Anomalous Spectral Lines in Space and Laboratory Plasmas - Studies with HST and CRYRING

University dissertation from Lund Observatory

Abstract: Eta Carinae is one of the most massive and luminous stars in the Galaxy. A huge bipolar nebula and an equatorial disk give the object a characteristic shape. Close to the star there are gas clouds, which emit intriguing emission line spectra. One such region, the strontium filament, is studied in more detail in this thesis, and the identities of 600 emission lines are reported. Some of these require extra treatment, viz. allowed and forbidden lines of Ti II and Sr II. Many thin astrophysical plasmas emit parity-forbidden lines, which can be used to diagnose the plasma. The upper levels of these lines are metastable states, which have radiative lifetimes of the order of 1 second compared to 1 nanosecond for ordinary states. We have performed measurements of metastable lifetimes in complex ions applying a laser probing technique on a stored ion beam at the storage ring CRYRING (MSL, Stockholm). This thesis reports on 4 lifetimes in Fe II and 2 in Ti II, the first measured in such complex systems. The lifetimes are in the range 0.23 to 28 s. Experimental absolute transition probabilities for forbidden lines in [Fe II] are derived by combining the experimental metastable lifetimes with astrophysical branching fractions (BF). The BF’s are derived from spectra of the Weigelt blobs of Eta Carinae, which contain strong forbidden [Fe II] lines. In some stars the intensity of emission lines from specific high-excitation levels is greatly enhanced. They are explained as fluoresence lines from energy levels, which have an enhanced population due to selective photoexcitation. This is caused by an accidental coincidence in wavelength between a strong emission line and the pumped transition. We report on fluorescence lines and pumped levels in Fe II observed in the symbiotic star RR Telescopii.

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