Water Maser Spots Research Articles

Observations of Water Masers and Radio Continuum Emission in AFGL 2591

We report results of continuum (1.3 and 3.6 cm) and H2O maser line high angular resolution observations, made with the Very Large Array (VLA) in the A configuration, toward the star-forming region AFGL 2591. Three radio continuum sources (VLA 1, VLA 2, and VLA 3) were detected in the region at 3.6 cm, and one source (VLA 3) at 1.3 cm. VLA 1 and VLA 2 appear resolved and their spectral indices suggest free-free emission from optically thin H II regions. VLA 3 is elongated in the east-west direction, along the axis of the bipolar molecular outflow observed in the region. Its spectral energy distribution is consistent with it being a ~200 AU optically thick disk plus a photoionized wind. In addition, we detected 85 water maser spots toward the AFGL 2591 region, which are distributed in three main clusters. Two of these clusters are spatially associated with VLA 2 and VLA 3, respectively. The third cluster of masers, including the strongest water maser of the region, does not coincide with any known continuum source. We suggest that this third cluster of masers is excited by an undetected protostar that we predict to be located ≃05 (500 AU) north from VLA 3. The maser spots associated with VLA 3 are distributed along a shell-like structure of 001 size, showing a peculiar velocity-position helical distribution. We propose that VLA 3 is the powering source of the observed molecular outflow in this region. Finally, we support the notion that the AFGL 2591 region is a cluster of B0-B3 type stars.

VLBI Observations of Water Masers in the Circumstellar Envelope of IRC$ +$60169

Abstract Water masers around an AGB star, IRC$ +$60169, were observed at four epochs using the Japanese VLBI networks. The distribution of the maser features is limited in a thick-shell region, which has inner and outer expansion velocities of $ 7 \,\mathrm{km} \,\mathrm{s}^{-1}$ and $ 14 \,\mathrm{km} \,\mathrm{s}^{-1}$ at radii of 25 mas and 120 mas, respectively. The distribution of the red-shifted features exhibits a ring-like structure, the diameter of which is 30 mas, and corresponds to the inner radius of the maser shell. This implies that dense gas around the star obscures red-shifted emission. Although a position–radial velocity diagram for the maser features is consistent with a spherical shell model, the relative proper motions do not indicate an expansion motion of the shell. A remarkable property has been found that is a possible periodic change of the alignment pattern of water maser spots.

The distribution of the warm and dense molecular gas around Cepheus A HW 2

We present VLA observations of the (J, K)=(1, 1), (2, 2), (3, 3) and (4, 4) inversion transitions of NH3 toward the HW 2 object in Cepheus A, with 1-arcsec angular resolution. Emission is detected in the main hyperfine line of the first three transitions. The NH3(2, 2) emission shows a non-uniform ‘ring’ structure, which is more extended (3 arcsec) and intense than the emission seen in the (1, 1) and (3, 3) lines. A rotational temperature of ∼ 30–50 K and a lower limit to the mass of ∼ 1 (XNH3/10−8)−1 M⊙ are derived for the ring structure. The spatio-kinematical distribution of the NH3 emission does not seem to be consistent with a simple circumstellar disc around the HW 2 thermal biconical radio jet. We suggest that it represents the remnant of the parental core from which both the inner 300-au (0.4 arcsec) disc, traced by the water maser spots previously found in the region, and the central object have formed. The complex velocity field of this core is probably produced from bound motions (similar to those of the inner disc) and from interaction with outflowing material.

Single-dish and interferometer measurements of water-maser polarization

Linear polarization of water-maser emission at 22.235 GHz was measured for astronomical sources using a single-dish telescope and an interferometer (the VLA). Of the 25 star-forming regions observed using single-dish polarimetry, eight had linearly polarized features. None of the 17 stellar maser sources showed measurable (greater than a few percent) linear or circular polarization in the single-dish observations. No linear polarization stronger than 7 percent was detected from the galactic nucleus of NGC 3079. In current theories, the direction of linear polarization is predicted to be parallel or perpendicular to the projection of the magnetic field in protostellar clouds, and thus can potentially provide information on field configurations in these regions if high angular resolution can be achieved. The direction of polarization for a few water-maser spots toward Orion KL, Orion B, NGC 2071, and W51 was successfully mapped using the VLA in continuum mode. These observations are discussed within the context of the theory of molecualr alignment and maser beaming in magnetic fields. 26 refs.