 All five classes include sources with a range of inclinations between almost 0 • up to 60-70 •. Except for VY UMa (i=-1 • ), there are no objects with small inclination angles among the "eyes" (all have i ≥ 28 • ), whereas the "fermata", "rings" and "irregular" all have a more uniform distribution over inclination angles. However, we stress that at this point the sample is too small to derive any further conclusions.
For about one third of the "non-detection" class, the proper motions are not known and thus their space velocities are, at best, lower limits based on radial velocities. This is in part a distance bias. The objects with non-detections are on average further away and consequently their proper motions have been too small to be measured. This means also that the predicted stand-off distances are upper limits.

Binary interaction
There is little evidence for binary interaction in our sample. Even though for several stars in our sample, there is solid evidence for close companions (see Tables 1 to 3), none show suspicious features in their bow shock interfaces. However, many of these appear in the category "irregular", which could indicate that such wind-wind-ISM interaction is only visible on small spatial scales. It is difficult to arrive at any firm conclusion as the number of binaries in the survey is low. Excluding the optical "visual" binaries, as these are not yet confirmed, out of the 25 objects in the "fermata" class only one is a known binary (Mira) which indeed reveals a peculiar shape of the interaction zone. Three others, W Aql, EP Aqr and θ Aps are solid candidates for binarity. None of the "rings" are binaries. Noteworthy, 3 out of 6 of the "irregulars" are confirmed binaries, and 2 of the 6 "eyes" are potentially binaries. Finally, also 6 out of 30 non-detections are binary systems. Including visual binaries adds 3 binaries to each of the "fermata", "eyes", and "non-detection" classes, and 4 binaries to the "rings". In this case, 5 out of 7 "eyes" show evidence for binarity, whether this means there is a connection between binarity and the "eyes" morphology can not be confirmed nor excluded at this point.

Oxygen-rich versus carbon-rich chemistry
One key property of the AGB stars and red supergiants in our sample is their circumstellar envelope chemistry. This can be either carbon-rich (the dust is predominantly made up of amorphous carbon, graphite and silicon carbide) or oxygen-rich (the dust is composed of silicates and oxides). Although we do not find a strong dependence on the presence versus absence of bow shocks and rings with respect to chemistry, there does appear to be a distinction between the shape of the extended emission found around carbon and oxygen-rich objects. The "fermata" and "irregular" classes include a high fraction, 22 out of 31, of O-rich stars. The "eyes" and "rings", on the other hand, include only few, 3 out of 22, O-rich stars. It seems that at least the "ring" structure is typical of C-rich chemistry, as already pointed out by Olofsson et al. (2000). A further argument favor-ing such a link between "ring" structure and C-richness is that all "fermata" stars also displaying a "rings" structure are Crich stars (they are noted with an asterisk in Table 1, and are also listed in Table 3). Could the circumstellar envelope structure be related to chemistry through differences in mass loss rates? It has been shown (Knapp 1985) that oxygen-rich stars have a wider range of mass-loss rates than C-rich stars for which theṀ is globally more homogeneous. On average, mass loss rates of C stars are higher than those of MS and S stars (Guandalini 2010). Apart from the fact that the mass-loss rate standard deviation of O-rich stars is indeed found to be somewhat larger than that of C-rich stars, no clear dichotomy emerges between the mass loss rates of O-rich stars and C-rich stars in the present sample.
Furthermore, the higher emissivity (Draine & Lee 1984;Li & Draine 2001) and lower gas-to-dust ratio of 160 for oxygenrich dust compared to the higher ratio of 400 for carbon-rich dust (see e.g. Knapp 1985;Heras & Hony 2005) will, for O-rich dust, give rise to brighter infrared emission for a given total dust and gas mass. One could then argue that the O-rich stars mass loss is more easily detected even with a patchy structure. This could perhaps explain why O-rich stars are detected preferentially among both "irregulars" and "fermata" classes.
An alternative explanation is that the "Ring" (and possible the "Eyes") morphology, are explained through (i) the interaction between a fast wind sweeping out matter from a previous slower wind, or (ii) a phase of drastically enhanced mass loss, e.g. caused by a thermal pulse. If this explanation holds, and if one assumes that most thermal pulses events are followed by a third dredge-up (TDUP) episode, then the discriminant character would not be O-rich or C-rich, but instead pre-TDUP or post-TDUP (i.e., thermally-pulsing (TP) AGB) stars). All intrinsic Stype stars, C-type stars and technetium-rich M stars in Tables 1  and 3 are TP-AGB stars. In fact, all "Ring" stars are TP-AGB stars.

Stellar and interstellar magnetic fields
Some wind-ISM models include the effects of an interstellar magnetic field on the shaping of the bow shock region. Heiligman (1980) predicted that the ISM magnetic pressure could deform the outer shells of very large spherical halos of PNe into "lemon" shapes, with the axis of symmetry inclined to the ordered ISM magnetic field direction. Soker & Dgani (1997) and Dgani (1998) elaborated on this scenario predicting different bow shock shapes depending on the relative magnitudes of the star's space velocity, v, the wind velocity, v w, and the Alvén speed, v A. The double arc objects (Class II) such as VY UMa and AQ Sgr could perhaps provide evidence for this scenario, although both are at relatively high latitudes and their symmetry axes are not aligned with the Galactic plane (assuming that at these locations the magnetic field is also parallel to the Galactic plane). It is also possible that the star has its own magnetic field and thus may exhibit axis-symmetric mass loss. Preliminary simulations (private communication A.-J. Van Marle) indicate that double arcs as well as jets (tentatively identified for VY UMa and W Hya) could be formed by a (rotating) star with a magnetic field.

Detached spherical shells
The observed detached shell objects (Class III) show quite a range of expansion ages calculated out of their measured or assumed expansion velocities, distances and angular sizes. Ranging from the youngest shells like U Cam or R Scl with ages of the order of 1000 years and much older ones like AQ And, Y CVn or UX Dra with ages of a few 10 000 years we see also a significant trend in the detectability in fossil mm-CO. Whereas all objects with shell ages below some 1000 years are prominent in CO, no detached shell older than 10 000 years was successfully detected yet. This could be understood in terms of photodissociation by the interstellar radiation field in the older extended shells with sizes of 0.2 pc or more (Kerschbaum et al. 2010). Arimatsu et al. (2011) find that the detached shell of U Ant detected with PACS is not the outermost one found with AKARI. Thus, the shell detected with PACS is either a density enhancement due to a two-wind interaction or it could represent the termination shock, similar to the scenario proposed for Y CVn by Libert et al. (2007).
Another interesting finding with respect to Class III objects are the objects that have both a detached shell and a bow shock interaction region, with R Scl being the showcase object. Seeing the bow shock far out off the detached shell more or less excludes one of the explanations of detached shells, namely their interpretation as being the wind-ISM interface (Libert et al. 2007). 7.5. Comparison between predicted and observed R 0 :

Implications for the ISM density
For a number of objects in our sample, previous studies have reported on the detection of wind-ISM bow shocks with IRAS, Spitzer or AKARI. The measured deprojected angular stand-off distance obtained with PACS agree very well with earlier results ( Table 7). The predicted values for R 0 (as function of √ n H ) give ISM densities that are somewhat higher than those computed from Eq. 5. For α Ori, Ueta et al. (2008) predict n H = 1.5 -1.9 cm −3 which is indeed in line with n H = 1.9 cm −3 derived from Eq. 5, but higher than that inferred from the stand-off distance, n H = 4.6 cm −3 (Table 7). Ladjal et al. (2010) derive n H ≥ 2 cm −3 for CW Leo, which is a factor of 2 higher than derived from both our predicted stand-off distance as well as from Eq. 5 (n H = 0.5 -1.0 cm −