Messenger No. 35 (March 1984)
Report on the First Eso-Cern Symposium on Large scale Structure of the Universe Cosmology and Fundamental Physics
The first ESO-CERN Symposium was held at CERN, Geneva, from 21 st to 25th November 1983 and was attended by approximately 200 participants. The discussions concentrated on the general field of Cosmology, where the progress made in the past twenty years, both in elementary particles and astronomy, has shown that these two fields of basic research are merging toward a new and fundamental understanding of the laws that govern our Universe. A detailed account is contained in the Proceedings of the Symposium which will be available in a few months.
Tentative Time-table of Council Sessions and Committee Meetings in 1984
Second Announcement of an ESO Workshop on the Virgo Cluster of Galaxies - Garching - 1984SEP4-7
Richter, O. G.
AA(European Southern Observatory, Garching bei München)
Second Announcement of an ESO Workshop on the Virgo Cluster of Galaxies - Garching - 1984SEP4-7
Chromospheric emission, rotation and X-ray coronae of late-type stars
AA(Arcetri, Osservatorio Astrofisico, Florence, Italy)
X-ray observations have shown that chromospheres, transition regions and coronae are common to stars throughout the HR diagram, and that magnetic fields play a fundamental role in the heating of outer stellar atmospheres. The observed emission levels are in both qualitative and quantitative disagreement with the predictions of the standard theory of coronal formation via the generation and dissipation of acoustic waves. As a result of recent emphasis on heating mechanisms which are based on the stressing and dissipation of magnetic fields generated by dynamo action in the subphotospheric convection zones, stellar rotation has assumed a central role in the heating problem as a controlling factor in dynamo process efficiency.
List of Preprints Published at ESO Scientific Group (December 1983 - February 1984)
299. F. Caputo, V. Castellani and M. L. Quarta: A Self-consistent Approach to the Age of Globular Cluster M15. Astronomy and Astrophysics. December 1983.
Spectroscopic Study of a Sample of Visual Double Stars
Chmielewski, Y.; Jousson, M.
AA(Observatoire de Geneve) AB(Observatoire de Geneve)
We learn what we know about stars from the photons that originate in their atmospheres and eventually reach our telescopes. Therefore, if we want to account for the spectral distribution of the radiation received from a star we must know the physical properties in its atmosphere. One of the great achievements of the last twenty years in the theory of the stellar atmospheres has been the calculation of detailed models of their average physical properties. This theory teaches us that the atmosphere of a well-behaved star can be characterized by a small number of parameters. Once they are specified, the computation of the model stellar atmosphere follows in a unique way, within the assumed approximations. The most important of these parameters are the effective temperature, the surface gravity and the chemical composition. For the sake of completeness, two more parameters have to be mentioned: the mixing length and the microturbulence. They pertain to very crude approximations behind which is hidden our poor understanding of such phenomena as convection or turbulence in the atmospheres of the stars. In general, the microturbulence and the mixing length are adjusted in a more or less empirical way. In fact, there are indications that they might not be fully independent from the other parameters.
Quasar Surface Densities
The story of the discovery of quasars has been told many times (see e.g. the 24th Liege International Astrophysical Colloquium 1983), nevertheless, it is always exciting to recall the first uncertain steps taken around 1960, when very little was known about this major component of the universe. In that period the identification of several radio sources, listed in the 3C catalogue, with more or less distant galaxies had been performed, but for many of them the optical counterpart was still unknown. In 1960 Matthews et al. (1) investigated with the 200" telescope of Mt. Palomar the fields corresponding to the sources 3C48, 3C196 and 3C286. They could not find any trace of galaxies, the radio position indicating on the contrary three objects of stellar appearance. At that time no radio star was actually known besides the Sun, thus the discovery raised some questions, which became even more puzzling when spectroscopic observations revealed that each of these "stars" emitted a lot of ultraviolet and blue light with a few emission lines, different from case to case, which could not be plausibly identified with any known element. Many theoretical possibilities were opened, but, before any thorough examination could be performed, the nature of the problem was completely changed with the identification of the radio source 3C273, carried out by Hazard, MacKey and Shimmins in 1962 (2) with the 210ft Parkes radio telescope. By means of several lunar occultations, the position of the source was measured with an uncertainty less than 1" and its structure was shown to consist of two components separated by 19.5 arcsec. The relative accuracy of these measurements allowed an indisputable optical identification with a stellar object of about 13th V magnitude with an associated jet extending as far as 19.3 arcsec. Schmidt (3) took a spectrum of this object, which showed six broad emission lines which could be interpreted as being due to known elements assuming an unexpectedly large redshift of 0.158. It was possible to apply the same interpretation to 3C48, 3C196, and 3C286, when their spectra were reexamined, adopting respectively redshifts of 0.37, 0.87 and 0.85. At that time the radio galaxy 3C295 (z = 0.46) was already known, nevertheless the discovery was upsetting: if the redshift of 3C273 is cosmological, then its absolute magnitude is -27 (assuming a Hubble constant of 50 km/s/Mpc), that is about 40 times brighter than the brightest galaxies.
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and Astrophysics 5, 264.
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10. Cristiani, S., Veron-Cetty, M. P., and Veron, P., 1983, ESO
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The Story of the Eclipsing Double-Lined Binary HD224113
For an observing astronomer it is always very exciting to record an unexpected event, even if this is "only" the detection of the optical variability of a spectroscopic binary. This happened to me in July 1978 when I performed a photometrie programme at the ESO 50 cm telescope. Since the allotted observing time was a bit too late to follow my programme stars until the end of the night, I had prepared a list of about 20 radial velocity variables to check their photometrie behaviour during the remaining hours. The first object I selected was HD 224113, a B6V star with a magnitude of V - 6.1. Suddenly, after some minutes of observation the brightness dropped off and faded away continuously until the rising sun prevented further measurements. The nature and range of the variation (6 V - 0.2) indicated that an eclipse had been observed. Of Course, for the nights to come, the hours before dawn were devoted to further observations of this star. However, no further variations were recognized, HD 224113 showed a Constant brightness all the time.
Some old and new facts about the Local Group of galaxies and the extragalactic distance scale
AA(European Southern Observatory, Garching, West Germany)
The study of the sun's galactic neighbors allows the determination of global parameters and composition with the highest possible observational accuracy. Absolute parameters are dependent on exact knowledge of distances to galaxies, however, and the implicit requirement for objects having a small dispersion in intrinsic physical properties is a subject of controversy among contemporary astronomers. Only recently has H I data become complete for the spiral and irregular galaxies in the Local Group, allowing the invocation of the Tully-Fisher relation as an aid to reliable distance indication. Other indicators are the Sandage-Tammann, the deVaucouleurs, and that of type I supernovae.
Multiple Stars - a Nuisance to the Observers
Loden, L. O.
AA(Astronomical Observatory, Uppsala)
Already in popular textbooks you can read that double stars are frequent phenomena in the Milky Way. In the first instance this concerns the visual double stars that every one can admire through the telescope. They constitute a considerable fraction of the total stellar content, with a certain statistical frequency dependence upon spectral type and luminosity class that may partly be physically significant but, to an overwhelming extent, is conditioned by selection effects. If we add the spectroscopic binaries, we increase the number by at least an order of magnitude and if we take into account also the higher multiples, we may find that the number of stars in multiple systems exceeds the number of single stars.
Exciting Stars in the Omega Nebula
AA(MPI für Radioastronomie, Bonn)
Every astronomer has his favourite object, which he studies sometimes throughout many years. Whenever he gets a few nights for observation he looks at "his" object to see how it is doing. My favourite object is the Omega Nebula, also known as M 17.
Visiting Astronomers (April 1-October 1, 1984)
Magnesium Isotopes in Halo Stars of Various Metallicities
AA(Universidade de Sao Paulo)
Population II stars are very old objects, and their relative abundances can give clues on the chemical enrichment at early times. The elemental composition of stars depends on the initial mass function of the progenitor stars which enrich the gas from which they form. Some element ratios in the oldest stars are especially sensitive to the mass of the preceding stars, the so-called population 111 or population O, first generation of zero-metal stars, today dissappeared.
Arnett, W. D., Wefel, J. P.: 1978, Astrophysical Journal 224, L139.
Carney, B,: 1980, "A Catalogue of Field Population II Stars", unpublished.
Spite, M., Spite, F.: 1980, Astronomy and Astrophysies 89, 118.
Truran, J. W., Iben Jr, I.: 1977, Astrophysical Journal 216, 797.
The ultraviolet absorption spectrum of NGC 4151
Veron, P.; Veron-Cetty, M.-P.; Tarenghi, M.
AA(European Southern Observatory, Garching, West Germany), AB(European Southern Observatory, Garching, West Germany), AC(European Southern Observatory, Garching, West Germany)
An analysis of NGC 4151's absorption line behavior has been conducted on the basis of 90 of the ESA data base's low dispersion, high resolution and large aperture UV spectra for the April 1978-February 1982 period. Attention is also given to features of the visible and X-ray spectra of this source. It is found that the continuum source is double, with one constant component and the other variable. The absorbing clouds cover the variable continuum source, as well as the broad emission line region.
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Society 206, 221.
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Fosbury, R. A. E. 1979, Monthly Notices of the Royal Astronomical
Society 189, 45P.
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The nature of subdwarf B stars
Heber, U.; Hunger, K.
AA(Kiel, Universität, Institut für theoretische Physik und Sternwarte, Kiel, West Germany), AB(Kiel, Universität, Institut für theoretische Physik und Sternwarte, Kiel, West Germany)
A discussion is conducted concerning the characteristics of subdwarf B stars, including the subdwarf OB (sdOB) stars whose temperatures reach up to 40,000 K and above. Attention is given to the question of these stars' degree of He deficiency, which influences their classification as horizontal branch stars. The use of the IUE band for effective temperature determinations, the lg, T(eff)l diagram, the photospheric He content of such helium main sequence stars as the sdOBs, and metal abundances and evolutionary histories, are considered in turn.
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Envelopes, eds. Baschek, B., Kegel, W. H., Traving, G., Springer,
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Astronomy and Astrophysics 108, 387.
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Groth, H. G., Kudritzki, R. P.: 1983, Mitt. d. Astron. Ges. 60, 308.
Heber, U., Hunger, K., Jonas, G., Kudritzki, R. P.: 1984, Astronomy
and Astrophysics 130, 119.
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Stellar metallicity gradient in the direction of the south galactic pole determined from Walraven photometry
Trefzger, Ch. F.; Pel, J. W.; Blaauw, A.
AA(Basel, Universitaet, Basel, Switzerland), AB(Groningen, Rijksuniversiteit, Groningen, Netherlands), AC(Groningen, Rijksuniversiteit, Groningen, Netherlands)
The observations presently reported were aimed at determining the relation between stellar metal abundance and distance from the galactic plane in a wider solar neighborhood. The Basel RGU Survey is used for the selection of F- and G-type program stars, thereby extending earlier photoelectric work to greater distances. A semiempirical calibration of the (V-B)-(B-L) diagram is constructed by combining the theoretical Kurucz colors with observations of field stars that cover a wide metallicity range.
One-mm observations of BL Lacertae objects
AA(Max-Planck-Institut fuer Radioastronomie, Bonn, West Germany)
Observations of BL Lac objects at 1 mm wavelength are discussed. The objects in question are 1400 + 162, 1514 - 241, 1514 + 197, 1749 + 096, 2032 + 107, 2223 - 052, and 2155 304. Extrapolation of high frequency radio spectra towards 1 mm yields a close correlation between observed and extrapolated fluxes at 1 mm. The uniform spectral slope from 1 mm to the near-IR is most readily explainable as due to a single radiation mechanism.
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Royal Astronomical Society 199,969.
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IAU circular No. 3856 (1983).
Light curve Variations in Short-Period Eb-Type Contact Binaries
AA(Astronomisches Institut Tübingen)
The structure and evolution of contact binaries is still very poorly understood. If two stars are so close together that they are physically touching, then it is to be expected that the normal equilibrium configurations of the single stars are heavily disturbed. Mass and energy transfer between the components can occur which makes the theoretical calculations on stellar structure and evolution extremely difficult.
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Simposio ESO/CERN sobre la Estructura a Gran Escala del Universo, Cosmologia y Fisica Fundamental