Search for gravitational lensing in a sample of highly luminous quasars

in Kayser, R.; Schramm, T.; Nieser, L. (Eds.) Proceedings of the Hamburg conference on ’Gravitational Lenses’, Lecture Notes in Physics 406 (1992)

The status of the ESO survey for gravitational lensing among highly luminous quasars (HLQs) is briefly reviewed. The statistics of lensing, both concerning the multiple images and the associations of ... [more ▼]

The status of the ESO survey for gravitational lensing among highly luminous quasars (HLQs) is briefly reviewed. The statistics of lensing, both concerning the multiple images and the associations of galaxies with quasars, are examined. We find a significant overdensity of galaxies very close to the line-of-sight to the HLQs. We also report the discovery of a new multiply lensed quasar candidate. [less ▲]

The Search for Low-mass Companions of B Stars in the Carina Nebula Cluster Trumpler 16

in Astrophysical Journal. Supplement Series (2011), 194

We have developed lists of likely B3-A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of η Car, an appropriate V and B - V ... [more ▼]

We have developed lists of likely B3-A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of η Car, an appropriate V and B - V combination, and proper motion (where available). Color and magnitude cuts have been made assuming an E(B - V) = 0.55 mag ± 0.1, which is a good approximation close to the center of Trumpler 16. These lists have been cross-correlated with X-ray sources found in the Chandra Carina Complex Project. Previous studies have shown that only very rarely (if at all) do late main-sequence B stars produce X-rays. We present evidence that the X-ray-detected sources are binaries with low-mass companions, since stars less massive than 1.4 M [SUB]sun[/SUB] are strong X-ray sources at the age of the cluster. Both the median X-ray energies and X-ray luminosities of these sources are in good agreement with values for typical low-mass coronal X-ray sources. We find that 39% of the late B stars based on a list with proper motions have low-mass companions. Similarly, 32% of a sample without proper motions have low-mass companions. We discuss the X-ray detection completeness. These results on low-mass companions of intermediate-mass stars are complementary to spectroscopic and interferometric results and probe new parameter space of low-mass companions at all separations. They do not support a steeply rising distribution of mass ratios to low masses for intermediate-mass (5 M [SUB]sun[/SUB]) primaries, such as would be found by random pairing from the initial mass function. Based on observations made with the Chandra X-ray Observatory. [less ▲]

A search for quasars in a field around NGC 520

in Monthly Notices of the Royal Astronomical Society (1990), 245

An objective-prism search for quasars was performed in a field around the galaxy NGC 520. The automated quasar detection software has been applied, and a sample of 175 highly rated quasar candidates has ... [more ▼]

An objective-prism search for quasars was performed in a field around the galaxy NGC 520. The automated quasar detection software has been applied, and a sample of 175 highly rated quasar candidates has been selected. The two- and three-dimensional distributions of the candidates have been analyzed. The distribution on the celestial sphere turns out to be nonrandom. The deviations from randomness are both a tendency to exhibit anticorrelation at the scale of a few arcmin and a significant excess of objects at separations of about 20 arcmin. Finally, in order to test the claims by Arp and Duhalde (1985) that an excess of quasars exists near NGC 520 and that there is a preferential NE-SW alignment of bright quasars across this amorphous galaxy, various statistical analyses of the distribution of the high-grade quasar candidates with respect to NGC 520 were performed. No sign of any possible relation is present in the data. [less ▲]

A Search for Rotationally Modulated Halpha Variability in OB Supergiants

in Stellar Rotation (2004, June 01)

Not Available

A Search for Water Vaporization on Ceres

in Astronomical Journal (The) (2011), 142

There are hints that the dwarf planet (1) Ceres may contain a large amount of water ice. Some models and previous observations suggest that ice could be close enough to the surface to create a flux of ... [more ▼]

There are hints that the dwarf planet (1) Ceres may contain a large amount of water ice. Some models and previous observations suggest that ice could be close enough to the surface to create a flux of water outward through the regolith. This work aims to confirm a previous detection of OH emission off the northern limb of Ceres with the International Ultraviolet Explorer (IUE). Such emission would be evidence of water molecules escaping from the dwarf planet. We used the Ultraviolet and Visual Echelle Spectrograph of the Very Large Telescope to obtain spectra off the northern and southern limbs of Ceres at several epochs. These spectra cover the 307-312 nm wavelength range corresponding to the OH (0,0) emission band, which is the brightest band of this radical, well known in the cometary spectra. These new observations, five times more sensitive than those from IUE, did not permit detection of OH around Ceres. We derive an upper limit for the water production of about ~7 × 10[SUP]25[/SUP] molecules s[SUP]-1[/SUP] and estimate the minimum thickness of the dust surface layer above the water ice layer (if present) to be about 20 m. . [less ▲]

A search for X-ray sources around WR 22 in the Carina region

in Astronomy and Astrophysics (2011), 525

We present the results of a deep search for X-ray sources in a circular field of 30' in diameter situated around WR 22 in the Carina region and observed with the XMM-Newton observatory. This field is ... [more ▼]

We present the results of a deep search for X-ray sources in a circular field of 30' in diameter situated around WR 22 in the Carina region and observed with the XMM-Newton observatory. This field is broadly located to the west of the main part of the Carina nebula. On the basis of six pointings (nominal exposure time: 10 ks each) centred on the WR+O binary star WR 22, we perform a survey with an effective exposure time of 68.8 ks. We introduce a catalogue of 43 bona-fide X-ray point sources, most of which were unknown before the XMM-Newton observations, and perform the first steps towards their identifications by cross-correlating the positions with optical/infrared catalogues. We investigated the possible variability of these sources in the X-ray domain and we extracted a few X-ray spectra for the brightest ones. A short description of the diffuse X-ray emission present in the region is also given. Based on observations with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). [less ▲]

Searching and oviposition behavior of aphidophagous hoverflies (Diptera: Syrphidae): a review

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2009), 13(3), 467-481

Aphidophagous hoverflies forage according two different host-finding mechanisms: they forage for suitable food sources (for their energy-expensive hovering flight, and for protein to mature their ... [more ▼]

Aphidophagous hoverflies forage according two different host-finding mechanisms: they forage for suitable food sources (for their energy-expensive hovering flight, and for protein to mature their reproductive system), and for suitable oviposition sites. Syrphids are highly mobile, enabling them to lay eggs over large areas, and to locate aphid colonies earlier in the season than other aphidophaga. The result is that most syrphid eggs tend to be laid close to aphid colonies. The choice of oviposition sites may be crucial for offspring performance because the neonate larvae have limited dispersal ability. Selection of aphid patches should therefore reflect nutritional value, risk of predation and competition pressure. Several factors are known to affect the choice of oviposition site: habitat, host plant, aphid species, aphid availability, semiochemicals, the presence of intra-or interspecific competitors and female age. We review here the available information on these factors in order to understand the mechanisms of decision-making by syrphid females during their egg-laying behavior, a crucial aspect of their effective use in strategies of the biological control of aphids. [less ▲]

Searching for Colliding-Wind Signatures in a Sample of O-Star Binaries

in Interacting Winds from Massive Stars (2002)

Not Available

Searching for faint companions with VLTI/PIONIER. I. Method and first results

in Astronomy and Astrophysics (2011), 535

Context. A new four-telescope interferometric instrument called PIONIER has recently been installed at VLTI. It provides improved imaging capabilities together with high precision. <BR /> Aims: We search ... [more ▼]

Context. A new four-telescope interferometric instrument called PIONIER has recently been installed at VLTI. It provides improved imaging capabilities together with high precision. <BR /> Aims: We search for low-mass companions around a few bright stars using different strategies, and determine the dynamic range currently reachable with PIONIER. <BR /> Methods: Our method is based on the closure phase, which is the most robust interferometric quantity when searching for faint companions. We computed the χ[SUP]2[/SUP] goodness of fit for a series of binary star models at different positions and with various flux ratios. The resulting χ[SUP]2[/SUP] cube was used to identify the best-fit binary model and evaluate its significance, or to determine upper limits on the companion flux in case of non-detections. <BR /> Results: No companion is found around <ASTROBJ>Fomalhaut</ASTROBJ>, <ASTROBJ>tau Cet</ASTROBJ> and <ASTROBJ>Regulus</ASTROBJ>. The median upper limits at 3σ on the companion flux ratio are respectively of 2.3 × 10[SUP]-3[/SUP] (in 4 h), 3.5 × 10[SUP]-3[/SUP] (in 3 h) and 5.4 × 10[SUP]-3[/SUP] (in 1.5 h) on the search region extending from 5 to 100 mas. Our observations confirm that the previously detected near-infrared excess emissions around Fomalhaut and tau Cet are not related to a low-mass companion, and instead come from an extended source such as an exozodiacal disk. In the case of <ASTROBJ>del Aqr</ASTROBJ>, in 30 min of observation, we obtain the first direct detection of a previously known companion, at an angular distance of about 40 mas and with a flux ratio of 2.05 × 10[SUP]-2[/SUP] ± 0.16 × 10[SUP]-2[/SUP]. Due to the limited u,v plane coverage, its position can, however, not be unambiguously determined. <BR /> Conclusions: After only a few months of operation, PIONIER has already achieved one of the best dynamic ranges world-wide for multi-aperture interferometers. A dynamic range up to about 1:500 is demonstrated on unresolved targets, but significant improvements are still required to reach the ultimate goal of directly detecting hot giant extrasolar planets. Based on observations obtained at the European Southern Observatory (ESO) Very Large Telescope Interferometer (VLTI), Paranal, Chile. [less ▲]

Searching the Latin texts with Hyperbase and TXM

Scientific conference (2011)