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Magnetic Field and Morphology of OH/IR Star OH 44.8-2.3: SiO Maser Observations

This study presents VLBA observations of SiO masers in the OH/IR star OH 44.8-2.3, revealing the magnetic field and morphology. The masers show a ring-like structure, and the magnetic field is parallel or perpendicular to the polarization vectors. Circular polarization analysis suggests a magnetic field strength of 1.5±0.5 G. The study also explores the relationship between asymmetries in SiO and OH masers and the consistency of SiO gaps over time.

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Magnetic Field and Morphology of OH/IR Star OH 44.8-2.3: SiO Maser Observations

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  1. VLBA SiO Maser Observations of the OH/IR Star OH 44.8-2.3: Magnetic Field and Morphology Huib Jan van Langevelde (JIVE/ Leiden Observatory) Wouter Vlemmings (Chalmers University) Athol Kemball (University of Illinois) Nikta Amiri (University of Colorado Boulder)

  2. TX Cam (73 Epochs) I. Gonidakis, P. J. Diamond, A. J. Kemball (2010)

  3. SiO Masers in Evolved Stars • SiO in OH/IR stars? • Bigger dust shell,Larger CSE,Longer periodsSiO Masers in OH/IR stars the same as Miras? • SiO emission Mechanism the same as Mira variables? Credit: Markus Wittkowski Credit: Makus Wittkowski TX Cam, Credit: Athol Kemball

  4. SiO Masers- Magnetic Fields TX Cam, SiO Kemball and Diamond, 1997, ApJ 481 L111

  5. SiO masers of the OH/IR star OH 44.8-2.3 • The first SiO maser map of an OH/IR • The masers appear to be absent from the eastern and western parts of the ring Amiri et al. 2012

  6. SiO masers of the OH/IR star OH 44.8-2.3- Continued • Distance:1.13±0.34 kpc (Van Langevelde et al. 1990). • Ring with a radius of ~5.4 AU around the star. • Similar distance from the star as Mira variables (3-7 AU Cotton et al. 2008). • Distance determination using parallax 5.4 AU Amiri et al. 2012

  7. Polarization properties-linear • Highly linearly polarized, up to 100% • Magnetic field is parallel or perpendicular to the polarization vectors (Goldreich et al. 1973). • The polarization vectors are consistent with a dipole magnetic field • Other complex morphologies (Toroidal or Solar type ) • OH and H2O polarimetric observations B B 100% Amiri et al. 2012

  8. Linear Polarization • No tangential morphology • Tangential Polarization Morphology is not a generic property of SiO masers!! TX Cam Credit: Athol Kemball

  9. Circular Polarization Analysis-Zeeman Splitting • Zeeman Splitting: The most direct way to measure magnetic field • The Zeeman splitting causes a velocity shift between the RCP and LCP spectra Zeeman Effect Velocity offset

  10. Circular Polarization Analysis • Both methods require careful polarization Calibration!!! • S-curve fitting • V=(LCP-RCP)/2 • Cross-Correlation Method • Sensitivity of this method is comparable to the S-curve fitting

  11. Polarization properties-circular • Tentative detection of circular polarization for brightest maser feature at ~0.7%. • This corresponds to a magnetic field strength of 1.5+/0.5 G. • The magnetic field was measured from the S-curve fitting and the cross-correlation method • Non-Zeeman effects (Wiebe & Watson 1998) Amiri et al. 2012

  12. OH Maser Observations of OH 44.8-2.3 • Are both asymmetries related? • A mechanism can support asymmetries on many scales? • Are SiO gaps consistent in Time? Amiri et al. 2012 1471 AU 5.4 AU

  13. Morphology of the CSE of OH 44.8-2.3 1471 AU B B

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