Search Publications
The Discovery of a High-Redshift X-Ray-Emitting QSO Very Close to the Nucleus of NGC 7319
Zibetti, Stefano; Burbidge, E. M.; Galianni, Pasquale +3 more
A strong X-ray source only 8" from the nucleus of the Seyfert 2 galaxy NGC 7319 in Stephan's Quintet has been discovered by Chandra. We have identified the optical counterpart and show that it is a QSO with ze=2.114. It is also an ultraluminous X-ray source with LX=1.5×1040 ergs s-1. From the optical spe…
Predicted and Empirical Radii of RR Lyrae Stars
Marconi, M.; Bono, G.; Caputo, F. +2 more
We present new theoretical period-radius-metallicity relations for RR Lyrae stars. Current predictions are based on a large set of nonlinear, convective models that cover a broad range of chemical abundances and input parameters. We also provide new and homogeneous estimates of angular diameters for a sample of field RR Lyrae stars using a recent …
To Be or Not to Be: Very Young Globular Clusters in M31
Matthews, Keith; Cohen, Judith G.; Cameron, P. Brian
We present observations made with the newly commissioned Keck laser guide star adaptive optics (LGSAO) system of six objects in M31 that are alleged in multiple recent studies to be young globular clusters (GCs); all are supposed to have ages <=5 Gyr. The resulting FWHM of the PSF core in our images is ~70 mas. The four youngest of these object…
A HST Study of the Stellar Populations in the Cometary Dwarf Irregular Galaxy NGC 2366
Thuan, Trinh X.; Izotov, Yuri I.
We present V and I photometry of the resolved stars in the cometary dwarf irregular galaxy NGC 2366, using Wide Field Planetary Camera 2 images obtained with the Hubble Space Telescope. The resulting color-magnitude diagram reaches down to I~26.0 mag. It reveals not only a young population of blue main-sequence stars (age <~30 Myr) but also an …
UVCS Observation of Sungrazer C/2001 C2: Possible Comet Fragmentation and Plasma-Dust Interactions
Lamy, P.; Raymond, J. C.; Biesecker, D. A. +5 more
In this paper we analyze SOHO Ultraviolet Coronagraph Spectrometer (UVCS) observations of the sungrazing comet C/2001 C2, a member of the Kreutz family, observed on 2001 February 7 at heliocentric distances of 4.98 and 3.60 Rsolar. This comet apparently went through sequential fragmentation events along its path: further indication of f…
BIMA Millimeter-Wave Observations of the Core-Jet and Molecular Gas in the FR I Radio Galaxy NGC 3801
Baum, Stefi A.; O'Dea, Christopher P.; Vogel, Stuart N. +2 more
We present BIMA 3 mm observations of the radio continuum source and the molecular gas disk in the radio-loud Fanaroff and Riley type I (FR I) galaxy NGC 3801. We have detected a continuum source in the nucleus and determined that it has a flat millimeter-wave spectrum, suggesting that the emission is nonthermal and due to an AGN; the radio core is…
X-Ray and Optical Emission from Radio Hot Spots of Powerful Quasars
Maraschi, L.; Cheung, C. C.; Tavecchio, F. +4 more
In a survey with Chandra and HST of a sample of 17 radio sources with bright radio jets (16 powerful FR II and one nearby FR I), we detected X-ray and optical emission from a number of radio hot spots and lobes. Six hot spots on the near sides of powerful FR II galaxies (as determined from the jet asymmetry) were detected at X-rays, while none wer…
X-Ray Variability Characteristics of the Seyfert 1 Galaxy NGC 3783
Markowitz, A.
We have characterized the energy-dependent X-ray variability properties of the Seyfert 1 galaxy NGC 3783 using archival XMM-Newton and Rossi X-Ray Timing Explorer data. The high-frequency fluctuation power spectral density function (PSD) slope is consistent with flattening toward higher energies. Light-curve cross-correlation functions yield no si…
Properties of Remote Flare Ribbons Associated with Coronal Mass Ejections
Wang, Haimin
To understand the large-scale structure of flares and coronal mass ejections, we studied the motion and properties of remote flare ribbons of three major events: 2003 May 27 X1.3, 2000 November 24 X1.8, and 2000 November 25 X1.9 flares. The remote ribbons are in addition to the typical two-ribbon pairs in the flare cores. We found two common prope…
Nanodiamond Dust and the Far-Ultraviolet Quasar Break
Krongold, Yair; Morisset, Christophe; Binette, Luc +5 more
We explore the possibility that the steepening observed shortward of 1000 Å in the energy distribution of quasars may result from absorption by dust, being either intrinsic to the quasar environment or intergalactic. We find that a dust extinction curve consisting of nanodiamonds, composed of terrestrial cubic diamonds or with surface impurities a…