The doubly eclipsing quintuple low-mass star system 1SWASP J093010.78+533859.5

Abstract

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 and collaborators confirmed the detached binary spectroscopically, and identified a fifth set of static spectral lines at its location, corresponding to an additional noneclipsing 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 ± 0.008 and 0.674 ± 0.007 M , with radii of 0.832 ± 0.018 and 0.669 ± 0.018 R and effective temperatures of 5185 +25 −20and 4325 +20 −15 K, respectively; the contact system has masses 0.86 ± 0.02 and 0.341 ± 0.011 M , radii of 0.79 ± 0.04 and 0.52 ± 0.05 R , respectively, and a common effective temperature 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 −1 , 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 ± 0.3 • and 86 ± 4 • ) may also indicate that they originally formed by fragmentation (around 9-10 Gyr ago) from a single protostellar disk, and subsequently remained in the same orbital plane.

The Arches cluster revisited

“…R 2 is perhaps rather large and hence log L L is rather high for an O hypergiant secondary: comparable single stars studied in Martins et al (2008) (F10 and F15) are modelled as having radii ∼30 R . However, an inflated secondary radius is expected in lower-mass contact binaries due to the shared envelope (Lohr et al 2015), and a comparable mechanism may be in operation here.…”

Photometric study of three ultrashort-period contact binaries

“…The possibility of a third body in J200059 could not be excluded due to the low quality of the O-C diagram, although Lohr et al (2013a) did not detect any evidence for period change in J200059. In fact, another system, 1SWASP J093010.78+533859.5 which had been not found period variations by Lohr et al (2013b) either, could be a multiple system (Koo et al 2014;Lohr et al 2015).…”

The Quadruple-lined, Doubly Eclipsing System V482 Persei

“…Furthermore, this second binary is also eclipsing (although the eclipses are very shallow), and both systems orbit a common center of mass with the 16-year period inferred earlier from the light-travel time effect. Such quadruple, doubly-eclipsing systems are relatively rare, though several have been discovered in recent years based on the high-precision and nearly uninterrupted observations collected between 2009 and 2013 by NASA's Kepler spacecraft, as well as from ground-based surveys (see, e.g., Pawlak et al 2013;Koo et al 2014;Lohr et al 2015).…”