Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue

Abstract

Aims. We present the results of our spectroscopic and photometric analysis of two newly discovered low-mass detached eclipsing binaries found in the All-Sky Automated Survey (ASAS) catalogue: ASAS J093814-0104.4 and ASAS J212954-5620.1. Methods. Using the Grating Instrument for Radiation Analysis with a Fibre-Fed Echelle (GIRAFFE) on the 1.9-m Radcliffe telescope at the South African Astronomical Observatory (SAAO) and the University College London Echelle Spectrograph (UCLES) on the 3.9-m Anglo-Australian Telescope, we obtained high-resolution spectra of both objects and derived their radial velocities (RVs) at various orbital phases. The RVs of both objects were measured with the two-dimensional cross-correlation technique (TODCOR) using synthetic template spectra as references. We also obtained V and I band photometry using the 1.0-m Elizabeth telescope at SAAO and the 0.4-m Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT) located at the Cerro Tololo Inter-American Observatory (CTIO). The orbital and physical parameters of the systems were derived with PHOEBE and JKTEBOP codes. We compared our results with several sets of widely-used isochrones. Results. Our multi-epoch photometric observations demonstrate that both objects show significant out-of-eclipse modulations, which vary in time. We believe that this effect is caused by stellar spots, which evolve on time scales of tens of days. For this reason, we constructed our models on the basis of photometric observations spanning short time scales (less than a month). Our modeling indicates that (1) ASAS J093814-0104.04 is a main sequence active system with nearly-twin components with masses of M 1 = 0.771 ± 0.033 M , M 2 = 0.768 ± 0.021 M and radii of R 1 = 0.772 ± 0.012 R and R 2 = 0.769 ± 0.013 R . (2) ASAS J212954-5620.1 is a main sequence active binary with component masses of M 1 = 0.833 ± 0.017 M , M 2 = 0.703 ± 0.013 M and radii of R 1 = 0.845 ± 0.012 R and R 2 = 0.718 ± 0.017 R . Conclusions. Both systems seem to confirm the well-known characteristic of active low-mass stars, for which the observed radii are larger and the temperatures lower than predicted by evolutionary models. Other parameters agree within errors with the models of main sequence stars. The time-varying spot configuration may imply a variable level of activity, which may manifest itself in small changes of the measured radii.

An Empirical Correction for Activity Effects on the Temperatures, Radii, and Estimated Masses of Low-Mass Stars and Brown Dwarfs

“…The vast majority of masses for stars and BDs in young clusters can only be determined by comparison with theoretical evolutionary tracks in H-R diagrams, using either luminosity or T eff or both (e.g., Kenyon & Hartmann 1995;Hillenbrand 1997;Luhman et al 1998;Moraux et al 2007;Scholz et al 2012a). While direct mass measurements are available for calibration of these models at higher masses (M 0.3 M ; e.g., Hillenbrand & White 2004), at the lowest stellar masses and into the substellar regime these models are essentially untested.…”

Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue - IV. A 0.61 + 0.45 M⊙ binary in a multiple system

“…The eclipsing system ASAS J011328–3821.1 (2MASS J01132817–3821024, 1RXS J011328.8–382059, hereafter ASAS‐01) has the shortest orbital period of all the objects in our sample of low‐mass detached eclipsing binaries (LMDEBs; see: Hełminiak & Konacki ; Hełminiak et al ) found in the All‐Sky Automated Survey (ASAS) Catalogue of Variable Stars (ACVS; Pojmański ), and it is one of the shortest among the LMDEBs known to date (i.e. P ASAS = 0.44559 d).…”

“…To directly derive the masses of the components of ASAS‐01, we obtained a series of high‐resolution spectra in order to measure their radial velocities (RVs). Most of the spectroscopic observations come from the 1.9‐m Radcliffe telescope and its Grating Instrument for Radiation Analysis with a Fibre‐Fed Echelle (GIRAFFE) spectrograph at the South African Astronomical Observatory (SAAO), with settings the same as described in the previous papers of this series (Hełminiak et al , ). Five spectra of R ∼ 40 000 were obtained during three consecutive nights in 2006 September.…”

“…The last spectrum was obtained in 2008 September with the 3.9‐m AAT and its University College London Echelle Spectrograph (UCLES) at the Siding Spring Observatory, with the same settings as described in Hełminiak et al (, ). This spectrum was not binned, and after 900 s of exposure we reached S/N ratio ∼20 at λ = 6530 Å.…”

New high-precision orbital and physical parameters of the double-lined low-mass spectroscopic binary BY Draconis

“…Let us note that spots can easily induce RV variations at the level of a few hundreds of m s −1 so the RV variability of BY Dra is not surprising (see e.g. Hełminiak & Konacki 2011; Hełminiak et al 2011). We also had to adopt small shifts between each data set as is explained in Konacki et al (2010).…”