Search Publications
HUBBLE SPACE TELESCOPE Imaging of Globular Clusters in the Edge-on Spiral Galaxies NGC 4565 and NGC 5907
Zepf, Stephen E.; Freeman, Kenneth C.; Kissler-Patig, Markus +1 more
We present a study of the globular cluster systems of two edge-on spiral galaxies, NGC 4565 and NGC 5907, from WFPC2 images in the F450W and F814W filters. The globular cluster systems of both galaxies appear to be similar to the Galactic globular cluster system. In particular, we derive total numbers of globular clusters of N_GC(4565)=204+/-38^+8…
The Structure and Morphology of the Ionized Gas in Starburst Galaxies: NGC 5253/5236
Conselice, Christopher J.; Calzetti, Daniela; Gallagher, John S., III +1 more
We investigate the interplay between starbursts and host galaxies by studying the structure and physical characteristics of the ionized gas surrounding the central starbursts in the two nearby galaxies NGC 5253 and NGC 5236. The two systems form a pair that presumably interacted about 1 Gyr ago. They represent very different galactic environments,…
HUBBLE SPACE TELESCOPE Observations of Galactic Globular Cluster Cores. I. NGC 6362 and NGC 6934
Djorgovski, S. G.; Zoccali, M.; Rich, R. M. +5 more
We present observations of the centers of the Galactic globular clusters NGC 6362 and NGC 6934 obtained with the Hubble Space Telescope/Wide Field Planetary Camera 2 as part of the snapshot program GO-7470. The B, V color-magnitude diagrams (CMDs) are presented for 4104 stars in NGC 6362 and for 8187 stars in NGC 6934. From the CMDs, we obtain (m-…
The Structure and Temporal Stability of Jupiter's Zonal Winds: A Study of the North Tropical Region
Simon, Amy A.
This paper investigates possible long-term zonal wind variations using Voyager (1979), Hubble Space Telescope (HST; 1995, 1997, 1998), and Galileo Orbiter (1997) data that has all been processed and analyzed in the same manner for consistency. Previous attempts to measure the zonal wind profile in Voyager data had yielded inconsistent results for …
A distance to the galaxy NGC4258 from observations of Cepheid variable stars
Zepf, Stephen E.; Davis, Marc; Madore, Barry F. +5 more
Cepheid variable stars pulsate in a way that is correlated with their intrinsic luminosity, making them useful as `standard candles' for determining distances to galaxies; the potential systematic uncertainties in the resulting distances have been estimated to be only 8-10%. They have played a crucial role in establishing the extragalactic distanc…
Stellar Populations in the Dwarf Spheroidal Galaxy Leo I
Cassisi, Santi; Castellani, Marco; Caputo, Filippina +2 more
We present a detailed study of the color-magnitude diagram (CMD) of the dwarf spheroidal galaxy Leo I, based on archival Hubble Space Telescope data. Our photometric analysis, confirming previous results on the brighter portion of the CMD, also allow us to obtain an accurate sampling of the stellar populations at the faint magnitudes corresponding…
Activity cycle and surface differential rotation of the single Pleiades star HD 82443 (DX Leo)
Lanza, A. F.; Messina, S.; Guinan, E. F. +1 more
The results of a long-term photometric monitoring of the young Pleiades moving group member HD 82443 are presented. A sequence of fifteen optical light curves obtained from 1989 to 1998 confirms the presence of a rotational modulation with a mean period of 5.377 days attributable to cool photospheric spots. The Maximum Entropy and the Tikhonov reg…
Strong optical line variability in MKN 110
Kollatschny, W.; Bischoff, K.
We present results of a long-term variability campaign on the Seyfert 1 galaxy Markarian 110. Mkn 110 is a narrow-line Seyfert 1 object hosted in a morphological peculiar galaxy. We monitored the optical continuum and the line intensities as well as their profiles over a time interval of nearly ten years. The continuum and the Balmer lines varied …
A study of solar wind acceleration based on gyrotropic transport equations
Leer, Egil; Olsen, Espen Lyngdal
The gyrotropic transport equations are used to describe an electron-proton solar wind from the 500,000 K level in the upper transition region and out to 30 solar radii. These equations allow for different temperatures parallel and perpendicular to the magnetic field, as well as transport of parallel and perpendicular thermal energy along the field…
Strange velocities in the equatorial ejecta of eta Carinae
Humphreys, Roberta M.; Davidson, Kris; Ishibashi, Kazunori +3 more
We report HST/HRS observations of gas that appears to have been ejected in the equatorial zone of eta Carinae. Some of the observed emission lines are produced by Fe II fluorescence processes, which, for unknown reasons, are uniquely intense near eta Carinae. Surprisingly low velocities are found, most likely representing ejection events hundreds …