Photometric and kinematic study of SA9.

We study a galactic area, SA 9, in order to determine the galactic structure and rotation towards longitude 1" = 139?3. We give here spectral types, distances and radial velocities of stars between magnitudes 7.5 and 11.8 in a field of 16 square degrees. Plates used were taken at Observatoire de Haute Provence, with the two Fehrenbach's objective prism astrographs of 15 and 40 cm. We are especially interested in OBA stars, as these types are known to be good spiral arms tracers. A complete spectral classification of the field has therefore been made, to recognize young stars among others. We obtain distances for 93 of them. Apparent magnitudes are given by Bigay's photometric results, and, if not available, by our own measures of plate density at = 4215 A (Martin, 1964). Absolute magnitudes are derived from the spectrophotometric method described by Martin (1964) including calculation of the Oilman's quantities 1/2 (H7 + H6); distances obtained in this way are known with probable error of 15% (sign* is used in Table 2 to spot them) When spectrophotometric results were not available, we derived absolute magnitudes from visual spectral classification joined to Boulon's calibration (1963); probable error is then 25%. Some color excesses are known by Bigay's photoelectric measurements; others have been determined through a general survey of interstellar absorption in the field: we distinguish 5 zones of different extinction (Fig. 1), the characteristics of which are given. Spiral structure obtained is in good agreement with H I results: we can notice a gap between 1000 and 2000 pc. Stars at further distances are present in our optical material, but the peak in the star repartition corresponding to the Perseus arm is not well observed, the field transparency being not high enough to get better results. We measure radial velocities of 126 stars, 84 of them being OBA stars, after Fehrenbach's method. Radial velocity of H r region S202 has been measured in order to compare it with radial velocities of supposed exciting stars. We derive circular velocities 0 for 70 stars; we plot 0 against B (distance to galactic center) and show it seems to be no agreement with Schmidt's curve for remote OBA stars: they lie far above the curve in a systematic way. Key words: OBA stars - distances - radial velocities - S202 - spiral structure - galactic rotation