1 / 27

VLBI observations of two 43-GHz SiO masers in R Cas

VLBI observations of two 43-GHz SiO masers in R Cas. Jiyune Yi 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.

landen
Download Presentation

VLBI observations of two 43-GHz SiO masers in R Cas

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. VLBI observations of two 43-GHz SiO masers in R Cas Jiyune Yi 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. HartebeesthoekRadio Astronomy Observatory 8th EVN Symposium 2006

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

  3. Stellar masers & Evolved stars • SiO, H2O 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

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

  5. Scientific goalsVLBA 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. 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. 10 mas ~ 1.07 AU EpochI (F~ 0.25)

  9. EpochII (F ~0.68)

  10. Epoch III (F~ 0.95) 10 mas ~ 1.07 AU

  11. EpochIV (F~ 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. 1996 36 mas(700 nm), 49 mas(714) • Hofmann et al. 2000 44 mas(671), 37 mas(700) 49 mas(714), 30 mas(1045) • Mennesson et al. 2002 24.78 mas (F~ 0.09) at 2.16 mm 31.09 mas (F ~ 0.17) at 3.79 mm  • 700 nm R Cas • 714 nm R Cas Weigelt et al. 1996

  14. Stellar photospheric size versus SiO maser shell sizeof R Cas • Angular diameter < 30 mas, at near IR continuum • Angular diameter > 30 mas, at visible  • Comparison with 3.8& 2.2mm radii, R(3.8) & R(2.2) at F=0.17 & 0.09, respectively (obs. by Mennesson et al. 2002)

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

  17. Analysis of MASER ring radius

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

  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 atIV  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 thering radius twice thicker in the v=1 ring (M)

  20. 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 3600 K

  21. Velocity field of the masers Epoch III V=1 V=2

  22. V=1 V=2 Spoke-like features EpochIV

  23. 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 Radial Spokes Rectangles  spokes of gas flowing outward at different angle Thick rect.  the brightest spokes which we observe

  24. 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

  25. Diamond & Kemball 2003 Desmurs et al. 2000 Comparison with other observations

  26. 43.1-GHz SiO maser & NIR observations in S Orionis SiO maser at ~ 2 photospheric radii (Boboltz & Wittkowski 2005)

More Related