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- 저자 : Østensen, Roy H. (검색결과 2 건)
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Silvotti, R.,Schuh, S.,Kim, S.-L.,Lutz, R.,Reed, M.,Benatti, S.,Janulis, R.,Lanteri, L.,Østensen, R.,Marsh, T. R.,Dhillon, V. S.,Paparo, M.,Molnar, L. Springer-Verlag 2018 Astronomy and astrophysics Vol.611 No.-
<P>V391 Peg (alias HS 2201+2610) is a subdwarf B (sdB) pulsating star that shows both <I>p</I>- and <I>g</I>-modes. By studying the arrival times of the <I>p</I>-mode maxima and minima through the O-C method, in a previous article the presence of a planet was inferred with an orbital period of 3.2 years and a minimum mass of 3.2 <I>M</I>Jup. Here we present an updated O-C analysis using a larger data set of 1066 h of photometric time series (~2.5× larger in terms of the number of data points), which covers the period between 1999 and 2012 (compared with 1999-2006 of the previous analysis). Up to the end of 2008, the new O-C diagram of the main pulsation frequency (<I>f</I>1) is compatible with (and improves) the previous two-component solution representing the long-term variation of the pulsation period (parabolic component) and the giant planet (sine wave component). Since 2009, the O-C trend of <I>f</I>1 changes, and the time derivative of the pulsation period (<I>p</I><SUP>.</SUP>) passes from positive to negative; the reason of this change of regime is not clear and could be related to nonlinear interactions between different pulsation modes. With the new data, the O-C diagram of the secondary pulsation frequency (<I>f</I>2) continues to show two components (parabola and sine wave), like in the previous analysis. Various solutions are proposed to fit the O-C diagrams of <I>f</I>1 and <I>f</I>2, but in all of them, the sinusoidal components of <I>f</I>1 and <I>f</I>2 differ or at least agree less well than before. The nice agreement found previously was a coincidence due to various small effects that are carefully analyzed. Now, with a larger dataset, the presence of a planet is more uncertain and would require confirmation with an independent method. The new data allow us to improve the measurement of <I>p</I><SUP>.</SUP> for <I>f</I>1 and <I>f</I>2: using only the data up to the end of 2008, we obtain <I>p</I><SUP>.</SUP>1 = (1.34 ± 0.04) × 10<SUP>−12</SUP> and <I>p</I><SUP>.</SUP>2 = (1.62 ± 0.22) × 10<SUP>−12</SUP>. The long-term variation of the two main pulsation periods (and the change of sign of <I>p</I><SUP>.</SUP>1) is visible also in direct measurements made over several years. The absence of peaks near <I>f</I>1 in the Fourier transform and the secondary peak close to <I>f</I>2 confirm a previous identification as <I>l</I> = 0 and <I>l</I> = 1, respectively, and suggest a stellar rotation period of about 40 days. The new data allow constraining the main <I>g</I>-mode pulsation periods of the star.</P>
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EXOTIME: searching for planets around pulsating subdwarf B stars
Schuh, Sonja,Silvotti, Roberto,Lutz, Ronny,Loeptien, Bjö,rn,Green, Elizabeth M.,Østensen, Roy H.,Leccia, Silvio,Kim, Seung-Lee,Fontaine, Gilles,Charpinet, Sté,phane,Francœur, Myriam,Randall, Springer-Verlag 2010 Astrophysics and space science Vol. No.
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