Search for Pulsations in Hydrogen-Deficient Planetary Nebula Nuclei Jan-Erik Solheim, ITA,Oslo Jose M. Gonzalez Perez, IAC, Tenerife Gerard Vauclair, Obs-MiP, Toulouse

Content Introduction, why search for variability? selection of targets - bipolar nebulae results of first campaigns – the non pulsators 3 years of NGC variability on many time scales repeated studies of two “hybrid PG 1159 stars” new results conclusions

The Inspiration In this paper: 6 new pulsators, making a total of 14 PG pulsators or GW Vir stars

The basic (1996) results The hot PNNs with O VI (early WC) have: --longer periods than GW Vir white dwarfs --low amplitudes --highly variable temporal spectra on time scales months or less Bond and Ciardullo 1996

Our Search Criteria Hot Hydrogen-Deficient PNNs with PG1159 or O VI spectra Non sperical planetary nebulae shape Question: Is there any sign of binarity in the temporal spectra? Ex: harmonics

Selection of objects – 11 targets

First results: “ 7 Non Pulsators”

Possible Non Pulsators ? PG NGC 7094 NGC 5765 NGC FAP = 1/20 IsWe 1 Abell 43 Abell 21

Pulsators detected (or studied in detail): NameT eff (kK) log gPeriods (min) Comments Jn , 31Suspected (BC) NGC Variable-known VV Variable Abell Stable? NGC Stable?? NGC 6852 (K1-14 type) ??18, 85:Unconfirmed NGC Maybe var. PN G , 170Long period Teff and log g from Werner and Herwig 2006

NGC 6852 Observed two nights, First night: No Pulsations Next night: At least one pulse

VV 47 – highly variable temporal spectra:

VV 47 comparison of peaks of different runs 1,2) Harmonics  Sign of binarity 3) Ratio 0.87  sign of trapped modes  The high frequency spectrum: g-modes driven by ε- mechanism (unstable)  Change during the same night

Corsico et al.2006 VV 47 compared with predictions P = s ( ) And 261s ( )

NGC followed 3 years ( ) 16 runs Changes the same night, July 21, 2000 Changes between two nights, July 21-24,2000

NGC 246: Changes from night to night –and possible harmonics of 227 μHz (73 min) May we interprete 227 μHz as an orbital period (73 min) ?

NCC pulse in burst -morlet wavelet - sudden appearance of periodic signal

NGC 246 Rapid change of temporal spectrum

Harmonics of 227 μHz – sometimes with low amplitudes

NGC 246 – pulse shape with period P=4349 s = 72.5 min

NGC 246 P=72.5 min is stable over 3 yrs: Orbital period  Most stable Superhump period (in disk)  most harmonics Rotation period  too fast if single star

NGC 246 – a binary system with P=72.5 min? Stable period over 3 yrs Pulse form varies between single, double and triple humped Period is close to expected CV minium He II in emission – sign of accretion Strong wind works against accretion Shape of nebulae indicate common envelope interaction with substellar companion – planet or brown dwarf (Soker 1997)

Corsico et al.2006 NGC 246 compared with predictions P = s No short periods

Abell 43 – pulsate or not pulsate? Ciardullo & Bond, 1996: possible variations P~2473s Schuh et al, 2000: P~5500s (2473 is an artifact) Gonalez Perez et al, 2007: no variations(obs 2000) Quirion et al. 2004: no pulsations expected (composition) Vauclair et all, 2005: 2 periods: 2600 and 3035s(not in model with X C =0.05) Quirion et al. 2005: (new atmosphere –> X C =0.23) predict P l=1: s Corsico et al 2006, predictions P > 2500 s Solheim et al., 2007: 6 periods: s  (2680 s and 5442s are the strongest ~ 2 mma)

Abell 43 in June 2004 P=2600,3035s

A43 model (Quirion et al 2005) X(H)=0.35 X(He)=0.42 X(C)=0.22 X(O)=0 X(Z)=0.01

Abell 43 observed in 2005: -4 n. (24 hrs) No high freq. peaks, 3 or more low freq. peaks

Abell 43: prewhitening – combined light curve

Abell 43 Observed and simulated light curve (6 periods)

NGC 7094 –almost identical to Abell 43 T= K, log g= 5.7, X(H)=0.35, X(C)=0.23 Abell 43: X(He)=0.42, X(O)=0.00 NGC 7094: X(He)=0.41, X(O)=0.01 Predictions (Quirion et al 2005):  Pl=1(Abell 43): s  NGC 7094: s

Freq (μHz) Per (s) Ampl (mma)

NGC 7094 –almost identical to Abell 43 T= K, log g= 5.7, X(H)=0.35, X(C)=0.23 Abell 43: X(He)=0.42, X(O)=0.00 NGC 7094: X(He)=0.41, X(O)=0.01 Predictions (Quirion et al 2005):  P(l=1) Abell 43: s  NGC 7094: s Observations:  Abell 43: s somewhat wider than predicted  NGC 7094: shorter as predicted

Corsico et al.2006 Abell 43 and NGC 7094 compared with predicitions Abell 43: s NGC 7094: s No short periods NGC 7094

New pulsator? NGC 2242 – possible of rapid change type P~11 min First part of night All night

New pulsator? PNG (Vy 1-1) – long period Strong modulations (P~5 000s and s ) not present in comparison stars: Double humped orbital period of about 3hrs?

Conclusions I Abell 43 and NGC 7094 are stable long period pulsators (P > 2000s) PNG (Vy 1-1): maybe also long period variable, needs confirmation VV 47 and NGC 246 are rapidly variable – short timescale modulations – long and short periods  Stable long period – maybe orbital (P=72 min for NGC 246)  NGC 2242: maybe rapidly variable, needs confirmation JN1 and NGC 5852 need confirmation

Conclusions II Need better analytical tools for analysis of the unstable light curves....  Wavelet analysis..or better  Ratios 0.87 for trapped modes  Harmonics related to orbital periods  Model predictions  Multisite campaigns