Hour-Scale Variability in NGC 663 and NGC 1960
Abstract
Since 2010 we have been monitoring massive emission-line (mainly Be) stars in young open clusters using narrowband imaging at Hα (656nm) and the nearby continuum (645nm) (Souza, Davis, and Teich 2013, BAAS. 45, PM354.22; Souza, Beltz-Mohrmann, and Sami 2014. JAAVSO, 42, 154). To supplement longer-timescale data taken at Williams College we obtained high-cadence observations, in both filters, of NGC 663 on the night of 12/10/15, and of NGC 1960 on the nights of 12/10/14, 1/23/15, 1/25/15, 11/11/15, and 12/13/15 at the 0.5m ARCSAT at Apache Point Observatory. After raw magnitude extraction using Aperture Photometry Tool (Laher et al. 2012, PASP, 124, 737), we used inhomogeneous ensemble photometry (Bhatti et al., 2010, ApJ Supp., 186, 233) to correct for transparency and seeing variations. The NGC 663 field is crowded; of 29 known Be stars in the observed field, 10 have nearby interferers. None of the remaining 19 Be stars showed significant variation during ~5.5 hours of observation. 1σ uncertainty estimates range from 0.02mag at R~10 to 0.15mag at R~14. To verify the observing and reduction procedure, we recovered hour-scale variability in known variables BY Cas (δ Cephei type, ~0.05mag decline) and V1155 Cas (β Cephei type, ~0.04mag amplitude). In NGC 1960, of 5 known and suspect Be stars observed, two not previously reported as variable (BD+34 1110 and USNOB1.0 1241-0103450) showed irregular variation on timescales of hours. In NGC 1960 we also report the incidental discovery of two non-Be suspect variables: a likely eclipsing binary (0.07mag), and a possible δ Scuti star (maximum amplitude ~0.02mag). We gratefully acknowledge support for student research from NSF grant AST-1005024 to the Keck Northeast Astronomy Consortium, and the Office of the Dean of Faculty and the DIII Research Funding Committee of Williams College. Based on observations obtained with Apache Point Observatory's 0.5-m Astrophysical Research Consortium Small Aperture Telescope.
- Publication:
-
American Astronomical Society Meeting Abstracts #228
- Pub Date:
- June 2016
- Bibcode:
- 2016AAS...22831903S