ner_tags: 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-Wavelength O O O O O O O O O B-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject 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 O O O O B-Wavelength I-Wavelength 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 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 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 O O O O O B-Wavelength 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 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 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 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 B-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject 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 B-Model I-Model O B-Citation I-Citation O O O O O O O B-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O
tokens: part of the diagram to the bottom-right, stable nuclear burning of hydrogen is not possible and this region should be populated with other types of soft X-ray sources. Indeed, Fig. 5 shows that in late-type galaxies (M 83, M 51, M 101 and M 81), there is a distinct group of rare soft and luminous sources located above these line. These sources have temperatures of approximately several tens of eV and seem to clearly stand out in the populations of soft sources in these galaxies. When interpreting the results shown in Fig. 5 , one should bear in mind that it shows absorbed luminosities in the 0.3−2.0 keV band and that absorption and bolometric corrections increase roughly exponentially with decreasing color temperature, and therefore the softest sources are truly luminous. For this reason, we classify sources to the left of the red line in Fig. 5 as classical SSSs. We also include those sources that are located outside the stable nuclear burning boundary but whose error bars cross this boundary. In addition, we added to this list two sources in M 101 that are located outside but close to the stable nuclear burning boundary (the two sources in the upper right panel of Fig. 5 with kT ≳ 100 eV and L X ≳ 10 37 erg s −1 ). The catalog of SSSs is presented in Table C.1 , and their numbers in galaxies from our sample are listed in Table 2 . 6.2. Specific frequency of super-soft X-ray sources across morphological types From Fig. 5 , it is evident that SSSs are considerably more abundant in late-type galaxies than in early-type galaxies. However, for a statistically sound conclusion one needs to take into consideration the completeness limits of the various data sets. To this end we used the sensitivity limit for M 51 corrected for the difference in the absorption column density as described in Sect. 5.2 to select SSSs. In each galaxy, we selected sources to the left of the thick red line and above the dashed blue line in Fig. 5 . This selection is within the 20 counts flux limit (solid black line in Fig. 5 ) in all galaxies, except for M 83 where at the low temperature end the 20 counts limit for this galaxy is higher by a factor of about two. This may result in slight underestimation of the specific frequency of super-soft sources in late-type galaxies. In Centaurus A, we used different criteria for sources located in and outside the dust lanes (cf. dotted line in Fig. 5 ), although this does not change the final result. In order to estimate specific frequencies of SSSs, we group the data separately for early- and late-type galaxies. There are 29 super-soft sources in late-type galaxies (M 83, M 51, M 81, M 101), which, for the total stellar mass of 13.9 × 10 10 M ⊙ yield the specific frequency of In computing statistical errors we used Gehrels approximation ( Gehrels 1986 ). Counting lenticular and elliptical galaxies together (Centaurus A, NGC 3115, NGC 3379, NGC 4278, NGC 4697), we find seven SSSs for the total stellar mass of 28.3 × 10 10 M ⊙ ,