Letters of Intent for 2015

LoI 2015-179
The General Assembly of the Galactic Halo


3 August 2015 to 7 August 2015


Hawaii Convention Center, 1801 Kalakaua Avenue, Honolulu, HI 96814, United States


Angela Bragaglia (

Coordinating division:

Division H Interstellar Matter and Local Universe

Co-Chairs of SOC:

Angela Bragaglia (INAF-OA Bologna)
Kenji Bekki (U Western Australia, Crawley)
Doug Geisler (U Conception)
Chris Sneden (McDonald Obs & U Texas, Austin)

Chair of LOC:




- First stars and stochastic enrichment in the early Galaxy
- Correlations between abundances and kinematics in Galactic field halo stars
- Galactic archaeology with (ongoing and future) large spectroscopic surveys
- Star clusters and their stellar populations
- Chemical signature and stellar kinematics in dwarf galaxies
- Satellite systems and haloes in the Local Group
- The Dwarf galaxy - Ultra Compact Dwarf - Ultra Faint Dwarfs - Globular
Cluster Connection
- The dark matter content of the Galaxy satellites
- Formation scenarios for small stellar systems
- Chemical and dynamical evolution of star clusters and dwarfs
and connection with the Galactic halo assembly



Full understanding of how galaxies form and evolve remains one of the greatest
challenges in astrophysics. There is a galaxy which is nearer to us than any
other: the Milky Way. Individual stars are resolved by modern instrumentation
out to its farthest outskirts. The bright conglomerates of its oldest stars
(globular clusters, GCs) have been studied for many decades. After pioneering
efforts, the analyses of the chemical composition and kinematics of individual
stars, even of the most distant bound satellites of the Galaxy, are now
routinely performed. Yet, we still do not have a solid understanding of the
exact mechanism(s) that gave birth and shape to the Galaxy we are immersed in.
Observations provide precious snapshots of the movie of our Galaxy's assembly,
back to its earliest epochs. Modern theories of galaxy formation try to fit all
of them in a coherent picture of structure formation and evolution.

Efficient and multi-object spectrographs mounted at 8-10m class telescopes
enabled measurement of detailed abundances for the first stars formed in the
Galaxy, provided the chemical tagging of distinct multiple stellar generations
in GCs, and even led to the detailed abundance patterns of dwarf satellite
galaxies in the Local Group. Detailed chemical abundances and kinematics are now
known for thousands of stars of the halo, bulge, thick and thin disks of the
Galaxy. On-going and future surveys and facilities (the combined Sloan surveys,
the Gaia-ESO survey, GALAH, etc; the Gaia satellite; the proposed 4MOST, MOONS,
WEAVE surveys, etc) will make this information available for millions of stars.
This will greatly improve our mapping of the Galactic subpopulations and of
stellar streams, relic proofs of past accretion events. Theoreticians are
developing more and more sophisticated structure formation and evolution models
to account for the striking, unexpected features that emerge from the data. In
particular, the Galactic halo is a much more lively environment than thought in
the past: it is revealing a dual nature, with its stars belonging to two
distinct components (accreted and formed in situ); abundance gradients are
present in the inner halo; substructures are present everywhere; GCs host
multiple populations with peculiar chemical composition, indicative of a complex
formation mechanism. In addition, some of the stars in the Galactic halo seem to
show a composition similar to the stars in the dwarf satellites of the Milky Way
while some are similar to the primordial generation in GCs.

The gathering of experts in different, yet contiguous fields, is a promising
route to a coherent picture for the formation and early evolution of the
Galactic halo, as the most accessible example of the building of such structures
in disk galaxies. The IAU General Assembly is the ideal opportunity to devote a
Symposium to the global assembly of the Galactic halo. This meeting will have
the right critical mass and synergy to probe many unsolved issues. At the same
time, it will provide impulse to future studies and understanding of this
Galactic component and its original constituents.

We plan to divide the Symposium in four main sessions, plus a final session
devoted to sum up what we learned and to devise future steps:

Session 1: Abundances in field stars
Session 2: Star clusters and their populations
Session 3: The stellar populations in dwarf galaxies
Session 4: Chemical and dynamical evolution; simulations
Session 5: Status going forward: building a consistent picture of the
Milky Way's formation

We plan to have both review and summary talks, as well as contributed talks and posters.

Proposed SOC members:
W. Aoki, K. Bekki, A. Bragaglia, J. Cohen, K. Freeman, D. Geisler, R. Gratton, A. Helmi, V. Hill, A. McConnachie, P. Nissen, D. Romano, C. Sneden, E. Starkenburg, E. Vesperini


IAU General Assembly 2015
IAU General Assembly
Honolulu, 3-14 August 2015

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