2009/07/14 by Tim Naylor · 2 citations
Physics and Astronomy · Social Sciences · #Astronomy and Astrophysical Research #Educational Leadership and Practices #Hertzsprung–Russell diagram #Main sequence #Scale (ratio) #Sequence (biology) #Stars #Statistic #Stellar, planetary, and galactic studies #astro-ph.IM #astro-ph.SR
paper · pdf · doi:10.1111/j.1365-2966.2009.15295.x
13 pages, 9 figures, accepted form MNRAS
arxiv created 2009/07/14 · openalex publication_date 2009/08/19 · arxiv updated 2015/05/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We fit the colour–magnitude diagrams of stars between the zero-age main-sequence and terminal-age main sequence in young clusters and associations. The ages we derive are a factor of 1.5–2 longer than the commonly used ages for these regions, which are derived from the positions of pre-main-sequence stars in colour–magnitude diagrams. From an examination of the uncertainties in the main-sequence and pre-main-sequence models, we conclude that the longer age scale is probably the correct one, which implies that we must revise upwards the commonly used ages for young clusters and associations. Such a revision would explain the discrepancy between the observational lifetimes of protoplanetary discs and theoretical calculations of the time to form planets. It would also explain the absence of clusters with ages between 5 and 30 Myr. We use the τ2 statistic to fit the main-sequence data, but find that we must make significant modifications if we are to fit sequences which have vertical segments in the colour–magnitude diagram. We present this modification along with improvements to the methods of calculating the goodness-of-fit statistic and parameter uncertainties. Software implementing the methods described in this paper is available from http://www.astro.ex.ac.uk/people/timn/tau-squared/.