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标题：CoRoT photometry and STELLA spectroscopy of an eccentric, eclipsing, and spotted HgMn binary with sub-synchronized rotation
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作者：K. G. Strassmeier ; K. G. Strassmeier ; T. Granzer 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2017
卷号：597
页码：1-13
DOI：10.1051/0004-6361/201629150
语种：English
出版社：EDP Sciences
摘要：Context. We report the discovery and analysis of very narrow transits in the eccentric spectroscopic binary HSS 348 (IC 4756). Aims. The aim is to characterize the full HSS 348 system. Methods. We obtained high-precision CoRoT photometry over two long runs and multi-epoch high-resolution échelle spectroscopy and imaging with STELLA. Standard radial-velocity extraction, spectrum synthesis, Fourier analysis, and light-curve inversions are applied to the data. Results. HSS 348 is found to be an eccentric (e = 0.18) double-lined spectroscopic binary with a period of 12.47 d in which at least the primary component is a peculiar B star of the HgMn class. The orbital elements are such that the system undergoes a grazing eclipse with the primary in front but no secondary eclipse. The out-of-eclipse light variations show four nearly equidistant but unequal minima stable in shape and amplitude throughout our observations. Their individual photometric periods are all harmonics of the same fundamental period which happens to agree with the transit period to within the errors. We interpret the fundamental period to be the rotation period of at least one if not both stars due to surface inhomogeneities. Due to the non-zero eccentricity of the orbit the two components are rotating sub-synchronously. Conclusions. It appears that HSS 348 is not a member of the IC 4756 cluster but a background B8+B8.5 binary system. Its sharp eclipses every 12.47 days just mimic a small-body transit but are in reality the grazing eclipses of a B-star binary and thus a classical false positive. The system seems to be pre-main sequence with the primary possibly just arrived on the ZAMS. The light curve with four unequal minima can be explained with four cool spots of different size equidistantly positioned in longitude. Our data do not allow to uniquely assign the spots to either of the two stars.
关键词：binaries: eclipsing;stars: chemically peculiar;stars: rotation;starspots;stars: individual: TYC 455-791-1;open clusters and associations: individual: IC 4756