eSMA science case for evolved stars (AGB, post-AGB, proto-PNe and PNe)

1. eSMA science case for evolved stars(AGB, post-AGB, proto-PNe and PNe) Wouter Vlemmings With various levels of input by: Albert Zijlstra (Manchester) Anita Richards (Manchester) Rebeca Soria-Ruiz (JIVE) Dinh Van Trung (ASIAA) Hans Olofsson (Onsala)

2. Asymmetry of the CSE • AGB stars and their envelopes are nicely spherical ?? • CO (Castro-Carrigo et al.; Olofsson et al. 2000) • Masers • PNe formed by fast wind overtaking initial slow wind. • <20% of the PNe are spherical ! • Several indications of asymmetry already during the AGB phase • IR interferometry (IOTA) reveals asymmetries in large sample at ~10 mas level (Ragland et al. 2006) • mid-IR shows asymmetric dust distribution around IK Tau (Weiner et al. 2006) • NIR speckle interferometry (Wittkowski et al. 1998) • And CO & maser observations • But origin and onset of asymmetries unknown • Companions / magnetic field / ‘star’spots

3. Evolved star: dust Polarization • AGB/PPNe observations find strong magnetic fields might be responsible for driving and shaping mass-loss • Understanding essential in studies of ISM enrichment and PNe shaping • Submm dust polarization observations are needed to confirm suspected magnetic shaping • Polarization originates from asymmetric dust grain distribution aligned with magnetic field • PNe NGC 6537: • Timescale for dust alignment t  B-2, which for 1 mG fields is ~106 yr • However, nebula timescale is ~104 yr • Alignment occurs closer to the star and is maintained in the outflow  magnetic shaping of the outflow NGC 6537 850 m SCUBA polarization (Sabin et al. 2007, Greaves 2002)

4. Evolved star: dust Polarization CRL 2688 • The values: • Linear polarization: 5-15% • Envelope extent: 1-10 arcsec • Larger for PNe (~20 arcsec) • Flux (at 1 kpc) varies wildly • Most sources of interest have fluxes of several hundred mJy • For significant detection of polarization we need rms of ~10mJy • Current observational problems: • Only high angular resolution observations (subarcsec) can probe inner region of the envelope where dust alignment occurs without suffering badly from beam depolarization • In the inner part of PNe, besided beam depolarization, linear polarization is reduced due to ionization. Weaker linear polarization down to ~1% needs to be accessible • Shorter wavelengths emission is stronger but in single dish the resolution insufficient  eSMA combination of polarization sensitivity and angular resolution essential NGC 7027

5. Submm dust polarization Cold Dust (50 K) 3  detection limit of 1% linear polarization in 1 eSMA observing track PNe NGC 6537 (~1.5 kpc; Matsuura et al. 2005)

6. Weighing the dust NGC 6302 • Recent paper by Peretto et al. (2007) find massive dust torus in a PNe using JCMT and SMA observations • Need to determine how widespread this phenomenon is • Including its relation to magnetic field and binaries • Many sources need higher angular resolution • NGC 6302 only barely resolved • CO observations at high angular resolution can resolve and weigh the dust torus • Using 12CO and 13CO ratio at same line transition (J=3-2, 330 and 345 GHZ) SMA CO map (top) and CO ratio (bottom)

7. CO observations • CO observations at high angular resolution can resolve circumstellar asymmetries while not being limited to only the most nearby objects • CO observations are fairly straightforward probes of the envelope kinematics • And thus good comparison for the widespread maser observations • Spatial variation in CO ratio can illuminate mass-loss history • i.e. Thermal pulses • Possibility for CO polarization studies up to now only done at lower transitions in star-forming regions Castro-Carrizo, PdB Olofsson, PdB at 115 GHz

8. Conclusions • Main project would consist of continuum dust observations of evolved stars. • Mapping the dust distribution of PPNe and AGB stars to find disks/outflows etc. is well suited for eSMA as: • Optimal frequency around 350 GHz • Sources are compact  high angular resolution • Sources are weak  high sensitivity • Linear polarization of the circumstellar dust around evolved stars, in particular (P-)PNe • Essential to determine the driving forces behind the AGB mass-loss • Current observations limited by low resolution, beam depolarization and sensitivity (Sabin et al. 2007, Greaves et al. 2002). • eSMA can uniquely map the distribution of 12CO and 13CO (J=3-2), resolve massive dusty disks and determine mass-loss history