Examinando por Autor "Cerrigone, L."
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Ítem Exploring the multifaceted circumstellar environment of the luminous blue variable HR Carinae(OXFORD UNIV PRESS, 2016-12) Buemi, C.S.; Trigilio, C.; Leto, P.; Umana, G.; Ingallinera, A.; Cavallaro, F.; Cerrigone, L.; Agliozzo, C.; Bufano, F.; Riggi, S.; Molinari, S.; Schillirò, F.We present a multiwavelength study of the Galactic luminous blue variable HR Carinae, based on new high-resolution mid-infrared (IR) and radio images obtained with the Very Large Telescope (VLT) and the Australia Telescope Compact Array (ATCA), which have been complemented by far-infrared Herschel-Photodetector Array Camera and Spectrometer (PACS) observations and ATCA archive data. The Herschel images reveal the large-scale distribution of the dusty emitting nebula, which extends mainly to the north-east direction, up to 70 arcsec from the central star, and is oriented along the direction of the space motion of the star. In the mid-infrared images, the brightness distribution is characterized by two arcshaped structures, tracing an inner envelope surrounding the central star more closely. At radio wavelengths, the ionized gas emission lies on the opposite side of the cold dust with respect to the position of the star, as if the ionized front were confined by the surrounding medium in the north-south direction. Comparison with previous data indicates significant changes in the radio nebula morphology and in the mass-loss rate from the central star, which has increased from 6.1 × 10-6M⊙ yr-1 in 1994-1995 to 1.17 × 10-5M⊙ yr-1 in 2014. We investigate possible scenarios that could have generated the complex circumstellar environment revealed by our multiwavelength data.Ítem SCORPIO - II. Spectral indices of weak Galactic radio sources(Oxford University Press, 2018-01) Cavallaro, F.; Trigilio, C.; Umana, G.; Franzen, T.M.O.; Norris, R.P.; Leto, P.; Ingallinera, A.; Buemi, C.S.; Marvil, J.; Agliozzo, C.; Bufano, F.; Cerrigone, L.; Riggi, S.In the next few years the classification of radio sources observed by the large surveys will be a challenging problem and spectral index is a powerful tool for addressing it. Here we present an algorithm to estimate the spectral index of sources from multiwavelength radio images. We have applied our algorithm to SCORPIO, a Galactic plane survey centred around 2.1 GHz carried out with Australian Telescope Compact Array and found we can measure reliable spectral indices only for sources stronger than 40 times the rms noise. Above a threshold of 1 mJy, the source density in SCORPIO is 20 per cent greater than in a typical extragalactic field, like Australia Telescope Large Area Survey because of the presence of Galactic sources. Among this excess population, 16 sources per square degree have a spectral index of about zero suggesting optically thin thermal emission such as H II regions and planetary nebulae, while 12 per square degree present a rising spectrum, suggesting optically thick thermal emission such as stars and UCH II regions. © 2017 The Author(s).Ítem The Luminous Blue Variable RMC 127 as Seen with ALMA and ATCA(Institute of Physics Publishing, 2017-06) Agliozzo, C.; Trigilio, C.; Pignata, G.; Phillips, N.M.; Nikutta, R.; Leto, P.; Umana, G.; Ingallinera, A.; Buemi, C.; Bauer, F.E.; Paladini, R.; Noriega-Crespo, A.; Prieto, J.L.; Massardi, M.; Cerrigone, L.We present ALMA and ATCA observations of the luminous blue variable RMC 127. The radio maps show for the first time the core of the nebula and evidence that the nebula is strongly asymmetric with a Z-pattern shape. Hints of this morphology are also visible in the archival Hubble Space Telescope image, which overall resembles the radio emission. The emission mechanism in the outer nebula is optically thin free-free in the radio. At high frequencies, a component of point-source emission appears at the position of the star, up to the ALMA frequencies. The rising flux density distribution () of this object suggests thermal emission from the ionized stellar wind and indicates a departure from spherical symmetry with. We examine different scenarios to explain this excess of thermal emission from the wind and show that this can arise from a bipolar outflow, supporting the suggestion by other authors that the stellar wind of RMC 127 is aspherical. We fit the data with two collimated ionized wind models, and we find that the mass-loss rate can be a factor of two or more smaller than in the spherical case. We also fit the photometry obtained by IR space telescopes and deduce that the mid-to far-IR emission must arise from extended, cool () dust within the outer ionized nebula. Finally, we discuss two possible scenarios for the nebular morphology: the canonical single-star expanding shell geometry and a precessing jet model assuming the presence of a companion star. © 2017. The American Astronomical Society.