Examinando por Autor "Bordiu, C."

Mostrando 1 - 3 de 3

Restringido
A warm molecular ring in AG Car: composing the mass-loss puzzle
(Oxford Academics: Oxford University Press, 2021-02-20) Bordiu, C.; Bufano, F.; Cerrigone, L.; Umana, G.; Rizzo, J. R.; Buemi, C. S.; Leto, P.; Cavallaro, F.; Ingallinera, A.; Loru, S.; Trigilio, C.; Riggi, S.; Agencia Estatal de Investigación (AEI); Rizzo, J. R. [0000-0002-8443-6631]; Cavallaro, F. [0000-0003-1856-6806]; Umana, G. [0000-0002-6972-8388]
We present APEX observations of CO J = 3 → 2 and ALMA observations of CO J = 2 → 1, 13CO J = 2 → 1, and continuum towards the Galactic luminous blue variable AG Car. These new observations reveal the presence of a ring-like molecular structure surrounding the star. Morphology and kinematics of the gas are consistent with a slowly expanding torus located near the equatorial plane of AG Car. Using non-LTE line modelling, we derived the physical parameters of the gas, which is warm (∼50 K) and moderately dense (∼103 cm−3). The total mass of molecular gas in the ring is 2.7 ± 0.9 M⊙. We analysed the radio continuum map, which depicts a point-like source surrounded by a shallow nebula. From the flux of the point-like source, we derived a current mass-loss rate of M˙=(1.55±0.21)×10−5M⊙ yr−1. Finally, to better understand the complex circumstellar environment of AG Car, we put the newly detected ring in relation to the main nebula of dust and ionized gas. We discuss possible formation scenarios for the ring, namely, the accumulation of interstellar material due to the action of the stellar wind, the remnant of a close binary interaction or merger, and an equatorially enhanced mass-loss episode. If molecular gas formed in situ as a result of a mass eruption, it would account for at least a 30 per cent of the total mass ejected by AG Car. This detection adds a new piece to the puzzle of the complex mass-loss history of AG Car, providing new clues about the interplay between LBV stars and their surroundings.
Restringido
Evolutionary map of the Universe (EMU): Compact radio sources in the SCORPIO field towards the galactic plane
(Oxford Academics: Oxford University Press, 2021-02-08) Riggi, S.; Umana, G.; Trigilio, C.; Cavallaro, F.; Ingallinera, A.; Leto, P.; Bufano, F.; Norris, R. P.; Hopkins, A. M.; Filipovic, M. D.; Andernach, H.; Van Loon, J.; Michalowski, M. J.; Bordiu, C.; An, T.; Buemi, C. S.; Carretti, E.; Collier, J. D.; Joseph, T.; Koribalski, B. S.; Kothes, R.; Loru, S.; McConnell, D.; Pommier, M.; Sciacca, E.; Schillirò, F.; Vitello, F.; Warhurst, K.; Whiting, M.; Universidad de Guanajuato; National Science Centre, Poland (NCN); European Research Council (ERC); Filipovic, M. [0000-0002-4990-9288]; Koribalski, B. [0000-0003-4351-993X]
We present observations of a region of the Galactic plane taken during the Early Science Program of the Australian Square Kilometre Array Pathfinder (ASKAP). In this context, we observed the SCORPIO field at 912 MHz with an uncompleted array consisting of 15 commissioned antennas. The resulting map covers a square region of ∼40 deg2, centred on (l, b) = (343.5°, 0.75°), with a synthesized beam of 24 × 21 arcsec2 and a background rms noise of 150–200 μJy beam−1, increasing to 500–600 μJy beam−1 close to the Galactic plane. A total of 3963 radio sources were detected and characterized in the field using the CAESAR source finder. We obtained differential source counts in agreement with previously published data after correction for source extraction and characterization uncertainties, estimated from simulated data. The ASKAP positional and flux density scale accuracy were also investigated through comparison with previous surveys (MGPS, NVSS) and additional observations of the SCORPIO field, carried out with ATCA at 2.1 GHz and 10 arcsec spatial resolution. These allowed us to obtain a measurement of the spectral index for a subset of the catalogued sources and an estimated fraction of (at least) 8 per cent of resolved sources in the reported catalogue. We cross-matched our catalogued sources with different astronomical data bases to search for possible counterparts, finding ∼150 associations to known Galactic objects. Finally, we explored a multiparametric approach for classifying previously unreported Galactic sources based on their radio-infrared colours.
Acceso Abierto
The peculiar chemistry of the inner ejecta of Eta Carina
(Oxford Academics: Oxford University Press, 2019-12-19) Bordiu, C.; Rizzo, J. R.; Ministerio de Economía y Competitividad (MINECO); Agencia Estatal de Investigación (AEI); Rizzo, J. R. [0000-0002-8443-6631]; Bordiu, C. [0000-0002-7703-0692]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
We investigated continuum and molecular line emission of four species (CO, HCN, H13CN, and HCO+) at 0.8 mm in the inner region around η Car, using ALMA archival observations at a resolution better than 0.2 arcsec. We report the discovery of an asymmetric extended structure north-west of the star, independent from the continuum point source. The structure is only traced by continuum and HCO+, and not detected in the other lines. Kinematics of this structure reveal that the HCO+ gas likely arises from ejecta expelled in the 1890s eruption. The ejecta is propagating outwards within the cavity produced by the current wind–wind interaction of η Car A and its companion. Chemical analysis of the ejecta reveals an apparent lack of CO and nitrogen-bearing species. We explore possible explanations for this peculiar chemistry, that differentiates this structure from the ejecta of the Great Eruption, rich in HCN and H13CN. We also report an absorption component near the continuum point source, only traced by HCN and H13CN in their vibrational-ground and vibrationally excited states. This absorbing gas is attributed to a hot bullet of N-enriched material expelled at a projected velocity of 40 km s−1.