Monitoring of OH maser emission from late-type stars

Jewell, P. R.; Elitzur, Moshe; Webber, J. C.; Snyder, L. E.

doi:10.1086/190615

Cited by 21 publications

(15 citation statements)

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“…U Ori showed dramatic variations in the OH lines in 1974, when the type of its OH emission changed (Cimerman 1979;Jewell et al 1979Jewell et al , 1981. The events consisted of the sudden appearance of strong 1612-MHz radiation, coinciding with the disappearance of the 1667-MHz radiation.…”

Section: Discussionmentioning

confidence: 99%

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Variability of the H₂O maser associated with U Orionis

Rudnitskij¹,

Lekht

Mendoza-Torres

et al. 2000

Astron. Astrophys. Suppl. Ser.

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Abstract. H 2 O line observations at λ = 1.35 cm of the Mira Ceti-type variable star U Ori are reported. The observations cover the time interval from March, 1980, to September, 1999. Variations of the integral flux and velocity centroid of the H 2 O line are analysed. The flux in general correlates with the visual light curve, following it with some phase delay ∆ϕ ∼ 0.2 − 0.4P (P is the period of the star). The maser emission is generated in a quasistationary layer of gas and dust at a distance of about 10 14 cm from the stellar centre. The maser variability is explained by the action of periodic shocks, driven by stellar pulsation and arriving to the maser in each stellar cycle. The shocks provide the maser pumping, whereas the sink of the waste energy is controlled by the dust, periodically heated by the stellar radiation near the light maximum; this accounts for the correlation of the maser radiation maximum with the descending branch of the light curve. Temporary weakness of the maser emission may be due to decay of the quasi-stationary layer, which is then rebuilt by a powerful shock, carrying away from the star a portion of the lost mass, once per a few stellar periods -the "superperiod". In its turn, the superperiod may reflect multiperiodic pulsation of the star or the presence of a long-term activity cycle, connected with restructuring of the stellar magnetic field, which is known to be strong in U Ori.

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Section: Discussionmentioning

confidence: 99%

“…In particular, in mid-1970s U Ori changed its type of the OH emission from IIb to I (Cimerman 1979;Jewell et al 1979Jewell et al , 1981. In 1980 U Ori experienced a strong flare in the H 2 O line λ = 1.35 cm (Lekht et al 1981), the flare lasted almost 1 year.…”

Section: Introductionmentioning

confidence: 99%

Variability of the H₂O maser associated with U Orionis

Rudnitskij¹,

Lekht

Mendoza-Torres

et al. 2000

Astron. Astrophys. Suppl. Ser.

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“…Thus, for our present study of superradiance we will only focus on OH samples that are believed to be inverted through radiative processes. The studies of pumping mechanisms of OH masers show that the 1612 MHz masers associated with evolved stars are pumped by far-infrared photons at 35 and 53 mm (Litvak 1969;Jewell et al 1979;Elitzur 1992;Gray 2012). These photons are emitted from dust shells formed by mass losses from the central star.…”

Section: Requirements For Superradiancementioning

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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“…Early observations of Miras and OH/IR objects showed that OH maser emission follows the optical and infrared emission Send offprint requests to: M. Szymczak, e-mail: msz@astro.uni.torun.pl Figures A1-A3 are only available in electronic form at http://www.edpsciences.org Present address: Jodrell Bank Observatory, University of Manchester, Jodrell Bank, Macclesfield, Cheshire SK11 9DL, UK. (Harvey et al 1974;Fillit et al 1977;Jewell et al 1979). They show evidence for radiative coupling of the OH maser with stellar variability.…”

Section: Introductionmentioning

confidence: 99%

“…Long term studies of Miras spanning about 15 years (Etoka 1996;Etoka & Le Squeren 2000) revealed that the integrated OH flux densities show cyclic variations superimposed on slow changes lasting several stellar cycles. There are some Mira variables which experienced eruptive variability in the OH lines (Jewell et al 1979;Le Squeren & Sivagnanam 1985;Etoka & Le Squeren 1996;.…”

Section: Introductionmentioning

confidence: 99%

Monitoring of long term behaviour of OH masers in semiregular variables: R Crt, W Hya and RT Vir

Etoka

Błaszkiewicz

Szymczak

et al. 2001

A&A

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Abstract. We present and interpret the results of a long-term OH variability study of three semiregular stars, one type a (SRa), W Hya, and two type b (SRb), R Crt and RT Vir. The 1665 and 1667 MHz OH masers of the three semiregulars were observed at intervals in the period 1982 January-1995 December using the Nançay radio telescope, and we searched for 1612 MHz emission. The OH maser profiles of the studied stars significantly deviated from a standard double-peaked profile. The timescale of profile changes in the two SRb stars R Crt and RT Vir was as short as a month. The OH profiles of the SRa star W Hya were much more stable but since November 1986 a very blue-shifted feature appeared at 1667 MHz. Our phase-lag measurements suggest that this feature comes from a detached OH shell of radius ∼3 × 10 16 cm. Faint 1612 MHz emission was found in W Hya only. Weak emission at velocities very close to the systemic velocity usually appeared during some intervals of high maser activity in R Crt and RT Vir and was almost always present in W Hya. For R Crt we estimated that this tangential emission disappeared when the kinetic temperature in the OH maser regions dropped below 150−200 K. For a few features, line narrowing and re-broadening were observed on timescales of 90−200 days. The linewidth was inversely proportional to the peak flux density, suggesting unsaturated amplification. Cyclic variations in the integrated flux density were observed in all the three stars. The OH variability curves were generally characterised by large amplitude (4−6 m ) variations over 400−800 days superimposed with 100−300-day variations of 0.2−2 m . Only the measured OH period of W Hya, of 362 ± 7 days, was in agreement with the optical period. The two SRb stars exhibited multi-periodic OH variability including with two statistically significant periods. The behaviour of their red-and blue-shifted emission was less correlated than in W Hya. The ratios of the flux densities at 1667 MHz to that at 1665 MHz in all the three stars were about 2 at epochs of high OH activity and usually increased during weak maser emission. Long term behaviour of the OH masers from W Hya resembled that of standard OH Miras, while that of R Crt and RT Vir suggested thin and clumpy envelopes where unsaturated emission was sustained in some clouds.

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Monitoring of OH maser emission from late-type stars

Cited by 21 publications

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Variability of the H₂O maser associated with U Orionis

Variability of the H₂O maser associated with U Orionis

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

Monitoring of long term behaviour of OH masers in semiregular variables: R Crt, W Hya and RT Vir

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Monitoring of OH maser emission from late-type stars

Cited by 21 publications

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Variability of the H2O maser associated with U Orionis

Variability of the H2O maser associated with U Orionis

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

Monitoring of long term behaviour of OH masers in semiregular variables: R Crt, W Hya and RT Vir

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Variability of the H₂O maser associated with U Orionis

Variability of the H₂O maser associated with U Orionis