Toshihiro Omodaka

Solar brightness distribution at 8.6 mm from interferometer observations

The radial brightness distribution of the quiet Sun at 8.6 mm is synthesized from observations using a sixteen element east-west interferometer in Nagoya. The observed brightness is flat from the disk center to 0.8R⊙. A slight darkening appeared between 0.8R⊙ and the limb. No evidence of the bright ring near the limb is found. The radio radius at 8.6 mm is 1.015±0.005R⊙. In addition there exists a coronal component just outside the radio limb.

AN INTERPRETATION OF THE DECAY CHARACTERISTICS OF SOLAR HARD X-RAY BURSTS

A simple trap model of solar hard X-ray bursts is discussed in which nonthermal electrons trapped in a magnetic bottle precipitate into the lower chromosphere through the resonant scattering by whistlers. In such a model, the X-ray spectra produced from trapped and precipitating electrons have different spectral shape, and both of the spectra will initially soften with time, provided the precipitation dominates over collisional degradation.

Interferometer observations of a radio burst at 8.6 mm associated with a polarized hard X-ray event

Observations of a radio burst at 8.6 mm wavelength on 1970 November 5, are described with the particular interest on the correspondence between radio and polarized X-ray events. The radio observations were carried out using an interferometer with a half power width of 2.9′ at the Dept. of Physics, Nagoya University, and indicated that the location of the radio burst coincided with preceding sunspots and the size of the burst source must be very small, less than about 1′. Mechanisms of radio and X-ray emissions are discussed briefly.

Rising motion of a behind-the-limb flare at 35 GHz

Interferometer observation of a behind-the-limb flare on 7 September, 1977, at 35 GHz (λ = 8.6 mm) shows that the microwave non-thermal radio source of the burst is located in the coronal region at the height higher than 7000 km above the photosphere and rises gradually with the velocity of about 30 km s-1.

ASTROMETRY OF IRAS 22555+6213 WITH VERA: A 3-DIMENSIONAL VIEW OF SOURCES ALONG THE SAME LINE OF SIGHT

We report results of the measurement of the trigonometric parallax of an H2O maser source in IRAS 22555+6213 with the VLBI Exploration of Radio Astrometry (VERA). The annual parallax was determined to be 0.278±0.019 mas, corresponding to a distance of 3.66 −0.26 kpc. Our results confirm that IRAS 22555+6213 is located in the Perseus arm. We computed the peculiar motion of IRAS 22555+6213 to be (Usrc, Vsrc,Wsrc) = (0 ± 1,−32 ± 1, 9 ± 1) km s−1, where Usrc, Vsrc, and Wsrc are directed toward the Galactic center, in the direction of Galactic rotation and toward the Galactic north pole, respectively. IRAS 22555+6213, NGC 7538 and Cepheus A lie along the same line of sight, and are within 2◦ on the sky. Their parallax distances, with which we derived their absolute position in the Milky Way, show that IRAS 22555+6213 and NGC 7538 are associated with the Perseus arm, while Cepheus A is located in the Local arm. We compared the kinematic distances of IRAS 22555+6213 derived with flat and non-flat rotation curve with its parallax distance and found the kinematic distance derived from the non-flat rotation assumption (−32 km s−1 lag) to be consistent with the parallax distance.

RADIO ASTROMETRIC OBSERVATIONS AND THE GALACTIC CONSTANT AS THE BASIS OF A GALACTIC KINEMATICS STUDY

We made phase-referencing Very Long Baseline Interferometry (VLBI) observations of Galactic 22 GHz H2O maser sources with VLBI Exploration of Radio Astrometry (VERA). We measured the parallax dis-tances of G48.61+0.02, G48.99-0.30, G49.19-0.34, ON1, IRAS 20056+3350, IRAS 20143+3634, ON2N, and IRAS 20126+4104, which are located near the tangent point and the Solar circle. The angular ve-locity of the Galactic rotation at the LSR (i.e. the ratio of the Galactic constants) is derived using the measured parallax distances and proper motions of these sources. The derived value of nΩ 0 = 28.8 ± 1.7 km s -1 kpc -1 is consistent with recent values obtained using VLBI astrometry but 10% larger than the International Astronomical Union (IAU) recommended value of 25.9 km s -1 kpc -1 = (220 km s -1 ) / (8.5 kpc).

ASTROMETRIC OBSERVATION OF MIRA VARIABLES WITH VERA

The calibration of the period luminosity relation (PLR) for Galactic Mira variables is one of the principle aims of the VERA project. We observe H2O maser emission at 22 GHz associated with Mira variables in order to determine their distances based on annual parallaxes. We conduct multi-epoch VLBI observations over 1{2 years with a typical interval of one month using VERA in order to obtain annual parallaxes with an accuracy of better than than 10%. Recently, the annnual parallax of T Lep was determined to be 3.06 0.04 mas corresponding to a distance of 327 4 pc (Nakagawa et al., 2014). The circumstellar distribution and kinematics of H2O masers was also revealed. With accurate distances to the sources, calibrations of K-band absolute magnitudes (MK) can be improved compared to conventional studies. By compiling Mira variables whose distances were determined with astrometric VLBI, we obtained a PLR of MK = 3.51 logP + 1.37 0.07.

VLBI Observations and NH3 Mapping of the Star-forming Region NGC2264

We have measured the annual parallax of the water maser source associated with star forming region NGC2264 from observations with VLBI Exploration of Radio Astrometry (VERA). We detected masers at VLSR = 7.2 km s−1 . We discussed its driving sources of detected maser spots. One of the maser spots was associated with a centimeter continuum source observed with VLA. Neither optical, infrared nor X-ray sources is catalogued near the spot. The other maser spot is located close to an X-ray source, although there is no optical or infrared counterpart. The proper motion of the former spot was (μα , μδ ) = (23.91± 4.29,−29.81± 4.27) and the proper motion of latter spot was (μα , μδ ) = (−0.96± 0.58,−6.05± 3.06). For the latter spot, the peculiar motion is ∼ 150 km s−1 and it has the high velocity and this may be a jet or an outflow from a young star. The observed parallax is 1.365 ± 0.098 mas, corresponding to the distance of 738 −50 pc. This value is constant with the photometric distance of NGC2264 previously measured. The fitting result of the parallax is shown in figure 1. We also observed in NH3 (1,1), (2,2), (3,3) lines of NGC2264 with the Kashima 34m telescope. We estimated the star formation efficiency (SFE) of NGC2264 from the dense molecular mass of NH3 and the stellar mass calculated by Teixeira et al.(2012). The SFE is 9 – 12 % which is consistent with previous results.

A Near Infrared Camera Refrigerated by Two Stirling Machines – an Alternative to Robotic Telescopes

We have developed and tested a new near infrared camera equipped with a 512 × 512 PtSi CCD and cooled by two independent Stirling Cycle refrigerators. The camera, installed on the 60 cm reflector telescope of the Nishi-Harima Astronomical Observatory (NHAO) since April 2000, has begun regular observations toward infrared objects. Since the reasonable cost and lower maintenance needs of the camera make it more attractive, we introduce it as an alternative to robotic telescopes.