Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt.........1t&link_type=abstract
Ph.D. Thesis California Inst. of Tech., Pasadena.
Astronomy and Astrophysics
Astronomy
5
Astronomical Catalogs, Infrared Photometry, Infrared Spectra, Sky Surveys (Astronomy), Star Formation, Brown Dwarf Stars, Dwarf Stars, Emission Spectra, Stellar Luminosity, Stellar Magnitude, Stellar Mass
Scientific paper
A 270 square degree photometric catalogue from plate material of the UKSRC and POSSII surveys was constructed. The procedures used and quality checks applied are described in detail, and should be considered as illustrative for those planning scientific programs with the forthcoming scans of these surveys. Infrared JHKLL photometry and low resolution infrared spectra (lambda is approximately equal to 1.0-2.5 microns) 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. Some of the current problems associated with the effective temperature scale for very low mass stars was examined. First results are presented from a CCD trigonometric parallax program at the Palomar 60 in telescope. The number of extremely late M-dwarfs (Mbol greater than 13) with directly measured distances was doubled. Structure in the main-sequences so constructed suggest that the faintest known stars may not be stably supported by nuclear burning. It is shown that sigma(pi) less than or equal to 0.004 in. can be obtained in a few years using standard CCD's on a common-user telescope. Infrared K-band photometry of complete samples of VLM candidates selected by our photographic catalogues are presented, and a bolometric luminosity function which extends to Mbol = 13.75 was constructed. Significant evidence for a luminosity function decreasing towards these luminosities was found. The data are consistent with the results of studies based on the Nearby Star sample. The observed LF was converted into the form of a mass function which extends with reasonable statistics to 0.08 solar mass - the H-burning minimum mass. The mass function 'turns over' at approximately 0.25 solar mass, goes through a local minimum at approximately 0.15 solar mass, and seems to increase again below 0.1 solar mass - none of these features are predicted by any of the current theories of star formation. Lastly, the mass density observed 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.
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