3,324 research outputs found
On the highly reddened members in 6 young galactic star clusters - a multiwavelength study
The spectral and reddening properties of 211 highly reddened proper motion
members with mag in 6 young galactic star clusters are investigated
using low resolution spectroscopic, broad-band and mid-IR data. We
report emission features in CaII HK and HI lines for a sample of 29 stars
including 11 stars reported for the first time and also provide either a new or
more reliable spectral class for a sample of 24 stars. CaII triplet width
measurements are used to indicate the presence of an accretion disk for a dozen
stars and to hint luminosity for a couple of stars. On the basis of spectral
features, near-IR excesses, dereddened color-color diagrams and mid-IR spectral
indices we identify a group of 28 pre-main sequence cluster members including 5
highly probable Herbig Ae/Be and 6 classical T Tauri star. A total of 25
non-emission MS stars, amounting to 10 % early type MS members, appears
to show Vega-like characteristics or are precursors to such a phenomenon. The
various membership indicators suggest that 16% of the PM members are
non-members. A significant fraction (70%) of program stars in NGC 1976, NGC
2244, NGC 6530 and NGC 6611 show anomalous reddening with =
, , and , respectively,
indicating the presence of grain size dust larger than that typical to the
diffuse medium. A small number of stars in NGC 1976, NGC 2244 and NGC 6611 also
show normal behavior while the cluster NGC 6823 appears to have a normal
reddening. Three highly luminous late type giants, one in NGC 2244 and two in
NGC 6530, appears to be member and are in post-hydrogen-core-burning stages
suggesting a prolonged duration ( 25 Myrs) of star formation.Comment: 12 pages, 13 figures, submitted to MNRA
The Variation of Integrated Star IMFs among Galaxies
The integrated galaxial initial mass function (IGIMF) is the relevant
distribution function containing the information on the distribution of stellar
remnants, the number of supernovae and the chemical enrichment history of a
galaxy. Since most stars form in embedded star clusters with different masses
the IGIMF becomes an integral of the assumed (universal or invariant) stellar
IMF over the embedded star-cluster mass function (ECMF). For a range of
reasonable assumptions about the IMF and the ECMF we find the IGIMF to be
steeper (containing fewer massive stars per star) than the stellar IMF, but
below a few Msol it is invariant and identical to the stellar IMF for all
galaxies. However, the steepening sensitively depends on the form of the ECMF
in the low-mass regime. Furthermore, observations indicate a relation between
the star formation rate of a galaxy and the most massive young stellar cluster
in it. The assumption that this cluster mass marks the upper end of a
young-cluster mass function leads to a connection of the star formation rate
and the slope of the IGIMF above a few Msol. The IGIMF varies with the star
formation history of a galaxy. Notably, large variations of the IGIMF are
evident for dE, dIrr and LSB galaxies with a small to modest stellar mass. We
find that for any galaxy the number of supernovae per star (NSNS) is suppressed
relative to that expected for a Salpeter IMF. Dwarf galaxies have a smaller
NSNS compared to massive galaxies. For dwarf galaxies the NSNS varies
substantially depending on the galaxy assembly history and the assumptions made
about the low-mass end of the ECMF. The findings presented here may be of some
consequence for the cosmological evolution of the number of supernovae per
low-mass star and the chemical enrichment of galaxies of different mass.Comment: 27 pages, accepted for publication by Ap
Antiepileptic drugs: newer targets and new drugs
Epilepsy is a common neurological disorder affecting 0.5-1% of the population in India. Majority of patients respond to currently available antiepileptic drugs (AEDs), but a small percentage of patients have shown poor and inadequate response to AEDs in addition to various side effects and drug interactions while on therapy. Thus there is a need to develop more effective AEDs in drug resistant epilepsy which have a better safety profile with minimal adverse effects. The United States food and drug administration (USFDA) has approved eslicarbazepine acetate, ezogabine, perampanel and brivaracetam which have shown a promising future as better AEDs and drugs like ganaxolone, intranasal diazepam, ICA- 105665, valnoctamide, VX-765, naluzotan are in the pipeline
CCD photometric and mass function study of 9 young Large Magellanic Cloud star clusters
We present CCD photometric and mass function study of 9 young Large
Magellanic Cloud star clusters namely NGC 1767, NGC 1994, NGC 2002, NGC 2003,
NGC 2006, SL 538, NGC 2011, NGC 2098 and NGC 2136. The BVRI data reaching down
to V ~ 21 mag, are collected from 3.5-meter NTT/EFOSC2 in sub-arcsec seeing
conditions. For NGC 1767, NGC 1994, NGC 2002, NGC 2003, NGC 2011 and NGC 2136,
broad band photometric CCD data are presented for the first time. Seven of the
9 clusters have ages between 16 to 25 Myr while remaining two clusters have
ages Myr (NGC 2098) and Myr (NGC 2136). For 7 younger
clusters, the age estimates based on a recent model and the integrated spectra
are found to be systematically lower ( 10 Myr) from the present estimate.
In the mass range of , the MF slopes for 8 out of nine
clusters were found to be similar with the value of ranging from
to . For NGC 1767 it is flatter with . Mass segregation effects are observed for NGC 2002, NGC 2006,
NGC 2136 and NGC 2098. This is consistent with the findings of Kontizas et al.
for NGC 2098. Presence of mass segregation in these clusters could be an
imprint of star formation process as their ages are significantly smaller than
their dynamical evolution time. Mean MF slope of
derived for a sample of 25 young ( Myr) dynamically unevolved LMC
stellar systems provide support for the universality of IMF in the intermediate
mass range .Comment: To appear in MNRA
Work probability distribution and tossing a biased coin
We show that the rare events present in dissipated work that enters Jarzynski
equality, when mapped appropriately to the phenomenon of large deviations found
in a biased coin toss, are enough to yield a quantitative work probability
distribution for Jarzynski equality. This allows us to propose a recipe for
constructing work probability distribution independent of the details of any
relevant system. The underlying framework, developed herein, is expected to be
of use in modelling other physical phenomena where rare events play an
important role.Comment: 6 pages, 4 figures
GRB Energetics and the GRB Hubble Diagram: Promises and Limitations
We present a complete sample of 29 GRBs for which it has been possible to
determine temporal breaks (or limits) from their afterglow light curves. We
interpret these breaks within the framework of the uniform conical jet model,
incorporating realistic estimates of the ambient density and propagating error
estimates on the measured quantities. In agreement with our previous analysis
of a smaller sample, the derived jet opening angles of those 16 bursts with
redshifts result in a narrow clustering of geometrically-corrected gamma-ray
energies about E_gamma = 1.33e51 erg; the burst-to-burst variance about this
value is a factor of 2.2. Despite this rather small scatter, we demonstrate in
a series of GRB Hubble diagrams, that the current sample cannot place
meaningful constraints upon the fundamental parameters of the Universe. Indeed
for GRBs to ever be useful in cosmographic measurements we argue the necessity
of two directions. First, GRB Hubble diagrams should be based upon fundamental
physical quantities such as energy, rather than empirically-derived and
physically ill-understood distance indicators. Second, a more homogeneous set
should be constructed by culling sub-classes from the larger sample. These
sub-classes, though now first recognizable by deviant energies, ultimately must
be identifiable by properties other than those directly related to energy. We
identify a new sub-class of GRBs (``f-GRBs'') which appear both underluminous
by factors of at least 10 and exhibit a rapid fading at early times. About
10-20% of observed long-duration bursts appear to be f-GRBs.Comment: Accepted to the Astrophysical Journal (20 May 2003). 19 pages, 3
Postscript figure
Analysis of Box Culvert to Reduce Stress Values
At the time of construction of roads, highways a structure is placed (commonly used) to transfer the traffic, rain water, drainage from one side to another of the road is called a culvert placed beneath the road. Due to the structural use, multiple loads are placed on the box causing various types of stress which occurs on it. The paper tries to reduce the stress occurred in the box by flaring the box partially
A Raman study of the Charge-Density-Wave State in AMoO (A = K,Rb)
We report a comparative Raman spectroscopic study of the
quasi-one-dimensional charge-density-wave systems \ab (A = K, Rb). The
temperature and polarization dependent experiments reveal charge-coupled
vibrational Raman features. The strongly temperature-dependent collective
amplitudon mode in both materials differ by about 3 cm, thus revealing the role
of alkali atom. We discus the observed vibrational features in terms of
charge-density-wave ground state accompanied by change in the crystal symmetry.
A frequency-kink in some modes seen in \bb between T = 80 K and 100 K supports
the first-order lock-in transition, unlike \rb. The unusually sharp Raman
lines(limited by the instrumental response) at very low temperatures and their
temperature evolution suggests that the decay of the low energy phonons is
strongly influenced by the presence of the temperature dependent charge density
wave gap.Comment: 13 pages, 7 figure
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