Variability of the H<sub>2</sub>O maser associated with the M-supergiant S Persei

Lekht, E. E.; Rudnitskij, G. M.; Mendoza-Torres, J. E.; Толмачев, А. М.

doi:10.1051/0004-6361:20052635

Cited by 14 publications

(15 citation statements)

References 38 publications

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“…The central peak around −37.8 km s −1 exceeds 40 Jy and is spatially compact at both MERLIN epochs. However, it has faded in Pushchino spectra taken at 19940810, a few months after the 1994 MERLIN epoch, and is absent for most of 1995-6 and all of 1997 (Lekht et al 2005). It re-appears in the 19981228 and later Pushchino spectra as well as in the MERLIN 1999 data.…”

Section: Maser Features and Their Parent Cloudsmentioning

confidence: 96%

Evolved star water maser cloud size determined by star size

Richards

Etoka

Gray

et al. 2012

A&A

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Context. Cool, evolved stars undergo copious mass loss but the detailed mechanisms and the form in which the matter is returned to the ISM are still under debate. Aims. We investigated the structure and evolution of the wind at 5 to 50 stellar radii from asymptotic giant branch and red supergiant stars. Methods. 22-GHz water masers around seven evolved stars were imaged using MERLIN, at sub-AU resolution. Each source was observed at between 2 and 7 epochs, covering several stellar periods. We compared our results with long-term single dish monitoring provided by the Pushchino radio telescope. Results. The 22-GHz emission is located in approximately spherical, thick, unevenly filled shells. The outflow velocity increases twofold or more between the inner and outer shell limits. Water maser clumps could be matched at successive epochs separated by less than two years for AGB stars, or at least 5 years for RSG. This is much shorter than the decades taken for the wind to cross the maser shell, and comparison with spectral monitoring shows that some features fade and reappear. In five sources, most of the matched maser features brighten or dim in concert from one epoch to the next. A number of individual maser features show idiosyncratic behaviour, including one cloud in W Hya caught in the act of passing in front of a background cloud leading to 50-fold, transient amplification. The masing clouds are one or two orders of magnitude denser than the wind average and contain a substantial fraction of the mass loss in this region, with a filling factor <1%. The RSG clouds are about ten times bigger than those round the AGB stars. Conclusions. Proper motions are dominated by expansion, with no systematic rotation. The maser clouds presumably survive for decades (the shell crossing time) but the masers are not always beamed in our direction. Only radiative effects can explain changes in flux density throughout the maser shells on short timescales. The size of the clouds is proportional to that of the parent star, being of a similar radius to the star once the clumps reach the 22-GHz maser shell. Stellar properties such as convection cells must determine the clumping scale.

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Section: Maser Features and Their Parent Cloudsmentioning

confidence: 96%

Evolved star water maser cloud size determined by star size

Richards

Etoka

Gray

et al. 2012

A&A

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“…Shock waves driven by stellar pulsations are postulated as possible causes of H 2 O variations in S Per (Lekht et al 2005). In this model an increase of integrated H 2 O flux detected at a given epoch should be correlated with one of the previous visual maxima depending on the shock travel time from the stellar surface to the maser layers.…”

Section: Origin Of the Outburstsmentioning

confidence: 97%

“…In this model an increase of integrated H 2 O flux detected at a given epoch should be correlated with one of the previous visual maxima depending on the shock travel time from the stellar surface to the maser layers. For instance, a shock of velocity ∼10 km s −1 affects the H 2 O and OH maser region ∼40 yr later Lekht et al 2005). An inspection of the AVVSO data from interval of 60-30 yr earlier than our observations failed to show any correlation.…”

Section: Origin Of the Outburstsmentioning

confidence: 99%

“…Both targets are semiregulars with mean visual periods of 832 and 732 days (Kholopov et al 1987). Their general properties were summarized elsewhere (Szymczak & Cohen 1997;Richards et al 1999;Lekht et al 2005). Optical and near-infrared images of high resolution showed a slight deviation from circularity (Monnier et al 2004;Schuster et al 2006).…”

Section: Introductionmentioning

confidence: 99%

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Outburst OH maser activity in the envelopes of S Persei and VX Sagittarii

Szymczak

Wolak

Gérard

et al. 2010

A&A

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Context. OH masers from the envelopes of M-type supergiants show a significant degree of polarization, implying magnetic fields of a few mG. Nothing is known about the temporal characteristics of the magnetic fields or how such changes may affect stellar mass loss. Aims. We therefore observed two supergiant stars in order to quantify the long-term polarization behaviour of the maser emission. Methods. Full-polarization spectra at 1612 and 1667 MHz were obtained with the Nançay radio telescope at intervals over periods of 4 and 6 years for S Per and VX Sgr, respectively. Results. Time series of OH maser full polarization spectra are presented. Semiregular variations of the integrated flux densities generally follow the visual light curves as expected for radiative pumping cycles. For both sources the variability indices of individual features are higher at 1667 MHz than at 1612 MHz and their extreme values occur for the blue-shifted emission. The degrees of polarization at 1667 MHz show diverse behaviours usually uncorrelated with the total flux, whereas those at 1612 MHz are commonly stable on time scales of 4−6 yr. Several outbursts of the 1667 MHz emission on time scales of 0.5−2 yr were found in both targets. The bursting features are highly polarized and show drifts in velocity. Small changes of the degrees of polarization and smooth variations of position angle of linear polarization during the bursts were observed in S Per but they are more dramatic in VX Sgr. Conclusions. The OH outbursts do not seem to have any direct link to stellar events, but seem to be localized in the wind.

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“…ground-state OH [47]), Effelsberg (e.g. excited OH [34]) or Puschino (H 2 O [85,86]), nor blind surveys, notably for methanol [43,122,23]. …”

Section: What Are Masers?mentioning

confidence: 99%

Beaming in on some stimulating issues in stellar evolution

Richards

2007

Proceedings of 8th European VLBI Network Symposium — PoS(8thEVN)

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This review discusses some recent maser observations and their interpretation, with the emphasis on physical processes in star formation and mass loss from evolved stars. I draw attention to issues where high-resolution observations have led to new, surprising or controversial developments. I also mention some results and prospects for maser studies arising from new instruments and surveys. Highlights include measurements of Zeeman splitting in non-paramagnetic species such as water and methanol. The water maser results often indicate a much stronger magnetic field than is seen by nearby OH masers, suggesting that the former arise from overdense clumps. Maser scattering or Faraday rotation implicates a significant ionised fraction. The increasing number of axisymmetric outflows from evolved stars, often with no signs of rotation, are likely to be shaped by magnetic fields, but there is no agreement on their origin. Extraordinary thousand-AU filaments have been seen in e.g. W3(OH) in OH and methanol, and in S128 in water. At the other extreme, compact 6-GHz OH and methanol are associated on sub-arcsec, but not milli-arcsec scales; does this indicate chemical chronology or competitive maser amplification? Another surprise is the increasing number of weak methanol and water masers associated with low-mass young stellar objects. Masers are still an ideal tool to probe the chemistry, kinematics, density, magnetic field and ionised fraction, and hence the rate and clumping scales of star formationbut the process is intrinsically a lot more complex than it once seemed.

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Variability of the H₂O maser associated with the M-supergiant S Persei

Cited by 14 publications

References 38 publications

Evolved star water maser cloud size determined by star size

Evolved star water maser cloud size determined by star size

Outburst OH maser activity in the envelopes of S Persei and VX Sagittarii

Beaming in on some stimulating issues in stellar evolution

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Variability of the H2O maser associated with the M-supergiant S Persei

Cited by 14 publications

References 38 publications

Evolved star water maser cloud size determined by star size

Evolved star water maser cloud size determined by star size

Outburst OH maser activity in the envelopes of S Persei and VX Sagittarii

Beaming in on some stimulating issues in stellar evolution

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Product

Resources

About

Variability of the H₂O maser associated with the M-supergiant S Persei