Eclipse timing variations in 7 post-common envelope binaries: an update on recent circumbinary models

TL;DR

This work analyzes eclipse timing variations (ETVs) in seven short-period post-common-envelope binaries to test circumbinary-planet models. By compiling 355 new minima and re-evaluating 18 recent models, the authors show that none reliably predict future eclipses, and that TESS data, while informative, introduce scatter that complicates ephemeris fitting. They systematically assess secular changes (AML, gravitational radiation, mass transfer) and quasi-cyclical magnetic effects, finding that magnetic energy requirements are generally prohibitive and that planetary models alone cannot explain the observed timing variations. The study concludes that, if circumbinary bodies exist, their influence must be combined with other processes, and that ETVs alone are insufficient for robust planetary confirmations in these systems.

Abstract

Eclipsing, short-period post-common envelope binaries (PCEBs) have been studied for several decades by eclipse timing variations (ETVs) which have been interpreted as being caused by circumbinary bodies. In this paper we report 355 new observations of 7 PECBs (HS0705+6700, NN Ser, NSVS 07826147, NSVS 14256825, NY Vir, QS Vir and RR Cae) and examine how the recent proposed models of these systems compare with our new observations. We find that none of the 18 recent models fit accurately with our data. We review alternative mechanisms of the ETVs, including magnetic effects, but conclude that they do not predict our results. Although we cannot exclude the presence of circumbinary bodies a combination of several mechanisms may be required to explain the observed ETVs.

Figures (17)

• Figure 1: O – C chart for HS0705+6700 showing the two models from Er_Özdönmez_Nasiroglu_Kenger_2024 updated with new data from this paper. Historical data $\mathrm{\sim}$ black filled triangles; TESS data $\mathrm{\sim}$ blue filled circles; Our new data $\mathrm{\sim}$ red open circles; Quadratic with 2 bodies model $\mathrm{\sim}$ red dashed line; Linear with 3 bodies model $\mathrm{\sim}$ black dashed line. Vertical axis is seconds and horizontal axis cycle number.
• Figure 2: O – C chart for HS0705+6700 showing the quadratic ephemeris of Eq. 1. Historical data $\mathrm{\sim}$ black filled triangles; Our new data $\mathrm{\sim}$ red open circles. Vertical axis is seconds and horizontal axis cycle number.
• Figure 3: O - C chart for NN Ser showing the two models from ozdonmez2023investigation updated with new data from this paper. Historical data $\mathrm{\sim}$ black filled triangles; Our new data $\mathrm{\sim}$ red open circles; 1-planet model $\mathrm{\sim}$ red dashed line; 2-planet model $\mathrm{\sim}$ black dashed line; Vertical axis seconds; Horizontal axis cycle number.
• Figure 4: O - C chart for NN Ser showing the updated quadratic ephemeris in Eq. \ref{['NN_Ser_ephem_quad']}. Historical data $\mathrm{\sim}$ black filled triangles; Our new data $\mathrm{\sim}$ red open circles; Vertical axis seconds; Horizontal axis cycle number.
• Figure 5: NSVS 07826147 O - C residuals for wolf2021possible). Model $\mathrm{\sim}$ red line; Primary eclipses are shown with solid triangles and open triangles are secondary eclipses. Part of SuperWASP unbinned data $\mathrm{\sim}$ blue circles; Our new data $\mathrm{\sim}$ red circles. Note, wolf2021possible did not use the SuperWASP data or secondary minima in their analysis. Vertical axis seconds; Horizontal axis cycle number.