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Reserch Results


The 2006 Radio Outburst of a Microquasar Cyg X-3



Figure: Spectral Evolution of the First Flare in the 2006 Active Phase of a Microquasar Cyg X-3.

M. Tsuboi et al. made the multi-frequency observations of radio outburst of the microquasar Cyg X-3 in February and March 2006 with the Nobeyama 45-m telescope, the Nobeyama Millimeter Array, and the Yamaguchi 32-m telescope. Since the prediction of a flare by RATAN-600 in Russia, the source has been monitored from Jan 27 (UT) with these radio telescopes. At the eighteenth day after the quench of the activity, expected flare was observed successfully. Flare occurred firstly at mm-wave. The radio flux at lower frequency increased within 1 day. The increase at mm-wave decayed quickly. Then the time scale of the variability in the active phase is presumably shorter in higher frequency bands. We also made the follow-up VLBI observation at 8.4 GHz with the Japanese VLBI Network (JVN) 2.6 days after the first rise. They detected a single core with a size of 8 mas (80 AU). The observed image size was almost stable, although the flux density showed rapid variation. No jet-like structure was detected at a sensitivity of Tb = 7.5x105 K. (Tsuboi et al. 2008, PASJ, 60, 465).

Detection of a Negative Ion in a Star Forming Region


Figure: C6H- emission line detected in L1527.

N. Sakai (Univ. of Tokyo) and her collaborators have detected the lines of C6H- toward low-mass protostar, L1527, in Taurus Molecular Cloud, with the Nobeyama 45-m telescope and the NRAO 100-m telescope in US (Sakai et al. 2007, ApJ, 667, L65). Although about 100 neutral molecules and 10 positive molecular ions have been found in various star-forming cores, no molecular anion has been detected so far. The present detection of C6H- in L1527 demonstrates importance of the anion chemistry in the dense part of star forming regions.

Tracing Chemical Reactions of Interstellar Molecules Using Abundance Variations of Their Isotopic Species


Figure: Production pathway for CCS.

CCS is a linear carbon chain molecule, and is known as an abundant interstellar molecule. The spectral lines of its two 13C isotopic species (13CCS, C13CS) are detected in interstellar molecular clouds by observations of their rotational spectral lines with the Nobeyama 45-m telescope and the NRAO 100-m telescope in US. The abundances of the two isotopic species are found to be much different, and this shows that the two carbon atoms in CCS are not equivalent in the dominant formation process. As a result, it is established that CH + CS reaction is the main production pathway. Since the spectral lines of CCS are frequently used for tracing the early evolutionary stage of star formation, detailed understanding of its formation pathway would give a substantial impact not only on astrochemistry, but also on astrophysics. In particular, using isotopic species is a very unique method exploring the interstellar chemical reactions in a molecule-to-molecule base, and will be more and more important in future observations, as sensitivity of observations will increase (Sakai, N., Ikeda, M., Morita, M., Sakai, T., Takano, S., Osamura, Y., and Yamamoto, S. 2007, ApJ, 663, 1174).

Candidates of Starless Cores for High - or Intermediate-Mass Stars



Figure: Integrated intensity maps of N2H+ (left) and CCS (center), and the Spitzer 24 μm image (right).

In order to understand the formation scenario of high-mass stars, which is not well established, it is important to investigate the initial condition of high-mass star formation. However, a genuine high-mass starless core has not been found so far. By using the Nobeyama Radio Observatory 45-m telescope, T. Sakai (Nobeyama Radio Observatory) and colleagues have found chemically and physically young high-mass cores in the AFGL 333 cloud. The high-mass cores are thought to be good candidates of high- or intermediate-mass starless cores, and are important target to understand the initial condition of high- or intermediate-mass star formation (Sakai, Oka & Yamamoto 2007, ApJ, 662, 1043).

Is a Star-Forming Cloud Core Initially Stable or Unstable?



Figure: Dense molecular gas surrounding the extremely young protostar GF9-2 obtained by the Nobeyama 45m-telescope (left), the OVRO mm-array (center) and the combined image (right).

For an isolated low-mass star, such as the Sun, two extreme paradigms of the gravitational collapse of a parental cloud core have been proposed; one model predicts that a core is gravitationally unstable when a protostar is born, while the other stable. However, observational test for validity of the two models have not successfully been made as hampered by difficulties in observations. R. Furuya (Subaru Telescope, NAOJ) and colleagues identified an extraordinary young protostar, GF9-2. They combined data from the Nobeyama 45m-telescope and the Owens Valley Millimeter Array in California, U.S.A., which allowed them to obtain high fidelity images of the natal core. Detailed analysis of the velocity structure of the core gas reinforces the assertion that the initial state of a star-forming core is gravitationally unstable (Furuya, Kitamura & Shinnaga 2006, ApJ 653, 1369).

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



Figure: The Orion Nebula and methyl formate.

Researchers from the University of Toyama and Nobeyama Radio Observatory, NAOJ have assigned 7 unidentified lines in Orion KL from previous line surveys around 97 GHz with Nobeyama 45 m radio telescope to the first torsionally excited methyl formate (Kobayashi et al. 2007 ApJL 657, L17). Recent progress on the assignment of laboratory spectra of methyl formate made it possible the successful assignments and 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 signal comes from. It is quite likely that many unidentified lines can be explained by this kind of organic molecules in the torsionally excited states.

Nobeyama CO Atlas of Nearby Spiral Galaxies


Figure: Optical image (left) and molecular gas distribution (right) of a spiral galaxy M83.

N. Kuno (Nobeyama Radio Observatory) and collaborators have revealed distribution of molecular gas in 40 nearby spiral galaxies (Kuno et al. 2007, PASJ 59). By using the multi-beam receiver "BEARS", they could get the largest data set observed with a large single-dish telescope that can resolve spiral arm and bar in nearby galaxies. The data are very useful to study the mechanism of molecular cloud and star formation in spiral galaxies. The data are available from the CO Atlas web page.

Detection of HCOOCH3 Toward a Low-Mass Protostar, NGC1333 IRAS4B



Figure: Spectral line profile of HCOOCH3 toward NGC1333IRAS4B.

Sakai (Univ. of Tokyo) and collaborators have detected the lines of HCOOCH3 with NRO 45m-telescope toward a low-mass protostar, NGC1333 IRAS4B (Sakai et al. 2006, PASJ, 58, L15). This source is extremely young, and hence, it seems likely that the complex organic molecules appear from the very early stage of protostellar evolution. This is the third detection of HCOOCH3 toward a low-mass star forming region, demonstrating importance of the complex organic molecules in the chemical evolution of solar-type protostars.