Search Publications
Stellar Populations and Evolution of Early-type Cluster Galaxies: Constraints from Optical Imaging and Spectroscopy of z = 0.5-0.9 Galaxy Clusters
Jørgensen, Inger; Chiboucas, Kristin
We present an analysis of stellar populations and evolutionary history of galaxies in three similarly rich galaxy clusters MS0451.6-0305 (z = 0.54), RXJ0152.7-1357 (z = 0.83), and RXJ1226.9+3332 (z = 0.89). Our analysis is based on high signal-to-noise ground-based optical spectroscopy and Hubble Space Telescope imaging for a total of 17-34 member…
Hubble Tarantula Treasury Project: Unraveling Tarantula's Web. I. Observational Overview and First Results
Panagia, N.; Anderson, J.; Zaritsky, D. +18 more
The Hubble Tarantula Treasury Project (HTTP) is an ongoing panchromatic imaging survey of stellar populations in the Tarantula Nebula in the Large Magellanic Cloud that reaches into the sub-solar mass regime (<0.5 M ⊙). HTTP utilizes the capability of the Hubble Space Telescope to operate the Advanced Camera for Surveys and the Wide …
Space Velocities of Southern Globular Clusters. VII. NGC 6397, NGC 6626 (M28), and NGC 6656 (M22)
Casetti-Dinescu, Dana I.; Girard, Terrence M.; van Altena, William F. +3 more
We have measured the absolute proper motions of globular clusters NGC 6397, NGC 6626 (M22), and NGC 6656 (M28) as part of our ongoing Southern Proper-Motion Program. The reference system is the ICRS via Hipparcos stars for these three low-Galactic-latitude clusters. Formal errors range between ~0.3 and 0.7 mas yr-1. Notable is the resul…
The Star Formation History of the Very Metal-poor Blue Compact Dwarf I Zw 18 from HST/ACS Data
Cignoni, M.; Tosi, M.; Clementini, G. +7 more
We have derived the star formation history (SFH) of the blue compact dwarf galaxy I Zw 18 through comparison of deep HST/ACS data with synthetic color-magnitude diagrams (CMDs). A statistical analysis was implemented for the identification of the best-fit SFH and relative uncertainties. We confirm that I Zw 18 is not a truly young galaxy, having s…
Statistical Properties of Galactic δ Scuti Stars: Revisited
Byun, Y. -I.; Kim, D. -W.; Protopapas, P. +1 more
We present statistical characteristics of 1578 δ Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from work by Rodríguez and collected the remaining 54% of stars (860 stars) from other literature. We updated the entries with the latest information of sky coordinates,…
Binary Cepheids: Separations and Mass Ratios in 5 M ⊙ Binaries
Schaefer, Gail H.; Bond, Howard E.; Karovska, Margarita +3 more
Deriving the distribution of binary parameters for a particular class of stars over the full range of orbital separations usually requires the combination of results from many different observing techniques (radial velocities, interferometry, astrometry, photometry, direct imaging), each with selection biases. However, Cepheids—cool, evolved stars…
The Distance to the Massive Galactic Cluster Westerlund 2 from a Spectroscopic and HST Photometric Study
Kobulnicky, Henry A.; Vargas Álvarez, Carlos A.; Bradley, David R. +4 more
We present a spectroscopic and photometric determination of the distance to the young Galactic open cluster Westerlund 2 using WFPC2 imaging from the Hubble Space Telescope (HST) and ground-based optical spectroscopy. HST imaging in the F336W, F439W, F555W, and F814W filters resolved many sources previously undetected in ground-based observations …
Variable Stars in the Globular Cluster NGC 2808
Kunder, Andrea; Walker, Alistair R.; Stetson, Peter B. +2 more
The first calibrated broadband BVI time-series photometry is presented for the variable stars in NGC 2808, with observations spanning a range of 28 years. We have also redetermined the variability types and periods for the variable stars identified previously by Corwin et al., revising the number of probable fundamental-mode RR Lyrae variables (RR…
Studies of NGC 6720 with Calibrated HST/WFC3 Emission-line Filter Images. I. Structure and Evolution
O'Dell, C. R.; Henney, W. J.; Ferland, G. J. +1 more
We have performed a detailed analysis of the Ring Nebula (NGC 6720) using Hubble Space Telescope WFC3 images and derived a new three-dimensional model. Existing high spectral resolution spectra played an important supplementary role in our modeling. It is shown that the Main Ring of the nebula is an ionization-bounded irregular non-symmetric disk …
Anomalously Steep Reddening Law in Quasars: An Exceptional Example Observed in IRAS 14026+4341
Wang, Jianguo; Bai, Jinming; Shu, Xinwen +7 more
A fraction of the heavily reddened quasars require a reddening curve that is even steeper than that of the Small Magellanic Cloud. In this paper, we thoroughly characterize the anomalously steep reddening law in quasars via an exceptional example observed in IRAS 14026+4341. By comparing the observed spectrum to the quasar composite spectrum, we d…