Yerkes Observatory Research Articles

Planetary Atmospheres

The Atmospheres of the Earth and Planets Papers presented at the Fiftieth Anniversary Symposium of the Yerkes Observatory, September 1947. Edited by Gerard P. Kuiper. Pp. vii + 366 + 16 plates. (Chicago: University of Chicago Press; London: Cambridge University Press, 1949.). 60s net.

OH Emission Bands in the Spectrum of the Night Sky.

High-resolution spectra of the infrared night sky obtained at Yerkes Observatory have shown conclusively that the previously unidentified infrared emissions are due to the rotation-vibration spectrum of OH. The agreement between the vibrational spacing, the rotational constants, and the doublet structure of the emissions and the predicted OH structure is excellent. The observation of vibrational levels up to v = 9 shows that small inaccuracies exist in the currently accepted vibrational constants. A more accurate determination of these constants could be made, despite the low dispersion of the spectrograph. Other bands of this system of OH occur in the region of 1 j# and may account for the radiation detected by Stebbins, Whitford, and Swings, which has been attributed to N2.

On the Doppler broadening of Fraunhofer lines by turbulence and by multiple interstellar clouds.

On the Doppler broadening of Fraunhofer lines by turbulence and by multiple interstellar clouds.

The absolute magnitude of R Puppis.

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The absolute magnitude of R Puppis. Bidelman, William P. Abstract Three very luminous stars appear to be associated with the distant B star galactic cluster, NGC 2439; the brightest of these is the Go Ia star R Puppis. The others are an early B super- giant star spectroscopically intermediate between ~ Per and E CMa, CPD 3101785, and a red supergiant of type M2 la-Ib, CPD 3101790. The estimated spectroscopic visual absolute magnitude of the B-type star is about -5.2, which implies a visual absolute magnitude of -7.2 for R Puppis and of -5.6 for the M-type supergiant star. Though the main sequence of the cluster has not been observed, at least one fainter cluster member of intermediate luminosity at class B2 is consistent with these values. The three supergiant stars are not greatly different in bolometric magnitude. NGC 2439 is the only known case of the simultaneous presence of a B-, a G-, and an M-type supergiant star in a cluster containing predominantly stars of early type. Yerkes Observatory, WiWiams Bay, Wis. Publication: The Astronomical Journal Pub Date: 1950 DOI: 10.1086/106423 Bibcode: 1950AJ.....55Q.165B full text sources ADS | data products SIMBAD (5)

Some results on planets.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Some results on planets. Kuiper, Gerard P. Abstract Three topics are discussed: (I) Pluto, Triton, Titania and Oberon were photographed with low dispersion up to 88oo A. No methane or other absorptions were detected, though the test is much sharper than that made previously on pan- chromatic plates. Saturn and its rings were observed up to 12000A (on Z plates), but the spectrum stops near the first, rather weak, absorption band of snow so that nothing significant is added to previous results with the PbS cell. (2) In a systematic survey of planetary spectra a system of four or five new narrow bands was found near 7500 A in the spectra of Uranus and Neptune; they appear to be not due to CH4, C2H4, C2H6, CO, CO2, H20, 02, N2, N20, H28, NH1 and probably not to CH2. (3) The second satellite of Neptune was confirmed; its period is about two years, its semimajor axis 400", its orbital plane inclined 60 to the ecliptic, but its direction of motion as yet undetermined. Yerkes Observatory, Williams Bay, Wis. Publication: The Astronomical Journal Pub Date: September 1949 DOI: 10.1086/106258 Bibcode: 1949AJ.....54..191K full text sources ADS |

A THIRD FLARE OF L 726-8B

When the large proper motion of L 726-8 was first found, arrangements were made with the Yerkes Observatory to take parallax plates of it with the 40-inch telescope. It was hoped that the scale of the Yerkes plates would be sufficient to separate the two components completely, and therefore one of the parallax plates had an exposure of Selected Area 92 added to determine accurately the difference in magnitude between the components. Unfortunately, the low altitude of the star at Yerkes and the concomitant poor seeing render the image so blurred that the components are never clearly separated, although the image usually appears elongated. Through a stroke of good luck, the plate with the Selected Area shows the star in the process of one of its flares. Since the plate was taken for parallax measurements, it contains three images of the star ; the first shows the star at normal brightness, with the components fairly well separated ; the second shows it very much brighter, but completely blurred ; and the third shows it fainter than the second, though still brighter than normal. Measurement shows that the center of light of these last two images is shifted eastward by about 80 'i, indicating that the flare must be attributed to the fainter component. The difference in magnitude of the components was estimated to be 0.5 pv from three Yerkes plates where the images are almost separated. The magnitudes, mT, are given below, with the conclusions drawn from them concerning the total light of the system, LT ; the light of the fainter component, LB ; and the light of this component in units of its normal light.

Physics at the National Research Council, Canada : Dr. G. Herzberg

DR. GERHARD HERZBERG has been appointed directer, Division of Physics, National Research Council, Canada, in succession to Dr. R. W. Boyle, who retired in October 1948. Dr. Herzberg is a Canadian citizen who has been on the staff of the Division of Physics for some months as a principal research officer, having gone to this post from the Yerkes Observatory, University of Chicago, where he had been professor of spectroscopy for nearly three years. During the preceding ten years, he was research professor of physics at the University of Saskatchewan, Saskatoon, Sask. Before that, he had worked in Germany at Darmstadt and Gottingen, and in the University of Bristol. Dr. Herzberg is a leading authority on spectroscopy and molecular structure, and is the author of three standard textbooks and numerous scientific papers. At Saskatoon he established a spectroscopy laboratory for graduate research and thus greatly strengthened the graduate school in physics and chemistry. He and his co-workers made important contributions to interpretation of data on spectral lines of distant stars and of comets. These investigations led up to his work at the Yerkes Observatory, where he built the world‘s longest multiple optical path (5,000 m. at atmospheric pressure) for the study of planetary atmospheres and to gain information on molecular structure. Using this equipment, he carried out important work on the infra-red absorption spectra of hydrogen, which has made it possible to detect hydrogen in planetary atmospheres. Dr. Herzberg will continue his varied researches in his new post.

Polarization of Radiation from Distant Stars by the Interstellar Medium

PHOTOMETRIC observations for the detection of partially polarized radiation from eclipsing binary stars have been in progress at Yerkes Observatory, of the University of Chicago, for several years with the view of establishing observationally the effect pointed out by Chandrasekhar that the continuous radiation of early-type stars should be polarized1,2. On the assumption that the opacity of early-type stars is due to scattering by electrons, the continuous radiation emerging from a star should be polarized with a maximum of polarization of 11 per cent at the limb. Since the presence of this polarization can be detected only when the early-type star is partially eclipsed by a larger late-type companion of the system, the effect is masked by radiation from this companion, so that the expected maximum observable effect is only of the order of 1·2 per cent in the one case investigated (RY Persei).

The astrometric orbit of Procyon.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The astrometric orbit of Procyon. Strand, K. Aa. Abstract From a series of 105 plates taken with the ~o-inch Yerkes refractor between 1916 and 1949 and a series of 85 plates taken with the ~6-inch McCormick refractor between 1915 and 1942 the astrometric orbit of the brighter component of Procyon and its parallax have been derived. Since the photographic material does not cover the entire period of 40.3 years the micrometer measures made by Aitken and Barnard between 1897 and 1913 were used in establishing the period. The photographic material gives the relative parallax "293 ~ `1006 (p.e.) in close agreement with the value given by Schlesinger's catalogue, and the value I `1194 ~ `1010 for the semi-major axis of the astrometric orbit. Utilizing the series of relative distances between the components observed by Barnard and Aitken the semi-major axis is 4'1520. The adopted value `1295 for the absolute parallax gives the masses 1.630 and .590 for the visual components. The mass for the brighter component is of the expected order of value for an F~ IV star with a bolometric magnitude 2.73. For an independent check on the derived orbital motion and the parallax a series of 17 spectrograms taken at the coude' focus of the 100-inch reflector between 1926 and 1946 have been measured but as yet not fully reduced. Dearborn Observatory, Evanston, Ill. Publication: The Astronomical Journal Pub Date: September 1949 DOI: 10.1086/106262 Bibcode: 1949AJ.....54..196S full text sources ADS | data products SIMBAD (1)

The H-R diagram and space distribution of the members of the Ursa Major cluster.

Introduction. In two papers on the Ursa Major cluster, published in 1939, Smart examined the claim to cluster membership of 136 stars. He concluded that 42 of these stars are definitely members of the cluster while the status of 52 was doubtful. The purpose of this investigation has been to obtain spectroscopic parallaxes of these stars and, combining these with the remaining data in Smart's papers, to reexamine the question of the membership of the cluster and to give a revised H-R diagram. A number of stars with small proper motions, for which the data are inconclusive, have been excluded by the limits on the position angle residual of 100 for definite members and 200 for probable members. The more accurate spectroscopic parallaxes have also excluded a few stars; the number has been reduced to 32 definite members and 12 probable members. There are probably also several members south of ~3o0 which have not been considered in this investigation. Space distribution. The cluster has a fairly compact nucleus containing I I stars within nine parsecs. The remaining stars are scattered up to a distance of 135 parsecs from this nucleus. The Coma and the Hyades clusters are included in the volume of space occupied by the Ursa Major cluster; Praesepe and the Pleiades are almost within it. In contrast to the Ursa Major cluster, the Coma cluster contains about 30 stars of similar absolute magnitude, Praesepe and the Hyades, about 75, and the Pleiades, several hundred members, each in a region less than eight parsecs across. H-i? Diagram. Nine of the nucleus stars give a smooth main sequence; the others include a metallic line star, a peculiar A star, and probably a Go subdwarf. The latter was discovered in an attempt to find the fainter members of the cluster in the vicinity of the nucleus from their proper motion, and has no radial velocity. The outlying members are also primarily main sequence stars with no stars in the cluster earlier than Ao. The cluster also probably contains an Mo giant, six late G giants, two early F giants, and four peculiar stars. Dynamical considerations. If the distribution of velocities near the sun were actually random, 575 of the stars in the Bright Star Catalogue within a hundred parsecs would have speeds within 4 km/sec of the cluster speed. However, only four of these would be moving within 100 of the direction of the cluster motion. A calculation of the effect of stellar encounters shows that a cluster star will probably change its kinetic energy with respect to the nucleus of the cluster by less than 20 per cent in 3 X IO~ years. This means that the life time of the cluster is of the same order as the galactic time scale. Yerkes Observatory, Williams Bay, Wis.

Spectrographic observations of the eclipsing binaries of the W Ursae Majoris type, AH Virginis and TZ Bootis.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectrographic observations of the eclipsing binaries of the W Ursae Majoris type, AH Virginis and TZ Bootis. Chang, Y. C. Abstract Over 30 spectrograms for each of these eclipsing binaries have been obtained at the McDonald Observatory with a dispersion of 76 A/mm at H~. The spectral lines of AH Vir break up into components at quadrature. The difference in intensity of the components is greatest at phase 0.75 P and is least at phase 0.25 P. Assuming a ~ircular orbit, it has been found from the velocity curve that ~ = QIo km/sec; Kb = 105 km/sec; = 250 km/sec. In many respects, the spectroscopic behavior of this binary bears close resemblance to YY Eri, another eclipsing variable of the W Ursae Majoris type. The mass-functions are mbSin3i = i.~~.and m~S~~3~ = 0.56. It appears to be fairly general that the mass ratio as given by Kb and Kf differs from unity by a greater amount than can be reconciled with the mass-luminosity relation. The spectral lines of TZ Boo do not become double at quadrature. There does not seem to be any correlation between the radial velocity and phase as calculated from the period of light variation. The mean velocity is - ~8 km/sec. Yerkes Observatory, Williams Bay, Wis. Publication: The Astronomical Journal Pub Date: February 1948 DOI: 10.1086/106066 Bibcode: 1948AJ.....53..111C full text sources ADS |

Spectral photometry of the dark lane of NGC 4594.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectral photometry of the dark lane of NGC 4594. van de Huist, H. C. Abstract NGC 4594 is a beautiful example of a spiral nebula seen nearly edgewise. Its major axis, of about 10', is in the east-west direction. It has a very bright nucleus and at 16" north of the center a dark lane is seen that has a width of about 8". The light in the minor axis can be traced on either side of the nucleus to about 90" from the center. The dark lane is probably caused by a well defined, flat ring of obscuring matter in the equator plane of the nebula. Photometry of the light in this dark lane at various wave lengths may therefore give information about the properties of the obscuring particles. The photometric problem is difficult, however, because the immediate neighborhood of the bright nucleus tends to introduce serious errors arising from imperfect guiding and from photographic effects, in particular Eberhard effect. Last April I took several spectrograms of this object with the Cassegrain spectrograph of the McDonald Observatory. The slit was a step slit placed along the minor axis. Its length was 20 mm = 148". The part covering the bright nucleus had a width of 0.30 mm, while the parts at either side that covered the faint outer parts of the nebula and the dark lane had a width of 2.55 mm. At the southern part, opposite the dark lane, there was an intermediate step, I .o6 mm wide. The spectrum, taken with the F/I Schmidt camera in 22' hours exposure time, shows the streaks due to the various steps and to the dark lane, all of them very nicely of measurable density. The further reduction follows the usual scheme; its preliminary results may be reported here. By making a microphotometer tracing across the spectrum at a certain wave length, then converting the densities into intensities and, finally, reducing the intensities to one slit width, the intensity curve along the minor axis of the nebula is found. This curve is of the same type as that found by Oort' from direct photographs. Its most striking property is that the northern and southern halves are, except for the dip due to the dark lane, exactly symmetrical. The depth of this dip is found to range from a factor 3 at 4000A to a factor 3.5 at ~oooA, in striking contrast with Oort's value of a factor 12. The latter difference may be due to Eberhard effect on the direct photographs. The further result that the light in the dark lane is slightly bluish would seem to indicate that this is light scattered by the dark clouds (mainly from the nucleus) and not light from the deeper layers coming through these clouds. I.M. N. io6, 159, 1946. Yerkes Observatory, Williams Bay, Wis,. Publication: The Astronomical Journal Pub Date: February 1948 DOI: 10.1086/106078 Bibcode: 1948AJ.....53..118V full text sources ADS |

The spectrum of gamma Pegasi.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The spectrum of gamma Pegasi. Underhill, Anne B. Abstract About 56 per cent of the 896 lines found from measurement of two coude' plates of ~ Pegasi covering the region ~3965 to X4935 have been identified. The results show generally that the spectrum of any element of reasonably high abundance on the earth may be found if its excitation potential is around 2~25 volts. The spectrum of K II has not been found in spite of favorable excitation conditions and high abundance on the earth. Further knowledge of the third and fourth spectra of the metals would aid greatly in the identification of many of the weak lines. A quantitative comparison between observed and predicted displacements of the He I lines by Stark effect shows that the observed displacements are smaller than theory predicts. The observations may be affected by stratification and by blending. Some [He IJ lines of the ~`P-m'P series are tentatively identified. A possible luminosity effect at X4026 between dwarf and intermediate B-type stars is explained in terms of the relative strengths of the [He IJ lines. Yerkes Observatory, Williams Bay, Wis Publication: The Astronomical Journal Pub Date: February 1948 DOI: 10.1086/106079 Bibcode: 1948AJ.....53..119U full text sources ADS |

Spectra of high-velocity giants.

view Abstract Citations (5) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectra of high-velocity giants. Keenan, P. O. ; Morgan, W. W. ; Münch, G. Abstract From a comparison of Yerkes, McDonald and Perkins spectrograms it is found that the characteristic differences between high-velocity giants (space motion > 75 km/sec) and the ordinary giants assigned to population I by Baade are: (I) In types G and K the bands of CN are definitely weaker in high-velocity stars than in ordinary stars of the same luminosity. The stronger metallic lines appear nearly normal in the high-velocity stars. The Balmer lines of H and the G-band (N4300) of CH are at least as strong as in ordinary stars and may be slightly strengthened in high-velocity stars. (2) Among the carbon stars (Type R) the high-velocity (?nes are marked by such tremendous strengthening of the G-band that they have been called CH-stars. The CN-bands appear on the average to be somewhat weaker than in ordinary carbon stars. The Balmer lines and N4554 of Ba+ are slightly strengthened. In both of these groups the peculiarities shown by the high-velocity stars are more pronounced in molecular features (CH, CN) than in atomic lines. The elements most affected are H, C, N and possibly 0 (because of the great influence of CO abundance upon the equilibrium concentration of CN). It is significant that these are among the abundant light elements the concentration of which appears to be a determining factor in the structure of a star. Twenty stars of types C and K having space motions estimated at more than 75 km/sec in Miczaika's catalogue were examined on the Yerkes spectrograms. Sixteen of them definitely showed the peculiarities, while, in the spectra of the remaining four, differences from normal stars could not be established with certainty. When revised spectroscopic absolute magnitudes were estimated from the new plates, however, the corresponding space velocities for these four stars were reduced to less than 75 km/sec, and their assignment to the high-velocity group was accordingly thrown into doubt. It is concluded that the appearance of the peculiarities to at least some degree is a quite general feature of the spectra of high-velocity stars. If the metallic lines are used in preference to the N42 15 band of CN, fairly reliable spectroscopic absolute magnitudes can be found for the high-velocity stars. For this purpose sp3ctro- grams of moderate dispersion appear most efficient. On the other hand, the fact that the peculiarities become more conspicuous on smallscale spectrograms suggests that objective-prism plates can be used to discover faint stars having the high-velocity characteristics. Perksns Observatory, Delaware, Ohio, and Yerkes Observatory, Wittianis Bay, Wis. Publication: The Astronomical Journal Pub Date: January 1948 DOI: 10.1086/106117 Bibcode: 1948AJ.....53Q.194K full text sources ADS |

The peculiar star, HD 30353.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The peculiar star, HD 30353. Bidelman, W. P. Abstract A discussion of the peculiar absorption-line spectrum of HD 30353 (m0 = 7.7) is presented on the basis of a spectrogram of dispersion 76 A/mm at H~ taken at the McDonald Observatory. This star appears to be an extremely luminous A-type supergiant, the spectrum of which is characterized by very strong lines of the ionized metals, comparatively weak Ca II lines, and extraordinarily weak hydrogen lines. A comparison with normal supergiants of luminosity class Ia on the Morgan, Keenan, Kellman system indicates that this star is probably of even higher luminosity than the A~ star, ~ Cas. The abnormal weakness of the hydrogen lines makes more appropriate, however, a comparison with two other stars showing this peculiarity, v Sgr and R CrB. It is shown that nearly all lines which appear in the spectrum of v Sgr, except those of hydrogen and helium, are greatly enhanced in the spectrum of HD 30353. It is considered possible that the helium lines at ~X4o26 and 4471 are also present in this star, although this cannot be definitely stated because of blending with strong lines of the ionized metals. The high luminosity which can be inferred from the spectrum of HD 30353 is confirmed to some extent by the radial velocity which has been determined from a single spectrogram. The velocity measured using eleven presumably unblended lines is -35 ~ 3 km/sec, which, if assumed to be entirely a consequence of galactic rotation, gives a minimum absolute visual magnitude, uncorrected for interstellar absorption, of about -5.5. Yerkes Observatory, Williams Bay, Wis. Publication: The Astronomical Journal Pub Date: 1948 DOI: 10.1086/106129 Bibcode: 1948AJ.....53R.110B full text sources ADS |

The determination of the parallax and mass-ratio of 99 Herculis.

For the determination of the empirical mass- luminosity relation, it is essential to establish accurate individual masses of the components of selected double star systems. Under a joint program between the Yerkes and Dearborn Observatories the orbital motions as well as parallaxes and mass-ratios of several double star systems are being determined. For 99 Herculis, 55 plates have been taken on 48 nights with the ~o-inch Yerkes refractor during the past thirty years. From these plates a parallax of `1066 ~ `1006 (p.e.) and the mass of the fainter component in terms of the total mass of .400 ~ .011 (p.e.) have been determined. These results agree closely with results obtained recently at the Sproul Observatory. If we combine the latest available data for this system we find that the brighter component of spectral class F8 has an absolute visual magnitude of 4.25 and a mass of .83 that of the sun. This indicates that the brighter component is less luminous and less massive than a star of the same spectral class belonging to the main sequence. For the fainter component no spectrum is available and while its luminosity is still somewhat uncertain its mass corresponds to a dK~ star. Dearborn Observatory, Evanston, Ill.

The Yerkes Observatory: Past, Present, and Future

The Yerkes Observatory: Past, Present, and Future

Total Solar Eclipse of May 20: Preliminary Reports

Contrary to all expectation, based on the usual weather conditions in May, the expeditions to the west coast of Africa to observe the total solar eclipse of May 20 were uniformly successful, whereas those to Brazil were upset by cloudy conditions. In Santiago in Chile, conditions were cloudy but observations were made from an aeroplane above the clouds. The corona was reported as of the minimum type with equatorial streamers and polar plumes—an unusual form so near sunspot maximum. At Araxá in Brazil, the Czechoslovak party and the Swedish party under Dr. Öhman were clouded out. At Bocayuva, the Finnish party was able to carry out its time observations for the geodetic programme. The party at the same place from the American Geographical Society, the Georgetown University, Washington, and the Yerkes Observatory reports only partial success owing to clouds. Dr. van Biesbroeck secured plates of the star-field around the sun for the Einstein effect, and photographs of the corona and of its spectrum; accurate time observations of the contacts were obtained. Photographs were taken from an A.A.F. B 17 plane flying at 30,000 ft.; also a programme of ionospheric observations was successfully carried through.

PHOTOGRAPHING THE CANALS OF MARS

Mars has generally been photographed through suitable color filters on fine-grain plates dyed to give maximum sensitivity in the spectral region transmitted. The plate holder usually permitted multiple exposures. C. O. Lampland, E. C. Slipher, and others at the Lowell Observatory, and E. E. Barnard at the Yerkes Observatory used a negative enlarger to magnify the telescope image several fold. W. H. Wright at the Lick Observatory used a microscope objective for the same purpose at the Crossley reflector and a similar arrangement was used by E. P. Hubble with the 100-inch at Mount Wilson. R. S. Trumpler and Η. Μ. Jeffers, however, photographed the image at the 36-inch refractor without enlargement. Focusing seems to have been accomplished largely by trial photographs of stars. To allow for changes due to temperature or mechanical displacements in the enlarging system used on the 36-inch refractor at the Lick Observatory, a deliberate variation of the focal position over a range of about 2 mm has been used to secure chance good focus. Table I shows some of the physical conditions that have obtained in photographing Mars. The diameter of the image on the plate was specifically stated by only two of the observers; the diameters in Table I were computed from the enlargement, focal length of the telescope, and an apparent diameter of 24 for Mars.

A WoIf-Rayet star of special interest.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A WoIf-Rayet star of special interest. Hiltner, W. A. Abstract The spectrographic orbit of the faint ~VolfRayet star (1945) ot = 22h07i~6, ~ = t57026' has been determined at the McDonald Observatory. The period of the system is 2.1 days and the semi-amplitude is 290 km/sec. The early type companion is probably responsible for the source of lines of the Balmer series of hydrogen in the ultraviolet. Yerkes Observatory, Williams Bay, Wis. Publication: The Astronomical Journal Pub Date: March 1947 DOI: 10.1086/105975 Bibcode: 1947AJ.....52..153H full text sources ADS |