Discovery of Two New Class II Methanol Maser Transitions in G345.01+1.79

We have used the Swedish ESO Submillimetre Telescope (SEST) to search for new class II methanol maser transitions towards the southern source G345.01+1.79. Over a period of 5 days we observed 11 known or predicted class II methanol maser transitions. Emission with the narrow line width and characteristic velocity of class II methanol masers (in this source) was detected in 8 of these transitions, two of which have not previously been reported as masers. The new class II methanol maser transitions are the 13(-3)-12(-4)E transition at 104.1 GHz and the 5(1)-4(2)E transition at 216.9 GHz. Both of these are from transition series for which there are no previous known class II methanol maser transitions. This takes the total number of known class II methanol maser series to 10, and the total number of transitions (or transition groups) to 18. The observed 104.1 GHz maser suggests the presence of two or more regions of masing gas with similar line of sight velocities, but quite different physical conditions. Although these newly discovered transitions are likely to be relatively rare, where they are observed combined studies using the Australia Telescope Compact Array and the Atacama Large Millimeter Array offer the prospect to be able to undertake multi-transition methanol maser studies with unprecedented detail.Comment: 8 pages, 3 figures, accepted for publication in ApJ Letter

Transverse radiation force in a tailored optical fiber

We show, by means of simple model calculations, how a weak laser beam sent through an optical fiber exerts a transverse radiation force if there is an azimuthal asymmetry present in the fiber such that one side has a slightly different refractive index than the other. The refractive index difference $\Delta n$ needs only to be very small, of order $10^{-3}$, in order to produce an appreciable transverse displacement of order 10 microns. We argue that the effect has probably already been seen in a recent experiment of She et al. [Phys. Rev. Lett. 101, 243601 (2008)], and we discuss correspondence between these observations and the theory presented. The effect could be used to bend optical fibers in a predictable and controlled manner and we propose that it could be useful for micron-scale devices.Comment: 4 pages, 3 figures. Accepted for publication as Rapid Communication in Phys. Rev.

A Search for 6.7 GHz Methanol Masers in M33

We report the negative results from a search for 6.7 GHz methanol masers in the nearby spiral galaxy M33. We observed 14 GMCs in the central 4 kpc of the Galaxy, and found 3 sigma upper limits to the flux density of ~9 mJy in spectral channels having a velocity width of 0.069 km/s. By velocity shifting and combining the spectra from the positions observed, we obtain an effective 3sigma upper limit on the average emission of ~1mJy in a 0.25 km/s channel. These limits lie significantly below what we would expect based on our estimates of the methanol maser luminosity function in the Milky Way. The most likely explanation for the absence of detectable methanol masers appears to be the metallicity of M33, which is modestly less than that of the Milky Way

Multi-transition study and new detections of class II methanol masers

We have used the ATNF Mopra antenna and the SEST antenna to search in the directions of several class II methanol maser sources for emission from six methanol transitions in the frequency range 85-115 GHz. The transitions were selected from excitation studies as potential maser candidates. Methanol emission at one or more frequencies was detected from five of the maser sources, as well as from Orion KL. Although the lines are weak, we find evidence of maser origin for three new lines in G345.01+1.79, and possibly one new line in G9.62+0.20. The observations, together with published maser observations at other frequencies, are compared with methanol maser modelling for G345.01+1.79 and NGC6334F. We find that the majority of observations in both sources are consistent with a warm dust (175 K) pumping model at hydrogen density ~10^6 cm^-3 and methanol column density ~5 x 10^17 cm^-2. The substantial differences between the maser spectra in the two sources can be attributed to the geometry of the maser region.Comment: 13 pages, 6 figures, Accepted for publication in MNRA

Methanol Masers as Tracers of Circumstellar Disks

We show that in many methanol maser sources the masers are located in lines, with a velocity gradient along them which suggests that the masers are situated in edge-on circumstellar, or protoplanetary, disks. We present VLBI observations of the methanol maser source G309.92+0.48, in the 12.2 GHz transition, which confirm previous observations that the masers in this source lie along a line. We show that such sources are not only linear in space but, in many cases, also have a linear velocity gradient. We then model these and other data in both the 6.7 GHz and the 12.2 GHz transition from a number of star formation regions, and show that the observed spatial and velocity distribution of methanol masers, and the derived Keplerian masses, are consistent with a circumstellar disk rotating around an OB star. We consider this and other hypotheses, and conclude that about half of these methanol masers are probably located in edge-on circumstellar disks around young stars. This is of particular significance for studies of circumstellar disks because of the detailed velocity information available from the masers.Comment: 38 pages, 13 figures accepted by Ap

A bilateral shear layer between two parallel Couette flows

We consider a shear layer of a kind not previously studied to our knowledge. Contrary to the classical free shear layer, the width of the shear zone does not vary in the streamwise direction but rather exhibits a lateral variation. Based on some simplifying assumptions, an analytic solution has been derived for the new shear layer. These assumptions have been justified by a comparison with numerical solutions of the full Navier-Stokes equations, which accord with the analytical solution to better than 1% in the entire domain. An explicit formula is found for the width of the shear zone as a function of wall-normal coordinate. This width is independent of wall velocities in the laminar regime. Preliminary results for a co-current laminar-turbulent shear layer in the same geometry are also presented. Shear-layer instabilities were then developed and resulted in an unsteady mixing zone at the interface between the two co-current streams.Comment: 6 pages, 7 figures. Accepted for publication in Phys. Rev.

The Arecibo Methanol Maser Galactic Plane Survey - III: Distances and Luminosities

We derive kinematic distances to the 86 6.7 GHz methanol masers discovered in the Arecibo Methanol Maser Galactic Plane Survey. The systemic velocities of the sources were derived from 13CO (J=2-1), CS (J=5-4), and NH3 observations made with the ARO Submillimeter Telescope, the APEX telescope, and the Effelsberg 100 m telescope, respectively. Kinematic distance ambiguities were resolved using HI self-absorption with HI data from the VLA Galactic Plane Survey. We observe roughly three times as many sources at the far distance compared to the near distance. The vertical distribution of the sources has a scale height of ~ 30 pc, and is much lower than that of the Galactic thin disk. We use the distances derived in this work to determine the luminosity function of 6.7 GHz maser emission. The luminosity function has a peak at approximately 10^{-6} L_sun. Assuming that this luminosity function applies, the methanol maser population in the Large Magellanic Cloud and M33 is at least 4 and 14 times smaller, respectively, than in our Galaxy.Comment: Accepted by Ap

A search for 85.5- and 86.6-GHz methanol maser emission

We have used the Australia Telescope National Facility Mopra 22m millimetre telescope to search for emission from the 85.5-GHz and 86.6-GHz transitions of methanol. The search was targeted towards 22 star formation regions which exhibit maser emission in the 107.0-GHz methanol transition, as well as in the 6.6-GHz transition characteristic of class II methanol maser sources. A total of 22 regions were searched at 85.5 GHz resulting in 5 detections, of which 1 appears to be a newly discovered maser. For the 86.6-GHz transition observations were made of 18 regions which yielded 2 detections, but no new maser sources. This search demonstrates that emission from the 85.5- and 86.6-GHz transitions is rare. Detection of maser emission from either of these transitions therefore indicates the presence of special conditions, different from those in the majority of methanol maser sources. We have observed temporal variability in the 86.6-GHz emission towards 345.010+1.792, which along with the very narrow line width, confirms that the emission is a maser in this source. We have combined our current observations with published data for the 6.6-, 12.1-, 85.5-, 86.6-, 107.0-, 108.8- and 156.6-GHz transitions for comparison with the maser model of Sobolev & Deguchi (1994). This has allowed us to estimate the likely ranges of dust temperature, gas density, and methanol column density, both for typical methanol maser sources and for those sources which also show 107.0-GHz emission.Comment: 11 pages, accepted for publication in MNRAS, Latex, mn2e.cl

A high-sensitivity 6.7 GHz methanol maser survey toward H2O sources

We present the results of a high sensitivity survey for 6.7 GHz methanol masers towards 22 GHz water maser using the 100 m Efflesberg telescope. A total of 89 sources were observed and 10 new methanol masers were detected. The new detections are relatively faint with peak flux densities between 0.5 and 4.0 Jy. A nil detection rate from low-mass star forming regions enhances the conclusion that the masers are only associated with massive star formation. Even the faintest methanol maser in our survey, with a luminosity of 1.1 $10^{-9} L_\odot$ is associated with massive stars as inferred from its infrared luminosity.Comment: Accepted for publication in A&