Medium-resolution Spectrograph Research Articles

R Coronae Borealis Stars: Long-Term Photometric & Spectroscopic Studies

For more than a decade we have been able to acquire and analyse a significant amount of photometric data of the highly variable R Coronae Borealis (RCB) stars. This has made been possible by a photometric service observing programme instigated at the Observatory. These photometric data have been combined with less extensive spectroscopic coverage, particularly of the decline phase of these stars. These have been supplemented by observations obtained at Mount Stromlo and Siding Spring Observatories for a radial velocity study. Significantly more spectroscopic observations are now being acquired with the development of a new medium resolution spectrograph at Mount John University Observatory.In this poster we will present recent photometric and spectroscopic results for a number of the RCB stars in our sample. This observational and analysis work can be used to provide further insight into the nature of these stars, their likely progeny and progenitors and the processes that are involved in the formation and evolution of the obscuring dust clouds which cause the decline phase.

Use of an intensified photodiode array detector for the acquisition of rotationally resolved laser-induced fluorescence spectra of OH in flames

The possibility of recording rotationally resolved fluorescence spectra in atmospheric pressure flames, with an intensified diode array detector (PDA), is described. Measurements have been performed with a medium resolution spectrograph coupled with a 1024 diodes array detector and with an IBM-PC for data acquisition and processing. The signal-to-noise ratio achievable with this detection system has been investigated, and the best experimental conditions were determined. The rotational population as resulting from a computer code data elaboration is also presented. This work confirms the capabilities of PDA detectors for acquiring large amounts of data in experiments involving fluorescence measurements.

Spectroscopic Investigations of Halos of Planetary Nebulae

Different ESO-telescopes with medium resolution spectrographs and CCD-detectors were used to look for emission from extended halos around Planetary Nebulae. In three out of four cases the search was successful. The ratio Rhalo/Rneb ranges from 2 to about 10. Assuming that the halos have been produced by the winds of the Red Giant progenitor stars, we determine Ṁ/VAGB of these progenitors, using the measured Hα- and Hβ-fluxes. These values scatter in a relatively narrow range around 2‥5 · 10−7 (M⊙/y)/(km/s). In some objects emission line fluxes were measured at two ore more radial distances and radial density profiles were derived from them. These are in good agreement with the expected n∼r−2 density law expected for a freely expanding wind.