6,273 research outputs found
Revising the kinematics of 12GHz CH3OH masers in W3(OH)
We derive accurate proper motions of the CH3OH 12 GHz masers towards the
W3(OH) UCHII region, employing seven epochs of VLBA observations spanning a
time interval of about 10 yr. The achieved velocity accuracy is of the order of
0.1 km/s, adequate to precisely measure the relative velocities of most of the
12 GHz masers in W3(OH), with amplitude varying in the range 0.3 - 3 km/s.
Towards W3(OH), the most intense 12 GHz masers concentrate in a small area
towards the north (the northern clump) of the UCHII region. We have compared
the proper motions of the CH3OH 12 GHz masers with those (derived from
literature data) of the OH 6035 MHz masers, emitting from the same region of
the methanol masers. In the northern clump, the two maser emissions emerge from
nearby (but likely distinct) cloudlets of masing gas with, in general, a rather
smooth variation of line-of-sight and sky-projected velocities, which suggests
some connection of the environments and kinematics traced by both maser types.
The conical outflow model, previously proposed to account for the 12 GHz maser
kinematics in the northern clump, does not reproduce the new, accurate
measurements of 12 GHz maser proper motions and has to be rejected. We focus on
the subset of 12 GHz masers of the northern clump belonging to the "linear
structure at P.A. = 130-140 degree", whose regular variation of LSR velocities
with position presents evidence for some ordered motion. We show that the
3-dimensional velocities of this "linear distribution" of 12GHz masers can be
well fitted considering a flat, rotating disk, seen almost edge-on.Comment: 32 pages, 10 figures; accepted in ApJ (Main Journal
Very Large Array Detection of the 36 GHz Zeeman Effect in DR21W Revisited
We report on the observation of the 36 GHz methanol maser line in the star
forming region DR21W to accurately measure the Zeeman effect. The reported
Zeeman signature by Fish et al. (2011) became suspicious after an instrumental
effect was discovered in the early days of the Very Large Array Wide-band
Digital Architecture (WIDAR) correlator commissioning. We conclude that the
previously reported magnetic field strength of 58 mG ((1.7 Hz/mG)/z) is
instrumental in nature and thus incorrect. With the improved performance of the
array, we now deduce a 3 sigma limit of -4.7 to +0.4 mG ((1.7 Hz/mG)/z) for the
line-of-sight component of the magnetic field strength in DR21W.Comment: 6 pages, 1 figure, accepted for publication in Ap
Lithium abundances in nearby FGK dwarf and subgiant stars: internal destruction, Galactic chemical evolution, and exoplanets
We derive atmospheric parameters and lithium abundances for 671 stars and
include our measurements in a literature compilation of 1381 dwarf and subgiant
stars. First, a "lithium desert" in the effective temperature (Teff) versus
lithium abundance (A_Li) plane is observed such that no stars with Teff~6075 K
and A_Li~1.8 are found. We speculate that most of the stars on the low A_Li
side of the desert have experienced a short-lived period of severe surface
lithium destruction as main-sequence or subgiant stars. Next, we search for
differences in the lithium content of thin-disk and thick-disk stars, but we
find that internal processes have erased from the stellar photospheres their
possibly different histories of lithium enrichment. Nevertheless, we note that
the maximum lithium abundance of thick-disk stars is nearly constant from
[Fe/H]=-1.0 to -0.1, at a value that is similar to that measured in very
metal-poor halo stars (A_Li~2.2). Finally, differences in the lithium abundance
distribution of known planet-host stars relative to otherwise ordinary stars
appear when restricting the samples to narrow ranges of Teff or mass, but they
are fully explained by age and metallicity biases. We confirm the lack of a
connection between low lithium abundance and planets. However, we find that no
low A_Li planet-hosts are found in the desert Teff window. Provided that subtle
sample biases are not responsible for this observation, this suggests that the
presence of gas giant planets inhibit the mechanism responsible for the lithium
desert.Comment: ApJ, in press. Complete Tables 1 and 3 are available upon reques
Use of Earth Resources Technological Satellite (ERTS) data in a natural resource inventory
There are no author-identified significant results in this report
Discovery of 6.035GHz Hydroxyl Maser Flares in IRAS18566+0408
We report the discovery of 6.035GHz hydroxyl (OH) maser flares toward the
massive star forming region IRAS18566+0408 (G37.55+0.20), which is the only
region known to show periodic formaldehyde (4.8 GHz H2CO) and methanol (6.7 GHz
CH3OH) maser flares. The observations were conducted between October 2008 and
January 2010 with the 305m Arecibo Telescope in Puerto Rico. We detected two
flare events, one in March 2009, and one in September to November 2009. The OH
maser flares are not simultaneous with the H2CO flares, but may be correlated
with CH3OH flares from a component at corresponding velocities. A possible
correlated variability of OH and CH3OH masers in IRAS18566+0408 is consistent
with a common excitation mechanism (IR pumping) as predicted by theory.Comment: Accepted for publication in the Astrophysical Journa
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
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