Search Publications
Testing three derivative methods of stellar population synthesis models
Han, Zhanwen; Zhang, Yu; Liu, Jinzhong +2 more
The number of methods used to study the properties of galaxies is increasing, and it is very important to test these methods. Galactic globular clusters (GCs) provide an excellent medium for such tests, because they can be considered as simple stellar populations. We present ages and metallicities for 40 Galactic GCs as determined from three publi…
On the cooling trend of SGR 0526-66
Göǧüş, Ersin; Güver, Tolga; Özel, Feryal
We present a systematic analysis of all archival Chandra observations of the soft gamma repeater SGR 0526-66. Our results show that the X-ray flux of SGR 0526-66 decayed by about 20 per cent between 2000 and 2009. We employ physically motivated X-ray spectral models and determine the effective temperature and the strength of the magnetic field at …
The distribution of metals in hot DA white dwarfs
Barstow, M. A.; Hubeny, I.; Dickinson, N. J.
The importance to stellar evolution of understanding the metal abundances in hot white dwarfs is well known. Previous work has found the hot DA white dwarfs REJ 1032+532, REJ 1614-085 and GD 659 to have highly abundant, stratified photospheric nitrogen, due to the narrow absorption-line profiles of the far-ultraviolet (FUV) N V doublet and the lac…
INTEGRAL and Swift/XRT observations of IGR J18179-1621
Torres, D. F.; Papitto, A.; Zhang, S. +3 more
IGR J18179-1621 is a hard X-ray binary transient discovered recently by INTEGRAL. Here we report on detailed timing and spectral analysis of IGR J18179-1621 in X-rays based on available INTEGRAL and Swift data. From the INTEGRAL analysis, IGR J18179-1621 is detected with a significance of 21.6σ in the 18-40 keV band by ISGRI and 15.3σ in the 3-25 …
The characterization of the distant blazar GB6 J1239+0443 from flaring and low activity periods
Costa, E.; Mereghetti, S.; Barbiellini, G. +64 more
In 2008, AGILE and Fermi detected gamma-ray flaring activity from the unidentified EGRET source 3EG J1236+0457, recently associated with a flat spectrum radio quasar (GB6 J1239+0443) at z = 1.762. The optical counterpart of the gamma-ray source underwent a flux enhancement of a factor of 15-30 in six years, and of ∼10 in six months. We interpret t…
Exploring the effects of high-velocity flows in abundance determinations in H II regions: bidimensional spectroscopy of HH 204 in the Orion nebula
García-Rojas, J.; Mesa-Delgado, A.; Luridiana, V. +3 more
We present results from integral field optical spectroscopy with the Potsdam Multi-Aperture Spectrograph of the Herbig-Haro (HH) object HH 204, with a spatial sampling of 1 × 1 arcsec2. We have obtained maps of different emission lines, physical conditions and ionic abundances from collisionally excited lines. The ionization structure o…
The contribution of star-forming galaxies to fluctuations in the cosmic background light
Efstathiou, G.; Kim, Han-Seek; Lacey, C. G. +3 more
Star-forming galaxies which are too faint to be detected individually produce intensity fluctuations in the cosmic background light. This contribution needs to be taken into account as a foreground when using the primordial signal to constrain cosmological parameters. The extragalactic fluctuations are also interesting in their own right as they d…
Hydrogen two-photon continuum emission from the Horseshoe filament in NGC 1275
Fabian, A. C.; Ferland, G. J.; Johnstone, R. M. +5 more
Far-ultraviolet emission has been detected from a knot of Hα emission in the Horseshoe filament, far out in the NGC 1275 nebula. The flux detected relative to the brightness of the Hα line in the same spatial region is very close to that expected from hydrogen two-photon continuum emission in the particle heating model of Ferland et al. if reddeni…
The ballistic transport instability in Saturn's rings - I. Formalism and linear theory
Ogilvie, Gordon I.; Latter, Henrik N.; Chupeau, Marie
Planetary rings sustain a continual bombardment of hypervelocity meteoroids that erode the surfaces of ring particles on time-scales of 105-107 years. The debris ejected from such impacts re-accretes on to the ring, though often at a slightly different orbital radius from the point of emission. This 'ballistic transport' lead…
Constraints on fast ejecta in the Crab supernova remnant from optical spectral lines
Lundqvist, P.; Tziamtzis, A.
The low kinetic energy and mass of the Crab supernova remnant challenge our understanding of core-collapse supernova explosions. A possibility is that the Crab nebula is surrounded by a shell of fast ejecta containing the ‘missing’ kinetic energy and mass. The only direct evidence for such a fast shell comes from an absorption feature in the Crab …