Table A9 'E(B-V)-and-R-ratio-vsn-7' Direct E(B-V) and R-ratio determinations for HR8752 from measurements of (B-V) and contemporary-time-estimate of spectral MK classification. In this section we discuss 1) obtaining E(B-V) and 2) obtaining R-ratio from Johnson (1968, ch. 5, "Interstellar Extinction", in Stars and Stellar Systems, Vol. VII, "Nebulae and Interstellar Matter", Middlehurst, B.M., & Aller, L.H., editors, The University of Chicago Press, Chicago) data using a time-synchronization for comparing MK- and B-V-data and 3) a note on R-ratio for yellow hypergiants (Section 3). 1) E(B-V) and R-ratio determinations from Johnson (1968, ch. 5, "Interstellar Extinction", in Stars and Stellar Systems, Vol. VII, "Nebulae and Interstellar Matter", Middlehurst, B.M., & Aller, L.H., editors, The University of Chicago Press, Chicago) for HR8752 (BS8752) are based on a comparison of observed (B-V) with the (standard value) MK type G0. However, the spectral type changes in time and a comparison should be done with the 'best estimated spectral type' for the given time or period. We interpolate for the colour observation date JD 2438300 in the sequence of MK measurements between JD 2436462-2439080 (cf. our Table in Appendix A5 subsections 3:-6a:) with MK F9-G0Ia (s=4.95+/-0.5) resp. G3 (s=5.15) to get a spectral parameter s=5.9 (G1.8) which we take to be spectral type G2. With Schmidt-Kaler (1982, in Landolt-Boernstein, Neue Serie, Group 6, Volume 2, Astronomy and Astrophysics, External Supplement to Vol. 1, Subvolume b, K. Schaifers and H.H. Voigt, editors, Springer Verlag, Berlin, also in Lang, K.R. 1992, Astrophysical Data, Planets and Stars, section 9.7 Stellar Temperature, Bolometric Correction and Absolute Luminosity, pp. 137-142, Springer Verlag, New York, section 4.1.2.1), and Johnson (1966A&A.....4..193J, Table III) this leads to E(B-V)=0.70+/-~0.02. The two techniques to time-synchronize the different types of observations (cf. also Section 3.2 in the main paper) result in the same number for E(B-V) and enhance the confidence in the found value. 2) To find the R-ratio, the table of Johnson (1968, ch. 5, "Interstellar Extinction", in Stars and Stellar Systems, Vol. VII, "Nebulae and Interstellar Matter", Middlehurst, B.M., & Aller, L.H., editors, The University of Chicago Press, Chicago, Table 20 for BS 8752) has to be corrected for the value of E(B-V) found here. This leads to a revised table: Corrections for BS 8752: E(U-V) E(B-V) E(V-R) E(V-I) E(V-J) E(V-K) E(V-L) E(V-M) E(V-N) E(V-O) ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ E(B-V) E(B-V) E(B-V) E(B-V) E(B-V) E(B-V) E(B-V) E(B-V) E(B-V) E(B-V) =2.07 =1.00 =0.79 =1.40 =2.00 =2.33 =2.60 =---- =3.37 =---- With these values we derive a R-ratio=4.4+/-~0.2, following the construction for Cepheus 'mean', mimicking Johnson's (1968, ch. 5, "Interstellar Extinction", in Stars and Stellar Systems, Vol. VII, "Nebulae and Interstellar Matter", Middlehurst, B.M., & Aller, L.H., editors, The University of Chicago Press, Chicago, Fig. 31). A new figure is shown as Fig.A9.1 in http://www.aai.ee/HR8752, and in the online appendix as Fig.A1. Note 3) below considers the high value of R-ratio and thus also of Av=RxE(B-V). 3) Note on R-ratio for yellow hypergiants: The high value for the R-ratio contrasts with the values of R = 3.0 to 3.1 that are usually attributed to O, B stars (cf. e.g. Fitzpatrick & Massa 2007ApJ...663..320F). There are 2 possible reasons for this: 1)- This high value (if it is true) points un-ambiguously to the non-canonical IS reddening curve in the line-of-sight towards HR 8752 whatever the reason for that (it may well be the parameters of dust close to HR 8752), cf. also Johnson (1968, ch. 5, "Interstellar Extinction", in Stars and Stellar Systems, Vol. VII, "Nebulae and Interstellar Matter", Middlehurst, B.M., & Aller, L.H., editors, The University of Chicago Press, Chicago) who indicates stark variations in line-of-sight variations for different regions in Cepheus. This last issue should indeed be the topic of a separate investigation. 2)- On the other hand studies show that the R-ratio does depend on spectral type, as is shown by Schmidt-Kaler (1961ZA.....53....1S), Lee (1970), Stothers (1972), that find deviations from R-ratio ~3.1 to ~3.6, while Olson (1975PASP...87..349O), Gutierrez-Moreno & Moreno (1975PASP...87..425G), Crawford & Mandwewala (1976PASP...88..917C cf. Fig. 7) and Buser (1978A&A....62..411B) give values that go higher than the R-ratio ~4.2. These authors combine stellar energy fluxes for various spectral types with the filter transmission curves (Olson, 1975PASP...87..349O) and different interstellar absorption laws (Crawford & Mandwewala, 1976PASP...88..917C) to obtain values of the R-ratio of total-to-selective absorption for (B-V) and other colour systems (cf. also below). We mention some authors: Schmidt-Kaler (1961AN....286..113S) finds that R follows an approximate linear function of (B-V)0 and E(B-V). Lee (1970ApJ...162..217L) finds R=3.6+/-0.3 derived from reddened M supergiants. In a paper on recalibration of absolute magnitudes of supergiants, Stothers (1995ApJ...451L..61S) takes the "distance moduli of stellar groups that have been determined from the magnitudes of B-type main sequence stars, using an extinction ratio of Av/E(B-V)=3.0." He proposes and uses R=3.0 for O,B,A stars, R=3.3 for F,G,K stars and R=3.6 for M stars, basically using the earlier references. The variation of the ratio of total-to-selective absorption of a star's intrinsic color and color excess has been examined and put into a numerical relation by Olson (1975PASP...87..349O). Calculations of the influence of several different laws of interstellar absorption for various spectral types combined with filter transmission curves to obtain reddening relations and the ratio of total-to-selective absorption have been published by Crawford & Mandwewala (1976PASP...88..917C) where they show R against E(B-V) for some spectral types: e.g. a G5 Ib star with E(B-V)=0.70 gives R~3.76. [In principle we could add our value adopted from Johnson (1968, ch. 5, "Interstellar Extinction", in Stars and Stellar Systems, Vol. VII, "Nebulae and Interstellar Matter", Middlehurst, B.M., & Aller, L.H., editors, The University of Chicago Press, Chicago): HR 8752, G2 Ia+ and R=4.4, with E(B-V)=0.7 (our determinations).] Buser (1978A&A....62..411B, Table 2) gives for a G2 Ib star: R=3.515 + 0.059*E(B-V) or R=3.556 for HR8752, whereas Gutierrez-Moreno & Moreno (1975PASP...87..425G), for a star of luminosity class I with standard color index system (d), gives R=3.558+0.155*E(B-V) or R=3.667 for HR8752. It seems that both later types and higher luminosities give higher R-ratios, as is demonstrated by of Crawford & Mandwewala (1976PASP...88..917C, Fig.8), but their examples include no hypergiants. (end)