1,027 research outputs found
The stellar metallicity distribution in intermediate latitude fields with BATC and SDSS data
Based on the Beijing-Arizona-Taiwan-Connecticut (BATC) and Sloan Digital Sky
Survey (SDSS) photometric data, we adopt SEDs fitting Method to evaluate the
metallicity distribution for \sim40,000 main-sequence stars in the Galaxy.
According to the derived photometric metallicities of these sample stars, we
find that the metallicity distribution shift from metal-rich to metal-poor with
the increase of distance from the Galactic center. The mean metallicity is
about of 1.5 \pm 0.2dex in the outer halo and 1.3 \pm 0.1 dex in the inner
halo. The mean metallicity smoothly decreases from -0.4 to -0.8 in interval 0 <
r \leq 5 kpc. The fluctuation in the mean metallicity with Galactic longitude
can be found in interval 4 < r \leq 8 kpc. There is a vertical abundance
gradients d[Fe/H]/dz\sim -0.21 \pm 0.05 dex kpc-1 for the thin disk (z \leq 2
kpc). At distance 2 < z \leq 5 kpc, where the thick disk stars are dominated,
the gradients are about of -0.16 \pm0.06 dex kpc-1, it can be interpreted as a
mixture of stellar population with different mean metallicities at all z
levels. The vertical metallicity gradient is - 0.05 \pm0.04 dex kpc-1 for the
halo (z > 5 kpc). So there is little or no metallicity gradient in the halo
A CCD Study of High Latitude Galactic Structure: Testing the Model Parameters
We interpret published CCD UBVI data to deduce the stellar density
distribution and metallicity distribution function in the region from 2-8 kpc
from the Galactic Plane, and compare our results to several star count models.
A feature of extant star count models is degeneracy between the adopted scale
heights of the thin and thick disks, and their local normalisation. We
illustrate the utility of this small data set, and future larger sets (e.g.
SDSS), by explicitly considering consistency between the derived density laws,
and the implied solar neighbourhood luminosity function. Our data set, from
Hall et al.(1996) (l=52, b=-39) contains 566 stars, selected to be consistent
with stellar loci in colour-colour diagrams. Our analysis supports the
parameterisation of the recent SDSS galaxy model of Chen et al.(2001), except
in preferring the stellar halo axis ratio to be 0.84. Photometric
metal-abundances have been derived for 329 stars using a new calibration. The
vertical distance-dependent metallicity distribution function, if parameterised
by a single mean value, can be described by a metallicity gradient -0.2 dex/kpc for the inner halo.
The data are however better described as the sum of three discrete distribution
functions, each of which has a small or zero internal gradient. The changing
mix of thin disk, thick disk and halo populations with distance from the plane
generates an illusion of a smooth gradient.Comment: 14 pages, 43 gif figures, accepted for publication in MNRA
The metallicity distributions in high-latitudes with SDSS
We present metallicities and their variations with different parameters for
36 high-latitude fields covering Galactic longitudes 0<l<360. The metallicities
for relatively short vertical distances (z<2.5 kpc) show systematic
fluctuations with Galactic longitude, similar to those of the thick-disc
scaleheight, which may be interpreted as indicating a common origin, viz., the
flare effect of the disc. This suggestion is supported by the metallicity
variations which we find as functions of radial distance. The metallicity
variation at larger vertical distances (6.5<z<9.5 kpc) is small but monotonic.
Three different vertical metallicity gradients could be detected:
d[M/H]/dz=-0.22(+/-0.03), d[M/H]/dz=-0.38 (+/-0.06), and d[M/H]/dz=-0.08
(+/-0.07) dex/kpc for the intervals z<3, 3<z<5, and 5<z<10 kpc, respectively.
Since our data cover the whole Galactic longitude interval, the resulting
metallicity gradients can be interpreted as properties of the larger-scale
Galaxy. The first gradient confirms the dissipational formation of the disc at
short z-distances. The steeper gradient corresponds to the transition region
between different population components of the Galaxy, and finally, the lowest
value provides an adequate description of the inner-halo metallicity gradient.Comment: 14 pages, 7 figures and 2 tables, accepted for publication in New
Astronom
Estimation of Galactic Model Parameters and Metalicity Distribution in Intermediate Latitudes with SDSS
We estimated the galactic model parameters for a set of 20
intermediate-latitude fields with galactic longitudes 0<l<100 and 160<l<240,
included in the currently available Data Release 6 (DR6) of SDSS, to explore
their possible variation with galactic longitude. The local space densities of
the thick disc and halo are almost the same for all fields,
=6.52% and =0.35%, respectively, a result
different than the one cited for high-latitude fields. The thin disc's
scaleheight is 325 pc in the galactic centre changes to 369 pc in the third
quadrant, which confirms the existence of disc flare, whereas the thick disc
scaleheight is as large as 952 pc at galactic longitude l=20 and 10% lower at
l=160, which confirms the existence of the disc long bar in the direction l=27.
Finally, the variation of the axis ratio of the halo with galactic longitude is
almost flat, =0.56, except a slight minimum and a small maximum in the
second and third quadrants, respectively, indicating an effect of the long bar
which seems plausible for a shallow halo. We estimated the metallicities of
unevolved G-type stars and discussed the metallicity gradient for different
vertical distances. The metallicity gradient is d[M/H]/dz=-0.30 dex kpc
for short distances, confirming the formation of this region of the Galaxy by
dissipational collapse. However, its change is steeper in the transition
regions of different galactic components. The metallicity gradient is almost
zero for inner halo (5<z<10 kpc), indicating a formation of merger or accretion
of numerous fragments such as dwarf galaxies.Comment: 31 pages, 18 figures and 4 tables, accepted for publication in New
Astronom
Local stellar kinematics from RAVE data - II. Radial metallicity gradient
We investigate radial metallicity gradients for a sample of dwarf stars from the RAdial Velocity Experiment (RAVE) Data Release 3 (DR3). We select a total of approximately 17 000 F-type and G-type dwarfs, using a selection of colour, log g and uncertainty in the derived space motion, and calculate for each star a probabilistic (kinematic) population assignment to a thick or thin disc using space motion and additionally another (dynamical) assignment using stellar vertical orbital eccentricity. We additionally subsample by colour, to provide samples biased toward young thin-disc and older thin-disc stars. We derive a metallicity gradient as a function of Galactocentric radial distance, i.e. d[M/H]/dRm=−0.051 ± 0.005 dex kpc−1, for the youngest sample, F-type stars with vertical orbital eccentricities ev≤ 0.04. Samples biased toward older thin-disc stars show systematically shallower abundance gradients
Galactic model parameters for field giants separated from field dwarfs by their 2MASS and V apparent magnitudes
We present a procedure which separates field dwarfs and field giants by their
2MASS and V apparent magnitudes. The procedure is based on the
spectroscopically selected standards, hence it is confident. We applied this
procedure to stars in two fields, SA 54 and SA 82, and we estimated a full set
of Galactic model parameters for giants including their total local space
density. Our results are in agreement with the ones appeared recently in the
literature.Comment: 10 pages, 4 figures and 5 tables, accepted for publication in A
Local stellar kinematics from RAVE data: III. Radial and Vertical Metallicity Gradients based on Red Clump Stars
We investigate radial and vertical metallicity gradients for a sample of red
clump stars from the RAdial Velocity Experiment (RAVE) Data Release 3. We
select a total of 6781 stars, using a selection of colour, surface gravity and
uncertainty in the derived space motion, and calculate for each star a
probabilistic (kinematic) population assignment to a thin or thick disc using
space motion and additionally another (dynamical) assignment using stellar
vertical orbital eccentricity. We derive almost equal metallicity gradients as
a function of Galactocentric distance for the high probability thin disc stars
and for stars with vertical orbital eccentricities consistent with being
dynamically young, e_v<=0.07, i.e. d[M/H]/dR_m = -0.041(0.003) and d[M/H]/dR_m
= -0.041(0.007) dex/kpc. Metallicity gradients as a function of distance from
the Galactic plane for the same populations are steeper, i.e. d[M/H]/dz_{max} =
-0.109(0.008) and d[M/H]/dz_{max} = -0.260(0.031) dex/kpc, respectively. R_m
and z_{max} are the arithmetic mean of the perigalactic and apogalactic
distances, and the maximum distance to the Galactic plane, respectively.
Samples including more thick disc red clump giant stars show systematically
shallower abundance gradients. These findings can be used to distinguish
between different formation scenarios of the thick and thin discs.Comment: 27 pages, including 15 figures and 4 tables, accepted for publication
in MNRA
Restoring Ureagenesis in Hepatocytes by CRISPR/Cas9-mediated Genomic Addition to Arginase-deficient Induced Pluripotent Stem Cells.
Urea cycle disorders are incurable enzymopathies that affect nitrogen metabolism and typically lead to hyperammonemia. Arginase deficiency results from a mutation in Arg1, the enzyme regulating the final step of ureagenesis and typically results in developmental disabilities, seizures, spastic diplegia, and sometimes death. Current medical treatments for urea cycle disorders are only marginally effective, and for proximal disorders, liver transplantation is effective but limited by graft availability. Advances in human induced pluripotent stem cell research has allowed for the genetic modification of stem cells for potential cellular replacement therapies. In this study, we demonstrate a universally-applicable CRISPR/Cas9-based strategy utilizing exon 1 of the hypoxanthine-guanine phosphoribosyltransferase locus to genetically modify and restore arginase activity, and thus ureagenesis, in genetically distinct patient-specific human induced pluripotent stem cells and hepatocyte-like derivatives. Successful strategies restoring gene function in patient-specific human induced pluripotent stem cells may advance applications of genetically modified cell therapy to treat urea cycle and other inborn errors of metabolism
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
Analysis of UBV Photometry in Selected Area 133
We interpret the de-reddened UBV data for the field SA 133 to deduce the
stellar density and metallicity distributions function. The logarithmic local
space density for giants, , and the agreement of the luminosity
function for dwarfs and sub-giants with the one of Hipparcos confirms the
empirical method used for their separation. The metallicity distribution for
dwarfs gives a narrow peak at [Fe/H]=+0.13 dex, due to apparently bright
limiting magnitude, , whereas late-type giants extending up to kpc from the galactic plane have a multimodal distribution. The
metallicity distribution for giants gives a steep gradient
dex kpc for thin disk and thick disk whereas a smaller value for the
halo, i.e. dex kpc.Comment: 7 pages, 7 figures and 3 tables, accepted for publication in A
- …