The faintest stars

Citation

Tinney, Christopher G. (1993) The faintest stars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/0wrn-f607. https://resolver.caltech.edu/CaltechETD:etd-09242008-091045

Abstract

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We construct a 270 square degree photometric catalogue from plate material of the UKSRC and POSSII surveys. The procedures used and quality checks applied are described in detail, and should be considered as illustrative for those planning scientific programmes with the forthcoming scans of these surveys.

Infrared JHKLL' photometry and low resolution infrared spectra (λ ≈ 1.0-2.5μm) for a selection of the latest stars known are presented. The combined photometric and spectral data are used to evaluate bolometric corrections and bolometric magnitudes for late type M-dwarfs almost 2-magnitudes fainter than the faintest previously measured objects. We examine some of the current problems associated with the effective temperature scale for very low mass stars.

First results are presented from a CCD trigonometric parallax programme at the Palomar 60" telescope. We double the number of extremely late M-dwarfs (M[subscript bol] > 13) with directly measured distances. Structure in the main sequences so constructed suggest that the faintest known stars may not be stably supported by nuclear burning. We show that σ(π) ≤ 0.004" can be obtained in a few years using standard CCDs on a common-user telescope.

We present infrared K-band photometry of complete samples of VLM candidates selected by our photographic catalogues, and construct a bolometric luminosity function which extends to M[subscript Bol] = 13.75. We find significant evidence for a luminosity function decreasing towards these luminosities. We also find that our data are consistent with the results of studies based on the Nearby Star sample. We convert our observed LF into the form of a mass function which extends with reasonable statistics to 0.08M[...] — the H-burning minimum mass. The mass function 'turns over' at ≈ 0.25M[...], goes through a local minimum at ≈ 0.15M[...], and seems to increase again below 0.1M[...] — none of these features are predicted by any of the current theories of star formation. Lastly, the mass density we observe just above the H-burning minimum mass makes it difficult to envisage brown dwarfs contributing significant quantities of missing mass without invoking either a mass function in this region significantly steeper than that seen for main sequence stars, or an extremely low cut-off mass to the mass function.

Thesis Files