The post-common-envelope, binary central star of the planetary nebula Hen 2-11

Abstract

We present a detailed photometric study of the central star system of the planetary nebula Hen 2-11, selected for study because of its low-ionisation filaments and bipolar morphology -traits which have been strongly linked with central star binarity. Photometric monitoring with NTT-EFOSC2 reveals a highly irradiated, double-eclipsing, post-common-envelope system with a period of 0.609 d. Modelling of the lightcurve indicates that the nebular progenitor is extremely hot, while the secondary in the system is probably a K-type main sequence star. The chemical composition of the nebula is analysed, showing Hen 2-11 to be a medium-excitation nonType i nebula. A simple photoionisation model is constructed determining abundance ratios of C/O and N/O which would be consistent with the common-envelope cutting short the AGB evolution of the nebular progenitor. The detection of a post-common-envelope binary system at the heart of Hen 2-11 further strengthens the link between binary progeny and the formation of axisymmetric planetary nebulae with patterns of low-ionisation filaments, clearly demonstrating their use as morphological indicators of central star binarity.

The post-common envelope central stars of the planetary nebulae Henize 2-155 and Henize 2-161

“…1) are extremely similar to those found in NGC 6326, NGC 6778, Hen 2-11, and NGC 5189 (Miszalski et al 2011b;Jones et al 2014a;Manick et al 2015). The geometrically opposed pairs of "knots" seen marking the ends of the major axis of the nebula are relatively typical of high velocity outflows or "jets" which are believed to be typical of central star binarity.…”

“…Similarly, other systems have been modelled based on photometry alone, but here masses can only be estimated via indirect means (e.g. Hen 2-11; Jones et al 2014a). It is also worth noting that the majority of the other systems listed in Table 11 are double-lined spectroscopic binaries, meaning that a more direct constraint can be placed on their mass ratios than in the case of a single-lined binary (as is the case for Hen 2-155, where the parameter is constrained by the modelling).…”

“…This is to be expected because the Zanstra method depends on accurate measurement of broadband central star magnitudes which will, of course, be contaminated by the contribution from the companion star (as seen in Jones et al 2014a). Furthermore, the Zanstra temperature determinations assume an optically thick nebula, which would not necessarily be the case for such a hot central star.…”

Dawes Review 6: The Impact of Companions on Stellar Evolution

“…On the other hand, jets from accretion disks formed during binary activity could explain the observations (Blackman & Lucchini, 2014). Other interesting cases are the collimated structures seen in PNe with post-CE central star binaries studied by Jones et al (2014a, 2014b. Their kinematics were used by Tocknell et al (2014) to impose constraints on the CE interaction energies, timescales, and magnetic fields.…”

Planetary Nebulae: What Can They Tell Us About Close Binary Evolution?

“…The use of these selectors (namely jets, filaments & rings) has led to a further increased rate of discovery led by the author and collaborators (e.g. Corradi et al 2011;Miszalski et al 2011aMiszalski et al , 2011bBoffin et al 2012;Jones et al 2014Jones et al , 2015. Now, as we approach a statistically significant sample of close binary central stars (∼50, figure 1), it is important to begin to look for further connections between these systems -not only to understand the role binarity plays in the formation of planetary nebulae, but also what these systems can tell us about binary evolution in general.…”