58 research outputs found
PSR B0329+54: Statistics of Substructure Discovered within the Scattering Disk on RadioAstron Baselines of up to 235,000 km
We discovered fine-scale structure within the scattering disk of PSR B0329+54
in observations with the RadioAstron ground-space radio interferometer. Here,
we describe this phenomenon, characterize it with averages and correlation
functions, and interpret it as the result of decorrelation of the
impulse-response function of interstellar scattering between the
widely-separated antennas. This instrument included the 10-m Space Radio
Telescope, the 110-m Green Bank Telescope, the 14x25-m Westerbork Synthesis
Radio Telescope, and the 64-m Kalyazin Radio Telescope. The observations were
performed at 324 MHz, on baselines of up to 235,000 km in November 2012 and
January 2014. In the delay domain, on long baselines the interferometric
visibility consists of many discrete spikes within a limited range of delays.
On short baselines it consists of a sharp spike surrounded by lower spikes. The
average envelope of correlations of the visibility function show two
exponential scales, with characteristic delays of and , indicating the presence of two scales of
scattering in the interstellar medium. These two scales are present in the
pulse-broadening function. The longer scale contains 0.38 times the scattered
power of the shorter one. We suggest that the longer tail arises from
highly-scattered paths, possibly from anisotropic scattering or from
substructure at large angles.Comment: 15 pages, 6 figures, 3 tables; accepted by Astrophysical journa
Evolved star water maser cloud size determined by star size
Cool, evolved stars undergo copious mass loss but the details of how the
matter is returned to the ISM are still under debate. We investigated the
structure and evolution of the wind at 5 to 50 stellar radii from Asymptotic
Giant Branch and Red Supergiant stars. 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 (several stellar periods). We compared our results
with long-term Pushchino single dish monitoring. The 22-GHz emission is located
in ~spherical, thick, unevenly filled shells. The outflow velocity doubles
between the inner and outer shell limits. Water maser clumps could be matched
at successive epochs separated by <2 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 5 sources, most of the matched features brighten or dim
in concert from one epoch to the next. One cloud in W Hya was caught in the act
of passing in front of a background cloud leading to 50-fold, transient
amplification. The masing clouds are 1-2 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 ~10x bigger than those
round the AGB stars. Proper motions are dominated by expansion, with no
systematic rotation. The maser clouds survive for decades (the shell crossing
time) but the masers are not always beamed in our direction. Radiative effects
cause changes in flux density throughout the maser shells on short timescales.
Cloud size is proportional to parent star size; clouds have a similar radius to
the star in the 22-GHz maser shell. Stellar properties such as convection cells
must determine the clumping scale.Comment: Accepted by A&A 2012 July 10 Main text 29 pages, 62 figures Appendix
44 pages, 23 figure
Results of Long-Term Monitoring of Maser Emission in the Star-forming Region G 10.623–0.383
International audienc
H2O and OH masers associated with cold infrared sources
International audienc
Evolution of the H2O and OH Maser Emission in W75 N
International audienc
Long-term monitoring and interpretation of flares in the H2O maser emission of IRAS 16293–2422
International audienc
Investigation of the OH and H2O maser emission from the semiregular variable HU puppis
International audienc
Evolution of Maser Emission in the Region of Active Star Formation G43.8–0.1. I. OH Maser Emission at 18 cm
International audienc
Variability of the OH and H2O maser emission toward AS 501
International audienc
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