The origin of R CrA variability

• Published in: Astronomy and astrophysics (Berlin) 2019-10, Vol.630
• Main Authors: Sissa, E., Gratton, R., Alcalà, J. M., Desidera, S., Messina, S., Mesa, D., D’Orazi, V., Rigliaco, E.
• Format: Article
• Language: English
• Subjects: Absorption; accretion; Accretion disks; Attenuation; Binary stars; circumstellar matter; Companion stars; Light curve; Luminosity; planets and satellites: formation; Pollution monitoring; protoplanetary disks; Star formation; stars: pre-main sequence; Stellar age
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201936101

Context. R CrA is the brightest member of the Coronet star-forming region and is the closest Herbig AeBe star with a spectrum dominated by emission lines. Its luminosity has been monitored since the end of the nineteenth century, but the origin of its variability, which shows a stable period of 65.767 ± 0.007 days, is still unknown. Aims. We studied photometric and spectroscopic data for this star to investigate the nature of the variability of R CrA. Methods. We exploited the fact that the near-infrared luminosity of the Herbig AeBe stars is roughly proportional to the total luminosity of the stars to derive the absorption, and then mass and age of R CrA. In addition, we modeled the periodic modulation of the light curve as due to partial attenuation of a central binary by a circumbinary disk. This model reproduces the observations very well. Results. We found that the central object in R CrA is a very young (1.5 ± 1.5 Myr) highly absorbed (AV = 5.47 ± 0.4 mag) binary; we obtain masses of MA = 3.02 ± 0.43 M⊙ and MB = 2.32 ± 0.35 M⊙ for the two components. We propose that the secular decrease of the apparent luminosity of R CrA is due to a progressive increase of the disk absorption. This might be related to precession of a slightly inclined disk caused by the recently discovered M-dwarf companion. This means that R CrA might be a triple system hosting a disk.