Search Publications
Discovery of the Narrow-Line Seyfert 1 Galaxy Markarian 335 in a Historical Low X-Ray Flux State
Gallo, Luigi C.; Grupe, Dirk; Komossa, Stefanie
We report the discovery of the narrow-line Seyfert 1 galaxy Mrk 335 in an extremely low X-ray state. A comparison of Swift observations obtained in 2007 May and June/July with all previous X-ray observations between 1971 and 2006 show the AGN to have diminished in flux by a factor of more than 30, the lowest X-ray flux Mrk 335 has ever been observ…
On the Evolution of Coronal Mass Ejections in the Interplanetary Medium
Webb, D. F.; Fry, C. D.; Howard, T. A. +1 more
Two coronal mass ejections (CMEs) are presented which were tracked through the LASCO field of view (FOV) within 30 Rsolar and later as interplanetary CMEs (ICMEs) through the SMEI FOV from 80 to 150 Rsolar. They were also associated with erupting filaments observed by EIT, providing information on trajectory of propagation. T…
The Eruption from a Sigmoidal Solar Active Region on 2005 May 13
Liu, Chang; Wang, Haimin; Yurchyshyn, Vasyl +4 more
This paper presents a multiwavelength study of the M8.0 flare and its associated fast halo CME that originated from a bipolar NOAA AR 10759 on 2005 May 13. The source active region has a conspicuous sigmoid structure at the TRACE 171 Å channel as well as in the SXI soft X-ray images, and we mainly concern ourselves with the detailed process of the…
The Spitzer Survey of the Small Magellanic Cloud: Discovery of Embedded Protostars in the H II Region NGC 346
Stanimirović, Snežana; Bolatto, Alberto D.; Simon, Joshua D. +6 more
We use Spitzer Space Telescope observations from the Spitzer Survey of the Small Magellanic Cloud (S3MC) to study the young stellar content of N66, the largest and brightest H II region in the SMC. In addition to large numbers of normal stars, we detect a significant population of bright, red infrared sources that we identify as likely …
Metallicity and Ionization in High-Velocity Cloud Complex C
Shull, J. Michael; Giroux, Mark L.; Collins, Joseph A.
We analyze HST and FUSE ultraviolet spectroscopic data for 11 sight lines passing through the infalling high-velocity cloud (HVC) Complex C. These sight lines pass through regions with H I column densities in the range NHI=1018.1-1020.1 cm-2. From [O I/H I] abundances, we find that Complex C metallicitie…
The Leo Elliptical NGC 3379: A Metal-Poor Halo Emerges
Layden, Andrew C.; Harris, William E.; Wehner, Elizabeth M. H. +1 more
We have used the ACS camera on HST to obtain (V, I) photometry for 5300 red giant stars in the halo of the dominant Leo group member NGC 3379, a galaxy usually regarded as a classic normal giant elliptical. We use this data to derive the metallicity distribution function (MDF) for its outer-halo field stars at a location centered 33 kpc from the g…
Superresolving Distant Galaxies with Gravitational Telescopes: Keck Laser Guide Star Adaptive Optics and Hubble Space Telescope Imaging of the Lens System SDSS J0737+3216
Treu, Tommaso; Gavazzi, Raphaël; Marshall, Philip J. +13 more
We combine high-resolution images in four optical/infrared bands, obtained with the laser guide star adaptive optics (LGSAO) system on the Keck telescope and with the Hubble Space Telescope (HST), to study the gravitational lens system SDSS J0737+3216 (lens redshift 0.3223, source redshift 0.5812). We show that (under favorable observing condition…
A Keck Spectroscopic Survey of MS 1054-03 (z = 0.83): Forming the Red Sequence
Franx, Marijn; Kelson, Daniel D.; Illingworth, Garth D. +4 more
Using a magnitude-limited, spectroscopic survey of the X-ray-luminous galaxy cluster MS 1054-03, we isolate 153 cluster galaxies and measure MS 1054's redshift and velocity dispersion to be z=0.8307+/-0.0004 and σz=1156+/-82 km s-1. The absorption-line, poststarburst (``E+A''), and emission-line galaxies, respectively, make u…
Shock Heating in the Nearby Radio Galaxy NGC 3801
Hardcastle, M. J.; Croston, J. H.; Kraft, R. P.
We report the Chandra detection of shock-heated shells of hot gas surrounding the radio lobes of the nearby (DL~53 Mpc) low-power radio galaxy NGC 3801. The shells have temperatures of 1 and 0.7 keV, compared to an ISM temperature of 0.23 keV. The estimated expansion speed of the shells is ~850 km s-1, corresponding to a Mach…
The Solar Eclipse of 2006 and the Origin of Raylike Features in the White-Light Corona
Koutchmy, S.; Sheeley, N. R., Jr.; Wang, Y. -M. +3 more
Solar eclipse observations have long suggested that the white-light corona is permeated by long fine rays. By comparing photographs of the 2006 March 29 total eclipse with current-free extrapolations of photospheric field measurements and with images from the Solar and Heliospheric Observatory (SOHO), we deduce that the bulk of these linear featur…