%R 2000A&AS..145..187C
%J-195
%A Chavarria-K C.
%A Terranegra L.
%A Moreno-Corral M.A.
%A de Lara E.
%T Photometric observations of weak-line T Tauri stars. II. WTTS in Taurus-Auriga, Orion and Scorpius OB2-2.
%M ds1711
%F 2000.07.25
%B We present uvby-{beta} photometry of 116 X-ray flux-selected active stars in the directions of the Orion (40), Taurus-Auriga (58) and Scorpius OB2-2 (18) star forming regions. Additionally, we give near IR JHK photometry of 20 active stars in the Taurus-Auriga direction. The program stars were selected from the ROSAT All Sky Survey and EINSTEIN X-ray surveys and are spectroscopically confirmed weak-line T Tauri stars and weak-line T Tauri star candidates. The photometry confirms
the young nature of the program stars and also indicates that a significant fraction of the sample could be foreground objects. The data given here probably represent the largest homogeneous uvby-{beta} photometric sample of new WTTS and WTTS candidates. Many objects in the sample are observed photometrically for the first time.
%K stars: activity - stars: evolution - stars: pre-main sequence

%R 2000A&AS..145..197B
%J-214
%A Brandi E.
%A Garcia L.G.
%A Piirola V.
%A Scaltriti F.
%A Quiroga C.
%T Linear polarization of a group of symbiotic systems.
%M ds9671
%F 2000.07.25
%B We report linear polarization measurements of a set of symbiotic stars, made at several epochs during the period 1994-1998. Evidence of intrinsic polarization is looked for from the wavelength dependence of the polarization degree and position angle in UBVRI bands. The results have also been analysed to search for temporal variability of polarization. Several objects have shown a polarization spectrum different from that produced by interstellar dust grains and/or
polarimetric variations on time scales as short as several days or months, indicating the presence of polarization component of circumstellar origin.
%K stars: binaries: symbiotic - stars: binaries eclipsing - stars: variable stars - polarization

%R 2000A&AS..145..215P
%J-222
%A Pourbaix D.
%T Resolved double-lined spectroscopic binaries: A neglected source of hypothesis-free parallaxes and stellar masses.
%M ds9259
%F 2000.07.25
%B Double-lined spectroscopic binaries, once visually resolved (VB-SB2), provide hypothesis-free orbital parallaxes and masses of both components. Unlike eclipsing-spectroscopic binaries for which many accurate masses are already known (Andersen, 1991A&ARv...3...91A; Andersen, 1997, in Bedding T.R., Booth A.J., Davis J. (eds.), Fundamental Stellar Properties: The Interaction between Observation and Theory. Kluwer Academic Publishers), the number of VB-SB2 remains rather small. This paper presents 40 such systems for which published visual observations and radial velocities allow a simultaneous adjustment of both data sets. The precision of the
individual masses as well as the evolution of that precision with respect to the published precision is investigated.
%K methods: data analysis - stars: binaries: spectroscopic, visual; distances; fundamental parameters

%R 2000A&AS..145..223C
%J-228
%A Chen L.
%A Geffert M.
%A Wang J.J.
%A Reif K.
%A Braun J.M.
%T A proper motion study of the globular cluster M 10.
%M ds1790
%F 2000.07.25
%B We present the first proper motion study of M 10 (NGC 6254). Absolute proper motions of about 532 stars in the field of the globular cluster M 10 were determined with respect to Hipparcos and ACT reference stars. In addition to photographic plates of Bonn and Shanghai also wide field CCD observations as second epoch plates were used. The wide field CCD observations show an accuracy comparable to that of the photographic plates. A good coincidence of the solutions based on
reference stars from Hipparcos and from ACT was found. Our final proper motions allow a sufficient separation of cluster and field stars. Two population II Cepheids were confirmed to be members of M 10. The absolute proper motion of M 10 was determined and combined with its distance from the Sun and its radial velocity. The space motion and metallicity of M 10 indicates the characteristics of a halo object with an orbit reaching to a maximal z-distance of less than 3kpc.
%K astrometry - globular clusters: individual: M 10 - Galaxy: kinematics and dynamics

%R 2000A&AS..145..229F
%J-242
%A Froebrich D.
%A Meusinger H.
%T A search for LSB dwarf galaxies in the M81 group on digitally stacked Schmidt plates.
%M ds1831
%F 2000.07.25
%B We present a search for low surface brightness (LSB) dwarf galaxies in a region of 10 square degrees around M 81. The survey is based on the digital co-addition of Schmidt plates where algorithms for sub-arcsecond co-centering, quality-weighting and sigma-clipping ``bad pixel'' rejection are applied. The 3{sigma} surface brightness limit is {mu}_lim_=25.6mag/''^2^. In a substantial fraction of the surveyed area, the detection of LSB objects is limited by ``Galactic cirrus''
rather than by the limiting magnitude of the stacked image. Optimum search parameters for an automated detection of dwarf galaxies are derived from simulations. The final selection of LSB dwarf candidates relies on a combination of automated detection and visual inspection. We present six new dwarf galaxy candidates with {mu}_B_(0)>=23mag/''^2^. Photometric data and best fitting parameters for the exponential model are derived both for the new candidates and for some
previously known LSB dwarf galaxies in the field. For the most likely new dwarf member of the M81 group, a central surface brightness of {mu}_B_(0)=25.4mag/''^2^ and a scale-length of 0.3kpc are derived.
%K galaxies: clusters: individual: \objS{NAME M 81 GROUP}{M81 group} - galaxies: general - galaxies: photometry - galaxies: fundamental parameters

%R 2000A&AS..145..243K
%J-254
%A Kouwenhoven M.L.A.
%T Pulsars in the Westerbork Northern Sky Survey.
%M h2123
%F 2000.07.25
%B I have searched the Westerbork Northern Sky Survey (WENSS) source list for detections of known radio pulsars. A source with a flux density greater than five times the local noise level is found near the positions of 25 pulsars. The probability that one out of these 25 sources is a chance coincidence is about 10%. I have looked at the WENSS maps of the non-detected pulsars. A flux density between three and five times the local noise level is found near the positions of 14
of these non-detected pulsars. There is a 50 percent probability that (at least) one of these marginal detections is just a noise fluctuation. Fourteen radio pulsars, which according to earlier flux measurements have flux densities above three times the WENSS noise level, are not detected. Of the 39 pulsars detected in the WENSS 19 are also detected in the NRAO VLA Sky Survey (NVSS). By combining the WENSS and NVSS flux densities for these 19 pulsars spectral indices are
obtained that differ by up to 50% from the long term averaged values reported in the literature. This affects the reliability of pulsar candidates that are selected on the basis of their WENSS-NVSS spectral index.
%K pulsars: general - surveys - radio continuum: stars - scattering

%R 2000A&AS..145..255L
%J-261
%A Lopez-Gonzalez M.J.
%A Rodriguez E.
%T Lightcurves of 10 Hygiea, 241 Germania and 509 Iolanda.
%M ds1854
%F 2000.07.25
%B The asteroids 10 Hygiea, 241 Germania and 509 Iolanda have been studied photometrically. From their lightcurves, synodic periods of 27.63+/-0.02, 15.51+/-0.01 and 12.72+/-0.02 hours, and amplitudes of 0.28mag, 0.17mag and 0.45mag, have been deduced for 10 Hygiea, 241 Germania and 509 Iolanda, respectively. The period found for 241 Germania is a significant revision from one previously published, and we present a first indication of pole orientation and shape. A
synodic period is obtained for 509 Iolanda. The solution obtained for the sense of rotation, sidereal period, pole orientation and shape properties for 10 Hygiea confirms previous results.
%K minor planets, asteroids - techniques: photometric

%R 2000A&AS..145..263S
%J-267
%A Simien F.
%A Prugniel P.
%T Kinematical data on early-type galaxies. V.
%M ds1874
%F 2000.07.25
%B We present kinematical data for a sample of 26 galaxies. Rotation curves and velocity-dispersion profiles are determined for all objects. This is our fifth paper in a series devoted to the presentation of data on elliptical and S0 galaxies, derived from long-slit absorption spectroscopy; the series now gathers 119 galaxies with homogeneous data.
%K galaxies: elliptical & lenticular, cD - galaxies: kinematics and dynamics - galaxies: fundamental parameters - galaxies: general

%R 2000A&AS..145..269P
%J-274
%A Parthasarathy M.
%A Vijapurkar J.
%A Drilling J.S.
%T Low resolution spectroscopy of hot post-AGB candidates.
%M ds9644
%F 2000.07.25
%B Spectral types are determined from low resolution optical spectra of 40 IRAS sources with far-infrared colours similar to planetary nebulae. The presence of circumstellar dust, high galactic latitude, and early supergiant or giant spectral type, sometimes with emission in the Balmer lines, indicate that some of these stars are low mass stars in the post-AGB stage of evolution.
%K stars: AGB and post-AGB - stars: evolution - stars: early-type - stars: emission-line - stars: atmospheres

%R 2000A&AS..145..275N
%J-281
%A Nitschelm C.
%A Lecavelier des Etangs A.
%A Vidal-Madjar A.
%A Ferlet R.
%A Olsen E.H.
%A Dennefeld M.
%T A three-year Stroemgren photometric survey of suspected {beta} Pictoris-like stars.
%M ds9544
%F 2000.07.25
%B We carried out a Stroemgren photometric survey of thirteen southern bright stars, including {beta} Pictoris itself, during three years, d'Astrophysique de Paris, in order to detect possible weak photometric variations. {beta} Pictoris presents a small long-term variation with a change of brightness by -2.1x10^-3^ mag per year, over about two years from beginning of 1996, a situation relatively similar to the one about 18 years ago. Among the other stars, only HD 38392
presents weak photometric variations with a period of 21.4 days, probably related to the star rotation period. The negative result concerning photometric variations of all other stars suggests that those stars are actually really stable and strengthens the reality of the variations discovered in the case of {beta} Pictoris and HD 38392.
%K stars: \object{beta Pic} - circumstellar matter - planetary systems - Stroemgren photometry

%R 2000A&AS..145..283K
%J-292
%A Kiss L.L.
%A Szatmary K.
%A Szabo G.
%A Mattei J.A.
%T Multiperiodicity in semiregular variables. II. Systematic amplitude variations.
%M h2107
%F 2000.07.25
%B We present a detailed lightcurve analysis for a sample of bright semiregular variables based on long-term (70-90 years) visual magnitude estimates carried out by amateur astronomers. Fundamental changes of the physical state (amplitude and/or frequency modulations, mode change and switching) are studied with the conventional Fourier and wavelet analysis. The light curve of the carbon Mira Y Per showing a gradual amplitude decrease has been re-analysed after collecting and
adding current data to earlier ones. The time scales of the sudden change and convection are compared and their similar order of magnitude is interpreted to be a possible hint for strong coupling between pulsation and convection. The periods of the biperiodic low-amplitude light curve and their ratios suggest a pulsation in the first and third overtone modes. An alternative explanation of the observed behaviour could be a period halving due to the presence of weak chaos.
Beside two examples of repetitive mode changes (AF Cyg and W Cyg) we report three stars with significant amplitude modulations (RY Leo, RX UMa and RY UMa). A simple geometric model of a rotationally induced amplitude modulation in RY UMa is outlined assuming low-order nonradial oscillation, while the observed behaviour of RX UMa and RY Leo is explained as a beating of two closely separated modes of pulsation. This phenomenon is detected unambiguously in V CVn, too. The period
ratios found in these stars (1.03-1.10) suggest either high-order overtone or radial+non-radial oscillation.
%K stars: pulsation - stars: AGB

%R 2000A&AS..145..293E
%J-304
%A Ehgamberdiev S.A.
%A Baijumanov A.K.
%A Ilyasov S.P.
%A Sarazin M.
%A Tillayev Y.A.
%A Tokovinin A.A.
%A Ziad A.
%T The astroclimate of Maidanak Observatory in Uzbekistan.
%M ds1885
%F 2000.07.25
%B The atmospheric turbulence and meteorology of the Maidanak Observatory in Uzbekistan are reviewed. Night time seeing was measured during the period August 1996 - November 1999 with the ESO Differential Image Motion Monitor. The median zenith seeing (FWHM) for the entire period of observations is 0.69'' at 0.5 {mu}m. A maximum clear sky season for Maidanak is July - September, with about 90% of possible clear time and a median seeing of 0.69''. The best monthly median
seeing, 0.62'', is observed in November. The winter maximum of clear time is usually observed in February (up to 50%) with a FWHM of 0.77''. During an additional site testing campaign (9 nights) organized in July 1998, the median wavefront outer scale L_0_ of 25.9 m and a median isoplanatic angle {theta}_0_ of 2.48'' were measured with the Generalized Seeing Monitor developed at the University of Nice. The temporal evolution of the wavefront can be described by several layers
moving at slow velocities with predominant direction from the West. This corresponds to a remarkably large atmospheric time constant. No correlation between wavefront velocity and the wind velocity at ground level was found. The good seeing, large isoplanatic angle and, especially, slow wind, place Maidanak Observatory among the best international astronomical sites for high angular resolution observations by interferometry and adaptive optics.
%K atmospheric effects - site testing

%R 2000A&AS..145..305C
%J-310
%A Coude du Foresto V.
%A Faucherre M.
%A Hubin N.
%A Gitton P.
%T Using single-mode fibers to monitor fast Strehl ratio fluctuations. Application to a 3.6m telescope corrected by adaptive optics.
%M ds9289
%F 2000.07.25
%B The theory of starlight coupling into single-mode fibers is reviewed to show how i) the central obstruction in a telescope pupil deteriorates coupling efficiency much more than one would expect from the loss of collecting area, and ii) a single-mode fiber and a photometer can be used to monitor fast Strehl ratio fluctuations. This last point is illustrated with experimental data obtained at the 3.6m La Silla telescope corrected with the ADONIS adaptive optics system. A 37
x gain in coupling efficiency was demonstrated by turning on the adaptive optics system, but periodic fluctuations in the coupled signal revealed a vibration of the telescope tube that could not have been detected otherwise.
%K telescopes - techniques: interferometric, adaptive optics - instrumentation: large telescopes - optical fibers: single-mode - infrared: general

%R 2000A&AS..145..311B
%J-321
%A Boggs S.E.
%A Jean P.
%T Event reconstruction in high resolution Compton telescopes.
%M h2143
%F 2000.07.25
%B The development of germanium Compton telescopes for nuclear {gamma}-ray astrophysics (~0.2-20 MeV) requires new event reconstruction techniques to accurately determine the initial direction and energy of photon events, as well as to consistently reject background events. This paper describes techniques for event reconstruction, accounting for realistic instrument/detector performance and uncertainties. An especially important technique is Compton Kinematic Discrimination,
which allows proper interaction ordering and background rejection with high probabilities. The use of these techniques are crucial for the realistic evaluation of the performance and sensitivity of any germanium Compton telescope configuration.
%K gamma rays: observations - telescopes - techniques: spectroscopic - techniques: image processing - instrumentation: detectors

%R 2000A&AS..145..323M
%J-340
%A Mandolesi N.
%A Bersanelli M.
%A Burigana C.
%A Gorski K.M.
%A Hivon E.
%A Maino D.
%A Valenziano L.
%A Villa F.
%A White M.
%T On the performance of Planck-like telescopes versus mirror aperture.
%M ds9530
%F 2000.07.25
%B Future space mission like MAP and Planck will be able to shade new light on our knowledge of the Universe thanks to their unprecedented angular resolution and sensitivity. The far sub-degree angular resolution is obtained coupling usual detectors, radiometers and/or bolometers, to an optical system, namely a telescope. The wealth of cosmological information is encoded at high l values (~1000) which can be reached with resolution of about 10'. Distortions of the main beam
resulting from the current focal plane arrangement and the optical design of the Planck satellite will degrade angular resolution and sensitivity per resolution element possibly compromising the final results. The detailed design of the Planck telescope is continuously changing with the aim of optimizing its performance. In the present work we present a methodological study on the relation between telescope optical design, focal plane arrangement and optical performances,
focussing on the dependence of angular resolution on primary mirror aperture. Different independent approaches have been developed to quantify the impact of main beam distortions on cosmic microwave background (CMB) science yielding nearly the same results. The so-called PHASE-A telescope is unacceptable with respect mission main goals. Larger telescopes (namely with effective aperture > 1.5 m) are therefore preferable. This paper is based on the Planck LFI activities.
%K cosmology: cosmic microwave background - methods: data analysis - telescopes

%R 2000A&AS..145..341B
%J-350
%A Baudoz P.
%A Rabbia Y.
%A Gay J.
%A Burg R.
%A Petro L.
%A Bely P.
%A Fleury B.
%A Madec P.-Y.
%A Charbonnier F.
%T Achromatic interfero coronagraphy. II. Effective performance on the sky.
%M ds9360
%F 2000.07.25
%B We report on the first observation run with the Achromatic Interfero Coronagraph (AIC) developed at Observatoire de la Cote d'Azur, France. Observations took place during Fall 97 at Observatoire de Haute Provence, France, with the 1.52 m telescope equipped at that time with adaptive optics. The Achromatic Interfero Coronagraph (AIC) is an imaging device providing the extinction of a star so as to detect and to image faint features of its close environment. Extinction
results from a destructive interference process. Morphological features located as close to the star as the first angular Airy ring can be detected, thus breaking a limitation of the classical Lyot coronagraphs. The working spectral band was K. Observation results demonstrate the validity of the AIC approach with ground-based telescopes and illustrates close-sensing capabilities. After a short reminding of the principle of AIC, conditions of observations are reported and
first results are discussed. Finally, limitations are evaluated and expected results are compared with effective performance.
%K methods: observational - instrumentation: interferometers - atmospheric effects - stars: binaries: close

%R 2000A&AS..145..351R
%J-364
%A Royer P.
%A Manfroid J.
%A Gosset E.
%A Vreux J.-M.
%T Simulations of observations with the Optical Monitor of the X-ray Multi-Mirror Satellite.
%M ds9582
%F 2000.07.25
%B This paper addresses the question of the observations to be performed with the Optical Monitor (OM) of the X-ray Multi-Mirror Satellite (XMM) under several aspects. First, we discuss XMM-OM's photometric system and its colour transformations towards the standard UBV system. Second, we establish a set of procedures to determine the temperature and the amount of interstellar absorption affecting the observed stars. Last, we address the possibility of isolating quasars in
multidimensional colour diagrams based on the XMM-OM filter set.
%K satellite: XMM - photometry: colour transformations; interstellar absorption; quasars: identification of candidates