Observatory sees vistas in heart of Orion Nebula
Posted: April 2, 2001

A new astronomical instrument, TIMMI2, has just been installed on the ESO 3.6-m telescope at La Silla. The first images have just been obtained and hold great promise for future research programmes with this facility.

The Thermal Infrared MultiMode Instrument was built in a collaboration between ESO and a consortium headed by the Jena University Observatory (Germany). It detects infrared radiation in the 5-24 microns mid-IR spectral region.

The area of a star-forming region deep inside the Orion Nebula has been imaged with ESO's new Thermal Infrared MultiMode Instrument (TIMMI2). It is located close to the Trapezium cluster and is identified on this view obtained with the ISAAC instrument at the 8.2-m VLT ANTU telescope. Photo: ESO
It is particularly well suited for observations of the complex processes that take place in the innermost regions of star-forming clouds. It is also a forerunner of a similar, but even more powerful instrument to be installed at the 8.2-m VLT telescopes on Paranal during the next years.

Among the first images are some of the most penetrating, mid-infrared views ever obtained of the central region of the Orion Nebula.

A group of astronomers has recently imaged a star-forming region in the Orion Nebula with a new and powerful astronomical instrument, the Thermal Infrared MultiMode Instrument (TIMMI2), now available at the La Silla Observatory. In addition to being scientifically very interesting, these observations also provide a demonstration of the impressive capabilities of this new facility.

It has been known for some time that the "BN/KL Complex" is a site of recent, massive star formation. It is located deep inside the Orion Nebula and is observed as a cluster of infrared-emitting objects and compact regions of ionized Hydrogen ("H II regions"), associated with intricate interstellar dust filaments and circumstellar dust clouds. There are also several hot and large stars in this heavily obscured area - together they shine as bright as 100,000 suns.

It is a difficult task to identify the main sources of heating in this region - the "heart" of the Orion BN/KL star-forming complex. For this, a combination of sharp images (at 1 arcsec resolution or better) at different wavelengths is required. This is now possible with ISAAC near-infrared and TIMMI2 mid-infrared images that together show the energy distribution of the individual sources.

  10.3 microns
The dust cloud covering the central region of Orion is more transparent at longer wavelengths and the complex is clearly seen on images obtained with TIMMI2 at wavelengths of 10.3 microns. Photo: ESO
The present TIMMI2 images of the BN/KL Complex were obtained at two different wavelengths, 10.3 microns (photo above) and 20.0 microns.

These mid-infrared photos are powerful tools for the astronomers' attempts to analyze the very early processes of star formation. They mainly show the thermal radiation from the dust in the area that is heated by the UV and visible light from the stars, and especially the comparatively warm, dense dust cocoons around the very young stars. Contrarily, the slightly older stars in this area have already blown away most of their dust shell and can therefore be seen at shorter wavelengths, e.g. in the ISAAC image, but not in the TIMMI2 photos.

The dust clouds through which we can now look with TIMMI2 are extremely dense. The obscuration in the visual region of the spectrum is enormous, about 60 magnitudes (i.e., a factor of 1024). No wonder that even the largest telescopes cannot get through to those "hidden" objects in visual light!

The ratio between the TIMMI2 images ("20microns/10microns" -- below) provides a temperature map of the dust in this region. The "hottest" (brightest in this photo) areas mostly correspond to the cocoons around the very young stars. With the excellent image sharpness (about 1 arcsec) provided by TIMMI2, it was possible to identify ten new mid-infrared sources on this photo. From the image ratio, dust temperatures of up to about 190 C (460 K) are measured.

The ratio of these images from 20microns and 10microns illustrates how the temperature of the dust in this area varies. The brighter areas are the hotter ones. Photo: ESO
The new Thermal Infrared MultiMode Instrument (TIMMI2) is a second-generation instrument for the ESO 3.6-m telescope on La Silla. It is the most sensitive and most versatile instrument of its kind available in the world and puts European astronomy at the forefront of research in this field.

TIMMI2 is a combined camera and spectrometer that is able to register radiation ("light") in the mid-infrared spectral range from 5-24 microns. It is the successor to the most productive TIMMI instrument that was used at La Silla and decommissioned in 1998, cf. e.g., the reports about the first observations of structures in the disk around the star Beta Pictoris pointing to the presence of planets (article in Nature 369, p.628; 1994), the impact of Comet SL-9 on Jupiter and also about Comet Hale-Bopp.

To achieve sufficient sensitivity for thermal radiation from celestial objects, TIMMI2 must be cooled (as a normal camera for visible light must be black inside and light-tight). It operates at -230C and the detector is kept at -260C.

Mid-infrared astronomy is a very promising field
Quite apart from its own capabilities, TIMMI2 also represents an important step towards the VLT Mid Infrared Spectrometer/Imager VISIR, a similar, but even more advanced mid-infrared instrument for ESO's Very Large Telescope at Paranal. VISIR is now being constructed under ESO contract at research institutes in France and the Netherlands. It is planned to install it on the 8.2-m MELIPAL in 2002. The sensitivity will be five times higher than that of TIMMI2 and it will produce images that are twice as sharp. Until then, the ESO astronomers and engineers as well as many visiting astronomers will have gained invaluable experience with TIMMI2, ensuring them a fast and efficient entry into this largely unexplored field of astronomy.

Mid-infrared observations like these are a most valuable tool for studying the birth of stars and the formation of circumstellar disks and planets. As such it is complementary to submm observations, e.g. with the future ALMA facility.

Later, an extremely large telescope with similar instrumentation - like the 100-m OWL for which a concept study is now underway at ESO - may be used to image earth-size planets orbiting stars in our cosmic neighbourhood.