arXiv subjects

M. T. Beltran

Publications and source records attributed to M. T. Beltran.

40 records · Page 3Linked to original sources

arXiv2007

Candidate Rotating Toroids around High-Mass (Proto)Stars

Using the OVRO, Nobeyama, and IRAM mm-arrays, we searched for ``disk''-outflow systems in three high-mass (proto)star forming regions: G16.59-0.05, G23.01-0.41, and G28.87+0.07. These were selected from a sample of NH3 cores associated with OH and H2O maser emission and with no or very faint continuum emission. Our imaging of molecular line (including rotational transitions of CH3CN and 3mm dust continuum emission revealed that these are compact, massive, and hot molecular cores (HMCs), that is likely sites of high-mass star formation prior to the appearance of UCHII regions. All three sources turn out to be associated with molecular outflows from CO and/or HCO+ J=1--0 line imaging. In addition, velocity gradients of 10 -- 100 km/s per pc in the innermost densest regions of the G23.01 and G28.87 HMCs are identified along directions roughly perpendicular to the axes of the corresponding outflows. All the results suggest that these cores might be rotating about the outflow axis, although the contribution of rotation to gravitational equilibrium of the HMCs appears to be negligible. Our analysis indicates that the 3 HMCs are close to virial equilibrium due to turbulent pressure support. Comparison with other similar objects where rotating toroids have been identified so far shows that in our case rotation appears to be much less prominent; this can be explained by the combined effect of unfavorable projection, large distance, and limited angular resolution with the current interferometers.

astro-ph↗

arXiv2007

The hyperyoung HII region in G24.78+0.08 A1

Context. G24.78+0.08 A1 is a 20 Msun star surrounded by a hypercompact (HC) HII region, driving a CO bipolar outflow, and located at the center of a massive rotating toroid undergoing infall towards the HC region. Recent water maser observations suggest that the HC region is expanding and accretion onto the star is halted. Aims. This study aims to confirm the expansion scenario proposed for the HC region on the basis of recent H2O maser observations. Methods. We carried out continuum VLA observations at 1.3cm and 7mm with the A array plus Pie Town configuration to map the HC region towards G24 A1. Results. The emission of the HC region has been resolved and shows a ring shape structure. The profiles of the emission obtained by taking slices at different angles passing through the barycenter of the HC region confirm the shell structure of the emission. The ratio between the inner and the outer radius of the shell, Ri/Ro, derived fitting the normalized brightness temperature profile passing through the peak of the 7mm emission, is 0.9, which indicates that the shell is thin. The deconvolved outer radius estimated from the fit is 590 AU. These results imply that the HC region in G24 A1 cannot be described in terms of a classical, homogeneous HII region but is instead an ionized shell. This gives support to the model of an expanding wind-driven, ionized shell suggested by the kinematics and distribution of the H2O masers associated with the HC region. According to this model, the HC region is expanding on very short times scales, 21-66 yr.

astro-ph↗

arXiv2004

Search for massive protostellar candidates in the southern hemisphere: I. Association with dense gas

(Abridged) We have observed CS and C17O lines, and 1.2 mm cont. emission towards a sample of 130 high-mass protostellar candidates with DEC<-30 deg. This is the first step of the southern extension of a project started more than a decade ago aimed at the identification of massive protostellar candidates. We selected from the IRAS PSC 429 sources which potentially are compact molecular clouds. The sample is divided into two groups: the 298 sources with [25-12]>0.57 and [60-12]>1.30 we call 'High' sources, the remaining 131 we call 'Low' sources. In this paper, we check the association with dense gas and dust in 130 'Low' sources. We find a detection rate of ca. 85% in CS, demonstrating a tight association with dense molecular clumps. Among the sources detected in CS, ca. 76% have also been detected in C17O and ca. 93% in the 1.2 mm cont. Mm-cont. maps show the presence of clumps with diameters 0.2-2 pc and masses from a few Msun to 10^5 Msun; H2 volume densities lie between ca. 10^{4.5} and 10^{5.5} cm^{-3}. The L(bol) are 10^3-10^6 Lsun, consistent with embedded high-mass objects. Based on our results and those found in the literature for other samples, we conclude that our sources are massive objects probably in a stage prior to the formation of an HII region. We propose a scenario in which 'High' and 'Low' sources are both made of a massive clump hosting a high-mass protostellar candidate and a nearby stellar cluster. The difference might be due to the fact that the IRAS 12mu flux, the best discriminant between the two groups, is dominated by the emission from the cluster in 'Lows' and from the massive protostellar object in 'Highs'.

astro-ph↗

arXiv2003

L1157: Interaction of the molecular outflow with the Class~0 environment

We present high angular resolution interferometric observations of the dust continuum at 2.7 and 1.3 mm, and of the HC3N (12-11) and C18O (2-1) emission around L1157-mm, a Class~0 object that drives a spectacular molecular outflow. The millimeter dust emission is clearly resolved into two components, a flattened compact source of ~450 x 250 AU at 1.3 mm, and mass ~0.1 Msun, plus an extended envelope of ~3000 AU at 1.3 mm, and mass ~1.1 Msun. The millimeter spectral index varies throughout the region, with the lower value found toward the compact protostar, possibly indicating grain growth in the denser regions. A strong interaction between the molecular outflow and the close protostellar environment is taking place and affects the structure of the innermost parts of the envelope. This is shown by the spatial coincidence between the molecular outflow and the dust (1.3 mm continuum) and HC3N emission: both tracers show structures associated to the edges of the outflow lobes. Basically, the global picture sketched for the Class 0 object L1157-mm by Gueth et al. (1997) is supported. We find possible evidence of infall, but we do not detect any velocity gradient indicative of a rotating circumstellar disk.

astro-ph↗