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Paper: Optical Spectroscopy and Photometry of the Draco Molecular Cloud
Volume: 166, Stromlo Workshop on High-Velocity Clouds
Page: 56
Authors: Penprase, Bryan E.; Harris, Eirik; Covino, Elvira; Palazzi, Eliana; Rhodes, Jason D.; Schwarz, Hugo
Abstract: To investigate the distance and linear dimensions of the Draco Molecular Cloud (MBM 41) we have obtained new CCD photometry and optical spectra for a selection of stars toward regions near the center of the cloud. A catalog of photometry for 362 stars in 20 selected areas has been developed, in which V and B magnitudes for stars are presented down to the limiting magnitude of V = 19. The photometric sample V and B-V magnitudes are compared with star counts predicted by the galactic model of Bahcall and Soneria (1980). We find from the star counts a best fit of 2.0 < Av < 3.0, and 800 < d < 1300 pc. We have also observed 15 stars at medium resolution (R = 30,000) with the SOFIN spectrograph of the Nordic Optical Telescope (NOT). In our sample we positively detect the Draco Cloud in Na I D absorption in 6 of the spectra, where the stellar radial velocity has allowed the interstellar Na I D line to be resolved. Our observations detect the absorption from the cloud at -17.7 < vlsr < -26.5 km s^{-1}, and with column densities of Na I ranging from 3.31x10^{-12} < N(NaI) < 2.1x10 cm^{-2}. Synthesized stellar spectra from Kurucz models are compared with observed stellar absorption lines to derive an MK spectral classification. The luminosity effects in the regions of the spectra near the lines of H alpha, Mg I, Na I D, Ca II triplet, and KI are used to determine the 2D MK type for our stars, and the corresponding spectroscopic parallax is used to help constrain the distance to the Draco cloud. The results suggest distances between 800 < d < 1000 pc, or 500 < |z| < 615 pc, making the Draco molecular cloud the most distant known high galactic latitude molecular cloud.
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