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…
The XMM-Newton view of three X-ray weak quasars: Iron emission and strong ionized absorption
Clavel, J.; Guainazzi, M.; Schartel, N. +4 more
We present the analysis of XMM-Newton observations of three X-ray weak quasars: PG 1001+054, PG 1535+547 and PG 2112+059. All objects are absorbed by ionized material showing high column densities, NH = 2.9 × 1022~cm-2 to NH = 1.9 × 1023~cm-2, and ionization parameters, ξ = 147 ~erg…
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…
Determination of Cepheid parameters by light-curve template fitting
Berdnikov, L. N.; Tanvir, N. R.; Ngeow, C. C. +3 more
We describe techniques to characterize the light curves of regular variable stars by applying principal component analysis (PCA) to a training set of high-quality data, and to fit the resulting light-curve templates to sparse and noisy photometry to obtain parameters such as periods, mean magnitudes etc. The PCA approach allows us to efficiently r…
CORONAS-F/SPIRIT EUV observations of October-November 2003 solar eruptive events in combination with SOHO/EIT data
Grechnev, V. V.; Chertok, I. M.; Kuzin, S. V. +6 more
The extraordinary solar activity of October-November 2003 manifested itself in many powerful eruptive events, including large coronal mass ejections (CMEs) and extremely powerful flares. A number of major events were accompanied by practically all known phenomena of the solar activity, both local and large-scale, and caused severe space weather di…
Exploring the structure of galaxy clusters: XMM-Newton observations of the REFLEX-DXL clusters at z ∼ 0.3
Zhang, Y. -Y.; Finoguenov, A.; Böhringer, H. +5 more
The precise determination of global properties of galaxy clusters, and their scaling relations, is a task of prime importance for the use of clusters as cosmological probes. We performed a detailed XMM-Newton study of 14 X-ray luminous REFLEX Survey clusters at z ∼ 0.3. We found that the properties of the galaxy clusters show a self-similar behavi…
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…
The calm after the storm: XMM-Newton observation of SGR 1806-20 two months after the Giant Flare of 2004 December 27
Tiengo, A.; Mereghetti, S.; Stella, L. +5 more
XMM-Newton observed the soft gamma repeater SGR 1806-20 about two months after its 2004 December 27 giant flare. A comparison with the previous observations taken with the same instrument in 2003-2004 shows that the pulsed fraction and the spin-down rate have significantly decreased and that the spectrum slightly softened. These changes may indica…