arXiv subjects

Leonardo Testi

Publications and source records attributed to Leonardo Testi.

184 records · Page 11Linked to original sources

arXiv1999

Young massive stars in the ISOGAL survey I. VLA observations of the ISOGAL l=+45 field

We present VLA radio continuum observations at 3.6 and 6 cm of a ~0.65 sq.deg. field in the galactic plane at l=+45deg . These observations are meant to be used in a comparison with ISO observations at 7 and 15 um of the same region. In this paper we compare the radio results with other radio surveys and with the IRAS-PSC. At 3.6 and/or 6 cm we detect a total of 34 discrete sources, 13 of which are found in five separate extended complexes. These are all multiple or single extended thermal ultra-compact HII (UCHII) regions. While for each of these complexes an IRAS counterpart could be reliably found, no IRAS counterpart could be reliably identified for any of the remaining 21 sources. Of these 21 compact sources, six are candidate UCHII regions, and the other 15 are most probably background extragalactic non-thermal sources. The five IRAS sources associated with the radio continuum complexes all satisfy the Wood & Churchwell (1989; WC89) color criteria for UCHII. None of the other 38 IRAS point sources present in our surveyed field show the same colors. This fraction of WC89 type to total IRAS sources is consistent with what is found over the entire galactic plane. The fact that, when observed with a compact VLA configuration, the IRAS sources with "UCHII colors" are found to be associated with arcminute-scale extended sources, rather than with compact or unresolved radio sources, may have important implications on the estimated lifetime of UCHII regions.

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arXiv1998

Star formation in clusters: a survey of compact mm-wave sources in the Serpens core

We report the results of a millimeter interferometric survey of compact 3 mm continuum sources in the inner 5.5'x5.5' region of the Serpens core. We detect 32 discrete sources above 4.0 mJy/beam, 21 of which are new detections at millimeter wavelengths. By comparing our data with published infrared surveys, we estimate that 26 sources are probably protostellar condensations and derive their mass assuming optically thin thermal emission from dust grains. The mass spectrum of the clumps, dN/dM~M^(-2.1), is consistent with the stellar initial mass function, supporting the idea that the stellar masses in young clusters are determined by the fragmentation of turbulent cloud cores.

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arXiv1998

IRAS 23385+6053: A Prototype Massive Class 0 Object

IRAS 23385+6053 is a Young Stellar Object with luminosity 16,000 solar luminosities at a kinematic distance of 4.9 kpc. This candidate precursor of an ultracompact HII region is associated with a millimeter source detected at the JCMT but is undetected at centimeter wavelengths with the VLA. We observed this source with the OVRO millimeter array at 3.4 mm in the continuum, HCO+(1-0), H13CO+(1-0) and SiO(v=0, 2-1) line emission, and with CAM aboard ISO at 6.75 and 15 um. The IRAS source is coincident with a 3.4 mm compact (r~0.048 pc) and massive (M~370 solar masses) core, which is undetected at 15 um to a 3 sigma level of 6 mJy; this is compatible with the derived H2 column density of 2x10(24) and the estimated visual extinction of about 2000 mag. We find L(submm)/L(bol)>10(-3) and M(env)/M(star)>>1, typical of Class 0 objects. The source is also associated with a compact outflow characterized by a size similar to the core radius, a dynamical timescale of about 7,000 years, and a mass loss rate of about 10(-3) solar masses/year. The axis of the outflow is oriented nearly perpendicular to the plane of the sky, ruling out the possibility that the non-detection at 15 um is the result of a geometric effect. All these properties suggest that IRAS 23385+6053 is the first example of a bona fide massive Class 0 object.

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arXiv1995

A Multiwavelength Picture of the AFGL 5142 Star-forming Region

We present molecular line, H2O maser, radio continuum and near infrared maps of the bipolar outflow source AFGL5142. The high resolution of our molecular CO observations enables us to define the morphology of the large-scale bipolar outflow into a two lobe structure extending for 2' on each side of the center. In the perpendicular direction, we find consistent evidence for a second, more compact (<0.5') outflow in the form of a spatial velocity offset in the CO map and of an H2 jet-like structure derived from a near infrared narrow band image. On a smaller scale size, the radio and infrared continuum observations reveal the engines of the molecular outflows. The maser emission occurs near the position of the most embedded source of the cluster, IRS1. This is located at the center of the compact outflow and jets of shocked H2 and coincides with an ultra compact radio continuum source (most probably an ionized stellar wind). The H2O cluster is composed of five spatial components: two are within 0.3'' from the YSO (a few hundred AU) and three are at larger distance (1.5--2'', a few thousand AU). A marginal detection of proper motion of the two more distant masers may suggest a high expansion velocity at a distance 4000 AU from the YSO, similar to what is found in Orion KL and W49N. The brightest NIR source of the cluster (IRS2) is associated with an IRAS point source and lies along the axis of the large-scale bipolar outflow. We propose that the masers and the compact molecular outflow are powered concurrently by the wind from the YSO associated with IRS1, while the large-scale outflow could be the remnant from the formation of IRS2.

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