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Observational technology is now reaching the point where optical absorption-line studies of dark interstellar clouds are becoming feasible. Such studies are of great interest. In particular, it will be important to discover the degree of depletion which has occurred in dark clouds. In order to assess depletions on the basis of observations of a limited range of ionization stages, it is necessary to analyze the ionization balance. The present investigation is concerned with such an analysis. The two key parameters necessary for deducing the ionization balance are the electron density and the radiation field intensity. A summary is provided regarding the existing data on the cloud density using data from the literature, and the radiation field intensity is derived from the observed H2 rotational excitation. The implications of both the density and radiation field data for the ionization balance of several species are discussed. It is found that for all species treated the first ion is dominant in the line of sight toward HD 147889.

Neutral nitrogen and oxygen column densities or limits are derived for 53 path lengths through the diffuse interstellar medium and compared with column densities of neutral hydrogen. For neither N nor O is a systematic increase of depletion found as reddening increases. The value found for forbidden O/N is 8, and the abundances of N and O are both between 40% and 70% of the solar values. Implications of these results for models of interstellar grains are briefly discussed.

Data on the interstellar Ca II H and K lines toward HD 147889, a star deeply embedded in the rho Ophiuchi dark cloud, were obtained at the Mauna Kea Observatory of the University of Hawaii, using a multi-anode microchannel array (MAMA) detector. An upper limit on the Ca II column density of 1.7 x 10 to the 11th/sq cm was derived, which, together with ionization considerations and an estimated lower limit on the total hydrogen column density, implies that the calcium-to-hydrogen ratio in this line of sight is 0.00000795 or less, relative to the solar value. The logarithmic depletion is up to -5.10, the largest yet measured, and implies that gas-grain interaction in this region has proceeded to a much greater degree than is typical of diffuse clouds.

Twenty stars classified as either Ap or Am have been imaged by the Imaging Proportional Counter on the Einstein Observatory in a search for evidence of coronal emission. It is found that an Am star will not be a source (at the 10 to the 28th ergs/sec level) unless it is in a spectroscopic binary with a period below about 10 days. The X-rays in the close binaries can be explained by the RS CVn effect in the late-type secondary, and the evidence is against strong emission from Am stars. Among the nine Ap stars observed, four were detected. While it is possible that the X-rays are being generated by undetected late-type dwarf companions, the large fraction of detections makes the Ap stars themselves the likely source of emission.

(Previously announced in STAR as N82-30203)

The presence of narrow, shifted absorption features superposed on the wide P Cygni profiles of the UV resonance lines in the spectra of O and B stars is studied and possible explanations of the narrow components are discussed. Spectra from 26 stars of spectral types O4f to B1 Ib were examined for the presence of narrow components in the absorption part of the profiles, and positive evidence was detected in 17. The central velocities of the features are found to be similar for different ions of the same star, and typically equal to 0.75 times the terminal velocity of the stellar wind. The width of the narrow absorptions is about 18% of the terminal stellar wind velocity, with a column density generally not correlated with the effective temperature or mass loss rate. Possible explanations for the narrow components include peaks in the degree of ionization, a stationary stellar shell, a plateau in the stellar wind velocity law, a decelerating stellar wind, a variable mass loss rate or a two component stellar wind with low-velocity, low-density material found at a distance greater than 2 stellar radii, which explanation appears most likely.

Mass loss rates for a number of early-to-mid-B main-sequence stars are compared with extrapolations of recently derived empirical correlations between M and stellar parameters for luminous OB stars. The order of magnitude of the rates for the B stars is consistent with a simple dependence on luminosity over the range from Of to mid-B, and is not consistent with previously derived correlations involving a dependence on mass or radius, which implies that luminosity is the dominant factor in driving the mass loss throughout the range of spectral types from mid-B main-sequence to Of. The winds in Be stars may represent a straightforward extension of the OB wind phenomenon to lower luminosities, and there appears to be no significant difference between B and Be stars in terms of their wind characteristics.

An analysis for the effects of stellar winds concerning Copernicus scans of Si III and Si IV resonance lines in the spectra of 22 early B stars, of which 19 have Be characteristics, yields line asymmetries in all but one of the stars to which theoretical profiles were fitted. The resulting wind parameters were used to calculate mass-loss rates. Most of the silicon in the winds of the cooler stars is in the form of Si III and Si IV, leading to a mass loss rate value ranging from 10 to the -11th to 3 x 10 to the -9th solar masses/year. Equatorial gravity darkening is seen in the relative velocity widths of ultraviolet and visible photospheric lines. The measured photospheric Si III and Si IV resonance-line equivalent widths do not agree with those predicted by current stellar atmosphere calculations. Be star mass loss rates are probably insufficient to affect either their own evolution or that of the galaxy, since their winds do not significantly contribute to the enrichment of the interstellar medium.

Intensive Copernicus scans of the 1(11)-0(00) line of the F-X band of H2O were carried out, resulting in a 2 sigma upper limit of 1.04 mA for this line at 1114.225 A. The recently published f-value implies a column density limit of 5.3 x 10 to the 12th/sq cm, marginally above the level expected from recent chemical model calculations. A 1.8 sigma feature appears at the expected position of the H2O line, implying a column density for the ground rotational state of 2.8 x 10 to the 12th/sq cm.

The 6196.0 A diffuse feature is observed in various directions towards moderately and slightly reddened stars at high spectral resolution and signal to noise ratio. The feature is found to be symmetric with no fine structure with an equivalent-width upper unit paralleling that of H2. The feature is as narrow as 0.4 A, although much broader in other stars due to cloud blending in the line of sight, and is absent in all observed stars with E(B-V) less than 0.1, and upper limits more than an order of magnitude below values extrapolated from more reddened stars. Upper limits are determined by multiplying the square root of the number of channels in which the line may lie, and another narrow feature, although highly asymmetric, is observed at 6194.6 A. It is concluded that the results increase the possibility of at least one of the diffuse band carriers being a molecule.

Ultraviolet line profiles are fitted with theoretical line profiles in the cases of 25 stars covering a spectral type range from O4 to B1, including all luminosity classes. Ion column densities are compared for the determination of wind ionization, and it is found that the O VI/N V ratio is dependent on the mean density of the wind and not on effective temperature value, while the Si IV/N V ratio is temperature-dependent. The column densities are used to derive a mass-loss rate parameter that is empirically correlated against the mass-loss rate by means of standard stars with well-determined rates from IR or radio data. The empirical mass-loss rates obtained are compared with those derived by others and found to vary by as much as a factor of 10, which is shown to be due to uncertainties or errors in the ionization fractions of models used for wind ionization balance prediction.

The resonance line of F I at 954.825 A is detected in the interstellar spectra of Delta Sco, and possibly Delta Ori, and upper limits are obtained toward five other stars. It is noted that the equivalent width for Delta Sco of 10.9(+4.5, -3.1) in milliangstroms corresponds to a column density of 1.52(+0.60, -0.43) x 10 to the 13th/sq cm and a depletion of -0.53(+0.15, -0.14) dex. For the other lines of sight, depletions of at least 0.1-0.5 dex are inferred. The results are discussed in the context of current theories of the depletion process.

Si II oscillator strengths for eight resonance lines from the ground state have been determined using a curve-of-growth analysis of interstellar data from the Copernicus and International Ultraviolet Explorer satellites. The oscillator strengths for 1526 A and 1808 A increase by factors of 3.0 and 1.5, respectively, from previously tabulated values; those for 989 A and 1020 A decrease by factors of 0.55 and 0.60, respectively. These new values result in better silicon abundances for interstellar clouds and resolve a long-standing puzzle in the interpretation of quasar absorption line data.

Data from the International Ultraviolet Explorer (IUE) have been used to derive extinction curves for several stars chosen because of unusual diffuse band strength or location within dense clouds. Both the strength and position of the 2200 A extinction maximum were assessed, as well as the level of extinction in the far-ultraviolet. A variety of combinations of these features were found, ranging from near or complete absence of a 2200 A bump (HD 29647), to low far-ultraviolet extinction (Rho Oph), to unusually steep, far-ultraviolet extinction (HD 169454). Anomalous extinction apparently shows up frequently in stars associated with nebulosity or dense clouds. The apparent independence of 2200 A and far-ultraviolet extinction supports earlier suggestions that these two features are created by distinct populations of grains.

Seven O stars known to have strong, and sometimes variable, stellar winds have been observed repeatedly with the Imaging Proportional Counter on the Einstein Observatory, in a program designed to determine whether the X-ray fluxes from these stars are variable. In three cases, definite changes were seen, either on a time scale of a year (Iota Ori and Delta Ori) or five days (15 Mon). In two of these cases, the X-ray spectrum was harder when the overall flux was higher, indicating that some of the fluctuations may take place in a hot (approximately 10 to the 7th K) emitting region at the bottom of the winds.

Data from IUE have been used to derive an ultraviolet extinction curve for HD 29647, a B star embedded in the Taurus dark cloud complex. The curve appears normal, except that the 2200 A extinction bump is absent. Arguments are developed to show that this is most likely due to a modification of the grain optical properties through the accretion of mantles in this dense cloud. If this conclusion is correct, it will have some impact on models for the formation of the 2200 A bump.

From a study of the UV lines in the spectra of 25 stars from 04 to B1, the empirical relations between the mean density in the wind and the ionization fractions of O VI, N V, Si IV, and the excited C III (2p 3P0) level were derived. Using these empirical relations, a simple relation was derived between the mass-loss rate and the column density of any of these four ions. This relation can be used for a simple determination of the mass-loss rate from O4 to B1 stars.

Copernicus ultraviolet data on six stars embedded in the well-studied Rho Ophiuchi cloud complex have been analyzed for interstellar abundances, densities, and far-ultraviolet extinction parameters, in an effort to determine how interstellar depletions depend on physical conditions. While there are variations within the cloud in the overall depletions, the pattern of depletions from element to element is constant for all six lines of sight. A picture is suggested in which the cloud core has a small velocity dispersion or is either so strongly depleted or so dense (hence not ionized) that the lines of first ions of heavy elements do not arise there, but rather form in a less-dense or less-depleted outer region. The cloud as a whole has substantial depletions, average to low far-ultraviolet extinction, and a low ratio of molecular to atomic hydrogen.

Chemical abundances and physical conditions in the interstellar gas toward Omicron Per are analyzed using Copernicus UV spectrophotometric data on 69 lines due to ions and atoms as well as 19 lines of H2 and HD. The UV extinction toward the star is determined along with the column densities of atomic and molecular hydrogen, the atomic column densities and temperature in the H I region, and the nature of the ionized regions along the line of sight. It is concluded that: (1) Omicron Per is apparently embedded in the near edge of an extended dense molecular cloud, the outer parts of which give rise to the observed absorption lines; (2) the H I region may consist of more than one cloud; (3) the far-UV extinction rise is unusually steep, indicating a high proportion of small grains; (4) the element depletions are somewhat greater than in Zeta Oph, particularly for sulfur and argon; and (5) the molecular abundances are generally consistent with gas-phase formation models rather than with molecular formation on grain surfaces, unless a substantial amount of small grains is present to increase the available surface area.

Ultraviolet spectra of intermediate resolution have been obtained with Copernicus for 12 objects classified as Be or shell stars and for 19 additional early B dwarfs. Some of these spectra show marked asymmetries in certain resonance lines, especially the Si IV doublet at 1400 A, indicating the presence in some cases of outflowing material with maximum velocities of nearly 1000 km/s. Direct evidence for mass loss at these velocities is seen for the first time in dwarf stars as late as B1.5; the only objects later than B0.5 which show this effect are Be or shell stars. Among the stars considered, there is a correlation between the presence of mass-loss effects and projected rotational velocity, suggesting that the ultraviolet flux from B1-B2 dwarfs is sufficient to drive high-velocity stellar winds only if rotational effects reduce the effective gravity near the equator. The mass-loss rate for one of the most active Be stars, 59 Cyg, is crudely estimated to be one billionth or one ten-billionth of a solar mass per year. The data suggest that the extended atmospheres associated with Be-star phenomena may be formed by mass ejection.

Observational data obtained by the Copernicus satellite and ground-based facilities are discussed which show that the depletion of interstellar elements apparently varies with cloud density in the way to be expected if the depletions were due to accretion of gas atoms or ions onto grains. It is shown that the depletion-by-accretion mechanism is supported by a good correlation between depletions and first ionization potentials of the elements (except for lithium, sodium, and potassium) and that this mechanism offers an alternative to the grain-condensation hypothesis in which most of the interstellar medium is required to have been processed through stellar nebulae. It is noted that if the grains do not normally carry positive charges, ion-grain encounters are the most important interactions between gas and dust and may be significant in determining ionization equilibrium, especially if there is a large population of very small grains.

Extensive scanning of the B1 III star omicron Per has been done with the Copernicus telescope-spectrometer in an effort to determine column densities or meaningful upper limits for several molecules expected to be relatively abundant in H I regions of moderate density. The combination of radio H II, OH, and CO emission-line data with the optical absorption measurements indicates that omicron Per is embedded in the near edge of a dense molecular cloud and that the material seen in front of the star must be close to it. Molecules detected in ultraviolet absorption are H2, HD, CO, and possibly OH. The CO rotational temperature is between 2.2 and 3.8 K. The observed column densities and upper limits from Copernicus and ground-based data are compared with recent models for molecular formation in diffuse clouds.

Assuming that chi Oph is an extreme Be star, some consequences are investigated for the interpretation that the IR excesses in such stars are produced by H(-) free-bound emission. The column density of H(-) in the shell surrounding chi Oph is estimated from the observed IR excess, and Copernicus UV spectrophotometric data are used to search for a predicted absorption feature at 1129.54 A due to H(-) and to derive an upper limit to the H(-) column density. No feature resembling the predicted H(-) line is seen in the spectrum of chi Oph, and a marked discrepancy is noted between the estimated column density and the derived upper limit. Possible causes of these discrepancies are discussed, including incorrect interpretation of the IR excess in extreme Be stars, incorrect theoretical calculations describing the predicted H(-) UV absorption line, and the possibility that the line of sight through the shell does not intersect the regions where the IR excess originates.

Data are presented which show that the strengths of the diffuse interstellar bands at 4430, 5780, and 5797 A tend to be deficient with respect to color excess in the lines of sight to stars lying behind dense interstellar clouds. In addition, diffuse-band data for ten stars in the well-studied rho Ophiuchi cloud complex are presented, and systematic variations of band strengths with optical depth are discussed. It is found that the band strength per grain in the line of sight apparently decreases with increasing grain size, taking the ratio of total-to-selective absorption and the wavelength of maximum polarization as indicators of the latter. It is concluded that diffuse-band formation probably takes place most efficiently in the outer regions of interstellar clouds. This may be consistent with a diffuse-band origin in small grains which are coated by mantles in cloud interiors; or in some molecule or molecules which are most abundant in the outer portions of interstellar clouds.

Detailed simultaneous visible and ultraviolet spectroscopy of Zeta Puppis was carried out in order to study the time scale of variations in its stellar wind and to assess the relationship between fluctuations in lines of ions formed at different heights. The observed variations were most striking in the He II 4686 A profile, but were also seen in H alpha and in the resonance doublets of Si IV and O VI. Fluctuations in the visible features occurred in times of about one hour, while the ultraviolet profiles showed changes which took several hours to develop. No evidence of periodicity was seen, but the time coverage is not sufficiently complete to preclude it. Specific changes, particularly in H alpha and 4686 A, may have been caused by the passage of density enhancements from the stellar surface outward through the wind. The profile variations, when compared with recent model calculations, imply changes in the mass-loss rate by no more than a factor of two in times of a few hours.

The resonance line of Sc II at 3642.785 A has been sought in the interstellar spectrum of Zeta Oph, resulting in an upper limit N(Sc II) not greater than 8.6 billion/sq cm and a depletion of this element at least by a factor of 200, if Sc III contributes a negligible column density. The present upper limit may be somewhat below the level expected under the grain-formation model for interstellar depletions, and is consistent with the abundance expected if the depletions are due to gas-grain collisions. The new limit on this element helps to support the hypothesis that species within a specific range of ionization potential are preferentially depleted.

Observations of a few selected wavelength regions in the ultraviolet spectrum of the Be star 59 Cyg, obtained in 1975 November, are compared with the complete low-resolution Copernicus scan of the same star obtained in 1972 October. Changes in the spectrum between the two times are discussed and interpreted in terms of the two distinct shell episodes revealed by optical data. A wide range of ionization exists from Fe III to N V, with a range in radial velocity of approximately 1000 km/s. Changes in the Si III, Si IV, and N V absorption arising in the stellar wind show that the velocity structure of the wind may have changed, and that the ionization balance also was altered over the 3 year interim.

New observations of interstellar lines of boron, vanadium, chromium, and cobalt in the spectra of Zeta Oph and Xi Per have been obtained with the Copernicus satellite. Chromium has been detected for the first time toward a reddened star, and cobalt has been seen for the first time in any interstellar line of sight. New limits have been obtained for boron and vanadium. These new data, along with limits on scandium and other species from the literature, have been compared with models for the depletion process. No fully conclusive test of depletion models is yet possible, but the new data on boron appear to favor the hypothesis that the depletions are dominated by accretion of gas-phase particles onto grains, rather than being due to grain condensation under pressure equilibrium. The impact of these new data on the study of grain surface properties is described.

Using the HEAO 1 soft X-ray sky survey, a search was conducted for X-ray emission from 18 stars in the spectral range B5-A7. The detection of 0.25 keV X-ray sources consistent with the positions of Pi Ceti, a normal B7 V star, and Phi Herculis, a classic Ap star was reported. The detection of these stars argues for large mass motions in the upper layers of stars in this spectral range, and argues against radiative diffusion as the source of abundance anomalies in Ap stars.

The velocity component structure of UV interstellar absorption line profiles observed toward Zeta Ophiuchi clouds has been analyzed; column densities of Mg II, P II, Mn II and Fe II are found for the clouds at -14.4 km/sec (the principal component) and those at about -30 km/sec (a blend of two components). Little or no depletion is noted in the secondary component, suggesting that the grain mantles have been sputtered off, perhaps by a shock front, in this moderately high-velocity cloud. Residual depletion of calcium and titanium in the shocked cloud provides information on the nature of the grain surfaces. In the low-velocity cloud, the relative abundances of neutral atoms may indicate a differential depletion within the cloud.

An intensive search for OH and H2O in the directions of Sigma Sco, Alpha Cam, and Omicron Per was undertaken with the Copernicus satellite. Multiple scans were carried out over the wavelength region for the expected absorption features due to the OH D-X and H2O C-X transitions. The feature due to OH was possibly detected toward Sigma Sco, and only an upper limit can be given toward Alpha Cam. H2O was not detected in any of the stars at the signal level accumulated. The OH abundance toward Sigma Sco and the respective lower limits for the OH/H2O ratios are discussed with regard to the extant models for the steady-state abundances of OH and H2O, and shown not to be inconsistent with ion-molecule schemes.

Copernicus ultraviolet scans of the peculiar mass-losing star P Cyg are described. From the L-alpha profile and diffuse band strengths reported in the literature, a value of interstellar reddening E(B V) of approximately 0.35 mag is derived, leading to the conclusion that the star is intrinsically reddened. This value for the color excess leads to an estimated distance for P Cyg of 0.6-1.8 kpc, on the basis of which a revised visual absolute magnitude of -7.6 to -5.2 is obtained. The wind from P Cyg is quite unlike that for other early B supergiants, displaying a low terminal velocity and low ionization. This difference is connected with the great extension of its photosphere and with the fact that the acceleration of the flow begins below the photosphere. It is suggested that the wind in P Cyg results from dynamical instabilities quite distinct from the mechanism which initiates the winds in other OB stars.

Multiple Copernicus scans of two N2 band regions (near 958.5 and 960.2A) of Delta Sco and Epsilon Per are reported. The observations indicate upper limits for the number of N2 molecules equal to 1.0-3.8 times 10 to the -12th/sq cm and 1.2-4.4 times 10 to the -12th/sq cm, respectively; the limits depend on the cloud temperature. It is suggested that the limits are consistent with the column densities predicted by chemical models for diffuse interstellar clouds, and the predicted relative abundances are presented in terms of the ratio of N(N2)/(2N(H2) + N(Hl)).

Spectra of He II 4686 A and H-alpha in Zeta Pup were obtained simultaneously with Copernicus ultraviolet scans of several P Cygni profiles in this O4 If supergiant with strong mass loss. The visible-wavelength data show significant variations in the profiles of both lines, consisting of doubling of the emission over times of less than a day. Recent theoretical calculations show that the observed profile variations in 4686 A can be produced by significant fluctuations in the wind density. The Copernicus data show less variability, although in one scan of the 1400-A Si IV doublet there appears to be a significant enhancement of the emission which may be correlated with one of the doublings observed in 4686 A and H-alpha, as though a density enhancement formed at low levels and then moved outward in the wind.

Simultaneous scans of the ultraviolet Si IV and Mg II resonance doublets in the spectrum of Gamma Cas with the Copernicus satellite during 64 continuous hours of observation, and H-alpha scans from a ground station, are described. No evidence is found for a rotation period of Gamma Cas, but narrow emission components in both ultraviolet doublets are reported along with a sudden emission increase on January 29.1, 1977 UT which appeared to be present in both H-alpha and the ultraviolet lines.

This paper reports the presence of Mg II emission, the probable presence of Si IV emission, and the possible presence of N V absorption in the UV spectrum of the B0.5 IVe star Gamma Cas. Changes in these features on time scales of several months are described. The detached-ring and mass-exchange binary models are briefly discussed and shown to be inadequate for Gamma Cas. An ad hoc generalization of the detailed stellar-wind model of Poeckert and Marlborough (1978) is presented and suggested as being qualitatively compatible with the UV data as well as with photoelectric H-alpha observations and the X-ray outburst observed in 1976. The presence of a 1-solar-mass neutron star companion with an orbital period of about 4 yr is hypothesized.

Broad-band infrared photometric measurements have been gathered for 105 stars which exhibit diffuse interstellar bands in their spectra. All normal stars obey a single reddening law, and a value of R equal to 3.08 + or - 0.15 is derived. This value is consistent with other recent determinations of R. The diffuse band indicators, the central depth of the 4430-A feature and the equivalent widths of the 5780-A and 6284-A features, show as large a scatter with the infrared color excesses as they do with E(B - V). No single-valued relation between the color excesses and the diffuse band strengths appears to exist. This casts doubt on whether dust grains which produce the visual and infrared extinctions are the carriers for the diffuse interstellar features.

Satellite observations of transitions of C2 at 2312 Angstroms in the spectrum of Xi Ophiuchi were carried out to evaluate the kinetic temperature of the interior cloud. A column density of 1.22 x 10 to the 12th per sq cm is derived from an absorption feature at the 4 sigma level of significance at the position of the R(0) line. This would imply a rotational temperature of not more than 22 K, with a more probable value of less than 16 K. Since total column density (3.2 x 10 to the 12th per sq cm) is found to be lower by a factor of approximately 4 than that which had been previously reported, substantial photo-dissociation of C2 is assumed.

Curve-of-growth analysis is used to derive chemical abundances in Alpha Lyr and Alpha CMa, based on ultraviolet spectra obtained with Copernicus. This analysis is part of a program to study the abundances of the heavy elements mercury and platinum and the short-lived element technetium in the atmospheres of Ap and Am stars. Ultraviolet Fe II lines are used to establish the curves of growth for Alpha Lyr and Alpha CMa A; abundances of a variety of elements, along with upper limits on Hg, Pt, and Tc, are derived. In cases where previous studies based on visual spectra have included elements in common with the present analysis, the agreement is good within the known uncertainties. One new element, cadmium, is observed for these two stars. The upper limits on Pt and Hg, as well as Tc, show that these elements are probably not enhanced in Alpha CMa A by more than about one order of magnitude.

The incidence and nature of variability occurring on time scales of years in the ultraviolet P Cygni profiles of 15 O and B stars are investigated using spectrophotometric data obtained with the Copernicus satellite. It is found that some change in at least a few details of the P Cygni profiles is evident in almost every case, that the changes in a few stars appear to represent substantial variations in the column densities of the particular ions observed, and that the changes in other stars are minor in nature and do not result from significant alterations in the quantity of material in the stellar winds. Most of the narrow absorption features are shown to be invariant in velocity, although their strengths have apparently changed in certain cases. The nature of the changes observed in each of the program stars is briefly described, the time scale for variability in the stellar winds is considered, and two stars (Zeta Pup and Delta Ori A) are identified for which some alteration in the total amount of material in the stellar wind has taken place. It is suggested that the narrow absorption features probably represent temperature gradients or plateaus in the stellar-wind velocity fields or may be caused by flat regions in the height dependence of the wind velocity.

Most work in recent years on the unidentified diffuse interstellar bands has been concentrated on the hypothesis that they are produced by some process in solid grains. We review that hypothesis and the arguments which support it, and find that diffuse band formation by certain classes of molecules should not yet be ruled out. Since several relevant observations have been made in the last four years, the observational data on the bands are reviewed. It would appear that these data are as consistent with molecular origins for the bands as with grain origins. Types of molecular transitions which give rise to 'diffuse' bands are described. These transitions can occur in relatively simple molecules composed of cosmically abundant elements and can produce broad, unresolvable profiles without destroying the molecule. New observations are suggested which could produce decisive evidence with which to determine whether the diffuse bands originate in grains, molecules, or both.

The paper reports on a search for the (8, 0) R(0) line of the A-X transition of NaH at 3990.88 A toward Zeta Oph and Sigma Sco, which was performed using a spectroscopic photoelectric imaging Fabry-Perot interferometer at the coude focus of a 2.2-m telescope. One-sigma upper limits on the NaH equivalent width are derived (0.26 mA for Zeta Oph and 0.69 mA for Sigma Sco), and two-sigma upper limits on the NaH column densities are obtained which imply that the formation rate for NaH cannot be large. It is noted that the latter upper limits are only about one order of magnitude higher than the most optimistic expectation of the NaH column density for formation of this molecule on grains.

Ultraviolet spectrophotometric data obtained with Copernicus are used to analyze the distribution, composition, density, temperature, and kinematics of the interstellar material along the line of sight to Zeta Persei. The far-UV extinction curve for the star is evaluated along with the kinematics of the interstellar gas, observations of atomic and molecular hydrogen, curves of growth for neutral and ionized species, atomic abundances and depletions, ionization equilibria, and observations of CO and OH lines. The results show that there are apparently three clouds along the line of sight to Zeta Persei: a main cloud at approximately +13 km/s which contains most of the material and forms all the neutral and molecular lines as well as most of the ionic lines, a second component at +22 km/s which must contribute to the strong UV lines of most ions, and a third component at roughly +2 km/s which gives rise to a strong Si III line at 1206 A. It is also found that the UV extinction curve has a somewhat steep far-UV rise, indicating the presence of a substantial number of small grains, and that about 30% of the hydrogen nuclei over the entire line of sight are in molecular form.

Near-ultraviolet radiation from Nova Cygni 1975 was detected by the Copernicus satellite on five occasions from 1975 September 1 to 1975 September 9. The nova was not seen in the UV after this date. The principal result was the observation of a broad emission feature from the Mg II doublet at 2800 A. The absence of strong UV radiation at shorter wavelengths suggests that these lines are produced by collisional excitation in the outer layers of an expanding shell with electron temperature of approximately 4000 K. The absence of observed emission lines from highly ionized species indicates that the amount of material with log T between 4.4 and 5.7 is less than 0.001 times that which produces the Mg II emission. The continuum flux in the near-UV decreased as the nova evolved, showing that the total luminosity decreased as the nova faded in the visible.

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.