Yazar "Paparo, M." seçeneğine göre listele

Listeleniyor 1 - 3 / 3
  • Küçük Resim Yok
    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.
  • Küçük Resim Yok
    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.
  • Küçük Resim Yok
    Öğe
    Whole Earth Telescope observations of the subdwarf B star KPD 1930+2752: a rich, short-period pulsator in a close binary
    (Oxford Univ Press, 2011) Reed, M. D.; Harms, S. L.; Poindexter, S.; Zhou, A. -Y.; Eggen, J. R.; Morris, M. A.; Quint, A. C.; McDaniel, S.; Baran, A.; Dolez, N.; Kawaler, S. D.; Kurtz, D. W.; Moskalik, P.; Riddle, R.; Zola, S.; Ostensen, R. H.; Solheim, J. -E.; Kepler, S. O.; Costa, A. F. M.; Provencal, J. L.; Mullally, F.; Winget, D. W.; Vuckovic, M.; Crowe, R.; Terry, D.; Avila, R.; Berkey, B.; Stewart, S.; Bodnarik, J.; Bolton, D.; Binder, P. -M.; Sekiguchi, K.; Sullivan, D. J.; Kim, S. -L.; Chen, W. -P.; Chen, C. -W.; Lin, H. -C.; Jian, X. -J.; Wu, H.; Gou, J. -P.; Liu, Z.; Leibowitz, E.; Lipkin, Y.; Akan, C.; Cakirli, O.; Janulis, R.; Pretorius, R.; Ogloza, W.; Stachowski, G.; Paparo, M.; Szabo, R.; Csubry, Z.; Zsuffa, D.; Silvotti, R.; Marinoni, S.; Bruni, I.; Vauclair, G.; Chevreton, M.; Matthews, J. M.; Cameron, C.; Pablo, H.
    KPD 1930+2752 is a short-period pulsating subdwarf B (sdB) star. It is also an ellipsoidal variable with a known binary period of 2.3 h. The companion is most likely a white dwarf and the total mass of the system is close to the Chandresekhar limit. In this paper, we report the results of Whole Earth Telescope (WET) photometric observations during 2003 and a smaller multisite campaign of 2002. From 355 h of WET data, we detect 68 pulsation frequencies and suggest an additional 13 frequencies within a crowded and complex temporal spectrum between 3065 and 6343 mu Hz (periods between 326 and 157 s). We examine pulsation properties including phase and amplitude stability in an attempt to understand the nature of the pulsation mechanism. We examine a stochastic mechanism by comparing amplitude variations with simulated stochastic data. We also use the binary nature of KPD 1930+2752 for identifying pulsation modes via multiplet structure and a tidally induced pulsation geometry. Our results indicate a complicated pulsation structure that includes short-period (approximate to 16 h) amplitude variability, rotationally split modes, tidally induced modes and some pulsations which are geometrically limited on the sdB star.