Search Publications
The Age-dependent Luminosities of the Red Giant Branch Bump, Asymptotic Giant Branch Bump, and Horizontal Branch Red Clump
Sarajedini, Ata; Alves, David R.
Color-magnitude diagrams of globular clusters usually exhibit a prominent horizontal branch (HB) and may also show features such as the red giant branch (RGB) bump and the asymptotic giant branch (AGB) bump. Stellar evolution theory predicts that the luminosities of these features will depend on the metallicity and age of the cluster. We calculate…
Correlated Errors in HIPPARCOS Parallaxes toward the Pleiades and the Hyades
Gould, Andrew; Narayanan, Vijay K.
We show that the errors in the Hipparcos parallaxes toward the Pleiades and the Hyades open clusters are spatially correlated over angular scales of 2°-3°, with an amplitude of up to 2 mas. This correlation is stronger than expected based on the analysis of the Hipparcos catalog. We predict the parallaxes of individual cluster members, πpm
Gravitationally Lensed Gamma-Ray Bursts as Probes of Dark Compact Objects
Hurley, K.; Norris, J. P.; Marani, G. F. +2 more
If dark matter in the form of compact objects comprises a large fraction of the mass of the universe, then gravitational lensing effects on gamma-ray bursts are expected. We utilize BATSE and Ulysses data to search for lenses of different mass ranges, which cause lensing in the milli, pico, and femto regimes. Null results are used to set weak limi…
The Young Age of the Extremely Metal-deficient Blue Compact Dwarf Galaxy SBS 1415+437
Thuan, Trinh X.; Izotov, Yuri I.; Foltz, Craig B.
We use Multiple Mirror Telescope (MMT) spectrophotometry and Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) spectra and Wide Field and Planetary Camera 2 (WFPC2) V and I images to study the properties and evolutionary status of the nearby (D=11.4 Mpc) extremely metal-deficient blue compact dwarf (BCD) galaxy SBS 1415+437 (≡CG 389). T…
The Extragalactic Distance Scale Key Project. XVIII. The Discovery of Cepheids and a New Distance to NGC 4535 Using the Hubble Space Telescope
Kelson, D. D.; Ford, H. C.; Ferrarese, L. +23 more
We report on the discovery of Cepheids in the Virgo spiral galaxy NGC 4535, based on observations made with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 4535 is one of 18 galaxies observed as a part of The HST Key Project on the Extragalactic Distance Scale, which aims to measure the Hubble constant to 10% a…
Cataclysmic Variables and a Candidate Helium White Dwarf in the Globular Cluster NGC 6397
Edmonds, Peter D.; Grindlay, Jonathan E.; Cool, Adrienne +3 more
We have used the Hubble Space Telescope (HST) and the Faint Object Spectrograph (FOS) to study faint UV stars in the core of the nearby globular cluster NGC 6397. We confirm the presence of a fourth cataclysmic variable (CV) in NGC 6397 (hereafter CV 4), and we use the photometry of Cool et al. to present evidence that CVs 1-4 all have faint disks…
Detection of Evolved High-Redshift Galaxies in Deep NICMOS/VLT Impages
Broadhurst, Tom; Rosati, Piero; Benítez, Narciso +2 more
A substantial population of high-redshift, early-type galaxies is detected in very deep UBVRIJHK images. Four elliptical profile galaxies are identified in the redshift range 1<z<2, with very red spectral energy distributions implying ages of >~2 Gyr for standard passive evolution. We also find later type IR-luminous galaxies at similarly…
Starburst in the Intragroup Medium of Stephan's Quintet
Xu, Cong; Sulentic, Jack W.; Tuffs, Richard
Based on new Infrared Space Observatory midinfrared observations and ground-based Hα and near-infrared observations, we report the detection of a bright starburst in the intragroup medium (IGM) of the famous compact group of galaxies known as Stephan's Quintet (source A in Fig. 1). We demonstrate that this starburst is caused by a colli…
The Host Galaxies of Three Radio-loud Quasars: 3C 48, 3C 345, and B2 1425+267
Schneider, Donald P.; Bahcall, John N.; Kirhakos, Sofia +1 more
Observations with the Wide-Field/Planetary Camera-2 of the Hubble Space Telescope are presented for three radio-loud quasars: 3C 48 (z=0.367), B2 1425+267 (z=0.366), and 3C 345 (z=0.594). All three quasars have luminous (~4×L*) galaxies as hosts, which are either elliptical (B2 1425+267 and 3C345) or interacting (3C 48), and all hosts a…
Quasars and Ultraluminous Infrared Galaxies: At the Limit?
McLeod, K. K.; Rieke, G. H.; Storrie-Lombardi, L. J.
We have detected the host galaxies of 16 nearby, radio-quiet quasars using images obtained with the Near-Infrared Camera and MultiObject Spectrometer. We confirm that these luminous quasars tend to live in luminous, early-type host galaxies, and we use the host-galaxy magnitudes to refine the luminosity/host-mass limit inferred from ground-based s…