AAVSO: American Association of Variable Star Observers

On the Classification of V3798 Sgr (Abstract)

Volume 36 number 2 (2008)

David Sliski

Abstract

(Abstract only) In 1972 D. Hoffleit classified V3798 Sgr as an RV Tau variable star. However Springob et al. (1998) suggested that it could be an UXOR—a star with sporadic drops of brightness. A retrospective study of the variability of the star was conducted using the Harvard Plate Collection. More than 250 plates were looked at with more than 120 measurements made. The plates were exposed as early as 1895 and as late as 1949. In addition the star was monitored in BVRI with a CCD camera on the Maria Mitchell Observatory (MMO) 24-inch telescope in 2007. In our study of V3798 Sgr, in both our CCD photometry and the plate study, sporadic drops of brightness were confirmed, measuring up to 1.3 magnitudes, within a broad range of time scales—from a year to an hour. No periodicity was detected. Spectra of the star showed typical early A absorption line spectrum with variable narrow emission in the cores of H-α and other absorption lines. A dramatic emission line flare was observed on September 19, 2007, with an increase of H-α equivalent width by a factor of 4 relative to the previous observation, five nights before. No continuum photometry is available for September 19 but the brightness in R two days before and one day after that date differs by only 0.07 magnitude. A closer synchronism of spectroscopy and photometry is needed to verify the lack of correlation between the variations of the emission lines and continuum. So far, the lack of periodicity and an early spectral type seem to disprove the classification of V3798 Sgr as an RV Tau star and support the hypothesis that it is an UXOR. We thank A. Doane for help with measuring the plates and P. Berlind, M. Calkins and O. Shemmer for taking the spectra. This project was supported by the NSF/REU grant AST-0354056 and the Nantucket Maria Mitchell Association.