January 14, 12:00 hr: Dr. Vanessa DOUBLIER
Abstract The galaxy formation simulations, and galaxy counts at different redshift tell us that dwarf galaxies are negligible bystanders in the overall picture of Galaxy Formation, at best are they recognized to be useful to explain the excess of blue faint objects in the galaxy counts at low redshifts. Moreover, those objects are not found in the most fashionable place of the Universe: they are found in low density environments and they don't interact much with their neighbors. But their star formation rates honestly compare with those of the giant starburst galaxies, their metal contents would bluff an old globular cluster ... If we assume as theoreticians tell us, that most of the large galaxies are build from small units, there was a time when dwarf galaxies accounted for most of the "baryon mass", and the "blue excess" at the faint end of the luminosity function of the galaxies are the left-overs of galaxy formation. Or, if we assume as simulations of the intensity of the UV background in the early stage of the universe tell us, that units of masses less than 10^9 solar mass could not collapse before a redshift of 1-2 then BCDGs may be still in the process of formation/collapse. I will try to highlight a few intriguing properties of BCDGs which put them back into the vast perspective of galaxy formation and evolution.
January 12, 16:30 hr: Dr. John PRITCHARD
Abstract For most of this century eclipsing binary star systems have been used to measure the properties of the individual stars that compose these systems. For the past couple of decades, such analyses have yielded the most precise measurements of stellar masses, radii and luminosities with which theoretical models for stellar structure and evolution have been tested and improved. With the advent of the VLT (and the other 8-m class telescopes) studies of similar precision and accuracy can at last be brought to bear on eclipsing binaries in the Magellanic Clouds. In my presentation I will discuss the efforts our collaboration, based in Copenhagen, is making to carry out this work.
January 19, 16:30 hr: Dr. Frederic PONT
Abstract Local group dwarf galaxies exhibit an amazing variety of star-formation histories. This has become obvious recently with the measurement of deep Colour-Magnitude Diagrams for the Milky Way satellites dwarfs. The very nature or these tiny galaxies is also an open question: are they dark-matter dominated systems, or tidal debris? Are they able to recycle and retain their own gas for subsequent star formation? To answer these questions requires a good knowledge of the chemical history of the dwarf galaxies. The next observational step is to derive metal abundances for individual stars in these galaxies. The new generation of 8-m class telescope has opened up this possibility, though high S/N, high-resolution spectra still require prohibitive observing time. Metallicity measurements can be made practical either by lowering the resolution, and using strong spectral features such as the CaII infrared triplet, or lowering the S/N, and using cross-correlation techniques. We apply both methods to the Carina, Fornax and Leo dwarf galaxies, three systems with very different morphologies, star formation histories and apparent dark matter content.
January 24, 11:30 hr: Dr. Eva GREBEL
Abstract I shall review the star formation histories of Local Group (LG) dwarf galaxies. Interestingly, no two dwarfs, irrespective of morphological type, show the same evolutionary history, and all vary widely in ages of their subpopulations and in their enrichment history. Based on the observed star formation episodes and properties I suggest that we see continuous evolution from low-mass dwarf irregulars (dIrrs) to dwarf spheroidal galaxies (dSph) in the LLG. The recently proposed detections of gas around six of the dSphs in the LG may be explained by a new photoionization scenario. Old populations,often spatially very extended, appear to be a common property of dwarf galaxies, though the fraction of these populations can be very small. Almost all types of dwarf galaxies studied in detail so far show spatial variations in ages and abundances such as radial age/metallicity gradients. I compare the properties of Milky Way dSphs to the M31 dSphs, some of which were only discovered last year, and discuss them in the framework of the ram pressure/tidal stripping scenario. The newly discovered LG dwarfs follow the same relationship for central surface brightness, mean metallicity, and absolute magnitude as the other LG dwarfs.
January 24, 16:00 hr: Dr. Richard B. LARSON
Abstract How did the first stars in the universe form? This talk will review some recent theoretical work on this problem, and it will discuss the expected properties of the first stars and some possible consequences for galaxy and quasar formation.
February 1st, 16:30 hr:Dr. Jan BRAND
Abstract First results will be presented of a study that aims to identify precursors of UC HII regions, with emphasis on what might be the first example of a bona fide massive protostar.
February 4, 16:30 hr: Dr. Duccio Macchetto
Abstract The HST has made many contributions to all areas of research in the field of AGN, and I have selected three topics where major progress in our understanding has been made over the last two years. The study of the NLR is key to understanding to what extent the unified model for AGN is applicable. In particular, understanding how the NLR is ionized and how its morphology is defined makes an important contribution to clarify the differences between Seyfert1 and Seyfert2. The main conclusion in this field is that the radio-jet is responsible for defining the morphology, both through the expanding cocoon and at the working surface of the radio lobe, and is largely responsible for the observed ionization. The ionization parameter in these sources is either constant or actually increases with distance from the nucleus; therefore, nuclear ionization alone cannot explain the observations, whereas local ionization by shocks is fully capable of providing the required flux of ionizing photons. Many HST observations have shown the presence of extended accretion disks (200--300pc). For the first time however, we have been able to show that in the case of M87 we are dealing with a true Keplerian disk. We carried out long-slit spectroscopy with the FOC and developed a sophisticated model which took into account the impact parameter, the shape of the PSF, the unknown SED of the nucleus in the 0.06'' inner region, and built a set of models which best fitted the data and were fully self-consistent. We derived the inclination of the disk to our line-of-sight and the black-hole mass. We showed that this mass is concentrated within the inner 3pc and cannot be uniformly distributed; therefore, it must be a black hole. We have investigated the optical counterparts of all the 3C radio jets and discovered a number of new optical jets. By comparing the radio and optical data we conclude that beaming is responsible for the optical visibility of these objects. We have also measured the proper motions of the jet in M87 over a 3-year period, and we find apparent velocities of features which vary from 1.5c to 6c for different knots. This observation shows among other things that the bulk and pattern velocities differ.
February 9, 16:30 hr: Dr. Philippe LAMY
Abstract I shall describe a novel technique of detecting and characterizing cometary nuclei even when they are active. It relies on high spatial resolution such as offered by the Planetary Camera of the Hubble Space Telescope for which the seeing is no longer the limiting factor, contrary to ground-based observations. As the signal from the surrounding coma decreases as the spatial resolution increases, that of the nucleus remains preserved as the Point Spread Function (PSF) of the telescope. The central pixels of the cometary images, scattered light or thermal emission, can therefore contain a significant component from the nucleus superimposed on that of the coma. The key problem is to correctly separate these two components. Various techniques which have applied to date will be described. I shall present the results obtained on the nuclei detected so far with HST and ISO, size, rotational state and active fraction and discuss their implications for cometary science.
February 15, 16:30 hr: Dr. Marc MONIEZ
Abstract EROS (Experience de Recherche d'Objets Sombres) searches for compact dark objects through microlensing from La Silla observatory. A combination of the revisited EROS1 data with the recently published results from EROS2 toward the LMC and the SMC will be presented and compared with the latest MACHO measurements. The need for complementary observations to clarify the question of the location of the lenses will be demonstrated. EROS has recently discovered several microlensing events towards new directions in the Galactic plane. The corresponding optical depth estimates will be given, as well as the analysis of possible deviations to the standard microlensing. Consequences concerning the galactic structure and its dark matter will be discussed.
February 18, 12:00 hr: Benoit JOGUET
Abstract I present new medium-resolution long-slit spectroscopy of 10 Seyfert 2 galaxies from near-UV to optical wavelengths. All these galaxies show strong absorption features from an integrated cool star spectrum on which is superimposed the high-order Balmer series absorption features and HeI absorption lines, both characterictic of hot massive stars. After analyzing in details the properties of the nuclear and circumnuclear stellar population, I focus the talk on the origin of dilution in Seyfert 2 galaxies.
February 23, 16:30 hr:Dr.Stefano BAGNULO (Vienna University and ESO Visiting Astronomer)
Abstract The large majority of astrophysical techniques are aimed at measuring the *intensity* of the observed radiation, and analysing its variability with time, position, and wavelength. Comparatively little attention is paid to the way the photons oscillate. The measurement of this latter feature of the radiation is the object of polarimetric observations. Polarisation originates whenever any kind of anisotropy occurs in the radiative source, e.g., presence of a magnetic field, scattering by matter, presence of collimated beams of particles. The analysis of polarised radiation can provide a much deeper insight into the nature of astronomical objects than what can be obtained with a ``simple'' intensity measurement. In many cases, some characteristics of the observed objects can *only* be recovered via polarimetric measurements. I will explain how polarised radiation can be measured, introducing the Stokes parameters, and the principles for building an ideal polarimeter. I will present the applications of the polarimetric techniques to some cases of astrophysical interest.
March 1, 16:30 hr: Dr. Angela IOVINO
Abstract Compact groups of galaxies are an extreme class of objects, ideal to study galaxy interactions and their effects. The redshift survey of a new southern sample of Compact Groups of Galaxies has just been completed, and this new sample has the great advantage of having been selected in an automated fashion through an algorithm applied to the COSMOS galaxy catalogue. We will present results on dynamics properties of such sample, comparing them with those of the compact groups sample originally selected by Hickson through visual search on POSS plates.
March 8, 16:30 hr:Dr. Stefano BAGNULO
Abstract Magnetic fields are ubiquitous in stars, and are characterised by various strength-scales and topologies which enormously change from one class of objects to the other. Magnetic fields are firmly detected, e.g., in pulsars (up to 10^{15} G), white dwarfs (from a few ten kG up to a few ten MG), chemically peculiar (CP) stars (from a few hundred G up to a few ten kG).Obviously, the weaker and more complex the field, the more difficult the magnetic diagnostic. A solar-like magnetic field, probably a quite common magnetic structure in main-sequence late-type stars, is virtually undetectable in stars other than the Sun. I will present some diagnostic techniques for stellar magnetic fields, and show the results of their applications to various stellar objects, with particular attention to the case of nondegenerate upper main sequence stars. I will also outline some problematics related to the role of the magnetic field in the physics of stellar objects.
March 21, 16:30 hr: Dr. Daniel SCHAERER
Abstract DLA systems provide currently the best in-situ probes of the metal content at high redshift. Their analysis is important for the understanding of cosmic chemical evolution, nucleosynthesis and others. The current status of abundance studies in DLAs will be reviewed. Two different pictures emerge from these analysis with different implications on nucleosynthesis and/or the nature of DLA systems. We here present a new study of ionisation effects on abundance determinations in DLA systems. Indeed the presence of ionised gas is suggested by the similarity between observed velocity structures of Al III and singly ionized species. A two component model of DLA systems is constructed.We demonstrate the importance of ionisation effects and discuss their implications on DLA abundance ratios, comparisons with Galactic stars and metal-poor HII regions, and various nucleosynthetic aspects (origin of N etc.).
March 22, 16:30 hr: Dr. Catherine CESARSKY
Abstract The counts derived from the five mid-IR 15mm (12-18mm LW3 band) ISOCAM Guaranteed Time Extragalactic Surveys performed in the regions of the Lockman Hole and Marano Field, the HDF-North and South (plus flanking fields), together with those of the lensing cluster A2390 at low fluxes and those of IRAS at high fluxes, cover four decades in flux from 50mJy to ~0.3Jy. The roughly 1000 sources detected with ISOCAM, 600 of which have a flux above the 80% completeness limit, guarantee a very high statistical significance for the integral and differential source counts from 0.1mJy up to ~5mJy. The slope of the differential counts is very steep (a = -3.0) in the flux range 0.4-4mJy, hence much above the Euclidean expectation of a= -2.5. When compared with no-evolution models based on IRAS, our counts show a factor ~ 10 excess at 400mJy, and a fast convergence, with a = - 1.6 at lower fluxes. Multiwavelength studies of a subsample of the ISOCAM sources in HDF and CFRS fields indicate that they are intrinsically bright galaxies (Luminous Infrared Galaxies, LIRGs), with median redshift 0.7. These galaxies, despite their low surface density, are responsible for a large part of star formation at z 1 and contribute substantially to the cosmic infrared background at 140mm.
March 27, 16:30 hr: Dr. David VALLS-GABAUD
Abstract After a brief introduction to the basic concepts of gravitational microlensing, we review the results obtained so far by the different groups. We discuss in detail three important outcomes: (1) the nature of dark compact obejcts, MACHOS or otherwise; (2) the constraints on Galactic structure, and in particular the bar in the Bulge; (3) the three-dimensional imaging of stellar photospheres. We conclude with a discussion of the expected results from ongoing and future microlensing experiments, from astrometric measures (GAIA) to the detection of planetary systems and extragalactic MACHOs.
March 29, 16:00 hr: Dr. Maxime BOCCHAS
Abstract Archaeoastronomy is a multidisciplinary scientific theme which is progressively gaining some maturity. We will review classical examples of both "very likely" and "dubious" examples of archaeoastronomical discoveries worldwide, including sites and practices in South America.
April 3, 16:00 hr: Dr. Peter CLAES
Abstract FIRST, ESA's fifth "Great Observatory", will be a large cryogenic Submillimeter Observatory in space open to the General Astronomical Community. FIRST's photometric and spectroscopic capabilities will have a revolutionary impact on the fields of formation of stars and galaxies by opening a new spectral window on the universe with very good sensitivity. FIRST will be complementary to ground-based and airborne (SOFIA) observatories. This talk presents the challenges of the FIRST-satellite and its instruments from a scientific and engineering perspective.
April 5, 16:30 hr: Dr. David Andre ERASMUS
Abstract While the meteorological conditions that determine atmospheric water vapour and cloud cover in Northern Chile are reasonably well understood, forecasting these quantities at remote locations such as La Silla and Paranal presents a considerable challenge. Weather satellites provide the only means for continuous monitoring of atmospheric conditions in the data-sparse areas of the Southern Hemisphere and coarse-grid global meteorological forecast models provide the only information on predicted data fields. By synthesizing data from these two sources, an automated system has been developed to forecast selected atmospheric moisture and cloud cover parameters at La Silla and Paranal. The results from two feasibility studies and a verification of the operational forecasts show that forecasts of cloud cover and water vapour parameters above ESO telescope sites can indeed be made with an accuracy suitable for use in telescope scheduling. In this presentation information will be provided to users and potential users on the general meteorology of the area, the logic behind the forecasts, how the forecasted parameters are derived, forecast accuracy and interpretation of the forecast products, particularly from an astronomers perspective. Further, the limitations of the current version of the forecast system and the impact this has on forecasted parameters will be discussed. An upgrade of the forecast programme, presently underway, will be described.
April 12, 16:30 hr: Dr. Gustavo PORTO de MELLO
Abstract The solar distribution of element abundances is very often taken as typical or representative of the local Galactic environment. This straightforward interpretation rests upon assumptions which are seldom questioned. In this talk, we will present the results of a very detailed abundance survey for a small sample of solar- type, solar neighborhood stars. The errors of the abundance determinations were kept very low by strictly differential techniques applied to very high S/N spectra. We show that deviations from the solar abundance pattern do occur in the Galactic vicinity, and that we cannot really claim that the solar chemical composition can be taken as typical. The results suggest that the Galactic chemical enrichment has been more complicated than commonly postulated and that heterogeneities in time and space probably work against the efficient mixing of the various nucleosynthetic products throughout the Galaxy.
April 19, 16:30 hr: Dr. Angela IOVINO
Abstract We have applied a new cluster detection algorithm to the ESO Imaging Survey, producing a new catalogue of cluster candidates up to z ~ 1. Such a catalogue enables one to perform statistically significant studies as well as detailed research on some of these systems individually and on their member galaxies. In this talk we will discuss the advantages of our search technique with respect to those already available in the literature and we will present ongoing observational projects on our cluster candidates.
April 24, 12:00 hr: Dr. Gustavo PORTO de MELLO
Abstract Solar twin stars are, by definition, non-binary stars identical to the Sun in all astrophysical parameters, within the observational uncertainties. Such objects can help us understand more clearly the solar place in the general stellar context. Recent data suggest that some of the solar characteristics are not typical of the local population of G-dwarfs. Solar twins can also help solve a long lasting problem: the Sun is the most fundamental calibrating object in stellar astrophysics, but its photometric colors remain poorly known. Also, such objects are presumably privileged candidates to possess planetary systems similar to our own and to be abodes for lifeforms based on carbon-chain chemistry and water oceans. No star is presently known to be a perfect solar twin, but the G2V nearby star HR6060 is shown to come extremely close. In this talk, we discuss the solar twin subject and present the preliminary results of our systematic survey to reveal all solar twin stars within 50 parsecs of the Sun.
April 27, 16:30 hr: Dr. Roberto GILMOZZI
Abstract The next generation of ground based telescopes will break the 20th century paradigm of the "factor of two" diameter increase. Taking advantage of the enormous advances in technology that the present generation of 8-10m telescopes has fostered, they will be fully adaptive, fully stearable behemoths of up to 100m diameter performing at the diffraction limit in the optical and near infrared. At ten times the collecting area of every telescope ever built put together, they will have limiting magnitudes of 37-38, angular resolutions of 1-2 milliarcseconds, and a price tag that does NOT follow the historical D^2.6 cost law. I will discuss some of the possible science cases (ranging from the determination of H [not Ho] unencumbered by local effects, to the study of every SN ever exploded at any z10, and including spectroscopy of extrasolar planets, studies of ultrahigh frequency phenomena, detection of brown dwarfs in external galaxies etc.) and show the design status of some of the proposed projects, in particular ESO's 100m concept (called OWL, for its sharp night vision and for OverWhelmingly Large telescope).
May 2, 16:30 hr: Dr. David VALLS-GABAUD
Abstract Current cosmological scenarios for the the formation of galaxies predict widely different histories for the evolution of their star formation rates, and which differ substantially from the standard picture of galaxy evolution. At the scale of the Local Group, these histories are reflected in the colour-magnitude diagrams of the stars resolved within these galaxies. I will present a new inversion method, which couples variational calculus with standard maximum likelihood techniques, to extract from these observations their star formation histories. After reviewing the biases, limitations and systematics of the method, with synthetic diagrams, I will discuss its application to WFPC2 observations of five dwarf spheroidal galaxies. In the same way, I will analyse the solar neighbourhood, as observed by HIPPARCOS, to reconstruct with unprecedented detail the variations of the star formation rate in the Galactic disc.
May 4, 16:30 hr: Dr. Andreas REISENEGGER
Abstract The Shapley Supercluster is the largest mass concentration in the local Universe, z 0.1, containing more than 30 Abell clusters within a radius of 25 Mpc. This makes it an interesting object to constrain cosmological models, study interactions between clusters of galaxies, and as a possible contributor to the motion of the Local Group with respect to the cosmic microwave background. Within about 10 h^{-1} Mpc of its center, the galaxy density in redshift space is about 50 times higher than the cosmic average (Bardelli et al. 2000), strongly implying that this region is presently undergoing gravitational collapse. A much increased sample of galaxy redshifts in the Shapley area (Quintana et al. 2000), now nearly 5000 redshifts in total, indeed shows the signature of gravitational collapse in its center. For the first time in a region containing more than one cluster of galaxies, a spherical collapse model is used to constrain the radial mass density profile. Comparisons are given to the masses of individual clusters, and the possible contribution to the Local Group motion is discussed.
May 5, 12:00 hr: Dr. Alberto BUZZONI
Abstract We will briefly assess the problem of a fair recognition of primeval galaxies from unbiased interpretation of high-redshift data. Energetic constraints from evolutionary population synthesis models will also be discussed in the light of a more appropriate use of this tool in cosmological research.
May 10, 16:30 hr: Dr. Tom RICHTLER
Abstract I will present the morphological appearance of star clusters in different types of host galaxies, elliptical, spiral and interacting galaxies. Physical mechanisms of cluster formation shall be discussed and possible ways of relating the understanding of star formation and cluster formation shall be indicated.
May 15, 16:30 hr: Dr. Ralph NEUHAEUSER
Abstract We have started a program to search for substellar companions, both brown dwarfs and giant planets, by ground-based direct imaging in the infrared (H and K), using SHARP and SOFI at the NTT, ISAAC at the VLT, and ALFA at the Calar Alto 3.5m. We search for such companions next (sub-arc sec to few arc sec) to young (up to 100 Myrs) nearby (up to 75 pc) stars, where substellar companions are still relativelly hot (and hence bright) and well separated. There are roughly 100 such stars known.
We have already found several such companion candidates, which we can best check by IR spectroscopy. We will present an ISAAC spectrum of TWA-7B, a companion candidate to TWA-7A, which is just 2.5 arc sec (138 AU) from the primary, but 9.5 mag fainter in H and K; give the magnitude of TWA-7B and age and distance of TWA-7A, the faint object (if really a companion) could be a three jupiter-mass planet. Hopefully, we will show ISAAC spectra a few more candidates, be taken in service mode in April 2000.
May 17, 16:30 hr: Dr. Tom RICHTLER
Abstract In this seminar I will discuss the construction of the distance ladder, starting from Baade-Wesselink parallaxes of Cepheids, which calibrate the P-L relation, and, via the LMC distance, also the horizontal branch magnitudes of globular clusters. These in turn are used to calibrate the globular cluster luminosity function. With this tool it is possible to measure the brightness of Ia supernovae and determine the Hubble constant.
May 24, 16:30hr: Dr. Norbert CHRISTLIEB
Abstract With the advent of several 8m class telescopes (e.g. VLT), and dedicated survey telescopes (e.g., VST), I predict that an era of astronomy starts in which the data flow (in terms of GB per Astronomer) will be so large that automated analysis techniques have to be used in many fields of research, in order to produce scientific results. I will focus my talk on one such technique, namely, automatic classification. After providing some mathematical background, I'll review where and how techniques of automatic classification have been used, and are used, in astronomy, and what future applications might be.
June 7, 16:30 hr: Dr. Norbert CHRISTLIEB
Abstract The Hamburg/ESO survey (HES) is an objective prism survey covering the total southern (delta +2.5 deg) extragalactic (|b| > 30 deg) sky in the magnitude range 1217.5. It's main aim is to find bright quasars. However, at its spectral resolution of 15 A at Hgamma, the strongest stellar absorption lines are visible, so that the HES data base of ~4 million digital spectra is a valuable source for automated selection of many different types of interesting stellar objects, e.g. extremely metal-poor stars, carbon stars or white dwarfs. I'll present a few research projects dealing with HES stars, and present results obtained so far.
June 9, 12:00 hr: Dr. Jerome OROSZ
Abstract There is very strong evidence for the presence of stellar-mass black holes in at least 12 objects. I will give an introduction to these objects and show how we use optical observations to derive mass estimates for these black holes. In addition, I will show how optical observations can also be of use in the study of accretion flows around the black holes.
June 15, 16:30 hr: Dr. Gianni MARCONI
Abstract Dwarf Galaxies represent the most numerous class of objects inside the Local Group. They are the least massive self-enriching stellar systems, thus representing the most basic "units" of independent evolution of matter in galactic form. From this particular point of view, they can be considered as a test particles for the cosmology at redshift 0. In the last few years, thanks to the new instrumentations, the feeling about the importance of these objects in the evolutionary path of galaxies has grown fast, but their role is still largely unclear. This talk will illustrate the main results recently obtained in this field. In order to clarify the framework on these galaxies, an overview of ongoing and future research projects will also given.
June 21, 16:30 hr: Dr. Thomas SZEIFERT
Abstract With the new generation of 8m-class telescopes and the available instruments one can obtain high accuracy polarisation measurements (up to S/N ~10000) or polarisation measurements of quite faint objects in a very reasonable amount of time. In the first part of the talk I will summarize the optical methods and data analyses methods, then continue by a brief summary of the physical processes which cause the polarisation of astronomical objects. As an example I will finally present some very preliminary results based on very recently released measurements of Seyfert galaxies and other objects taken with FORS1 at UT1.
July 5, 16:30 hr: Dr. Howard YEE
Abstract The photometric properties of cluster galaxies from 45 Abell clusters and the brightest cluster galaxies (BCGs) from a subset of 24 are examined using B and R CCD images. We derive the luminosity function and color-magnitude relation for the cluster galaxies, and measure the profiles and color gradients of the BCGs. I will discuss the correlations between the properties of the cluster galaxies and the BCGs and the implications on the formation of cD galaxies.
July 7, 12:00 hr: Michael ENDL
Abstract A search for extrasolar planets was begun in November 1992 using the Coude Echelle Spectrometer (CES) on La Silla. For more than five years the observations were performed with the 1.4m CAT telescope and are currently continued with the 3.6m telescope. I will review the project, outline the data modeling technique we use to obtain high precision stellar radial velocities (RV), and present the results of the whole survey. The discovery of a planet orbiting the young star iota Horologii and limits for the presence of Jovian planets in the Alpha Centauri system will be described in detail. Furthermore, a pilot study is currently in progress to determine the RV precision of UVES for a planet search using the VLT UT2 (KUEYEN) 8.2m telescope.
July 11, 16:30 hr: Dr. Georges MEYLAN
Abstract Galactic globular clusters, which are ancient building blocks of our Galaxy, represent a very interesting family of stellar systems in which some fundamental dynamical processes have taken place on time scales shorter than the age of the universe. In contrast with galaxies, these clusters represent unique laboratories for learning about two-body relaxation, mass segregation from equipartition of energy, stellar collisions, stellar mergers, and core collapse. All these phenomena, combined with the effects of disk and bulge crossing suffered by each globular cluster along its orbital path, favor the regular escape of stars from these stellar systems, leading to their slow evaporation. I shall present recent observational results which confirm the fact that globular clusters are not the everlasting swarm of stars that, not so long ago, we thought they were.
July 13, 16:30 hr: Dr. George PRESTON
Abstract Blue metal-poor (BMP) stars are metal-poor ([Fe/H]-1) main sequence stars with colors that place them blueward of the halo turnoff. They could be blue stragglers or intermediate age main sequence stars captured from satellite galaxies like the Carina dwarf. Their high specific frequency compared to the specific frequencies of blue stragglers in globular clusters suggested the latter in 1995. However, a radial velocity survey of 62 of these objects conducted at LCO during the past 8 years produced a high (60%) proportion of spectroscopic binaries, mostly with periods longer than 100 days. We conclude that (1) about half of the BMP stars must be blue stragglers and (2) that globular clusters either destroyed most of their primordial binaries with large separations or never possessed them.
July 17, 16.30 hr: Dr. Paulo GARCIA
Abstract The collimated jets observed in some active pre-main-sequence stars are commonly interpreted as caused by MHD collimation. The physical mechanism underlying the collimation is the transport of current by the jets. Current models suppose that the thermal pressure has no effect in the dynamics of the jets and therefore lack the ability to compute the temperature evolution along the jet -- a crucial parameter when trying to compare theory with observations. We will present results for the temperature evolution along MHD jets. We assume that it is the current that heats the jet through the well known Ohmic heating and the less well know ambipolar diffusion heating (the analogue of Ohmic heating for the neutrals). Our thermal description doesn't have any free parameters and is thus completly controlled by the underlying MHD dynamical model. We show that for this "minimal" heating and for the MHD models considered, the gas can be heated up to temperatures of ~1e4 but cannot be highly ionized. This suggests the need for other heating sources such as shocks. We show that collimated structures with a morphology very similar to the one observed are predicted and underline bias caused by imaging with limited resolution (current AO/HST).
July 31, 16:30 hr: Drs. M. TALLON, E. THIEBAUT, A. BLAZIT
Abstract As long as adaptive optics cannot achieve a full correction in the visible, speckle interferometry is the only way to get diffraction-limited images in this spectral domain. The instrument SPID works in short-exposure mode (speckle imaging) but offering more than the other optical specklegraphs: a high spectral resolution with continuously tunable wavelength. It also includes a wavefront sensor for post-compensation processing. It will soon be able to work in long-exposure mode with high spectral resolution, allowing observations with adaptive optics with partial compensation. SPID gives images in two spectral bandwidths simultaneously - the width and the central wavelength of each bandwidth can be chosen independently-, with an adjustable spectral resolution from 60 up to 3000, in the range 400-750nm. We shall present the instrumental concept and observational performances, the data processing, as well as the astrophysical programs our team is driving. After its validation by the first results, we intend to open our instrument to collaborations for all observational programs which could benefit from its potential.
August 3, 12:00 hr:Drs. Christian COUTURES and Pascal FOUQUE
Microlensing events of stars in the galactic bulge or in the Magellanic Couds are rare events. Anomalous events are even less frequent and happen for instance when the lens is a binary star. We will report on such an event, discovered and followed by EROS recently (June and July 2000), and present a first guess of the lens geometry.
August 23, 16:30 hr: Dr. Damien HUTSEMEKERS
Abstract About 10% of QSOs show broad absorption lines (BALs) in their spectra, revealing outflows with large velocities (0.1c). The origin of these outflows, their true occurence among QSOs as well as their role in the Starburst / AGN phenomenons are still largely unknown. Recent progress based on polarization, radio and infrared observations will be presented.
August 30, 16:30 hr: Dr. Leonardo TESTI
Abstract I will review recent observational studies on the structure and fragmentation of molecular clouds. Particular emphasis will be devoted to high spatial resolution millimeter continuum and spectral line observations of cluster forming clumps within molecular clouds. These observations show that the mass spectrum of prestellar cores within cloud clumps resembles the field stars initial mass function and thus suggests that the mass spectrum of stars in clusters may be determined by the clump fragmentation process.
September 1, 12:00 hr: Dr. Vanessa HILL
Abstract During UVES science verification, giants in 4 LMC star clusters in a wide age range were observed, providing the opportunity to determine for the first time, the chemical evolution of the LMC. Measuring abundance ratios in stars of various ages give in fact strong constrains on the rate and also the manner in which the gas of the parent galaxy has been processed through star formation (star formation rate but also relative contribution of SNI, SNII, AGBs,...). First results from the analysis of these 4 clusters will be discussed.
September 6, 16:30 hr: Dr. Leonardo TESTI
Abstract Massive stars are usually found in dense stellar clusters. We present recent infrared and radio observations that suggest that massive stars are preferentially produced in dense stellar clusters, possibly by dynamical interaction, rather than by standard gas accretion as lower mass stars. The possibility that the observed correlation between young massive stars and cluster richness could be the results of randomly sampling the cluster size spectrum and the stellar IMF is also discussed.
September 22, 16:30 hr: Sebastian ELS
Abstract Measuring stellar radial velocities has reached a precision (a few m/s) which allows to detect substellar companions with planetary masses. At this level of precision the measured RV is not only affected by companions and going to more active stars shows the influence of stellar surface features like spots and granulation patterns. The correction of these effects would offer the possibility to search for planets around active and thus young stars. We used the ESO> Coude-Echelle-Spectrometer to observe several active stars to search for rotational modulation of the RV and for a correlation with changes of the stellar absorption line asymmetries caused by stellar surface features. First results of these observations will be presented and future applications of such a correction method will be discussed.
October 6, 16:30 hr: Dr. Riccardo SCARPA
Abstract Results from the HST survey of BL Lacertae objects and ground based observations of radio galaxies, and non-radio ellipticals are compared. It is found that BL Lac hosts galaxies and galaxies hosting powerful radio sources are in all respect indistinguishable, sharing the same size, luminosity, ellipticity, isophotal twist, and isophotal displacement. This result strongly favors the proposed unification schemes. Moreover, comparing the same properties with data for a control sample of normal, non-radio ellipticals, it is found that all three samples are indistinguishable, supporting a picture in which all giant ellipticals are similar and periodically experience a phase of activity.
October 11, 16:30 hr: Dr. Jurgen SCHMITT
Abstract The last two decades have seen the emergence of a new field in stellar astrophysics: Stellar X-ray astronomy. With soft X-ray imagery X-ray emission was found from many thousands of solar-like stars. I will summarize the most important findings of X-ray surveys of late type stars and put those into the context of the solar-stellar connection. Similarities and difference between solar and stellar X-ray emission will be discussed. The results of eclipse observations to determine stellar structure will be reviewed, and recent results of X-ray spectroscopy (with Chandra and XMM-Newton) will be discussed mostly from the point of view of density diagnostics.
October 20, 16:30 hr: Dr. Monique SPITE
Abstract 40 nights have been granted on UVES to the Large Program "First Stars". What can we learn from these very ��d galactic stars? The analysis of extremely metal deficient stars offers us a glimpse at the earliest epoch of the galactic history. The chemical composition of the atmosphere of these stars is essentially unchanged since their birth. They are so old that their chemical composition is the result of the enrichment by a very small number of supernovae (only one ?). By comparing their chemical composition to the prediction of various nucleosynthetic processes we hope to gain a better picture of conditions around the time of Galactic formation. Some of the very first results are presented.
October 25, 16:30 hr: Dr. Chantal BALKOWSKI
Abstract Ram pressure stripping which can affect galaxies moving inside an Intracluster Medium has been invoked to explain the observed HI deficiency of spiral galaxies in clusters. The best place to study the gas removal due to Ram pressure stripping is the Virgo Cluster as this is the closest cluster. Multiwavelength observations in HI, Halpha and CO are now available as well as simulations of galaxies entering into a cluster. We will present these new results which show that the stripping event happens when the galaxy is close to the cluster center and that some of the stripped gas could be re-accreted on the galaxy, inducing local enhanced star formation.
November 2, 16:30 hr: Dr. Jean-Paul KNEIB
Abstract Cluster cores distort and magnify distant galaxies. I shall review the latest observations and results and shall discuss future prospects.
November 3, 12:00 hr: Dr. Chantal BALKOWSKI
Abstract I will present new optical observations of HI rich dwarf galaxies in the Hydra cluster and the search for tidal dwarf galaxies in the Stephan's quintet.
November 9, 16:30 hr: Dr. Christophe DUMAS
Abstract The recent observations of Neptune's inner satellites and ring-arcs and Pluto's satellite Charon, are a good illustration of the use of high-angular resolution to the field of planetary science, either from space with HST, or from the ground with adaptive optics. [1.1-2.4] micron spectra of Charon's leading and trailing hemispheres obtained with HST/NICMOS reveal a non-uniform distribution of NH3 on the surface, although the attribution of a 2.21 mic band in the spectrum of Charon to ammonia hydrate is not fully secured yet. Near-IR photometric measurements of the neptunian system confirm that the ring-arcs and inner satellites are made from similar material, with the possible presence of water frost on Proteus. The astrometry of the satellites agrees with the predictions based on Voyager, while the ring-arcs were found nearly 20 degrees away from the expected location, putting into question their confinement by the sole action of the nearby satellite Galatea.
November 13, 14:30 hr: Dr. Giuseppe BONO
Abstract Both evolutionary and pulsational properties of variable stars will be discussed by taking into account theoretical predictions based on homogeneous sets of evolutionary tracks and on nonlinear, convective models. We will also discuss the pulsation properties of variables located inside the Cepheid instability strip and compare them with current data available in the literature.
November 15, 16:30 hr: Dr. Karen MEECH
Abstract The growing field of "Bioastronomy" or "Astrobiology" combines the studies of planetary astronomy, astrophysics, and biology in an exciting field which encompasses the search for extra-solar planetary systems, the study of extreme environments on Earth and other solar system planets and moons where life might exist, the origin and evolution of life, and the search for extra-terrestrial intelligence. Planned and proposed future NASA missions are more and more strongly combining astronomy and biology in their mission goals. This talk will focus discussion on 2 missions, and the implications for biohazards. The first mission will be the recently approved Discovery mission "Deep Impact", to be launched on 6 Jan 2004, for an encounter with comet P/Tempel 1 on 4 Jul 2005. The spacecraft will deliver a half ton impactor to the nucleus to excavate a crater >20m deep and >100m in diameter. This will be the first experiment to sample deeply below the surface of a comet, an object thought to be a primordial remnant from the epoch of solar system formation. We will also be examining the mechanics and energies of impact crater formation -- a phenomenon which has played a large role in the development of life on Earth, as well as for mass extinctions of life on Earth. Chemical evidence from Earth's atmosphere and the study of comet composition will be shown to give clues about the origin of our atmosphere, and its evolution during the early Earth as life was developing. Recent discoveries of complex organics (fullerenes) which have survived impact on Earth in meteorites will be discussed, as this has implications for the transport of pre-biotic material to Earth. The series of Mars Global Surveryor missions will also be discussed, highlighting recent images from the red planet, and outlining the planned sequence of science goals for the Mars exploration in the next decade. Included in the Mars exploration are plans for a future sample return mission. The goal of these 2 missions will be to search for organic materials and signs of past or extant life. The samples will be launched into Mars orbit, where they will be collected and returned to Earth. I will discuss the new NASA plans for the Mars exploration architecture and missions. In anticipation of the NASA Mars sample returns, scientists are discussing the best means of protecting Earth from the samples (should life be extant) and protecting the samples from Earth to avoid contamination. This talk will present a brief discussion of the biohazard protocols (biohazard safety level 4) being considered, in conjunction with the need for early release of samples for study by the scientific community.
November 20, 14:30 hr: Dr. Giuseppe BONO
Abstract We present the results of a detailed comparison between predicted and empirical Period-Luminosity (PL) and Period-Luminosity-Color PLC) relations in different photometric bands. In particular, we discuss the dependence of current distance estimates on the intrinsic width of the instability strip, on the reddening, and on the metallicity.
November 21, 16:30 hr: Dr. Massimo TURATTO
Abstract The attention of the astronomers is nowadays focused on the use of (type Ia) SNe as distance indicators up to cosmological distances. This talk will discuss the other kinds of SN explosions which are not directly related to the determination of the geometry of the Universe, i.e. Core Collapse SNe. Within the wide variety of objects, I will try to describe the physical unity of these objects and to highlight some points of major interest in their study.
November 22, 16:30 hr: Dr. Karen MEECH
Abstract The earliest stages of collapse of our solar nebula are not subject to direct observational constraints. However, cometary nuclei can give us some information from this early era. Comet nucleus size distributions may preserve a record of the outer nebula mass distributions in the late stages of planetary formation, as well as a record of collisional evolution. The rate of proto-planetary growth and scattering as a function of heliocentric distance depended on the size and mass distribution of the km-size planetesimals that have survived as today's comets, their nebular surface density and their velocity distributions. Likewise, comparisons of the development and cessation of activity as a function of heliocentric distance for comets originating in different regions of the outer solar nebula can help us understand the volatile distribution and physical processes in the outer nebula and the planet formation environment. Observations are showing that there is a possible preservation of an interstellar ice / dust component within nuclei, yet at the same time the cometary material has undergone processing during its formation. This review will discuss the possible formation scenarios for comets, and how observations are giving us information about the volatile distribution in the nebula, and the role that the comets have played in the formation of planets. Comparison will be drawn between the different dynamical classes of outer solar system bodies, e.g. the short-period comets, the long-period comets, the Centaurs, the dynamically new comets and the Edgeworth-Kuiper Belt objects.
November 24, 12:00 hr: Gloria ANDREUZZI
Abstract During the last few years it has been a renewed interest in white dwarfs: these stars represent the final evolutionary phase of both metal-poor and metal-rich low-mass stars. The main reason we are interested in these objects is because during their thermonuclear evolution, they must shed an amount of material equal to the difference between the WD remnant and the mean-sequence progenitors mass. Therefore we can use these objects to improve our knowledge on the chemical evolution of the Galaxy by using: i) the initial-final mass relation; ii) the upper limit of the progenitor mass. The latter measurement also supplies useful hints on Mup i.e. the stellar mass above which stars end up their evolution as SN type II. A key observable to understand the evolutionary properties of white dwarfs is the luminosity function, because it presents a sharp truncation at a luminosity which is determined by the time since formation of the first white dwarfs in that cluster. The dependence of this limiting luminosity on age relies on relatively well-understood physical mechanisms and it is independent of the stellar evolutionary models. As a consequence, measurements of this termination can supply an indipendent estimate of the cluster ages. I will briefly summarize the main results recently obtained in this field and in particular the detection and measurement of the white dwarfs cooling sequence in galactic globular and open clusters. The talk will be focused on white dwarfs in the old open cluster NGC188.
November 27, 14:30 hr: Dr. Giuseppe BONO
Abstract The pulsation behavior of both metal-poor and metal-rich RR Lyrae stars in globular clusters and in the Galactic field will be discussed. We also point out pros and cons of the Luminosity-Metallicity relation and PL_K relation to derive stellar distance. Finally, we present a new approach to simultaneously estimate physical parameters and distance of RR Lyrae stars.
November 29, 16:30 hr: Dr. Mark ALLEN
Abstract I will present early results from the HST STIS UV snapshot survey of low redshift 3CR radio galaxies. This survey is designed to provide a zero redshift comparison sample for the extraordinary radio galaxy morphologies found at high redshift. These images show UV morphologies that are strikingly different from that seen at optical wavelengths. I will discuss the effects of dust, star formation and scattering of blazar jets.
December 1st, 14:30 hr: Dr. Giuseppe BONO
Abstract We present a series of open problems concerning radial variable stars. We will outline in particular the observational data which could constrain the physical assumptions adopted for constructing non-linear pulsations models. We will also discuss the thorny problems still affecting the accuracy of the distance scale.
December 1st, 17:00 hr: Dr. Karen MEECH
Abstract *Have you ever wondered about the physical plausibility of some of the "science" portrayed in modern movies? *Do the big budgets for recent films include any shred of scientific reality, scientific advice? *Have you been curious? Come see the truth on December 1, when we will discuss 2 recent "doomsday" movies, "DEEP IMPACT" and "ARMAGEDDON" and critically look at how good the science in these movies was. The theme of both movies deals with mankind�s response to learning about the imminent impact of a large comet on Earth and what we might be able to do about this. Comet and asteroid impacts, while unpleasant prospects now, actually were very important in development of life on Earth., as well as for mass extinctions of life on Earth (e.g. the KT impact 65 million years ago which was believed to be the cause of the extinction of the dinosaurs). In addition to having some fun, and some (perhaps surprising) insight into just how well our movie makers portray science, you will also learn about the real impact hazard to Earth and what we are doing about it. In addition you will also learn about the REAL Deep Impact --a new NASA mission to be launched in 2004. Karen Meech is one of the co-investigators on this mission. Come find out why NASA is willing to spend $100 million dollars to go throw a chunk of copper at a comet. Come find out why we should (or should not) lay awake at night wondering about these beautiful celestial wanderers. The talk will begin with a brief overview of comet history, how we came to understand what comets and then will highlight the most recently approved mission to a comet, and will be highlighted with a lively discussion of what the movies got right and wrong, illustrated with excerpts from the movies. After the talk, by popular vote, we will watch one of the two movies.
December 4, 14:30 hr: Dr. Anne DUTREY
Abstract After a brief introduction on interferometry, I will mainly focus on mm interferometry by describing its principles and presenting the current mm arrays (and ALMA). Then I will briefly explain the differences between mm and optical interferometry.
December 5, 16:30 hr: Dr. Micol BOLZONELLA
Abstract The photometric redshift method is not only a promising technique to study the galaxy evolution up to faint magnitudes, but it becomes a necessity in view of the large photometric databases that will be obtained by the present and future deep surveys. I will describe the technique developed in the realization of the public code "hyperz" (http://webast.ast.obs-mip.fr/hyperz/) and the accuracy tests aimed at studying the performances of the code, its drawbacks and the possible degeneracy in the parameter space. The applications of this method are numerous. I will show the results on HDF Luminosity Functions in different bands, computed consistently with the characteristics of the photometric redshift technique.
December 6, 16:30 hr: Dr. Ariane LANCON
Abstract Between ~10^8 and ~10^9 years after a starburst, the near-IR light of the evolving stellar population is provided to ~50% by upper Asymptotic Giant Branch stars. These stars are difficult to model: their structure and surface chemistry is affected by thermal pulses every ~10^4 years, their radii, luminosities and effective temperatures vary with periods of 100-1000 days. However, these properties have their positive sides. The extended atmospheres of pulsating stars display molecular features that distinguish them from luminous red stars in other (younger or older) evolutionary stages. The progressive evolution from M spectral types to carbon stars acts as a metallicity sensitive clock. I will discuss the status of investigations in this area of "stellar population synthesis". Applications range from intermediate age clusters as found in merging galaxies (now) to "E+A" galaxies (in the future).
December 18, 14:30 hr: Dr. Anne DUTREY
Abstract Using several well known astronomical examples, I will present the main problems and biases of data analysis which can be encountered when using mm arrays. Particularly, I will show examples of UV data analysis, mosaicing, low S/N images...
December 20, 16:30 hr: Dr. Mark ALLEN
Abstract Unified models for active galaxies explain the differences between Seyferts type 1 and 2 as an orientation effect. In Seyfert 2s the nucleus and broad line region (BLR) are obscured by a molecular torus, whereas in Seyfert 1s the nucleus and BLR are viewed directly. The appearance of NGC 4151 however presents a challenge to this simple model. Its biconical shaped narrow line region (NLR) suggests a Seyfert 2 orientation, yet prominent broad lines characteristic of a Seyfert 1 indicate a direct view of the nucleus. One interpretation of this is that we have a "special" sight line to this object, close to the opening angle of the ionization cone. I discuss how this unique perspective may allow us to probe the transition between the broad and narrow line regions. THIS IS A TEST.
December 22, 11:30 hr: Dr. Ariane LANCON
Abstract NGC 7714 is an interacting starburst galaxy included both in UV selected samples and in IRAS samples. We have collected spectra for the central ~2" (330 pc) in the UV, the optical and the K band. The UV spectrum is so blue that the dominant population at that wavelength must be very young and on a line of sight with hardly any obscuration. All other stellar components are reddened more severly. A variety of models (star formation history, dust distribution) are consistent with the spectroscopic data as well as with other boundary conditions (far-IR luminosity, X ray and radio emission). We discuss the common features of the collection of satisfactory solutions. More generally, the case of NGC7714 is used to illustrate some of the difficulties one encounters when attempting to ajust the integrated spectrum of a part of a galaxy with "simple" synthetic galaxy spectra.