61 research outputs found
Volume-Limited Dependent Galactic Model Parameters
We estimate 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 confirm 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 < M g ≤ 5, and 5 < M g ≤ 6, whereas for the third field (l = 60°) a larger absolute-magnitude interval is adopted, 4 < M g ≤ 10. The limiting apparent magnitudes of the star samples are g 0 = 15 and g 0 = 22.5 mag, which provide space densities within distances in the line of sight of ∼0.9 and 25 kpc. The Galactic model parameters for the thin disc are not volume dependent. However, the ones for the thick disc and halo do show spectacular trends in their variation 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 relative local space density of the halo estimated by fitting the density laws to the space densities evaluated for all volumes is constant, except for the small ones. However it is absolute-magnitude and Galactic longitude dependent. The axial ratio of the halo increases abruptly for the volumes where a thick disc is dominant, whereas it approaches an asymptotic value gradually for larger volumes, indicating a continuous transition from a disc-like 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 analysi
A New Procedure for the Photometric Parallax Estimation
We present a new procedure for photometric parallax estimation. The data for
1236 stars provide calibrations between the absolute magnitude offset from the
Hyades main-sequence and the UV-excess for different (B-V)o colour-index
intervals, i.e.: (0.3 0.4), (0.4 0.5), (0.5 0.6), (0.6 0.7), (0.7 0.8), (0.8
0.9), (0.9 1.0), and (1.0 1.1). The mean difference between the original and
estimated absolute magnitudes and the corresponding standard deviation are
rather small, +0.0002 and +/-0.0613 mag. The procedure has been adapted to the
Sloan photometry by means of colour equations and applied to a set of
artificial stars with different metallicity. The comparison of the absolute
magnitudes estimated by the new procedure and the canonical one indicates that
a single colour-magnitude diagram does not supply reliable absolute magnitudes
for stars with large range of metallicity.Comment: 26 pages, including 12 tables and 6 figures, accepted for publication
in PAS
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
A Universal Vertical Stellar Density Distribution Law for the Galaxy
We reduced the observational logarithmic space densities in the vertical
direction up to 8 kpc from the galactic plane, for stars with absolute
magnitudes (5,6], (6,7] and [5,10] in the fields #0952+5245 and SA114, to a
single exponential density law. One of three parameters in the quadratic
expression of the density law corresponds to the local space density for stars
with absolute magnitudes in question. There is no need of any definition for
scaleheights or population types. We confirm with the arguments of non-discrete
thin and thick discs for our Galaxy and propose a single structure up to
several kiloparsecs from the galactic plane. The logarithmic space densities
evaluated by this law for the ELAIS field fit to the observational ones.
Whereas, there are considerable offsets for the logarithmic space densities
produced by two sets of classical galactic model parameters from the
observational ones, for the same field.Comment: 9 pages, 1 figure and 10 tables, accepted for publication in
Astrophysics & Space Scienc
A different approach for the estimation of Galactic model parameters
We estimated the Galactic model parameters by means of a new approach based
on the comparison of the observed space density functions per absolute
magnitude interval with a unique density law for each population individually,
and via the procedure in situ for the field SA 114 (,
; 4.239 square-degree; J2000). The separation of stars into
different populations has been carried out by their spatial distribution. The
new approach reveals that model parameters are absolute magnitude dependent.
The scale height for thin disk decreases monotonously from absolutely bright to
absolutely faint stars in a range 265-495 pc, but there is a discontunity at
the absolute magnitude where the squared secans hiperbolicus
density law replaces the exponential one. The range of the scale-height for
thick disk, dominant in the absolute magnitude interval , is
less: 805-970 pc. The local space density for thick disk relative to thin disk
decreases from 9.5% to 5.2% when one goes from the absolutely bright to faint
magnitudes. Halo is dominant in three absolute magnitude intervals and the
axial ratio for this component is almost the same for these intervals where
. The same holds for the local space density relative to the thin
disk with range (0.02-0.15)%. The model parameters estimated by comparison of
the observed space density functions combined for three populations per
absolute magnitude interval with the combined density laws agree with the cited
values in the literature. Also each parameter is equal to at least one of the
corresponding parameters estimated for different absolute magnitude intervals
by the new approach. We argue that the most appropriate Galactic model
parameters are those, that are magnitude dependent.Comment: 14 pages, including 16 figures and 16 tables, accepted for
publication in MNRA
Phytosociological Studies on the Halophytic Communities of Central Anatolia
Central Anatolia belongs to the Irano-Turanian region in terms of phytogeography. Salt marshes occupy a significant place in this province. Halophytic vegetation which develops around the salt lakes is floristically very rich and includes many endemic taxa. In this study, five different phytosociological researches, carried out on the salt marsh communities of Central Anatolia were taken as a whole. In all these researches, the vegetation analyses were carried out according to the traditional Braun-Blanquet approach. The nomenclature and classification of syntaxa follow the "International Code of Phytosociological Nomenclature". Plant associations misevaluated and/or not considered as validly published were renamed and reclassified. The salt marsh communities which are dealt with in this study belong to the Halostachyetalia and Juncetalia maritimi orders of the Salicomictea classis. These orders are represented by the alliances of Lepidio caespitosi-Limonion iconici and Inulo aucheranae-Elymion salsi in the salt marshes of Central Anatolia
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