A proper-motion separation of M4 members from field stars, using deep HST observations separated by a time base-line of 5 years, allows us to study a pure sample of cluster main-sequence stars almost to the minimum mass for hydrogen burning. High-precision photometry shows how badly current theoretical models fail to reproduce the color-magnitude diagram of low-mass stars of moderate metallicity ([M/H] ~ -1). This inability of theory to reproduce the luminosity-radius relation casts doubt on the theoretical mass-luminosity relation, which is needed to convert the observed luminosity function (LF) into a mass function (MF), as well as to convert our locally determined LF into a global MF. To the extent that we trust theoretical M-L relations for such transformations, we obtain a flat MF from the LF, and some indication that theoretical masses might be too low at a given luminosity, near the H-burning limit.
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view Abstract Citations (63) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Gap in the Color-Magnitude Diagram of NGC 2420:...
We present a catalog containing the measurements of 2262 sources, including 334 extended sources, 1915 point sources, and 13 known QSOs, in five SDSS passbands. Of these objects...
view Abstract Citations (282) References (125) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Uncertainties in the Modeling of Old Stellar Popu...
In this paper, we use the general theory worked out within the past few years for the structure and the evolution of low-mass stars to derive the stellar mass-function in the Ga...
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