EARLY RESULTS FROM ISO

28 November 1996
Source: European Space Agency

EARLY RESULTS FROM ISO

European Space Agency
Paris, France                   28 November 1996

PRESS INFORMATION NOTE Nr. 21-96

Enthusiasm for Europe's space telescope ISO

A special issue of the journal Astronomy and Astrophysics, published in the
latter part of November 1996, is devoted to early results from the European
Space Agency's Infrared Space Observatory. Ninety-one scientific papers tell
of unprecedented inspections of the cool universe and its hidden corners, as
ISO and its four excellent instruments rewrite the astronomical textbooks.

"Are the most luminous galaxies powered by extreme rates of star formation,
or do they harbour black-hole-powered active nuclei as well?" Scientists
lead by Reinhard Genzel at Max Planck Institut fur extra terrestrische
Physik in Garching, Germany, have used ISO's Short Wavelength Spectrometer
to give an answer. Writing in the London journal Nature, an independent
commentator, Gerry Gilmore of the Institute of Astronomy in Cambridge,
considers that their papers in Astronomy and Astrophysics give a clear
answer to this question. The "remarkable result" according to Gilmore is
that none of three ultra-luminous infrared galaxies studied by ISO requires
an active nucleus to account for the emissions, which arise from rapid star
formation. About another ISO target Gilmore writes:

"In one lovely example, of two intersecting disk galaxies known as the
Antennae, it is even possible to resolve the spot where the two disks
currently cross, and to see the progression of star formation across the
disk as the two galaxies orbit through each other." (Nature, 21 November
1996, p. 211)

One year after its launch, ISO is exceptionally popular among astronomers,
not only in Europe but worldwide. A panel of American astronomers, reporting
to NASA on the scientific merits of eight astrophysical space missions,
gives ISO the highest ranking and calls it "the major infrared mission of
the decade". At a time when NASA is reducing its budgets for some
astrophysical missions, its funding of ISO-related research is increasing.

The demand for a share in ISO's unique view of the infrared universe is
insatiable. ESA has been overwhelmed by new proposals for observations,
coming from 511 groups of astronomers in ESA's own Member States and in the
USA and Japan. Although ISO is extremely efficient, performing an average of
45 observations a day, it could not cope with 16,000 observations requested
as additions to ISO's already busy programme for 1997. The time allocation
committee has had to turn down 75 per cent of the proposed observations.
Nevertheless the allocations announced this month will meet the wishes of
most groups of applicants at least in part.

ISO is now about half way through its operating life. An Ariane 44P launcher
put it into orbit on 17 November 1995. ISO's superfluid helium which keeps
the telescope and instruments cold, will last about six months longer than
required in the specification. Operations are expected to continue until
December 1997, with the benefit that the chemically rich and starmaking
clouds of the important Orion region of the sky will be observable by ISO.

Tracing the origin of planets

Observations of the Antennae galaxies, and some of the other ISO results now
described in full technical detail in Astronomy and Astrophysics, were
outlined in earlier ESA Information Notes, 02-96 and 14-96. These include
examinations of star formation in many galaxies and within dust clouds in
our own Galaxy, the Milky Way. ISO has also given a big boost to
astrochemistry by identifying infrared signatures of many materials, which
play a physical as well as a chemical role in the evolution of galaxies and
stars. The materials seen by ISO include ionized carbon atoms, sooty carbon
compounds, hydrogen molecules, water molecules, and frozen carbon dioxide
and methane. The latest results tell of mineral crystals, which may shed
light on the origin of the Earth itself.

Disks of dust around some stars, of the kind from which planets might
evolve, were a major discovery in infrared astronomy by ISO's predecessor,
the Dutch US UK satellite IRAS (1983). The prototype was the bright northern
star Vega. It showed excess emissions of long-wavelength infrared rays,
which could not come from the star itself. Subsequent studies confirmed the
dust disks of Vega and a few other stars, and the search for more such disks
is a major programme for ISO, relying particularly on measurements by the
photometer ISOPHOT across a wide range of infrared wavelengths.

Several new candidate Vega-like dust disks are reported in Astronomy and
Astrophysics by Harm Habing of Leiden in the Netherlands, and his
colleagues. Their preliminary conclusion is that the dust disks are a common
feature of ordinary stars as massive as the Sun or heavier, but they are by
no means ubiquitous. Further measurements on Vega itself show relatively low
emissions at the longest wavelengths, which implies that the dust grains are
small.

In a related programme, a Belgian-led team has used ISO's Short-Wavelength
Spectrometer to probe the composition of dust near very young stars. It
reports the discovery of crystals of olivine, a silicate mineral and a major
constituent of the Earth's own rocky mantle. The firm detection of olivine
crystals builds a bridge from the stars to the minerals of the solar system.

Most mineral grains in interstellar space lack the crystalline forms of
common minerals, even if they have the same chemical composition. Hints of
infrared emissions from olivine crystals, detected by ground-based
telescopes at around 11 microns wavelength, are confused by emissions coming
also from carbon compounds. ISO, with its unhampered view at longer
wavelengths, sees signatures of magnesium-rich olivine crystals at 20, 24
and 34 microns.

The minerals crystallize when gravity concentrates them near a young star,
and intense radiation from the star modifies the grains. ISO also sees
similar materials in the dust shells of old stars, in a project headed by
the Dutch astronomer Rens Waters, who is also closely involved in the work
on young stars. Apparently the mineral crystals do not survive in
interstellar space, but have to be refashioned near young stars.

The most clear-cut evidence for olivine crystals comes from the vicinity of
HD 100546, a young blue star about 500 light-years away near the Southern
Cross. It is thought to be only a few million years old and it is a strong
infrared emitter. The star also shows peculiar ultraviolet absorptions,
recorded by the NASA ESA UK International Ultraviolet Explorer, which
apparently result from comets or asteroids splashing into HD 100546.

"A tremendous cloud of comets seems to surround this young star," says
Christoffel Waelkens of Leuven, Belgium, who leads the project that
discovered the olivine crystals. "We believe that it was from just such a
comet cloud, around the young Sun, that the Earth and the other planets were
born. Now we compare notes with colleagues who study minerals in our local
comets and meteorites. ISO has seen olivine in Comet Hale-Bopp. So not the
least of ISO's successes is a reunification of stellar astrophysics and
solar-system science."

Newborn stars and stellar jets

Astronomers in Stockholm, Sweden, are the lead authors of papers concerning
the search for newborn stars and related phenomena in the southern
constellation Chamaeleon. At about 800 light-years a feature called the
Chamaeleon Dark Clouds, sprawling across more than one degree of the sky, is
one of the closest regions of present-day star formation. The camera ISOCAM
has obtained more than 23,000 images of the region, in two wavelength bands
around 7 and 15 microns. Out of hundreds of objects detected, the team
identified 65 young stars, of which more than 40 per cent were not
previously known.

Another lead author from Stockholm reports on the use of ISO's
Long-Wavelength Spectrometer to examine a strange luminous patch in the
Chamaeleon Dark Clouds called HH 54. It is a Herbig-Haro object, named after
an American and a Mexican astronomer, in which a jet of gas from a very
young star creates luminosity by shock waves, at a great distance from the
star. ISO has for the first time detected emissions from water vapour in an
HH object.

This result not only confirms ISO's pioneering role as a cosmic water
diviner, but gives new insight into the mechanisms creating the HH object.
Practically all of the energy of a 10 kilometre-per-second shock is
dissipated by infrared emissions from water vapour, hydroxyl and carbon
monoxide molecules. A related paper, with a lead author from Frascati,
Italy, compares HH 54 with other nearby objects HH 52 and HH 53, again using
the Long-Wavelength Spectrometer. A conclusion is that HH 54 is energized by
a young star different from the one that may be responsible for the other
two objects.

"The 91 papers published this month, covering observations from planets to
galaxies, are still only a foretaste of many hundreds to be expected as the
observing programmes and the data-processing mature," says Martin Kessler,
ISO's project scientist based at Villafranca, Spain. "For example, ISOCAM is
engaged on a systematic survey of a section of the Milky Way. In Astronomy
and Astrophysics only one per cent of the survey is reported yet already
there are thousands of infrared sources and plenty of surprises. Although
ISO has only one more year of operation, its impact on astronomy will
continue for many years."

For further information about ISO contact:

ESA PR (Paris): Simon Vermeer +33 1 5369 7106
ESA Project Scientist: Dr Martin Kessler +34 1 813 1253
Principal Investigator, Camera (ISOCAM): Prof. Catherine Cesarsky +33 1 6908
7515
Principal Investigator, Photometer (ISOPHOT): Prof. Dietrich Lemke +49 6221
528259
Principal Investigator, Short-Wavelength Spectrometer (SWS): Dr Thijs de
Graauw +31 50 363 4074
Principal Investigator, Long-Wavelength Spectrometer (LWS): Prof. Peter
Clegg +44 171 975 5038

For further information on the science discussed in this press release
contact :

The Nature article summarising the Astronomy and Astrophysics papers Dr
Gerry Gilmore, +44 1 223 337 548
What powers ultraluminous galaxies ? Prof. Reinhard Genzel +49 89 329 93280
The Antenna interacting galaxies Dr Laurent Vigroux + 33 1 69 08 65 77
Vega-like dust disks around stars Prof. Harm Habing + 31 71 527 5803
Dust shells around old stars Dr Rens Waters + 31 20 525 7468
Clouds of Comets around the star HD 100546 Prof. Christoffel Waelkens +32 16
32 70 36


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