The Keele-Exeter young cluster survey - I. Low-mass pre-main-sequence stars in NGC 2169
Monthly Notices of the Royal Astronomical Society
Oxford University Press (OUP) / Royal Astronomical Society
We have used RCIC CCD photometry from the Isaac Newton telescope and intermediate-resolution spectroscopy from the Gemini North telescope to identify and characterize low-mass (0.15 < M/M⊙ < 1.3) pre-main-sequence stars in the young open cluster NGC 2169. Isochrone fitting to the high- and low-mass populations yields an intrinsic distance modulus of 10.13+0.06−0.09 mag and a model-dependent age of 9 ± 2 Myr. Compared to the nearby, kinematically defined groups of a similar age, NGC 2169 has a large low-mass population which potentially offers a more precise statistical investigation of several aspects of star formation and early stellar evolution. By modelling the distribution of low-mass stars in the IC versus RC−IC diagram, we find that any age spread among cluster members has a Gaussian full width at half-maximum (FWHM) ≤ 2.5 Myr. A young age and a small age spread (<10 Myr) are supported by the lack of significant lithium depletion in the vast majority of cluster members. There is no clear evidence for accretion or warm circumstellar dust in the low-mass members of NGC 2169, bolstering the idea that strong accretion has ceased and inner discs have dispersed in almost all low-mass stars by ages of 10 Myr.
Based on observations obtained at the Gemini Observatory (program GN-2005B-Q-30), which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Particle Physics and Astronomy Research Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil) and CONICET (Argentina). Also based on observations made with the INT which is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. This publication makes use of data products from the 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. NJM acknowledges the receipt of a studentship funded by the UK Particle Physics and Astronomy Research Council.
This is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this record.
Vol. 376 (2), pp. 580 - 598