2019A&A...630A.132S

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±1.5Myr) highly absorbed (A_V=5.47±0.4mag) binary; we obtain masses of M_A=3.02±0.43M_☉ and M_B=2.32±0.35M_☉ 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.