The central star of NGC 2392 shows the hardest X-ray emission among central stars of planetary nebulae (CSPNe). The recent discovery of a spectroscopic companion with an orbital period of 1.9 days could provide an explanation for its hard X-ray emission, as well as for the collimation of its fast outflow. Here we analyse the available Chandra and XMM-Newton X-ray observations to determine accurately the spectral and temporal variation properties of the CSPN of NGC 2392. The X-ray emission can be described by an absorbed thermal plasma model with temperature 26$^{+8}_{-5}$ MK and X-ray luminosity (8.7$\pm$1.0)$\times$10$^{30}$ erg s$^{-1}$. No long-term variability is detected in the X-ray emission level, but the Chandra light curve is suggestive of short-term variations with a period $\sim$0.26 days. The possible origins of this X-ray emission are discussed. X-ray emission from the coronal activity of a companion or shocks in the stellar wind can be ruled out. Accretion of material from an unseen main-sequence companion onto the CSPN or from the CSPN wind onto a white dwarf companion are the most plausible origins for its hard X-ray emission, although the mismatch between the rotational period of the CSPN and the modulation time-scale of the X-ray emission seems to preclude the former possibility.
Aquila X-1 is a prototypical neutron star low mass X-ray binary and one of the most studied X-ray transients. We present optical spectroscopy obtained with the Gran Telescopio Canarias (10.4 m) during the 2016 outburst, the brightest in recent times, which showed a standard evolution with hard and soft accretion states. Our data set includes a dense coverage of the brightest phases of the event, as well as the decay towards quiescence. We searched for optical winds by studying the profiles and evolution of the main emission lines and found no indisputable wind signatures, such as P-Cyg profile…
We reassess the historical $L_{X}/L_{Bol}$ relation for early-type stars from a comparison between T-ReX, the Chandra ACIS X-ray survey of the Tarantula Nebula in the LMC, and contemporary spectroscopic analysis of massive stars obtained primarily from VLT/FLAMES, VLT/MUSE and HST/STIS surveys. For 107 sources in common (some host to multiple stars), the majority of which are bolometrically luminous (40% exceed $10^6 L_{\odot}$), we find an average $\log L_{X} /L_{Bol} = -6.90 \pm 0.65$. Excluding extreme systems Mk 34 (WN5h+WN5h), R140a (WC4+WN6+) and VFTS 399 (O9 IIIn+?), plus four WR source…
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. …
Planetary nebulae (PNe) were expected to be filled with hot pressurized gas driving their expansion. ROSAT hinted at the presence of diffuse X-ray emission from these hot bubbles and detected the first sources of hard X-ray emission from their central stars, but it was not until the advent of Chandra and XMM-Newton that we became able to study in detail their occurrence and physical properties. Here I review the progress in the X-ray observations of PNe since the first WORKshop for PLAnetary Nebulae observationS (WORKPLANS) and present the perspective for future X-ray missions with particular …
Ancient 'ghost' planetary nebulae discovered with amateur telescopes
Asociación Astronómica AstroHenares（AstroHenares天文协会）；Instituto de Astrofísica de Canarias（加那利天体物理学研究所）；Departamento de Astrofísica, Universidad de La Laguna（拉帕尔马大学天体物理系）；Observatorio Astronómico Nacional (OAN-IGN)（国家天文台（OAN-IGN））；Zentrum für Astronomie der Universität Heidelberg, Landessternwarte（海德堡大学天文中心，州立天文台）
Jets (fast collimated outflows) are claimed to be the main shaping agent of the most asymmetric planetary nebula (PNe) as they impinge on the circumstellar material at late stages of the asymptotic giant branch (AGB) phase. The first jet detected in a PN was that of NGC 2392, yet there is no available image because its low surface brightness contrast with the bright nebular emission. Here we take advantage from the tomographic capabilities of GTC MEGARA high-dispersion integral field spectroscopic observations of the jet in NGC 2392 to gain unprecedented details of its morphology and kinematic…
The ACIS-S camera on board the Chandra X-ray Observatory has been used to discover a hot bubble in the planetary nebula (PN) IC4593, the most distant PN detected by Chandra so far. The data are used to study the distribution of the X-ray-emitting gas in IC 4593 and to estimate its physical properties. The hot bubble has a radius of ~2$^{\prime\prime}$ and is found to be confined inside the optically-bright innermost cavity of IC 4593. The X-ray emission is mostly consistent with that of an optically-thin plasma with temperature $kT\approx0.15$ keV (or $T_\mathrm{X}\approx1.7\times10^{6}$ K), e…
