Showing papers by "European Southern Observatory published in 1991"
Computer Sciences Corporation1, Johns Hopkins University2, University of California, Los Angeles3, Tel Aviv University4, Ohio State University5, Sapienza University of Rome6, Rutherford Appleton Laboratory7, Autonomous University of Madrid8, University of California, Berkeley9, University of Michigan10, Western Kentucky University11, Columbia University12, Space Telescope Science Institute13, University of Toronto14, Max Planck Society15, Bowling Green State University16, University College London17, Complutense University of Madrid18, University of California, San Diego19, Agnes Scott College20, University of Arizona21, Goddard Space Flight Center22, European Southern Observatory23, Uppsala University24, University of Alabama25
TL;DR: In this paper, an 8-month campaign of monitoring NGC 5548 with IUE is described, with the goal of determining the size and structure of the broad-line region in active galactic nuclei.
Abstract: This is an electronic version of an article published in The Astrophysical Journal. Clavel, J. et al. Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. I. An 8 month campaign of monitoring NGC 5548 with IUE. The Astrophysical Journal 366 (1991): 64-81
396 citations
TL;DR: In this paper, the optical filaments in Centaurus A were analyzed using both narrow-band imaging and long-slit spectroscopy, showing that the line-emitting filaments are complex and highly structured at the limit of ground-based resolution.
Abstract: New observations, including both narrow-band imaging and long-slit spectroscopy, of the optical filaments in Centaurus A are presented. The line-emitting filaments which compose part of the well-known optical-jet are complex and highly structured at the limit of ground-based resolution. Variations in the surface brightness, line intensity ratios and the velocity field occur on spatial scales ∼ 100 pc. No evidence of [O III] λ5007 emission associated with either the inner jet or a possible counter jet are found. The emission line spectra of the filaments are very similar in character to those of the spatially extended nebulosities in more distant radio galaxies and radio quasars.
99 citations
TL;DR: In this paper, high-resolution observations of the core of the globular cluster 47 Tucanae with the Faint Object Camera on the Hubble Space Telescope reveal a high density of "blue straggler" stars, occupying the upper end of the main sequence from which all stars in the cluster should have long since evolved.
Abstract: High-resolution observations of the core of the globular cluster 47 Tucanae with the Faint Object Camera on the Hubble Space Telescope reveal a high density of 'blue straggler' stars, occupying the upper end of the main sequence from which all stars in the cluster should have long since evolved. Their presence in the dense core supports the hypothesis that they formed by stellar collision and coalescence, and, as the heaviest objects in the cluster, have drifted to the core.
66 citations
TL;DR: B and V CCD photometry for 1565 stars in the low-concentration globular cluster NGC 6171=M107 is presented in this paper, where the authors present a CCD image for each star in the cluster.
Abstract: B and V CCD photometry is presented for 1565 stars in the low-concentration globular cluster NGC 6171=M107.
48 citations
TL;DR: In this article, spectroscopic observations of the He II line at 4,686 A from which they deduced a new estimate of the orbital speed of the compact object was obtained, together with the mass ratio of the binary components, derived from X-ray observations.
Abstract: THE unusual galactic object SS433 is well known because of the periodic red and blueshifts, corresponding to velocities of 50,000 kms–1, of some of its emission lines1,2. It is now believed to be a binary system that emits two oppositely directed precessing jets moving with a speed of 0.26c. The jets are produced and controlled by an accretion disk, probably geometrically thick, around a compact object whose nature is still controversial. Several arguments have been advanced21–23suggesting that it is a black hole. Here we report spectroscopic observations of the He II line at 4,686 A from which we deduce a new estimate of the orbital speed of the compact object. Together with the mass ratio of the binary components, derived from X-ray observations, we find that the compact object is a neutron star, not a black hole. Analysis of the double-peaked profile of the He II line suggests that it is emitted by the accretion disk (or its corona), which is partly obscured by an opaque wind from the hot-spot region.
45 citations
TL;DR: In this paper, a detailed description of the set-up and optimization of the optical system, based on the three levels (i.e. time frequencies) of active correction, is given.
Abstract: This paper is the fourth, and last, in the series on active optics as realized in the ESO New Technology Telescope (NTT). It gives a detailed description of the set-up and optimization of the optical system, based on the three levels (i.e. time frequencies) of active correction. The first results in direct imagery with the telescope optimized only near zenith (‘Astronomical First Light’) yielded immediately the best star images ever recorded in ground-based astronomy with a full-width-half-maximum of 0·33 arcsec on a CCD detector with pixels of 0·123 arcsec diameter.
44 citations
TL;DR: In this article, a large set of numerical simulations has been performed by using two different N-body codes to derive detailed properties of the end-product of dissipationless collapse.
Abstract: A large set of numerical simulations has been performed by using two different N-body codes to derive detailed properties of the end-product of dissipationless collapse. Three classes of initial mass distribution have been adopted, characterized by different inhomogeneity scales, with velocity dispersion corresponding to a virial ratio in a range 5 × 10 −4 -0.2. The results show that the phase space properties of the final equilibrium state depend strongly on the initial mass distribution.
35 citations
TL;DR: For thin meniscus mirrors, the modes which correct arbitrary wavefront aberrations in the most efficient way are derived as mentioned in this paper, which are similar to the free-vibration modes of the mirror.
Abstract: For thin meniscus mirrors the modes which correct arbitrary wave-front aberrations in the most efficient way are derived These modes are similar to the free-vibration modes of the mirror The relationship between the two types of modes is shown The most important features such as orthogonality and energy of the modes are discussed This modal approach is applied to a few practical problems in connection with the primary mirrors of the Very Large Telescope of the European Southern Observatory
33 citations
TL;DR: In this paper, the optical position, light-curve and early spectral development of the outburst support the identification of Nova Muscae 1991 as a binary, and similarities with A0620−00 (known optically as V616 Mon) in its early evolutionary stages led them to classify NovaMuscae1991 as a candidate black-hole binary.
Abstract: X-RAY novae form a subclass of low-mass X-ray binaries, which typically consist of a neutron star accreting material from a low-mass, late-type companion. In a few cases, however—notably A0620–00 (ref. 1)—, the accreting object may be a black hole. The detection and study of the optical counterpart is then of great importance in understanding the origin of the X-ray emission and the nature of the companion. We report here the discovery of a new X-ray nova, Nova Muscae 1991, which we found in a search for the optical counterpart of the new transient X-ray source GRS1121–68. The optical position, light-curve and early spectral development of the outburst support the identification of Nova Muscae 1991 as a binary, and similarities with A0620–00 (known optically as V616 Mon) in its early evolutionary stages led us to classify Nova Muscae 1991 as a candidate black-hole binary.
29 citations
TL;DR: In this paper, the spectral properties of the polar haze and CH4 absorption lines in the range 4200-4700 cm−1 were investigated and it was found that the haze is widely distributed in the south and north polar region, and is not particularly associated with auroral activities.
29 citations
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TL;DR: A review of the current understanding of the Herbig-Haro phenomenon can be found in this article, where the history of the phenomenon is outlined and observations at various wavelengths summarized.
Abstract: This article reviews our current understanding of the Herbig-Haro phenomenon. HH objects are shocks occurring in supersonic flows from very young stars. The history of HH research is outlined, and observations at various wavelengths summarized. Particular attention is paid to the highly collimated Herbig-Haro jets, whose morphology, kinematics and physical properties are discussed. Shock models for the jet structure and the working surface of jets are reviewed, and two regions with HH jets are examined in detail. The energy sources of HH flows are, as a class, among the youngest stars known, and it is argued that HH objects are related to disk accretion events in their driving sources.
TL;DR: A method for testing the surfaces of large mirrors has been developed at the National Astronomy Observatories (NOAO) to be used even when conditions of vibration and thermal turbulence in the light path cannot be eliminated, and was shown to have a sensitivity equal to a Foucault test.
Abstract: A method for testing the surfaces of large mirrors has been developed at the National Astronomy Observatories (NOAO) to be used even when conditions ofvibration and thermal turbulence in the light path cannot be eliminated. The full aperture ofthe mirror under test is examined by means of a scatterplate interferometer that has the property of being a quasi-common-path method, although any means for obtaining interference fringes will do. The improvements in the NOAO method lie in the means for capturing the fringe pattern and the analysis that follows. The method uses a remotely operated CCD camera system to record the fringe pattern from the workpiece. Recording the spot pattern resulting from a Hartmann test screen placed over the workpiece is also possible, but the analysis methods will differ from those discussed. By operating the test equipment remotely, the optician does not cause unnecessary vibrations or heat in the testing area. The typical test is done with a camera exposure of about a millisecond to "freeze" the fringe pattern on the detector. Averaging up to 10 separate exposures effectively eliminates the turbulence effects. The analysis program is based on a method originally developed for examining telescope images affected by atmospheric seeing. From the intensity information, a phase map of the wavefront reflected from the surface is obtained using a new phase-unwrapping technique. The resolution is limited only by the number of fringes in the test aperture. The method described provides the optician with complete numerical information and visual plots for the surface under test and the diffracted image the method will produce, all within a few minutes, to an accuracy of 0.01 μm measured peak-to-valley. The method has been extensively used for a variety of tests of a 1.8-m-diam borosilicate glass honeycomb mirror, where the method was shown to have a sensitivity equal to a Foucault test. The test setup is described, including the analysis technique, and examples of the results obtainable are provided. The method continues to be used at NOAO for testing large optics (currently a 3.5-m honeycomb mirror).
TL;DR: In this paper, a preliminary analysis of these images is reported, which includes measurements of the relative positions and magnitudes of the lensed images of the QSO, and of the galaxy.
Abstract: Images of the gravitational lens system G2237 + 0305 have been obtained with the Faint Object Camera on board the Hubble Space Telescope A preliminary analysis of these images is reported here and includes measurements of the relative positions and magnitudes of the lensed images of the QSO, and of the lensing galaxy No evidence is found for a fifth lensed image
TL;DR: In this paper, the 12 C/13 C abundance ratio in the direction of ζ Oph was determined to be 67.6±4.5 using the equivalent widths of 12 CH + and 13 CH + lines used for this determination.
Abstract: Observations of the molecular ion CH + at 4232 A in the direction of ζ Oph have determined the 12 CH + / 13 CH + abundance ratio to be 67.6±4.5. The equivalent widths of 12 CH + and 13 CH + lines used for this determination were 23.246±0.068 mA and 0.410±0.022 mA, respectively. The line profiles show a very broad component with Gaussian velocity dispersion parameter b=9.9±1.3 km s −1 . These data provide strong evidence that the 12 C/ 13 C abundance ratio in the direction of ζ Oph is close to 70
TL;DR: The first high-resolution observations of R136 with the Faint Object Camera on board the Hubble Space Telescope are reported in this paper, showing that R136a is a very compact star cluster consisting of more than eight stars within 0.7 arcsec diameter.
Abstract: R136 is the luminous central object of the giant H II region 30 Doradus in the LMC. The first high-resolution observations of R136 with the Faint Object Camera on board the Hubble Space Telescope are reported. The physical nature of the brightest component R136a has been a matter of some controversy over the last few years. The UV images obtained show that R136a is a very compact star cluster consisting of more than eight stars within 0.7 arcsec diameter. From these high-resolution images a mass upper limit can be derived for the most luminous stars observed in R136.
TL;DR: The first fully active telescope, the ESO NTT, produced its first astronomical images (first light) in March 1989 as discussed by the authors, and the background work leading to them is described.
Abstract: The first fully ‘active’ telescope, the ESO NTT, produced its first astronomical images (‘First Light’) in March 1989. The spectacular results and the background work leading to them are described. The origins of the development of the active optics concept are reviewed and a description of the NTT system is given. Recent operational results and limitations to optical quality are discussed, as well as the steps taken to establish a fully automatic correction system. Finally, the optical efficiency of telescopes is considered in the light of the NTT experience and the implications for future ground- and space-based telescopes summarized.
TL;DR: In this paper, the authors present a tracking system that stabilizes atmospheric and instrumental image motion in vacuum tower telescopes, which is designed to lock on low contrast features, such as solar granulation or other small scale structure.
Abstract: We present a tracking system that stabilizes atmospheric and instrumental image motion in vacuum tower telescopes. The system is designed to lock on low contrast features, such as solar granulation or other small scale structure. A matrix diode array rapidly scans the scene of interest, usually with a field of 5 arcsec. Images are cross-correlated in real time with a previously recorded reference image of the same area. The drive signal for the image motion corrector, a small, articulated mirror, is generated by measuring the position of the cross correlation maximum. Reference pictures are updated every 30 s in order to adapt to the changing small scale solar features. Performance tests show that the residual image motion in the tracked image is 0.05 arcsec rms compared to a typical 0.5 arcsec rms for the untracked image. The system locks on any small scale structure anywhere on the sun. The bandwidth of the servo system is 40 Hz, or sufficient to stabilize image motion on a meter-class solar telescope.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this paper, a spectral analysis of the infrared sky radiance at λ ≈ 10μm was made at the ESO-site of La Silla in Northern Chile.
Abstract: A spectral analysis of the fluctuations of the infrared sky radiance at λ ≈ 10μm was made at the ESO-site of La Silla in Northern Chile. The data are compared to literature. The consequences of the results on infrared observing for future large telescopes are discussed: our data suggest that in order to achieve background noise limited performance in the 10μm atmospheric window chopping with frequencies of ≈8 Hz and amplitudes of ≈10 arcsec is mandatory.
TL;DR: Several estimators of inclination dependence of galaxy brightnesses, diameters and average surface brightnesses have been introduced in the literature as discussed by the authors, and some of them are shown to be biased.
Abstract: Several new estimators of inclination dependence of galaxy brightnesses, diameters and average surface brightnesses have been introduced. Estimators from the literature are also reviewed and some of them are shown to be biased. The analysis presented takes into account selection effects which take place in the two most popular kinds of galaxy samples : magnitude- and diameter-limited.
TL;DR: In this article, the authors presented deep BVRIK images of PKS 1413+135 and tentatively classified it as an S0b-c galaxy using the DDO system.
Abstract: Deep BVRIK images of PKS 1413+135 are presented. The K-band image is dominated by the unresolved BL Lac core, although the surrounding galaxy is visible. The optical images are completely dominated by the host galaxy. The radial surface brightness distributions in R and I are best fitted by a combination of a large exponential disc and a small central bulge. The disc/bulge ratio is ∼ 4-7 and the colours of the host galaxy are quite red so it is tentatively classifed as an S0b-c galaxy (using the DDO system). This is the first BL Lac object for which there is conclusive evidence for an underlying disc galaxy and only the second object for which a disc-type host has been reported at all
TL;DR: This paper presents descriptions of four informa tion/system interface projects in progress at ESRIN, the establishment of the European Space Agency (ESA) in Italy, which suggest that next generation scientific information systems will have to be designed for direct access by end users to a large number of information sources, through a common interface.
Abstract: This paper presents descriptions of four information-system interface projects in progress at ESRIN, each demonstrating a somewhat different approach to interface design, but ali sharing the commonality of responding to user goals, tasks and characteristics. It is suggested that next-generation scientific information systems will have to be designed for direct access by end users to a large variety of information sources, through a commom interface. Design of such systems, including their interfaces, should be based on a multi-level analysis of user goals, tasks and domain views.
TL;DR: In this article, the authors present descriptions of four informa tion/system interface projects in progress at ESRIN, the estab lishment of the European Space Agency (ESA) in Italy.
Abstract: This paper presents descriptions of four informa tion/system interface projects in progress at ESRIN, the estab lishment of the European Space Agency (ESA) in Italy. Each project demonstrates a somewhat different approach to mter face design, but all share the commonality of responding to user goals, tasks and charactenstics. It is suggested that next generation scientific information systems will have to be designed for direct access by end users to a large vanety of information sources, through a common interface. Design of such systems, including their interfaces, should be based on a multi-level analysis of user goals, tasks and domain views.
TL;DR: The Come-On Plus adaptive optics system as mentioned in this paper is an upgrade of the original COMON-ON instrument, with a 52 actuator deformable mirror and 30 Hz correction bandwidth.
Abstract: This paper is a presentation of the Come-On-Plus adaptive optics system, based on the Come-On
prototype. Come-On-PIus will be set up in 1992 on the ESO 3.6 m telescope in La Silla (Chile). It is an
upgrade of the Come-On instrument, with a 52 actuator deformable mirror, and 30 Hz correction
bandwidth. But the main improvement concerns the wavefront sensing, designed in this instrument for
astronomical applications, with a high detectivity wavefront sensor and a specific mirror control
algorithm. This system is planned for routine astronomical observing as well as providing design
parameters for the adaptive optics system of the ESO Very Large Telescope (VLT).
TL;DR: In this article, the authors discussed the implications of the ESO VLT and the latest developments in the design of its active optics and discussed the most important remaining problem is the local air condition.
Abstract: The latest developments of active optics of the ESO NTT include the reduction of friction in the lateral supports of the primary mirror and in the positioning system of the secondary mirror. The most important remaining problem is the local air condition. The implications for the ESO VLT and the latest developments in the design of its active optics are discussed.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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TL;DR: The first proposal of a flexible image transport system for astronomy was made by Wells and Greisen (1979) as discussed by the authors, which described a general way to encode both a definition of the data and the data itself in a machine independent way using magnetic tape as the standard transport medium.
Abstract: The first proposal of a Flexible Image Transport System for astronomy was made by Wells and Greisen (1979). It described a general way to encode both a definition of the data and the data itself in a machine independent way using magnetic tape as the standard transport medium. The advantage of using a standard format for transport of astronomical images was soon realized and most major observatories implemented it as the prime format for data exchange. Subsequently, the FITS tape format (Wells et al., 1981) was recommended as the standard format for interchange of image data between all observatories by Commission 5 at the 1982 General Assembly of International Astronomical Union (IAU) in Patras (IAU Inf. Bull. 49, 1983). The first extension of the FITS format was also recommended during that meeting. This “random-groups” extension (Greisen and Harten, 1981) defined the way to transport a large number of data matrices with irregular spacing.
Journal Article•
TL;DR: In this article, the yttrium and zirconium abundances were determined in a sample of 20 metal-poor stars on the basis of high resolution, high signal-to-noise spectra.
Abstract: The yttrium and zirconium abundances are determined in a sample of 20 metal-poor stars on the basis of high resolution, high signal-to-noise spectra. Significant differences between the behaviours of these two neighbouring elements are found, zirconium being less deficient than yttrium in Population II stars. Moreover, there is a genuine cosmic scatter in the abundances of these two elements relative to iron, of the order of 20%. The scatter is lower when these elements are compared to titanium, which might indicate that a significant fraction of the lighter neutro-capture elements are produced in massive stars
01 Jan 1991
TL;DR: The best known extragalactic distance of the Virgo cluster (21.2 ± 0.6 Mpc) from seven independent methods is presently the best known.
Abstract: The distance of the Virgo cluster (21.2 ± 0.6 Mpc) from seven independent methods is presently the best known extragalactic distance. On the other hand the cosmic recession velocity of the cluster (v = 1144 ±18 km s-1) within a nearly Machian frame can be determined using relative distances to more distant clusters. The resulting value of the Hubble constant — freed from all velocity perturbations — is Ho = 52 km s-1Mpc-1. The formal error of this determination is very small.
TL;DR: In this article, the radio-bright 'knots' are spatially extended, and there is significant emission in the regions between the knots, suggesting that the jet propagates essentially free of losses, generating radio and optical emission at its edges, where interstellar material may be encountered.
Abstract: THE jet in the nearby elliptical galaxy NGC4486 (M87) is a prototype of this kind of nuclear activity1. High-resolution observations over a wide wavelength range have been used to investigate the propagation of energy along the jet and the radiation mechanism, but these studies have been hampered by the much lower resolution available at optical compared with radio wavelengths. Here we present high-resolution multi-colour images of the jet, obtained using image reconstruction techniques. Morphological features in the jet known from radio observations are seen in our optical images. In particular, we find that the radio-bright 'knots' are spatially extended, and that there is significant emission in the regions between the knots. There is also evidence for limb-brightening at a number of positions along the jet. Taken together, our observations suggest that the jet propagates essentially free of losses, generating radio and optical emission at its edges, where interstellar material may be encountered.
TL;DR: In this article, the authors examined different options to achieve blind operation of optical interferometers, focussing on the application to the very large Telescope Interferometer (VLTI).
Abstract: Maximum sensitivity for optical interferometers is achieved only when the optical pathlengths between the different arms can be equalized without using interference fringes on the research object itself. This is called “blind operation” of the interferometer. In this paper I examine different options to achieve this, focussing on the application to the Very Large Telescope Interferometer (VLTI). It is proposed that blind operation should be done using a so-called “coherence autoguider”, working on an unresolved star of magnitude V=11 to 13 within the “isoplanatic patch for coherencing”, which has a diameter of about 1 degree. Estimates of limiting magnitudes for the VLTI are also derived.