%R 1995A&AS..109..201G
%J-262
%A Garcia J.R., Cebral J.R., Scoccimarro E.R., Wahnon P., Arena R., Bazterra V., Pellizza L., Risi A., Rodriguez M.L., Zimmermann M.
%T A catalogue of variable stars in the lower instability strip.
%F 1995.01.17
%B Identifications, positions, photometry, spectra, some pulsational features, other astrophysical parameters and literature for 302 pulsating variable stars in the lower instability strip, near the ZAMS, are given. About 185 stars have near homogeneous photometric information in the Stroemgren's uvby-{beta} photometric system. This catalogue/database covers information published until November 1993.
%K catalogs - stars: variable: {delta} Sct; others

%R 1995A&AS..109..263B
%J-264
%A Brett J.M.
%T Opacity sampling model photospheres for M dwarfs. II. The grid.
%F 1995.01.17
%B We present a table of new `classical' model photospheres for M dwarfs computed with an extensive set of atomic and molecular opacities treated with the accurate and realistic opacity sampling technique. The models of this grid are described and analysed in a companion paper (Brett 1995).
%K stars: atmospheres - stars: late type - stars: low mass - stars: fundamental parameters

%R 1995A&AS..109..265H
%J-265
%A Heck A.
%T StarHeads. (Announcement of a database).
%F 1995.01.17
%B Another database has been made available on-line through the CDS WWW server. StarHeads is a resource providing links to individual web pages of astronomers and related space scientists.
%K database: miscellaneous
%X At URL <http://cdsweb.u-strasbg.fr/starheads.html>

%R 1995A&AS..109..267G
%J-291
%A Giommi P., Ansari S.G., Micol A.
%T Radio to X-ray energy distribution of BL Lacertae objects.
%F 1995.01.17
%B We present multifrequency spectra of a large number of radio and X-ray selected BL Lacertae objects constructed using non-simultaneous archival data. The data were obtained using the European Space Information System (ESIS) and are from several radio and optical catalogues, the IRAS Faint Source Catalogue, the Einstein and the EXOSAT databases. The sample includes 121 BL Lacs that have been extracted from the 1Jy and the S4 radio surveys (Stickel et al. 1991; Stickel &
Kuehr 1994), the Einstein IPC Slew Survey, the Einstein Extended Medium Sensitivity Survey (EMSS), the EXOSAT High Galactic Latitude Survey, and from the compilations of Giommi et al. (1990), and Veron & Veron (1993). We find that the shape of the radio to infra-red spectrum of Radio Selected and X-ray Selected BL Lacs is very similar. The difference between these two classes of objects is instead evident in the optical/X-ray part of the spectrum. The classical radio
discovered BL Lacs are characterized by an energy spectrum with a sharp cutoff in the IR/optical band while in most of the X-ray discovered objects the turnover is located near the UV/X-ray band or at higher frequencies. For a given X-ray flux this diversity can give rise to radio fluxes different by a factor of 100 or more. We argue that BL Lac objects may be a single population of sources characterized by a wide range of energy cutoffs. In this scenario BL Lacs discovered
in radio surveys are representative of the entire population, while objects characterized by an energy break near the X-ray band, which are abundantly detected at X-ray frequencies, are intrinsically a small minority.
%K BL Lacertae objects: general - radio continuum: galaxies - X-ray: galaxies

%R 1995A&AS..109..293G
%J-312
%A Grebel E.K., Roberts W.J.
%T Heterochromatic extinction. I. Dependence of interstellar extinction on stellar temperature, surface gravity, and metallicity.
%F 1995.01.17
%B Techniques used to remove atmospheric extinction cannot be used for interstellar extinction, because objects can be observed at only a single extinction, which varies from object to object. The interstellar extinction is thus unknowable without the use of prior information about the object. In this paper we show how to apply such knowledge in the case of normal stars. Using standard passbands, an accepted average optical interstellar extinction law, and Kurucz flux tables,
we derive useful colour-dependent interstellar extinction relations for synthetic versions of two widely used sets of broad band photometric passbands, Johnson-Cousins UBVRI and Washington CMT_1_T_2_. For the Washington system, we define a new internal reddening system. For bands blueward of 500 nm in either photometric system the reddenings for main sequence stars and evolved stars are quite different, and even can be non-linear as a function of temperature colour. These
corrections are important for the correct characterisation of the intrinsic reddening properties of interstellar dust, for fitting isochrones accurately, for determining stellar metallicities, for obtaining correct standard reddenings for reddened galactic clusters, and indeed for the determination of basic stellar parameters for single stars such as T_eff_ and M_bol_. To make the reddenings to different objects comparable, we standardise the reddening on that of a solar
metallicity main sequence star of T_eff_=17000 K (B3-4 V). The functional dependence of the extinction curves on abundance is not as important in the Johnson-Cousins as in the Washington system. We compute new theoretical reddening vectors in both systems, and evaluate the size of the nonlinearity with extinction (Forbes effect).
%K ISM: dust, extinction - techniques: photometric - stars: fundamental parameters

%R 1995A&AS..109..313R
%J-328
%A Roberts W.J., Grebel E.K.
%T Heterochromatic extinction. II. Dependence of atmospheric extinction on stellar temperature, surface gravity, and metallicity.
%F 1995.01.17
%B In synthetic versions of two broadband photometric systems, Johnson-Cousins and Washington, we find the dependence of atmospheric extinction corrections on colour and on macro features in the spectra of stars, such as the Balmer jump, as parameterised by T_eff_, logg, and [Fe/H]. We use standard passbands, a mean atmospheric extinction law measured at ESO/La Silla, extended and modified by us, and the Kurucz library of synthetic spectra. The true broadband atmospheric
extinction is far more complicated than any current reduction (transformation) methods consider. Hence all broadband magnitude systems are fundamentally unphysical - they contain not the extra-atmospheric magnitudes, but unobservable magnitudes whose relation to physical magnitudes is unknown, but may differ by 0.05mag or more for hot and cool stars. Hence, it is hazardous to compare them to any synthetic magnitude system derived from either synthetic spectra or spectral
scans. These problems exist to a lesser degree in intermediate band systems, but narrow band systems are relatively immune from these complexities. We do not treat either kind of system here. If our results were incorporated into a photometric reduction program, and standard stars and program stars stars carefully selected by metallicity and luminosity class, a standard magnitude system could be established that would be directly comparable to synthetic systems. As a bonus,
measurements of intrinsic flux variations at the millimagnitude level would become more secure. We describe our own operational photometric transformation program that incorporates only the linear part of the dependence on colour of atmospheric extinction. Our results and prescriptions are useful for aperture photoelectric photometry, but our implementation is aimed at CCD photometry of stellar populations.
%K atmospheric effects - techniques: photometric - stars: fundamental parameters

%R 1995A&AS..109..329M
%J-332
%A Manfroid J., Sterken C., Cunow B., de Groot M., Jorissen A., Kneer R., Krenzin R., Kruijswijk M., Naumann M., Niehues M., Schoeneich W., Sevenster M., Vos N., Vogt N.
%T Long-term photometry of variables at ESO. III. The third data catalogue (1990-1992).
%F 1995.01.17
%B In this paper we present the third catalogue of photometric data in the Stroemgren system obtained during the period October 1990-January 1992 in the framework of the Long-Term Photometry of Variables (LTPV) program at the European Southern Observatory. The catalogue is available in computer readable form at the Centre de Donnees de Strasbourg.
%K catalogs - stars: variables: other - techniques: photometric

%R 1995A&AS..109..333P
%J-340
%A Pirogov L., Zinchenko I., Lapinov A., Myshenko V., Shul'ga V.
%T H^13^CN, H^13^CO^+^, HCN and HCO^+^ observations of dense gas in galactic molecular clouds.
%F 1995.01.17
%B The results of the observations of several galactic dense molecular cloud cores in the J=1-0 H^13^CN, H^13^CO^+^, HCN and HCO^+^ lines along with the J=1-0 HCN observations of some high-latitude clouds are presented. In the optically thin approximation the H^13^CN and H^13^CO^+^ column densities (N) are evaluated. HCN and HCO^+^ column densities are derived from N(H^13^CN) and N(H^13^CO^+^) using the [^12^C]/[^13^C] ratios for each cloud calculated from its galactocentric
dependence. HCN abundances are found for two objects. The H^13^CO^+^, HCO^+^ and HCN emission region sizes are estimated for some cores. HCO^+^ and H^13^CO^+^ model calculations for S140 show that either the [HCO^+^]/[H^13^CO^+^] abundance ratio is rather low, ~30, or the object has inhomogeneous structure. The J=1-0 HCN line was detected towards MBM 55B high-latitude cloud. HCN column density in this source is N(HCN)>=10^11^cm^-2^, the HCN abundance is X(HCN)>10^-10^.
%K stars: formation - ISM: clouds - ISM: molecules - radio lines: ISM

%R 1995A&AS..109..341R
%J-345
%A Rifatto A., Longo G., Capaccioli M.
%T The UV properties of normal galaxies. II. The ``non-IUE'' data.
%F 1995.01.17
%B In the last decade several satellite and balloon borne experiments have collected a large number of ultraviolet fluxes of normal galaxies measured through apertures of various sizes and shapes. We have homogenized this data set by deriving scale corrections with respect to IUE. In a forthcoming paper these data will be used to derive standard luminosity profiles and total magnitudes.
%K galaxies: general; photometry - catalogs - ultraviolet: galaxies

%R 1995A&AS..109..347L
%J-353
%A Li K.J., Zhong S.H., Ding Y.J., Bai J.M., Li Q.Y.
%T The sunspotless flare on April 12, 1991 and the evolution of the neighboring filaments.
%F 1995.01.17
%B On April 12, 1991, a 2N sunspotless flare was observed by using the spectra-spectroheliograph at Yunnan Observatory. H_{alpha}_ filtergrams and sequence H_{alpha}_ and H_{gamma}_ spectra were obtained. In this paper, the morphology of the sunspotless flare and the evolution of the nearby filaments are studied. The results show that the arch-shaped filament which appears on the neutral line to separate the active region from the solar quiet region is activated several days
before the onset of the sunspotless flare, and disappears several hours before the onset. It is suggested that the sunspotless flare is associated with the filament, i.e. its activation, disparition brusque and so forth. The sunspotless flare is of unusual long duration (about 80min in the H_{alpha}_ emission) and exhibits a slow rise to maximum intensity (about 20min in the H_{alpha}_ emission) i.e. a `long duration effect' and a `gradual rise-and-fall effect' in both the
H_{alpha}_ emission and the soft X-ray radiation, and the flash phase is poorly defined or absent. The energy released by the sunspotless flare may come from the magnetic energy stored in the corresponding plage region. The velocity along the line-of-sight is small for the sunspotless flare (less than several kilometers per second), but rather large for the nearby corridor filament (about a hundred km/s). The horizontal extension velocity of the sunspotless flare is not
large. Compared with the general major H_{alpha}_ flare of the same importance, the sunspotless flare is relatively gentle.
%K Sun: activity - Sun: flare, filament

%R 1995A&AS..109..355B
%J-373
%A Bumba V., Klvana M., Kalman B.
%T NOAA 6850: an inactive delta-configuration and its magnetic and velocity fields.
%F 1995.01.17
%B We present the results of a detailed study of evolution of photospheric features, longitudinal magnetic and velocity fields and proper motions of sunspots in one complex (NOAA 6850) and one simple (NOAA 6853) active region of September/October 1991, being part of a long-lasting complex of activity. We bring evidence of the changes of all the studied quantities with the sudden renewal and then subsequent weakening of magnetic activity in the larger group. We discuss the
reasons why the complex delta-configuration group did not produced larger flares, assuming that the observed phase of the complex's development represented only a preparatory stage, which matured during the next disk passage. We underline the physical importance of the coincidence of magnetic field, line-of-sight and proper motion singularities with regions of the fastest changes of penumbral and umbral structures.
%K Sun: sunspots - Sun: flares

%R 1995A&AS..109..375A
%J-382
%A Ahumada J., Lapasset E.
%T Catalogue of blue stragglers in open clusters.
%F 1995.01.17
%B An extensive survey of blue straggler candidates in galactic open clusters of both hemispheres is presented. The blue stragglers were selected considering their positions in the cluster colour-magnitude diagrams.They were categorized according to the accuracy of the photometric measurements and membership probabilities. An amount of 959 blue straggler candidates in 390 open clusters of all ages were identified and classified. A set of basic data is given for every cluster
and blue straggler. The information is arranged in the form of a catalogue. Blue stragglers are found in clusters of all ages. The percentage of clusters with blue stragglers generally grows with age and richness of the clusters. The mean ratio of the number of blue stragglers to the number of cluster main sequence stars is approximately constant up to a cluster age of about 10^8.6^ yr and rises for older clusters. In general, the blue stragglers show a remarkable degree of
central concentration.
%K catalogues - open clusters and associations: general - blue stragglers

%R 1995A&AS..109..383K
%J-387
%A Keller C.U., Gschwind R., Renn A., Rosselet A., Wild U.P.
%T The spectral hole-burning device: a 3-dimensional photon detector.
%F 1995.01.17
%B We present the principles of a new device that combines a high-resolution spectrometer (0.001nm spectral resolution, 10nm bandwidth) with maximum efficiency, a large detector (pixel size 1{mu}m by 1{mu}m, overall size 2cm by 2cm), and a very high density data storage device (up to 400TB) in a single optical device. This device is based on persistent spectral hole-burning in a dye-doped polymer at temperatures of a few K. It is called a Spectral Hole-Burning Device
(SHBD) in analogy to Charge Coupled Devices (CCD). A SHBD can be thought of as a color film with extremely high spectral resolution: it records the intensity in the visible or the near-infrared according to the two-dimensional position and the wavelength. Therefore it is a 3-dimensional photon detector. We show first results from laboratory measurements that prove the feasibility of a SHBD.
%K spectroscopy - detector - spectral hole burning

%R 1995A&AS..109..389C
%J-399
%A Chelli A., Petrov R.G.
%T Model fitting and error analysis for differential interferometry. I. General formalism.
%F 1995.01.17
%B A combination between high angular and high spectral resolution techniques, Differential Interferometry (DI) yields seeing independent information with a resolution much higher than the telescope diffraction limit. This paper, first in a series of two, presents a formalism for the estimation of the parameters modelling the brightness and velocity fields of unresolved or partially resolved astronomical candidates. We use the average cross spectrum of speckle patterns
recorded in different spectral channels to define an estimator which contains all the seeing independent DI data and is to be minimised in a non linear iterative least square fit of the model parameters. From this general estimator, we derive a simpler one based on the phase of the average cross spectrum which remains seeing independent whatever the spectral bandwidth is. We apply it to non resolved sources, when all the information is contained in the object spectrum and in
the angular vectorial function {epsilon}({lambda}) representing the variation of the object photocenter with wavelength. Then, we give a simple formal expression of the parameters errors and, as a first application, we determine the optimum size for the slit of the spectrograph used in a one dimensional DI experiment. In the second paper, we describe the application of this general formalism to rotating stars and binary systems and discuss its performances as a function of
the visual magnitude.
%K atmospheric effects - techniques: interferometric - techniques: image processing - methods: data analysis

%R 1995A&AS..109..401C
%J-415
%A Chelli A., Petrov R.G.
%T Model fitting and error analysis for differential interferometry. II. Application to rotating stars and binary systems.
%F 1995.01.17
%B A combination between high angular and high spectral resolution techniques, Differential Interferometry (DI) yields seeing independent information with a resolution eventually much higher than the telescope diffraction limit. A first paper presented a formalism for the estimation of the parameters modelling the brightness and velocity distribution of any astronomical candidate, even partially resolved. Here we describe the application of this general method to the
measurement of the angular diameters, rotation velocities and position angles of the rotation axes of rotating stars and to the measurement of the angular vectorial separation and radial velocity differences in binary systems. A method to compute the uncertainties on this parameters is presented and used for a numerical computation of the limiting performances of DI for this two kinds of applications.
%K atmospheric effects - techniques: interferometric - techniques: image processing - methods: data analysis - binaries: general - stars: rotation

%R 1995A&AS..109..417S
%J-423
%A Sanchez Almeida J.
%T Uncertainties in the determination of the Stokes parameters due to photon noise.
%F 1995.01.17
%B We derive inequalities which restrict the precision of the Stokes parameters imposed by photon noise. The signal-to-noise ratio of the measured Stokes parameters is never better than the square root of the number of detected photons. In case of weakly polarized sources (i.e., most astronomical sources), such an inequality imposes no practical limit and it should be replaced by the intensity-to-noise ratio, which approximately follows the same square root law. Besides these
general results, we also find relationships between the errors of the Stokes parameters which apply to particular (although fairly common) analyzers. The equations are presented in a device-independent fashion, so that they can be used to tell, in an absolute sense, whether photon noise allows the measurement of small polarimetric signals.
%K polarization - techniques: polarimetric