Yazar "Handler, G." seçeneğine göre listele
Listeleniyor 1 - 5 / 5
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Multimode pulsations of the lambda bootis star 29 Cygni: The 1995 and 1996 multisite campaigns(Univ Chicago Press, 2007) Mkrtichian, D. E.; Kusakin, A. V.; De Coca, P. Lopez; Krisciunas, K.; Akan, C.; Malanushenko, V. P.; Paparo, M.; Percy, J.; Rolland, A.; Costa, V.; Olivares, J. I.; Koval, V. A.; Hobart, M. A.; Ibanoglu, C.; Ozturk, A.; Thompson, S.; Paunzen, E.; Handler, G.; Burnashev, V.; Weiss, W. W.; Kuratov, K. S.; Kang, Y. W.In this paper we present the results of multisite photometric and spectroscopic campaigns, carried out during the years 1995 and 1996, to study the pulsations of a typical lambda Bootis star, 29 Cyg. During the 1995 campaign we found well-defined multiperiodicity in 29 Cyg, which was studied in detail during a multilongitude campaign covering a 65 day time interval in 1996. The frequency analysis of the 1996 campaign's data easily revealed 11 excited low l degree modes with frequencies of oscillation ranging from 20.3 to 37.4 cycles day(-1) and mean photometric amplitudes ranging from 10.65 to 0.96 mmag in the V filter. After removing the well-identified frequencies, the discrete Fourier transform of the residuals showed excess power in the 20-40 cycle day(-1) domain, which indicates the probable existence of unresolved rich p-mode spectra with photometric V amplitudes below 0.5 mmag. We found a regular spacing of 2.41 cycles day(-1) within the modes of 29 Cyg, which was interpreted as the spacing of consecutive even and odd l-values. The asteroseismic luminosity log L/L-circle dot = 1.12, calculated from the frequency spacing, is in good agreement with the Hipparcos luminosity log L/L-circle dot = 1.16 and with luminosities from photometric and spectroscopic calibrations. Using our multicolor photometry we tentatively identified the dominant f(1) 37.425 cycle day(-1) mode as an l = 2, n = 5mode, and made radial overtone identification for all frequencies. These ranged from n 2 to 5. Analysis of the photometric data shows the long-term ( years) and probable short-term ( days) variability of amplitudes for all of these modes in 29 Cyg. Using our multicolor WBVR filter photometry, we found the wavelength dependence of the pulsation amplitudes for the five highest amplitude modes. Based on the H alpha line radial velocity observations of 29 Cyg, we detected multiperiodic radial velocity variations with frequencies of 38.36 and 29.99 cycles day(-1) and semiamplitudes of 1.0 and 0.8 km s(-1), respectively. These frequencies coincide within the errors with the photometric frequencies of the two highest amplitude modes, 37.425 and 29.775 cycles day(-1). For the highest amplitude l = 2, n= 5 mode ( 37.425 cycles day(-1)), the radial velocity-to-light amplitude ratio and velocity-to-light phase shift are equal to 2K(H alpha)/Delta V 94 km mag(-1) s(-1) and Phi(f1) = phi(Vr) - phi V = +0: 08 +/- 0.01, respectively, and are in good agreement with values for delta Scuti stars. The rich multiperiodic spectrum makes 29 Cyg a promising target for future multisite campaigns.Öğe Photometric multi-site campaign on massive B stars in the open cluster chi Persei (NGC 884)(Iop Publishing Ltd, 2008) Saesen, S.; Pigulski, A.; Carrier, F.; De Ridder, J.; Aerts, C.; Handler, G.; Narwid, A.; Fu, J. N.; Zhang, C.; Jiang, X. J.; Kopacki, G.; Vanautgaerden, J.; Steslicki, M.; Acke, B.; Poretti, E.; Uytterhoeven, K.; De Meester, W.; Reed, M. D.; Kolaczkowski, Z.; Michalska, G.; Schmidt, E.; Ostensen, R.; Gielen, C.; Yakut, K.; Leitner, A.; Kalomeni, B.; Prins, S.; Van Helshoecht, V.; Zima, W.; Huygen, R.; Vandenbussche, B.; Lenz, P.; Ladjal, D.; Antolin, E. Puga; Verhoelst, T.; Niarchos, P.; Liakos, A.; Lorenz, D.; Dehaes, S.; Reyniers, M.; Davignon, G.; Kim, S-L; Kim, D. H.; Lee, Y-J; Lee, C-U; Kwon, J-H; Broeders, E.; Van Winckel, H.; Vanhollebeke, E.; Raskin, G.; Blom, Y.; Eggen, J. R.; Beck, P.; Puschnig, J.; Schmitt, L.; Gelven, G. A.; Steiniger, B.; Drummond, R.; Gizon, L; Roth, MIn 2005 a photometric observation campaign started on the open cluster chi Persei, involving 13 telescopes spread over the whole northern hemisphere. After two years we gathered almost 1200 hours of data. We present here preliminary results on the variability search, especially from the 60-cm telescope in Bialkow (Poland), which show seven confirmed beta Cephei stars, four candidate B-type pulsators and other interesting variable stars.Öğe Photometric multi-site campaign on the open cluster NGC 884 I. Detection of the variable stars(Edp Sciences S A, 2010) Saesen, S.; Carrier, F.; Pigulski, A.; Aerts, C.; Handler, G.; Narwid, A.; Fu, J. N.; Zhang, C.; Jiang, X. J.; Vanautgaerden, J.; Kopacki, G.; Steslicki, M.; Acke, B.; Poretti, E.; Uytterhoeven, K.; Gielen, C.; Ostensen, R.; De Meester, W.; Reed, M. D.; Kolaczkowski, Z.; Michalska, G.; Schmidt, E.; Yakut, K.; Leitner, A.; Kalomeni, B.; Cherix, M.; Spano, M.; Prins, S.; Van Helshoecht, V.; Zima, W.; Huygen, R.; Vandenbussche, B.; Lenz, P.; Ladjal, D.; Antolin, E. Puga; Verhoelst, T.; De Ridder, J.; Niarchos, P.; Liakos, A.; Lorenz, D.; Dehaes, S.; Reyniers, M.; Davignon, G.; Kim, S. -L.; Kim, D. H.; Lee, Y. -J.; Lee, C. -U.; Kwon, J. -H.; Broeders, E.; Van Winckel, H.; Vanhollebeke, E.; Waelkens, C.; Raskin, G.; Blom, Y.; Eggen, J. R.; Degroote, P.; Beck, P.; Puschnig, J.; Schmitzberger, L.; Gelven, G. A.; Steininger, B.; Blommaert, J.; Drummond, R.; Briquet, M.; Debosscher, J.Context. Recent progress in the seismic interpretation of field beta Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. Aims. To improve our comprehension of the beta Cep stars, we studied the young open cluster NGC 884 to discover new B- type pulsators, besides the two known beta Cep stars, and other variable stars. Methods. An extensive multi-site campaign was set up to gather accurate CCD photometry time series in four filters (U, B, V, I) of a field of NGC 884. Fifteen different instruments collected almost 77 500 CCD images in 1286 h. The images were calibrated and reduced to transform the CCD frames into interpretable differential light curves. Various variability indicators and frequency analyses were applied to detect variable stars in the field. Absolute photometry was taken to deduce some general cluster and stellar properties. Results. We achieved an accuracy for the brightest stars of 5.7 mmag in V, 6.9 mmag in B, 5.0 mmag in I and 5.3 mmag in U. The noise level in the amplitude spectra is 50 mu mag in the V band. Our campaign confirms the previously known pulsators, and we report more than one hundred new multi- and mono- periodic B-, A- and F-type stars. Their interpretation in terms of classical instability domains is not straightforward, pointing to imperfections in theoretical instability computations. In addition, we have discovered six new eclipsing binaries and four candidates as well as other irregular variable stars in the observed field.Öğe The pulsation modes of the pre-white dwarf PG 1159-035(Edp Sciences S A, 2008) Costa, J. E. S.; Kepler, S. O.; Winget, D. E.; O'Brien, M. S.; Kawaler, S. D.; Costa, A. F. M.; Giovannini, O.; Kanaan, A.; Mukadam, A. S.; Mullally, F.; Nitta, A.; Provencal, J. L.; Shipman, H.; Wood, M. A.; Ahrens, T. J.; Grauer, A.; Kilic, M.; Bradley, P. A.; Sekiguchi, K.; Crowe, R.; Jiang, X. J.; Sullivan, D.; Sullivan, T.; Rosen, R.; Clemens, J. C.; Janulis, R.; O'Donoghue, D.; Ogloza, W.; Baran, A.; Silvotti, R.; Marinoni, S.; Vauclair, G.; Dolez, N.; Chevreton, M.; Dreizler, S.; Schuh, S.; Deetjen, J.; Nagel, T.; Solheim, J. -E.; Gonzalez Perez, J. M.; Ulla, A.; Barstow, M.; Burleigh, M.; Good, S.; Metcalfe, T. S.; Kim, S. -L.; Lee, H.; Sergeev, A.; Akan, M. C.; Cakirli, O.; Paparo, M.; Viraghalmy, G.; Ashoka, B. N.; Handler, G.; Huerkal, O.; Johannessen, F.; Kleinman, S. J.; Kalytis, R.; Krzesinski, J.; Klumpe, E.; Larrison, J.; Lawrence, T.; Meistas, E.; Martinez, P.; Nather, R. E.; Fu, J. -N.; Pakstiene, E.; Rosen, R.; Romero-Colmenero, E.; Riddle, R.; Seetha, S.; Silvestri, N. M.; Vuckovic, M.; Warner, B.; Zolao, S.; Althaus, L. G.; Corsico, A. H.; Montgomery, M. H.Context. PG 1159-035, a pre-white dwarf with T-eff similar or equal to 140000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters. Methods. We used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods. Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M-circle dot = 0.59 +/- 0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r(c)/R-*, = 0.83 +/- 0.05. From the multiplet splitting, we calculated the rotational period P-rot = 1.3920 +/- 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for l = 1 modes and less than 50% for l = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.Öğe Towards ensemble asteroseismology of the young open clusters chi Persei and NGC 6910(Wiley-V C H Verlag Gmbh, 2010) Saesen, S.; Pigulski, A.; Carrier, F.; Michalska, G.; Aerts, C.; De Ridder, J.; Briquet, M.; Handler, G.; Kolaczkowski, Z.; Acke, B.; Bauwens, E.; Beck, P. G.; Blom, Y.; Blommaert, J.; Broeders, E.; Cherix, M.; Davignon, G.; Debosscher, J.; Degroote, P.; Decin, L.; Dehaes, S.; De Meester, W.; Deroo, P.; Desmet, M.; Drummond, R.; Eggen, J. R.; Fu, J.; Gazeas, K.; Gelven, G. A.; Gielen, C.; Huygen, R.; Jiang, X.; Kalomeni, B.; Kim, S. -L.; Kim, D. H.; Kopacki, G.; Kwon, J. -H.; Ladjal, D.; Lee, C. -U.; Lee, Y. -J.; Lefever, K.; Leitner, A.; Lenz, P.; Liakos, A.; Lorenz, D.; Narwid, A.; Niarchos, P.; Ostensen, R.; Poretti, E.; Prins, S.; Provencal, J.; Antolin, E. Puga; Puschnig, J.; Raskin, G.; Reed, M. D.; Reyniers, M.; Schmidt, E.; Schmitzberger, L.; Spano, M.; Steininger, B.; Steslicki, M.; Uytterhoeven, K.; Vanautgaerden, J.; Vandenbussche, B.; Van Helshoecht, V.; Vanhollebeke, E.; Van Winckel, H.; Verhoelst, T.; Vuckovic, M.; Waelkens, C.; Wolf, G. W.; Yakut, K.; Zhang, C.; Zima, W.As a result of the variability survey in chi Persei and NGC 6910, the number of beta Cep stars that are members of these two open clusters is increased to twenty stars, nine in NGC 6910 and eleven in chi Persei. We compare pulsational properties, in particular the frequency spectra, of beta Cep stars in both clusters and explain the differences in terms of the global parameters of the clusters. We also indicate that the more complicated pattern of the variability among B-type stars in chi Persei is very likely caused by higher rotational velocities of stars in this cluster. We conclude that the sample of pulsating stars in the two open clusters constitutes a very good starting point for the ensemble asteroseismology of beta Cep-type stars and maybe also for other B-type pulsators. (C) 2010 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim
