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THE VLBI MONITORING PROJECT FOR 6.7 GHz METHANOL MASERS USING THE JVN/EAVN
SUGIYAMA, KOICHIRO,FUJISAWA, KENTA,HACHISUKA, KAZUYA,YONEKURA, YOSHINORI,MOTOGI, KAZUHITO,SAWADA-SATOH, SATOKO,MATSUMOTO, NAOKO,SAITO, YU,HIRANO, DAIKI,HAYASHI, KYONOSUKE,SHEN, ZHIQIANG,HONMA, MAREKI The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
We have initiated a Very Long Baseline Interferometer (VLBI) monitoring project of 36 methanol maser sources at 6.7 GHz using the Japanese VLBI Network (JVN) and East-Asian VLBI Network (EAVN), starting in August 2010. The purpose of this project is to systematically reveal 3-dimensional (3-D) kine-matics of rotating disks around forming high-mass protostars. As an initial result, we present proper mo- tion detections for two methanol maser sources showing an elliptical spatial morphology, G 002.53+00.19 and G 006.79-00.25, which could be the best candidates associated with the disk. The detected proper motions indicate a simple rotation in G 002.53+00.19 and rotation with expansion in G 006.79-00.25, respectively, on the basis of disk model fits with rotating and expanding components. The expanding motions might be caused by the magnetic-centrifugal wind on the disk.
SUGIYAMA, KOICHIRO,YONEKURA, YOSHINORI,MOTOGI, KAZUHITO,SAITO, YU,FUJISAWA, KENTA,ISHII, SHOTA,MOMOSE, MUNETAKE,HONMA, MAREKI,TAZAKI, FUMIE,TANAKA, KEI E.I.,HOSOKAWA, TAKASHI,UCHIYAMA, MIZUHO,INAYOSHI The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
We have initiated single-dish monitoring observations of ~400 methanol maser sources at 6.7 GHz using the Hitachi 32-m radio telescope from December 2012 to systematically research periodic flux variations, which are observed in some methanol maser sources associated with high-mass (proto-)stars. In our monitoring, we have made daily monitoring, so that each source has been observed every nine days with an integration time of 5 min (typical $3{\sigma}$ detection sensitivities of 0.9 Jy). The monitoring observations help us statistically understand periodic flux variations with a period longer than 50 days. As an initial result, we present a new detection of periodic flux variations in the 6.7 GHz methanol maser source G 036.70+00.09. The period of the flux variations is ~53 days (~0.019 cycles $day^{-1}$), and seems to be stable over 9 cycles, at least until the middle of August 2014.
Matsumoto, Naoko,Hirota, Tomoya,Sugiyama, Koichiro,Kim, Kee-Tae,Kim, Mikyoung,Byun, Do-Young,Jung, Taehyun,Chibueze, James O.,Honma, Mareki,Kameya, Osamu,Kim, Jongsoo,Lyo, A-Ran,Motogi, Kazuhito,Oh, C IOP Publishing 2014 ASTROPHYSICAL JOURNAL LETTERS - Vol.789 No.1
<P>We have carried out the first very long baseline interferometry (VLBI) imaging of a 44 GHz class I methanol maser (70-61A(+)) associated with a millimeter core MM2 in a massive star-forming region IRAS 18151-1208 with KaVA (KVN and VERA Array), which is a newly combined array of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We have succeeded in imaging compact maser features with a synthesized beam size of 2.7 milliarcseconds x 1.5 milliarcseconds (mas). These features are detected at a limited number of baselines within the length of shorter than approximate to 650 km corresponding to 100 M. in the uv-coverage. The central velocity and the velocity width of the 44 GHz methanol maser are consistent with those of the quiescent gas rather than the outflow traced by the SiO thermal line. The minimum component size among the maser features is similar to 5 mas x 2 mas, which corresponds to the linear size of similar to 15 AU x 6 AU assuming a distance of 3 kpc. The brightness temperatures of these features range from similar to 3.5 x 10(8) to 1.0 x 10(10) K, which are higher than the estimated lower limit from a previous Very Large Array observation with the highest spatial resolution of similar to 50 mas. The 44 GHz class I methanol maser in IRAS 18151-1208 is found to be associated with the MM2 core, which is thought to be less evolved than another millimeter core MM1 associated with the 6.7 GHz class II methanol maser.</P>