Examinando por Autor "Rizzo, J. R."

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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.
Acceso Abierto
SiO, 29SiO, and 30SiO Emission from 67 Oxygen-rich Stars: A Survey of 61 Maser Lines from 7 to 1 mm
(IOP Science Publishing, 2021-03-26) Rizzo, J. R.; Cernicharo, J.; García Miró, C.; Agencia Estatal de Investigación (AEI); European Commission (EC); 0000-0002-8443-6631; 0000-0002-3518-2524
Circumstellar environments of oxygen-rich stars are among the strongest SiO maser emitters. Physical processes such as collisions, infrared pumping, and overlaps favor the inversion of level population and produce maser emission at different vibrational states. Despite numerous observational and theoretical efforts, we still do not have a unified picture including all of the physical processes involved in SiO maser emission. The aim of this work is to provide homogeneous data in a large sample of oxygen-rich stars. We present a survey of 67 oxygen-rich stars from 7 to 1 mm, in their rotational transitions from J = 1 → 0 to J = 5 → 4, for vibrational numbers v from 0 to 6 in the three main SiO isotopologs. We have used one of the 34 m NASA antennas at Robledo and the IRAM 30 m radio telescope. The first tentative detection of a v = 6 line is reported, as well as the detection of new maser lines. The highest vibrational levels seem confined to small volumes, presumably close to the stars. The J = 1 → 0, v = 2 line flux is greater than the corresponding v = 1 in almost half of the sample, which may confirm a predicted dependence on the pulsation cycle. This database is potentially useful in models which should consider most of the physical agents, time dependency, and mass-loss rates. As a by-product, we report detections of 27 thermal rotational lines from other molecules, including isotopologs of SiS, H2S, SO, SO2, and NaCl.
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.