Draco Molecular Cloud

Draco Molecular Cloud
archived 10-25-99
Archive file# o102599c
donated by L. Savage

Detection of Optical Absorption Lines from the Draco Molecular Cloud
Bryan Penprase (Pomona College)
Friday August 14th; 15:50-16:15

We present results from a campaign of observations with the Nordic Optical Telescope (NOT) in La Palma in which we have obtained definite detections of the Draco Molecular CLoud in absorption toward 6 stars, and possible detection in several other stars.

Analysis of the spectral types for the program stars has enabled us to develop a 2D spectral classification algorithm, and from this we present spectroscopic parallax distances for the stars. New photometric observations combined with the spectral types allow us to contrain the estinction from the Draco Cloud among our sightlines with absorption line detections to 0.07 < E(B-V) < 0.43, suggesting Av within the cloud ranging from 0.25 < Av < 1.3 magnitudes. With the stellar distances, we may constrain the distance to the Draco cloud to 800 < d < 1000 pc, making this the most distant high galactic latitude cloud known.

The Draco cloud appears to be infalling into the plane of the galaxy, and at our estimated distance appears at a height 500 < |z| < 615 pc. The Na I absorption lines have been fit with a line profile model, and we have found column densities of Na I ranging from from 3.31x10^12 < N(NaI) < 2.1x10^13 cm^-2 . Comparison with H I emission shows that the velocity of the Na I absorption coincides with the HI emission from the cloud. We also present a spectrum in which stellar absorption lines from a high velocity star creates the appearance of a high velocity cloud, and discuss the relation between the Draco molecular cloud with other nearby high velocity cloud complexes.

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