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

HCOOCH3 as a probe of temperature and structure of Orion-KL

We studied the O-bearing molecule HCOOCH3 to characterize the physical conditions of the different molecular source components in Orion-KL. We identify 28 methyl formate emission peaks throughout the 50" field of observations. The two strongest peaks are in the Compact Ridge (MF1) and in the SouthWest of the Hot Core (MF2). Spectral confusion is still prevailing as half of the expected transitions are blended over the region. Assuming that the transitions are thermalized, we derive the temperature at the five main emission peaks. At the MF1 position we find a temperature of 80K in a 1.8"x0.8" beam size and 120K on a larger scale (3.6" x2.2"), suggesting an external source of heating, whereas the temperature is about 130K at the MF2 position on both scales. Transitions of HCOOCH3 in vt=1 are detected as well and the good agreement of the positions on the rotational diagrams between the vt=0 and the vt=1 transitions suggests a similar temperature. The velocity of the gas is between 7.5 and 8.0km/s depending on the positions and column density peaks vary from 1.6x10^16 to 1.6x10^17cm^-2. A second velocity component is observed around 9-10 km/s in a North-South structure stretching from the Compact Ridge up to the BN object; this component is warmer at the MF1 peak. The two other C2H4O2 isomers are not detected and the derived upper limit for the column density is <3x10^14cm^-2 for glycolaldehyde and <2x10^15cm^-2 for acetic acid. From the 223GHz continuum map, we identify several dust clumps with associated gas masses in the range 0.8 to 5.8Msun. Assuming that the HCOOCH3 is spatially distributed as the dust, we find relative abundances of HCOOCH3 in the range <0.1x10^-8 to 5.2x10^-8. We suggest a relation between the methyl formate distribution and shocks as traced by 2.12 mum H2 emission.Comment: Accepted for publication in A&

Full-Polarization Observations of OH Masers in Massive Star-Forming Regions: I. Data

We present full-polarization VLBA maps of the ground-state, main-line, 2 Pi 3/2, J = 3/2 OH masers in 18 Galactic massive star-forming regions. This is the first large polarization survey of interstellar hydroxyl masers at VLBI resolution. A total of 184 Zeeman pairs are identified, and the corresponding magnetic field strengths are indicated. We also present spectra of the NH3 emission or absorption in these star-forming regions. Analysis of these data will be presented in a companion paper.Comment: 111 pages, including 42 figures and 21 tables, to appear in ApJ

Silicon isotopic abundance toward evolved stars and its application for presolar grains

Galactic chemical evolution (GCE) is important for understanding the composition of the present-day interstellar medium (ISM) and of our solar system. In this paper, we aim to track the GCE by using the 29Si/30Si ratios in evolved stars and tentatively relate this to presolar grain composition. We used the APEX telescope to detect thermal SiO isotopologue emission toward four oxygen-rich M-type stars. Together with the data retrieved from the Herschel science archive and from the literature, we were able to obtain the 29Si/30Si ratios for a total of 15 evolved stars inferred from their optically thin 29SiO and 30SiO emission. These stars cover a range of masses and ages, and because they do not significantly alter 29Si/30Si during their lifetimes, they provide excellent probes of the ISM metallicity (or 29Si/30Si ratio) as a function of time. The 29Si/30Si ratios inferred from the thermal SiO emission tend to be lower toward low-mass oxygen-rich stars (e.g., down to about unity for W Hya), and close to an interstellar or solar value of 1.5 for the higher-mass carbon star IRC+10216 and two red supergiants. There is a tentative correlation between the 29Si/30Si ratios and the mass-loss rates of evolved stars, where we take the mass-loss rate as a proxy for the initial stellar mass or current stellar age. This is consistent with the different abundance ratios found in presolar grains. We found that older objects (up to possibly 10 Gyr old) in our sample trace a previous, lower 29Si/30Si value of about 1. Material with this isotopic ratio is present in two subclasses of presolar grains, providing independent evidence of the lower ratio. Therefore, the 29Si/30Si ratio derived from the SiO emission of evolved stars is a useful diagnostic tool for the study of the GCE and presolar grains.Comment: 7 pages, 4 figure

The HI shell G132.6-0.7-25.3: A Supernova Remnant or an Old Wind-Blown Bubble?

Data from the Canadian Galactic Plane Survey reveal an abundance of HI shells and arcs in the disk of our galaxy. While their shape is suggestive of stellar winds or supernovae influence, very few of these structures have been examined in detail thus far. A fine example is an HI shell in the outer Galaxy with no continuum counterpart discovered in the survey's pilot project. Its size and kinematics suggest that it was created by the winds of a single late-type O star which has since evolved off the main sequence or by a supernova explosion. A B1 Ia star at the centre of the shell, in projection, is a possible candidate for energy source if the shell is assumed to be wind-blown. The shell's shape implies a surprisingly small scale height of less than about 30 pc for the surrounding gas if the elongation is due to evolution in a density gradient.Comment: 25 pages, 6 figures. Accepted for publication in the Astronomical Journa

Hot gas and dust in a protostellar cluster near W3(OH

We used the IRAM Interferometer to obtain sub-arcsecond resolution observations of the high-mass star-forming region W3(OH) and its surroundings at a frequency of 220 GHz. With the improved angular resolution, we distinguish 3 peaks in the thermal dust continuum emission originating from the hot core region about 6 arcsec (0.06 pc) east of W3(OH). The dust emission peaks are coincident with known radio continuum sources, one of which is of non-thermal nature. The latter source is also at the center of expansion of a powerful bipolar outflow observed in water maser emission. We determine the hot core mass to be 15 solar masses based on the integrated dust continuum emission. Simultaneously many molecular lines are detected allowing the analysis of the temperature structure and the distribution of complex organic molecules in the hot core. From HNCO lines, spanning a wide range of excitation, two 200 K temperature peaks are found coincident with dust continuum emission peaks suggesting embedded heating sources within them.Comment: 12 pages, 3 figure

Editorial: Neuromechanics in Movement and Disease With Physiological and Pathophysiological Implications: From Fundamental Experiments to Bio-Inspired Technologies.

SCOPUS: ed.jinfo:eu-repo/semantics/publishe

Expansion of W 3(OH)

A direct measurement of the expansion of W 3(OH) is made by comparing Very Large Array images taken about 10 yr apart. The expansion is anisotropic with a typical speed of 3 to 5 km/s, indicating a dynamical age of only 2300 yr. These observations are inconsistent with either the freely expanding shell model or a simple bow shock model. The most favored model is a slowly expanding shell-like HII region, with either a fast rarefied flow or another less massive diffuse ionized region moving towards the observer. There is also a rapidly evolving source near the projected center of emission, perhaps related to the central star.Comment: LaTeX file, 28 pages, includes 8 figures. To appear in ApJ in December 10 (1998) issue. Also available at http://www.submm.caltech.edu/~kawamura/w3oh_pp.p

OH far-infrared emission from low- and intermediate-mass protostars surveyed with Herschel-PACS

OH is a key species in the water chemistry of star-forming regions, because its presence is tightly related to the formation and destruction of water. This paper presents OH observations from 23 low- and intermediate-mass young stellar objects obtained with the PACS integral field spectrometer on-board Herschel in the context of the Water In Star-forming Regions with Herschel (WISH) key program. Most low-mass sources have compact OH emission (< 5000 AU scale), whereas the OH lines in most intermediate-mass sources are extended over the whole PACS detector field-of-view (> 20000 AU). The strength of the OH emission is correlated with various source properties such as the bolometric luminosity and the envelope mass, but also with the OI and H2O emission. Rotational diagrams for sources with many OH lines show that the level populations of OH can be approximated by a Boltzmann distribution with an excitation temperature at around 70 K. Radiative transfer models of spherically symmetric envelopes cannot reproduce the OH emission fluxes nor their broad line widths, strongly suggesting an outflow origin. Slab excitation models indicate that the observed excitation temperature can either be reached if the OH molecules are exposed to a strong far-infrared continuum radiation field or if the gas temperature and density are sufficiently high. Using realistic source parameters and radiation fields, it is shown for the case of Ser SMM1 that radiative pumping plays an important role in transitions arising from upper level energies higher than 300 K. The compact emission in the low-mass sources and the required presence of a strong radiation field and/or a high density to excite the OH molecules points towards an origin in shocks in the inner envelope close to the protostar.Comment: Accepted for publication in Astronomy and Astrophysics. Abstract abridge

Formation of disclination lines near a free nematic interface

We have studied the nucleation and the physical properties of a -1/2 wedge disclination line near the free surface of a confined nematic liquid crystal. The position of the disclination line has been related to the material parameters (elastic constants, anchoring energy and favored anchoring angle of the molecules at the free surface). The use of a planar model for the structure of the director field (whose predictions have been contrasted to those of a fully three-dimensional model) has allowed us to relate the experimentally observed position of the disclination line to the relevant properties of the liquid crystals. In particular, we have been able to observe the collapse of the disclination line due to a temperature-induced anchoring angle transition, which has allowed us to rule out the presence of a real disclination line near the nematic/isotropic front in directional growth experiments. 61.30.Jf,61.30.G