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J.J.B. Harlow (Penn State)
An optical/near infrared CCD imaging survey was used to estimate the space density of low mass stars in the Galactic disk. The survey data, taken at the Palomar 5m telescope, covered 39.3 square degrees of sky over a large range of Galactic latitudes. Two custom filters were used, yielding limiting apparent magnitudes of approximately R=22 and I=20. A total 24,652 point-like objects with colors of M dwarfs were identified.
Palomar instrumental fluxes were converted to standard VRI magnitudes. Classification spectra were obtained for 278 of the stars in the survey. The contamination rate by non-dwarfs in the color range V-I between +1.1 and +3.9 was found to be less than one percent. Distances were estimated based on the inferred V-I color and I apparent magnitude. Statistical uncertainties in fluxes and color transformations led to 1\sigma distance uncertainties less than or equal to 37 percent.
To model the selection effects present in the catalog and derive empirical estimates of the uncertainties 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 instrumental apparent magnitudes, which was directly compared with the observed catalog.
The measured luminosity function is presented for absolute magnitudes MI between 7 and 14.Agreement is seen with previous measurements for MI brighter than 11, but with smaller error bars. For MI near 12, a higher number density is measured than has been reported for previous photometric studies. The corresponding Mass Function is slowly rising for decreasing mass near the brown dwarf limit of 0.08 solar masses. Future work is needed to obtain spectra of all of the stars with MI near 12, to confirm their dwarf nature.
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The author(s) of this abstract have provided an email address for comments about the abstract: jharlow@uop.edu