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Pushing the ground-based limit : 14-μmag photometric precision with the definitive Whole Earth Telescope asteroseismic data set for the rapidly oscillating Ap star HR 1217

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Pushing the ground-based limit : 14-μmag photometric precision with the definitive Whole Earth Telescope asteroseismic data set for the rapidly oscillating Ap star HR 1217

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Título Pushing the ground-based limit : 14-μmag photometric precision with the definitive Whole Earth Telescope asteroseismic data set for the rapidly oscillating Ap star HR 1217
Autor Kurtz, Donald W.
Cameron, C.
Cunha, Margarida S.
Dolez, Noël
Vauclair, Gérard
Pallier, E.
Ulla, Ana
Kepler, Souza Oliveira
Costa, Alex Fabiano Murillo da
Kanaan Neto, Antonio Nemer
Fraga, Luciano
Giovannini Junior, Odilon
Wood, Matthew A.
Silvestri, Nicole M.
Kawaler, Steven D.
Riddle, Reed L.
Reed, M. D.
Watson, Todd K.
Metcalfe, Travis S.
Mukadam, Anjum Shagufta
Nather, R. Edward
Winget, Donald Earl
Nitta, Atsuko
Kleinman, Scot James
Guzik, Joyce Ann
Bradley, Paul A.
Matthews, Jaymie M.
Sekiguchi, Kazuhiro
Sullivan, Denis J.
Sullivan, Terry
Shobbrook, Robert R.
Jiang, Xiaojun
Birch, P.
Ashoka, B.N.
Seetha, S.
Girish, V.
Joshi, Santosh
Moskalik, Pawel
Zola, Staszek
O'Donoghue, Darragh
Handler, Gerald
Mueller, M.
Gonzalez Perez, Jose Miguel
Solheim, Jan-Eric
Johannessen, F.
Bigot, L.
Abstract HR1217 is one of the best-studied rapidly oscillating Ap (roAp) stars, with a frequency spectrum of alternating even-and odd-l modes that are distorted by the presence of a strong, global magnetic field. Several recent theoretical studies have found that within the observable atmospheres of roAp stars the pulsation modes are magneto-acoustic with significant frequency perturbations that are cyclic with increasing frequency. To test these theories a Whole Earth Telescope extended coverage campaign obtained 342 h of JohnsonBdata at 10-s time resolution for the roAp starHR1217 over 35 d with a 36 per cent duty cycle in 2000 November–December. The precision of the derived amplitudes is 14 μmag, making this one of the highest precision ground-based photometric studies ever undertaken. Substantial support has been found for the new theories of the interaction of pulsation with the strong magnetic field. In particular, the frequency jump expected as the magnetic and acoustic components cycle through 2π rad in phase has been found. Additionally, comparison of the new 2000 data with an earlier 1986 multisite study shows clear amplitude modulation for some modes between 1986 and 2000. The unique geometry of the roAp stars allows their pulsation modes to be viewed from varying aspect with rotation, yielding mode identification information in the rotational sidelobes that is available for no other type of pulsating star. Those rotational sidelobes in HR1217 confirm that two of the modes are dipolar, or close to dipolar; based on the frequency spacings and Hipparcos parallax, three other modes must be either l = 0 or 2 modes, either distorted by the magnetic field, or a mix of m-modes of given l where the mixture is the result of magnetic and rotational effects. A study of all high-speed photometric Johnson B data from 1981 to 2000 gives a rotation period Prot =12.4572d, as found in previous pulsation and photometric studies, but inconsistent with a different rotation period found in magnetic studies. We suggest that this rotation period is correct and that zero-point shifts between magnetic data sets determined from different spectral lines are the probable cause of the controversy over the rotation period. This WET data set is likely to stand as the definitive ground-based study of HR1217. It will be the baseline for comparison for future space studies of HR1217, particularly the MOST satellite observations.
Contido em Monthly notices of the royal astronomical society. Vol. 358, no. 2 (Apr. 2005), p. 651-664
Assunto Asterosismologia
Estrelas magneticas
Fotometria estelar
Pulsacoes estelares
Rotacao estelar
[en] Stars: individual: HR 1217
[en] Stars: magnetic fields
[en] Stars: oscillations
[en] Stars: variables: other
Origem Estrangeiro
Tipo Artigo de periódico
URI http://hdl.handle.net/10183/90268
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