Establishing binarity amongst Galactic RV Tauri stars with a disc

Abstract

Context. During the last few decades, it became more evident that binarity is a prevalent phenomenon amongst RV Tauri stars with a disc. This study is a contribution in comprehending the role of binarity upon late stages of stellar evolution. Aims. In this paper we determine the binary status of six Galactic RV Tauri stars, namely DY Ori, EP Lyr, HP Lyr, IRAS 17038−4815, IRAS 09144−4933 and TW Cam, which are surrounded by a dusty disc. The radial velocities are contaminated by high amplitude pulsations. We disentangle the pulsations from the orbital signal in order to determine accurate orbital parameters. We also place them on the HR diagram, thereby establishing their evolutionary nature. Methods. We used high resolution spectroscopic time series obtained from the HERMES and CORALIE spectrographs mounted on the Flemish Mercator and Swiss Leonhard Euler Telescopes, respectively. An updated ASAS/AAVSO photometric time series is analysed to complement the spectroscopic pulsation search and to clean the radial velocities from the pulsations. The pulsation-cleaned orbits are fitted with a Keplerian model to determine the spectroscopic orbital parameters. We also calibrated a PLC relationship using type II cepheids in the LMC and apply the relation to our Galactic sample to obtain accurate distances and hence luminosities. Results. All the six Galactic RV Tauri stars included in this study are binaries with orbital periods ranging between ∼ 650 and 1700 days and with eccentricities between 0.2 and 0.6. The mass functions range between 0.08 to 0.55 M which points to an unevolved low mass companion. In the photometric time series we detect a long-term variation on the time-scale of the orbital period for IRAS 17038−4815, IRAS 09144−4933 and TW Cam. Our derived stellar luminosities indicate that all except DY Ori and EP Lyr, are post-AGB stars. DY Ori and EP Lyr are likely examples of the recently discovered dusty post-RGB stars.Conclusions. The orbital parameters strongly suggest that the evolution of these stars was interrupted by a strong phase of binary interaction during or even prior to the AGB. The observed eccentricities and long orbital periods among these stars provides a challenge to the standard theory of binary evolution.

The period-luminosity and period-radius relations of Type II and anomalous Cepheids in the Large and Small Magellanic Clouds

“…The RVT stars that show IR excess are brighter in W than those without (also remarked by Manick et al (2017)), but excluding those there is well defined W(VI) relation for BLH, WVIR and non-dusty RVT, as illustrated in Figure 1.…”

The orbits of subdwarf-B + main-sequence binaries

“…9 the period-eccentricity distribution of post-AGB (pAGB) binaries are plotted. This sample contains dusty pAGB binaries with known orbital parameters from Waters et al (1993); Van Winckel et al (1995); Pollard et al (1996); Gonzalez & Wallerstein (1996); Van Winckel et al (1998, 1999; Maas et al (2002Maas et al ( , 2005 Manick et al (2017), and barium (Ba) and Tcpoor S stars for which orbital parameters were derived by Van der Swaelmen et al (2017). The Ba stars are giant stars in binary systems with a WD companion where the giant has an overabundance in s-process elements caused by mass transfer from WD progenitor during its AGB phase (Bidelman & Keenan 1951;Jorissen et al 1998).…”

“…9. The period-eccentricity distribution of different types of post-AGB binaries that have undergone a mass-loss phase in their past: dusty pAGB binaries (green squares, Waters et al 1993;Van Winckel et al 1995;Pollard et al 1996;Gonzalez & Wallerstein 1996;Van Winckel et al 1998, 1999Maas et al 2002Maas et al , 2005Van Winckel 2007;van Winckel et al 2009;Gorlova et al 2014;Gezer et al 2015;De Smedt et al 2016;Manick et al 2017), Ba stars (blue circles, Van der Swaelmen et al 2017), Tc-poor S stars (black x's, Van der Swaelmen et al 2017) and the wide sdB binaries (red crosses, this article). See section 6.2.…”

The stellar photosphere–hydrogen ionization front interaction in classical pulsators: a theoretical explanation for observed period–colour relations

“…The classical picture of the theory of stellar evolution suggests that the progenitors of T2Cs evolve redward from the blue edge of the HB and may move up the Asymptotic Giant Branch (AGB) going through the BL Her-type and W Vir-type pulsation stages (Gingold 1985;Wallerstein 2002). However, recent work by Gezer et al (2015); Groenewegen & Jurkovic (2017a,b); Manick et al (2017) among others questions this classical picture and the origin and evolution of T2Cs is not as well-understood as was once thought to be. Iwanek et al (2018) confirmed BL Her stars to be as old as RR Lyraes while W Vir stars could be a mixture of old and intermediate-age stars.…”