UK astronomers have pinpointed for the first time hundreds
of newborn stars inside their dusty cocoons, with the help
of “Michelle” — one of the most ambitious and technically
complicated ground-based instruments ever built. Michelle
is a youngster too: it has just celebrated its first
birthday on the United Kingdom Infrared Telescope (UKIRT)
in Hawaii.

Tamara King, a student from Leeds University, has been
using Michelle to look for hundreds of stellar nurseries.
Young stars are enshrouded in the dust and gas clouds out
of which they formed. These clouds block their light,
making it extremely hard to spot the stars.

King first looked at what she suspected was a Massive
Young Stellar Object (MYSO) at near-infrared wavelengths
with UFTI, the UKIRT Fast-Track Imager. The object is
about 10,000 years old — young in stellar terms. She saw
what looked like an outflowing jet of material, a third
of a light year long, and 3000 light years from Earth. She
explains “This could be material coming from a young star,
but until the star itself is seen we’re in the dark.”

Enter “Michelle” — short for “Mid-Infrared Echelle
Spectrograph”. Michelle gathers light with wavelengths in
the mid-infrared range, between 8 and 25 microns. It can
see through the dust to pinpoint the star. King says “The
star shone clearly through the murk, lined up with the
outflowing jet. This implies that it is indeed the
source of the jet. Our project is looking at hundreds of
candidate MYSOs. By unveiling these stellar birthplaces,
we’re getting one step closer to understanding the
complexities of how stars are born and evolve.”

Michelle has also been used to study the remnants of old
stars known as planetary nebulae, as well as planets,
asteroids and comets, the centre of our Galaxy, and
other galaxies millions of light years away.

Unfortunately, these are not the only things that shine
brightly in the mid-infrared. Every object at or around
room temperature shines too, including the Earth’s
atmosphere, and the telescope itself. Mid-infrared
astronomy has been compared to “observing in the
daylight, with the telescope on fire”!

Michelle was designed to overcome this — its detector and
optics are cooled by liquid helium to temperatures as low
as -269 degrees C, just 4 degrees above absolute zero. It
is also fitted to UKIRT, an infrared telescope with
excellent image quality and thermal stability. Situated
4194 metres above sea level, atop Mauna Kea in Hawaii,
UKIRT takes Michelle above much of the Earth’s atmosphere.

Unlike most astronomical instruments, the multi-talented
Michelle is so flexible that it can quickly switch
between the three main types of astronomical observation:
imaging, spectroscopy, and polarimetry. Dr Tom Kerr, the
UKIRT Michelle Scientist, says “Michelle is a boon to
infrared astronomers. Switching from one Michelle mode
to another is simple and quick, allowing us to carry out
different types of observations in one night. Previously
we’d have to use three separate instruments to do this.”

Dr Andy Adamson, the Director of UKIRT, adds “Michelle
opens up mid-infrared astronomy for the UK astronomy
research community. It’s a perfect match both for UKIRT
and for the excellent skies of Mauna Kea.”

Michelle was designed and built at the UK Astronomy
Technology Centre (ATC) in Edinburgh, Scotland. Having
spent a year on UKIRT, it will be shared with the
Gemini North telescope, also on Mauna Kea in Hawaii.

Notes to Editors

Massive Young Stellar Objects:

A Massive Young Stellar Object (MYSO) is a star in the
early stages of its life, still embedded in the material
from which it has formed. The exact evolutionary stage
of the young star is difficult to discern because of the
extreme obscuration by the surrounding material. The
MYSO is still gaining mass, as the surrounding gas
spirals down onto it. At the same time, jets of gas are
pushed outwards from its poles. Once the star reaches
the ‘main sequence’ of its life, it will be more than
ten times as massive as our own Sun.

Michelle:

The Mid-Infrared Echelle Spectrograph (Michelle) is
designed to work between the wavelengths of 8 and 25
microns, and is one of the most versatile astronomical
instruments ever built. It is the first common-user
mid-infrared instrument to use a large 320×240-pixel
SBRC Si:As detector array, and to have such a high
spectral resolution. Michelle is capable of separating
two wavelengths of mid-infrared light which differ by
only one part in 30,000.

UKIRT:

The world’s largest telescope dedicated solely to infrared
astronomy, the 3.8-metre UK Infrared Telescope (UKIRT) is
sited near the summit of Mauna Kea, Hawaii, at an altitude
of 4194 meters above sea level. It is operated by the
Joint Astronomy Centre in Hilo, Hawaii, on behalf of the
UK Particle Physics and Astronomy Research Council.

The UK ATC:

The UK Astronomy Technology Centre is located at the
Royal Observatory, Edinburgh (ROE). It is a scientific
site belonging to the Particle Physics and Astronomy
Research Council (PPARC). The mission of the UK ATC is
to support the mission and strategic aims of PPARC and
to help keep the UK at the forefront of world astronomy
by providing a UK focus for the design, production and
promotion of state of the art astronomical technology.

Images

UKIRT images of the Massive Young Stellar Object (MYSO)
candidate. On the left is the near infrared image of the
surrounding material, made with the UKIRT Fast-Track
Imager (UFTI). On the right is the mid-infrared image
made with Michelle, showing the deeply embedded star.
Images courtesy of Tamara King, University of Leeds, and
the Joint Astronomy Centre, Hawaii.

* [JPEG, 35KB]
http://outreach.jach.hawaii.edu/pressroom/2002_michellemyso/michellemyso.jpg

* [Large JPEG, 96KB]
http://outreach.jach.hawaii.edu/pressroom/2002_michellemyso/michellemyso_large.jpg

* [Large TIFF, 7.5MB]
http://outreach.jach.hawaii.edu/pressroom/2002_michellemyso/michellemyso_large.tif

Web links

* JAC press release and information
http://outreach.jach.hawaii.edu/pressroom/2002_michellemyso/

* JAC outreach home page
http://outreach.jach.hawaii.edu/