ALMA OBSERVATIONS OF THE LARGEST PROTO-PLANERARY DISK IN THE ORION NEBULA, 114-426: A CO SILHOUETTE

• Published in: The Astrophysical journal 2015-07, Vol.808 (1), p.1-8
• Main Authors: Bally, John, Mann, Rita K, Eisner, Josh, Andrews, Sean M, Di Francesco, James, Hughes, Meredith, Johnstone, Doug, Matthews, Brenda, Ricci, Luca, Williams, Jonathan P
• Format: Article
• Language: English
• Subjects: Continuums; Disks; Dust; Emission; Grains; Molecular clouds; Orion nebula; Stars
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/808/1/69

We present ALMA observations of the largest protoplanetary disk in the Orion Nebula, 114-426. Detectable 345 GHz (856 [mu]m) dust continuum is produced only in the 350 AU central region of the ~1000 AU diameter silhouette seen against the bright H[alpha] background in Hubble Space Telescope images. Assuming optically thin dust emission at 345 GHz, a gas-to-dust ratio of 100, and a grain temperature of 20 K, the disk gas-mass is estimated to be 3.1 + or - 0.6 Jupiter masses. If most solids and ices have been incorporated into large grains, however, this value is a lower limit. The disk is not detected in dense-gas tracers such as HCO super(+) J = 4-3, HCN J = 4-3, or CS = 7-6. These results may indicate that the 114-426 disk is evolved and depleted in some light organic compounds found in molecular clouds. The CO J = 3-2 line is seen in absorption against the bright 50-80 K background of the Orion A molecular cloud over the full spatial extent and a little beyond the dust continuum emission. The CO absorption reaches a depth of 27 K below the background CO emission at V sub(LSR) approximately 6.7 km s super(-1) ~ 0."52 (210 AU) northeast and 12 K below the background CO emission at V sub(LSR) approximately 9.7 km s super(-1) ~ 0".34(140 AU) southwest of the suspected location of the central star, implying that the embedded star has a mass less than 1 M sub([middot in circle]).