Search Publications
Occultation of the Quiescent Emission from Sgr A* by IR Flares
Dowell, C. D.; Yusef-Zadeh, F.; Wardle, M. +2 more
We have investigated the nature of flare emission from Sgr A* during multi-wavelength observations of this source that took place in 2004, 2005, and 2006. We present evidence for dimming of submillimeter and radio flux during the peak of near-IR flares. This suggests that the variability of Sgr A* across its wavelength spectrum is phenomenological…
The distance to the C component of I Zw 18 and its star formation history. A probabilistic approach
Luridiana, V.; Cerviño, M.; Pérez, E. +2 more
Aims: We analyzed the resolved stellar population of the C component of the extremely metal-poor dwarf galaxy I Zw18 in order to evaluate its distance and star formation history as accurately as possible. In particular, we aimed at answering the question of whether this stellar population is young.
Methods: We developed a probabilistic a…
Spectral studies of asteroids 21 lutetia and 4 vesta as objects of space missions
Busarev, V. V.
Asteroid 21 Lutetia is one of the objects of the Rosetta mission carried out by the European Space Agency (ESA). The Rosetta spacecraft launched in 2004 is to approach Lutetia in July 2010, and then it will be directed to the comet Churyumov-Gerasimenko. Asteroid 4 Vesta is planned to be investigated in 2011 from the Dawn spacecraft launched by th…
Quantifying the importance of ram-pressure stripping in a galaxy group at 100 Mpc
Croston, J. H.; Freeland, E.; Sengupta, C.
We examine two members of the NGC 4065 group of galaxies: a bent-double (aka wide angle tail) radio source and an H I-deficient spiral galaxy. Models of the X-ray-emitting intragroup gas and the bent-double radio source, NGC 4061, are used to probe the density of intergalactic gas in this group. H I observations reveal an asymmetric, truncated dis…
On the Light-Bending Model of X-Ray Variability of MCG -6-30-15
Ebisawa, Ken; Niedźwiecki, Andrzej; Miyakawa, Takehiro +1 more
We have applied the light-bending model of X-ray variability to Suzaku data of the Seyfert 1 galaxy MCG -6-30-15. We analyzed the energy dependence of the root mean square variability, and discussed conditions necessary for the model to explain the characteristic decrease of the source variability at around 5-8 keV. A model, where the X-ray source…
X-ray emission from O-type stars: DH Cep and HD 97434
Pandey, J. C.; Singh, K. P.; Kumar, Brijesh +2 more
We present X-ray emission characteristics of the massive O-type stars DH Cep and HD 97434 using archival XMM-Newton observations. There is no convincing evidence for short-term variability in the X-ray intensity during the observations. However, the analysis of their spectra reveals X-ray structure being consistent with two-temperature plasma mode…
New Precision Orbits of Bright Double-lined Spectroscopic Binaries. IV. 66 Andromedae, HR 6979, and HR 9059
Williamson, Michael H.; Fekel, Francis C.; Tomkin, Jocelyn
We have determined improved spectroscopic orbits for three double-lined binaries, 66 And (F4 V), HR 6979 (Am), and HR 9059 (F5 IV) using radial velocities from the 2.1 m telescope at McDonald Observatory, the coudé feed telescope at Kitt Peak National Observatory, and 2 m telescope at Fairborn Observatory. The orbital periods range from 11.0 to 14…
Differential Proper-motion Study of the Circumstellar Dust Shell of the Enigmatic Object, HD 179821
Ueta, Toshiya; Ferguson, Brian A.
HD 179821 is an enigmatic evolved star that possesses characteristics of both a post-asymptotic giant branch (post-AGB) star and a yellow hypergiant, and there has been no evidence that unambiguously defines its nature. These two hypotheses are products of an indeterminate distance, presumed to be 1 kpc or 6 kpc. We have obtained the two-epoch Hub…
New Fe VIII Line Identifications using Observations of the Quiet Sun
Young, P. R.; Landi, E.
In this work, we study Fe VIII lines emitted in the 1000-1200 Å wavelength range that originate from levels that also emit transitions observed in the 190-200 Å wavelength range. The intensity ratios between such lines depend on atomic physics parameters only and not on the physical parameters of the emitting plasma: they are excellent tools to ve…
Quasar radio-loudness and the elliptical core problem
Hamilton, Timothy S.
The dichotomy between radio-loud and radio-quiet quasi-stellar objects (QSOs) is not simply one of host morphology. While spiral galaxies almost exclusively host radio-quiet QSOs, ellipticals can host either radio-louds or radio-quiets. We find that a combination of accretion rate and host scale determines which type of QSO a given elliptical gala…