1 VERA による近傍星形成領域の 位置天文観測 Tomoya Hirota (Mizusawa-VLBI, NAOJ)
2 Nearby SFRs project Astrometry of H 2 O masers in nearby SFRs (<1 kpc) One of the VERA initial scientific programs Aim of this project Fundamental database Refine physical processes in star/planet-formation Reveal 3-D structure of Gould belt and local bubble Distribution of nearby SFRs (based on Dame et al. 1987 and Ward-Thompson et al. 2007)
3 First example: Orion KL Nearest massive star-forming region D=480 pc (Genzel et al. 1981) Best laboratory for star-formation studies Subaru NIR image H 2 O maser map with (Kaifu et al. 2000) VERA (Hirota et al. 2007)
4 Distance to Orion KL The first VERA result by Hirota et al. (2007) Single H 2 O maser 2.29+/-0.10 mas = 437+/-19 pc Smaller than well known value =480 pc (Genzel et al. 1981)
5 Orion Nebula cluster VERA: H 2 O and SiO masers in Orion KL 437+/-19 pc (H 2 O maser: Hirota et al. 2007) 418+/-6 pc (SiO maser: Kim et al. 2008) VLBA: continuum from WTTSs 1’ = 0.12pc 389 +24/-21 pc (GMR-A: Sandstrom et al. 2007) 414+/-7 pc (4 WTTSs: Menten et al. 2007) Consistent with each other Source I (masers) (NIR image of ONC; Menten et al. 2007)
6 Perseus molecular cloud NGC1333 (Hirota et al. 2008): 235+/-18 pc L1448C (Hirota et al. 2011): 232+/-18 pc Photometric distance: 220 pc (Cernis 1990) HIPPARCOS: 318 pc for Per OB2 (de Zeeuw et al. 1999) Proper motions similar to VLA/HIPPARCOS results Optical image of the Perseus region (Bally et al. 2008)
7 Perseus molecular cloud 3D structure of Perseus molecular cloud Consistent with previously suggested by photometric observations (Cernis 1993) PerOB2 Taurus NGC1333 B1 IC348 Schematic view proposed by Cernis (1993)
8 Cepheus-Cassiopeia region New distance to L1204G/IRAS22198+6336 (Hirota et al. 2008) 1.3 kpc 0.7 kpc; MYSO? Intermediate-mass YSO 3D structure ranging from 0.7-3 kpc 0.7kpc 0.7kpc 2kpc 1kpc 3kpc 2-3kpc
9 Other sources in Cepheus region CO map (Yonekura et al. 1997) VLBI astrometry (compiled by Chibueze et al. 2014)
10 Other researches (not all) Ophiuchus VERA: 178 +18 / -37 pc (Imai et al. 2007) VLBA: 120.0 +4.5 / -4.2 pc (Loinard et al. 2008) Orion-Monoceros VERA: 738 +57 / -50 pc for NGC2264 (Kamezaki et al. 2014) VLBA Bessel project (Wu et al. 2014) Nearby sources (including ~1 kpc) in Sagittarius Arm VLBA Gould belt survey (Loinard et al. ) Continuum sources in nearby SFRs surveyed by JVLA Taurus, Perseus, Ophiuchus, Orion, Serpens, (Cepheus)
11 New VLBI target sources Non-thermal radio emitting stars Magnetic activities Strong shock by stellar wind Possible target sources Pulsar Micro quasar Supernovae (remnant) X(g)-ray binary RS CVn binary Weak-line T-Tauri star (WTTS) Relationship between X-ray O star, Wolf-Rayet star and radio luminosity (Gudel 2002)
12 Observations Japanese VLBI Network (JVN) OCTAVE (Optically ConnecTed Array for Vlbi Exploration) 筑波 32m Usuda 64 m, Tsukuba 32 m, Hitachi 32 m, Yamaguchi 32 m Maximum baseline ~ 900 km 臼田 64m 10 mas resolution at 8 GHz Recording rate = 2 Gbps (512 MHz bandwidth) Real-time data transfer to Mitaka 日立 32m 山口 32m
13 Observations Survey of young stellar objects and massive stars Date: 2008 March, 3 stations (WTTSs, HAeBe) Date: 2011 November/December, 3 stations (O/WR stars) Source selection Relatively compact/strong radio emission detected with VLA Time variation Negative spectral energy distribution Polarization Association of X-ray Not systematic samples
14 Results(1) WTTSs Example of the results (for VLBI experts) FRING (solint=1) solutions with SNR=10-30 for ~10mJy Detection of 3 sources (V773 Tau, GMR-12, VSSG14) Many non-detection Insufficient calibration Insufficient position accuracy Extended thermal sources (UCHII regions, thermal jets); short-baseline (<50 km) is essential (e.g. Ibaraki array)
15 Results(2) O/WR stars Detected 5/23 sources of O/WR stars No flux calibration applied Cep-A Cyg OB2 Hitachi Hitachi GMR-12 HW9 NO9 GMR- WR140 WR146 12 Tsukuba Usuda Time=1hr Time=30min Yamaguchi Yamaguchi SNR=40
16 Summary and future Summary of VERA Maser astrometry revealed 3D structure of molecular clouds Summary of JVN/OCTAVE Radio emitting stars will be new probes of astrometry Complete survey of WR stars is on-going Future astrometry with VLBI, ALMA and SKA Star-forming regions not only with masers but also with continuum emission from (low-mass) WTTSs and (high- mass) O stars in clusters will be promising Stellar radio astrometry will be developed for various classes/populations of sources at different environments
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