Hiroshi Imai Graduate School of Science and Engineering Kagoshima University East Asian VLBI Workshop, 2009 March 20

Stellar maser: the movie SiO masers around TX Cam (Diamond & Kemball 2003) Maser movie visualizes… expansion contraction rotation acceleration ballistic and non-ballistic motions Maser motions visualize giant gas clumps floating from giant convective cells? jets or spurs? shock wave transfer?

Circumstellar envelope and masers SiO/H 2 O/OH masers in VX Sgr (Chapman & Cohen 1986) SiO/H 2 O/OH masers in VX Sgr (Chapman & Cohen 1986) 1 arcsec (1500 AU)

Periodic variation in H 2 O maser emission ~ light curve ~ Collisionally excited Phase lag 0.7 ≦ Δφ( H 2 O—opt) ≦ 1.5 (Shintani+08) 0.5 ≦ Δφ( H 2 O—SiO) ≦ 1.4 (Ueda+09 in prep.) H 2 O velocity-integrated flux Optical magnitude

Periodic variation in H 2 O maser emission ~ distribution ~ RR Aql (Bowers & Johnston 94)

Shock wave transfer in the envelope Model of dust-induced pulsation-driven shock waves ( Hofner+95 ) Acceleration by shock waves (ΔV~10 km s -1 /2-3 months) Acceleration by shock waves (ΔV~10 km s -1 /2-3 months)

Detection of a shock wave? RT Vir (Imai+03)

Acceleration in a maser proper motion (rather than in a radial velocity) RT Vir (Imai+03)

Target: W Hydrae Distance ~90 pc SRa variable (P~360d) small Δm regular periodicy Bright maser source OH, H2O, SiO (v=1,2,3) Elongation of the radio photosphere Radio photosphere SiO maser emission Reid & Menten (2007)

Regular periodicity of H 2 O masers in W Hya Shintani+08 H 2 O velocity-integrated flux Optical magnitude

Periodic variation in angular and velocity distributions?

VERA cannot map, but KVN can VERA: 1000—2300 km baselines KNIFE (Kashima—Nobeyama): 200 km baseline KVN: 200—400 km baselines VERA KNIFE

Monitoring observations of stellar masers with interferometers Array N tel maserθ beam [mas] (min-max) N obs [/source] (valid) ΔT [month] T total [month] Reference J-Net4H2O3—143—4~1~4 Imai+97 Ishitsuka+01 VERA4H2O SiO 3—6 2—4 6— —4 1—9 12—24 15 Nakagawa+08 Kamohara+09 VLBA VLBA+VLA OH H2O SiO 7— — — — —60 3 ~55 Vlemmings+07 Imai+03 Diamond+03 MERLIN5H2O14— Richards+01 VLA27H2O100—10 4 4—54—30<60 Winnberg+08 KVN3 or 4 H2O SiO 15—10>500.5 >25Target

Conclusions: stellar masers in the movie Very attractive in science and public outreach in astronomy Direct approach to dynamics in stellar surface and envelope Asymmetic stellar mass loss driven by giant convection cells? Pulsation-driven shock waves transferred in envelope? Mass loss dependence on circumstellar dust abundance? Technical requirements Tight ( 1 pulsation period) monitor Short—intermediate baselines (50—400 km) Image quality (>3 baselines) Automatic data analysis (pipeline, automatic data flagging) Visualization tool (image interporation, etc.) Most possible key science target for KVN