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Post Info TOPIC: HD 181068
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Title: Dynamical masses, absolute radii and 3D orbits of the triply eclipsing star HD 181068 from Kepler photometry
Authors: Tamás Borkovits, Aliz Derekas, László L. Kiss, Amanda Király, Emese Forgács-Dajka, Imre Barna Bíró, Timothy R. Bedding, Stephen T. Bryson, Daniel Huber, Róbert Szabó

HD 181068 is the brighter of the two known triply eclipsing hierarchical triple stars in the Kepler field. It has been continuously observed for more than 2 years with the Kepler space telescope. Of the nine quarters of the data, three have been obtained in short-cadence mode, that is one point per 58.9 s. Here we analyse this unique dataset to determine absolute physical parameters (most importantly the masses and radii) and full orbital configuration using a sophisticated novel approach. We measure eclipse timing variations (ETVs), which are then combined with the single-lined radial velocity measurements to yield masses in a manner equivalent to double-lined spectroscopic binaries. We have also developed a new light curve synthesis code that is used to model the triple, mutual eclipses and the effects of the changing tidal field on the stellar surface and the relativistic Doppler-beaming. By combining the stellar masses from the ETV study with the simultaneous light curve analysis we determine the absolute radii of the three stars. Our results indicate that the close and the wide subsystems revolve in almost exactly coplanar and prograde orbits. The newly determined parameters draw a consistent picture of the system with such details that have been beyond reach before.

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Blobrana


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Light Curve of Triple Star HD 181068

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Title: HD 181068: A Red Giant in a Triply-Eclipsing Compact Hierarchical Triple System
Authors: A. Derekas, L. L. Kiss, T. Borkovits, D. Huber, H. Lehmann, J. Southworth, T. R. Bedding, D. Balam, M. Hartmann, M. Hrudkova, M. J. Ireland, J. Kovacs, Gy. Mezo, A. Moor, E. Niemczura, G. E. Sarty, Gy. M. Szabo, R. Szabo, J.H. Telting, A. Tkachenko, K. Uytterhoeven, J. M. Benko, S. T. Bryson, V. Maestro, A. E. Simon, D. Stello, G. Schaefer, C. Aerts, T. A. ten Brummelaar, P. De Cat, H. A. McAlister, C. Maceroni, A. Merand, M. Still, J. Sturmann, L. Sturmann, N. Turner, P. G. Tuthill, J. Christensen-Dalsgaard, R. L. Gilliland, H. Kjeldsen, E. V. Quintana, P. Tenenbaum, J. D. Twicken

Hierarchical triple systems comprise a close binary and a more distant component. They are important for testing theories of star formation and of stellar evolution in the presence of nearby companions. We obtained 218 days of Kepler photometry of HD 181068 (magnitude of 7.1), supplemented by groundbased spectroscopy and interferometry, which show it to be a hierarchical triple with two types of mutual eclipses. The primary is a red giant that is in a 45-day orbit with a pair of red dwarfs in a close 0.9-day orbit. The red giant shows evidence for tidally-induced oscillations that are driven by the orbital motion of the close pair. HD 181068 is an ideal target for studies of dynamical evolution and testing tidal friction theories in hierarchical triple systems.

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HD 181068 is a triple star system comprising a red giant: HD 181068A and two red dwarfs: HD 181068B and HD 181068C. The system is notable for the unique triply eclipsing variations that are observed as each star passes behind or in front of the others. The primary star HD 181068A is also unusual in that it does not exhibit internal seismic oscillations as have been detected in other red giants. HD 181068A is estimated to be 12.4 times larger than our Sun.
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Kepler star trio find is mystery to astroseismologists

The graceful dance between three stars seen by the Kepler telescope has drawn the attention of astronomers because it is not accompanied by a song.
Most stars are known to generate great booming sounds in their interiors, and Kepler can spot the resulting change in the light that they emit.
However, astronomers reporting in Science say a red giant they have spotted is unexpectedly quiet.
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Kepler discovery of a unique triply eclipsing triple star
       
While the quest for Earth-like planets around other stars using the NASA's Kepler space telescope has recently produced many exciting discoveries, other branches of stellar astrophysics also benefit from the ultraprecise space photometry offered by the revolutionary Kepler satellite. An international group of European, Australian and American researchers report on the discovery of a unique stellar system in a paper accepted for publication in the Science magazine. The object, catalogued as HD 181068 and known as Trinity' within the authorship team, is a 7th magnitude star that is almost visible to the naked eye, and the seemingly single star is in reality a complex triple system in which three stars reside in a very special geometry, showing mutual eclipses as each of the stars gets behind or in front of the others. The most luminous object is a red giant star around which a close pair of two red dwarfs orbits with a period of 45,5 days.
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