Evidence found for elusive chemistry from the universe’s first minutes

Source: Composition: NIESYTO design; Image NGC 7027: William B. Latter (SIRTF Science Center/Caltech) and N An image showing the spectrum of HeH as observed with Great on board of Sofia towards the planetary nebula NGC 7027

 BY ANDY EXTANCE

https://www.chemistryworld.com/news/helium-hydride-ion-detected-in-space-for-the-first-time/3010394.article

Despite the helium hydride ion HeH+ first appearing 13.8 billion years ago, following the big bang, from humanity’s perspective it had been lost in space. Hydrogen and helium were the two first elements, and in the universe’s extreme birth conditions astrochemists presumed they formed the first ever molecular bond in HeH+.. Rolf Güsten from the Max Planck Institute for Radioastronomy in Germany, and colleagues knew HeH+ can exist – it was spotted in the lab in 1925. But now, they have convincingly spied it in space for the first time, in a nebula that exists in the current universe.

‘The lack of evidence of HeH+ caused some doubts whether we do understand the formation and destruction of this special molecule as well as we thought,’ Güsten tells Chemistry World. ‘This concern is gone now.’

Güsten and colleagues observed the HeH+ rotational ground state in a planetary nebula using a terahertz (THz) spectrometer flying on the airborne Stratospheric Observatory for Infrared Astronomy (Sofia). In fact, this study is one of the reasons why the German Receiver for Astronomy at Terahertz Frequencies instrument was built.

Scientists previously failed to find vibrational infrared spectroscopy evidence for HeH+despite great effort. Terahertz spectrometry is a difficult alternative. The HeH+ rotational ground state has a wavelength of 149.137µm. Ozone and water in Earth’s atmosphere block out all this light, meaning researchers had to take to the stratosphere.

Source: Left: © Carlos Duran/MPIfR; Right: © NASA Photo/Jim Ross

The Great far-infrared spectrometer (left) is mounted to the telescope flange of the flying observatory Sofia (right)

Meanwhile, spectroscopic features from much more common carbon–hydrogen bonds appear at 149.09µm and 149.39µm. Success therefore required high spectral resolution, and very sensitive sensors, as Güsten’s team expected the signal to be weak. Reaching the 2THz frequency range of the 149.137µm signal also ‘took several years of technological advancements’.

‘This is a great first detection of a molecular species that is certainly of interest and relevance to a wider astronomical community, and this detection opens the door for further studies,’ comments astronomer Jan Cami from the University of Western Ontario, Canada.

For example, Güsten and colleagues will search for more HeH+ when Sofia next flies, in June. But now they know HeH+ exists, they can start looking for it further back in time towards the big bang. They will exploit cosmological redshifts, similar to how wavelengths emitted by objects moving away from observers expand in the Doppler shift. That will multiply the HeH+ wavelength approximately tenfold, he explains, making the light from the young universe visible ‘from large ground-based observatories’, Güsten says.

Abstract-Unveiling the chemistry of interstellar CH: Spectroscopy of the 2 THz N=2←1 ground state line

Helmut Wiesemeyer, Rolf Güsten, Karl M. Menten, Carlos A. Durán, Timea Csengeri, Arshia M. Jacob, Robert Simon, Jürgen Stutzki, Friedrich Wyrowski

https://arxiv.org/abs/1804.04707

The methylidyne radical CH is commonly used as a proxy for H2 in the cold, neutral phase of the interstellar medium. The optical spectroscopy of CH is limited by interstellar extinction, whereas far-infrared observations provide an integral view through the Galaxy. While the HF ground state absorption, another H2 proxy in diffuse gas, frequently suffers from saturation, CH remains transparent both in spiral-arm crossings and high-mass star forming regions, turning this light hydride into a universal surrogate for H2. However, in slow shocks and in regions dissipating turbulence its abundance is expected to be enhanced by an endothermic production path, and the idea of a "canonical" CH abundance needs to be addressed. The N=2←1 ground state transition of CH at λ149μm has become accessible to high-resolution spectroscopy thanks to GREAT aboard SOFIA. Its unsaturated absorption and the absence of emission makes it an ideal candidate for the determination of column densities with a minimum of assumptions. Here we present an analysis of four sightlines towards distant, far-infrared bright Galactic star forming regions. If combined with the sub-millimeter line of CH at λ560μm, environments forming massive stars can be analyzed. For this we present a case study on the "proto-Trapezium" cluster W3 IRS5, and demonstrate that the sub-millimeter/far-infrared lines of CH reliably trace not only diffuse but also dense, molecular gas. While we confirm the global correlation between the column densities of HF and those of CH, clear signposts of an over-abundance of CH are observed towards lower densities. A quiescent ion-neutral chemistry alone cannot account for this over-abundance. Vortices forming in turbulent, diffuse gas may be the setting for an enhanced production path.

Abstract-SOFIA/GREAT Discovery of Terahertz Water Masers

David A. Neufeld Gary J. Melnick, Michael J. Kaufman,  Helmut Wiesemeyer, Rolf Güsten, Alex Kraus4, Karl M. Menten,  Oliver Ricken, and Alexandre Faure, 

http://iopscience.iop.org/article/10.3847/1538-4357/aa7568/meta

We report the discovery of water maser emission at frequencies above 1 THz. Using the GREAT instrument on SOFIA, we have detected emission in the 1.296411 THz  transition of water toward three oxygen-rich evolved stars: W Hya, U Her, and VY CMa. An upper limit on the 1.296 THz line flux was obtained toward R Aql. Near-simultaneous observations of the 22.23508 GHz  water maser transition were carried out toward all four sources using the Effelsberg 100 m telescope. The measured line fluxes imply 22 GHz/1.296 THz photon luminosity ratios of 0.012, 0.12, and 0.83, respectively, for W Hya, U Her, and VY CMa, values that confirm the 22 GHz maser transition to be unsaturated in W Hya and U Her. We also detected the 1.884888 THz transition toward W Hya and VY CMa, and the 1.278266 THz  transition toward VY CMa. Like the 22 GHz maser transition, all three of the THz emission lines detected here originate from the ortho-H₂O spin isomer. Based upon a model for the circumstellar envelope of W Hya, we estimate that stimulated emission is responsible for ~85% of the observed 1.296 THz line emission, and thus that this transition may be properly described as a terahertz-frequency maser. In the case of the 1.885 THz transition, by contrast, our W Hya model indicates that the observed emission is dominated by spontaneous radiative decay, even though a population inversion exists

SOFIA Airborne Telescope Heads South

Image Credit: With the large door over its 2.5-meter German-built telescope wide open, NASA's Stratospheric Observatory for Infrared Astronomy 747SP aircraft soars over Southern California's high desert during a test flight in 2010 in preparation for its Early Science missions. Credit: NASA / Jim Ross
http://www.redorbit.com/news/space/1112901471/nasa-sofia-airborne-telescope-south-new-zealand-southern-hemisphere-magellanic-clouds-071813/

Lee Rannals for redOrbit.com – Your Universe Online

NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) telescope has moved south to New Zealand for the next two weeks to take advantage of the Southern Hemisphere’s orientation.

The space agency said the airborne observatory would be utilizing its southern position to take advantage of studying celestial objects that are difficult or impossible to see in the northern sky. SOFIA is a telescope attached to a modified Boeing 747SP aircraft with an effective diameter of 100 inches. It provides astronomers with visible, infrared and sub millimeter spectrum views of the night sky.

Astronomers used SOFIA on its first New Zealand flight to observe the disk of gas and dust orbiting the black hole at the center of our Milky Way galaxy. The airborne telescope was also able to take a peek at two dwarf galaxies and the Large and Small Magellanic Clouds. The Magellanic Clouds can be seen with the naked eye in the southern sky.

“SOFIA’s deployment to the Southern Hemisphere shows the remarkable versatility of this observatory, which is the product of years of fruitful collaboration and cooperation between the U.S. and German space agencies,” said Paul Hertz, director of NASA’s Astrophysics Division in Washington. “This is just the first of a series of SOFIA scientific deployments envisioned over the mission’s planned 20-year lifetime.”

Astronomers will be using a far-infrared spectrometer known as the German Receiver for Astronomy at Terahertz Frequencies (GREAT) mounted on SOFIA to study interstellar gas and the life cycle of stars.

“The success of the GREAT spectrometer in addressing exciting scientific questions at far-infrared wavelengths was demonstrated during SOFIA’s earlier, Northern Hemisphere flights,” said Rolf Guesten of the Max Planck Institute for Radio Astronomy in Bonn, Germany, and leader of the German researchers who developed the spectrometer. “Now, we are turning the instrument to new frontiers such as the Magellanic Clouds, including the Tarantula Nebula — that is the most active star-forming region known in the local group of galaxies.”

Pamela Marcum, the project scientists for SOFIA, said the results anticipated from these southern observations will further scientists’ understanding of star formation, stellar evolution and chemistry in the stellar clouds.

“The deployment exemplifies the synergistic relationship between SOFIA’s international partners, with NASA playing a crucial role in the planning and execution of the science observations,” Marcum said.

SOFIA received major upgrades back in December to its observatory and avionics systems. These upgrades will significantly improve the systems’ efficiency and operability.

Abstract-Enhancing the stability of a continuous-wave terahertz system by photocurrent normalization

Axel Roggenbuck, Malte Langenbach, Komalavalli Thirunavukkuarasu, Holger Schmitz, Anselm Deninger, Iván Cámara Mayorga, Rolf Güsten, Joachim Hemberger, and Markus Grüninger  »View Author Affiliations

http://www.opticsinfobase.org/josab/abstract.cfm?uri=josab-30-6-1397

In a continuous-wave terahertz system based on photomixing, the measured amplitude of the terahertz signal shows a variability due to drifts of the responsivities of the photomixers and of the optical power illuminating the photomixers. We report a simple method to substantially reduce this variability. By normalizing the amplitude to the DC photocurrents in both the transmitter and receiver photomixers, we achieve a significant increase in stability. If, e.g., the optical power of one laser is reduced by 10%, the normalized signal is expected to change by only 0.3%, i.e., less than the typical uncertainty due to short-term fluctuations. This stabilization can be particularly valuable for terahertz applications in nonideal environmental conditions outside of a temperature-stabilized laboratory.

© 2013 Optical Society of America

New Molecules and Star Formation in the Milky Way

Optical color image of the rho Ophiuchi star formation region, about 400 light-years from Earth, with dark dusty filamentary gas clouds. The position of the optically obscured low-mass protostar IRAS16293-2422 towards which interstellar deuterated hydroxyl OD has been detected is marked with a red circle. The absorption line spectrum, observed with GREAT onboard SOFIA, displays the molecule’s fingerprint at a frequency of 1.3915 Terahertz (or 0.215 mm wavelength). The inset shows the OD molecule (red: oxygene, gray: deuterium), an isotopic substitute of hydroxyl (OH) with the hydrogen atom replaced by heavier deuterium. This deuterated molecule is an important marker in the formation of interstellar water and may serve as a chemical clock in the early star formation process.The bright yellowish star in the bottom left is Antares, one of the brightest stars in the sky. Below and to Antares’ right is the globular cluster Messier 4. (Credit: Spectrum: MPIfR/B. Parise, Photo: ESO/S. Guisard

http://www.sciencedaily.com/releases/2012/05/120510100221.htm

ScienceDaily (May 10, 2012) — SOFIA, the "Stratospheric Observatory for Infrared Astronomy," completed its first series of science flights, using the German Receiver for Astronomy at Terahertz Frequencies (GREAT). The scientific results are now being published in a special issue of the journalAstronomy & Astrophysics (Volume 542, May 10) along with reports on GREAT's advanced technologies. They include first detections of new interstellar molecules and important spectral lines in space, and address different stages of the star formation process.

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The first series of astronomical observations with GREAT on board of SOFIA were successfully completed in November 2011. Now, six months later, the scientific results have been published in a special issue of the European journal Astronomy & Astrophysics. In total, 22 articles by an international group of scientists report on the first astronomical results as well as the technologies employed in the GREAT instrument on board SOFIA.

As a joint project between NASA and the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, DLR), SOFIA operates a 2.7-m telescope in a modified Boeing 747SP aircraft and is the world's largest ever airborne infrared observatory. SOFIA flies at altitudes as high as 13700 meters to provide access to astronomical signals at far-infrared wavelengths that would otherwise be blocked due to absorption by water vapour in the atmosphere. The SOFIA observatory and the GREAT instrument open the far-infrared skies for high-resolution spectroscopy, and GREAT pushes its technology to higher frequencies and sensitivities than ever reached before.

Many of the contributed papers study the star formation process in its earliest phases, first when the protostellar molecular cloud is contracting and condensing, and then when the embryonic star is vigorously interacting with its surrounding parental molecular cloud -tearing it apart and ionizing it. The high spectral resolution capabilities of GREAT enabled scientists to resolve the velocity field of gas in the parental molecular clouds traced by the important cooling line radiation of ionized carbon in several star forming regions.

GREAT detected the velocity signature of infalling gas motion ("collapse") in the envelopes of three protostars, directly probing the dynamics of a forming star. Two interstellar molecular species were detected for the first time ever: OD, an isotopic substitute of hydroxyl (OH) with the hydrogen atom replaced by the heavier deuterium, and the mercapto radical SH. Observations of the ground-state transition of OH at a frequency of 2.5 Terahertz (120 microns wavelength) explored new astrochemical territories while pushing the technological frontier.

The remnant envelope of an evolved star, ionized by its hot stellar core, was also investigated as was the violent shock interaction of a supernova remnant and the surrounding interstellar medium. Furthermore, the circumnuclear accretion disk, ultimately feeding the black hole in the centre of the Milky Way galaxy was studied, as well as star formation in the circumnuclear region of the nearby galaxy IC342.

"The rich harvest of scientific results from this first observing campaign with SOFIA and the GREAT instrument gives a first glimpse of the tremendous scientific potential of this observatory and promises unique astronomical observations for years to come, particularly in the topical research areas of star formation and astrochemistry" states the Deputy Director of the SOFIA Science Mission, Hans Zinnecker, from DSI. In parallel with Rolf Güsten from the Max-Planck-Institut für Radioastronomie, the Principal Investigator of the GREAT project, Zinnecker organized the selection process and ultimately selected some of the most exciting observing proposals from the German astronomical community.

"The high resolving power of the GREAT spectrometer is designed for studies of interstellar gas and the stellar life cycle, from a protostar's early embryonic phase when still embedded in its parental cloud to an evolved star's death when the stellar envelope is ejected back into space," says Güsten. "This stunning collection of first scientific results is reward for the many years of development work, and underlines the huge scientific potential of airborne far-infrared spectroscopy."

The "Deutsches SOFIA Institut" (DSI) of the University of Stuttgart coordinates SOFIA's science mission and operation on behalf of the German partners.

GREAT, the German Receiver for Astronomy at Terahertz Frequencies is a receiver for spectroscopic observations in the far-infrared spectral regime between frequencies of 1.25 and 5 terahertz (60-240 microns), which are not accessible from the ground due to absorption by water vapour in the atmosphere. GREAT is a first generation German SOFIA instrument, developed by the Max-Planck Institute for Radio Astronomy (MPIfR) and the KOSMA at the Universität zu Köln, in collaboration with the Max-Planck Institute for Solar System Research and the DLR Institute for Planetary Research. Rolf Güsten (MPIfR) is the Principal Investigator for GREAT.

SOFIA, the "Stratospheric Observatory for Infrared Astronomy" is a joint project of the National Aeronautics and Space Administration (NASA) and the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR; German Aerospace Centre, grant: 50OK0901).

Links to articles:

http://www.aanda.org/index.php?option=com_toc&url=/articles/aa/abs/2012/06/contents/contents.html

http://www.mpifr.de/div/submmtech/heterodyne/great/GREA

Sofia The observatory above the clouds

Image via Wikipedia

© NASA/C. Thomas

If you want to reach for the stars, you have to lift off. This could be the motto of Sofia, a jumbo jet which has been converted into an observatory. On board it carries a 2.7-metre telescope, which the researchers use to observe the birthplaces of distant suns, galactic molecular clouds or the envelopes of planets in the infrared as they fly above Earth’s disturbing atmosphere at an altitude of 15 kilometres.

If you look up to the sky on a clear starlit night, you see only a single octave of the mighty keyboard which makes up the cosmos. This is because our eyes perceive only the visible light. And also because the Earth’s atmosphere blocks out a large part of the radiation from space such as gamma rays, X-rays or infrared light. It is in this spectral region that exploded suns, infant planetary systems or the cores of distant galaxies appear to be especially interesting. The astronomers therefore work with an armada of satellite telescopes above the terrestrial blanket of smog. And a short while ago they also opened an observation post directly above the clouds: Sofia.
The name of the flying observatory stands for Stratospheric Observatory for Infrared Astronomy. Sofia is a passenger on a converted Boeing 747SP jumbo jet and has a telescope with a mirror measuring 2.7 metres in diameter. This giant eye surveys the universe in the infrared spectral region from a height of 12 to 15 kilometres. At this altitude, above the troposphere, Sofia leaves almost all the water vapour behind which otherwise swallows up the long wavelength light from space.
The telescope is mounted in the tail of the plane and hermetically sealed off from the cabin. Once the plane has reached its flying altitude, doors in the fuselage slide apart and the instrument observes in the open air, at low pressure and outside temperatures of around minus 60 degrees. The primary mirror with the above-mentioned 2.7-metre diameter weighs roughly 800 kg; it captures the radiation from space and projects it onto the smaller secondary mirror, which focuses it and sends it to a tertiary mirror, which finally guides it to the image plane of the scientific instrument to which it is connected.

The Forcast infrared camera developed at Cornell University in the US was the first of nine instruments of the “first light generation” to go into operation. At the beginning of April it was then the turn of Great, Germany’s contribution. This spectrometer surveys the universe in the far-infrared region at wavelengths between 60 and 250 micrometres, which are not accessible from the surface of the Earth because of the water vapour absorption in the atmosphere.

As Sofia touched down on the runway of Dryden Aircraft Operations Facility in Palmdale, California at 6:40 a.m. local time on 6 April 2011 it heralded a new era for observing astronomy: “Even the first spectra show the outstanding scientific potential of airborne far-infrared spectroscopy,” says Rolf Güsten, the delighted head of the Great project and a scientist at the Max Planck Institute for Radio Astronomy in Bonn, Germany after the maiden flight. The telescope’s large collecting area coupled with enormous advances in Terahertz technologies in recent years allow Great to collect data 100 times faster than in earlier experiments. “This opens up the way for unique scientific observations.”

The programme back then consisted of the molecular cloud M 17, a region with enhanced star formation in our Milky Way, and also the IC 342 galaxy only few million light years away. In both sources Great not only registered the radiation of ionised carbon at a wavelength of 0.158 millimetres, but also spectral lines of warm carbon monoxide at high excitation. These lines are evidence of atomic processes which lead to a cooling of the interstellar matter.
The balance between heating and cooling processes, on the other hand, regulates the temperature of the interstellar medium, thereby controlling the initial conditions for the formation of new stars. Such processes occur at low temperatures – way below minus 200 degrees Celsius – and can thus only be followed in the infrared. The researchers are therefore concentrating on the birth of stars and planets. Sofia will be able to follow such cosmic delivery rooms in our galaxy and also in neighbouring galaxies with an accuracy never achieved before.
To operate at optimum performance, the observatory must have absolute calm; even the slightest vibrations would ruin any measurement. So the engineers developed a system to insulate against vibrations which is made of air springs, silicon-filled damping elements and high-tech control electronics. This mechanically decouples the plane from the telescope.
The astronomers work in the area in front of the pressure bulkhead and between the wings. And 1st class has been replaced with space for guest observers and teachers, students or journalists. This is how it came about that in the night before 15 July there were two German teachers on board for the first time. Wolfgang Viesser from Christoph-Probst Gymnasium in Munich and Jörg Trebs from Thomas Mann Oberschule in Berlin were able to experience at close hand how the scientists used Great to scrutinise L1157, a newly forming star in the Draco constellation.
The jumbo jet is based in Palmdale near Los Angeles. Sofia will also take off from Christchurch in New Zealand and from Stuttgart airport on its cosmic excursions.
Provided by Max-Planck-Gesellschaft (news : web)