Abstract
Abstract Wide-field near-infrared (NIR) polarimetry was used to examine disk systems around two brown dwarfs (BDs) and two young stellar objects (YSOs) embedded in the Heiles Cloud 2 (HCl2) dark molecular cloud in Taurus as well as numerous stars located behind HCl2. Inclined disks exhibit intrinsic NIR polarization due to scattering of photospheric light, which is detectable even for unresolved systems. After removing polarization contributions from magnetically aligned dust in HCl2 determined from the background star information, significant intrinsic polarization was detected from the disk systems of one BD (ITG 17) and both YSOs (ITG 15, ITG 25), but not from the other BD (2M0444). The ITG 17 BD shows good agreement of the disk orientation inferred from the NIR and from published Atacama Large Millimeter/submillieter Array dust continuum imaging. ITG 17 was also found to reside in a 5200 au wide binary (or hierarchical quad star system) with the ITG 15 YSO disk system. The inferred disk orientations from the NIR for ITG 15 and ITG 17 are parallel to each other and perpendicular to the local magnetic field direction. The multiplicity of the system and the large BD disk nature could have resulted from formation in an environment characterized by misalignment of the magnetic field and the protostellar disks.
Highlights
Disks around low-mass objects offer unique insights into star and planet formation processes, especially regarding low-mass star and brown dwarf formation
Near-infrared (NIR) polarimetry may offer an efficient way to survey, detect, and identify low-mass star or BD disks for follow-up examination by millimeter and submillimeter wavelength interferometers. This current study sought to use NIR polarimetry to probe two brown dwarf (BD) disks and two young stellar object (YSO) disks in Taurus to assess the efficacy of this method and to compare NIR and mm disk orientation findings
Observations of the CFHT Tau 4 and 2M0444 fields were obtained with the Mimir instrument in its imaging polarimetry mode, which had a pixel field of view of 0.6 × 0.6 arcsec onto a 1024 × 1024 pixel ALADDIN III InSb detector array, at the Perkins Telescope Observatory (PTO), located on Anderson Mesa, outside Flagstaff, AZ on the UT nights of 2019 December 13 and 21 as well as 2020 January 6, February 12 and 14
Summary
Disks around low-mass objects offer unique insights into star and planet formation processes (see reviews by Luhman 2012; Andrews 2020), especially regarding low-mass star and brown dwarf formation. The Taurus star-forming region is one of the best studied laboratories for low-mass star formation (e.g., Elias 1978; Beckwith et al 1990; Kenyon et al 1990) and sprawls across about 12 × 16◦ of the sky (see the Figure 18-5-6 extinction map of Dobashi et al 2005) It has been only recently, with the release of Gaia DR2 (Gaia Collaboration et al 2016, 2018) and the studies by Luhman (2018) and Galli et al (2019), that accurate distances to the constituent dark clouds in Taurus and their associated groupings of stars, YSOs, and BDs have been established. Analysis of the NIR data, in combination with Gaia Early Data Release 3 (EDR3: Gaia Collaboration et al 2016, 2020) proper motions and parallaxes as well as archival NIR and mid-infrared photometry were used to ascertain foreground, embedded, and background polarization and extinction properties These were used to deduce the intrinsic NIR polarization properties of the disks around the two BDs and two YSOs. The remainder of this paper is organized as follows.
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