Showing papers by "European Southern Observatory published in 1982"

Giant voids in the Universe

Abstract: Recent observations indicate that most galaxies are concentrated in superclusters consisting of galaxies, and clusters of galaxies, aligned along strings. Giant volumes exist between superclusters which are almost empty of visible objects. Theories of galaxy formation predict the formation of non-spherical superclusters and giant voids. Large-scale structure changes very slowly, so the currently observed structure reflects the whole history of galaxy formation and structural evolution.

Steps toward the Hubble constant. VIII - The global value

Abstract: The problem of determining the global Hubble constant is approached by using two distance indicators whose dispersion in absolute magnitude is small, and hence which are virtually free of the Malmquist bias. New data are presented on the mean absolute-magnitude of the brightest individual red and blue supergiant stars in very nearby galaxies, calibrated relative to the Cepheids. The results are used to calibrate the maximum absolute blue magnitude for two well-observed Type I supernovae (SNe I). The velocity-relative distance diagram for 16 SNe I with known maximum apparent blue magnitudes is then calibrated using distances for IC 4182 and NGC 4214, with the result that the global Hubble constant equals 50 + or - 7 km per second per megaparsec. The result is compared with the known age of globular clusters in the Galaxy to show that the cosmological and the evolutionary time scales now closely agree.

Simultaneous optical and x-ray bursts from 4U/MXB 1636-53

Abstract: Methods of obtaining information about the geometry of X-ray burster systems from simultaneous optical and X-ray observations are discussed, and such simultaneous observations of 4U/MXB 1636-53 are reported. The physical idea of an optical burst being due to reprocessing of an X-ray burst in material in the vicinity of the compact object is discussed. The resulting modification of the X-ray burst signal is described in terms of an optical response function. Delay and smearing due to radiative processes are discussed along with those due to the geometry. For 4U/MXB 1636-53, the estimated delay is 2.5 seconds, the smearing is less than four seconds, and the maximum temperature of the reprocessing region is about 75,000 K. The projected area of the reprocessing region is about 6 x 10 to the 21st square cm. The neutron star is about 1.4 solar masses, the radius of the accretion disk is greater than 1.5 lt-sec, and the mass of the Roche lobe filling companion star is less than 2.0 solar masses, corresponding to a binary period between about one and ten hours.

Optical bursts from 4U/MXB 1636-53

Abstract: The results of observations of 15 and 26 optical bursts detected during June and July 1979 and June and July 1980, respectively, from the X-ray burst source 4U/MXB 1636-53 in a 'white light' passband are presented. The maximum burst fluxes above the persistent optical flux and integrated burst fluxes are correlated, and it appears that the maximum optical and X-ray burst fluxes are related according to a power law, consistent with optical emission from blackbody reprocessing of X-rays. The approximately linear relationship between the integrated optical and X-ray burst fluxes argues against this simple picture. The correlation of burst fluxes with waiting time since the previous burst suggests that large optical bursts come after a long waiting time. Short burst intervals observed both for optical and X-radiation suggest that not all available nuclear fuel is consumed in the thermonuclear flash which gives rise to the X-ray burst.

Status Of The European Southern Observatory New Technology Telescope Project

Abstract: The ESO NTT project is still in the conceptual phase but it is hoped early in 1982 to enter the engineering phase. With an aperture of 3.5 m it is seen also as a basic development aspect of our Very Large Telescope (VLT) project. The basic characteristics of the NTT are briefly reviewed with particular reference to the nature of the primary and its support system, which is strongly influenced by the active optics approach. Some relevant results of image analysis of existing conventional telescopes as well as some dome seeing and imaging monitoring results at the present ESO 3.6 m telescope are given. Brief comments are made on the concept of the ESO VLT.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

European Southern Observatory (ESO) Coude Echelle Spectrometer

Abstract: A powerful high resolution spectrometer has been developed, and is installed at the Coude Focus of ESO's 3.6 m telescope. It can also be fed by a 1.4 m auxiliary telescope dedicated to the instrument. With this latter telescope magnitude 10 stars can be observed at a resolving power of 100.000 and with a good instrumental profile. The CES also features a single channel scanner mode which can attain a resolving power of 300.000 with an extremely high spectral purity.

Universal spectrophotometer for determining the efficiency of optical components and systems.

Abstract: An instrument has been developed to measure the absolute reflectance or transmittance of optical elements or systems. Contrary to existing spectrophotometers, it is not limited by the size or by the optical power of the element to be analyzed.

Detection of radio emission from optically identified supernova remnants in M31

Abstract: The Very Large Array was used to conduct a radio search at a wavelength of 20 cm for ten optically identified supernova remnants (SNRs) in M31. Five SNRs were detected, and for the other objects, upper limits to the emission were determined. On the average, the surface brightness of an SNR in M31 appears to be fainter than that of an SNR in the Galaxy. It is suggested that the median surface brightness at a given diameter is higher in late-type spirals than in Sb systems.

Environmental effects on galaxies in clusters

Abstract: This study is part of a program to investigate consequences to a galaxy of its orbiting within a cluster of galaxies. Numerical experiments have been conducted to study the tidal influences on the internal dynamics of a galaxy (Miller and Smith 1982). The present first cut at the general problem treats effects of the cluster’s tidal potential on the pattern motion and observable properties of a galaxy (shape, density contours, velocity fields, velocity dispersions) for a fixed external potential. The first-order cluster force field is balanced by the galaxy’s acceleration in the real cluster, leaving tidal terms as the leading terms in a Taylor series expansion of the cluster force field about the center of the galaxy. The cluster tidal force field is usually stretching along a line toward the cluster center and compressive at right angles.

A photometric study of the short-period eclipsing binary BW Eridani

Abstract: UBV observations of the short-period eclipsing binary BW Eri are reported and analyzed. The photometric parameters are determined. BW Eri is a detached or semidetached system.

Discovery of a new BL Lacertae object /1E 1402.3 + 0416/ with the Einstein Observatory

Abstract: It is noted that only one BL Lac object, designated 1E 1402.3 + 0416, has so far been discovered as part of an optical identification program for a complete sample of faint X-ray sources detected with the Einstein Observatory. Consistent with previously X-ray-discovered BL Lacs, this object is blue and radio weak (17 mJy at 6 cm). It is pointed out that the percentage of BL Lacs in the faint extragalactic X-ray sample (2%) is smaller than the percentage at higher X-ray fluxes (6%). Over the same range in X-ray flux, the percentage of emission-line active galaxy nuclei (QSO + Seyferts) rises from 40% to 74%). This is seen as suggesting that BL Lacs do not evolve in a manner similar to quasars and are, therefore, not substantial contributors to the X-ray background.

On the linearity of the SWP camera of the international ultraviolet explorer /IUE/ - A correction algorithm

Abstract: An algorithm is presented for correcting IUE low resolution spectral images obtained with the SWP camera for some of the non-linearity effects reported by Bohlin et al. (1980). The non-linearity problem, which affects SWP images processed at Goddard Space Flight Center in the period May 22, 1978 to July 7, 1979 and at VILSPA in the period June 14, 1978 to August 6, 1979, was essentially due to the use of an Intensity Transfer Function (ITF) that erroneously included a blank image in the 20 percent exposure level. The correction algorithm described here was adopted by the three IUE Agencies in November 1979 as being suitable for most IUE users. It has the advantages to be applicable to any kind of low resolution SWP spectra, to introduce errors which are usually less than the intrinsic photometric errors, and to be of simple application. The results obtained by applying the method to a representative set of spectra of both point and extended sources are reported. In addition, a new evaluation of linearity and reproducibility of the SWP spectral data is provided, based on the improved ITF.

A Complete Sample of Radio Galaxies

Abstract: We report here some preliminary results of a multi-wavelength study of a complete sample of radio galaxies. The sample is comprised of 93 radio sources from the Parkes 11 cm catalog which are identified with galaxies of 17th magnitude or brighter in the declination zone -17° to -40°. Our objective is to cross-correlate the radio, infrared, optical, and other properties of a properly defined sample of radio galaxies.

21 CM line observations of cD galaxies

Abstract: A small 21 cm line survey of five cD galaxies, all first ranked cluster members, and all except one known to be centered on an extended X-ray source, is reported. Rms noise values for each object as obtained after smoothing the signals are listed. Estimated upper limits of the H I flux and an average flux upper limit of twice the rms over the whole width are used to estimate an upper limit of the neutral hydrogen mass. Hydrogen mass is computed to photographic luminosity ratios, with no correction applied to the optical luminosity of the galaxies except the one that allows for galactic extinction. Dressler's (1979) three component cD galaxy model is scaled to the sample galaxies and, assuming that the H I velocity distribution follows that of the stars, an upper limit to the hydrogen mass to total mass ratio in

Wolf-Rayet Stars Associated to Giant Regions of Star Formation

Abstract: Data on Wolf-Rayet(WR) stars in extragalactic H II regions and emission line galaxies are presented and discussed. The sample is still limited and inhomogeneous but two important points appear to be already established: a) The WR stars are more numerous than the blue super-giants at least in same phase of the evolution of the stellar clusters which ionize the giant H II regions, b) when the WR stars are detected, two cases are apparently observed, one in which only WN, the other in which both WN and WC, are present.

Problems of Modern Optical Coatings for Astronomy

Abstract: A significant improvement in instrument efficiency can be obtained through the use of high-efficiency coatings. Their implications on cost, complexity and operation of the instrument are discussed. Moreover, it is essential to have the possibility of assessing the real performances of such coatings. An instrument able to measure coating efficiency on almost any kind of substrate has been successfully built.

Remarks on the Evolutionary Status of Cataclysmic Variables

Abstract: The basic binary parameters (masses, system dimensions) of all cataclysmic variables are essentially identical, but there is a great variety in the outburst behaviour. Since there is no evident physical reason for this, it is suggested that nova and dwarf nova variability are periodically repeating states of activity of the same binary. After the nova eruption first follows a postnova state (very low disc mass), later the dwarf nova states BV Pup, U Gem and Z Cam (slowly increasing disc mass and outburst frequency, finally standstills), and finally the UX UMa state (permanent standstill) which is terminated by a new nova outburst. The mass of the disc increases continuously during this cycle. Also the mean mass transfer and accretion rates vary slowly from 1018 g s−1 at beginning and end of the cycle to 1016 g s−1 at mid-cycle, as a U Gem star. The nova outburst is understood in terms of a thermonuclear runaway near the surface of the white dwarf, the dwarf nova outburst is due to intermittent accretion of gas which was accumulated in the outer disc during quiescence (several arguments in favor of this model are given). The time interval between consecutive nova outbursts is of the order of 105 years. The secular evolution of a cataclysmic binary is characterized by a period decrease from 10h to 1h5 in a time scale of 1010 years. The star probably passes the period gaps in the ultra-short period domain in form of no-contact configurations.

UV Spectroscopy of the Novalike Variable TT Arietis

Abstract: TT Ari was detected by Strohmeier et al (1957) and is classified as a novalike variable It was hitherto unclear whether TT Ari is a special type of dwarf nova (Warner, 1976) or an old nova (Cowley et al, 1975) Our group obtained a total of four IUE spectra between 1979 and 1981 in the short and long wavelength region The first spectrum was taken in July 1979, when the system had a visual brightness of 113 magnitudes The following two IUE observations in November 1980 revealed TT Ari in the lowest optical state (V = 14m3) observed so far The fourth spectrum was obtained during the rise to maximum in January 1981, when the system had an apparent magnitude of V = 11m8 From this behavior, Krautter et al (1981) concluded that TT Ari is a dwarf nova with extremely extended standstills as they are typical for Z Cam s t ar s

NGC 604 — A Giant H II Region Dominated by Many WR Stars

Abstract: NGC 604, the largest H II region in M 33, is comparable in many respects (eg. ionized mass, total extent of a few hundered pc) with the giant H II complex 30 Doradus of the LMC. Recently D’Odorico and Rosa (1981) discovered broad WR emission features at 4640 A, 4660 A, He II 4686 A and 5812 A in a number of the bright knots in the core of NGC 604. In that paper it was concluded, that about 50 WR stars, mainly of the transition type WN 7 but WC characteristica seen as well, are present in the H II region. These findings were confirmed by the observations by Conti and Massey (1981).

The Near Infrared Properties of Selected WN Stars in the Large Magellanic Cloud

Abstract: We report here on preliminary infrared photometry of six WN stars in the Large Magellanic Cloud. Besides R136, the central object of the 30 Doradus Nebula, the sample includes three stars (R139, R140, R145) located near the center of the region (within ∿ 1 arcmin) and two more stars (R144, R147) at a distance of ∿ 5 arcmin from R136.

Absolute Magnitudes of Wolf-Rayet Stars: The WN3 and WN4 Sub-Classes in the Large Magellanic Cloud

Abstract: After the systematic survey carried out by Azzopardi and Breysacher (1979, 1980) at La Silla, Chile, with the 40- cm Objective Prism Astrograph, the census of the Wolf-Rayet population (101 stars) in the Large Magellanic Cloud (LMC) can probably be considered as quite complete except, perhaps, for stars located in the core of dense HII regions. The catalogue by Breysacher (1981) includes 100 stars to which one has to add one star of the WN type discovered by Sanduleak (private communication) outside of the survey limits.

The Wolf-Rayet Eclipsing Binary HD 5980 in the Small Magellanic Cloud

Abstract: The Wolf-Rayet star HD 5980, which is probably associated with the bright HII region NGC 346 of the Small Magellanic Cloud, was found to be an eclipsing binary by Hoffmann, Stift and Moffat (1978). Breysacher and Perrier (1980) determined the orbital period, P=19.266±0.003d, of the system whose light curve reveals a strongly eccentric orbit (e=0.47 for i=80o). The behaviour of the light curve outside the eclipses shows that we are dealing with a rather complex binary system. An analysis of the spectroscopic data is presented here.

New Developments in Data Storage

Abstract: It is estimated that up to 100 Gbytes of primary data from digital detectors have to be stored each year. The amount of reduced data is at least one order of magnitude smaller. Although the storage density for magnetic recording can be made higher only the optical technic can provide a substantial denser medium than the photographic emulsion. It seems likely that optical read-only devices will be developed for archival storage of data in this decade. Magnetic recording of data will still be preferred whenever changing of the information is important.