2,057 research outputs found
Stellar populations in the Galactic bulge
AIMS:The aim of this paper is to study the characteristics of the stellar
populations and the metallicity distribution in the Galactic bulge. We study
the entire stellar population, but also retrieve information using only the red
clump stars. METHODS: To study the characteristics of the stellar populations
and the metallicity distribution in the Galactic bulge, we compared the output
of the galaxy model TRILEGAL, which implements the Binney et al. (1997) bulge
model, with observations from 2MASS and OGLE-II. A minimisation procedure has
been set up to retrieve the best fitting model with different stellar
populations and metallicity distributions. RESULTS: Using the TRILEGAL code we
find that the best model resembling the characteristics of the Galactic bulge
is a model with the distance to the Galactic centre kpc, the major axis ratios of the bar , and the angle between the
Sun-centre line and the bar . Using these
parameters the best model is found for a burst of 8 Gyr, although it is almost
indistinguishable from models with ages of 9 and 10 Gyr. The metallicity
distribution found is consistent with metallicity distributions in the
literature based on spectroscopic results.Comment: A&A accepte
The Garching-Bonn Deep Survey (GaBoDS) Wide-Field-Imaging Reduction Pipeline
We introduce our publicly available Wide-Field-Imaging reduction pipeline
THELI. The procedures applied for the efficient pre-reduction and astrometric
calibration are presented. A special emphasis is put on the methods applied to
the photometric calibration. As a test case the reduction of optical data from
the ESO Deep Public Survey including the WFI-GOODS data is described. The
end-products of this project are now available via the ESO archive Advanced
Data Products section.Comment: 6 pages, 3 figures, proceedings of ESO Calibration Workshop 200
Gravitational Lensing in the metric theory proposed by Sobouti
Recently, Y. Sobouti (2007) has provided a metric theory f(R) that can
account for certain dynamical anomalies observed in spiral galaxies. Mendoza &
Rosas-Guevara (2007) have shown that in this theory there is an extra-bending
as compared to standard general relativity. In the present work we have
developed in more specific detail this additional lensing effect and we have
made evaluations of the alpha parameter used in the model adjusting the theory
to observations in X-rays of 13 clusters of galaxies with gravitational lensing
(Hoekstra (2007)).Comment: 7 pages, 2 figure
Integrated parameters of star clusters: A comparison of theory and observations
(Abridged) This paper presents integrated magnitude and colours for synthetic
clusters. The integrated parameters have been obtained for the whole cluster
population as well as for the main-sequence (MS) population of star clusters.
We have also estimated observed integrated magnitudes and colours of MS
population of galactic open clusters, LMC and SMC star clusters. It is found
that the colour evolution of MS population of star clusters is not affected by
the stochastic fluctuations, however these fluctuations significantly affect
the colour evolution of the whole cluster population. The fluctuations are
maximum in colour in the age range 6.7 log (age) 7.5. Evolution
of integrated colours of MS population of the clusters in the Milky Way, LMC
and SMC, obtained in the present study are well explained by the present
synthetic cluster model. The observed integrated colours of MS
population of LMC star clusters having age 500 Myr seem to be
distributed around 0.004 model, whereas colours are found to be
more bluer than those predicted by the 0.004 model. vs
two-colour diagram for the MS population of the Milky Way star clusters shows a
fair agreement between the observations and present model, however the diagrams
for LMC and SMC clusters indicate that observed colours are relatively
bluer. Possible reasons for this anomaly have been discussed.Comment: 35 pages, 20 figs, accepted for publication in MNRA
Photometric Analysis of the Optical Counterpart of the Black Hole HMXB M33 X-7
Aims: Study the high-mass X-ray binary X-7 in M33 using broad-band optical
data.
Methods: We used recently published CFHT r' and i' data for variable stars in
M33 to extract the light curve of the optical counterpart of X-7. We combined
these data with DIRECT B and V measurements in order to search for an
independent optical modulation with the X-ray periodicity. The periodic
modulation is modelled with the ellipsoidal effect. We used UBVRr'i' magnitudes
of the system to constrain the temperature and radius of the optical component.
Results: The optical data revealed a periodicity of 3.4530 +- 0.0014 days,
which is consistent with the known X-ray period. Double modulation, which we
attributed to ellipsoidal modulation, is clearly seen in four different optical
bands. The absolute magnitude in six optical bands is most consistent with a
stellar counterpart with 33000 < T_{eff} < 47000 K and 15 < R < 20 R_{\sun}. We
modelled the optical periodic modulation and derived the masses of the two
components as a function of the orbital inclination and the radius of the
stellar component. The resulting mass range for the compact object is 1.3 < M <
23 M_{\sun}.
Conclusions: The system is probably a black hole HMXB, similar to Cyg X-1,
LMC X-1 and LMC X-3.Comment: Accepted for publication in A&
Galactic Archaeology with CoRoT and APOGEE: Creating mock observations from a chemodynamical model
In a companion paper, we have presented the combined
asteroseismic-spectroscopic dataset obtained from CoRoT lightcurves and APOGEE
infra-red spectra for 678 solar-like oscillating red giants in two fields of
the Galactic disc (CoRoGEE). We have measured chemical abundance patterns,
distances, and ages of these field stars which are spread over a large radial
range of the Milky Way's disc. Here we show how to simulate this dataset using
a chemodynamical Galaxy model. We also demonstrate how the observation
procedure influences the accuracy of our estimated ages.Comment: 5 pages, 6 figures. To appear in Astronomische Nachrichten, special
issue "Reconstruction the Milky Way's History: Spectroscopic surveys,
Asteroseismology and Chemo-dynamical models", Guest Editors C. Chiappini, J.
Montalb\'an, and M. Steffe
Mapping low-latitude stellar substructure with SEGUE photometry
Encircling the Milky Way at low latitudes, the Low Latitude Stream is a large
stellar structure, the origin of which is as yet unknown. As part of the SEGUE
survey, several photometric scans have been obtained that cross the Galactic
plane, spread over a longitude range of 50 to 203 degrees. These data allow a
systematic study of the structure of the Galaxy at low latitudes, where the Low
Latitude Stream resides. We apply colour-magnitude diagram fitting techniques
to map the stellar (sub)structure in these regions, enabling the detection of
overdensities with respect to smooth models. These detections can be used to
distinguish between different models of the Low Latitude Stream, and help to
shed light on the nature of the system.Comment: To appear in the proceedings of IAU Symposium 254 "The Galaxy disk in
a cosmological context", Copenhagen, June 200
Efeito de diferentes tecnologias de armazenamento na qualidade de maçãs.
O objetivo desse estudo foi avaliar as mudanças físico-químicas, sensoriais e moleculares associadas às condições de armazenamento e a relação dessas características com a perda de qualidade em maçãs
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