Extinction, polarization, and star formation in clouds at high galactic latitude

Details Extinction, polarization, and star formation in clouds at high galactic latitude Extinction, polarization, and star formation in clouds at high galactic latitude

Oct 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.........1l&link_type=abstract

Thesis (PhD). RENSSELAER POLYTECHNIC INSTITUTE, Source DAI-B 60/04, p. 1650, Oct 1999, 168 pages.

Computer Science

Dust

Scientific paper

The goal of this project is to characterize interstellar dust in the environment of high-latitude translucent molecular clouds. I determine absolute extinction from near-infrared color excess of background stars and compare the shape of the near-infrared extinction curve and the value of the ratio of total-to-selective extinction (RV) to averages observed closer to the Galactic plane. Parameters characterizing high-latitude extinction span a much larger range than in diffuse lines of sight or in dense clouds, including unusually low values of RV. Observed extinction due to dust in molecular clouds is underestimated by the Burstein & Heiles method and depends more on local cloud environment than on global Galactic conditions. The shape of the polarization curve is similar to the average curve observed in the diffuse ISM, with less variation than is observed in the extinction curve. There is little correlation between extinction and polarization at high latitude, including the grain size parameters RV, and the wavelength of maximum polarization (λ max). I show how the various data observed toward the star HD 210121 are consistent with an enhanced abundance of small grains in the foreground cloud. I also show that variation in polarization efficiency in the high-latitude molecular cloud MBM 18 suggests that the cloud may have a complex structure. Identifying young stellar objects (YSOs) in the translucent environment will provide insight into the limits of conditions that lead to star formation. A search for infrared color excess in the Chamaeleon II region identifies four new T Tauri stars, all located at the translucent north-east boundary of the cloud. All of the known YSOs at high latitude have mid-infrared excess emission, but the isolated YSOs do not have near-infrared excess. I obtain near-infrared photometry of the most promising candidates from a catalog of IRAS-selected YSO candidates at high-latitude and find eight new YSOs. In general, these objects are not associated with any known molecular clouds and their origin is still not known.

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