Peering into the interior of a dark interstellar cloud with the APEX telescope

December 17, 2010
The Rho Ophiuchi dark cloud is a star forming region at a distance of approx. 400 light years. The inlet shows spectra of the rare molecule D2H+, detected with the APEX telescope in Chile, overlaid onto an infrared image of this region. Compilation: Bérengčre Parise. Background image: Spitzer Space Telescope. NASA/JPL-Caltech/L. Allen (CfA) & D. Padgett (SSC-Cattech). Inlett: D2H+ Spectra (Champ+/APEX). (Click image for higher resolution).

Rare molecular species like H2D+ and D2H+, built from the hydrogen atom H and its heavier isotope deuterium D have gained great attention as probes of cold and dense molecular cloud cores. Since deuterium in space is about 100000 times rarer than hydrogen, these molecules are very difficult to detect. Thanks to the conjunction of powerful instrumentation at APEX, the "Atacama Pathfinder EXperiment", and an optimal site over 5000 meters above sea level, a research team from the Max Planck Institute for Radio Astronomy in Bonn led by Bérengère Parise achieved to map the spatial distribution of the rare D2H+ species in a prestellar core in the Rho Ophiuchi cloud, a star-forming region at a distance of approx. 400 light years.

Stars form in clouds of dust and gas. Before the birth of the star, these clouds are dense and extremely cold (temperatures of about 10 Kelvin, corresponding to approx. -260 degrees Celsius), causing most of the gaseous to be frozen on the surface of solid dust grains, very similarly to the condensation of water vapor onto the solid walls of our kitchen freezers. The disappearance of most molecules from the gas makes the observation of molecular emission from these objects very difficult. At the same time, these conditions leave room for the development of a peculiar chemistry between the remaining gaseous species, leading to the formation of light molecules containing atoms, in particular the light triatomic species H2D+ and D2H+.

These peculiar molecules have been the target of many observational searches in the last decade. "This is because their emission can help astronomers to understand the extreme physical conditions in stellar cocoons", says Bérengère Parise, the Emmy Noether group leader driving this research project. "They can be considered as the "light in the freezer" and their study is essential for understanding the processes that lead to the formation of stars and their planetary systems."

The APEX telescope in 5100 m above sealevel in Chile where the observations were performed. Image: Bérengčre Parise (Click image for higher resolution).

The observation of these peculiar molecules is however very difficult in view of the high frequency of the light they emit. The wavelength of the emission, shorter than one millimetre and therefore referred to as "submillimetre", lies in a frequency window where the earth atmosphere is transparent only under the best weather conditions. These observations thus require the best submillimetre telescopes located at the best observing sites, conjugated with sensitive instruments that can detect those faint signals.

In this respect, the observation of D2H+ is even more tricky than that of H2D+, because of an even higher frequency. This explains why most observational searches for this molecule have been unsuccessful, leading to date to only one claimed detection with another submillimetre telescope, with an uncertain frequency calibration.

"Our state-of-art CHAMP+ receiver is a very sensitive and powerful submillimetre instrument", says Rolf Güsten, head of the submillimetre technology group of MPIfR where CHAMP+ was built. "It can record astronomical signal on seven different positions of the sky simultaneously, and at two different frequencies." This increased performance compared to previous instruments makes the observation of faint signals on several positions much more efficient. It was therefore possible to observe the emission of D2H+ simultaneously on seven positions in a cold core for the first time, an observation that would have been nearly impossible with a single-pixel instrument, because of the long integration times required for the detection on a single position (a full night of observing time per position).

The observation resulted in a surprising discovery: the molecule was not only detected in the coldest center of the core, as expected by the MPIfR team, but also in some of the side pixels, showing that the distribution of this molecule is extended, and not only confined to the innermost region of the core. This finding is an important piece of information for understanding the peculiar chemistry taking place in the extreme environments from which stars form. It implies that the freezing of molecules on dust grains is extremely efficient, a result that the team will try to confirm by independent observations in the coming months.

"This is the definitive confirmation of the existence of this rare molecule in space", says Bérengère Parise. "The information on its spatial distribution provided by the CHAMP+ observation opens the possibility to investigate in details the chemical and physical processes taking place during the early phases of star formation."

Explore further: First light for word's largest 'thermometer camera'

More information: Extended emission of D2H+ in a prestellar core , B. Parise, et al, 2010, Astronomy & Astrophysics, DOI:10.1051/0004-6361/20101547

Related Stories

First light for word's largest 'thermometer camera'

August 6, 2007

The world's largest bolometer camera for submillimetre astronomy is now in service at the 12-m APEX telescope, located on the 5100m high Chajnantor plateau in the Chilean Andes. LABOCA was specifically designed for the study ...

Black hole outflows from Centaurus A detected with APEX

January 28, 2009

( -- Astronomers have a new insight into the active galaxy Centaurus A (NGC 5128), as the jets and lobes emanating from the central black hole have been imaged at submillimetre wavelengths for the first time. ...

Studying a Star Before it is Born

December 4, 2009

( -- The first phase of a star's formation are thought to begin deep inside a natal cloud of gas and dust. In the earliest stages, material coalesces under the influence of gravity into so-called "dense cores," ...

Water around massive young stars

September 16, 2010

Water is critical to human life, but also plays an important role in the life of stars and their planetary systems. As a gas, water helps to cool collapsing clouds of interstellar material so that they can form new stars.

Recommended for you

Rosetta captures comet outburst

August 25, 2016

In unprecedented observations made earlier this year, Rosetta unexpectedly captured a dramatic comet outburst that may have been triggered by a landslide.

ALMA finds unexpected trove of gas around larger stars

August 25, 2016

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) surveyed dozens of young stars—some Sun-like and others approximately double that size—and discovered that the larger variety have surprisingly ...

35 years on, Voyager's legacy continues at Saturn

August 25, 2016

Saturn, with its alluring rings and numerous moons, has long fascinated stargazers and scientists. After an initial flyby of Pioneer 11 in 1979, humanity got a second, much closer look at this complex planetary system in ...

Rocky planet found orbiting habitable zone of nearest star

August 24, 2016

An international team of astronomers including Carnegie's Paul Butler has found clear evidence of a planet orbiting Proxima Centauri, the closest star to our Solar System. The new world, designated Proxima b, orbits its cool ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.