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Description
Variable red- and blue-shifted absorption features observed in the CaII K line towards the A-type shell star {phi} Leo have been suggested by us in a previous work to be likely due to solid, comet-like bodies in the circumstellar (CS) environment. Our aim is to expand our observational study of this object to other characteristic spectral lines of A-type photospheres as well as to lines arising in their CS shells. We have obtained more than 500 high-resolution optical spectra collected at different telescopes during 37 nights in several observing runs from December 2015 to January 2019. Time series consecutive spectra were taken, covering intervals of up to ~9 hours in some nights. We have analysed some photospheric lines, in particular CaI 4226{AA} and MgII 4481{AA}, as well as the circumstellar shell lines CaII H&K, CaII IR triplet, FeII 4924, 5018 and 5169{AA}, TiII 3685, 3759 and 3761{AA}, and the Balmer lines H{alpha} and H{beta}. Our observational study reveals that {phi} Leo is a variable delta Scuti star whose spectra show remarkable dumps and bumps superimposed on the photospheric line profiles, which vary their strength and sharpness, propagate from blue- to more red-shifted radial velocities and persisting during a few hours. Similarly t o other delta Scuti stars, these features are likely produced by non-radial pulsations. At the same time, all shell lines present an emission at ~3km/s centered at the core of the CS features, and two variable absorption minima at both sides of the emission; those absorption minima occur at practically the same velocity for each line, i.e., no apparent dynamical evolution is observed. The variations observed in the CaII H&K, FeII and TiII lines occur at any time scale from minutes to days and observing run, but without any clear correlation or recognizable temporal pattern among the different lines. In the case of H{alpha} the CS contribution is also variable in just one of the observing runs. Summarizing, we suggest that {phi} Leo is a rapidly rotating delta Scuti star surrounded by a variable, (nearly) edge-on CS disk possibly re-supplied by the delta Scuti pulsations. The behaviour of the CS shell lines is reminiscent of the one observed in rapidly rotating Be shell stars with an edge-on CS disk, and clearly points out that the variations observed in the CS features of {phi} Leo are highly unlikely to be produced by exocomets. In addition, the observational results presented in this work, together with some recent results concerning the shell star HR 10, suggest the need of a critical revision of the CaII K features which have been attributed to exocomets in other shell stars.
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