196 CARNEGIE INSTITUTION OF WASHINGTON. 



which range from 05 to 08 on H. H. Plaskett's classification. N. G. C. 40 

 and B. D. +30° 3639 are the only cases among the brighter nuclei in which 

 emission bands predominate. 



RESEARCHES ON STARS. 

 TRIGONOMETRIC PARALLAXES AND PROPER MOTIONS. 



In continuation of his work on trigonometric parallaxes, van Maanen has 

 obtained during the year 173 photographs with 401 exposures at the 80-foot 

 focus of the 60-inch reflector, and 147 photographs with 263 exposures at the 

 42-foot (primary) focus of the 100-inch telescope. The plates necessary for 

 the derivation of parallaxes have been secured for 20 fields, thus bringing 

 the total number of completed fields to 180. 



Among the objects of especial interest for which parallaxes have been 

 determined are a Orionis and /3 Andromedse. The measurement of the 

 diameter of a Orionis by the interferometer method makes an accurate value 

 of its parallax of great importance. Including the Mount Wilson result 

 and the spectroscopic value, six determinations are now available for this 

 star, and the weighted mean, +0''017±0''002, is probably one of the most 

 accurate parallaxes known at present. The linear diameter of the star 

 using this value is about 245,000,000 miles. 



The star New Draper Catalogue 4143 of M-type spectrum, magnitude 

 8.8, and a proper motion of 0''027 annually was placed on the observing 

 list because of the possibility that it might prove to be an M-type star of 

 absolute magnitude intermediate between the giants and dwarfs. The 

 parallax, however, shows it to be a giant star of absolute magnitude 4-1.2. 



Three stars of very large proper motion discovered by Wolf, Nos. 1037, 

 1039, and 1040, were observed with the 100-inch reflector. Their parallaxes 

 show them to be dwarf stars of absolute magnitude about 13 on the photo- 

 graphic scale, with linear velocities at right angles to the line of sight of about 

 110 km. a second. 



A very extraordinary result was found in the case of o Ceti, the relative 

 parallax proving to be — 0''081±0''036. The large negative value and high 

 probable error make it very likely that this result is due to the remarkable 

 asymmetry of the star near minimum of light which was discovered by Adams 

 and Joy from spectroscopic observations and referred to in the annual report 

 for 1921. 



Parallaxes have been determined for two of the giant planetary nebulae, as 

 follows : 



Dumbbell Nebula, N. G. C. 6853: TTrd = +0':011±0'r004. 

 Helical nebula, N. G. C. 7293: 7rrei. = +0':058±0':005. 



These values would give for the absolute magnitudes of the central stars 

 +8.8 and +11.2, respectively, and diameters of 700 and 375 times that of the 

 orbit of Neptune. 



The measurement of the proper motions of the comparison stars in the fields 

 of the stars under observation for parallax* has been continued by Mrs. Marsh, 

 under the direction of van Maanen, and a total of 30 fields has been completed. 

 Mrs. Marsh has also measured the proper motions of four planetary nebulae 

 and three faint stars of large proper motion discovered by van Maanen. One 

 of these has an absolute magnitude of +11.3 and appears to be a companion 

 of Pi 5^ 146. 



