Age Of Pre-main Sequence Stars Research Articles

Lithium and age of pre-main sequence stars: the case of Parenago 1802

With the aim to test the present capability of the stellar surface lithium abundance in providing an estimation for the age of PMS stars, we analyze the case of the detached, double-lined, eclipsing binary system PAR 1802. For this system, the lithium age has been compared with the theoretical one, as estimated by applying a Bayesian analysis method on a large grid of stellar evolutionary models. The models have been computed for several values of chemical composition and mixing length, by means of the code FRANEC updated with the Trojan Horse reaction rates involving lithium burning.

Star formation in the starburst cluster in NGC 3603

We have used new, deep, visible and near infrared observations of the compact starburst cluster in the giant HII region NGC 3603 and its surroundings with the WFC3 on HST and HAWK-I on the VLT to study in detail the physical properties of its intermediate mass (~ 1 - 3 M_sun) stellar population. We show that after correction for differential extinction and actively accreting stars, and the study of field star contamination, strong evidence remains for a continuous spread in the ages of pre-main sequence stars in the range ~ 2 to ~ 30 Myr within the temporal resolution available. Existing differences among presently available theoretical models account for the largest possible variation in shape of the measured age histograms within these limits. We also find that this isochronal age spread in the near infrared and visible Colour-Magnitude Diagrams cannot be reproduced by any other presently known source of astrophysical or instrumental scatter that could mimic the luminosity spread seen in our observations except, possibly, episodic accretion. The measured age spread and the stellar spatial distribution in the cluster are consistent with the hypothesis that star formation started at least 20-30 Myrs ago progressing slowly but continuously up to at least a few million years ago. All the stars in the considered mass range are distributed in a flattened oblate spheroidal pattern with the major axis oriented in an approximate South-East - North-West direction, and with the length of the equatorial axis decreasing with increasing age. This asymmetry is most likely due to the fact that star formation occurred along a filament of gas and dust in the natal molecular cloud oriented locally in this direction.

The Initial Mass Function and Young Brown Dwarf Candidates in NGC 2264. I. The Initial Mass Function around S Monocerotis

The young open cluster NGC 2264 was observed on 2002 January 6–7 with the CFH12K mosaic CCD on the 3.6 m Canada-France-Hawaii Telescope to investigate the shape of the initial mass function (IMF). In order to select the pre–main-sequence (PMS) members more completely, Chandra X-Ray Observatory archival data were retrieved and used for the identification of X-ray–emitting weak-line T Tauri stars. In addition, the (R-I, V-I) diagram was used to exclude background late-type giants, and a statistical approach was applied to estimate the number of contaminating foreground main-sequence stars. The shape of the IMF of the Chandra field of view is flat between log m = -0.4 and ∼-1.0 (m in solar mass units), with a weak signature of a dip near log m = -0.2. The overall shape of the IMF is very similar to those obtained for the Pleiades or the Trapezium. The fraction of disked PMS stars, as noted by Rebull and coworkers, does not show any signature of mass dependency. The age of PMS stars between log m = 0 and -1 is 3.1 ± 0.5 Myr.