Seiji Kameno

THE 2014 ALMA LONG BASELINE CAMPAIGN: FIRST RESULTS FROM HIGH ANGULAR RESOLUTION OBSERVATIONS TOWARD THE HL TAU REGION

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0. ′′ 075 (10 AU) to 0. ′′ 025 (3.5 AU), revealing an astonishing level of detail in the cir cumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72 ◦ ± 0.05 ◦ ) and position angle (+138.02 ◦ ± 0.07 ◦ ). We obtain a high-fidelity image of the 1.0 mm spectral index (�), which ranges from � � 2.0 in the optically-thick central peak and two brightest ring s, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation incl ude an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO + (1-0) which exhibits a pattern over LSR velocities from 2-12 km s -1 consistent with Keplerian motion around a �1.3M⊙ star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protost ars XZ Tau (A/B) and LkH�358 at 2.9 mm. Subject headings: stars: individual (HL Tau, XZ Tau, LkH�358) — protoplanetary disks — stars: formation — submillimeter: planetary systems — techniques: interferometric

Distance to Orion KL Measured with VERA

We present the initial results of multiepoch VLBI observations of 22 GHz H2O masers in the Orion KL region with VERA (VLBI Exploration of Radio Astrometry). With the VERA dual-beam receiving system, we carried out phase-referencing VLBI astrometry, and successfully detected the annual parallax of Orion KL to be 2.29 ˙ 0.10 mas, corresponding to a distance of 437 ˙ 19 pc from the Sun. The distance to Orion KL was determined for the first time with the trigonometric parallax method in these observations. Although this value is consistent with that previously reported, 480 ˙ 80 pc, which was estimated from a statistical parallax method using the proper motions and radial velocities of the H2O maser features, our new results provide a much more accurate value with an uncertainty of only 4%. In addition to the annual parallax, we detected an absolute proper motion of the maser feature, suggesting an outflow motion powered by the radio source I along with the systematic motion of source I itself.

A Helical Magnetic Field in the Jet of 3C 273

Both in the Faraday Rotation Measure and the intrinsic polarization angle, new features are revealed to indicate a helical magnetic field operating along the jet of the bright active galactic nucleus 3C 273. The helical field has been suggested to be related to the formation and collimation of jets by magnetohydrodynamic models. The distribution of the rotation measure shows a systematic gradient with respect to the jet axis, which is expected by a helical magnetic field. In addition, the helical field can consistently explain two types in the direction of the projected magnetic field: parallel and perpendicular to the jet axis. Further, if the helical magnetic field is generated by winding up of an initial field by rotation of the accretion disk, we can uniquely determine the direction of the disk rotation, since the jet is approaching us.

Distance to VY Canis Majoris with VERA

We report astrometric observations of H2O masers around the red supergiant VY Canis Majoris (VY CMa) carried out with VLBI Exploration of Radio Astrometry (VERA). Based on astrometric monitoring for 13 months, we successfully measured a trigonometric parallax of 0.88 ± 0.08 mas, corresponding to a distance of 1.14 +0.11 −0.09 kpc. This is the most accurate distance to VY CMa and the first one based on an annual parallax measurement. The luminosity of VY CMa has been overestimated due to a previously accepted distance. With our result, we re-estimate the luminosity of VY CMa to be (3 ± 0.5) × 10 5 L⊙ using the bolometric flux integrated over optical and IR wavelengths. This improved luminosity value makes location of VY CMa on the Hertzsprung-Russel (HR) diagram much closer to the theoretically allowable zone (i.e. the left side of the Hayashi track) than previous ones, though uncertainty in the effective temperature of the stellar surface still does not permit us to make a final conclusion.

Astrometry of H2O Masers in Nearby Star-Forming Regions with VERA III. IRAS22198+6336 in Lynds1204G

We present results of multi-epoch VLBI observations with VERA (VLBI Exploration of Radio Astrometry) of the 22 GHz H2O masers associated with a young stellar object (YSO) IRAS 22198+6336 in a dark cloud, L 1204 G. Based on phase-referencing VLBI astrometry, we derived an annual parallax of IRAS 22198+6336 to be 1.309˙ 0.047 mas, corresponding to the distance of 764˙ 27 pc from the Sun. Although the most principal error source of our astrometry is attributed to the internal structure of the maser spots, we successfully reduced the errors in the derived annual parallax by employing position measurements for all of the 26 detected maser spots. Based on this result, we reanalyzed the spectral energy distribution of IRAS 22198+6336 and found that the bolometric lumi— —

Time Variation of the Rotation Measure Gradient in the 3C 273 Jet

The existence of a gradient in the Faraday rotation measure (RM) of the quasar 3C 273 jet is confirmed by follow-up observations. A gradient transverse to the jet axis is seen for more than 20 mas in projected distance. Taking account of the viewing angle, we estimate it to be more than 100 pc. Comparing to the distribution of the RM in 1995, we detect a time variation of it at the same distance from the core over 7 yr. We discuss the origin of the Faraday rotation based on this rapid time variation. We rule out foreground media such as a narrow-line region, and suggest a helical magnetic field in the sheath region as the origin of this gradient of the RM.

Distance to NGC 281 in a Galactic Fragmenting Superbubble: Parallax Measurements with VERA

We have used the Japanese VLBI array VERA to perform high-precision astrometry of an H2O maser source in the Galactic star-forming region NGC 281 West, which has been considered to be part of a 300-pc superbubble. We successfully detected a trigonometric parallax of 0.355 ˙ 0.030 mas, corresponding to a source distance of 2.82 ˙ 0.24 kpc. Our direct distance determination of NGC 281 has resolved a large distance discrepancy between previous photometric and kinematic studies; likely NGC 281 is in the far side of the Perseus spiral arm. The source distance as well as the absolute proper motions were used to demonstrate the 3D structure and expansion of the NGC 281 superbubble, � 650 pc in size parallel to the Galactic disk and with a shape slightly elongated along the disk or spherical, but not vertically elongated, indicating that the superbubble expansion may be confined to the disk. We estimate the expansion velocity of the superbubble as being � 20 km s � 1 , both perpendicular to and parallel to the Galactic disk with a consistent timescale of � 20 Myr.

The Kinematic and Spectral Ages of the Compact Radio Source CTD 93

We present a study of the kinematic and spectral ages of the gigahertz-peaked spectrum (GPS) source CTD 93. Measurements of the hot-spot separation over 8.5 yr show evidence of an increase. The separation rate along the source axis is (0.34 ± 0.11)c (H0 = 72 km s-1 Mpc-1), which results in a kinematic age of 2200 ± 700 yr. Assuming that two hot spots are moving apart at equal speeds, we derive an advance speed of (0.17 ± 0.06)c. The radio-lobe spectra show a high-frequency steepening, as expected if energetic electrons lose energy by synchrotron radiation. The spectral break decreases with the distance from the hot spot in the northern component of CTD 93. This tendency is expected from the basic scenario of radio-lobe evolution involving particle acceleration at the hot spots, with the radio lobes populated by high-energy electrons that have leaked from the hot spots. Although a core-jet morphology for CTD 93 has previously been proposed, these results indicate that the morphology is similar to that of compact symmetric object (CSO). From the spectral fits in the northern component we found a break frequency of 3.7 GHz at the edge of the lobe. The resultant spectral age is ~300 yr, assuming the equipartition magnetic field. This requires the advance speed of 0.26c, which shows a good agreement of the hot-spot motion of (0.17 ± 0.06)c. Our results strongly support the hypothesis that CSOs are young radio sources.

A high-frequency radio survey of low-luminosity active galactic nuclei

ABSTRACT We investigate the high-frequency radio spectra of twenty low-luminosity activegalactic nuclei (LLAGNs) with compact radio cores. Our millimetre survey withthe Nobeyama Millimetre Array (NMA) and analyses of submillimetre archivaldata that had been obtained with the Submillimetre Common User BolometerArray (SCUBA) on the James Clerk Maxwell Telescope (JCMT) reveal the fol-lowing properties. At least half of the LLAGNs show inverted spectra between 15and 96 GHz; we use published data at 15 GHz with the Very Large Array (VLA)in a 0.15-arcsec resolution and our measurements at 96 GHz with the NMA ina 7-arcsec resolution. The inverted spectra are not artificially made due to theirunmatched beam sizes, because of little diffuse contamination from dust, Hii re-gions, or extended jets in these LLAGNs. Such high-frequency inverted spectraare apparently consistent with a ‘submillimetre bump’, which is predicted by anadvection-dominated accretion flow (ADAF) model. We find a strong correlationbetween the high-frequency spectral index and low-frequency core power mea-sured with very-long-baseline-interferometry (VLBI) instruments. The invertedspectra were found exclusively in low-core-power sources, while steep spectrawere in high-core-power ones with prominent pc-scale jets. This suggests thatthe ADAF and nonthermal jets may coexists. The flux ratios between disc andjet seem to be different from LLAGN to LLAGN; disc components can be seenin nuclear radio spectra only if the jets are faint.Key words: galaxies: active – galaxies: Seyfert – radio continuum: galaxies –submillimetre.

VLBI Astrometry of AGB Variables with VERA — A Semiregular Variable S Crateris—

We present a distance measurement for the semiregular variable S Crateris (S Crt) based on its annual parallax. With the unique dual beam system of the VLBI Exploration for Radio Astrometry (VERA) telescopes, we measured the absolute proper motion of a water maser spot associated with S Crt, referred to the quasar J1147� 0724 located . .. . .. . .. . ..