‐sensitive indices derived from the spectra, we compare the η Cha stars to standard dwarfs. We find that the VRI colours of the PMS stars are indistinguishable from those of main‐sequence stars, but that a B ‐band excess attaining ≈0.2 mag for late‐M cluster stars is present, which might be an indicator of gravity, metallicity and/or activity differences between the two samples of stars. The narrow‐band spectral indices for the η Cha stars possibly indicate higher metallicity and strongly indicate lower surface gravity than the dwarf indices, consistent with the elevated location of the cluster in the Hertzsprung–Russell evolutionary diagram. Using the derived synthetic colours and indices, we adopt spectral types for the late‐type η Cha stars. We then produce a table of absolute optical magnitudes and colours representing the cluster isochrone for comparison with PMS evolutionary models. From our results we also conclude that the η Cha stars are unreddened, consistent with the group being a sample of older PMS stars distant from obscuring molecular clouds, except for the A1 member HD 75505 for which we confirm A V = 0.4 mag likely due to the presence of circumstellar material.