Physical parameters and multiplicity of five southern close eclipsing binaries

Abstract

Aims. We detected tertiary components of close binaries from spectroscopy and light curve modelling, investigated the lighttravel time effect and the possibility of magnetic activity cycles, measured mass ratios for unstudied systems, and derived absolute parameters. Methods. We carried out new photometric and spectroscopic observations of five bright ( V < 10.5 mag) close eclipsing binaries, predominantly in the southern skies. We obtained full Johnson BV light curves, which were modelled with the Wilson-Devinney code. Radial velocities were measured with the cross-correlation method using IAU radial velocity standards as spectral templates. Period changes were studied with the O−C method, utilising published epochs of minimum light (XY Leo) and ASAS photometry (VZ Lib). Results. For three objects (DX Tuc, QY Hya, V870 Ara), absolute parameters have been determined for the first time. We spectroscopically detected the tertiary components in XY Leo and VZ Lib and discovered one in QY Hya. For XY Leo we updated the light-time effect parameters and detected a secondary periodicity of about 5100 d in the O−C diagram that may hint at the existence of short-period magnetic cycles. A combination of recent photometric data shows that the orbital period of the tertiary star in VZ Lib is likely to be over 1500 d. QY Hya is a semi-detached X-ray active binary in a triple system with K and M-type components, while V870 Ara is a contact binary with the third smallest spectroscopic mass ratio for a W UMa star to date (q = 0.082 ± 0.030). Being close to the theoretical minimum for contact binaries, this small mass ratio suggests that V870 Ara has the potential of constraining evolutionary scenarios of binary mergers. The inferred distances to these systems are compatible with the Hipparcos parallaxes.

Rotation, activity, and lithium abundance in cool binary stars

“…References. a: Griffin (2009), b: Griffin (1987, c: Cutispoto et al (2003), d: Climenhaga et al (1951), e: Favata et al (1993), f: Fekel (1997), g: Fekel et al (2004, h: Latham et al (2002), i: Henry et al (1995), j: Wright et al (2004), k: Karatas et al (2004), l: Cutispoto et al (1999), m: Griffin (2005), n: Griffin & Keenan (1992), o: Halbwachs et al (2003), p: Morales et al (2009), q: Otero & Dubovsky (2004), r: Fekel et al (1999), s: Duemmler et al (2002, t: Duquennoy & Mayor (1988), u: Gálvez et al (2006), v: Barnes (2007), w: Montes et al (2000), x: Strassmeier (1994, y: Gálvez et al (2005), z: Griffin (2010), 29: Szalai et al (2007), 30: Gálvez et al (2009), 31: Gálvez et al (2007, 32: Griffin & Filiz Ak (2010), 33: Goldberg et al (2002), 34: Griffin (2003), 35: Griffin (2012). Table 2 STELLA radial velocities of standard stars.…”

“…www.an-journal.org HD 105575 = QY Hya. Szalai et al (2007) presented a photometric and spectroscopic study of this 0.29 d eclipsing binary and derived a complete system's solution from BV light curves and radial velocities. These authors also announced the discovery of a tertiary component in the cross correlation function and listed absolute parameters appropriate for a (K5/M1)/G4 system.…”

“…The secondary's K amplitude is 158 km s −1 , and both stars have a v sin i of around 40 km s −1 ; and accordingly large are the orbital residuals. The disagreement with the elements given by Szalai et al (2007) possibly comes from the different ways the cross correlation is determined. Our photometric orbital period is 0.292386 d and agrees with the orbital period within its uncertainties.…”

Cyclical period changes in HT Cassiopeiae: a difference between systems above and below the period gap

“…The period gap is indicated by vertical dashed lines. The crosses depict ∆P/P values for 56 other close binaries with cyclical period modulations (Lanza & Rodonó 1999;Qian et al 1999Qian et al , 2000aQian et al ,b, 2002Qian et al , 2007aLanza et al 2001;Kang et al 2002;Qian 2002aQian ,b, 2003Yang & Liu 2002, 2003aZavala et al 2002;Çakırlı et al 2003;Kim et al 2003;Qian & Boonrucksar 2003;Afşar et al 2004;Lee et al 2004;Yang et al 2004Yang et al , 2007Zhu et al 2004;Borkovits et al 2005;Erdem et al 2007;Pilecki et al 2007;Szalai et al 2007). Systems with independent evidence that the observed (O−C) modulations can be explained by a third body were excluded (actually, it is not possible to exclude the possibility that the observed modulation of some of the systems plotted may still be caused by a third body.…”

Possible solution to the problem of the extreme mass ratio W UMa-type binaries

“…However, spectroscopic and photometric analyses of observational data show that there are systems with lower q values: V870 Ara ( q = 0.082; Szalai et al 2007), SX Crv ( q = 0.079; Zola et al 2004), AW UMa ( q = 0.075; Rucinski 1992), 1 V857 Her ( q = 0.065; Qian et al 2006). If we want theory to match observations, the only solution is to set k 2 1 < 0.075 ( k 2 1 ≈ 0.06, Rasio 1995; Li & Zhang 2006).…”