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D. Hammond (U. of Delaware & Maria Mitchell Obs.), J. Lawless (Grove City Coll. & Maria Mitchell Obs.)
ES Aql, initially classified as a semi-regular variable, is now suspected to belong to RCB stars - a small (only about 30 cases known) group of carbon-rich supergiants that undergo dramatic declines in brightness at irregular intervals. In order to restore the long time-scale light curve of the star and clear up the suspicions of its alleged RCB nature, an in-depth study of the Harvard photographic plates containing this star was undertaken. We carried out eye photometry of several hundred plates, which resulted in 396 reliable estimates of the relative magnitude of ES Aql covering almost a 100-year period - from 1893 to 1989. We detected as many as 89 events of considerable fading of the star, including total disappearing from the plate, which means that the star had a photographic magnitude of about 15 or fainter in the brightness minimum. In the relatively long periods of time off minima, the star resides with a magnitude of around 13.2. From our data, the duration of the time that the star was in recession varies from two to five months, but we cannot exclude shorter fadings. A preliminary analysis shows no periodicity in the fading events. Based on this extensive photometric study, we conclude that ES Aql is indeed an RCB star. We thank Dr. G. Clayton, Ms. Alison Doane, Dr. N. Samus, and Dr. V. Strelnitski for help in our work on the project. This project was supported by the NSF/REU grant AST-9820555 and the Nantucket Maria Mitchell Association.
The author(s) of this abstract have provided an email address for comments about the abstract: danakh@udel.edu