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Measurements are presented and analysed of the strength of the Ca II triplet lines in red giants in Galactic globular and open clusters, and in a sample of red giants in the LMC disc that have significantly different [Ca/Fe] abundance ratios to the Galactic objects. The Galactic objects are used to generate a calibration between Ca II triplet line strength and [Fe/H], which is then used to estimate [Fe/H]CaT for the LMC stars. The values are then compared with the [Fe/H]spec determinations from high-dispersion spectroscopy. After allowance for a small systematic offset, the two abundance determinations are in excellent agreement. Further, as found in earlier studies, the difference is only a very weak function of the [Ca/Fe] ratio. For example, changing [Ca/Fe] from +0.3 to -0.2 causes the Ca II-based abundance to underestimate [Fe/H]spec by only ~0.15 dex, assuming a Galactic calibration. Consequently, the Ca II triplet approach to metallicity determinations can be used without significant bias to study stellar systems that have substantially different chemical evolution histories. [ABSTRACT FROM AUTHOR]

Context. The study of globular clusters is one of the most powerful ways to learn about a galaxy's chemical evolution and star formation history. They preserve a record of chemical abundances at the time of their formation and are relatively easy to age date. The most detailed knowledge of the chemistry of a star is given by high resolution spectroscopy, which provides accurate abundances for a wide variety of elements, yielding a wealth of information on the various processes involved in the cluster's chemical evolution. Aims. We studied red giant branch (RGB) stars in an old, metal-poor globular cluster of the LargeMagellanic Cloud (LMC), Hodge 11 (H11), in order to measure as many elements as possible. The goal is to compare its chemical trends to those in the Milky Way halo and dwarf spheroidal galaxies in order to help understand the formation history of the LMC and our own Galaxy. Methods. We have obtained high resolution VLT/FLAMES spectra of eight RGB stars in H11. The spectral range allowed us to measure a variety of elements, including Fe, Mg, Ca, Ti, Si, Na, O, Ni, Cr, Sc, Mn, Co, Zn, Ba, La, Eu and Y. Results. We derived a mean [Fe/H] = -2.00 ± 0.04, in the middle of previous determinations. We found low [α/Fe] abundances for our targets, more comparable to values found in dwarf spheroidal galaxies than in the Galactic halo, suggesting that if H11 is representative of its ancient populations then the LMC does not represent a good halo building block. Our [Ca/Fe] value is about 0.3 dex less than that of halo stars used to calibrate the Ca IR triplet technique for deriving metallicity. A hint of a Na abundance spread is observed. Its stars lie at the extreme high O, low Na end of the Na:O anti-correlation displayed by Galactic and LMC globular clusters. [ABSTRACT FROM AUTHOR]

ABSTRACT We report on the results of observations in the CO(1-0) transition of a complete sample of Southern, intermediate-redshift ( z= 0.2-0.5) ultraluminous infrared galaxies (ULIRGs) using the Mopra 22-m telescope. The 11 ULIRGs with LFIR > 1012.5 L⊙ south of δ=−12° were observed with integration times that varied between 5 and 24 h. Four marginal detections were obtained for individual targets in the sample. The 'stacked' spectrum of the entire sample yields a high significance, 10σ detection of the CO(1-0) transition at an average redshift of z= 0.38. The tightest correlation of LFIR and LCO for published low-redshift ULIRG samples ( z < 0.2) is obtained after normalization of both these measures to a fixed dust temperature. With this normalization the relationship is linear. The distribution of dust-to-molecular hydrogen gas mass displays a systematic increase in dust-to-gas mass with galaxy luminosity for low-redshift samples, but this ratio declines dramatically for intermediate-redshift ULIRGs down to values comparable to that of the Small Magellanic Cloud. The upper envelope to the distribution of ULIRG molecular mass as function of look-back time demonstrates a dramatic rise by almost an order of magnitude from the current epoch out to 5 Gyr. This increase in maximum ULIRG gas mass with look-back time is even more rapid than that of the star formation rate density. [ABSTRACT FROM AUTHOR]

Far-infrared [C ii] 158-μm, [O i] 145-μm and [O i] 63-μm fine structure emission-line fluxes were measured from archival Infrared Space Observatory Long Wavelength Spectrometer spectra of 46 extragalactic sources, with 28 sources providing detections in all three lines. For 12 of the sources, the contribution to the [C ii] 158-μm line flux from H ii regions could be estimated from their detected [N ii] 122-μm line fluxes. The measured [C ii]/[O i] and [O i] 63/145-μm line flux ratios were compared with those from a grid of photodissociation region (PDR) models previously computed using theucl_pdr code. Persistent offsets between the observed and modelled line ratios could be partly attributed to the effects of [O i] 63-μm self-absorption. Using the Spherical Multi-Mol (smmol) code, we calculated model [O i] line profiles and found that the strength of the [O i] 63-μm line was reduced by 20–80 per cent, depending on the PDR parameters. We conclude that high PDR densities and radiation field strengths, coupled with the effects of [O i] 63-μm self-absorption, are likely to provide the best match to the observed line flux ratios. [ABSTRACT FROM AUTHOR]

We present synthetic spectral energy distributions (SEDs) for single-age, single-metallicity stellar populations (SSPs) covering the full optical spectral range at moderately high resolution [full width at half-maximum (FWHM) 2.3 Å]. These SEDs constitute our base models, as they combine scaled-solar isochrones with an empirical stellar spectral library [Medium resolution INT Library of Empirical Spectra (MILES)], which follows the chemical evolution pattern of the solar neighbourhood. The models rely as much as possible on empirical ingredients, not just on the stellar spectra, but also on extensive photometric libraries, which are used to determine the transformations from the theoretical parameters of the isochrones to observational quantities. The unprecedented stellar parameter coverage of the MILES stellar library allowed us to safely extend our optical SSP SED predictions from intermediate- to very-old-age regimes and the metallicity coverage of the SSPs from super-solar to . SSPs with such low metallicities are particularly useful for globular cluster studies. We have computed SSP SEDs for a suite of initial mass function shapes and slopes. We provide a quantitative analysis of the dependence of the synthesized SSP SEDs on the (in)complete coverage of the stellar parameter space in the input library that not only shows that our models are of higher quality than those of other works, but also in which range of SSP parameters our models are reliable. The SSP SEDs are a useful tool to perform the analysis of stellar populations in a very flexible manner. Observed spectra can be studied by means of full spectrum fitting or by using line indices. For the latter, we propose a new line index system to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. Apart from constant resolution as a function of wavelength, the system is also based on flux-calibrated spectra. Data can be analysed at three different resolutions: 5, 8.4 and 14 Å (FWHM), which are appropriate for studying globular cluster, low- and intermediate-mass galaxies, and massive galaxies, respectively. Furthermore, we provide polynomials to transform current Lick/IDS line index measurements to the new system. We provide line index tables in the new system for various popular samples of Galactic globular clusters and galaxies. We apply the models to various stellar clusters and galaxies with high-quality spectra, for which independent studies are available, obtaining excellent results. Finally, we designed a web page from which not only these models and stellar libraries can be downloaded but which also provides a suite of on-line tools to facilitate the handling and transformation of the spectra. [ABSTRACT FROM AUTHOR]

Weak emission line quasars are a rare and puzzling group of objects. In this paper, we present one more object of this class found in the Sloan Digital Sky Survey (SDSS). The quasar SDSS J094533.99+100950.1, lying at , has practically no C iv emission line, a red continuum very similar to the second steepest of the quasar composite spectra of Richards et al., is not strongly affected by absorption and the Mg ii line, although relatively weak, is strong enough to measure the black hole mass. The Eddington ratio in this object is about 0.45, and the line properties are not consistent with the trends expected at high accretion rates. We propose that the most probable explanation of the line properties in this object, and perhaps in all weak emission line quasars, is that the quasar activity has just started. A disc wind is freshly launched so the low ionization lines which form close to the disc surface are already observed but the wind has not yet reached the regions where high ionization lines or narrow line components are formed. The relatively high occurrence of such a phenomenon may additionally indicate that the quasar active phase consists of several subphases, each starting with a fresh build-up of the broad-line region. [ABSTRACT FROM AUTHOR]

We present optical and infrared (IR) integrated colours and surface brightness fluctuation (SBF) magnitudes, computed from stellar population synthesis models that include emission from the dusty envelopes surrounding thermally pulsing asymptotic giant branch (TP-AGB) stars undergoing mass loss. We explore the effects of varying the mass-loss rate by one order of magnitude around the fiducial value, modifying accordingly both the stellar parameters and the output spectra of the TP-AGB stars plus their dusty envelopes. The models are single burst, and range in age from a few Myr to 14 Gyr, and in metallicity between and 0.07; they combine new calculations for the evolution of stars in the TP-AGB phase, with star plus envelope spectral energy distributions (SEDs) produced with the radiative transfer codedusty. We compare these models to optical and near-IR data of single AGB stars and Magellanic star clusters. This comparison validates the current understanding of the role of mass loss in determining stellar parameters and spectra in the TP-AGB. However, neither broad-band colours nor SBF measurements in the optical or the near-IR can discern global changes in the mass-loss rate of a stellar population. We predict that mid-IR SBF measurements can pick out such changes, and actually resolve whether a relation between metallicity and mass loss exists. [ABSTRACT FROM AUTHOR]

We report the results of a near-infrared survey for long-period variables in a field of view of 20× 30 arcmin2 towards the Galactic Centre (GC). We have detected 1364 variables, of which 348 are identified with those reported in Glass et al. We present a catalogue and photometric measurements for the detected variables and discuss their nature. We also establish a method for the simultaneous estimation of distances and extinctions using the period–luminosity relations for the JHKs bands. Our method is applicable to Miras with periods in the range 100–350 d and mean magnitudes available in two or more filter bands. While J band means are often unavailable for our objects because of the large extinction, we estimated distances and extinctions for 143 Miras whose H- and -band mean magnitudes are obtained. We find that most are located at the same distance to within our accuracy. Assuming that the barycentre of these Miras corresponds to the GC, we estimate its distance modulus to be , corresponding to . We have assumed the distance modulus to the Large Magellanic Cloud to be 18.45 mag, and the uncertainty in this quantity is included in the above systematic error. We also discuss the large and highly variable extinction. Its value ranges from 1.5 mag to larger than 4 mag in except towards the thicker dark nebulae and it varies in a complicated way with the line of sight. We have identified mid-infrared counterparts in the Spitzer/IRAC catalogue of Ramírez et al. for most of our variables and find that they follow rather narrow period–luminosity relations in the 3.6–8.0 μm wavelength range. [ABSTRACT FROM AUTHOR]

We present preliminary results from spectral observations of four (4) candidate radio sources co-identified with known planetary nebulae (PNe) in the Small Magellanic Cloud (SMC). These were made using the Radcliffe 1.9-meter telescope in Sutherland, South Africa. These radio PNe were originally found in Australia Telescope Compact Array (ATCA) surveys of the SMC at 1.42 and 2.37 GHz, and were further confirmed by new high resolution ATCA images at 6 and 3 cm (4"/2"). Optical PNe and radio candidates are within 2" and may represent a sub-population of selected radio bright objects. Nebular ionized masses of these objects may be 2.6 M☉ or greater, supporting the existence of PNe progenitor central stars with masses up to 8 M☉. [ABSTRACT FROM AUTHOR]

We present an analysis of three strong, intervening Mg II absorption systems towards the optical afterglow of gamma-ray burst (GRB) 060418. From high-resolution Ultraviolet and Visual Echelle Spectrograph (UVES) spectra we measure metal column densities and find that the highest redshift absorber exhibits a large amount of dust depletion compared with damped Lyman absorbers (DLAs) seen in quasi-stellar object (QSO) spectra. The intervening absorber is also unusual in exhibiting a clear 2175-Å bump, the first time this feature has been definitively detected in a GRB spectrum. The GRB afterglow spectrum is best fitted with a two-component extinction curve: a Small Magellanic Cloud (SMC) extinction law at (the redshift of the host) with and a Galactic extinction curve at with . We also present a moderately deep New Technology Telescope (NTT) R-band image of the GRB 060418 field and spectroscopy of four galaxies within 1 arcmin. None of these objects has a redshift that matches any of the intervening absorbers, and we conclude that the galaxies responsible for the two intervening Mg ii absorbers at have luminosities . [ABSTRACT FROM AUTHOR]

We present a Spitzer Space Telescope spectroscopic survey of mass-losing carbon stars (and one oxygen-rich star) in the Large Magellanic Cloud (LMC). The stars represent the superwind phase on the asymptotic giant branch (AGB), which forms a major source of dust for the interstellar medium (ISM) in galaxies. Bolometric magnitudes indicate progenitor masses of . The spectra cover the wavelength range 5–38 μm. They show varying combinations of dust continuum, dust emission features (SiC, MgS) and molecular absorption bands (C2H2, HCN). A 10-μm absorption feature is attributed to C3. A weak band at 5.8 μm is suggestive of carbonyl. The circumstellar 7.5-μm C2H2 band is found to be stronger at lower metallicity, explained by higher C/O ratios at low metallicity. The versus colours, used to select the sample, are shown to be relatively insensitive in separating carbon versus oxygen-rich AGB stars. The predominance of carbon stars therefore indicates that in the range , LMC AGB stars become carbon-rich before onset of the superwind. A set of four narrow bands, dubbed the Manchester system, is used to define the infrared continuum for dusty carbon stars. We investigate the strength and central wavelength of the SiC and MgS dust bands as a function of colour and metallicity. The line-to-continuum ratio of these bands shows some indication of being lower at low metallicity. The MgS band is only seen at dust temperatures below 600 K. Metal-poor carbon stars can form amorphous carbon dust from self-produced carbon. The formation efficiency of oxygen-rich dust depends more strongly on metallicity. In lower-metallicity environments, the dust input into the ISM by AGB stars may be strongly biased towards carbonaceous dust. [ABSTRACT FROM AUTHOR]

We reinvestigate the massive stellar content of the irregular dwarf galaxy NGC 3125 (Tol 3) using Very Large Telescope (VLT)/FORS1 imaging and spectroscopy, plus archival VLT/ISAAC, Hubble Space Telescope ( HST)/FOC and HST/STIS data sets. FORS1 narrow-band imaging confirms that the NGC 3125-A and -B knots represent the primary sites of Wolf–Rayet (WR) stars, whilst HST imaging reveals that both regions host two clusters. Both clusters within region A host WR stars (A1 and A2), for which the optically fainter cluster A2 is heavily reddened. It is not clear which cluster within region B hosts WR stars. Nebular properties are in good agreement with previous studies and infer a Large Magellanic Cloud (LMC) like metallicity of log(O/H)+12∼8.3. LMC template mid-type WN and early-type WC spectra are matched to the observed blue and red WR bumps of A1 and B, permitting the contribution of WC stars to the blue bump to be quantified. From our FORS1 spectroscopy, we obtain N(WN5–6:WC4) = 105:20, ∼55:0 and 40:20 for the clusters A1, A2 and B1 + 2, respectively. Our results are a factor of ∼3 lower than previously reported by optical studies as a result of a lower Hα/Hβ derived interstellar reddening. Using Starburst99 theoretical energy distributions to estimate O star populations for each cluster, we find N(WR)/ N(O) = 0.2 for A1 and 0.1 for A2 and the clusters within region B. From Hα narrow-band imaging, the O star content of the Giant H ii regions A and B is found to be a factor of 5–10 times higher than that derived spectroscopically for the ultraviolet (UV)/optically bright clusters, suggesting that NGC 3125 hosts optically obscured young massive clusters, further supported by VLT/ISAAC K-band imaging. Archival HST/STIS UV spectroscopy confirms the low interstellar reddening towards A1, for which we have determined a Small Magellanic Cloud (SMC) extinction law for NGC 3125, in preference to an LMC or starburst law. We obtain N(WN5–6) = 110 from the slit loss corrected He iiλ1640 line flux. This is in excellent agreement with optical results, although it is a factor of 35 times lower than that inferred from the same data set by Chandar, Leitherer & Tremonti. The discrepancy is due to an anomalously high interstellar reddening derived from their use of the generic starburst extinction law. Highly discrepant stellar populations may result in spatially resolved star-forming regions from UV and optical studies through the use of different extinction laws. [ABSTRACT FROM AUTHOR]

We present spectroscopic observations, taken with the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph telescope/instrument, of the unusual Small Magellanic Cloud X-ray binary system SXP 323 = AX J0051−733. This system shows a clear modulation at 0.71 d in long-term optical photometry, which has been proposed as the binary period of this system. The high-resolution optical spectra, taken at a range of phases during the 0.71-d cycle, rule out this possibility. Instead it is suggested that this long-term effect is due to non-radial pulsations in the Be star companion to SXP 323. In addition, the spectra show clear evidence for major changes in the ( V/ R) ratio of the double peaks of the Balmer lines indicative of asymmetries in the circumstellar disc. The complex structure of the interstellar lines is also discussed in the context of the SMC structure. [ABSTRACT FROM AUTHOR]