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Ultraviolet Imaging Telescope Photometry of Massive Stars: The OB Association NGC 206 in M31
O'Connell, Robert W.; Bohlin, Ralph C.; Smith, Andrew M. +6 more
The Ultraviolet Imaging Telescope (UIT) obtained UV images of the giant M31 OB association NGC 206. Magnitudes in bands at 1520 and 2490 A were obtained for 30 massive stars, which demonstrate the effectiveness of UIT for photometry of moderately crowded hot stars to V ~ 21. The UV colors and magnitudes observed for stars in NGC 206 place them in …
X-Ray Observations of the Seyfert 1 Galaxy MCG 2-58-22
Ghosh, K. K.; Soundararajaperumal, S.
Results of the detailed X-ray (0.1-10 keV) spectral analysis of the Seyfert 1 galaxy, MCG 2-58-22, are presented based on the EXOSAT observations on 1984 November 16-26. X-ray spectra of this source were obtained from the EXOSAT archives. Weak, soft flux (0.1-2 keV) variations were found on time scales of 2-3 days, and no variations of the hard fl…
The Cramer-Rao lower bound and stellar photometry with aberrated HST images
Jakobsen, P.; Greenfield, P.; Jedrzejewski, R.
The Cramer-Rao lower bound theorem of statistics is applied to the problem of extracting 2D stellar photometry from aberrated Hubble Space Telescope camera images. The theorem is used to derive a simple and general expression for the best possible photometric precision that can be derived from a given image, regardless of what image processing or …
The UV and IR Jovian aurorae
Prange, Renee
Although the Jovian aurorae have been widely considered as due to the interaction of the Io torus with the magnetosphere, rather little had been learnt until the last few years from the remote UV observations as far as generation mechanisms are concerned, due both to the complexity of the observation analysis and the deficiency of the theoretical …
Cool star flux spectra for population studies in galaxies.
Parthasarathy, M.; Morossi, C.; Malagnini, M. L. +1 more
Five solar-composition cool giant stars have been observed with the IUE low resolution mode. The UV energy distributions were merged with visual spectrophotometry from the literature and compared with predictions from two new grids of model atmospheres. Atmospheric parameters were derived consistent with the literature data by matching observation…
Effective temperature of B-type stars from the SI II lines of the UV multiplet 13.04 at 130.5-130.9 nm.
Castelli, F.; Singh, J.
An analysis was performed for the 129.3-132.0 nm region of ten normal and two helium-weak peculiar B-type stars of spectral types ranging from B2 to B9 and luminosity classes IV-V. Computations of spectra made it possible to determine the Si abundance from the Si III lines and to estimate the effective temperature from the Si III profiles. The rot…
X-ray variability in the Seyfert galaxy Markarian 618.
Singh, K. P.; Rao, A. R.; Vahia, M. N.
We report X-ray observations of the Seyfert type I galaxy Markarian 618, using the low-energy (LE) and the medium-energy (ME) detectors of the EXOSAT observatory. The 0.1-10 keV X-ray spectrum is adequately explained by a simple power law with the photon index {GAMMA} = 1.8^+0.7^_-0.5_( 90 per cent confidence), similar to that observed from variou…
A Deconvolution Technique for Hubble Space Telescope FGS Fringe Analysis
Hershey, John L.
A technique has been developed for directly transforming interferometer fringe visibility functions (``S-curves") from the HST Fine Guidance Sensors (FGSs) into intensity profiles of the program object. In a process analogous to Fourier transform image deconvolution, an S-curve from a double star yields a pair of narrow profiles containing informa…
The HIPPARCOS Input Catalogue. II. Astrometric Data.
Le Poole, R. S.; Jahreiß, H.; Argue, A. N. +12 more
A positional accuracy of 1.5 arcsec rms at the epoch of observation was required for the stars proposed for observation by the Hipparcos satellite. How this was achieved by collecting and investigating already available positions and proper motions in a special compilation catalog, carrying out new ground-based measurements, and a detailed analysi…
The Luminosity of the Classical Cepheid T VUL
Evans, Nancy R.
The classical Cepheid T Vul has been discovered to have a hot companion on International Ultraviolet Explorer satellite spectra. The companion has a spectral type of A0.8 V. The absolute magnitude of the Cepheid determined from the companion is Mv = -3.43 mag. Because the companion is significantly fainter and less massive than the Ceph…