Mathematics – Logic
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21440405c&link_type=abstract
American Astronomical Society, AAS Meeting #214, #404.05; Bulletin of the American Astronomical Society, Vol. 41, p.667
Mathematics
Logic
Scientific paper
We report on the development of a software tool (PROMOTIONS) to streamline the process of measuring proper motions of material in expanding nebulae. Our tool makes use of IDL's widget programming capabilities to design a unique GUI that is used to compare images of the objects from two epochs. The software allows us to first orient and register the images to a common frame of reference and pixel scale, using field stars in each of the images. We then cross-correlate specific morphological features in order to determine their proper motions, which consist of the proper motion of the nebula as a whole (PM-neb), and expansion motions of the features relative to the center. If the central star is not visible (quite common in bipolar nebulae with dense dusty waists), point-symmetric expansion is assumed and we use the average motion of high-quality symmetric pairs of features on opposite sides of the nebular center to compute PM-neb. This is then subtracted out to determine the individual movements of these and additional features relative to the nebular center. PROMOTIONS should find wide applicability in measuring proper motions in astrophysical objects such as the expanding outflows/jets commonly seen around young and dying stars. We present first results from using PROMOTIONS to successfully measure proper motions in several pre-planetary nebulae (transition objects between the red giant and planetary nebula phases), using images taken 7-10 years apart with the WFPC2 and ACS instruments on board HST.
The authors are grateful to NASA's Undergradute Scholars Research Program (USRP) for supporting this research.
Caleb Wherry John
Sahai Raghvendra
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