Ammonia observations of the nearby molecular cloud MBM 12

We present NH3(1,1) and NH3(2,2) observations of MBM 12, the closest known molecular cloud (65 pc distance), aimed to find evidence for on-going star formation processes. No local temperature (with a T_rot upper limit of 12 K) nor linewidth enhancement is found, which suggests that the area of the cloud we mapped (~ 15' size) is not currently forming stars. Therefore, this close ``starless'' molecular gas region is an ideal laboratory to study the physical conditions preceding new star formation. A radio continuum source was found in Very Large Array archive data, close but outside the NH3 emission. This source is likely to be a background object.Comment: 8 pages, 3 figures, accepted by MNRA

New Non-Abelian Reissner-Nordstr\"{o}m Black Hole Solutions in the Generalized SU(2) Proca Theory And Some Astrophysical Implications

The Generalized SU(2) Proca theory is a vector-tensor theory of gravity whose action is invariant under global transformations of the SU(2) group and includes second-order derivative self-interactions of the vector field beyond the massive Yang-Mills theory. We find that the presence of two Lagrangian pieces consisting of four gauge fields minimally coupled to gravity gives rise to an exact Reissner-Nordstr\"{o}m black hole solution endowed with two different non-Abelian effective charges that depend on the specific combination, $\chi = 2\chi_1 + \chi_2$, of the respective coupling constants. After studying the spacetime structure of the black hole, some astrophysical implications of the black hole solutions are investigated. First, joint analysis of observations of the EHT's first images of Sagittarius A$^{\star}$ of our Galaxy set the first serious constraint on the free parameters of the theory beyond the theoretical bounds found. Second, we investigate the accretion properties of spherical steady flows around this class of non-Abelian Reissner-Nordstr\"{o}m black hole. Specifically, we examine the general conditions under which transonic flow is allowed. Analytical solution for critical accretion is found in terms of the coupling constant. In addition, we explore numerically the effect of changing $\chi$ on the radial velocity and mass density, and show how the extremal Reissner-Nordstr\"{o}m and the standard Schwarzschild solutions as limit cases are achieved. Lastly, working in the fully relativistic regime, an analytical expression for the critical mass accretion rate of a polytropic fluid onto a black hole is derived. As a main result, we find that the critical accretion rate efficiency can be noticeably improved compared to the Schwarzschild case for a specific region of the parameter space where the non-Abelian charge becomes imaginary.Comment: 17 pages, 8 figure

A survey for water maser emission towards planetary nebulae. New detection in IRAS 17347-3139

We report on a water maser survey towards a sample of 27 planetary nebulae (PNe) using the Robledo de Chavela and Medicina single-dish antennas, as well as the Very Large Array (VLA). Two detections have been obtained: the already known water maser emission in K 3-35, and a new cluster of masers in IRAS 17347-3139. This low rate of detections is compatible with the short life-time of water molecules in PNe (~100 yr). The water maser cluster at IRAS 17347-3139 are distributed on a ellipse of size ~ 0.2" x 0.1", spatially associated with compact 1.3 cm continuum emission (simultaneously observed with the VLA). From archive VLA continuum data at 4.9, 8.4, and 14.9 GHz, a spectral index alpha = 0.76 +- 0.03 is derived for this radio source, which is consistent with either a partially optically thick ionized region or with an ionized wind. However, the latter scenario can be ruled out on mass-loss considerations, thus indicating that this source is probably a young PN. The spatial distribution and the radial velocities of the water masers are suggestive of a rotating and expanding maser ring, tracing the innermost regions of a torus formed at the end of the AGB phase. Given that the 1.3 cm continuum emission peak is located near one of the tips of the major axis of the ellipse of masers, we speculate on a possible binary nature of IRAS 17347-3139, where the radio continuum emission could belong to one of the components and the water masers would be associated with a companion.Comment: Accepted by The Astrophysical Journal. 25 pages, 6 figure

Molecular Line Emission from Accretion Disks Around YSOs

In this work we model the expected molecular emission from protoplanetary disks, modifying different physical parameters, such as dust grain size, mass accretion rate, viscosity, and disk radius, to obtain observational signatures in these sources. Having in mind possible future observations, we study correlations between physical parameters and observational characteristics. Our aim is to determine the kind of observations that will allow us to extract information about the physical parameters of disks. We also present prospects for molecular line observations of protoplanetary disks, using millimeter and submillimeter interferometers (e.g., SMA or ALMA), based on our results.Comment: 6 pages, 2 figures. Proceeding of the workshop "Magnetic fields and star formation: theory versus observation", Madrid (Spain), April 21 - 25, 200