arXiv subjects

A. M. Magalhaes

Publications and source records attributed to A. M. Magalhaes.

21 records · Page 2Linked to original sources

arXiv2001

S 111 and the polarization of the B[e] supergiants in the Magellanic Clouds

We have obtained linear polarization measurements of the Large Magellanic Cloud B[e] supergiant S 111 using optical imaging polarimetry. The intrinsic polarization found is consistent with the presence of an axisymmetric circumstellar envelope. We have additionally estimated the electron density for S 111 using data from the literature and revisited the correlation between polarization and envelope parameters of the B[e] supergiant stars using more recent IR calibration color data. The data suggest that the polarization can be indeed explained by electron scattering. We have used Monte Carlo codes to model the continuum polarization of the Magellanic B[e] supergiants. The results indicate that the electron density distribution in their envelopes is closer to a homogeneous distribution rather than an r$^{-2}$ dependence. At the same time, the data are best fitted by a spherical distribution with density contrast than a cylindrical distribution. The data and the model results support the idea of the presence of an equatorial disk and of the two-component wind model for the envelopes of the B[e] supergiants. Spectropolarimetry would help further our knowledge of these envelopes.

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arXiv1999

Spectropolarimetry of the Luminous Narrow-Line Seyfert Galaxies IRAS 20181-2244 and IRAS 13224-3809

We observed the narrow-line Seyfert 1 galaxies IRAS 20181-2244 and IRAS 13324-3809 with a new spectropolarimeter on the RC spectrograph at the CTIO 4m telescope. Previously it had been suggested that IRAS 20181-2244 was a Type 2 QSO and thus might contain an obscured broad-line region which could be detected by the presence of broad Balmer lines in the polarized flux. We found the object to be polarized at about 2%, and constant with wavelength, (unlike most narrow-line Seyfert 1s), but with no evidence of broad Balmer lines in polarized flux. The spectropolarimetry indicates that the scattering material is inside the BLR. IRAS 13224-3809, notable for its high variability in X-ray and UV wavelengths, has a low polarization consistent with a Galactic interstellar origin.

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arXiv1997

Dust in the Small Magellanic Cloud: Interstellar Polarization and Extinction

To elucidate the dust properties in the SMC we have for the first time measured linear polarization in five colors in the optical region of the spectrum for a sample of reddened stars. For two of these stars, for which there were no existing UV spectrophotometric measurements, but for which we measured a relatively large polarization, we have also obtained data from the International Ultraviolet Explorer (IUE) in order to study the extinction. The main results are: (1) the wavelength of maximum polarization, $λ_{max}$, in the SMC is typically smaller than that in the Galaxy; (2) however, AZV 456, which shows the UV extinction bump, has a $λ_{max}$ typical of that in the Galaxy, its polarization curve is narrower, its bump is shifted to shorter wavelengths as compared to the Galaxy and its UV extinction does not conform to the Galactic analytical interpolation curve based on the ratio of total to selective extinction; (3) the 'typical', monotonic SMC extinction curve can be best fit with amorphous carbon and silicate grains; (4) the extinction towards AZV456 may only be explained by assuming a larger gas-to-dust ratio than the observed N(HI)/A(V) value, with a small amount of the available carbon in graphite form; (5) from an analysis of both the extinction and polarization data and our model fits it appears that the SMC has typically smaller grains than those in the Galaxy.

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