Other
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21533503n&link_type=abstract
American Astronomical Society, AAS Meeting #215, #335.03; Bulletin of the American Astronomical Society, Vol. 42, p.435
Other
Scientific paper
V3798 Sgr is an irregular variable that was first classified as an RV Tau (Hoffleit 1972) and later as a candidate UXor (Springob et al. 1997). We reduced 11 spectra of the star taken on three epochs with the spectrometer of the Hiltner reflector at MDM Obs. on Kitt Peak, AZ, and with the FAST Spectrometer on the Tillinghast Reflector at the Whipple Obs. on Mount Hopkins, AZ. The spectra show strong hydrogen and other absorption lines and a strongly variable emission in the core of Hα. The strength of the CaII K line and the presence of Hα emission allow us to classify the star as Herbig Ae, which is compatible with being an UXor. Photometric monitoring of the star with the 0.6-m telescope of the Maria Mitchell Observatory shows irregular drops of brightness typical of UXors, up to 1m in the R band. However, during the periods where the spectra were taken, the star did not exhibit variations greater than 0.2m in R, and the equivalent width of the hydrogen absorption lines did not vary by more than ≈ 5%, whereas the Hα emission varied dramatically, up to a factor of 7 on a time scale of a few days. This is an apparent contradiction to the widely accepted model of UXors, according to which the drops of continuum brightness are due to occasional occultations of the star by circumstellar dust clouds and the emission lines originate in a virtually invariable ionized shell. We explore the possibility to explain the observations by a combination of the dust occultation model with the less popular model involving accretion. The authors thank D. Latham for help with obtaining spectra on the Tillinghast telescope. This project was supported by the NSF/REU grant AST-0851892 and the Nantucket Maria Mitchell Association.
Nielsen Jennifer
Strelnitski Vladimir
Thorstensen John
Walker Gabrielle
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