1 / 25

OH26.5+0.6 : Insight into the circumstellar structure of an extreme OH/IR star

OH26.5+0.6 : Insight into the circumstellar structure of an extreme OH/IR star. Sandra Etoka In collaboration with Philip Diamond. Outline. Introduction Maser emission extent Geometric and polarimetric structure Discussion/Summary. Introduction.

mab
Download Presentation

OH26.5+0.6 : Insight into the circumstellar structure of an extreme OH/IR star

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. OH26.5+0.6 :Insight into the circumstellar structure of an extreme OH/IR star Sandra Etoka In collaboration with Philip Diamond

  2. Outline • Introduction • Maser emission extent • Geometric and polarimetric structure • Discussion/Summary

  3. Introduction • OH26.5+0.6 is: an extreme 8M OH/IR star with a mass-loss rate on the order of 5 x 10-4 M/yr. It is one of the brightest OH maser emitters in our Galaxy and is suspected of experiencing a superwind which emerged less than 150 years ago (Justtanont et al. 1996).

  4. Introduction • OH26.5+0.6 is: an extreme 8M OH/IR star with a mass-loss rate on the order of 5 x 10-4 M/yr. It is one of the brightest OH maser emitters in our Galaxy and is suspected of experiencing a superwind which emerged less than 150 years ago (Justtanont et al. 1996). • MERLIN OH observations at 18 cm in the 1667, 1665 and 1612 MHz maser line allowed the first combined insight into the geometric and polarimetric structure of the circumstellar material surrounding this object.

  5. Introduction • OH26.5+0.6 is: an extreme 8M OH/IR star with a mass-loss rate on the order of 5 x 10-4 M/yr. It is one of the brightest OH maser emitters in our Galaxy and is suspected of experiencing a superwind which emerged less than 150 years ago (Justtanont et al. 1996). • MERLIN OH observations at 18 cm in the 1667, 1665 and 1612 MHz maser line allowed the first combined insight into the geometric and polarimetric structure of the circumstellar material surrounding this object. • This work intends to bring a new insight into the structural changes undergone by the circumstellar material of an evolved star when it enters the OH/IR stage.

  6. Maser emission extent • The spot located at the centre of the maser distribution at 1612 at a velocity of 41 km/s is quite likely to be on the stellar position. 1612 MHz velocity integrated image in Stokes I

  7. Maser emission extent • The total extent of the OH masing shell at 1612 MHz is ~ 5 arcsec corresponding to a linear extent of ~7000 au at 1.4 kpc • It is an ellipsoid elongated in the E-W direction 1612 MHz velocity integrated image in Stokes I without the strong central maser spot

  8. Maser emission extent • The 1667 MHz extends ~1 arcsec further than the 1612 MHz. This is surprising since maser theory predict the 1665/67 MHz emission to be internal to that at 1612 MHz • Also, the orientation of the long axis at 1612 and 1667 MHz maser distribution does not seem to coincide • Why is that so ? 1667 MHz velocity integrated image in Stokes I

  9. Maser emission extent • the 1665 MHz maser emission is totally asymmetric: • a strong central maser spot + a filament oriented NW • the total extent is less than 2 arcsec 1665 MHz velocity integrated image in Stokes I

  10. 1665 MHz maser spot distribution • Maser spot distribution criteria: • 3 consecutive channels • 1665 MHz: 3σ • 1667 & 1612 MHz: 4σ • P only shown if ≥3σ

  11. 1665 MHz maser spot distribution • Maser spot distribution criteria: • 3 consecutive channels • 1665 MHz: 3σ • 1667 & 1612 MHz: 4σ • P only shown if ≥3σ • The 2 blue-shifted central spots are quite likely an amplification of the stellar radiation

  12. 1665 MHz maser spot distribution • Maser spot distribution criteria: • 3 consecutive channels • 1665 MHz: 3σ • 1667 & 1612 MHz: 4σ • P only shown if ≥3σ • The 2 blue-shifted central spots are quite likely an amplification of the stellar radiation • a clear filament is traced by the red shifted maser spots

  13. 1667 MHz maser spot distribution • 81 maser spots • Only the 2 strongest red shifted maser spots show P≥3σ • The south part of the shell is dominated by blue shifted maser emission while the N-NE part by the red shifted emission

  14. 1612 MHz maser spot distribution • Out of the 277 maser spots at 4σ 106 show P ≥ 3σ • The southern part of the maser distribution is clearly dominated by blue-shifted emission • B=3-4 mG inferred by Zeeman splitting

  15. 1612 MHz maser spot distribution • Out of the 277 maser spots at 4σ 106 show P ≥ 3σ • The southern part of the maser distribution is clearly dominated by blue-shifted emission • B=3-4 mG inferred by Zeeman splitting • The distribution of the vectors of polarization is a mixture of radial (N) and tangential (S).

  16. 1612 MHz maser spot distribution • Out of the 277 maser spots at 4σ 106 show P ≥ 3σ • The southern part of the maser distribution is clearly dominated by blue-shifted emission • B=3-4 mG inferred by Zeeman splitting • The distribution of the vectors of polarization is a mixture of radial (N) and tangential (S). This is consistent with a poloidal magnetic field titled ~40-60º to the LOS 40-60º (Elitzur 1992; Kemball & Diamond 1997)

  17. 1667 MHz radial velocity distribution • V=f(θ) allow us to infer the thickness of the OH masing shell (~1.5-2 arcsec) and that acceleration takes place

  18. 1612 MHz radial velocity distribution

  19. 1612 MHz radial velocity distribution

  20. 1612 MHz radial velocity distribution • V=f(θ) for both the 1667 and 1612 MHz is well explained by a prolate shell titled about 45º - 65º to the line of sight (Bower’s model 1991)

  21. 1612 MHz radial velocity distribution • V=f(θ) for both the 1667 and 1612 MHz is well explained by a prolate shell titled about 45º - 65º to the line of sight (Bower’s model 1991)

  22. Discussion/Summary • Polarization structure consistent with a poloidal magnetic field inclined ~ 40-60º to the line of sight

  23. Discussion/Summary • Polarization structure consistent with a poloidal magnetic field inclined ~ 40-60º to the line of sight • This coincides with the geometrical major-axis of the ellipsoidal maser distribution inferred from V=f(θ)

  24. Discussion/Summary • Polarization structure consistent with a poloidal magnetic field inclined ~ 40-60º to the line of sight • This coincides with the geometrical major-axis of the ellipsoidal maser distribution inferred from V=f(θ) • Magnetic field strength inferred from Zeeman splitting: 3-4 mG at 7000 au. Similar to what was found for the super massive evolved star NML Cyg at similar distance (Etoka & Diamond 2004)

  25. Discussion/Summary • Polarization structure consistent with a poloidal magnetic field inclined ~ 40-60º to the line of sight • This coincides with the geometrical major-axis of the ellipsoidal maser distribution inferred from V=f(θ) • Magnetic field strength inferred from Zeeman splitting: 3-4 mG at 7000 au. Similar to what was found for the super massive evolved star NML Cyg at similar distance (Etoka & Diamond 2004) The end: Thanks !

More Related