Computer Science
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000phdt........62h&link_type=abstract
Thesis (PhD). THE PENNSYLVANIA STATE UNIVERSITY, Source DAI-B 61/12, p. 6514, Jun 2001, 244 pages.
Computer Science
1
Scientific paper
A digital survey was used to estimate the space density of nearby stars. Survey data were taken at the Palomar 5m telescope in 1994 and 1996. The data were CCD images which covered 39.3 square degrees of sky. The observations were done in transit mode, and span Galactic latitudes from -60° to -25° and +25° to +78°. Two custom filters were used, yielding limiting magnitudes of approximately R = 22 and I = 20. The original purpose of these data was to calibrate the positions of high redshift quasars found with grism surveys. Software was developed which searched through the data for red point-like objects which could be M dwarfs. A total of 36.51 square degrees of the survey was searched and analyzed and 31,786 M dwarf candidates were identified. Standard VRI magnitudes were measured for 5.1% of the stars in the survey. This allowed for conversion from Palomar instrumental fluxes in custom filters to standard VRI magnitudes. Classification spectra were obtained for 278 of the stars in the survey, confirming the relation of color to Spectral Type. The contamination rate by non-dwarfs in the color range +1.1 < V-I < +3.9 was found to be less than 1%. Distances were estimated based on the inferred V-I color and I apparent magnitude. A relation from the literature was used to determine the absolute magnitude, MI based on V-I. For the 24,652 M dwarf candidates used in the measurement of the luminosity function, statistical uncertainties in distance estimation were less than 37%. To model the selection effects present in this catalog and derive empirical estimates of the errors in the desired parameters, a Monte Carlo simulation of the Galaxy was created. The input parameters to the Galaxy simulation included the stellar luminosity function and the density structure of the Galaxy. The output was an artificial catalog of objects with positions and ri and zz apparent magnitudes, which could be compared directly with the observed catalog. These input parameters were adjusted to yield an artificial catalog which best matched the observed catalog, thereby measuring the local stellar luminosity function.
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