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New high-sensitivity, milliarcsecond resolution results from routine observations of lunar occultations at the ESO VLT
Context. Lunar occultations (LO) are a very efficient and powerfultechnique that achieves the best combination of high angular resolutionand sensitivity possible today at near-infrared wavelengths. Given thatthe events are fixed in time, that the sources are occulted randomly,and that the telescope use is minimal, the technique is very well suitedfor service mode observations. Aims: We have established aprogram of routine LO observations at the VLT observatory, especiallydesigned to take advantage of short breaks available in-between otherprograms. We have used the ISAAC instrument in burst mode, capable ofproducing continuous read-outs at millisecond rates on a suitablesubwindow. Given the random nature of the source selection, our aim hasbeen primarily the investigation of a large number of stellar sources atthe highest angular resolution in order to detect new binaries.Serendipitous results such as resolved sources and detection ofcircumstellar components were also anticipated. Methods: We haverecorded the signal from background stars for a few seconds, around thepredicted time of occultation by the Moon's dark limb. At millisecondtime resolution, a characteristic diffraction pattern can be observed.Patterns for two or more sources superimpose linearly, and this propertyis used for the detection of binary stars. The detailed analysis of thediffraction fringes can be used to measure specific properties such asthe stellar angular size and the presence of extended light sources suchas a circumstellar shell. Results: We present a list of 191 starsfor which LO data could be recorded and analyzed. Results include thedetection of 16 binary and 2 triple stars, all but one of which werepreviously unknown. The projected angular separations are as small as 4milliarcsec and magnitude differences as high as ? K = 5.8 mag.Additionally we derive accurate angular diameters for 2 stars andresolve circumstellar emission around another one, also all for thefirst time. We have established upper limits on the angular size of 177stars, mostly in the 1 to 5 mas range, and we plan to include them in afuture list of sources well suited for the calibration ofinterferometers. Conclusions: We confirm the performance of thetechnique already established in our previous work. LO at an 8 m-classtelescope can achieve an angular resolution close to 0farcs001 with asensitivity K ? 12 mag.Based on observations made with ESO telescopes at Paranal Observatory.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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