PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC Vol. 55 S;m Francisco, California, December 1943 No. 327 SURVEY OF THE YEAR'S WORK AT MOUNT WILSON* W. S. Adams Seven members of the scientific staff of the Observatory have been on leave of absence throughout the year to engage in research upon military problems and two members of the operat- ing staff are in the armed services. In addition numerous others, while remaining at the Observatory, have devoted much time to assisting in the solution of specific optical and instrumental ques- tions brought to their attention. Essentially the entire activities of the instrument and optical shops have been devoted to con- tracts with the Army and the Office of Scientific Research and Development. The astronomical work of the Observatory, but slightly reduced in amount, has been maintained chiefly by the older members of the staff. The essential solar observations, in which continuity of records is especially important, have been carried on without interruption, and the 60-inch and 100-inch telescopes have been used regularly throughout the year. An interesting result of the dimout regulations in the valley area including Pasadena and Los Angeles has been a darkening of the sky to the south and southwest of Mount Wilson which has made pos- sible a doubling of exposure times on very faint objects without increase of fog on the plates. This has been especially valuable in the study of faint variables and other stars in extragalactic nebulae. The year was characterized by exceptionally favorable ob- * For a complete report covering the period July 1, 1942—June 30, 1943, see Carnegie Institution of Washington Year Book, No. 42, 1943. 253 © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 254 PUBLICATIONS OF THE serving conditions, solar observations being made on 327 days and stellar observations on 294 nights. Although the precipita- tion during the winter season was unusually high, amounting to nearly 66 inches, it was almost wholly in the form of rain largely concentrated in three heavy storms. A mild winter appears to favor good astronomical definition. Sunspot activity decreased materially during the year and is now at a very low stage. As the minimum is approached, special interest attaches to the discovery of the first spot of the new cycle. This was found on December 20, 1942, in north latitude 32°. On May 16, 1943 a group appeared in south latitude 41° which was the largest group ever photographed in latitudes higher than 40°. Polarity observations indicated the expected reversal of sign as compared with spots of the previous cycle. In the course of an extensive study of solar prominences, Pettit has found clear evidence of an interchange of gases be- tween interactive prominences. He found also that interactive prominences may become eruptive. In general the angle of ejec- tion of eruptive prominences shows but a small inclination to the solar radius, although exceptions occur. Two-thirds of the 39 trajectories available show an angle of less than 20°. Eruptive prominences move great distances without change of velocity, distances of 200,000 km or more having been observed for 18 prominences, with two exceeding a solar radius. The frequency of eruptive prominences is found to be of the order of 400 per year at sunspot maximum and 25 to 50 per year at sunspot minimum. This investigation has also dealt with motions in prominences of the tornado type and with the structure of quiescent promi- nences. A palisade-like form seems to be characteristic of the quiescent type with as many as 20 or 30 columns or withes, 2000 km wide, and as much as 50,000 km high. Spectroscopic observations of the sun have included studies of the extreirfe ultraviolet spectrum of the disk and spots, photo- graphs of a portion of the green region with a Lummer plate for measurements of the general magnetic field and the solar rota- tion, and an investigation of the presence of additional com- pounds in disk and spot spectra. This last investigation, carried © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System ASTRONOMICAL SOCIETY OF THE PACIFIC 255 on by Babcock and Mrs. Coffeen, has resulted in the identifica- tion of O 2 in the sun where it appears in several faint extensions of the Schumann-Runge band system, and the probable recog- nition of NH in two low states of electronic excitation. The presence of O 2 in the solar atmosphere, even if greatly diluted, must very profoundly reduce the outflow of solar radiation in the region λ 670-λ 2000 A because of its enormous absorptive power. A study still in progress is a comparison by Richardson of the Η and Κ lines at times of violent magnetic storms and of magnetic calm to test the suggestion by Chapman that a cloud containing ionized calcium atoms moving toward the earth dur- ing a magnetic storm might be detected by the presence of a faint absorption component on the violet side of the lines. A satisfac- tory method of determining the intensities of the lines has been devised and the measures are being collected. A search for the asteroid Adonis was made by Nicholson on photographs with the 100-inch telescope covering a range of 14 days in the time of perihelion passage, but no definite evidence of the presence of the asteroid was found. Nicholson has also reobserved the positions of the fainter satellites of Jupiter and has recalculated and improved the orbit of Satellite IX. Cometary observations have included photographs by Baade of periodic comet Wolf I, which was found close to the predicted position, and of Whipple's comet (1942/). The latter showed remarkably rapid changes in the structure of the tail in the course of a few hours. Spectrograms of Whipple's comet by Minkowski enabled him to identify several previously unidentified features in the visual region with bands of Ν Η 2. In the broad field of stellar investigation van Maanen has completed measurements of parallax for 14 faint stars of large proper motion, and has increased his second-epoch material for the determination of proper motions of Cepheid variables to a total of 91 objects. The proper motions of about 800 stars in the distant open cluster h Persei have been measured on two pairs of photographs separated by intervals of 27 and 17 years, respectively. In spite of the small motion of but 0^004 for the cluster, the accuracy of measurement is such as to make it pos- © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 256 PUBLICATIONS OF THE sible to separate to a very large extent the cluster stars from the field stars. An interesting study of the physical characteristics of the companion of small mass in the system of 61 Cygni has been made by Dr. Russell. The use of theories applicable to normal lucid stars for an object of such mass necessarily involves extra- polation and may result in considerable uncertainties. Calcula- tions of the radius of the star based upon the mass given by Strand yield wide possible limits, but the assumption of the rea- sonable intermediate value of three-fourths the radius of the sun indicates a central temperature of 1,600,000° K, a surface tem- perature below self-luminosity, and a radiation which could be supplied by contraction alone for a period of 5 X 109 years at a cost of but 1/400 of its radius. Several photometric investigations have been completed dur- ing the year. In one of these Dr. Stebbins has used a combina- tion of a photoelectric cell with suitable filters to isolate six spectral regions between λ 3500 and λ 10,000. About one hun- dred fifty stars of all types have been measured, most of which are found to radiate much like black bodies. The chief devia- tions are due to strong hydrogen absorption in the ultraviolet region in A-type stars, and to the strong red and infrared bands in M-type stars. The color temperatures range from about 24,000° Κ for stars of types O and early Β to 2,000° Κ for the reddest M-type stars. The value for type A is 11,000° K. The completion of the investigations of stars in the north polar region by Dr. Seares and Miss Joyner has confirmed the provisional results for the spectrum-color relationship and the color temperatures of the stars. The general uniformity of the obscuring cloud over the polar cap 20° in diameter seems to be well established, the solar system lying close to if not actually within the cloud. The color excess increases at a nearly linear rate to a value of 0.27 magnitude at about 450 parsecs where the cloud apparently ends. The constancy of the zero point of the color indices of the Polar Catalogue is well shown by an intercomparison of the results for small individual fields within the polar cap. An important astrophysical result of this study is the evi- © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System ASTRONOMICAL SOCIETY OF THE PACIFIC 257 dence for the small dispersion in color index for stars of the same spectral type, the upper limit being 0.035 magnitude for types KO and earlier, and about 0.1 magnitude for types K5-M. The accidental error in the various systems of spectral classification may also be derived from the results of the investigation. Visual observations of the light-curve of Nova Puppis (1942) were made by Pettit over a period of about six months with a modified form of wedge photometer.