... Observing . ... Solar Observing . ... April 3 (SUN) - Solar Observing, Central Park , Manhattan . ... APRIL'S SKY . ... Lecture Series at the American Museum of Natural History The Amateur Astronomers Association is proud to present an astronomy lecture series from October through May each year for our members and the .. ... The€аAmateur Astronomers Association of New York€аwas organized in 1927 to promote the study of Astronomy, emphasizing its cultural and inspirational value. ...

... This paper discusses evidence for and properties of disks associated to brown dwarfs in the star-forming region rho-Oph. ... We present low-resolution near-infrared spectra in the J, H and K bands, and determine for each source spectral type, extinction, effective temperature a nd luminosity by comparing the spectra to those of field dwarfs and to the most recent model stellar atmospheres. ... The coolest object in our sample has mass in the range 8-12 Mjup (0.008-0.012 Msun). ...

... Using a simple 2-D Gaussian Point Spread Function (PSF) on a constant (flat) sky background, I derive a theoretical photometric and astrometric performance model for analytical and digital PSF-fitting stellar photometry. ... The photometric performance is maximized when either the effective background area or the effective-background-level measurement error is minimized. ... An important, but frequently ignored, noise source is the uncertainty of the measurement of the effective background level ( )...

We review the evidence, from rotational modulation, for association of plages and spots on active binaries. ... There is a similar lack of evidence for BY Dra systems. The results can be interpreted as evidence for: (a) the presence of active longitudes which persist on some RS CVn stars for several years, (b) high filling factors in MgII emission and (c) lower filling factors, and therefore greater contrast, in SWP emission. ...

... Early studies of PMS stars focused on T associations, especially Taurus-Auriga. However, one might expect low mass star formation to be different in OB associations. ... He identified Orion OB1a as the stars northwest of the belt. Orion OB1b is composed of the stars near the belt, including the belt stars and Orionis. ... He finds no perceptible distance change within the Orion OB1b association and finds the distance modulus to be 7.8 and 7.9 for Orion OB1a and OB1b respectively. ...

... The normal m 1 , c 1 indices and metallicities have been calculated for 2472 F-stars from the uvby and H fotometry. ... It is shown that the metallicity distribution of F6-G0 dwarfs is not a Gaussian one, but may be considered as a sum of two normal distributions. At the centre, the distribution shows a gap which subdivides all the stars into two metallicity groups. ... По данным uvby , H - фотометрии вычислены нормальные индексы m 1 , c 1 и определена металличность 2472 F-зыезд. ...

... The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s -1 . ... 1S We present a summary of an identification program of the more than 2000 X-ray sources detected during the ROSAT All-Sky Survey (Voges et al. 1999) at high galactic latitude, |b| > 30degr , with countrate above 0.2 s -1 . This program, termed the ROSAT Bright Survey RBS, is to more than 99.5% complete. ...