179 research outputs found
Circumstellar dust model for infrared stars
The expected thermal emission from the shell around stars has been calculated on the graphite model. The calculated spectral distribution is in reasonable agreement with the observed infrared emission from some of the infrared stars
Atmospheres of extreme metal-deficient stars
Atmospheric models have been constructed for effective temperatures 4000° , 4500° and 5000° and for hydrogen-to-metal ratios of 1, 102, 103 and 104 times the solar values, and for surface gravities of 2×104 and 2×102. The effect of metal deficiency on the atmospheric structure of these stars are studied
A multicomponent model of the infrared emission from Comet Halley
A model based on a mixture of coated silicates and amorphous carbon grains produces a good spectral match to the available Halley data and is consistent with the compositional and morphological information derived from interplanetary dust particle studies and Halley flyby data. The dark appearance of comets may be due to carbonaceous coatings on the dominant (by mass) silicates. The lack of a 10 micrometer feature may be due to the presence of large silicate grains. The optical properties of pure materials apparently are not representative of cometary materials. The determination of the optical properties of additional silicates and carbonaceous materials would clearly be of use
Opacity means and stellar atmospheres
The three kinds of means which are generally used in construction of a model of a 'nongrey atmosphere' of a star are compared for three effective temperatures, 41',700, 20,400 and 10,700° K, with log g = 4.2. It is found that the kind of mean used does not show any wild influence on the physical parameters of the model. Thus, in general, for the study of 'nongrey stellar atmospheres' in mechanical equilibrium any kind of mean may be a good approximation
UrbanFly: Uncertainty-Aware Planning for Navigation Amongst High-Rises with Monocular Visual-Inertial SLAM Maps
We present UrbanFly: an uncertainty-aware real-time planning framework for
quadrotor navigation in urban high-rise environments. A core aspect of UrbanFly
is its ability to robustly plan directly on the sparse point clouds generated
by a Monocular Visual Inertial SLAM (VINS) backend. It achieves this by using
the sparse point clouds to build an uncertainty-integrated cuboid
representation of the environment through a data-driven monocular plane
segmentation network. Our chosen world model provides faster distance queries
than the more common voxel-grid representation, and UrbanFly leverages this
capability in two different ways leading to as many trajectory optimizers. The
first optimizer uses a gradient-free cross-entropy method to compute
trajectories that minimize collision probability and smoothness cost. Our
second optimizer is a simplified version of the first and uses a sequential
convex programming optimizer initialized based on probabilistic safety
estimates on a set of randomly drawn trajectories. Both our trajectory
optimizers are made computationally tractable and independent of the nature of
underlying uncertainty by embedding the distribution of collision violations in
Reproducing Kernel Hilbert Space. Empowered by the algorithmic innovation,
UrbanFly outperforms competing baselines in metrics such as collision rate,
trajectory length, etc., on a high fidelity AirSim simulator augmented with
synthetic and real-world dataset scenes.Comment: Submitted to IROS 2022, Code available at
https://github.com/sudarshan-s-harithas/UrbanFl
Development of Novel Character in Okra [Abelmoschus esculentus (L.) Moench]
Transgressive segregation in the population of IIHR-31-1-2 x Arka Anamika BC3 F1-F6 generations led to the development of, various novel characters such as, ridgeless fruits (round fruit) and enhanced nodal productivity bearing short internodal length in okra selection-1, which was found to be promising for cultivation with high yield and good fruit quality. It can be grown both during Kharif and summer seasons. Okra selection-1 was also found to exhibit smooth fruits, high yield potential with sturdy plant habit and field tolerance to fusarium wilt and YVMV. Due to rapid rate of increase of processing in okra by freezing and canning, Okra selection I may be an ideal fruit type for freezing because of its short, smooth, dark green and round or multifaceted fruits with low mucilage content
Magnetic anomalies of offshore Krishna-Godavari basin, eastern continental margin of India
The marine magnetic data acquired from offshore Krishna-Godavari (K-G) basin, eastern continental margin of India (ECMI), brought out a prominent NE-SW trending feature, which could be explained by a buried structural high formed by volcanic activity. The magnetic anomaly feature is also associated with a distinct negative gravity anomaly similar to the one associated with 85°E Ridge. The gravity low could be attributed to a flexure at the Moho boundary, which could in turn be filled with the volcanic material. Inversion of the magnetic and gravity anomalies was also carried out to establish the similarity of anomalies of the two geological features (structural high on the margin and the 85°E Ridge) and their interpretations. In both cases, the magnetic anomalies were caused dominantly by the magnetization contrast between the volcanic material and the surrounding oceanic crust, whereas the low gravity anomalies are by the flexures of the order of 3-4 km at Moho boundary beneath them. The analysis suggests that both structural high present in offshore Krishna-Godavari basin and the 85°E Ridge have been emplaced on relatively older oceanic crust by a common volcanic process, but at discrete times, and that several of the gravity lows in the Bay of Bengal can be attributed to flexures on the Moho, each created due to the load of volcanic material
An Exploration of the Paradigm for the 2-3 Hour Period Gap in Cataclysmic Variables
We critically examine the basic paradigm for the origin of the 2-3 hr period
gap in cataclysmic variables (CVs). We carry out an extensive population
synthesis study of CVs starting from ~ 3 x 10^6 primordial binaries, and
evolving some ~ 2 x 10^4 surviving systems through their CV phase. In
particular we study current-epoch distributions of CVs in the ,
R_{2}-P_{orb}, M_{2}-P_{orb}, q-P_{orb}, T_{eff}-P_{orb}, and L_{2}-P_{orb}
planes, where is the mass transfer rate, q is the mass ratio M_2/M_1,
and M_2, R_2, T_{eff}, and L_2 are the donor star mass, radius, effective
temperature, and luminosity, respectively. This work presents a new perspective
on theoretical studies of the long-term evolution of CVs. In particular, we
show that if the current paradigm is correct, the secondary masses in CVs just
above the period gap should be as much as ~ 50% lower than would be inferred if
one assumes a main-sequence radius-mass relation for the donor star.Comment: Accepted in Ap
Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members. II. age dependencies and new insights
Models of stellar structure and evolution can be constrained by measuring
accurate parameters of detached eclipsing binaries in open clusters. Multiple
binary stars provide the means to determine helium abundances in these old
stellar systems, and in turn, to improve estimates of their age. In the first
paper of this series, we demonstrated how measurements of multiple eclipsing
binaries in the old open cluster NGC6791 sets tighter constraints on the
properties of stellar models than has previously been possible, thereby
potentially improving both the accuracy and precision of the cluster age. Here
we add additional constraints and perform an extensive model comparison to
determine the best estimates of the cluster age and helium content, employing
as many observational constraints as possible. We improve our photometry and
correct empirically for differential reddening effects. We then perform an
extensive comparison of the CMDs and eclipsing binary measurements to Victoria
and DSEP isochrones to estimate cluster parameters. We also reanalyse a
spectrum of the star 2-17 to improve [Fe/H] constraints. We find a best
estimate of the age of ~8.3 Gyr while demonstrating that remaining age
uncertainty is dominated by uncertainties in the CNO abundances. The helium
mass fraction is well constrained at Y = 0.30 \pm 0.01 resulting in dY/dZ ~ 1.4
assuming that such a relation exists. During the analysis we firmly identify
blue straggler stars, including the star 2-17, and find indications for the
presence of their evolved counterparts. Our analysis supports the RGB mass-loss
found from asteroseismology and we determine precisely the absolute mass of
stars on the lower RGB, 1.15\pm0.02Msun. This will be an important consistency
check for the detailed asteroseismology of cluster stars.Comment: 18 Pages, 9 Figures, accepted for publication in A&
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