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arXiv · 2107.00662

ASASSN-21co: A detached eclipsing binary with an 11.9 year period

D. M. Rowan·K. Z. Stanek·Z. Way·C. S. Kochanek·T. Jayasinghe·Todd A. Thompson·H. Barker·F. -J. Hambsch·T. Bohlsen·Stella Kafka·B. J. Shappee·T. W. -S. Holoien·J. L. Prieto
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Abstract

We use ASAS V-band and ASAS-SN g-band observations to model the long-period detached eclipsing binary ASASSN-21co. ASAS observations show an eclipse of depth V ~ 0.6 mag in April of 2009. ASAS-SN g-band observations from March of 2021 show an eclipse of similar duration and depth, suggesting an orbital period of 11.9 years. We combine the g-band observations with additional BVRI photometry taken during the eclipse to model the eclipse using PHOEBE. We find that the system is best described by two M giants with a ratio of secondary radius to primary radius of ~0.61. Optical spectra taken during the eclipse are consistent with at least one component of the binary being an M giant, and we find no temporal changes in the spectral features. The eclipse itself is asymmetric, showing an increase in brightness near mid-eclipse, likely due to rotational variability that is too low amplitude to be observed out-of-eclipse.

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D. M. Rowan, K. Z. Stanek, Z. Way, C. S. Kochanek, T. Jayasinghe, Todd A. Thompson, H. Barker, F. -J. Hambsch, T. Bohlsen, Stella Kafka, B. J. Shappee, T. W. -S. Holoien, J. L. Prieto. 2021-07-01. ASASSN-21co: A detached eclipsing binary with an 11.9 year period. https://doi.org/10.3847/2515-5172%2Fac0c83

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