Search Publications
The Wolf-Rayet Content of M33
Massey, Philip; Neugent, Kathryn F.
Wolf-Rayet (WR) stars are evolved massive stars, and the relative number of WC-type and WN-type WRs should vary with metallicity, providing a sensitive test of stellar evolutionary theory. The observed WC/WN ratio is much higher than that predicted by theory in some galaxies but this could be due to observational incompleteness for WN types, which…
A Hubble Space Telescope Study of Lyman Limit Systems: Census and Evolution
Lehner, Nicolas; Howk, J. Christopher; Ribaudo, Joseph
We present a survey for optically thick Lyman limit absorbers at z < 2.6 using archival Hubble Space Telescope observations with the Faint Object Spectrograph and Space Telescope Imaging Spectrograph. We identify 206 Lyman limit systems (LLSs), increasing the number of cataloged LLSs at z < 2.6 by a factor of ~10. We compile a statistical sa…
Observational Constraints on Red and Blue Helium Burning Sequences
McQuinn, Kristen B. W.; Dolphin, Andrew E.; Skillman, Evan D. +4 more
We derive the optical luminosity, colors, and ratios of the blue and red helium burning (HeB) stellar populations from archival Hubble Space Telescope observations of nineteen starburst dwarf galaxies and compare them with theoretical isochrones from Padova stellar evolution models across metallicities from Z = 0.001 to 0.009. We find that the obs…
Lifting the Veil on Obscured Accretion: Active Galactic Nuclei Number Counts and Survey Strategies for Imaging Hard X-Ray Missions
Rigby, J. R.; Treister, E.; Ballantyne, D. R. +2 more
Finding and characterizing the population of active galactic nuclei (AGNs) that produces the X-ray background (XRB) is necessary to connect the history of accretion to observations of galaxy evolution at longer wavelengths. The year 2012 will see the deployment of the first hard X-ray imaging telescope which, through deep extragalactic surveys, wi…
Images of the Extended Outer Regions of the Debris Ring around HR 4796 A
Kuzuhara, M.; Tamura, M.; Ishii, M. +48 more
We present high-contrast images of HR 4796 A taken with Subaru/HiCIAO in the H band, resolving the debris disk in scattered light. The application of specialized angular differential imaging methods allows us to trace the inner edge of the disk with high precision and reveals a pair of "streamers" extending radially outward from the ansae. Using a…
Thermodynamics of the Solar Corona and Evolution of the Solar Magnetic Field as Inferred from the Total Solar Eclipse Observations of 2010 July 11
Morgan, Huw; Habbal, Shadia Rifai; Daw, Adrian +7 more
We report on the first multi-wavelength coronal observations, taken simultaneously in white light, Hα 656.3 nm, Fe IX 435.9 nm, Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, Fe XIV 530.3 nm, and Ni XV 670.2 nm, during the total solar eclipse of 2010 July 11 from the atoll of Tatakoto in French Polynesia. The data enabled temperature differenti…
Numerical Simulation of Dust in a Cometary Coma: Application to Comet 67P/Churyumov-Gerasimenko
Combi, Michael R.; Rubin, Martin; Tenishev, Valeriy
The Rosetta spacecraft is en route to comet 67P/Churyumov-Gerasimenko for a rendezvous, landing, and extensive orbital phase beginning in 2014. With a limited amount of available observational data, planning of the mission as well as the interpretation of measurements obtained by instruments on board the spacecraft requires modeling of the dusty/g…
The Temperature Dependence of Solar Active Region Outflows
Stenborg, Guillermo; Warren, Harry P.; Ugarte-Urra, Ignacio +1 more
Spectroscopic observations with the EUV Imaging Spectrometer (EIS) on Hinode have revealed large areas of high-speed outflows at the periphery of many solar active regions. These outflows are of interest because they may connect to the heliosphere and contribute to the solar wind. In this paper, we use slit rasters from EIS in combination with nar…
Multi-scale Anti-correlation Between Electron Density and Magnetic Field Strength in the Solar Wind
Tu, C. -Y.; Marsch, E.; Rème, H. +4 more
This work focuses on the relation between the electron density and the magnetic field strength in the solar wind, and aims to reveal its compressive nature and to determine the level of compressibility. For this purpose, we choose a period of quiet solar wind data obtained at 1 AU by the Cluster C1 satellite. The electron density is derived with a…
Twist and Connectivity of Magnetic Field Lines in the Solar Active Region NOAA 10930
Kusano, K.; Shiota, D.; Inoue, S. +2 more
Twist and connectivity of magnetic field lines in the flare-productive active region NOAA 10930 are investigated in terms of the vector magnetograms observed by the Solar Optical Telescope on board the Hinode satellite and the nonlinear force-free field (NLFFF) extrapolation. First, we show that the footpoints of magnetic field lines reconstructed…