Either 1) Far IR SED of Seyfert Galaxies: detecting starformation at high z or/and 2) The IAC survey of starburst galaxies

1) J.M. Rodríguez Espinosa and Ana Perez García 2) Ana Pérez García, B. García Lorenzo*, V. Melo, C. Muñoz-Tuñón and J.M. Rodríguez Espinosa 1) IAC, Spain 2) IAC, Spain except for *) ING, Spain espinosa@ll.iac.es (Oral) 1)Far IR SED of Seyfert Galaxies: detecting starformation at high z The Far IR SEDs of a complete sample of Seyfert Galaxies have been measured with ISO. The analysis performed on this sample allows to unambiguously identify the starburst emission in these galaxies. The method allows to derive other important parameters as well as its application to the measurement of star formation rates of galaxies a t high redshifts. 2)The IAC survey of starburst galaxies

PDIBENE@IFCTR.MI.CNR.IT (None)

Cosmological origin of the lowest metallicity halo stars

X. Hernandez$^{1,2}$ and A. Ferrara$^{2,3}$ $^1$ IAUNAM, Universidad Nacional Aut\'onoma de M\'exico. $^2$ Osservatorio Astrofisico di Arcetri. $^3$ Center for Computational Physics, University of Tsukuba.. xavier@arcetri.astro.it (Oral) We explore the predictions of the standard hierarchical clustering scenario of galaxy formation, regarding the numbers and metallicities of PopIII stars likely to be found within our Galaxy today. By PopIII we shall be referring to stars formed at large redshift ($z>4$), with low metallicities ($[Z/Z_{\odot}]<-2.5$) and in small systems (total mass $\simlt$ $2\times 10^{8} M_{\odot}$) that are extremely sensitive to stellar feedback, and which through a prescribed merging history (Lacey \& Cole 1993) end up becoming part of the Milky Way today. An analytic, extended Press-Schechter formalism is used to get the mass functions of halos which will host PopIII stars at a given redshift, and which will end up in Milky Way sized systems today. Each of these is modeled as a mini galaxy, with a detailed treatment of the dark halo structure, angular momentum distribution, final gas temperature and disk instabilities, all of which determine the fraction of the baryons which are subject to star formation. Use of new primordial metallicity stellar evolutionary models allows us to trace the history of the stars formed, give accurate estimates of their expected numbers today, and their location in $L/L_{\odot}$ vs. $T/K$ HR diagrams. A first comparison with observational data suggests that the IMF of the first stars was increasingly high mass weighted towards high redshifts, levelling off at $z\simgt 9$ at a characteristic stellar mass scale $m_s=10-15 M_\odot$.

fidel@astro.ugto.mx (None)

tszeifer@eso.org (None)

ptorres@ccip.udg.mx (Oral)

Systematic Errors: A Few Things We Do Not Know About Stars and Model Atmospheres

Robert L. Kurucz CFA, USA rkurucz@cfa.harvard.edu (Oral) \centerline{\bf Systematic Errors:} \centerline {\bf A Few Things We Do Not Know About Stars and Model Atmospheres} \vskip 10pt We do not know how to make realistic model atmospheres. We do not understand convection. We do not consider the variation in microturbulent velocity. We do not understand spectroscopy. We do not have good spectra of the sun or any other star. We do not have energy distributions for the sun or any other star. We do not know how to determine abundances. We do not know the abundances of the sun or any other star. We do not have good atomic and molecular data. One half the lines in the solar spectrum are not identified. Cepheids have convective pulsation but the models do not. We do not have high quality spectra over phase for any Cepheid. We do not understand how abundances evolve in early stars. Many early stars are oblate fast rotators with polar UV hotter. \vskip 10pt These are all hard problems. We can learn more cosmology by working on them to reduce the systematic errors they introduce than by trying to derive cosmological results that are highly uncertain.

Population Synthesis in the Blue

Ricardo Schiavon Sandra Faber UCO/Lick Observatory ripisc@ucolick.org (Oral) We present a new set of models for stellar population synthesis in the optical. These models are aimed at determining the luminosity-weighted ages and metal abundances of galaxies at $z\sim$1, as part of the DEEP project. The models are based on a comprehensive high-resolution stellar library (1.8$\rm\AA}$ FWHM) and state-of-the-art theoretical isochrones. The adoption of a stellar library of unprecedent resolution and coverage in stellar parameter space allows us to throw a new light on the dependence of absorption features as a function of both stellar and stellar population parameters. We provide first tests of the models by comparing their predictions to the observations of Galactic globular clusters and galaxies from the Local Universe. In special, we concentrate on calibrating age indicators such as higher order Balmer lines (H$\gamma$ through H$\epsilon$), as a function of stellar population parameters.

gnedin@casa.colorado.edu (None)

see Dr. M. Chavez malagnini@ts.astro.it (Oral)

Simulated Millimetre and Submillimetre Galaxy Surveys

E. L. Chapin, D. H. Hughes, E. Gaztañaga INAOE, Mexico echapin@inaoep.mx (Poster) Current submillimetre surveys are hindered in their ability to reveal detailed information on the epoch of galaxy formation and the evolutionary history of a high-redshift starburst population. The difficulties are due to the small primary apertures (D < 15 m) of existing submillimetre telescopes and the limited sensitivities of their first generation of bolometer cameras. This situation is changing rapidly due to a variety of powerful new ground-based, airborne and satellite FIR to millimetre wavelength facilities. Improving our understanding of the luminosity and clustering evolution provides the motivation for conducting cosmological submillimetre and millimetre surveys. It is therefore important that we quantify the limitations of the future surveys and the significance of the results that can be drawn from them. Here we present simulated surveys which are made as realistic as possible in order to address some key issues confronting existing and forthcoming surveys. We discuss the results from simulations specifically for the Large Millimetre Telescope. We address how the measured source counts could be affected by resolution and confusion, by the survey sensitivity and noise, and by the sampling variance due to clustering and shot-noise.

To be defined

Lorenzo Olguin and Jesus Gonzalez IA-UNAM, Mexico IA-UNAM, Mexico lorenzo@astroscu.unam.mx (Poster) To be defined

Spectroscopic analyses of early B supergiants in nearby galaxies

A.Herrero(1,2), M.A.Urbaneja(1), S.J.Smartt (3), F.Najarro (4), D.J.Lennon (5) (1) IAC, La Laguna, Spain (2) ULL, La Laguna, Spain (3) IoA, Cambridge, UK (4) IEM, CSIC, Madrid, Spain (5) ING, La Palma, Spain ahd@ll.iac.es (Oral) We present new results of our spectroscopic analyses of early B supergiants in Local Group galaxies, which include determination of stellar parameters and abundances from moderate S/N ratio (100) observations obtained at intermediate resolutions (1-2 \AA) with the William Herschel Telescope. Special attention is paid to M33, where abundance gradients for several elements are derived and compared with data existing in the literature. A comparison between results obtained using plane parallel hydrostatic model atmospheres and spherical ones with mass-loss is also presented. Techniques suitable for carrying on the analyses at lower resolutions are discussed.

Review talk on: The evolutionary properties of the first stellar generation (from the intermediate to the massive stars) and their final yields.

A.Chieffi, M.Limongi, O. Straniero, I. Dominguez IAS-CNR, Italy, ; OAR, Italy : OACT, Italy ; DFTC, Spain achieffi@ias.rm.cnr.it (Oral) I will review the evolutionary properties of stars deprived of metals (Z=0) in the mass range 0.6-100 $M_\odot$ together to the final yields produced in the various mass ranges.

sole@inaoep.mx (None)

delfin-x@inaoep.mx (None)

eurrutia@upaep.mx (None)

Star formation history in the solar neighbourhood: the link between stars and cosmology

V. Avila-Reese, C. Firmani, X. Hernández Instituto de Astronomía, UNAM, México avila@astroscu.unam.mx (Oral) The star formation (SF) history derived from observations for the solar neighbourhood is compared with predictions of a model of galaxy formation and evolution in the cosmological context. In this model, galactic disks form inside-out within growing dark matter halos with a gas accretion rate proportional to the hierarchical mass aggregation rate, and under the assumption of detailed angular momentum conservation. Global SF is induced by gravitational instabilities (Toomre criterion) and self-regulated by a disk vertical energy balance. For a model that resembles very well the present-day properties of the Milky Way, we find that the SF history at the Galactocentric radius of 8.5 kpc is qualitatively similar to that inferred from comparing a sample of stars from the Hipparcos catalog with synthetic CMDs. The model disk at this radius forms roughly 11.5 Gyr ago. The SF rate increases up to a broad maximum between 8 and 6 Gyr, gently decreasing then by a factor of $\sim 2.5$ until its present-day value of 3 $M_{\odot} Gyr^{-1} pc^{-2}$ (a flat universe with $\Omega_{\Lambda}=h=0.7$ was used). The SF history in our models is tightly related to the cosmological structure formation scenario and the cosmological parameters. We discuss other (secondary) physical ingredients which could produce bursts of SF and a faster decrease of the SF history during the last 3 Gyr.

Update on Globular Cluster Ages

P. Demarque, Y.-C. Kim & S. Yi Yale University, New Haven , CT, USA Center for Space Astrophysics, Yonsei Univ., Seoul, Korea California Institute of Technology, Pasadena, CA, USA demarque@astro.yale.edu (Oral) The ages of the globular clusters in the Galaxy are considered in the light of Hipparcos, HST photometry, and the recently completed Yale-Yonsei isochrones. The ages of the oldest clusters and the issue of the age spread among Galactic globular clusters are discussed. Finally, progress on the dating of globulars using their integrated spectral energy distribution is described.

Gamma-ray bursts as the collapse of massive stars: mapping the Universe to greater depths

Enrico Ramirez-Ruiz, Neil Trentham and Andrew W. Blain IoA, Cambridge enrico@ast.cam.ac.uk (Oral) \begin{abstract} One of the major achievements in extra-galactic astronomy in recent time has been the dramatic transformation in our understanding of gamma-ray bursts (GRBs). There is now consensus that the most common GRBs are linked with massive stars. Those stars that shed their envelopes most readily have short jet crossing times and are more likely to produce a GRB. In this context, GRBs will become invaluable probes of the history of massive star formation and galaxy evolution. Because gamma-rays are not attenuated by intervening dust and gas, the bursts provide an unbiased sampling of cosmic sites of massive star-formation at all look-back times. These advances have opened new vistas and questions regarding the nature of the earliest generation of stars, the evolution of metallicity in the Universe and the large-scale structure at very high redshifts. Some key theoretical issues are highlighted, along with the types of observations that can be used to answer some of these open questions. \end{abstract}

The first stars, the IMF and nucleosynthetic constraints

C. Abia(1), I. Dominguez(1), O. Straniero(2),M.Limongi(3),A. Chieffi(4), J. Isern(5) (1) Universidad de Granada (Spain) (2) Osservatorio de Teramo (Italy) (3) Osservatorio di Monte-Porzio (Italy) (4) IAS, Frascati (Italy) (5) IEEC-CSIC, Barcelona (Spain) cabia@ugr.es (Oral) \begin{abstract} Motivated by the recent detection of metals in different components of the high redshift universe and by the abundance ratios measured in the extremely metal-poor stars of our Galaxy, we study the nucleosynthesis constraints that this imposes on an early generation of stars (Population III). To do so we take into account the chemical yields computed by our group from homogeneous evolutionary calculations of zero metal stars in the mass range $3\la m/M_\odot\la 40$. We also consider the role played by metal-free very massive objects (m$>100$ M$_\odot$). Using both analytical and numerical chemical evolution models, we confront model predictions from the different choices of the mass function proposed for Population III with the observational constraints. We show that low values of star formation efficiency ($<1\%$) are required so as not to exceed the minimum metallicity ([C/H]$\approx -2.4$) measured in the high redshift systems for any of the IMFs proposed. We show that the observational constraints also require $\Omega_{sr}<10^{-3}\Omega_b$, confirming previous claims that the possible contribution of the stellar remnants from Population III to the baryonic dark matter is insignificant. At present, however, the scarcity of abundance measurements for high redshift systems does not permit us to put severe limitations on the nature of the initial mass function for Population III. In fact, overabundances of alpha-elements with respect to iron of the order of these measured in damped Lyman-$\alpha$ systems are obtained for any of the IMFs tested. Nevertheless, to account for the very large [C,N/Fe] ratios found in a considerable number of extremely metal-poor stars of our Galaxy, an IMF peaking at the intermediate stellar mass range ($4-8$ M$_\odot$) is needed. \end{abstract}

Cosmology with Supernovae

Geoffrey Burbidge UCSD, USA gburbidge@ucsd.edu (Oral) abstract not available yet

Explosive Nucleosynthesis and Yields of Low Metallicity Massive Stars

Marco Limongi(1), Alessandro Chieffi(2) and Oscar Straniero(3) (1) Osservatorio Astronomico di Roma, Italy (2) Istituto di Astrofisica Spaziale (CNR), Roma, Italy (3) Osservatorio Astronomico di Teramo, Italy marco@nemo.mporzio.astro.it (Oral) The presupernova evolutions and the explosive yields of massive stars in the range $\rm 13-80~M_\odot$ with metallicity Z=0 and $\rm Z=10^{-3}$ are presented. Differences in the final elemental yields between the two sets of models are addressed and discussed in terms of differences in the presupernova evolutionary properties. Implications on the enrichment of the interstellar medium for the various generations of stars are also discussed.

Cosmological origin of the lowest metallicity halo stars

Xavier Hernandez (1,2) and Andrea Ferrara (1) (1) Osservatorio Astrofisico di Arcetri, Florence Italy (2) IAUNAM, Mexico City, Mexico xavier@arcetri.astro.it (Oral) We explore the predictions of the standard hierarchical clustering scenario of galaxy formation, regarding the numbers and metallicities of PopIII stars likely to be found within our Galaxy today. By PopIII we shall be referring to stars formed at large redshift ($z>4$), with low metallicities ($[Z/Z_{\odot}]<-2.5$) and in small systems (total mass $\simlt$ $2\times 10^{8} M_{\odot}$) that are extremely sensitive to stellar feedback, and which through a prescribed merging history (Lacey \& Cole 1993) end up becoming part of the Milky Way today. An analytic, extended Press-Schechter formalism is used to get the mass functions of halos which will host PopIII stars at a given redshift, and which will end up in Milky Way sized systems today. Each of these is modeled as a mini galaxy, with a detailed treatment of the dark halo structure, angular momentum distribution, final gas temperature and disk instabilities, all of which determine the fraction of the baryons which are subject to star formation. Use of new primordial metallicity stellar evolutionary models allows us to trace the history of the stars formed, give accurate estimates of their expected numbers today, and their location in $L/L_{\odot}$ vs. $T/K$ HR diagrams. A first comparison with observational data suggests that the IMF of the first stars was increasingly high mass weighted towards high redshifts, levelling off at $z\simgt 9$ at a characteristic stellar mass scale $m_s=10-15 M_\odot$.

Stellar metallicities beyond the Local Group with VLT/FORS

N. Przybilla (1), F. Bresolin (1), R.H. Mendez (1), R.P. Kudritzki (2) (1) USM, Munich, Germany, (2) IfA, Hawaii, USA nob@usm.uni-muenchen.de (Oral) Luminous BA-type supergiants are the visually brightest stars in spiral and irregular galaxies. Substantial progress in their theoretical modelling has been achieved by the application of sophisticated non-LTE spectrum synthesis. After the testing of the method on Local Group objects at high resolution, the next step is taken. First results from medium resolution spectroscopy of supergiants in NGC\,3621 at a distance of 7\,Mpc, obtained with the {\sc Fors} instrument on the VLT, are presented. Parameters such as metallicity, colour excess and extinction have been determined for the first time from individual stars at such distances. Analyses of these objects in other galaxies in the future will have an impact on studies on chemical abundances, galactic evolution and abundance gradients. This will also impact the determination of the cosmic distance scale through its implications for the Cepheid distances and the application of the complementary wind momentum- luminosity relationship after proper empirical calibration.

Cepheid Distance Scale and the Virgo Cluster

Anwesh Mazumdar TIFR, Mumbai, India anwesh@astro.tifr.res.in (Oral) A careful study of the various systematic effects plaguing the Cepheid distance scale is extremely important in the context of the recent extension of this standard candle to distances up to the Virgo cluster with the HST. Some of these effects are estimated from analysis of the observed stellar characteristics of Cepheid variables in our Galaxy and the Magellanic Clouds. We devise simple formalisms to account for such effects while using Cepheids to determine extragalactic distances. The distance to the Virgo cluster is estimated from the Cepheid data in six Virgo spirals after correcting for systematic effects such as the flux-limited incompleteness bias. The results underline the importance of bridging the gap between the physical understanding of Cepheid variables as pulsating stars and their application as a powerful cosmological tool.

The peculiar evolution of low-mass Population III stars

Helmut Schlattl (1), Santi Cassisi (2), Achim Weiss (1) and Maurizio Salaris (3) (1) MPA, Garching, Germany (2) OACT, Teramo, Italy (3) ARI, LJMU, Birkenhead, United Kingdom schlattl@mpa-garching.mpg.de (Oral) We have followed the evolution of low-mass, initially metal-free stars from the zero-age main sequence to the white dwarf stage under the assumption of pollution with external, metal-rich material and in the presence of diffusion. We identify conditions under which helium-flash induced mixing between the envelope and carbon-rich layers occurs and compare the resulting surface abundances and post-flash stellar parameters with those of observed extremely metal-poor stars.

angela.j.kopp@lawrence.edu (None)

Evolution of Cosmological Type Ia Supernovae and G

E.Gaztanaga, E.Garcia-Berro, J.Isern , O.Benvenuto, L.Althaus INAOE, Puebla, Mexico IEEC/CSIC/UPC, Barcelona, Spain FCAG, La Plata, Argentina gazta@inaoep.mx (Oral) There are at least three ways in which a varying gravitational constant $G$ could affect the interpretation of the recent high-redhisft Type Ia supernovae results. If the local value of $G$ at the space-time location of distant supernovae is different, it would change both the thermonuclear energy release and the time scale of the supernova outburst. In both cases the effect is related to a change in the Chandrasekhar mass $M_{\rm Ch}\propto G^{-3/2}$. In addition the integrated variation of $G$ with time would also affect cosmic evolution and therefore the luminosity distance relation. Here we investigate in a consistent way how these different effects of a varying $G$ could change the current interpretation of the Hubble diagram of Type Ia supernovae and use the results to set upper bounds on an hypothetical variation of $G$. It is nonetheless remarkable that Dirac's hypothesis that $G$ should decrease with time can qualitatively explain the observed $\Delta m \simeq 0.2$ mag increase at $z\simeq 0.5$ (with respect to a decelerating universe) and, at the same time, reduce the duration of the risetimes of distant Type Ia supernovae as initialy reported.

marna@inaoep.mx (None)

ary@inaoep.mx (None)

The Proper Motion of the Globular Cluster NGC~6553 and of Bulge Stars with HST

M. Zoccali(1), A. Renzini(1), S. Ortolani(2), E. Bica(3), B. Barbuy(4) (1) ESO-Garching, (2) Dip. Astron. Padova, Italy, (3) Dep. Astron. Porto Alegre, Brazil, (4) Dep. Astron. Sao Paulo, Brazil mzoccali@eso.org (Poster) WFPC2 images obtained with HST 4.16 years apart have allowed us to measure the proper motion of the metal rich globular cluster NGC6553 with respect to the background bulge stars. With a space velocity of (${\Pi},~{\Theta},~W$) = (-3.5, 230, -3) km s$^{-1}$, NGC~6553 follows the mean rotation of both disk and bulge stars at a Galactocentric distance of 2.7 kpc. While the kinematics of the cluster is consistent with either a bulge or a disk membership, the virtual identity of its stellar population with that of the bulge cluster NGC~6528 makes its bulge membership more likely. The astrometric accuracy is high enough for providing a measure of the bulge proper motion dispersion and confirming its rotation. A selection of stars based on the proper motions produced an extremely well defined cluster color-magnitude diagram (CMD), essencially free of bulge stars. The improved turnoff definition in the decontaminated CMD confirms an old age for the cluster ($\sim 13$ Gyr) indicating that the bulge underwent a rapid chemical enrichment while being built up at in the early Universe. An additional interesting feature of the cluster color-magnitude diagram is a significant number of blue stragglers stars, whose membership in the cluster is firmly established from their proper motions.

The dusty SF history of distant galaxies and modelling tools

Gian Luigi Granato Osservatorio astronomico di Padova (OAPD) granato@pd.astro.it (Oral) In this review I summarize recent advances in the determination of the cosmic history of star formation and other properties of high-z galaxies, and the relevance of this information in our understanding of the formation of structures. I emphasize the importance of dust reprocessing in the high--z universe, as demonstrated in particular by IR and sub-mm data. This demand a panchromatic approach to observations and suitable modelling tools, which I discuss. I also summarize what it is to be expected from future instruments.

The Upper End of The Galactic Metallicity Scale

Benjamin J. Taylor BYU taylorb@physc3.byu.edu (Oral) Among North American stellar astronomers, it is widely agreed that the upper end of the galactic metallicity scale is well understood. For $\mu$ Leo and NGC 6791 in particular, metallicities are thought to be about $+0.46$ and $+0.40$ dex, respectively. In fact, neither of these results is trustworthy, and the prevailing impression about the upper end of the metallicity scale is mistaken. For NGC 6791, there is a high-dispersion analysis of a cluster star by Peterson and Green (1998, ApJ 502, L39) and a conspicuous color-magnitude analysis by Chaboyer et al. (1999, AJ 117, 1360). Both analyses are based on non-statistical procedures, fail to explore solution space adequately, and yield formally meaningless results. At present, the actual range of permitted metallicities allowed by these and other analyses extends down to $+0.16$ dex. For $\mu$ Leo, the analysis recognized as definitive in North America was published by Castro et al.\ (1996, AJ 111, 2439). However, the zero-point technique in that analysis is fallacious. In fact, it was repudiated by one of the Castro et al.\ co-authors (namely, Bell) some fifteen years before Castro et al.\ was published (see Trimble and Bell 1981, QJRAS 22, 361). In addition, Castro et al.\ continue two pertinent traditions: $a)$ discussion of an arbitrary set of published results which changes arbitrarily from one data review to another, and $b)$ adoption of an a priori requirement that $\mu$ Leo shall have a metallicity of about $+0.3$ dex or greater. A third North American tradition excludes statistics from analyses of ``super-metal-rich'' (SMR) stars. To counter these and other self-defeating traditions, the present author has introduced a ``statistical paradigm'' for treating published high-dispersion metallicities. When this paradigm is applied, SMR dwarfs and subgiants can be identified, bu no SMR giants are discovered. It is concluded that at present, the existence of SMR giants can neither be proved nor disproved. In addition, a review is given of serious shortcomings in the high-dispersion and color-magnitude disciplines that are highlighted by the SMR problem.

Modelling the x-ray to radio SED of galaxies

silva@ts.astro.it (Oral)

A Precise New Method of Correcting the Temperature in Stellar Atmospheres

O. Cardona(1), L. Crivellari (2), E. Simonneau(3) 1 Instituto Nacional de Astrofísica, Óptica y Electrónica, México. 2 Osservatorio Astronomico di Trieste, Italy, Instituto de Astrofísica de Canarias, Spain. 3 Institute d'Astrophysique de Paris, CNRS, France. ocardona@inaoep.mx (Oral) When one includes the frequencies of the continuum and of the lines of Lyman when establishing the conditions of energy balance in the calculation of models of stellar atmospheres for cold and moderately cold stars it is found that the energy gained or lost in those frequencies can be 15 or 20 orders of magnitude bigger that the rest of the spectrum. However, due to the great optical depth corresponding to those frequencies - for almost all the layers of the model, the monochromatic mean intensity of the radiation and the corresponding source function are numerically equal with many significant figures. Consequently the radiation field absorbed and emitted in these frequencies do not collaborate to the energy balance. We can say that these frequencies are passive ( at least in the layers where the corresponding radiative field is in numerical radiative equilibrium ). But, unfortunately, in all the temperature correction methods, the source functions - and accordingly the total emission terms -, and the radiation mean intensities are calculated independently. Then, in both terms, i.e., in both integrals, the dominant collaboration ( some times of 15 to 20 orders of magnitud ) corresponds to the passive frequencies, and therefore, the determination of the new temperature could be falsified. We present a method to calculate the correction of the temperature in stellar atmospheres that overcomes the aforesaid difficulty. We intend to obtain the maximum precision of the calculations using as variable the non local mean intensity $ \varphi (\nu )=J(\nu )-S(\nu ) $. Once this variable is calculated one can calculate the mean intensity $ J(\nu ) $ and the source function $ S(\nu ) $ independently. Defining the non local intensities $ y^{+}(\nu ,\mu ) $ and $ y^{-}(\nu ,\mu ) $ in terms of the differences among the specific intensities upward $ I^{+}(\nu ,\mu ) $ and downward $ I^{-}(\nu ,\mu ) $ with the source function $ S(\nu ,\mu ) $ respectively, we can obtain an equation similar to that of the standard radiation transport equation which can be solved with any method. Thus, when the variable $ \varphi (\nu )=J(\nu )-S(\nu ) $ is numerically zero in the transfer computation, it means that the frequency $ \nu $ is passive, and consequently it can be taken out of the balance integral. We solve here the transport equation with the Implicit Integral Method for an atmosphere in LTE, for physical conditions close to solar.

The primordial lithium abundance

Piercarlo Bonifacio Osservatorio Astronomico di Trieste bonifaci@ts.astro.it (Oral) The recent observations of the cosmic microwave background (CMB) by the baloon experiments BOOMERANG and MAXIMA favour a rather high value of the baryonic density $h^2\Omega_b \approx 0.03$. This value is in fact higher than allowed by the observed primordial abundances of light elements and Standard Big Bang Nucleosynthesis (SBBN). In this contribution we review the problem of the primordial Li abundance from an observational point of view, addressing the possibility of inferring a higher primordial Li value than currently accepted. We shall also discuss the possible existence of a slope in the plateau, which would lead to a very low primordial Li abundance. We discuss results based on new photometric and spectroscopic data, for a sample of field stars on the Spite plateau and new observations in metal--poor Globular Clusters. ~ ~

Sara L. Ellison, Sean Ryan, Jason X. Prochaska ESO (Chile), Open University (UK), Carnegie Observatories (USA) sellison@eso.org (Oral) The study of metal abundances in Damped Lyman Alpha systems (DLAs) and susbsequent comparison with Galactic stellar populations represents one of the best opportunities to probe galaxy formation and chemical evolution at early times. Here, I present the first ever detection of Cobalt in a $z \sim 2$ DLA. I discuss the possible implications that further such detections may have for understanding both the star formation histories of high redshift galaxies and stellar nucleosynthetic processes.

Cosmological Chemistry and the Formation of the First Objects

Anton Lipovka Julio Saucedo Julio Campos Ilie Soto CIFUS, UNI-SON CIFUS, UNI-SON CIFUS, UNI-SON CIFUS, UNI-SON CIFUS, UNI-SON CIFUS, UNI-SON Ingenieria Quimica, UNI-SON jsaucedo@cosmos.cifus.uson.mx (Poster) In the present report we discuss the role of primordial molecules in the evolution of the Universe at epochs 10 < Z <300. The last results of the "BOOMERANG" and "MAXIMA" experiments argue in favor of a non standard big bang nucleosynthesis, so it is of great importance to take into consideration not only primordial molecules formed by H, D, He, and Li, but also by primordial Nitrogen, Carbon, and Oxygen. Molecular abundances in protoobjects under different circumstances are estimated and possible changes in their evolution are discussed. It is stressed that under reasonable assumptions of the relative abundance of oxygen and carbon = 10^{-9} - 10^{-10}, one can obtain observable optical depths for the lines of primordial molecules due to the luminescence and scattering of CMBR by molecules of protoobjects moving with peculiar velocities at high redshift. By taking into account the formation of the first stars at redshift 10 < Z <100 it is possible to observe results of their evolution in lines.

Deep Studies of the Resolved Stellar Populations in the Outskirts of M31

Annette Ferguson Kapteyn Institute, University of Groningen, The Netherlands ferguson@astro.rug.nl (Oral)

A Survey of Open Clusters in the Northen Hemisphere

A. Moitinho W.J. Schuster C. Chavarría IA-UNAM, Mexico IA-UNAM, Mexico IA-UNAM, Mexico andrem@astrosen.unam.mx (Poster) The ladder that links stars to cosmology is composed of several steps. Following the closest stars, whose trigonometric paralaxes can be directly measured, the next step in the cosmic distance scale is composed of star clusters. Star clusters are ideal objects for the study of many astrophysical problems because they are groups of stars with a broad range in mass, formed under the same conditions, at approximately the same time, and located at a common distance. As a group, star clusters have proven to be valuable probes of the structure and development of our Galaxy and beyond. Individually, they provide observational constraints to theories of star formation and evolution. In this contribution the first results of a UBVRI survey of open clusters that is being conducted at the Observat\'orio Astron\'omico Nacional at Sierra de San Pedro M\'artir (SPM) are presented. Most of the clusters visible from SPM and will be surveyed using the same instrumentation (telescope, CDD, filters) and reduction procedures. This survey will, therefore, provide a highly homogeneous database of open cluster photometry. With this database we expect to \\ (1) establish a set of local standards that will allow other work to be transformed onto a common system; \\ (2) obtain an atlas of colour-colour and colour-magnitude diagrams for the clusters;\\ (3) determine a homogeneous set of cluster reddenings, distances and ages;\\ (4) provide selection criteria for further studies (reddening, distance and age ranges; clusters containing certain types of stars; etc.)

Accurate distance to the Andromeda Galaxy using eclipsing binaries as standard candles

Ignasi Ribas Villanova University (USA) iribas@ast.villanova.edu (Oral) The Andromeda Galaxy (M31) is crucial for the calibration of the Cosmic Distance Scale and thus for determining the evolution and age of the Universe. Yet, currently its distance is known to no better than $10-15$\%. We have demonstrated in our work on the LMC distance that double-line eclipsing binaries can serve as excellent ``standard candles''. Distances derived from eclipsing binaries are basically geometric and essentially free from many assumptions and uncertainties that plague other less direct methods. For example, Guinan et al. (1998) and Fitzpatrick et al. (2001) recently obtained distances of $45.7\pm1.6$ kpc and $45.9\pm2.1$ kpc from the analysis of two LMC systems. Here we discuss the extension of our program of using eclipsing binaries as standard candles to determine an accurate distance to M31. HST/STIS low-resolution spectrophotometry will be used to determine $T_{\rm eff}$, $[Fe/H]$, and $A_{\lambda}$. HST/STIS or Keck observations will provide accurate radial velocities of these double-line systems which, when combined with our light curves and $T_{\rm eff}$, yield the stellar radii, luminosities, and distances. Based on our previous experience, we expect to reduce the uncertainty of the M31 distance to better than 5\%, thereby firmly calibrating the Cosmic Distance Scale.

Calibrating the Cosmic Meter Stick: The Distance to the LMC Using Eclipsing Binaries

Edward Guinan, Ignasi Ribas, Edward Fitzpatrick Department of Astronomy & Astrophysics Villanova University edward.guinan@villanova.edu (Oral) The Cosmic Distance Scale is anchored to the distance to the LMC. However, there is considerable disagreement about this fundamental measurement, with discrepancies among different approaches of $\approx$10\% ($m-M = 18.2-18.7$ mag). To overcome this problem we have been carrying out a program to measure accurately the distance to the LMC using eclipsing binaries as standard candles. The analysis combines the ``classical'' study of light and radial velocity curves, which yield stellar masses and radii, with a new analysis of the observed energy distributions, which yield effective temperatures, metallicities, and reddenings of the systems plus the distance. This robust method consists of a detailed study of well-understood objects (B stars) in a well-understood evolutionary phase (core H burning). There are no ``zeropoint'' uncertainties as, for example, with the use of Cepheid variables. Neither is the result subject to sampling biases, as may affect techniques which utilize whole stellar populations, such as red giant branch stars. Moreover, the analysis is insensitive to stellar metallicity (although the metallicity of the stars is explicitly determined) and the effects of interstellar extinction are determined for each object studied. Results of three eclipsing systems analyzed so far yield an LMC distance modulus of $(V_0-M_V)_{\rm LMC}=18.35\pm0.06$ mag. Analysis of several more well-suited eclipsing binaries potentially can result in an LMC distance with a net uncertainty of $(V_0-M_V)_{\rm LMC} \simeq 0.03$~mag ($<1.5\%$). Within the next few years we hope to expand the program to include about 20 systems. The ensemble of targets, in addition to nailing down the distance to the LMC, will provide a detailed probe of the structure and spatial extent of this important galaxy.

Halpha luminosity function of H II regions: preliminary calibration of a powerful standard candle

Maite Rozas, Almudena Zurita, John Beckman IAUNAM-Mexico IAC-Espana maite@astrosen.unam.mx (Poster) We propose the use of the H II region luminosity function as a posible refined powerful standard candle for extragalactic distances. We have found evidence that there is a change in the properties of H II regions in spirals at a fixed luminosity in Halpha which we call the Stromgrem luminosity (L= 10e38.6 erg/s in Halpha). The key piece of evidence is the presence in the Halpha LF of a change in gradient and a glitch (local sharp peak). The invariance and high luminosity of the change.peak measured in the LF was proposed in previous studies as a possible secondary standard candle, but it is calibrated here for the first time using the LFs of NGC 925 and M100, whose Cepheid distances have been determined in the Hubble Space Telescope (HST) Extragalactic Distance Scale Key Project.

chasobel@yahoo.com (None)

Abundances in high redshift Damped Ly$\alpha$ systems

Paolo Molaro Trieste Observatory molaro@ts.astro.it (Oral) Absorption due to clouds along the line of sight to quasars, with large enough hydrogen column density to be shielded from intergalactic ionizing photons, probes the chemistry of the cosmic gas with unique accuracy. The status of available chemical abundances in Damped Ly$\alpha$ systems is reviewed and compared with those of other astrophysical sites such as halo stars and interstellar medium of the Milky-Way, or Blue Compact galaxies. Some implications for the very early stellar formation and the nature of the high redshift gas giving rise to the Damped Ly$\alpha$ systems are discussed.

On the properties of massive population III stars and metal-free stellar populations

Daniel Schaerer Observatoire Midi-Pyrenees Toulouse/France schaerer@ast.obs-mip.fr (Oral) We have calculated extended grids of model atmospheres appropriate for massive popIII stars, based on both plane parallel and spherically expanding non-LTE models. These are used to discuss the spectral properties and ionising fluxes of metal-free stars and their dependence on poorly known parameters, such as possible stellar winds. The above model atmospheres are combined with recent metal-free evolutionary tracks from the Geneva and Padova group and included in our evolutionary synthesis models to predict the observational properties (SED, colors, and emission lines) of massive stellar populations, representative of potential metal-free clusters or galaxies. We discuss the dependence of these properties on the main parameters such as the mass limits and slope of the IMF and the star formation history, as well as the sensitivity to the stellar tracks (mass loss) and uncertainties in the atmosphere models. The results for popIII populations are compared to predictions of metal-poor objects which have already extensively been compared to observations of metal-poor HII regions and starbursts. The models presented here are of interest for a variety of studies on reionisation, the first generation of stars and galaxies, early stellar populations and others.

Dust and nebular emission in star-forming galaxies

P. Panuzzo (1), A. Bressan (2), G. L. Granato (2), L. Silva (3), L. Danese (1) (1) SISSA/ISAS, (2) Astronomical Observatory of Padova, Italy, (3) Astronomical Observatory of Trieste, Italy panuzzo@sissa.it (Oral) Star forming galaxies exhibit a variety of physical conditions, from quiescent normal spirals to the most powerful dusty starbursts. In order to study these complex systems, we need a suitable tool to analyze the information coming from observations at all wavelengths. We present a new spectro-photometric model which considers in a consistent way starlight as reprocessed by gas and dust. We discuss preliminary results for a sample of local starbursts and ULIRGS.

Reconstructing star formation episodes in the Local Group

D. Valls-Gabaud(1), X. Hernandez(2), G. Gilmore(3) (1) Observatoire Midi-Pyrenees, Toulouse, France (2) Obs. Astr. Arcetri, Florence, Italy (3) Institute of Astronomy, Cambridge, UK dvg@ast.obs-mip.fr (Oral) The colour-magnitude diagrams (CMDs) of resolved stellar populations within the Local Group provide unique constraints on the cosmological models of galaxy formation. The unprecedented quality of recent CMDs, probing environments as different as the Hipparcos solar neighbourhood, the dense cores of globular clusters and the diffuse, galaxy-wide samples of nearby dwarf spheroidal galaxies, requires proper techniques to infer their star formation histories. Our state-of-the-art method, based on a coupling of maximum likelihood with variational calculus, allows us to infer -for the first time- a robust, non-parametric reconstruction of the evolution of the star formation rate which gave rise to the observed CMDs. Uncertainties in the IMF, fraction of binaries and metallicity are studied with Monte Carlo simulations, showing that the dating of star formation episodes is robust against changes in these quantities. We apply our method to the best CMDs available, where crowding effects and blending are minimal. In the solar neighbourhood we find evidence for a regularity of about 50 Myr in the star formation activity over the past 3 Gyr, possibly linked to interactions with spiral arms. In nearby globular clusters we derive very stringent upper limits to the spread of the burst which formed their stars. The case of the five Local Group dwarfs studied so far shows an unexpected wide variety in their star formation histories. We interpret these results within the framework of galaxy formation models in the CDM paradigm.

Surveys for variable stars in M31 and M33

D. Bersier, L. Macri, K. Stanek, B. Mochejska, J. Kaluzny, D. Sasselov, J. Tonry Harvard CfA; Warsaw; IfA, Hawaii dbersier@cfa.harvard.edu (Oral) Nearby galaxies are the best laboratories to test current theories of stellar evolution and star formation. They are also anchor points of the extragalactic distance scale. I will describe two projects looking for variable stars in M31 and M33, with the goal of obtaining direct distances to these galaxies. The DIRECT project has discovered several hundreds of new Cepheids in each galaxy, many eclipsing binaries, and numerous other variables. In a complementary program, I have obtained BVI data from the WIYN telescope over three years. I will present the current status of each project and emphasize the results that have an impact on the distance scale. I will also mention an abundance analysis of two M33 Cepheids based on Keck spectra.

tbd

bertone@merate.mi.astro.it (Poster)

luisrg@inaoep.mx (None)

On the Stellar Initial Mass Function in Very Metal-Poor Environments

Fumitaka Nakamura (1) and Masayuki Umemura (2) (1) Astronomy Dept., UC Berkeley (2) RCCP, University of Tsukuba nakamura@astro.berkeley.edu (Oral) We studied the collapse of filamentary gas clouds by 1D hydro simulations coupled with H$_2$ and HD molecular formation. [This is an extension of Nakamura \& Umemura (2001, ApJ, 548, 19).] The numerical results show that the cloud evolution depends mainly on the initial density and H$_2$ abundance. For low-density filaments, there is a critical H$_2$ abundance of $3\times 10^{-3}$, beyond which HD cooling becomes effective. When the H$_2$ abundance is lower than the critical value, H$_2$ cooling determines the cloud evolution and then the cloud tends to fragment into dense cores with masses of$10^3 M_\odot > M > $ a few $\times 10M_\odot$. (They might evolve into very massive or massive stars.) In contrast, when the H$_2$ abundance is higher than the critical value, the fragment masses reduce to a few $\times 10M_\odot$ owing to effective HD cooling (They might evolve into massive stars). On the other hand, for high-density filaments, HD cooling does not play a role in the thermal evolution of the cloud. The cloud contraction is accelerated by effective three-body H$_2$ formation and the fragmentation does not take place until the cloud becomes optically thick to H$_2$ lines. Then, the fragment masses are estimated as $\approx 1M_\odot$ (They might evolve into low-mass or intermediate-mass stars). Our results are applicable to star formation in very metal-poor environments ($Z<10^{-2}Z_\odot$) because the metal cooling does not play a role in the thermal evolution of the gas. The initial H$_2$ abundance of the filament can be related to the ionization degree of a parent cloud because the H$_2$ molecules form efficiently in highly-ionized gas. Thus, the numerical results imply that the bimodality might be a characteristic of the IMF in very metal-poor environments and the IMF may depend strongly on intergalactic environments such as UV radiation and intergalactic shocks which can ionize the intergalactic gas. We will discuss the implications for the first star formation and galaxy formation.

Reconstructing the star formation history in the halo of NGC 5128

Francine R. Marleau, Jan Kleyna, James R. Graham Saint Mary's University, Canada IoA, University of Cambridge, UK University of California, Berkeley, USA marleau@maia.stmarys.ca (Poster)

On the Calibration of Star Formation Rates

Daniel Rosa González Elena Terlevich Roberto Terlevich INAOE, México INAOE, Mexico IoA, Cambridge, UK. danrosa@inaoep.mx (Oral) A central problem in the "Madau--Lilly" diagram, i.e. the evolution of the Star Formation Rates (SFR) with redshift, is that the SFR is estimated using several different estimators at different redshift ranges that potentially can have systematic differences among them. I will address the question: How much of the observed change of the SFR with redshift may be due to systematic differences in the SFR calibrators. I have used a well calibrated sample of star forming galaxies in the local Universe to establish a self--consistent system of SFR estimators. The application of the new system to a high redshift sample shows an increase of the SFR by a factor of 14 from the local Universe to redshift one and a slow decrease from redshift one to five with a median value of approximately 0.3 solar masses per year per cubic megaparsec (for h=.5, $\Omega_{\rm M}$=1 and $\Lambda$=0).

toa@inaoep.mx (None)

ahtramop@inaoep.mx (None)

HI Emission from the Damped Lyman-alpha absorber SBS 1543+593

David V. Bowen(1), Elias Brinks(2), Walter Huchtmeier(3), Todd M. Tripp(1), and Edward B. Jenkins(1) (1) Princeton University Observatory, USA (2) Universidad de Guanajuato, Mexico (3) MPI fuer Radioastronomie, Germany ebrinks@astro.ugto.mx (Poster) We detect 21 cm emission from the Low Surface Brightness (LSB) galaxy SBS~1543+593. The neutral gas gives rise in the optical to a Damped--Ly$\alpha$ (DLy$\alpha$) line in the spectrum of the background QSO HS~1543+5921 ($z_e = 0.807). We derive an accurate measure of the systemic velocity of the intervening LSB galaxy, its HI mass, and an estimate for its dynamical mass. Comparison with upper limits reported in the literature towards two other DLy$\alpha$ systems, we show that even if the LSB were put at only a modest redshift, of order 0.1, it would not be detectable in HI.

ovega@inaoep.mx (None)

Modelling of cool stellar atmospheres: an update

Peter Hauschildt University of Georgia Dept. of Physics + Astronomy yeti@hal.physast.uga.edu (Oral)

raqueld@inaoep.mx (None)

miyang@inaoep.mx (None)

Estimation of H0 using Cepheid PL relations at maximum light

S. M. Kanbur and S. Nikolaev Department of Astronomy, University of Massachusetts Department of Astronomy, University of Massachusetts shashi@fcrao1.astro.umass.edu (Oral) We use the pulsational properties of Cepheids at maximum light to suggest the use of Cepheid PL relations at maximum light. We show that these relations exist and have smaller dispersion than their counterparts at mean light in the LMC. Further, we estimate the distance to 4 HST KP observed galaxies and by using the recession velocity of NGC 1365, we obtain a crude estimate of H0 = 73.3 plus or minus 16.9 km/sec/Mpc. The error on this estimate is dominated by the error on the recession velocity of NGC 1365. We discuss future prospects with PL relations at maximum light.

chasobel@yahoo.com (None)

yamil@inaoep.mx (None)

papaqui@inaoep.mx (None)

dferrus@inaoep.mx (None)

jantonio@inaoep.mx (Oral)

jcgc@inaoep.mx (None)

grimaldi@inaoep.mx (None)

jperez@inaoep.mx (None)

calvarez@inaoep.mx (None)

dhuos@inaoep.mx (None)

abelmh@inaoep.mx (None)

maac@inaoep.mx (None)

montana@inaoep.mx (None)

A Grid of Synthetic Stellar UV Fluxes

L. H. Rodriguez (1), M. Chavez (1), A. Buzzoni (2), E. Bertone (3) (1) INAOE-Mexico (2) TNG La Palma-Spain (3) Osservatorio di Merate-Italy lino@inaoep.mx (Poster) We present preliminary results of the inicial steps towards building an extensive theoretical and observational stellar data base in the UV. This data base will be based on IUE low and high dispersion data (complemented with Voyager data) and Kurucz model fluxes. We compare high dispersion images of three stars; HD 36512, HD 17081 and HD 90839 with the corresponding high resolution synthetic spectra computed using the SYNTHE series of codes developed by Kurucz (CD-ROM 18). The goal of this comparison is to identify spectral regions that are well represented by model fluxes and to calibrate line intensities in terms of the basic atmospheric parameters. In this poster paper we present a solar chemical composition grid covering the parameter space from 10000 K to 50000 K, and surface gravity from 2.0 to 5.0 dex.

aviles@inaoep.mx (None)

rosariop@inaoep.mx (None)

HII region luminosity functions: Preliminary calibration of a new secondary standard candle.

M. Rozas(1), A. Cardwell(2)(3), A. Zurita(2)(4), J.E. Beckman(2)(5) (1) Observatorio de San Pedro Martir, Mexico (2) Instituto de Astrofísica de Canarias, Spain (3) The Open University, United Kingdom (4) Isaac Newton Group of Telescopes, La Palma, Spain (5) CSIC, Spain cardwell@ll.iac.es (Poster) Recent studies of the HII region luminosity function, made using high quality data, have revealed a break in the luminosity function which is both invariant and at a high luminosity. We present a preliminary calibration of this feature, for use as a new secondary standard candle, using the HII region LFs of NGC 925, M 100, NGC 4535 and NGC 4725, whose Cepheid distances have been determined by the HST Extragalactic Distance Scale Key Project.

The massive, interacting multiple system HD 5980 in the SMC

Koenigsberger, G. IA-UNAM gloria@astroscu.unam.mx (Poster) The binary system HD5980 is located in the Small Magellanic Cloud, in the periphery of the young stellar cluster NGC 346. HD 5980 is the visually brightest object of the cluster and it consists of at least three stars: Star A (the LBV/WR) and Star B (a WR star) constitute a physically bound, eclipsing system with a short orbital period (19.266 days), and a modest eccentricity (e=0.27); the third component, Star C, an O4-6 spectral type.There is as yet no evidence that Star C is physically bound, nor that it is interacting in any way with the A+B system. In 1993 and 1994, HD 5980 underwent two sudden eruptions, the second of which was similar to the Luminous Blue Variable (LBV) eruptions. This is the first, and up-to-now the only case of an observed LBV-like transition involving a WR star. The location of Star A on the HR diagram implies a ZAMS mass above 140 M$_{\odot}$ (similar to $\eta$ Car), although its actual mass is close to 50 M$_{\odot}$ implying that a large fraction of its original mass has already been lost, possibly resulting from instabilities driven by tidal oscillations. We will present an update of this remarkable extragalactic binary system.

In preparation

Valdez-Gutierrez, M., Rosado, M. INAOE, Mexico. IA-UNAM, Mexico. mago@inaoep.mx (Poster) In preparation

leonardo@inaoep.mx (None)

aporras@inaoep.mx (None)

Where did the gas and stars in the intracuster medium come from?

Omar López-Cruz (1,2) (1) INAOE (2) D.A. U de Guanajuato omar@inaoep.mx (Oral) will review the current ideas regarding the enrichment the intracluster medium (ICM) in rich clusters of galaxies. It has been proposed that the main agent for the enrichement of the ICM are the cluster ellipticals. New observations seem to contradict, or at least complement, this view, we will argue that disrupted cluster dwarfs are more likely to have contributed to a significant fraction of the light and gas in the ICM. _________________________________________________________________

Luminosity Evolution in Cluster Elliptical Galaxies

Omar López-Cruz (1,2), David Schade (3), and Felipe Barrientos (4) (1) INAOE (2) D.A. U de Guanajuato (3) National Research Council Canada, HIA/DAO. (4) Departamento de Astronomia, PUC de Chile omar@inaoep.mx (Oral) I review the current status of the observations from the ground and from HST that show that elliptical galaxies have undergone a significant amount of luminosity evolution. The results presented here come from two-dimensional surface photometry derived from HST, CFHT and KPNO. After confrontation with the models of Buzzoni (1995) we conclude that the observed luminosity evolution is consistent with passive evolution, and a formation epoch of 15 Gyr ago and a Salpeter IMF. At the end of this review I will discuss the relevance of these results in the context of the universality of the IMF.

Dust-Penetrated morphology in the high-redshift universe

D.L. Block (1), I. Puerari (2), M. Takamiya (3), R. Abraham (4), A. Stockton (5), I. Robson (6), W. Holland (6) (1) University of Witwatersrand, South Africa (2) INAOE, Mexico (3) Gemini Observatory, USA (4) University of Toronto, Canada (5) University of Hawaii, USA (6) Joint Astronomy Center, USA puerari@inaoep.mx (Poster) Results from the Hubble Deep Field (HDF) North and South show a large percentage of high-redshift galaxies whose appearance falls outside traditional classification systems. The nature of these objects is poorly understood, but sub-mm observations indicate that at least some of these systems are heavily obscured (Sanders 2000). This raises the intriguing possibility that a physically meaningful classification system for high-redshift galaxies might be more easily devised at rest-frame infrared wavelengths, rather than in the optical regime. Practical realization of this idea will become possible with the advent of the Next Generation Space Telescope (NGST). In order to explore the capability of NGST for undertaking such science, we present NASA-IRTF and SCUBA observations of NGC 922, a chaotic system in our local Universe which bears a striking resemblance to objects such as HDF 2-86 (z = 0.749) in the HDF North. If objects such as NGC 922 are common at high-redshifts, then this galaxy may serve as a local morphological ``Rosetta stone'' bridging low and high-redshift populations. In this paper we demonstrate that quantitative measures of galactic structure are recoverable in the rest-frame infrared for NGC 922 seen at high redshifts using NGST, by simulating the appearance of this galaxy at redshifts z = 0.7 and z = 1.2 in rest-frame K$'$. While this object cannot be classfied within any optical Hubble bin, simulated NGST images at these redshifts can be readily classified using the dust penetrated z = 0 template of Block \& Puerari (1999) and Buta \& Block (2001). The near-infrared disk of NGC 922 is not peculiar at all; rather, it is remarkably regular, even presenting spiral arm modulation, a characteristic signature of several grand design galaxies. Our results suggest that the capability of efficiently exploring the rest-wavelength IR morphology of high-z galaxies should probably be a key factor in deciding the final choice of instruments for the NGST.

Cosmological origin of the lowest metallicity halo stars

xavier@arcetri.astro.it (Oral)

To be communicated

Sergio A. Cellone (1) Alberto Buzzoni (2) (1) FCAG - UNLP. Argentina (2) OAB, Italy and TNG, Spain scellone@fcaglp.unlp.edu.ar (Poster)

cade@inaoep.mx (None)

quantumrem@yahoo.com (None)

Nucleosynthesis of the Light Elements

Ann Merchant Boesgaard Univ. of Hawaii boes@ifa.hawaii.edu (Oral) The light isotope $^7$Li is made during the nuclear reactions in the first few minutes after the Big Bang both by reactions with $^3$H and via $^7$Be reactions. The amount of $^7$Li in stellar atmospheres is the result of Big Bang nucleosynthesis, synthesis by other means e.g. in AGB stars and supernovae, by galactic cosmic ray spallation, and destruction by nuclear reactions during stellar evolution. The best way to find the value of the primordial component is to look at the Li abundance in the oldest stars where the other effects of Li enrichment and destruction are thought to be at a minimum. After a review of Li in halo stars, new results on Li in globular cluster turn-off stars will be presented. The element Be maybe formed during the Big Bang according to some models of an early inhomogeneous universe. Results of Be in the oldest stars will be shown; there seems to be no evidence for primordial Be. The evolution of both Be and B (and the ratio B/Be) may reveal the contribution of spallation reactions to the Li abundance and the ratio of Li to Be in F stars may reveal the amount of Li destruction; this knowledge helps to clarify the primordial Li value. Knowledge of the amount of the light elements in stars in the solar vicinity is one step to understanding the prevailing conditions at the time of the Big Bang.

violetaguzmanj@hotmail.co (None)

dalba@udgserv.cencar.udg.mx (None)

bressan@pd.astro.it (Oral)

lafisicarifa@yahoo.com (None)

aortuno@fismat1.fcfm.buap.mx (Oral)

Cosmological parameters from the recent CMB anisotropies measurements.

R. Stompor Dept. of Astronomy, University of California, Berkeley, CA, USA radek@cfpa.berkeley.edu (Oral) I will discuss the constraints one can put on the viable cosmologies using the results of the most recent CMB experiments in particular MAXIMA and BOOMERANG.

memomemo36@hotmail.com (Oral)

tinocofisica@hotmail.com (Oral)

High Redshift Galaxies and the Intergalactic Medium

Rupert Croft Harvard-CfA, USA rcroft@cfa.harvard.edu (Oral) I will present results from high resolution cosmological simulations of galaxy formation in a cold dark matter universe, focussing on redshifts of around 3. At these early times, star formation is occuring vigorously, but most of the baryons in the universe are still diffuse, and have yet to form into galaxies. Absorption lines due to neutral hydrogen in the spectra of nearby quasars provide a useful way to probe physical conditions in the gas around these galaxies. I will explore the relationship between this intergalactic material and the sites of stars formation, in order to understand how these high redshift galaxies form, and to provide data which can be compared to observations.

harry.blom@wkap.nl (None)

The value of Omega

Roman Juszkiewicz 1. Kepler Institute, Zielona Gora, POLAND 2. Copernicus Center, Warsaw,. POLAND 3. Universite de Geneve, SWITZERLAND roman@camk.edu.pl (Oral) I will describe a new technique for estimating the cosmological mass density parameter, $\Omega_m$ . I will also discuss a range of other dynamical measures of $\Omega_m$ as well as the current state of our knowledge about the vacuum contribution, $\Omega_{\Lambda}$, and the measure of the curvature, $\Omega = \Omega_m + \Omega_{\Lambda}$.

fer_fab@hotmail.com, ferfab@inaoep.mx (None)

STARS AND GAS IN HIGH REDSHIFT GALAXIES

Max Pettini IoA, Cambridge, England pettini@ast.cam.ac.uk (Oral) Recent advances in instrumentation and observing techniques have made it possible to begin to study in detail the stellar populations and the interstellar media of galaxies at redshift z = 3, when the universe was still in its `teen years'. In keeping with the theme of this conference, I will show how our knowledge of local star-forming regions can be applied directly to these distant galaxies to deduce their ages, metallicities, initial mass function, and masses. I will also discuss areas where current limitations in stellar astrophysics have a direct bearing on the interpretation of the data being gathered, at an ever increasing rate, on the high redshift universe.

New phenomena discovered in the atmospheres of normal late-B type stars

S. Hubrig (1), G.M. Wahlgren (2), & F. Castelli (3) (1) ESO, Chile, (2) University of Lund, Sweden, (3) CNR-Gruppo Nazionale Astronomia and Osservatorio Astronomico di Trieste, Italy shubrig@eso.org (Poster) We report detection of weak emission lines in main sequence B star spectra observed at high spectral resolution and high signal-to-noise ratio. The emission lines originate from highly excited states of singly-ionized species. The mechanism for populating these excited states is currently under investigation and the results may have a significant bearing upon our understanding of the outmost atmospheric regions of B type stars. Another intriguing result of our study is that stars in our sample show evidence for magnetic intensification.

Heating the Quiet Corona by Nanoflares: Results from SUMER on board SoHO.

Dr. Jose Eduado Mendoza Torres and Juan Pablo Torres Papaqui INAOE, Mexico, INAOE, Mexico. papaqui@inaoep.mx (Poster) The observations analyzed in this work were carried out by the SUMER telescope on board of the SoHO satellite, during 1996 November 14, 15 and 16. The observations cover a wavelength range from 749 to 789 \AA. This range includes Chromospheric and Chromosphere-Corona Transition Region spectral lines. One of the goals of this thesis is to study whether the explosive events (EE) tend to begin in a given line or indistinctly in any line in the range of temperatures between 0.8 and 6.3$\times 10^5$ K. This would give us the possibility to know if the explosions begin preferably at a certain height on the solar atmosphere. This has a lot of implications for a better understanding of the stellar atmospheres since the explosions have been proposed as a mechanism for the heating of the Corona. Among the EE we selected those where three spectral components were clearly distinguished. The red and blue components denote the presence of plasma flows which originate in the region of the explosion. The lateral spectral components (red and blue) were characterized by Doppler shifts from 48 to 74 km/s, a timelife of 1 minute and a size of approximately 2100 km. We find that the EE originate preferably at temperature of $1.5\times 10^5$ K, which corresponds to the low part of the Transition Region, indicates that they really give an important contribution to the heating of the Corona.

rosannagua@yahoo.com (None)

Population Synthesis and Diagnostic of High-redshift Galaxies

Stellar Abundances in Dwarf Galaxies

New Insights on the Nature of the Lowest Metallicity Stars

Either 1) Far IR SED of Seyfert Galaxies: detecting starformation at high z or/and 2) The IAC survey of starburst galaxies

Cosmological origin of the lowest metallicity halo stars

Systematic Errors: A Few Things We Do Not Know About Stars and Model Atmospheres

Population Synthesis in the Blue

Simulated Millimetre and Submillimetre Galaxy Surveys

To be defined

Spectroscopic analyses of early B supergiants in nearby galaxies

Review talk on: The evolutionary properties of the first stellar generation (from the intermediate to the massive stars) and their final yields.

Star formation history in the solar neighbourhood: the link between stars and cosmology

Update on Globular Cluster Ages

Gamma-ray bursts as the collapse of massive stars: mapping the Universe to greater depths

The first stars, the IMF and nucleosynthetic constraints

Cosmology with Supernovae

Explosive Nucleosynthesis and Yields of Low Metallicity Massive Stars

Cosmological origin of the lowest metallicity halo stars

Stellar metallicities beyond the Local Group with VLT/FORS

Cepheid Distance Scale and the Virgo Cluster

The peculiar evolution of low-mass Population III stars

Evolution of Cosmological Type Ia Supernovae and G

The Proper Motion of the Globular Cluster NGC~6553 and of Bulge Stars with HST

The dusty SF history of distant galaxies and modelling tools

The Upper End of The Galactic Metallicity Scale

Modelling the x-ray to radio SED of galaxies

A Precise New Method of Correcting the Temperature in Stellar Atmospheres

The primordial lithium abundance

Cosmological Chemistry and the Formation of the First Objects

Deep Studies of the Resolved Stellar Populations in the Outskirts of M31

A Survey of Open Clusters in the Northen Hemisphere

Accurate distance to the Andromeda Galaxy using eclipsing binaries as standard candles

Calibrating the Cosmic Meter Stick: The Distance to the LMC Using Eclipsing Binaries

Halpha luminosity function of H II regions: preliminary calibration of a powerful standard candle

Abundances in high redshift Damped Ly$\alpha$ systems

On the properties of massive population III stars and metal-free stellar populations

Dust and nebular emission in star-forming galaxies

Reconstructing star formation episodes in the Local Group

Surveys for variable stars in M31 and M33

tbd

On the Stellar Initial Mass Function in Very Metal-Poor Environments

Reconstructing the star formation history in the halo of NGC 5128

On the Calibration of Star Formation Rates

HI Emission from the Damped Lyman-alpha absorber SBS 1543+593

Modelling of cool stellar atmospheres: an update

Estimation of H0 using Cepheid PL relations at maximum light

A Grid of Synthetic Stellar UV Fluxes

HII region luminosity functions: Preliminary calibration of a new secondary standard candle.

The massive, interacting multiple system HD 5980 in the SMC

In preparation

Where did the gas and stars in the intracuster medium come from?

Luminosity Evolution in Cluster Elliptical Galaxies

Dust-Penetrated morphology in the high-redshift universe

Cosmological origin of the lowest metallicity halo stars

To be communicated

Nucleosynthesis of the Light Elements

Cosmological parameters from the recent CMB anisotropies measurements.

High Redshift Galaxies and the Intergalactic Medium

The value of Omega

STARS AND GAS IN HIGH REDSHIFT GALAXIES

New phenomena discovered in the atmospheres of normal late-B type stars

Heating the Quiet Corona by Nanoflares: Results from SUMER on board SoHO.