Departamento de Física
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/785
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2 resultados
Resultados da Pesquisa
- Near-infrared Spectroscopy of Ultracompact H ii Regions in W51A with NIFS/ALTAIR(2022-12-01) Cassio Barbosa; NAVARETE, F.; BLUM, R. D.; DAMINELI, A.; CONTI, P. S.© 2022. The Author(s). Published by the American Astronomical Society.W51A is the most active star formation region of the giant H ii region W51. It harbors the two massive protoclusters W51e and W51 IRS2, which are very rare in the Galaxy. We aim to identify the newborn massive stars and ultracompact H ii regions to derive its distance and age. We performed Integral Field Unit observations with NIFS+ALTAIR of nine targets in the W51A subregion. The distance modulus was obtained using the spectral classification in the K band and a reddening law appropriate to the inner Galactic plane. We derived the distance and the spectral types for five of the targets, ranging from O8 to O9.5, similar to those derived from radio continuum data, except for two sources to which we assigned a somewhat later spectral type. We included another seven objects with precise spectral classification from other works, which allowed us to better constrain the distance estimate. Our spectrophotometric distance d = 4.80 ± 1.27 kpc is in good agreement with those derived from the Galactic rotation model and trigonometric parallaxes, placing the region near the tangent point of the Sagittarius arm. We conclude that the stars studied in this work have an age spread of 1.5-4 Myr, substantially older than thought to date.
- Planetary Transits at Radio Wavelengths: Secondary Eclipses of Hot Jupiter Extended Atmospheres(2020-05-20) SELHORST, C. L.; Cassio Barbosa; SIMES, P. J. A.; VIDOTTO, A. A.; VALIO, A.© 2020. The American Astronomical Society. All rights reserved..When a planet transits in front of its host star, a fraction of its light is blocked, decreasing the observed flux from the star. The same is expected to occur when observing the stellar radio flux. However, at radio wavelengths, the planet also radiates, depending on its temperature, and thus modifies the transit depths. We explore this scenario simulating the radio lightcurves of transits of hot Jupiters, Kepler-17b, and WASP-12b, around solar-like stars. We calculated the bremsstrahlung radio emission at 17, 100, and 400 GHz originating from the star, considering a solar atmospheric model. The planetary radio emission was calculated modeling the planets in two scenarios: as a blackbody or with a dense and hot extended atmosphere. In both cases the planet radiates and contributes to the total radio flux. For a blackbody planet, the transit depth is in the order of 2%-4% and it is independent of the radio frequency. Hot Jupiters planets with atmospheres appear bigger and brighter in radio, thus having a larger contribution to the total flux of the system. Therefore, the transit depths are larger than in the case of blackbody planets, reaching up to 8% at 17 GHz. Also the transit depth is frequency-dependent. Moreover, the transit caused by the planet passing behind the star is deeper than when the planet transits in front of the star, being as large as 18% at 400 GHz. In all cases, the contribution of the planetary radio emission to the observed flux is evident when the planet transits behind the star.