Coincidence of maser emission from OH at 6.035 GHz and methanol at 6.668 GHz

Caswell, J. L.

doi:10.1093/mnras/289.1.203

Cited by 148 publications

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“…345.010+1.792 is associated with an UCHII region (Caswell 1997), and many other class II methanol maser transitions . Breen et al (2010a) detected water maser emission in 2003 with a peak flux density of 2.0 Jy, but it was not detected in their 2004 observations (detection limit of 0.2 Jy) or in our observations.…”

Section: Resultsmentioning

confidence: 99%

“…The astrometric accuracy of ATCA measurements of water masers is, under ideal conditions, around 0.4 arcseconds (Caswell 1997) and is set by the precision to which the coordinates of the phase calibrators have been measured and other systematics such as the antenna positions. For observations at 22 GHz, varying water vapour content in the atmosphere degrades the phase calibration and the typical astrometric accuracy for the current observations is estimated to be within an arcsecond in good weather conditions.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

“…Water masers are pumped by collisions with H2 molecules within shocks associated with outflows or accretion (Elitzur et al 1989;Garay & Lizano 1999) and may reside further away from their parent YSO than 6.7-GHz methanol masers (see Forster & Caswell (1989) c.f. Caswell (1997)). …”

Section: Introductionmentioning

confidence: 99%

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A search for water masers associated with class II methanol masers – II. Longitude range 341° to 6°

Titmarsh

Ellingsen

Breen

et al. 2016

Mon. Not. R. Astron. Soc.

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This is the second paper in a series of catalogues of 22-GHz water maser observations towards the 6.7-GHz methanol masers from the Methanol Multibeam (MMB) Survey. In this paper we present our water maser observations made with the Australia Telescope Compact Array towards the masers from the MMB survey between l = 341 • through the Galactic centre to l = 6 • . Of the 204 6.7-GHz methanol masers in this longitude range we found 101 to have associated water maser emission (∼ 50 per cent). We found no difference in the 6.7-GHz methanol maser luminosities of those with and without water masers. In sources where both maser species are observed, the luminosities of the methanol and water masers are weakly correlated. Studying the mid-infrared colours from GLIMPSE we found no differences between the colours of those sources associated with both methanol and water masers and those associated with just methanol. Comparing the column density and dust mass calculated from the 870-µm thermal dust emission observed by ATLASGAL, we found no differences between those sources associated with both water and methanol masers and those with methanol only. Since water masers are collisionally pumped and often show emission further away from their accompanying YSO than the radiatively pumped 6.7-GHz methanol masers, it is likely water masers are not as tightly correlated to the evolution of the parent YSO and so do not trace such a well defined evolutionary state as 6.7-GHz methanol masers.

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Section: Resultsmentioning

confidence: 99%

Section: Observations and Data Reductionmentioning

confidence: 99%

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A search for water masers associated with class II methanol masers – II. Longitude range 341° to 6°

Titmarsh

Ellingsen

Breen

et al. 2016

Mon. Not. R. Astron. Soc.

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“…ATCA follow-up to provide precise (sub-arcsecond) positional accuracy for masers discovered in single dish surveys has been made by Caswell, Vaile, Forster (1995b) ;Ellingsen, Norris, McCulloch (1996a);Caswell (1997) ;Phillips, Norris, Ellingsen, McCulloch (1998) ;Walsh, Burton, Hyland, Robinson (1998), and others.…”

Section: Methanol Maser Surveysmentioning

confidence: 99%

Recent southern maser surveys

Caswell

2007

Proc. IAU

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Abstract. This discussion of recent maser surveys in the southern sky will allow us to see the context of the new methanol multibeam survey, which is currently in progress and described elsewhere at this symposium. My emphasis will be on masers that arise in star-forming regions in the disc of our Galaxy. I discuss outcomes from existing surveys, and comparison of different maser species, with special attention to the recognition of blue-shifted outflows.

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“…The maser emission is typically observed as a series of "spots" with bright cores of a few-10 AU, surrounded by weaker emission on scales of 10s-100s of AU [9], but sometimes extending to 1000s of AU [10]. The maser spots usually arise in clusters with linear scales of 6000 AU [11]. There are relatively few cases where the spatial structure of individual maser spots has been investigated in different coincident transitions towards the same source, however, where they have it has been found that the structure as measured by plots of the visibility versus baseline length differ [9].…”

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confidence: 99%

Practical Limitations on Astrophysical Observations of Methanol to Investigate Variations in the Proton-to-Electron Mass Ratio

2011

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The possibility of using astrophysical observations of rotational transitions in the methanol molecule to measure, or constrain temporal and spatial variations in the proton-to-electron mass ratio (µ) has recently been investigated by several groups. Here we outline some of the practical considerations of making such observations, including both the instrumental and astrophysical limitations which exist at present. This leads us to conclude that such observations are unlikely to be able to improve evidence either for, or against the presence of variations in the proton-to-electron mass ratio by more than an order of magnitude beyond current limits.PACS numbers: 06.20. Jr, 98.38.Er, 98.58.Ec The possibility of using astrophysical observations of rotational transitions in the methanol molecule to measure, or constrain temporal and spatial variations in the proton-to-electron mass ratio (µ) has recently been suggested by several groups [1,2]. The first attempts to use astronomical observations of methanol masers to constrain µ within the Milky Way show that |∆µ/µ| < 28 × 10 −9 [2].The hindered internal rotation exhibited by methanol produces the degeneracy which makes the different rotational transitions particularly sensitive to the protonto-electron mass ratio [1]. It also leads to the rich rotational and vibrational spectrum, which due to quantum mechanical selection rules produces a large number of centimetre and millimetre maser transitions in interstellar space. The strongest and most common of these is the 5 1 → 6 0 A + transition which has a rest frequency of approximately 6.7 GHz. It has been detected towards more than 900 sites of high-mass star formation in the Milky Way [see for example 3, 4]. The second strongest astrophysical transition of methanol is from the 2 0 → 3 −1 E transition which has a rest frequency of approximately 12.2 GHz, and is observed towards 43% of those sources showing 6.7 GHz emission [5]. In most methanol maser regions multiple spectral features are observed in the spectra of 6.7 or 12.2 GHz methanol masers at different Doppler shifted velocities [3,4]. The spectral features typically have near-Gaussian profiles (although spectral blending between spatially unresolved components affects most observations), and FWHM (full-width half maximum) of a few tenths of kilometers per second.The K µ coefficient measures the sensitivity of a transition to the proton-to-electron mass ratio and for the 6.7 and 12.2 GHz methanol transitions these have been calculated to be -42 and -33 respectively [1]. To improve constraints on |∆µ/µ|, beyond those already achieved [2], requires measurement of the relative Doppler shifted velocities of the different transitions to an accuracy of better than 100 ms −1 . When the 6.7 and 12.2 GHz methanol transitions exhibit peaks at the same velocity they have been demonstrated to arise from the same locations at the milliarcsecond level (corresponding to linear scales of a few AU at distances of a few kpc) [6,7]. The large number of 6.7 and 12.2 GHz methanol...

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Coincidence of maser emission from OH at 6.035 GHz and methanol at 6.668 GHz

Cited by 148 publications

References 0 publications

A search for water masers associated with class II methanol masers – II. Longitude range 341° to 6°

A search for water masers associated with class II methanol masers – II. Longitude range 341° to 6°

Recent southern maser surveys

Practical Limitations on Astrophysical Observations of Methanol to Investigate Variations in the Proton-to-Electron Mass Ratio

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