25 research outputs found
Distances of Stars by mean of the Phase-lag Method
Variable OH/IR stars are Asymptotic Giant Branch (AGB) stars with an
optically thick circumstellar envelope that emit strong OH 1612 MHz emission.
They are commonly observed throughout the Galaxy but also in the LMC and SMC.
Hence, the precise inference of the distances of these stars will ultimately
result in better constraints on their mass range in different metallicity
environments. Through a multi-year long-term monitoring program at the Nancay
Radio telescope (NRT) and a complementary high-sensitivity mapping campaign at
the eMERLIN and JVLA to measure precisely the angular diameter of the
envelopes, we have been re-exploring distance determination through the
phase-lag method for a sample of stars, in order to refine the
poorly-constrained distances of some and infer the currently unknown distances
of others. We present here an update of this project.Comment: 4 pages, 1 figure, 2 tables, to appear in the Proceedings of the IAU
Symposium No. 336: Astrophysical Masers: Unlocking the Mysteries of the
Univers
OH masers in the Milky Way and Local Group galaxies in the SKA era
The intense line emission of OH masers is a perfect tracer of regions where
new stars are born aswell as of evolved stars, shedding large amounts of
processed matter into the interstellar medium. From SKA deep surveys at 18 cm,
where the maser lines from the ground-state of the OH molecule arise, we
predict the discovery of more than 20000 sources of stellar and interstellar
origin throughout the Galaxy. The study of this maser emission has many
applications, including the determination of magnetic field strengths from
polarisation measurements, studies of stellar kinematics using the precisely
determined radial velocities, and distance determinations from VLBI astrometry.
A new opportunity to study shocked gas in different galactic environments is
expected to arise with the detection of lower luminosity masers. For the first
time, larger numbers of OH masers will be detected in Local Group galaxies. New
insights are expected in structure formation in galaxies by comparing maser
populations in galaxies of different metallicity, as both their properties as
well as their numbers depend on it. With the full capabilities of SKA, further
maser transitions such as from excited OH and from methanol will be accessible,
providing new tools to study the evolution of star-forming regions in
particular.Comment: Contribution to the conference on "Advancing Astrophysics with the
Square Kilometre Array" for the SKA science book, Giardini-Naxos, Sicily,
June 2014; in Proceedings of Science, 14 page
OH maser towards IRAS 06056+2131: polarization parameters and evolution status
We present high angular resolution observations of OH maser emission towards
the high-mass star forming region IRAS 06056+2131. The observations were
carried out using the UK radio interferometer array, Multi-Element Radio Linked
Interferometer Network (MERLIN) in the OH main lines at 1665- and 1667-MHz, in
addition to the OH satellite line at 1720-MHz. The results of this study
revealed emission in the 1665 MHz line with an estimated total intensity of
Jy. We did not detect any emission from the 1667-MHz and 1720-MHz
lines.
The full polarization mode of MERLIN enables us to investigate the magnetic
field in the OH maser region. Our results show that IRAS 06056+2131 is a highly
circularly polarized source. In this transition, a Zeeman pair is identified
from which a magnetic strength of mG is inferred. The orientation
of the linear polarization vectors suggests that the magnetic field lines at
the location of the OH maser emission \textbf{might be} in agreement with the
orientation of the outflow thought to be associated with this source. The star
forming evolutionary status of the embedded proto-stellar object is discussed.Comment: 10 pages, 5 figure
Flaring Miras
Product is a conference poster, not in proceedings.Long-term monitoring have allowed the discovery of a new class of OH masers towards thin-shell Miras. The 2 main characteristics of these events are their high degree of polarisation and indications that the OH flaring zones are more internal than the standard OH ones. This latter fact has been confirmed by recent mapping. These flaring events have now being recorded towards objects believed to be isolated as well as belonging to a binary system. The overall characteristics of such events and the implications with respect to the standard models will be discussed