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We present five morphological and kinematic criteria to aid in asserting the binary nature of a protoplanetary disc, based on 3D hydrodynamical simulations of circumbinary discs post-processed with Monte Carlo radiative transfer. We find that circumbinary discs may be identified by i) a central cavity, ii) spiral arms both in and outside of their central cavities, iii) non-localised perturbations in their iso-velocity curves, iv) asymmetry between the lines of maximum speed of the blue and red-shifted wings and v) asymmetry between the area of the blue and red-shifted wings. We provide quantitative metrics for the last two criteria that can be used, in conjunction with the morphological criteria, to signal whether a protoplanetary disc is likely to be a circumbinary disc., Comment: 26 pages, 26 figures, accepted to MNRAS

We report kinematic and thermal signatures associated with the directly imaged protoplanet candidate in the Elias 2-24 disc. Using the DSHARP ALMA observations of the $^{12}$CO J=2-1 line, we show that the disc kinematics are perturbed, with a detached CO emission spot at the location of the planet candidate and traces of spiral wakes, and also that the observed CO emission intensities require local heating. While the foreground extinction hides the velocity channels associated with the planet, preventing a planet mass estimate, the level of gas heating implied by the CO emission indicates the presence of a warm, embedded giant planet. Comparison with models show this could either be a $\gtrsim 5$M$_\mathrm{Jup}$, or a lower mass ( $\gtrsim 2$M$_\mathrm{Jup}$) but accreting proto-planet., Comment: 6 pages, 3 figures, accepted for publication in MNRAS Letters

Companions at sub-arcsecond separation from young stars are difficult to image. However their presence can be inferred from the perturbations they create in the dust and gas of protoplanetary disks. Here we present a new interpretation of SPHERE polarised observations that reveal the previously detected inner spiral in the disk of HD 100546. The spiral coincides with a newly detected 12CO inner spiral and the previously reported CO emission Doppler-flip, which has been interpreted as the signature of an embedded protoplanet. Comparisons with hydrodynamical models indicate that this Doppler-flip is instead the kinematic counterpart of the spiral, which is likely generated by an inner companion inside the disk cavity., Comment: Accepted to ApJL, 14 pages, 10 figures

We present detailed abundance measurements for 45 globular clusters (GCs) in galaxies in (and, in one case, beyond) the Local Group. The measurements are based on new high-resolution integrated-light spectra of GCs in NGC 185, NGC 205, M31, M33, and NGC 2403, combined with reanalysis of previous observations of GCs in the Fornax dSph, WLM, NGC 147, NGC 6822, and the Milky Way. The GCs cover the range -2.8 < [Fe/H] < -0.1 and we determined abundances for Fe, Na, Mg, Si, Ca, Sc, Ti, Cr, Mn, Ni, Cu, Zn, Zr, Ba, and Eu. Corrections for non local thermodynamic equilibrium effects are included for Na, Mg, Ca, Ti, Mn, Fe, Ni, and Ba. For several of the galaxies, our measurements provide the first quantitative constraints on the detailed composition of their metal-poor stellar populations. Overall, the GCs in different galaxies exhibit remarkably uniform abundance patterns of the alpha-, iron-peak, and neutron-capture elements, with a dispersion of less than 0.1 dex in [alpha/Fe] for the full sample. There is a hint that GCs in dwarf galaxies are slightly less alpha-enhanced (by about 0.04 dex on average) than those in larger galaxies. One GC in M33 (HM33-B) resembles the most metal-rich GCs in the Fornax dSph (Fornax 4) and NGC 6822 (SC7) by having alpha-element abundances closer to scaled-solar values, possibly hinting at an accretion origin. We find that the alpha-element abundances strongly correlate with those of Na, Sc, Ni, and Zn. Several GCs with [Fe/H]<-1.5 are deficient in Mg compared to other alpha-elements. We find no GCs with strongly enhanced r-process abundances as reported for metal-poor stars in some ultra-faint dwarfs and the Magellanic Clouds. The similarity of the abundance patterns for metal-poor GCs in different environments points to similar early enrichment histories and only allow for minor variations in the initial mass function., Comment: 34 pages + 6 appendices. Accepted for publication in Astronomy & Astrophysics

We map the planetary wake associated with the embedded protoplanet creating the CO kink in the disk of HD~163296. We show that the wake can be traced by a series of correlated perturbations in the peak velocity map. The sign change of the perturbations across the disk major axis confirm that the wake induces predominantly radial motion, as predicted by models of planet-disk interaction. These results provide the first direct confirmation of planet wakes generated by Lindblad resonances. Mapping the wake provides a constraint on the disk aspect ratio, which is required to measure the mass of the planet., Comment: 10 Pages, 6 figures. Accepted in ApJL

Millimetre continuum observations of debris discs can provide insights into the physical and dynamical properties of the unseen planetesimals that these discs host. The material properties and collisional models of planetesimals leave their signature on the grain size distribution, which can be traced through the millimetre spectral index. We present 8.8 mm observations of the debris discs HD 48370, CPD 72 2713, HD 131488, and HD 32297 using the Australian Telescope Compact Array (ATCA) as part of the PLanetesimals Around TYpicalPre-main seqUence Stars (PLATYPUS) survey. We detect all four targets with a characteristic beam size of 5 arcseconds and derive a grain size distribution parameter that is consistent with collisional cascade models and theoretical predictions for parent planetesimal bodies where binding is dominated by self-gravity. We combine our sample with 19 other millimetre-wavelength detected debris discs from the literature and calculate a weighted mean grain size power law index which is close to analytical predictions for a classical steady state collisional cascade model. We suggest the possibility of two distributions of q in our debris disc sample; a broad distribution (where q is approximately 3.2 to 3.7) for "typical" debris discs (gas-poor/non-detection), and a narrow distribution (where q is less than 3.2) for bright gas-rich discs. Or alternatively, we suggest that there exists an observational bias between the grain size distribution parameter and absolute flux which may be attributed to the detection rates of faint debris discs at cm wavelengths., Comment: 10 pages, 4 figures, accepted

We recently found the globular cluster (GC) EXT8 in M31 to have an extremely low metallicity of [Fe/H]=-2.91+/-0.04 using high-resolution spectroscopy. Here we present a colour-magnitude diagram (CMD) for EXT8, obtained with the Wide Field Camera 3 on board the Hubble Space Telescope. Compared with the CMDs of metal-poor Galactic GCs, we find that the upper red giant branch (RGB) of EXT8 is about 0.03 mag bluer in F606W-F814W and slightly steeper, as expected from the low spectroscopic metallicity. The observed colour spread on the upper RGB is consistent with being caused entirely by the measurement uncertainties, and we place an upper limit of sigma(F606W-F814W)=0.015 mag on any intrinsic colour spread. The corresponding metallicity spread can be up to sigma([Fe/H])=0.2 dex or >0.7 dex, depending on the isochrone library adopted. The horizontal branch (HB) is located mostly on the blue side of the instability strip and has a tail extending to at least M(F606W)=+3, as in the Galactic GC M15. We identify two candidate RR Lyrae variables and several UV-luminous post-HB/post AGB star candidates, including one very bright (M(F300X)=-3.2) source near the centre of EXT8. The surface brightness of EXT8 out to a radius of 25 arcsec is well fitted by a Wilson-type profile with an ellipticity of epsilon=0.20, a semi-major axis core radius of 0.25", and a central surface brightness of 15.2 mag per square arcsec in the F606W band, with no evidence of extra-tidal structure. Overall, EXT8 has properties consistent with it being a "normal", but very metal-poor GC, and its combination of relatively high mass and very low metallicity thus remains challenging to explain in the context of GC formation theories operating within the hierarchical galaxy assembly paradigm., Comment: Accepted for publication in Astronomy & Astrophysics

We investigate the kinematic properties of nine nearby early-type galaxies with evidence of a disk-like component. Three of these galaxies are located in the field, five in the group and only one in the cluster environment. By combining the kinematics of the stars with those of the globular clusters (GCs) and planetary nebulae (PNe), we probe the outer regions of our galaxies out to $\sim$4-6 Re. Six galaxies have PNe and red GCs that show good kinematic alignment with the stars, whose rotation occurs along the photometric major-axis of the galaxies, suggesting that both the PNe and red GCs are good tracers of the underlying stellar population beyond that traced by the stars. Additionally, the blue GCs also show rotation that is overall consistent with that of the red GCs in these six galaxies. The remaining three galaxies show kinematic twists and misalignment of the PNe and GCs with respect to the underlying stars, suggesting recent galaxy interactions. From the comparison with simulations, we propose that all six aligned galaxies that show similar dispersion-dominated kinematics at large radii (>2-3 Re) had similar late ($z<1$) assembly histories characterised by mini mergers (mass-ratio <1:10). The different Vrot/$\sigma$ profiles are then the result of an early ($z>1$) minor merger (1:10< mass-ratio <1:4) for the four galaxies with peaked and decreasing Vrot/$\sigma$ profiles and of a late minor merger for the two galaxies with flat Vrot/$\sigma$ profiles. The three mis-aligned galaxies likely formed through multiple late minor mergers that enhanced their velocity dispersion at all radii, or a late major merger that spun-up both the GC sub-populations at large radii. Therefore, lenticular galaxies can have complex merger histories that shape their characteristic kinematic profile shapes., Comment: 31 pages, 12 figures. Accepted for publication in MNRAS on 2021 April 09

The origin of the inner dust cavities observed in transition discs remains unknown. The segregation of dust and size of the cavity is expected to vary depending on which clearing mechanism dominates grain evolution. We present the results from the Discs Down Under program, an 8.8 mm continuum Australia Telescope Compact Array (ATCA) survey targeting 15 transition discs with large (> 20 au) cavities, and compare the resulting dust emission to Atacama Large millimetre/sub-millimetre Array (ALMA) observations. Our ATCA observations resolve the inner cavity for 8 of the 14 detected discs. We fit the visibilities and reconstruct 1D radial brightness models for 10 sources with a S/N > 5sigma. We find that, for sources with a resolved cavity in both wavebands, the 8.8 mm and sub-mm brightness distributions peak at the same radius from the star. We suggest that a similar cavity size for 8.8 mm and sub-mm dust grains is due to a dust trap induced by the presence of a companion., Comment: 18 pages, 11 figures

Globular clusters (GCs) are dense, gravitationally bound systems of thousands to millions of stars. They are preferentially associated with the oldest components of galaxies, and measurements of their composition can therefore provide insight into the build-up of the chemical elements in galaxies in the early Universe. We report a massive GC in the Andromeda Galaxy (M31) that is extremely depleted in heavy elements. Its iron abundance is about 800 times lower than that of the Sun, and about three times lower than in the most iron-poor GCs previously known. It is also strongly depleted in magnesium. These measurements challenge the notion of a metallicity floor for GCs and theoretical expectations that massive GCs could not have formed at such low metallicities., Comment: Accepted for publication in Science. For supplementary materials, see under ancillary files

We put forward a co-axial pump(optical)-probe(X-rays) experimental concept and show performance of the optical component. A Bessel beam generator with a central 100 micrometers-diameter hole (on the optical axis) was fabricated using femtosecond (fs) laser structuring inside a silica plate. This flat-axicon optical element produces a needle-like axial intensity distribution which can be used for the optical pump pulse. The fs-X-ray free electron laser (X-FEL) beam of sub-1 micrometer diameter can be introduced through the central hole along the optical axis onto a target as a probe. Different realisations of optical pump are discussed. Such optical elements facilitate alignment of ultra-short fs-pulses in space and time and can be used in light-matter interaction experiments at extreme energy densities on the surface and in the volume of targets. Full advantage of ultra-short 10 fs X-FEL probe pulses with fs-pump(optical) opens an unexplored temporal dimension of phase transitions and the fastest laser-induced rates of material heating and quenching. A wider field of applications of fs-laser-enabled structuring of materials and design of specific optical elements for astrophotonics is presented.

Here we present the discovery of 895 s-process-rich candidates from 454,180 giant stars observed by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) using a data-driven approach. This sample constitutes the largest number of s-process enhanced stars ever discovered. Our sample includes 187 s-process-rich candidates that are enhanced in both barium and strontium, 49 stars with significant barium enhancement only and 659 stars that show only a strontium enhancement. Most of the stars in our sample are in the range of effective temperature and log g typical of red giant branch (RGB) populations, which is consistent with our observational selection bias towards finding RGB stars. We estimate that only a small fraction (0.5 per cent) of binary configurations are favourable for s-process enriched stars. The majority of our s-process-rich candidates (95 per cent) show strong carbon enhancements, whereas only five candidates (less than 3 percent) show evidence of sodium enhancement. Our kinematic analysis reveals that 97 percent of our sample are disc stars, with the other 3 percent showing velocities consistent with the Galactic halo. The scaleheight of the disc is estimated to be zh=0.634kpc, comparable with values in the literature. A comparison with the yields from asymptotic giant branch (AGB) models suggests that the main neutron source responsible for the Ba and Sr enhancements is the 13C(alpha,n)16O reaction. We conclude that the s-process-rich candidates may have received their overabundances via mass transfer from a previous ABG companion with an initial mass in the range 1-3Msun., Comment: 9 pages, 6 figures

We present new deep imaging of the central regions of the remote globular cluster NGC 2419, obtained with the F343N and F336W filters of HST/WFC3. The new data are combined with archival imaging to constrain nitrogen and helium abundance variations within the cluster. We find a clearly bimodal distribution of the nitrogen-sensitive F336W-F343N colours of red giants, from which we estimate that about 55% of the giants belong to a population with about normal (field-like) nitrogen abundances (P1), while the remaining 45% belong to a nitrogen-rich population (P2). On average, the P2 stars are more He-rich than the P1 stars, with an estimated mean difference of Delta Y = 0.05, but the P2 stars exhibit a significant spread in He content and some may reach Delta Y = 0.13. A smaller He spread may be present also for the P1 stars. Additionally, stars with spectroscopically determined low [Mg/Fe] ratios ([Mg/Fe]<0) are generally associated with P2. We find the P2 stars to be slightly more centrally concentrated in NGC 2419 with a projected half-number radius of about 10% less than for the P1 stars, but the difference is not highly significant (p=0.05). We find evidence of rotation for the P1 stars, whereas the results are inconclusive for the P2 stars, which are consistent with no rotation as well as the same average rotation found for the P1 stars. Because of the long relaxation time scale of NGC 2419, the radial trends and kinematic properties of the populations are expected to be relatively unaffected by dynamical evolution. Hence, they provide constraints on formation scenarios for multiple populations, which must account not only for the presence of He spreads within sub-populations identified via CNO variations, but also for the relatively modest differences in the spatial distributions and kinematics of the populations., Comment: 16 pages, 19 figures. Accepted for publication in A&A

Stars with unusual elemental abundances offer clues about rare astrophysical events or nucleosynthetic pathways. Stars with significantly depleted magnesium and enhanced potassium ([Mg/Fe] < -0.5; [K/Fe] > 1) have to date only been found in the massive globular cluster NGC 2419 and, to a lesser extent, NGC 2808. The origin of this abundance signature remains unknown, as does the reason for its apparent exclusivity to these two globular clusters. Here we present 112 field stars, identified from 454,180 LAMOST giants, that show significantly enhanced [K/Fe] and possibly depleted [Mg/Fe] abundance ratios. Our sample spans a wide range of metallicities (-1.5 < [Fe/H] < 0.3), yet none show abundance ratios of [K/Fe] or [Mg/Fe] that are as extreme as those observed in NGC 2419. If confirmed, the identified sample of stars represents evidence that the nucleosynthetic process producing the anomalous abundances ratios of [K/Fe] and [Mg/Fe] probably occurs at a wide range of metallicities. This would suggest that pollution scenarios that are limited to early epochs (such as Population III supernovae) are an unlikely explanation, although they cannot be ruled out entirely. This sample is expected to help guide modelling attempts to explain the origin of the Mg-K abundance signature.

In previous papers, we introduced our method for measuring chemical abundances from integrated-light spectra of globular clusters and applied it to a variety of extragalactic star clusters. Here we extend our analysis technique to the infrared. We simultaneously analyse an optical spectrum of the massive globular cluster G280 in M31, obtained with the HIRES spectrograph on the Keck I telescope, and an H-band spectrum obtained with NIRSPEC on Keck II. We discuss the sensitivity of our results to various modifications of the input assumptions, such as different line lists and isochrones and the possible presence of a metallicity spread in G280. When using the most recent version of the Kurucz line list, we measure iron abundances of [Fe/H]=-0.68+/-0.02 from the optical spectrum and [Fe/H]=-0.60+/-0.07 from the infrared spectrum. These values agree well with previous spectroscopic determinations of the metallicity of G280. While the small difference between the optical and infrared measurements is insignificant given the uncertainties, it is also consistent with a metallicity spread similar to that observed in massive GCs such as Omega Cen and G1, and also hinted at by the colour-magnitude diagram of G280. The optical and infrared spectra both indicate an alpha-enhancement of about 0.3-0.4 dex relative to solar-scaled abundances, as typically also observed in Milky Way GCs. It appears that our integrated-light analysis technique also performs well in the H-band. However, complications due to the presence of molecular bands and telluric contamination are more severe in the infrared, and accurate modelling of the coolest giants is more critical., Comment: Accepted for publication in Astronomy & Astrophysics

We present new abundance measurements for eleven GCs in the Local Group galaxies NGC 147, NGC 6822, and Messier 33. These are combined with previously published observations of four GCs in the Fornax and WLM galaxies. The abundances were determined from analysis of integrated-light spectra, obtained with HIRES on the Keck I telescope and with UVES on the VLT. We find that the clusters with [Fe/H]<-1.5 are all alpha-enhanced at about the same level as Milky Way GCs. Their Na abundances are also generally enhanced relative to Milky Way halo stars, suggesting that these extragalactic GCs resemble their Milky Way counterparts in containing significant fractions of Na-rich stars. For [Fe/H]>-1.5, the GCs in M33 are also alpha-enhanced, while the GCs that belong to dwarfs (NGC 6822 SC7 and Fornax 4) have closer to Solar-scaled alpha-element abundances, thus mimicking the abundance trends observed in field stars in nearby dwarf galaxies. The abundance patterns in SC7 are remarkably similar to those in the Galactic GC Ruprecht 106, including significantly sub-solar [Na/Fe] and [Ni/Fe] ratios. In NGC 147, the GCs with [Fe/H]<-2.0 account for about 6% of the total luminosity of stars in the same metallicity range, a lower fraction than those previously found in the Fornax and WLM galaxies, but substantially higher than in the Milky Way halo., Comment: Accepted for publication in A&A. Updated Table 5 with metallicities for Hodge II and SD7 determined from continuum shape fitting (Sharina & Davoust 2009). Added comparison with M33 GC metallicities from Beasley et al. (2015)

We test the performance of our analysis technique for integrated-light spectra by applying it to seven well-studied Galactic GCs that span a wide range of metallicities. Integrated-light spectra were obtained by scanning the slit of the UVES spectrograph on the ESO Very Large Telescope across the half-light diameters of the clusters. We modelled the spectra using resolved HST colour-magnitude diagrams (CMDs), as well as theoretical isochrones, in combination with standard stellar atmosphere and spectral synthesis codes. The abundances of Fe, Na, Mg, Ca, Ti, Cr, and Ba were compared with literature data for individual stars in the clusters. The typical differences between iron abundances derived from our integrated-light spectra and those compiled from the literature are less than 0.1 dex. A larger difference is found for one cluster (NGC 6752), and is most likely caused primarily by stochastic fluctuations in the numbers of bright red giants within the scanned area. As expected, the alpha-elements (Ca, Ti) are enhanced by about 0.3 dex compared to the Solar-scaled composition, while the [Cr/Fe] ratios are close to Solar. When using up-to-date line lists, our [Mg/Fe] ratios also agree well with literature data. Our [Na/Fe] ratios are, on average, 0.08-0.14 dex lower than average values quoted in the literature, and our [Ba/Fe] ratios may be overestimated by 0.20-0.35 dex at the lowest metallicities. We find that analyses based on theoretical isochrones give very similar results to those based on resolved CMDs. Overall, the agreement between our integrated-light abundance measurements and the literature data is satisfactory. Refinements of the modelling procedure, such as corrections for stellar evolutionary and non-LTE effects, might further reduce some of the remaining offsets., Comment: 35 pages, 16 figures, accepted for A&A

We use measurements of nitrogen abundances in red giants to search for multiple stellar populations in the four most metal-poor globular clusters (GCs) in the Fornax dwarf spheroidal galaxy (Fornax 1, 2, 3, and 5). New imaging in the F343N filter, obtained with the Wide Field Camera 3 on the Hubble Space Telescope, is combined with archival F555W and F814W observations to determine the strength of the NH band near 3370 AA. After accounting for observational errors, the spread in the F343N-F555W colors of red giants in the Fornax GCs is similar to that in M15 and corresponds to an abundance range of Delta([N/Fe])=2 dex, as observed also in several Galactic GCs. The spread in F555W-F814W is, instead, fully accounted for by observational errors. The stars with the reddest F343N-F555W colors (indicative of N-enhanced composition) have more centrally concentrated radial distributions in all four clusters, although the difference is not highly statistically significant within any individual cluster. From double-Gaussian fits to the color distributions we find roughly equal numbers of "N-normal" and "N-enhanced" stars (formally about 40% N-normal stars in Fornax 1, 3, and 5 and 60% in Fornax 2). We conclude that GC formation, in particular regarding the processes responsible for the origin of multiple stellar populations, appears to have operated similarly in the Milky Way and in the Fornax dSph. Combined with the high ratio of metal-poor GCs to field stars in the Fornax dSph, this places an important constraint on scenarios for the origin of multiple stellar populations in GCs., Comment: 16 pages, 7 figures, accepted for publication in ApJ

We determine the metallicities for globular clusters (GCs) in the WLM and IKN dwarf galaxies, using VLT/UVES and Keck/ESI spectroscopy. For the WLM GC we also measure detailed abundance ratios for a number of light, alpha, Fe-peak and n-capture elements. We find low metallicities of [Fe/H]=-2.0 and -2.1 for the WLM GC and the GC IKN-5, respectively. We estimate that 17%-31% of the metal-poor stars in WLM belong to the GC, and IKN-5 may even contain a similar number of metal-poor stars as the whole of the IKN dwarf itself. These high ratios of metal-poor GCs to field stars are in tension with GC formation scenarios that require GCs to have lost a very large fraction of their initial mass. The GCs in the WLM and IKN dwarf galaxies resemble those in the Fornax dSph by being significantly more metal-poor than a typical halo GC in the Milky Way and other large galaxies. They are also substantially more metal-poor than the bulk of the field stars in their parent galaxies. The overall abundance patterns in the WLM GC are similar to those observed for GCs in the Fornax dSph: [Ca/Fe] and [Ti/Fe] are super-Solar at about +0.3 dex, while [Mg/Fe] is less elevated than [Ca/Fe] and [Ti/Fe]. The [Na/Fe] ratio is similar to the averaged [Na/Fe] ratios in Milky Way GCs, but higher than those of Milky Way halo stars. Fe-peak (Mn, Sc, Cr) and heavy elements (Ba, Y, La) generally follow the trends seen in the Milky Way halo. The relatively high Na abundance in the WLM GC suggests that the [Na/O] anti-correlation is present in this cluster., Comment: 15 pages, 12 figures. Accepted for publication in A&A. Minor corrections by language editor taken into account

The chemo-dynamics of galaxy halos beyond the Local Group may now be mapped out through the use of globular clusters and planetary nebulae as bright tracer objects, along with deep multi-slit spectroscopy of the integrated stellar light. We present results from surveying nearby early-type galaxies, including evidence for kinematically distinct halos that may reflect two-phase galaxy assembly. We also demonstrate the utility of the tracer approach in measuring the kinematics of stellar substructures around the Umbrella Galaxy, which allow us to reconstruct the progenitor properties and stream orbit., Comment: Multi-Spin Galaxies, ASP conference Series, in press, eds. E. Iodice et al., 4 pages, 2 figures

We study the Globular Cluster (GC) system of the nearby elliptical galaxy M87 using the newly available dataset with accurate kinematics (Strader et al.2011). We find evidence for three distinct sub-populations of GCs in terms of colours, kinematics and radial profiles. We show that a decomposition into three populations (blue, intermediate and red GCs) is statistically preferred to one with two or four populations, and relate them to the stellar profile. We exploit the sub-populations to derive dynamical constraints on the mass and Dark Matter (DM) content of M87 out to $\sim100$ kpc. We use a class of global mass-estimators (from Paper I), obtaining mass measurements at different locations. M87's DM fraction changes from $\approx$0.2 at the starlight's effective radius (6 kpc) to $\approx$0.95 at the distance probed by the most extended, blue GCs (135 kpc). We supplement this with \textit{virial decompositions}, exploiting the dynamical model to produce a separation into multiple components. These yield the luminous mass as $5.5^{+1.5}_{-2.0}\times 10^{11}M_\odot$ and the DM within 135 kpc as $8.0^{+1.0}_{-4.0}\times 10^{12}M_\odot.$ The inner DM density behaves as $\rho \sim r^{-\gamma}$ with $\gamma\approx 1.6$. This is steeper than the cosmologically preferred cusp $\rho \sim r^{-1},$ providing evidence of DM contraction. Finally, we combine the GC separation into three sub-populations and the Jeans equations, obtaining information on the orbits of the GC system. The centrally concentrated red GCs exhibit tangential anisotropy, consistent with radial-orbit depletion by tidal shredding. The most extended blue GCs have an isotropic velocity dispersion tensor in the central parts, which becomes more tangential moving outwards, consistent with adiabatic contraction of the DM halo., Comment: MNRAS (submitted), 16 pages, 10 figures

We investigate the radial distribution of the low-mass X-ray binary (LMXB) population in the elliptical galaxy NGC 4649, using Chandra and Hubble data to separate the field and globular cluster (GC) populations. GCs with LMXBs have the same radial distribution as the parent red and blue GCs. The radial profile of field LMXBs follows the V-band profile within the D25 of NGC 4649. Using the spatial information provided by our data, we find that the global galaxy-wide relations between cumulative number and luminosity of LMXBs and the integrated stellar mass hold on local scales within D25. An excess of field LMXBs with respect to the V-light is observed in the galaxy's outskirt, which may be partially due to unidentified GC sources or to a rejuvenated field LMXB population caused by past merging interactions., Comment: 15 pages, 10 figures, 3 tables, accepted by ApJ

The Fornax dwarf spheroidal galaxy is well known for its very high globular cluster specific frequency, SN=26. Furthermore, while the field star metallicity distribution peaks at [Fe/H]=-1, four of the five GCs have [Fe/H]<-2. Only about 5 percent of the field stars have such low metallicities. Hence, a very large fraction of about 1/5-1/4 of the most metal-poor stars belong to the four most metal-poor GCs. This implies that these clusters could, at most, have been a factor of 4-5 more massive initially. A second, even more extreme case may be the IKN dwarf galaxy where SN=124. Although metallicities are not accurately known, the GCs account for about 13 percent of the total V-band luminosity of IKN., Comment: 4 pages, 1 figure, to appear in the proceedings of the meeting "Reading the book of globular clusters with the lens of stellar evolution", Rome, Nov. 26-28, 2012, to be published in Memorie della Societa' Astronomica Italiana

We present the X-ray source catalog for the Chandra monitoring observations of the elliptical galaxy, NGC 4649. The galaxy has been observed with Chandra ACIS-S3 in six separate pointings, reaching a total exposure of 299 ks. There are 501 X-ray sources detected in the 0.3-8.0 keV band in the merged observation or in one of the six individual observations; 399 sources are located within the D_25 ellipse. The observed 0.3-8.0 keV luminosities of these 501 sources range from 9.3x10^{36} erg/s to 5.4x10^{39} erg/s. The 90% detection completeness limit within the D_25 ellipse is 5.5x10^{37} erg/s. Based on the surface density of background active galactic nuclei (AGNs) and detection completeness, we expect ~45 background AGNs among the catalog sources (~15 within the D_25 ellipse). There are nine sources with luminosities greater than 10^{39} erg/s, which are candidates for ultraluminous X-ray sources. The nuclear source of NGC 4649 is a low-luminosity AGN, with an intrinsic 2.0-8.0 keV X-ray luminosity of 1.5x10^{38} erg/s. The X-ray colors suggest that the majority of the catalog sources are low-mass X-ray binaries (LMXBs). We find that 164 of the 501 X-ray sources show long-term variability, indicating that they are accreting compact objects. We discover four transient candidates and another four potential transients. We also identify 173 X-ray sources (141 within the D_25 ellipse) that are associated with globular clusters (GCs) based on Hubble Space Telescope and ground-based data; these LMXBs tend to be hosted by red GCs. Although NGC 4649 has a much larger population of X-ray sources than the structurally similar early-type galaxies, NGC 3379 and NGC 4278, yet the X-ray source properties are comparable in all three systems., Comment: 14 pages, 12 figures, 10 tables. ApJS in press. Full tables available in the published version or upon request

We report the discovery of a new ultraluminous X-ray source (ULX) associated with a globular cluster in the elliptical galaxy NGC 4649. The X-ray source was initially detected with a luminosity below 5 x 10^38 erg/s, but in subsequent observations 7 and 11 years later it had brightened substantially to 2 - 3 x 10^39 erg/s. Over the course of six separate observations it displayed significant spectral variability, in both continuum slope and absorption column. Short-term variability in the X-ray flux was also present in at least one observation. The properties of this object appear consistent with a stellar-mass black hole accreting at super-Eddington rates (i.e. in the ultraluminous accretion state), although a highly super-Eddington neutron star cannot be excluded. The coincidence of an increase in absorption column with a possible enhancement in short-term variability in at least one observation is suggestive of a clumpy radiatively-driven wind crossing our line-of-sight to the object, Comment: 7 pages, 4 figures, accepted for publication in ApJ

Aims: We describe our newly developed approach to detailed abundance analysis from integrated-light high-dispersion spectra of star clusters. As a pilot project, we measure abundances of several elements for three globular clusters (GCs) in the Fornax dSph, using VLT/UVES spectra. Methods: We divide the cluster colour-magnitude diagrams into about 100 bins and compute synthetic spectra for each bin. The individual model spectra are co-added and the abundances are iteratively adjusted until the best match to the observed spectra is achieved. Results: We find [Fe/H] = -2.3, -1.4 and -2.1 for Fornax 3, 4 and 5, with +/-0.1 dex uncertainties. Fornax 3 and 5 are thus similar in metallicity to the most metal-poor Milky Way GCs and fall near the extreme metal-poor end of the field star metallicity distribution in Fornax. The [alpha/Fe] ratios, as traced by Ca and Ti, are enhanced with respect to the Solar composition at the level of about +0.25 dex for Fornax 3 and 5, and possibly slightly less (about +0.12 dex) for Fornax 4. For all three clusters the [Mg/Fe] ratio is significantly less elevated than [Ca/Fe] and [Ti/Fe], possibly an effect of the abundance anomalies that are well-known in Galactic GCs. We thus confirm that Mg may be a poor proxy for the overall alpha-element abundances for GCs. The abundance patterns of heavy elements (Y, Ba and Eu) indicate a dominant contribution to nucleosynthesis from the r-process in all three clusters, with a mean [Ba/Eu]=-0.7, suggesting rapid formation of the GCs. Conclusions: Combining our results with literature data for Fornax 1 and 2, four of the five Fornax GCs fall in the range -2.5<[Fe/H]<-2, while Fornax 4 is substantially more metal-rich than the others. The indications that abundance anomalies are detectable in integrated light are encouraging, particularly for the prospects of detecting such anomalies in young, massive star clusters., Comment: 18 pages, accepted for publication in A&A

Recently, high-dispersion spectroscopy has demonstrated conclusively that four of the five globular clusters (GCs) in the Fornax dwarf spheroidal galaxy are very metal-poor with [Fe/H]<-2. The remaining cluster, Fornax 4, has [Fe/H]=-1.4. This is in stark contrast to the field star metallicity distribution which shows a broad peak around [Fe/H]=-1 with only a few percent of the stars having [Fe/H]<-2. If we only consider stars and clusters with [Fe/H]<-2 we thus find an extremely high GC specific frequency, SN=400, implying by far the highest ratio of GCs to field stars known anywhere. We estimate that about 1/5-1/4 of all stars in the Fornax dSph with [Fe/H]<-2 belong to the four most metal-poor GCs. These GCs could, therefore, at most have been a factor of 4-5 more massive initially. Yet, the Fornax GCs appear to share the same anomalous chemical abundance patterns known from Milky Way GCs, commonly attributed to the presence of multiple stellar generations within the clusters. The extreme ratio of metal-poor GC- versus field stars in the Fornax dSph is difficult to reconcile with scenarios for self-enrichment and early evolution of GCs in which a large fraction (90%-95%) of the first-generation stars have been lost. It also suggests that the GCs may not have formed as part of a larger population of now disrupted clusters with an initial power-law mass distribution. The Fornax dSph may be a rosetta stone for constraining theories of the formation, self-enrichment and early dynamical evolution of star clusters., Comment: 4 pages, 2 figures, accepted for A&A Letters

The interpretation that bimodal colour distributions of globular clusters (GCs) reflect bimodal metallicity distributions has been challenged. Non-linearities in the colour to metallicity conversions caused by the horizontal branch (HB) stars may be responsible for transforming a unimodal metallicity distribution into a bimodal (optical) colour distribution. We study optical/near-infrared (NIR) colour distributions of the GC systems in 14 E/S0 galaxies. We test whether the bimodal feature, generally present in optical colour distributions, remains in the optical/NIR ones. The latter colour combination is a better metallicity proxy than the former. We use KMM and GMM tests to quantify the probability that different colour distributions are better described by a bimodal, as opposed to a unimodal distribution. We find that double-peaked colour distributions are more commonly seen in optical than in optical/NIR colours. For some of the galaxies where the optical (g-z) distribution is clearly bimodal, the (g-K) and (z-K) distributions are better described by a unimodal distribution. The two most cluster-rich galaxies in our sample, NGC4486 and NGC4649, show some interesting differences. The (g-K) distribution of NGC4649 is better described by a bimodal distribution, while this is true for the (g-K) distribution of NGC4486 GCs only if restricted to a brighter sub-sample with small K-band errors (< 0.05 mag). Formally, the K-band photometric errors cannot be responsible for blurring bimodal metallicity distributions to unimodal (g-K) colour distributions. However, simulations including the extra scatter in the colour-colour diagrams (not fully accounted for in the photometric errors) show that such scatter may contribute to the disappearance of bimodality in (g-K) for the full NGC4486 sample. For the less cluster-rich galaxies results are inconclusive due to poorer statistics. [Abridged], Comment: A&A accepted, 15 pages, 10 figures, 4 tables

We present colour-magnitude diagrams (CMDs) for a sample of seven young massive clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC 7793. The clusters have ages in the range 5-50 million years and masses of 10^5 -10^6 Msun. Although crowding prevents us from obtaining photometry in the central regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters, along with the brighter main sequence stars. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible. In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the He-burning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergiants from the main sequence complicates this comparison. In several cases we observe a large spread (1-2 mag) in the luminosities of the supergiant stars that cannot be accounted for by observational errors. This spread can be reproduced by including an age spread of 10-30 million years in the models. However, age spreads cannot fully account for the observed morphology of the CMDs and other processes, such as the evolution of interacting binary stars, may also play a role., Comment: 15 pages, 12 figures, accepted for publication in A&A

Variable X-ray and gamma-ray emission is characteristic of the most extreme physical processes in the Universe, and studying the sources of these energetic photons has been a major driver in astronomy for the past 50 years. Here we present multiwavelength observations of a unique gamma-ray selected transient, discovered by Swift, which was accompanied by bright emission across the electromagnetic spectrum, and whose properties are unlike any previously observed source. We pinpoint the event to the center of a small, star-forming galaxy at redshift z=0.3534. Its high-energy emission has lasted much longer than any gamma-ray burst, while its peak luminosity was about 100 times higher than the brightest active galactic nuclei. The association of the outburst with the center of its host galaxy suggests that this phenomenon has its origin in a new, rare mechanism associated with a massive black hole in the nucleus of a galaxy.

Context: Some photometric studies of extragalactic globular cluster (GC) systems using the optical and near-infrared colour combination have suggested the presence of a large fraction of intermediate-age (2-8 Gyrs) GCs. Aims: We investigate the age distributions of GC systems in 14 E/S0 galaxies. Methods: We carry out a differential comparison of the (g-z) vs. (g-K) two-colour diagrams for GC systems in the different galaxies in order to see whether there are indications of age differences. We also compare the different GC systems with a few simple stellar population models. Results: No significant difference is detected in the mean ages of GCs among elliptical galaxies. S0 galaxies on the other hand, show evidence for younger GCs. Surprisingly, this appears to be driven by the more metal-poor clusters. The age distribution of GCs in NGC4365 seems to be similar to that of other large ellipticals (e.g. NGC4486, NGC4649). Padova SSPs with recently released isochrones for old ages (14 Gyrs) show less of an offset with respect to the photometry than previously published models. Conclusions: We suggest that E type galaxies assembled most of their GCs in a shorter and earlier period than S0 type galaxies. The latter galaxy type, seems to have a more extended period of GC formation/assembly., Comment: A&A accepted, 16 pages, 18 figures

Context: The combination of optical and near-infrared (NIR) colours has the potential to break the age/metallicity degeneracy and offers a better metallicity sensitivity than optical colours alone. Previous studies of extragalactic globular clusters (GCs) with this colour combination, however, have suffered from small samples or have been restricted to a few galaxies. Aims: We compile a homogeneous and representative sample of GC systems with multi-band photometry to be used in subsequent papers where ages and metallicity distributions will be studied. Methods: We acquired deep K-band images of 14 bright nearby early-type galaxies. The images were obtained with the LIRIS near-infrared spectrograph and imager at the William Herschel Telescope (WHT) and combined with optical ACS g and z images from the Hubble Space Telescope public archive. Results: For the first time GC photometry of 14 galaxies are observed and reduced homogeneously in this wavelength regime. We achieved a limiting magnitude of K~20-21. For the majority of the galaxies we detect about 70 GCs each. NGC4486 and NGC4649, the cluster-richest galaxies in the sample contain 301 and 167 GCs, respectively. We present tables containing coordinates, photometry and sizes of the GCs available., Comment: A&A accepted, 18 pages, 13 figures

{Aims.} We present the main results of an imaging survey of possible young massive clusters (YMC) in M31 performed with the Wide Field and Planetary Camera2 (WFPC2) on the Hubble Space Telescope (HST). We present the images and color magnitude diagrams (CMDs) of all of our targets. {Methods.} The reddening, age and, metallicity of the clusters were estimated by comparing the observed CMDs and luminosity functions with theoretical models. Stellar masses were estimated by comparison with theoretical models in the log(Age) vs. absolute integrated magnitude plane. {Results.} Nineteen of the twenty surveyed candidates were confirmed to be real star clusters. Three of the clusters were found not to be good YMC candidates from newly available integrated spectroscopy and were in fact found to be old from their CMD. Of the remaining sixteen clusters, fourteen have ages between 25 Myr and 280 Myr, two have older ages than 500 Myr (lower limits). By including ten other YMC with HST photometry from the literature we have assembled a sample of 25 clusters younger than 1 Gyr, with mass ranging from 0.6 x 10^4 M_sun to 6 x 10^4 M_sun, with an average of ~ 3 x 10^4 M_sun. {Conclusions.} The clusters considered here are confirmed to have masses significantly higher than Galactic open clusters in the same age range. Our analysis indicates that YMCs are relatively common in all the largest star-forming galaxies of the Local Group., Comment: 31 pages, 21 figures (quality of Figures 1 and 2 reduced), uses longtable.sty. Accepted for publication in Astronomy and Astrophysics. A high-resolution version of the paper is available at http://www.bo.astro.it/M31/YMC