Search Publications
Hubble Space Telescope Observations of Element Abundances in Low-Redshift Damped Lyα Galaxies and Implications for the Global Metallicity-Redshift Relation
York, Donald G.; Fall, S. Michael; Kulkarni, Varsha P. +4 more
Most models of cosmic chemical evolution predict that the mass-weighted mean interstellar metallicity of galaxies should rise with time from a low value ~1/30 solar at z~3 to a nearly solar value at z=0. In the absence of any selection effects, the damped Lyα absorbers (DLAs) in quasar spectra are expected to show such a rise in global metallicity…
The Low-z Intergalactic Medium. I. O VI Baryon Census
Shull, J. Michael; Danforth, Charles W.
Intergalactic absorbers along lines of sight to distant quasars are a powerful diagnostic for the evolution and content of the intergalactic medium (IGM). In this study, we use the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite to search 129 known Lyα absorption systems at z<0.15 toward 31 active galactic nuclei (AGNs) for correspondin…
Coronal Evolution of the Sun in Time: High-Resolution X-Ray Spectroscopy of Solar Analogs with Different Ages
Skinner, Stephen L.; Güdel, Manuel; Ness, Jan-Uwe +3 more
We investigate the long-term evolution of X-ray coronae of solar analogs based on high-resolution X-ray spectroscopy and photometry with XMM-Newton. Six nearby main-sequence G stars with ages between ~0.1 and ~1.6 Gyr and rotation periods between ~1 and 12.4 days have been observed. We use the X-ray spectra to derive coronal element abundances of …
Evolution of the Near-Infrared Tully-Fisher Relation: Constraints on the Relationship between the Stellar and Total Masses of Disk Galaxies since z~1
Conselice, Christopher J.; Ellis, Richard S.; Bundy, Kevin +3 more
Using a combination of Keck spectroscopy and near-infrared imaging, we investigate the K-band and stellar-mass Tully-Fisher relation for 101 disk galaxies at 0.2<z<1.2, with the goal of placing the first observational constraints on the assembly history of halo and stellar mass. Our main result is a lack of evolution in either the K-band or …
From Radio to X-Ray: Flares on the dMe Flare Star EV Lacertae
Hawley, Suzanne L.; Johns-Krull, Christopher M.; Osten, Rachel A. +2 more
We present the results of a campaign to observe flares on the M dwarf flare star EV Lacertae over the course of two days in 2001 September, utilizing a combination of radio continuum, optical photometric and spectroscopic, ultraviolet spectroscopic, and X-ray spectroscopic observations to characterize the multiwavelength nature of flares from this…
The Low End of the Supermassive Black Hole Mass Function: Constraining the Mass of a Nuclear Black Hole in NGC 205 via Stellar Kinematics
Joseph, Charles L.; Ferrarese, Laura; Merritt, David +1 more
Hubble Space Telescope (HST) images and spectra of the nucleated dwarf elliptical galaxy NGC 205 are combined with three-integral axisymmetric dynamical models to constrain the mass MBH of a putative nuclear black hole. This is only the second attempt, after M33, to use resolved stellar kinematics to search for a nuclear black hole with…
An Overdensity of Galaxies at z = 5.9 +/- 0.2 in the Hubble Ultra Deep Field Confirmed Using the ACS Grism
Daddi, E.; Panagia, N.; Ferguson, H. C. +17 more
We present grism spectra taken with the Advanced Camera for Surveys (ACS) to identify 29 red sources with (i775-z850)>=0.9 in the Hubble Ultra Deep Field (HUDF). Of these, 23 are found to be galaxies at redshifts between z=5.4 and 6.7, identified by the break at 1216 Å due to intergalactic medium (IGM) absorption; two are …
High-Resolution Radio Observations of the Colliding-Wind Binary WR 140
Dougherty, S. M.; Claussen, M. J.; Zauderer, B. A. +2 more
Milliarcsecond resolution Very Long Baseline Array (VLBA) observations of the archetype W-R+O star colliding-wind binary (CWB) system WR 140 are presented for 23 epochs between orbital phases 0.74 and 0.97. At 8.4 GHz, the emission in the wind-collision region (WCR) is clearly resolved as a bow-shaped arc that rotates as the orbit progresses. We i…
Coronal Mass Ejection Shock and Sheath Structures Relevant to Particle Acceleration
Gombosi, T. I.; Tóth, G.; Zurbuchen, T. H. +6 more
Most high-energy solar energetic particles are believed to be accelerated at shock waves driven by coronal mass ejections (CMEs). The acceleration process strongly depends on the shock geometry and the structure of the sheath that forms behind the shock. In an effort to understand the structure and time evolution of such CME-driven shocks and thei…
Relationship between Magnetic Power Spectrum and Flare Productivity in Solar Active Regions
Abramenko, V. I.
Power spectra of the line-of-sight magnetograms were calculated for 16 active regions of different flare activity. Data obtained by the Michelson Doppler Imager instrument on board the Solar and Heliospheric Observatory in high-resolution mode were used in this study. For each active region, the daily soft X-ray flare index, A, was calculated. Thi…