from Central Stars of Planetary Nebulae Hard X-ray Emission from Central Stars of Planetary Nebulae Martín A. Guerrero Instituto de Astrofísica de Andalucía, IAA-CSIC, Spain You-Hua Chu & Robert A. Gruendl University of Illinois at Urbana-Champaign, USA The X-ray Universe 2011 Berlin, June 29, 2011

Talk Outline  X-ray emission expected from central stars of planetary nebulae (CSPNe)  Photospheric X-ray emission.  Coronal emission from a companion.  Detection of unexpected hard X-ray emission from CSPNe  Possible mechanisms for hard X-ray production:  Pros and cons.  Implications for PN formation and evolution. Martín A. Guerrero, Hard X-ray Emission from CSPNe 2

PNe descend from low- and intermediate-mass stars: 0.8 M < Mi < 10 M 3

Photospheric X-ray Emission from Hot Central Stars Photospheric emission from hot (Teff > 100,000 K) CSPNe have high-energy tails that may extend into the X-ray domain. T. Rauch NLTE model Martín A. Guerrero, Hard X-ray Emission from CSPNe 4

Photospheric X-ray Emission from Hot Central Stars Einstein, EXOSAT and ROSAT detections of soft X-rays: A 36, K 1-16, K 1-27, LoTr 5, NGC 246, NGC 1360, NGC 3587, NGC 4361, NGC 6853, NGC 7293 (de Korte et al. 1985; Tarafdar & Apparao 1988; Apparao & Tarafdar 1989; Kreysing et al. 1992; Rauch et al. 1994; Hoare et al. 1995) Search of the entire ROSAT archive for X-ray emission from PNe (Guerrero, Chu & Gruendl 2000)  Point source (at the PSPC spatial resolution of 30”)  Soft X-rays peaking below 0.2 keV (BB or photospheric models) Martín A. Guerrero, Hard X-ray Emission from CSPNe 5

Photospheric X-ray Emission from Hot Central Stars Einstein, EXOSAT and ROSAT detections of soft X-rays: A 36, K 1-16, K 1-27, LoTr 5, NGC 246, NGC 1360, NGC 3587, NGC 4361, NGC 6853, NGC 7293 (de Korte et al. 1985; Tarafdar & Apparao 1988; Apparao & Tarafdar 1989; Kreysing et al. 1992; Rauch et al. 1994; Hoare et al. 1995) Search of the entire ROSAT archive for X-ray emission from PNe (Guerrero, Chu & Gruendl 2000)  Ideal conditions for detection Small distance Low ISM extinction  Nebulae and central stars at late evolutionary stage High Teff Low photospheric metal content Large and optically thin nebulae Martín A. Guerrero, Hard X-ray Emission from CSPNe 6

Unexpected Hard X-ray Emission at CSPNe [N II] NGC 6543 H X-rays NGC 6543 (Chu et al. 2001) kT1 = 0.1 keV, kT2 = 0.8 keV Lx = 1.0×1030 erg s-1 NGC 2392 (Guerrero et al. in prep.) kT = 2.8 keV Lx= 3.0×1030 erg s-1 X-rays [N II] H [N II] NGC 2392 0.3-0.7 keV 0.7-1.5 keV 1.5-3.0 KeV Martín A. Guerrero, Hard X-ray Emission from CSPNe 7

Does Hard X-ray Emission Implies a Companion?  Coronal emission from a late type companion.  Accretion:  From a companion (as for quiescent novae or cataclysmic variables).  From a debris disk. Martín A. Guerrero, Hard X-ray Emission from CSPNe 8

GISW Density Gradient and Collimated Outflows The (Generalized) Interacting-Stellar Winds (G)ISW model of PN formation Symmetric AGB mass loss U Cam (Oloffson et al. 2010) U Cam Origin of the density gradient in the GISW model? Companion: preferential AGB mass loss @ equator  Collimated outflows Accretion disk and launch of fast collimated outflows Effects on nebular morphology Martín A. Guerrero, Hard X-ray Emission from CSPNe M 2-48

LoTr 5: When a galaxy group meets a PN Serendipitous Chandra and XMM-Newton observations (RX J1256.0+2556) X-rays peaking at ≈1 keV with secondary peak at ≈1.5 keV and high energy tail kT1=0.61 keV, kT2=3.1 keV Lx= 8.0 × 1030 ergs s-1 Notable X-ray variability (Montez et al. 2010; Guerrero et al., in prep.) XMM observations give similar spectral shape (kT1=0.6 keV, kT2=2.3 keV), but Lx = 2.2×1030 ergs s-1 and no clear variability 10

LoTr 5: a bipolar PN with a multiple central star Multiple system IN Comae including a G5 III star Rotation speed close to break-up velocity: vrot sin(i) ≈ 67 km s-1 Saturated coronal activity from a G5 III star: Lx/Lbol ≈ 10-3 LoTr 5 is an almost pole-on bipolar PNe (Graham et al. 2004) Bipolar axis and binary orbital plane are orthogonal Martín A. Guerrero, Hard X-ray Emission from CSPNe 11

Two post-common envelope close binary CSPNe Montez et al. (2010) has detected X-ray emission from the O-type subdwarf + late-type companion CSPNe of HFG 1 and DS 1 kT ≈ 0.5 - 2.0 keV Lx ≈ 1030 ergs s-1 Saturated coronal activity Lx/Lbol ≈ 10-3 DS 1 DS 1 (Miszalski et al. 2009) Martín A. Guerrero, Hard X-ray Emission from CSPNe 12

PNe with Collimated Outflows and Hard X-ray CSPNe NGC 2392 Mz 3 NGC 6543 NGC 6826 13

Late Type Stars Coronal Activity and Age In late type stars, Lx is related to rotation and declines with age !!! Lx≈ v2rot (Pallavicini et al. 1981) Lx≈ t-β 1.5 < β < 2.0 (Güedel et al. 1997) Mi=3M Mi=1.5M Enhanced X-ray emission (Lx/Lbol = 10-3 – 10-5.21):  Massive PN progenitor for companions to stay active longer enough  Evolution towards the PN phase sped up by the companion  Angular momentum transfer from the PN progenitor to the companion  Rotation of companion abnormally fast: LoTr 5  Giants in symbiotic stars rotate faster (Zamanov et al. 2006)  Rapid-rotating companions of WDs: 2RE J0044+093, 2RE J0357+283  Tidal synchronization (close binaries), wind accretion (wide binaries) (Jeffries & Stevens 1996)  F7-M4 can be spun up to P ≈ 3 days (Soker & Kastner 2002) for AGB and RGB 14

Hard X-ray Emission from the Helix Central Star ROSAT: Hard (> 0.5 keV) component (Leahy et al. 1994) - not a known binary system; spectrophotometric standard ! not a powerful stellar wind to produce a hot bubble Spatial coincidence? Background source? Diffuse emission?

Chandra and XMM-Newton Observations of the Helix A point source at the central star X-ray emission peaking at 0.9 keV and decline of X-ray emission: kT1 = 0.65 keV, kT2 = 1.3 keV, Lx = (6.4 – 7.7)×1029 ergs s-1 (Guerrero et al. 2001) Serendipitous XMM-Newton observations: even lower Lx KT1 = 0.65 keV, KT2 = 1.3 keV, LX= 5.2×1029 ergs s-1 (Guerrero et al., in prep.) Martín A. Guerrero, Hard X-ray Emission from CSPNe 16

Hard X-rays from the Helix CSPN: Not What You Expected Variability of stellar H and [N II]: possible evidence for dMe companion (Gruendl et al. 2001) Spitzer detection of a point source in all IRAC and MIPS bands up to 70 μm  IRAC 3.6, 4.5, and 5.8 μm emission consistent with the CSPN Rayleigh- Jeans tail, but no sign of the dwarf companion!  IRAC 8.0 μm and MIPS emission: cold, 100-130 K thin debris disk of dust distributed between 35-150 AU  Disk origin: Collisions of Kuiper Belt- like objects, or to the breakup of comets from an Oort-like cloud? (Su et al. 2007) X-ray emission and H and [N II] variability product of intermittent accretion of material from the disk Martín A. Guerrero, Hard X-ray Emission from CSPNe 17

Enigmatic Hard X-ray Emission from WDs PG 1159 and KPD 0005+5106 (O’Dwyer et al 2003; Chu et al 2004)  Among the two hottest WDs  PG 1159 is a pulsator -> no binary  KPD 0005+5106 not a background source: O VIII lines (Werner et al. 1996) Chandra observations (Chu et al., in prep.)  Very low metal content: - X-ray transparent atmospheres - tight constrain on accretion  Very small fraction of single WDs shows hard X-rays (Bilíková et al. 2010) Leakage of the Wien high-energy tail from deep in the stellar atmosphere? Detailed ad-hoc NLTE models by T. Rauch at the Teff and with precise surface abundances have failed so far to reproduce it. 18

Shock-in Winds: OB and WR stars NGC 2392*, NGC 6543 and NGC 6826 also have fast stellar winds DACs (Discrete Absorption Components) moving outwards in the wind of NGC 6543 with ~0.17 days modulation (Prinja et al. 2007) Variability of the P Cygni profiles of high-excitation UV lines in NGC 2392 and NGC 6826 similar to those seen in OB stars (Guerrero & De Marco, in prep.) v ~ 1,100 km s-1 Martín A. Guerrero, Hard X-ray Emission from CSPNe 19

Shock-in Winds: OB and WR stars Instabilities of the driving mechanism of the stellar wind can lead to shocks in the wind of single O, early B, and WR stars. (Lucy & White 1980; Gayley & Owocki 1995) Lx = 1031 – 1033 ergs s-1 Tx ≈ a few 106 K (kT = 0.2-0.5 keV) log Lx/Lbol = -6.912 ± 0.153 log LX = 0.574×log Lw + 11.45 (Sana et al. 2006) Martín A. Guerrero, Hard X-ray Emission from CSPNe 20

Shock-in Winds: OB and WR stars The fast stellar winds of NGC 2392*, NGC 6543, and NGC 6826 WR stars: Lw ≈ 1037-1038 ergs s-1 CSPNe: Lw ≈ 1032-1034 ergs s-1 NGC 6543 and NGC 6826 have lower Lx/Lw: log Lx/Lw = -4.1 – -4.9 OB stars log Lx/Lw = -2.5 – -3.1 NGC 2392: kTshock = (3/16) m v2 v∞ = 420 km s-1  kT = 1.3 [v/1,000 km s-1]2 keV = 0.23 keV !! Martín A. Guerrero, Hard X-ray Emission from CSPNe 21

Other Possible Origins of the Hard X-ray Emission  Accretion:  From a companion (quiescent novae or cataclysmic variables).  From a debris disk. CVs and quiescent recurrent novae have large optical/IR/UV and X- ray variability. Accretion is inhibited by fast stellar winds: dMac/dT > 10-5 M yr-1  Stellar winds:  Interacting winds (WR+OB binary systems or symbiotic stars). Orbital radius dependence, but basically noticeable wind and unseen companion -> <-  Wind ablation of a stellar or sub-stellar companion. Orbital radius changes with stellar evolution: the lower the mass of the companion, the stronger dependence Martín A. Guerrero, Hard X-ray Emission from CSPNe 22

Possible Origins of the Hard X-ray Emission CSPN Coronal Wind WD Accretion shock-in colliding ablation companion dust LoTr 5 ✓ ✗ ✗ ✗ ✓ ✗ ✗ Mz 3 ✓ ? ? ? ✗ ✗ ✗ NGC 2392 ✓ ✗ ✗ ? ✗ ✗ ✗ NGC 6543 ✓ ✓ ✓wb ✓cb ✗ ✗ ✗ NGC 6826 ✓ ✓ ✓wb ✓cb ✗ ✗ ✗ NGC 7293 ✗ ✗ ✗ ✗ ✓ ✗ ✓ DS 1 ✓ HFG 1 ✓ Martín A. Guerrero, Hard X-ray Emission from CSPNe 23

Conclusions  Coronal emission from a late-type companion Enhanced coronal activity and rotation late in the star life  Shock-in winds as in OB stars Scaled down versions of OB winds: Lx/Lbol, Lx/Lw Wind variability  Other wind interactions Dwarf stellar (no sub-stellar or giant planet) companion  Leaking from underneath the atmosphere as in hot WDs Unlikely due to “relatively” low Teff and surface abundances  Accretion Not a viable mechanism in general Accretion from a debris disk as a last resource to explain Helix CSPN X-ray emission: abundances, variability Martín A. Guerrero, Hard X-ray Emission from CSPNe 24