The post-common-envelope X-ray binary nucleus of the planetary nebula NGC 2392

Abstract

The Chandra X-ray Observatory has detected relatively hard X-ray emission from the central stars of several planetary nebulae (PNe). A subset have no known late-type companions, making it very difficult to isolate which of several competing mechanisms may be producing the X-ray emission. The central star of NGC 2392 is one of the most vexing members, with substantial indirect evidence for a hot white dwarf (WD) companion. Here we report on the results of a radial velocity (RV) monitoring campaign of its central star with the HERMES échelle spectrograph of the Flemish 1.2 m Mercator telescope. We discover a single-lined spectroscopic binary with an orbital period of 1.902208 ± 0.000013 d and a RV semi-amplitude of 9.96 ± 0.13 km s −1 . The high degree of nebula ionisation requires a WD companion (M 0.6M ), which the mass-function supports at orbital inclinations 7 deg, in agreement with the nebula orientation of 9 deg. The hard component of the X-ray spectrum may be explained by the companion accreting mass from the wind of the Roche lobe filling primary, while the softer component may be due to colliding winds. A companion with a stronger wind than the primary could produce the latter and would be consistent with models of the observed diffuse X-ray emission detected in the nebula. The diffuse X-rays may also be powered by the jets of up to 180 km s −1 and active accretion would imply that they could be the first active jets of a post-common-envelope PN, potentially making NGC 2392 an invaluable laboratory to study jet formation physics. The 1.9 d orbital period rules out a double-degenerate merger leading to a Type Ia supernova and the weak wind of the primary likely also precludes a single-degenerate scenario. We suggest that a hard X-ray spectrum, in the absence of a late-type companion, could be a powerful tool to identify accreting WD companions.

Two’s company, three’s a crowd: SALT reveals the likely triple nature of the nucleus of the extreme abundance discrepancy factor planetary nebula Sp 3

“…This is one of the longest orbital periods known in PNe (Miszalski et al 2019b) and higher than expected for post-CE WD main-sequence binaries (Nebot Gómez-Morán et al 2011), further supporting the possibility that there may be a larger population of longer orbital period binary central stars waiting to be found. Sp 3 is the third binary we have identified in the list of RV variables identified by Afšar & Bound Afšar & Bond (2005), after NGC 1360 (Miszalski et al 2018a) and NGC 2392 (Miszalski et al 2019a). • The TMAP NLTE model atmosphere analysis of the SALT HRS spectra shows the primary to be a relatively fast rotator (v rot = 80 ± 20 km s −1 ) with T eff = 68 000 +12 000 −6 000 K and log g = 4.6 ± 0.2.…”

“…Sp 3 is a relatively unstudied PN notable for the probable association between the V = 13.20 mag central star and a V = 16.86 mag visual companion (Ciardullo et al 1999). As in the case of NGC 1360 (Miszalski et al 2018a) and NGC 2392 (Miszalski et al 2019a), Afšar & Bond (2005) detected RV variability in nine observations of Sp 3, but did , and (d) is a version of (a) with another unsharp mask filter applied. A logarithmic scale and an unsharp mask filter was applied to all images to enhance faint features.…”

“…therein) and alignment of the nebula orientation with orbital inclination (Hillwig et al 2016). Low-ionisation filaments also appear to be associated with post-CE PNe (Miszalski et al 2009b(Miszalski et al , 2011a2019a), particularly in ring configurations (e.g. Corradi et al 2011;Boffin et al 2012;Miszalski et al 2018a).…”

Tomography of the unique on-going jet in the planetary nebula NGC 2392

“…The launch mechanism of the jet of NGC 2392 is thus presently active, i.e., it is an on-going jet (Miszalski et al 2019). This is also the case of the late-AGB jets in BD+46 • 442 and IRAS 19135+3937 (Bollen et al 2019).…”

The post-common-envelope binary nucleus of the planetary nebula IC 4776: neither an anomalously long orbital period nor a Wolf–Rayet binary

“…The nearest post-CE PNe in the ADF versus orbital period diagram to IC 4776 (ADF=1.75, Sowicka et al 2017) are now NGC 2392 (P =1.9 d, Miszalski et al 2019;ADF=1.65, Zhang et al 2012) and NGC 5189 (P =4.05 d, Miszalski et al 2015;ADF=1.6, García-Rojas et al 2013). The newly determined 3.11 d orbital period of IC 4776 does not dramatically alter the conclusions of Wesson et al (2018), however we consider the sample size still too small to draw any correlation between ADF and orbital period.…”