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RISS 인기검색어
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- 저자 : Kunder, Andrea (검색결과 4 건)
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THE RR LYRAE VARIABLES AND HORIZONTAL BRANCH OF NGC 6656 (M22)<sup>,</sup>
Kunder, Andrea,Stetson, Peter B.,Cassisi, Santi,Layden, Andrew,Bono, Giuseppe,Catelan, Má,rcio,Walker, Alistair R.,Paredes Alvarez, Leonardo,Clem, James L.,Matsunaga, Noriyuki,Salaris, Maurizio American Institute of Physics 2013 The Astronomical journal Vol.146 No.5
<P>The first calibrated broadband UBVI time-series photometry is presented for the RR Lyrae variable stars in NGC 6656 (M22), with observations spanning a range of 22 years. We have also redetermined the variability types and periods for the RR Lyrae stars identified previously by photographic observations, revising the number of fundamental-mode RR Lyrae variables (RR0) to 10 and the number of first-overtone variables (RR1) to 16. The mean periods of the RR0 and RR1 variables are ⟨P⟩<SUB>RR0</SUB> = 0.66 ± 0.02 days and ⟨P⟩<SUB>RR1</SUB> = 0.33 ± 0.01 days, respectively, supporting an Oosterhoff II classification for the cluster. The number ratio of RR1-type to all RR-type variables is N<SUB>1</SUB>/N<SUB>RR</SUB> = 0.61, also consistent with an Oosterhoff II designation. Both the RR Lyrae stars' minimum light colors and the blue edge of the RR Lyrae instability strip suggest E( B – – V) = 0.36 ± 0.02 mag toward M22. Regarding the HB morphology of M22, we find (B-R)/(B+V+R) = +0.97 ± 0.1 and at least one 'gap' located in an unusual part of the blue HB, in the middle of the so-called hot HB stars.</P>
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Evaluation of Acute and Chronic Effects of D-Galactose on Memory and Learning in Wistar Rats
Bharti Chogtu,Avinash Arivazhahan,Sushil Kiran Kunder,Amod Tilak,Ravi Sori,Amruta Tripathy 대한정신약물학회 2018 CLINICAL PSYCHOPHARMACOLOGY AND NEUROSCIENCE Vol.16 No.2
Objective: D-galactose has been commonly used in rodent models to induce accelerated effects of aging, including those on learning, memory, and muscular tone and coordination. This is normally seen on chronic administration of D-galactose. However, there is minimal suggestive evidence on the short-term effects of the same. The aim of the study was to study the acute and chronic effects of D-galactose on learning and memory in Wistar rats. Methods: Twenty four male Wistar rats were randomly assigned to the control, standard (rivastigmine), oral D-galactose (200 mg/kg/day) and subcutaneous D-galactose (200 mg/kg/day) for a total duration of 8 weeks. Effects on learning and memory were assessed at 2 weeks, 4 weeks and 8 weeks by Morris water maze model and passive avoidance testing. Results: Both oral and subcutaneous D-galactose showed positive effects on learning and memory on acute dosing, whereas this beneficial effect was lost during chronic dosing. Conclusion: Short-term administration of D-galactose showed positive effects, while long-term administration nullified these effects.
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Nemec, J. M.,Smolec, R.,Benkő,, J. M.,Moskalik, P.,Kolenberg, K.,Szabó,, R.,Kurtz, D. W.,Bryson, S.,Guggenberger, E.,Chadid, M.,Jeon, Y.‐,B.,Kunder, A.,Layden, A. C.,Kinemuchi, K.,Kis Blackwell Publishing Ltd 2011 Monthly notices of the Royal Astronomical Society Vol.417 No.2
<P><B>ABSTRACT</B></P><P>Nineteen of the ∼40 RR Lyr stars in the <I>Kepler</I> field have been identified as candidate non‐Blazhko (or unmodulated) stars. In this paper we present the results of Fourier decomposition of the time‐series photometry of these stars acquired during the first 417 d of operation (Q0–Q5) of the <I>Kepler</I> telescope. Fourier parameters based on ∼18 400 long‐cadence observations per star (and ∼150 000 short‐cadence observations for FN Lyr and for AW Dra) are derived. None of the stars shows the recently discovered ‘period‐doubling’ effect seen in Blazhko variables; however, KIC 7021124 has been found to pulsate simultaneously in the fundamental and second overtone modes with a period ratio <I>P</I><SUB>2</SUB>/<I>P</I><SUB>0</SUB>∼ 0.593 05 and is similar to the double‐mode star V350 Lyr. Period change rates are derived from O − C diagrams spanning, in some cases, over 100 years; these are compared with high‐precision periods derived from the <I>Kepler</I> data alone. Extant Fourier correlations by Kovács, Jurcsik et al. (with minor transformations from the <I>V</I> to the <I>Kp</I> passband) have been used to derive underlying physical characteristics for all the stars. This procedure seems to be validated through comparisons of the <I>Kepler</I> variables with Galactic and Large Magellanic Cloud (LMC) RR Lyr stars. The most metal‐poor star in the sample is NR Lyr, with [Fe/H] =−2.3 dex; and the four most metal‐rich stars have [Fe/H] ranging from −0.6 to +0.1 dex. Pulsational luminosities and masses are found to be systematically smaller than <I>L</I> and <IMG src='/wiley-blackwell_img/equation/MNR_19317_mu1.gif' alt ='inline image'/> values derived from stellar evolution models, and are favoured over the evolutionary values when periods are computed with the Warsaw linear hydrodynamics code. Finally, the Fourier parameters are compared with theoretical values derived using the Warsaw non‐linear convective pulsation code.</P>
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VARIABLE STARS IN LARGE MAGELLANIC CLOUD GLOBULAR CLUSTERS. III. RETICULUM
Kuehn, Charles A.,Dame, Kyra,Smith, Horace A.,Catelan, Má,rcio,Jeon, Young-Beom,Nemec, James M.,Walker, Alistair R.,Kunder, Andrea,Pritzl, Barton J.,De Lee, Nathan,Borissova, Jura American Institute of Physics 2013 The Astronomical journal Vol.145 No.6
<P>This is the third in a series of papers studying the variable stars in old globular clusters in the Large Magellanic Cloud. The primary goal of this series is to look at how the characteristics and behavior of RR Lyrae stars in Oosterhoff-intermediate systems compare to those of their counterparts in Oosterhoff-I/II systems. In this paper we present the results of our new time-series BVI photometric study of the globular cluster Reticulum. We found a total of 32 variables stars (22 RRab, 4 RRc, and 6 RRd stars) in our field of view. We present photometric parameters and light curves for these stars. We also present physical properties, derived from Fourier analysis of light curves, for some of the RR Lyrae stars. We discuss the Oosterhoff classification of Reticulum and use our results to re-derive the distance modulus and age of the cluster.</P>
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