Improving PARSEC models for very low mass stars

Abstract

Many stellar models present difficulties in reproducing basic observational relations of very low mass stars (VLMS), including the mass-radius relation and the optical colour-magnitudes of cool dwarfs. Here, we improve PARSEC models on these points. We implement the T -τ relations from PHOENIX BT-Settl model atmospheres as the outer boundary conditions in the PARSEC code, finding that this change alone reduces the discrepancy in the mass-radius relation from 8 to 5 per cent. We compare the models with multi-band photometry of clusters Praesepe and M 67, showing that the use of T -τ relations clearly improves the description of the optical colours and magnitudes. But anyway, using both Kurucz and PHOENIX model spectra, model colours are still systematically fainter and bluer than the observations. We then apply a shift to the above T -τ relations, increasing from 0 at T eff = 4730 K to ∼14% at T eff = 3160 K, to reproduce the observed mass-radius radius relation of dwarf stars. Taking this experiment as a calibration of the T -τ relations, we can reproduce the optical and near infrared CMDs of low mass stars in the old metal-poor globular clusters NGC 6397 and 47 Tuc, and in the intermediate-age and young solar-metallicity open clusters M 67 and Praesepe. Thus, we extend PARSEC models using this calibration, providing VLMS models more suitable for the lower main sequence stars over a wide range of metallicities and wavelengths. Both sets of models are available on PARSEC webpage.

The search for multiple populations in Magellanic Cloud clusters – I. Two stellar populations in the Small Magellanic Cloud globular cluster NGC 121

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The embedded clusters DBS 77, 78, 102, and 160−161, and their link with the interstellar medium

“…3.4). We employed the ZAMS obtained from Bressan et al (2012), Chen et al (2014Chen et al ( , 2015, Tang et al (2014) and we interpolated the stellar mass using the algorithm given by Steffen (1990). This procedure is valid only for MS stars.…”

Kepler-432: A Red Giant Interacting With One of Its Two Long-Period Giant Planets

“…Using the asteroseismically derived mass, radius, and age of the primary (see Section 5), we place the primary star on an appropriate Padova PARSEC isochrone (Bressan et al 2012;Chen et al 2014). We then use the observed magnitude differences between the stars to search for an appropriate match to the companion in the isochrone.…”