Space instrument HIFI delivers crystal clear observations

’We can investigate the universe’s thermostat’

The first measurement data from the Dutch space instrument HIFI are of such a good quality that they can be used for more than just fine-tuning the instruments. According to scientific leader Frank Helmich and project leader Peter Roelfsema they can be used straightaway for scientific research: ’We shall be keeping dozens of European astronomers busy for a long time to come.’

Deeply hidden in the giant molecular cloud, DR21, newly formed massive stars are wreaking havoc on their stellar nursery. In this Spitzer image, in false colors, of the DR 21 star forming region, the green reveals the emission from large molecules set aglow by the newly formed stars. The large bubbles and striated appearance of the cloud are caused by the complex dynamical interaction of the newly formed massive stars and the environment from which they formed. To the right we see a blow up of the active region.

After 10 years of development the HIFI instrument, one of the three science instruments on board of the Herschel Space Observatory, has now observed its first objects in the sky and obtained its first spectra. Principal Investigator Frank Helmich (SRON, Groningen,The Netherlands) is very enthusiastic. HIFI, the “Heterodyne Instrument for the Far-Infrared”, is a high-resolution spectrometer, aimed at obtaining detailed information from spectral lines, the fingerprints of atoms and molecules in the interstellar medium. “These first spectra really show the versatility of the instrument. We have looked at objects in the sky and obtained spectra, which already now caused a lot of excitement. We are only in the phase that we are fine-tuning the instrument and already now these observations are of unheard quality.” Project leader Peter Roelfsema (SRON, Groningen, The Netherlands) ascribes the immediate success of HIFI to the close cooperation between instrument specialists and astronomers. Only in this way were we able to make the best spectrometer in the world.”

“Spectra are always awkward to understand for the general public, explains Emmanuel Caux, French leader for HIFI (CESR, Toulouse, France), “but the power contained in these measurements is coming from the fact that the spectra in fine detail reflect the conditions of the object we study. As such we use the lines as probes. Probes we can apply at the vast distances astronomy has.” German lead Juergen Stutzki (University of Koeln, Germany) confirms this. “in our laboratory we have gone through great efforts to determine the fingerprints of many molecules. These fingerprints we can now match to the spectra obtained with HIFI in unprecedented quality.” “People are quite familiar with the popular series Crime Scene Investigation,” Tom Phillips (CalTech, Pasadena, USA), American lead, says. “Where in CSI we often see that DNA analysis give final clues, we see the same with HIFI.” “If a match is obtained between the laboratory spectrum and the HIFI spectrum we solved a puzzle, a puzzle at astronomical distances!”

The first proposal for the Herschel Space Observatory is already more than 25 years old. Former Principal Investigator for HIFI Thijs de Graauw (ALMA, Chile) says: "Far-Infrared spectroscopy is a powerful tool to study the role of gas and dust in the formation of stars and planets and the evolution of galaxies. The high quality of these first spectra carry the promise of great new insight in these questions. It is a great pleasure to see that HIFI works so well.”

HIFI, the Heterodyne Instrument for the Far-Infrared is a very complex instrument and no single institute or even single country had all the expertize required. As a result HIFI had to be built by a large consortium. Twenty five institutes from 13 countries shared their top technological knowledge to develop the HIFI instrument. In fact, several components in HIFI would not have been possible to be built 10 years ago. Key technologies enabling the construction of these components, of which some exist only in 4 pieces, has been advanced within the HIFI instrument consortium.

“The first sources were expected to be luminous in their lines.” HIFI Project Scientist Xander Tielens (Leiden University, The Netherlands) says. “But I was still surprised at the strength of the lines.” We have been searching the large star-forming region DR21 in Cygnus for warm molecular gas heated by nearby newly-formed massive stars and we discovered that it was much stronger than expected. This reveals that the interaction of newly formed stars with their natal environment is very important for the further evolution of these regions.”

“We confirmed this with the observation of a line of singly ionized Carbon in the same area,” scientist Volker Ossenkopf (University of Koeln, Germany) says. Never ever has this line been measured with such high accuracy and at such high angular resolution. It bears great promise for the scientific program my colleagues and myself have developed for a better understanding of the star forming activity in these regions.”

The third line measured by HIFI is in fact its “raison d’etre”. The water molecule, being abundant in the Earth’s atmosphere, can therefore not be observed from Earth at all, but only from an instrument located on a spacecraft. HIFI was specifically built to observe water in all kinds of celestial objects and the observation of water in DR21 is the start of a whole industry of water studies. HIFI commissioning manager David Teyssier (ESA) realized that this complex line profile is a reflection of the just as complex underlying physics in the source. “We have measured this line, but a straightforward explanation is not easily given. There is no doubt in my mind that soon the explanation comes, revealing a lot about DR21.” Project leader Peter Roelfsema confirms this: “HIFI is a very powerful instrument, giving relatively simple data. However, interpretation of the data needs the intimate collaboration between astrophysicists and spectroscopists like we see in our consortium”. “We will continue with our engineering observations, to ensure high quality in all HIFI’s observing modes and frequencies. We have only just started to do that.”