Showing papers by "European Southern Observatory published in 1988"
84 citations
TL;DR: In this article, the authors presented the theory and practical basis of a complete system for active control of optical quality, with particular application to large telescopes, using a thin model mirror of 1 m diameter.
Abstract: Part I of this paper [1] presented the theory, and practical basis, of a complete system for active control of optical quality, with particular application to large telescopes. Reference was made to an experimental verification using a thin model mirror of 1 m diameter. Part II now gives a complete account of these experiments which consisted essentially of two parts: the verification of the theoretical modal calibrations and their orthogonality in practice, and the application of the calibrations to achieve the active modal correction of the mirror. Both aspects of the experiment were successful, with a precision higher than expected. The residual errors left after final correction are, by definition, of a higher order than the five corrected low spatial frequency terms and are small. However, one residual term is dominant (fifth-order astigmatism) but this was omitted in the correction process as being probably too high a mode to appear in practice. A calibration for this term will be performed...
62 citations
TL;DR: In this paper, the authors observe the presence of 2 systemes cinematiques which sont interpretes comme l'interaction de deux nuages HI in a galaxie compacte bleue II Zwicky 40.
Abstract: L'observation VLA a 21 cm de la galaxie compacte bleue II Zwicky 40 revele la presence de 2 systemes cinematiques qui sont interpretes comme l'interaction de deux nuages HI. La masse totale de chaque nuage est estimee a 3•10 9 M ○. ; cette valeur excede la masse visible observee d'un ordre de grandeur indiquant la presence de matiere sombre dans cette galaxie
60 citations
43 citations
TL;DR: The European Southern Observatory Very Large Telescope (ESOVLSTM) project as mentioned in this paper is a project for a linear array of four independent 8m telescopes with adaptive optics applied for a real-time phase compensation of the individual pupils for atmospheric distortions.
Abstract: The European Southern Observatory Very Large Telescope is a project for a linear array of four independent 8-m telescopes. This concept offers the possibility of operating the telescopes in the synthetic-aperture mode as an interferometer with a maximum baseline of approximately 112 m. The first target for the interferometric operation is phasing in the infrared range, with a gradual expansion toward shorter wavelengths. Two smaller movable telescopes are added to the linear array for a complete filling of the spatial-frequency plane. Adaptive optics is applied for a real-time phase compensation of the individual pupils for atmospheric distortions. The whole array, in addition to the individual pupils of the independently mounted telescopes, must be phased, including pupil position corrections due to pupil foreshortening and shift effects, in order to reach a reasonable phased field of view.
40 citations
39 citations
01 Dec 1988
TL;DR: In this article, the discovery of a probable gravitational lens associated with the quasar UM 425 = QSO 1120+019 is reported and the velocity difference between the two brightest components from the cross-correlation technique is shown to be 200 + or - 100 km/s and is consistent with zero.
Abstract: The discovery of a probable gravitational lens associated with the quasar UM 425 = QSO 1120+019 is reported. BVR images of the object were obtained with a CCD using a 1.5-m telescope in March, 1987. Three close companions were observed around the bright image of the quasar. Follow-up spectroscopy suggests that the brightest companion has the same emission lines as the quasar. The velocity difference between the two brightest components from the cross-correlation technique is shown to be 200 + or - 100 km/s and is consistent with zero. Subtracting a scaled spectrum of the brighter component from the brightest companion leaves a residual which is interpreted as the spectrum of a lensing galaxy at a redshift of about 0.6. 18 refs.
24 citations
TL;DR: In this paper, the main periodic solutions of a 4-dimensional symplectic mapping composed of two coupled 2-dimensional mappings were calculated numerically and also theoretically for small values of the coupling parameter μ.
Abstract: We study the main periodic solutions of a 4-dimensional symplectic mapping composed of two coupled 2-dimensional mappings. Their bifurcations were calculated numerically and also theoretically for small values of the coupling parameter μ. Most bifurcating families of period 2n (n≻0) have complex unstable regions that extend from μ=0 to the maximum allowed value of μ for each family. These complex unstable regions do not allow the transmisssion of the stability of the corresponding families to families of higher order. We found only one family with a complex unstable region not extending to the maximum μ, but in this case also the transmission of the stability is stopped at an inverse bifurcation. Thus although there are infinite sequences of bifurcations (of the Feigenbaum type) in the limiting 2-dimensional case μ=0, all such sequences are interrupted when the system is 4-dimensional (i.e. for μ≠0). The appearance of complex instability for μ=0 can be predicted by studying the cases μ=0 and applying the Krein-Moser theorem.
24 citations
01 Jan 1988
TL;DR: The observational work which has been done to date on young low-mass binaries is reviewed in this article, and results from - as well as some limitations of - various techniques are discussed.
Abstract: The observational work which has been done to date on young low-mass binaries is reviewed. Much effort is currently put into surveys of such binaries, and results from - as well as some limitations of - various techniques are discussed. Statistical analysis of a sufficiently large sample of pre-main sequence binaries will eventually provide essential information on how stars form.
22 citations
TL;DR: In this article, the spectrum, the timescale and the luminosity of the event may be interpreted as the first direct evidence for a supernova explosion in the nuclear region of a spiral galaxy.
Abstract: Peterson and Ferland1 have reported observations of the low-luminosity variable Seyfert galaxy NGC5548, which they interpret as the first direct evidence for an accretion event in the nucleus of an active galaxy. Here we show that the spectrum, the timescale and the luminosity of the event may be better interpreted as the first direct evidence for a supernova explosion in the nuclear region of a spiral galaxy.
21 citations
TL;DR: In this article, the relation entre la source radio and le profil particulier des raies d'emission is investigated en comparant les donnees radio aux observations spectroscopiques.
Abstract: Des cartes radio du noyau Seyfert dans NGC 7674, obtenues par des observations VLBI et VLA revelent une source radio triple possedant une etendue angulaire totale d'environ 0,7 arcsec. La relation entre la source radio et le profil particulier des raies d'emission est discutee en comparant les donnees radio aux observations spectroscopiques
TL;DR: The ESO400-G43 ( = 2034-356) is one of the brightest and largest blue compact galaxies known as discussed by the authors, and its morphology and spectral properties are consistent with a predominantly young stellar population and an extremely low mass to light ratio (M/LB = 0.1).
Abstract: Blue compact galaxies (BCGs) are characterized by their compact appearance and very blue colours1,2 indicative of a high star-formation rate. The metal abundances are low, suggesting that the present rate of star formation cannot have lasted for very long3 (unless the gas is being replenished). These galaxies are thus either truly young or their star formation takes place in short bursts3,4. ESO400-G43 ( = 2034–356) is one of the brightest and largest BCGs known. Observations in the 21-cm line with the Very Large Array (VLA) of the National Radio Astronomy Observatory reveal a massive (5×109 M⊙) slowly rotating H I halo. Optical observations obtained at the European Southern Observatory (ESO) show that the morphology and spectral properties are consistent with a predominantly young stellar population and an extremely low mass to light ratio (M/LB = 0.1). The luminous stars seem to be concentrated in a rapidly spinning central disk. Dark matter is dominating the mass at large radii.
01 Jan 1988
TL;DR: Two different approaches - one based on supervised Bayesian classification, the other on unsupervised data-driven classification - are presented and some preliminary results are reported.
Abstract: Progress is reported on a project which aims at mapping the extragalactic sky in order to derive the large scale distribution of luminous matter. Our approach consists in selecting from the IRAS Point Source Catalog a set of galaxies which is as clean and as complete as possible. The decision and discrimination problems involved lend themselves to a treatment using methods from multivariate statistics, in particular statistical pattern recognition. Two different approaches - one based on supervised Bayesian classification, the other on unsupervised data-driven classification - are presented and some preliminary results are reported.
TL;DR: In this paper, a combinaison d'observations spectrophotometriques entre 3600 and 7100 A, with a radio a 21 cm and d'une photographie optique permet d'etudier la morphologie de la galaxie a raies d'emission Michigan 160.
Abstract: La combinaison d'observations spectrophotometriques entre 3600 et 7100 A, d'observations radio a 21 cm et d'une photographie optique permet d'etudier la morphologie de la galaxie a raies d'emission Michigan 160. Elle apparait comme un systeme riche en gaz domine par quatre regions HII massives. Son contenu en gaz neutre represente 50% de la masse totale
01 Jan 1988
TL;DR: Multivariate statistical methods deal with the inherently very difficult problem of detecting patterns in data and different methods bring different features of the data to light.
Abstract: Multivariate statistical methods deal with the inherently very difficult problem of detecting patterns in data These patterns can take many forms — natural groups, inherent dimensionality, correlations, dependencies, and so on Often, therefore, different methods bring different features of the data to light
TL;DR: The 21 cm absorption through the disk of M31 has been observed, using the VLA to study the cool atomic phase of the interstellar medium in this nearby spiral galaxy as discussed by the authors.
Abstract: The 21-cm absorption through the disk of M31 has been observed, using the VLA to study the cool atomic phase of the interstellar medium in this nearby spiral galaxy. It is found that the abundance of diffuse clouds with tau between 0.125 and 1 in M31 is no higher than in the solar neighborhood of the Milky Way. The mean spin temperature, 300 K, is similar to or higher than the local value. The fraction of the neutral atomic hydrogen in the cool phase is about 0.25 or less. These results imply that M31 has a mixture of warm and cool interstellar phases similar to that in our vicinity of the Milky Way, which suggests either that the heating and cooling balance occurs in a similar pressure environment, or that whatever dynamical processes determine the mixture of warm and cool gas reach a similar equilibrium in M31 as here. Specifically, the warm neutral medium seems to be a robust phase, with a much larger filling-factor than the cool clouds.
03 May 1988
TL;DR: In this article, photovoltaic CMT-Si CCD hybrid focal plane arrays for the IRAC currently developed at ESO have been tested and data on efficiency, fill factor, dark current, limiting noise performance and uniformity are presented.
Abstract: Photovoltaic CMT-Si CCD hybrid focal plane arrays for the Infrared Array Camera IRAC currently developed at ESO have been tested. The arrays have a format of 32 x 32 and 64 x 64 pixels. The cutoff wavelength of the detector is 3.9 microns but can be custom designed between 2.5 and 5 microns. The detectors consist of cylindrically shaped p-n junctions which are connected to a buried channel CCD by a special loophole interconnect technology. The input stage of the CCD is a direct injection circuit. Test results of the arrays relevant to ground based astronomy will be discussed and data on efficiency, fill factor, dark current, limiting noise performance and uniformity are presented. The tests were performed on reject engineering arrays. Scientific arrays are under development. Yet, test results obtained so far are promissing and demonstrate the potential of these devices for IR astronomy.
01 Jan 1988
TL;DR: A qualitative description of spectral properties, dynamical behaviour and morphology of a selection of mainly southern radio galaxies which have been observed to have extended ionized gas in their vicinity is given in this article.
Abstract: A qualitative description is given of spectral properties, dynamical behaviour and morphology of a selection of mainly southern radio galaxies which have been observed to have extended ionized gas in their vicinity. The question of the significance of this gas in relation to cooling flows is still very much an open one.
11 Apr 1988
TL;DR: In this paper, an adaptive optics prototype for infrared imaging using a visible wavefront sensor and its expected performances in astronomy is described, which employs a real-time phase compensation with a phase shifting optical element, which is usually a deformable mirror.
Abstract: High resolution imaging in ground-based astronomy is limited by the wave front degradation through the turbulent atmosphere. Adaptive optics offers the possibility to overcome these limitations. It employs a real-time phase compensation with a phase shifting optical element, which is usually a deformable mirror. The information for the control of the mirror surface is gained from a wavefront sensor. Thispaper describes an adaptive optics prototype for infrared imaging using a visible wavefront sensor and its expected performances in astronomy.
Journal Article•
Journal Article•
TL;DR: The presence of a galaxie formant lentille gravitationnelle is confirmed by the detection of faibles raies d'absorptions H and K de Ca II (et probablement aussi des raies D1 et D2 de Na I) in the spectre du quasar UM 673 as discussed by the authors.
Abstract: Le quasar UM 673 est resolu en 2 images quasi stellaires separees de 2.22 arc sec, de meme redshift Z=2.72 et de raies spectrales en emission et absorption identiques. La presence d'une galaxie formant lentille gravitationnelle est confirmee par la detection de faibles raies d'absorptions H et K de Ca II (et probablement aussi des raies D1 et D2 de Na I) avec un redshift de Z=0.493 dans le spectre du quasar. Un modele gravitationnel est presente ici et son application donne une masse de 2.4 10 11 M ○. pour la galaxie situee sur la ligne de visee de UM 673
Journal Article•
TL;DR: A list of 25 new Herbig-Haro objects, HH 58 to HH 82, in the Orion molecular clouds and in southern molecular cloud complexes has been compiled as mentioned in this paper, together with a few spectra and some IR observations.
Abstract: A list of 25 new Herbig-Haro objects, HH 58 to HH 82, in the Orion molecular clouds and in southern molecular cloud complexes has been compiled. CCD images in the S II 6717, 6731 forbidden lines are presented for the objects, together with a few spectra and some IR observations. The individual objects and, when identified, their energy sources are discussed. HH 65 is located in the red lobe of the bipolar outflow associated with the highly variable reflection nebula Re 50. HH 67 is a 22-arcsec long sinusoidal jet. HH 68/69 consists of a long, linear chain of four HH knots. HH 72 emerges from a 120-solar luminosity IRAS source embedded in a Bok globule. HH 79 is the first HH object discovered in the Ophiuchus clouds. HH 80/81 in Sagittarius are among the brightest HH objects known, have complex velocities, high excitation conditions and emerge from a 6000-solar luminosity young B-star. HH 82 is associated with the bright variable star S Coronae Australis.
Journal Article•
02 Dec 1988
TL;DR: In this paper, a two-dimensional infrared speckle camera operating at wavelengths of 1μm 5μm was adapted for use as a 2D infrared camera at the National Optical Astronomy Observatories (NOAO).
Abstract: The infrared imager currently in use at the National Optical Astronomy Observatories (NOAO) has been adapted for use as a two-dimensional infrared speckle camera operating at wavelengths of 1μm 5μm Data have been obtained at the Kitt Peak National Observatory (KPNO) Mayall telescope (effective aperture ti 38m) for a number of different sources Diffraction-limited images are presented for two objects, the "Red Rectangle" and NML Cygnus, using the Knox-Thompson algorithm to recover the Fourier phases A comparison of phase-relaxation techniques applied to the integrated phase differences is presented using both the Hudgin method and successive over-relaxation
01 Jan 1988
TL;DR: In this paper, a very high resolution (0.015 nm) image of comet P/Halley was taken with a view to evaluating the contamination of the forbidden oxygen doublet at 630 nm by NH2 features at low resolution.
Abstract: Spectra of comet P/Halley have been taken at very high resolution (0.015 nm) with a view to evaluating the contamination of the forbidden oxygen doublet at 630 nm by NH2 features at low resolution. Comparison is made with a few other bright comets.
TL;DR: In this paper, a multimass anisotropic dynamical model is applied to the observational constraints given by the surface brightness profile and the central velocity dispersion of NGC 1835, an old globular cluster in the Large Magellanic Cloud.
Abstract: A multimass anisotropic dynamical model is applied to the observational constraints given by the surface brightness profile and the central velocity dispersion of NGC 1835, an old globular cluster in the Large Magellanic Cloud. The total mass obtained for this cluster is larger than the previous determinations by at least a factor of five. The method most frequently used to determine the total mass of Magellanic Clouds globular clusters consists of transforming the observed tidal radius into mass, under the assumption of circular orbit of the clusters, due to rotation. Taking into account the above new results, this former method should be used only with great care in the case of Magellanic clusters. 39 references.
Journal Article•
TL;DR: In this paper, the infrared photometry of Comet P/Halley is presented over a period ranging from September 1985 to June 1986, prehelion and posthelion, and short-term variations are observed in the intervals Dec. 25, 1985 - Jan. 3, 1986 and Feb.17 - March 3,1986.
Abstract: Infrared photometry of Comet P/Halley is presented over a period ranging from September 1985 to June 1986, prehelion and posthelion. Short-term variations are observed in the intervals Dec. 25, 1985 - Jan. 3, 1986 and Feb.17 - March 3, 1986. When the comet is in a quiescent state, the infrared flux increases linearly with the diaphragm size, which implies a dust expansion at constant velocity up to a distance to the nucleus of at least 10,000 km. The temperature measured in April 1986 ranges between 250 and 300 K, in reasonable agreement with the expected equilibrium temperature of the grains. Between September 1985 and June 1986, no evidence of variation in the dust nature is observed.
01 Jan 1988
TL;DR: In this paper, the authors compare some basic families of orbits in a number of galactic models and in the restricted three body problem and show that the long period orbits are connected to the short period orbits (SPO) by an infinity of bridges.
Abstract: We compare some basic families of orbits in a number of galactic models and in the restricted three body problem. In plane rotating barred galaxies the orbits around the Lagrangian points L4, L5, L1, L2 are qualitatively similar to the orbits around L4, L5, L3 of the restricted three body problem. The long period orbits are connected to the short period orbits (SPO) by an infinity of bridges. The limit of the sequence of bridges is a family of heteroclinic (in the galactic problem), or homoclinic (in the restricted problem) orbits. In various galactic models the SPO families are connected with the families around L1 L2 by one or more bridges. All these families end at retrograde orbits around the centre. This behaviour is compared with the restricted problem, in which the SPO families join the family around L3, which ends at retrograde orbits around the larger primary.
01 Jan 1988
TL;DR: In this article, images of the dust tail of comet Halley were obtained with the ESO wide-field CCD camera during April 1986 with the Johnson B, V and R filters in polarized light.
Abstract: Images of the dust tail of comet Halley were obtained with the ESO wide-field CCD camera during April 1986 with the Johnson B, V and R filters in polarized light. An analysis of selected images taken on April 6 and 11, processed for photometric analysis, is presented. Results are given for the absolute brightness, the color, the polarization and its variation with wavelength.