DEPARTMENT OF MERIDIAN ASTROMETRY.* 



Benjamin Boss, Director. 



As in previous years, the work of the Department of Meridian 

 Astrometry falls principally under three headings: investigation of 

 stellar motions, observations, and reduction of observations. 



INVESTIGATIONS OF STELLAR MOTIONS. 



The investigation of the dependence of solar motion upon the type 

 and the mean magnitude of the stars employed has been finished, as 

 far as present data would permit. The published results indicate the 

 following conclusions : 



1. There is little if any shift in galactic longitude in the position of 

 the apex of solar motion dependent upon the mean magnitude of the 

 stars employed in its determination, though a slight and possibly 

 fictitious shift in galactic latitude is noted. 



2. There seems to be a considerable dependence of the position of the 

 apex of solar motion upon spectral type, probably due to a relative 

 shift between early and late type stars. It manifests itself in a separa- 

 tion in galactic longitude of about 12° between the positions of the solar 

 apex as derived from early and late type stars, the galactic latitude 

 remaining constant at about +22°. The evidence on this point is 

 satisfactorily corroborated by a similar treatment of radial velocities. 

 It also manifests itself in a difference of about 6 kilometers between the 

 values of solar velocity as determined from early and late type stars. 



3. There is a systematic difference between the position of the apex 

 of solar motion as determined from proper-motions and that determined 

 from radial velocities, apparently of the same order as the difference 

 due to types. 



4. The close agreement of the solar apex as deduced from B-type stars 

 from both proper-motions and radial velocities indicates one of two ex- 

 tremes. Either the small real velocities of these stars fit them especially 

 for a solar-motion determination, or there exists among them a one 

 drift which entirely unfits them for such a determination. Until the 

 real cause of the agreement can be established it might be advisable 

 to exclude the B-type stars from the determinations of solar motion. 



5. If there is any real effect on solar motion due to the distribution 

 of the stars according to galactic longitude or latitude, the existing 

 material is not capable of revealing it. 



6. In the future, discussions of solar motion should take into account 

 the effect of spectral type, as manifestly a change in ratio between 

 early and late type stars will cause a shift in the position of the solar 

 apex. It might be well temporarily to adopt as the position of the 

 solar apex a mean value between early and late type solutions : A = 272°, 



♦Address Dudley Observatory, Albany, N. Y. (For previous reports see Year Books Nos. 2-12.) 

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