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Multi-site, multi-year monitoring of the oscillating Algol-type eclipsing binary CT Herculis
Lampens, P.,Strigachev, A.,Kim, S.-L.,Rodrí,guez, E.,Ló,pez-Gonzá,lez, M. J.,Vidal-Saí,nz, J.,Mkrtichian, D.,Koo, J.-R.,Kang, Y. B.,Van Cauteren, P.,Wils, P.,Kraicheva, Z.,Dimi EDP Sciences 2011 Astronomy and astrophysics Vol.534 No.2
<P>We present the results of a multi-site photometric campaign carried out in 20042008 for the Algol-type eclipsing binary system CT Her, the primary component of which displays δ Scuti-type oscillations. Our data consist of differential light curves collected in the filters B and V, which were analysed using the method of Wilson-Devinney (PHOEBE). After identifying an adequate binary model and removing the best-fit light-curve solution, we performed a Fourier analysis of the residual B and V light curves to investigate the pulsational behaviour. We confirm the presence of rapid pulsations with a main period of 27.2 min. Up to eight significant frequencies with semi-amplitudes in the range 3 to 1 mmag were detected, all of which lie in the frequency range 43.553.5 d<SUP>−1</SUP>. This result is independent of the choice of the primary’s effective temperature (8200 or 8700 K) since the light-curve models of the binary are very similar in both cases. This is yet another case of a complex frequency spectrum observed for an accreting δ Scuti-type star (after Y Cam). In addition, we demonstrate that the amplitudes of several pulsation frequencies provide evidence of variability on timescales as short as 12 years, perhaps even less. Moreover, our analysis takes into account some recently acquired spectra, from which we obtained the corresponding radial velocities for the years 20072009. Investigation of the OC diagram shows that further monitoring of the epochs of eclipse minima of CT Her will cast new light on the evolution of its orbital period.</P>
<i>δ</i> Sct-type pulsations in eclipsing binary systems: Y Cam
Rodrí,guez, E.,Garcí,a, J. M.,Costa, V.,Lampens, P.,van Cauteren, P.,Mkrtichian, D. E.,Olson, E. C.,Amado, P. J.,Daszyń,ska-Daszkiewicz, J.,Turcu, V.,Kim, S.-L.,Zhou, A. Y.,Ló,p Blackwell Publishing Ltd 2010 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.408 No.4
<P>ABSTRACT</P><P>We present the results of a three-continent multisite photometric campaign carried out on the Algol-type eclipsing binary system Y Cam, in which the primary component is a multiperiodic δ Sct-type pulsator. The observations consist of 86 nights and more than 450 h of useful data collected mainly during the Northern winter 2002–2003. This means that this is the most extensive time series for such kind of systems obtained so far. These observations were collected mostly in the Johnson V filter, but they also include, for the first time, nearly complete binary light curves in simultaneous Strömgren <I>uvby</I> filters together with a few Crawford Hβ data obtained around the orbital phase of the first quadrature. A detailed photometric analysis is presented for both binarity and pulsation. The results indicate a semidetached system with the secondary filling its Roche lobe. No significant contribution from a third body is found. The residuals from the computed binary solution were then used to investigate the pulsational content of the primary component. The frequency analysis of the out-of-primary-eclipse data leads to a set of eight significant and independent pulsational peaks in a well-defined region of the frequency domain. This means that this is the largest set of excited modes discovered so far in the pulsating component of such kind of systems. The possibility of aliasing problems during the present run or short-term time-scale amplitude variations in some of them was investigated with null results. Indeed the results indicate that <I>f</I><SUB>1</SUB> and <I>f</I><SUB>3</SUB> form a frequency doublet with a beat period of <I>P</I><SUB>beat</SUB>= 17.065 d. Our results confirm the frequencies already detected by earlier authors and show the presence of some additional significant peaks. The observed amplitudes during the present run are also consistent with those derived from older data sets. We perform a preliminary mode identification for most of the frequencies on the basis of the collected multicolour photometry, the observed frequency spacings and the mode visibility in eclipsing binaries.</P>
Phan, T. L.,Thanh, T. D.,Ho, T. A.,Manh, T. V.,Tran, Q. T.,Lampen, P.,Phan, M. H.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.11
<P>This paper points out that the magnetic-phase transition and magnetocaloric effect of La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> (LCMO) can be easily controlled by using the mechanical milling method. Changing the milling time from 5 to 30 min, we have obtained LCMO nanoparticles (NPs) with average crystallite sizes (d, determined by the Williamson-Hall method) ranging from 100 to 45 nm. The magnetic studies (based on a superconducting quantum interference device) and simple analyses (based on Banerjee's criteria) prove the magnetic-phase transformation from the first-order to the second-order, which takes place at a threshold value of d located in the range 60-70 nm. Compared with the as-prepared LCMO sample (a first-order magnetic phase transition), though the d decrease reduces the values of the T<SUB>C</SUB>, magnetization, magnetic-entropy change, and refrigerant capacity, but the width of the magnetic phase transition is increased remarkably. This widens the working range of LCMO NPs in magnetic refrigeration applications. We believe that the presence of surface-related effects, lattice strain, and distortions leads to Mn<SUP>3+</SUP>-Mn<SUP>4+</SUP> ferromagnetic interactions in LCMO NPs weaker than that in the as-prepared sample.</P>