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VLBI observations of two 43-GHz SiO masers in R Cas Jiyune Yi KVN Korea VLBI Network ( KVN ) group Korea Astronomy and Space Science Institute In collaboration.

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Presentation on theme: "VLBI observations of two 43-GHz SiO masers in R Cas Jiyune Yi KVN Korea VLBI Network ( KVN ) group Korea Astronomy and Space Science Institute In collaboration."— Presentation transcript:

1 VLBI observations of two 43-GHz SiO masers in R Cas Jiyune Yi KVN Korea VLBI Network ( KVN ) group Korea Astronomy and Space Science Institute In collaboration with R. Booth 1,2 and J. Conway 1 1. Onsala Space Observatory, Sweden 2. Hartebeesthoek Radio Astronomy Observatory 8 th EVN Symposium 2006

2 M5 Asymptotic Giant Branch AGB star C/O core He burning inner shell H burning outer shell

3 Stellar masers & Evolved stars SiO, H 2 O and OH masers form in the extended stellar atmosphere & circumstellar envelope of evolved star (AGB stars)  High resolution studies of SiO masers ☞ unique tool to study extended stellar atmosphere of AGB stars ☞ unique tool to study extended stellar atmosphere of AGB stars

4 SiO maser in AGB star adopted by J. Hron, original idea by T. Le Bertre

5 Scientific goals VLBA observations of SiO masers To find significant constraints on SiO maser modellings  evidence of stellar phase dependence To provide highly plausible inputs for new models To extend our understanding on the physical and dynamical properties of CSEs  positions of individual maser clumps measured down to sub- milliarcsecond accuracy To put confidence in non-standard VLBI techniques, (both observations and calibrations)

6 6 Technical challenge To track the delay across the 301 MHz frequency gap between the v=1 and v=2 transitions  Simultaneous observations of the two maser transitions required To determine the relative position of the masers in the two transitions  Imaging the two maser maps relative to each other using cross-phase referencing

7 4 epochs of VLBA observations : R Cas R Cas Light curve (courtesy,AAVSO)

8 Epoch I (  ~ 0.25) 10 mas ~ 1.07 AU

9 9 Epoch II (  ~ 0.68)

10 10 Epoch III (  ~ 0.95) 10 mas ~ 1.07 AU

11 11 Epoch IV (  ~ 0.23)

12 R Cas image at 671 nm (Weigelt et al. 1996)

13 R Cas photospheric size measured by optical/IR Weigelt et al mas(700 nm), 49 mas(714) Hofmann et al mas(671), 37 mas(700) 49 mas(714), 30 mas(1045) Mennesson et al mas (  ~ 0.09) at 2.16  m mas (  ~ 0.17) at 3.79  m  Weigelt et al  700 nm R Cas  714 nm R Cas

14 Stellar photospheric size versus SiO maser shell size of R Cas Angular diameter < 30 mas, at near IR continuum Angular diameter > 30 mas, at visible  Comparison with 3.8  & 2.2  m radii, R(3.8) & R(2.2) at  0.17 & 0.09, respectively (obs. by Mennesson et al. 2002)  0.17  0.09 Epoch I (  0.25) 1.01 x R(3.8)1.3 x R(2.2) Epoch II (  0.68) 1.4 x R(3.8)1.8 x R(2.2) Epoch III & IV (  0.95 & 0.23) 1.6 x R(3.8)2.0 x R(2.2)

15 Summary : R Cas Instead of ring disruption at near maser minimum (Epoch II ) both masers formed circular rings. Both maser rings expanded and contracted depending on the stellar phase. At maser maximum, both masers showed many coincident masers. Outward-extending flare-like structure of emission survived over 2 epochs (~ 0.3 stellar phase). SiO maser shell diameters estimated around 1 ~ 2 stellar diameter. Asymmetry found at Epoch I, asymmetric ejection of material directed away from us ? Models which are predominantly collisionally pumped are in good agreement with our results. Missing flux (typically more than 50 %) density found, estimated a lower limit of the structure, 3~4 mas

16 16 TX Cam maps at 4 epochs (Jiyune Yi et al. 2005) 10 mas ~3.8 AU

17 17 Analysis of MASER ring radius

18 18 Comparison with models Epoch III Epoch IV v = 1 v = 2 v = 1 v = 2

19 19 Comparison with models Ring shape  Disruption of the ring structure at maser minimum development of the ring afterwards Ring radius  Expansion and contraction along the stellar cycle Ratio of the ring radius, v=2/v=1  96 % ( III ) vs 94 % (M) ; 91 % ( IV ) vs 92 %(M) relatively smaller R at IV  v=2, contracting while v=1, constant Ring thickness (25~75% percentiles), v=1 vs v=2  15.6 % vs 14.9 % ( III ) ; 19.5 % vs 18.6 % ( IV ) of the ring radius  twice thicker in the v=1 ring (M)

20 20

21 3600 K 1800 K Constraint on SiO maser models To excite the lowest vibrational state,v=1  Required temperature >1800 K  Unable to have spatial coincidence of masers in various v- states by radiative pumping

22 Velocity field of the masers V=1V=2 Epoch III

23 Spoke-like features Epoch IV V=1V=2

24 Radial Spokes Rectangles  spokes of gas flowing outward at different angle Thick rect.  the brightest spokes which we observe All spokes have the same velocity field, decelerating with radius. LOS1  LOS through a spoke in the sky plane, having a velocity coherent path equal to the spoke width LOS2  LOS through a spoke, having a maximum velocity coherent path length LOS3  LOS, velocity coherent path length decreasing because of the large velocity gradient along the path

25 Models of SiO masers in M-Miras (Humphreys et al. 2002: Gray & Humphreys 2000) 86 GHz v=1,J=1-0 v=2,J=1-0

26 Comparison with other observations Desmurs et al Diamond & Kemball 2003

27 GHz SiO maser & NIR observations in S Orionis  SiO maser at ~ 2 photospheric radii (Boboltz & Wittkowski 2005)


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