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Nancy Grace Roman Space Telescope will revolutionize our understanding of the Galactic Bulge with its Galactic Bulge Time Domain survey. At the same time, Rubin Observatories's Legacy Survey of Space and Time (LSST) will monitor billions of stars in the Milky Way. The proposed Roman survey of the Galactic Plane, with its NIR passbands and exquisite spacial resolution, promises groundbreaking insights for a wide range of time-domain galactic astrophysics. In this white paper, we describe the scientific returns possible from the combination of the Roman Galactic Plane Survey with the data from LSST., Comment: 8 pages, 1 figure, submitted to the 2024 Call for Community Input into the Definition of a Roman Galactic Plane Survey

PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5 %, 10 %, 10 % for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO's target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile at the beginning of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

The Nancy Grace Roman Telescope's High Latitude Wide Area Survey will have a number of synergies with the Vera Rubin Observatory's Legacy Survey of Space and Time (LSST), particularly for extragalactic star clusters. Understanding the nature of star clusters and star cluster systems are key topics in many areas of astronomy, chief among them stellar evolution, high energy astrophysics, galaxy assembly/dark matter, the extragalactic distance scale, and cosmology. One of the challenges will be disentangling the age/metallicity degeneracy because young ($\sim$Myr) metal-rich clusters have similar SEDs to old ($\sim$Gyr) metal-poor clusters. Rubin will provide homogeneous, $ugrizy$ photometric coverage, and measurements in the red Roman filters will help break the age-metallicity and age-extinction degeneracies, providing the first globular cluster samples that cover wide areas while essentially free of contamination from Milky Way stars. Roman's excellent spatial resolution will also allow measurements of cluster sizes. We advocate for observations of a large sample of galaxies with a range of properties and morphologies in the Rubin/LSST footprint matching the depth of the LSST Wide-Fast-Deep field $i$ band limit (26.3 mag), and recommend adding the F213 filter to the survey., Comment: white paper submitted for Roman CCS input

The Vera C. Rubin Legacy Survey of Space and Time holds the potential to revolutionize time domain astrophysics, reaching completely unexplored areas of the Universe and mapping variability time scales from minutes to a decade. To prepare to maximize the potential of the Rubin LSST data for the exploration of the transient and variable Universe, one of the four pillars of Rubin LSST science, the Transient and Variable Stars Science Collaboration, one of the eight Rubin LSST Science Collaborations, has identified research areas of interest and requirements, and paths to enable them. While our roadmap is ever-evolving, this document represents a snapshot of our plans and preparatory work in the final years and months leading up to the survey's first light., Comment: 202 pages (in book format) 34 figures plus chapter heading figures (13)

The revolutionary power of future Rubin-LSST observations will allow us to significantly improve the physics of pulsating stars, including RR Lyrae. In this context, an updated theoretical scenario predicting all the relevant pulsation observables in the corresponding photometric filters is mandatory. The bolometric light curves based on a recently computed extensive set of nonlinear convective pulsation models for RR Lyrae stars, covering a broad range in metal content and transformed into the Rubin-LSST photometric system. Predicted Rubin-LSST mean magnitudes and pulsation amplitudes have been adopted to built the Bailey diagrams (luminosity amplitude vs period) and the color-color diagrams in these bands. The current findings indicate that the gLSST-rLSST, rLSST-iLSST colors obey to a well defined linear relation with the metal content. Moreover, the Period Luminosity relations display in the reddest filters (rLSST,iLSST,zLSST,yLSST) a significant dependence on the assumed metal abundance. In particular, more metal-rich RR Lyrae are predicted to be fainter at fixed period. Metal-dependent Period-Wesenheit relations for different combinations of optical and NIR filters are also provided. These represent powerful tools to infer individual distances independently of reddening uncertainties, once the metal abundance is known and no relevant deviations from the adopted extinction law occur. Finally, we also derived new linear and quadratic absolute magnitude metallicity relations (gLSST vs [Fe/H]) and the metallicity coefficient is consistent with previous findings concerning the B and the V band., Comment: Accepted for publication on ApJ

In the globular cluster NGC2808, a quasi-standard initial lithium abundance is derived for a red giant belonging to the `extreme' population, characterized by a large helium overabundance, and by abundances of proton capture elements typical of nuclear processing in gas at very high temperatures, where the initial lithium has been fully destroyed. The observations of lithium in such extreme cluster stars are important to test different models for the formation of multiple populations in old Globular Clusters. In the asymptotic giant branch (AGB) scenario, fresh lithium is synthetized during the initial phases of hot bottom burning which, afterwards, synthetize the other p-capture elements. We model the abundance of lithium in the ejecta of superAGB models, finding values consistent or larger than observed in the `extreme' giant; these same models describe correctly the magnesium depletion and silicon enrichment of the extreme population of NGC 2808, so the overall agreement provides further support to the AGB scenario. In the models involving massive or supermassive stars, the Lithium observed requires a mixture of the lithium-free ejecta of the polluting population with more than 40% of standard-lithium pristine gas. The extended chemical anomalies of NGC 2808 stars are then to be all explained within at most 60% of the possible dilution range, the initial helium mass fraction in the ejecta should be Y >= 0.5, to account for the Ye 0.38-0.40 of the extreme population, and further observations of p-process elements are needed to check the model., Comment: accepted for publication in The Astrophysical Journal Letters

We propose a combination of a modified Wide-Fast-Deep survey, a mini-survey of the South Celestial Pole, and a Deep Drilling-style survey to produce a 3-D map of the Magellanic System and to provide a detailed census of the transient and variable populations in the Clouds. We support modifying the Wide-Fast-Deep survey to cover the declination range $-72.25\deg<{\rm Dec}<12.4\deg$ and the Galactic latitude range $|b|>15\deg$, as proposed in a separate white paper. We additionally propose a mini-survey covering the 950$\deg^2$ with ${\rm Dec} < -72.25$ in $ugriz$ to the standard LSST single-exposure depth and with 40 visits per filter per field. Finally, we propose a mini-survey covering $\sim100 \deg^2$ of the main bodies of the Clouds with twelve total pointings, 2000 total visits per field, and shorter exposure time., Comment: 11 pages, 3 figures, submitted to Call for White Papers on LSST Cadence Optimization

The LSST survey was designed to deliver transformative results for four primary objectives: constraining dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. While the LSST Wide-Fast-Deep survey and accompanying Deep Drilling and mini-surveys will be ground-breaking for each of these areas, there remain competing demands on the survey area, depth, and temporal coverage amid a desire to maximize all three. In this white paper, we seek to address a principal source of tension between the different LSST science collaborations, that of the survey area and depth that they each need in the parts of the sky that they care about. We present simple tools which can be used to explore trades between the area surveyed by LSST and the number of visits available per field and then use these tools to propose a change to the baseline survey strategy. Specifically, we propose to reconfigure the WFD footprint to consist of low-extinction regions (limited by galactic latitude), with the number of visits per field in WFD limited by the LSST Science Requirements Document (SRD) design goal, and suggest assignment of the remaining LSST visits to the full visible LSST sky. This proposal addresses concerns with the WFD footprint raised by the DESC (as 25 percent of the current baseline WFD region is not usable for dark energy science due to MW dust extinction), eases the time required for the NES and SCP mini-surveys (since in our proposal they would partially fall into the modified WFD footprint), raises the number of visits previously assigned to the GP region, and increases the overlap with DESI and other Northern hemisphere follow-up facilities. This proposal alleviates many of the current concerns of Science Collaborations that represent the four scientific pillars of LSST and provides a Big Sky approach to cadence diplomacy., Comment: 12 page, 5 figures, submitted to Call for White Papers on LSST Cadence Optimization

Almost several decades after the discovery of the first multiple populations in galactic globular clusters (GC) the debate on their formation is still extremely current and NGC2808 remains one of the best benchmark to test any scenario for their origin and the evolution. In this work we focus on the chemical composition of stars belonging to the extreme He-rich population populated by stars with the most extreme abundance of Mg, Al, Na, O and Si. We checked whether the most recent measures are consistent with the AGB yields of stars of $6.5-8~M_{\odot}$. These stars evolve on time scales of the order of 40-60 Myr and eject matter strongly enriched in helium, owing to a deep penetration of the surface convective zone down to regions touched by CNO nucleosynthesis occurring after the core He-burning phase. Since the big unknown of the AGB phase of massive stars is the mass loss, we propose a new approch that takes into account the effects of the radiation pressure on dust particles. We show that this more realistic description is able to reproduce the observed abundances of Mg, Al, Na and Si in these extreme stars. The large spread in the oxygen abundances is explained by invoking deep mixing during the RGB phase. It will be possible to check this work hypothesis as soon as the oxygen measurements of the main sequence stars of NGC2808 will be available., Comment: 12 pages, 5 figures, accepted 2018 June 29 by MNRAS

A critical issue in the asymptotic giant branch (AGB) self-enrichment scenario for the formation of multiple populations in Globular Clusters (GCs) is the inability to reproduce the magnesium isotopic ratios, despite the model in principle can account for the depletion of magnesium. In this work we analyze how the uncertainties on the various p-capture cross sections affect the results related to the magnesium content of the ejecta of AGB stars. The observed distribution of the magnesium isotopes and of the overall Mg-Al trend in M13 and NGC 6752 are successfully reproduced when the proton-capture rate by 25Mg at the temperatures 100 MK, in particular the 25Mg(p, gamma)26Alm channel, is enhanced by a factor 3 with respect to the most recent experimental determinations. This assumption also allows to reproduce the full extent of the Mg spread and the Mg-Si anticorrelation observed in NGC 2419. The uncertainties in the rate of the 25Mg(p,gamma)26Alm reaction at the temperatures of interest here leave space for our assumption and we suggest that new experimental measurements are needed to settle this problem. We also discuss the competitive model based on the super massive star nucleosynthesis., Comment: accepted for publication on MNRAS

We present deep spectroscopic observations of a Lyman-break galaxy candidate (hereafter MACS1149-JD) at $z\sim9.5$ with the $\textit{Hubble}$ Space Telescope ($\textit{HST}$) WFC3/IR grisms. The grism observations were taken at 4 distinct position angles, totaling 34 orbits with the G141 grism, although only 19 of the orbits are relatively uncontaminated along the trace of MACS1149-JD. We fit a 3-parameter ($z$, F160W mag, and Ly$\alpha$ equivalent width) Lyman-break galaxy template to the three least contaminated grism position angles using an MCMC approach. The grism data alone are best fit with a redshift of $z_{\mathrm{grism}}=9.53^{+0.39}_{-0.60}$ ($68\%$ confidence), in good agreement with our photometric estimate of $z_{\mathrm{phot}}=9.51^{+0.06}_{-0.12}$ ($68\%$ confidence). Our analysis rules out Lyman-alpha emission from MACS1149-JD above a $3\sigma$ equivalent width of 21 \AA{}, consistent with a highly neutral IGM. We explore a scenario where the red $\textit{Spitzer}$/IRAC $[3.6] - [4.5]$ color of the galaxy previously pointed out in the literature is due to strong rest-frame optical emission lines from a very young stellar population rather than a 4000 \AA{} break. We find that while this can provide an explanation for the observed IRAC color, it requires a lower redshift ($z\lesssim9.1$), which is less preferred by the $\textit{HST}$ imaging data. The grism data are consistent with both scenarios, indicating that the red IRAC color can still be explained by a 4000 \AA{} break, characteristic of a relatively evolved stellar population. In this interpretation, the photometry indicate that a $340^{+29}_{-35}$ Myr stellar population is already present in this galaxy only $\sim500~\mathrm{Myr}$ after the Big Bang., Comment: Accepted to ApJ. This is the accepted version

The color-magnitude diagrams of many Magellanic Cloud clusters (with ages up to 2 billion years) display extended turnoff regions where the stars leave the main sequence, suggesting the presence of multiple stellar populations with ages which may differ even by hundreds million years (Mackey et al. 2008, Milone et al. 2009, Girardi et al. 2011). A strongly debated question is whether such an extended turnoff is instead due to populations with different stellar rotations (Girardi et al. 2011, Goudfrooij et al. 2011, Rubele et al. 2013, Li et al. 2014). The recent discovery of a `split' main sequence in some younger clusters (about 80--400Myr) added another piece to this puzzle. The blue (red) side of the main sequence is consistent with slowly (rapidly) rotating stellar models (D'Antona et al. 2015, Milone et al. 2016, Correnti et al. 2017, Milone et al 2016), but a complete theoretical characterization of the observed color-magnitude diagram appeared to require also an age spread (Correnti et al. 2017). We show here that, in three clusters so far analyzed, if the blue main sequence stars are interpreted with models that have been always slowly rotating, they must be about 30% younger than the rest of the cluster. If they are instead interpreted as stars initially rapidly rotating, but that have later slowed down, the age difference disappears, and "braking" also helps to explain the apparent age differences of the extended turnoff. The age spreads in Magellanic Cloud clusters are a manifestation of rotational stellar evolution. Observational tests are suggested., Comment: Accepted for publication and in state of Advance Online Publication (from 24 July 2017) on Nature Astronomy

We investigate the relation between the star formation rate (SFR) and the stellar mass (M), i.e. the Main Sequence (MS) relation of star-forming galaxies, at 1.3<=z<6 in the first four HST Frontier Fields, based on rest-frame UV observations. Gravitational lensing combined with deep HST observations allows us to extend the analysis of the MS down to stellar masses as low as logM/Msun~7.5 at z<~4 and logM/Msun~8 at higher redshifts, a factor of ~10 below most previous results. We perform an accurate simulation to take into account the effect of observational uncertainties on the MS and correct for the Eddington bias. This step allows us to reliably measure the MS and in particular its slope. While the normalization increases with redshift, we fit an unevolving and approximately linear slope. We nicely extend to lower masses the results of brighter surveys. Thanks to the large dynamic range in mass and by making use of the simulation, we analyzed any possible mass dependence of the dispersion around the MS. We find tentative evidence that the scatter decreases with increasing stellar masses, suggesting a larger variety of star formation histories in low mass galaxies. This trend agrees with theoretical predictions, and is explained as either a consequence of the smaller number of progenitors of low mass galaxies in a hierarchical scenario and/or of the efficient but intermittent stellar feedback processes in low mass halos. Finally, we observe an increase in the SFR per unit stellar mass with redshift milder than predicted by theoretical models, implying a still incomplete understanding of the processes responsible for galaxy growth.

We interpret the stellar population of $\omega$ Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time with the main sequences, sub-giant and horizontal branch data. The reproduction of the observed colour magnitude features is very satisfying and bears interesting hints concerning the evolutionary history of this peculiar stellar ensemble. Our main results are: 1) no significant spread in age is required to fit the colour-magnitude diagram. Indeed we can use coeval isochrones for the synthetic populations, and we estimate that the ages fall within a $\sim 0.5$ Gyr time interval; in particular the most metal rich population can be coeval (in the above meaning) with the others, if its stars are very helium--rich (Y$\sim$0.37) and with the observed CNO enhancement ([(C+N+O)/Fe] = + 0.7); 2) a satisfactory fit of the whole HB is obtained, consistent with the choice of the populations providing a good reproduction of the main sequence and sub giant data. 3) the split in magnitude observed in the red HB is well reproduced assuming the presence of two stellar populations in the two different sequences observed: a metal poor population made of stars evolving from the blue side (luminous branch) and a metal richer one whose stars are in a stage closer to the zero age HB (dimmer branch). This modelization also fits satisfactorily the period and the [Fe/H] distribution of the RR Lyrae stars., Comment: 13 pages, 7 figure, 3 tables

Horizontal Branch stars belong to an advanced stage in the evolution of the oldest stellar galactic population, occurring either as field halo stars or grouped in globular clusters. The discovery of multiple populations in these clusters, that were previously believed to have single populations gave rise to the currently accepted theory that the hottest horizontal branch members (the blue hook stars, which had late helium-core flash ignition, followed by deep mixing) are the progeny of a helium-rich "second generation" of stars. It is not known why such a supposedly rare event (a late flash followed by mixing) is so common that the blue hook of {\omega} Cen contains \sim 30% of horizontal branch stars 10 , or why the blue hook luminosity range in this massive cluster cannot be reproduced by models. Here we report that the presence of helium core masses up to \sim 0.04 solar masses larger than the core mass resulting from evolution is required to solve the luminosity range problem. We model this by taking into account the dispersion in rotation rates achieved by the progenitors, whose premain sequence accretion disc suffered an early disruption in the dense environment of the cluster's central regions where second-generation stars form. Rotation may also account for frequent late-flash-mixing events in massive globular clusters., Comment: 44 pages, 8 figures, 2 tables in Nature, online june 22, 2015

We compare theoretical dust yields for stars with mass 1 Msun < mstar < 8 Msun, and metallicities 0.001 < Z < 0.008 with observed dust production rates (DPR) by carbon- rich and oxygen-rich Asymptotic Giant Branch (C-AGB and O-AGB) stars in the Large and Small Magellanic Clouds (LMC, SMC). The measured DPR of C-AGB in the LMC are reproduced only if the mass loss from AGB stars is very efficient during the carbon-star stage. The same yields over-predict the observed DPR in the SMC, suggesting a stronger metallicity dependence of the mass-loss rates during the carbon- star stage. DPR of O-AGB stars suggest that rapid silicate dust enrichment occurs due to efficient hot-bottom-burning if mstar > 3 Msun and Z > 0.001. When compared to the most recent observations, our models support a stellar origin for the existing dust mass, if no significant destruction in the ISM occurs, with a contribution from AGB stars of 70% in the LMC and 15% in the SMC., Comment: 12 pages, 8 figures, accepted by MNRAS

We present new models for the evolution of stars with mass in the range 1Msun < M < 7.5Msun, followed from the pre-main-sequence through the asymptotic giant branch phase. The metallicity adopted is $Z=3*10^{-4} (which, with an alpha-enhancement of +0.4, corresponds to [Fe/H]=-2). Dust formation is described by following the growth of dust grains of various types as the wind expands from the stellar surface. Models with mass M>3Msun experience Hot Bottom Burning, thus maintaining the surface C/O below unity. Unlike higher Z models, the scarcity of silicon available in the envelope prevents the formation of silicates in meaningful quantities, sufficient to trigger the acceleration of the wind via radiation pressure on the dust grains formed. No silicate formation occurs below a threshold metallicity of Z=10^{-3}. Low--mass stars, with M< 2.5Msun become carbon stars, forming solid carbon dust in their surroundings. The total dust mass formed depends on the uncertain extent of the inwards penetration of the convective envelope during the Third Dredge--Up episodes following the Thermal Pulses. Carbon grains have sizes 0.08 micron < a_C < 0.12 micron and the total amount of dust formed (increasing with the mass of the star) is M_C=(2-6)*10^{-4}Msun. Our results imply that AGB stars with Z=3*10^{-4} can only contribute to carbon dust enrichment of the interstellar medium on relatively long timescales, > 300 Myr, comparable to the evolutionary time of a 3Msun star. At lower metallicities the scarcity of silicon available and the presence of Hot Bottom Burning even in M< 2Msun, prevents the formation of silicate and carbon grains. We extrapolate our conclusion to more metal--poor environments, and deduce that at Z < 10^{-4} dust enrichment is mostly due to metal condensation in supernova ejecta., Comment: 13 pages, 8 figures, accepted for publication on MNRAS

We follow the scenario of formation of second generation stars in globular clusters by matter processed by hot bottom burning (HBB) in massive asymptotic giant branch (AGB) stars and Super AGB stars (SAGB). In the cluster NGC 2419 we assume the presence of an extreme population directly formed from the AGB and SAGB ejecta, so we can directly compare the yields for a metallicity Z=0.0003 with the chemical inventory of the cluster NGC 2419. At such a low metallicity, the HBB temperatures (well above 108K) allow a very advanced nucleosynthesis. Masses of about 6Mo deplete Mg and synthesize Si, going beyond Al, so this latter element results only moderately enhanced; sodium can not be enhanced. The models are consistent with the observations, although the predicted Mg depletion is not as strong as in the observed stars. We predict that the oxygen abundance must be depleted by a huge factor in the Mg poor stars. The HBB temperatures are close to the region where other p capture reactions on heavier nuclei become possible. We show that high potassium abundance found in Mg poor stars can be achieved during HBB, by p captures on the argon nuclei, if the relevant cross section(s) are larger than listed in the literature or if the HBB temperature is higher. Finally, we speculate that some calcium production is occurring owing to proton capture on potassium. We emphasize the importance of a strong effort to measure a larger sample of abundances in this cluster., Comment: 5 pages, 2 figures, accepted by Astrophysical Journal Letter

We present the first extensive and detailed theoretical scenario for the interpretation of Cepheid properties observed in the SDSS filters. Three sets of nonlinear convective pulsation models, corresponding to the chemical compositions of Cepheids in the Milky Way, the Large Magellanic Cloud and the Small Magellanic Cloud respectively, are transformed into the SDSS bands by relying on updated model atmospheres. The resulting observables, namely the instability strip boundaries and the light curves, as well as the Period-Luminosity, the Wesenheit and the Period-Luminosity-Colour relations, are discussed as a function of the metal content, for both the fundamental and the first overtone mode. The fundamental PL relations are found to deviate from linear relations when computed over the whole observed Cepheid period range, especially at the shorter wavelenghts, confirming previous findings in the Johnson-Cousins bands. The obtained slopes are found to be mildly steeper than the ones of the semiempirical and the empirical relations available in the literature and covering roughly the same period range, with the discrepancy ranging from about 13% in u-band to about 3% in z., Comment: Accepted for publication in MNRAS

We have used new, deep, visible and near infrared observations of the compact starburst cluster in the giant HII region NGC 3603 and its surroundings with the WFC3 on HST and HAWK-I on the VLT to study in detail the physical properties of its intermediate mass (~ 1 - 3 M_sun) stellar population. We show that after correction for differential extinction and actively accreting stars, and the study of field star contamination, strong evidence remains for a continuous spread in the ages of pre-main sequence stars in the range ~ 2 to ~ 30 Myr within the temporal resolution available. Existing differences among presently available theoretical models account for the largest possible variation in shape of the measured age histograms within these limits. We also find that this isochronal age spread in the near infrared and visible Colour-Magnitude Diagrams cannot be reproduced by any other presently known source of astrophysical or instrumental scatter that could mimic the luminosity spread seen in our observations except, possibly, episodic accretion. The measured age spread and the stellar spatial distribution in the cluster are consistent with the hypothesis that star formation started at least 20-30 Myrs ago progressing slowly but continuously up to at least a few million years ago. All the stars in the considered mass range are distributed in a flattened oblate spheroidal pattern with the major axis oriented in an approximate South-East - North-West direction, and with the length of the equatorial axis decreasing with increasing age. This asymmetry is most likely due to the fact that star formation occurred along a filament of gas and dust in the natal molecular cloud oriented locally in this direction., Comment: 21 pages, 19 figures, accepted for publication in Astrophysics & Space Science

On May 27th 2010, the Italian astronomical community learned with concern that the National Institute for Astrophysics (INAF) was going to be suppressed, and that its employees were going to be transferred to the National Research Council (CNR). It was not clear if this applied to all employees (i.e. also to researchers hired on short-term contracts), and how this was going to happen in practice. In this letter, we give a brief historical overview of INAF and present a short chronicle of the few eventful days that followed. Starting from this example, we then comment on the current situation and prospects of astronomical research in Italy., Comment: Also available at http://adoptitaastronom.altervista.org/index.html