Search Publications
Very Blue Stars and Mass Segregation in the Core of M15
Paresce, Francesco; de Marchi, Guido
The core of the globular cluster M15 (NGC 7078) has been observed with the COSTAR-corrected Faint Object Camera on board the Hubble Space Telescope (HST), through medium-band ultraviolet filters centered at 255 nm and 348 nm. A total of about 1200 stars are detected in a region of size 7" x 7" located just west of the cluster center, to form a col…
Distant Ring Galaxies as Evidence for a Steeply Increasing Galaxy Interaction Rate with Redshift
Da Costa, G. S.; Seitzer, Patrick; Walker, Alistair R. +2 more
Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) images of the Local Group dwarf galaxy Tucana reveal an unbiased sample of distant field galaxies. While a large number of these galaxies can be classified according to standard Hubble types, a significant number of these galaxies can be identified as "ring" galaxies, a morphology likely…
Ultraviolet Imagery of NGC 6752: A Test of Extreme Horizontal Branch Models
O'Connell, Robert W.; Sweigart, Allen V.; Bohlin, Ralph C. +5 more
We present a 1620 A image of the nearby globular cluster NGC 6752 obtained with the Ultraviolet Imaging Telescope (UIT) during the Astro-2 mission of the Space Shuttle Endeavour in 1995 March. An ultraviolet-visible color-magnitude diagram (CMD) is derived for 216 stars matched with the visible photometry of Buonanno et al. This CMD provides a nea…
The Mid-Infrared Evolution of Nova V1974 Cygni
Hayward, T. L.; Saizar, P.; Gehrz, R. D. +6 more
We observed nova V1974 Cygni (1992) at mid-infrared wavelengths λ = 7.5-13 µm nine times between 1992 April (54 days after the outburst) and 1994 July (day 882). Low- and medium-resolution spectra recorded the evolution of hydrogen recombination lines, free-free continuum emission, and the [Ne II] 12.8 µm, [Ne VI] 7.6 µm, and [Mg…
Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images. III. Photometric properties.
Tagliaferri, G.; Pasquini, L.; Pallavicini, R. +2 more
We present high-precision UBV(RI)_c_ photometry for a sample of active stars detected serendipitously by the EXOSAT satellite. Fourteen objects, out of 47 likely optical counterparts, turned out to be clearly variable, with periods in the range 1-8 days, including a newly discovered eclipsing binary. For most of them the optical variability is con…
Observations of galactic cosmic rays and the anomalous helium during ULYSSES passage from the south to the north solar pole.
Simpson, J. A.; McKibben, R. B.; Zhang, M. +2 more
We compare observations of the modulated intensities and spectra of galactic cosmic ray nuclei and anomalous helium above 30 MeV/n measured by the COsmic and Solar Particle INvestigations (COSPIN) High Energy Telescope (HET) on Ulysses with similar observations from the IMP-8 earth-orbiting satellite between September 1994 and August 1995. During …
The SWS survey for rotational H_2_ lines in late-type galaxies. Observations of the central regions of NGC 6946.
de Graauw, T.; van der Werf, P. P.; de Jong, T. +1 more
We report the first extragalactic detection of the pure rotational H_2_ S(0) and S(1) lines at 28.2 and 17.0µm in the central 130pc molecular complex of the nearby Scd galaxy NGC 6946. We deduce a temperature of this gas component of 170K and a mass of 5x10^6^Msun_ for an ortho/para ratio of 3, corresponding to the ratio of statis…
The globular clusters in M87: a bimodal colour distribution
Elson, Rebecca A. W.; Santiago, Basilio X.
We present V and I photometry for ~150 globular clusters with 20<<e1>V<</e1>27 about 2.5 arcmin from the centre of M87, the cD galaxy in the Virgo cluster. The data were acquired with the Hubble Space Telescope which, with an effective resolution of 0.1 arcsec, allows us for the first time to distinguish between globular clusters…
HST photometry of 47 TUC and analysis of the stellar luminosity function in Milky Way clusters
Elson, Rebecca A. W.; Gilmore, Gerard F.; Santiago, Basilio X.
We present V and I photometry for over 1000 stars in a region 5 arcmin from the centre of the globular cluster 47 Tuc. The field was imaged with the Wide Field and Planetary Camera 2 (WFPC-2) as part of the Hubble Space Telescope's Medium Deep Survey key project. The luminosity function (LF) continually rises in the domain 5<~<e1>M_I<~…
Solving the mystery of the heavy-element opacity in the DA white dwarf GD 394.
Barstow, M. A.; Bruhweiler, F. C.; Holberg, J. B. +3 more
The white dwarf GD 394 is one of a very small number of bright hot DAs which have detectable quantities of highly ionized heavy elements in their spectra. Whether this material resides in the photosphere of GD 394 or is in the form of a circumstellar shell has been the subject of much debate, with the large discrepancy between the published radial…