Search Publications
Identifying Lenses with Small-Scale Structure. I. Cusp Lenses
Keeton, Charles R.; Gaudi, B. Scott; Petters, A. O.
The inability of standard models to explain the flux ratios in many four-image gravitational lens systems has been presented as evidence for significant small-scale structure in lens galaxies. That claim has generally relied on detailed lens modeling, so it is both model dependent and somewhat difficult to interpret. We present a more robust and g…
The Magnetic Helicity Budget of Solar Active Regions and Coronal Mass Ejections
Zhang, H.; Zhang, J.; Nindos, A.
We compute the magnetic helicity injected by transient photospheric horizontal flows in six solar active regions associated with halo coronal mass ejections (CMEs) that produced major geomagnetic storms and magnetic clouds (MCs) at 1 AU. The velocities are computed using the local correlation tracking (LCT) method. Our computations cover time inte…
The Effects of UV Continuum and Lyα Radiation on the Chemical Equilibrium of T Tauri Disks
Herczeg, Gregory J.; Calvet, Nuria; Bergin, Edwin +1 more
We show in this Letter that the spectral details of the far-ultraviolet (FUV) radiation fields have a large impact on the chemistry of protoplanetary disks surrounding T Tauri stars. We show that the strength of a realistic stellar FUV field is significantly lower than typically assumed in chemical calculations and that the radiation field is domi…
Evidence of a Significant Intermediate-Age Population in the M31 Halo from Main-Sequence Photometry
Ferguson, Henry C.; Brown, Thomas M.; Rich, R. Michael +5 more
We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M31), 51' (11 kpc) from the nucleus. These observations, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, are the deepest optical images yet obtained, attaining 50% completeness at mV=30.7 mag. The CMD, c…
The Initial Helium Content of Galactic Globular Cluster Stars from the R-Parameter: Comparison with the Cosmic Microwave Background Constraint
Salaris, Maurizio; Cassisi, Santi; Irwin, Alan W.
Recent precise determinations of the primordial He abundance (Yp) from cosmic microwave background (CMB) analyses and cosmological nucleosynthesis computations provide Yp=0.248+/-0.001. On the other hand, recent works on the initial He abundance of Galactic globular cluster (GGC) stars, making use of the R-parameter as an He …
The Hubble Constant from the Gravitational Lens B1608+656
Treu, T.; Blandford, R. D.; Koopmans, L. V. E. +2 more
We present a refined gravitational lens model of the four-image lens system B1608+656 based on new and improved observational constraints: (1) the three independent time delays and flux ratios from Very Large Array observations, (2) the radio-image positions from Very Large Baseline Array observations, (3) the shape of the deconvolved Einstein rin…
Giant Lyα Nebulae Associated with High-Redshift Radio Galaxies
Dey, Arjun; Bland-Hawthorn, Joss; Stanford, S. A. +7 more
We report deep, Keck narrowband Lyα images of the luminous z>3 radio galaxies 4C 41.17, 4C 60.07, and B2 0902+34. The images show giant, 100-200 kpc scale, emission-line nebulae, centered on these galaxies, that exhibit a wealth of morphological structure, including extended low surface brightness emission in the outer regions, radially directe…
Solar Seismic Models and the Neutrino Predictions
Kosovichev, A. G.; Turck-Chièze, S.; Couvidat, S.
This paper focuses on the solar neutrino fluxes, the g-mode predictions, and the possible impact of the magnetic fields on the neutrino emission and transport. The Solar and Heliospheric Observatory (SOHO) spacecraft has allowed astrophysicists to achieve a major breakthrough in the knowledge of the solar core. Both GOLF and MDI instruments on SOH…
Lyα Emission in Starbursts: Implications for Galaxies at High Redshift
Mas-Hesse, J. M.; Kunth, D.; Leitherer, C. +3 more
We present the results of a high-resolution UV two-dimensional spectroscopic survey of star-forming galaxies observed with Hubble Space Telescope Space Telescope Imaging Spectrograph. Our main aim is to map the Lyα profiles to learn about the gas kinematics and its relation with the escape of Lyα photons and to detect extended Lyα emission due to …
The Evolution of a Mass-selected Sample of Early-Type Field Galaxies
Peng, C. Y.; Keeton, C. R.; Kochanek, C. S. +7 more
We investigate the evolution of mass-selected early-type field galaxies using a sample of 28 gravitational lenses spanning the redshift range 0<~z<~1. Based on the redshift-dependent intercept of the fundamental plane in the rest-frame B band, we measure an evolution rate of dlog(M/L)B/dz=-0.56+/-0.04 (all errors are 1 σ unless no…