Dinah M. Cragg

Models of class II methanol masers based on improved molecular data

The class II masers of methanol are associated with the early stages of formation of high-mass stars. Modelling of these dense, dusty environments has demonstrated that pumping by infrared radiation can account for the observed masers. Collisions with other molecules in the ambient gas also play a significant role, but have not been well modelled in the past. Here we examine the effects on the maser models of newly available collision rate coefficients for methanol. The new collision data do not alter which transitions become masers in the models, but do influence their brightness and the conditions under which they switch on and off. At gas temperatures above 100 K the effects are broadly consistent with a reduction in the overall collision cross-section. This means, for example, that a slightly higher gas density than identified previously can account for most of the observed masers in W3(OH). We have also examined the effects of including more excited-state energy levels in the models, and find that these play a significant role only at dust temperatures above 300 K. An updated list of class II methanol maser candidates is presented.

A search for propylene oxide and glycine in Sagittarius B2 (LMH) and Orion

We have used the Mopra Telescope to search for glycine and the simple chiral molecule propylene oxide in the Sgr B2 (LMH) and Orion KL, in the 3-mm band. We have not detected either species, but have been able to put sensitive upper limits on the abundances of both molecules. The 3 sigma upper limits derived for glycine conformer I are 3.7 x 10(14) cm(-2) in both Orion-KL and Sgr B2 ( LMH), comparable to the reported detections of conformer I by Kuan et al. However, as our values are 3s upper limits rather than detections we conclude that this weighs against confirming the detection of Kuan et al. We find upper limits for the glycine II column density of 7.7 x 10(12) cm(-2) in both Orion-KL and Sgr B2 ( LMH), in agreement with the results of Combes et al. The results presented here show that glycine conformer II is not present in the extended gas at the levels detected by Kuan et al. for conformer I. Our ATCA results have ruled out the detection of glycine ( both conformers I and II) in the compact hot core of the LMH at the levels reported, so we conclude that it is unlikely that Kuan et al. have detected glycine in either Sgr B2 or Orion-KL. We find upper limits for propylene oxide abundance of 3.0 x 10(14) cm(-2) in Orion-KL and 6.7 x 10(14) cm(-2) in Sgr B2 (LMH). We have detected fourteen features in Sgr B2 and four features in Orion-KL which have not previously been reported in the interstellar medium, but have not been able to plausibly assign these transitions to any carrier.

A Search for biomolecules in Sagittarius B2 (LMH) with the Australia Telescope Compact Array

We have used the Australia Telescope Compact Array to conduct a search for the simplest amino acid, glycine (conformers I and II), and the simple chiral molecule propylene oxide at 3-mm in the Sgr B2 LMH. We searched 15 portions of spectrum between 85 and 91 GHz, each of 64 MHz bandwidth, and detected 58 emission features and 21 absorption features, giving a line density of 75 emission lines and 25 absorption lines per GHz stronger than the 5σ level of 110 mJy. Of these, 19 are transitions previously detected in the interstellar medium, and we have made tentative assignments of a further 23 features to molecular transitions. However, as many of these involve molecules not previously detected in the ISM, these assignments cannot be regarded with confidence. Given the median line width of 6.5 km/s in Sgr B2 LMH, we find that the spectra have reached a level where there is line confusion, with about 1/5 of the band being covered with lines. Although we did not confidently detect either glycine or propylene oxide, we can set 3σ upper limits for most transitions searched. We also show that if glycine is present in the Sgr B2 LMH at the level of N = 4×10 cm found by Kuan et al. (2003) in their reported detection of glycine, it should have been easily detected with the ATCA synthesized beam size of 17.0 x 3.4 arcsec, if it were confined to the scale of the LMH continuum source (< 5 arcsec). This thus puts a strong upper limit on any small-scale glycine emission in Sgr B2, for both of conformers I and II.

Discovery of new 19.9-GHz methanol masers in star-forming regions

We have used the NASA Tidbinbilla 70-m antenna to search for emission from the 21‐30 E (19.9-GHz) transition of methanol. The search was targeted towards 22 star formation regions that exhibit maser emission in the 107.0-GHz 31‐40 A + methanol transition, and in the 6.6-GHz 51‐60 A + transition characteristic of class II methanol maser sources. A total of seven sources were detected in the 21‐30 E transition, six of these being new detections. Many of the new detections are weak (0.5 Jy), however, they appear to be weak masers rather than thermal or quasi-thermal emission. We find a strong correlation between sources that exhibit 19.9-GHz methanol masers and those that both have the class II methanol masers projected against radio continuum emission and have associated 6035-MHz OH masers. This suggests that the 19.9-GHz methanol masers arise in very specific physical conditions, probably associated with a particular evolutionary phase. In the model of Cragg, Sobolev & Godfrey these observations are consistent with gas temperatures of 50 K, dust temperatures of 150‐200 K and gas densities of 10 6.5 ‐10 7.5 cm −3 . Ke yw ords: masers ‐ stars: formation ‐ ISM: molecules ‐ radio lines: ISM.

Search for class II methanol masers at 23.1 GHz

In the early days of methanol maser discoveries, the 9 2 -10 1 A + transition at 23.1 GHz was found to exhibit maser characteristics in the northern star-forming region W3(OH) and probable maser emission in two other sources. Attention subsequently turned to the 6.6-GHz 5 1 -6 0 A + methanol maser transition, which has proved a valuable tracer of early high-mass star formation. We have undertaken a new search for 23.1 -GHz methanol masers in 50 southern star formation regions using the Parkes radio telescope. The target sources all exhibit class II methanol maser emission at 6.6 GHz, with 20 sources also displaying maser features in the 107.0-GHz 3 1 -4 0 A + methanol line. Strong emission at 23.1 GHz in NGC 6334F was confirmed, but no emission was detected in the remaining sources. Thus the 23.1-GHz methanol masers are rare. A maser model in which methanol molecules are pumped to the second torsionally excited state by radiation from warm dust can account for class II maser activity in all the transitions in which it is observed. According to this model the 23.1-GHz maser is favoured by conditions representing low gas temperature, high external dust temperature, low gas density and high column density of methanol; the scarcity of this maser indicates that such combinations of conditions are uncommon. We have undertaken new model calculations to examine the range of parameters compatible with the upper limits on 23.1-GHz emission from our survey. Further constraints apply in sources with upper limits to maser emission at 107.0 GHz and the combination of data for the two transitions delineates a narrow range of gas density and methanol abundance if the dust temperature is 175 K or greater. While the results are subject to the uncertainties of the chosen model, they may be applicable to the majority of methanol maser sites in the vicinity of newborn high-mass stars, in which methanol masers other than the 6.6- and 12.1-GHz transitions are not detected.

Discovery of two new class II methanol maser transitions in G 345.01+1.79

We have used the Swedish ESO Submillimetre Telescope (SEST) to search for new class II methanol maser transitions toward the southern source G 345.01+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 eight 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 51-42 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.

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

ABSTRACT We have used the Australia Telescope National Facility Mopra 22m millimetretelescope to search for emission from the 6 −2 -7 −1 E (85.5-GHz) and 7 2 -6 3 A − (86.6-GHz) transitions of methanol. The search was targeted towards 22 star formationregions which exhibit maser emission in the 107.0-GHz 3 1 -4 0 A + methanol transition,as well as in the 6.6-GHz 5 1 -6 0 A + transition characteristic of class II methanol masersources. A total of 22 regions were searched at 85.5 GHz resulting in 5 detections, ofwhich 1 appears to be a newly discovered maser. For the 86.6-GHz transition observa-tions were made of 18 regions which yielded 2 detections, but no new maser sources.This search demonstrates that emission from the 6 −2 -7 −1 E and 7 2 -6 3 A − transitionsis rare. Detection of maser emission from either of these transitions therefore indicatesthe presence of special conditions, different from those in the majority of methanolmaser sources. We have observed temporal variability in the 86.6-GHz emission to-wards 345.010+1.792, which along with the very narrow line width, confirms that theemission 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 masermodel of Sobolev & Deguchi (1994). Both detections and nondetections are usefulfor setting limits on the physical conditions in star forming regions which containmethanol maser emission. This has allowed us to estimate the likely ranges of dusttemperature, gas density, and methanol column density, both for typical methanolmaser sources and for those sources which also show 107.0-GHz emission. The gastemperature can also be estimated for those sources exhibiting masers at 85.5 and/or86.6 GHz.Key words: masers – stars:formation – ISM: molecules – radio lines : ISM

Investigating high-mass star formation through maser surveys

Interstellar masers are unique probes of the environments in which they arise. In studies of high-mass star formation their primary function has been as signposts of these regions and they have been used as probes of the kinematics and physical conditions in only a few sources. With a few notable exceptions, we know relatively little about the evolutionary phase the different maser species trace, nor their location with respect to other star formation tracers. While detailed studies of a small number of maser regions can reveal much about them, other information can only be obtained through large, systematic searches. In particular, such surveys are vital in efforts to determine an evolutionary sequence for the common maser species, and there is growing evidence that methanol masers may trace an earlier phase than the other common maser species of OH and water.

How do methanol masers manage to appear in the youngest star vicinities and isolated molecular clumps

General characteristics of methanol (CH3OH) maser emission are summarized. It is shown that methanol maser sources are concentrated in the spiral arms. Most of the methanol maser sources from the Perseus arm are associated with embedded stellar clusters and a consid- erable portion is situated close to compact Hii regions. Almost 1/3 of the Perseus Arm sources lie at the edges of optically identified Hii regions which means that massive star formation in the Perseus Arm is to a great extent triggered by local phenomena. A multiline analysis of the methanol masers allows us to determine the physical parameters in the regions of maser forma- tion. Maser modelling shows that class II methanol masers can be pumped by the radiation of the warm dust as well as by free-free emission of a hypercompact region (hcHii) with a turnover frequency exceeding 100 GHz. Methanol masers of both classes can reside in the vicinity of hcHiis. Modelling shows that periodic changes of maser fluxes can be reproduced by variations of the dust temperature by a few percent which may be caused by variations in the brightness of the central young stellar object reflecting the character of the accretion process. Sensitive observations have shown that the masers with low flux densities can still have considerable amplification factors. The analysis of class I maser surveys allows us to identify four distinct regimes that differ by the series of their brightest lines.

Pumping the interstellar (6, 3) ammonia maser

A numerical model of the excitation of ammonia in dense interstellar clouds predicts strong maser emission in various inversion doublet lines when infrared pumping to the lowest vibrationally excited state is included. Specifically the (6,3) transition mases, while the (5,3) and (4,3) transitions are in normal emission, as observed in W51. Model conditions are H 2 density between 10 8 and 10 10 cm −3 , NH 3 column density 10 18 cm −2 , and infrared temperature greater than 200 K, comparable with conditions required for OH and H 2 O masing in regions of star formation.