[en] 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.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Charpinet, Stéphane; Institut de Recherche en Astrophysique et Planétologie (IRAP)
Fontaine, Gilles; Université de Montréal - UdeM > Département de Physique
Brassard, Pierre; Université de Montréal - UdeM > Département de Physique
Green, Elizabeth M.; University of Arizona
Van Grootel, Valérie ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique stellaire théorique et astérosismologie
Randall, Suzanna K.; European Southern Observatory (ESO)
Silvotti, Roberto; INAF-Osservatorio Astronomico di Torino
Baran, Andrzej; Mt. Suhora Observatory
Ostensen, Roy H.; Katholieke Universiteit Leuven - KUL > Instituut voor Sterrenkunde
Kawaler, Steve D.; Iowa State University
Telting, John H.; Nordic Optical Telescope
Language :
English
Title :
A compact system of small planets around a former red giant star
Publication date :
22 December 2011
Journal title :
Nature
ISSN :
0028-0836
eISSN :
1476-4687
Publisher :
Nature Publishing Group, Basingstoke, United Kingdom
Udry, S. & Santos, N. C. Statistical properties of exoplanets. Annu. Rev. Astron. Astrophys. 45, 397-439 (2007).
Setiawan, J. et al. A giant planet around a metal-poor star of extragalactic origin. Science 330, 1642-1644 (2010).
Silvotti, R. et al. A giant planet orbiting the 'extreme horizontal branch' star V391 Pegasi. Nature 449, 189-191 (2007). (Pubitemid 47402374)
Lee, J. W. et al. The sdB1M eclipsing system HW Virginis and its circumbinary planets. Astron. J. 137, 3181-3190 (2009).
Maxted, P. F. L., Napiwotzki, R., Dobbie, P. D. & Burleigh, M. R. Survival of a brown dwarf after engulfment by a red giant star. Nature 442, 543-545 (2006). (Pubitemid 44167909)
Geier, S. et al. Binaries discovered by the MUCHFUSS project: SDSS J0820510008-aneclipsing subdwarfBbinary witha brown dwarf companion. Astrophys. J. 731, L22-L26 (2011).
D'Cruz, N. L., Dorman, B., Rood, R. T. & O'Connell, R. W. The origin of extreme horizontal branch stars. Astrophys. J. 466, 359-371 (1996).
Heber, U. Hot subdwarf stars. Annu. Rev. Astron. Astrophys. 47, 211-251 (2009).
Soker, N. Can planets influence the horizontal branch morphology? Astron. J. 116, 1308-1313 (1998).
Gilliland, R. L. et al. Kepler asteroseismology program: introduction and first results. Publ. Astron. Soc. Pacif. 122, 131-143 (2010).
Østensen, R. H. et al. First Kepler results on compact pulsators-I. Survey target selection and the first pulsators. Mon. Not. R. Astron. Soc. 409, 1470-1486 (2010).
Reed, M. D. et al. First Kepler results on compact pulsators-III. Subdwarf B stars withV1093Her and hybrid(DWLyn)type pulsations. Mon. Not. R. Astron. Soc. 409, 1496-1508 (2010).
Green, E. M. et al. Discovery of a new class of pulsating stars: gravity-mode pulsators among subdwarf B stars. Astrophys. J. 583, L31-L34 (2003). (Pubitemid 37394398)
Charpinet, S. et al. Progress in sounding the interior of pulsating hot subdwarf stars. AIP Conf. Proc. 1170, 585-596 (2009).
Van Grootel, V. et al. Early asteroseismic results from Kepler: structural and core parameters of the hot B subdwarf KPD 194314058 as inferred from g-mode oscillations. Astrophys. J. 718, L97-L101 (2010).
Knutson, H. A. et al. A map of the day-night contrast of the extrasolar planet HD 189733b. Nature 447, 183-186 (2007). (Pubitemid 46763083)
Snellen, I. A. G., Mooij, E. J. W. & Albrecht, S. The changing phases of extrasolar planet CoRoT-1b. Nature 459, 543-545 (2009).
Leigh, C. et al. A new upper limit onthe reflected starlight from t Bootisb. Mon. Not. R. Astron. Soc. 344, 1271-1282 (2003). (Pubitemid 37316664)
Rowe, J. F. et al. The very low albedo of an extrasolar planet: MOST space-based photometry of HD209458. Astrophys. J. 689, 1345-1353 (2008).
Mallama, A. Characterization of terrestrial exoplanets based on the phase curves and albedos of Mercury, Venus and Mars. Icarus 204, 11-14 (2009).
Wolszczan, A. & Frail, D. A. A planetary system around the millisecond pulsar PSR1257 1 12. Nature 355, 145-147 (1992).
Villaver, E. & Livio, M. The orbital evolution of gas giant planets around giant stars. Astrophys. J. 705, L81-L85 (2009).
Han, Z. et al. The origin ofsubdwarfB stars-I. The formation channels. Mon. Not. R. Astron. Soc. 336, 449-466 (2002).
Maxted, P. F. L. et al. The binary fraction of extreme horizontal branch stars. Mon. Not. R. Astron. Soc. 326, 1391-1402 (2001). (Pubitemid 33620904)
Bear, E. &Soker, N. Connectingplanetsaroundhorizontalbranch starswithknown exoplanets. Mon. Not. R. Astron. Soc. 411, 1792-1802 (2011).
Nordhaus, J. et al. Tides and tidal engulfment in post-main-sequence binaries: period gapsfor planetsandbrowndwarfs aroundwhitedwarfs. Mon. Not. R. Astron. Soc. 408, 631-641 (2010).
Hébrard, G., Lecavelier Des Étangs, A., Vidal-Madjar, A., Désert, J.-M. & Ferlet, R. Evaporation rate of hot Jupiters and formation of chthonian planets. ASP Conf. Proc. 321, 203-204 (2004).
Silvotti, R. The subdwarfB1giantplanet systemV391 Peg:Different scenariosfor its previous evolution. ASP Conf. Ser. 392, 215-219 (2008).
Léger, A. et al. Transiting exoplanets from the CoRoT spacemission. VIII. CoRoT-7b: the first super-Earth with measured radius. Astron. Astrophys. 506, 287-302 (2009).
Batalha, N. M. et al. Kepler's first rocky planet: Kepler-10b. Astrophys. J. 729, 27-47 (2011).
