Press release Mar. 22nd 2007

Organic Molecule (Methyl Formate) in the First Torsionally Excited State Identified in Orion!!


Mar. 1st, 2007 Published in the Astrophysical Journal Letters, Vol. 657, L17-L19
Mar. 22nd, 2007 National Astronomical Observatory of Japan internet release
Mar. 29th, 2007 Presentation at the spring annual meeting of the Astronomical Society of Japan.

Researchers involved(affiliations)
Kaori Kobayashi (University of Toyama), Kazumi Ogata (University of Toyama), Shozo Tsunekawa (University of Toyama)
Shuro Takano (Nobeyama Radio Observatory, National Astronomical Observatory of Japan, and the Graduate University for Advanced Studies (Sokendai))

Summary

Researchers from the University of Toyama and Nobeyama Radio Observatory, National Astronomical Observatory of Japan (NAOJ) have assigned 7 unidentified radio lines in Orion molecular cloud (Orion KL) from previous line surveys around 97 GHz with Nobeyama 45 m radio telescope to the first torsionally excited methyl formate (Chemical formula: HCOOCH3) (Kobayashi et al. 2007 ApJL 657, L17).
There are regions with large amount of gas or molecules in space and Orion molecular cloud is one good example. The emitted radio signals from the molecules are observed by radio telescopes. There are many radio signals whose origin is unknown and efforts to identify these signals are under progress.
Recently researchers in the University of Toyama succeeded to assign the laboratory spectra of methyl formate in the torsionally excited state (See below). This success made it possible the comparison with the data observed in 1988 with Nobeyama 45 m radio telescope and successful assignments of 7 former unidentified lines in collaboration with the researcher from National Astronomical Observatory of Japan. In addition, at least 13 lines from other line surveys were also identified. The detection helps to estimate the temperature and the abundance of this molecule and chemical reaction where the radio signals come from. It is quite likely that many unidentified lines can be explained by this kind of organic molecules in the torsionally excited states.
Figure 1. Orion molecular cloud and methyl formate
Photo of Orion is here

Orion molecular cloud

The constellation Orion is shining in the winter sky at night. Orion molecular cloud, which exists in this constellation, is gas rich and many stars are still forming (Figure 1.). Many active researches are in progress with infrared and radio telescopes to understand the star-forming processes from gas. At the same time, many organic molecules have been found in this gas. The emitted radio lines from these molecules are also used as probes to understand these processes. There still remain, however, many radio lines without identifications.

Methyl formate and laboratory measurement

The structure of methyl formate is shown in Figure 2. The torsional motion is also shown. Large amount of this molecule has been found in Orion molecular cloud and recent researches have revealed that this molecule exists in the early stage of star-formation. However, all the observations were limited to methyl formate without this kind of large torsional motion. We report the first observation of methyl formate in torsionally excited state. Torsional motion requires higher energy and it indicates that the observed region is warmer.
Figure 2. Methyl formate with torsional motion
(gray: carbon, red: oxygen, pale blue: hydrogen)
To prove the existence of this kind of molecules in space requires laboratory spectroscopy is indispensible. Quantum chemical calculations are still not precise enough to predict the frequencies, because the observed radio frequencies in laboratories and telescopes have very high precision. In University of Toyama, spectra of methyl formate were observed and one example is shown in Figure 3. Radio signals from methyl formate in torsionally excited state were identified.
Figure 3. Laboratory spectrum
of methyl formate


Observation with Nobeyama 45 m radio telescope and data analysis

This successful assignment of laboratory spectra made it possible the detailed comparison with the data observed in 1988 with Nobeyama 45 m radio telescope. After about 20years, 7 former unidentified lines were assigned to methyl formate in torsionally excited state in collaboration with the researcher from Nobeyama Radio Observatory, NAOJ. The quality of observational data with Nobeyama telescope is very good and helped to prove the first identification. In addition, at least 13 lines from other line surveys were also identified.
Detailed analysis of the data observed with Nobeyama telescope determined that the temperature is about -230 Celsius degrees. In dark clouds where no stars are forming, the temperature is generally very low and about -263 Celsius degrees. Our higher value indicates that the star-forming activity warms up the gas.

Future expectation

Methyl formate in torsionally excited state emits many more radio lines. In the future, it seems conceivable that other unidentified lines could be attributed to the molecule.
In the University of Toyama, researches of laboratory spectroscopy of organic molecules in torsionally excited states have been carried out. The emitted signal of this kind of molecules in torsionally excited state observed with radiotelescopes is generally weak. The new telescope, ALMA, currently under construction in Chile has higher sensitivity, and many weaker lines will be observed soon. Part of the origin would be found to be due to such a large organic molecules in the torsionally excited states. The basic information is provided by the researchers in the University of Toyama. The results would help to understand the temperature, abundance, and chemical reactions there.

Link

  • Tsunekawa Laboratory, Department of Physics, University of Toyama
  • National Astronomical Observatory of Japan [home, Nobeyama Radio Observatory, 45 m Telescope]

      Contact


      Kaori Kobayashi (Department of Physics, University of Toyama) Tel. +81-76-445-6595
      Shuro Takano (Nobeyama Radio Observatory, National Astronomical Observatory of Japan, and Graduate University for Advanced Studies (Sokendai)) Tel. +81-267-98-4377

      Last update, Mar. 22nd 2007