The blue supergiant Sher 25 and its intriguing hourglass nebula

The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumsteller nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here, we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + log O/H = 8.61 +/- 0.13 dex) is similar to that in the background nebula (8.56 +/- 0.07), suggesting that the composition of the host cluster is around solar. However, we confirm that the circumsteller nebula is very rich in nitrogen, with an abundance of 8.91 +/- 0.15, compared to the background value of 7.47 +/- 0.18. A new analysis of the stellar spectrum With the FASTWIND model atmosphere code suggests that the photospheric nitrogen and oxygen abundances in Sher 25 are consistent with the nebular results. While the nitrogen abundances are high, when compared to stellar evolutionary models, they do not unambiguously confirm that the star has undergone convective dredge-up during a previous red supergiant phase. We suggest that the more likely scenario is that the nebula was ejected from the star while it was in the blue supergiant phase. The star's initial mass was around 50 M-circle dot which is rather too high for it to have had a convective envelope stage as a red supergiant. Rotating stellar models that lead to mixing of core-processed material to the stellar surface during core H-burning can quantitatively match the stellar results with the nebula abundances.

Blue luminous stars in nearby galaxies: Quantitative spectral analysis of M33 B-type supergiant stars

We present the detailed spectral analysis of a sample of M33 B-type supergiant stars, aimed at the determination of their fundamental parameters and chemical composition. The analysis is based on a grid of non-LTE metal line-blanketed model atmospheres including the effects of stellar winds and spherical extension computed with the code FASTWIND. Surface abundance ratios of C, N, and O are used to discuss the chemical evolutionary status of each individual star. The comparison of observed stellar properties with theoretical predictions of massive star evolutionary models shows good agreement within the uncertainties of the analysis. The spatial distribution of the sample allows us to investigate the existence of radial abundance gradients in the disk of M33. The comparison of stellar and H II region O abundances ( based on direct determinations of the electron temperature of the nebulae) shows good agreement. Using a simple linear radial representation, the stellar oxygen abundances result in a gradient of -0.0145 +/- 0.005 dex arcmin(-1) (or -0.06 +/- 0.02 dex kpc(-1)) up to a distance equal to similar to 1.1 times the isophotal radius of the galaxy. A more complex representation cannot be completely discarded by our stellar sample. The stellar Mg and Si abundances follow the trend displayed by O abundances, although with shallower gradients. These differences in gradient slope cannot be explained at this point. The derived abundances of the three alpha-elements yield solar metallicity in the central regions of the disk of M33. A comparison with recent planetary nebula data from Magrini and coworkers indicates that the disk of M33 has not suffered from a significant O enrichment in the last 3 Gyr.

VLT FORS spectra of blue supergiants in the Local Group galaxy NGC 6822

Half hour exposures using the ESO VLT/FORS1 combination at Paranal in Chile have allowed us to obtain spectra for three B supergiants in the dwarf irregular galaxy NGC 6822. The spectra have been analysed using non-LTE techniques and temperatures, gravities, helium content and abundances have been obtained. Overall the metallicity of NGC 6822 is found to lie between that of the LMC and of the SMC, in agreement with previous observations of H II regions and in contrast to the earlier findings of Massey et al. (1995). The analysis of H-alpha yields estimates of the mass-loss rates and wind momenta. These results demonstrate that significantly longer exposures with the same instruments will allow us to perform quantitative spectroscopy of blue supergiants in galaxies far beyond the Local Group.

A UKST survey of blue objects towards the galactic centre - a search for early-type stars

We have begun a search for early-type stars towards the galactic centre which are potentially young objects situated within the inner few kiloparsecs of the disk. U and V (or I) band photographic photometry from the UK Schmidt Telescope has been obtained to identify the bluest candidates in nineteen Schmidt fields (centred close to the galactic centre). We have spectroscopically observed these targets for three fields with the FLAIR multi-fibre system to determine their spectral types. In particular; ten early B-type stars have been identified and equivalent width measurements of their Balmer and HeI lines have been used to estimate atmospheric parameters. These early-type objects have magnitudes in the range 11.5 less than or equal to V less than or equal to 16.0, and our best estimates of their distance (given probable highly variable reddening in this direction together with errors in the plate photometry) suggest that some of them originated close to (i.e R-g

New identifications for blue objects towards the Galactic center: post-AGE stars, Be/disk stars and others

As part of a programme to investigate spatial variations in the Galactic chemical composition, we have been searching for normal B-type stars and A-type supergiants near the Galactic center. During this search we have found eleven peculiar stars, and in some cases performed detailed abundance analyses of them which suggest that they may be at a post-AGB evolutionary stage.

LS 4825: A blue supergiant on the far side of the galaxy

We present high-resolution spectroscopic observations of LS 4825, a V = 12 B-type star in the Galactic center direction. On the basis of its stellar and interstellar spectra, we infer that it is likely to be a young supergiant at a distance of 21 +/- 5 kpc, and hence lying on the far side of the 'Galaxy. Adopting this hypothesis, a differential abundance analysis shows LS 4825 to have a chemical composition that is consistent with local B-type supergiants. These observations therefore represent the first detailed investigation of a star on the far side of the Galactic center. We trace multiple interstellar components in Ca II K and Na I D spectra, with velocities -206 less than or equal to v(lst) less than or equal to +93 km s(-1). We consider the likely origin of this gas and find that some components appear to trace matter lying close to the Galactic center. We discuss the possible use of such sight lines in furthering our understanding both of the nature of gas around the Galactic center and of the abundance gradient of the Galaxy.

Metallicities of 4 blue supergiants near the Galactic centre

High resolution optical spectra of four blue supergiants (HD148422 B0.5 Ib; HD178487 B0.5 Ib; HD179407 B1 Ib, HD163522 B1 Ib) which lie within 4.5 kpc of the Galactic centre are presented. Careful differential LTE model atmosphere analyses are used to quantify the differences in photospheric metal abundances between these stars and MK spectral standards in the solar neighborhood. A detailed non-LTE model atmosphere analysis of one star (HD163522) confirms that the LTE differential abundances should be reliable, provided we use a comparison star with similar atmospheric parameters.

Identification, expression, and DNA sequence of the GDP-mannose biosynthesis genes encoded by the O7 rfb gene cluster of strain VW187 (Escherichia coli O7:K1)

The O7-specific lipopolysaccharide (LPS) in strains of Escherichia coli consists of a repeating unit made of galactose, mannose, rhamnose, 4-acetamido-2,6-dideoxyglucose, and N-acetylglucosamine. We have recently cloned and characterized genetically the O7-specific LPS biosynthesis region (rfbEcO7) of the E. coli O7:K1 strain VW187 (C. L. Marolda, J. Welsh, L. Dafoe, and M. A. Valvano, J. Bacteriol. 172:3590-3599, 1990). In this study, we localized the gnd gene encoding gluconate-6-phosphate dehydrogenase at one end of the rfbEcO7 gene cluster and sequenced that end of the cluster. Three open reading frames (ORF) encoding polypeptides of 275, 464, and 453 amino acids were identified upstream of gndEcO7, all transcribed toward the gnd gene. ORF275 had 45% similarity at the protein level with ORF16.5, which occupies a similar position in the Salmonella enterica LT2 rfb region, and presumably encodes a nucleotide sugar transferase. The polypeptides encoded by ORFs 464 and 453 were expressed under the control of the ptac promoter and visualized in Coomassie blue-stained sodium dodecyl sulfate-polyacrylamide gels and by maxicell analysis. ORF464 expressed GDP-mannose pyrophosphorylase and ORF453 encoded a phosphomannomutase, the enzymes for the biosynthesis pathway of GDP-mannose, one of the nucleotide sugar precursors for the formation of the O7 repeating unit. They were designated rfbMEcO7 and rfbKEcO7, respectively. The RfbMEcO7 polypeptide was homologous to the corresponding protein in S. enterica LT2, XanB of Xanthomonas campestris, and AlgA of Pseudomonas aeruginosa, all GDP-mannose pyrophosphorylases. RfbKEcO7 was very similar to CpsG of S. enterica LT2, an enzyme presumably involved in the biosynthesis of the capsular polysaccharide colanic acid, but quite different from the corresponding RfbK protein of S. enterica LT2.

Outer membrane proteins of Bacteroides fragilis grown in vivo

The outer membrane protein (OMP) profiles of four different strains of Bacteroides fragilis, as determined by Coomassie blue stained polyacrylamide gels, were compared after growth in broth culture and in the mouse peritoneal cavity. There was no induction of the expression of large quantities of novel OMP after growth in vivo. Mouse immunoglobulin G and albumin were associated with the bacterial OMP, but could be removed by washing.

One-step synthesis of ZnO nanosheets: a blue-white fluorophore

Zinc oxide is synthesised at low temperature (80A degrees C) in nanosheet geometry using a substrate-free, single-step, wet-chemical method and is found to act as a blue-white fluorophore. Investigation by atomic force microscopy, electron microscopy, and X-ray diffraction confirms zinc oxide material of nanosheet morphology where the individual nanosheets are polycrystalline in nature with the crystalline structure being of wurtzite character. Raman spectroscopy indicates the presence of various defects, while photoluminescence measurements show intense green (centre wavelength approximately 515 nm) blue (approximately 450 nm), and less dominant red (approximately 640 nm) emissions due to a variety of vacancy and interstitial defects, mostly associated with surfaces or grain boundaries. The resulting colour coordinate on the CIE-1931 standard is (0.23, 0.33), demonstrating potential for use as a blue-white fluorescent coating in conjunction with ultraviolet emitting LEDs. Although the defects are often treated as draw-backs of ZnO, here we demonstrate useful broadband visible fluorescence properties in as-prepared ZnO. 

In vivo safety of trypan blue use in vitreoretinal surgery

Purpose: The purpose of this study was to evaluate "in vivo" safety of trypan blue (TB) in patients undergoing TB-assisted internal limiting membrane or epiretinal membrane peeling. Methods: Prospective study including 21 patients (21 eyes) with full-thickness macular hole and/or epiretinal membrane undergoing TB-assisted internal limiting membrane/epiretinal membrane peeling. Main outcome measures included distance visual acuity, near visual acuity, amplitude of P50 and N95 of the pattern electroretinogram, and fundus autofluorescence; these were assessed preoperatively, at 6 months (n = 21) and 12 months (n = 10) postoperatively. Results: There was a statistically significant improvement in distance visual acuity, near visual acuity, P50, and N95 amplitude at 6 months and 12 months postoperatively. The mean logarithm of the minimum angle of resolution distance visual acuity and near visual acuity improved from baseline by 0.31 (SD 0.37) and 0.17 (SD 0.31) at 6 months, respectively, and by 0.4 (SD 0.25) and 0.35 (SD 0.28) at 12 months, respectively. The mean P50 and N95 component amplitudes improved by 28% compared with baseline at 6 months (P50 0.4 [SD 0.8]; N95 0.53 [SD 1.07]) and by 63% at 12 months (P50 0.9 [0.85]; N95 1.04 [1.34]). Autofluorescence did not demonstrate damage to the retinal pigment epithelium attributable to TB. Conclusion: No deleterious effects of TB were observed in this study. Copyright © 2011 Lippincott Williams &Wilkins.