478 research outputs found
Testing the Hypothesis that Methanol Maser Rings Trace Circumstellar Disks: High Resolution Near-IR and Mid-IR Imaging
Milliarcsecond VLBI maps of regions containing 6.7 GHz methanol maser
emission have lead to the recent discovery of ring-like distributions of maser
spots and the plausible hypothesis that they may be tracing circumstellar disks
around forming high mass stars. We aimed to test this hypothesis by imaging
these regions in the near and mid-infrared at high spatial resolution and
compare the observed emission to the expected infrared morphologies as inferred
from the geometries of the maser rings. In the near infrared we used the Gemini
North adaptive optics system of Altair/NIRI, while in the mid-infrared we used
the combination of the Gemini South instrument T-ReCS and super-resolution
techniques. Resultant images had a resolution of approximately 150 mas in both
the near-infrared and mid-infrared. We discuss the expected distribution of
circumstellar material around young and massive accreting (proto)stars and what
infrared emission geometries would be expected for the different maser ring
orientations under the assumption that the masers are coming from within
circumstellar disks. Based upon the observed infrared emission geometries for
the four targets in our sample and the results of SED modeling of the massive
young stellar objects associated with the maser rings, we do not find
compelling evidence in support of the hypothesis that methanol masers rings
reside in circumstellar disks.Comment: 20 pages, 7 figures, accepted for publication by ApJ; article with
full-resolution figures can be downloaded at http://www.jim-debuizer.ne
Masers and the Massive Star Formation Process: New Insights Through Infrared Observations
Our mid-infrared and near-infrared surveys over the last five years have
helped to strengthen and clarify the relationships between water, methanol, and
OH masers and the star formation process. Our surveys show that maser emission
seems to be more closely associated with mid-infrared emission than cm radio
continuum emission from UC HII regions. We find that masers of all molecular
species surveyed trace a wide variety of phenomena and show a proclivity for
linear distributions. The vast majority of these linear distributions can be
explained by outflows or shocks, and in general do not appear to trace
circumstellar disks as was previously thought. Some water and methanol masers
that are not associated with radio continuum emission appear to trace
infrared-bright hot cores, the earliest observable stage of massive stellar
life before the onset of a UC HII region.Comment: 6 pages, 3 figures, to appear in the proceedings of IAU Symposium
227: "Massive Star Birth: A Crossroads of Astrophysics", version with
full-resolution images available at http://www.ctio.noao.edu/~debuize
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