NGC2169

NGC2169 is the first cluster to be observed under the auspices of the Keele-Exeter young cluster survey (KEY clusters). The idea is to find and investigate the properties of clusters with age between 5 and 30 Myr, which are poorly represented in the current literature. It is in these clusters that high mass stars of 8-20 solar masses evolve off the main sequence, that the majority of pre-main sequence evolution and lithium depletion takes place in 0.2-2 solar mass stars and where circumstellar discs are dispersed and planetary systems formed. We plan to compare ages derived from high- and low-mass stellar isochrones and from Li-depletion calculations. Any discrepancies will highlight weaknesses in the current generation of evolutionary models and stellar interior physics.

Using the new tau^2 techniques described in Naylor & Jeffries (2006) we have investigated previously published photometry for high mass stars in NGC2169 as well as a new RI survey of the low-mass pre main sequence. These data are supported by Gemini spectroscopy of low-mass cluster candidates to confirm their membership, search for circumstellar accretion discs and investigate Li depletion.

We have found an intrinsic distance modulus of 10.04-10.19 mag and a (model-dependent) age of 9+/-2 Myr that is consistent with the upper limit available from the turn-off age of the high-mass stars. In addition we find that the (lack of) Li depletion seen in the cluster is also consistent with this age. Importantly, the lack of spread in the low-mass colour-magnitude diagram and the limited spread in observed Li depletion point to a spread of age in the cluster members that is less than a Gaussian FWHM of 2.5 Myr. No evidence for accretion is seen in the cluster implying that circumstellar material has largely dispersed from around low-mass stars by ages of 10 Myr.

The RI catalogue which was presented as Table 3 in the paper can be downloaded from here. In addition there is a gzipped, tar saveset of the spectra in fits format. The spectra are wavelength calibrated with telluric correction and a relative flux calibration applied. They have been normalised to the continuum level between 6690-6703A. Warning: The spectra contain two gaps in coverage caused by gaps between detectors in GMOS (see paper). The gaps have been filled in these spectra with an obvious linear interpolation.