view Abstract Citations (13) References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effective Wave Lengths of Standard Magnitudes; Color Temperature and Spectral Type. Seares, Frederick H. ; Joyner, Mary C. Abstract The investigation is concerned primarily with (a) the derivation of effective wave lengths, Xp~, ?tPv, for the color system of the international Pg and Pv magnitudes; (b) calculation, for a series of tempera- tures, of black-body color indices C corresponding to XPg and Xiv; (c) derivation of color temperatures (of black-body radiators) corresponding to observed color indices for the standard spectral types B5, AO, etc. For control and comparison, similar calculations were also made for the Pe and Ci and C2 systems of Stebbins. The international system of color.-This is determined by sensitivity factors of the form s = f(X) = Tr2p, where r = atmospheric transmission at the altitude of the pole, r = coefficient of reflection of silver (r2, since two reflections are involved), and p = sensitivity factor of the plate-the Seed 27 for Pg mag- nitudes, the Instantaneous Iso exposed behind a certain filter for Pv. The effective wave length-This is the ordinary weighted mean Xe = ~Xsy/~sy, where y (Table 1) for a given temperature, also a function of A, is proportional to the intensity of radiation of wave length A. There is no direct determination of p for either of the standard plates. Mees's values for the Eastman 40 have been used, instead, for Pg m, and for Pv m a series obtained from low-dispersion spectrograms of northern skylight. Results for X~ and for the corresponding theoretical color indices are given in Ta- ble 3. Alternative values for aluminized mirrors are in Table 4. Effect of atmospheric extinction.-Calculated values of the extinction at the pole and the zenith for stars of different temperatures are given in Tables 5 and 6. The dependence on temperature is important, especially for Pg magnitudes, and should not be neglected, as is done in current photometric practice. Ratio of total Pg absorption to color excess.-Values computed from the effective wave lengths of Table 3 for an absorption varying as X-' are listed in Table 7. This table also gives, for the same absorption law, the influence of stellar temperature on color excess. Reduced color-spectrum relation-The values of Cs (Table 7 of the preceding Contribution) may be freed from the differential effects of stellar temperature on color excess and on atmospheric extinction by means of the corrections in Tables 9 and 9a. Color temperatures-The reduced values of Cs and the black-body color indices of Table 3 for different temperatures lead to the color temperatures in Tables 10 and 11. The zero point is fixed by adopting 11,000° K for type A5. The results from the photoelectric colors Ci and C2 agree well but are systemati- cally lower than those from the international C. For gKO the values are 37500 ± 640 (ME) and 41500 ± 800, respectively. The difference of 400° probably arises from departures from black-body radiation in the stars (sec. xi). Miscellaneous.-In section vi it is shown that for all practical problems the absorption A = pX~ calculated by the direct substitution of the effective wave length X~ is the same as that found by integrat- ing the losses over the entire range in X (Table 8). The same is also true for Rayleigh scattering in amounts comparable with the atmospheric extinction (up to 0.6 mag. at the pole). The use of sensitivity factors for the Eastman 40 plate instead of those for the Seed 27 and several other approximations are discussed in detail in section ix. None oi the errors thus introduced can ac- count for the systematic difference in the color temperatures found for the international and the photo- electric systems. The influence of observational errors in C, Ci, and C2 on the adopted temperatures is examined in section x. The relationship of Brill's isophotal wave lengths to the effective wave lengths of Table 3 is discussed in section xiii (cf. Table 12) Publication: The Astrophysical Journal Pub Date: November 1943 DOI: 10.1086/144573 Bibcode: 1943ApJ....98..302S full text sources ADS | Related Materials (1) Reprint: 1943CMWCI.685....1S