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Published January 1, 2015 | Published + Submitted
Journal Article Open

An ALMA Disk Mass for the Candidate Protoplanetary Companion to FW Tau


We present ALMA observations of the FW Tau system, a close binary pair of M5 stars with a wide-orbit (300 AU projected separation) substellar companion. The companion is extremely faint and red in the optical and near-infrared, but boasts a weak far-infrared excess and optical/near-infrared emission lines indicative of a primordial accretion disk of gas and dust. The component-resolved 1.3 mm continuum emission is found to be associated only with the companion, with a flux (1.78 ± 0.03 mJy) that indicates a dust mass of 1–2 M_⊕. While this mass reservoir is insufficient to form a giant planet, it is more than sufficient to produce an analog of the Kepler-42 exoplanetary system or the Galilean satellites. The mass and geometry of the disk-bearing FW Tau companion remains unclear. Near-infrared spectroscopy shows deep water bands that indicate a spectral type later than M5, but substantial veiling prevents a more accurate determination of the effective temperature (and hence mass). Both a disk-bearing "planetary-mass" companion seen in direct light or a brown dwarf tertiary viewed in light scattered by an edge-on disk or envelope remain possibilities.

Additional Information

© 2015 The American Astronomical Society. Received 9 September 2014; accepted for publication 4 December 2014; published 19 December 2014. The authors thank Gaspard Duchêne for an insightful discussion of the nature of the FW Tau companion, and the referee for a helpful critique of this Letter. This Letter makes use of the following ALMA data: ADS/JAO.ALMA#2012.1.00989.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The NRAO is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc.

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Submitted - 1412.2175v1.pdf

Published - 2041-8205_798_1_L23.pdf


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August 22, 2023
August 22, 2023