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Verma K.,Tata Institute of Fundamental Research | Faria J.P.,University of Porto | Antia H.M.,Tata Institute of Fundamental Research | Basu S.,Yale University | And 8 more authors.
Astrophysical Journal | Year: 2014

16 Cyg A and B are among the brightest stars observed by Kepler. What makes these stars more interesting is that they are solar analogs. 16 Cyg A and B exhibit solar-like oscillations. In this work we use oscillation frequencies obtained using 2.5 yr of Kepler data to determine the current helium abundance of these stars. For this we use the fact that the helium ionization zone leaves a signature on the oscillation frequencies and that this signature can be calibrated to determine the helium abundance of that layer. By calibrating the signature of the helium ionization zone against models of known helium abundance, the helium abundance in the envelope of 16 Cyg A is found to lie in the range of 0.231 to 0.251 and that of 16 Cyg B lies in the range of 0.218 to 0.266. © 2014. The American Astronomical Society. All rights reserved..


Aguirre V.S.,University of Aarhus | Ruchti G.R.,Lund Observatory | Hekker S.,Max Planck Institute for Solar System Research | Hekker S.,University of Amsterdam | And 10 more authors.
Astrophysical Journal Letters | Year: 2014

About 1% of giant stars have been shown to have large surface Li abundances, which is unexpected according to standard stellar evolution models. Several scenarios for lithium production have been proposed, but it is still unclear why these Li-rich giants exist. A missing piece in this puzzle is the knowledge of the exact stage of evolution of these stars. Using low- and-high-resolution spectroscopic observations, we have undertaken a survey of lithium-rich giants in the Kepler field. In this Letter, we report the finding of the first confirmed Li-rich core-helium-burning giant, as revealed by asteroseismic analysis. The evolutionary timescales constrained by its mass suggest that Li production most likely took place through non-canonical mixing at the RGB tip, possibly during the helium flash. © 2014. The American Astronomical Society. All rights reserved..


Bhattacharyya S.,Bhabha Atomic Research Center | Godambe S.,Bhabha Atomic Research Center | Bhatt N.,Bhabha Atomic Research Center | Mitra A.,Bhabha Atomic Research Center | Choudhury M.,Homi Bhabha Center for Science Education
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

We have recently studied LS 5039, a gamma-ray binary, with the Giant Metrewave Radio Telescope during its periastron and apastron passage. The results presented here show that the spectra are inverted at low frequency and the flux densities do not differ significantly for two different orbital phases. Assuming that the free-free absorption of radio in the stellar wind environment is responsible for the optically thick radio emission, we calculated the free-free absorption optical depth and constrained the height of the radio-emitting region from the orbital plane. The height is found to be around 1.6 au for a spherical stellar wind geometry. This estimate may change if the stellar wind is focused or the radio absorption is due to synchrotron self-absorption. © 2011 The Authors Monthly Notices of the Royal Astronomical Society. © 2011 RAS.


Hekker S.,University of Amsterdam | Elsworth Y.,University of Birmingham | Basu S.,Yale University | Mazumdar A.,Homi Bhabha Center for Science Education | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Asteroseismology, i.e. the study of the internal structures of stars via their global oscillations, is a valuable tool to obtain stellar parameters such as mass, radius, surface gravity and mean density. These parameters can be obtained using certain scaling relations which are based on an asymptotic approximation. Usually the observed oscillation parameters are assumed to follow these scaling relations. Recently, it has been questioned whether this is a valid approach, i.e. whether the order of the observed oscillation modes is high enough to be approximated with an asymptotic theory. In this work, we use stellar models to investigate whether the differences between observable oscillation parameters and their asymptotic estimates are indeed significant. We compute the asymptotic values directly from the stellar models and derive the observable values from adiabatic pulsation calculations of the same models. We find that the extent to which the atmosphere is included in the models is a key parameter. Considering a larger extension of the atmosphere beyond the photosphere reduces the difference between the asymptotic and observable values of the large frequency separation. Therefore, we conclude that the currently suggested discrepancies in the scaling relations might have been overestimated. Hence, based on the results presented here we believe that the suggestions of Mosser et al. should not be followed without careful consideration. ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Mazumdar A.,Homi Bhabha Center for Science Education | Michel E.,University Pierre and Marie Curie | Antia H.M.,Tata Institute of Fundamental Research | Deheuvels S.,University Pierre and Marie Curie | Deheuvels S.,Yale University
Astronomy and Astrophysics | Year: 2012

The technique of determining the acoustic location of layers of sharp changes in the sound speed inside a star from the oscillatory signal in its frequencies is applied to a solar-type star, the CoRoT target, HD 49933. We are able to determine the acoustic depth of the second helium ionisation zone of HD 49933 to be 794 -68 +55 s. The acoustic depth of the base of the convective zone is found to be 1855 -412 +173 s where the large error bars reflect the ambiguity in the result, which is difficult to determine with present precision on the frequencies because of the intrinsically weak nature of the signal. The positions of both these layers are consistent with those in a representative stellar model of HD 49933. © 2012 ESO.


Wu T.T.,Harvard University | Wu T.T.,CERN | Martin A.,CERN | Roy S.M.,Homi Bhabha Center for Science Education | Singh V.,Tata Institute of Fundamental Research
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

Recently, André Martin has proved a rigorous upper bound on the inelastic cross sectionσinel at high energy, which is one-fourth of the known Froissart-Martin-Lukaszuk upper bound on σtot. Here, we obtain an upper bound on σinel in terms of σtot and show that the Martin bound on σinel is improved significantly with this added information. © 2011 American Physical Society.


Pande P.,Homi Bhabha Center for Science Education | Sevian H.,University of Massachusetts Boston
Proceedings of International Conference of the Learning Sciences, ICLS | Year: 2016

We present preliminary analysis of chemistry graduate students' and secondary chemistry teachers' assumptions about mechanisms of chemical phenomena, around a set of threshold concepts. Chemistry education literature largely identifies pre-threshold assumptions as naive/alternative conceptions not particularly useful in understanding chemical phenomena. In the context of molecular dynamics, a threshold is considered to exist between thinking deterministically vs. probabilistically. We argue that (a) a deterministic perspective is as useful as a probabilistic one, (b) even experts implicitly exhibit (do not lose) deterministic assumptions, (c) probabilistic mental models are built on top of deterministic models, using multiple instances of the phenomena of interest, and (d) expertise involves willfully switching between pre- and post-threshold assumptions. © ISLS.


Kothiyal A.,Indian Institute of Technology Bombay | Murthy S.,Indian Institute of Technology Bombay | Chandrasekharan S.,Homi Bhabha Center for Science Education
Proceedings of International Conference of the Learning Sciences, ICLS | Year: 2016

Professional engineers are often required to make estimates of physical quantities and processes, as well as user requirements and system performance. However, engineering undergraduates, as part of their curriculum, do not learn how to make such estimates. In order to design a technology-enhanced course in engineering estimation, we conducted a study of experienced engineers working on estimation problems. A three-phase process for engineering estimation, and the cognitive mechanisms underlying them, emerged from the analysis of this data. We highlight the roles of mental simulation and external representation in the estimation process. These results will be used to design learning environments for engineering estimation. © 2016 ISLS.


Pathare S.R.,Homi Bhabha Center for Science Education | Pradhan H.C.,Homi Bhabha Center for Science Education
Physics Education | Year: 2010

Heat and thermodynamics is a conceptually rich area of undergraduate physics. In the Indian context in particular there has been little work done in this area from the point of view of misconceptions. This prompted us to undertake a study in this area. We present a study of students' misconceptions about heat transfer mechanisms, i.e. conduction, convection and radiation, and about elementary kinetic theory. © 2010 IOP Publishing Ltd.


Kharatmal M.,Homi Bhabha Center for Science Education | Nagarjuna G.,Homi Bhabha Center for Science Education
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

Although concept maps have been found to be effective in science education research, these are critiqued for being informal due to informal usage of relation and attribute names thereby resulting in ambiguity. Refined concept mapping, a development over the regular concept mapping is an approach towards introducing rigor and parsimony in representing knowledge. The method proposed suggests to substitute the ambiguous relation names with well-defined relation names to concepts consistently while mapping a domain. We suggest the use of this method for introducing rigor in concept mapping and position it among the other models of knowledge representation in an inverse semantic spectrum. © 2010 Springer-Verlag Berlin Heidelberg.

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