Abstract
Abstract The SR 24 multistar system hosts both circumprimary and circumsecondary disks, which are strongly misaligned with each other. The circumsecondary disk is circumbinary in nature. Interestingly, both disks are interacting, and they possibly rotate in opposite directions. To investigate the nature of this unique twin disk system, we present 0.″1 resolution near-infrared polarized intensity images of the circumstellar structures around SR 24, obtained with HiCIAO mounted on the Subaru 8.2 m telescope. Both the circumprimary disk and the circumsecondary disk are resolved and have elongated features. While the position angle of the major axis and radius of the near-IR (NIR) polarization disk around SR 24S are 55° and 137 au, respectively, those around SR 24N are 110° and 34 au, respectively. With regard to overall morphology, the circumprimary disk around SR 24S shows strong asymmetry, whereas the circumsecondary disk around SR 24N shows relatively strong symmetry. Our NIR observations confirm the previous claim that the circumprimary and circumsecondary disks are misaligned from each other. Both the circumprimary and circumsecondary disks show similar structures in 12CO observations in terms of its size and elongation direction. This consistency is because both NIR and 12CO are tracing surface layers of the flared disks. As the radius of the polarization disk around SR 24N is roughly consistent with the size of the outer Roche lobe, it is natural to interpret the polarization disk around SR 24N as a circumbinary disk surrounding the SR 24Nb–Nc system.
Highlights
There are many young binary stars hosting a circumprimary disk misaligned with respect to either a circumsecondary disk, a circumbinary disk, or a binary orbital plane (e.g., HK Tau, Jensen & Akeson 2014; L1551 NE, Takakuwa et al 2017; GG Tau, Aly et al 2018; IRS 43, Brinch et al 2016; GW Ori, Czekala et al 2017; HD 98800, Kennedy et al 2019)
Some promising mechanisms that have been claimed to address theoretically the origin of inner disks misaligned with respect to outer disks are as follows: (1) the rotation axis of the disk system is misaligned with respect to the magnetic field direction (e.g., Ciardi & Hennebelle 2010); (2) the anisotropic accretion of gas with different rotational axes (e.g., Bate 2018); and (3) a massive planet misaligned with respect to an outer disk tilting an inner disk (e.g., Nealon et al 2019; Zhu 2019)
As this morphology is symmetric to the bridge emanating from the east side of the SR 24N disk observed using both CIAO and Hubble Space Telescope (HST), this morphology might be attributed to binary formation
Summary
There are many young binary stars hosting a circumprimary disk misaligned with respect to either a circumsecondary disk, a circumbinary disk, or a binary orbital plane (e.g., HK Tau, Jensen & Akeson 2014; L1551 NE, Takakuwa et al 2017; GG Tau, Aly et al 2018; IRS 43, Brinch et al 2016; GW Ori, Czekala et al 2017; HD 98800, Kennedy et al 2019) These circumprimary and circumsecondary disks are directly imaged as two single disks. The planet is assumed to be sufficiently massive to open a gap in the disk Such planets can become misaligned with respect to an outer disk through secular interaction with an external misaligned companion (Lubow & Martin 2016; Martin et al 2016), or through precessional resonances (Owen & Lai 2017). The inner disk (within the planet/companion orbital radius) might become aligned to the orbital plane of the planet, becoming misaligned with respect to the outer disk
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