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Session 80 - Central Stars of Planetary Nebulae.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center

[80.01] Photometric Variability of Proto-Planetary Nebulae

B. J. Hrivnak, W. Lu, K. J. Vogler, P. Barajas, G. Lessmann, B. Spitzbart, J. Webb (Valparaiso U.)

We have undertaken at Valparaiso U. a program of CCD monitoring of Proto-Planetary Nebulae (PPN) candidates to search for light variability. PPN are post-AGB objects in transition to the planetary nebula phase. Several reasons motivated this study. The properties of PPN are not well known, and we thought it useful to search for light variability in these objects. It is known that other post-AGB objects, such at RV Tauri variables, vary periodically in brightness. In a related study, we have monitored a dozen PPN for radial velocity variation, and found then all to vary, some periodically. We wanted to see if there existed a correlation between the light and velocity variability.

We presently have 40 objects on this monitoring program. The observations began in earnest in July 1994 at the Valparaiso University Observatory, and continue through the present time. The PPN were chosen from an ongoing program of discovery and study of PPN candidates (Hrivnak, Kwok, amp; Volk 1989, ApJ, 346, 265; Hrivnak amp; Kwok 1992, BAAS, 24, 1175), based upon IRAS data.

>From an analysis of the data of the first season, we find the light curves to fall into four categories: clearly periodic variability, (2) clear variability, but not enough data to determine if periodic, (3) clear variability, but probably not periodic, and (4) not variable. The objects in the first category are particularly interesting, because in the three best cases the radial velocity also varies with the same period of between 80 and 120 days. The data from the second season are being reduced and will be incorporated into the results presented.

This study is well suited for a small telescope (0.4 m) equipped with a CCD. The objects studied have V magnitudes in the range of 9 to 15. It has also provided an excellent way for students to be involved in a research project, which they have done during the summer months. This research is supported by the NASA JOVE program and the NSF.

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