14,046 research outputs found
The Milky Way disk
This review summarises the invited presentation I gave on the Milky Way disc.
The idea underneath was to touch those topics that can be considered hot
nowadays in the Galactic disk research: the reality of the thick disk, the
spiral structure of the Milky Way, and the properties of the outer Galactic
disk. A lot of work has been done in recent years on these topics, but a
coherent and clear picture is still missing. Detailed studies with high quality
spectroscopic data seem to support a dual Galactic disk, with a clear
separation into a thin and a thick component. Much confusion and very
discrepant ideas still exist concerning the spiral structure of the Milky Way.
Our location in the disk makes it impossible to observe it, and we can only
infer it. This process of inference is still far from being mature, and depends
a lot on the selected tracers, the adopted models and their limitations, which
in many cases are neither properly accounted for, nor pondered enough. Finally,
there are very different opinions on the size (scale length, truncation radius)
of the Galactic disk, and on the interpretation of the observed outer disk
stellar populations in terms either of external entities (Monoceros,
Triangulus-Andromeda, Canis Major), or as manifestations of genuine disk
properties (e.g., warp and flare).Comment: 7 pages, 9 figures. Full text in English. To be published in the 57
Bulletin of the Argentinian Association of Astronomy (BAAA 57
Gaia 1 cannot be a Thick Disk Galactic cluster
In this note I show how the recently suggested membership of the open cluster
Gaia 1 to the Galactic thick disk is based on incorrect assumptions about the
structure of the disk itself, and neglect well-known observational evidences on
the disk warp and flare.Comment: 2 pages, 1 figure, in press as a Research Note of the American
Astronomical Societ
Morphological transformation of dwarf galaxies in the Local Group
In the Local Group there are three main types of dwarf galaxies: Dwarf Irregulars, Dwarf Spheroidals, and Dwarf Ellipticals. Intermediate/transitional types are present as well. This contribution reviews the idea that the present day variety of dwarf galaxy morphologies in the Local Group might reveal the existence of a transformation chain of events, of which any particular dwarf galaxy represents a manifestation of a particular stage. In other words, all dwarf galaxies that now are part of the Local Group would have formed identically in the early universe, but then evolved differently because of morphological transformations induced by dynamical processes like galaxy harassment, ram pressure stripping, photo-evaporation, and so forth. We start describing the population of dwarf galaxies and their spatial distribution in the LG. Then, we describe those phenomena that can alter the morphology of a dwarf galaxies, essentially by removing, partially or completely, their gas content. Lastly, we discuss morphological signatures in the Local Group Dwarf Galaxies that can be attributed to different dynamical phenomena. While it is difficult to identify a unique and continuous transformation sequence, we have now a reasonable understanding of the basic evolutionary paths that lead to the various dwarf galaxy type
Properties and origin of the old, metal rich, star cluster, NGC 6791
In this contribution I summarize the unique properties of the old, metal
rich, star cluster NGC 6791, with particular emphasis on its population of
extreme blue horizontal branch stars. I then conclude providing my personal
view on the origin of this fascinating star cluster.Comment: 7 pages, 4 eps figures, paper presented at the 10th Pacific Rim
Conference on Stellar Astrophysics, Seoul, May 27-31, 2013, ASP Conference
Series, in pres
The Milky Way thin disk structure as revealed by stars and young open clusters
In this contribution I shall focus on the structure of the Galactic thin
disk. The evolution of the thin disk and its chemical properties have been
discussed in detail by T. Bensby's contribution in conjunction with the
properties of the Galactic thick disk, and by L.Olivia in conjunction with the
properties of the Galactic bulge. I will review and discuss the status of our
understanding of three major topics, which have been the subject of intense
research nowadays, after long years of silence: (1) the spiral structure of the
Milky Way, (2) the size of the Galactic disk, and (3) the nature of the Local
arm (Orion spur), where the Sun is immersed. The provisional conclusions of
this discussion are that : (1) we still have quite a poor knowledge of the
Milky Way spiral structure, and the main dis-agreements among various tracers
are still to be settled; (2) the Galactic disk does clearly \textit{not} have
an obvious luminous cut-off at about 14 kpc from the Galactic center, and next
generation Galactic models need to be updated in this respect, and (3) the
Local arm is most probably an inter-arm structure, similar to what we see in
several external spirals, like M~74. Finally, the impact of GAIA and LAMOST in
this field will be briefly discussed as well.Comment: 12 pages, 8 eps figure, invited review, to appear in Proceedings of
the IAU Symposium No. 298, "Setting the scene for Gaia and LAMOST", eds. S.
Feltzing, G. Zhao, N. A. Walton, and P. A. Whiteloc
The intermediate-age open cluster NGC 2112
We report on CCD photometry of a field centered on the region of the
intermediate-age open cluster NGC 2112 down to V=21. Due to the smaller field
coverage, we are able to limit the effect of field star contamination which
hampered in the past precise determinations of the cluster age and distance.
This way, we provide updated estimates of NGC 2112 fundamental parameters.
Having extended the photometry to the pass-band, we are able to construct a
colour-colour diagram, from which we infer a reddening
mag. The comparison of the Colour-Magnitude Diagram (CMD) with theoretical
isochrones leads to a distance of pc, and an age of
Gyr. While the distance is in agreement with previous determinations, the age
turns out to be much better constrained and significantly lower than previous
estimates.Comment: 7 pages, 7 eps figures, in press in MNRA
The Road to Copenhagen: What Agreement Can Actually Be Effective and Stable? by Carlo Carraro
KlimaverÀnderung; Umweltabkommen; Internationale Zusammenarbeit; Welt
Incentives and Institutions. A Bottom-up Approach to Climate Policy
This paper comments and assesses âFragmented Carbon Markets and Reluctant Nations: Implications for the Design of Effective Architecturesâ, a paper that David Victor presented at the international workshop on "Architectures for Agreement: Addressing Global Climate Change in the Post-Kyoto World", organized by Joe Aldy and Rob Stavins at the J.F. Kennedy School of Government in May 2006. By analyzing Victorâs proposals for an effective climate agreement post 2012, this paper emphasizes the contribution that game-theoretical analyses have provided to the design of climate agreements. It therefore emphasizes how incentives and institutions play a crucial role in affecting the final outcome of negotiations on climate change control, and how incentives and institutions can be modified to achieve a better control of climate change. This paper also discusses a wider policy approach that can enhance the effectiveness of measures designed to address the climate change problem.Agreements, Climate, Incentives, Negotiations, Policy
Old open clusters in the outer Galactic disk
The outer parts of the Milky Way disk are believed to be one of the main
arenas where the accretion of external material in the form of dwarf galaxies
and subsequent formation of streams is taking place. The Monoceros stream and
the Canis Major and Argo over-densities are notorious examples. VLT high
resolution spectra have been acquired for five distant open clusters. We derive
accurate radial velocities to distinguish field interlopers and cluster
members. For the latter we perform a detailed abundance analysis and derive the
iron abundance [Fe/H] and the abundance ratios of several elements.
Our analysis confirms previous indications that the radial abundance gradient
in the outer Galactic disk does not follow the expectations extrapolated from
the solar vicinity, but exhibits a shallower slope. By combining the
metallicity of the five program clusters with eight more clusters for which
high resolution spectroscopy is available, we find that the mean metallicity in
the outer disk between 12 and 21 kpc from the Galactic center is [Fe/H]
, with only marginal indications for a radial variation. In
addition, all the program clusters exhibit solar scaled or slightly enhanced
elements, similar to open clusters in the solar vicinity and thin disk
stars. We investigate whether this outer disk cluster sample might belong to an
extra-galactic population, like the Monoceros ring. However, close scrutiny of
their properties - location, kinematics and chemistry - does not convincingly
favor this hypothesis. On the contrary, they appear more likely genuine
Galactic disk clusters. We finally stress the importance to obtain proper
motion measurements for these clusters to constrain their orbits.Comment: 19 pages, 9 eps figure, in press in A&A, abstract rephrased to fit i
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