1,409 research outputs found
Old stellar systems in UV: resolved and integrated properties
The UV properties of old stellar populations have been subject of intense
scrutiny from the late sixties, when the UV-upturn in early type galaxies was
first discovered. Because of their proximity and relative simplicity, Galactic
globular clusters (GGCs) are ideal local templates to understand how the
integrated UV light is driven by hot stellar populations, primarily horizontal
branch stars and their progeny. Our understanding of such stars is still
plagued by theoretical uncertainties, which are partly due to the absence of an
accurate, comprehensive, statistically representative homogeneous data-set. To
move a step forward on this subject, we have combined the HST and GALEX
capabilities and collected the largest data-base ever obtained for GGCs in UV.
This data-base is best suited to provide insights on the HB second parameter
problem and on the first stages of GCs formation and chemical evolution and to
understand how they are linked to the observed properties of extragalactic
systems.Comment: 8 pages, 7 figures; ESO/NUVA/IAG Workshop on Challenges in UV
Astronomy, ESO Garching, 7-11 October 2013; to be published in Astrophysics
and Space Scienc
The non-segregated population of blue straggler stars in the remote globular cluster Palomar 14
We used deep wide-field observations obtained with the Canada-France-Hawaii
Telescope to study the blue straggler star (BSS) population in the innermost
five arcminutes of the remote Galactic globular cluster Palomar 14. The BSS
radial distribution is found to be consistent with that of the normal cluster
stars, showing no evidence of central segregation. Palomar 14 is the third
system in the Galaxy (in addition to OmegaCentauri and NGC 2419) showing a
population of BSS not centrally segregated. This is the most direct evidence
that in Palomar 14 two-body relaxation has not fully established energy
equipartition yet, even in the central regions (in agreement with the estimated
half-mass relaxation time, which is significantly larger than the cluster age).
These observational facts have important implications for the interpretation of
the shape of the mass function and the existence of the tidal tails recently
discovered in this cluster.Comment: 5 pages, 4 figures, accepted for publication in ApJ Letter
COCOA Code for Creating Mock Observations of Star Cluster Models
We introduce and present results from the COCOA (Cluster simulatiOn
Comparison with ObservAtions) code that has been developed to create idealized
mock photometric observations using results from numerical simulations of star
cluster evolution. COCOA is able to present the output of realistic numerical
simulations of star clusters carried out using Monte Carlo or \textit{N}-body
codes in a way that is useful for direct comparison with photometric
observations. In this paper, we describe the COCOA code and demonstrate its
different applications by utilizing globular cluster (GC) models simulated with
the MOCCA (MOnte Carlo Cluster simulAtor) code. COCOA is used to synthetically
observe these different GC models with optical telescopes, perform PSF
photometry and subsequently produce observed colour magnitude diagrams. We also
use COCOA to compare the results from synthetic observations of a cluster model
that has the same age and metallicity as the Galactic GC NGC 2808 with
observations of the same cluster carried out with a 2.2 meter optical
telescope. We find that COCOA can effectively simulate realistic observations
and recover photometric data. COCOA has numerous scientific applications that
maybe be helpful for both theoreticians and observers that work on star
clusters. Plans for further improving and developing the code are also
discussed in this paper.Comment: 18 pages, 12 figures, accepted for publication in MNRAS. Revised
manuscript has a new title, better quality figures and many other
improvements. COCOA can be downloaded from: https://github.com/abs2k12/COCOA
(comments are welcome
Tensor approximation of generalized correlated diffusions and applications
This thesis documents my research activity conducted in the past three years at the Department of Statistical Science at the University College London. My investigation is focused on functional-analytic methods applied to the characterization of generalized correlated Markov processes. The main objective of the research is to formalize the properties of such a class of stochastic processes when approximated in a tensor space. This lead to the development of a new interpretation of the correlation among processes that is exploited for the analysis of copula functions and their statistical properties
Hook of Hamate Removal in a Collegiate Baseball Player
In volume 4, Issue 1 of the JSMAHS you will find Professional Research Abstracts, as well as Bachelor Student Research Abstracts and Case Reports.
Thank you for viewing this 4th Annual OATA Special Editio
Evidence of tidal distortions and mass loss from the old open cluster NGC 6791
We present the first evidence of clear signatures of tidal distortions in the
density distribution of the fascinating open cluster NGC 6791. We used deep and
wide-field data obtained with the Canada-France-Hawaii-Telescope covering a 2x2
square degrees area around the cluster. The two-dimensional density map
obtained with the optimal matched filter technique shows a clear elongation and
an irregular distribution starting from ~300" from the cluster center. At
larger distances, two tails extending in opposite directions beyond the tidal
radius are also visible. These features are aligned to both the absolute proper
motion and to the Galactic center directions. Moreover, other overdensities
appear to be stretched in a direction perpendicular to the Galactic plane.
Accordingly to the behaviour observed in the density map, we find that both the
surface brightness and the star count density profiles reveal a departure from
a King model starting from ~600" from the center. These observational evidence
suggest that NGC 6791 is currently experiencing mass loss likely due to
gravitational shocking and interactions with the tidal field. We use this
evidence to argue that NGC 6791 should have lost a significant fraction of its
original mass. A larger initial mass would in fact explain why the cluster
survived so long. Using available recipes based on analytic studies and N-body
simulations, we derived the expected mass loss due to stellar evolution and
tidal interactions and estimated the initial cluster mass to be M_ini=(1.5-4) x
10^5 M_sun.Comment: Accepted for publication in the MNRAS (9 pages, 8 Figures
- …