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

Long-term Variability of H2_2CO Masers in Star-forming Regions

We present results of a multi-epoch monitoring program on variability of 6$\,$cm formaldehyde (H$_2$CO) masers in the massive star forming region NGC$\,$7538$\,$IRS$\,$1 from 2008 to 2015 conducted with the GBT, WSRT, and VLA. We found that the similar variability behaviors of the two formaldehyde maser velocity components in NGC$\,$7538$\,$IRS$\,$1 (which was pointed out by Araya and collaborators in 2007) have continued. The possibility that the variability is caused by changes in the maser amplification path in regions with similar morphology and kinematics is discussed. We also observed 12.2$\,$GHz methanol and 22.2$\,$GHz water masers toward NGC$\,$7538$\,$IRS$\,$1. The brightest maser components of CH$_3$OH and H$_2$O species show a decrease in flux density as a function of time. The brightest H$_2$CO maser component also shows a decrease in flux density and has a similar LSR velocity to the brightest H$_2$O and 12.2$\,$GHz CH$_3$OH masers. The line parameters of radio recombination lines and the 20.17 and 20.97$\,$GHz CH$_3$OH transitions in NGC$\,$7538$\,$IRS$\,$1 are also reported. In addition, we observed five other 6$\,$cm formaldehyde maser regions. We found no evidence of significant variability of the 6$\,$cm masers in these regions with respect to previous observations, the only possible exception being the maser in G29.96$-$0.02. All six sources were also observed in the H$_2^{13}$CO isotopologue transition of the 6$\,$cm H$_2$CO line; H$_2^{13}$CO absorption was detected in five of the sources. Estimated column density ratios [H$_2^{12}$CO]/[H$_2^{13}$CO] are reported.Comment: 29 pages, 9 figure

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

Mira's wind explored in scattering infrared CO lines

We have observed the intermediate regions of the circumstellar envelope of Mira (o Ceti) in photospheric light scattered by three vibration-rotation transitions of the fundamental band of CO, from low-excited rotational levels of the ground vibrational state, at an angular distance of beta = 2"-7" away from the star. The data were obtained with the Phoenix spectrometer mounted on the 4 m Mayall telescope at Kitt Peak. The spatial resolution is approximately 0.5" and seeing limited. Our observations provide absolute fluxes, leading to an independent new estimate of the mass-loss rate of approximately 3e-7 Msun/yr, as derived from a simple analytic wind model. We find that the scattered intensity from the wind of Mira for 2" < beta < 7" decreases as beta^-3, which suggests a time constant mass-loss rate, when averaged over 100 years, over the past 1200 years.Comment: accepted for publication in the Astrophysical Journa

Possible magnetic field variability during the 6.7 GHz methanol maser flares of G09.62+0.20

(Abridged) Recently, the magnetic field induced Zeeman splitting was measured for the strongest known 6.7 GHz methanol maser, which arises in the massive star forming region G09.62+0.20. This maser is one of a handful of periodically flaring methanol masers. The 100-m Effelsberg telescope was used to monitor the 6.7 GHz methanol masers of G09.62+0.20. With the exception of a two week period during the peak of the maser flare, we measure a constant magnetic field of B_||~11+-2 mG in the two strongest maser components of G09.62+0.20 that are separated by over 200 AU. In the two week period that coincides exactly with the peak of the maser flare of the strongest maser feature, we measure a sharp decrease and possible reversal of the Zeeman splitting. The exact cause of both maser and polarization variability is still unclear, but it could be related to either background amplification of polarized emission or the presence of a massive protostar with a close-by companion. Alternatively, the polarization variability could be caused by non-Zeeman effects related to the radiative transfer of polarized maser emission.Comment: 4 pages, 3 figures, accepted for publication Astronomy and Astrophysic

A New Galactic 6cm Formaldehyde Maser

We report the detection of a new H2CO maser in the massive star forming region G23.71-0.20 (IRAS 18324-0820), i.e., the fifth region in the Galaxy where H2CO maser emission has been found. The new H2CO maser is located toward a compact HII region, and is coincident in velocity and position with 6.7 GHz methanol masers and with an IR source as revealed by Spitzer/IRAC GLIMPSE data. The coincidence with an IR source and 6.7 GHz methanol masers suggests that the maser is in close proximity to an embedded massive protostar. Thus, the detection of H2CO maser emission toward G23.71-0.20 supports the trend that H2CO 6cm masers trace molecular material very near young massive stellar objects.Comment: Accepted for publication in The Astrophysical Journal Letter

Discovery of 6.035GHz Hydroxyl Maser Flares in IRAS18566+0408

We report the discovery of 6.035GHz hydroxyl (OH) maser flares toward the massive star forming region IRAS18566+0408 (G37.55+0.20), which is the only region known to show periodic formaldehyde (4.8 GHz H2CO) and methanol (6.7 GHz CH3OH) maser flares. The observations were conducted between October 2008 and January 2010 with the 305m Arecibo Telescope in Puerto Rico. We detected two flare events, one in March 2009, and one in September to November 2009. The OH maser flares are not simultaneous with the H2CO flares, but may be correlated with CH3OH flares from a component at corresponding velocities. A possible correlated variability of OH and CH3OH masers in IRAS18566+0408 is consistent with a common excitation mechanism (IR pumping) as predicted by theory.Comment: Accepted for publication in the Astrophysical Journa

Excited Hydroxyl Outflow in the High-Mass Star-Forming Region G34.26+0.15

G34.26+0.15 is a region of high-mass star formation that contains a broad range of young stellar objects in different stages of evolution, including a hot molecular core, hyper-compact HII regions and a prototypical cometary ultra-compact HII region. Previous high-sensitivity single dish observations by our group resulted in the detection of broad 6035 MHz OH absorption in this region; the line showed a significant blue-shifted asymmetry indicative of molecular gas expansion. We present high-sensitivity Karl G. Jansky Very Large Array (VLA) observations of the 6035 MHz OH line conducted to image the absorption and investigate its origin with respect to the different star formation sites in the region. In addition, we report detection of 6030 MHz OH absorption with the VLA and further observations of 4.7 GHz and 6.0 GHz OH lines obtained with the Arecibo Telescope. The 6030 MHz OH line shows a very similar absorption profile as the 6035 MHz OH line. We found that the 6035 MHz OH line absorption region is spatially unresolved at $\sim 2$" scales, and it is coincident with one of the bright ionized cores of the cometary HII region that shows broad radio recombination line emission. We discuss a scenario where the OH absorption is tracing the remnants of a pole-on molecular outflow that is being ionized inside-out by the ultra-compact HII region.Comment: 19 pages, 6 figures. Accepted for publication in The Astrophysical Journa

An H2CO 6cm Maser Pinpointing a Possible Circumstellar Torus in IRAS18566+0408

We report observations of 6cm, 3.6cm, 1.3cm, and 7mm radio continuum, conducted with the Very Large Array towards IRAS18566+0408, one of the few sources known to harbor H2CO 6cm maser emission. Our observations reveal that the emission is dominated by an ionized jet at cm wavelengths. Spitzer/IRAC images from GLIMPSE support this interpretation, given the presence of 4.5um excess emission at approximately the same orientation as the cm continuum. The 7mm emission is dominated by thermal dust from a flattened structure almost perpendicular to the ionized jet, thus, the 7mm emission appears to trace a torus associated with a young massive stellar object. The H2CO 6cm maser is coincident with the center of the torus-like structure. Our observations rule out radiative pumping via radio continuum as the excitation mechanism for the H2CO 6cm maser in IRAS18566+0408.Comment: 20 pages, 4 figures, ApJ (in press