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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…
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…
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…
N-Body Simulations of Compact Young Clusters near the Galactic Center
Lee, Hyung Mok; Figer, Donald F.; Kim, Sungsoo S. +1 more
We investigate the dynamical evolution of compact young star clusters (CYCs) near the Galactic center using Aarseth's Nbody6 codes. The relatively small number of stars in the cluster (5000-20,000) makes real-number N-body simulations for these clusters feasible on current workstations. Using Fokker-Planck (F-P) models, Kim, Morris, & Lee made…
High-Resolution Hubble Space Telescope STIS Spectra of C I and CO in theβ Pictoris Circumstellar Disk
Roberge, A.; Feldman, P. D.; Ferlet, R. +5 more
High-resolution far-ultraviolet (FUV) echelle spectra showing absorption features arising from C I and CO gas in the β Pic circumstellar (CS) disk were obtained on 1997 December 6 and 19 using the Space Telescope Imaging Spectrograph (STIS). An unsaturated spin-forbidden line of C I at 1613.376 Å not previously seen in spectra of β Pic was detecte…
Infrared Space Observatory Mid-Infrared Spectra of Reflection Nebulae
Werner, M. W.; Sellgren, K.; Uchida, K. I. +1 more
We present 5-15 µm imaging spectroscopy of the reflection nebulae vdB 17 (NGC 1333), vdB 59 (NGC 2068), vdB 101, vdB 111, vdB 133, and vdB 135, obtained with the infrared camera and circular variable filter wheel on the Infrared Space Observatory (ISO). These nebulae are illuminated by stars with Teff=3,600-19,000 K, implying UV (…
Solar and Heliospheric Observatory Observations of a Helical Coronal Mass Ejection
Thompson, B. J.; Raymond, J. C.; Ciaravella, A. +8 more
The EUV Imaging Telescope (EIT), Large Angle Spectrometric Coronagraph (LASCO), and Ultraviolet Coronagraph Spectrometer (UVCS) instruments aboard the SOHO satellite observed a prominence eruption (coronal mass ejection) on 1997 December 12. Ejected plasma moved at about 130 km s-1 in the plane of the sky and showed Doppler shifts betwe…