Seminar of RPg Student:- A Morpho-kinematic and Ionization Study of the Helix Planetary Nebula (NGC 7293)
In the proposed program of study, a pseudo-integral field spectroscopic unit (pseudo-IFU) study of the well-known “Helix” planetary nebula (PN), also known as NGC 7293, will be carried out using data from the 2DF 400-fibred instrument on the 3.9m Anglo-Australian Telescope (AAT). Some preliminary has already been obtained by Prof. Q.Parker but more is needed. This is in order to study its morphology, kinematic properties and ionization structures. Also sought is the pertinent information that would reveal the extent and location of signatures of the so-called “abundance discrepancy factor” (ADF) between abdundances independently derived from the optical recombination lines and collisionally excited lines. This factor can vary from a few up to several hundred and is known for this and many other PNe (eg. Wesson et al. 2017) and seems strongly correlated to central star binarity. This factor will be instrumental in a potential indirect confirmation of the binary nature of the central star of the Helix nebula. No proven binary has been shown to exist for this well studied PN but it seems likely based on current limited evidence. This needs to be buttressed by more data and investigation such as will be provided by this project.
The aim of this study is to generate an “atlas-quality” legacy data set that is based on AAT’s deep AAOmega low-resolution and HERMES high-resolution “stepped” 2dF spectra for this PN. The Helix is an interesting candidate for this one-of-a-kind study because of its larger angular size (>0.5degrees in size) as it is quite evolved and also close to Earth (being one of the closest PNe to the Sun). This would normally pose a challenge for any standard type of IFU study intended to sample across the entire object due to their limited angular extent on the sky. Such studies are easier for distant celestial objects that are farther away and thus have smaller angular sizes. Very few optical spectral studies on the Helix nebula presently exists in the literature and none have undertaken a large scale point-to-point spectroscopic investigation such as we are undertaking. This unique study will provide 1200 spectral pointings across the Helix that both high and low spectral resolution with the powerful AAT 2dF instrument in both HERMES and AAOmega modes. The results and findings of the proposed study will form the basis of a refereed publilcation that would be a valuable addition to the existing literature.
講者：Kris Akira STERN(香港大學)