Showing papers by "European Southern Observatory published in 1986"
TL;DR: In this paper, les donnees spectroscopiques concernant 32 galaxies HII were presented, and certain conditions comportent des sursauts de formation stellaire (36 ont ete observes au total) for lesquels on a obtenu les temperatures electroniques and les abondances de loxygene and de lazote.
Abstract: On presente les donnees spectroscopiques concernant 32 galaxies HII. Certaines comportent des sursauts de formation stellaire (36 ont ete observes au total) pour lesquels on a obtenu les temperatures electroniques et les abondances de l'oxygene et de l'azote. On examine les relations existant entre les parametres
238 citations
100 citations
TL;DR: In this paper, optical spectra of the black hole candidate X-ray binary LMC X-l reveal that the system is surrounded by an extended, highly ionized He III region, N159F, which appears to be the long-sought-for example of an Xray-photo ionized nebula.
Abstract: Optical spectra of the black hole candidate X-ray binary LMC X-l reveal that the system is surrounded by an extended, highly ionized He III region, N159F, which appears to be the long-sought-for example of an X-ray-photoionized nebula The spatially resolved temperature and ionization structure allows us to measure the previously unobservable extreme ultraviolet (EUV) luminosity of an accreting compact object
89 citations
TL;DR: The determination of the pregalactic helium mass fraction from a constant parameter dY/dZ has been studied in this article, and it is concluded that helium may correlate better with nitrogen than with oxygen.
Abstract: The determination of the pregalactic helium mass-fraction is addressed. Previous attempts to empirically determine Yp from a constant parameter dY/dZ are critically discussed, and new results based on extensive spectroscopy of emission-line galaxies by Terlevich and Melnick (1981) are examined. It is concluded from these new results that helium may correlate better with nitrogen than with oxygen. If Y is plotted against N/H, a single relationship holds for all objects, all the relationships extrapolating back to Yp = 0.237 + or - 0.005. It is suggested that the large value of dY/dZ in blue compact galaxies and the (Y, N/H) relation are due to local contamination by winds from Wolf-Rayet stars.
74 citations
TL;DR: In this paper, the authors describe the instruments and procedures and provisionally summarize the major structures and events that were seen at the time of closest approach of the various spacecraft, between 5 March and 14 March 1986.
Abstract: The near-nucleus and large-scale activity of comet Halley has been monitored at the ESO La Silla Observatory since mid-February 1986. During an 8-week period with excellent observing conditions, images obtained with three telescopes documented the post-perihelion behaviour on a daily basis. We describe the instruments and procedures and provisionally summarize the major structures and events that were seen at the time of closest approach of the various spacecraft, between 5 March and 14 March 1986.
72 citations
13 Oct 1986
TL;DR: The ESO New Technology Telescopy (NTT) as mentioned in this paper has two Nasmyth foci, one for IRSPEC and the other for an instrument operating in the 3000 - 10000 A region.
Abstract: The ESO New Technology Telescopy (NTT) (1),(2) to be operative by the end of 1988, will have two Nasmyth foci. The telescope diameter is 3.5 m and the Nasmyth F-no is F/11, corresponding to a scale of 187 um/arosec. At one focus the Infrared Spectrograph (IRSPEC) will be installed, while the other focus is reserved for an instrument operating in the 3000 - 10000 A region.
54 citations
53 citations
TL;DR: In this article, a strong correlation was found between the Hγ emission and the soft X-ray flux, over several hours of observation of UV Ceti and EQ Peg, suggesting that much of the low level Xray flux which has previously been considered quiescent, in fact derives from small flare events.
Abstract: We present some preliminary results of simultaneous monitoring of the two flare stars, UV Ceti and EQ Peg with EXOSAT and ground based optical spectro-scopy. A strong correlation, found between the Hγ emission and the soft X-ray flux, over several hours of observation of UV Ceti, suggests that much of the low level X-ray flux which has previously been considered ‘quiescent’, in fact derives from small flare events. The implication is that coronal heating in M type dwarfs may result directly from the frequent occurrence of micro-flares.
48 citations
TL;DR: Modeles stellaires pour differentes metallicites permettant de calculer le taux de supernovae de type I dans le cadre du modele de naine CO double degeneree.
Abstract: Modeles stellaires pour differentes metallicites permettant de calculer le taux de supernovae de type I dans le cadre du modele de naine CO double degeneree
42 citations
TL;DR: In this paper, high-resolution measurements of the interstellar lines of CN near 3874 A toward the star Zeta Oph provide a new measurement of the cosmic background radiation temperature of 2.74 + or - 0.5 mA, which is substantially smaller than previously reported and requires larger saturation corrections than used in previous work to determine the CN excitation temperature.
Abstract: Precise high-resolution measurements of the interstellar lines of CN near 3874 A toward the star Zeta Oph provide a new measurement of the cosmic background radiation temperature of 2.74 + or - 0.05 K at 2.64 mm and 2.75 (+0.24, -0.29) K at 1.32 mm. Using a spectral resolution of 156,000, the intrinsic width of these lines is found to be 19.0 + or - 0.5 mA, which is substantially smaller than previously reported and requires larger saturation corrections than used in previous work to determine the CN excitation temperature. 16 references.
38 citations
TL;DR: The occultation of a star by Neptune on August 20, 1985 was observed at 22 micron wavelength with telescopes at the European Southern Observatory (ESO) and the Cerro Tololo Inter-American Observatory (CTIO).
Abstract: The occultation of a star by Neptune on August 20, 1985 was observed at 22 micron wavelength with telescopes at the European Southern Observatory (ESO) and the Cerro Tololo Inter-American Observatory (CTIO) The detection of a 'central flash' midway between immersion and emersion has allowed the determination of Neptune's oblateness and the atmospheric extinction at 22 microns, which is related to the stratospheric methane mixing ratio An oblateness of (208 +019 or -018) x 10 to the 2nd is found and, assuming a stratospheric temperature of 120 K, a value of 06 percent is inferred (with an uncertainty of a factor of 10) for the methane mixing ratio (CH4/H2) at 03 mbar The latter value may indicate supersaturation of methane in Neptune's stratosphere
TL;DR: In this article, the evolution of model stellaires has been studied and a 2,5 a 8 M ϋ (n 2.5 ) log Z = −8, −6, −4, depuis la sequence principale jusqu'a lignition du centre de carbone ou la degenerescence du cœur de CO
Abstract: Calcul de l'evolution de modeles stellaires de masse 2,5 a 8 M○. et log Z=−8, −6, et −4, depuis la sequence principale jusqu'a l'ignition du centre de carbone ou la degenerescence du cœur de CO
TL;DR: In this article, the bifurcations of families of double and quadruple period orbits in a simple Hamiltonian system of three degrees of freedom were studied, depending on whether a stability curve crosses or is tangent to the axis b =−2.
Abstract: We study the bifurcations of families of double and quadruple period orbits in a simple Hamiltonian system of three degrees of freedom. The bifurcations are either ‘simple’ or ‘double’, depending on whether a stability curve crosses or is tangent to the axis b=−2. We have also generation of a new family whenever a given family has a maximum or minimum e or ∌.
TL;DR: In this article, a deep image of the Kepler SNR has been obtained in the light of H-alpha + N II forbidden-line with the faint object spectrograph and camera (EFOSC) and a CCD detector at the ESO 3.6 m telescope.
Abstract: A deep image of the Kepler SNR has been obtained in the light of H-alpha + N II forbidden-line with the faint object spectrograph and camera (EFOSC) and a CCD detector at the ESO 3.6 m telescope. The visibility of the optically emitting knots of ionized gas has been greatly enhanced by subtraction of the continuum radiation. Features as faint as 2 percent of the night-sky brightness have been identified and a half-shell of emission is clearly revealed. The total H-alpha luminosity of the ionized gas is estimated to be 8.3 x 10 to the 45th photons/s at a distance of 5 kpc implying a mass of ionized hydrogen of about 0.02 solar mass. An automatic searching program has been used to identify and list individual emission features in the continuum-subtracted image. A catalog with accurate celestial positions and approximate fluxes for 64 emission-line knots is given. 13 references.
TL;DR: In this article, the similarity between the two spectra in a hitherto unobserved range was reported, suggesting that the two images are in fact distinct quasars located close together in space.
Abstract: It has recently been suggested1 that the quasars 1146 + 111B,C, separated on the sky by 2.6 arc min, are actually two images of a single object produced by an extremely massive gravitational lens. The basis for this suggestion is the similarity in redshifts (within 100–200 km s−1) and spectral features. Here we report differences between the two spectra in a hitherto unobserved range, suggesting that the two images are in fact distinct quasars located close together in space.
TL;DR: In this article, a noyau stellaire variable and brillant of magnitude V∼13.5 is described as the object PKS 2005-489, which is one of the most popular stellaires of the type BL.
Abstract: La galaxie PKS 2005-489 a un noyau stellaire variable et brillant de magnitude V∼13. On rapporte des observations RX, UV, optiques et radio qui indiquent une variabilite et un continuum en loi de puissance dans chacune de ces bandes, montrant que PKS 2005-489 est l'un des objets du type BL les plus brillants
TL;DR: In this article, the outward motion of the thin wall of laser-heated small gold cavities was investigated using 6-frame optical and single-frame x-ray backlighting, and the measured velocity was attributed to the pressure produced by an ablative heat wave which was driven into the wall by thermal soft-X-ray radiation generated in the cavity.
Abstract: The outward motion of the thin wall of laser-heated small gold cavities was investigated using 6-frame optical and single-frame x-ray backlighting. The measured velocity is attributed to the pressure produced by an ablative heat wave which is driven into the wall by thermal soft-X-ray radiation generated in the cavity.
01 Jan 1986
TL;DR: In the case of multi-mode oscillations amplitude ratios can be variable as discussed by the authors, and there are even first indications of systematic differences between different groups of stars in terms of their spectral properties.
Abstract: Thanks to the fast rotation which via the Doppler effect permits one to indirectly resolve the stellar disk in one dimension and amplitudes often reaching 10 km/s or more, nonradial oscillations with degrees up to m = 20 are easily detected in high S/N (better than 200) observations of early type stars. Recent work by Smith (1981, 1985), Vogt and Penrod (1983), Penrod and Smith (1985), Penrod (1985), Baade (1982, 1984, and unpublished data), and Baade and Ferlet (1984) show the ubiquity of nonradial oscillations in the upper left part of the HRD. With the increasing amount of data some general properties of these pulsations are emerging, and there are even first indications of systematic differences between different groups of stars. The latter is encouraging in the context of this workshop because it could mean that from the analysis of the oscillations additional insight can be gained into the stars’ internal structure, i.e. seismology of early-type stars may in fact become a reality. From the above references the following can be extracted as the most important results obtained thus far:
Virtually all “normal” stars with spectral type B6 or earlier are nonradial oscillators, at least occasionally (for supergiants the spectroscopic evidence is still less complete).
Observations have not so far succeeded in restricting the range of possible excitation mechanisms suggested by various theoretical models. But the rotation rate may play an important role.
Simultaneously excited modes are are often coupled: Pm x m = const (m = mode degree; the constant is different for different stars).
The modes with the longest wavelengths have typical periods between 0.5 and 2 days. If they are g-modes, very high radial overtones are implied. On the other hand, the nonradial modes observed in some of the radially pulsating s Cephei stars all fall into the range 0.13 to 0.3 day and thus are almost identical to those of the radial modes.
For modes with periods much longer than the radial fundamental mode, in some slow to moderately fast rotators a horizontal-to-vertical amplitude ratio, K, of only 0.15 has been deduced. This is in conflict with the characteristics of g and r modes as the only ones with so long periods. At least in most Be stars, K appears to be much larger.
The mode spectra of Be and Bn stars seem to differ in that symmetry variations of the overall profiles have been found only in Be stars - but also in the narrow lined 53 Per stars (however, the modes causing these variations are probably different in 53 Per and Be stars).
Mass loss episodes from Be stars are correlated with temporarily decreased (often vanishing) pulsation amplitudes.
The V/R ratio of the double emission in the Hel λ6678 profile of many Be stars varies with the period of the slowest pulsation mode.
In the case of multi-mode oscillations amplitude ratios can be variable. In some stars also a mode switching has been diagnosed.
In many stars pulsation cycles are not always all alike. Various deviations from the mean occur. At least in some cases these are very unlikely to be due to multi-mode beating.
TL;DR: In this article, the authors confirm the suggestion de Greenstein et Sargent of l'existence d'une connexion entre les sous-naines B du champ and les etoiles bleues de la branche horizontale.
Abstract: L'analyse confirme la suggestion de Greenstein et Sargent de l'existence d'une connexion entre les sous-naines B du champ et les etoiles bleues de la branche horizontale. On discute des implications relatives a l'evolution
TL;DR: On a trouve 49 raies d'observation entre 3500 and 6000 A and on a identifie sept deplacements vers le rouge for ces raies as discussed by the authors.
Abstract: On a trouve 49 raies d'observation entre 3500 et 6000 A et on a identifie sept deplacements vers le rouge pour ces raies. Six des systemes d'absorption se situent dans le domaine restreint z abs =1,971 a z abs =2,138
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TL;DR: In the quarter century since the first optical identification of a "radio star" (3C 48), astronomers have come to general agreement that the underlying quasar energy source is accretion onto a massive black hole.
Abstract: In the quarter century since the first optical identification of a "radio star" (3C 48), astronomers have come to general agreement that the underlying quasar energy source is accretion onto a massive black hole. There is much less agreement on the detailed physics of the processes by which this energy is converted to the forms observed, but this has not prevented the objects from serving as valuable probes of the universe at distant times and places.
TL;DR: In this article, the best signal-to-noise ratio stellar occultations have been reanalysed to look for yet undetected dark matter around Uranus and Neptune using stellar occulations observed at the European Southern Observatory (ESO) on 22 April 1982 and at the Canada France Hawaii Telescope (CFHT) on 15 June 1983.
Abstract: In addition to their natural satellites, the giant planets possess a surprisingly rich population of moonlets, rings, arcs and diffuse haloes of dust1–6, the dynamics of which involves gravitational interactions7 and radiation and magnetic forces8,9. Recent analyses (by A.B., W. Hubbard, F.R. and B.S.) of isolated events observed around Neptune indicate the existence of an incomplete or at least a highly azimuthally variable ring or ‘arc’ around Neptune. Similar phenomena may be detectable around Uranus. In order to look for yet undetected dark matter around Uranus and Neptune, the best signal-to-noise ratio stellar occultations have been reanalysed. To be confirmed, an ‘event’ should be observed with more than one telescope on the same site since the Fresnel scale (see below) is about 2–3 km at the level of Uranus and Neptune, and it should also be observed from widely separated observatories (100–1,000 km) to have an idea of the spatial extent of the occulting object, and to distinguish between satellites and ring-like structures. Moreover, theoretical models of diffracting bars or circular objects provide useful tests to reject some isolated events as being incompatible with real and celestial events10. We report here an investigation of the surroundings of Uranus and Neptune using stellar occulations observed at the European Southern Observatory (ESO) on 22 April 1982 and at the Canada France Hawaii Telescope (CFHT) on 15 June 1983, respectively. The high signal-to-noise ratio of these observations sets stringent limits on the presence of matter around these planets.
TL;DR: In this paper, variability represented one of the most important tools for the understanding of the physical processes involved in Active Galactic Nuclei (AGN) in the early days, and it has been used extensively since then.
Abstract: Since the early days, variability represented one of the most important tools for the understanding of the physical processes involved in Active Galactic Nuclei.
Journal Article•
20 Aug 1986
TL;DR: In this paper, the linear relationship between the applied support force and the deformation of the mirror resting on a force-based support system has been investigated with a lm diameter spherical mirror with a thickness of 18,9 mm and 78 supports.
Abstract: Active optics, as envisaged for the ESO NTT, is based on four principles: 1. The linear relationship between the applied support force and the deformation of the mirror resting on a force based support system. 2. The orthogonality of the corrected aberrations. 3. The restriction to correct only those aberrations for which small forces are necessary, i.e. long wavelength aberrations as e.g. astigmatism and spherical aberration, which are also those modes induced by errors in the system. 4. The use of precalibrated forces for these corrections. Using the Shack-Hartmann test method for the analysis of the wavefront, we have confirmed these principles in an experiment with a lm diameter spherical mirror with a thickness of 18,9 mm and 78 supports.
13 Oct 1986
TL;DR: This paper critically examines the current software development scenario, in the academic as well as in the industrial environment, and identifies areas where improvements should be made, and suggest possible techniques which can be used.
Abstract: Next generation software techniquesR. Albrecht ( *), H. -M. Adorf, A. RichmondSpace Telescope European Coordinating Facility, European Southern ObservatoryKarl -Schwarzschild -Str. 2, D -8046 Garching, F.R.G.( *) Affiliated to the Astrophysics Division, Space Science Department,European Space AgencyAbstractThis paper critically examines the current software development scenario, in the academicas well as in the industrial environment. We identify areas where improvements should bemade, and suggest possible techniques which can be used. The use of knowledge -based systemsis considered, and their application to software development and to scientific research isexamined.IntroductionEnormous advances have occurred during the last 20 years in the area of hardware. Throughan evolution of both the technology as well as the manufacturing techniques, main memoriesincreased from typically kilobits to many megabits, external storage from kilobytes to giga-bytes, and processing speed is now measured in megaflops. VHSI approaches, right now beingdeveloped for military applications, will spin off even more processing prower.The question is: have the hardware improvements been paralleled by equivalent improve-ments in the software area? We contend that the answer is: no. Although the need exists forsoftware systems that are orders of magnitude more sophisticated that those that were incommon use in past years, most development teams attempt to use basically the same tech-niques that were used in those simpler times. Sure, flowcharts have been replaced by PDL,and programming languages are getting more comfortable. However, we are not developing soft-ware orders of magnitude faster than we used to, nor have we progressed very much in thearea of software quality control. We have not changed software techniques as radically ashardware changed from TTL to CMOS, we have not introduced software changes equivalent tochanges from IC to LSI to VHSI.Within the area of astronomy the initial single -user, stand -alone programs of earlierdays are currently integrated into or replaced by rather complex image processing systemslike AIPS, GIPSY, IRAF /SDAS, and MIDAS to name only a few. Recent achievements, especiallythe advent of space -born observatories like IUE, and the forthcoming Hubble Space Telescopeand ROSAT, present a challenge to the existing software systems. National and internationalcollaborations form which develop a natural need to share software resources, but they areplagued with software portability problems'.Current software development methodologyThere are two major areas in which large scale software projects are being developed:industry and academia.In industry, attempts to enforce rigid methodologies upon what is essentially a creativeprocess have for the most part backfired, turning software development into a managementheavy bureaucracy. In fact, software is being produced using the management methodologiesdeveloped in a hardware producing environment. While this might be justifiable in limited -scope projects with well defined, stable requirements, this approach is guaranteed to failin projects which need to get close to the state -of- the -art.Academia has succeeded in retaining more of the intellectual challenge, which the devel-opment of software undoubtedly is. However, there is a definite tendency to always startfrom scratch, thereby unnecessarily duplicating the efforts of other people. The NotInvented Here" syndrome thrives. Of course there is a reason for this: most software systemsdeveloped in academia are of such poor engineering that they barely survive upgrades of thehost operating system, cannot be used on other computers, and usually die with the departureof the original author.It is evident that in both areas an inordinate amount of resources are being wasted. Inindustry we have to accept software production figures in the order of one line of code perman -day; in academia, all investments in software efforts usually have to be written off atthe end of a research project.
20 Aug 1986
TL;DR: The New Technology Telescope (NTT) as discussed by the authors is an anoptical telescope with a primary mirror of 3.5 meters and two Nasmyth foci, designed at ESO's LaSilla Observatory.
Abstract: 8046 GarchingFederal Republic of GermanyAbstractThis paper describes of the basic concepts and current status of the ESO NTT Project. The NTT is anoptical telescope with a primary mirror of 3.5 meters and two Nasmyth foci. It will operate at ESO's LaSilla Observatory, and is planned for installation in 1988. The project combines a number of innovativetechnical solutions.IntroductionAs an intermediate step towards a very large telescope (VLT), ESO decided to design and build a NewTechnology Telescope (NTT) with a mirror measuring 3.5 m in diameter. This telescope will help reduce demandon the 3.6 m telescope on La Silla and will offer an opportunity for practical testing of new ideas fortelescope design.Until fairly recently, a telescope of the 3 to 4 m class was considered as the largest telescope for amajor observatory. Telescopes of this size were therefore built as universal instruments with considerablecapital investment. The new approach, taken also by the NTT Project, aims at achieving a large telescope at
20 Aug 1986
TL;DR: In this paper, an extensive geographical survey of Northern Chile led to the selection of a few representative summits for comparison with the observatory of La Silla, and a technical description of the instrumentation developed by ESO including the differential Hartmann open air monitor.
Abstract: Very large telescope projects, due to their increased expected performances and cost, have prompted several campaigns to compare existing and potential observatory sites throughout the world.ln the frame of the ESO-VLT studies, an extensive geographical survey of Northern Chile led to the selection of a few representative summits for comparison with the observatory of La Silla. Standard meteorological towers, acoustic radar, Rawinsondes, microthermal sensors and optical seeing monitors will be collecting experimental data in the years to come. After a brief review of the relations between atmospheric and optical seeing parameters, the particular case of Northern Chile is described with the help of data collected up to naw..Then follows a technical description of the instrumentation developed by ESO including the differential Hartmann open air monitor.© (1986) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.