Found 42 talks archived in The Galaxy

Tuesday March 6, 2018
Dr. Giuseppina Battaglia


In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this talk I will first give an overview of some of the main properties of the Milky Way stellar halo based on literature studies. I will then present results concerning the chemical properties of the outer regions of the Milky Way stellar halo, based on the elemental abundances of halo stars with large present-day Galactocentric distances, >15 kpc. The data-set we acquired consists of high resolution HET/HRS, Magellan/MIKE and VLT/UVES spectra for 28 red giant branch stars covering a wide metallicity range, -3.1 ≲ [Fe/H] ≲-0.6. We show that the ratio of α-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H] ≳-1.5 when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples. 

Thursday June 16, 2016
Mrs. Sara Bertran de Lis
Instituto de Astrofísica de Canarias (IAC)


The detection of chemical inhomogeities in the Galactic disk requires an oustanding precision in the abundance measurements and a thorough estimation of the uncertainties. So far, studies in alpha-elements in disk stars either do not reach the required precision, or comprise too small samples in the solar neighborhood. Thanks to the Apache Point Galactic Evolution Experiment (APOGEE), we have for the first time a large spectroscopic sample of about 100.000 disk stars, with data homogeneously obtained, reduced, and analyzed. Taking advantage of such database, we examine the distribution of oxygen-to-iron abundance ratio in stars across the Galactic disk. These data reveal that the square root of the star-to-star cosmic variance in the [O/Fe] at a given metallicity is about 0.03 to 0.04 dex in both the thin- and thick-disk populations. Measuring the spread in [O/Fe] and other abundance ratios can provide strong constraints for models of Galactic chemical evolution. In this talk we will describe how we arrived at this result, the calculation of uncertainties, and implications regarding the chemical evolution of the Galaxy.

Tuesday February 25, 2014
Dr. Carmela Lardo
INAF-Osservatorio Astronomico di Bologna


In this talk I present an overview of the structure, activity and goals
of the Gaia-ESO survey, a large public spectroscopic survey aimed at investigating
the origin and formation history of our Galaxy by collecting high quality spectroscopy
of representative samples (about 105 Milky Way stars) of all Galactic stellar populations,
in the field and in clusters. Briefly, I discuss the most relevant results obtained so far.
In particular, I present our study on the internal kinematics of Galactic globular clusters based on the radial estimates obtained from the survey complemented with ESO archive data.

Thursday February 6, 2014
Dr. Elena Pancino
INAF - Osservatorio Astronomico di Bologna


Gaia - the ESA cornerstone astrometric mission - was launched in December 2013, with the goal of censing the Milky Way population in a 6D space (positions and velocity) of 10^9 point-like obects, with errors
100-1000 times smaller than Hipparcos, with three color magnitudes and spectra as well. The scientific impact of its data will be large in many fields of astrophysics, from Galactic science, to Solar system objects, to stellar astrophysics, to galaxies and Quasars; from the distance ladder revision to fundamental physics. I will describe the mission concept, the scientific goals, and the present status of the mission, with special attention to the flux calibration of Gaia data.

Thursday January 9, 2014
Dr. Manuela Zoccali
Universidad Católica de Chile


The structure, kinematics and stellar population of the Galactic bulge is very complex. Only three years ago the bulge was discovered to be X-shaped, a structure believed to originate from the dynamical instabilities of a disk, through the formation and posterior heating of a bar. The study of its kinematics reveals a cylindrical rotation, typical of a bar, suggesting the absence of a spheroidal component. Nevertheless, the bulge stellar population is old, has a radial metallicity gradient, and element ratio indicative of a short formation timescale. All these elements conflict with a simplistic view of the bulge as a heated bar, formed via "secular" evolution of a disk. I will review our knowledge of the bulge properties as traced by the 3D structure, kinematics, and chemical composition of its red clump stars.

Friday September 6, 2013
Dr. Carlos Allende Prieto
Instituto de Astrofisica de Canarias, Tenerife, Spain


3- Other spectroscopic surveys and analysis strategies


- data mashup: astrometry,  photometry and spectroscopy together

- reconstructing the Galaxy

- 'observing' galaxy simulations

- discovery and follow-up of interesting/exotic targets: HVS, UMPS, CEMPS, RCrBs...

Friday September 6, 2013
Dr. Leo Girardi
Osservatorio Astronomico di Padova, INAF, Italy


5- Some current problems and opportunities

- simulating kinematics

- simulating variables

- simulating non-solar scaled populations

- simulating rare and extreme populations (e.g. X-ray sources, PNe,

  hot-WDs, AGB-manque', C stars, IR-emission by mass-losing stars)

- opportunities opened by asteroseismology

Friday September 6, 2013
Dr. Ortwin Gerhard
Max-Planck-Institut fuer extraterrestrische Physik, Germany


5-   The Galactic halo

- mass, extent, shape

- substructure, inner/outer halo

Friday September 6, 2013
Dr. Ken Freeman
Australian National University, Australia


5- The Galactic bulge

- observational status on bulge kinematics and chemical properties in the context of other bulges

- ideas about the formation of the bulge

Friday September 6, 2013
Dr. Jerry Sellwood
Rutgers University, USA


5- SPH basics

- numerical viscosity

- Kelvin-Helmholtz instabilities

- other problems and their amelioration