The orbits of subdwarf-B + main-sequence binaries: III. The period - eccentricity distribution

Abstract

The predicted orbital-period distribution of the subdwarf-B (sdB) population is bi-modal with a peak at short (< 10 days) and long (> 500 days) periods. Observationally, many short-period sdB systems are known, but only few wide sdB binaries have been studied in detail. Based on a long-term monitoring program the wide sdB sample has been increased, finding an unexpected correlation between the eccentricity and period. In this article we present the orbital solution and spectral analysis of four new systems, BD-7.5977, EC11031-1348, TYC2084-448-1 and TYC3871-835-1, and update the orbital solution of PG1104+243. Using the whole sample of wide sdBs, we aim at finding possible correlations between orbital and spectral properties, with as goal improving theoretical models of Roche-lobe overflow. High-resolution spectra were obtained to determine the radial velocities of both the sdB and MS components. Surface gravities and temperatures of both component were derived from photometric spectral-energy distributions. Spectral parameters of the cool companion were verified using the GSSP code. Furthermore the amount of accreted mass was estimated. Orbital parameters matching the earlier observed period-eccentricity relation were found for three systems, while TYC 2084-448-1 is found to have a lower eccentricity than expected from the period-eccentricity trend indicated by the other systems. Based on new observations, the orbit of PG 1104+243 has a small but significant eccentricity of 0.04 $\pm$ 0.02, matching other systems with similar periods. Furthermore, a correlation between accreted mass and orbital period was found, as well as a possible relation between the initial mass-ratio and the final period-eccentricity. The wide sdB-binary sample shows interesting possible correlations between orbital and spectral properties. However, a larger sample is necessary to statistically validate them.

18 pages, 9 figures, Accepted for publication in A&A

References in corpus (8)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Hot subdwarf binaries from the MUCHFUSS project - Analysis of 12 new systems and a study of the short-period binary population
• Orbital eccentricities of binary systems with a former AGB star
• New binaries among UV-selected, hot subdwarf stars and population properties
• Testing eccentricity pumping mechanisms to model eccentric long period sdB binaries with MESA
• The orbits of subdwarf B + main-sequence binaries. I: The sdB+G0 system PG 1104+243
• Establishing binarity amongst Galactic RV Tauri stars with a disc
• The mass-ratio and eccentricity distributions of barium and S stars, and red giants in open clusters

Cited by in corpus (18)

• Barium & related stars and their white-dwarf companions II. Main-sequence and subgiant stars
• Forming Hot Subluminous Stars from Hierarchical Triples -- I. The Role of an Outer Tertiary on Formation Channels
• A Roche Lobe-filling hot Subdwarf and White Dwarf Binary: possible detection of an ejected common envelope
• Flares hunting in hot subdwarf and white dwarf stars from Cycles 1-5 of TESS photometry
• Blue Stragglers and Friends: Initial Evolutionary Pathways in Close Low-Mass Binaries: Literature Review
• The first heavy-metal hot subdwarf composite binary SB 744
• Pulsating subdwarf B stars observed with K2 during Campaign 7 and an examination of seismic group-properties
• Evolutionary Constraints on the Long-period Subdwarf B Binary PG 1018-047
• Rethinking mass transfer: a unified semi-analytical framework for circular and eccentric binaries. I. Orbital evolution due to conservative mass transfer
• Gaia Barium Dwarfs and Their Ostensibly Ordinary Counterparts
• Detection of Ubiquitous Circumbinary Matter in Hot Subdwarfs Formed from Common-Envelope Ejections
• Identifying and characterising the population of hot sub-luminous stars with multi-colour MeerLICHT data
• Distinct Rotational Evolution of Giant Planets and Brown Dwarf Companions
• Post-AGB Binaries as Interacting Systems
• Wide sdB binaries. I. Orbital and atmospheric parameters
• HD 26172: an active solar-type subgiant in a close binary system
• EC 22536-5304: a lead-rich and metal-poor long-period binary
• Stellar Parameters and Orbital Period Estimates for Composite-Spectrum sdB+MS Binaries from LAMOST