5,831 research outputs found
Do phase transitions survive binomial reducibility and thermal scaling?
First order phase transitions are described in terms of the microcanonical
and canonical ensemble, with special attention to finite size effects.
Difficulties in interpreting a "caloric curve" are discussed. A robust
parameter indicating phase coexistence (univariance) or single phase
(bivariance) is extracted for charge distributions.Comment: 10 pages, TeX type, psfig, also available at
http://csa5.lbl.gov/moretto/ps/lgm.ps, to appear in the Proceedings of the
1st Catania Relativistic Ion Studies: Critical Phenomena and Collective
Observables, Acicastello, May 27-31, 199
Measurements of streaming motions of the Galactic bar with Red Clump Giants
We report a measurement of the streaming motion of the stars in the Galactic
bar with the Red Clump Giants (RCGs) using the data of the Optical
Gravitational Lensing Experiment II (OGLE-II). We measure the proper motion of
46,961 stars and divide RCGs into bright and faint sub-samples which on average
will be closer to the near and far side of the bar, respectively. We find that
the far-side RCGs (4,979 stars) have a proper motion of \Delta ~ 1.5 +-
0.11 mas yr^{-1} toward the negative l relative to the near-side RCGs (3,610
stars). This result can be explained by stars in the bar rotating around the
Galactic center in the same direction as the Sun with v_b ~ 100 km s^{-1}. In
the Disc Star (DS) and Red Giant (RG) samples, we do not find significant
difference between bright and faint sub-samples. For those samples \Delta
\~ 0.3 +- 0.14 mas yr^{-1} and ~ 0.03 +- 0.14 mas yr^{-1}, respectively. It is
likely that the average proper motion of RG stars is the same as that of the
Galactic center. The proper motion of DSs with respect to RGs is ~ 3.3 mas
yr^{-1} toward positive l. This value is consistent with the expectations for a
flat rotation curve and Solar motion with respect to local standard of rest.
RGs have proper motion approzimately equal to the average of bright and faint
RCGs, which implies that they are on average near the center of the bar. This
pilot project demonstrates that OGLE-II data may be used to study streaming
motions of stars in the Galactic bar. We intend to extend this work to all 49
OGLE-II fields in the Galactic bulge region.Comment: 7 pages, 9 figures, submitted to MNRA
The formation of young B/PS bulges in edge-on barred galaxies
We report about the fact that the stellar population that is born in the gas
inflowing towards the central regions can be vertically unstable leading to a
B/PS feature remarkably bluer that the surrounding bulge. Using new
chemodynamical simulations we show that this young population does not remain
as flat as the gaseous nuclear disc and buckles out of the plane to form a new
boxy bulge. We show that such a young B/PS bulge can be detected in colour
maps.Comment: 2 pages, 5 figures, to appear in IAU Symposium 245, Formation and
Evolution of Galaxy Bulges, M. Bureau, E. Athanassoula, and B. Barbuy (eds.),
Oxford, 16-20 July 200
Disc galaxies with multiple triaxial structures. II. JHK surface photometry and numerical simulations
We present detailed JHK surface photometry with ellipse fits of 13 galaxies
selected from previous optical observations as likely candidates for having a
secondary bar or a triaxial bulge within the primary bar. We have found 7
double-barred galaxies, 3 double-barred galaxies with an additional
intermediate structure with twisted isophotes, and 3 galaxies with a bar and
central twisted isophotes. A global analysis of the structural parameter
characteristics in the I- and K-bands is presented. Various numerical models of
galaxies with bars within bars are also analysed using the ellipse fitting
technique and compared to the observations. A thorough review of the possible
hypotheses able to explain this phenomenon is given with emphasis on the most
likely ones.Comment: 12 pages, AATEX. Accepted for publication in A&A. Large color
postscript figures omitted (Figs. 1), figures 2-9 included; gzip'ed
postscript files of the paper and Figs. 1 available via anonymous ftp at
ftp://obsftp.unige.ch/pub/fri/aasjhk/ , files fri_aasjhk.ps.gz and ngc*.ps.g
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