Distances to PNe using angular

expansion parallaxLizette 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

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.

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)

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.

M2-43

• VLA-A, 1995.65 & 1999.72

• At 8Ghz (3.6 cm)

• Angular resolution of 0.3”

t=4.07 yr

Model

IC 418

• VLA-B, 1986.49 & 2007.85

• At 5GHz (6 cm)

• Angular resolution of 3”

t=21.36 yr

NGC 6881

• VLA-A, 1984.99 & 1994.24

• At 4.8GHz (6 cm)

• Angular resolution of 0.8”

t=9.25 yr

Angular Expansiond/dt = /t,

where is the size of the nebula (“) and t is the difference between the two epochs.

• M2-43 d/dt = 0.61 +/- 0.09 mas/yr.• IC418 d/dt = 5.80 +/- 1.50 mas/yr.• NGC 6881 d/dt = 2.10 +/- 0.70 mas/yr.

D = 211(vexp / d/dt ),• M2-43 D = 6.9 +/- 1.5 kpc.• IC 418 D = 1.3 +/- 0.4 kpc.• NGC 6881 D = 1.6 +/- 0.5 kpc.

Important Parameters

M2-43• Ionised MassMion = 0.03 M

• Electronic Density ne = 1.1 x 105 cm-3 • Emission Measure EM = 4 x 108 cm-6pc• Kinematic AgeT = 500 yr

IC 418• Ionised MassMion = 8.7 M

• Electronic Density ne = 6.2 x 103 cm-3 • Emission Measure EM = 5 x 106 cm-6pc• Kinematic AgeT = 1200 yr

NGC 6881• Ionised MassMion = 0.002 M

• Electronic Density ne = 5 x 104 cm-3

• Emission Measure EM = 28 x 106 cm-6pc• Kinematic AgeT = 350 yr

Name D (kpc) ReferenceBD+303639 1.69 +/- 1.30 2.80 +/- 3 Masson (1989)BD+303639 1.73 +/- 0.51 2.68 +/- 0.81 Hajian et al. (1993)NGC 3242 13.2 +/- 4.7 0.42 +/- 0.16 Hajian et al. (1995)NGC 6302 1.7 +/- 0.3 1.60 +/- 0.6 Gómez et al. (1993)NGC 6210 3.10 +/- 0.42 1.57 +/- 0.40 Hajian et al. (1995)NGC 6572 2.51 +/- 0.76 1.49 +/- 0.62 Hajian et al. (1995)NGC 7027 4.7 +/- 7 0.94 +/- 0.2 Masson (1986)NGC 7662 5.6 +/- 5 0.79 +/- 0.75 Hajian y Terzian (1996)VY 2-2 1.13 +/- 0.12 3.60 +/- 0.4 Christianto y Seaquist (1998)M2-43 0.61 +/- 0.09 6.9 +/- 1.5 Guzman et al (2006)IC 418 5.8 +/- 1.5 1.3 +/- 0.4 Guzman et al (2009)NGC 6881 2.1 +/- 0.7 1.6 +/- 0.5 Guzman et al (2011)

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.

Thank you!

Radial velocity• M2-43, radial velocity

of 111 +/- 40 km/s (Schneider et al., 1983),

• Galactic model from Brand & Blitz (1993).