1,536 research outputs found
A high-sensitivity OH 5-cm line survey in late-type stars
We have undertaken a comprehensive search for 5-cm excited OH maser emission
from evolved stars representative of various stages of late stellar evolution.
Observed sources were selected from known 18-cm OH sources. This survey was
conducted with the 100-m Effelsberg telescope to achieve high signal to noise
ratio observations and a sensitivity limit of about 0.05 to 0.1 Jy. A total of
64 stellar sources were searched for both main line and satellite line
emission. We confirm the previous detection of 5 cm OH in Vy 2-2, do not
confirm emission from NML-Cyg and do not report any other new detection within
the above sensitivity limit.
Implications of these results on the pumping mechanism of the OH radical in
circumstellar envelopes are briefly discussed.Comment: 8 pages, 5 figures, A&A in pres
Effelsberg Observations of Excited-State (6.0 GHz) OH in Supernova Remnants and W3(OH)
While masers in the 1720 MHz transition of OH are detected toward many
supernova remnants (SNRs), no other OH transition is seen as a maser in SNRs.
We present a search for masers at 6049 MHz, which has recently been predicted
to produce masers by pure collisional excitation at conditions similar to that
required for 1720 MHz masing. The Effelsberg 100 m telescope was used to
observe the excited-state 6016, 6030, 6035, and 6049 MHz lines of OH toward
selected SNRs, most of which have previously-detected bright 1720 MHz masers.
No excited-state masers are found toward SNRs, consistent with previous
observations of the 6049 MHz and other excited-state transitions. We do not see
clear evidence of absorption toward SNR target positions, although we do see
evidence of absorption in the molecular cloud at +50 km/s near Sgr A East. Weak
absorption is detected at 6016 MHz toward W3(OH), while stronger, narrower
emission is seen at 6049 MHz, suggesting that the 6049 MHz emission is a
low-gain maser. We conclude that conditions in SNRs are not conducive to
excited-state maser emission, especially in excited-state satellite lines.Comment: 4 pages using emulateapj.cls including 2 tables and 1 figure,
accepted to ApJ
Structure of W3(OH) from Very High Spectral Resolution Observations of 5 Centimeter OH Masers
Recent studies of methanol and ground-state OH masers at very high spectral
resolution have shed new light on small-scale maser processes. The nearby
source W3(OH), which contains numerous bright masers in several different
transitions, provides an excellent laboratory for high spectral resolution
techniques. We present a model of W3(OH) based on EVN observations of the
rotationally-excited 6030 and 6035 MHz OH masers taken at 0.024 km/s spectral
resolution. The 6.0 GHz masers are becoming brighter with time and show
evidence for tangential proper motions. We confirm the existence of a region of
magnetic field oriented toward the observer to the southeast and find another
such region to the northeast in W3(OH), near the champagne flow. The 6.0 GHz
masers trace the inner edge of a counterclockwise rotating torus feature.
Masers at 6030 MHz are usually a factor of a few weaker than at 6035 MHz but
trace the same material. Velocity gradients of nearby Zeeman components are
much more closely correlated than in the ground state, likely due to the
smaller spatial separation between Zeeman components. Hydroxyl maser peaks at
very long baseline interferometric resolution appear to have structure on
scales both smaller than that resolvable as well as on larger scales.Comment: 21 pages using emulateapj.cls including 16 figures and 2 tables,
accepted to Ap
Nanorheology : an Investigation of the Boundary Condition at Hydrophobic and Hydrophilic Interfaces
t has been shown that the flow of a simple liquid over a solid surface can
violate the so-called no-slip boundary condition. We investigate the flow of
polar liquids, water and glycerol, on a hydrophilic Pyrex surface and a
hydrophobic surface made of a Self-Assembled Monolayer of OTS
(octadecyltrichlorosilane) on Pyrex. We use a Dynamic Surface Force Apparatus
(DSFA) which allows one to study the flow of a liquid film confined between two
surfaces with a nanometer resolution. No-slip boundary conditions are found for
both fluids on hydrophilic surfaces only. Significant slip is found on the
hydrophobic surfaces, with a typical length of one hundred nanometers.Comment: 8 pages, 7 figures, 2 tables. Accepted for European Physical Journal
E - Sofr Mate
EVLA Observations of OH Masers in ON 1
This Letter reports on initial Expanded Very Large Array (EVLA) observations
of the 6035 MHz masers in ON 1. The EVLA data are of good quality, lending
confidence in the new receiver system. Nineteen maser features, including six
Zeeman pairs, are detected. The overall distribution of 6035 MHz OH masers is
similar to that of the 1665 MHz OH masers. The spatial resolution is sufficient
to unambiguously determine that the magnetic field is strong (~ -10 mG) at the
location of the blueshifted masers in the north, consistent with Zeeman
splitting detected in 13441 MHz OH masers in the same velocity range. Left and
right circularly polarized ground-state features dominate in different regions
in the north of the source, which may be due to a combination of magnetic field
and velocity gradients. The combined distribution of all OH masers toward the
south is suggestive of a shock structure of the sort previously seen in W3(OH).Comment: 4 pages using emulateapj.cls including 2 tables and 2 color figure
5cm OH masers as diagnostics of physical conditions in star-forming regions
We demonstrate that the observed characteristics of the 5 cm OH masers in
star-forming regions can be explained with the same model and the same
parameters as the 18 cm and the 6 cm OH masers. In our already published study
of the 18 cm and the 6 cm OH masers in star-forming regions we had examined the
pumping of the 5 cm masers, but did not report the results we had found because
of some missing collision rate coefficients, which in principle could be
important. The recently published observations on the 5 cm masers of OH
encourage us to report our old calculations along with some new ones that we
have performed. These calculations, in agreement with the observations, reveal
the main lines at 5 cm as strong masers, the 6049 MHz satellite line as a weak
maser, and the 6017 MHz satellite line as never inverted for reasonable values
of the parametersComment: TeX 15 pages, 30 postscript figures, accepted by Ap
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