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The Galactic B[e] supergiant MWC 137 is surrounded by a large-scale optical nebula. To shed light on the physical conditions and kinematics of the nebula, we analyze the optical forbidden emission lines [NII] 6548,6583 and [SII] 6716,6731 in long-slit spectra taken with ALFOSC at the Nordic Optical Telescope. The radial velocities display a complex behavior but, in general, the northern nebular features are predominantly approaching while the southern ones are mostly receding. The electron density shows strong variations across the nebula with values spreading from about zero to ~800 cm$^{-3}$. Higher densities are found closer to MWC~137 and in regions of intense emission, whereas in regions with high radial velocities the density decreases significantly. We also observe the entire nebula in the two [SII] lines with the scanning Fabry-Perot interferometer attached to the 6-m telescope of the Special Astrophysical Observatory. These data reveal a new bow-shaped feature at PA = 225-245 and a distance 80" from MWC 137. A new H$\alpha$ image has been taken with the Danish 1.54-m telescope on La Silla. No expansion or changes in the nebular morphology appear within 18.1 years. We derive a mass of 37 (+9/-5) solar masses and an age of $4.7\pm0.8$ Myr for MWC 137. Furthermore, we detect a period of 1.93 d in the time series photometry collected with the TESS satellite, which could suggest stellar pulsations. Other, low-frequency variability is seen as well. Whether these signals are caused by internal gravity waves in the early-type star or by variability in the wind and circumstellar matter currently cannot be distinguished., Comment: 18 pages, 12 figures, Table 1 is only available in electronic form, submitted to AJ

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.

About 786.4 thousand stars were observed by LAMOST twice or more during the first stage of its spectroscopic survey. The radial velocity differences for about 256 thousand targets are larger than 10 km s−1 and they are possible spectroscopic binary or variable candidates (SBVCs). It is shown that most SBVCs are slightly metal poorer than the Sun. There are two peaks in the temperature distribution of SBVCs around 5760 K and 4870 K, while there are three peaks in the distribution of the gravitational acceleration at 2.461, 4.171 and 4.621 cm s−2. The locations of SBVCs on the [Fe/H]-T, [Fe/H]-log g, log g-T and H-R diagrams are investigated. It is found that the detected SBVCs could be classified into four groups. The first group has higher log g ∼4.621 and lower T ∼ 4870 K which are mainly cool red dwarf binaries. The second group of SBVCs has log g around 4.171 cm s−2 that includes binaries and pulsating stars such as δ Sct and γ Dor variables. The gravitational accelerations of the third group of SBVCs are higher and some of them are below the zero-age main sequence. They may be contact binaries in which the primary components are losing energy to the secondaries in the common envelopes and are at a special stellar evolutionary stage. The last group is composed of giants or supergiants with log g around 2.461 cm s−2 that may be evolved pulsating stars. One target (C134624.29+333921.2) is confirmed as an eclipsing binary with a period of 0.65 days. A preliminary analysis suggests that it is a detached binary with a mass ratio of 0.46. The primary fills its critical Roche lobe by about 89%, indicating that mass transfer will occur between the two components.

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 present new deep photometry of the globular cluster system (GCS) around NGC 6166, the central supergiant galaxy in Abell 2199. HST data from the ACS and WFC3 cameras in F475W, F814W are used to determine the spatial distribution of the GCS, its metallicity distribution function (MDF), and the dependence of the MDF on galactocentric radius and on GC luminosity. The MDF is extremely broad, with the classic red and blue subpopulations heavily overlapped, but a double-Gaussian model can still formally match the MDF closely. The spatial distribution follows a Sersic-like profile detectably to a projected radius of at least $R_{gc} = 250$ kpc. To that radius, the total number of clusters in the system is N_{GC} = 39000 +- 2000, the global specific frequency is S_N = 11.2 +- 0.6, and 57\% of the total are blue, metal-poor clusters. The GCS may fade smoothly into the Intra-Cluster Medium of A2199; we see no clear transition from the core of the galaxy to the cD halo or the ICM. The radial distribution, projected ellipticity, and mean metallicity of the red (metal-richer) clusters match the halo light extremely well for R > 15 kpc, both of them varying as \sigma_{MRGC} ~ \sigma_{light} ~ R^-1.8. By comparison, the blue (metal-poor) GC component has a much shallower falloff \sigma_{MPGC} ~ R^-1.0 and a more nearly spherical distribution. This strong difference in their density distributions produces a net metallicity gradient in the GCS as a whole that is primarily generated by the population gradient. With NGC 6166 we appear to be penetrating into a regime of high enough galaxy mass and rich enough environment that the bimodal two-phase description of GC formation is no longer as clear or effective as it has been in smaller galaxies., Comment: 19 pages, 22 figures. In press for Astrophysical Journal

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.

Sodium overabundance in yellow supergiants has stumped people for more than 20 years. The purpose of this paper is to explore this problem from the perspective of nuclear physics. We investigate carefully the CNO and NeNa cycles that are responsible for sodium production. We investigate some key reactions in the appropriate network. We show whether and how the sodium output can be affected by the rate uncertainties in these reactions. In this way, we evaluate if a reaction is important enough to deserve a better determination of its rate in terrestrial laboratories.

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.

Hubble Space Telescope observations of the site of the supernova (SN) SN 2008ax obtained in 2011 and 2013 reveal that the possible progenitor object detected in pre-explosion images was in fact multiple. Four point sources are resolved in the new, higher-resolution images. We identify one of the sources with the fading SN. The other three objects are consistent with single supergiant stars. We conclude that their light contaminated the previously identified progenitor candidate. After subtraction of these stars, the progenitor appears to be significantly fainter and bluer than previously measured. Post-explosion photometry at the SN location indicates that the progenitor object has disappeared. If single, the progenitor is compatible with a supergiant star of B to mid-A spectral type, while a Wolf-Rayet (W-R) star would be too luminous in the ultraviolet to account for the observations. Moreover, our hydrodynamical modeling shows that the pre-explosion mass was 4-5 M⊙ and the radius was 30-50 R⊙, which is incompatible with a W-R progenitor. We present a possible interacting binary progenitor computed with our evolutionary models that reproduces all the observational evidence. A companion star as luminous as an O9-B0 main-sequence star may have remained after the explosion., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

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.

Multifrequency behaviour of the very slow nova V723 Cas is reviewed. The long-term photometry of the object revealed the orbital period 0.693265 days of the binary, quasi-periodic oscillations in the envelope of the outbursted white dwarf and 182 days periodicity of activity due to the mass transfer bursts from the red to the white dwarf probably caused by a periastron passage of the third body. The photometry at the maximum of brightness was used to calculate the velocity v = 210 {r km s}^{-1} of ejection of an expanding supergiant photosphere -- main inner envelope of the nova. The emission line profiles in nebular stage show multiple peaks formed in an expanding equatorial ring and polar blobs of this envelope. The HeI line profile and radio observations suggest the existence of the outer envelope, shaped and accelerated by the spherical and polar winds, detected as absorption components of the HI and HeI P Cygni type line profiles. Radio observations allowed to determine ejected mass 2.5 x 10 -4 M o and confirmed the clumpy structure of the ejecta.

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.

Variations of the Hα line in the spectra of the star HD14134 are investigated using observations carried out in 2013–2014 and in 2016 with the 2-m telescope at Shamakhy Astrophysical Observatory. In the spectra of this star, the absorption and emission components of Hα are found to disappear and an inverse P Cyg profile of Hα is seen on some observational epochs. Our observations showed that when the Hα line disappeared or an inversion of the P-Cyg-type profile is observed in the spectra, the Hβ line is redshifted. When these events appeared, no synchronous variabilities were observed in the spectral parameters of other spectral lines formed in deeper atmospheric layers. In addition, the structures of Hα, CII (6578.05 A, 6582.88 A), SiII (6347.1 A, 6371.36 A) and Hβ lines are variable on a timescale of hours, but we did not detect significant variations in the other photospheric lines, as well as in the HeI (5875.72 A) line. It is suggested that observational evidence for the non-stationary atmosphere of HD14134 can be associated in part with non-spherical stellar wind.

We present the first results from our HST Brightest Cluster Galaxy (BCG) survey of seven central supergiant cluster galaxies and their globular cluster (GC) systems. We measure a total of 48000 GCs in all seven galaxies, representing the largest single GC database. We find that a log-normal shape accurately matches the observed luminosity function (LF) of the GCs down to the GCLF turnover point, which is near our photometric limit. In addition, the LF has a virtually identical shape in all seven galaxies. Our data underscore the similarity in the formation mechanism of massive star clusters in diverse galactic environments. At the highest luminosities (log L > 10^7 L_Sun) we find small numbers of "superluminous" objects in five of the galaxies; their luminosity and color ranges are at least partly consistent with those of UCDs (Ultra-Compact Dwarfs). Lastly, we find preliminary evidence that in the outer halo (R > 20 kpc), the LF turnover point shows a weak dependence on projected distance, scaling as L_0 ~ R^-0.2, while the LF dispersion remains nearly constant., To appear in Astrophysical Journal, December 2014

We present Hubble Space Telescope (HST) observations of the field of the Type IIb supernova (SN) 2011dh in M51 performed at ≈1161 rest-frame days after explosion using the Wide Field Camera 3 and near-UV filters F225W and F336W. A star-like object is detected in both bands and the photometry indicates it has negative (F225W-F336W) color. The observed object is compatible with the companion of the now-vanished yellow supergiant progenitor predicted in interacting binary models. We consider it unlikely that the SN is undergoing strong interaction and thus estimate that it makes a small contribution to the observed flux. The possibilities of having detected an unresolved light echo or an unrelated object are briefly discussed and judged unlikely. Adopting a possible range of extinction by dust, we constrain parameters of the proposed binary system. In particular, the efficiency of mass accretion onto the binary companion must be below 50%, if no significant extinction is produced by newly formed dust. Further multiband observations are required in order to confirm the identification of the object as the companion star. If confirmed, the companion star would already be dominant in the UV-optical regime, so it would readily provide a unique opportunity to perform a detailed study of its properties., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

B[e] supergiants (B[e]SGs) are transitional objects in the post-main sequence evolution of massive stars. The small number of B[e]SGs known so far in the Galaxy and the Magellanic Clouds indicates that this evolutionary phase is short. Nevertheless, the strong aspherical mass loss occurring during this phase, which leads to the formation of rings or disk-like structures, and the similarity to possible progenitors of SN1987 A emphasize the importance of B[e]SGs for the dynamics of the interstellar medium as well as stellar and galactic chemical evolution. The number of objects and their mass-loss behavior at different metallicities are essential ingredients for accurate predictions from stellar and galactic evolution calculations. However, B[e]SGs are not easily identified, as they share many characteristics with luminous blue variables (LBVs) in their quiescent (hot) phase. We present medium-resolution near-infrared K-band spectra for four stars in M 31, which have been assigned a hot LBV (candidate) status. Applying diagnostics that were recently developed to distinguish B[e]SGs from hot LBVs, we classify two of the objects as bonafide LBVs; one of them currently in outburst. In addition, we firmly classify the two stars 2MASS J00441709+4119273 and 2MASS J00452257+4150346 as the first B[e]SGs in M 31 based on strong CO band emission detected in their spectra, and infrared colors typical for this class of stars., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

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.

In this paper, we investigate the problem of supersonic convection caused by the application of the usual Mixing Length Theory (MLT), and give a modification to the original expression of the MLT. In the case of the usual MLT, a zone of supersonic convection exists when the stellar model goes into yellow-red supergiant phase. When the modification is applied, the models of late type supergiants possess shallower convective envelopes for a given temperature compared with the normal formalism of the MLT. Therefore the stellar models made with our new formalism move to lower effective temperature by 100-400 K depending on the luminosity of the star. Such a modification does not affect the convective envelope structure of lower luminosity late type stars, as both expressions of the MLT give the same result. in these stars.

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

International audience; Titanium dioxide, TiO2, is a refractory species that could play a crucial role in the dust-condensation sequence around oxygen-rich evolved stars. We present and discuss the detections of 15 emission lines of TiO2 with ALMA in the complex environment of the red supergiant VY CMa. The observations reveal a highly clumpy, anisotropic outflow in which the TiO2 emission likely traces gas exposed to the stellar radiation field. We find evidence for a roughly east-west oriented, accelerating bipolar-like structure, of which the blue component runs into and breaks up around a solid continuum component. We see a distinct tail to the south-west for some transitions, consistent with features seen in the optical and near-infrared. We find that a significant fraction of TiO2 remains in the gas phase outside the dust-formation zone and suggest that this species might play only a minor role in the dust-condensation process around extreme oxygen-rich evolved stars like VY CMa.

SAO 244567 is an unusually fast evolving star. Within twenty years only, it had turned from a B-type supergiant into the central star of the Stingray Nebula. Space- and ground-based observations obtained over the last decades have revealed that its spectrum changes noticeably over just a few years, showing stellar evolution in real time. The low mass of SAO 244567 is, however, in strong contradiction with canonical post-asymptotic giant branch evolution. Thus, its fast evolution has been a mystery for decades. We present preliminary results of the non-LTE spectral analyis of the recently obtained HST/COS observations, which finally allow us to shed light on the evolutionary history of this extraordinary object., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

In this paper, we report on Chandra observations of the starburst galaxy NGC 922. NGC 922 is a drop-through ring galaxy with an expanding ring of star formation, similar in many respects to the Cartwheel galaxy. The Cartwheel galaxy is famous for hosting 12 ultraluminous X-ray sources (ULXs), most of which are in the star-forming ring. This is the largest number of ULXs seen in a single system and has led to speculation that the low metallicity of the Cartwheel (0.3 Z ☉) may optimize the conditions for ULX formation. In contrast, NGC 922 has metallicity near solar. The Chandra observations reveal a population of bright X-ray sources, including seven ULXs. The number of ULXs in NGC 922 and the Cartwheel scales with the star formation rate: we do not find any evidence for an excess of sources in the Cartwheel. Simulations of the binary population in these galaxies suggest that the ULX population in both systems is dominated by systems with strong wind accretion from supergiant donors onto direct-collapse black holes. The simulations correctly predict the ratio of the number of sources in NGC 922 and the Cartwheel. Thus, it would appear that the metallicity of the Cartwheel is not low enough to see a difference in the ULX population compared to NGC 922.

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.

The water maser emission from the unusual supergiant, VY CMa, has been observed with the Urumqi 25m radio telescope. A simple redshifted maser spectrum was detected in the 1.6 Jy noise level during our monitoring observations. All of the H2O maser features are redshifted with respect to the VY CMa stellar velocity of I 7.6 km .s(-1). The spectrum appears to consist of two striking like groups and each group has three features. The appearances and the ratio of these three features in the two maser groups are very similar. The H2O maser emission arises from a region close to the supergiant, about 10 stellar radii of the star. The simple redshifted spectrum could be due to infall masing gas on the near side of the disk. Pulsation of the central star causes oscillations in this portion of the envelope, with the shock wave propagating outward and with material falling inward. The masing gas motions are very complex, by which the dramatic changes or the quasi-sinusoidal fluctuation in Aux may be explained.

3EG J1837-0423 and HESS J1841-055 are two unidentified and peculiar high-energy sources located in the same region of the sky, separated by 1.4°. Specifically, 3EG J1837-0423 is a transient MeV object detected by EGRET only once during flaring activity that lasted a few days while HESS J1841-055 is a highly extended TeV source. We attempted to match the high-energy emission from the unidentified sources 3EG J1837-0423 and HESS J1841-055 with X-rays (4-20 keV) and soft γ-rays (20-100 keV) candidate counterparts detected through deep International Gamma-Ray Astrophysics Laboratory observations of the sky region. As a result we propose the Supergiant Fast X-ray Transient (SFXT) AX J1841.0-0536 as a possible candidate counterpart of 3EG J1837-0423, based on spatial proximity and transient behavior. Alternatively, AX J1841.0-0536 could be responsible for at least a fraction of the entire TeV emission from the extended source HESS J1841-055, based on a striking spatial correlation. In either case, the proposed association is also supported from an energetic standpoint by a theoretical scenario where AX J1841.0-0536 is a low magnetized pulsar which, due to accretion of massive clumps from the supergiant companion donor star, undergoes sporadic changes to transient Atoll-states where a magnetic tower can produce transient jets and as a consequence high-energy emission. In either case (by association with 3EG J1837-0423 or alternatively with HESS J1841-055), AX J1841.0-0536 might be the prototype of a new class of Galactic transient MeV/TeV emitters., Universidad Nacional De La Plata

An optical spectroscopic observation was made towards the circumstellar nebula of the supergiant VI Cyg 12, for the first time to the best of our knowledge. Several emission lines appear in the spectrum. Based on the spectra of the star and its circumstellar matter, as well as the IRAS and NVSS data, we conclude that VI Cyg 12 has an expanding shell with an expansion velocity 3100 km s(-1) due to strong stellar wind. It is an older star that possibly evolved from a very massive O-type star. The stellar wind and mass loss may take an important part in the evolution of this star.

The derivation of high precision/accuracy parameters and chemical abundances of massive stars is of utmost importance to the fields of stellar evolution and Galactic chemical evolution. We concentrate on the study of OB-type stars near the main sequence and their evolved progeny, the BA-type supergiants, covering masses of ∼6 to 25 solar masses and a range in effective temperature from ∼8000 to 35 000 K. The minimization of the main sources of systematic errors in the atmospheric model computation, the observed spectra and the quantitative spectral analysis play a critical role in the final results. Our self-consistent spectrum analysis technique employing a robust non-LTE line formation allows precise atmospheric parameters of massive stars to be derived, achieving 1σ-uncertainties as low as 1% in effective temperature and ∼0.05–0.10 dex in surface gravity. Consequences on the behaviour of the chemical elements carbon, nitrogen and oxygen are discussed here in the context of massive star evolution and Galactic chemical evolution, showing tight relations covered in previous work by too large statistical and systematic uncertainties. The spectral analysis of larger star samples, like from the upcoming Gaia-ESO survey, may benefit from these findings.

Massive stars are extremely luminous and characterized by mass loss through radiation-driven stellar winds. The radiation emitted at the stellar surface may interact with the wind, making the analysis of the emerging spectrum a very challenging task. In addition to the luminosity, effective temperature, and surface gravity, several other stellar parameters impact the spectral morphology of these objects, remarkably the mass-loss rate and the wind terminal velocity. That is generally the case for OB supergiants, Luminous Blue Variables, and WR stars. CMFGEN [1] comprises the state-of-the-art in non-LTE radiative transfer and has been successfully applied to the above classes of objects over the last decade. The code assumes spherical symmetry, stationary outflow, and both photospheric and wind lines can be treated in non-LTE. Full line blanketing due to hundreds of thousands of spectral lines is included, as well as wind clumping. Here I discuss the assumptions behind CMFGEN and present examples of models and spectroscopic analyses.

We report on progress in determining the chemical composition of the photospheres of massive, cool supergiant stars for the purpose of investigating whether by-products from recent slow neutron capture nucleosynthesis have been transported up to the photosphere by convective processes. Our initial work has been focused on identifying atomic transitions that are useful for stellar abundance work at near-infrared wavelengths and in gathering accurate atomic data for these transitions. The latter task includes the determination of experimental oscillator strengths, which represents a vital role for laboratory astrophysics. We use high-resolution optical and near-infrared spectra of the massive, cool star α. Orionis as the prototype for our study for line identification and synthetic spectrum modeling. Abundances have been determined for a number of heavy elements, and our early results illuminate the problems with atomic data that must be overcome before we are able to derive chemical abundances with the accuracy required for meaningful comparison with calculations for s-process nucleosynthesis.