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A Snapshot Survey for Gravitational Lenses among z>=4.0 Quasars. I. The z>5.7 Sample
Strauss, Michael A.; Brinkmann, J.; Fan, Xiaohui +7 more
Over the last few years, the Sloan Digital Sky Survey (SDSS) has discovered several hundred quasars with redshift between 4.0 and 6.4. Including the effects of magnification bias, one expects a priori that an appreciable fraction of these objects are gravitationally lensed. We have used the Advanced Camera for Surveys on the Hubble Space Telescope…
Long-term variability in the X-ray emission of RX J0720.4-3125
de Vries, C. P.; Vink, J.; Verbunt, F. +1 more
We detect a gradual, long-term change in the shape of the X-ray spectrum of the isolated neutron star RX J0720.4-3125, such that the spectrum of the source can no longer be described as a blackbody spectrum. The change is accompanied by an energy-dependent change in the pulse profile. If the X-ray emission is influenced by the magnetic field of th…
Evidence of Magnetic Reconnection along Coronal Hole Boundaries
Doyle, J. G.; Madjarska, M. S.; van Driel-Gesztelyi, L.
The present study reveals for the first time the existence of bidirectional jets, which are a signature of magnetic reconnection, occurring along coronal hole boundaries. The Solar Ultraviolet Measurement of Emitted Radiation spectrometer observations obtained in the N IV 765.15 Å (1.3×105 K) and Ne VIII 770.42 Å (6×105 K) em…
Properties of the background of EPIC-pn onboard XMM-Newton
Freyberg, M. J.; Matsushita, K.; Takahashi, I. +2 more
We have investigated the background properties of EPIC-pn onboard XMM-Newton to establish the background subtraction method. Count rates of the background vary violently by two orders of magnitude at the maximum, while during the most quiet period, these are stable within 8% at a 1σ level. The overall spectrum is dominated by particle events above…
The dust environment of comet 67P/Churyumov-Gerasimenko
Rauer, H.; Fulle, M.; Barbieri, C. +4 more
The new target of the ESA Rosetta Mission is comet 67P/Churyumov-Gerasimenko, which passed its last perihelion on 18 August 2002 and was well observed from fall 2002 to spring 2003. Its most prominent feature was a thin dust tail, which is best fitted by the Neck-Line model. Fits of the whole tail provide the dust environment of 67P during a year …
Chandra Observations of the Three Most Metal Deficient Blue Compact Dwarf Galaxies Known in the Local Universe, SBS 0335-052, SBS 0335-052W, and I Zw 18
Bauer, Franz E.; Thuan, Trinh X.; Izotov, Yuri I. +1 more
We present an X-ray study of the three most metal deficient blue compact dwarf (BCD) galaxies known in the local universe, based on deep Chandra observations of SBS 0335-052 (0.025 Zsolar), SBS 0335-052W (0.02 Zsolar), and I Zw 18 (0.02 Zsolar). All three are detected, with more than 90% of their X-ray emission ari…
On the light echo in V838 Mon
Tylenda, R.
We present a theoretical outline of the light echo phenomenon and results of simple numerical simulations and we study the available images of the light echo in V838 Mon obtained with HST. An investigation of the observed expansion of the light echo leads us to conclude that the distance to V838 Mon is ⪆5 kpc. From an analysis of the inner bright …
The Iron Unresolved Transition Array in Active Galactic Nuclei
Netzer, Hagai
The unresolved transition array (UTA) of iron M-shell ions is a prominent absorption feature in the X-ray spectrum of many active galactic nuclei (AGNs). Modeling photoionized plasmas in an attempt to match the observed silicon and oxygen lines fails to predict the level of ionization of iron as inferred by this feature. It is suggested that the d…
Jupiter's Atmospheric Composition from the Cassini Thermal Infrared Spectroscopy Experiment
Smith, M. D.; Strobel, D. F.; Lellouch, E. +39 more
The Composite Infrared Spectrometer observed Jupiter in the thermal infrared during the swing-by of the Cassini spacecraft. Results include the detection of two new stratospheric species, the methyl radical and diacetylene, gaseous species present in the north and south auroral infrared hot spots; determination of the variations with latitude of a…
Hubble Space Telescope Observations of the Main Sequence of M4
Stetson, P. B.; Rich, R. M.; Shara, M. +8 more
We present new results from a photometric study of the main-sequence stars in M4 (NGC 6121=C1620-264), the closest globular cluster to the Sun. Multifield, multiepoch observations at approximately 1, 2, and 6 core radii were obtained with WFPC2 on the Hubble Space Telescope through either the F606W filter or the F555W (V) and F814W (I) filters. Th…