Weak OH Masers in the Direction of H<sup>2</sup>0 Masers

Haynes, R. F.; Caswell, J. L.; Goss, W. M.

doi:10.1017/s132335800001465x

Cited by 4 publications

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“…6). This source was first discovered by Haynes et al (1976). The emission is still similar to that seen in 1976.…”

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confidence: 60%

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Survey of OH Masers at 1665 MHz. II. Galactic Longitude 340o to the Galactic Centre

Caswell¹,

Haynes²

1983

Aust. J. Phys.

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Aust. J. Phys., 1983,36, 361-99 The galactic plane from longitude 340° through the galactic centre to longitude + 2° has been searched for OH on the 1665 MHz transition. Forty-nine OH maser emission sources were detected and these have now been studied on all four OH ground-state transitions. Most of the masers are associated with regions of star formation (type I) while three may be examples of late-type stars (type II OH/IR) with unusually strong main-line emission.Two especially interesting type I masers discovered are: OH351·78-0·54, which is now the strongest OH maser known, with a peak intensity of nearly 1000 Jy (= 10-23 W m-2 Hz-i), and OH340·78-0·1O, which displays an unusual velocity structure suggestive of a shell of emission.Combining the present results with those of our earlier survey of longitudes 326° to 340 0 (Part I) doubles the number of well-studied type I OH sources. We have thus been able to improve our previous estimate of the luminosity function and have also now derived a galactic radial distribution extending to the galactic centre; this shows that while the inner 5 kpc of the Galaxy is generally deficient in type I OH masers, the immediate vicinity of the centre has a quite high density of such sources.The conclusions of Part I were reassessed in the light of the new results. In the total sample of 85 type I sources six show accompanying strong 1720 MHz maser emission and nine show strong 1612 MHz maser emission; this significantly alters the statistics of Part I alone, which showed no 1720 MHz masers but six 1612 MHz masers. However, our earlier results regarding velocity structure, polarization and variability are generally corroborated; in particular, the present data reinforce our conclusions that a surprisingly large proportion of masers (including the exceptionally strong OH351'78-0'54) have no closely rdated prominent HII region and quite likely pinpoint sites of the very early stages in star formation. The quite common occurrence of the masers within extensive OH clouds (as indicated by weak but spatially extended emission at 1612 or 1720 MHz) is also suggestive of dense molecular clouds in which star formation and HII region development are just beginning.

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“…6). This source was first discovered by Haynes et al (1976). The emission is still similar to that seen in 1976.…”

supporting

confidence: 60%

“…...., C RCG, Robinson et al (1974); CHGM, Caswell et al (1981); HCG, Haynes et al (1976); CHG, Caswell et al (1977); CR, Caswell and Robinson (1974);WWDL, Weaver et al (1965); CH, Caswell and Haynes (1980);CF, Cohen and Few (1976);GW, Gardner and Whiteoak (1975);MRGB, McGee et al (1965).…”

Section: (B) Notes On Some Individual Oh Sourcesmentioning

confidence: 99%

Survey of OH Masers at 1665 MHz. II. Galactic Longitude 340o to the Galactic Centre

Caswell¹,

Haynes²

1983

Aust. J. Phys.

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“…8). This OH maser was discovered by Haynes et al (1976) (see also Caswell et al 1977), and is coincident with an H 2 0 maser. The high-resolution continuum map (at 1·4 GHz) and the red photograph reproduced by Shaver et al (1981) show that these masers are slightly displaced from the HII region.…”

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confidence: 62%

Survey of OH Masers at 1665 MHz. III. Galactic Longitudes 233° to 326°

Caswell

Haynes

1987

Aust. J. Phys.

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Aust. J. Phys., 1987, 40, 215-38 We have searched the galactic plane from longitude 233° to 326° for OH emission on the 1665 MHz transition. Between longitudes 270° and 326°, where the survey zone was a uniformly sampled grid, we detected 35 OH maser sources, including 24 new ones; most are of the Type I variety that delineates sites of current star formation, and many of the sites are young, with no well-developed HII regions in the vicinity. By combining the present results with those of earlier surveys Oongitudes 326° -+ 360° -+ 2°: Parts I and II) we have improved on previous estimates of the galactic distribution of these masers.All sources were studied in both circular polarisations on the 1665 and 1667 MHz transitions of the OH ground state; measurements of the 1612 and 1720 MHz transitions will be needed to single out any masers of different varieties, such as those associated with late-type stars rather than regions of star formation.Three individually interesting discoveries are: OH301·14-0·23, which shows weak 'highvelocity' emission displaced more than 20 km s -1 from the main features, similar to the displacements seen in the associated H 2 0 maser; OH310·06-3.02, which is probably an unusual variety of late-type star; and OH 311·64 -0· 38, whose systemic velocity of + 34 kms -1 .indicates a location outside the solar circle, in a previously uncharted extension of the Carina spiral arm, 16· 3 kpc from the Sun.

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“…Current spectra (2004 displayed, and 2005) show stable spectra with no net circular or linear polarization. The relatively smooth absorption spectra seen at 1667 MHz have been stable over all high spectral resolution measurements since first recorded in 1976 (Haynes, Caswell & Goss 1976), and are assumed as a baseline to derive the peak intensity of 1665-MHz emission given in Table 1. 1665-MHz spectra are barely distinguishable from those in 1989 (unpublished Parkes data), but significant changes have occurred since 1976 when the feature at 21.5 km s −1 was stronger and showed net RHCP, and was used for the VLA position measurement by Forster & Caswell (1989).…”

Section: 113+0050mentioning

confidence: 99%

Parkes full polarization spectra of OH masers – I. Galactic longitudes 350° through the Galactic Centre to 41°

Caswell

Green

Phillips

2013

Monthly Notices of the Royal Astronomical Society

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Full polarization measurements of 1665 and 1667-MHz OH masers at sites of massive star formation have been made with the Parkes 64-m radio telescope. Here we present the resulting spectra for 104 northerly sources, from Galactic longitude 350 • through the Galactic Centre to 41 • . Some maser positions were previously uncertain by many arcseconds, and thus for more than 20 masers we made new measurements with the ATCA (which also revealed several hitherto unreported masers), in most cases yielding arcsecond precision to match the majority of sites. Position improvements have assisted us in distinguishing OH masers with accompanying methanol masers from those without (thought to be at a later stage of evolution). There was no existing linear polarization information at many sites, and spectral resolution was sometimes poor, or velocity coverage incomplete. These inadequacies are addressed by the present Parkes spectra. The whole OH maser sample exhibit the well-known predominance of highly circularly polarized features. We find that linear polarization is also common, but usually much weaker, and we highlight the rare cases of very pronounced linear polarization that can extend to 100 per cent. Unusually large velocity ranges of at least 25 km s −1 are present at seven sites. Our spectra measurements for most sources are at two epochs spaced by nearly one year, and reveal high stability at most sites, and marked variability (more than factors of two in the strongest feature) at only five sites. The spectra also provide a valuable reference for longer term variability, with high stability evident over the past decades at 10 sites and marked variability for four of the sample. Future systematic monitoring of these variables may uncover further examples of periodicity, a phenomenon so far recognised in only one source.

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Weak OH Masers in the Direction of H²0 Masers

Cited by 4 publications

References 6 publications

Survey of OH Masers at 1665 MHz. II. Galactic Longitude 340o to the Galactic Centre

Survey of OH Masers at 1665 MHz. II. Galactic Longitude 340o to the Galactic Centre

Survey of OH Masers at 1665 MHz. III. Galactic Longitudes 233° to 326°

Parkes full polarization spectra of OH masers – I. Galactic longitudes 350° through the Galactic Centre to 41°

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Weak OH Masers in the Direction of H20 Masers

Cited by 4 publications

References 6 publications

Survey of OH Masers at 1665 MHz. II. Galactic Longitude 340o to the Galactic Centre

Survey of OH Masers at 1665 MHz. II. Galactic Longitude 340o to the Galactic Centre

Survey of OH Masers at 1665 MHz. III. Galactic Longitudes 233° to 326°

Parkes full polarization spectra of OH masers – I. Galactic longitudes 350° through the Galactic Centre to 41°

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Weak OH Masers in the Direction of H²0 Masers