Anomalous Intensity Ratios of the Interstellar Lines of OH in Absorption and Emission

McGee, R. X.; Robinson, B. J.; Gardner, F. F.; Bolton, J. G.

doi:10.1038/2081193a0

Cited by 35 publications

(15 citation statements)

References 6 publications

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“…Line intensity ratios for the absorption at +1·3 km/sec are close to those given previously (McGee et al 1965); 2·2: 2·8 : 1 for 1665, 1667, and 1720 MHz respectively. No observations were taken at 1612 MHz.…”

Section: (Iii) Row 38supporting

confidence: 65%

“…OR emission was observed on all four lines (1612( , 1665( , 1667( , and 1720. The profiles have been given by McGee et al (1965).…”

Section: (Ix) Sagittarius B2mentioning

confidence: 99%

“…by McGee et al (1965) and Dieter, Weaver, and Williams (1966). In the present investigation we have made observations at the OH frequencies on about 30 of the stronger thermal sources within the declination range of the Parkes radiotelescope (i.e.…”

Section: Introductionmentioning

confidence: 99%

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Oh Observations in the Directions of Galactic Thermal Sources

McGee¹,

Gardner²,

Robinson³

1967

Aust. J. Phys.

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SummaryA survey for the hydroxyl line radiation has been made in the directions of 30 radio sources (most of them thermal) with the 210 ft telescope of beamwidth 12'· 2 and the multichannel line receiver of bandwidths 10 and 37 kHz. The line at frequency 1665·401 MHz was observed for all sources and the other three lines at 1612, 1667, and 1720 MHz were observed for 10 of the more important sources. The latter were investigated for circular and linear polarization.Twenty·six sources showed absorption lines in their directions, many at two or more radial velocities. Apparent opacities ranged from 0·4 to less than 0·002.Fourteen sources showed emission lines. In general, the emission was strongly circularly polarized.Linear polarization was low except for a value of 45 % in one source.An attempt was made to locate the OH clouds in space with the aid of a model of galactic rotation. OH gas appeared to be spread throughout the spiral arms of hydrogen. The ratio of OH to HI was less in the outer arms than towards the centre source Sagittarius A but it varied somewhat randomly in the inner arms. There is little doubt that OH emission and in many cases OH absorption occur close to HII regions.

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Section: (Iii) Row 38supporting

confidence: 65%

“…OR emission was observed on all four lines (1612( , 1665( , 1667( , and 1720. The profiles have been given by McGee et al (1965).…”

Section: (Ix) Sagittarius B2mentioning

confidence: 99%

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Oh Observations in the Directions of Galactic Thermal Sources

McGee¹,

Gardner²,

Robinson³

1967

Aust. J. Phys.

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“…In optically thin regions under conditions of local thermodynamic equilibrium (LTE), the expected intensity ratios are approximately 1:5:9:1 for the 1612, 1665, 1667, and 1720MHz lines, respectively (Elitzur 1992. However, in several observations different line ratios were measured (McGee et al 1965), and in some cases the intensity of a given line significantly exceeded that predicted using LTE (Weaver et al 1965). The strong anomalous line intensities were explained by postulating maser action for the corresponding transitions.…”

Section: Introductionmentioning

confidence: 99%

DICKE’S SUPERRADIANCE IN ASTROPHYSICS. II. THE OH 1612 MHz LINE

Rajabi

Houde

2016

ApJ

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We apply the concept of superradiance that was introduced by Dicke in 1954 to the OH molecule 1612 MHz spectral line, which is often used for the detection of masers in the circumstellar envelopes of evolved stars. Because the detection of 1612 MHz OH masers in the outer shells of envelopes of these stars implies the existence of a population inversion and a high level of velocity coherence, and that these are two necessary requirements for superradiance, we investigate whether superradiance can also happen in these regions. Superradiance is characterized by high-intensity, spatially compact, burst-like features taking place over timescales on the order of seconds to years, depending on the size and physical conditions present in the regions harboring such sources of radiation. Our analysis suggests that superradiance provides a valid explanation for previous observations of intensity flares detected in that spectral line for the U Orionis Mira star and the IRAS 18276-1431 preplanetary nebula.

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“…Weaver et al (1965) discovered both emission and absorption in the direction of NGC 6334 at 1665 and 1667 MHz. McGee et al (1965) observed emission also at 1720 MHz and absorption at all four frequencies; they found that the main source of emission at 1665 MHz was of small angular extent and located towards the edge of the group of nebulae.…”

Section: Introductionmentioning

confidence: 99%

18 cm OH-Line Radiation from NGC 6334

Gardner¹,

McGee²,

Robinson³

1967

Aust. J. Phys.

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SummaryA survey of the OH·line radiation from the region of NGC 6334 has been made with the Parkes 210 ft telescope (beamwidth 12'· 2 arc, bandwidth 10 kHz). Observations of both circular and linear polarization were made at 1665 MHz, and less completely at 1667 MHz.Two centres of OH-line emission, A and B, are clearly distinguished, one on either side of the nebulosity. Each centre may consist of three or more neighbouring regions with radial velocities in the range -6 to -12·5 km/sec. OH·line absorption observed at radial velocities of -4·5 and + 5· 5 km/sec probably takes place in gas complexes between the nebula and the Sun.Strong circular polarization is present, especially in A, the more northern source, but the polarization characteristics of the two main centres are markedly different. Linear polarization is less than 10% for A. There is no clear evidence for secular variation of the line intensities.

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Anomalous Intensity Ratios of the Interstellar Lines of OH in Absorption and Emission

Cited by 35 publications

References 6 publications

Oh Observations in the Directions of Galactic Thermal Sources

Oh Observations in the Directions of Galactic Thermal Sources

DICKE’S SUPERRADIANCE IN ASTROPHYSICS. II. THE OH 1612 MHz LINE

18 cm OH-Line Radiation from NGC 6334

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