Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983a%26as...51...17p&link_type=abstract
Astronomy and Astrophysics Supplement Series, vol. 51, Jan. 1983, p. 17-25. In German.
Astronomy and Astrophysics
Astrophysics
5
Astronomical Photography, Brightness Distribution, Galactic Nuclei, Milky Way Galaxy, Ultraviolet Photometry, Angular Resolution, Atmospheric Effects, Data Reduction, Galactic Structure, Photographic Plates
Scientific paper
6 photographic plates, taken at La Silla, Chile, with the spherical mirror super-wide-angle camera of the Astronomisches Institut der Ruhr Universität Bochum (see paper I: Schmidt-Kaler, Th. et al., 1982) were measured to study the surface brightness distribution in the area around the centre of the Milky Way, between galactic longitudes 297° and 27°, and latitudes - 30° to + 30°, with an angular resolution of 0.°3 × 0.°3 (Fig. 5).
In section 2 the plate material and details of the reductions are presented, so far as not already given in paper I. During the photometric scanning of the plates all stars brighter than a limiting magnitude mlim were marked by hand, and the corresponding data points were replaced by an average from neighbouring points (section 3). Defined at the level of 50% elimination, mlim ≌ 8.m0 (in U). Figure 4 shows the effect of various methods of eliminating bright stars. The errors of the surface photometry are discussed in section 4. The internal mean error of the intensity of one data point, as determined from the scatter from the 6 plates, is ± 9.4%. This error is split into an additive component ± 8 S10U (S10 = intensity of a star of 10m), mostly due to the contributions of airglow and scattered light, and a multiplicative component of ± 7.5%, mostly due to the uncertainty of the photographic characteristic curve. Possible systematic errors are estimated and upper limits for these are given in table II.
Section 5 presents the results of the photometry. For the sake of clear representation in the isophote map (Fig 5) data with intermediate intensities 110 < Igal ≦ 250 S10U were smoothed over 0.°9 × 0.°9, data with Igal ≦ 110 S10U were smoothed over 1.°2 × 1.°2. The mean error of the isophotes is about ± 6%. We then compare our photometry with existing ultraviolet surface photometries. Apart from the area l = 320° to 330°, b = -25° to -20° where our intensities are probably vitiated by some remaining airglow influence, there is generally very good agreement with the results of Seidensticker, Schinidt-Kaler and Schlosser (= paper II), their values being smaller by a statistically insignificant additive difference of -14(± 15) S10U. The comparison (Fig 6) with the photoelectric surface photometry of Pfleiderer and Mayer (1971) shows a negligible additive difference of -8 (± 12) S10U, but a large scale difference of 24(± 9)%, the Bochum values being larger. The comparison with the measurements of Leinert and Richter (1981), obtained by the satellite Helios, shows very good agreement in the run of the intensities (Fig. 7). Computation of a point by point correlation reveals their values being smaller by an additive difference of -5 (± 2) S10U and a scale difference of 17(± 2)%. As obvious from figure 7 the main difference in the two photometry results from the finer structures in our data, due to different resolution and different completeness in eliminating background stars. Thus we constructed a lower envelope to our data. This reveals an additive difference of 0 (± 0.3) S10U and a scale difference of 2.4 (± 9)% in the same sense as above.
In the last paragraph we discuss the structure of the Milky Way central region in U, in particular those spiral filaments which appear inclined to the galactic equator (shingles, corrugations). The three shingles discovered by Schmidt-Kaler and Schlosser (1973) in the next-inner spiral arm-I and an additional feature appear if the data-field of the UV photometry is spatially differentiated (Fig. 8).
Proell H.-J.
Schlosser Wolfgang
Schmidt-Kaler Theodor
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