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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