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We combine Stromgren-Crawford uvby beta photometry with Gaia-DR2 parallaxes for a sample of 880 supergiants of O-B9 spectral types to explore the potential of these data in providing physical parameters of such stars. We obtained reddening corrections and photometric absolute magnitudes via the existing uvby beta calibrations. We calculated Gaia-based absolute magnitudes applying individual photometric reddening corrections for each star. The uvby beta photometry is particularly useful in this case, since it provides color excess independent of spectral classification, thus overcoming possible MK classification inconsistencies. After evaluating and correcting the effect of luminosity class mis-classifications on the photometric absolute magnitudes, we found a reasonable agreement between the photometric and Gaia-based absolute magnitudes for this sample. At this point, the color-magnitudeM(V)versus (b-y)(0)diagrams based on photometry and Gaia show slight discrepancies, which have to be addressed in the light of the next Gaia data releases. The derived precise reddening corrections should further help to refine the physical parameters of these stars and address their connection to OB-associations and regions of star formation.

Seventeen years of V-band and intermediate Wing near-IR TiO (λ719-nm to λ1024-nm) time-series photometry of the M1-4 Iab supergiant TV Geminorum are presented. The observations were conducted from 1997 to 2014 with the primary goals of determining both long-term (years) and short-term (months) periodicities and estimating temporal changes in temperature, luminosity, and radius as the star varies in brightness. Our results suggest a dominant short-term V-band period of ~411 days (~1.12 years) that is superimposed on a long-term cycle of ~3137 days (~8.59 years). Over this long-term cycle, the effective temperature varies between ~3500 K to ~3850 K and, at an adopted distance of 1.5 ± 0.2 kpc, the luminosity varies from ~6.2 × 104 L⊙ to ~8.9 × 104 L⊙ and the radius varies from ~620 R⊙ to ~710 R⊙. Variations in temperature and luminosity are indicative of a semi-regular long-term pulsation with imposed short-term periods similar to the V-band variations. However, the calculated radius variations are apparently not generally inversely correlated with respect to the long-term temperature and luminosity changes as typically found in Cepheids and Mira-type variables. This observation suggests other undetermined mechanisms, such as the formation and subsequent dissipation of supergranules or possible complex pulsations, are taking place in this evolved red supergiant to account for these variations. Like other young, massive luminous red supergiants such as Betelgeuse (α Orionis) and Antares (α Scorpii), TV Gem shows complicated light variations on time scales that range from months to several years. These evolved high massive stars are important to study because they are nearby, bright progenitors of core-collapsed Type II supernovae.

We report the fifth confirmed Luminous Blue Variable/S Doradus variable in M31. In 2006, J004526.62+415006.3 had the spectrum of hot Fe ii emission line star with strong P Cygni profiles in the Balmer lines. In 2010, its absorption line spectrum resembled an early A-type supergiant with H and Fe ii emission lines with strong P Cygni profiles, and in 2013, the spectrum had fully transitioned to an F-type supergiant due to the formation of the optically thick, cool wind which characterizes LBVs at maximum light. The photometric record supports the LBV/S Doradus nature of the variability. Its bolometric luminosity of ~-9.65 mag places it on the H-R diagram near the known LBVs, AE And, Var C in M33, and S Dor.

This study of new CCD spectra of ε Aur recorded in the blue and near-UV during the 2010 eclipse has been reinforced and extended by the inclusion of some 130 digitized historic spectra from MountWilson (dating back to the 1930s) and from the DAO (dating from 1971). The precise repetition of disk-related spectral-line changes during three successive eclipses indicates that the structure of the disk does not alter appreciably on a time-scale of a least a century.We deduce that the disk has an extensive but optically thin outer layer, and a flat structure that is tilted near to edge-on. We discover that it is receiving from the supergiant a very confined stream of material that is enriched in rare-earth elements. The stream has an approach velocity very similar to the projected rotational velocity of the F star; it has an extremely small velocity dispersion, and is only visible between specific egress phases. We surmise that the F star is a horizontal-branch star though its own photosphere appears, on average, to have a solar composition.We also uncover variable broad emission in the system and find a possible correlation with the F-star's Cepheid-like ~67-day pulsations that cause its photometric variations. © 2013. The Astronomical Society of the Pacific. All rights reserved.

We have examined the Wilson–Bappu effect, a relationship between the absolute magnitude of the star, MVMV, and the logarithm of the Ca ii emission width, W0W0, over the largest MVMV range to date, +13+13 to -5-5, covering MM-dwarfs to type Ia supergiants. We used an extensive literature, the latest Hipparcos reduction, data from two globular clusters, and new observations from Apache Point Observatory to compile a sample that allowed us to study the effect of [Fe/H] on the Wilson–Bappu relationship. Our results include reporting the deviations from linearity and demonstrating that the Wilson–Bappu relationship is insensitive to metallicity.

We present multiwavelength broadband photometry and V, I time resolved photometry for two variable bright stars in the SMC, OGLE004336.91-732637.7 (SMC-SC3) and OGLE004633.76-731204.3 (SMC-SC4). The light curves span 12 years and show long-term periodicities (SMC-SC3) and modulated eclipses (SMC-SC4) that are discussed in terms of wide-orbit intermediate mass interacting binaries and associated envelopes. SMC-SC3 shows a primary period of 238.1 days along with a complicated waveform suggesting ellipsoidal variablity influenced by an eccentric orbit. This star also shows a secondary variability with an unstable periodicity that has a mean value of 15.3 days. We suggest this could be associated with nonradial pulsations., Comment: To be published in Publications of the Astronomical Society of the Pacific (PASP).

V725 Sgr is a rather peculiar variable that showed a period increase during part of the twentieth century. Its behavior is attributed to rapid stellar evolution. V725 Sgr was monitored in V, R, I and J, H, K with the REM telescope, on La Silla, from 2008 August to 2009 November. Its light variation does not show a well-defined cyclic behavior. Its current V is similar to what it was 30-40 yrs ago. Its published motion suggests that V725 Sgr is located at a few kiloparsecs from the Sun. This implies that V725 Sgr is a giant rather than a supergiant star. From its mean colors we conclude that V725 Sgr is now an irregular variable of spectral type ~K4 III.

We have obtained differential uvby and UBV photometry of the B8Iae variable HD 199478 (HR 8020) over 2500 days, in order to study the photometric variability of this star, and to compare it with various aspects of the spectroscopic variability. The total peak-to-peak amplitude was about 0.15 mag in each filter. Color variability was present, but complex. The photometric data were analyzed using self-correlation and Fourier analysis; the latter was hampered by the complexity of the variability, and by the presence of two annual seasonal gaps in the data. Although the variability was not strictly periodic, there are characteristic time scales of 20 days, and occasionally 50 days, in many seasons. These are consistent with the time scales of spectroscopic variability. There was no obvious photometric counterpart to the unusual spectroscopic behavior in 2000 October. We discuss the results in the context of recent theoretical studies of hot supergiant variability.

This paper discusses data reduction for an echelle spectrograph we have developed for an automatic telescope at Tennessee State University and are using to monitor radial velocities and line profiles of cool giant and supergiant stars. Although our approach to data reduction is rather conventional, we discuss flat-fielding and extraction of velocities in ways that should be of general interest, establish a transformation to the IAU radial velocity system (+0.35 ± 0.09 km s–1), and determine the external precision for measured velocities (0.10-0.11 km s–1). Also, we present results of the first 2-3 years of monitoring radial velocities in about 120 cool giants and compare those results with the level of variability found with photometry. These new data confirm the widely held understanding that K and M giants are all radial velocity variables at the level of 0.1 km s–1.

The long-term brightness changes in the M supergiant, type C semiregular variable, Type II supernova progenitor BC Cyg from 1890 to the present are examined using archival data obtained from photographic plates in the collections of Harvard College Observatory and Sternberg Astronomical Institute, in conjunction with AAVSO observations. BC Cyg pulsates with a period close to 700 days but underwent a 0.5 mag increase in brightness between 1900 and 2000, in conjunction with a decrease in pulsation period from 699 to 687 days. Such changes appear to be evolutionary in origin, representing a small contraction of the star associated with a slight decrease in luminosity. Its evolutionary mass is estimated to be ~19 M⊙ from its membership in Berkeley 87, a feature that also permits it to be used to test the M supergiant period-luminosity relation.

We have added data for 16 distant Cepheids observed with the echelle spectrograph of the Apache Point 3.5 m telescope to improve the correlations of abundance parameters with pulsation period and distance from the Galactic center (RG). While we see no important trends with pulsation period, some important ratios are closely related to the evolution of stars through the instability strip. The most interesting is the N/C ratio, which is predicted to be enhanced by a factor of 4 when an evolving supergiant cools to Teff = 4000 K and the outer convection zone reaches the depth at which CN processing has converted C to N. We find a Gaussian distribution around a value of [N/C] = 0.6, just as predicted. The ratio of about 30:1 mixed to unmixed stars can be taken as the ratio of evolutionary time spent on the blue loop to the time spent on the first crossing through the instability strip. According to stellar models, the main mixing event takes place when Teff drops below 4000 K, which is outside the red edge of the instability strip; i.e., after stars have crossed the instability strip for the first time. We have confirmed previously known correlations of [Fe/H] with RG. We find that [Fe/H] shows a gradient of –0.06 Kpc–1. The only other significant gradient is that of [Eu/Fe], which increases with RG, thereby showing an increasing ratio of SN II/SN Ia in the outer Galaxy.

A large set of deep, near‐IR, objective‐prism plates taken along the southern Galactic plane was searched for cool supergiants and carbon stars. Accurate coordinates and charts for 759 carbon stars in two Galactic longitude sectors within 75 of the plane, 248°

Identifying the massive progenitor stars that give rise to core-collapse supernovae (SNe) is one of the main pursuits of supernova and stellar evolution studies. Using ground-based images of recent, nearby SNe obtained primarily with KAIT, astrometry from 2MASS, and archival images from HST, we have attempted the direct identification of the progenitors of 16 SNe II and SNe Ib/c. We may have identified the progenitors of the SNe II 1999br, 1999ev, and 2001du as supergiant stars with M^0_V ~ -6 mag in all three cases. We may have also identified the progenitors of the SNe Ib 2001B and 2001is as very luminous supergiants with M^0_V ~ -8 to -9 mag, and possibly the progenitor of the SN Ic 1999bu as a supergiant with M^0_V ~ -7.5 mag. Additionally, we have recovered at late times SNe 1999dn, 2000C, and 2000ew, although none of these had detectable progenitors on pre-SN images. In fact, for the remaining SNe only limits can be placed on the absolute magnitude and color (when available) of the progenitor. The detected SN II progenitors and limits are consistent with red supergiants as progenitor stars, although possibly not as red as we had expected. Our results for the SNe Ib/c do not strongly constrain either Wolf-Rayet stars or massive interacting binary systems as progenitors., 19 pages, 23 figures, to appear in PASP (2003 Jan)

ES Aql, initially classified as a semiregular variable, is now believed to be a member of the R Coronae Borealis (RCB) class of stars, a small group of carbon-rich supergiants that undergo dramatic declines in brightness at irregular intervals. We present photometry of ES Aql going back as far as 1893 using plates from the Harvard College Observatory as well as more recent photoelectric and visual observations. ES Aql displays the typical behavior of an RCB star, consisting of sharp declines at irregular intervals. The spectrum of ES Aql is also typical of a cool ( K) RCB star, showing strong absorption bands of C2 and CN, along T ∼ 5000 eff with weak hydrogen and no detectable 13 C. ES Aql is also an IRAS source indicating the presence of dust. Based on these data, we conclude that ES Aql is indeed an RCB star.

Spectroscopic observations of the M supergiant star Betelgeuse were taken at the Elginfield Observatory over 17 months in the 1999–2000 observing seasons in order to search for giant convection cells. Although the photospheric spectral lines show some temporal variations, mainly in their depths (consistent with a previously study), the Doppler shift distribution inferred from them is remarkably stable. The spectral lines show characteristic macroturbulence dispersion ∼15 km s−1 and cover a full span of ±50–60 km s−1. The widths of the lines show occasional as well as longer term changes of a few percent but no evidence for giant convection cells. These spectroscopic observations are more consistent with a classical picture of nonthermal photospheric velocities in which large numbers of convection cells appear on the stellar disk at all times.

Interstellar C IV absorption line studies of the hot gaseous halo of the Large Magellanic Cloud (LMC) have been hindered by non-ideal selections of early-type probe stars in regions where C+3 can be produced locally via photoionization, fast stellar winds, or supernovae. To observe stars outside such regions, precise spectral classifications of OB stars in the field are needed. Therefore, we have obtained medium-dispersion spectra of 42 early-type stars in the LMC that are distributed outside superbubbles or supergiant shells. The spectral classification of these stars is presented in this paper. Nineteen of these program stars have spectral types between B1 and O7, and are thus suitable probes for interstellar C IV absorption line studies of the hot gaseous halo of the LMC.

We present revised orbital elements for the massive interacting binary HD 163181, and we offer the first evidence of apsidal motion in the orbit (apsidal period U = 510±100 yr). We searched for but found no obvious evidence of the secondary's spectral lines in our optical spectra. We do observe, however, systematic profile variations with orbital phase that probably result from a gas stream from the Roche lobe-filling supergiant to the faint secondary. The relatively small projected rotational velocity of the primary (V sin i = 88±3 km s–1), the faintness of the secondary, the reported lack of orbital motion in the Hα emission, and the presence of an IR excess all suggest that the system is surrounded by an extensive circumbinary disk (as is found in a similar binary, RY Scuti).

HD 223960, an A0 Ia-type supergiant in the Cas OB5 association, is unusual among Galactic supergiants of its class in having an Hα profile with double-peaked emission entirely above the continuum. We analyzed 12 high-resolution echelle spectra obtained in 1993-1995 and in 1999 with the 1 m telescope of Ritter Observatory. The radial velocities of photospheric Si, C, He, Ne, and S lines were found to be constant to within ±2 km s–1, but the data suggest variability in the equivalent widths of Si ii λλ6347, 6371 and several other photospheric lines. The radial velocities and equivalent widths and, especially, the ratio V/R of the Hα components vary. The present data do not indicate a binary explanation for the double-peaked emission feature. Alternative explanations are considered, but none is completely satisfactory. The available evidence is consistent with the star having a weak, fast wind.

The striking correlation between Ca ii K-line emission width and absolute visual magnitude has not previously been well calibrated for stars more luminous than giants. From a sample of binary systems fit to isochrones, we find deviations of more than 2 mag, correlated with spectral class, between these binarity Mv values and the Wilson-Bappu relation. Additional Mv values derived from Hipparcos parallaxes are used to explore the systematics. The spectral class dependence vanishes for K-line parameter log W0 ≤ 1.80. Linear spectral class corrections are derived for the more luminous stars, with log W0 ≥ 2.00, while a table is provided for the transition region. The dispersion from these relations is about ±0.6 mag. This recalibration extends the demonstrated applicability of the Wilson-Bappu technique to Mv -5 or distance ≈20 kpc.

High signal-to-noise, optical digital classiÐcation spectrograms of three northern very early O supergiants and four late O supergiants with CNO anomalies are illustrated and discussed. Several of these exceptional objects either are the prototypes of their classes, originally discovered photographically, or are unique representatives of them in the northern hemisphere. The full blue-violet and yellow-red spectrum of the extreme ON supergiant BD )36i4063, discovered by G. Mathys with limited wavelength coverage, is shown for the Ðrst time. Extensive line identiÐcations are provided, and the high quality of these data reveals numerous new absorption and emission features corresponding either to the high ionization in the case of the very early objects, or to the chemical abundance anomalies in the later ones. These data provide standards for digital classiÐcation of related objects in the north and guidance for subsequent astrophysical analyses with higher spectral resolution.

CCD-based BVR photometry of 123 previously unobserved stars drawn from volumes I, II, III, and V of the Luminous Stars in the Northern Milky Way catalog (LS catalog) is reported. In addition, the Galactic distribution of over 400 LS-catalog supergiants as derived from spectroscopic parallaxes is examined.

Recent observations of S Doradus, the archetype of luminous blue variables (LBVs), reveal that the star's optical spectrum now resembles an F-type supergiant, with a rich complex of absorption lines. Despite nearly 50 years of spectroscopic monitoring, such a spectrum has never before been seen for S Dor despite numerous occasions when the star was equally bright. However, such F-type spectra have been seen in other LBVs, including Var B in M33 during a recent outburst, and in η Carina during an outburst in 1893. The singly ionized metal lines arise in a layer moving away from the star (toward us) at 50 km s–1, consistent with the lines forming in a "pseudophotosphere" originating in the stellar wind. The temperature suggested by the F-type spectrum is as cool as an LBV can get. Our CCD UBV photometry shows that the star has brightened only 0.3 mag in V since 1996, at which time it showed an emission-line spectrum characteristic of LBVs at minimum. The dereddened B–V color is consistent with an effective temperature suggested by the spectrum (7500 K), but there is a pronounced UV excess as evidenced by U–B. Why the behavior of S Dor has suddenly changed remains a mystery.

The International Ultraviolet Explorer (IUE) satellite observed VV Cephei (M2 Iab) B? ) over nearly a full 20.3 year orbital period, but all the observations were obtained outside total eclipse. Egress of the chromospheric eclipse was the only portion of the eclipse observed by IUE. We have examined all 124 high-resolution IUE spectra of VV Cephei and describe the spectrum and its variations. Contrary to initial expectations, the spectrum remained complex throughout the entire orbit, and Ðve line components have been identiÐed : (1) emission lines ; (2) neutral, low-excitation (e.g., Fe I) lines, which disappear as the hot component emerges from eclipse ; (3) broad, high-ionization (e.g., Si IV and Fe III) lines arising from the hot component or nearby circumstellar material ; (4) narrow absorption cores from the circumstellar envelope of the M supergiant ; and (5) "" shell II absorption lines with variable proÐles which do not absorb below a minimum depth. Mg II h and k emission broadens and strengthens when the system is near periastron and secondary eclipse. Most of the variation in the other emission features appears to be stochastic rather than phase dependent. The continuum shows rapid variations on timescales as short as 2 weeks. At any one time, the continuum Nux between 1400 and 3000 is fairly constant but varies, apparently stochastically, in the range A � (2E7) ) 10~12 ergs s~1 cm~2 for observations obtained outside of chromospheric eclipse. The dered- A � ~1 dened continuum Nuxes vary as Dj~0.8, implying that the source is not purely stellar. Radial velocity measurements of the circumstellar and shell lines show that neither follows the radial velocity curve of the two stars. Circumstellar line velocities range from the systemic velocity to D15 km s~1 more negative, consistent with their formation in an extended circumstellar envelope of the M supergiant which is large compared to the scale of the orbit. The shell lines are redshifted from the systemic velocity by D30 km s~1 .T he lastIUE observations (near phase 0.9) showed shell lines with greater redshifts and deeper absorption than around the rest of the cycle. The ultraviolet spectrum of VV Cep is compared to spectra of stars showing similar features : the Be shell star 28 Tauri, the B(e) star HD 45677, and the M supergiant)B binary systems a Scorpii and KQ Puppis. A table detailing the appearance and behavior of numerous line multiplets is presented.

Reliable prediction of stellar diameters, particularly angular diameters, is a useful and necessary tool for the increasing number of milliarcsecond resolution studies being carried out in the astronomical community. A new and accurate technique of predicting angular sizes is presented for main sequence stars, giant and supergiant stars, and for more evolved sources such as carbon stars and Mira variables. This technique uses observed $K$ and either $V$ or $B$ broad-band photometry to predict V=0 or B=0 zero magnitude angular sizes, which are then readily scaled to the apparent angular sizes with the $V$ or $B$ photometry. The spread in the relationship is 2.2% for main sequence stars; for giant and supergiant stars, 11-12%; and for evolved sources, results are at the 20-26% level. Compared to other simple predictions of angular size, such as linear radius-distance methods or black-body estimates, zero magnitude angular size predictions can provide apparent angular sizes with errors that are 2 to 5 times smaller., Comment: 28 pages, 4 figures, accepted by PASP

Chemical compositions are derived from high-resolution spectra for three stars classed as SRd variables in the General Catalogue of Variable Stars. These stars are shown to be metal-poor supergiants: WY And with [Fe/H] = -1.0, VW Eri with [Fe/H] = -1.8, and UW Lib with [Fe/H] = -1.2. Their compositions are identical to within the measurement errors with the compositions of subdwarfs, subgiants, and less evolved giants of the same FeH. The stars are at the tip of the first giant branch or in the early stages of evolution along the asymptotic giant branch (AGB). There is no convincing evidence that these SRd variables are experiencing thermal pulsing and the third dredge-up on the AGB. The SRds appear to be the cool limit of the sequence of RV Tauri variables., 14 pages, 1 figure, 4 tables

We present a spectrophotometric imaging study of the emission bubble N70 (DEM 301) in the Large Magellanic Cloud. N70 is approximately 100 pc in size with a nearly circular shell-like morphology. The nebular emission is powered by an uncertain combination of EUV photons, intense winds, and supernova shock waves from the central population of high-mass stars (the OB association LH 114). We have obtained narrowband images (FWHM ~ 6 A) of N70 in the light of Hα λ6563, [N ii] λ6584, [S ii] λλ6717, 6731, and [O iii] λ5007, along with the corresponding red and green continua. The resulting line fluxes and flux ratios are used to derive ionization rates, nebular densities, volume filling fractions, and excitation indices. The photoionizing luminosity inferred from the embedded stellar population is more than adequate to account for the observed hydrogen ionization rate.We compare the emission-line photometry with that derived from similar imaging of the Orion Nebula and with data collected from the literature on other emission-line regions in the LMC. Compared with the Orion Nebula, N70 shows much higher [S ii]/Hα intensity ratios that increase smoothly with radius—from less than 0.3 near the center to greater than 1.0 toward the outer filamentary shell. The measured intensity ratios in N70 more closely match the range of excitation spanned by giant and supergiant H ii shells and by some of the supernova remnants observed in the LMC. The contending ionization and excitation processes in the interior and outer shell of N70 are evaluated in terms of the available data. EUV photons probably contribute most of the inner nebula's ionization, whereas a combination of photoionization plus collisional ionization and excitation of sulfur atoms by low-velocity shocks seems to best fit the emission-line luminosities and intensity ratios observed in the outer shell. Considerations of the radiative and mechanical energetics that are involved may indicate the need for one or two supernova explosions having occurred during the last ~Myr.

We have used Hipparcos parallaxes to derive absolute visual magnitudes of G, K, and M stars with Ca ii emission line widths previously measured by O. C. Wilson. A linear relationship similar to the one derived originally by Wilson & Bappu and improved by Lutz & Kelker was found from Mv = +7 to –2. For stars brighter than Mv = -2 a substantial number of stars show Ca ii emission lines that are broader than expected from the linear fit. Most of those stars are bright giants and supergiants of type G. In appendices we show some sample Ca ii profiles and identify emission lines of Fe ii as well as the H line in some stars.

MK spectral classifications of over 2500 Case-Hamburg luminous stars are examined to determine whether those for which Ha was reported in emission in the original surveys (but for which blue-region emission was not noted) are more likely to have MK classifications indicating blue-region emission than their non-Ha counterparts; this proves to be the case. In addition, stars with Ha emission are less likely to be supergiants than their non-Ha counterparts, and, when emission is indicated in the MK classification, one is much more likely to be dealing with a luminosity class V or III star than a bright giant or supergiant.

Chemical compositions are derived from high-resolution spectra for four stars classed as SRd variables in the General Catalogue of Variable Stars. Two stars—XY Aquarii and RX Cephei—are of solar metallicity and most likely not variable stars. Their spectroscopic effective temperatures and surface gravities correspond to the spectral types G0 V for XY Aqr and G8 III for RX Cep. Two stars are undisputed variables and shown here to be metal-poor supergiants: AB Leonis with (Fe/H) and SV Ursae Majoris with . 21.6 (Fe/H) . The metallicities and high radial velocities show them to be halo stars. . 21.4

We present the current (2000 February) status of the optical spectrum of the irregularly variable M supergiant VY CMa, based on high‐resolution CCD spectra. The emission spectrum is largely unchanged over the past 43 yr, with low‐lying atomic lines as well as the molecules TiO and ScO in emission. Tables of observed wavelengths for both identified and unidentified lines are presented.

Supergiants are the most luminous stars in galaxies that are currently forming many stars. Reliable abundance determinations, for the most part, reflect the values of the interstellar material out of which they formed. Thus, they can be used to trace the chemical history of their parent galaxies. This study derived the stellar atmospheric parameters and elemental abundances of the early spectral type supergiants 4 Lac (B9 Iab) (HR 8541, HD 212593) and n Cep (A2 Ia) (HR 8334, HD 207260) from Reticon and CCD exposures obtained with the long camera of the 1.22 m telescope of the Dominion Astrophysical Observatory in Victoria, British Columbia. They cover 3830–4950 A with signal-to-noise ratios of at least 200 and a 2 pixel resolution of 0.072 A. The spectra were measured with the graphics spectroscopic analysis program REDUCE (G. Hill & W. A. Fisher 1986, Publ. Dominion Astrophys. Obs., 16, 193). The tailored analyses were performed using the LTE plane-parallel model atmospheres code ATLAS9 (R. L. Kurucz 1993, Kurucz CD-ROM 13 [Cambridge: Smithsonian Astrophys. Obs.]). They are similar to those performed by K. A. Venn (1995, ApJS, 99, 659) and B. Albayrak (2000, A&A, 364, 237), who studied supergiants with similar and cooler effective temperatures. The study of 4 Lac extends this type of analysis to a slightly hotter effective temperature. For weak features, the lines were measured using profiles whose width was found from medium-strength unblended lines to aid the process of trying to deconvolve blended lines. For each spectrogram, I identified the cleanest spectral features and found the radial velocity using the laboratory wavelengths. The remaining lines were identified with A Multiplet Table of Astrophysical Interest (C. E. Moore 1945, Princeton: Princeton Univ. Obs.) and more recent references. The adopted values Teff p 10,250 K and log g p 1.85 for 4 Lac and Teff p 8400 K and log g p 1.10 for n Cep were determined using the wings of Hb, and Fe i/ii and Si ii/iii ionization equilibria for 4 Lac and the wings of Hb and Fe i/ii and Cr i/ii ionization equilibria for n Cep. A microturbulence of 2.8 km s for 4 Lac was found from Fe ii lines using WIDTH9 1

During recent years, there has been a growing interest in active galactic nuclei and starburst galaxies. These two spectacular phenomena can dominate completely the total spectrum of their host, and they are present in a significant fraction of the local galaxy population. There is growing evidence that they might play an important part in the galaxy evolution at high redshift (e.g., A. Dey et al. 1997, ApJ, 490, 698; A. Cimatti et al. 1999, A&A, 352, L45), prompting us to carry out a detailed study of nearby galaxies with active nuclei and starbursts in order to take advantage of the more detailed analysis that can be carried out in the local universe. Seyfert galaxies.—We used new infrared (IR) spectroscopy of the CO band at 2.3 mm of 46 Seyfert galaxies from the CfA sample (J. Huchra & R. Burg, 1992, ApJ, 393, 90) to constrain the populations of young stars in their central regions. This is the first set of IR spectra of a complete sample of Seyfert galaxies. The CO band appears diluted by a nonstellar featureless component, most likely warm dust near the central engine. We devised a technique based on JHKL colors to separate the stellar and nonstellar components at 2.3 mm and corrected 16 Seyfert galaxies for dilution. A comparison with the CO indices of ellipticals and pure starburst galaxies indicates that no red supergiant phase starbursts dominate the Seyfert galaxies currently. The best Seyfert-starburst separator in the near-IR appears to be the [Fe ii] (1.26 mm)/Pab versus H2 (2.12 mm)/Brg diagram. The narrow emission line properties of our sample are significantly different from those of ultraluminous IR galaxies from the sample of T. W. Murphy, Jr., et al. (2001, AJ, 121, 97), implying that most of the latter (∼ ) cannot contain 23 hidden active nuclei. The other ∼ can still harbor completely 13 obscured AGNs, invisible even in the K band. Spectral library.—We have compiled a moderately high resolution ( ) H(1.6 mm) and K-band (2.2 mm) R ≈ 2000–3000 spectral atlas containing 218 stars. The atlas spans most of the ranges of , and [Fe/H] relevant for modeling starburst T log g, eff galaxies. We report indices for 19 spectral features and develop new diagnostic techniques for estimating parameters of individual stars. Magnesium indices are the best near-IR metallicity indicators because they are less sensitive to the stellar than Teff the others. The IR Mg i indices are just as good indicators for the abundance in composite systems as their optical counterparts. We have calibrated the strength of Mg i at 1.50 mm as function of the stellar [Fe/H]. We also calibrated a number of line ratios as indicators and luminosity class separators. Teff Despite the lack of suitable iron lines, the light-to-heavy element abundance ratio can be estimated in the IR by using the Ca i at 2.26 mm, because it has been shown from optical observations (G. Worthey 1998, PASP, 110, 888) that the calcium abundance follows the iron abundance. Evolutionary population synthesis.—The spectral library was incorporated into an evolutionary population synthesis model for young stellar populations (≤30 Myr) aimed specifically at starbursts. The model is based on Starburst99, developed by C. Leitherer et al. (1999, ApJ, 123, 3). It predicts the time evolution of near-IR features for single bursts of star formation (SF). They all are very weak during the first 5–7 Myr, while most of the flux comes from hot blue supergiants. The indices become stronger as the red supergiants begin to develop at 7–10 Myr. The indices weaken as the supergiants explode as supernovae at 12–15 Myr and stabilize at to 13 of the peak values after that. Our models, when combined 12 with age estimates from hydrogen recombination emission lines, can be used to probe directly the abundance of the starbursts, because the index strengths are scaled by the metallicity. Metallicities of starbursts.—We applied the Mg i 1.50 mm indicator to determine the metallicity of the starbursts from C. Engelbracht (1997, Ph.D. thesis, Univ. Arizona) and derived near-solar abundances for the majority of them. The technique yielded [Fe/H] p 0.3–0.4 for giant ellipticals. Our estimates correlate very well with the optical iron indices. We demonstrated by means of a simple chemical enrichment model that the fraction of iron peak elements can be influenced significantly by the preceding SF history. This poses a problem for [Fe/H] estimates based on a-elements (e.g., Mg) but also opens up a possibility to explore the previous SF history.

This study presents a detailed model atmosphere abundance analysis of Deneb which was performed using Ku- rucz LTE ATLAS9 model atmospheres. The atmospheric pa- rameters were determined from Mg I/II and Fe I/II equilibrium, and by fitting the H profile and optical region spectrophotom- etry. The compromise values which best satisfy these criteria are Te = 9000 K and log g = 1.45. The Mg I, Mg II, Si II, Ti II, Cr II, Fe I, and Fe II lines yield microturbulences of 3.60, 6.50, 8.50, 8.00, 11.90, 3.60, and 10.40 km s 1 , respectively. An average microturbulence of 7 kms 1 was used for the other atomic species. From a comparision of the synthetic spectrum with the ob- servations, the best value for the rotational velocity is v sin i = 25 km s 1 , and for the macroturbulent velocity is =1 4 km s 1 , which are similar to those of some earlier derived values. Also, the individual spectrograms have a range of radial veloc- ity variation of 15 km s 1 which is approximately equal to macroturbulent velocity. These values of the macroturbulence and the range of radial velocity variation are close to the sum of the amplitudes (10.44 kms 1 ) of all the pulsation periods found by Lucy (1976), who also suggested that the surface motions of the atmosphere of Deneb can be identified with macroturbu- lence. Deneb showed a definite helium underabundance with a well determined He/H value = 0.071. The CNO values (C being mildly deficient, N being in moderate excess, and an O being slightly deficient) are consistent with the mixing of the CNO- cycled products into the surface layers from the processed ma- terials presumably dredged-up from the interior. Aluminium is mildly deficient by 0.24 dex with respect to solar value, while sulfur is moderately underabundant by 0.43 dex in Deneb. Mg and Si have the solar abundances. The metal abundances (Ca to Ni) tend to be greater than solar except for Sc which is slightly deficient. The heavy elements abundances (Sr, Y, and Zr) are all greater than solar. These abundance patterns conform to the common tendency seen with other normal Populatio nIAs u- Send offprint requests to: B. Albayrak ? Based on data obtained at the Dominion Astrophysical Observa- tory, Herzberg Institute of Astrophysics, National Research Council of Canada. ?? Table A.1 is only available electronically with the On-Line publi- cation at http://link.springer.de/link/service/00230/ pergiants found by Venn (1995a). The rare-earth elements (Ba, La, and Eu) which have been unexplored in other Galactic early A-type supergiants are significantly overabundant relative the Sun.

Spectroscopic abundance determinations for a sample of seven F-G stars have been carried out. The majority of them have large galactic latitudes. One objective in deriving spectroscopic abundances is to differentiate evolved objects seen at high galactic latitudes from the young population I supergiant stars that happened to have large galactic latitudes but actually belong to the galactic disk. Secondly, it is important to get good calibrators for photometric metallicity indices. It has been suggested in the past that many high galactic latitude F-G stars that are classified as supergiants are in reality subgiants or dwarfs. Our spectroscopically derived gravities show that two of the stars studied in this paper, HR 5165 and HD 114520, are not supergiants as classified in Bright Star Catalogue but are subgiants belonging to the solar neighbourhood. In our sample, HR 3229 and HR 8470 display solar abundances and the derived gravities support the bright giant luminosity class ascribed to them. HR 4114, HR 4912 and HR 7671 have abundances significantly different from those of young supergiants of galactic disk. The evolutionary status of these objects is discussed.

Observations on the 13-color photometric system are reported for 71 A0-K0 supergiant stars brighter than V = 6.0. Three independent methods to determine the effective temperatures for A0-K0 supergiants from their 13C photometry are discussed: 1) Calibrations between Teff and reddening-free indices are developed; temperatures were collected from the literature for the calibration stars, and most of them were spectroscopically determined. 2) An empirical correlation between intrinsic colors in the 13C system and Teff has been derived. 3) The unreddened colors are compared with synthetic colors calculated by Kurucz (1989); this leads to simultaneous estimates for Teff and log g. The estimated uncertainties in Teff by the three methods are comparable and are approximately plus or minus 200-300K

Attracted by an earlier claim (Thiessen 1956) that BM Cas is an eclipsing binary with one component a classical Cepheid, we have obtained new photometry and IUE ultraviolet spectra of the system. While we verify that there is variability in addition to the eclipses, we conclude that there is no classical Cepheid present. The variability is irregular, and, since it is present in the uv spectra as well as in the V photometry, we believe it is associated with the hotter component. We find the latter to be a high-luminosity star of spectral type of A6, in close agreement with the MK assignment of A7 Iab (Bidelman 1982), and the secondary component most likely to be a late-K or early-M giant. The latter appears to fill or nearly fill it Roch lobe, while the primary star is not far from doing so as well, implying a complex evolutionary history for the syste.

HD 105262 has a spectrum like that of HR 4049 in having Balmer liens as in a Ib supergiant but very weak lines due to He I, Ca II, Si II, Ti II, fe I, Fe II, and Mg II. It has a published proper motion of 0.057" ± 0.011" yr-1. If the star had the luminosity of a Ib supergiant, its space motion would be several times the escape velocity from the Galaxy. HD 105262 does not have the spectral appearance of a horizontal-branch or post AGB star. The most likely explanation for the spectrum is the model proposed for HR 4049 by Lamers et al. (1986), Waelkens et al. (1987), and Lambert et al. (1988), namely a low-mass proto-planetary nebula star in which the narrow Balmer lines are formed in an extended atmosphere.

The Virgo spiral NGC 4569 has a very compact optical nucleus whose spectrum is highly composite, which strong Balmer absorption indicating that A stars dominate the optical light. Recent HST imaging shows that the nucleus is extremely compact in the mid-ultraviolet, so that either there must be a central AGN or an extraordinarily luminous and compact central star cluster. I present here IUE and ground-based spectrophotometry and high-resolution optical spectra, which are used to decompose the nucleus into possible stellar and AGN contributions. Accounting for the asymmetric contamination by Balmer emission, at a velocity different from the stellar absorption lines, removes the apparent discrepancy between radial velocities for different stellar components. The nuclear spectrum shows contributions from ordinary bulge light and from a young population. This young component has effective spectral type of mid-A, and the Balmer lines are so narrow that A-type supergiants are the most important contributors to the optical light. The young population is therefore much younger than the spectral type would suggest if interpreted as a main-sequence turnoff age, and the asociated OB stars might account for much of the UV flux. In this case, the nucleus contains an extraordinarily bright star cluster about as large as the core of 30 Doradus but more than 6 magnitudes brighter. While some less luminous supergiant-dominated star clusters have been found, current models of starburst evolution do not give a natural explanation for such a bunching in effective temperature. Evidence for an AGN is equivocal; M/L arguments show that only for the most extreme conditions of timing and burst duration could stars alone give a small enough value to satisfy the observational limit on velocity dispersion, and this condition would be eased if some of the UV radiation and the ionization of the nuclear gas can be attributed to an AGN. While, for very favorable conditions the Balmer absorption might be interpreted as coming from an unusually extensive and face-on accretion disk (rather than stars), the small linewidths and dominance of a single photospheric temperature place very stringent geometric and size constraints on this possibility.

Copernicus low-resolution (0.2A) observations of 16 O stars, 10 B stars (mostly supergiants), and one WN-A star with the highest data quality between 1000 and 1200A are presented in the form of a classical spectral atlas. The purpose is to survey the systematic spectral-type/luminosity-class dependence of the line features, including those from the stellar winds, in this relatively less studied wavelength range. Perhaps the most important new contribution is the demonstration of the pronounced luminosity effect in the S IV lambda-lambda-1063, 1073 wind profiles, identical to those previously recognized in Si IV lambda-lambda-1394, 1403 and C III lambda-1176, which share essentially the same ionization potential. The stellar-wind effects in O VI lambda-lambda-1032, 1038; P V lambda-lambda-1118, 1128; Si IV lambda-lambda-1122, 1128; and C III lambda-1176 are also described. Attention is redrawn to the unidentified feature at 1099A, which is one of the strongest absorption lines in this range of mid-O through early-B spectra. The atlas will facilitate interpretations of recent Hopkins Ultraviolet Telescope and future Far Ultraviolet Spectroscopic Explorer observations in this wavelength range, as well as sharpen the stellar-wind phenomenology for astrophysical analysis.

The A-type supergiants have an interesting location on the HR-diagram for testing stellar evolution theories since various evolution scenarios describe vastly different histories for these stars. In particular, the predicted abundances of carbon and nitrogen in the stellar atmospheres differ significantly since these stars may have evolved directly from the main-sequence or may be returning from the red giant branch where they would undergo the first dredge-up of CN-cycled H-burned gas from the stellar interior. This thesis provides new elemental abundances for a large group of Galactic A-type supergiants in the 5 to 20 solar mass range, while also addressing the difficulties in determining reliable abundances in these stars. The atmospheric analysis of each star was performed using the most recent Kurucz LTE model atmospheres. Atmospheric parameters (Teff and log g) have been determined from ionization equilibrium of weak Mg I and Mg II lines and fitting the wings of the H-gamma line profiles; the final parameters were chosen at the intersection of the loci of possible Teff-gravity values from each indicator. Calculations show that NLTE effects on the weak Mg I and Mg II spectral lines used in this analysis are small, therefore they are ideal atmospheric parameter indicators. The metal abundances, log epsilon (O, Mg, Si, Ca, Sc, Ti, Cr, Fe, Ni) are solar to within about ±0.2~dex, calculated assuming LTE. Overabundances of Na are found, which are discussed as a combination of possible NLTE effects and/or pollution of newly synthesized Na from a NeNa proton capture reaction that could occur in the stellar core. Otherwise, we see no evidence of slight overall metal enrichments in these young stars that might be expected due to Galactic chemical evolution. More details of the atmospheric and LTE metal abundance analyses can be found in Venn 1994 (ApJS, 99, 659). The carbon and nitrogen abundances are examined in order to study the evolutionary status of these stars. LTE abundances show that nitrogen is enriched and carbon depleted, as expected after the first dredge-up, however the quantities are much greater than predicted and there is a very strong trend in the nitrogen abundances with Teff. New NLTE line formation calculations have been carried out for nitrogen and carbon to investigate these results (details in Venn 1994 ApJ, 449, 839). For nitrogen, it was necessary to construct a new and detailed N I/II model atom (which was calibrated with respect to Vega, see Lemke & Venn 1995, A&A, in press). Application to the A-supergiants shows that departures from LTE strongly affect the nitrogen abundances, even for weak lines. NLTE corrections (=log (X)NLTE - log epsilonXLTE) for the weak lines used in this analysis range from -1.0 dex in the A0 supergiants to -0.3 in the F0 supergiants. The NLTE corrections remove the strong trend with effective temperature seen in the LTE nitrogen abundances. The average NLTE abundance is log epsilon (N)NLTE = 8.05 ± 0.19 for the 22 A0-F0 supergiants analyzed. For carbon, the Sturenburg & Holweger (1990, A&A, 237, 125) model atom was adopted and tested extensively. Again, the NLTE corrections are significant, ranging from -0.1 in the F0 stars to -0.5 in the A3 stars. For the hotter stars, we show that the only observable C I lines, near 9100A, do not yield reliable elemental abundances. The mean NLTE carbon abundance is log epsilon (C)NLTE =8.14 ± 0.13 for the 14 A3-F0 supergiants. The A-supergiant NLTE abundances are compared to the mean carbon and nitrogen abundances in unevolved B-stars in the same mass range, which are not the same as solar ([C/H]B*= -0.35 and [N/H]B*= -0.21). We find log epsilon (N/C)A I - log epsilon (N/C)B* =+0.38 ± 0.26. This value is significantly less than the first dredge-up ratio (~0.65 for 10 solar mass stars and ~0.98 for 20 solar mass stars) predicted by several evolution scenarios, including the popular Geneva tracks. However, the non-zero [N/C] ratio suggests that the A-type supergiants have undergone some partial mixing of CN-cycled gas, which is not currently predicted by Galactic metallicity evolution tracks. Therefore, Galactic A-type supergiants are not evolving from the red giant branch - they have evolved directly from the main-sequence, but have undergone some mixing of CN-cycled gas not currently predicted by stellar evolution theory.

Observations of the emission line object Bl 3-14, classified by Allen (1982, 1984) as a symbiotic star, are presented. The spectra obtained in 1987, 1990, and 1991, show clearly the binary nature of the object, with a hot component with strong absorption lines and a late component with TiO absorption bands, plus a few emission lines. It is concluded that Bl 3-14 is a symbiotic star which has suffered an outburst, showing now a gM6 late component, an expanding envelope which mimics an A-F supergiant spectrum, and a gaseous envelope with a few emission lines. More observations are needed to ascertain the real behavior of this object.

Pulsation models for the enigmatic F-type supergiant variable, UU Her are investigated. It is shown that irregular pulsations with small amplitude is realized, if UU her is assumed to be an intermediate mass F type supergiant star which has evolved with mass-loss and rotation mixing and thus highly luminous, compared with what is obtained by conventional evolution.

Some of the most luminous stars have sporadic, violent mass-loss events whose cuases are not understood. These evolved hot stars are called Luminous Blue Variables (LBV's), and their instability may shape the appearance of the upper HR diagram. LBV eruptions are interestingly reminiscent of geysers, or even volcanos. They have received considerable observational attention since 1980, but theoretical work to explain the instability has been scarce. In a typical LBV eruption, the star's photosphere expands and the apparent temperature decreases to near 8000 K. During these normal eruptions the bolometric luminosity remains constant, as typified by S Dor, AG Car and R127. A few LBV's, specifically eta Car, P Cyg, V12 in NGC 2403 and SN1961V, have giant eruptions in which the total luminosity actually increases by more than one or two magnitudes. The star may expel as much as a solar mass or more with a total luminous output rivalling a supernova. The classical LBV's have luminosities greater than MBol approaching -9.6 mag, suggesting initial mass greater than 50 Solar Mass. These stars have very lkikely not been red supergiants as there are no evolved cool stars of comparable luminosity. Their instaibility may prevent their evolution to the red supergiant region. There is also a group of less luminous LBV's (MBol approaching -8 to -9 mag) with low temperatuers, smaller amplitudes and lower mass loss rates. These stars have probably been red supergiants and have shed a lot of mass prior to their current unstable state. Although the physical cuase of the LBV instability is not yet understood, the most likely mechanism involve radiation pressure (the opacity-modified Eddington limit) or dynamical instabilities in the outer layers as the star evolves off the main sequence. In this review, we summarize the physical characteristics and behavior of LBV's, and discuss their brief but critical role in massive star evolution, and possible mechanisms for their remarkable instability.

Completion of long-term astrometric plate series yields revised results on the orbits and parallaxes. The subdwarf mu Cas seems to be overluminous; the distance of the supergiant epsilon Aur is near 600 pc. The unresolved companion in the red dwarf pair BD +6degree398 is of very low mass, and the companion of BD +67degree552 massive but probably underluminous.

Star formation properties in Giant Extragalactic H II Regions (GEHRs) are investigated using optical photometry and evolutionary population synthesis models. Photometric data in $BVR$ bands and in the emission line of H-alpha are obtained by CCD imaging at Vainu Bappu Observatory, Kavalur. Aperture photometry is performed for 180 GEHRs in galaxies NGC 1365, 1566, 2366, 2903, 2997, 3351, 4303, 4449, 4656 and 5253. Thirty six of these GEHRs having published spectroscopic data are studied for star formation properties. The population synthesis model is constructed based on Maeder's stellar evolutionary and Kurucz stellar atmosphere models, to synthesize observational quantities of embedded clusters in GEHRs. The observed H-alpha luminosity is a measure of the number of massive stars while the contribution to BVR bands is from intermediate mass (5-15 solar mass) stars when the cluster is young and from evolving supergiants when the cluster is old (age >/= 6~Myr). Differential reddening between gas and embedded stars is essential to constrain the dereddened cluster colors within the range of youngest clusters. Obscuring dust closely associated with gas, which is distributed in filaments and clumps, as in the case of 30 Doradus, is the most likely configuration giving rise to net reduction of extinction towards stars. The fraction of the stellar photons escaping the nebula unattenuated is estimated to be 50%. GEHRs are rarely found to be simple systems containing stars from single generation. In the present sample such regions in addition to being older than 3~Myr, have their Lyman continuum luminosity reduced by as much as 60%, compared to the observed $B$ band luminosity for a normal IMF. The missing ionizing photons may be escaping the nebula, leading to the ionization of extra-H II region ionized medium. Co-existence of young (age

Spectrophotometry of 36 Long Period Variable stars in M33 is presented. Most of them show strong TiO bands. These spectra together with published photometry indicate that the red variables exceeding 5 x 104 L are M supergiants, evolved from young massive stars which are prominent in this galaxy. A small number of lower luminosity stars are present in this sample. These are asymptotic giant branch stars. We identify 2 of them as carbon stars. There are no strong S stars.

This dissertation addresses several issues concerning stellar oxygen abundances. The 7774 {A} O I triplet equivalent widths of Abia & Rebolo [1989, AJ, 347, 186] for metal-poor dwarfs are found to be systematically too high. I also argue that current effective temperatures used in halo star abundance studies may be ~150 K too low. New color-Teff relations are derived for metal-poor stars. Using the revised Teff values and improved equivalent widths for the 7774A O I triplet, the mean [O/Fe] ratio for a handful of halo stars is found to be +0.52 with no dependence on Teff or [Fe/H]. Possible cosmological implications of the hotter Teff scale are discussed along with additional evidence supporting the need for a higher temperature scale for metal-poor stars. Our Teff scale leads to a Spite Li plateau value of NLi=2.28 ± 0.09. A conservative minimal primordial value of NLi=2.35 is inferred. If errors in the observations and models are considered, consistency with standard models of Big Bang nucleosynthesis is still achieved with this larger Li abundance. The revised Teff scale raises the observed B/Be ratio of HD 140283 from 10 to 12, making its value more comfortably consistent with the production of the observed B and Be by ordinary spallation. Our Teff values are found to be in good agreement with values predicted from both the Victoria and Yale isochrone color-Teff relations. Thus, it appears likely that no changes in globular cluster ages would result. Next, we examine the location of the break in the [O/Fe] versus [Fe/H] plane in a quantitative fashion. Analysis of a relatively homogeneous data set does not favor any unique break point in the range -1.7 /= -3), in agreement with the new results for halo dwarfs. We find that the gap in the observed [O/H] distribution, noted by Wheeler et al. [1989, ARAA, 27, 279], persists despite the addition of more O data and may betray the occurrence of a hiatus in star formation between the end of halo formation and the beginning of star formation in the disk. It is noted that the slope of the [O/Fe] versus [Fe/H] relation for [Fe/H] >/= -1 depends on the statistical regression utilized. Hence, alleged "observed" [O/H] - age relations, which do not use truly observed O abundances (but, rather, adopt O abundances based on Fe abundances), should be regarded with caution. Systematic effects on O abundances derived from the 6300A [O I] and 7774A O I lines are considered next. While our Solar observations confirm the disagreement between the observed 7774A O I equivalent widths and LTE model calculations at low microns, we stress that Solar O abundance determinations made from flux spectra are in very good agreement with the meteoritic value. We find the 6300A [O I] equivalent width value appears to be uncertain for the Sun. Given this uncertainty, the inability of authors to reproduce each others' 6300A O abundances, and the results of recent quasi-two-stream calculations, we do not believe it can be readily claimed (as is usually done) that these abundances are more reliable than those derived from the 7774A O I triplet. In a sample of relatively metal-rich F and G dwarfs, we find no systematic difference between the 6300 and 7774A O abundances for Teff

Several searches for periodicities in the historical visible light curves of RCB stars have found that the intervals between declines are random. This paper reexamines 70 declines of R Coronae Borealis since 1853 using one homogeneous data set, the AAVSO light curve. In this data set, pairs of consecutive declines also show a random distribution of intervals. However, if the sequence of declines is examined, there are semiperiodic variations between times of high- and low-decline activity on a time scale of a few years. Near-IR photometry of RCB stars indicates that there are large semiperiodic variations in the amount of dust being produced which have similar time scales. Possible interpretations of a semiperiodic variation in dust formation rates in RCB stars are presented. One is a magnetic activity cycle resulting in 'spots' on the star over which dust formation takes place. Such a magnetic activity cycle is similar to the solar cycle. Another is the changes in the period and amplitude of the pulsations over several years affecting the efficiency of dust production.

V441 Herculis (89 Herculis) and V814 Herculis (HD 161796) are among the best-known UU Herculis stars (high latitutde, often seemingly young, F supergiants). Most, if not all, members of hte class exhibit long-period, low amplitude light variability, which potentially could be a useful diagnostic in establishing the nature of these poorly understood stars. The periods, shaps, mean levels, and stability of the light curves and their relation to corresponding velocity curves all provide information on the type of pulsation, and the type of star. To this end, one of us (JDF) has a long-term program running on the Automatic Photoelectric Telesocpe Service, whereby UBV photometry of V441 Her and V814 Her is obtained on about 100 nights a year eventually for some ten years. The date are now being published every second year, and the program will conclude with ane xtensive analysis of the findings. This paper represents the fifth data report; the previous one was in Fernie 1991 and earlier ones are cited therein. A preliminary synoptic overview of results to 1991 is given in Fernie 1993.

Biweekly ultraviolet observations of the red supergiant-hot dwarf binary VV Cephei during 1991, obtained near third quadrature, have revealed the existence of short-term continuum variations. We infer these are superposed on an underlying emission-line spectrum. The viewing geometry of this long-period system suggests we are seeing a process associated with nonuniform mass transfer to an accretion disk. This rapid variability can be related to global instabilities in the stellar wind and mass loss from the red supergiant.