Author name code: wilson-olin ADS astronomy entries on 2022-09-14 author:"Wilson, Olin C." ------------------------------------------------------------------------ Title: VizieR Online Data Catalog: Ca II H and K Measurements Made at MWO (Duncan+ 1991) Authors: Duncan, D. K.; Vaughan, A. H.; Wilson, O. C.; Preston, G. W.; Frazer, J.; Lanning, H. H.; Misch, A.; Mueller, J.; Soyumer, D.; Woodard, L.; Baliunas, S. L.; Noyes, R. W.; Hartmann, L. W.; Porter, A.; Zwaan, K.; Middelkoop, F.; Rutter, R.; Mihalas, D. Bibcode: 2005yCat.3159....0D Altcode: Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during the years 1966-1983. These results are derived from 65,263 individual observations of 1296 stars. For each star, for each observing season, the maximum, minimum, mean, and variation of the instrumental H and K index "S" are given, as well as a measurement of the accuracy of observation. A total of 3110 seasonal summaries are reported.

These observations were obtained with two instruments, HKP-1 and HKP-2. The HKP-2 instrument is a four-channel chopping spectrometer which records counts in 1.09{AA} FWHM triangular bandpasses centered in the H and K lines as well as in two 20{AA} reference bandpasses centered on 3901.067 and 4001.067{AA}. The stellar activity is expressed by the index S defined as

S = {alpha} (Nh+Nk)/(Nr+Nv)

where Nh and Nk are the counts (corrected from background) in the H and K lines, Nr and Nv those in the reference continuum bandpasses, and {alpha} is a constant of proportionality used to correct for night-to-night instrumental variations. Higher values of S generally correspond to higher levels of chromospehric activities.

Factors which effect the ability to detect stellar activity variations and accurately measure their amplitudes such as the accuracy of the H and K measurements and scattered light contamination are discussed. Relations are given which facilitate intercomparison of "S" values with residual intensities from ordinary spectrophotometry, and for converting measurements to absolute fluxes.

(1 data file). Title: Chromospheric Variations in Main-Sequence Stars. II. Authors: Baliunas, S. L.; Donahue, R. A.; Soon, W. H.; Horne, J. H.; Frazer, J.; Woodard-Eklund, L.; Bradford, M.; Rao, L. M.; Wilson, O. C.; Zhang, Q.; Bennett, W.; Briggs, J.; Carroll, S. M.; Duncan, D. K.; Figueroa, D.; Lanning, H. H.; Misch, T.; Mueller, J.; Noyes, R. W.; Poppe, D.; Porter, A. C.; Robinson, C. R.; Russell, J.; Shelton, J. C.; Soyumer, T.; Vaughan, A. H.; Whitney, J. H. Bibcode: 1995ApJ...438..269B Altcode: The fluxes in passbands 0.1 nm wide and centered on the Ca II H and K emission cores have been monitored in 111 stars of spectral type F2-M2 on or near the main sequence in a continuation of an observing program started by O. C. Wilson. Most of the measurements began in 1966, with observations scheduled monthly until 1980, when observations were scheduled sevral times per week. The records, with a long-term precision of about 1.5%, display fluctuations that can be identified with variations on timescales similar to the 11 yr cycle of solar activity as well as axial rotation, and the growth and decay of emitting regions. We present the records of chromospheric emission and general conclusions about variations in surface magnetic activity on timescales greater than 1 yr but less than a few decades. The results for stars of spectral type G0-K5 V indicate a pattern of change in rotation and chromospheric activity on an evolutionary timescale, in which (1) young stars exhibit high average levels of activity, rapid rotation rates, no Maunder minimum phase and rarely display a smooth, cyclic variation; (2) stars of intermediate age (approximately 1-2 Gyr for 1 solar mass) have moderate levels of activity and rotation rates, and occasional smooth cycles; and (3) stars as old as the Sun and older have slower rotation rates, lower activity levels and smooth cycles with occasional Maunder minimum-phases. Title: CA II H and K Measurements Made at Mount Wilson Observatory, 1966--1983 Authors: Duncan, Douglas K.; Vaughan, Arthur H.; Wilson, Olin C.; Preston, George W.; Frazer, James; Lanning, Howard; Misch, Anthony; Mueller, Jean; Soyumer, David; Woodard, L.; Baliunas, Sallie L.; Noyes, Robert W.; Hartmann, Lee W.; Porter, Alain; Zwaan, Cornelis; Middelkoop, Frans; Rutten, Rene G. M.; Mihalas, Dimitri Bibcode: 1991ApJS...76..383D Altcode: Summaries are presented of the photoelectric measurements of stellar Ca II H and K line intensity made at Mount Wilson Observatory during the years 1966-1983. These results are derived from 65,263 individual observations of 1296 stars. For each star, for each observing season, the maximum, minimum, mean, and variation of the instrumental H and K index 'S' are given, as well as a measurement of the accuracy of observation. A total of 3110 seasonal summaries are reported. Factors which affect the ability to detect stellar activity variations and accurately measure their amplitudes, such as the accuracy of the H and K measurements and scattered light contamination, are discussed. Relations are given which facilitate intercomparison of 'S' values with residual intensities derived from ordinary spectrophotometry, and for converting measurements to absolute fluxes. Title: Ca II H and K Flux Monitoring in Cool Stars: Rotation and Activity Cycles Authors: Robinson, C. R.; Baliunas, S. L.; Bennett, W.; Briggs, J.; Frazer, J.; Noyes, R. W.; Shelton, C.; Woodard, L.; Vaughan, A. H.; Wilson, O. C. Bibcode: 1989BAAS...21.1115R Altcode: No abstract at ADS Title: The Mount Wilson Observatory HK Project: The Continuing Analysis of Rotation and Stellar Magnetic Cycles Authors: Baliunas, S. L.; Bennett, W.; Briggs, J.; Frazer, J.; Noyes, R. W.; Robinson, C. R.; Shelton, C.; Woodard, L.; Vaughan, A. H.; Wilson, O. C. Bibcode: 1988BAAS...20Q.994B Altcode: No abstract at ADS Title: Stellar Activity Cycles and Rotation in Cool Stars Observed from Mt. Wilson Observatory Authors: Baliunas, S. L.; Briggs, J.; Frazer, J.; Noyes, R. W.; Robinson, C. R.; Carroll, S.; Donahue, R. A.; Shelton, C.; Woodard, L.; Vaughan, A. H.; Wilson, O. C. Bibcode: 1988BAAS...20Q.697B Altcode: 1988BAAS...20Z.697B No abstract at ADS Title: Recognition and classification of strong-CN giants. Authors: Keenan, Philip C.; Yorka, Sandra B.; Wilson, Olin C. Bibcode: 1987PASP...99..629K Altcode: Fifty of the stars designated as super-metal-rich by Spinrad and Taylor (1969) are classified here on the Revised MK System. Positive CN indices are assigned in recognition of the characteristic excesses of carbon and nitrogen in their atmospheres, as compared to normal Population I stars. For only a few of the stars, an abnormal strength of the iron lines or of Ca 4226 A is so noticeable that they need to be distinguished by positive indices for these metals. Title: Activity Cycles of Lower Main-Sequence Stars: Eighteen Years of Research Authors: Baliunas, S. L.; Donahue, R. A.; Horne, J. H.; Noyes, R. W.; Porter, A.; Gilliland, R.; Duncan, D. K.; Frazer, J.; Lanning, H.; Misch, A.; Mueller, J.; Soyumer, D.; Vaughan, A. H.; Wilson, O. C.; Woodard, L. A. Bibcode: 1984BAAS...16R.899B Altcode: No abstract at ADS Title: Photoelectric measures of chromospheric H and K and He in giant stars. Authors: Wilson, O. C. Bibcode: 1982ApJ...257..179W Altcode: The coude scanner of the 100-inch telescope was used to measure the fluxes at the centers of H and K of Ca II and at the position of H-epsilon, and its antiposition, in about 200 late-type giant stars. For the large majority of class III giants, it was found that the total chromospheric radiation of H and K and of H-epsilon is constant in amount for G8 to early M-type stars with respect to the energy in the V band, and that the two Ca II lines together emit about three times as much energy as does H-epsilon. In the Hyades main sequence the efficiency of the transfer of energy from the total outflow into the chromosphere increases from the bluer to the redder stars, whereas the converse is true in the normal giants. Evidence is given that main-sequence stars with H and K emission also have emission in H-epsilon that is considerably weaker, with respect to H and K, than in the giants. Title: Activity Cycles in Other Stars Authors: Wilson, O.; Vaughan, A.; Kraft, R.; Preston, G. Bibcode: 1981S&T....62..312W Altcode: No abstract at ADS Title: The activity cycles of stars. Authors: Wilson, O. C.; Vaughan, A. H.; Mihalas, D. Bibcode: 1981SciAm.244b..82W Altcode: 1981SciAm.244...82W No abstract at ADS Title: The activity cycles of stars Authors: Wilson, O. C.; Vaughan, A. H.; Mihalas, D. Bibcode: 1981SciAm.244b.104W Altcode: 1981SciAm.244..104W The activity cycle of the sun is reviewed with attention to the contributions of Galileo, Schwabe, Wolf, Maunder, Carrington, Hale, Babcock and Parker. The use of the H-K photometer in the observation of the chromospheric variability of 91 sun-like stars at the Mount Wilson Observatory is discussed. It is estimated that more than half of the main-sequence stars less massive than 1.5 solar masses may show cyclic behavior. The chromospheric variations for 12 sunlike stars are given. Title: Stellar Spectroscopy - Stellar Chromospheres - Magnetic Ap-Star - Dwarf Novae - Variable Stars Authors: Wilson, O.; Vaughan, A.; Preston, G.; Wolff, S. C.; Borne, K.; Wade, R.; Greenstein, J.; Schneider, D. P.; Mochnacki, S.; Oke, J. B. Bibcode: 1979haob.rept..724W Altcode: No abstract at ADS Title: Chromospheric variations in main-sequence stars. Authors: Wilson, O. C. Bibcode: 1978ApJ...226..379W Altcode: An analysis is given of fluxes measured in 1-A bands centered on the Ca II H and K lines for a sample of 91 main-sequence stars, extending from about F5 to M2, over time intervals of nine to 11 years. The results are discussed separately for a set of 18 stars with minimal chromospheric fluxes used as standards, the program stars of spectral types F7 to G3, the program stars of types G5 and later, as well as the sun. K/H ratios are determined and compared for the different groups of stars. It is tentatively concluded that: (1) no stellar chromospheres are likely to be constant in time; (2) short-term fluctuations tend to increase in size with average flux; (3) cyclical variations occur with periods ranging from about 7 years to probably at least twice as long; (4) the stellar cycles observed in H and K flux should be regarded as evidence for analogs of the solar cycle; and (5) the incidence of complete or probable partial cycles increases toward later spectral types. Title: Flux measurements of Ca II and K emission. Authors: Vaughan, A. H.; Preston, G. W.; Wilson, O. C. Bibcode: 1978PASP...90..267V Altcode: A four-channel photon-counting spectrophotometer (designated HKP-2) is described which is designed for measuring stellar chromospheric calcium emission. The HKP-2 is calibrated, and its performance and accuracy evaluated, by observing 63 of Wilson's (1968) program stars on the same nights with both the HKP-2 and a coude scanner designated HKP-1. The results of the observations are discussed in terms of the calibration of mean H-K flux indices, variations in individual stellar fluxes, the flux ratio for H and K, and the instrument color index. It is shown that the HKP-2 provides satisfactory performance in the measurement of stellar chromospheric emission in a manner closely analogous to the method of Wilson and that a single observation yields a color index as well as flux indices for H and K that can be calibrated and transferred unambiguously to Wilson's system of measurement. Title: Stellar chromospheres for fun and profit. Authors: Wilson, O. C. Bibcode: 1977BAAS....9..585W Altcode: No abstract at ADS Title: Effects of heavy element abundance on spectroscopic luminosities of G5 - K0 giants. Authors: Keenan, P. C.; Wilson, O. C. Bibcode: 1977ApJ...214..399K Altcode: Spectral classification has been carried out on coude' spectrograms (9 A mm -1) for 13 semibarium stars (stars with slight excesses of heavy metals) and for two barium stars. The luminosity classes assigned from ratios of lines of iron-peak elements should be independent of chemical composition. These luminosity classes place the observed semibarium stars on, or very slightly above, the main giant sequence, in agreement with the K-line absolute magnitudes. The two barium stars (o Vir and HD 205011) are also typical giants in luminosity. Subject headings: stars: abundances - stars: late-type - stars: luminosities Title: Absolute magnitudes of stars from widths of chromospheric Ca II emission lines. Authors: Wilson, O. C. Bibcode: 1976ApJ...205..823W Altcode: Absolute magnitudes of about 700 late-type subgiants, giants, and supergiants are derived from measures of the widths of the chromospheric emission components of the Ca ii K line. They are tabulated along with other pertinent information. The data are essentially complete for all suitable stars down to m = 5.0 and declination 250. The moduli derived from the Mv(K) are plotted against the trigonometric parallaxes for all stars for which the latter have weights >20. It is found that there is a systematic difference in the fit to the m - M = -s - 5 log curve for stars with b < 250 compared to those with b > 250. Since the numbers of stars in these two groups are equal, the difference is believed to originate with the parallaxes. Estimates against nearby Fe i lines have been made for the strength of Sr ii A4077, which is a luminosity criterion for these stars. When the logarithms of the A4077 intensities are plotted against the Mv(K), the bulk of the stars in the diagram fall approximately along a linear relationship. However, there is a group of stars between Mv(K) = +1.5 and -3 for which the estimated A4077 intensities are too strong, compared to the average for the other stars, by amounts well in excess of the errors of estimation. Further investigation indicates that the G-K stars in this group are probably barium stars, but M-type stars also participate in the Sr ii anomaly. The color-magnitude diagram constructed from the Mv(K) has several interesting features which are discussed in the text. In particular, the C-M diagram of NGC 188 by Sandage forms an excellent lower boundary to the assemblage of field stars. Subject headings: Ca ii emission - stars: late-type - stars: luminosities Title: Chromospheric Variations in Main Sequence Stars Authors: Wilson, O. C. Bibcode: 1976IAUS...71..447W Altcode: No abstract at ADS Title: Ira S. Bowen (1898-1973) Authors: Wilson, O. C. Bibcode: 1973S&T....45..212W Altcode: No abstract at ADS Title: Summary Authors: Wilson, O. C. Bibcode: 1973NASSP.317..305W Altcode: 1973stch.coll..305W; 1973IAUCo..19..305W No abstract at ADS Title: I. S. Bowen 1898 - 1973 Februar 6th. Authors: Wilson, O. C. Bibcode: 1973S&T....45R.212W Altcode: No abstract at ADS Title: Ira Sprague Bowen (1898 - 1973). Authors: Wilson, O. C. Bibcode: 1973S&T....45Q.212W Altcode: No abstract at ADS Title: A Preliminary Investigation of the Dependence of Mv (K) on [Fe/H] Authors: Wilson, O. C.; Olsen, E. H.; Kjaergaard, P. Bibcode: 1972QJRAS..13..161W Altcode: No abstract at ADS Title: Widths of CA II Chromospheric Emission Lines as a Measure of Stellar Luminosity Authors: Wilson, Olin C. Bibcode: 1970PASP...82..865W Altcode: No abstract at ADS Title: Dependence of Chromospheric Emission upon Bolometric Luminosity for the Hyades Authors: Wilson, O. C. Bibcode: 1970ApJ...160..225W Altcode: Fluxes in the centers of the H and K lines were measured for sixty-five Hyades stars between F4 and KS. Analysis of these measures shows that, in terms of bolometric luminosity, theradiation in the chromospheric H and K emission lines increases by a factor of 2 between B - V = 0.45 and B - V = 1.25. Other results give the emission as a function of the local continuum, as well as the true emission ratios for stars in this color range. Title: Calcium emission intensities as indicators of stellar age. Authors: Wilson, O.; Woolley, R. Bibcode: 1970MNRAS.148..463W Altcode: Fresh data are presented concerning the calcium emission intensities of 325 main-sequence late-type stars estimated by one of the authors (0. W.). These are compared with parameters of the galactic orbits of the stars according to methods worked out at R.G.O. A very clear correlation is found between the calcium emission intensities and the eccentricities and box angles (inclinations) of the orbits. This reinforces the view that main-sequence stars with strong calcium reversals are young stars, and have near circular orbits with low inclinations to the galactic plane; while stars with feeble emissions are old stars which have, statistically, high eccentricities and high inclinations to the galactic plane. Title: High-Dispersion Classification of K2-M6 Giants of High and Low Velocity Authors: Deutsch, A. J.; Wilson, O. C.; Keenan, P. C. Bibcode: 1969ApJ...156..107D Altcode: The classification of early M-type giants by the usual criteria of TiO band strengths has been tested by estimating ratios of weak atomic lines on coudé spectrograms of scale 9-10 A mm1. No systematic dif- ferences are found between the types given by the two methods for Population I stars and for high- velocity stars of intermediate Population II. Published V - I and U - I colors also give sequences in agreement with the spectral types. Although there is thus no evidence that TiO bands differ in strength between giants of the two popula- tions studied, in several of the M stars of high velocity a slight weakening of the stronger atomic lines ap- pears to be present. In several stars representing both populations, the absorption lines at Hy and Ho show intensity changes on a time scale of weeks or months; but other absorption lines and bands appear not to vary Title: Calibration Apparatus at Mt. Wilson and Mt. Palomar Authors: Wilson, Olin C. Bibcode: 1969BAAS....1..154W Altcode: No abstract at ADS Title: Chromospheric variations in main-sequence stars Authors: Wilson, O. C. Bibcode: 1969lls..symp..103W Altcode: No abstract at ADS Title: Flux Measurements at the Centers of Stellar H- and K-Lines Authors: Wilson, O. C. Bibcode: 1968ApJ...153..221W Altcode: The coudé scanner of the 100-inch telescope has been used as a two-channel photometer to measure the fluxes at the centers of stellar H- and K-lines, for the purpose of initiating a search for stellar ana- logue~ of the solar cycle. From the Stromgren-Perry catalogue 139 stars previously observed at 10 A mm1 dispersion were selected for this purpose and included most of those in which H-K emission had been seen on the spectrograms. Reasonable agreement between eye-estimated intensities and the photometric results shows that the procedure adopted is suitable for specifying chromospheric activity, but with an accuracy much improved over eye estimates. The probable error of a single measurement of a line is a little less than 2 per cent. No undoubted variations have been observed during a year's observation. However, the measures are discussed in connection with the Stromgren-Perry photometric parameters b - y, in1, C1. In this way it is possible to trace in some detail the course of chromospheric evolution as stars begin to move off the zero-age main sequence (ZAMS) toward the giant region. Doublet ratios of the chromospheric compo- nents of H and K are one of the by-products of the observations. They show that, in general, the optical thickness of the gas masses involved cannot be very great Title: Radial velocities of dK and dM stars. Authors: Wilson, O. C. Bibcode: 1967AJ.....72..905W Altcode: No abstract at ADS Title: Distance of the Hyades and Relation between Luminosity and CA II Emission-Line Widths Authors: Wilson, O. C. Bibcode: 1967PASP...79...46W Altcode: No abstract at ADS Title: Dwarf k- and m- Stars from the Catalogue of Vyssotsky et AL. Authors: Wilson, O. C. Bibcode: 1967IAUS...30..145W Altcode: No abstract at ADS Title: The masses of nine visual binary systems Authors: Wilson, O. C. Bibcode: 1967mamt.book..241W Altcode: No abstract at ADS Title: Age-Helium Content Correlations for Two Low-Mass Field Binary Systems Authors: Faulkner, John; Iben, Icko, Jr.; Wilson, Olin C. Bibcode: 1966ApJ...146..271F Altcode: It is shown that knowledge of a well-determined mass for a star ascending the subgiant branch would provide an important test of theories of stellar evolution. Recently determined masses for the systems ADS 755 and ADS 11479 suggest that the component stars formed from material that was richer in helium than would be thought appropriate to the relevant period of formation. In particular, the assumption that these stars are as old as the Galaxy itself implies initial helium contents >= 30 per cent, in agreement with a recently proposed theory of the evolution of Population II stars. Title: Stellar Convection Zones, Chromospheres, and Rotation Authors: Wilson, O. C. Bibcode: 1966ApJ...144..695W Altcode: This paper is an attempt to connect the rotations of main-sequence stars with their chrom osheric properties and, hence, with the extent of their hydrogen convection zones. It is based on 10/mm spectrograms of 308 stars, with b - y > 0 240 from the -Perry catalogue. On the zero-age main sequence it is found that rotational velocities of the order of V sin i > 50 km/sec set in very abruptly at b - y = 0.285, and Kraft's observations show that this is true also in the Hyades. However, similar rotational velocities are found among the field stars at the upper edge of the main- sequence band among spectral types G0-G5, and it is logical to suppose that these objects have evolved from the zero-age line near b - y = 0.285. A curve can be drawn in the (b - y) - Ci plane which separates the large from the small rotations, and this curve, therefore, approximates the evolutionary track of stars originating at b - y = 0.285 on the zero-age line. This curve, which divides the larger from the smaller angular momenta, applies to the members of spectroscopic binary systems as well as to single stars. Stars showing emission at H and K have a strong concentration to the zero-age line and extend up the main sequence to b - y = 0.30. It cannot be stated definitely that stellar chromospheres terminate near this point, but the evidence indicates that it is quite possible that they do. If so, the close agreement between the onset of larger rotations and the termination of chromospheres is very suggestive of the braking mechanism described by Schatzman. The implication, then, is that deep hydrogen convection ends at b - y = 0 285 on the zero-age line (spectral type F4), and the observations show that the change from deep to shallow convection must occur within a mass range of the order of 5 per cent. Title: Stellar Chromospheres Authors: Wilson, O. C. Bibcode: 1966Sci...151.1487W Altcode: No abstract at ADS Title: Chromospheric Activity as a Function of Age in Main-Sequence Stars Authors: Wilson, O. C.; Skumanich, A. Bibcode: 1966IAUS...24...40W Altcode: No abstract at ADS Title: A Preliminary Investigation of Lithium in Main Sequence Visual Binaries Authors: Wilson, O. C.; Baum, W. A.; Ford, W. K., Jr.; Purgathofer, A. Bibcode: 1965PASP...77..359W Altcode: No abstract at ADS Title: Stellar Chromospheres and Ca II H and K Emission Authors: Wilson, O. C. Bibcode: 1965SAOSR.174..381W Altcode: No abstract at ADS Title: The Strength of the li i Line in the Spectra of Main-Sequence f- and G-Type Stars. Authors: Kraft, Robert P.; Wilson, Olin C. Bibcode: 1965ApJ...141..828K Altcode: No abstract at ADS Title: Dependence of Chromospheric Activity upon Age in Main-Sequence Stars: Additional Evidence. Authors: Wilson, O. C.; Skumanich, Andrew Bibcode: 1964ApJ...140.1401W Altcode: Spectrograms of 10 A/mm dispersion have been obtained of 142 field stars from the catalogue of Str6mgren and Perry for those objects with b - y > 0.325. Mter elimination of known spectroscopic binaries and stars of higher luminosity, a sample of 114 main-sequence stars remains. In this sample seventeen stars showing H and K bright reversals are found, and all but two of these lie close to the lower boundary (zero-age edge) of the distribution in a Ci - (b - y) diagram. This result is taken as evidence in support of the view that chromospheric activity of main-sequence stars decreases with age. In particular, it removes the possibility that stars formed in large clusters differ significantly in respect to their chromospheric properties from those formed in small groups or singly. Title: Chromospheric Activity and Lithium Authors: Wilson, O. C. Bibcode: 1964PASP...76..238W Altcode: No abstract at ADS Title: Retirement of Dr. Ira S. Bowen Authors: Wilson, O. C. Bibcode: 1964PASP...76..193W Altcode: No abstract at ADS Title: The Distribution of Intensities of Bright H and K in dK Stars and the Rate of Star Production in the Galaxy Authors: Wilson, O. C. Bibcode: 1964PASP...76...28W Altcode: No abstract at ADS Title: Strength of the Li I Line in the Spectra of Main-Sequence F- and G-Type Stars. Authors: Kraft, Robert P.; Wilson, Olin C. Bibcode: 1964AJ.....69Q.549K Altcode: The strength of the Li I feature at X6708 has been estimated against X6703 of Fe I and X6718 of Ca I in the spectra of about 30 main- sequence F- and G-type stars. The stars were selected from Stro~mgren and Perry's photometric catalog on the b-y, c,, m1, system in the interval 0.33<b-y<0.42, without regard to c, or m1, or Ca II emission strength. From the limited material at hand, we conclude the following: (1) All stars showing strong Ca II emission show strong Li I in absorption, but Li I absorption occurs in strength in many stars without Ca II emission. (2) If, following Stro~mgren, we interpret the index c, as a nuclear age parameter, then there is no correlation between Li I strength and nuclear age. (3) There is no correlation between the Li I strength and the metal index mi. Title: The Spectrum of NGC 7027. Authors: Aller, L. H.; Bowen, I. S.; Wilson, O. C. Bibcode: 1963ApJ...138.1013A Altcode: Additional spectrograms of NGC 7027 have been obtained which extend the observations to substantially fainter lines than earlier studies. Photoelectric measurements were made of the stronger lines in the region between X 3100 and X 4700 and were used to calibrate the photographically determined intensities of all lines. Title: A Probable Correlation Between Chromospheric Activity and Age in Main-Sequence Stars. Authors: Wilson, O. C. Bibcode: 1963ApJ...138..832W Altcode: Observation shows that the average intensity of H and K emission is much higher for main-sequence stars of types G0-K2 in the Hyades, Praesepe, Coma, and Pleiades clusters than for similar local field stars and that it is appreciably higher for the Pleiades than for the other clusters. It is also found, from observations of local visual binaries, that the H-K intensities in the members of such pairs tend to be very similar when allowance is made for spectral-type differences. It is concluded that the most probable explanation of these facts is that the H-K intensity in a main-sequence star and hence the general degree of its chromospheric activity bear an inverse relationship to its age. This concept of chromospheric evolution is consistent with all the observations presented here, as well as with the known kinematical differences between dMe and ordinary dM stars. If, however, stars can be formed in the general field, as well as in clusters, then the observed differences in chromospheric activity would be related to place of origin rather than to age. The probable bearing of average surface magnetic-field strength on the question of chromospheric activity is discussed briefly. Title: Nebular absorption of He 3889 A. Authors: Munch, G.; Wilson, O. C. Bibcode: 1963AJ.....68..287M Altcode: No abstract at ADS Title: Lithium in a Main Sequence Star Authors: Wilson, O. C. Bibcode: 1963PASP...75...62W Altcode: No abstract at ADS Title: Nebular Absorption of He I λ3889. Authors: Münch, G.; Wilson, O. C. Bibcode: 1963AJ.....68Q.287M Altcode: The presence of an absorption line arising from the 2~5 metastable level of neutral helium in the spectra of the stars imbedded in the Orion Nebula was noticed long ago by 0. C. Wilson. Lately it has been shown by G. Mu~nch and 0. C. Wilson (Z. Astrophys. 56, 127, 1962) how the strength of this nebular absorption line may be related to the surface brightness of a homogeneous emission nebula. The lack of agreement between the surface brightness thus computed for the Orion Nebula with the observed value, has been interpreted in terms of density inhomogeneities in the nebula, independently postulated by Osterbrock on other grounds. Because this interpretation has been criticized by K. Wurm (Z. Astrophys. 52,149, 1961), new observational evidence related to the line in question is being obtained. In this communicatioi~, besides new data for the Orion stars, the results of the search for the absorption line in other emission nebulae are presented. So far the line has been detected in a number of stars in the complex M8- M20, in BD +6601675, exciting NGC 6822, in BD +6002522 exciting NGC 7635, and in HD 64315, exciting star of NGC 2467. The stars imbedded in 20 other H II regions do not have detectable He I nebular absorption. Although a complete discussion of the data requires surface brightness determinations (corrected for interstellar and internebular extinction) not available yet, it is shown how the recent observations fully support the interpretation advanced earlier by Wilson and Mu~nch. Title: Internal Motions in the Planetary Nebula IC 4997 Authors: Wilson, Olin C.; O'dell, C. R. Bibcode: 1962PASP...74..511W Altcode: No abstract at ADS Title: Relationship Between Colors and Spectra of Late Main-Sequence Stars. Authors: Wilson, O. C. Bibcode: 1962ApJ...136..793W Altcode: Spectrograms of 109 main-sequence stars of types G5 and later have been obtained at a dispersion of 10 A/mm and have been used to derive spectral types on the Yerkes system, based on ratios of metallic lines. A plot of the revised types against the old Mount Wilson types shows a very considerable scatter, which is believed to be due chiefly to errors in the Mount Wilson values. Nevertheless, even with the revised types, it is found that there is not a one-to-one correspondence between spectral type and photoelectric color for these field stars. Spectral types of 69 Hyades main-sequence stars have been estimated from 38 A/mm spectrograms. For these objects the correlation of type and color is appreciably closer than for the field stars. It is suggested, following an argument based on the Vogt-Russell theorem, that these facts imply a greater degree of chemical non-uniformity in the local main sequence than in that of the Hyades. A number of instances of anomalous intensities of the hydrogen lines and of CN bands among the local main-sequence stars are indicated. Title: On the Structure of the Orion Nebula. A Reply to K. WURM. With 2 Figures in the Text Authors: Münch, G.; Wilson, O. C. Bibcode: 1962ZA.....56..127M Altcode: No abstract at ADS Title: An Interpretation of the Late Main Sequence. Authors: Wilson, O. C. Bibcode: 1961ApJ...133..457W Altcode: Eggen's photoelectrically measured c6lors are plotted against spectral type for the main sequence below AS. It is found that the distribution of points in this diagram is fairly narrow from AS to G5, at which point it begins to widen. This width, which extends at least as far as Mi, is much too large to be attributable to errors in either the colors or the spectral types. It is noted also that the widening occurs in that region of the spectral sequence where the supply of electrons fiom hydrogen is diminishing to the point where the metals are coming into equilbrium with their own electrons. This leads to an attempt to account for the major features of the (P- V) -type diagram on the basis of a series of stellar atmospheres in which the metal-hydrogen radio is not constant and within which,for a given spectral type, there is an appreciable spread of temperature. The results are encouraging to a considerable degree, and, where discrepancies occur in the range G8-K2, they are in the sense to be reduced if differential blanketing effects are still appreciable It turns out that among main-sequence K-type stars a total range in the metal-hydrogen ratio of the order 1:100 is necessary to account for the observed spread in the plot referred to above. Observations at 10 A/mm of stars of the same types near the upper and lower boundaries of the diagram show that they are spectroscopically distinguishable. All stars near the upper boundary (red stars) have much stronger H and K emission than do stars of the same types near the lower boundary (blue stars). Conversely, except at G8, the blue stars of given types all have stronger Balmer absorption lines than the corresponding red stars. These latter facts are accounted for, semiquantitatively, by the same assumptions as those which explain the spread in the (P - V) spectral-type diagram. Title: Spectrographic Observations of a Flare Star Authors: Wilson, O. C. Bibcode: 1961PASP...73...15W Altcode: No abstract at ADS Title: A New Scale of Stellar Distances Authors: Wilson, O. C. Bibcode: 1961SciAm.204a.107W Altcode: No abstract at ADS Title: Observational Limitations to Mass Loss by Normal Late-Type Giants. Authors: Wilson, O. C. Bibcode: 1960ApJ...132..136W Altcode: Spectroscopic observations of H and K lines of Ca ii in several hundred late-type stars are discussed, and it is shown that the measured displacements provide no evidence for ejection of matter from normal giants earlier than MO. Also, some simple calculations show that the absence of true circumstellar lines from the spectra of these objects implies a rate of mass loss less than 10-10 0 per year. Hence if these stars must lose a substantial portion of their masses before becoming wbite dwarfs there appear to be only two alternatives: either they all must eventually evolve to M-type stars and remain such long enough to eject the necessary amount of matter; or they are ejecting matter at present but by some unknown mechanism which permits the process to escape observation. There is also a brief discussion of mass loss in genera] and with reference to a Herculis in particular. Title: A Suggested Mechanism for the Ejection of Matter from M-Type Stars. Authors: Wilson, O. C. Bibcode: 1960ApJ...131...75W Altcode: It is suggested that matter is ejected from M-type stars by the outward force due to a strong chromospheric Ly-a radiation A brief examination of the mechanism indicates that it may be capable of meeting the requirements set by the observations of expanding envelopes around these stars Title: Eclipses by Extended Atmospheres Authors: Wilson, O. C. Bibcode: 1960stat.book..436W Altcode: 1960S&SS....6..436W; 1960stat.conf..436W No abstract at ADS Title: A Color-Magnitude Diagram for Late-Type Stars Near the Sun. Authors: Wilson, O. C. Bibcode: 1959ApJ...130..496W Altcode: A color-magnitude diagram for late-type stars in the solar neighborhood is derived from measures of the widths of the bright H and K reversals in the spectra of stars for which photoelectric values of B - V are available. The diagram is filled out by the inclusion of stars with trigonometric parallaxes >0'oso. From the plotted points it is possible to delineate with fair accuracy the limiting evolutionary track for the oldest galactic stars and to estimate the location of the break-off point from the main sequence. The corresponding age of the galaxy is about lOiS years, but this estimate is subject to improvement with the addition of further observations. Title: Accuracy of Absolute Magnitudes Derived from Widths of H and K Emission Components. Authors: Wilson, O. C. Bibcode: 1959ApJ...130..499W Altcode: Measures of the dths of the bright reversals in H and K in the sun and in the yellow giants of the Hyades are used to establish a calibration of absolute visual magnitude as a function of emission-line width. For giant and subgiant stars the probable error of a single measurement is j 0.26 mag., and the probable error due to intrinsic scatter is about I 0.20 mag. The latter quantity is determined from comparison with 24 stars for which dir/ir < 6 . A comparison with 29 main-sequence stars gives larger values of both measuring error and intrinsic scatter. It is suggested that the principal source of intrinsic scatter for all stars may be rotational widening. Further comparison with H and K measures in three supergiants in h and x Persei and in the K-type component of Aurigae indicates that the calibration is valid for stars as bright as Mv -6. Title: Location of Late Type High-Velocity Stars in the Color-Magnitude Diagram Authors: Wilson, O. C. Bibcode: 1959PASP...71..338W Altcode: No abstract at ADS Title: Internal Kinematics of the Orion Nebula. Authors: Wilson, O. C.; Minich, Guido; Flather, Edith; Coffeen, Mary F. Bibcode: 1959ApJS....4..199W Altcode: No abstract at ADS Title: A preliminary color-magnitude diagram for late-type stars in the solar neighborhood Authors: Wilson, O. C. Bibcode: 1959IAUS...10...39W Altcode: 1959SAnAp...8...39W No abstract at ADS Title: Some Theoretical Apsects of H and K Emission in Late-Type Stars. Authors: Hoyle, F.; Wilson, O. C. Bibcode: 1958ApJ...128..604H Altcode: A velocity is defined in the subphotospheric convection zones of late-type stars that varies from star to star in the same way as the width of the emission lines H and K of Ca ii The quantity is tentatively identified as the velocity of hydromagnetic waves. Title: Internal Kinematics of the Planetary Nebulae Authors: Wilson, O. C. Bibcode: 1958RvMP...30.1025W Altcode: 1958IAUS....8.1025W No abstract at ADS Title: Limitations on Physical Theories of H and K Emission Lines. Authors: Wilson, O. C. Bibcode: 1957ApJ...126..525W Altcode: A satisfactory physical theory of the H and K emission lines in the sun and stars has not yet been developed. By consideration of existing observations, certain requirements of and limitations upon such theories are established. If rO is the optical thickness in the line center, N the number of Ca ii ions per square centimeter vertical column, L the luminosity (visual), and AXD the Doppler width, the following items must be accounted for: A. Emission produced in optically thin layers (ro 1). (1) AXD L1/6. (2) N unrestricted except for upper limit on ro. (3) Mechanism for adequate emission from thin layers. B. Emission produced in optically thick layers (10 < ro <- l0 ). (1) Both AXD and N must vary appropriately with L. (2) The rate of variation of AXD with L must lie within the maximum and minimum rates, which, together with the corresponding variations of N, are, respectively, AXD L1/5, N L-1/4, and AXD L1/9, N L1/2. Title: H Emission in Late-Type Star. Authors: Wilson, O. C. Bibcode: 1957ApJ...126...46W Altcode: Intensities of HE emission are estimated in 185 late-type stars and compared with those of the K line of Ca ii. Although there is a statistical tendency toward a correlation between the HE and K intensities, there is also a large scatter, indicating that the ratio of HE to K is widely variable. Title: H and K Emission in Late-Type Stars: Dependence of Line Width on Luminosity and Related Topics. Authors: Wilson, O. C.; Vainu Bappu, M. K. Bibcode: 1957ApJ...125..661W Altcode: The H and K emission lines of Ca II have been studied on 10-A/mm spectrograms of 185 stars of types G, K, and M. Nearly all stars of type G0 or later in the list of MK standards (Johnson and Morgan 1953) have been included. Emission-line widths have been measured, as well as displacements of the emission and absorption components. Tb e displacements are determined with respect to nearby low-excitation reversing- layer absorption lines.

When the logarithms of the emission-line widths (corrected for instrumental width) are plotted against the Yerkes absolute spectroscopic magnitudes, the points define a straight line which extends over a 15-mag. range of Mv and which indicates that the line width varies as the one-sixth power of the luminosity. Stars with weak or strong lines and of all spectral types later than G0 seem to fit the linear relationship equally well. The widths therefore cannot be dependent upon line intensity or stellar surface temperature.

Evidence from the solar spectrum, from ζ Aurigae, from Hyades stars, and from four visual binaries point to the conclusion that the relationship described here is not of a statistical nature. Therefore, it is probable that the Ca II emission-line widths can be used as luminosity indicators. Internal consistency considerations indicate that one good spectrogram should fix the absolute magnitude of any late-type star with suitable lines to within ±05 mag.

It is found that,for displacements within ±6 km/sec, negative values are more frequent than positive for the emission components of H and K. On the other hand, between +4 and -4 km/sec, positive values are more common for the absorption components. The naive interpretation is that the emitting layer is rising and that the absorbing material is falling slowly inward. Statistics of the larger displacements common among the intrinsically luminous stars are discussed briefly. In particular, it is found that among the M-type giants and supergiants the negative displacements of the absorption components are not correlated with absolute magnitude. Title: The Analysis of the Chromosphere of Zeta Aurigae Authors: Wilson, O. C. Bibcode: 1957JRASC..51...70W Altcode: No abstract at ADS Title: Simultaneous Spectrographic and Photometric Observations of the Short-Period Variables SX Phoenicis and CC Andromedae. Authors: Wilson, O. C.; Walker, Merle F. Bibcode: 1956ApJ...124..325W Altcode: Radial velocity-curves and light-curves in three colors are derived from simultaneous spectrographic and photoelectric observations made at Palomar in 1953 and 1954. For both SX Phoenicis and CC Andromedae maximum brightness lags behind maximum size, as deduced from the radial velocities, by a quarter-period, as is true of the cepheid variables. The light-amplitude of SX Phoenicis is widely variable, but corresponding variations in the velocity-amplitude cannot be established with certainty. On the other hand, there is an obvious relationship between the light- and velocity-amplitudes of CC Andromedae, which seems to be the same as that for Scuti. It is probable that these two stars, together with DQ Cephei, belong to the same class of variable and that they may be considerably brighter than main-sequence stars of the same spectral type. Title: The New Cassegrain Spectrograph for the Mount Wilson 60-Inch Telescope Authors: Wilson, O. C. Bibcode: 1956PASP...68..346W Altcode: No abstract at ADS Title: Proportionality of Nebular Red Shifts to Wave Length. Authors: Minkowski, R.; Wilson, O. C. Bibcode: 1956ApJ...123..373M Altcode: Measures of the red shift /Xo for the colliding galaxies Cygnus A give the value 16812 + 9 km/sec for the mean wave length 3830 A and 16798 + 7 km/sec for the mean wave length 6472 A. The relative change in the red shift with wave length is less than 3 X 10- per 1000 A. Combination of the optical results with those by Lilley and McClain for the 21-cm hydrogen line shows that the relative change is lessthan3 X 10- per 1000A Title: Complex Lines in the Spectrum of RW Cephei. Authors: Merrill, Paul W.; Wilson, Olin C. Bibcode: 1956ApJ...123..392M Altcode: The spectrum of this extreme supergiant M-type star observed with dispersion of 9 A/mm shows many absorption lines apparently with two components separated by a narrow central maximum. The maximum is probably actual emission superposed on an absorption line considerably widened by turbulence. In certain lines, especially the resonance lines of Ca i, Cr i, Mn 1, and Sr ii, the shortward component is greatly reinforced by the absorption of an upper expanding shell of gas. Shortward of X 4000 A there appear numerous narrow emission lines, chiefly of Fe i and Ti 1, without accompanying dark lines. The peculiar relative intensities of these lines are probably due to strong differential . The spectrum is compared with that of a Orionis. Title: The Radial Velocity of DQ Cephei = HD 199908. Authors: Sahade, J.; Struve, O.; Wilson, O. C.; Zebergs, V. Bibcode: 1956ApJ...123..399S Altcode: The radial velocities measured on 215 spectrograms taken on sixteen nights confirm Walker's photoelectric period of 0.0788650 day. The mean velocity of the star is - 21 9 km/sec. There is a beat period of 0.3751 day. The total range of the principal oscillation is 9.2 km/sec; that of the interfering oscillation is 2.6 km/sec. The period of the interfering oscillation is 0 06516 or 0.09986 day. The spectrum is approximately Fl IV-V. The maximum brightness occurs halfway on the descending branch of the velocity- curve. Near minimum radial velocity a narrow space of continuous spectrum is visible between Ca H and HE. This feature is absent at other phases. Title: Award of the Bruce Gold Medal to Dr. Albrecht Unsöld Authors: Wilson, O. C. Bibcode: 1956PASP...68...89W Altcode: No abstract at ADS Title: The Possible Occurrence of λ5876 of He I in Absorption in the Spectra of Certain Late-Type Stars Authors: Wilson, O. C.; Aly, M. K. Bibcode: 1956PASP...68..149W Altcode: No abstract at ADS Title: The Award of the Bruce Gold Medal to Dr. Walter Baade Authors: Wilson, O. C. Bibcode: 1955PASP...67...57W Altcode: No abstract at ADS Title: Introductory remarks: THE ATMOSPHERES OF GIANT AND SUPERGIANT STARS Authors: Wilson, O. C. Bibcode: 1955stat.conf..147W Altcode: 1954stat.conf..147W No abstract at ADS Title: Chromospheric Structure of the K-Type Component of Zeta Aurigae. Authors: Wilson, O. C.; Abt, Helmut A. Bibcode: 1954ApJS....1....1W Altcode: Spectrograms of 10 A/mm dispersion taken during the 1947-1948 eclipse have been measured for line intensities and for radial velocities, and the results are compared with those obtained previously for the 1939-1940 eclipse. Egress of 1947-1948 is found to he quite similar to ingress and egress of 1939-1940; ingress at the more recent eclipse differs, however, from the other three transits in the direction of a considerably slower gradient, particularly at the greater chromospheric heights. This effect is found from lines of all types. However, ingress of 1947-1948 is not distinguishable from the other transits in the values of any of the derived parameters: excitation temperature, turbulent velocity, or degree of ionization. It is shown that the apparent rise of AXD with height found in 1939-1940 is really due to a systematic difference in this quantity between the neutral and ionized lines. Ions indicate slightly higher turbulent velocities than do neutral atoms. The excitation temperature increases with height at about the same rate as indicated by the earlier results. Ionization in the chromosphere is studied in some detail, and 's theory of the penetration of ionizing radiation from the B star into the chromosphere of the K star is applied to the roblem. The outcome is that it appears impossible to account for the spectroscopic phenomena on t e basis of a smooth distribution of the chromospheric material. In fact, it is necessary to assume that the matter occurs in condensations of rather small size (thickness of the order of 10 km) and high density (log n[H] = 13.8) in order to keep the ionization at the required level and to avoid discordance with the solar abundance ratios. The model is in accord with all but one of the observed spectroscopic features, as well as with the recent interpretation of the photometric eclipse by Roach and Wood. Title: Spectrophotometry of the Central Stars of Four Planetary Nebulae. Authors: Aller, L. H.; Wilson, O. C. Bibcode: 1954ApJ...119..243A Altcode: An analysis of coud spectrograms of the nuclei of four planetary nebulae with predoininanily absorption spectra, viz., IC 418, IC 2149, NGC 2392, and IC 4593, yields spectral classes of on R. M. Petrie's system. The proffles of the hydrogen lines are compared with those of the O9 star 10 Lacertae. Electron densities somewhat lower than those previously obtained for other planetary nuclei with absorption4ine spectra seem to be indicated. It is suggested that the He/H ratio can be greater in the planetary nuclei than in normal 0 stars and that the excitation temperatures can be systematically lower than those derived from Petrie's scale. A final decision will requlre a much more detailed analysis, involving the calculation of model atmospheres. Title: The Mass of the Globular Cluster M92. Authors: Wilson, O. C.; Coffeen, Mary F. Bibcode: 1954ApJ...119..197W Altcode: Radial-velocity measurements of 23 spectrograms of 15 red giant stars in M92 are discussed. A mass of 3.3 X t 0 is derived for the cluster, and the corresponding mass-to-luminosity ratio is 2.0 in solar units. It is probable that there are intrinsic velocity variations in some of the cluster stars. Title: Some Remarks on the Spatial and Kinematic Structure of the Planetary Nebula IC 418. Authors: Wilson, O. C. Bibcode: 1953ApJ...117..264W Altcode: Recent high-dispersion spectrograms have resolved the [N ii] and [0 llJ lines in this nebula which had appeared single with the lower dispersion previously used. On collecting and discussing the kinematic data for this low-excitation nebula and correlating them with the results from slitless spectrograms, it becomes highly probable that IC 418 is built upon the same spatiokinematic model as are the high-excitation ring nebulae. A brief consideration of ring nebulae in general leads to two alternative explanations for them: (1) If the density inside the shell is higher than the density in the shell, then the flow of matter is from the inner mass into the shell. In this case the electron temperature in the inner mass must be much higher than that in the shell. (2) If, on the other hand, the inner mass consists of matter expelled inward from the shell, a relatively higher density in the shell, as compared to the interior, is adequate to account for the appearance of the ring nebulae. Title: Monochromatic isophotic contours of planetary nebulae. Authors: Wilson, O. C.; Aller, L. H. Bibcode: 1953AJ.....58R.235W Altcode: Slitless spectrograms of a number of bright planetary nebulae including NGC 1535, 2392, 2440, 6210, 6752, 6741, 7009, 7662, and tC 418, 4593 were obtained with the coude' spectrograph and image rotator at the 100-inch telescope. Monochromatic images of EOIII~, LNe~IIj, ENevJ, Hei, Heii, and H have been analyzed with the balanced-beam isophotometer invented by Hiltner and Williams. A comparison of results secured by tal~ing successive tracings across the image with the isophotic contours traced by the machine showed good agreement. The greatest inacctiracy in the contours is introduced by internal motions in the nebula which prodtice a distortion of the slitless images. Direct photographs obtained with suitable plate and filter combinations can overcome this difficulty. Observations obtained with the multislit, which gives not only the velocities of the forward and backward sides of the shell in the line of sight, but also the relative amounts of material in the two sides of the shell, may be combined with the isophotic contour data to calculate three-dimensional models of some of the more regular nebulae. When multislit data are not available, assumptions about the symmetry of the nebula must be made. The contours obtained illustrate single and double ring structures, single nuclear and binuclear strticttires, as well as somewhat irregular objects. Observatory, University of Michigan, Ann Arbor, Mich. Title: The Structure of the Planetary Nebula IC 418. Authors: Wilson, O. C.; Aller, Lawrence H. Bibcode: 1951ApJ...114..421W Altcode: Slitless coude' spectrograms of the small, low-excitation, planetary nebula IC 418 are analyzed to determine the intensity distribution across the disk in various monochromatic images. From an analysis of these intensity distributions an attempt is made to find the emission per unit volume. The emission in ergs/cm3/sec is expressed in c.g.s. units, and the approximate ionic densities of H, He, N IT, 0 II, 0 III, Ne iii and Sir are derived. Title: The Of-Type Spectroscopic Binary BD+40°4220. Authors: Wilson, O. C.; Abt, Arthur Bibcode: 1951ApJ...114..477W Altcode: The components of the spectroscopic binary BD+ are of spectral types Of and 09 and the period is 6.600 + 0.002 days. The mass of the 09 star (probably a giant or supergiant) is about four times that of the Of. Rather pronounced periodic variations in visibility of some of the spectral features are briefly discussed. Title: The structural features of certain planetary nebulae. Authors: Aller, Lawrence H.; Wilson, Olin C. Bibcode: 1950AJ.....55...70A Altcode: Guided slitless spectrograms obtained with the aid of an image rotator at the coude' focus of the 100-inch reflector are used for a study of the structure of NGC 6572 and NGC 7662. The outer portions of NGC 6572 possess an amorphous structure. The nebula is not at all elliptically symmetrical as earlier observations with smaller telescopes indicated. Mg I X457I and S ii show a shell structure, whereas N iii X4640 and A iv X4740 apparently do not. The intensity distribution across the nebula, corrected for bad seeing and guiding, has been obtained for lines of hydrogen and helium. Isophotal contours of 0 iii X4959, Ne iii X3865, Hp, and Heii X4686 in NGC7662 have been drawn. The two forbidden lines show similar contours whereas the distribution of H and He ii is similar in the inner portions of the nebula. A three-night exposure shows that He ii does not appear in the outer shell at all. On the assumption that the structure of the nebula, in the first approximation, can be represented as circularly symmetrical in the plane containing the major axis of the ring and the observer, the radial emission distribution is derived by a method employed by Wallenquist in his study of star clusters. The hydrogen and Ne iii shells appear to be hollow, whereas there is some suggestion that He ii emission appears within the inner shell. Similar studies are in progress for other planetary nebulae, among them XGC62Io, 7009, and IC 418 and 4543. Observatory, University of Michigan, Ann Arbor, Mich. and Mt. Wilson and Palomar Observatories, Pasadena, Ca 1sf. Title: A Survey of Internal Motions in the Planetary Nebulae. Authors: Wilson, O. C. Bibcode: 1950ApJ...111..279W Altcode: Slit spectrograms (dispersion 10 A/mm) of twenty-six bright planetary nebulae have been obtained with the coude' spectrograph of the 100-inch telescope. For thirteen of the nebulae, slitiess spectrograms have been secured with the same instrument. he main observational results are the separations of the components of the double nebular lines and the dimensions of corresponding slitless images. Analysis of these data leads to the following principal conclusions: 1. There is no correlation between the relative intensities (V/R) of the red and violet components of the nebular lines and the general level of nebular excitation. 2. The number of nebulae with V/R> 1 is about equal to the number with V/R < 1; hence the nebulae are probably transparent in the observed wave4ength range. 3. The most reliable measure of expansion velocity is shown to be the mean of the values given by lines of H, [0 ni], and [Ne in]. There may be a very weak positive correlation between this quantity and the level of excitation. 4. Where differences in component separation exist in the spectrum of a planetary nebula (and they are quite common), tife particles show smaller separations than the low-excitation particles. Extreme examples are [Ne v], for which the separations are often close to zero, and [0 n] and [N n], which sometimes show large separations. Hydrogen presents an outstanding exception to the general run of separation with excitation, agreeing closely with [0 in] and [Ne in]. Available evidence is against any marked dependence of component separation upon transition probability. 5. There is generally a positive correlation between component separation and monochromatic image size. Usually, though not always, differences in image size are much less than differences in separation. 6. Components of the nebular lines are often quite sharp, their apparent width being frequently determined by the resolving power of the emulsion; but components of H lines are noticeably diffuse in all nebulae. By-products of the investigation include improved wave lengths of twenty nebular lines and radial velocities of twelve nebulae. Two models have been investigated in attempting to explain the observations. The basic assumption of the first model is that the velocity given by the lines of any ion is a measure of the velocity of the abundant H and He in the region where the lines in question are produced. In this model the material is supposed to have originally a velocity equal to that measured for [Ne v], which is, in some nebulae, probably less than 5 km/sec. The increments in velocity between [Ne v] and He ii and between He ii and H are assumed to be due to the increases in momentum flux carried by the gas upon absorption of nuclear radiation below x 228 A and between x 912 and x 228 A, respectively. Reasonable values of the radius and temperature of the central star lead, on this model, to the correct orders of magnitude both for the velocity changes and for the total nebular brightness. The second model assumes that measured velocity differences are due to selective forces acting upon some of the rare ions and maintaining them in relative motion with respect to the abundant H and He. It appears possible in this fashion to construct a model which can account for the [Ne v] anomaly on the basis of an inward flux of Lyman continuum from the bright hydrogen shell. This model leads, however, to nebulae about 5 mag. too faint, and for this reason the first one seems preferable. Title: Planetary Nebulae Authors: Wilson, Olin C. Bibcode: 1950ASPL....6...20W Altcode: 1950ASPL..253.....W No abstract at ADS Title: Proportionality of Nebular Red Shifts to Wave Length Authors: Wilson, O. C. Bibcode: 1949PASP...61..132W Altcode: No abstract at ADS Title: The Wolf-Rayet Spectroscopic Binary HD 190918. Authors: Wilson, O. C. Bibcode: 1949ApJ...109...76W Altcode: The emission and absorption components of this star are of types close to WN5 and BO, respectively. Many observations made in 1946, 1947, and 1948 have been combined by graphical methods to yield ap- proximate spectrographic orbits. Only the X 4686 band of Heii was measured in the W spectrum, while five or six absorption lines due to the B-type component were regularly used. Derived constants of the system are: YB = -21.8 km/sec, KB = 10.0 km/sec; ~yw = -f 88 km/sec, K~ = 38 km/sec; (mB -f mw) sin3 i = 0.986 0. Since the spectra of the components of HD 190918 are not very different from those of HD 193576, whose minimum total masses are 35 0, it is probable that the value of i for HD 190918 does not exceed 18°. It is concluded, therefore, that the red shift of the X 4686 He ii band in WN stars is probably inde- pendent of the orientation of the polar axes of the stars with respect to the line of sight and that its origin is to be sought in processes occurring within the WN atmospheres Title: Book Review: Centennial Symposia, December, 1946 Authors: Wilson, O. C. Bibcode: 1949PA.....57...48W Altcode: No abstract at ADS Title: No. 755. The Wolf-Rayet spectroscopic binary HD 190918. Authors: Wilson, O. C. Bibcode: 1949CMWCI.755....1W Altcode: 1949QB4.M93n755.... No abstract at ADS Title: Three Interesting Spectroscopic Binaries Authors: Wilson, O. C. Bibcode: 1948PASP...60..385W Altcode: No abstract at ADS Title: Variations in the Spectrum of the Wolf-Rayet Star HD 50896 Authors: Wilson, O. C. Bibcode: 1948PASP...60..383W Altcode: No abstract at ADS Title: Nova Serpentis 1948 Authors: Wilson, O. C. Bibcode: 1948PASP...60..327W Altcode: No abstract at ADS Title: The Nuclear and Nebular Spectra of the Planetary Nebula NGC 2392. Authors: Wilson, O. C. Bibcode: 1948ApJ...108..201W Altcode: Eighteen stellar absorption lines and three wide emission lines were measured on an excellent spectro- gram of the nucleus of NGC 2392. Seven nebular lines also were measured. The two nebular lines of [Ne vi, X 3346 and X 3426, are single and nearly monochromatic. Other nebular lines are double, with a separation of about 100 km/sec between the components. Radial velocities of the system given by the single [Ne vi lines, by means of the components of the double nebular lines, and by the stellar emission lines are, respectively, +70.8, +71.1, and +70.9 km/sec. When the stellar absorption lines are grouped according to total excitation requirements, it is found that those of highest excitation (N iv) give approximately the velocity of the system. Lines of lower ex- citation show progressively larger displacements toward the violet. The lines of lowest excitation (H) yield a velocity of +45 km/sec. These results indicate a variation of outward velocity with depth in the atmosphere of the nuclear star such that the N iv lines are formed at the greatest depth, those of H at the least depth. The single nebular lines of [Ne v} are unexplained. A slitless spectrogram indicates that these lines, as well as the double lines of [Ne m}, [011], etc., are all formed in the inner nebular ring. Some of the obvious problems raised by these observations are mentioned Title: The Nuclear and Nebular Spectra of the Planetary Nebula NGC 2392 Authors: Wilson, Olin C. Bibcode: 1948PASP...60..247W Altcode: No abstract at ADS Title: A Preliminary Lower Limit to the Ratio C12/C13 in Interstellar Matter Authors: Wilson, O. C. Bibcode: 1948PASP...60..198W Altcode: No abstract at ADS Title: The Structure of the Atmosphere of the K-Type Component of Zeta Aurigae. Authors: Wilson, O. C. Bibcode: 1948ApJ...107..126W Altcode: This investigation is based upon spectrograms of 10.4 A/mm dispersion obtained during the 1939- 1940 eclipse. * Curves of growth were constructed for four atmospheric levels observed during ingress and for three during egress. Relative gf-values for Fe I lines were taken from the laboratory data of King and King. For other elements the relative gf's were calculated from the measures of lines in the solar-flash spectrum made by H. H. Lane. Doppler widths, L~XD, of the theoretical curves of growth which best fit the observations, range from 0.08 A for a height above the limb of 0.8 X 106 km to 0.16 A for a height of 20.6 X 1O°km, with cor- responding turbulent velocities of 6.5 and 13.0 km/sec, respectively. It appears, therefore, that the turbu- lence increases with height in theatmosphere. Excitation temperatures determined by comparison of the populations of the a~F and a3F states of Fe i with that of the ground state, a5D, also increase with height. Mean values range from 37800 at h = 0.8 X 106 km to 5660° at Ii = 13.5)< 10~ km. Density gradients in the atmosphere are readily evaluated by means of the curves of growth. For all atomic and ionic states included in this investigation the gradients are steepest at the lowest levels and tend to become less steep with increasing height. Moreover, except for Ca i in the lowest level, all the density gradients are nearly the same. If the densities are expressed as a function of height by means of the formula n = noe~, the observations yield a mean value of a = 2.3 X 1012 cm'. The observed gradient is compared with those calculated on the assumption of hydrostatic equilibrium. The latter hypothesis leads to gradients of the order of twenty times larger than observed for H to one thousand times larger for Fe and elements of similar atomic weight. McCrea's theory of turbulent support is also investigated. If the turbulent velocities obtained from the curves of growth are used in McCrea's equa- tion, the resulting gradient is still about ten times too large. It cannot be decided at the present time whether this discrepancy is real or due to an accumulation of errors in the data. The ionization in the atmosphere of the K-type component is investigated, chiefly at heights of 7 X 10~ km and 14 X 1O~ km, for which the data appear most reliable. Thermodynamic equilibrium is first assumed; the combination of the Boltzmann and Saha equations for H, together with the standard ionization equation for Ca, then permit an evaluation of the temperature, T. The latter is found to be nearly the same as that of the K-type star itself, and the electron density at height 7 X 10~ km is 1O~ per cm3, on the assumption that hydrogen supplies effectively all the electrons. It is next assumed that the ionization of Ca is governed by the dilute radiation of the B-type star and Pannekoek's equation is applied. It is shown that the observed ionization of Ca requires a higher electron density than appears to be available for H, and hence it is unlikely that the B-type star is responsible for the ionization of Ca and atoms of similar I.P. This conclusion leads to an investigation of the opacity of the atmosphere of the K-type star as a function of wave length. Menzel's opacity formula is shown to provide ample opacity at X «= 2000 A to screen most of the atmosphere from the ionizing radiation of the companion, while still insuring transparency in the regions ordinarily observed. On the basis of the same equation it is suggested that the eclipses may begin appreciably earlier in the ultraviolet than in the ordinary photo- graphic region. A tentative explanation of the rise of excitation temperature with height is based upon the metastability of the atomic states concerned and the variation of atmospheric opacity with height and wave length. INTRODUCTIO Title: No. 749. The nuclear and nebular spectra of the planetary nebula NGC 2392. Authors: Wilson, O. C. Bibcode: 1948CMWCI.749....1W Altcode: 1948QB4.M93n749.... No abstract at ADS Title: No. 742. The structure of the atmosphereof the K-type component of Zeta Aurigae. Authors: Wilson, O. C. Bibcode: 1948CMWCI.742....1W Altcode: 1948QB4.M93n742.... No abstract at ADS Title: Components of Interstellar Sodium Lines Authors: Merrill, Paul W.; Wilson, O. C. Bibcode: 1947PASP...59..132M Altcode: No abstract at ADS Title: Spectrum of the Planetary Nebula NGC 3242 Authors: Wilson, O. C. Bibcode: 1946PASP...58..210W Altcode: No abstract at ADS Title: Absolute Dimensions of a Wolf-Rayet Star and the Expanding-Envelope Hypothesis. Authors: Wilson, O. C. Bibcode: 1942ApJ....95..402W Altcode: Measures of the equivalent width of the Hy absorption line of the B-type component of RD 193576 have been made during and outside of eclipse. These data, combined with a preliminary unpublished light-curve by G. E. Kron and the spectrographic orbit by the writer, permit the derivation of the abso- lute dimensions of the system with fair accuracy. It is found that the Woif-Rayet star is the larger and brighter of the pair, although it has the smaller mass, and Gaposchkin has shown it to have the smaller surface brightness. The hypothesis that the Woif-Rayet emission bands are formed in an expanding envelope surrounding the star is discussed critically. Arguments based upon observations, although not decisive, tend to throw doubt on the validity of the hypothesis. The binary character of HD 193576 offers a means of deciding whether or not the emission bands of the Woif-Rayet component are produced in an expanding envelope. In view of the facts that the band width corresponds to an ejection velocity of 2000 km/sec and that the character of the Woif-Rayet spectrum is not seriously modified by the presence of the companion, it is assumed that the ejected particles follow linear trajectories. As a consequence of this assumption, the radial velocity measured by the displacement of the emission band must differ from the true radial velocity of the star. The chief consequence of this transit-time effect is a difference between the observed times of eclipse and the times predicted by the spectrographic orbit. Formulae are derived from the transit-time effect and computa- tions of its magnitude are made for three velocity distributions and for a variety of inner and outer radii of the envelope, with the aid of the absolute dimensions of the system derived in section I. Similar com- putations are made of the magnitude of the violet shift of the bands due to occultation. The existing observations limit the difference between the observed and the computed times of eclipse to O.O1P, which requires that the supposed envelope be so small as to lead to violet shifts of some hundreds of km/sec. Since such shifts are not observed, it is concluded that the emission bands are probably not formed in an expanding envelope. The measured intensities of the X 4686 band of He ix are investigated as a function of phase. The intensity is very nearly the same at phases 0.25, 0.50, and 0.75, but the band is about 19 per cent weaker at primary minimum. Perhaps there is a "reflection effect," which causes the Woif-Rayet star to radiate more strongly in the X 4686 band from the hemisphere facing the companion. A few tentative remarks are made concerning possible alternatives to the expanding-envelope hy- pothesis, although no satisfactory solution is found. A zone of turbulence might be invoked to account for the great widths of the emission bands. This explanation, however, leads to difficulties with the dis- placed absorption components sometimes observed in Woif-Rayet spectra. Moreover, it leaves unex- plained the red shift of the bands in HD 193576 and their periodic changes in shape Title: No. 660. Absolute dimensions of a Wolf-Rayet star and the expanding-envelope hypothesis. Authors: Wilson, O. C. Bibcode: 1942CMWCI.660....1W Altcode: 1942QB4.M93n660.... No abstract at ADS Title: Three Wolf-Rayet Spectroscopic Binaries Authors: Wilson, O. C. Bibcode: 1941PASP...53..295W Altcode: No abstract at ADS Title: Some Results from the 1939-40 Eclipse of ζ Aurigae Authors: Wilson, O. C. Bibcode: 1941PASP...53..228W Altcode: No abstract at ADS Title: Narrow Lines in the Spectrum of γ Cassiopeiae Authors: Merrill, Paul W.; Wilson, O. C. Bibcode: 1941PASP...53..125M Altcode: No abstract at ADS Title: On the Determination of Mass Ratios of Spectroscopic Binaries. Authors: Wilson, O. C. Bibcode: 1941ApJ....93...29W Altcode: A method is described which permits the determination of the mass ratio and systemic velocity of a double-lined spectroscopic binary from much less observational material than that required for a com- plete orbit determination Title: Narrow lines in the spectrum of gamma Cassiopeiae. Authors: Merrill, P. W.; Wilson, O. C. Bibcode: 1941PASP...53R.125M Altcode: No abstract at ADS Title: No. 640. On the determination of mass ratios of spectroscopic binaries. Authors: Wilson, O. C. Bibcode: 1941CMWCI.640....1W Altcode: 1941QB4.M93n640.... No abstract at ADS Title: A Wolf-Rayet Visual Binary Authors: Wilson, O. C. Bibcode: 1940PASP...52..404W Altcode: No abstract at ADS Title: Physical Characteristics of the Wolf-Rayet Stars. Authors: Wilson, O. C. Bibcode: 1940ApJ....91..394W Altcode: The red shift of the emission bands of the Woif-Rayet component of HD 193576, noted in the preceding Con1ri&ut~on, suggests that similar displacements may be a com- mon feature of Woif-Rayet spectra. Examination of the wave lengths derived by Beals from measures of a number of Woif-Rayet stars lends strong support to this view, at least for stars of the nitrogen sequence. A discussion of the possible origins of such a shift leads to the conclusion that only two of them are at all likely. One of these possi- bilities, namely, that the red shift is due to a weakening of the violet sides of the bands by absorption of the light of the central star in the expanding envelope, does not require any modification of the current view as to the nature of a Woif-Rayet star. The other possible interpretation is that the observed displacements represent a gravitational red shift. If the latter is correct, the radii of the gaseous envelopes in which the emission bands arise cannot exceed approximately one-tenth that of the sun, and the nuclei themselves must be considerably smaller and extremely dense. Some elementary com- putations of the physical conditions in these small gaseous envelopes do not lead to any inherent impossibilities. The one grave objection appears to lie in the extraordinarily high surface temperatures demanded of the nuclei in order to produce the observed continuous spectra. In fact, it is suggested that, if the gravitational interpretation is adopted, the continuous spectra cannot be the black-body radiations of the nuclei at all but must be fluorescent spectra arising in the inner portions of the gaseous envelopes. The data available at present are insufficient to decide between the two possible interpretations of the red shift. It may only be said that the absorption explanation does not receive much support, since visual inspection of spectrograms indicates that absorption components on the violet edges of He u bands are quite rare. Probably careful photometric investigation of the contours of emission bands in Woif-Rayet spectra wifi, in the future, decide the question Title: The Wolf-Rayet Spectroscopic Binary HD 193576. Authors: Wilson, O. C. Bibcode: 1940ApJ....91..379W Altcode: Spectrographic orbits have been derived for the double-lined binary HP 193576. The Woff-Rayet component is of type WN5, while that of the absorption-line com- ponent is somewhat uncertainly estimated as Bi. The minimum masses of the Wolf- Rayet and B-type components are 9.740 and 24.80, respectively. A curious feature of the results is that the y-axes for the two stars differ by 90 km/sec, the two values being +56 and -34 km/sec, respectively, for the Woif-Rayet and the B components. Neither erroneous wave lengths nor blends seem to afford an explanation of this difference. Since a velocity for the system of -~4 km/sec is much more in keeping with the velocities of other early-type stars in the vicinity of HD 193576 than is one of +56 km/sec, it is probable that the emission bands of the Woif-Rayet star are shifted toward the red by an amount equal to the difference between the y-axes. The nature of the red shift is discussed in the following Contribution. The significance of certain rather minor periodic variations in the He Ii 4686 band is discussed. In particular, no evidence for an eclipse is found in the spectrographic ma- terial, and, therefore, no est mate of the inclination of the orbit plane is possible. The absolute magnitude of the system has been previously derived from the intensi- ties of the interstellar H and K lines. It is found necessary to assume the stars to be 1-2 mag. brighter in order to bring the density of the B-type component into line with the known densities of other massive stars of early type. When this is done, the density of the Woif-Rayet star is found to be of the same order as that of the sun, if it has a surface temperature of 8o,ooo°. Also, the Woif-Rayet star appears to be about 4 mag. brighter than would be estimated from its mass on the basis of the empirical mass-luminosity relation Title: Relative Populations of 2^{1}S and 2^{3}S States of Helium in the Orion Nebula. Authors: Wilson, O. C. Bibcode: 1940ApJ....91..360W Altcode: The observed equivalent width of X 3889 of He i produced by the Orion nebula, together with the absence of X 3965, leads to a lower limit for the ratio of populations of the 2~S and 2'S states of N3/Ni »= 25. This is considerably in excess of the values calculated by Struve and Wurm on the assumption of strict metastabifity for both levels, and thus points toward a shorter mean life for 2'S than for 2~S. The matter may be complicated, however, by the selective absorption by the nebula of the light from the Trapezium stars Title: No. 623. The Wolf-Rayet spectroscopic binary HD 193576. Authors: Wilson, O. C. Bibcode: 1940CMWCI.623....1W Altcode: No abstract at ADS Title: No. 625. Relative populations of 21S and 23S states of Helium in the Orion Nebula. Authors: Wilson, O. C. Bibcode: 1940CMWCI.625....1W Altcode: No abstract at ADS Title: The Wolf-Rayet spectroscopic binary HD 193576. Authors: Wilson, Olin Chaddock Bibcode: 1940wrsb.book.....W Altcode: 1940QB4.M93........ No abstract at ADS Title: No. 624. Physical characteristics of the Wolf-Rayet stars. Authors: Wilson, O. C. Bibcode: 1940CMWCI.624....1W Altcode: No abstract at ADS Title: Possible Applications of Supernovae to the Study of the Nebular Red Shifts. Authors: Wilson, O. C. Bibcode: 1939ApJ....90..634W Altcode: No abstract at ADS Title: Intercomparison of Doublet Ratio and Line Intensity for Interstellar Sodium and Calcium. Authors: Wilson, O. C. Bibcode: 1939ApJ....90..244W Altcode: No abstract at ADS Title: On the Doublet Ratio of Interstellar H and K and the Absolute Magnitudes of Wolf-Rayet Stars. Authors: Sanford, Roscoe F.; Wilson, O. C. Bibcode: 1939ApJ....90..235S Altcode: Observations-The total absorptions of the interstellar Ca ii lines, H and K, have been measured in 400 and B stars with weak H and in i8 Woif-Rayet stars (Table i). The difficulty so often encountered in measuring the total absorption of H in the pres- ence of strong He in absorption has therefore been largely obviated, and it is hoped that these measures are an improvement upon earlier ones. Ratio of K to H-K/H appears to be approximately 2 for very weak lines and to de- crease, on the average, as lines of greater strength are considered, reaching 1.56 for H 0.4 A, with little apparent tendency to diminish thereafter. See Figures i and 2. Ratios D2/K and Di/H.-Twenty-f our stars in Table i provide measures of the total absorptions of the interstellar D2 and Di of Na I. The mean D2/K and Di/H derived therefrom are 1.63 and 2.18, respectively, which closely check earlier results, i.6 and the tentative value 2.1, respectively. Absolute magnitudes of Woif-Rayet stars-The curve which relates distance with K- line intensity has been used to derive the distances of the i8 Woif-Rayet stars from which mean visual absolute magnitudes for 6 stars of the carbon sequence and 12 of the nitrogen sequence have been derived. They are -2.8 and -2.1, respectively. Masses of the Woif-Rayet stars-Plausible values of temperature, together with our derived absolute magnitudes and what appears to be a reasonable allowance for the contribution of bright bands to the apparent magnitudes, give masses approximately thirty times that of the sun. The assumptions and guesses involved make such values highly speculative, even though the mass-luminosity relation itself is unqualifiably ac- cepted Title: No. 613. On the doublet ratio of interstellar H and K and the absolute magnitudes of Wolf-Rayet stars. Authors: Sanford, Roscoe F.; Wilson, O. C. Bibcode: 1939CMWCI.613....1S Altcode: 1939QB4.M93n613.... No abstract at ADS Title: Velocities and intensities of absorption lines produced by helium in the Orion Nebula Authors: Wilson, O. C. Bibcode: 1939PAAS....9R.274W Altcode: No abstract at ADS Title: No. 614. Inter comparison of doublet ratio and line intensity for interstellar sodium and calcium. Authors: Wilson, O. C. Bibcode: 1939CMWCI.614....1W Altcode: 1939QB4.M93n614.... No abstract at ADS Title: Hɛ Emission in the Spectrum of Arcturus Authors: Wilson, O. C. Bibcode: 1938PASP...50..245W Altcode: No abstract at ADS Title: The Radial Velocities of 600 Stars and Measures of 69 Spectroscopic Binaries. Authors: Christie, William H.; Wilson, O. C. Bibcode: 1938ApJ....88...34C Altcode: The radial velocities of 600 stars observed with the 60- and 100-inch reflectors are given. This list is in no way homogeneous and contains stars from several observing lists made up for various investigations. In addition, measures are given for 69 variable-velocity stars, some of which have been observed elsewhere Title: Double Interstellar Sodium Lines Authors: Sanford, R. F.; Merrill, P. W.; Wilson, O. C. Bibcode: 1938PASP...50...58S Altcode: No abstract at ADS Title: No. 582. Unidentified interstellar lines in the yellow and red. Authors: Merrill, Paul W.; Wilson, O. C. Bibcode: 1938CMWCI.582....1M Altcode: No abstract at ADS Title: No. 593. The radial velocities of 600 stars and measures of 69 spectroscopic binaries. Authors: Christie, William H.; Wilson, O. C. Bibcode: 1938CMWCI.593....1C Altcode: 1938QB4.M93n593.... No abstract at ADS Title: Unidentified Interstellar Lines in the Yellow and Red Authors: Merrill, Paul W.; Wilson, O. C. Bibcode: 1938ApJ....87....9M Altcode: Six unidentified interstellar lines (Table i) are discussed. Following a brief history of previous observations, Tables 2 and 3 give widths and central absorptions of three of the lines. The total intensity of X 6284, which, in the mean, equals the average for the detached lines Di and D2, shows a somewhat stronger correlation with stellar color excess than does the intensity of the D lines. The widths of the unidentified lines, which are rather diffuse and not sharp like the D lines, and other facts make an atomic origin improbable. The lines may be portions of molecular bands, as yet unidentified. Several facts, however, suggest that the lines are produced by small solid particles, per- haps closely related to those that cause space reddening Title: Helium Absorption Due to the Orion Nebula Authors: Wilson, O. C. Bibcode: 1937PASP...49..338W Altcode: No abstract at ADS Title: Intensities and Displacements of Interstellar Lines Authors: Merrill, Paul W.; Sanford, Roscoe F.; Wilson, O. C.; Burwell, Cora G. Bibcode: 1937ApJ....86..274M Altcode: The main purpose of this ConirThution is to record measurements of the intensities and displacements of the interstellar lines Di, D2, H, and K in the spectra of numerous early-type stars. Intensities of the unidentified lines XX 5780, 5797, and 6284 are in- cluded. Observational methods and the technique of measurement are fully described, and the accuracy of the results is discussed. Comparison of the Mount Wilson values of the intensities of the D lines with those of Beals (Table 3, Fig. i) indicates a fairly small accidental error in both series but a con- siderable systematic difference between them. Displacements of the D lines measured at various observatories (Table 7) are in good agreement. The Catalogue, Table 6, includes 254 stars brighter than apparent magnitude 7.0, 147 fainter stars, and, in addition, 3 novae. The numbers of objects with the various kinds of data are as follows Title: Intensities of the Infrared Cα II Triplet in Stellar Spectra Authors: Wilson, O. C.; Merrill, Paul W. Bibcode: 1937ApJ....86..162W Altcode: The equivalent widths of the infrared Ca n triplet, XX 8498, 8542, and 8662, have been measured on spectrograms of the sun and of several stars taken with a grating spectrograph having a dispersion of 33 A/mm. The results for the solar lines agree well with those of other observers and are nearly proportional to t~he square roots of the theore~ica1muitip1et int~nsities. In the stars, however, particularly the late-type giants, there is a strong tendency for the three lines to be more nearly equal in strength. The cause of the variation in gradient is not clear, and more extensive observations will be of interest Title: Forbidden Iron Lines in the Spectrum of the Companion of α Scorpii Authors: Wilson, O. C.; Sanford, R. F. Bibcode: 1937PASP...49..221W Altcode: No abstract at ADS Title: Analysis of the Intensities of the Interstellar D Lines Authors: Wilson, O. C.; Merrill, Paul W. Bibcode: 1937ApJ....86...44W Altcode: Previous investigations of interstellar lines are briefly reviewed. The interstellar D-line intensities measured at Mount Wilson in the spectra of over 200 early-type stars are critically discussed with the object of deducing the distribution and motions of the sodium atoms in space. If the atoms are assumed to have no rela- tive motions other than those due to temperature, the D-line intensities should follow a normal curve of growth. This assumption is shown to be incorrect because (i) the curve derived from the measured intensities does not have the proper shape and (2) it leads to very improbable d~istances for the stars with strong lines as compared to those with weak lines. The introduction of galactic rotation gives a good representation of the mean de- crease of the doublet ratio D2/DI from 2.0 to 1.2 with increasing intensity. A more de- tailed examination proves conclusively, however, that the rotational velocity gradient cannot be responsible for the widths of the lines because, for a given distance, the line intensities an~I the doublet ratio are essentially the same for all galactic longitudes. The observations can be accounted for by making the hypothesis that interstellar sodium occurs in discrete aggregations or clouds, which, while participating in the gen- eral galactic rotation, have in addition considerable random motions. This assumption requires no dependence upon t~ie galactic longitude and succeeds in explaining how the D lines can strengthen almost linearly with the distance, while the ratio of D 2 to Di is only 1.2. By fitting computed curves to the observational data, the following numerical results are obtained: an upper limit to the temperature is 44,000°; the density of sodium atoms in the ground state is approximately io-3' gm/cc; the linear dimensions of the clouds, in the galactic plane, are of the order of 700 parsecs; and the spread of the ran- dom cloud velocities need not exceed 15 or 20 km/sec Title: The System of β Capricorni Authors: Adams, W. S.; Sanford, R. F.; Wilson, O. C. Bibcode: 1937PASP...49...25A Altcode: No abstract at ADS Title: No. 575. Intensities of the infrared CaII triplet in stellar spectra. Authors: Wilson, O. C.; Merrill, Paul W. Bibcode: 1937CMWCI.575....1W Altcode: 1937QB4.M93n575.... No abstract at ADS Title: No. 570. Analysis of the intensities of the interstellar D-lines. Authors: Wilson, O. C.; Merrill, Paul W. Bibcode: 1937CMWCI.570....1W Altcode: 1937QB4.M93n570.... No abstract at ADS Title: No. 576. Intensities and displacements of interstellar lines. Authors: Merrill, Paul W.; Sanford, Roscoe F.; Wilson, O. C.; Burwell, Cora G. Bibcode: 1937CMWCI.576....1M Altcode: 1937QB4.M93n576.... No abstract at ADS Title: The Blending of H and Hɛ in the Spectrum of α Lyrae Authors: Wilson, O. C.; Thackeray, A. D. Bibcode: 1936PASP...48..329W Altcode: No abstract at ADS Title: Radial Velocity Curves of Nova Lacertae 1936 Authors: Adams, W. S.; Sanford, R. F.; Wilson, O. C. Bibcode: 1936PASP...48..325A Altcode: No abstract at ADS Title: Variations in the Spectrum of P Cygni Authors: Wilson, O. C. Bibcode: 1936ApJ....84..296W Altcode: An examination of spectrograms of P Cygni taken at the Lick and Mount Wilson observatories has shown that the Balmer lines in this star consist of an emission com- ponent and two absorption components, instead of one, as formerly supposed. These two absorption components vary in intensity (and probably in position) in such a way that on some occasions both are visible, while on others only one or the other is to be seen. No period for the variation can be deduced from the available material, but it is demonstrated that significant changes have occasionally occurred within intervals of the order of one month. The helium lines also appear to pass through a similar cycle in step with those of hydrogen Title: Note on the Absolute Magnitudes at Maximum of Nova Aquilae 1918 and Nova Cygni 1920 Authors: Wilson, O. C. Bibcode: 1936PASP...48..229W Altcode: No abstract at ADS Title: Distance of Nova Lacertae 1936 Derived from the Intensities of Interstellar Lines Authors: Merrill, P. W.; Wilson, O. C. Bibcode: 1936PASP...48..230M Altcode: No abstract at ADS Title: Contour or profile? Authors: Wilson, O. C.; Williams, E. G. Bibcode: 1936Obs....59...49W Altcode: No abstract at ADS Title: Intensities of interstellar lines Authors: Merrill, P. W.; Wilson, O. C. Bibcode: 1936PAAS....8R.249M Altcode: No abstract at ADS Title: No. 550. Variations in the spectrum of P Cygni. Authors: Wilson, O. C. Bibcode: 1936CMWCI.550....1W Altcode: 1936QB4.M93n550.... No abstract at ADS Title: Note on the recent eclipse of ζ Auriage Authors: Christie, W. H.; Wilson, Olin C. Bibcode: 1935AN....257..183C Altcode: No abstract at ADS Title: Absorption Lines due to an Expanding Star Authors: Wilson, O. C. Bibcode: 1935ApJ....82..233W Altcode: The modification of the shape of an absorption line produced by an expansion or con- traction of a star is investigated. It is shown that Carroll's approximation is valid only for small velocities and that for large velocities important changes in the shape and strength of a line occur. Applications to giant stars and Cepheid variables are discussed briefly and to Woif-Rayet stars and novae with more detail. A method is indicated by which, if the geometrical explanation of certain features in the spectrum of Nova Her- culis is considered valid, the linear dimensions of the star may be computed. A pre- liminary calculation gives for the radius of the photosphere of Nova Herculis in its earlier stages a value of the order of iooX 106 km Title: Radial velocities from absorption lines in the spectrum of Nova Herculis. Authors: Adams, W. S.; Christie, W. H.; Joy, A. H.; Sanford, R. F.; Wilson, O. C. Bibcode: 1935PASP...47..205A Altcode: No abstract at ADS Title: ζ Aurigae: the Structure of a Stellar Atmosphere Authors: Christie, William H.; Wilson, O. C. Bibcode: 1935ApJ....81..426C Altcode: From the measures of spectrograms of ~ Aurigae taken during the 1934 eclipse a ~iumber of new and interesting results have been obtained. By combining the measures of the light of the star made at Mount Wilson and Madi- son with the spectroscopic elements derived by Harper and by the authors, new ele- ments for the system have been obtained. A method has been devised whereby the effects of the light of the K star in the corn- posite spectrum of the two bodies may be eliminated from measures of microphotometer tracings of the spectra. This possibility has enabled us to measure the total absorption of the continuous spectrum of the B star produced by the various elements in the atmos- phere of the K star. From a number of microphotometer tracings made from the most suitable plates, the claanges in the total absorption have been measured for nearly a hundred lines in the spectra. These measures have been used to determine the effect of the B star shining through the atmosphere of the K star alone, thus affording means of obtaining the rela- tive numbers of atoms of the various elements existing at different levels above the photosphere of the K star. These results are grouped into six distinct classes: neutral metals; Mg; Ti~ (two groups); H; Cat Comparison of these results with theory reveals that there is, in most cases, no ade- quate hypothesis to account for the observed distribution. The measures of the bydro- gen lines indicate that the hydrogen shell surrounding the star is of uniform density Title: Cyanogen Absorption in the Spectrum of Nova Herculis, 1934 Authors: Wilson, O. C.; Merrill, P. W. Bibcode: 1935PASP...47...53W Altcode: No abstract at ADS Title: No. 519. &Zeta Aurigae: The structure of a stellar atmosphere. Authors: Christie, William H.; Wilson, O. C. Bibcode: 1935CMWCI.519....1C Altcode: 1935QB4.M93n519.... No abstract at ADS Title: Spectrophotometry of RS Ophiuchi (nova Ophiuchi no. Authors: Wilson, O. C.; Williams, E. G. Bibcode: 1934ApJ....80..344W Altcode: From one good plate taken with the three-prism violet spectrograph on August 30, 1933, the apparent color temperature of RS Ophiuchi is found to be 4000° K. Contours of the hydrogen emission bandshave been determined from several plates covering the period August i6-September ii, ~ On the assumption that the red sides of the bands present the true unmodified shapes, the following facts emerge: a) The contours are roughly exponential in form. The earlier ones can be represented approximately by the formula 1= e-(u/u~, where n-~ r+k(uo/u)-k and k =0.125. The value u0 decreases rapidly with time at first, then more slowly, ftnally attaining a more or less constant value; k also decreases and may be considered to vanish for the later contours. b) In addition to a sharp absorption component present on the short-wave-length sides of the band maxima in the early stages, there appears to be a general deficiency of intensity over the violet halves of the bands relative to that of the red halves. The sup- position that this is due to the complete suppression of the continuous spectrum under the violet sides is not in entire agreement with the facts, but there may be complicating factors. This hypothesis would require a large velocity range among the atoms directly in front of the star, and leaves no room for the monochromatic hydrogen absorption components or for the sharp nebular lines. It is suggested that the latter arise in a quies- cent shell around the star left over from its previous outburst. The Balmer decrement has been obtained from two accordant plates, and is found to be appreciably faster than the mean of those found by Plaskett and by Berman for planetary and diffuse nebulae. The observed decrement is brought into good agreement with the latter by applying the differential factors necessary to reduce a true tempera- ture of 35,0000 to an apparent one of 40000. From several spectrograms it appears that the ratio of the area of Hy to the intensity in the underlying continuous spectrum did not vary greatly between August i6 and September 2, 1933. Zanstra's method gives a photo-electric temperature of 35,000°, calculated from the measures on plate V4o4, August i8. If this is a real measure of the temperature, it fol- lows from the preceding paragraph that, while the star decreased in brightness by about two magnitudes from August i6 to September 2, its temperature remained constant. This conclusion would imply that the fading of the star was due to a shrinkage in the radiating surface. From the measured intensity of the K line, with an approximate allowance for a probable stellar blend, a distance of 95o parsecs is deduced. This is shown to be fairly consistent with the recent results of Stebbins and Huffer on the assumption that the difference between the photo-electric and apparent temperatures is due to space redden- ing Title: The Analysis of Nova Emission Bands Authors: Wilson, O. C. Bibcode: 1934ApJ....80..259W Altcode: It is assumed, following Gerasimovi~ and Chandrasekhar, that nova emission bands originate in spherical expanding gaseous envelopes having internal velocity gradients; also that the matter in the envelope is transparent to its own radiation and that Chandrasekhar's occultation effect may be neglected. A method is then developed by which the velocity gradient can easily be found from the observed band shapes; all that is required is a simple integration. The analysis is applied to the hydrogen emission contours recently measured in the spectrum of RS Ophiuchi Title: Comparison of the Paschen and the Balmer Series of Hydrogen Lines in Stellar Spectra Authors: Merrill, Paul W.; Wilson, Olin C. Bibcode: 1934ApJ....80...19M Altcode: Introduction-The structure of the hydrogen spectrum and previous observations of the Paschen series are briefly described. The behavior of the Paschen lines m= 12 to m = 24, recently photographed at Mount Wilson in various types of stellar spectra, resembles in general that of the Bahner lines in the same types. The Paschen series is very conspicuous in the c stars $ Orionis and a Cygni. Photometric data-Measurements of structure and intensity have been made by the usual photometric methods on numerous lines in both hydrogen series in the spectra of a Leonis B8n, a Lyrae Ao, a Canis Majoris Ao, j3 Orionis cB8, and a Cygni cA2. Structure of lines-Most lines not affected by the overlapping of neighboring lines have contours of the simple exponential form, although in a Leonis the centers are flattened. In the broad-line stars a Leonis and a Lyrae considerable departure from the exponential form is exhibited by the wings of lines near the heads of the series. In ~3 On- onis, a Cygni, a Leonis, and in the emission-line stars `y Cassiopeiae and P Cygni the shapes of Balmer and Paschen lines are similar, with the dimensions proportional to wave-length; but this is not true of a Lyrae, in whose spectrum the Balmer lines have relatively more intense wings. Central intensities-Measured values for numerous lines are given in Table VI. In general the central intensities of Paschen lines are less than those of the corresponding Balmer lines. In a Leonis the Paschen series is relatively intense and has a slow decre- ment. In j3 Orionis and a Cygni both series exhibit slow decrements and little overlap- ping. Problem of overlapping lines-The shapes as well as the central intensities of many lines, particularly in the Balmer series, are probably seriously modified by the over- lapping wings of adjacent lines. The problem is to find the shapes and intensities of the "true" or original lines which by their mutual interaction produce the observed curve. A physically reasonable sequence of lines has been found which yields close ap- proximations to the observed shapes and intensities in a Lyrae but gives too great a reduction of the general intensity of the whole spectrum toward the head of the series. This difficulty, which appears to be of a rather general nature, is briefly discussed. Total line absorption-Measured values for lines of both series in a Cygni, /3 Orionis, and a Leonis are given in Table VII. From these data Unsold's equation gives the num- bers of atoms in the second and third levels. The numbers computed for a given level from various lines differ systematically, indicating that the theory is incomplete. The maximum numbers, used in Boltzmann's equation for thermal equilibrium, give reason- able values of the temperature of the absorbing hydrogen. Intensities of emission lines-Several bright lines in both series were measured in y Cassiopeiae and P Cygni. The relative importance of induced and spontaneous emis- sion is discussed. The photospheric temperatures computed from the intensities of pairs of lines having a common upper level depend on the assumed distribution of the atoms with respect to azimuthal quantum number. An assumed distribution corresponding to thermal equilibrium leads to reasonable temperatures for both stars. The possibility of determining the amount of space absorption by comparison with other data is pointed out. * Contributions from the Mount Wilson Observatory, Carnegie Institution of Washing- ton, No. 494 Title: No. 501. Spectrophotometry of RS Ophiuchi (Nova Ophiuchi No. 3). Authors: Wilson, O. C.; Williams, E. G. Bibcode: 1934CMWCI.501....1W Altcode: 1934QB4.M93n501.... No abstract at ADS Title: Comparison of the Balmer and Paschen series of hydrogen in stellar spectra Authors: Wilson, Olin Chaddock, Jr. Bibcode: 1934PhDT........16W Altcode: No abstract at ADS Title: Comparison of the Balmer and Paschen Series of Hydrogen in Stellar Spectra. Authors: Wilson, Olin C. Bibcode: 1934PhDT.........7W Altcode: No abstract at ADS Title: No. 494. Comparison of the Paschen and the Balmer series of hydrogen lines in stellar spectra. Authors: Merrill, Paul W.; Wilson, Olin C., Jr. Bibcode: 1934CMWCI.494....1M Altcode: 1934QB4.M93n494.... No abstract at ADS Title: No. 500. The analysis of nova emission bands. Authors: Wilson, O. C. Bibcode: 1934CMWCI.500....1W Altcode: 1934QB4.M93n500.... No abstract at ADS Title: Contours of Absorption Lines in Nova Aquilae 1918 before Maximum Authors: Wilson, O. C. Bibcode: 1932PASP...44..388W Altcode: No abstract at ADS Title: An Application of the Radiometer: a Registering Microphotometer Authors: Smith, Sinclair; Wilson, Olin C., Jr. Bibcode: 1932ApJ....76..117S Altcode: A registering microphotometer is described in which a radiometer is used as the light- sensitive element. The instrument has been made as simple as possible without sacrifice of performance, and tests seem to show that it is both fast and precise, besides being very easy to operate. The details of construction are discussed and some typical records are reproduced Title: The Velocity of Light Authors: Wilson, Olin C. Bibcode: 1932Natur.130...25W Altcode: IN NATURE for April 4, 1931, M. E. J. Gheury de Bray points out that the determinations of the velocity of light made in this century seem to tend towards smaller and smaller values the more recent the time of observation. Title: Three New Be Stars Authors: Wilson, Olin C., Jr. Bibcode: 1932PASP...44..124W Altcode: No abstract at ADS Title: No. 454. An application of the radiometer: A registering microphotometer. Authors: Smith, Sinclair; Wilson, Olin. C., Jr. Bibcode: 1932CMWCI.454....1S Altcode: 1932QB4.M93n454.... No abstract at ADS