ANGULAR EXPANSION IN PLANETARY NEBULAE FROM RADIO INTERFEROMETRIC DATA

ANGULAR EXPANSION IN PLANETARY

NEBULAE FROM RADIO INTERFEROMETRIC DATA

Yolanda Gómez

Centro de Radioastronomía y Astrofísica, UNAM

México

Asymmetrical Planetary Nebulae IV, La Palma, España

Colaborators

Lizette Guzmán (CRyA, UNAM, México)Luis F. Rodríguez (CRyA, UNAM, México)


Angular expansion techniqueA geometrical method in which we substract two

images, taken over a period of a few years, to estimate the angular expansion rate of the nebula,

First applied by Masson (1986) to radio interferometric data to estimate distances to PNe.

1

//211 exp

yrmasskm

VpcD

v

D=v/D


Some examples

This technique has been applied with success to several PNe: e.g. NGC6302 (Gómez et al. 1993) , NGC6572 (Hajian

et al. 1995) , Vy 2-2 (Christianto & Seaquist 1998).

For PNe with distances > 1 kpc the expected angular expansion rate is < 2 mas/yr.

NGC 7027

yrmas /7.4

yrt 8.2

skmV /21exp

kpcD 2.094.0

(Masson 1986; 1989)


Planetary Nebula M 2-43

This is the largest distance for a PN measured, up to now, with the angular expansion technique.

yrmas /61.0

yrt 4

kpcD 5.19.6

(Guzmán, Gómez & Rodríguez 2006)

See poster by Guzmán et al.

skmV /20exp

VLA 3.6 cm

1999.72–1995.651999.72+1995.65


Other application for the angular expansion technique


The “Saturn Nebula” NGC 7009 The ansae (handles) are present in PNe with bipolar, rotating, episodic jets ( BRETS; e.g. López et al. 1995) and fast, low ionization emission regions (FLIERS; Balick et al. 1993).

In NGC 7009 the ansae are moving at about 100 km/s in the plane of the sky, relative to the nucleus (Reay & Atheton 1985; Balick et al. 1987).

The ansae are possibly the termination points of the jets (Balick et al. 1987; López et al. 2000; Steffen et al. 2001).

ansae

HST

Red [NII]; green [OIII]; blue [He II]


Proper motions of ansae

NGC 7009 Few measurements of proper motions of ansae: KjPn 8 (Meaburn

1997), Hen 2-90 (Sahai et al. 2002), NGC7009 (Fernández et al. 2004).

NGC 7009: From photographic plates a PM of 16 3 mas/yr (Liller 1965)

From HST images a PM for the eastern ansa of 28 8 mas/yr (Fernández et al. 2004) is derived.

HST images of the east ansa (Fernández, Monteiro & Schwarz 2004)


• Archive VLA data for NGC 7009 at 3.6 cm in two epochs: 1989.24 and 1997.33

Observations

NGC 7009yrt 09.8

VLA

Applying the angular expansion technique to NGC 7009 to measure proper motions of the ansae at radio.

VLA 3.6 cm


Western

Eastern

23 +/- 6 mas/yr

34 +/- 10 mas/yr

Ansae proper motions

(Rodríguez & Gómez 2007, RevMexAA, 43, 173)


Derived parameters for the ansae NGC 7009

• Assuming D= 860 +/- 340 pc, the velocities of the ansae in the plane of the sky are:

EAST ansa 100 +/- 50 km/s

WEST ansa 140 +/- 70 km/s• If the ansae are moving ballistically the estimated

age is:

~300 years if they originated from the main body

~850 years if they originated from the central star.


Upper limit to the expansion

Difference image

D 700 pc

Lower limit consistent with the average of 14 available values (Acker et al. 1992; Fernández et al.

2004), 860 +/- 340 pc.

The flux density of the main body remains constant.

The flux density of the jets decreased in 30%. With an electron density 1000 – 4000 cm-3 (Bohigas et al. 1994; Goncalves et al. 2003) the recombination timescales are between 30 to 120 yrs.


Conclusions Interferometric data taken with a few years of

separation can reveal the angular expansion of the nebula and it is possible to estimate its distance (e.g. M 2-43; Guzmán et al. 2006).

This is the first time that proper motions of ansae in PNe are determined with radio observations (NGC 7009; Rodríguez & Gómez 2007).


Thank you

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ANGULAR EXPANSION IN PLANETARY NEBULAE FROM RADIO INTERFEROMETRIC DATA