Binarity as the Origin of Long Secondary Periods in Red Giant Stars

Long secondary periods (LSPs), observed in a third of pulsating red giant stars, are the only unexplained type of large-amplitude stellar variability known at this time. Here we show that this phenomenon is a manifestation of a substellar or stellar companion orbiting the red giant star. Our investi...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2021-04, Vol.911 (2), p.L22
Main Authors: Soszyński, I., Olechowska, A., Ratajczak, M., Iwanek, P., Skowron, D. M., Mróz, P., Pietrukowicz, P., Udalski, A., Szymański, M. K., Skowron, J., Gromadzki, M., Poleski, R., Kozłowski, S., Wrona, M., Ulaczyk, K., Rybicki, K.
Format: Article
Language:English
Subjects:
Amplitudes
Extrasolar planets
Giant stars
Infrared radiation
Light curve
Magellanic clouds
Milky Way
Red giant stars
Stars
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Summary:Long secondary periods (LSPs), observed in a third of pulsating red giant stars, are the only unexplained type of large-amplitude stellar variability known at this time. Here we show that this phenomenon is a manifestation of a substellar or stellar companion orbiting the red giant star. Our investigation is based on a sample of about 16,000 well-defined LSP variables detected in the long-term OGLE photometric database of the Milky Way and Magellanic Clouds, combined with the mid-infrared data extracted from the NEOWISE-R archive. From this collection, we selected about 700 objects with stable, large-amplitude, well-sampled infrared light curves and found that about half of them exhibit secondary eclipses, thus presenting an important piece of evidence that the physical mechanism responsible for LSPs is binarity. Namely, the LSP light changes are due to the presence of a dusty cloud orbiting the red giant together with the companion and obscuring the star once per orbit. The secondary eclipses, visible only in the infrared wavelength, occur when the cloud is hidden behind the giant. In this scenario, the low-mass companion is a former planet that has accreted a significant amount of mass from the envelope of its host star and grown into a brown dwarf.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/abf3c9