1. Distances to PNe using angular expansion parallax Lizette Guzman-Ramirez (JBCA, University of Manchester) Yolanda Gomez and Laurent Loinard (CRyA, UNAM, Mexico) 41st YERAC University of Manchester/Jodrell Bank Observatory, 18-20 July 2011

2. Why distances are important? Essential parameter for studying the stellar and nebular parameters as well as the evolution of the central star. While the total number of PNe in the Milky Way has been estimated to be somewhere between 5000 and 25,000, less than 50 have distances with reasonable accuracy. Used to measure the rotational curve in other galaxies, dark matter halos and using the PNLF estimate the distance to this galaxies.

4. PNe M2-43 [WC8] –Distance estimations 1.4 kpc (Cahn et al. 1992) to 4.45 kpc (Van de Steen et al. 1994b) IC 418 –Distances estimations 0.36 kpc (Acker et al. 1978) to 5.74 kpc (Phillips et al. 1984) NGC 6881 –Distance estimations 1.5 kpc (Cahn et al. 1984) to 6.4 kpc (Zhang et al. 1995)

5. Angular Expansion in Radio Masson (1986), was the first person to use this technique. Observed NGC 7027 in two epochs with a 2.8 years gap. Because you are trying to observe very small changes in the nebula, this technique requires very high resolution data. Interferometry is the way to go.

6. M2-43 VLA-A, 1995.65 & 1999.72 At 8Ghz (3.6 cm) Angular resolution of  0.3”  t=4.07 yr Model

7. IC 418 VLA-B, 1986.49 & 2007.85 At 5GHz (6 cm) Angular resolution of  3”  t=21.36 yr

8. NGC 6881 VLA-A, 1984.99 & 1994.24 At 4.8GHz (6 cm) Angular resolution of  0.8”  t=9.25 yr

9. Angular Expansion d  /dt =  /  t, where  is the size of the nebula (“) and  t is the difference between the two epochs. M2-43d  /dt = 0.61 +/- 0.09 mas/yr. IC418 d  /dt = 5.80 +/- 1.50 mas/yr. NGC 6881d  /dt = 2.10 +/- 0.70 mas/yr. D = 211(v exp / d  /dt ), M2-43D = 6.9 +/- 1.5 kpc. IC 418D = 1.3 +/- 0.4 kpc. NGC 6881D = 1.6 +/- 0.5 kpc.

10. Important Parameters M2-43 Ionised Mass M ion = 0.03 M  Electronic Density n e = 1.1 x 10 5 cm -3 Emission Measure EM = 4 x 10 8 cm -6 pc Kinematic Age T = 500 yr IC 418 Ionised Mass M ion = 8.7 M  Electronic Density n e = 6.2 x 10 3 cm -3 Emission Measure EM = 5 x 10 6 cm -6 pc Kinematic Age T = 1200 yr NGC 6881 Ionised Mass M ion = 0.002 M  Electronic Density n e = 5 x 10 4 cm -3 Emission Measure EM = 28 x 10 6 cm -6 pc Kinematic Age T = 350 yr

12. Conclusions and Future Work Distances are important! Angular expansion technique give us reliable distances with a good accuracy. Proposal for eMerlin for a few more objects that have already been observed so we only need a second epoch.

13. Thank you!

14. Radial velocity M2-43, radial velocity of 111 +/- 40 km/s (Schneider et al., 1983), Galactic model from Brand & Blitz (1993).