Apsidal Motion in Massive Binaries: CPD-41° 7742, an Extreme Case?

We study the apsidal motion in close eccentric massive binaries. We focus on CPD-41° 7742, located in the very young and rich open cluster NGC 6231. Measuring the rate of apsidal motion in such a binary system gives insight into the internal structure and evolutionary state of the stars composing it. Independent studies of CPD-41° 7742 in the past showed large discrepancies in the longitude of periastron of the orbit, hinting at the presence of apsidal motion (i.e. slow precession of the line of apsides with time). We perform a consistent analysis of all observational data explicitly accounting for the apsidal motion. We make use of the extensive set of spectroscopic and photometric observations of the binary to infer fundamental parameters of the stars and of the binary. The age estimates are in good agreement with estimates obtained for other massive binaries in NGC 6231. This study confirms the need for enhanced mixing inside the stellar evolution models of the most massive stars to reproduce the observational stellar properties. This points toward larger convective cores than usually considered.Apsidal Motion in Massive Binaries: constraining the internal structure of massive star

Apsidal motion in massive eccentric binaries: The case of CPD-41°7742, and HD 152218 revisited

peer reviewedContext. This paper is part of a study of the apsidal motion in close eccentric massive binary systems, which aims to constrain the internal structure of the stars. We focus on the binary CPD-41° 7742 and briefly revisit the case of HD 152218. Aims. Independent studies of CPD-41° 7742 in the past showed large discrepancies in the longitude of periastron of the orbit, hinting at the presence of apsidal motion. We here perform a consistent analysis of all observational data, explicitly accounting for the rate of change of the longitude of periastron. Methods. We make use of the extensive set of spectroscopic and photometric observations of CPD-41° 7742 to infer values for the fundamental parameters of the stars and of the binary. Applying a disentangling method to the spectra allows us to simultaneously derive the radial velocities (RVs) at the times of observation and reconstruct the individual spectra of the stars. The spectra are analysed by means of the CMFGEN model atmosphere code to determine the stellar properties. We determine the apsidal motion rate in two ways: First, we complement our RVs with those reported in the literature, and, second, we use the phase shifts between the primary and secondary eclipses. The light curves are further analysed by means of the Nightfall code to constrain the orbital inclination and, thereby, the stellar masses. Stellar structure and evolution models are then constructed with the Clés code for the two stars with the constraints provided by the observations. Different prescriptions for the mixing inside the stars are adopted in the models. Newly available photometric data of HD 152218 are analysed, and stellar structure and evolution models are built for the system as for CPD-41° 7742. Results. The binary system CPD-41° 7742, made of an O9.5 V primary (M_P = 17.8 ± 0.5 M⊙, R_P = 7.57 ± 0.09 R⊙, Teff,P = 31 800 ± 1000 K, Lbol,P = 5.28+0.67-0.68 × 10^4 L⊙) and a B1–2 V secondary (M_S = 10.0 ± 0.3 M⊙, R_S = 4.29+0.04-0.06 R⊙, Teff,S = 24 098 ± 1000 K, Lbol,S = 5.58+0.93−0.94 × 10^3 L⊙), displays apsidal motion at a rate of (15.38+0.42−0.51)° yr-1 . Initial masses of 18.0 ± 0.5 M⊙ and 9.9 ± 0.3 M⊙ are deduced for the primary and secondary stars, respectively, and the binary’s age is estimated to be 6.8 ± 1.4 Myr. Regarding HD 152218, initial masses of 20.6 ± 1.5 and 15.5 ± 1.1 M⊙ are deduced for the primary and secondary stars, respectively, and the binary’s age of 5.2 ± 0.8 Myr is inferred. Conclusions. Our analysis of the observational data of CPD-41° 7742 that explicitly accounts for the apsidal motion allows us to explain the discrepancy in periastron longitudes pointed out in past studies of this binary system. The age estimates are in good agreement with estimates obtained for other massive binaries in NGC 6231. This study confirms the need for enhanced mixing in the stellar evolution models of the most massive stars to reproduce the observational stellar properties; this points towards larger convective cores than usually considered

The puzzle of HD 104994 (WR 46)

Intense coordinated spectroscopic and photometric monitoring of the suspected Wolf-Rayet binary WR 46 in 1999 reveals clear periodic variations, P = 0.329 ± 0.013 days, in the radial velocities of the emission lines of highest ionization potential, O VI and N V, found deepest in the Wolf-Rayet wind and thus least likely to be perturbed by a companion. These are accompanied by coherent variability in the profiles of lines with lower ionization/excitation potential and in the continuum flux. Most probably originating from orbital motion of the Wolf-Rayet component of the binary, this periodic radial velocity signal disappears from time to time, thus creating a puzzle yet to be solved. We show that the entangled patterns of the line profile variability are mainly governed by transitions between high and low states of the system's continuum flux.Facultad de Ciencias Astronómicas y Geofísica

The puzzle of HD 104994 (WR 46)

Intense coordinated spectroscopic and photometric monitoring of the suspected Wolf-Rayet binary WR 46 in 1999 reveals clear periodic variations, P = 0.329 ± 0.013 days, in the radial velocities of the emission lines of highest ionization potential, O VI and N V, found deepest in the Wolf-Rayet wind and thus least likely to be perturbed by a companion. These are accompanied by coherent variability in the profiles of lines with lower ionization/excitation potential and in the continuum flux. Most probably originating from orbital motion of the Wolf-Rayet component of the binary, this periodic radial velocity signal disappears from time to time, thus creating a puzzle yet to be solved. We show that the entangled patterns of the line profile variability are mainly governed by transitions between high and low states of the system's continuum flux.Facultad de Ciencias Astronómicas y Geofísica

BRITE-Constellation reveals evidence for pulsations in the enigmatic binary η\eta Carinae

$\eta$ Car is a massive, eccentric binary with a rich observational history. We obtained the first high-cadence, high-precision light curves with the BRITE-Constellation nanosatellites over 6 months in 2016 and 6 months in 2017. The light curve is contaminated by several sources including the Homunculus nebula and neighboring stars, including the eclipsing binary CPD$-$59$^\circ$2628. However, we found two coherent oscillations in the light curve. These may represent pulsations that are not yet understood but we postulate that they are related to tidally excited oscillations of $\eta$ Car's primary star, and would be similar to those detected in lower-mass eccentric binaries. In particular, one frequency was previously detected by van Genderen et al. and Sterken et al. through the time period of 1974 to 1995 through timing measurements of photometric maxima. Thus, this frequency seems to have been detected for nearly four decades, indicating that it has been stable in frequency over this time span. These pulsations could help provide the first direct constraints on the fundamental parameters of the primary star if confirmed and refined with future observations.Comment: 8 pages, 4 figures, accepted to MNRA

Division IX: Optical and infrared techniques

This document introduces the reports by the Commissions and Working Groups of Division IX. © 2007 International Astronomical Union

The puzzle of HD 104994 (WR 46)

Intense coordinated spectroscopic and photometric monitoring of the suspected Wolf-Rayet binary WR 46 in 1999 reveals clear periodic variations, P = 0.329 ± 0.013 days, in the radial velocities of the emission lines of highest ionization potential, O VI and N V, found deepest in the Wolf-Rayet wind and thus least likely to be perturbed by a companion. These are accompanied by coherent variability in the profiles of lines with lower ionization/excitation potential and in the continuum flux. Most probably originating from orbital motion of the Wolf-Rayet component of the binary, this periodic radial velocity signal disappears from time to time, thus creating a puzzle yet to be solved. We show that the entangled patterns of the line profile variability are mainly governed by transitions between high and low states of the system's continuum flux.Facultad de Ciencias Astronómicas y Geofísica

Detection of solar-like oscillations from Kepler photometry of the open cluster NGC 6819

Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance and initial chemical composition allows strong tests of the theory of stellar evolution. We report results from the first 34 days of science data from the Kepler Mission for the open cluster NGC 6819 -- one of four clusters in the field of view. We obtain the first clear detections of solar-like oscillations in the cluster red giants and are able to measure the large frequency separation and the frequency of maximum oscillation power. We find that the asteroseismic parameters allow us to test cluster-membership of the stars, and even with the limited seismic data in hand, we can already identify four possible non-members despite their having a better than 80% membership probability from radial velocity measurements. We are also able to determine the oscillation amplitudes for stars that span about two orders of magnitude in luminosity and find good agreement with the prediction that oscillation amplitudes scale as the luminosity to the power of 0.7. These early results demonstrate the unique potential of asteroseismology of the stellar clusters observed by Kepler.Comment: 5 pages, 4 figures, accepted by ApJ (Lett.

Beyond Paradigms in Cultural Astronomy. Proceedings of the 27th SEAC conference held together with the EAA

Proceedings of the 27th SEAC conference held together with the EAA.-- Editors: A. César González-García, Roslyn M. Frank, Lionel D. Sims, Michael A. Rappenglück, Georg Zotti, Juan A. Belmonte, Ivan Šprajc.Cultural Astronomy is the endeavour to understand the role of the sky in past and present societies, and how these societies incorporated the sky into their culture. This broad ranging discipline is closely related to archaeology when investigating material remains of the past. Cultural Astronomy also explores the role of the heavens from the perspectives of the anthropological sciences. In recent decades the discipline has been concerned with methodological and theoretical issues. This volume offers chapters based on presentations at the 27th SEAC meeting held in Bern (2019). These chapters provide a vivid image of front-line research in diverse areas, from Roman light and shadow effects to highlight power, to Maya city organization, Etruscan temple orientation or the ontology of the sky.Peer reviewe