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 echelle spectrograph of the Flemish 1.2 m Mercator telescope. We discover a single-lined spectroscopic binary with an orbital period of $1.902208\pm 0.000013$ d and a RV semi-amplitude of $9.96\pm 0.13$ km/s. The high degree of nebula ionisation requires a WD companion ($M\gtrsim 0.6M_{\odot }$), which the mass-function supports at orbital inclinations $\lesssim$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 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.

12 pages, 7 figures, 2 tables. Accepted for publication in PASA

References in corpus (6)

• Observational Confirmation of a Link Between Common Envelope Binary Interaction and Planetary Nebula Shaping
• The Chandra Planetary Nebulae Survey (ChanPlaNS): III. X-ray Emission from the Central Stars of Planetary Nebulae
• The Chandra Planetary Nebula Survey (ChanPlaNS). II. X-ray Emission from Compact Planetary Nebulae
• A radial velocity survey for post-common-envelope Wolf-Rayet central stars of planetary nebulae: First results and discovery of the close binary nucleus of NGC 5189
• X-Ray Emission from Jet-Wind Interaction in Planetary Nebulae
• Rummaging inside the Eskimo's parka: Variable asymmetric PN fast wind and a binary nucleus?

Cited by in corpus (9)

• Catalogue of central stars of planetary nebulae: Expanded edition
• Space Velocity and Time Span of Jets in Planetary Nebulae
• Tomography of the unique on-going jet in the planetary nebula NGC 2392
• Towards a more complete sample of binary central stars of planetary nebulae with Gaia
• The post-common-envelope binary central star of the planetary nebula ETHOS 1
• The post-common-envelope binary nucleus of the planetary nebula IC~4776: Neither an anomalously long orbital period nor a Wolf-Rayet binary
• The binary central star of the bipolar pre-planetary nebula IRAS 08005-2356 (V510 Pup)
• Planetary Nebulae in the eROSITA eRASS1 catalog
• Two hot pre-white dwarfs inside the red-giant-branch planetary nebula Pa 13 -- Double core evolution or common envelope-induced rejuvenation?