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Post Info TOPIC: 1SWASP J093010.78+533859.5
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Rare system of five stars discovered

Astronomers have discovered a very rare system of five connected stars.
The quintuplet consists of a pair of closely linked stars - binaries - one of which has a lone companion; it is the first known system of its kind.
The pair of stars orbit around a mutual centre of gravity, but are separated by more than the distance of Pluto's orbit around the Sun.
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Title: The doubly eclipsing quintuple low-mass star system 1SWASP J093010.78+533859.5
Author: M. E. Lohr (1), A. J. Norton (1), E. Gillen (2), R. Busuttil (1), U. C. Kolb (1), S. Aigrain (2), A.McQuillan (2 and 3), S. T. Hodgkin (4), E. González (5) ((1) The Open University, Milton Keynes, UK, (2) University of Oxford, Oxford, UK, (3) Tel Aviv University, Tel Aviv, Israel, (4) Institute of Astronomy, Cambridge, UK, (5) Observatori Astronómic de Mallorca, Costitx, Mallorca)

Our discovery of 1SWASP J093010.78+533859.5 as a probable doubly eclipsing quadruple system containing a contact binary with P~0.23 d and a detached binary with P~1.31 d was announced in 2013. Subsequently Koo et al. confirmed the detached binary spectroscopically and identified a fifth set of static spectral lines at its location, corresponding to a further non-eclipsing component of the system. Here we present new spectroscopic and photometric observations, allowing confirmation of the contact binary and improved modelling of all four eclipsing components. The detached binary is found to contain components of masses 0.837(8) and 0.674(7) M_sol, with radii of 0.832(18) and 0.669(18) R_sol and effective temperatures of 5185(-20,+25) and 4325(-15,+20) K respectively, the contact system has masses 0.86(2) and 0.341(11) M_sol, radii of 0.79(4) and 0.52(5) R_sol respectively, and a common T_eff of 4700(50) K. The fifth star is of similar temperature and spectral type to the primaries in the two binaries. Long-term photometric observations indicate the presence of a spot on one component of the detached binary, moving at an apparent rate of approximately one rotation every two years. Both binaries have consistent system velocities around -11 to -12 km/s, which match the average radial velocity of the fifth star, consistent distance estimates for both subsystems of d=78(3) and d=73(4) pc are also found, and (with some further assumptions) of d=83(9) pc for the fifth star. These findings strongly support the claim that both binaries (and very probably all five stars) are gravitationally bound in a single system. The consistent angles of inclination found for the two binaries (88.2(3) and 86(4) degrees) may also indicate that they originally formed by fragmentation (~9-10 Gyr ago) from a single protostellar disk and subsequently remained in the same orbital plane.

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Title: 1SWASP J093010.78+533859.5: A Possible Hierarchical Quintuple System
Author: Jae-Rim Koo, Jae Woo Lee, Byeong-Cheol Lee, Seung-Lee Kim, Chung-Uk Lee, Kyeongsoo Hong, Dong-Joo Lee, Soo-Chang Rey

We present the observational results of this kind of rare object 1SWASP J093010.78+533859.5, for which the doubly eclipsing feature had been detected previously from the SuperWASP photometric archive. Individual PSF photometry for two objects with a separation of about 1.9 arcsec was performed for the first time in this study. Our time-series photometric data confirms the finding of Lohr et al. (2013) that the bright object A is an Algol-type detached eclipsing binary and the fainter B is a W UMa-type contact eclipsing. Using the high- resolution optical spectra, we obtained well-defined radial velocity variations of system A. Furthermore, stationary spectral lines were detected that must have originated from a further, previously unrecognized stellar component. It was confirmed by the third object contribution from the light curve analysis. No spectral feature of the system B was detected, probably due to motion blur by long exposure time. We obtained the binary parameters and the absolute dimensions of the systems A and B from light curve synthesis with and without radial velocities, respectively. The primary and secondary components of system A have a spectral type of K1 and K5 main sequences, respectively. Two components of system B have nearly the same type of K3 main sequence. Light variations for both binaries are satisfactorily modeled by using two-spot models with one starspot on each component. We estimated the distances to systems A and B individually. Two systems may have similar distances of about 70 pc and seem to be gravitationally bound with a separation of about 130 AU. In conclusion, we suggest that 1SWASP J093010.78+533859.5 is a quintuple stellar system with a hierarchical structure of a triple system A(ab)c and a binary system B(ab).

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