A Dramatic Change in the Polarization of V Hya

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Session 84 -- Variable Stars
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[84.08] A Dramatic Change in the Polarization of V Hya

J.J. Johnson (University of Wisconsin-Madison, Space Astronomy Lab)

The unusual carbon star, V Hydrae, is a semiregular variable with a period of 530 days superimposed on a longer, large amplitude period of 6500 days. It has been observed to have bipolar CO outflow (Kahane et al., 1988), and is believed to be an early precursor of a bipolar planetary nebula (Tsuji et al., 1988). In an earlier program (Johnson and Jones, 1991), we observed V Hya with a broad-band polarimeter. We found that it was intrinsically polarized with P on the order of 0.7\% at V. We re-observed V Hya at the University of Wisconsin's Pine Bluff Observatory using a spectropolarimeter, and found that the polarization has increased dramatically to 10\% at V, with a near 90 degree rotation in position angle from the earlier observation. Near the epoch when we observed V Hya for the second time, it was reported by T. L. Evans that V Hya was experiencing a decline in visible light. The infrared colors have also become redder, suggesting a possible dust ejection episode. V Hya is expected to reach a deep minimum sometime in 1994. We combine our polarimetric observations with our infrared and optical photometry and optical spectroscopy to propose a possible explanation for the polarimetric variations.

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