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Our purpose is to study the effect of binary companions located within the first 10 stellar radii from the primary AGB star. In this work, we target the mass-losing carbon star V Hydrae (V Hya), looking for signatures of its companion in the dust forming region of the atmosphere. The star was observed in the L- and N-bands with the VLTI/MATISSE instrument at low spectral resolution. We reconstructed images of V Hya's photosphere and surroundings using the two bands and compared our interferometric observables with VLTI/MIDI and VISIR archival data. To constrain the dust properties, we used DUSTY to model the spectral energy distribution. The star is dominated by dust emission in the L- and N- bands. The VISIR image confirms the presence of a large-scale dusty circumstellar envelope surrounding V Hya. The MATISSE reconstructed images show asymmetric and elongated structures in both infrared bands. In the L-band, we detected an elongated shape of approximately 15 mas, likely to be of photospheric origin. In the N-band, we found a 20 mas extension North-East from the star, and perpendicular to the L-band elongated axis. The position angle and the size of the N-band extension match the prediction of the companion position at MATISSE epoch. By comparing MATISSE N-band with MIDI data, we deduce that the elongation axis in the N-band has rotated since the previous interferometric measurements 13 years ago, supporting the idea that the particle enhancement is related to the dusty clump moving along with the companion. The MATISSE images unveil the presence of a dust enhancement at the companion position, opening new doors for further analysis on the binary interaction with an AGB component., Comment: Accepted for publication in Astronomy & Astrophysics

12CO and 13CO lines, as well as a mm-wave continuum, have been observed for a sample of 22 OH/IR stars in directions within 2 degrees of the Galactic Centre. Photometry data have been gathered from the literature to construct SEDs and to determine pulsational variability. Radiative transfer models have been used to interpret the data. All stars in the sample were detected in at least one CO line, and 8 objects were detected in 324 GHz continuum. Based on luminosity criteria, the sample is divided into 17 objects that most likely lie within the inner Galactic Bulge, and 5 objects that are most likely foreground objects. The median luminosity of the inner-Galactic-Bulge objects, 5600 Lsun, corresponds to an initial mass in the range 1.2-1.6 Msun, indicating that these OH/IR stars descend from solar-type stars. The objects in this sub-sample are further divided into two classes based on their SED characteristics: 11 objects have SEDs that are well matched by models invoking dust envelopes extending from a few stellar radii and outwards, while 6 objects are better modelled as having detached dust envelopes with inner radii in the range 200-600 au and warmer central stars. The former objects have periodic variability, while the latter objects are predominantly non-periodic. The median gas-mass-loss rate, gas terminal expansion velocity, gas-to-dust mass ratio, and circumstellar 12CO/13CO abundance ratio have been estimated to be 2x10{-5} Msun/yr, 18 km/s, 200 (excluding the sources with detached dust envelopes, which show markedly lower gas-to-dust ratios), and 5, respectively, for the inner-Galactic-Bulge objects. The inner-Galactic-Bulge OH/IR stars studied here constitute an excellent sample of equidistant objects for the purpose of understanding the evolution of the mass-loss-rate characteristics at the tip of the AGB., Comment: 32 pages, 17 figures

We employed the {\it VISTA near-infrared $YJK_\mathrm{s}$ survey of the Magellanic System} (VMC), to analyse the $Y,\,J,\,K_\mathrm{s}$ light curves of $\delta$ Cepheid stars (DCEPs) in the Large Magellanic Cloud (LMC). Our sample consists of 4408 objects accounting for 97 per cent of the combined list of OGLE\,IV and {\it Gaia}\,DR2 DCEPs. We determined a variety of period-luminosity ($PL$) and period-Wesenheit $PW$ relationships for Fundamental (F) and First Overtone (1O) pulsators. We discovered for the first time a break in these relationships for 1O DCEPs at $P$=0.58 d. We derived relative individual distances for DCEPs in the LMC with a precision of $\sim$1 kpc, calculating the position angle of the line of nodes and inclination of the galaxy: $\theta$=145.6$\pm$1.0 deg and $i$=25.7$\pm$0.4 deg. The bar and the disc are seen under different viewing angles. We calculated the ages of the pulsators, finding two main episodes of DCEP formation lasting $\sim$40 Myr which happened 93 and 159 Myr ago. Likely as a result of its past interactions with the SMC, the LMC shows a non-planar distribution, with considerable structuring: the bar is divided into two distinct portions, the eastern and the western displaced by more than 1 kpc from each other. Similar behaviour is shown by the spiral arms. The LMC disc appears "flared" and thick, with a disc scale height of $h\sim 0.97$ kpc. This feature can be explained by strong tidal interactions with the Milky Way and/or the Small Magellanic Cloud or past merging events with now disrupted LMC satellites., Comment: 22 pages, 21 figures, accepted for publication on MNRAS. Tables 1 and 2 are available in advance of publication upon request from the first author

Classical Cepheids are the most popular distance indicators and tracers of young stellar populations. The key advantage is that they are bright and they can be easily identified in Local Group and Local Volume galaxies. Their evolutionary and pulsation properties depend on their chemical abundances. The main aim of this investigation is to perform a new and accurate abundance analysis of two tens of calibrating Galactic Cepheids using high spectral resolution (R$\sim$40,000-115,000) and high S/N spectra ($\sim$400) covering the entire pulsation cycle. We focus our attention on possible systematics affecting the estimate of atmospheric parameters and elemental abundances along the pulsation cycle. We cleaned the line list by using atomic transition parameters based on laboratory measurements and by removing lines that are either blended or display abundance variations along the pulsation cycle. The spectroscopic approach that we developed brings forward small dispersions in the variation of the atmospheric parameters ($\sigma$($T_{\rm eff}$)$\sim$50 K, $\sigma$($\log{g}$)$\sim$0.2 dex, and $\sigma$($\xi$)$\sim$0.2 km/s) and in the abundance of both iron ($\lesssim$ 0.05 dex) and alpha elements ($\lesssim$0.10 dex) over the entire pulsation cycle. We also provide new and accurate effective temperature templates by splitting the calibrating Cepheids into four different period bins, ranging from short to long periods. For each period bin, we performed an analytical fit with Fourier series providing $\theta = 5040/{T_{\rm eff}}$ as a function of the pulsation phase. The current findings are a good viaticum to trace the chemical enrichment of the Galactic thin disk by using classical Cepheids and a fundamental stepping stone for further investigations into the more metal-poor regime typical of Magellanic Cepheids., Comment: 31 pages, 23 figures (out of which 11 are in the appendices A and B), to be published in the Astronomy & Astrophysics journal

We aim to constrain the sizes of the CO circumstellar envelopes (CSEs) of 16 S-type stars, along with an additional 7 and 4 CSEs of C-type and M-type AGB stars, respectively. We map the emission from the CO J=2-1 and 3-2 lines observed with the Atacama Compact Array (ACA) and its total power (TP) antennas, and fit with a Gaussian distribution in the uv- and image planes for ACA-only and TP observations, respectively. The major axis of the fitted Gaussian for the CO(2-1) line data gives a first estimate of the size of the CO-line-emitting CSE. We investigate possible signs of deviation from spherical symmetry by analysing the line profiles, the results from visibility fitting, and by investigating the deconvolved images. The sizes of the CO-line-emitting CSEs of low-mass-loss-rate (low-MLR) S-stars fall between the sizes of the CSEs of C-stars, which are larger, and those of M-stars, which are smaller, as expected because of the differences in their respective CO abundances. The sizes of the low-MLR S-type stars show no dependence on circumstellar density, while a steeper density dependence is observed at high MLR. Furthermore, our results show that the CO CSEs of most of the S-stars in our sample are consistent with a spherically symmetric and smooth outflow. The CO envelope sizes obtained in this paper will be used to constrain detailed radiative transfer modelling to directly determine more accurate MLR estimates for the stars in our sample. For several of our sources that present signs of deviation from spherical symmetry, further high-resolution observations would be necessary to investigate the nature of, and the physical processes behind, these asymmetrical structures. This will provide further insight into the mass-loss process and its related chemistry in S-type AGB stars., Comment: 8 pages, 2 figures, 4 appendices, accepted in A&A

We present results from an analysis of $\sim$ 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 OGLE (Optical Gravitational Lensing Experiment) 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 ~7,000 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=$22\pm4^{\circ }$ relative to the plane of the sky and position angle of the line of nodes $\theta=167\pm7^{\circ }$ (measured from north to east). The north-eastern part of the ellipsoid is closer to us and no particular associated substructures are detected as well as any metallicity gradient., Comment: accepted for publication in MNRAS

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 ($\sim1$-$10$ Gyr) red clump stars to map the three-dimensional 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. Red clump stars are selected from near-infrared colour-magnitude diagrams based on data from the VISTA 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 red clump stars has an inclination $i=35\deg$-$48\deg$ and position angle PA$=170\deg$-$186\deg$. 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 red clump 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., Comment: 16 pages, 11 figures; accepted for publication in MNRAS

Carbon stars have been and are extensively studied, given their complex internal structure and their peculiar chemical composition, which make them living laboratories to test stellar structure and evolution theories of evolved stars. They are the most relevant dust manufacturers, thus playing a crucial role in the evolution of galaxies. We study the dust mineralogy of circumstellar envelope (CE) of C-stars in the Large Magellanic Cloud (LMC), to achieve a better understanding of the dust formation process in the outflow of these objects. We investigate the expected distribution of C-stars in the observational planes built with the MIRI filters mounted onboard the James Webb Space Telescope (JWST), to select the best planes allowing an exhaustive characterisation of the stars. We compare the synthetic spectral energy distributions, obtained by the modelling of asymptotic giant branch stars and of the dust formation process in the wind, with the spectra of carbon stars in the LMC, taken with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. From the detailed comparison between synthetic modelling and observation we characterise the individual sources and derive the detailed mineralogy of the dust in the CE. We find that precipitation of MgS on SiC seeds is common to all non metal-poor carbon stars. Solid carbon is the dominant dust component, with percentages above $80\%$ in all cases; a percentage between $10\%$ and $20\%$ of carbon dust is under the form of graphite, the remaining being amorphous carbon. Regarding the observational planes based on the MIRI filters, the colour-magnitude ([F770W]-[F1800W], [F1800W]) plane allows the best understanding of the degree of obscuration of the stars, while the ([F1800W]-[F2550W], [F1800W]) diagram allows a better discrimination among stars of different metallicity., Comment: 28 pages, 18 figures 2 tables. Accepted for publication in A&A

Modelling dust formation in single stars evolving through the carbon-star stage of the asymptotic giant branch (AGB) reproduces well the mid-infrared colours and magnitudes of most of the C-rich sources in the Large Magellanic Cloud (LMC), apart from a small subset of extremely red objects (EROs). The analysis of EROs spectral energy distribution suggests the presence of large quantities of dust, which demand gas densities in the outflow significantly higher than expected from theoretical modelling. We propose that binary interaction mechanisms that involve common envelope (CE) evolution could be a possible explanation for these peculiar stars; the CE phase is favoured by the rapid growth of the stellar radius occurring after C$/$O overcomes unity. Our modelling of the dust provides results consistent with the observations for mass-loss rates $\dot M \sim 5\times 10^{-4}~\dot M/$yr, a lower limit to the rapid loss of the envelope experienced in the CE phase. We propose that EROs could possibly hide binaries of orbital periods $\sim$days and are likely to be responsible for a large fraction of the dust production rate in galaxies., Comment: Accepted for publication in MNRAS Letter

Stars on the asymptotic giant branch (AGB) lose considerable amounts of matter through their dust-driven stellar winds. A number of such sources have been imaged by Herschel/PACS, revealing a diverse sample of different morphological types. Among them are a few examples which show geometrically thin, spherically symmetric shells which can be used to probe the mass loss history of their host stars. We aim to determine the physical properties of the dust envelope around the two carbon stars U Hya and W Ori. With the much-improved spatial constraints from the new far-infrared maps, our primary goal is to measure the dust masses contained in the shells and see how they fit the proposed scenarios of shell formation. We calculated the radiative transfer of the circumstellar dust envelope using the 1D code More of DUSTY (MoD). Adopting a parametrised density profile, we obtained a best-fit model in terms of the photometric and spectroscopic data, as well as a radial intensity profile based on Herschel/PACS data. For the case of U Hya, we also computed a grid of circumstellar envelopes by means of a stationary wind code and compare the results of the two modelling approaches. The Herschel/PACS maps show U Hya surrounded by a detached shell of $114''\ (0.12\,\mathrm{pc})$ in radius, confirming the observations from previous space missions. The dust masses calculated for the shell by the two approaches are consistent with respect to the adopted dust grain properties. In addition, around W Ori, we detect for the first time a weak spherically symmetric structure with a radius of $92''\ (0.17\,\mathrm{pc})$ and a dust mass of $(3.5\pm0.3)\times10^{-6}\,\mathrm{M_\odot}$.

High-angular-resolution observations of asymptotic giant branch (AGB) stars often reveal non-spherical morphologies for the gas and dust envelopes. We aim to make a pilot study to quantify the impact of different geometries (spherically symmetric, spiral-shaped, and disc-shaped) of the dust component of AGB envelopes on spectral energy distributions (SEDs), mass estimates, and subsequent mass-loss rate (MLR) estimates. We also estimate the error made on the MLR if the SED is fitted by an inappropriate geometrical model. We use the 3D Monte-Carlo-based radiative-transfer code RADMC-3D to simulate emission from dusty envelopes with different geometries (but fixed spatial extension). We compare these predictions with each other, and with the SED of the AGB star EP Aqr that we use as a benchmark since its envelope is disc-like and known to harbour spiral arms, as seen in CO. The SEDs involving the most massive envelopes are those for which the different geometries have the largest impact, primarily on the silicate features at 10 and 18 um. These different shapes originate from large differences in optical depths. Massive spirals and discs appear akin to black bodies. Optically thick edge-on spirals and discs (with dust masses of 1e-4 and 1e-5 Msun) exhibit black-body SEDs that appear cooler than those from face-on structures and spheres of the same mass, while optically thick face-on distributions appear as warmer emission. We find that our more realistic models, combined spherical and spiral distributions, are 0.1 to 0.5 times less massive than spheres with similar SEDs. More extreme, less realistic scenarios give that spirals and discs are 0.01 to 0.05 times less massive than corresponding spheres. This means that adopting the wrong geometry for an AGB circumstellar envelope may result in a MLR that is incorrect by as much as 1 to 2 orders of magnitude when derived from SED fitting., Comment: 15 pages, 9 figures, and 8 tables, accepted for publication in A&A in August 2020

This is the first publication of the DEATHSTAR project. The goal of the project is to reduce the uncertainties of observational estimates of mass-loss rates from Asymptotic Giant Branch (AGB) stars. Line emission from 12CO J=2-1 and 3-2 were mapped using the ACA. In this initial analysis, the emission distribution was fit to a Gaussian distribution in the uv-plane. Detailed radiative transfer analysis will be presented in the future. The axes of the best-fit Gaussian at the line center of the 12CO J=2-1 emission gives a first indication of the size of the emitting region. Furthermore, the fitting results, such as the major and minor axis, center position, and the goodness of fit across both lines, constrain the symmetry of the emission distribution. We find that the CO envelope sizes are, in general, larger for C-type than for M-type AGB stars, which is expected if the CO/H2 ratio is larger in C-type stars. Furthermore, a relation between the 12CO J=2-1 size and circumstellar density is shown that, while in broad agreement with photodissociation calculations, reveals large scatter and systematic differences between the stellar types. The majority of the sources have CO envelopes that are consistent with a spherically symmetric, smooth outflow. For about a third of the sources, indications of strong asymmetries are found. This is consistent with previous interferometric investigations of northern sources. Smaller scale asymmetries are found in a larger fraction of sources. These results for CO envelope radii and shapes can be used to constrain detailed radiative transfer modeling of the same stars so as to determine mass-loss rates that are independent of photodissociation models. For a large fraction of the sources, observations at higher spatial resolution will be necessary to further investigate the complex circumstellar dynamics revealed by our ACA observations., Comment: 10 pages, 5 figures, 5 appendices, accepted in A&A

The flux-weighted gravity-luminosity relation (FWGLR) is investigated for a sample of 477 classical Cepheids (CCs), including stars that have been classified in the literature as such but are probably not. The luminosities are taken from the literature, based on the fitting of the spectral energy distributions (SEDs) assuming a certain distance and reddening. The flux-weighted gravity (FWG) is taken from gravity and effective temperature determinations in the literature based on high-resolution spectroscopy. There is a very good agreement between the theoretically predicted and observed FWG versus pulsation period relation that could serve in estimating the FWG (and $\log g$) in spectroscopic studies with a precision of 0.1~dex. As was known in the literature, the theoretically predicted FWGLR relation for CCs is very tight and is not very sensitive to metallicity (at least for LMC and solar values), rotation rate, and crossing of the instability strip. The observed relation has a slightly different slope and shows more scatter (0.54~dex). This is due both to uncertainties in the distances and to the pulsation phase averaged FWG values. Data from future Gaia data releases should reduce these errors, and then the FWGLR could serve as a powerful tool in Cepheid studies., Comment: A&A in press

(abridged)Variability is a key property of stars on the asymptotic giant branch (AGB). Their pulsation period is related to the luminosity and mass-loss rate of the star. The long-period variables (LPVs) and Mira variables are the most prominent of all types of variability of evolved stars. The reddest, most obscured AGB stars are too faint in the optical and have eluded large variability surveys. Selection criteria are derived based on colour-colour and colour-magnitude diagrams from the combination of VISTA Magellanic Cloud (VMC) survey, Spitzer IRAC and AllWISE data. After eliminating LPVs with known periods shorter than 450 days, a sample of 1299 candidate obscured AGB stars is selected. K-band LCs are constructed combining the epoch photometry available in the VMC survey with literature data, analysed for variability and fitted with a single period sine curve to derive mean magnitudes, amplitudes and periods. A subset of 254 stars are either new variables, or known variables where the period we find is better determined than the literature value, or longer than 1000 days. The spectral energy distributions (SEDs) of these stars are fitted to a large number of templates. For this purpose the SEDs and Spitzer IRS spectra of some non-AGB stars are also fitted to have templates of the most likely contaminants in the sample. A sample of 217 likely LPVs is found. Thirty-four stars have periods longer than 1000 days although some of them have alternative shorter periods. Mass-loss rates and luminosities are estimated from the template fitting. Period-luminosity relations are presented for C- and O-rich Miras that appear to be extensions of relations derived in the literature for shorter periods. The fit for the C-stars is particularly well defined (with 182 objects) and reads Mbol = (-2.27 \pm 0.20) log P + (1.45 \pm 0.54)mag with an rms of 0.41 mag., Comment: A&A accepted

(abridged) Spectral energy distributions (SEDs) were constructed for a sample of 477 classical cepheids (CCs). The SEDs were fitted with a dust radiative transfer code. Four stars showed a large mid- or far-infrared excess and the fitting then included a dust component. These comprise the well-known case of RS Pup, and three stars that are (likely) Type-II cepheids (T2Cs), AU Peg, QQ Per, and FQ Lac. The remainder of the sample was fitted with a stellar photosphere to derive the best-fitting luminosity and effective temperature. Distance and reddening were taken from the literature. The stars were plotted in a Hertzsprung-Russell diagram and compared to evolutionary tracks for cepheids and theoretical instability strips. For the large majority of stars, the position in the HRD is consistent with the instability strip for a CC or T2C. About 5% of the stars are outliers in the sense that they are much hotter or cooler than expected. A comparison to effective temperatures derived from spectroscopy suggests in some cases that the photometrically derived temperature is not correct and that this is likely linked to an incorrectly adopted reddening. In this work the presence of a small NIR excess, as has been proposed in the literature for a few well-known cepheids, is investigated. Firstly, this was done by using a sample of about a dozen stars for which a mid-infrared spectrum is available. Secondly, the SEDs of all stars were fitted with a dust model to see if a statistically significant better fit could be obtained. The results were compared to recent work. Eight new candidates for exhibiting a NIR excess are proposed, solely based on the photometric SEDs. Obtaining mid-infrared spectra would be needed to confirm this excess. Finally, period-bolometric luminosity and period-radius relations are presented for samples of over 370 fundamental-mode CCs., Comment: Accepted A&A

We study the M-type asymptotic giant branch (AGB) population of the Large Magellanic Cloud (LMC) by characterizing the individual sources in terms of the main properties of the progenitors and of the dust present in the circumstellar envelope. To this aim, we compare the combination of the spectroscopic and photometric data collected by Spitzer, complemented by additional photometric results available in the literature, with results from AGB modelling that include the description of dust formation in the wind. To allow the interpretation of a paucity stars likely evolving through the post-AGB phase, we extended the available evolutionary sequences to reach the PN phase. The main motivation of the present analysis is to prepare the future observations of the evolved stellar populations of Local Group galaxies that will be done by the James Webb Space Telescope (JWST), by identifying the combination of filters that will maximize the possibilities of characterizing the observed sources. The present results show that for the M-star case the best planes to be used for this purpose are the colour-magnitude ([F770W]-[F2550W], [F770W]) and (Ks-[F770W], [F770W]) planes. In these observational diagrams the sequences of low-mass stars evolving in the AGB phases before the achievement of the C-star stage and of massive AGBs experiencing hot bottom burning are clearly separated and peculiar sources, such as post-AGB, dual-dust chemistry and iron-dust stars can be easily identified

We study a group of evolved M-stars in the Large Magellanic Cloud, characterized by a peculiar spectral energy distribution. While the $9.7~\mu$m feature arises from silicate particles, the whole infrared data seem to suggest the presence of an additional featureless dust species. We propose that the circumstellar envelopes of these sources are characterized by a dual dust chemistry, with an internal region, harbouring carbonaceous particles, and an external zone, populated by silicate, iron and alumina dust grains. Based on the comparison with results from stellar modelling that describe the dust formation process, we deduce that these stars descend from low-mass ($M < 2~M_{\odot}$) objects, formed $1-4$ Gyr ago, currently evolving either in the post-AGB phase or through an after-pulse phase, when the shell CNO nuclear activity is temporarily extinguished. Possible observations able to confirm or disregard the present hypothesis are discussed.

We present MWFitting, a method to fit the stellar components of the Galaxy by comparing Hess Diagrams (HDs) from TRILEGAL models to real data. We apply MWFitting to photometric data from the first three years of the Dark Energy Survey (DES). After removing regions containing known resolved stellar systems such as globular clusters, dwarf galaxies, nearby galaxies, the Large Magellanic Cloud and the Sagittarius Stream, our main sample spans a total area of $\sim$2,300 deg$^2$ distributed across the DES footprint. We further explore a smaller subset ($\sim$ 1,300 deg$^2$) that excludes all regions with known stellar streams and stellar overdensities. Validation tests on synthetic data possessing similar properties to the DES data show that the method is able to recover input parameters with a precision better than 3\%. Based on the best-fit models, we create simulated stellar catalogues covering the whole DES footprint down to $g = 24$ magnitude. Comparisons of data and simulations provide evidence for a break in the power law index describing the stellar density of the Milky Way (MW) halo. Several previously discovered stellar over-densities are recovered in the residual stellar density map, showing the reliability of MWFitting in determining the Galactic components. Simulations made with the best-fitting parameters are a promising way to predict MW star counts for surveys such as LSST and Euclid., Comment: 18 pages, 6 figures

In this paper JK_s data from the VISTA Magellanic Cloud (VMC) survey are used to investigate the tip of the red giant branch (TRGB) as a distance indicator. A linear fit to recent theoretical models is used which reads M_{K_s} = -4.196 -2.013 (J-K_s), valid in the colour range 0.75 < (J-K_s) < 1.3 mag and in the 2MASS system. The observed TRGB is found based on a classical first-order and a second-order derivative filter applied to the binned luminosity function using the "sharpened" magnitude that takes the colour term into account. Extensive simulations are carried out to investigate any biases and errors in the derived distance modulus (DM). Based on these simulations criteria are established related to the number of stars per bin in the 0.5 magnitude range below the TRGB and related to the significance with which the peak in the filter response curve is determined such that the derived distances are unbiased. The DMs based on the second-order derivative filter are found to be more stable and are therefore adopted, although this requires twice as many stars per bin. The TRGB method is applied to specific lines-of-sight where independent distance estimates exist, based on detached eclipsing binaries in the LMC and SMC, classical Cepheids in the LMC, RR Lyrae stars in the SMC, and fields in the SMC where the star formation history (together with reddening and distance) has been derived from deep VMC data. The analysis shows that the theoretical calibration is consistent with the data, that the systematic error on the DM is approximately 0.045 mag, and that random errors of 0.015 mag are achievable. Reddening is an important element in deriving the distance: we find mean DMs ranging from 18.92 (for a typical E(B-V) of 0.15 mag) to 19.07 mag (E(B-V) about 0.04) for the SMC, and ranging from 18.48 (E(B-V) about 0.12 mag) to 18.57 mag (E(B-V) about 0.05) for the LMC., Comment: A&A accepted

We use parallax data from the Gaia second data release (GDR2), combined with parallax data based on Hipparcos and HST data, to derive the period-luminosity-metallicity (PLZ) relation for Galactic classical cepheids (CCs) in the V,K, and Wesenheit WVK bands. An initial sample of 452 CCs are extracted from the literature with spectroscopically derived iron abundances. Reddening values, pulsation periods, and mean magnitudes are taken from the literature. Based on nine CCs with a goodness-of-fit (GOF) statistic <8 and with an accurate non-Gaia parallax, a parallax zero-point offset of -0.049 +- 0.018 mas is derived. Selecting a GOF statistic <8 removes about 40\% of the sample most likely related due to binarity. Excluding first overtone and multi-mode cepheids and applying some other criteria reduces the sample to about 200 stars. The derived PL(Z) relations depend strongly on the parallax zero-point offset. The slope of the PL relation is found to be different from the relations in the LMC at the 3 sigma level. Fixing the slope to the value found in the LMC leads to a distance modulus (DM) to the LMC of order 18.7 mag, larger than the canonical distance. The canonical DM of around 18.5 mag would require a parallax zero-point offset of order $-0.1$ mas. Given the strong correlation between zero point, period and metallicity dependence of the PL relation, and the parallax zero-point offset there is no evidence for a metallicity term in the PLZ relation. The GDR2 release does not allow us to improve on the current distance scale based on CCs. The value of and the uncertainty on the parallax zero-point offset leads to uncertainties of order 0.15 mag on the distance scale. The parallax zero-point offset will need to be known at a level of 3 microas or better to have a 0.01 mag or smaller effect on the zero point of the PL relation and the DM to the LMC., Comment: Accepted 23 July by A&A

Context: At the end of their lives AGB stars are prolific producers of dust and gas. The details of this mass-loss process are still not understood very well. Herschel PACS and SPIRE spectra offer a unique way of investigating properties of AGB stars in general and the mass-loss process in particular. Methods: The HIPE software with the latest calibration is used to process the available PACS and SPIRE spectra of 40 evolved stars. The spectra are convolved with the response curves of the PACS and SPIRE bolometers and compared to the fluxes measured in imaging data of these sources. Custom software is used to identify lines in the spectra, and to determine the central wavelengths and line intensities. Standard molecular line databases are used to associate the observed lines. Because of the limited spectral resolution of the spectrometers several known lines are typically potential counterparts to any observed line. To help identifications the relative contributions in line intensity of the potential counterpart lines are listed for three characteristic temperatures based on LTE calculations and assuming optically thin emission. Result: The following data products are released: the reduced spectra, the lines that are measured in the spectra with wavelength, intensity, potential identifications, and the continuum spectra, i.e. the full spectra with all identified lines removed. As simple examples of how this data can be used in future studies we have fitted the continuum spectra with three power laws and find that the few OH/IR stars seem to have significantly steeper slopes than the other oxygen- and carbon-rich objects in the sample. As another example we constructed rotational diagrams for CO and fitted a two-component model to derive rotational temperatures., Comment: A&A accepted

The survey for DUST in Nearby Galaxies with Spitzer (DUSTiNGS) identified several candidate Asymptotic Giant Branch (AGB) stars in nearby dwarf galaxies and showed that dust can form even in very metal-poor systems (Z ~ 0.008 $Z_\odot$). Here, we present a follow-up survey with WFC3/IR on the Hubble Space Telescope (HST), using filters that are capable of distinguishing carbon-rich (C-type) stars from oxygen-rich (M-type) stars: F127M, F139M, and F153M. We include six star-forming DUSTiNGS galaxies (NGC 147, IC 10, Pegasus dIrr, Sextans B, Sextans A, and Sag DIG), all more metal-poor than the Magellanic Clouds and spanning 1 dex in metallicity. We double the number of dusty AGB stars known in these galaxies and find that most are carbon rich. We also find 26 dusty M-type stars, mostly in IC 10. Given the large dust excess and tight spatial distribution of these M-type stars, they are most likely on the upper end of the AGB mass range (stars undergoing Hot Bottom Burning). Theoretical models do not predict significant dust production in metal-poor M-type stars, but we see evidence for dust excess around M-type stars even in the most metal-poor galaxies in our sample (12+log(O/H) = 7.26-7.50). The low metallicities and inferred high stellar masses (up to ~10 $M_\odot$) suggest that AGB stars can produce dust very early in the evolution of galaxies (~30 Myr after they form), and may contribute significantly to the dust reservoirs seen in high-redshift galaxies., Comment: 18 pages, 9 figures, accepted for publication in ApJ

Context: Cepheids are excellent tracers of young stellar populations. They play a crucial role in astrophysics as standard candles. The chemistry of classical Cepheids in the Milky Way is now quite well-known. Despite a much larger sample, the chemical composition of Magellanic Cepheids has been only scarcely investigated. Aims: For the first time, we study the chemical composition of several Cepheids located in the same populous cluster: NGC 1866, in the Large Magellanic Cloud (LMC). To also investigate the chemical composition of Cepheids at lower metallicity, four targets are located in the Small Magellanic Cloud (SMC). Our sample allows us to increase the number of Cepheids with known metallicities in the LMC/SMC by 20%/25% and the number of Cepheids with detailed chemical composition in the LMC/SMC by 46%/50%. Methods: We use canonical spectroscopic analysis to determine the chemical composition of Cepheids and provide abundances for a good number of $\alpha$, iron-peak and neutron-capture elements. Results: We find that six Cepheids in the LMC cluster NGC 1866 have a very homogeneous chemical composition, also consistent with red giant branch (RGB) stars in the cluster. Period--age relations that include no or average rotation indicate that all the Cepheids in NGC 1866 have a similar age and therefore belong to the same stellar population. Our results are in good agreement with theoretical models accounting for luminosity and radial velocity variations. Using distances based on period-luminosity relations in the near- or mid-infrared, we investigate for the first time the metallicity distribution of the young population in the SMC in the depth direction. Preliminary results show no metallicity gradient along the SMC main body, but our sample is small and does not contain Cepheids in the inner few degrees of the SMC., Comment: Accepted in A&A

Carbon monoxide is the most abundant molecule after H$_2$ and is important for chemistry in circumstellar envelopes around late-type stars. The size of the envelope is important when modelling low-J transition lines and deriving mass-loss rates from such lines. Now that ALMA is coming to full power the extent of the CO emitting region can be measured directly for nearby asymptotic giant branch (AGB) stars. In parallel, it has become obvious in the past few years that the strength of the interstellar radiation field (ISRF) can have a significant impact on the interpretation of the emission lines. In this paper an update and extension of the classical Mamon et al. (1988; ApJ 328, 797) paper is presented; these authors provided the CO abundance profile, described by two parameters, as a function of mass-loss rate and expansion velocity. Following recent work an improved numerical method and updated H$_2$ and CO shielding functions are used and a larger grid is calculated that covers more parameter space, including the strength of the ISRF. The effect of changing the photodissociation radius on the low-J CO line intensities is illustrated in two cases., Comment: A&A in press

Aims. Our goal is to characterize the intermediate age, detached shell carbon star U Antliae morphologically and physically in order to study the mass-loss evolution after a possible thermal pulse. Methods. High spatial resolution ALMA observations of unprecedented quality in thermal CO lines allow us to derive first critical spatial and temporal scales and constrain modeling efforts to estimate mass-loss rates for both the present day as well as the ejection period of the detached shell. Results. The detached shell is remarkably thin, overall spherically symmetric, and shows a barely resolved filamentary substructure possibly caused by instabilities in the interaction zone of winds with different outflow velocities. The expansion age of the detached shell is of the order of 2700 years and its overall width indicates a high expansion-velocity and high mass-loss period of only a few hundred years at an average mass-loss rate of $\approx$ 10$^{-5}$ $M_\odot$ yr$^{-1}$. The post-high-mass-loss-rate-epoch evolution of U Ant shows a significant decline to a substantially lower gas expansion velocity and a mass-loss rate amounting to 4$\times$10$^{-8}$ $M_\odot$ yr$^{-1}$, at present being consistent with evolutionary changes as predicted for the period between thermal pulses.

The mass-loss process from evolved stars is a key ingredient for our understanding of many fields of astrophysics, including stellar evolution and the chemical enrichment of the interstellar medium via stellar yields. One the main unsolved questions is the geometry of the mass-loss process. Taking advantage of the results from the Herschel Mass loss of Evolved StarS (MESS) programme, we initiated a coordinated effort to characterise the geometry of mass loss from evolved red giants at various spatial scales. For this purpose we used the MID-infrared interferometric Instrument (MIDI) to resolve the inner envelope of 14 asymptotic giant branch stars (AGBs) in the MESS sample. In this contribution we present an overview of the interferometric data collected within the frame of our Large Programme, and we also add archive data for completeness. We studied the geometry of the inner atmosphere by comparing the observations with predictions from different geometric models. Asymmetries are detected for five O-rich and S-type, suggesting that asymmetries in the N band are more common among stars with such chemistry. We speculate that this fact is related to the characteristics of the dust grains. Except for one star, no interferometric variability is detected, i.e. the changes in size of the shells of non-mira stars correspond to changes of the visibility of less than 10%. The observed spectral variability confirms previous findings from the literature. The detection of dust in our sample follows the location of the AGBs in the IRAS colour-colour diagram: more dust is detected around oxygen-rich stars in region II and in the carbon stars in region VII. The SiC dust feature does not appear in the visibility spectrum of UAnt and SSct, which are two carbon stars with detached shells. This finding has implications for the theory of SiC dust formation., Comment: 43 pages, 31 figures; accepted for publication in Astronomy & Astrophysics. Abstract shortened for compilation reasons. Metadata corrected

Context: Low- and intermediate-mass stars lose most of their stellar mass at the end of their lives on the asymptotic giant branch (AGB). Determining gas and dust mass-loss rates (MLRs) is important in quantifying the contribution of evolved stars to the enrichment of the interstellar medium. Aims: Attempt to, for the first time, spectrally resolve CO thermal line emission in a small sample of AGB stars in the Large Magellanic Cloud. Methods: ALMA was used to observe 2 OH/IR stars and 4 carbon stars in the LMC in the CO J= 2-1 line. Results: We present the first measurement of expansion velocities in extragalactic carbon stars. All four C-stars are detected and wind expansion velocities and stellar velocities are directly measured. Mass-loss rates are derived from modelling the spectral energy distribution and Spitzer/IRS spectrum with the DUSTY code. Gas-to-dust ratios are derived that make the predicted velocities agree with the observed ones. The expansion velocities and MLRs are compared to a Galactic sample of well-studied relatively low MLRs stars supplemented with "extreme" C-stars that have properties more similar to the LMC targets. Gas MLRs derived from a simple formula are significantly smaller than derived from the dust modelling, indicating an order of magnitude underestimate of the estimated CO abundance, time-variable mass loss, or that the CO intensities in LMC stars are lower than predicted by the formula derived for Galactic objects. This could be related to a stronger interstellar radiation field in the LMC. Conclusions: Although the LMC sample is small and the comparison to Galactic stars is non-trivial because of uncertainties in their distances it appears that for C stars the wind expansion velocities in the LMC are lower than in the solar neighbourhood, while the MLRs appear similar. This is in agreement with dynamical dust-driven wind models., Comment: Accepted for publication by A&A

The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C2H2 at 7.5 um. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in the DPR at lower metallicities, but it is not statistically significant. The most deeply embedded carbon stars have lower variability amplitudes and show SiC in absorption. In some cases they have bluer colors at shorter wavelengths, suggesting that the central star is becoming visible. These deeply embedded stars may be evolving off of the AGB and/or they may have non-spherical dust geometries., Comment: Accepted for publication by ApJ, 20 pages, 20 figures. Full versions of the tables are available at: http://isc.astro.cornell.edu/~sloan/library/2016/mcc

The VISTA near infrared Y, J, Ks survey of the Magellanic System (VMC) is collecting deep Ks band time series photometry of pulsating variable stars hosted by the two Magellanic Clouds and their connecting Bridge. In this paper, we present Y, J, Ks light curves for a sample of 4172 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with literature V values, allowed us to construct a variety of period-luminosity (PL), period-luminosity-color (PLC), and period-wesenheit (PW) relationships, valid for Fundamental (F), First Overtone (FO) and Second Overtone (SO) pulsators. The relations involving V, J, Ks bands are in agreement with their counterparts in the literature. As for the Y band, to our knowledge we present the first CC PL, PW, and PLC relations ever derived using this filter. We also present the first near infrared PL, PW, and PLC relations for SO pulsators to date. We used PW(V,Ks) to estimate the relative SMC-LMC distance and, in turn, the absolute distance to the SMC. For the former quantity we find a value of Delta(mu)=0.55+-0.04 mag, in rather good agreement with other evaluations based on CCs, but significantly larger than the results obtained from older population II distance indicators. This discrepancy might be due to the different geometric distributions of young and old tracers in both Clouds. As for the absolute distance to the SMC, our best estimates are mu(SMC)=19.01+-0.05 mag and mu(SMC)=19.04+-0.06 mag, based on two distance measurements to the LMC, which rely on accurate CC and eclipsing Cepheid binary data, respectively., Comment: 24 Pages, 20 Figure, 6 tables. Accepted for publication on ApJS

Infrared Herschel imaging and spectroscopic observations of the nebula M1-67 around the Wolf-Rayet star WR 124 have been obtained along with optical imaging observations. The infrared images reveal a clumpy dusty nebula that extends up to 1 pc. The comparison with the optical images shows that the ionized gas nebula coincides with the dust nebula, the dust and the gas being mixed together. A photodissociation region is revealed from the infrared spectroscopic analysis. The analysis of the infrared spectrum of the nebula, where forbidden emission lines of ionized elements were detected, showed that the nebula consists of mildly processed material with the calculated abundance number ratios being N/O = 1.0 +/- 0.5 and C/O = 0.46 +/- 0.27. Based on a radiative transfer model, the dust mass of the nebula was estimated to be 0.22 Msun with a population of large grains being necessary to reproduce the observations. The comparison of the mass-loss rate and the abundance ratios to theoretical models of stellar evolution led to the conclusion that the nebular ejection took place during a RSG/YSG evolutionary phase of a central star with an initial mass of 32 Msun., Comment: 14 pages, 11 figures, accepted for publication in A&A

Context. The recent detection of warm H$_2$O vapor emission from the outflows of carbon-rich asymptotic giant branch (AGB) stars challenges the current understanding of circumstellar chemistry. Two mechanisms have been invoked to explain warm H$_2$O vapor formation. In the first, periodic shocks passing through the medium immediately above the stellar surface lead to H$_2$O formation. In the second, penetration of ultraviolet interstellar radiation through a clumpy circumstellar medium leads to the formation of H$_2$O molecules in the intermediate wind. Aims. We aim to determine the properties of H$_2$O emission for a sample of 18 carbon-rich AGB stars and subsequently constrain which of the above mechanisms provides the most likely warm H$_2$O formation pathway. Methods, Results, and Conclusions. See paper.

We present Ks -band light curves for 299 Cepheids in the Small Magellanic Cloud (SMC) of which 288 are new discoveries that we have identified using multi-epoch near-infrared photometry obtained by the VISTA survey of the Magellanic Clouds system (VMC). The new Cepheids have periods in the range from 0.34 to 9.1 days and cover the magnitude interval 12.9 <= Ks <= 17.6 mag. Our method was developed using variable stars previously identified by the optical microlensing survey OGLE. We focus on searching new Cepheids in external regions of the SMC for which complete VMC Ks-band observations are available and no comprehensive identification of different types of variable stars from other surveys exists yet., Comment: 12 pages, 7 figures. Accepted for publication in MNRAS

Context. We study the atmosphere of the carbon-rich Mira RU Vir using the mid-infrared high spatial resolution interferometric observations from VLTI/MIDI. Aims. The aim of this work is to analyse the atmosphere of the carbon-rich Mira RU Vir, with state of the art models, in this way deepening the knowledge of the dynamic processes at work in carbon-rich Miras. Methods. We compare spectro-photometric and interferometric measurements of this carbon-rich Mira AGB star, with the predictions of different kinds of modelling approaches (hydrostatic model atmospheres plus MOD-More Of Dusty, self-consistent dynamic model atmospheres). A geometric model fitting tool is used for a first interpretation of the interferometric data. Results. The results show that a joint use of different kind of observations (photometry, spectroscopy, interferometry) is essential to shed light on the structure of the atmosphere of a carbon-rich Mira. The dynamic model atmospheres fit well the ISO spectrum in the wavelength range {\lambda} = [2.9, 25.0] {\mu}m. Nevertheless, a discrepancy is noticeable both in the SED (visible), and in the visibilities (shape and level). A possible explanation are intra-/inter-cycle variations in the dynamic model atmospheres as well as in the observations. The presence of a companion star and/or a disk or a decrease of mass loss within the last few hundred years cannot be excluded but are considered unlikely., Comment: 15 pages. Accepted in A&A

We present the first results from the SAGE-Var program, a follow on to the Spitzer legacy program Surveying the Agents of Galaxy Evolution (SAGE; Meixner, et al. 2006). We obtained 4 epochs of photometry at 3.6 & 4.5 microns covering the bar of the Large Magellanic Cloud (LMC) and the central region of the Small Magellanic Cloud (SMC) in order to probe the variability of extremely red sources missed by variability surveys conducted at shorter wavelengths, and to provide additional epochs of observation for known variables. Our 6 total epochs of observations allow us to probe infrared variability on 15 different timescales ranging from ~20 days to ~5 years. Out of a full catalog of 1,717,554 (LMC) and 457,760 (SMC) objects, we find 10 (LMC) and 6 (SMC) large amplitude AGB variables without optically measured variability owing to circumstellar dust obscuration. The catalog also contains multiple observations of known AGB variables, type I and II Cepheids, eclipsing variables, R CrB stars and young stellar objects which will be discussed in following papers. Here we present infrared Period-Luminosity (PL) relations for classical Cepheids in the Magellanic Clouds, as well as improved PL relationships for AGB stars pulsating in the fundamental mode using mean magnitudes constructed from 6 epochs of observations.

Far-infrared Herschel PACS imaging and spectroscopic observations of the nebula around the luminous blue variable (LBV) star AG Car have been obtained along with optical imaging in the Halpha+[NII] filter. In the infrared light, the nebula appears as a clumpy ring shell that extends up to 1.2 pc with an inner radius of 0.4 pc. It coincides with the Halpha nebula, but extends further out. Dust modeling of the nebula was performed and indicates the presence of large grains. The dust mass is estimated to be ~ 0.2 Msun. The infrared spectrum of the nebula consists of forbidden emission lines over a dust continuum. Apart from ionized gas, these lines also indicate the existence of neutral gas in a photodissociation region that surrounds the ionized region. The abundance ratios point towards enrichment by processed material. The total mass of the nebula ejected from the central star amounts to ~ 15 Msun, assuming a dust-to-gas ratio typical of LBVs. The abundances and the mass-loss rate were used to constrain the evolutionary path of the central star and the epoch at which the nebula was ejected, with the help of available evolutionary models. This suggests an ejection during a cool LBV phase for a star of ~ 55 Msun with little rotation., Comment: accepted for publication in A&A

The DUSTiNGS survey (DUST in Nearby Galaxies with Spitzer) is a 3.6 and 4.5 micron imaging survey of 50 nearby dwarf galaxies designed to identify dust-producing Asymptotic Giant Branch (AGB) stars and massive stars. Using two epochs, spaced approximately six months apart, we identify a total of 526 dusty variable AGB stars (sometimes called "extreme" or x-AGB stars; [3.6]-[4.5]>0.1 mag). Of these, 111 are in galaxies with [Fe/H] < -1.5 and 12 are in galaxies with [Fe/H] < -2.0, making them the most metal-poor dust-producing AGB stars known. We compare these identifications to those in the literature and find that most are newly discovered large-amplitude variables, with the exception of approximately 30 stars in NGC 185 and NGC 147, one star in IC 1613, and one star in Phoenix. The chemical abundances of the x-AGB variables are unknown, but the low metallicities suggest that they are more likely to be carbon-rich than oxygen-rich and comparisons with existing optical and near-IR photometry confirms that 70 of the x-AGB variables are confirmed or likely carbon stars. We see an increase in the pulsation amplitude with increased dust production, supporting previous studies suggesting that dust production and pulsation are linked. We find no strong evidence linking dust production with metallicity, indicating that dust can form in very metal-poor environments., Comment: 18 pages, 16 figures, accepted for publication in ApJ

We present new Herschel photometric and spectroscopic observations of Supernova 1987A, carried out in 2012. Our dedicated photometric measurements provide new 70 micron data and improved imaging quality at 100 and 160 micron compared to previous observations in 2010. Our Herschel spectra show only weak CO line emission, and provide an upper limit for the 63 micron [O I] line flux, eliminating the possibility that line contaminations distort the previously estimated dust mass. The far-infrared spectral energy distribution (SED) is well fitted by thermal emission from cold dust. The newly measured 70 micron flux constrains the dust temperature, limiting it to nearly a single temperature. The far-infrared emission can be fitted by 0.5+-0.1 Msun of amorphous carbon, about a factor of two larger than the current nucleosynthetic mass prediction for carbon. The observation of SiO molecules at early and late phases suggests that silicates may also have formed and we could fit the SED with a combination of 0.3 Msun of amorphous carbon and 0.5 Msun of silicates, totalling 0.8 Msun of dust. Our analysis thus supports the presence of a large dust reservoir in the ejecta of SN 1987A. The inferred dust mass suggests that supernovae can be an important source of dust in the interstellar medium, from local to high-redshift galaxies., Comment: ApJ accepted, 8 pages

In our series of papers presenting the Herschel imaging of evolved planetary nebulae, we present images of the dust distribution in the Helix nebula (NGC 7293). Images at 70, 160, 250, 350, and 500 micron were obtained with the PACS and SPIRE instruments on board the Herschel satellite. The broadband maps show the dust distribution over the main Helix nebula to be clumpy and predominantly present in the barrel wall. We determined the spectral energy distribution of the main nebula in a consistent way using Herschel, IRAS, and Planck flux values. The emissivity index of 0.99 +/- 0.09, in combination with the carbon rich molecular chemistry of the nebula, indicates that the dust consists mainly of amorphous carbon. The dust excess emission from the central star disk is detected at 70 micron and the flux measurement agree with previous measurement. We present the temperature and dust column density maps. The total dust mass across the Helix nebula (without its halo) is determined to be 0.0035 solar mass at a distance of 216 pc. The temperature map shows dust temperatures between 22 and 42 K, which is similar to the kinetic temperature of the molecular gas, strengthening the fact that the dust and gas co-exist in high density clumps. Archived images are used to compare the location of the dust emission in the far infrared (Herschel) with the ionized (GALEX, Hbeta) and molecular hydrogen component. The different emission components are consistent with the Helix consisting of a thick walled barrel-like structure inclined to the line of sight. The radiation field decreases rapidly through the barrel wall., Comment: 8 pages, 9 figures, revised version A&A in press

Nearby resolved dwarf galaxies provide excellent opportunities for studying the dust-producing late stages of stellar evolution over a wide range of metallicity (-2.7 < [Fe/H] < -1.0). Here, we describe DUSTiNGS (DUST in Nearby Galaxies with Spitzer): a 3.6 and 4.5 micron post-cryogen Spitzer Space Telescope imaging survey of 50 dwarf galaxies within 1.5 Mpc that is designed to identify dust-producing Asymptotic Giant Branch (AGB) stars and massive stars. The survey includes 37 dwarf spheroidal, 8 dwarf irregular, and 5 transition-type galaxies. This near-complete sample allows for the building of statistics on these rare phases of stellar evolution over the full metallicity range. The photometry is >75% complete at the tip of the Red Giant Branch for all targeted galaxies, with the exception of the crowded inner regions of IC 10, NGC 185, and NGC 147. This photometric depth ensures that the majority of the dust-producing stars, including the thermally-pulsing AGB stars, are detected in each galaxy. The images map each galaxy to at least twice the half-light radius to ensure that the entire evolved star population is included and to facilitate the statistical subtraction of background and foreground contamination, which is severe at these wavelengths. In this overview, we describe the survey, the data products, and preliminary results. We show evidence for the presence of dust-producing AGB stars in 8 of the targeted galaxies, with metallicities as low as [Fe/H] = -1.9, suggesting that dust production occurs even at low metallicity., Comment: 18 pages, 13 figures. Accepted for publication in ApJS

The VISTA survey of the Magellanic Clouds System (VMC) is collecting deep $K_\mathrm{s}$--band time--series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper we have analysed a sample of 130 Large Magellanic Cloud (LMC) Type II Cepheids (T2CEPs) found in tiles with complete or near complete VMC observations for which identification and optical magnitudes were obtained from the OGLE III survey. We present $J$ and $K_\mathrm{s}$ light curves for all 130 pulsators, including 41 BL Her, 62 W Vir (12 pW Vir) and 27 RV Tau variables. We complement our near-infrared photometry with the $V$ magnitudes from the OGLE III survey, allowing us to build a variety of Period-Luminosity ($PL$), Period-Luminosity-Colour ($PLC$) and Period-Wesenheit ($PW$) relationships, including any combination of the $V, J, K_\mathrm{s}$ filters and valid for BL Her and W Vir classes. These relationships were calibrated in terms of the LMC distance modulus, while an independent absolute calibration of the $PL(K_\mathrm{s})$ and the $PW(K_\mathrm{s},V)$ was derived on the basis of distances obtained from $Hubble Space Telescope$ parallaxes and Baade-Wesselink technique. When applied to the LMC and to the Galactic Globular Clusters hosting T2CEPs, these relations seem to show that: 1) the two population II standard candles RR Lyrae and T2CEPs give results in excellent agreement with each other; 2) there is a discrepancy of $\sim$0.1 mag between population II standard candles and Classical Cepheids when the distances are gauged in a similar way for all the quoted pulsators. However, given the uncertainties, this discrepancy is within the formal 1$\sigma$ uncertainties., Comment: 18 pages + Appendix (14 pages). Accepted for publication on MNRAS

We report on the discovery of strong intensity variations in the high rotational lines of abundant molecular species towards the archetypical circumstellar envelope of IRC+10216. The observations have been carried out with the HIFI instrument on board \textit{Herschel}\thanks{\textit{Herschel} is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA} and with the IRAM\thanks{This work was based on observations carried out with the IRAM 30-meter telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain)} 30-m telescope. They cover several observing periods spreading over 3 years. The line intensity variations for molecules produced in the external layers of the envelope most probably result from time variations in the infrared pumping rates. We analyze the main implications this discovery has on the interpretation of molecular line emission in the envelopes of Mira-type stars. Radiative transfer calculations have to take into account both the time variability of infrared pumping and the possible variation of the dust and gas temperatures with stellar phase in order to reproduce the observation of molecular lines at different epochs. The effect of gas temperature variations with stellar phase could be particularly important for lines produced in the innermost regions of the envelope. Each layer of the circumstellar envelope sees the stellar light radiation with a different lag time (phase). Our results show that this effect must be included in the models. The sub-mm and FIR lines of AGB stars cannot anymore be considered as safe intensity calibrators.

We present new near-infrared (NIR) light-curve templates for fundamental (FU, JHK) and first overtone (FO, J) Cepheids. The new templates together with PL and PW relations provide Cepheid distances from single-epoch observations with a precision only limited by the intrinsic accuracy of the method adopted. The templates rely on a very large set of Galactic and Magellanic Clouds (MCs) Cepheids (FU,~600; FO,~200) with well sampled NIR (IRSF data) and optical (V,I; OGLE data) light curves. To properly trace the change in the shape of the light curve as a function of period, we split the sample of calibrating Cepheids into 10 different period bins. The templates for the first time cover FO Cepheids and the FU short-period Cepheids (P<5 days). Moreover, the zero-point phase is anchored to the phase of the mean magnitude along the rising branch. The new approach has several advantages in sampling the light curve of bump Cepheids when compared with the phase of maximum light. We also provide new estimates of the NIR-to-optical amplitude ratios for FU and FO Cepheids. We perform detailed analytical fits using both 7th-order Fourier series and multi-Gaussian periodic functions. The latter are characterized by a smaller number of free parameters (9 vs 15). Mean NIR magnitudes based on the new templates are up to 80% more accurate than single-epoch measurements and up to 50% more accurate than mean magnitudes based on previous templates, with typical associated uncertainties ranging from 0.015 mag (J) to 0.019 mag (K). Moreover, the errors on individual distances of Small MC Cepheids derived from NIR PW relations, are essentially reduced to the intrinsic scatter of the adopted relations. Thus, the new templates are the ultimate tool to estimate precise Cepheid distances from NIR single-epoch observations, which can be adopted to derive the 3D structure of the MCs., Comment: 23 pages, 16 figures

The evolution of low- and intermediate-mass stars on the asymptotic giant branch (AGB) is mainly controlled by the rate at which these stars lose mass in a stellar wind. Understanding the driving mechanism and strength of the stellar winds of AGB stars and the processes enriching their surfaces with products of nucleosynthesis are paramount to constraining AGB evolution and predicting the chemical evolution of galaxies. In a previous paper we have constrained the structure of the outflowing envelope of W Hya using spectral lines of the $^{12}$CO molecule. Here we broaden this study by modelling an extensive set of H$_{2}$O and $^{28}$SiO lines observed by the three instruments on board Herschel using a state-of-the-art molecular excitation and radiative transfer code. The oxygen isotopic ratios and the $^{28}$SiO abundance profile can be connected to the initial stellar mass and to crucial aspects of dust formation at the base of the stellar wind, respectively. The modelling of H$_{2}$O and $^{28}$SiO confirms the properties of the envelope model of W Hya derived from $^{12}$CO lines. We find an H$_2$O ortho-to-para ratio of 2.5\,$^{+2.5}_{-1.0}$, consistent with what is expected for an AGB wind. The O$^{16}$/O$^{17}$ ratio indicates that W Hya has an initial mass of about 1.5 M$_\odot$. Although the ortho- and para-H$_{2}$O lines observed by HIFI appear to trace gas of slightly different physical properties, a turbulence velocity of $0.7\pm0.1$ km s$^{-1}$ fits the HIFI lines of both spin isomers and those of $^{28}$SiO well. The ortho- and para-H$_2^{16}$O and $^{28}$SiO abundances relative to H$_{2}$ are $(6^{+3}_{-2}) \times 10^{-4}$, $(3^{+2}_{-1}) \times 10^{-4}$, and $(3.3\pm 0.8)\times 10^{-5}$, respectively. Assuming a solar silicon-to-carbon ratio, the $^{28}$SiO line emission model is consistent with about one-third of the silicon atoms being locked up in dust particles.

Context. The Mass loss of Evolved StarS (MESS) sample observed with PACS on board the Herschel Space Observatory revealed that several asymptotic giant branch (AGB) stars are surrounded by an asymmetric circumstellar envelope (CSE) whose morphology is most likely caused by the interaction with a stellar companion. The evolution of AGB stars in binary systems plays a crucial role in understanding the formation of asymmetries in planetary nebul{\ae} (PNe), but at present, only a handful of cases are known where the interaction of a companion with the stellar AGB wind is observed. Aims. We probe the environment of the very evolved AGB star $\pi^1$ Gruis on large and small scales to identify the triggers of the observed asymmetries. Methods. Observations made with Herschel/PACS at 70 $\mu$m and 160 $\mu$m picture the large-scale environment of $\pi^1$ Gru. The close surroundings of the star are probed by interferometric observations from the VLTI/AMBER archive. An analysis of the proper motion data of Hipparcos and Tycho-2 together with the Hipparcos Intermediate Astrometric Data help identify the possible cause for the observed asymmetry. Results. The Herschel/PACS images of $\pi^1$ Gru show an elliptical CSE whose properties agree with those derived from a CO map published in the literature. In addition, an arc east of the star is visible at a distance of $38^{\prime\prime}$ from the primary. This arc is most likely part of an Archimedean spiral caused by an already known G0V companion that is orbiting the primary at a projected distance of 460 au with a period of more than 6200 yr. However, the presence of the elliptical CSE, proper motion variations, and geometric modelling of the VLTI/AMBER observations point towards a third component in the system, with an orbital period shorter than 10 yr, orbiting much closer to the primary than the G0V star., Comment: 13 pages, 11 figures, accepted for publication in Astronomy & Astrophysics

The VISTA near-infrared YJKs survey of the Magellanic Clouds system (VMC) has entered its core phase: about 40% of the observations across the Large and Small Magellanic Clouds (LMC, SMC), the Magellanic Bridge and Stream have already been secured and the data are processed and analysed regularly. The initial analyses, concentrated in the first two completed tiles in the LMC (6_6 including 30 Doradus and 8_8 including the South Ecliptic Pole), show the superior quality of the data. The depth of the VMC survey allows the derivation of the star formation history (SFH) with unprecedented quality compared to previous wide-area surveys while reddening maps of high angular resolution are constructed using red clump stars. The multi-epoch Ks-band data reveal tight period-luminosity relations for variable stars and they permit the measurement of accurate proper motions of the stellar populations. The VMC survey continues to acquire data that will address many issues in the field of star and galaxy evolution., Comment: 3 pages, 4 figures

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 $

For the Mass-loss of Evolved StarS (MESS) programme, the unprecedented spatial resolution of the PACS photometer on board the Herschel space observatory was employed to map the dusty environments of asymptotic giant branch (AGB) and red supergiant (RSG) stars. Among the morphologically heterogeneous sample, a small fraction of targets is enclosed by spherically symmetric detached envelopes. Based on observations in the 70 {\mu}m and 160 {\mu}m wavelength bands, we investigated the surroundings of the two carbon semiregular variables S Sct and RT Cap, which both show evidence for a history of highly variable mass-loss. S Sct exhibits a bright, spherically symmetric detached shell, 138" in diameter and co-spatial with an already known CO structure. Moreover, weak emission is detected at the outskirts, where the morphology seems indicative of a mild shaping by interaction of the wind with the interstellar medium, which is also supported by the stellar space motion. Two shells are found around RT Cap that were not known so far in either dust emission or from molecular line observations. The inner shell with a diameter of 188" shows an almost immaculate spherical symmetry, while the outer ~5' structure is more irregularly shaped. MoD, a modification of the DUSTY radiative transfer code, was used to model the detached shells. Dust temperatures, shell dust masses, and mass-loss rates are derived for both targets.

The Helix Nebula (NGC 7293) is the closest planetary nebulae. Therefore, it is an ideal template for photochemical studies at small spatial scales in planetary nebulae. We aim to study the spatial distribution of the atomic and the molecular gas, and the structure of the photodissociation region along the western rims of the Helix Nebula as seen in the submillimeter range with Herschel. We use 5 SPIRE FTS pointing observations to make atomic and molecular spectral maps. We analyze the molecular gas by modeling the CO rotational lines using a non-local thermodynamic equilibrium (non-LTE) radiative transfer model. For the first time, we have detected extended OH+ emission in a planetary nebula. The spectra towards the Helix Nebula also show CO emission lines (from J= 4 to 8), [NII] at 1461 GHz from ionized gas, and [CI] (2-1), which together with the OH+ lines, trace extended CO photodissociation regions along the rims. The estimated OH+ column density is (1-10)x1e12 cm-2. The CH+ (1-0) line was not detected at the sensitivity of our observations. Non-LTE models of the CO excitation were used to constrain the average gas density (n(H2)=(1-5)x1e5 cm-3) and the gas temperature (Tk= 20-40 K). The SPIRE spectral-maps suggest that CO arises from dense and shielded clumps in the western rims of the Helix Nebula whereas OH+ and [CI] lines trace the diffuse gas and the UV and X-ray illuminated clumps surface where molecules reform after CO photodissociation. [NII] traces a more diffuse ionized gas component in the interclump medium., Comment: Accepted for publication in Astronomy and Astrophysics

We present 48 Herschel/PACS spectra of evolved stars in the wavelength range of 67-72 $\mu$m. This wavelength range covers the 69 $\mu$m band of crystalline olivine ($\text{Mg}_{2-2x}\text{Fe}_{(2x)}\text{SiO}_{4}$). The width and wavelength position of this band are sensitive to the temperature and composition of the crystalline olivine. Our sample covers a wide range of objects: from high mass-loss rate AGB stars (OH/IR stars, $\dot M \ge 10^{-5}$ M$_\odot$/yr), through post-AGB stars with and without circumbinary disks, to planetary nebulae and even a few massive evolved stars. The goal of this study is to exploit the spectral properties of the 69 $\mu$m band to determine the composition and temperature of the crystalline olivine. Since the objects cover a range of evolutionary phases, we study the physical and chemical properties in this range of physical environments. We fit the 69 $\mu$m band and use its width and position to probe the composition and temperature of the crystalline olivine. For 27 sources in the sample, we detected the 69 $\mu$m band of crystalline olivine ($\text{Mg}_{(2-2x)}\text{Fe}_{(2x)}\text{SiO}_{4}$). The 69 $\mu$m band shows that all the sources produce pure forsterite grains containing no iron in their lattice structure. The temperature of the crystalline olivine as indicated by the 69 $\mu$m band, shows that on average the temperature of the crystalline olivine is highest in the group of OH/IR stars and the post-AGB stars with confirmed Keplerian disks. The temperature is lower for the other post-AGB stars and lowest for the planetary nebulae. A couple of the detected 69 $\mu$m bands are broader than those of pure magnesium-rich crystalline olivine, which we show can be due to a temperature gradient in the circumstellar environment of these stars. continued..., Comment: Accepted for publication in A&A