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Session 7 - Molecular Clouds.
Display session, Wednesday, January 07
Exhibit Hall,

[7.08] Photometric Distances to Dark Clouds and Small Bok Globules: Reddening Law Sensitivities

D. E. Peterson, D. Clemens (Boston University)

A new method of distance determination to small molecular clouds has been developed and applied to CB24, a small Bok globule from the catalog of Clemens and Barvainis (ApJS 1988). Using a (V-I) versus (B-V) color-color diagram for stars in the 13.7^\prime field, fifteen M dwarfs were identified. The colors are dereddened, using a standard extinction law, back to a zero-extinction line whose position was established from published data. From the extinctions measured toward the M dwarf stars, distances to the stars can be estimated.

The focus of this poster is an examination of the effects of different reddening/extinction laws on the dereddening method performed and how changes in the extinction law affect calculations of the distance moduli of the stars. The slope of the reddening line depends on the ratio of total extinction to color excess: R_V = A_V/E(B-V), where values of R_V are known to range from under 3 to at least 6. Using the extinction law of He et al. (ApJS 1995), a relationship was obtained between the E(V-I)/E(B-V) slope and total extinction. By selecting various R_V values, a range of slopes were established and used to perform the dereddening of the fifteen candidate CB24 M dwarfs.

One of the candidate reddened M dwarfs in the field of CB24 is projected within the optical boundary of CB24, and therefore is located behind the CB24 cloud. Thus a maximum distance to CB24 can be found based on the distance modulus of this M dwarf. The distance to this M dwarf, and consequently the maximum distance to the CB24 cloud, was found for the mean R_V (3.08) to be 360 pc. However, changes in the reddening law were found to have relatively minor effects on the derived distance. Thus the method is largely immune to distance errors induced by grain growth in cloud peripheries.

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