Search Publications
Bar Evolution over the Last 8 Billion Years: A Constant Fraction of Strong Bars in the GEMS Survey
Bell, Eric F.; Ravindranath, Swara; Somerville, Rachel S. +25 more
One-third of present-day spirals host optically visible strong bars that drive their dynamical evolution. However, the fundamental question of how bars evolve over cosmological times has yet to be resolved, and even the frequency of bars at intermediate redshifts remains controversial. We investigate the frequency of bars out to z ~ 1 drawing on a…
Discovery of a Transient Magnetar: XTE J1810-197
Safi-Harb, Samar; Hurley, Kevin; Kouveliotou, Chryssa +10 more
We report the discovery of a new X-ray pulsar, XTE J1810-197, that was serendipitously discovered on 2003 July 15 by the Rossi X- Ray Timing Explorer (RXTE) while observing the soft gamma repeater SGR 1806-20. The pulsar has a 5.54 s spin period, a soft X-ray spectrum (with a photon index of ~4), and is detectable in earlier RXTE observations back…
Resistive Emergence of Undulatory Flux Tubes
Aulanier, G.; Schmieder, B.; Pariat, E. +3 more
During its 2000 January flight, the Flare Genesis Experiment observed the gradual emergence of a bipolar active region, by recording a series of high-resolution photospheric vector magnetograms and images in the blue wing of the Hα line. Previous analyses of these data revealed the occurrence of many small-scale, transient Hα brightenings identifi…
Resolution of the MACHO-LMC-5 Puzzle: The Jerk-Parallax Microlens Degeneracy
Gould, Andrew
By extending the constant-acceleration analysis of Smith, Mao, & Paczyński to include jerk, I show that microlens parallax measurements are subject to a four-fold discrete degeneracy. The new degeneracy is characterized by a projected velocity vj=-(3/4)cscβec(cos2ψsin2βec+sin2ψ)3/2v⊕, wher…
Interstellar Carbon in Translucent Sight Lines
Sofia, Ulysses J.; Meyer, David M.; Lauroesch, James T. +1 more
We report interstellar C II column densities or upper limits determined from weak absorption of the 2325.4029 Å intersystem transition observed in six translucent sight lines (AV>~1) with the Space Telescope Imaging Spectrograph (STIS). The sight lines sample a wide range of interstellar characteristics, including total to selective …
The Effect of Metallicity on Cepheid-based Distances
Ferrarese, Laura; Saha, Abhijit; Sakai, Shoko +1 more
We have used the Wide Field Planetary Camera 2 on board the Hubble Space Telescope to obtain V and I images of seven nearby galaxies. For each, we have measured a distance using the tip of the red giant branch (TRGB) method. By comparing the TRGB distances with published Cepheid distances, we investigate the metallicity dependence of the Cepheid p…
Magnetic Reconnection and Mass Acceleration in Flare-Coronal Mass Ejection Events
Qiu, Jiong; Wang, Haimin; Gary, Dale E. +1 more
An observational relationship has been well established among magnetic reconnection, high-energy flare emissions and the rising motion of erupting flux ropes. In this paper, we verify that the rate of magnetic reconnection in the low corona is temporally correlated with the evolution of flare nonthermal emissions in hard X-rays and microwaves, all…
A Probable z~7 Galaxy Strongly Lensed by the Rich Cluster A2218: Exploring the Dark Ages
Richard, Johan; Ellis, Richard S.; Kneib, Jean-Paul +1 more
We discuss the observational properties of a remarkably faint triply imaged galaxy revealed in a deep z'-band Advanced Camera for Surveys observation of the lensing cluster A2218 (z=0.175). A well-constrained mass model for the cluster, which incorporates the outcome of recent Keck spectroscopic campaigns, suggests that the triple syste…
A Composite Extreme-Ultraviolet QSO Spectrum from FUSE
Green, Richard F.; Shull, J. Michael; Scott, Jennifer E. +4 more
The Far Ultraviolet Spectroscopic Explorer (FUSE) has surveyed a large sample (>100) of active galactic nuclei (AGNs) in the low-redshift universe (z<1). Its response at short wavelengths makes it possible to measure directly the far-ultraviolet spectral properties of quasi-stellar objects (QSOs) and Seyfert 1 galaxies at z<0.3. Using arc…
ILCT: Recovering Photospheric Velocities from Magnetograms by Combining the Induction Equation with Local Correlation Tracking
Welsch, B. T.; Fisher, G. H.; Abbett, W. P. +1 more
We present three methods for deriving the velocity field in magnetized regions of the Sun's photosphere. As a preliminary step, we introduce a Fourier-based local correlation tracking (LCT) routine that we term ``FLCT.'' By explicitly employing the observation made by Démoulin & Berger, that results determined by LCT applied to magnetograms in…