UVES Abundances of Stars in Nearby Dwarf Spheroidal Galaxies     

Eline Tolstoy  Kim Venn  Matt Shetrone  Francesca Primas  Vanessa Hill  Andreas Kaufer  Thomas Szeifert 《Astrophysics and Space Science》2002,281(1-2):217-218

It is a truth universally acknowledged, that a galaxy in possession of a good quantity of gas must want to form stars. It is the details of how and why that baffle us all. The simplest theories either would have this process a carefully self-regulated affair, or one that goes completely out of control and is capable of wrecking the galaxy which hosts it. Of course the majority of galaxies seem to amble along somewhere between these two extremes, and the mean properties tend to favour a quiescent self-regulated evolutionary scenario. But there area variety of observations which require us to invoke transitory ‘bursts’ of star-formation at one time or another in most galaxy types. Several nearby dwarf spheroidal galaxies have clearly determined star-formation histories with apparent periods of zero star formation followed by periods of fairly active star formation. If we are able to understand what separated these bursts we would understand several important phenomena in galaxy evolution. Were these galaxies able to clear out their gas reservoir in a burst of star formation? How did this gas return? or did it? Have these galaxies receieved gas from the IGM instead? Could stars from these types of galaxy contribute significantly to the halo population in our Galaxy? To answer these questions we need to combine accurate stellar photometry and Colour-Magnitude Diagram interpretation with detailed metal abundances to combine a star-formation rate versus time with a range of element abundances with time. Different elements trace different evolutionary process (e.g., relative contributions of type I and II supernovae). We often aren't even sure of the abundance spread in these galaxies. We have collected detailed high resolution UVES spectra of four nearby dwarf spheroidal galaxies (Sculptor, Fornax, Leo I &; Carina) to begin to answer these questions. This is a precursor study to a more complete study with FLAMES. We presented at this meeting the initial results for the Sculptor and Fornax dwarf spheroidal galaxies which have been previously had single element (low resolution) calcium abundance studies (Tolstoy et al., 2001). See Figures 1 and 2.  相似文献   

Observations of Jet Diameter, Density and Dynamics     

Francesca Bacciotti  Thomas P. Ray  Jochen Eislöffel  Jens Woitas  Josef Solf  Reinhard Mundt  Christopher J. Davis 《Astrophysics and Space Science》2003,287(1-4):3-13

Collimated jets are believed to be an essential ingredient of the star formation process, and we are now able for the first time to test observationally the theories for their formation and propagation. The major advances achieved in recent years are reviewed, regarding the observed morphology, kinematics and excitation properties of jets, from the parsec-scale `giant outflows' down to the `microjets' from T Tauri stars. High angular resolution images and spectra have provided valuable estimates of jet diameter, space velocity, temperature, ionization fraction, electron and total density, both along and across the flow. We can thus calculate key physical quantites, as the shock excitation parameters, or the mass and momentum fluxes in the flow. The results obtained appear to validate the popular magneto-centrifugal models for jet launching, although some important issues are still under debate, as to the cause of knotty structures, observed wind thermal properties, and the dynamical relationship between jets and molecular outflows. Among the most interesting recent findings, we mention the observed indications for jet rotation, with inferred toroidal velocities consistent with the prescribed angular momentum balance between infall and outflow.  相似文献   

The evolution of cosmic star formation, metals and gas     

Francesco Calura  Francesca Matteucci 《Astrophysics and Space Science》2003,284(2):429-432

We reconstruct the history of the cosmic star formation as well as the cosmic production of metals in the universe by means of detailed chemical evolution models for galaxies of different morphological types. We consider a picture of coeval, non-interacting evolving galaxies where ellipticals experience intense and rapid starbursts within the first Gyr after their formation, and spirals and irregulars continue to form stars at lower rates up to the present time. We show that spirals are the main contributors to the decline of the luminosity density in all bands between z=1 and z=0. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

K dwarfs and the chemical evolution of the solar cylinder     

Eira Kotoneva  Chris Flynn  _&#; †  Cristina Chiappini  Francesca Matteucci 《Monthly notices of the Royal Astronomical Society》2002,336(3):879-891

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The Best Observables from the Point of View of a Model Maker     

Francesca Matteucci 《Astrophysics and Space Science》2001,277(1):17-26

We select and discuss the best observables to be used to constrain models of galactic chemical evolution. To this purpose, we discuss the observables in our Galaxy, which is the best studied system, as well as in external galaxies.  相似文献   

Chemical Evolution of Galaxies and Nature of High Redshift Objects     

Francesca Matteucci  Francesco Calura 《Astrophysics and Space Science》2004,294(1-2):29-35

We review the methodology adopted in computing chemical evolution models of galaxies of different morphological type (ellipticals, spirals and irregulars). We discuss the importance of the history of star formation in different galaxies in order to interpret the observed abundances. In particular, we discuss the time-delay model which allows us to interpret the observed abundance patterns in galaxies as due to the different contributions of supernovae II and Ia. We show that the time-delay model applied to galaxies of different morphological type predicts different [X/Fe] versus [Fe/H] relations in different galaxies. As a consequence of this, these relations can be used to infer the nature and to date high redshift objects. Finally, we show our predictions for the cosmic star formation rate.  相似文献   

Chemical evolution in a model for the joint formation of quasars and spheroids     

Donatella Romano  Laura Silva  Francesca Matteucci  Luigi Danese 《Monthly notices of the Royal Astronomical Society》2002,334(2):444-458

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Flow in coronal loops with a mass source     

Giancarlo Noci  Francesca Zuccarello 《Solar physics》1983,88(1-2):193-209

This research studies the flow of plasma inside a coronal loop in which an injection of plasma through the lateral surface is permitted. The flow is assumed steady and polytropic. The problem covers two cases: (a) upflow at one footpoint, downflow at the other; (b) downflow at both footpoints. The first case can be shown to be quite similar to that of a mass-conserving flow with variable cross section; the second, instead, is characterized by solutions with a different type of topology; its main new feature is the obvious fact that all the solutions pass through a single point going from negative to positive velocities. In this second case the density ratio between footpoints and top can be much smaller than in a mass conserving flow. This can explain some properties of observed loops.  相似文献   

Tracing Cosmic-Rays and SNe with Be Abundances     

Francesca Primas 《Astrophysics and Space Science》2002,281(1-2):195-198

We present the results of a new analysis of Be abundances in a large sample of stars, spanning the metallicity range -2.5 ≤ [Fe/H] ≤ - 0.7. The observations were taken with the Ultraviolet and Visible Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT). With this new set of high quality data we aim at further investigating the trend of Be with metallicity, the possible presence of dispersion, and their implications for cosmic-ray and supernovae physics. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Formation and evolution of late-type dwarf galaxies – I. NGC 1705 and NGC 1569     

Donatella Romano  Monica Tosi  Francesca Matteucci 《Monthly notices of the Royal Astronomical Society》2006,365(3):759-778

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