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Eight eclipse reappearances of the innermost Galilean satellite, Io, were observed during the fall of 1973. The measurements were made using photometers specially designed to cope with the problem of scattered light from Jupiter. Posteclipse brightening of Io was not detected and, if present, was less than our estimated detection threshold of about 0.02 mag.
The nucleus of M31 was photographed at a resolution of 0.2 sec with the 91-cm balloon-borne Stratoscope II telescope. At the half-intensity level, the nucleus was observed to be elliptical with its major axis lying in position angle of 63 (plus or minus 5) deg. The peak surface brightness was 12.7 plus or minus 0.3 V mag per square second of arc assuming B - V = 1.0. The nucleus appears to be a separate feature from the bulge with a scale height of approximately 0.5 pc. The mass of the nucleus is of the order of 100 million solar masses, and the apparent visual mass-to-light ratio is of the order of 20.
Recent y-filter photometry shows that Titan has brightened by about 0.04 mag between 1972.7 and 1974.2. The trend is consistent with that derived by Andersson.
New spectral types for 16 stars, UBVRI photometry for 13 stars and UBVRIHKL photometry for 35 stars in the Orion Nebula cluster are presented. Analysis of these data together with those of Penston (1973) shows that the reddening law in the cluster is normal. Previous claims for high ratios of total to selective absorption are caused by mistaking infrared emission for a hole in the absorption at that wavelength. The distance modulus of M42 is 8.0 + or - 0.1 mag. Star formation in the cluster has been in progress over the last 10 million yr. The infrared colors of cluster stars are correlated with their range of variation in the optical region.
The 3.5-micron magnitudes of R CrB and NML Cyg as a function of Julian date (over the period 1968-1974) are presented and briefly analyzed. They establish the variability of R CrB at this wavelength: during the interval studied, its magnitude varied approximately 1.4 units, in a definite cyclic pattern. The magnitude variations of NML Cyg were smaller (about 0.5 mag), but they may be cyclic with a period on the same order as that of R CrB.
An empirical relation between interstellar X-ray absorption and optical extinction is derived from the correlation of measurements made on objects of large intrinsic diameter. The result is Av = 4.5 times 10 to the -22nd power N(H) mag, with the principal error being largely systematic in origin, where N(H) represents the column density of interstellar matter in the Brown and Gould model for the X-ray absorption coefficient. Applying this ratio to optically identified compact sources, it is concluded that sources in binary systems showing pronounced X-ray occultations have an intrinsic absorption equivalent to about 10 to the 22-nd power atoms per sq cm of interstellar matter and that there are a few compact sources where the absorption seems to be primarily interstellar in origin. The interstellar absorption expected in Cyg X-1 from the extinction of its optical counterpart is much greater than that suggested by X-ray spectra, which may be due to a soft X-ray component greater than that predicted by the power law fitted to higher energy data.
Optical studies are reported for a representative sample of 10 unidentified high galactic latitude X-ray sources that are north of declination minus 25 deg and that have 3U error boxes less than or of the order of 0.5 square degrees. The source 3U 1410-03 is identified with a peculiar emission-line spiral galaxy, NGC 5506, and a distance group 4 rich cluster of galaxies, Abell 2142, is suggested as a possible identification for 3U 1555+27. It is shown that very few of the unidentified high galactic latitude sources are quasi-stellar sources brighter than 17.5 mag, although one possible X-ray quasar, NAB 0137-01, is reported.
New photoelectric observations of the B-magnitude of CV Ser made in 1973 and 1974 show no clear evidence of an eclipse, but they establish night-to-night variability of several percent, a systematic brightness change of 0.035 mag during a portion of the single orbit observed in 1973, and irregular flaring in 1974. We made iris photometer measurements of Harvard patrol plates taken between 1905 June and 1953 July, and find no evidence of a very deep eclipse such as observed by Hjellming and Hiltner. We present several new light curves and discuss then in the light of the recent results of Cowley et al.
We have obtained medium-resolution spectra in the yellow of seven stars in the error box of the binary radio pulsar PSR 1913 + 16, using the image-tube scanner at the Lick 3-m telescope. None of the objects is spectroscopically abnormal and thus a strong candidate for membership in the system. The data are used to establish the extinction in the field, which is modest for this low galactic latitude. For three of the stars, limits of the order V exceeding 23 mag on optical pulsations with the frequency of the radio pulsar are derived. X-ray observations of the field have been obtained in the 2.5-7.5 keV band, using the UCL experiment aboard OAO Copernicus. No source is detected, with a 2 sigma upper limit on the time-averaged flux of 1.0 times 10 to the -10th power ergs per sq cm per sec.
Investigation of blue-sensitive photographs of HDE 226868 = Cygnus X-1 reveal no (+ or - 0.06 mag) long-term changes in brightness since the beginning of the century nor any abrupt intensity changes similar to what was observed at X-ray and radio frequencies. From the double sinusoidal fluctuation with 5.6 day period, an attempt is made to derive a more precise value for the orbital period, but problems are encountered and discussed. There exists evidence that the amplitude of the orbital fluctuations is increasing slowly with time.
UBV photometry of WRA 977 on 36 nights between January and July of 1974 shows that this object is active on a time scale of days at the 0.1 mag level, but that it remains quite constant during monitoring intervals lasting up to 1 hour. Periodogram analysis reveals no significant periodic variation in the brightness of this object.
Basic heat transfer data for structural materials used in the Saturn 1B/V 1U component case structural design were obtained. The main emphasis is on thermal contact conductance between dissimilar metallic surfaces, since thermal conductivity values within solids have been sufficiently established previously. The test program outline and test results are described. The following materials were tested: aluminum 6061-T6 (12 samples), aluminum 356 (as cast), almag 35 (as cast), magnesium AZ91C-T4 (4 samples), and mag lithium LA-141 (2 samples).
Several spectra of the optical object identified with the X-ray flare source A0620-00 have been obtained at 5 A/mm with the Cassegrain echelle spectrograph on the 4-m Mayall telescope at Kitt Peak National Observatory. These spectra reveal no significant stellar lines, but the flux distribution in the range 4250-7400 A, dereddened for a color excess of 0.9 mag, is similar to that of an O star. The color excess, which is derived from the observed strength of the 5780-A diffuse interstellar band, and the velocities and strengths of the interstellar Na I D lines imply that the object is between 1.5 and 2.5 kpc from the sun. If a distance of 2 kpc is adopted, then the luminosity of the source in the observed wavelength region is roughly 5 by 10 to the 35th power erg/s. The possibility that this object is a slow nova is discussed.
Lasker (1976) has proposed to identify a B roughly equals 23.7 mag star as thermal radiation from the hot neutron star associated with the Vela pulsar. It is shown that this identification, if correct, together with existing X-ray surveys of the Vela supernova remnant, requires that the radius of this pulsar certainly exceed 45 km, and probably 95 km.
Light curves, UBV colors, rotational periods, phase coefficients, and absolute magnitudes are presented. The asteroids studied are (1) Ceres, (4) Vesta, (16) Psyche, (78) Diana, (281) Lucretia, (451) Patientia, (1212) Francette, and (1362) Griqua. The rotation axis of Lucretia is nearly perpendicular to the plane of the ecliptic. Ceres appears to be nearly spherical with an absolute magnitude of B(1,0)=4.42, which is 0.3 mag fainter than previously reported. The determination of the absolute magnitude for an asteroid depends on its aspect, and for each opposition there is, therefore, a different absolute magnitude.
A far-infrared map of the M8 region at 69 microns with a 1-arcmin resolution shows an unresolved source 19 arcmin east of the main component. This source is a strong near-infrared emitter, with K = 4.8 and K - L = 2.6 mag. An intense peak in (C-12)O emission (brightness temperature about 36 K) coincides with the new infrared source. Comparison of millimeter-wave and infrared observations suggest that this source is an extremely young compact H II region. Evidence for a depletion of dust opacity inside the H II region is also found.
Maps of a region 10 arcmin in diameter around the galactic center made simultaneously in three wavelength bands at 30, 50, and 100 microns with about 1 arcmin resolution are presented, and the distribution of far-IR luminosity and color temperature across this region is derived. The position of highest far-IR surface brightness coincides with the peak of the late-type stellar distribution and with the H II region Sgr A West. The high spatial and temperature resolution of the data is used to identify features of the far-IR maps with known sources of near-IR, radio continuum, and molecular emission. The emission mechanism and energy sources for the far-IR radiation are analyzed qualitatively, and it is concluded that all of the observed far-IR radiation from the galactic-center region can be attributed to thermal emission from dust heated both by the late-type stars and by the ultraviolet sources which ionize the H II regions. A self-consistent model for the far-IR emission from the galactic-center region is presented. It is found that the visual extinction across the central 10 pc of the Galaxy is only about 3 mag and that the dust density is fairly uniform in this region. An upper limit of 10 million suns is set on the luminosity of any still unidentified source of 0.1- to 1-micron radiation at the galactic center.
Seven Mira variable stars with silicon monoxide maser emission have been found. All are later than M4 and heavily reddened. Two were observed near maximum light. One, Y Cas, seems to bear out the correlation of 43-GHz SiO maser luminosity and mean spectral type at maximum light. RT Aql, however, falls about 1 mag below the expected brightness. A catalog of SiO maser stars is given.