Planetary Nebulae

People involved at OAB: Stanghellini

Planetary Nebulae in the Magellanic Clouds

This project is a major effort started in 1997, aimed to study the morphology and all the nebular and stellar properties of the Magellanic Cloud (MC) PNs. In collaboration with B. Balick (U. of Washington), C. Blades (STScI) and D. Shaw (NOAO) a series of observing programs to probe PN morphology in extra-galactic environments have been successfully executed. We use optical STIS slitless spectroscopy in snapshot mode, obtaining information on multi-wavelength morphology, size, ionization, and central star spectra of about 100 LMC and 30 SMC PNs (about one half the known PNs in those galaxies). Furthermore, we use UV spectroscopy to study the carbon emission and the central star spectra of a subsample of 30 LMC PNs.

Ultra-compact SMC HII regions

Our STIS snapshot survey of SMC PNs was aimed at observing all known ($\sim 60$) PNs previously identified in that galaxy. Given the nature of HST snapshot observations, only 30 targets were actually observed. Of those, two turned out to be misclassified PNs, and are indeed H II regions. An additional H II region was observed within the framework of these observations. A preliminary analysis of these H II regions shows that they are extremely compact (the largest one is less than 3 pc across), extremely reddened (much more than the typical SMC H II region), and well populated star forming regions. Previously, only three very compact H II regions were known in the SMC (Heydari-Malayeri 1999; Testor 2001), all of them less reddened and compact than those found by us. The importance of studying the ultra-compact H II regions in the SMC is multi-fold. First, they offer an ideal laboratory to study star formation in a low-metallicity environment. Second, the small sizes of these regions, compared to the average SMC H II regions (50 to 270 pc) are indicative of a very recent star formation process (Elmegreen 2000). Third, the low reddening toward the SMC, together with the high resolution of HST, allow us to measure the physical parameters of the ionizing stars, to build the appropriate evolutionary diagrams, and to study star formation at very low metallicity.