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Register a new userThe He II Fowler lines and the O III and N III Bowen fluorescence lines in the symbiotic nova RR Tel
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A new measure of reddening (E$_{(B-V)}$$sim$0.00) has been obtained from the comparison between the observed and the theoretical intensity decrement for 20 emission lines of the $ion{He}{ii}$ Fowler (n$to$3) series. This value has been confirmed by the STIS and IUE continuum distribution, and by the value of n$_H$ from the damped profile of the IS H Ly-$alpha$ line. We have obtained very accurate measurements for about thirty Bowen lines of $ion{O}{iii}$ and a precise determination of the efficiency in the O1 and O3 excitation channels (18 % and 0.7 %, respectively). The relative $ion{O}{iii}$ intensities are in good agreement with the predictions by Froese Fischer (1994). A detailed study of the decays from all levels involved in the Bowen mechanism has lead to the detection of two new $ion{O}{iii}$ Bowen lines near $lambda$ 2190. High resolution IUE data have shown a nearly linear decline with time, from 1978 to 1995, in the efficiency of the O1 and O3 processes, with a steeper slope for the O3 channel. A detailed study of the $ion{N}{iii}$ $lambda$ 4640 lines and of their excitation mechanism has shown that, recombination and continuum fluorescence being ruled out, line fluorescence remains the only viable mechanism to pump the 3d $^2D_{5/2}$ and 3d $^2D_{3/2}$ levels of $ion{N}{iii}$. We point out the important role of multiple scattering in the resonance lines of $ion{O}{iii}$ and $ion{N}{iii}$ near $lambda$ 374 and show that the observed $ion{N}{iii}$ line ratios and intensities can be explained in terms of line fluorescence by the three resonance lines of $ion{O}{iii}$ at $lambda$$lambda$ 374.432, 374.162 and 374.073 under optically thick conditions.
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The exceptional resolution of UVES has allowed the detection of weak spectral features and the separation of components in blended lines. The intensities of all of the OIII fluorescence lines produced by the O1, O3 and other channels, including the 5592 Angstrom charge-exchange line, have been measured and their ratios compared with models.
We present electron collision strengths and their thermally averaged values for the forbidden lines of the astronomically abundant doubly-ionized oxygen ion, O^{2+}, in an intermediate coupling scheme using the Breit-Pauli relativistic terms as implemented in an R-matrix atomic scattering code. We use several atomic targets for the R-matrix scattering calculations including one with 72 atomic terms. We also compare with new results obtained using the intermediate coupling frame transformation method. We find spectroscopically significant differences against a recent Breit-Pauli calculation for the excitation of the [O III] lambda 4363 transition but confirm the results of earlier calculations.
From the available STIS data of RR Tel, that have provided a coverage with absolutely calibrated data in a wide wavelength range, we have obtained a new determination of its reddening (E(B-V)=0.00) from the comparison of the observed HeII Paschen lines decrement relative to HeII lambda 4686 (for 24 HeII Paschen lines down to the region of the head of the series near lambda 2060 A) with the theoretical one as given in Storey and Hummer (1995) for case B, T=10,000 K and log Ne=6. This new E(B-V)=0.0 value has been confirmed from a re-analysis of the IUE low resolution data. We recall that the so far generally adopted value in the literature has been E(B-V)=0.10 as obtained by Penston et al. (1983).
The circumnuclear region of M31, consisting of multiphase interstellar medium, provides a close-up view of the interaction of the central supermassive black hole and surrounding materials. Far-infrared (FIR) line structure lines and their flux ratios can be used as diagnostics of physical properties of the neutral gas in this region. Here we present the first FIR spectroscopic mapping of the circumnuclear region of M31 in [C ii] 158 um, [O i] 63 um and [O iii] 88 um lines with the Herschel Space Observatory, covering a ~500 x 500 pc (2 x 2) field. Significant emissions of all three lines are detected along the so-called nuclear spiral across the central kpc of M31. The velocity field under a spatial resolution of ~50 pc of the three lines are in broad consistency and also consistent with previous CO(3-2) line observations in the central region. Combined with existing [C ii] and CO(3-2) observations of five other fields targeting on the disk, we derived the radial distribution of [C ii]/CO(3-2) flux ratio, and found that this ratio is higher in the center than the disk, indicating a low gas density and strong radiation field in the central region. We also found that the [C ii]/FIR ratio in the central region is 5.4 (+-0.8) x 10^-3, which exhibits an increasing trend with the galactocentric radius, suggesting an increasing contribution from old stellar population to dust heating towards the center.
We present preliminary results of a simultaneous X-ray/optical campaign of the prototypical LMXB Sco X-1 at 1-10 Hz time resolution. Lightcurves of the high excitation Bowen/HeII emission lines were obtained through narrow interference filters with ULTRACAM, and these were cross-correlated with X-ray lightcurves. We find evidence for correlated variability, in particular when Sco X-1 enters the Flaring Branch. The Bowen/HeII lightcurves lag the X-ray lightcurves with a light travel time which is consistent with reprocessing in the companion star.
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