tokens: on the velocity–luminosity relation for RSGs derived by Mauron Josselin ( 2011 ), we obtain a wind velocity of ∼35 km s −1 during the RSG state of ρ Cas. Considering that the enhanced mass-loss within the RSG phase took place about 10 000 yr ago, the material would have travelled over a length of roughly 0.36 pc, which corresponds to an angular distance of ∼24 arcsec at the distance of 3.1 kpc for ρ Cas (Lobel et al. 2003 ). This angular distance is too small to be seen on, e.g. WISE images, on which ρ Cas is saturated. This distance is also much smaller than the size of a regular wind-blown bubble resulting from the previous blue supergiant phase, so that we can exclude that the material is located within the astrosphere or shock region with the interstellar medium. On the other hand, this distance is too large to be seen on the HST images presented by Schuster et al. ( 2006 ), and too large to guarantee that the material is dense and hot enough to produce measurable amounts of CO band emission. Therefore, we believe that the post-RSG wind, which is faster but much less massive, interacts with the material released during the RSG phase. This interaction can lead to a compression and heating of the old material (with the appropriate carbon isotope ratio) and hence give rise to the observed, static CO band emission. The temperature of the CO gas is much higher than the dust sublimation temperature. In the region of CO band emission, the physical parameters within the environment might hence prevent the efficient formation of dust, which could be another reason for the lack of a detectable dusty nebula around ρ Cas. For its spectral type, and considering that ρ Cas is presumably a very slow rotator, it displays extremely broad absorption lines. These were suggested to be broadened by macroturbulence. This type of line broadening is typically found in early-type (OB) supergiants in which pulsations play a significant role together with stellar rotation (see e.g. Ryans et al. 2002 ; Aerts et al. 2009 ; Simón-Díaz et al. 2010 ; Kraus et al. 2015 ), and is one of the criteria to discriminate YHGs from YSGs (de Jager 1998 ). While ρ Cas is known to pulsate, not much is known about its real rotation velocity, although Lobel et al. ( 1998 ) derived a value of v sin i ≃ 25 km s −1 from line-profile fitting. To investigate the possible contribution of rotation to the line profile broadening of ρ Cas, we analysed photospheric lines using the method of Fourier transformation. This method only works properly for symmetric profiles. However, symmetric line profile shapes are rather rare in our data of ρ Cas and basically only seen in two nights. Also, given the spectral resolution of our data, the Fourier transformation can recover only rotation velocities projected to the line of sight higher than v sin i ∼ 15 km s −1 with high confidence. The results from our analysis are shown in Fig. 8 for different elements within the same night (top panel) and for the
ner_tags: O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O B-Telescope O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Telescope O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O B-Citation I-Citation I-Citation O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O