arXiv subjects

Riccardo Cesaroni

Publications and source records attributed to Riccardo Cesaroni.

22 records · Page 2Linked to original sources

arXiv2003

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.

astro-ph↗

arXiv2002

The Crab Nebula at 1.3 mm: evidence for a new synchrotron component

We present the results of 1.3 mm observations of the Crab Nebula, performed with the MPIfR bolometer arrays at the IRAM 30-m telescope. The maps obtained, of unprecedented quality at these wavelengths, allow a direct comparison with high-resolution radio maps. Although the spatial structure of the Crab Nebula does not change much from radio to millimetre wavelengths, we have detected significant spatial variations of the spectral index between 20 cm and 1.3 mm. The main effect is a spectral flattening in the inner region, which can be hardly explained just in terms of the evolution of a single population of synchrotron emitting electrons. We propose instead that this is the result of the emergence of a second synchrotron component, that we have tried to extract from the data. Shape and size of this component resemble those of the Crab Nebula in X rays. However, while the more compact structure of the Crab Nebula in X rays is commonly regarded as an effect of synchrotron downgrading, it cannot be explained why a similar structure is present also at mm wavelengths, where the electron lifetimes far exceed the nebular age. Our data, combined with published upper limits on spatial variations of the radio spectral index, also imply a low-energy cutoff for the distribution of electrons responsible for this additional synchrotron component. Although no model has been developed so far to explain the details of this component, one may verify that the total number of the electrons responsible for it is in agreement with what predicted by the classical pulsar-wind models, which otherwise are known to fail in accounting for the number of radio emitting electrons. We have also detected a spectral steepening at mm wavelengths in some elongated regions, whose positions match those of radio synchrotron filaments.

astro-ph↗

arXiv2000

A search for precursors of Ultracompact HII Regions in a sample of luminous IRAS sources. III: Circumstellar Dust Properties

The James Clerk Maxwell Telescope has been used to obtain submillimeter and millimeter continuum photometry of a sample of 30 IRAS sources previously studied in molecular lines and centimeter radio continuum. All the sources have IRAS colours typical of very young stellar objects (YSOs) and are associated with dense gas. In spite of their high luminosities (L>10000 solar units), only ten of these sources are also associated with a radio counterpart. In 17 cases we could identify a clear peak of millimeter emission associated with the IRAS source, while in 9 sources the millimeter emission was extended or faint and a clear peak could not be identified; upper limits were found in 4 cases only. Using simple greybody fitting model to the observed SED, we derive global properties of the circumstellar dust. The dust temperature varies from 24 K to 45 K, while the exponent of the dust emissivity vs frequency power-law spans a range 1.56<beta<2.38, characteristic of silicate dust; total circumstellar masses range up to more than 500 solar masses. We find that for sources with comparable luminosities, the total column densities derived from the dust masses do not distinguish between sources with and without radio counterpart. We interpret this result as an indication that dust does not play a dominant role in inhibiting the formation of the HII region. We examine several scenarios for their origin in terms of newborn ZAMS stars and although most of these fail to explain the observations, we cannot exclude that these sources are young stars already on the ZAMS with modest residual accretion that quenches the expansion of the HII region. Finally, we consider the possibility that the IRAS sources are high-mass pre-ZAMS (or pre-H-burning) objects deriving most of the emitted luminosity from accretion.

astro-ph↗

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.

astro-ph↗