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Astronomers find Paschen in the bar
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Robert Sharp (1), Ian Parry (1), Stuart Ryder (2), Johan H. Knapen (3) and Lisa Mazzuca (4)
(1) IoA Cambridge, (2) AAO, (3) Univ.of Hertfordshire, (4) NASA/GSFC
An international team of astronomers have used a unique instrument on
the 8m Gemini South Telescope to determine the ages of stars across
the central region of the barred spiral galaxy, M83. Preliminary
results provide the first hints of a domino model of star formation where star formation occurs in a time sequence, driven by the movements of gas and stars in the central bar.
The new instrument, called CIRPASS,
simultaneously produces 500 spectra, taken from across the whole
region of interest, which act as a series of 'fingerprints'.
Encoded in these 'fingerprints' is not only all the information the
team required to determine when individual groups of stars formed, but
also information on their movements and chemical properties. Dr.
Johan Knapen, project co-investigator, 'The unique combination of a
state-of-the-art instrument like CIRPASS with one of the most powerful
telescopes available is now providing us with truly sensational
observations.'
M83 is a grand design spiral galaxy undergoing an intense burst of
star formation in its central bar region. Large scale images, of the
visible light from the galaxy, taken with ground based telescopes,
show a pronounced bar across the middle of the galaxy) seen as
the diagonal white structure in figure 1
. Astronomers believe that it is the influence of this bar
which leads a concentration of gas in the central regions of the
galaxy from which stars are born. 'The central region of M83 is
enshrouded in dust, but by using CIRPASS, which operates in the
infra-red not the visible, we are able to see through this dust and
investigate the hidden physical processes at work in the galaxy,'
said Dr Ian Parry, leader of the CIRPASS instrumentation team.
Two competing theories strive to explain the burst of star formation
in the centre of the galaxy, M83. One theory suggests that stars form
randomly across the whole nuclear region. A second model, favoured by
the observational team, proposes that star-formation is triggered by
the bar structure. In this model, the rotation of gas and stars in the
bar causes stars to be formed sequentially, in a domino manner.
Using a technique first demonstrated by Dr. Stuart Ryder and
colleagues, the team searched for a hydrogen emission feature, the
Paschen-beta line, within the galaxy's
'fingerprints'. The measurement of this feature indicates the
presence of hot young stars. By comparing the strengths of the
Paschen-beta emission with the amount of absorption from
carbon-monoxide (arising in the cool atmospheres of old giant stars)
the team are able determine the age of the stars in each region of the
galaxy. 'A detailed analysis of the data is underway but initial
results hint at a complex sequence of star formation,' said Dr Robert
Sharp, instrument support scientist with CIRPASS.
Preliminary analysis of other emission features (due to Paschen-beta
and ionized iron) revealed a potentially intriguing result. 'Ionized
iron enables us to trace past supernova explosions. The observations
indicate that energy from exploding stars (supernovae) may be being passed into
regions of undisturbed gas causing further massive star formation.' said
Dr. Stuart Ryder, principle investigator.
While some members of the instrument team are presenting their work at the Royal Society Science Exhibition in
London, CIRPASS is back on the Gemini South Telescope in Chile, performing the next set of observations.
Contact information
Robert Sharp, email: rgs@ast.cam.ac.uk, Tel: +44 (0)1223 337148 (In Chile, until mid-July, contactable by e-mail)
Ian Parry, email: irp@ast.cam.ac.uk, Tel: +44 (0)1223 337092
Stuart Ryder, email: sdr@aaoepp.aao.gov.au
Johan Knapen, email: knapen@star.herts.ac.uk
Lisa M. Mazzuca, email : mazzuca@stargate.gsfc.nasa.gov
For general contact information and assistance
Lisa Wright, email:ljw@ast.cam.ac.uk, Tel: +44 (0)1223 337527
Scientific Publications:
Harris J. etal. 2001, ApJ, 122, 3046
Ryder S.D., Knapen J.H. and Takamiya M. 2001, MNRAS, 323, 663
Web Resources
1. Insitute of Astronomy, Cambridge, http://www.ast.cam.ac.uk
2. Anglo-Australian Observatory, http://www.aao.gov.au/
3. University of Hertfordshire Astronomy Research Group, http://star.herts.ac.uk
4. NASA Goddard Space Flight Centre, http://www.gsfc.nasa.gov/
5. Cambridge Infra-Red PAnoramic Survey Spectrograph, http://www.ast.cam.ac.uk/$\sim$optics/
6. The Gemini Observatory, http://www.gemini.edu
7. Hubble Space Telescope Science Institute, http://www.stsci.edu
Figures
A large scale image of
the barred spiral galaxy M83 as seen from a ground based telescope.
Right : The closer view of the Hubble space telescope gives a detailed
image of the nuclear region of the galaxy (Harris etal. 2001
ApJ 122 3046). The coloured outlines show the locations of the
CIRPASS cluster of 500 lenses during the three observations.
 |
 |
|
CIRPASS achieves it's wide, two
dimensional, field of view by employing a cluster of optical fibres.
The cluster, known as and integral field unit (IFU), shown to the
above left, is placed at the focus of the telescope. A spectrum is
recorded through each fibre, the ends of which can be seen as the
hexagonal array of dots in the picture. The 8m Gemini South telescope
(see to the right above is located at 10,000 feet on the peak of Cerro
Pachon in the Chilean Andes. Photo Courtesy of Gemini Observatory) |
 |
 |
| The maps above show the measured
intensity of the Paschen-Beta (left) and Ionised Iron [FeII](right)
emission lines. The [FeII] emission is rather clumpy, and confined
mainly to the outer edges of the more diffuse Paschen-Beta emission.
This %suggests that massive star formation is being propagated into
regions of undisturbed gas by the passage of supernova blasts. |
|
