Search

We present new radio continuum images and a source catalogue from the MeerKAT survey in the direction of the Small Magellanic Cloud. The observations, at a central frequency of 1.3 GHz across a bandwidth of 0.8 GHz, encompass a field of view ∼7° × 7° and result in images with resolution of 8 arcsec. The median broad-band Stokes I image Root Mean Squared noise value is ∼11  μ Jy beam−1. The catalogue produced from these images contains 108 330 point sources and 517 compact extended sources. We also describe a UHF (544–1088 MHz) single pointing observation. We report the detection of a new confirmed Supernova Remnant (SNR; MCSNR J0100–7211) with an X-ray magnetar at its centre and 10 new SNR candidates. This is in addition to the detection of 21 previously confirmed SNRs and two previously noted SNR candidates. Our new SNR candidates have typical surface brightness an order of magnitude below those previously known, and on the whole they are larger. The high sensitivity of the MeerKAT survey also enabled us to detect the bright end of the SMC Planetary Nebulae (PNe) sample – point-like radio emission is associated with 38 of 102 optically known PNe, of which 19 are new detections. Lastly, we present the detection of three foreground radio stars amidst 11 circularly polarized sources, and a few examples of morphologically interesting background radio galaxies from which the radio ring galaxy ESO 029–G034 may represent a new type of radio object. [ABSTRACT FROM AUTHOR]

We present new Hubble Space Telescope Wide-Field Camera 3/infrared medium-band photometry of the compact elliptical galaxy M32, chemically resolving its thermally pulsating asymptotic giant branch stars. We find 2829 M-type stars and 57 C stars. The carbon stars are likely contaminants from M31. If carbon stars are present in M32 they are so in very low numbers. The uncorrected C/M ratio is 0.020 ± 0.003; this drops to less than 0.007 after taking into account contamination from M31. As the mean metallicity of M32 is just below solar, this low ratio of C to M stars is unlikely due to a metallicity ceiling for the formation of carbon stars. Instead, the age of the asymptotic giant branch (AGB) population is likely to be the primary factor. The ratio of AGB to red giant branch stars in M32 is similar to that of the inner disc of M31 which contain stars that formed 1.5–4 Gyr ago. If the M32 population is at the older end of this age then its lack of C-stars may be consistent with a narrow mass range for carbon star formation predicted by some stellar evolution models. Applying our chemical classifications to the dusty variable stars identified with Spitzer , we find that the x-AGB candidates identified with Spitzer are predominately M-type stars. This substantially increases the lower limit to the cumulative dust-production rate in M32 to > 1.20 × 10−5 |${\rm M}_{\odot } \, {\rm yr}^{-1}$|⁠. [ABSTRACT FROM AUTHOR]

High-spatial-resolution H  i observations have led to the realization that the nearby (within few hundreds of parsecs) Galactic atomic filamentary structures are aligned with the ambient magnetic field. Enabled by the high-quality data from the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope for the Galactic ASKAP H  i survey, we investigate the potential magnetic alignment of the |$\gtrsim\!{10}\, {\rm pc}$| -scale H  i filaments in the Small Magellanic Cloud (SMC). Using the Rolling Hough Transform technique that automatically identifies filamentary structures, combined with our newly devised ray-tracing algorithm that compares the H  i and starlight polarization data, we find that the H  i filaments in the north-eastern end of the SMC main body ('Bar' region) and the transition area between the main body and the tidal feature ('Wing' region) appear preferentially aligned with the magnetic field traced by starlight polarization. Meanwhile, the remaining SMC volume lacks starlight polarization data of sufficient quality to draw any conclusions. This suggests for the first time that filamentary H  i structures can be magnetically aligned across a large spatial volume (⁠|$\gtrsim\!{\rm kpc}$|⁠) outside of the Milky Way. In addition, we generate maps of the preferred orientation of H  i filaments throughout the entire SMC, revealing the highly complex gaseous structures of the galaxy likely shaped by a combination of the intrinsic internal gas dynamics, tidal interactions, and star-formation feedback processes. These maps can further be compared with future measurements of the magnetic structures in other regions of the SMC. [ABSTRACT FROM AUTHOR]

The Nearby Evolved Stars Survey (NESS) is a volume-complete sample of ∼850 Galactic evolved stars within 3 kpc at (sub-)mm wavelengths, observed in the CO J  = (2–1) and (3–2) rotational lines, and the sub-mm continuum, using the James Clark Maxwell Telescope and Atacama Pathfinder Experiment. NESS consists of five tiers, based on distances and dust-production rate (DPR). We define a new metric for estimating the distances to evolved stars and compare its results to Gaia EDR3. Replicating other studies, the most-evolved, highly enshrouded objects in the Galactic Plane dominate the dust returned by our sources, and we initially estimate a total DPR of 4.7 × 10−5 M⊙ yr−1 from our sample. Our sub-mm fluxes are systematically higher and spectral indices are typically shallower than dust models typically predict. The 450/850 |$\mu$| m spectral indices are consistent with the blackbody Rayleigh–Jeans regime, suggesting a large fraction of evolved stars have unexpectedly large envelopes of cold dust. [ABSTRACT FROM AUTHOR]

Galaxy interactions distort the distribution of baryonic matter and can affect star formation. The nearby Magellanic Clouds are a prime example of an ongoing galaxy interaction process. Here, we use the intermediate-age (∼1–10 Gyr) red clump (RC) stars to map the 3D structure of the Small Magellanic Cloud (SMC) and interpret it within the context of its history of interaction with the Large Magellanic Cloud (LMC) and the Milky Way. RC stars are selected from near-infrared colour–magnitude diagrams based on data from the Visible and Infrared Survey Telescope for Astronomy survey of the Magellanic Clouds. Interstellar reddening is measured and removed, and the corrected brightness is converted to a distance, on a star-by-star basis. A flat plane fitted to the spatial distribution of RC stars has an inclination i = 35°–48° and position angle, PA=170°–186°. However, significant deviations from this plane are seen, especially in the periphery and on the eastern side of the SMC. In the latter part, two distinct populations are present, separated in distance by as much as 10 kpc. Distant RC stars are seen in the north of the SMC, and possibly also in the far west; these might be associated with the predicted 'Counter-Bridge'. We also present a dust reddening map, which shows that dust generally traces stellar mass. The structure of the intermediate-age stellar component of the SMC bears the imprints of strong interaction with the LMC a few Gyr ago, which cannot be purely tidal but must have involved ram pressure stripping. [ABSTRACT FROM AUTHOR]

We present results from an analysis of ∼29 000 RR Lyrae stars located in the Large Magellanic Cloud (LMC). For these objects, near-infrared time-series photometry from the VISTA survey of the Magellanic Clouds system (VMC) and optical data from the Optical Gravitational Lensing Experiment (OGLE) IV survey and the Gaia Data Release 2 catalogue of confirmed RR Lyrae stars were exploited. Using VMC and OGLE IV magnitudes we derived period–luminosity (PL), period–luminosity–metallicity (PLZ), period–Wesenheit (PW), and period–Wesenheit–metallicity (PWZ) relations in all available bands. More that  7000 RR Lyrae were discarded from the analysis because they appear to be overluminous with respect to the PL relations. The |$PL_{K_{\mathrm{s}}}$| relation was used to derive individual distance to |${\sim}22\, 000$| RR Lyrae stars, and study the three-dimensional structure of the LMC. The distribution of the LMC RR Lyrae stars is ellipsoidal with the three axis S 1 = 6.5 kpc, S 2 = 4.6 kpc, and S 3 = 3.7 kpc, inclination i  = 22 ± 4° relative to the plane of the sky and position angle of the line of nodes θ = 167 ± 7° (measured from north to east). The north-eastern part of the ellipsoid is closer to us and no particular associated substructures are detected and neither any metallicity gradient. [ABSTRACT FROM AUTHOR]

We present observations of a region of the Galactic plane taken during the Early Science Program of the Australian Square Kilometre Array Pathfinder (ASKAP). In this context, we observed the scorpio field at 912 MHz with an uncompleted array consisting of 15 commissioned antennas. The resulting map covers a square region of ∼40 deg2, centred on (l, b)  = (343.5°, 0.75°), with a synthesized beam of 24 × 21 arcsec2 and a background rms noise of 150–200  μ Jy beam−1, increasing to 500–600  μ Jy beam−1 close to the Galactic plane. A total of 3963 radio sources were detected and characterized in the field using the caesar source finder. We obtained differential source counts in agreement with previously published data after correction for source extraction and characterization uncertainties, estimated from simulated data. The ASKAP positional and flux density scale accuracy were also investigated through comparison with previous surveys (MGPS, NVSS) and additional observations of the scorpio field, carried out with ATCA at 2.1 GHz and 10 arcsec spatial resolution. These allowed us to obtain a measurement of the spectral index for a subset of the catalogued sources and an estimated fraction of (at least) 8 per cent of resolved sources in the reported catalogue. We cross-matched our catalogued sources with different astronomical data bases to search for possible counterparts, finding ∼150 associations to known Galactic objects. Finally, we explored a multiparametric approach for classifying previously unreported Galactic sources based on their radio-infrared colours. [ABSTRACT FROM AUTHOR]

We present Herschel Space Observatory Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver Fourier Transform Spectrometer (SPIRE FTS) spectroscopy of a sample of 20 massive Young Stellar Objects (YSOs) in the Large and Small Magellanic Clouds (LMC and SMC). We analyse the brightest far-infrared (far-IR) emission lines, that diagnose the conditions of the heated gas in the YSO envelope and pinpoint their physical origin. We compare the properties of massive Magellanic and Galactic YSOs. We find that [O  i ] and [C  ii ] emission, that originates from the photo-dissociation region associated with the YSOs, is enhanced with respect to the dust continuum in the Magellanic sample. Furthermore the photoelectric heating efficiency is systematically higher for Magellanic YSOs, consistent with reduced grain charge in low metallicity environments. The observed CO emission is likely due to multiple shock components. The gas temperatures, derived from the analysis of CO rotational diagrams, are similar to Galactic estimates. This suggests a common origin to the observed CO excitation, from low-luminosity to massive YSOs, both in the Galaxy and the Magellanic Clouds. Bright far-IR line emission provides a mechanism to cool the YSO environment. We find that, even though [O  i ], CO, and [C  ii ] are the main line coolants, there is an indication that CO becomes less important at low metallicity, especially for the SMC sources. This is consistent with a reduction in CO abundance in environments where the dust is warmer due to reduced ultraviolet-shielding. Weak H2O and OH emission is detected, consistent with a modest role in the energy balance of wider massive YSO environments. [ABSTRACT FROM AUTHOR]

We present results from the analysis of 2997 fundamental mode RR Lyrae variables located in the Small Magellanic Cloud (SMC). For these objects, near-infrared time series photometry from the VISTA survey of the Magellanic Clouds system (VMC) and visual light curves from the OGLE IV (Optical Gravitational Lensing Experiment IV) survey are available. In this study, the multi-epoch Ks-band VMC photometry was used for the first time to derive intensityaveraged magnitudes of the SMCRR Lyrae stars. We determined individual distances to theRR Lyrae stars from the near-infrared period-absolute magnitude-metallicity (PMKsZ) relation, which has some advantages in comparison with the visual absolute magnitude-metallicity (MV-[Fe/H]) relation, such as a smaller dependence of the luminosity on interstellar extinction, evolutionary effects and metallicity. The distances we have obtained were used to study the three-dimensional structure of the SMC. The distribution of the SMC RR Lyrae stars is found to be ellipsoidal. The actual line-of-sight depth of the SMC is in the range 1-10 kpc, with an average depth of 4.3 ± 1.0 kpc. We found that RR Lyrae stars in the eastern part of the SMC are affected by interactions of the Magellanic Clouds. However, we do not see a clear bimodality observed for red clump stars, in the distribution of RR Lyrae stars. [ABSTRACT FROM AUTHOR]

The Infrared Spectrograph (IRS) on the Spitzer Space Telescope observed nearly 800 point sources in the Large Magellanic Cloud (LMC), taking over 1000 spectra. 197 of these targets were observed as part of the SAGE-Spec Spitzer Legacy program; the remainder are from a variety of different calibration, guaranteed time and open time projects.We classify these point sources into types according to their infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information, using a decision-tree classification method.We then refine the classification using supplementary information from the astrophysical literature. We find that our IRS sample is comprised substantially of YSO and HII regions, post-main-sequence low-mass stars: (post-)asymptotic giant branch stars and planetary nebulae and massive stars including several rare evolutionary types. Two supernova remnants, a nova and several background galaxies were also observed. We use these classifications to improve our understanding of the stellar populations in the LMC, study the composition and characteristics of dust species in a variety of LMC objects and to verify the photometric classification methods used by mid-IR surveys.We discover that some widely used catalogues of objects contain considerable contamination and others are missing sources in our sample. [ABSTRACT FROM AUTHOR]

We present K-band integral field spectroscopic observations towards 17 massive young stellar objects (YSOs) in the low-metallicity SmallMagellanic Cloud (SMC) and two YSO candidates in the compact HII regions N81 and N88 A (also in the SMC). These sources, originally identified using Spitzer photometry and/or spectroscopy, have been resolved into 29 K-band continuum sources. By comparing Brγ emission luminosities with those presented for a Galactic sample of massive YSOs, we find tentative evidence for increased accretion rates in the SMC. Around half of our targets exhibit emission-line (Brγ, HeI and H2) morphologies that extend significantly beyond the continuum source and we have mapped both the emission morphologies and the radial velocity fields. This analysis also reveals evidence for the existence of ionized low-density regions in the centre outflows from massive YSOs. Additionally, we present an analysis of optical spectra towards a similar sample of massive YSOs in the SMC, revealing that the optical emission is photoexcited and originates near the outer edges of molecular clouds, and is therefore consistent with a high mean-free path of UV photons in the interstellar medium (ISM) of the SMC. Finally, we discuss the sample of YSOs in an evolutionary context incorporating the results of previous infrared and radio observations, as well as the near-infrared and optical observations presented in this work. Our spectroscopic analysis in both the K band and the optical regimes, combined with previously obtained infrared and radio data, exposes differences between properties of massive YSOs in our own Galaxy and the SMC, including tracers of accretion, discs and YSO-ISM interactions. [ABSTRACT FROM AUTHOR]

We present observations of CK Vul obtained with the Spitzer Space Telescope. The infrared spectrum reveals a warm dust continuum with nebular, molecular hydrogen and HCN lines superimposed, together with the 'Unidentified Infrared' features. The nebular lines are consistent with emission by a low-density gas. We conclude that the Spitzer data, combined with other information, are incompatible with CK Vul being a classical nova remnant in 'hibernation' after the event of 1670, a 'very late thermal pulse', a 'Luminous Red Variable', such as V838 Mon, or a 'diffusion-induced nova'. The true nature of CK Vul remains a mystery. [ABSTRACT FROM AUTHOR]

The Spitzer Surveying the Agents of Galaxy Evolution (SAGE) survey has allowed the identification and analysis of significant samples of Young Stellar Object (YSO) candidates in the Large Magellanic Cloud (LMC). However, the angular resolution of Spitzer is relatively poor meaning that at the distance of the LMC, it is likely that many of the Spitzer YSO candidates in fact contain multiple components. We present high-resolution K-band integral field spectroscopic observations of the three most prominent massive YSO candidates in the N113 HII region using Very Large Telescope/Spectrograph for INtegral Field Observations in the Near Infrared (VLT/SINFONI). We have identified six K-band continuum sources within the three Spitzer sources and we have mapped the morphology and velocity fields of extended line emission around these sources. Br γ, HeI and H2 emission is found at the position of all six K-band sources; we discuss whether the emission is associated with the continuum sources or whether it is ambient emission. H2 emission appears to be mostly ambient emission and no evidence of CO emission arising in the discs of YSOs has been found. We have mapped the centroid velocities of extended Br γ emission and He I emission and found evidence of two expanding compact HII regions. One source shows compact and strong H2 emission suggestive of a molecular outflow. The diversity of spectroscopic properties observed is interpreted in the context of a range of evolutionary stages associated with massive star formation. [ABSTRACT FROM AUTHOR]

Atacama Large Millimetre Array observations show a non-detection of carbon monoxide around the four most luminous asymptotic giant branch (AGB) stars in the globular cluster 47 Tucanae. Stellar evolution models and star counts show that the mass-loss rates from these stars should be ~1.2-3.5 × 10-7 M⊙ yr-1. We would naïvely expect such stars to be detectable at this distance (4.5 kpc). By modelling the ultraviolet radiation field from post-AGB stars and white dwarfs in 47 Tuc, we conclude that CO should be dissociated abnormally close to the stars. We estimate that the CO envelopes will be truncated at a few hundred stellar radii from their host stars and that the line intensities are about two orders of magnitude below our current detection limits. The truncation of CO envelopes should be important for AGB stars in dense clusters. Observing the CO (3-2) and higher transitions and targeting stars far from the centres of clusters should result in the detections needed to measure the outflow velocities from these stars. [ABSTRACT FROM AUTHOR]

The Magellanic Clouds are uniquely placed to study the stellar contribution to dust emission. Individual stars can be resolved in these systems even in the mid-infrared, and they are close enough to allow detection of infrared excess caused by dust. We have searched the Spitzer Space Telescope data archive for all Infrared Spectrograph (IRS) staring-mode observations of the Small Magellanic Cloud (SMC) and found that 209 Infrared Array Camera (IRAC) point sources within the footprint of the Surveying the Agents of Galaxy Evolution in the Small Magellanic Cloud (SAGE-SMC) Spitzer Legacy programme were targeted, within a total of 311 staring-mode observations. We classify these point sources using a decision tree method of object classification, based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information. We find 58 asymptotic giant branch (AGB) stars, 51 young stellar objects, 4 post-AGB objects, 22 red supergiants, 27 stars (of which 23 are dusty OB stars), 24 planetary nebulae (PNe), 10 Wolf-Rayet stars, 3 H II regions, 3 R Coronae Borealis stars, 1 Blue Supergiant and 6 other objects, including 2 foreground AGB stars. We use these classifications to evaluate the success of photometric classification methods reported in the literature. [ABSTRACT FROM AUTHOR]

Low-luminosity galaxies may be the building blocks of more luminous systems. Southern African Large Telescope observations of the low-luminosity, early-type galaxy NGC 59 are obtained and analysed. These data are used to measure the stellar population parameters in the centre and off-centre regions of this galaxy, in order to uncover its likely star formation history. We find evidence of older stars, in addition to young stars in the emission-line regions. The metallicity of the stellar population is constrained to be [Z/H] ~ - 1.1 to - 1.6, which is extremely low, even for this low-luminosity galaxy, since it is not classed as a dwarf spheroidal galaxy. The measured [α/Fe] ratio is subsolar, which indicates an extended star formation history in NGC 59. If such objects formed the building blocks of more massive, early-type galaxies, then they must have been gaseous mergers, rather than dry mergers, in order to increase the metals to observed levels in luminous, early-type galaxies. [ABSTRACT FROM AUTHOR]

We present the detection and analysis of molecular hydrogen emission towards ten interstellar regions in the Large Magellanic Cloud. We examined low-resolution infrared spectral maps of 12 regions obtained with the Spitzer infrared spectrograph (IRS). The pure rotational 0-0 transitions of H2 at 28.2 and 17.1 μm are detected in the IRS spectra for 10 regions. The higher level transitions are mostly upper limit measurements except for three regions, where a 3σ detection threshold is achieved for lines at 12.2 and 8.6 μm. The excitation diagrams of the detected H2 transitions are used to determine the warm H2 gas column density and temperature. The single-temperature fits through the lower transition lines give temperatures in the range 86-137 K. The bulk of the excited H2 gas is found at these temperatures and contributes ~5-17 per cent to the total gas mass. We find a tight correlation of the H2 surface brightness with polycyclic aromatic hydrocarbon and total infrared emission, which is a clear indication of photoelectric heating in photodissociation regions. We find the excitation of H2 by this process is equally efficient in both atomic- and molecular-dominated regions. We also present the correlation of the warm H2 physical conditions with dust properties. The warm H2 mass fraction and excitation temperature show positive correlations with the average starlight intensity, again supporting H2 excitation in photodissociation regions. [ABSTRACT FROM AUTHOR]

We present a catalogue of 1768 eclipsing binary stars (EBs) detected in the Large Magellanic Cloud (LMC) by the second generation of the EROS survey (hereinafter EROS-2); 493 of them are new discoveries located in outer regions (out of the central bar) of the LMC. These sources were originally included in a list of candidate classical Cepheids (CCs) extracted from the EROS-2 catalogue on the basis of the period (0.89 < PEROS < 15.85 d) versus luminosity [13.39 < 〈BEROS〉 < 17.82 mag] diagram. After visual inspection of the light curves we reclassified them as eclipsing binaries. They have blue colours (BEROS − REROS < 0.2 mag) hence we classed them as hot eclipsing binaries (HEBs) containing hot massive components: main sequence (MS) stars or blue giants. We present Ks-band light curves for 999 binaries from our sample that have a counterpart in the VISTA near-infrared ESO public survey of the Magellanic Clouds system (VMC). We provide spectral classifications of 13 HEBs with existing spectroscopy. We divided our sample into contact-like binaries and detached/semi-detached systems based on both visual inspection and the parameters of the Fourier decomposition of the light curves and analysed the period–luminosity (PL) relations of the contact-like systems using the REROS and Ks magnitudes at maximum light. The contact-like binaries in our sample do not follow PL relations. We analysed the sample of contact binaries from the OGLE III catalogue and confirmed that PLI and ${\rm PL}_{K_{\rm s}}$ sequences are defined only by eclipsing binaries containing a red giant component. [ABSTRACT FROM PUBLISHER]

We present new observations of 34 young stellar object (YSO) candidates in the Small Magellanic Cloud (SMC). The photometric selection required sources to be bright at 24 and 70 μm (to exclude evolved stars and galaxies). The anchor of the analysis is a set of Spitzer Infrared Spectrograph (IRS) spectra, supplemented by ground-based 3–5 μm spectra, Spitzer Infrared Array Camera and Multiband Imaging Photometer for Spitzer photometry, near-infrared (IR) imaging and photometry, optical spectroscopy and radio data. The sources’ spectral energy distributions and spectral indices are consistent with embedded YSOs; prominent silicate absorption is observed in the spectra of at least 10 sources, silicate emission is observed towards four sources. Polycyclic aromatic hydrocarbon (PAH) emission is detected towards all but two sources. Based on band ratios (in particular the strength of the 11.3-μm and the weakness of the 8.6-μm bands) PAH emission towards SMC YSOs is dominated by predominantly small neutral grains. Ice absorption is observed towards 14 sources in the SMC. The comparison of H2O and CO2 ice column densities for SMC, Large Magellanic Cloud and Galactic samples suggests that there is a significant H2O column density threshold for the detection of CO2 ice. This supports the scenario proposed by Oliveira et al., where the reduced shielding in metal-poor environments depletes the H2O column density in the outer regions of the YSO envelopes. No CO ice is detected towards the SMC sources. Emission due to pure rotational 0–0 transitions of molecular hydrogen is detected towards the majority of SMC sources, allowing us to estimate rotational temperatures and H2 column densities. All but one source are spectroscopically confirmed as SMC YSOs. Based on the presence of ice absorption, silicate emission or absorption and PAH emission, the sources are classified and placed in an evolutionary sequence. Of the 33 YSOs identified in the SMC, 30 sources populate different stages of massive stellar evolution. The presence of ice- and/or silicate-absorption features indicates sources in the early embedded stages; as a source evolves, a compact H ii region starts to emerge, and at the later stages the source’s IR spectrum is completely dominated by PAH and fine-structure emission. The remaining three sources are classified as intermediate-mass YSOs with a thick dusty disc and a tenuous envelope still present. We propose one of the SMC sources is a D-type symbiotic system, based on the presence of Raman, H and He emission lines in the optical spectrum, and silicate emission in the IRS spectrum. This would be the first dust-rich symbiotic system identified in the SMC. [ABSTRACT FROM AUTHOR]

ABSTRACT We present spectra of 1142 colour-selected stars in the direction of the Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy, of which 1058 were taken with VLT/FLAMES multi-object spectrograph and 84 were taken with the SAAO Radcliffe 1.9-m telescope grating spectrograph. Spectroscopic membership is confirmed (at >99 per cent confidence) for 592 stars on the basis of their radial velocity, and spectral types are given. Very slow rotation is marginally detected around the galaxy's major axis. We identify five S stars and 23 carbon stars, of which all but four carbon stars are newly determined and all but one (PQ Sgr) are likely Sgr dSph members. We examine the onset of carbon richness in this metal-poor galaxy in the context of stellar models. We compare the stellar death rate (one star per 1000-1700 yr) with the known planetary nebula dynamical ages and find that the bulk population produce the observed (carbon-rich) planetary nebulae. We compute average lifetimes of S and carbon stars as 60-250 and 130-500 kyr, compared to a total thermal-pulsing asymptotic giant branch lifetime of 530-1330 kyr. We conclude by discussing the return of carbon-rich material to the interstellar medium. [ABSTRACT FROM AUTHOR]

ABSTRACT The VISTA Magellanic Cloud (VMC; PI: M.-R. L. Cioni) survey is collecting deep Ks-band time series photometry of the pulsating variable stars hosted by the system formed by the two Magellanic Clouds (MCs) and the bridge connecting them. In this paper, we present the first results for classical Cepheids, from the VMC observations of two fields in the Large Magellanic Cloud (LMC), centred on the South Ecliptic Pole and the 30 Doradus star-forming regions, respectively. The VMC Ks-band light curves of the Cepheids are well sampled (12 epochs) and of excellent precision (typical errors of ∼0.01 mag). We were able to measure for the first time the Ks magnitude of the faintest classical Cepheids in the LMC ( Ks ∼ 17.5 mag), which are mostly pulsating in the first overtone (FO) mode, and to obtain FO period-luminosity ( PL), period-Wesenheit ( PW) and period-luminosity-colour ( PLC) relations, spanning the full period range from 0.25 to 6 d. Since the longest period Cepheid in our data set has a variability period of 23 d, we have complemented our sample with literature data for brighter F Cepheids. On this basis, we have built a PL relation in the Ks band that, for the first time, includes short-period - hence low-luminosity - pulsators, and spans the full range from 1.6 to 100 d in period.We also provide the first ever empirical PW and PLC relations using the ( V − Ks) colour and time series Ks photometry. The very small dispersion (∼0.07 mag) of these relations makes them very well suited to study the three-dimensional geometry of the Magellanic system. The use of 'direct' (parallax- and Baade-Wesselink-based) distance measurements to both Galactic and LMC Cepheids allowed us to calibrate the zero-points of the PL, PW and PLC relations obtained in this paper, and in turn to estimate an absolute distance modulus of ( m − M)0 = 18.46 ± 0.03 mag for the LMC. This result is in agreement with most of the latest literature determinations based on classical Cepheids. [ABSTRACT FROM AUTHOR]

ABSTRACT We present infrared spectra of the binary XX Oph obtained with the Infrared Spectrograph on the Spitzer Space Telescope. The data show some evidence for the presence of solid C60- the first detection of C60 in the solid phase - together with the well-known 'unidentified infrared' emission features. We suggest that, in the case of XX Oph, the C60 is located close to the hot component, and that in general it is preferentially excited by stars having effective temperatures in the range 15 000-30 000 K. C60 may be common in circumstellar environments, but unnoticed in the absence of a suitable exciting source. [ABSTRACT FROM AUTHOR]

ABSTRACT Dust production is explored around 14 metal-poor ([Fe/H]=−1.91 to −0.98) giant stars in the Galactic globular cluster ω Centauri using new Spitzer Infrared Spectrograph spectra. This sample includes the cluster's post-asymptotic giant branch (AGB) and carbon stars and is thus the first representative spectral study of dust production in a metal-poor ([Fe/H] < −1) population. Only the more metal-rich stars V6 and V17 ([Fe/H]=−1.08, −1.06) exhibit silicate emission, while the five other stars with mid-infrared excess show only a featureless continuum which we argue is caused by metallic iron dust grains. We examine the metallicity of V42, and find it is likely part of the metal-rich population ([Fe/H]∼−0.8). Aside from the post-AGB star V1, we find no star from the cluster's bulk, metal-poor ([Fe/H] < −1.5) population - including the carbon stars - to be producing detectable amounts of dust. We compare the dust production to the stars' Hα line profiles obtained at the Magellan/Clay telescope at Las Campanas Observatory, finding pulsation shocking in the strongest pulsators (V6, V17 and V42), but evidence of outflow in all other stars. We conclude that the onset of dust production does not signify a fundamental change in the material leaving the star. Our data add to a growing body of evidence that metallic iron dominates dust production in metal-poor, oxygen-rich stars, but that dust is probably not the primary accelerant of winds in this mass-metallicity regime. [ABSTRACT FROM AUTHOR]

We present the classification of 197 point sources observed with the Infrared Spectrograph in the SAGE-Spec Legacy programme on the Spitzer Space Telescope. We introduce a decision-tree method of object classification based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information, which is used to classify the SAGE-Spec sample of point sources. The decision tree has a broad application to mid-infrared spectroscopic surveys, where supporting photometry and variability information are available. We use these classifications to make deductions about the stellar populations of the Large Magellanic Cloud and the success of photometric classification methods. We find 90 asymptotic giant branch (AGB) stars, 29 young stellar objects, 23 post-AGB objects, 19 red supergiants, eight stellar photospheres, seven background galaxies, seven planetary nebulae, two H regions and 12 other objects, seven of which remain unclassified. [ABSTRACT FROM AUTHOR]

We present the comparison of the three most important ice constituents (water, CO and CO) in the envelopes of massive young stellar objects (YSOs), in environments of different metallicities: the Galaxy, the Large Magellanic Cloud (LMC) and, for the first time, the Small Magellanic Cloud (SMC). We present observations of water, CO and CO ice in four SMC and three LMC YSOs (obtained with Spitzer-IRS and VLT/ISAAC). While water and CO ice are detected in all Magellanic YSOs, CO ice is not detected in the SMC objects. Both CO and CO ice abundances are enhanced in the LMC when compared to high-luminosity Galactic YSOs. Based on the fact that both species appear to be enhanced in a consistent way, this effect is unlikely to be the result of enhanced CO production in hotter YSO envelopes as previously thought. Instead we propose that this results from a reduced water column density in the envelopes of LMC YSOs, a direct consequence of both the stronger UV radiation field and the reduced dust-to-gas ratio at lower metallicity. In the SMC the environmental conditions are harsher, and we observe a reduction in CO column density. Furthermore, the low gas-phase CO density and higher dust temperature in YSO envelopes in the SMC seem to inhibit CO freeze-out. The scenario we propose can be tested with further observations. [ABSTRACT FROM AUTHOR]

We present a search for long-period variable (LPV) stars among giant branch stars in M15 which, at [Fe/H]∼−2.3, is one of the most metal-poor Galactic globular clusters. We use multicolour optical photometry from the 0.6-m Keele Thornton and 2-m Liverpool Telescopes. Variability of mag is detected in K757 and K825 over unusually long time-scales of nearly a year, making them the most metal-poor LPVs found in a Galactic globular cluster. K825 is placed on the long secondary period sequence, identified for metal-rich LPVs, though no primary period is detectable. We discuss this variability in the context of dust production and stellar evolution at low metallicity, using additional spectra from the 6.5-m Magellan (Las Campanas) telescope. A lack of dust production, despite the presence of gaseous mass loss raises questions about the production of dust and the intracluster medium of this cluster. [ABSTRACT FROM AUTHOR]

The exploration of chemical abundances in globular cluster giant branch stars has revealed element-abundance inhomogeneities between the stars. This study has investigated a sample of giant branch stars in the globular cluster 47 Tucanæ, which were observed at a resolution of using the Ultraviolet Échelle Spectrograph on the Very Large Telescope. The analysis of these stars showed non-local thermodynamic equilibrium (non-LTE) effects on the abundances derived from the sample of atomic lines under an LTE approximation. The stellar parameters for each star were redetermined using only high-excitation-potential Fe i lines. The resulting chemical abundance analysis showed enhancements in both the light and heavy s-process element abundances with mean values of dex and dex. However, no trend was found between the ratio of the heavy to light s-process element abundances ([h s/l s] dex) and metallicity due to the small spread in both of these values. This indicates that the heavy-element-abundance enhancements are not due to third dredge-up of internal nucleosynthesis products in these evolved stars. The source of the heavy-element enhancements is therefore primordial or pollution event related in origin. [ABSTRACT FROM AUTHOR]

We present comprehensive photometric and spectroscopic observations of the faint transient SN 2008S discovered in the nearby galaxy NGC 6946. SN 2008S exhibited slow photometric evolution and almost no spectral variability during the first nine months, implying a long photon diffusion time and a high-density circumstellar medium. Its bolometric luminosity is low with respect to most core-collapse supernovae but is comparable to the faintest Type II-P events. Our quasi-bolometric light curve extends to 300 d and shows a tail phase decay rate consistent with that of 56Co. We propose that this is evidence for an explosion and formation of 56Ni . Spectra of SN 2008S show intense emission lines of Hα, [Ca ii] doublet and Ca ii near-infrared (NIR) triplet, all without obvious P-Cygni absorption troughs. The large mid-infrared (MIR) flux detected shortly after explosion can be explained by a light echo from pre-existing dust. The late NIR flux excess is plausibly due to a combination of warm newly formed ejecta dust together with shock-heated dust in the circumstellar environment. We reassess the progenitor object detected previously in Spitzer archive images, supplementing this discussion with a model of the MIR spectral energy distribution. This supports the idea of a dusty, optically thick shell around SN 2008S with an inner radius of nearly 90 au and outer radius of 450 au, and an inferred heating source of 3000 K. The luminosity of the central star is . All the nearby progenitor dust was likely evaporated in the explosion leaving only the much older dust lying further out in the circumstellar environment. The combination of our long-term multiwavelength monitoring data and the evidence from the progenitor analysis leads us to support the scenario of a weak electron-capture supernova explosion in a super-asymptotic giant branch progenitor star (of initial mass ) embedded within a thick circumstellar gaseous envelope. We suggest that all of main properties of the electron-capture SN phenomenon are observed in SN 2008S and future observations may allow a definitive answer. [ABSTRACT FROM AUTHOR]

We present spectroscopic observations from the Spitzer Space Telescope of six carbon-rich asymptotic giant branch (AGB) stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph) and two foreground Galactic carbon stars. The band strengths of the observed C2H2 and SiC features are very similar to those observed in Galactic AGB stars. The metallicities are estimated from an empirical relation between the acetylene optical depth and the strength of the SiC feature. The metallicities are higher than those of the Large Magellanic Cloud, and close to Galactic values. While the high metallicity could imply an age of around 1 Gyr, for the dusty AGB stars, the pulsation periods suggest ages in excess of 2 or 3 Gyr. We fit the spectra of the observed stars using thedusty radiative transfer model and determine their dust mass-loss rates to be in the range . The two Galactic foreground carbon-rich AGB stars are located at the far side of the solar circle, beyond the Galactic Centre. One of these two stars shows the strongest SiC feature in our present Local Group sample. [ABSTRACT FROM AUTHOR]

NGC 6611 is the massive young cluster (2–3 Myr) that ionizes the Eagle Nebula. We present very deep photometric observations of the central region of NGC 6611 obtained with the Hubble Space Telescope and the following filters: ACS/WFC F775W and F850LP and NIC2 F110W and F160W, loosely equivalent to ground-based IZJH filters. This survey reaches down to . We construct the initial mass function (IMF) from well into the brown dwarf regime (down to ). We have detected 30–35 brown dwarf candidates in this sample. The low-mass IMF is combined with a higher-mass IMF constructed from the ground-based catalogue from Oliveira et al. We compare the final IMF with those of well-studied star-forming regions: we find that the IMF of NGC 6611 more closely resembles that of the low-mass star-forming region in Taurus than that of the more massive Orion Nebula Cluster. We conclude that there seems to be no severe environmental effect in the IMF due to the proximity of the massive stars in NGC 6611. [ABSTRACT FROM AUTHOR]

The variable star DZ Cru was thought to be a nova when it was discovered in eruption in 2003 August. This explanation was later challenged, however, when the first spectra of the object were reported. We present near-infrared spectroscopy of DZ Cru obtained at the New Technology Telescope on three occasions, starting ∼1.5 yr after outburst, with the aim of establishing the nature of the object. The spectra display H i, O i, [N i] emission lines, together with He i P Cygni lines superposed on a dust continuum. These observations suggest the ‘peculiar variable in Crux’ is a classical nova. [ABSTRACT FROM AUTHOR]

We have observed five carbon-rich asymptotic giant branch (AGB) stars in the Fornax dwarf spheroidal (dSph) galaxy, using the Infrared Spectrometer on board the Spitzer Space Telescope. The stars were selected from a near-infrared survey of Fornax and include the three reddest stars, with presumably the highest mass-loss rates, in that galaxy. Such carbon stars probably belong to the intermediate-age population (2–8 Gyr old and metallicity of [Fe/H]∼−1) of Fornax. The primary aim of this paper is to investigate mass-loss rate, as a function of luminosity and metallicity, by comparing AGB stars in several galaxies with different metallicities. The spectra of three stars are fitted with a radiative transfer model. We find that mass-loss rates of these three stars are . The other two stars have mass-loss rates below . We find no evidence that these rates depend on metallicity, although we do suggest that the gas-to-dust ratio could be higher than at solar metallicity, in the range 240 to 800. The C2H2 bands are stronger at lower metallicity because of the higher C/O ratio. In contrast, the SiC fraction is reduced at low metallicity due to low silicon abundance. The total mass-loss rate from all known carbon-rich AGB stars into the interstellar medium (ISM) of this galaxy is of the order of . This is much lower than that of the dwarf irregular galaxy Wolf Lundmark Melotte (WLM), which has a similar visual luminosity and metallicity. The difference is attributed to the younger stellar population of WLM. The suppressed gas-return rate to the ISM accentuates the difference between the relatively gas-rich dwarf irregular and the gas-poor dSph galaxies. Our study will be useful to constrain gas and dust recycling processes in low-metallicity galaxies. [ABSTRACT FROM AUTHOR]

Dust radiative transfer models are presented for 60 carbon stars in the Magellanic Clouds (MCs) for which 5–35 μm Spitzer infrared spectrograph (IRS) spectra and quasi-simultaneous ground-based JHKL photometry are available. From the modelling, the luminosity and mass-loss rate are derived (under the assumption of a fixed expansion velocity and dust-to-gas ratio), and the ratio of silicon carbide (SiC) to amorphous carbon (AMC) dust is also derived. This ratio is smaller than observed in Galactic carbon stars, as has been noted before. Light curves for 36 objects can be retrieved from the massive compact halo object (MACHO) and optical gravitational lensing experiment (OGLE) data bases, and periods can be derived for all but two of these. Including data from the literature, periods are available for 53 stars. There is significant scatter in a diagram where the mass-loss rates are plotted against luminosity, and this is partly due to the fact that the luminosities are derived from single-epoch data. The mass-loss rates for the MC objects roughly scatter around the mean relation for Galactic C-stars. The situation is better defined when the mass-loss rate is plotted against pulsation period. For a given period, most of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) stars have mass-loss rates that are in agreement with that observed in Galactic carbon stars (under the assumption that these objects have an expansion velocity and dust-to-gas ratio typical of the mean observed in Galactic carbon Miras). For some SMC sources only, the IRS spectrum at longer wavelengths falls clearly below the model flux predicted by a constant mass-loss rate. An alternative model with a substantial increase of the mass-loss rate to its present-day value over a time-scale of a few tens of years is able to explain the spectral energy distribution (SED) and IRS spectra of these sources. However, the probability to have two such cases in a sample of 60 is small, and makes this not a likely explanation (and testable by re-observing these objects near the end of the lifetime of Spitzer). Alternative explanations are (ad hoc) changes to the dust emissivity at longer wavelengths, and/or deviations from spherical symmetry. [ABSTRACT FROM AUTHOR]

We investigate the conditions of star formation in the Large Magellanic Cloud (LMC). We have conducted a survey for water maser emission arising from massive young stellar objects in the 30 Doradus region (N 157) and several other H ii regions in the LMC (N 105A, N 113 and N 160A). We have identified a new maser source in 30 Dor at the systemic velocity of the LMC. We have obtained 3–4 μm spectra, with the European Southern Observatory (ESO)-Very Large Telescope (VLT), of two candidate young stellar objects. N 105A IRS1 shows H recombination line emission, and its Spectral Energy Distribution (SED) and mid-infrared colours are consistent with a massive young star ionizing the molecular cloud. N 157B IRS1 is identified as an embedded young object, based on its SED and a tentative detection of water ice. The data on these four H ii regions are combined with mid-infrared archival images from the Spitzer Space Telescope to study the location and nature of the embedded massive young stellar objects and signatures of stellar feedback. Our analysis of 30 Dor, N 113 and N 160A confirms the picture that the feedback from the massive O- and B-type stars, which creates the H ii regions, also triggers further star formation on the interfaces of the ionized gas and the surrounding molecular cloud. Although in the dense cloud N 105A star formation seems to occur without evidence of massive star feedback, the general conditions in the LMC seem favourable for sequential star formation as a result of feedback. In an Appendix , we present water maser observations of the galactic red giants R Doradus and W Hydrae. [ABSTRACT FROM AUTHOR]

We present an observation of the very late thermal pulse object V4334 Sgr (Sakurai's Object) with the Infrared Spectrometer (IRS) on the Spitzer Space Telescope. The emission from 5–38 μm is dominated by the still-cooling dust shell. A number of features are seen in absorption against the dust shell, which we attribute to HCN and polyyne molecules. We use these features to determine the 12C/13C ratio for the absorbing gas to be ; this implies that, despite the H-content of the molecules, the hydrocarbon-bearing gas must have originated in material produced in the very late thermal pulse. We see no evidence of emission lines, despite the recently-reported optical and radio observations that suggest the effective temperature of the stellar remnant is rising. [ABSTRACT FROM AUTHOR]

We investigate the molecular bands in carbon-rich asymptotic giant branch (AGB) stars in the Large Magellanic Cloud (LMC), using the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope ( SST) over the 5–38 μm range. All 26 low-resolution spectra show acetylene (C2H2) bands at 7 and 14 μm. The hydrogen cyanide (HCN) bands at these wavelengths are very weak or absent. This is consistent with low nitrogen abundances in the LMC. The observed 14 μm C2H2 band is reasonably reproduced by an excitation temperature of 500 K. There is no clear dilution of the 14 μm C2H2 band by circumstellar dust emission. This 14-μm band originates from molecular gas in the circumstellar envelope in these high mass-loss rate stars, in agreement with previous findings for Galactic stars. The C2H2 column density, derived from the 13.7 μm band, shows a gas mass-loss rate in the range 3 × 10−6 to 5 × 10−5 M⊙ yr−1. This is comparable with the total mass-loss rate of these stars estimated from the spectral energy distribution. Additionally, we compare the line strengths of the 13.7 μm C2H2 band of our LMC sample with those of a Galactic sample. Despite the low metallicity of the LMC, there is no clear difference in the C2H2 abundance among LMC and Galactic stars. This reflects the effect of the third dredge-up bringing self-produced carbon to the surface, leading to high carbon-to-oxygen ratio at low metallicity. [ABSTRACT FROM AUTHOR]

We present new K- and L′-band imaging observations for members of the young (3–5 Myr) σ Orionis cluster, obtained at the United Kingdom Infrared Telescope (UKIRT) with the UKIRT 1–5 micron Imager Spectrometer (UIST). We determine ( K− L′) colour excesses with respect to the photospheres, finding evidence for warm circumstellar dust around 27 out of 83 cluster members that have masses between 0.04 and . This indicates a circumstellar disc frequency of at least (33 ± 6) per cent for this cluster, consistent with previous determinations from smaller samples and also consistent with the 3-Myr disc half-life suggested by Haisch et al. There is marginal evidence that the disc frequency declines towards lower masses, but the data are also consistent with no mass dependence at all. There is no evidence for spatial segregation of objects with and without circumstellar discs. [ABSTRACT FROM AUTHOR]

We report optical and near-infrared spectroscopy, and optical spectropolarimetry, of the peculiar variable V838 Mon during the multiple outburst phase in early 2002. The spectral evolution is exceptional. Our earliest spectra (2002 January) are noteworthy for their strong absorption lines of barium and strontium in the optical, and bands of CO and circumstellar H2O in the near-infrared. All but the CO weaken or are absent in later spectra. The behaviour of the CO band during this phase is extraordinary: initially in absorption, it was observed two months later in optically thick emission. The excitation of the CO is probably the result of the propagation of a shock wave at the third maximum. The two spectropolarimetric epochs were taken 6 and 27 d after the second outburst on 2002 February 8. The polarization at both times was measured to be per cent. Nearly all of the measured polarization is believed to be due to interstellar dust, a conclusion that is consistent with previous studies. At both epochs, however, a weak and variable intrinsic component is thought to be present. Between January and March of 2002 the luminosity of V838 Mon increased by a factor of 15 and the apparent diameter increased fourfold. [ABSTRACT FROM AUTHOR]

We present moderate- and high-resolution infrared spectroscopy of the peculiar eruptive variable V838 Mon, which underwent a series of remarkable outbursts in early 2002. During the period covered by our observations, 2002 December–2003 December, the near-infrared spectrum continued to show many of the characteristics of a very cool supergiant. However, throughout this period the spectrum also revealed strong and variable SiO first overtone emission, and Paβ emission. The 2003 December spectrum contained a series of Ti ilines with inverse P Cygni profiles. This is clear evidence that some material is falling inward towards the star. [ABSTRACT FROM AUTHOR]

We have performed IZJHKL′ observations in NGC 6611, the young cluster that ionizes the Eagle Nebula. We have discovered a rich pre-main sequence concentrated around the O-stars in the cluster. As measured by their L′-band excesses, at least 58 ± 5 per cent of the pre-main sequence objects have circumstellar discs. By comparing this disc frequency with frequencies determined for regions where the pre-main sequence stars are subject to less ionizing radiation, we find no evidence that the harsher environment of NGC 6611 (approximately an order of magnitude more ionizing Lyman continuum radiation than the Trapezium cluster) significantly hastens the dissipation of circumstellar discs around solar mass stars. [ABSTRACT FROM AUTHOR]

It has been claimed that CK Vul (the remnant of Nova Vul 1670) may be the oldest recovered ‘old nova’ and as such provides evidence in support of the hibernation scenario for classical nova systems. However this interpretation has been challenged. We present 450- and 850-μm photometry of CK Vul which cast further doubt on its old nova status. It displays a large far infrared-submillimetre flux excess, inconsistent with the properties of an old nova. Furthermore, IRAS images show that CK Vul is located in a ‘cavity’ in the infrared emission, a feature often associated with planetary nebulae. It seems more likely that CK Vul – and hence Nova Vul 1670 – is (like V605 Aql and V4334 Sgr) an evolved star in the throes of a final thermal pulse. [ABSTRACT FROM AUTHOR]

Background: The objective of this study was to evaluate the cost-effectiveness of women undergoing IVF treatment with recombinant FSH (rFSH) in comparison with highly purified urinary FSH (uFSH-HP) and human menopausal gonadotrophins (HMG).Methods: A decision-analytic model was used to estimate cost-effectiveness ratios for 'the average cost per ongoing pregnancy' and 'incremental cost per additional pregnancy' for women entering into IVF treatment for a maximum of three cycles. The model was constructed based on a previously published large prospective randomized clinical trial comparing rFSH and uFSH-HP. Where necessary, these data were augmented with a combination of expert opinion, evidence from the literature and observational data relating to the management and cost of IVF treatment in the UK. The cost of rFSH, uFSH-HP and HMG were obtained from National Health Service list prices in the UK.Results: The model predicted a cumulative pregnancy rate after three cycles of 57.1% for rFSH and 44.4% for both uFSH-HP and HMG. The cost of IVF treatment was 5135 pounds sterling for rFSH, 4806 pounds sterling for uFSH-HP and 4202 pounds sterling for HMG. When assessed in association with outcomes, the average cost per ongoing pregnancy was more favourable with rFSH (8992 pounds sterling) than with either uFSH-HP (10 834 pounds sterling) or HMG (9472 pounds sterling). The incremental cost per additional pregnancy was 2583 pounds sterling using rFSH instead of uFSH-HP and 7321 pounds sterling using rFSH instead of HMG. These results were robust to changes in the baseline assumptions of the model.Conclusion: rFSH is a cost-effective treatment strategy in ovulation induction prior to IVF. [ABSTRACT FROM AUTHOR]