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At least 271 records · Page 15

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NASA NTRS1972

C-4 155 nm line in beta Cephei

The class of early B variable stars known as beta Cephei stars are characterized by short-period radial velocity and light variations. The coolest stars of this group have an effective temperature of about 20,000 K and the hottest, about 28,000 K. These stars are not related to the classical Cepheids whose temperatures are of the order of 6000 K. The amplitude of the radial velocity variation beta Cephei stars is in the tens of kilometers per second and the light variation is less than 0.2 mag, that is, less than 10 percent. The fastest pulsation interval is 3 hr and the slowest is 6 hr. The prototype beta Cephei has a period of 4 hr 34 min. Ultraviolet observations were taken using OAO 2 to investigate the relationship between the visual and the ultraviolet variations.

Fischel, D.↗

NASA NTRS1972

The absolute magnitudes and spectral types of the stars in the gamma Velorum system.

The ratio of the visual luminosities of the O and WC components of the binary system gamma (2) Vel has been derived by comparison of the emission-line strengths in the spectrum with those in the spectrum of a single WC8 star, HD 192103. The result is 1.4 mag, with the O star being brighter; the classification of the O star was found to be 09 I, so that the classification of gamma (2) Vel is WC8+09 I.

Conti, P. S.↗

NASA NTRS1972

Search for a Venus halo effect during 1970.

Photometric observations of Venus during 1970 inferior conjunction, in contrast to observations made during the 1969 inferior conjunction, show no evidence of a Venus halo effect at 158 phase angle. The upper limit to brightening is about 0.005 mag but can still be reconciled with earlier results. Because of the importance of the question of H2O-ice in the Venus clouds, further observations are encouraged to remove the marginality of most observations to date.

Ward, D.↗

NASA NTRS1972

The physical properties of the Jovian atmosphere inferred from eclipses of the Galilean satellites. II - 1971 apparition.

Further simultaneous two-color photoelectric photometry of Ganymede was carried out at blue (4500 A) and yellow (5790 A) wavelengths during its eclipse by Jupiter on Mar. 10, 1971. In both colors, the shape of the ingress light curve was again reliably determined for extinctions up to 9 mag. Neither curve showed any evidence of a refraction tail. The observations have been interpreted in terms of the local optical transmission properties of the Jovian atmosphere. At gas number densities of about 5 x 10 to the 18th power per cu cm the maximum photon scattering mean free path at visual wavelengths was 47 km atm. Evidence indicates that neither a simple reflecting-layer model or a semiinfinite homogeneous scattering model provides an adequate physical description of the atmosphere.

Price, M. J.↗

NASA NTRS1972

Underluminosity and magnetic fields in Beta Lyrae

A combination of available observational data for Beta Lyrae and theoretical models of evolution in close binary systems in used to show that the minimum underluminosity of the dark secondary component of this system is 1 to 4 mag. It is demonstrated that magnetic fields are probably relatively weak in massive main-sequence stars, including the two stellar components of Beta Lyrae, and therefore that a strong magnetic field is not a likely explanation for the underluminosity of the secondary component of Beta Lyrae.

Stothers, R.↗

NASA NTRS1973

UBV photometry of Iapetus.

UBV observations of Iapetus on 34 nights have revealed a 0.30-mag difference in the depths of two successive minima in the light curve of this satellite. The difference can be explained by a two-hemisphere model with the leading darker hemisphere having a much stronger variation in brightness with solar phase angle than the trailing brighter hemisphere. Aside from the variation in the depths of the minima, the general character of the light and color curves is similar to that reported by earlier investigators.

Millis, R. L.↗

NASA NTRS1973

Light curve of HZ Herculis.

The optical counterpart of Her X-1 was observed for B-magnitude on 34 nights between July 30 and October 10, 1972. The scatter in the light curve is about 0.5 mag and may be related to the 35-day cycle.-

Petro, L.↗

NASA NTRS1973

Evidence for the binary nature of 2U 1700-37.

Analysis of Uhuru data on the X-ray source 2U 1700-37 has revealed the presence of regular occultations. The period is 3.4 days with an occultation duration of 1.1 days. The source is highly variable on a time scale of minutes. Significant intensity variations have also been observed on a time scale of 0.1 second with a 3 sigma upper limit of 17 percent on the percentage periodically pulsed. The energy spectrum is flat and shows a large amount of low-energy absorption. The data indicate that 2U 1700-37 is an X-ray source in a binary system. The 6.6-mag O7f star HD 153919 is suggested as the optical candidate.-

Jones, C.↗

NASA NTRS1973

Model atmospheres for Betelgeuse.

Detailed comparison of a series of stellar atmospheric models at effective temperatures of 3800 and 3500 K with scanner observations of Betelgeuse (alpha Ori, M2 Iab). The atmospheres are hydrostatic, flux-constant, LTE atmospheres which include the opacity of H2O, CO, CN, and atomic line blanketing. To reduce the flux shortward of 6000 A enough to agree with observations requires either strong atomic line blanketing (or a similar opacity source) or significant reddening, or (likely) both. The visual extinction (an estimate of which depends strongly on the line blanketing, especially in the 1- to 2-micron region) lies between 0.4 and 2.0 mag. Comparison of predicted strengths of observed CO and CN features with observations and of predicted column densities of CO, OH, NH, and H2O with published column densities suggests that C/H may be less than its solar value by about a factor of 10 and C/O may be less than 0.6 in Betelgeuse.

Fay, T. D.↗

NASA NTRS1973

On the nature of the infrared point source in the Orion Nebula.

New photometric observations of the BN infrared source in the Orion Nebula eliminate the possibility that it is simply a highly reddened star, and undermine the conclusion that there are 80 mag of visual extinction to the source. We suggest that there is a generic relationship between it and the infrared source IRS 5 in the H II region W3.

Becklin, E. E.↗

NASA NTRS1973

The redshift-magnitude relation for quasi-stellar objects.

It is shown that the best-fitting slope of the redshift-magnitude relation for the most luminous quasi-stellar object in each redshift range is 4.3 plus or minus 0.4. However, the steepness of this slope is due primarily to the lowest redshift range including 3C 273, without which it is 2.1 plus or minus 0.6. The slopes of the second and third brightest QSOs are 3.1 plus or minus 0.6 and 3.2 plus or minus 0.6, respectively, markedly less than the slope of 5 which is expected for a Friedmann universe with q(0) = +1. Although the departure of the slope from 5 mag per decade is statistically significant at about 95% confidence, due to the heterogeneity and incompleteness of the sample there may be a systematic selectional bias not accounted for either in this analysis or in that of Bahcall and Hills. Consequently, no definite pronouncement can be made until a complete sample of adequate size is examined.

Burbidge, G. R.↗

NASA NTRS1973

Radio maps around five spiral and peculiar galaxies.

Areas of from 1 to 2 degrees square around five spiral and peculiar galaxies of apparent brightness between 10.3 and 12.7 mag have been mapped at a wavelength of 13 cm. In this small sample of observations it is found that, on the average, about two, counting the galaxy itself, radio sources of flux strength between 0.1 and 0.4 f.u. are physically associated with each spiral. This result supports the conclusion of De Jong that satellite radio sources are associated with spiral galaxies. If these preliminary results are indicative, then the radio sources associated with spiral galaxies differ from those classically associated with elliptical galaxies by being (1) intrinsically weaker and (2) not as accurately aligned as pairs across the central galaxy.

Arp, H.↗

NASA NTRS1973

Minor planets and related objects. IX - Photometry and polarimetry of /1685/ Toro.

UBV photometry, lightcurves, a polarization-phase relation, and rotational polarization curves of Toro were obtained, June-August 1972. The average colors are B-V = 0.87 and U-B = 0.47 mag, showing some reddening with phase. The geometric albedo of Toro in the B filter is 0.14 which corresponds to an effective mean radius of 2.2 km plus or minus 0.4 (p.e.). The rotational polarization curves indicate that the lightcurves are mostly due to shape, but some albedo variation over the surface is detected as well. The shape is elongated, and probably irregular, with a cross-sectional area ratio of about 3.2, the maximum effective radius is 2.8 km and the minimum, 1.6 km.

Dunlap, J. L.↗

NASA NTRS1973

The luminosity function of galactic X-ray sources - A cutoff and a 'standard candle'

Analysis of the 2- to 10-kev luminosity distribution of 36 X-ray sources in the Local Group having known or estimated distances, showing that there exists a luminosity cutoff of approximately 10 to the 37.7th ergs/sec in agreement with the theoretical (Eddington) limit for the luminosity of an approximately 1 solar mass star. Furthermore, among the complete sample of high-luminosity sources, there appears to be a statistically significant group of X-ray 'standard candles' at (within less than 0.8 mag) the critical luminosity. This finding (which is in agreement with the self-consistent mass flow accretion models) presents the possibility that X-ray sources may be used as extragalactic distance indicators in the next generation of X-ray astronomy experiments.

Margon, B.↗

NASA NTRS1974

Minor planets and related objects. XV - Asteroid /1620/ Geographos

Analysis of the light curves and color-phase and polarization-phase relations of Geographos according to observations over an eight-month period in 1969. The light curves are relatively smooth with two distinct maxima and minima. The largest amplitude of 2.03 mag is the largest observed on asteroids to date. The average B-V is 0.87 and the average U-B is 0.50. A laboratory model that best reproduced Geographos' light curves was a cylinder having hemispherical ends with a length to width ratio of 2.7; on the basis of this model and a relation of Bowell and Zellner (1973), Geographos was calculated to be approximately 1.50 km wide and 4.0 km long.

Dunlap, J. L.↗

NASA NTRS1974

Ultraviolet photometry from the Orbiting Astronomical Observatory. XI - The 1971 eclipse of 32 Cygni

We observed the 1971 eclipse of 32 Cyg at regular intervals from November 1 to 15 with the wide-band filter photometers aboard OAO-2. Data have been reduced for seven filter bands with effective wavelengths between 4250 and 1430 A. Both the constancy of the light near mid-eclipse for the shorter wavelengths, and the derived energy distribution of the B component over all of these wavelengths indicate that the eclipse was total. The spectral types determined from the photometry of the two components are B5 and K4 Ib, after correction for interstellar reddening of 0.10 mag in B-V.

Doherty, L. R.↗

NASA NTRS1974

OAO-2 observations of the helium spectrum variable a Centauri

Ultraviolet photometry and spectrometer data are presented for a Cen, which exhibits large variations in the strength of its He I lines. The photometry indicates that the star becomes brighter at the helium-weak phase by 0.05 mag throughout the ultraviolet and visual region. A model atmosphere analysis indicates that the photometric variations are not due to flux redistribution from back-warming effects, but can be interpreted as due to the rotation of a distorted stellar disk in the shape of a prolate spheroid.

Molnar, M. R.↗

NASA NTRS1974

Six-color photometry of Iapetus, Titan, Rhea, Dione and Tethys

Six-color photometric observations made during Saturn's 1972/73 opposition enable us to separate the solar phase and orbital phase contributions to the observed light variations of Iapetus, Titan, Rhea, Dione and Tethys. Titan shows no orbital variations, but has phase coefficients which range from negligible values in the infrared to 0.014 mag/deg in the ultraviolet. Rhea has a bright leading side, a light curve amplitude of about 0.2 mag, and surprisingly large phase coefficients. Combined with other available information, the observations suggest a very porous, texturally complex surface layer. Dione has a leading side which is a few tenths of a magnitude brighter than the trailing side, but the light curve amplitude has little wavelength dependence and the phase coefficients are significantly smaller than those of Rhea, suggesting a less intricate surface texture. The leading side of Tethys is probably a few tenths of a magnitude brighter than the trailing side. Our Iapetus observations generally supplement the earlier work by Millis.

Noland, M.↗