5,283 research outputs found
Comprehensive analysis of RGU photometry in the direction to M5
The RGU-photographic investigation of an intermediate latitude field in the
direction to the Galactic center is presented. 164 extra-galactic objects,
identified by comparison of Minnesota and Basel charts, are excluded from the
program. Also, a region with size 0.104 square-degrees, contaminated by cluster
(M5) stars and affected by background light of the bright star HD 136202 is
omitted. Contrary to previous investigations, a reddening of ,
corresponding to E(G-R)=0.07 mag is adopted. The separation of dwarfs and
evolved stars is carried out by an empirical method, already applied in some of
our works. A new calibration for the metallicity determination is used for
dwarfs, while the absolute magnitude determination for stars of all categories
is performed using the procedures given in the literature. There is good
agreement between the observed logarithmic space density histograms and the
galactic model gradients. Also, the local luminosity function agrees with
Gliese's (1969) and Hipparcos' (Jahreiss & Wielen 1997) luminosity functions,
for stars with mag. For giants, we obtained two different local
space densities from comparison with two Galactic models, i.e. ,
close to that of Gliese (1969), and . A metallicity gradient,
dex/kpc, is detected for dwarfs (only) with absolute
magnitudes , corresponding to a spectral type interval F5-K0.Comment: 17 pages, including 13 figures and 3 tables, accepted for publication
in PAS
Absolute magnitudes for late-type dwarf stars for Sloan photometry
We present a new formula for absolute magnitude determination for late-type
dwarf stars as a function of (g-r) and (r-i) for Sloan photometry. The absolute
magnitudes estimated by this approach are brighter than those estimated by
colour-magnitude diagrams, and they reduce the luminosity function rather close
to the luminosity function of Hipparcos.Comment: 11 pages, 9 figures and 5 tables, accepted for publication in A
Accurate fundamental parameters for Lower Main Sequence Stars
We derive an empirical effective temperature and bolometric luminosity
calibration for G and K dwarfs, by applying our own implementation of the
InfraRed Flux Method to multi-band photometry. Our study is based on 104 stars
for which we have excellent BVRIJHK photometry, excellent parallaxes and good
metallicities. Colours computed from the most recent synthetic libraries
(ATLAS9 and MARCS) are found to be in good agreement with the empirical colours
in the optical bands, but some discrepancies still remain in the infrared.
Synthetic and empirical bolometric corrections also show fair agreement. A
careful comparison to temperatures, luminosities and angular diameters obtained
with other methods in literature shows that systematic effects still exist in
the calibrations at the level of a few percent. Our InfraRed Flux Method
temperature scale is 100K hotter than recent analogous determinations in the
literature, but is in agreement with spectroscopically calibrated temperature
scales and fits well the colours of the Sun. Our angular diameters are
typically 3% smaller when compared to other (indirect) determinations of
angular diameter for such stars, but are consistent with the limb-darkening
corrected predictions of the latest 3D model atmospheres and also with the
results of asteroseismology. Very tight empirical relations are derived for
bolometric luminosity, effective temperature and angular diameter from
photometric indices. We find that much of the discrepancy with other
temperature scales and the uncertainties in the infrared synthetic colours
arise from the uncertainties in the use of Vega as the flux calibrator. Angular
diameter measurements for a well chosen set of G and K dwarfs would go a long
way to addressing this problem.Comment: 34 pages, 20 figures. Accepted by MNRAS. Landscape table available
online at http://users.utu.fi/luccas/IRFM
Open-cluster density profiles derived using a kernel estimator
Surface and spatial radial density profiles in open clusters are derived
using a kernel estimator method. Formulae are obtained for the contribution of
every star into the spatial density profile. The evaluation of spatial density
profiles is tested against open-cluster models from N-body experiments with N =
500. Surface density profiles are derived for seven open clusters (NGC 1502,
1960, 2287, 2516, 2682, 6819 and 6939) using Two-Micron All-Sky Survey data and
for different limiting magnitudes. The selection of an optimal kernel
half-width is discussed. It is shown that open-cluster radius estimates hardly
depend on the kernel half-width. Hints of stellar mass segregation and
structural features indicating cluster non-stationarity in the regular force
field are found. A comparison with other investigations shows that the data on
open-cluster sizes are often underestimated. The existence of an extended
corona around the open cluster NGC 6939 was confirmed. A combined function
composed of the King density profile for the cluster core and the uniform
sphere for the cluster corona is shown to be a better approximation of the
surface radial density profile.The King function alone does not reproduce
surface density profiles of sample clusters properly. The number of stars, the
cluster masses and the tidal radii in the Galactic gravitational field for the
sample clusters are estimated. It is shown that NGC 6819 and 6939 are extended
beyond their tidal surfaces.Comment: 17 pages, 15 figure
The second and third parameters of the Horizontal Branch in Globular Clusters
The Horizontal Branch (HB) second parameter of Globular Clusters (GCs) is a
major open issue in stellar evolution. Large photometric and spectroscopic
databases allow a re-examination of this issue. We derive median and extreme
(90% of the distribution) colours and magnitudes of stars along the HB for
about a hundred GCs. We transform these into median and extreme masses of stars
on the HB taking into account evolutionary effects, and compare these masses
with those expected at the tip of the Red Giant Branch to derive the total mass
lost by the stars. A simple linear dependence on metallicity of this total mass
lost explains well the median colours of HB stars. Adopting this mass loss law
as universal, we find that age is the main second parameter. However, at least
a third parameter is clearly required. The most likely candidate is the He
abundance, which might be different in GCs stars belonging to the different
stellar generations whose presence was previously derived from the Na-O and
Mg-Al anticorrelations. Variations in the median He abundance allow explaining
the extremely blue HB of some GCs; such variations are correlated with the
R-parameter. Suitable He abundances allow deriving ages from the HB which are
consistent with those obtained from the Main Sequence. Small corrections to
these latter ages are then proposed, producing a tight age-metallicity relation
for disk and bulge GCs. Star-to-star variations in the He content explain the
extension of the HB. There is a strong correlation between this extension and
the interquartile of the Na-O anticorrelation. The main driver for the
variations in the He-content within GCs seems the total cluster mass. 47 Tuc
and M3 exhibit exceptional behaviours; however, they can be accommodated in a
scenario for the formation of GCs that relates their origin to cooling flows
generated after very large episodes of star formation.Comment: 30 pages, 31 figures. In press on Astronomy and Astrophysics, version
after language editin
Optimizing Color-Difference Formulas for 3D-Printed Objects
Based on previous visual assessments of 440 color pairs of 3D-printed samples, we tested
the performance of eight color-difference formulas (CIELAB, CIEDE2000, CAM02-LCD, CAM02-SCD,
CAM02-UCS, CAM16-LCD, CAM16-SCD, and CAM16-UCS) using the standardized residual sum
of squares (STRESS) index. For the whole set of 440 color pairs, the introduction of kL (lightness
parametric factor), b (exponent in total color difference), and kL + b produced an average STRESS
decrease of 2.6%, 26.9%, and 29.6%, respectively. In most cases, the CIELAB formula was significantly
worse statistically than the remaining seven formulas, for which no statistically significant differences
were found. Therefore, based on visual results using 3D-object colors with the specific shape,
size, gloss, and magnitude of color differences considered here, we concluded that the CIEDE2000,
CAM02-, and CAM16-based formulas were equivalent and thus cannot recommend only one of
them. Disregarding CIELAB, the average STRESS decreases in the kL + b-optimized formulas from
changes in each one of the four analyzed parametric factors were not statistically significant and
had the following values: 6.2 units changing from color pairs with less to more than 5.0 CIELAB
units; 2.9 units changing the shape of the samples (lowest STRESS values for cylinders); 0.7 units
changing from nearly-matte to high-gloss samples; and 0.5 units changing from 4 cm to 2 cm samples.Beijing Institute of Graphic Communication BIGC Ec202003
BIGC Ec202102
BIGC Ec202302Ministry of Science and Innovation of the National Government of Spain PID2019-107816GB-I00/SR
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