[Special characters cannot be displayed. Please see the pdf version of the Abstract for an accurate reproduction.] We studied the circumstellar discs, the initial mass function (IMF), mass distribution, binarity and the fundamental properties of the [special character] 9 Myr-old pre-main sequence (PMS) [special character] Chamaeleontis cluster. Using JHKL colour-colour and colour-excess diagrams, we found the circumstellar disc fraction to be [special character] 0.60 among the late-type members. Four stars with [special character] (K - L) > 0.4 were identified as experiencing ongoing accretion which was later confirmed by high-resolution spectroscopic study. Quantitative analysis of the H[special character] profiles found accretion in these four stars at rates comparable to that of two members of the similarly-aged TW Hydrae Association (TWA); rates 1 - 3 orders of magnitude lower than in younger classical T Tauri stars. Together these results suggest that, while the mass accretion rate decreases with age, PMS stars can retain their inner discs for [special character] 10 Myr. An optical photometric survey spanning 1.3 ?? 1.3 pc added two low-mass stars to the cluster inventory. Together with other recent surveys the population is likely to be significantly complete for primaries with masses M > 0.15M[special character]. The cluster now consists of 18 primaries and 9 confirmed and candidate secondaries, with [special character] 2-4 times higher multiplicity than seen in field dwarfs. The cluster IMF is consistent with that of rich young clusters and field stars. By extending the IMF to lower masses, we predict 20-29 low-mass stars and brown dwarfs may remain undiscovered. From study of the cluster???s spatial and mass distribution, we find the [special character] Cha cluster has significant mass segregation, with > 50 per cent of the stellar mass residing within the central 0.17 pc. Lastly we classified members of the cluster with low-resolution spectra, providing information about the fundamental properties of the PMS stars by comparison to standard dwarfs. Broadband VRI colours and pseudocontinuum indices derived for the cluster stars are indistinguishable from dwarfs at visual and red wavelengths. This suggests the temperature sequence for the PMS [special character] Cha cluster is similar to that of the dwarf sequence. Narrow-band spectral indices for the [special character] Cha cluster possibly indicate higher metallicity and strongly indicate lower surface gravity than the dwarf indices.
| Identifer | oai:union.ndltd.org:ADTP/240789 |
| Date | January 2004 |
| Creators | Lyo, A-Ran, Physical, Environmental & Mathematical Sciences, Australian Defence Force Academy, UNSW |
| Publisher | Awarded by:University of New South Wales - Australian Defence Force Academy. School of Physical, Environmental and Mathematical Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright A-Ran Lyo, http://unsworks.unsw.edu.au/copyright |
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