Examinando por Autor "Nikutta, R."

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    New ATCA, ALMA and VISIR observations of the candidate LBV SK-67 266 (S61): The nebular mass from modelling 3D density distributions
    (Oxford University Press, 2016-11) Agliozzo, C.; Nikutta, R.; Pignata, G.; Phillips, N.M.; Ingallinera, A.; Buemi, C.; Umana, G.; Leto, P.; Trigilio, C.; Noriega-Crespo, A.; Paladini, R.; Bufano, F.; Cavallaro, F.
    We present new observations of the nebula around the Magellanic candidate Luminous Blue Variable S61. These comprise high-resolution data acquired with the Australia Telescope Compact Array (ATCA), the Atacama Large Millimetre/Submillimetre Array (ALMA), and the VLT Imager and Spectrometer for mid Infrared (VISIR) at the Very Large Telescope. The nebula was detected only in the radio, up to 17 GHz. The 17 GHz ATCA map, with 0.8 arcsec resolution, allowed a morphological comparison with the Ha Hubble Space Telescope image. The radio nebula resembles a spherical shell, as in the optical. The spectral index map indicates that the radio emission is due to free-free transitions in the ionized, optically thin gas, but there are hints of inhomogeneities. We present our new public code RHOCUBE to model 3D density distributions and determine via Bayesian inference the nebula's geometric parameters. We applied the code to model the electron density distribution in the S61 nebula. We found that different distributions fit the data, but all of them converge to the same ionized mass, ~0.1M⊙, which is an order of magnitude smaller than previous estimates. We show how the nebula models can be used to derive the mass-loss history with high-temporal resolution. The nebula was probably formed through stellar winds, rather than eruptions. From the ALMA and VISIR non-detections, plus the derived extinction map, we deduce that the infrared emission observed by space telescopes must arise from extended, diffuse dust within the ionized region.
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    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.
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    The mass-loss before the end : two luminous blue variables with a collimated stellar wind
    (Cambridge University Press, 2016-11) Agliozzo, C.; Trigilio, C.; Buemi, C.; Leto, P.; Umana, G.; Pignata, G.; Phillips, N.M.; Nikutta, R.; Prieto, J.L.; Eldridge, J.J.; Bray, J.C.; McClelland, L.A.S.; Xiao, L.
    We gathered a multiwavelength dataset of two well-known LBVs. We found a com plex mass-loss, with evidence of variability, such as has been seen previously. In addition, our data reveal signatures of collimated stellar winds. We propose a new scenario for these two stars where the nebula shaping is influenced by the presence of a companion star and/or fast rotation.