Arecibo Observations of Formaldehyde in L1551

We report observations of the formaldehyde (H2CO) 6 cm (4.8 GHz) line toward L1551. The observations were conducted with the Arecibo Telescope (beam FWHP ~ 1') to verify the tentative detection of H2CO thermal emission reported by Duncan and collaborators in 1987. The H2CO emission lines were expected to be present with a signal-to-noise ratio of 10 in our spectra. However, we did not detect H2CO emission; i.e., our data rule out their tentative detection. The absence of H2CO emission is also confirmed by the fact that the H2CO line profiles at the two positions of expected emission are well fitted by a single absorption component (accounting for the hyperfine structure of the line) in one of the positions and by a single absorption line plus a red-wing absorption component in the second position. The Orion BN/KL region remains the only H2CO 6 cm thermal emitter known. Our observations also demonstrate that the H2CO 6 cm absorption line traces not only the quiescent molecular cloud but also the kinematics associated with the star formation process in L1551-IRS 5

Thermal Methanol Observations of the Outflow from the G31.41+0.31 Hot Molecular Core

The G31.41+0.31 region hosts one of the most prominent hot molecular cores known. Coincident with the hot molecular core is an outflow whose orientation has been controversial. We report VLA-C observations of thermal methanol (70–61 A+, 44 GHz) toward the position of the G31.41+0.31 hot molecular core. Our goals are to clarify the orientation of the outflow and to study the properties of a molecular outflow from a very young region of massive star formation. We confirm that the outflow is indeed associated with the hot molecular core. Our observations strongly suggest that the outflow is oriented in the northeast-southwest direction. The outflow is massive (15 M☉), with a dynamical time of the order of ~4 × 103 yr, and has a wide-angle bipolar morphology

A Search for Formaldehyde 6 cm Emission toward Young Stellar Objects. II. H2CO and H110α Observations

We report the results of our second survey for Galactic H2CO maser emission toward young stellar objects. Using the GBT and the VLA in the A configuration we observed 58 star-forming regions and discovered the fifth H2CO 6 cm maser region in the Galaxy (G23.71-0.20). We have discussed the detection toward G23.71-0.20 in a previous paper. Here we present all the other results from our survey, including detection of H2CO absorption features toward 48 sources, detection of the H110α recombination line toward 29 sources, detection (including tentative detections) of the carbon recombination line C110α toward 14 sources, subarcsecond angular resolution images of 6 cm continuum emission toward five sources, and observations of the H2CO masers in IRAS 18566+0408 and NGC 7538. In the case of NGC 7538, we detected the two main H2CO maser components, and our observations confirm variability of the blueshifted component recently reported by Hoffman et al. The variability of both maser components in NGC 7538 could be caused by a shock wave that reached the redshifted component approximately 14 yr before reaching the blueshifted component. If that were the case, we would expect to detect an increase in the flux density rate of change of the blueshifted component sometime after the year 2009. Our data also support the use of H2CO/H110α observations as a tool to resolve the kinematic distance ambiguity of massive star-forming regions in the Galaxy

First Detection of an H2CO 6 cm Maser Flare: A Burst in IRAS 18566+0408

We report the discovery of a short-duration (less than 3 months) outburst of the H2CO 6 cm maser in IRAS 18566+0408 (G37.55+0.20). During the flare, the peak flux density of the maser increased by a factor of 4; after less than a month, it decayed to the preflare value. This is the first detection of a short, burstlike variability of an H2CO 6 cm maser. The maser shows an asymmetric line profile that is consistent with the superposition of two Gaussian components. We did not detect a change in the velocity or the line width of the Gaussian components during the flare. If the two Gaussian components trace two separate maser regions, then very likely an event outside the maser gas triggered simultaneous flares at two different locations