1. Hen 2-90: The Planetary Nebula which looks like a YSO Raghvendra Sahai Jet Propulsion Laboratory, Caltech 1.Discovered by Henize (1967), listed in Perek-Kohoutek catalog as PK 305+1#1 2.Optical spectra taken by Costa et al. (1993) – young PN with stellar Teff=50,000 K, low abundances of O, N, Ne and Ar Discovery of Jets in Hen 2-90 (Sahai & Nyman 2001) Included in Sahai & Trauger’s HST/ WFPC2 (H-alpha) imaging survey of young PNe (sample selected based on low [OIII]5007/H-alpha flux ratio) 1.HST Image showed (1) linear, knotty, bipolar, symmetric jet & (2) central bipolar nebula hstjet hstjet 2.Ground-based (ESO) images showed jet extending linearly to to about 40 arcsec on each side eso eso 3.Jet highly collimated (opening angle=4 deg), ionised, knot masses about 10^-6 Msun, jet mass ejection rate about 10^-8 (D/2.5kpc)^1.5 Msun/yr 4.Kinematic distance=2.8 kpc

2. Jet Radial Velocity and Proper Motions Long-slit spectroscopy from ground ( Guerrero et al. 2001, Sahai et al 2002 ) showed that jet radial velocity is remarkably constant (+/- 26 km/s) rv. rv Line-widths in knots indicate that latter expanding at roughly the sound velocity in ionised 10^4 K gas (10 km/s) ( Guerrero et al. 2001 ) 2 nd epoch HST imaging (2 yrs after discovery) clearly showed proper motions of 30 mas/yr ( Sahai et al 2002) pm pm Hence intrinsic jet speed = 360 (150) km/s, inclination to sky-plane is 4.2 (10.3) deg, if D=2.5 (1) kpc Minimum jet age (derived directly from proper motion and linear extent of jet) = 1400 yrs

3. The Nature Of Hen 2-90 and its Bipolar Jet Plausible Binary Model for Launching Jet: Accretion disk around a Binary Companion, plausible parameters – primary/companion each of 0.6 Msun, P=40 yr, semimajor axis 12 AU ( Sahai et al 2002 ). Models of Jet Propagation: MHD models of jet with periodic low- amplitude changes in outflow velocity ( Lee & Sahai 2003 ) produce knots, toroidal magnetic field in jet needed to keep knots confined Is Hen2-90 a symbiotic star? Guerrero et al. 2001 think so, based on near-IR colors (I-J, J-K), which, according to Schmeja & Kimeswenger (2001), can separate symbiotics from PNs. But no direct evidence of a red giant seen so far spectroscopically (e.g. strong red & near-IR continuum, molecular bands, etc.) For D roughly 1-3 kpc, luminosity is consistent with a young PN classification (latter also consistent with location in IRAS color-color diagram, emission-line diagnostic diagram), lack of a dense star- forming core makes massive-unevolved star hypothesis unlikely

4. The Knotty Bipolar Jet and Central Region intro intro

5. He2-90 – Extended Jet in [NII] Sahai et al. 2003, in prep. intro intro

6. Proper Motions of Jet Knots pmtxt pmtxt

7. Jet Radial Velocity pmtxt pmtxt

8. Extended Jet – Radial Intensity

9. Jet: Excitation