References of "Ostensen, Roy H"
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See detailA compact system of small planets around a former red giant star
Charpinet, Stéphane; Fontaine, Gilles; Brassard, Pierre et al

in Nature (2011), 480

Planets that orbit their parent star at less than about one astronomical unit (1AU is the Earth-Sun distance) are expected to be engulfed when the star becomes a red giant. Previous observations have ... [more ▼]

Planets that orbit their parent star at less than about one astronomical unit (1AU is the Earth-Sun distance) are expected to be engulfed when the star becomes a red giant. Previous observations have revealed the existence of post-red-giant host stars with giant planets orbiting as close as 0.116AU or with brown dwarf companions in tight orbits, showing that these bodies can survive engulfment. What has remained unclear is whether planets can be dragged deeper into the red-giant envelope without being disrupted and whether the evolution of the parent star itself could be affected. Here we report the presence of two nearly Earth-sized bodies orbiting the post-red-giant, hot B subdwarf star KIC 05807616 at distances of 0.0060 and 0.0076AU, with orbital periods of 5.7625 and 8.2293 hours, respectively. These bodies probably survived deep immersion in the former red-giant envelope. They may be the dense cores of evaporated giant planets that were transported closer to the star during the engulfment and triggered the mass loss necessary for the formation of the hot B subdwarf, which might also explain how some stars of this type did not form in binary systems. [less ▲]

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See detailDeep asteroseismic sounding of the compact hot B subdwarf pulsator KIC02697388 from Kepler time series photometry
Charpinet, Stéphane; Van Grootel, Valérie ULg; Fontaine, Gilles et al

in Astronomy and Astrophysics (2011), 530

Context. Contemporary high precision photometry from space provided by the Kepler and CoRoT satellites generates significant breakthroughs in terms of exploiting the long-period, g-mode pulsating hot B ... [more ▼]

Context. Contemporary high precision photometry from space provided by the Kepler and CoRoT satellites generates significant breakthroughs in terms of exploiting the long-period, g-mode pulsating hot B subdwarf (sdBVs) stars with asteroseismology. Aims: We present a detailed asteroseismic study of the sdBVs star KIC02697388 monitored with Kepler, using the rich pulsation spectrum uncovered during the ~27-day-long exploratory run Q2.3. Methods: We analyse new high-S/N spectroscopy of KIC02697388 using appropriate NLTE model atmospheres to provide accurate atmospheric parameters for this star. We also reanalyse the Kepler light curve using standard prewhitening techniques. On this basis, we apply a forward modelling technique using our latest generation of sdB models. The simultaneous match of the independent periods observed in KIC02697388 with those of models leads objectively to the identification of the pulsation modes and, more importantly, to the determination of some of the parameters of the star. Results: The light curve analysis reveals 43 independent frequencies that can be associated with oscillation modes. All the modulations observed in this star correspond to g-mode pulsations except one high-frequency signal, which is typical of a p-mode oscillation. Although the presence of this p-mode is surprising considering the atmospheric parameters that we derive for this cool sdB star (Teff = 25 395 ± 227 K, log g = 5.500 ± 0.031 (cgs), and log N(He) /N(H) = -2.767 ± 0.122), we show that this mode can be accounted for particularly well by our optimal seismic models, both in terms of frequency match and nonadiabatic properties. The seismic analysis leads us to identify two model solutions that can both account for the observed pulsation properties of KIC02697388. Despite this remaining ambiguity, several key parameters of the star can be derived with stringent constraints, such as its mass, its H-rich envelope mass, its radius, and its luminosity. We derive the properties of the core proposing that it is a relatively young sdB star that has burnt less than ~34% (in mass) of its central helium and has a relatively large mixed He/C/O core. This latter measurement is in line with the trend already uncovered for two other g-mode sdB pulsators analysed with asteroseismology and suggests that extra mixing is occurring quite early in the evolution of He cores on the horizontal branch. Conclusions: Additional monitoring with Kepler of this particularly interesting sdB star should reveal the inner properties of KIC02697388 and provide important information about the mode driving mechanism and the helium core properties. [less ▲]

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See detailEXOTIME: searching for planets around pulsating subdwarf B stars
Schuh, Sonja; Silvotti, Roberto; Lutz, Ronny et al

in Astrophysics & Space Science (2010, October), 329

In 2007, a companion with planetary mass was found around the pulsating subdwarf B star V391 Pegasi with the timing method, indicating that a previously undis- covered population of substellar companions ... [more ▼]

In 2007, a companion with planetary mass was found around the pulsating subdwarf B star V391 Pegasi with the timing method, indicating that a previously undis- covered population of substellar companions to apparently single subdwarf B stars might exist. Following this serendip- itous discovery, the EXOTIME (http://www.na.astro.it/ ~silvotti/exotime/) monitoring program has been set up to follow the pulsations of a number of selected rapidly pul- sating subdwarf B stars on time scales of several years with two immediate observational goals: (1) determine P ̇ of the pulsational periods P (2) search for signatures of substellar companions in O– C residuals due to periodic light travel time variations, which would be tracking the central star’s companion- induced wobble around the centre of mass These sets of data should therefore, at the same time, on the one hand be useful to provide extra constraints for classical asteroseismological exercises from the P ̇ (comparison with “local” evolutionary models), and on the other hand allow one to investigate the preceding evolution of a target in terms of possible “binary” evolution by extending the otherwise unsuccessful search for companions to potentially very low masses. While timing pulsations may be an observationally ex- pensive method to search for companions, it samples a dif- ferent range of orbital parameters, inaccessible through or- bital photometric effects or the radial velocity method: the latter favours massive close-in companions, whereas the timing method becomes increasingly more sensitive toward wider separations. In this paper we report on the status of the on-going ob- servations and coherence analysis for two of the currently five targets, revealing very well-behaved pulsational charac- teristics in HS 0444+0458, while showing HS 0702+6043 to be more complex than previously thought. [less ▲]

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See detailEarly asteroseismic results from Kepler: structural and core parameters of the hot B subdwarf KPD 1943+4058 as inferred from g-mode oscillations
Van Grootel, Valérie ULg; Charpinet, Stéphane; Fontaine, Gilles et al

in Astrophysical Journal Letters (2010), 718

We present a seismic analysis of the pulsating hot B subdwarf KPD 1943+4058 (KIC 005807616) on the basis of the long-period, gravity-mode pulsations recently uncovered by Kepler. This is the first time ... [more ▼]

We present a seismic analysis of the pulsating hot B subdwarf KPD 1943+4058 (KIC 005807616) on the basis of the long-period, gravity-mode pulsations recently uncovered by Kepler. This is the first time that g-mode seismology can be exploited quantitatively for stars on the extreme horizontal branch, all previous successful seismic analyses having been confined so far to short-period, p-mode pulsators. We demonstrate that current models of hot B subdwarfs can quite well explain the observed g-mode periods, while being consistent with independent constraints provided by spectroscopy. We identify the 18 pulsations retained in our analysis as low- degree (l = 1 and 2), intermediate-order (k = −9 through −58) g-modes. The periods (frequencies) are recovered, on average, at the 0.22% level, which is comparable to the best results obtained for p-mode pulsators. We infer the following structural and core parameters for KPD 1943+4058 (formal fitting uncertainties only): Teff = 28,050 ± 470 K, log g = 5.52 ± 0.03, M∗ = 0.496 ± 0.002 M⊙, log (Menv/M∗) = −2.55 ± 0.07, log (1 − Mcore/M∗) = −0.37 ± 0.01, and Xcore (C+O) = 0.261 ± 0.008. We additionally derive the age of the star since the zero-age extended horizontal branch 18.4 ± 1.0 Myr, the radius R = 0.203 ± 0.007 R⊙, the luminosity L = 22.9 ± 3.13 L⊙, the absolute magnitude MV = 4.21 ± 0.11, the reddening index E(B − V ) = 0.094 ± 0.017, and the distance d = 1180 ± 95 pc. [less ▲]

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