Astronomy and Astrophysics Supplement Series

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List of Papers (Total 1,649)

Blind source separation and analysis of multispectral astronomical images

Celestial sources are studied by means of multispectral analysis, for which a pixel value can be considered as a mixture of different sources. We show that the application of blind source separation methods can display interesting features, which can help astronomers to improve their description of celestial sources. Experiments were carried out on Hubble Space Telescope images...

Detection of scattered light in telescopes

We present a simple, but powerful method to test for the presence of scattered light in telescopes. Scattered light can seriously hamper any attempt to achieve a proper flat fielding of CCD data. The method consists of making a pinhole camera (camera obscura) by placing a pinhole mask in front of the CCD window. Exposing the CCD in this configuration gives an image of the light...

Time variability of five strong 12 GHz methanol masers

Five intense 12 GHz methanol masers with structured profile have been monitored during the period 90 Nov.-92 Apr., in order to study the variability on time scales ranging from one week to about 2 years. The integrated flux density of W3(OH), G188.94 +0.89, NGC 7538 remains constant (within the measurement uncertainties) during our period of observation. By amplitude...

VRI photometry of stars in the fields of 12 BL Lacertae objects

We present VRc Ic Johnson-Cousins magnitudes of field comparison stars for twelve BL Lacertae objects belonging to the largest sample of blazars which is monitored at the Perugia University Observatory. The sequences reported here can be used in the long–term CCD photometric monitoring of BL Lac objects aimed to understand the characteristics of their variability. Finding charts...

TU Bootis: An ambiguous W Ursae Majoris system

The W UMa system TU Boo has a period of 0.32438 days and a spectral type G3. We present here the first photometric analysis, based on photoelectric B and V light curves. The q-search method was used to find the preliminary range of the mass-ratio in order to search for the final solution. The unspotted solution was found by using the unperturbed part of the light curve and...

B[e] stars. I. HD 51585 (=OY Gem)

We analyse CCD spectroscopic material obtained at the Haute Provence Observatory between 1990 and 1993, covering the wavelength region 3800-11000 Å. 320 emission lines were measured and identified. Of these about 40% correspond to permitted or forbidden lines of ionized iron. Many forbidden lines (20% of the total) are present, including many classic nebular lines. We also...

Surface photometry of galaxies in low density regions

We perform detailed surface photometry, based on B- and/or R-band CCD images of 92 faint galaxies. They are a subsample of those galaxies which were studied by Hopp et al. (1994) in the direction of three nearby voids. We derive integral photometric parameters and radial surface brightness profiles and compare them to those of several faint galaxy samples, located in different...

Fractional abundances of molecules in dense interstellar clouds: A compendium of recent model results

In this paper we present calculated fractional abundances in dense interstellar clouds for selected atomic and molecular species using three different homogeneous, pseudo-time-dependent models discussed by Bettens, Lee, & Herbst (1995): the new standard model, the new neutral-neutral model, and model 4. We have run each model with 3 different hydrogen densities – 103, 104, and...

Multi-colour photometric and spectroscopic monitoring of the WN5 star EZ Canis Majoris

We present and analyse photometric and spectroscopic observations of the WN5 star EZ Canis Majoris obtained over a period of 7 years. We discuss the changing light curve, the shift in phase of the maxima and point to flare type variability seen in one night. Small amplitude variations are reported in another night. We have investigated the change of the average visual magnitude...

New weak-line T Tauri stars in Orion from the ROSAT all-sky survey

We present results of the spectroscopic and photometric follow-up observations of the ROSAT all-sky survey in the direction of the Orion cloud complex. The main goal of these observations is the search for X-ray emitting pre-main sequence stars. 820 X-ray sources were detected with high confidence in about 450 square degrees. The mean density of X-ray sources in this region is a...

Magnetic configuration of a sunspot region using the H line

The configuration of the magnetic field in an active region is analysed using a set of Hβ chromospheric magnetograms and narrow pass-band filtergrams taken at various positions on the line. We found that the chromospheric magnetic field is parallel to the chromospheric features and inhomogeneous. The photospheric magnetic field disappears abruptly in the edge of the penumbra; the...

UBVRI photometric monitoring of 7 rapidly rotating late-type dwarfs in the Alpha Persei cluster

The UBVRI light curves of 7 late-type dwarfs amongst the fastest rotators of the Alpha Per cluster (vsini ≥140 km s-1) are presented. The shape of the light curves suggests that the photometric variations are most often dominated by a single group of cool spots located at intermediate or high latitude on the stellar surface. Assuming that starspots are good tracers of the stellar...

A 15 years monitoring program at 408 MHz

This is the second paper based on the 408 MHz monitoring program with the East-West arm of the Bologna interferometer. The monitoring concerned 125 radio sources measured approximately once a month for 15 years. We present the summary of the variability analysis concerning all the sample and the monitoring data, not yet published, of the variable sources.

Light curves and periods of Mira variables

Good distance indicators are needed in studies of the galactic structure. Pulsating variables can be used, but the problem is to find a homogenous sample obeying a period-luminosity relation with low scatter. In this paper, we show how such a sample can be produced using the Terzan catalogue of Variables and available Schmidt plates. We have selected 150 large amplitude variables...

Optical structure and star formation in blue compact dwarf galaxies. I. Observations and profile decomposition

We present new B and R CCD surface photometry for a sample of 4 Blue Compact Dwarf Galaxies (BCDs) and 2 higher luminosity starburst galaxies. We find that the BCD surface brightness profiles (SBPs) can be generally well fitted by the sum of the light of 3 distinct components: 1) an exponential component at large radii, with or without a central flattening which describes the...

A spatial and spectral maximum entropy method as applied to OVRO solar data

We present first results of applying a Maximum Entropy Method (MEM) algorithm that acts in both the spatial and spectral domains to data obtained with the frequency-agile solar interferometer at Owens Valley Radio Observatory (OVRO) taken at 45 frequencies in the range . The traditional MEM algorithm does not exploit the spatial information available at adjacent frequencies in...

Absolute transition probabilities for the a6D y6P° multiplet (#8) of Fe II

We report the first laboratory measurement of absorption oscillator strengths (f-values) for 6 VUV () transitions of the multiplet (#8) in Fe II. We have also reconfirmed a recent measurement of the f-value of the Fe II resonance line at . These measurements are made with the high sensitivity absorption experiment at the University of Wisconsin-Madison. Measurements are also made...

TT Arietis: Photometric variability from 1985 to 1994

Results of photoelectric observations of TT Ari during the 1985–1994 interval are presented. Observations were carried out at the Rozhen and Belogradchik observatories as part of our programme for the study of anti-dwarf novae. The long-term light curve in the standard UBV system is constructed and peculiarities of the long-term behaviour of the star in this time interval are...

Multicolour deep CCD photometric study of the moderately young southern open star clusters NGC 3228, NGC 4103, NGC 5662 and NGC 6087

CCD observations in the U, B, V, R and I passbands have been used to generate colour-colour and deep colour-magnitude diagrams for the young open star clusters NGC 3228, NGC 4103,  NGC 5662 and NGC 6087. The sample consists of about 2000 stars reaching down to . The interstellar extinction across the face of the imaged cluster regions seems to be uniform with average values of...

The high energy instrument PDS on-board the BeppoSAX X–ray astronomy satellite

BeppoSAX/PDS experiment is one of four narrow field instruments of the BeppoSAX payload, that also includes two wide field cameras. The goal of PDS is to extend the energy range of BeppoSAX to hard X–rays. The operative energy range of PDS is 15 to 300 keV, where the experiment can perform sensitive spectral and temporal studies of celestial sources. The PDS detector is composed...

Two-band spectral filtering in instruments for measuring solar magnetic fields

In this paper we formulate the basic concept of a bichromatic image technique. Specific examples of its application are analyzed in the context of research into solar plasma characteristics by pinpointing its merits and demerits. Specialized requirements to the spectral devices are set forth, which may be summarized as: a) the presence of two nearby identical spectral passbands...

Mass determination of astrometric binaries with Hipparcos - I. Theory and simulation

The analysis of the observations of double stars made by the ESA satellite Hipparcos has involved a very specific processing to derive the relevant astrometric parameters. This required to distinguish between several categories of double stars according to the separation and orbital motion. We show that for close pairs with orbital period less than about 20 years, the concept of...

CLEAN and WIPE

Clean is a matching pursuit process which has two weak points: in situations of astrophysical interest, the "clean map

Optical positions and proper motions of radio stars

The optical positions of 31 radio stars were obtained with the 40 cm astrograph at Zô–Sè Section, Shanghai Observatory from 1985 to 1988. The observational positions and the proper motions of these radio stars in the FK5 system are given in this paper.

New theoretical yields of intermediate mass stars

We present theoretical yields of H, 4He, 12C, 13C, 14N, and 16O for stars with initial masses between 0.8 and 8 and initial metallicities , 0.004, 0.008, 0.02, and 0.04. We use the evolutionary tracks of the Geneva group up to the early asymptotic giant branch (AGB) in combination with a synthetic thermal-pulsing AGB evolution model to follow in detail the chemical evolution and...