254 research outputs found
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
86 GHz SiO maser survey of late-type stars in the Inner Galaxy. IV. SiO emission and infrared data for sources in the Scutum and Sagittarius-Carina arms, 20 deg < l < 50 deg
We present an 86 GHz SiO (v = 1, J = 2 ---> 1) maser search toward late-type
stars located within |b|<0.5 deg and 20 deg < l < 50 deg. This search is an
extension at longer longitudes of a previously published work. We selected 135
stars from the MSX catalog using color and flux criteria and detected 92 (86
new detections). The detection rate is 68%, the same as in our previous study.
The last few decades have seen the publication of several catalogs of point
sources detected in infrared surveys (MSX, 2MASS, DENIS, ISOGAL, WISE, GLIMPSE,
AKARI, and MIPSGAL). We searched each catalog for data on the 444 targets of
our earlier survey and for the 135 in the survey reported here. We confirm
that, as anticipated, most of our targets have colors typical of oxygen-rich
asymptotic giant branch (AGB) stars. Only one target star may have already left
the AGB. Ten stars have colors typical of carbon-rich stars, meaning a
contamination of our sample with carbon stars <=1.7%.Comment: 13 pages, 6 Figures, A&A accepte
Methanol as a tracer of fundamental constants
The methanol molecule CH3OH has a complex microwave spectrum with a large
number of very strong lines. This spectrum includes purely rotational
transitions as well as transitions with contributions of the internal degree of
freedom associated with the hindered rotation of the OH group. The latter takes
place due to the tunneling of hydrogen through the potential barriers between
three equivalent potential minima. Such transitions are highly sensitive to
changes in the electron-to-proton mass ratio, mu = m_e/m_p, and have different
responses to mu-variations. The highest sensitivity is found for the mixed
rotation-tunneling transitions at low frequencies. Observing methanol lines
provides more stringent limits on the hypothetical variation of mu than ammonia
observation with the same velocity resolution. We show that the best quality
radio astronomical data on methanol maser lines constrain the variability of mu
in the Milky Way at the level of |Delta mu/mu| < 28x10^{-9} (1sigma) which is
in line with the previously obtained ammonia result, |Delta mu/mu| < 29x10^{-9}
(1\sigma). This estimate can be further improved if the rest frequencies of the
CH3OH microwave lines will be measured more accurately.Comment: 7 pages, 1 table, 1 figure. Accepted for publication in Ap
- …