Strong magnetic field in W75N OH maser flare

A flare of OH maser emission was discovered in W75N in 2000. Its location was determined with the VLBA to be within 110 au from one of the ultracompact H II regions, VLA2. The flare consisted of several maser spots. Four of the spots were found to form Zeeman pairs, all of them with a magnetic field strength of about 40 mG. This is the highest ever magnetic field strength found in OH masers, an order of magnitude higher than in typical OH masers. Three possible sources for the enhanced magnetic field are discussed: (i) the magnetic field of the exciting star dragged out by the stellar wind; (ii) the general interstellar field in the gas compressed by the MHD shock; and (iii) the magnetic field of planets which orbit the exciting star and produce maser emission in gaseous envelopes.Comment: 5 pages, 3 figures. to be published in MNRA

X-rays from Cepheus A East and West

We report the discovery of X-rays from both components of Cepheus A, East and West, with the XMM-Newton Observatory. HH 168 joins the ranks of other energetic Herbig Haro objects that are sources of T~10^6 K X-ray emission. The HH 168 effective temperature is T = 5.8 (+3.5,-2.3) x 10^6 K and its unabsorbed luminosity is 1.1 x 10^29 erg s^-1, making it hotter and less luminous than other representatives of its class. We also detect prominent X-ray emission from the complex of compact radio sources believed to be the power sources for Cep A. We call this source HWX and it is distinguished by its hard X-ray spectrum, T = 1.2 (+1.2,-0.5) x 10^8 K, and complex spatial distribution. It may arise from one or more protostars associated with the radio complex, the outflows, or a combination of the two. We detect 102 X-rays sources; many presumed to be pre-main sequence stars based upon the reddening of their optical/IR counterparts.Comment: 15 pages, 8 figures, data table not included because of size limit

Total linear polarization in the OH maser W75N: VLBA polarization structure

W75N is a star-forming region containing various ultracompact HII regions and OH, water, and methanol maser emission. Our VLBA map shows that the OH masers are located in a thin disk rotating around an O-star which is the exciting star of the ultracompact HII region VLA1. A separate set of maser spots is connected with the ultracompact HII region VLA2. The radial velocity of OH maser spots varies across the disk from 3.7 km/s to 10.9 km/s. The diameter of the disk is 4000 A.U. All maser spots are strongly polarized. This are the first OH masers showing nearly 100 per cent linear polarization in several spots. Two maser spots seem to be Zeeman pairs corresponding to a magnetic field of 5.2 mgauss and 7.7 mgauss, and in one case we tentatively found a Zeeman pair consisting of two linearly polarized components. The linearly polarized maser spots are shown to be sigma-components which is the case of the magnetic field being perpendicular to the line of sight. The direction of the magnetic field as determined from linearly polarized spots is perpendicular to the plane of the disk, although the galactic Faraday rotation may significantly affect this conclusion.Comment: 14 figures, 1 table, 27 pages. accepted for publication in ApJ, scheduled for v.564, N1, 200

Space-VLBI observations of OH maser OH34.26+0.15: low interstellar scattering

We report on the first space-VLBI observations of the OH34.26+0.15 maser in two main line OH transitions at 1665 and 1667 MHz. The observations involved the space radiotelescope on board the Japanese satellite HALCA and an array of ground radio telescopes. The map of the maser region and images of individual maser spots were produced with an angular resolution of 1 milliarcsec which is several times higher than the angular resolution available on the ground. The maser spots were only partly resolved and a lower limit to the brightness temperature 6x10^{12} K was obtained. The maser seems to be located in the direction of low interstellar scattering, an order of magnitude lower than the scattering of a nearby extragalactic source and pulsar.Comment: 8 pages, 2 tables, 9 figures, accepted for publication in MNRA

Coexisting conical bipolar and equatorial outflows from a high-mass protostar

The BN/KL region in the Orion molecular cloud is an archetype in the study of the formation of stars much more massive than the Sun. This region contains luminous young stars and protostars, but it is difficult to study because of overlying dust and gas. Our basic expectations are shaped to some extent by the present theoretical picture of star formation, the cornerstone of which is that protostars acrete gas from rotating equatorial disks, and shed angular momentum by ejecting gas in bipolar outflows. The main source of the outflow in the BN/KL region may be an object known as radio source I, which is commonly believed to be surrounded by a rotating disk of molecular material. Here we report high-resolution observations of silicon monoxide (SiO) and water maser emission from the gas surrounding source I; we show that within 60 AU (about the size of the Solar System), the region is dominated by a conical bipolar outflow, rather than the expected disk. A slower outflow, close to the equatorial plane of the protostellar system, extends to radii of 1,000 AU.Comment: 10 pages, 2 figures. Accepted by Nature. To appear December 199

The Extreme Scattering Event Toward PKS 1741-038: VLBI Images

(Abridged) We report multi-epoch VLBI observations of the source PKS 1741-038 as it underwent an extreme scattering event. Observations at four epochs were obtained, and images were produced at three of these. During the event the source consisted of a dominant, compact component, essentially identical to the structure seen outside the event. However, the source's diameter increased slightly at 13 cm during the ESE. An increase in the source's diameter is inconsistent with a simple refractive model. We also see no evidence for ESE-induced substructure within the source or the formation of multiple images, as would occur in a strongly refractive lens. However, a model in which the decrease in flux density during the ESE occurs solely because of stochastic broadening within the lens requires a larger broadening diameter during the ESE than is observed. Thus, the ESE toward 1741-038 involved both stochastic broadening and refractive defocussing within the lens. If the structure responsible for the ESE has a size of order 1 AU, the level of scattering within an ESE lens may be a factor of 10^7 larger than that in the ambient medium. A filamentary structure could reduce the difference between the strength of scattering in the lens and ambient medium, but we conclude that, if ESEs arise from filamentary structures, they occur when the filamentary structures are seen lengthwise. We predict the amount of pulse broadening that would result from a comparable lens passing in front of a pulsar. The pulse broadening would be no more than 1.1 microseconds, consistent with the lack of pulse broadening detected during ESEs toward the pulsars PSR B1937+21 and PSR J1643-1224.Comment: 19 pages, LaTeX2e with AASTeX-4.0, 1 LaTeX table and 5 figures in 9 PostScript files, to be published in the ApJ, minor change in Figures 2a, 3a, and 4a to correct a labe