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Stellar Companions and the Age of HD 141569 and Its Circumstellar Disk
Zuckerman, B.; Rich, R. M.; Matthews, K. +2 more
We investigate the stellar environment of the β Pictoris-like star HD 141569 with optical spectroscopy and near-infrared imaging. The B9.5 Ve primary and two other stars (types M2 and M4) both located in projection less than 9" away have the same radial velocity and proper motion and therefore almost certainly form a triple star system. From their…
Solar wind electron suprathermal strength and temperature gradients: Ulysses observations
Maksimovic, Milan; Gary, S. Peter; Skoug, Ruth M.
We use observations from the Ulysses electron spectrometer to examine global trends of the electron suprathermal population and to study, for the first time, the electron core, halo, and total temperature gradients in the fast solar wind over the poles. We use a data set covering the period from the beginning of the mission (1990, day of year 322)…
Hubble Space Telescope Observations of New Horizontal-Branch Structures in the Globular Cluster ω Centauri
O'Connell, Robert W.; Hill, Robert S.; Bohlin, Ralph C. +6 more
The globular cluster ω Centauri contains the largest known population of very hot horizontal-branch (HB) stars. We have used the Hubble Space Telescope to obtain a far-UV/optical color-magnitude diagram of three fields in ω Cen. We find that over 30% of the HB objects are ``extreme'' HB or hot post-HB stars. The hot HB stars are not concentrated t…
Hubble Space Telescope/NICMOS Observations of I ZW 18: A Population of Old Asymptotic Giant Branch Stars Revealed
Östlin, G.
I present the first results from a Hubble Space Telescope/NICMOS imaging study of the most metal-poor blue compact dwarf galaxy, I Zw 18. The near-infrared color-magnitude diagram (CMD) is dominated by two populations, one 10-20 Myr population of red supergiants and one 0.1-5 Gyr population of asymptotic giant branch stars. Stars older than 1 Gyr …
Stellar Dynamics and the Implications on the Merger Evolution in NGC 6240
Genzel, R.; Tacconi, L. J.; Thatte, N. +3 more
We report near-infrared integral field spectroscopy of the luminous merging galaxy NGC 6240. Stellar velocities show that the two K-band peaks separated by 1.6" are the central parts of inclined, rotating disk galaxies with equal mass bulges. The dynamical masses of the nuclei are much larger than the stellar mass derived from the K-band light, im…
The Morphology of the Emission-Line Region Of Compact Steep-Spectrum Radio Sources
Capetti, A.; Morganti, R.; Axon, D. J. +3 more
We present the results of HST narrowband imaging of 11 compact steep-spectrum (CSS) radio sources. Five of them (3C 48, 3C 147, 3C303.1, 3C 277.1, and 4C 12.50) were observed as part of a dedicated ``pointed'' program of deep line imaging, at the redshifted wavelength of the [O III] λ5007 emission line. For six additional sources (3C 49, 3C 93.1, …
The All Sky Automated Survey. Catalog of about 3800 Variable Stars
Pojmanski, G.
Results of the first two years of observations using the All Sky Automated Survey prototype camera are presented. More than 140000 stars in 50 Selected Fields covering 300 square degrees were monitored each clear night in the I-band resulting in the ASAS Photometric I-band Catalog containing over 5*10^7 individual measurements. Nightly monitoring …
A New Spin on the Problem of Horizontal-Branch Gaps: Stellar Rotation along the Blue Horizontal Branch of Globular Cluster M13
Djorgovski, S. G.; Cohen, Judith G.; Côté, Patrick +4 more
We have determined the projected rotational velocities of 13 blue horizontal-branch (BHB) stars in the globular cluster M13 via rotational broadening of metal absorption lines. Our sample spans the photometric gap observed in the horizontal-branch distribution at Teff~=11,000 K and reveals a pronounced difference in stellar rotation on …
Observations of the Crab Nebula and Its Pulsar in the Far-Ultraviolet and in the Optical
Gull, Theodore R.; Pun, Chun S. J.; Fransson, Claes +5 more
We present far-UV observations of the Crab Nebula and its pulsar made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Broad, blueshifted absorption arising in the nebula is seen in C IV λ1550, reaching a blueward velocity of ~2500 km s-1. This can be interpreted as evidence for a fast outer shell surro…
A Coupled Model of Titan's Atmosphere and Ionosphere
Lara, L. M.; Rodrigo, R.; López-Moreno, J. J. +2 more
The paper deals with a coupled model of the upper atmosphere and ionosphere of Titan. The neutral atmosphere is described by a comprehensive photochemical model for 30° solar zenith angle with molecular and turbulent diffusive transport taken into account. At the upper boundary (1430 km) escaping flux of light molecules is included in boundary con…