Search Publications
Photospheric Magnetic Field Changes Associated with Transition Region Explosive Events
Wang, Haimin; Chae, Jongchul; Schühle, Udo +2 more
From a comparison of the Solar and Heliospheric Observatory SUMER spectral data and a time series of Big Bear Solar Observatory magnetograms, we present observational clues to the physical origin of transition region explosive events. First, explosive events rarely occur in the interior of strong magnetic flux concentrations but rather are prefere…
A Spectroscopic Survey of the Galaxy Cluster CL 1358+62 at Z = 0.328
Franx, Marijn; van Dokkum, Pieter; Fisher, David +1 more
We present a spectroscopic survey of the rich X-ray-selected galaxy cluster CL 1358+6245 at z = 0.328. When our 173 new multislit spectra of cluster galaxies are combined with data from the literature, we produce a catalog of 232 cluster members in a region 10' × 11' (3.5 Mpc × 3.8 Mpc) surrounding the brightest cluster galaxy. These data are used…
A Blind Test of Photometric Redshift Prediction
Dickinson, Mark; Sawicki, Marcin; Hogg, David W. +16 more
Results of a blind test of photometric redshift predictions against spectroscopic galaxy redshifts obtained in the Hubble Deep Field with the Keck Telescope are presented. The best photometric redshift schemes predict spectroscopic redshifts with a redshift accuracy of Deltaz < 0.1 for more than 68% of sources and with Deltaz < 0.3 for 100%,…
Hubble Space Telescope V-Band Imaging of the Bipolar Proto-Planetary Nebula IRAS 17150-3224
Kwok, Sun; Hrivnak, Bruce J.; Su, Kate Y. L.
We report Hubble Space Telescope Wide Field Planetary Camera 2 imaging of the bipolar proto-planetary nebula IRAS 17150-3224. We find a series of concentric arcs superposed on the two reflection nebular lobes, similar to those observed in AFGL 2688. This suggests that periodic mass-loss enhancement is a common phenomenon in the asymptotic giant br…
On the age of the nearby blue compact dwarf galaxy SBS 0335-052
Thuan, T. X.; Izotov, Y. I.; Papaderos, P. +2 more
UBVRI surface photometry and long-slit spectrophotometric observations are used to investigate the evolutionary status and put constraints on the age of the underlying stellar population of the eastern component of a nearby pair of dwarf galaxies, the blue compact dwarf galaxy SBS\ 0335-052E. We show that ionized gas emission extending out to dist…
A new analysis of the red giant branch `tip' distance scale and the value of the Hubble constant
Salaris, Maurizio; Cassisi, Santi
The theoretical evaluations of the red giant branch tip (TRGB) luminosity presented previously by Salaris & Cassisi are extended to higher metallicities, and compared with analogous independent results recently published. The present sets of stellar models agree quite well in the determination of the TRGB brightness. Relations between TRGB bol…
A Protocometary Cloud around HR 4796A?
Telesco, C.; Malkan, M.; Fisher, R. S. +3 more
We report both ROSAT observations and ground-based 10.8 µm imaging of the wide binary HR 4796, which consists of a main-sequence A-type star with a large amount of circumstellar dust, HR 4796A, and, at a separation of 7.7", a pre-main-sequence M-type companion, HR 4796B. From the ROSAT data, we find that the X-ray emission is centered on HR …
The Luminosity Function of the Globular Cluster NGC 6397 near the Limit of Hydrogen Burning
Anderson, Jay; Piotto, Giampaolo; Cool, Adrienne M. +1 more
Second-epoch Hubble Space Telescope observations of NGC 6397 have led to the measurement of proper motions accurate enough to separate the faintest cluster stars from the field, thus extending the luminosity function of this globular cluster far enough to approach the limit of hydrogen burning on the main sequence. We isolate a sample of 1385 main…
Strömgren Photometry of Globular Clusters: The Distance and Age of M13, Evidence for Two Populations of Horizontal-Branch Stars
Grundahl, Frank; VandenBerg, Don A.; Andersen, Michael I.
We present deep CCD photometry of the globular cluster M13 (NGC 6205) in the Strömgren uvbyβ system and determine a foreground reddening of E(b-y)=0.015+/-0.01 mag. From a fit to the main sequence of metal-poor subdwarfs with Hipparcos parallaxes, we derive (m-M)0=14.38+/-0.10, which implies an age near 12 Gyr assuming [Fe/H] = -1.61 an…
HIPPARCOS Parallaxes and the Cepheid Distance Scale
Madore, Barry F.; Freedman, Wendy L.
Hipparcos parallaxes have recently become available for a sample of Galactic Cepheids, and we have used these new distances to calibrate the Cepheid period-luminosity (PL) relation at six wavelengths (BVIJHK). Comparing these calibrations with previously published multiwavelength PL relations we find agreement to within 0.07 +/- 0.14 mag, or 4% +/…