W. R. J. Rolleston

The present-day chemical composition of the SMC from UVES spectra of the sharp-lined, B-type dwarf AV 304

High-resolution spectroscopic VLT/UVES observations are presented for the B-type main-sequence star, AV 304, in the Small Magellanic Cloud (SMC). These spectra have been analysed using LTE model-atmosphere techniques, to derive stellar atmospheric parameters and chemical compositions. As AV 304 is located within the hydrogen burning main-sequence band, its chemical composition should reflect that of the SMC interstellar medium (ISM). A detailed line-by-line differential analysis has been undertaken relative to a Galactic comparison star. A general metal deficiency for the a-process elements O, Si & S of -0.43 +/- 0.05 dex is found for AV 304, with iron having a similar underabundance. Oxygen may be relatively over-abundant by similar to0.1 dex and carbon and aluminium underabundant by similar to0.2 dex. A large nitrogen underabundance (of -1.2 dex relative to hydrogen and -0.7 dex relative to iron) is found. This is interpreted in terms of the CNO bi-cycle having been suppressed in the SMC. Furthermore, the large nitrogen deficiency is in excellent agreement with that found for SMC H II regions. Indeed, this represents a first for stellar astrophysics - confirming the low base-line nitrogen composition of the SMC ISM (viz. 12+log(N/H) similar to 6.66 +/- 0.10 dex).

The present-day chemical composition of the LMC

High-resolution observations of five OB-type main-sequence stars in the Large Magellanic Cloud (LMC) have been obtained with the UCLspectrograph on the 3.9-m Anglo-Australian Telescope. These spectra have been analysed using LTE model-atmosphere techniques, to derive stellar atmospheric parameters and chemical compositions. As these stars are located within the hydrogen burning main-sequence band, their surface abundances should reflect those of the present-day interstellar medium. Detailed line-by-line differential analyses have been undertaken relative to Galactic comparison stars. We conclude that there exists a general metal deficiency of −0.31 ± 0.04 dex within the LMC, and find no significant abundance variations between cluster and field stars. There is also tentative evidence to suggest a lower oxygen to iron abundance ratio, and an over-deficiency of magnesium relative to the other α-elements. These are discussed in terms of previous abundance analyses and models of discontinuous (or bursting) star formation within the LMC. Finally, there is some evidence to suggest a greater chemical enrichment of material within the H  region LH104.

Chemical abundances in the inner 5 kpc of the Galactic disk

High-resolution, high signal-to-noise spectral data are presented for four young B-type stars lying towards the Galactic Centre. Determination of their atmospheric parameters from their absorption line profiles, and uvby photometric measurement of the continua indicate that they are massive objects lying slightly out of the plane, and were probably born in the disk between 2.5-5 kpc from the Centre. We have carried out a detailed absolute and differential line-by-line abundance analyses of the four stars compared to two stars with very similar atmospheric parameters in the solar neighbourhood. The stars appear to be rich in all the well sampled chemical elements (C, N, Si, Mg, S, Al), except for oxygen . Oxygen abundances derived in the atmospheres of these four stars are very similar to that in the solar neighbourhood. If the photospheric composition of these young stars is reflective of the gaseous ISM in the inner Galaxy, then the values derived for the enhanced metals are in excellent agreement with the extrapolation of the Galactic abundance gradients previously derived by Rolleston et al. (2000) and others. However, the data for oxygen suggests that the inner Galaxy may not be richer than normal in this element, and the physical reasons for such a scenario are unclear.

An analysis of the optical spectra of the post-asymptotic giant branch stars LSIV -12 111 and HD 341617

High spectral resolution and signal-to-noise observations of the absorption and emission line spectra in two post- asymptotic-giant-branch (PAGB) stellar candidates, LSIV 12 111 and HD 314617 are discussed. The absorption line spectra have been analysed using non-LTE model atmosphere techniques to determine stellar atmospheric parameters and chemical compositions, both in absolute terms and relative to a standard star, HD 13841. The atmospheric parameters dier from previous estimates based on LTE model atmospheres, probably due to non-LTE eects. In turn these imply stellar masses that are generally larger than have been previously estimated. Both PAGB candidates have relative uniform underabundances of metals with mean values of 0.35 dex for LSIV 12 111 and 0.50 dex for HD 314617. Furthermore, their abundance patterns are remarkably similar to that observed for optically bright, F-type PAGBs. From the emission spectra, the plasma parameters and angular size of the circumstellar material are constrained, and these are consistent with previous estimates and with a PAGB evolutionary stage.

The Optical Spectral Line List of RR Telescopii

The symbiotic nova RR Telescopii has been observed with the 1.5 m telescope of the Cerro Tololo Inter-American Observatory (CTIO), using the 1.5 m bench-mounted echelle spectrograph in conjunction with a Tektronix CCD. It displays a rich emission-line spectrum, ranging in excitation from O I to [Ni VIII]. We present a list of 491 measured lines, with their suggested identifications, covering a wavelength range from 3430 to 9320 A. Of these, only nine are unidentified, and 70 lines are cataloged that were not given in the original line list of Thackeray. Absolute line intensities are also given, which have been derived by comparing the high-resolution data with a flux-calibrated low-resolution spectrum taken with the Cassegrain spectrograph on the 1.0 m telescope at CTIO.

Chemical compositions of four B-type supergiants in the SMC wing

High-resolution UCLES/AAT spectra of four B-type supergiants in the SMC South East Wing have been analysed using non-LTE model atmosphere techniques to determine their atmospheric parameters and chemical compositions. The prin- ciple aim of this analysis was to determine whether the very low metal abundances (−1.1 dex compared with Galactic value) previously found in the Magellanic Inter Cloud region (ICR) were also present in the SMC Wing. The chemical compositions of the four targets are similar to those found in other SMC objects and appear to be incompatible with those deduced previously for the ICR. Given the close proximity of the Wing to the ICR, this is difficult to understand and some possible explanations are briefly discussed.

Early-Type Stars in the Galactic Halo from the Palomar-Green Survey. I. A Sample of Evolved, Low-Mass Stars

We present high-resolution spectroscopic observations of early-type stars drawn from a complete sample based on low-resolution spectroscopy of targets from the Palomar-Green Survey by Green, Schmidt, & Liebert. Qualitatively, the metal-line spectra are sharp and are therefore indicative of extremely low projected rotational velocities. Hence the objects are characterized as members of an old, evolved population (for example, blue horizontal branch or post-asymptotic giant branch). By careful choice of Population I, Galactic disk B stars, we have computed differential abundances between the targets and their main-sequence analogs. The CNO abundances from model-atmosphere analyses suggest the presence of nucleosynthesis dredge-up products in the stellar photospheres. With one exception, the stars all have [Fe/H] abundances consistent with their progenitor objects being metal deficient. Some conclusions are drawn as to the previous evolution (red giant branch, horizontal branch, or asymptotic giant branch) of the stars.

Observations of the interstellar medium in the Magellanic Bridge.

We present ultraviolet and optical spectra of DI1388, a young star in the Magellanic Bridge, a region of gas between the Small and Large Magellanic Clouds. The data have signal-to-noise ratios of 20–45 and a spectral resolution of 6.5 kms −1 . Interstellar absorption by the Magellanic Bridge at vLSR ≈ 200 kms −1 is visible in the lines of C I, C II, C II*, C IV, N I, O I, Al II, Si II, Si III, Si IV, S II, Ca II, Fe II, and Ni II. The relative gas-phase abundances of C II, N I, O I, Al II, Si II, Fe II, and Ni II with respect to S II are similar to those found in Galactic halo clouds, despite a significantly lower metallicity in the Magellanic Bridge. The higher ionization species in the cloud have a column density ratio N(C +3 )/N(Si +3 ) ∼ 1.9, similar to that inferred for collisionally ionized Galactic cloud interfaces at temperatures ∼ 10 5 K. We identify sub-structure in the stronger interstellar lines, with a broad component (FWHM ∼ 20 kms −1 ) at ∼ 179 kms −1 and a sharp component (FWHM ∼ 11 kms −1 ) at 198 kms −1 . The abundance analysis for these clouds indicates that the feature at 198 kms −1 consists of a low electron density, mainly neutral gas that may be associated with an interface responsible for the highly ionized gas. The 179 kms −1 cloud consists of warmer, lower density gas that is partially ionized. Subject headings: Galaxies: abundances — ISM: abundances — Magellanic Bridge — ISM: structure

A non-LTE analysis of the spectra of two narrow lined main sequence stars in the SMC

An analysis of high-resolution VLT/UVES spectra of two B-type main sequence stars, NGC 346-11 and AV 304, in the Small Magellanic Cloud (SMC), has been undertaken, using the non-LTE tlusty model atmospheres to derive the stellar parameters and chemical compositions of each star. The chemical compositions of the two stars are in reasonable agreement. Moreover, our stellar analysis agrees well with earlier analyses of

High-resolution spectroscopy of globular cluster post-Asymptotic Giant Branch stars

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