An unprecedented source of planetary nebulae, the disk-like relics of
elderly, dying stars, has been discovered in the southern part of our Milky
Way galaxy.

With about 1000 planetary nebulae found so far and many more still to be
discovered, the number of aged stars in their death throes revealed by the
new survey is rapidly overtaking the entire population discovered over the
entire sky during the last 75 years.

The cosmic graveyard is revealed in deep survey images taken in H-alpha
light with the UK Schmidt Telescope at the Anglo-Australian Observatory
(AAO/UKST) in New South Wales, Australia. The survey was led by Quentin
Parker (Institute for Astronomy, Royal Observatory Edinburgh) and Steven
Phillipps (University of Bristol)

Dr. Parker will be showing the colourful new images obtained during his
survey to the UK National Astronomy Meeting in Bristol on Wednesday 10 April
2002, and explaining their significance for improving our understanding of
star formation and evolution.

“So far we have identified 1000 new planetary nebulae from visual scans of 70
percent of the southern Galactic plane,” said Parker. “This number is now
increasing rapidly as the plates are systematically scrutinised by the
SuperCOSMOS facility at the Royal Observatory, Edinburgh, so that more
compact, fainter candidates are being found.”

According to Parker, the doubling of the known population of planetary
nebulae will have a significant impact on many aspects of research into
stellar evolution and Galactic structure.

“Finding evolved planetary nebulae and their central stars can help us
understand stellar evolution during the critical transition phase between the
nebula and a white dwarf,” he said. “There is a currently a severe paucity of
observational data of evolved planetary nebulae which our new catalogue
should help address.”

The highlights from the new sample include identification of some rare and
unusual objects:

* 8 Wolf-Rayet stars (exceptionally hot stars rich in carbon or nitrogen)
have been discovered at the centres of new planetary nebulae from follow-up
spectroscopy. They include what may be the first nitrogen-rich central star
yet found in our Galaxy. Only 56 Wolf-Rayet stars are currently known.

* The discovery of several halo planetary nebulae travelling at more than 300
km/s towards the Galactic centre.

* The discovery of a planetary nebula in an old open star cluster. This is an
extremely rare and valuable find as the known cluster (and hence planetary
nebula) distance enables accurate estimates of planetary nebula parameters.

* The identification of large numbers of evolved planetary nebulae, many with
angular sizes from 100arcseconds to 8arcminutes.

* The discovery of several close pairs of planetary nebulae, with separations
of less than 2arcminutes.

* The discovery of additional shells, ansae (“handle-shaped” clouds) and
lobes around many known planetary nebulae. This may help to solve the problem
of missing mass in planetary nebulae, since they provide evidence of previous
episodes of material being ejected into space. Their new angular dimensions
should lead to re-evaluation of many distance estimates.

* The discovery of two faint equidistant lobes either side of the well known
butterfly-like planetary nebula NGC2899, probably making this object one of
the largest and closest planetary nebulae to the Sun.

* The discovery of several hundred planetary nebulae in the Galactic Bulge
region – the densely populated region of stars close to the centre of the
Galaxy.

NOTES FOR EDITORS:

Studies of planetary nebulae are essential for improving understanding of the
later evolution of low mass stars like our own Sun and of stellar evolution
in the critical phase prior to the creation of small, dead stars known as
white dwarfs. They provide vital probes for studying processes of
nucleosynthesis inside stars, abundances of chemical compounds and chemical
enrichment of interstellar space, acting as powerful indicators of our
Galaxy’s star formation history.

Planetary nebulae are also excellent tracers for Galactic Bulge dynamical
studies because they are less affected by metallicity bias than other tracers
and have strong emission lines permitting accurate velocity determinations.

The AAO/UKST H-alpha Survey was carried out using a filter that reveals hot,
hydrogen-rich clouds in the Galactic plane. It uses the world’s largest
optical interference filter for astronomy and covers a swathe approximately
20 degrees wide along the Galactic plane. This provides an unprecedented
combination of coverage, resolution and sensitivity that make it superior to
any previous survey of this type.

CONTACT DETAILS:

During the UK National Astronomy Meeting (9 – 12 April) Dr. Parker can be
contacted via the NAM press office (see above).

Normal contact details:

Dr. Quentin A Parker

Institute for Astronomy

Royal Observatory

Edinburgh

EH9 3HJ

Tel: +44 (0)131-668-8378 (switchboard): +44 (0)131-668-8100

Mobile: +44 (0)7714-143273

Fax: +44 (0)131-662-1668

E-mail: qap@roe.ac.uk

URL: http://www.roe.ac.uk/ifa/people/

>From 16 April 2002 Dr. Parker can be contacted at:

Dept. of Physics

University of Macquarie

Sydney

NSW 2109

Australia

E-mail: qap@physics.mq.edu.au

FURTHER INFORMATION AND AN H-ALPHA IMAGE OF THE VELA SUPERNOVA REMNANT CAN BE
FOUND ON THE WEB AT:
http://www-wfau.roe.ac.uk/sss/halpha/hapr.html

DETAILS OF THE H-ALPHA SURVEY CAN BE FOUND ONLINE AT:
http://www.roe.ac.uk/wfau/halpha/halpha.html

OTHER IMAGES OF PLANETARY NEBULAE AND BACKGROUND INFORMATION CAN BE FOUND AT:
http://www.astro.washington.edu/balick/WFPC2/index.html