Dippers from TESS Full-frame Images. II. Spectroscopic Characterization of Four Young Dippers (2201.09459v1)

Abstract: Photometric monitoring by the Transiting Exoplanet Survey Satellite (TESS) has discovered not only periodic signals by transiting exoplanets but also episodic or quasi-periodic dimming around young stellar objects. The mechanisms of the dimming of these objects, so-called "dippers", are thought to be related to the property of the accretion or the structure of protoplanetary disks especially in regions close to the host star. Recently, we have created the catalog of dippers from the one year of TESS Full Frame Image (FFI) data. In this paper, we report spectral features of four newly found dippers in that catalog and show that they potentially shed light on the dimming mechanisms. We found that all of the targets exhibit the H alpha emission line, which is an indicator of an ongoing accretion. Based on its line profiles and/or their variability, we characterized the properties of the disks of each source, which can support the dimming mechanisms due to a dusty disk wind or an accretion warp. Also, we found an interesting dipper (TIC 317873721), "close-in binary dipper," showing the complex variability of the line profile and the large radial velocity variation. Since the dimming intervals are similar to the orbital period of the binary, we suggest that the dips are caused by dust in the warp of accretion from a circumbinary disk onto stars. Such a close-in ($<$ 0.1 au) binary dipper is rarely reported so far, further investigation will reveal the new aspect of the disk evolution and planetary formation.