380 research outputs found
Absolute Magnitude Calibration for Giants based on the Colour-Magnitude Diagrams of Galactic Clusters. II-Calibration with SDSS
We present an absolute magnitude calibration for red giants with the colour
magnitude diagrams of six Galactic clusters with different metallicities i.e.
M92, M13, M3, M71, NGC 6791 and NGC 2158. The combination of the absolute
magnitudes of the red giant sequences with the corresponding metallicities
provides calibration for absolute magnitude estimation for red giants for a
given colour. The calibration is defined in the colour interval
0.45 1.30 mag and it covers the metallicity interval
+0.37 dex. The absolute magnitude
residuals obtained by the application of the procedure to another set of
Galactic clusters lie in the interval mag.
However, the range of 94% of the residuals is shorter,
mag. The mean and the standard deviation of (all) residuals are 0.169 and 0.140
mag, respectively. The derived relations are applicable to stars older than 2
Gyr, the age of the youngest calibrating cluster.Comment: 12 pages, including 5 figures and 10 tables, accepted for publication
in PASA. arXiv admin note: substantial text overlap with arXiv:1204.429
Galactic longitude dependent Galactic model parameters
We present the Galactic model parameters for thin disc estimated by Sloan
Digital Sky Survey (SDSS) data of 14 940 stars with apparent magnitudes
in six intermediate latitude fields in the first Galactic
quadrant. Star/galaxy separation was performed by using the photometric
pipeline and the isodensity contours in the two colour
diagram. The separation of thin disc stars is carried out by the bimodal
distribution of stars in the histogram, and the absolute magnitudes
were evaluated by a procedure presented in the literature Bilir et al. (2005).
Exponential density law fits better to the derived density functions for the
absolute magnitude intervals and , whereas
sech/sech laws are more appropriate for absolute magnitude intervals
and . We showed that the scaleheight and
scalelength are Galactic longitude dependent. The average values and ranges of
the scaleheight and the scalelength are pc ( pc)
and pc ( pc) respectively. This result would
be useful to explain different numerical values claimed for those parameters
obtained by different authors for the fields in different directions of the
Galaxy.Comment: 28 pages, including 12 figures and 7 tables, accepted for publication
in New Astronom
SDSS Absolute Magnitudes for Thin Disc Stars based on Trigonometric Parallaxes
We present a new luminosity-colour relation based on trigonometric parallaxes
for thin disc main-sequence stars in SDSS photometry. We matched stars from the
newly reduced Hipparcos catalogue with the ones taken from 2MASS All-Sky
Catalogue of Point Sources, and applied a series of constraints, i.e. relative
parallax errors (), metallicity
( dex), age ( Gyr) and surface gravity
(), and obtained a sample of thin disc main-sequence stars. Then, we
used our previous transformation equations (Bilir et al. 2008a) between SDSS
and 2MASS photometries and calibrated the absolute magnitudes to the
and colours. The transformation formulae between 2MASS
and SDSS photometries along with the absolute magnitude calibration provide
space densities for bright stars which saturate the SDSS magnitudes.Comment: 7 pages, including 7 figures and 2 tables, accepted for publication
in MNRA
Luminosity-Colours relations for thin disc main-sequence stars
In this study we present the absolute magnitude calibrations of thin disc
main-sequence stars in the optical (), and in the near-infrared
(). Thin disc stars are identified by means of Padova isochrones, and
absolute magnitudes for the sample are evaluated via the newly reduced
Hipparcos data. The obtained calibrations cover a large range of spectral
types: from A0 to M4 in the optical and from A0 to M0 in the near-infrared.
Also, we discuss the of effects binary stars and evolved stars on the absolute
magnitude calibrations. The usage of these calibrations can be extended to the
estimation of galactic model parameters for the thin disc individually, in
order to compare these parameters with the corresponding ones estimated by
statistics (which provides galactic model parameters for thin
and thick discs, and halo simultaneously) to test any degeneracy between them.
The calibrations can also be used in other astrophysical researches where
distance plays an important role in that study.Comment: 8 pages, including 12 figures and 4 tables, accepted for publication
in MNRA
Absolute Magnitude Calibration for Red Giants based on the Colour-Magnitude Diagrams of Galactic Clusters. III-Calibration with 2MASS
We present two absolute magnitude calibrations, and , for
red giants with the colour magnitude diagrams of five Galactic clusters with
different metallicities i.e. M92, M13, M71, M67, and NGC 6791. The combination
of the absolute magnitudes of the red giant sequences with the corresponding
metallicities provides calibration for absolute magnitude estimation for red
giants for a given colour. The calibrations for and are
defined in the colour intervals and mag, respectively, and they cover the metallicity
interval dex. The absolute
magnitude residuals obtained by the application of the procedure to another set
of Galactic clusters lie in the intervals and
mag for and , respectively.
The means and standard deviations of the residuals are
and , and and
mag. The derived relations are applicable to stars
older than 4 Gyr, the age of the youngest calibrating cluster.Comment: 20 pages, including 8 figures and 22 tables, accepted for publication
in PASA. arXiv admin note: substantial text overlap with arXiv:1206.275
Volume limited dependent Galactic model parameters
We estimated 34 sets of Galactic model parameters for three intermediate
latitude fields with Galactic longitudes l=60, l=90, and l=180, and we
discussed their dependence on the volume. Also, we confirmed the variation of
these parameters with absolute magnitude and Galactic longitude. The star
samples in two fields are restricted with bright and unit absolute magnitude
intervals, (4,5], and (5,6], whereas for the third field a larger absolute
magnitude interval is adopted, (4,10]. The limiting apparent magnitudes of star
samples are g=15 and g=22.5 mag which provide space densities within distances
in the line of sight 0.9 and 25 kpc. The Galactic model parameters for the thin
disc are not volume dependent. However, the ones for thick disc and halo do
show spectacular trends in their variations with volume, except for the
scalelength of the thick disc. The local space density of the thick disc
increases, whereas the scaleheight of the same Galactic component decreases
monotonically. However, both model parameters approach asymptotic values at
large distances. The axial ratio of the halo increases abruptly for the volumes
where thick disc is dominant, whereas it approaches an asymptotic value
gradually for larger volumes, indicating a continuous transition from disclike
structure to a spherical one at the outermost region of the Galaxy. The
variation of the Galactic model parameters with absolute magnitude can be
explained by their dependence on the stellar luminosity, whereas the variation
with volume and Galactic longitude at short distances is a bias in analysis.Comment: 12 pages, including 8 figures and 5 tables, accepted for publication
in PAS
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