29,966 research outputs found
Population I Cepheids and star formation history of the Large Magellanic Cloud
In this paper we study the Cepheids distribution in the Large Magellanic
Cloud (LMC) as a function of their ages using data from the OGLE III
photometric catalogue. To determine age of the Pop I Cepheids, we derived a
period-age (PA) relationship using the Cepheids found in the LMC star clusters.
We find two peaks in the period distribution at logP =0.49+/-0.01 and logP
=0.28+/-0.01 days which correspond to fundamental and first overtone pulsation
modes, respectively. Ages of the Cepheids are used to understand star formation
scenario in the LMC in last 30-600 Myr. The age distribution of the LMC
Cepheids is found to have a peak at log(Age)=8.2+/-0.1. This suggests that
major star formation event took place at about 125-200 Myr ago which may have
been triggered by a close encounter between the SMC and the LMC. Cepheids are
found to be asymmetrically distributed throughout the LMC and many of them lie
in clumpy structures along the bar. The frequency distribution of Cepheids
suggests that most of the clumps are located to the eastern side of the LMC
optical center.Comment: 2014, New Astronomy, 28, 2
Basic Parameters of Open Star Clusters DOLIDZE 14 and NGC 110 in Infrared bands
The basic physical parameters of a poorly studied open cluster NGC 110 and an
unstudied open cluster DOLIDZE 14 are estimated in the present study using the
archival PPMXL and WISE catalogues. The radius of both the clusters are
estimated by fitting the modified King's empirical model on their stellar
density profiles. The other basic parameters of the clusters such as distance,
reddening, and age are obtained by visual fitting of the Marigo's solar
metallicity isochrone on their IR colour-magnitude diagrams (CMDs). The
mean-proper motion of the clusters are estimated through the individual proper
motion of probable members identified through the dynamical and statistical
methods. The archival catalogues (JHKW1W2) are constructed for both the
clusters by compiling the extracted data from the PPMXL and WISE catalogues.
The various colour-excesses, such as E(J-H), E(H-K) and E(W1-W2), are estimated
using the best fit theoretical isochrone on the (J-H)-H, (H-K)-H and (W1-W2)-H
CMDs, respectively. The ratios of various infrared colours of the clusters are
obtained through their two-colour diagrams. We also identify the most probable
members in these clusters by estimating spatial, kinematic and spatio-kinematic
probabilities of stars within the cluster. A correlation between the E(H-K) and
E(W1-W2) is also established.Comment: 23 pages, 7figure
Asteroseismology of Pulsating Stars
The success of helioseismology is due to its capability of measuring p-mode
oscillations in the Sun. This allows us to extract informations on the internal
structure and rotation of the Sun from the surface to the core. Similarly,
asteroseismology is the study of the internal structure of the stars as derived
from stellar oscillations. In this review we highlight the progress in the
observational asteroseismology, including some basic theoretical aspects. In
particular, we discuss our contributions to asteroseismology through the study
of chemically peculiar stars under the "Nainital-Cape Survey" project being
conducted at ARIES, Nainital since 1999. This survey aims to detect new
rapidly-pulsating Ap (roAp) stars in the northern hemisphere. We also discuss
the contribution of ARIES towards the asteroseismic study of the compact
pulsating variables. We comment on the future prospects of our project in the
light of the new optical 3.6-m telescope to be install at Devasthal (ARIES).
Finally, we present a preliminary optical design of the high-speed imaging
photometers for this telescope.Comment: published in Journal of Astrophysics & Astronomy. arXiv admin note:
text overlap with arXiv:1405.3145, arXiv:1212.5084, arXiv:1205.6407,
arXiv:1212.2384, arXiv:1109.3455, arXiv:1104.5191, arXiv:1102.1884,
arXiv:1310.0696, arXiv:1310.2266 by other author
Complex stellar system ESO65SC03: Open cluster or remnant?
We present a complete spatial and dynamical study of the poorly populated
stellar system ESO65SC03. The radial distribution of the system gives a core
and cluster radii of 1.10+/-0.63 arcmin and 5.36+/-0.24 arcmin, respectively.
The surface number density profile (SNDP) does not show any clear enhancement
of the surface stellar number density between the stars of the system and the
field regions. We derive the optimum isochrone solution for a particular grid
size in the colour-magnitude diagram (CMD) using the statistical cleaning
procedure. Using the statistically cleaned CMDs, we find the distance modulus,
(m-M)_0, and reddening, E({B-V}), of the system to be 11.8+/-0.2 mag and 0.45
mag, respectively. The mean proper motion of this system is -5.37+/-0.81 mas/yr
and 0.31+/-0.40 in RA and DEC directions, respectively. The mean proper motion
of this system is found to be almost similar to the field region. The mass
function for the brighter stars is found to be too high for the system to be an
open cluster. These combined results place constraints on whether stellar
system ESO65SC03 is a possible open star cluster remnant (POCR) or an Asterism.
Our understanding is that the ESO65SC03 is in a stage of POCR by loosing their
main sequence stars in the dynamic evolution processes.Comment: 10 pages, 9 figures, accepted for publication in PAS
Population I Cepheids and understanding star formation history of the Small Magellanic Cloud
In this paper, we study the age and spatial distributions of Cepheids in the
Small Magellanic Cloud (SMC) as a function of their ages using the data from
the OGLE III photometric catalogue. A period-age (PA) relation derived for the
Classical Cepheids in the Large Magellanic Cloud (LMC) has been used to find
the ages of Cepheids. The age distribution of the SMC Classical Cepheids is
found to have a peak at log(Age) = 8.40+/-0.10 which suggests that a major star
formation event might have occurred in the SMC at about 250+/-50 Myrs ago. It
is believed that this star forming burst had been triggered by close
interactions of the SMC with the LMC and/or the Milky Way (MW). A comparison of
the observed spatial distributions of the Cepheids and open star clusters has
also been carried out to study the star formation scenario in the SMC.Comment: 10 pages, 7 figures, accepted for publication in Research in
Astronomy and Astrophysic
Photometric studies of two W UMa type variables in the field of distant open cluster NGC6866
We present photometric analysis of the two W UMa type binaries identified in
the field of distant open star cluster NGC6866. Although these systems, namely
ID487 and ID494, were reported in the Joshi et al. (2012), but a detailed study
of these stars has not been carried out earlier. The orbital periods of these
stars are found to be 0.415110+/-0.000001 day and 0.366709+/-0.000004 day,
respectively. Based on the photometric and infrared colours, we find their
respective spectral types as K0 and K3. The photometric light variations of
both the stars show O'Connell effect which could be explained by employing a
dark spot on the secondary components. The V and I bands light curves are
analyzed using the Wilson-Devinney (WD) code and relations given by Gazeas
(2009) which yield radii and mass of the primary and secondary components of
the star ID487 as R1 = 1.24+/-0.01 Rsun, R2 = 1.11+/-0.02 Rsun, and M1 =
1.24+/-0.02 Msun, M2 = 0.96+/-0.05 Msun, and for the star ID494 as R1 =
1.22+/-0.02 Rsun, R2 = 0.81+/-0.01 Rsun, and M1 = 1.20+/-0.06 Msun, M2 =
0.47+/-0.01 Msun.Comment: 12 pages, 7 figures, 2016, RAA, 16, 1
Probing nearby Galactic structure through open star clusters
Based on the most complete sample of Galactic open star clusters up to 1.8
kpc, we performed statistical analysis of the distribution of open cluster
parameters in order to understand the Galactic structure. The geometrical
characteristics of a large number of open clusters enable us to determine solar
offset and scale height and distribution of reddening material in the Galactic
neighbourhood.Comment: 4 pages, 1 figure, conference proceedings Stars: From Collapse to
Collapse, Proceedings of a conference held at Special Astrophysical
Observatory, Nizhny Arkhyz, Russia 3-7 October 2016. Edited by Yu. Yu.
Balega, D. O. Kudryavtsev, I. I. Romanyuk, and I. A. Yakunin. San Francisco:
Astronomical Society of the Pacific, 2017, p.8
Open star clusters and Galactic structure
In order to understand the Galactic structure, we perform a statistical
analysis of the distribution of various cluster parameters based on an almost
complete sample of Galactic open clusters yet available. The geometrical and
physical characteristics of a large number of open clusters given in the MWSC
catalogue are used to study the spatial distribution of clusters in the Galaxy
and determine the scale height, solar offset, local mass density and
distribution of reddening material in the solar neighbourhood. We also explored
the mass-radius and mass-age relations in the Galactic open star clusters. We
find that the estimated parameters of the Galactic disk are largely influenced
by the choice of cluster sample.Comment: Astrometry and Astrophysics in the Gaia sky, Proceedings of the
International Astronomical Union, IAU Symposium, Volume 330, pp. 227-22
Identification of Stellar Sequences in various Stellar Systems : ESO65-SC03, TEUTSCH 106, TURNER 6
The spatial morphological study of studied clusters is carried out through
the identified probable members within them. The field stars decontamination is
performed by the statistical cleaning approach (depends on the magnitude and
colour of stars within the field and cluster regions). The CMRD (colour
magnitude ratio diagram) approach is used to separate stellar sequences of the
cluster systems. The age, distance and reddening of each cluster are estimated
through the visual inspection of best fitted isochrone in colour magnitude
diagrams(CMDs). The mean proper motion values of clusters are obtained through
the extracted data from PPMXL and UCAC4 catalogs. Moreover, these values are
varying according to the extracted data-set from these catalogues. This
variation is occurred due to their different estimation efficiency of proper
motions. The TCR (two colour ratio) and TCMR (two colour magnitude ratio)
values of each cluster are determined by utilizing the WISE and PPMXL
catalogues, these values are found abnormal for TEUTSCH 106. In addition, the
TCMR values are similar to TCR values at longer wavelength, whereas both values
are far away to each other at shorter wavelength. The fraction of young stellar
objects (YSOs) is also computed for each cluster.Comment: 24 pages, 5 figure
TeV Scale Cross-Sections and the Pomeranchuck Singularity
We have investigated the detailed structure of -plane singularities of
scattering amplitude saturating the Froissart bound. A self-consistent analysis
of these singularities provides us secondary terms in the Froissart bound.
These secondary terms lead to ghosts in the -plane, which can only be
removed by introducing an odderon singularity. Phenomenological implications of
this analysis are also discussed
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