Galactic Bulge Research Articles

Chemical abundance analysis of symbiotic giants. Metallicity and CNO abundance patterns in 14 northern S-type systems

ABSTRACT In previous works, we computed abundances for the red giant in nearly four dozen S-type symbiotic systems (SySt). The abundances provide information about metallicity, evolutionary status, and possible memberships in Galactic stellar populations. Here, we extend our studies with a northern hemisphere sample of SySt. This northern sample is dominated by Galactic disc/halo objects, whereas our previous southern sample is heavily biased toward the bulge population. Spectrum synthesis of high-resolution (R ∼ 50 000), near-IR spectra using standard LTE analysis and atmospheric models have been used to measure abundances of CNO and elements around the iron peak (Fe, Ti, Ni, and Sc) in the atmospheres of the red giant component. The SySt sample shows generally slightly sub-solar metallicity, as expected for an older disc population, with a median at [Fe/H] ∼ −0.2 dex. Enhanced 14N, depleted 12C, and decreased 12C/13C, indicate that all these giants have experienced the first dredge-up. Comparison with theoretical predictions indicates that additional mixing processes had to occur to explain the observed C and N abundances. Relative O and Fe abundances agree with those represented by Galactic disc and bulge giant populations in the APOGEE data, with a few cases that can be attributed to membership in the extended thick-disc/halo. As an interesting byproduct of this study, we observed a blue-shifted additional component on the wings of absorption lines in the spectra of AG Peg, which could be connected with accretion on to the hot component.

On the likelihoods of finding very metal-poor (and old) stars in the Milky Way’s disc, bulge, and halo

ABSTRACT Recent observational studies have uncovered a small number of very metal-poor (VMP) stars with cold kinematics in the Galactic disc and bulge. However, their origins remain enigmatic. We select a total of 138 Milky Way (MW) analogues from the TNG50 cosmological simulation based on their z = 0 properties: discy morphology, stellar mass, and local environment. In order to make more predictive statements for the MW, we further limit the spatial volume coverage of stellar populations in galaxies to that targeted by the upcoming 4MOST high-resolution survey of the Galactic disc and bulge. We find that across all galaxies, ∼20 per cent of VMP ([Fe/H] < −2) stars belong to the disc, with some analogues reaching 30 per cent. About 50 ± 10 per cent of the VMP disc stars are, on average, older than 12.5 Gyr and ∼70 ± 10 per cent come from accreted satellites. A large fraction of the VMP stars belong to the halo (∼70) and have a median age of 12 Gyr. Our results with the TNG50 cosmological simulation confirm earlier findings with simulations of fewer individual galaxies, and suggest that the stellar disc of the MW is very likely to host significant amounts of very- and extremely-metal-poor stars that, although mostly of ex situ origin, can also form in situ, reinforcing the idea of the existence of a primordial Galactic disc.

Improved Galactic diffuse emission model strengthens the case for a Millisecond Pulsar explanation of the Fermi GeV excess

After more than a decade since its discovery, the Galactic center gamma-ray excess - discovered with the Fermi Large Area Telescope - remains puzzling. While the spectrum of the signal can be explained by either dark matter or an unresolved population of millisecond pulsars, the spatial morphology of this excess seems to hold the key to separate the two theories. In this contribution, we present the results of a recent study in which we use bleeding edge models for interstellar gas, inverse Compton emission, and stellar mass models to reanalyze the Galactic center excess. We find that the spatial morphology of the excess is highly correlated with stellar matter in the Galactic bulge, providing strong support for the millisecond pulsar hypothesis.

Persistent and occasional: Searching for the variable population of the ZTF/4MOST sky using ZTF Data Release 11

Aims. We present a variability-, color-, and morphology-based classifier designed to identify multiple classes of transients and persistently variable and non-variable sources from the Zwicky Transient Facility (ZTF) Data Release 11 (DR11) light curves of extended and point sources. The main motivation to develop this model was to identify active galactic nuclei (AGN) at different redshift ranges to be observed by the 4MOST Chilean AGN/Galaxy Evolution Survey (ChANGES). That being said, it also serves as a more general time-domain astronomy study. Methods. The model uses nine colors computed from CatWISE and Pan-STARRS1 (PS1), a morphology score from PS1, and 61 single-band variability features computed from the ZTF DR11 g and r light curves. We trained two versions of the model, one for each ZTF band, since ZTF DR11 treats the light curves observed in a particular combination of field, filter, and charge-coupled device (CCD) quadrant independently. We used a hierarchical local classifier per parent node approach-where each node is composed of a balanced random forest model. We adopted a taxonomy with 17 classes: non-variable stars, non-variable galaxies, three transients (SNIa, SN-other, and CV/Nova), five classes of stochastic variables (lowz-AGN, midz-AGN, highz-AGN, Blazar, and YSO), and seven classes of periodic variables (LPV, EA, EB/EW, DSCT, RRL, CEP, and Periodic-other). Results. The macro-averaged precision, recall, and F1-score are 0.61, 0.75, and 0.62 for the g-band model, and 0.60, 0.74, and 0.61, for the r-band model. When grouping the four AGN classes (lowz-AGN, midz-AGN, highz-AGN, and Blazar) into one single class, its precision-recall, and F1-score are 1.00, 0.95, and 0.97, respectively, for both the g and r bands. This demonstrates the good performance of the model in classifying AGN candidates. We applied the model to all the sources in the ZTF/4MOST overlapping sky (−28 ≤ Dec ≤ 8.5), avoiding ZTF fields that cover the Galactic bulge (|gal_b| ≤ 9 and gal_l ≤ 50). This area includes 86 576 577 light curves in the g band and 140 409 824 in the r band with 20 or more observations and with an average magnitude in the corresponding band lower than 20.5. Only 0.73% of the g-band light curves and 2.62% of the r-band light curves were classified as stochastic, periodic, or transient with high probability (Pinit ≥ 0.9). Even though the metrics obtained for the two models are similar, we find that, in general, more reliable results are obtained when using the g-band model. With it, we identified 384 242 AGN candidates (including low-, mid-, and high-redshift AGN and Blazars), 287 156 of which have Pinit ≥ 0.9.

Variable stars in the residual light curves of OGLE-IV eclipsing binaries towards the Galactic Bulge

Context. The Optical Gravitational Lensing Experiment (OGLE) observed around 450 000 eclipsing binaries (EBs) towards the Galactic Bulge. Decade-long photometric observations such as these provide an exceptional opportunity to thoroughly examine the targets. However, observing dense stellar fields such as the Bulge may result in blends and contamination by close objects. Aims. We searched for periodic variations in the residual light curves of EBs in OGLE-IV and created a new catalogue for the EBs that contain ‘background’ signals after the investigation of the source of the signal. Methods. From the about half a million EB systems, we selected those that contain more than 4000 data points. We fitted the EB signal with a simple model and subtracted it. To identify periodical signals in the residuals, we used a GPU-based phase dispersion minimisation python algorithm called cuvarbase and validated the found periods with Lomb-Scargle periodograms. We tested the reliability of our method with artificial light curves. Results. We identified 354 systems where short-period background variation was significant. In these cases, we determined whether it is a new variable or just the result of contamination by an already catalogued nearby one. We classified 292 newly found variables into EB, δ Scuti, or RR Lyrae categories, or their sub-classes, and collected them in a catalogue. We also discovered four new doubly eclipsing systems and one eclipsing multiple system with a δ Scuti variable, and modelled the outer orbits of the components.

GaiaData Release 3

Context.GaiaData Release 3 (DR3) provides a number of new data products that complement the early DR3 made available two years ago. Among these is the firstGaiacatalogue of eclipsing-binary candidates containing 2 184 477 sources with brightnesses from a few magnitudes to 20 mag in theGaiaG-band and covering the full sky.Aims.We present the catalogue, describe its content, provide tips for its use, estimate its quality, and show illustrative samples.Methods.Candidate selection is based on the results of variable object classification performed within theGaiaData Processing and Analysis Consortium. Candidates are then further filtered using eclipsing-binary-tailored criteria based on theG-band light curves. To find the orbital period, a large ensemble of trial periods is first acquired using three distinct period-search methods applied to the cleanedGlight curve of each source. TheGlight curve is then modelled with up to two Gaussians and a cosine for each trial period. The best combination of orbital period and geometric model is finally selected using Bayesian model comparison based on the BIC. A global ranking metric is provided to rank the quality of the chosen model between sources. The catalogue is restricted to orbital periods larger than 0.2 days.Results.Of ∼600 000 available crossmatches, about 530 000 of the candidates are classified as eclipsing binaries in the literature as well, and 93% of them have published periods compatible with theGaiaperiods. Catalogue completeness is estimated to be between 25% and 50%, depending on the sky region, relative to the OGLE4 catalogues of eclipsing binaries towards the Galactic Bulge and the Magellanic Clouds. The analysis of an illustrative sample of ∼400 000 candidates with significant parallaxes shows properties in the observational Hertzsprung-Russell diagram as expected for eclipsing binaries. The subsequent analysis of a subsample of detached bright candidates provides further hints for the exploitation of the catalogue. We also address the observed lack of short-period (less than a day) systems in the Magellanic Cloud in comparison to Galactic systems. The orbital periods, light-curve model parameters, and global rankings are all published in the catalogue with their related uncertainties where applicable.Conclusions.ThisGaiaDR3 catalogue of eclipsing-binary candidates constitutes the largest catalogue to date in terms of number of sources, sky coverage, and magnitude range.

Internal Kinematics and Structure of the Bulge Globular Cluster NGC 6569 ∗ ∗ Based on observations collected at the European Southern Observatory, Cerro Paranal (Chile), in the context of the ESO-VLT Multi-Instrument Kinematic Survey (MIKiS survey) under Large Programmes 106.21N5 (PI: Ferraro), 195.D-0750 (PI: Ferraro), 193.D-0232 (PI: Ferraro). This publication makes use of data products from the Two Micron All

In the context of a project aimed at characterizing the properties of star clusters in the Galactic bulge, here we present the determination of the internal kinematics and structure of the massive globular cluster NGC 6569. The kinematics has been studied by means of an unprecedented spectroscopic data set acquired in the context of the ESO-VLT Multi-Instrument Kinematic Survey of Galactic globular clusters, combining the observations from four different spectrographs. We measured the line-of-sight velocity of a sample of almost 1300 stars distributed between ∼0.″8 and 770″ from the cluster center. From a subsample of high-quality measures, we determined the velocity dispersion profile of the system over its entire radial extension (from ∼5″ to ∼200″ from the center), finding the characteristic behavior usually observed in globular clusters, with a constant inner plateau and a declining trend at larger radii. The projected density profile of the cluster has been obtained from resolved star counts, by combining high-resolution photometric data in the center, and the Gaia EDR3 catalog radially extended out to for a proper sampling of the Galactic field background. The two profiles are properly reproduced by the same King model, from which we estimated updated values of the central velocity dispersion, main structural parameters (such as the King concentration, the core, half mass, and tidal radii), total mass, and relaxation times. Our analysis also reveals a hint of ordered rotation in an intermediate region of the cluster (40″ < r < 90″, corresponding to 2r c < r < 4.5r c ), but additional data are required to properly assess this possibility.

Blanco DECam Bulge Survey (BDBS). VI. Extinction Maps Toward Southern Galactic Bulge Globular Clusters

We present wide-field, high resolution maps of the color excess for 14 globular clusters toward the Southern Galactic bulge. The maps were derived using Gaia EDR3 astrometry and stellar photometry from the Blanco DECam Bulge Survey, which is a deep, wide-field ugrizY photometric survey of the southern Galactic bulge. Comparisons with WISE 12 μm images of thermal continuum emission demonstrate that the maps presented here trace interstellar extinction by dust down to 5″ scales. We use the reddening-corrected photometry of proper motion-selected cluster stars to build color–magnitude diagrams for the target globular clusters, which show residual broadening in excess of that expected from the photometric errors alone. This residual broadening is likely to be driven by star-to-star elemental abundance variations.

Prediction of Planet Yields by the PRime-focus Infrared Microlensing Experiment Microlensing Survey

The PRime-focus Infrared Microlensing Experiment (PRIME) will be the first to conduct a dedicated near-infrared microlensing survey by using a 1.8 m telescope with a wide field of view of 1.45 deg2 at the South African Astronomical Observatory. The major goals of the PRIME microlensing survey are to measure the microlensing event rate in the inner Galactic bulge to help design the observing strategy for the exoplanet microlensing survey by the Nancy Grace Roman Space Telescope and to make a first statistical measurement of exoplanet demographics in the central bulge fields where optical observations are very difficult owing to the high extinction in these fields. Here we conduct a simulation of the PRIME microlensing survey to estimate its planet yields and determine the optimal survey strategy, using a Galactic model optimized for the inner Galactic bulge. In order to maximize the number of planet detections and the range of planet mass, we compare the planet yields among four observation strategies. Assuming the Cassan et al. mass function as modified by Penny et al., we predict that PRIME will detect planetary signals for 42–52 planets (1–2 planets with M p ≤ 1M ⊕, 22−25 planets with mass 1M ⊕ < M p ≤ 100M ⊕, 19–25 planets 100M ⊕ < M p ≤ 10, 000M ⊕), per year depending on the chosen observation strategy.

Predicting the Yield of Small Transiting Exoplanets around Mid-M and Ultracool Dwarfs in the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey

We simulate the yield of small (0.5–4.0 R ⊕) transiting exoplanets around single mid-M and ultracool dwarfs (UCDs) in the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey. We consider multiple approaches for simulating M3–T9 sources within the survey fields, including scaling local space densities and using Galactic stellar population synthesis models. These approaches independently predict ∼100,000 single mid-M dwarfs and UCDs brighter than a Roman F146 magnitude of 21 that are within the survey fields. Assuming planet occurrence statistics previously measured for early-to-mid-M dwarfs, we predict that the survey will discover small transiting planets around these sources, each to a significance of 7.1σ or greater. Significant departures from this prediction would test whether the occurrence rates of small planets increase or decrease around mid-M dwarfs and UCDs compared to early-M dwarfs. We predict the detection of habitable, terrestrial planets (R p < 1.23 R ⊕) in the survey. However, atmospheric characterization of these planets will be challenging with current or near-future space telescope facilities due to the faintness of the host stars. Nevertheless, accurate statistics for the occurrence of small planets around mid-M dwarfs and UCDs will enable direct tests of predictions from planet formation theories and will determine our understanding of planet demographics around the objects at the bottom of the main sequence. This understanding is critical given the prevalence of such objects in our galaxy, whose planets may therefore comprise the bulk of the galactic census of exoplanets.

60 Microlensing Events from the Three Years of Zwicky Transient Facility Phase One

Microlensing events have historically been discovered throughout the Galactic bulge and plane by surveys designed solely for that purpose. We conduct the first multiyear search for microlensing events on the Zwicky Transient Facility (ZTF), an all-sky optical synoptic survey that observes the entire visible northern sky every few nights. We discover 60 high-quality microlensing events in the 3 yr of ZTF-I using the bulk lightcurves in the ZTF Public Data Release 5.19 of our events are found outside of the Galactic plane (∣b∣ ≥ 10°), nearly doubling the number of previously discovered events in the stellar halo from surveys pointed toward the Magellanic Clouds and the Andromeda galaxy. We also record 1558 ongoing candidate events as potential microlensing that can continue to be observed by ZTF-II for identification. The scalable and computationally efficient methods developed in this work can be applied to future synoptic surveys, such as the Vera C. Rubin Observatory’s Legacy Survey of Space and Time and the Nancy Grace Roman Space Telescope, as they attempt to find microlensing events in even larger and deeper data sets.

On the dearth of C-enhanced metal-poor stars in the galactic bulge

ABSTRACTThe chemical fingerprints of the first stars are retained within the photospheres of ancient unevolved metal-poor stars. A significant fraction of these stellar fossils is represented by stars known as Carbon-Enhanced Metal-Poor (CEMP), $\mathrm{[C/Fe]} \gt +0.7$ and $\mathrm{[Fe/H]} \lt -2$, which are likely imprinted by low-energy primordial supernovae. These CEMP stars are largely observed in the Galactic halo and ultrafaint dwarf galaxies, with values reaching $\rm [C/Fe]=+4.5$. The Galactic bulge is predicted to host the oldest stars, but it shows a striking dearth of CEMP stars with $\rm [C/Fe]\gtrsim +2.0$. Here, we explore the possible reasons for this anomaly by performing a statistical analysis of the observations of metal-poor stars in combination with the predictions of Lambda cold dark matter models. We suggest that the dearth of CEMP stars with high $\mathrm{[C/Fe]}$ is not due to the low statistics of observed metal-poor stars but is the result of the different formation process of the bulge. N-body simulations show that the first star-forming haloes which end up in the bulge are characterized by the highest star formation rates. These rates enable the formation of rare massive first stars exploding as pair-instability supernovae (PISNe), which wash out the signature of primordial faint supernovae. We demonstrate that the mean $\mathrm{[C/Fe]}$ of first stars polluted environments decreases with the increasing contribution of PISNe. We conclude that the dearth of CEMP stars in the Galactic bulge indirectly probes the existence of elusive PISNe, and propose a novel method which exploits this lack to constrain the mass distribution of the first stars.

Periodic X-ray sources in the massive globular cluster 47 Tucanae: Evidence for dynamically formed cataclysmic variables

ABSTRACT We present a systematic study of periodic X-ray sources in the massive globular cluster 47 Tuc, utilizing deep archival Chandra observations that resolve the cluster core and recently available eROSITA observations that cover the cluster outskirt. By applying the Gregory-Loredo algorithm, we detect 20 periodic signals among 18 X-ray sources, ranging between 205–95731 s. Fourteen periods are newly discovered in the X-ray band. We classify these periodic sources into four quiescent low-mass X-ray binaries, 1 ms pulsar, two coronally-active binaries, and eleven cataclysmic variables (CVs) based on their X-ray temporal and spectral properties, as well as multiband information. Despite a small sample subject to potential selection bias against faint and non-magnetic CVs, the 11 CVs together define an orbital period distribution significantly different from that of the CVs previously found in the solar neighbourhood and the Galactic bulge. In particular, there exists in 47 Tuc an apparent paucity of short-period CVs below the period gap, which might be attributed to a high occupation fraction of non-magnetic CVs. Also characteristic of the 47 Tuc CVs are an overabundance of long-period CVs with a subgiant donor, a substantial fraction of CVs within the period gap, and a steep radial surface density profile. These are best understood as a group of CVs having recently formed via dynamical interactions in the dense cluster core. Despite sufficient sensitivity of the X-ray data, only one periodic source is found between one-third of the half-light radius and the tidal radius, the nature of which is unclear.

Detailed α abundance trends in the inner Galactic bulge

Context. Until now, heavy interstellar extinction has meant that only a few studies of chemical abundances have been possible in the inner Galactic bulge. However, it is crucial to learn more about this structure in order to better understand the formation and evolution of the centre of the Galaxy and galaxies in general. Aims. In this paper, we aim to derive high-precision α-element abundances using CRIRES high-resolution IR spectra of 72 cool M giants of the inner Galactic bulge. Methods. Silicon, magnesium, and calcium abundances were determined by fitting a synthetic spectrum for each star. We also incorporated recent theoretical data into our spectroscopic analysis (i.e. updated K-band line list, better broadening parameter estimation, non-local thermodynamic equilibrium (NLTE) corrections). We compare these inner bulge α abundance trends with those of solar neighbourhood stars observed with IGRINS using the same line list and analysis technique; we also compare our sample to APOGEE DR17 abundances for inner bulge stars. We investigate bulge membership using spectro-photometric distances and orbital simulations. We construct a chemical-evolution model that fits our metallicity distribution function (MDF) and our α-element trends. Results. Among our 72 stars, we find four that are not bulge members. [Si/Fe] and [Mg/Fe] versus [Fe/H] trends show a typical thick disc α-element behaviour, except that we do not see any plateau at supersolar metallicities as seen in other works. The NLTE analysis lowers [Mg/Fe] typically by ∼0.1 dex, resulting in a noticeably lower trend of [Mg/Fe] versus [Fe/H]. The derived [Ca/Fe] versus [Fe/H] trend has a larger scatter than those for Si and Mg, but is in excellent agreement with local thin and thick disc trends. With our updated analysis, we constructed one of the most detailed studies of the α abundance trends of cool M giants in the inner Galactic bulge. We modelled these abundances by adopting a two-infall chemical-evolution model with two distinct gas-infall episodes with timescales of 0.4 Gyr and 2 Gyr, respectively. Conclusions. Based on a very meticulous spectral analysis, we have constructed detailed and precise chemical abundances of Mg, Si, and Ca for cool M giants. The present study can be used as a benchmark for future spectroscopic surveys.

Chrono-chemodynamical analysis of the globular cluster NGC 6355: Looking for the fundamental bricks of the Bulge

The information on Galactic assembly time is imprinted on the chemodynamics of globular clusters. This makes them important probes that help us to understand the formation and evolution of the Milky Way. Discerning between in-situ and ex-situ origin of these objects is difficult when we study the Galactic bulge, which is the most complex and mixed component of the Milky Way. To investigate the early evolution of the Galactic bulge, we analysed the globular cluster NGC 6355. We derived chemical abundances and kinematic and dynamic properties by gathering information from high-resolution spectroscopy with FLAMES-UVES, photometry with the Hubble Space Telescope, and Galactic dynamic calculations applied to the globular cluster NGC 6355. We derive an age of 13.2 ± 1.1 Gyr and a metallicity of [Fe/H] = − 1.39 ± 0.08 for NGC 6355, with α-enhancement of [α/Fe] = + 0.37 ± 0.11. The abundance pattern of the globular cluster is compatible with bulge field RR Lyrae stars and in-situ well-studied globular clusters. The orbital parameters suggest that the cluster is currently confined within the bulge volume when we consider a heliocentric distance of 8.54 ± 0.19 kpc and an extinction coefficient of RV = 2.84 ± 0.02. NGC 6355 is highly likely to come from the main bulge progenitor. Nevertheless, it still has a low probability of being formed from an accreted event because its age is uncertain and because of the combined [Mg/Mn] [Al/Fe] abundance. Its relatively low metallicity with respect to old and moderately metal-poor inner Galaxy clusters may suggest a low-metallicity floor for globular clusters that formed in-situ in the early Galactic bulge.

The Ages of Galactic Bulge Stars with Realistic Uncertainties

Using modern isochrones with customized physics and carefully considered statistical techniques, we recompute the age distribution for a sample of 91 microlensed dwarfs in the Galactic bulge presented by Bensby et al. and do not produce an age distribution consistent with their results. In particular, our analysis finds that only 15 of 91 stars have ages younger than 7 Gyr, compared to their finding of 42 young stars in the same sample. While we do not find a constituency of very young stars, our results do suggest the presence of an ∼8 Gyr population at the highest metallicities, thus contributing to the long-standing debate about the age–metallicity distribution of the Galactic bulge. We supplement this with attempts at independent age determinations from two sources of photometry, BDBS and Gaia, but find that the imprecision of photometric measurements prevents reliable age and age uncertainty determinations. Lastly, we present age uncertainties derived using a first-order consideration of global modeling uncertainties in addition to standard observational uncertainties. The theoretical uncertainties are based on the known variance of free parameters in the 1D stellar evolution models used to generate isochrones, and when included, result in age uncertainties of 2–5 Gyr for this spectroscopically well-constrained sample. These error bars, which are roughly twice as large as typical literature values, constitute realistic lower limits on the true age uncertainties.

The Complex Structure of the Bulge of M31

The bulge of M31 is of interest regarding the nature of galactic bulges and how their structure relates to bulge formation mechanisms and their subsequent evolution. With the UVIT instrument on AstroSat, we have observed the bulge of M31 in five far-ultraviolet (FUV) and near-ultraviolet (NUV) filters at 1″ spatial resolution. Models for the luminosity distribution of the bulge are constructed using the UVIT data and the galaxy image fitting algorithm GALFIT. We fit the bulge without the nuclear region with a Sérsic function for the five images and find Sérsic indices (≃2.1–2.5) similar to previous studies but smaller R e values (≃0.5–0.6 kpc). When fitting the images including the nuclear region, a multicomponent model is used. We use an eight-component model for the FUV 148 nm image, which has the highest sensitivity. The other images (169–279 nm) are fit with four-component models. The dust lanes in the bulge region are recovered in the residual images, which have subtraction of the bright bulge light using the multicomponent models. The dust lanes show that M31's nuclear spiral is visible in absorption at NUV and FUV wavelengths. The bulge images show boxy contours in all five UVIT wave bands, which is confirmed by fitting using GALFIT. The Sérsic indices of ∼2.1–2.5 are intermediate between the expected values for a classical bulge and for a pseudobulge. The boxiness of the bulge provides further evidence that M31's bulge has contributions from a classical bulge and a pseudobulge.

The ESO-VLT MIKiS Survey Reloaded: Exploring the Internal Kinematics of NGC 6440* * Based on observations collected at the European Southern Observatory, Cerro Paranal (Chile), under proposal 193.D-0232 (PI: Ferraro), 195.D-0750 (PI: Ferraro), 60.A-9489 (PI: Ferraro), and 093.D-0319 (PI: Lanzoni).

In the context of the ESO-VLT Multi-Instrument Kinematic Survey of Galactic globular clusters, here we present the line-of-sight velocity dispersion profile of NGC 6440, a massive globular cluster located in the Galactic bulge. By combining the data acquired with four different spectrographs, we obtained the radial velocity of a sample of ∼1800 individual stars distributed over the entire cluster extension, from ∼0.″1 to 778″ from the center. Using a properly selected sample of member stars with the most reliable radial velocity measures, we derived the velocity dispersion profile up to 250″ from the center. The profile is well described by the same King model that best fits the projected star density distribution, with a constant inner plateau (at σ 0 ∼ 12 km s−1) and no evidence of a central cusp or other significant deviations. Our data allowed us to study the presence of rotation only in the innermost regions of the cluster (r < 5″), revealing a well-defined pattern of ordered rotation with a position angle of the rotation axis of ∼132° ± 2° and an amplitude of ∼3 km s−1 (corresponding to V rot/σ 0 ∼ 0.3). In addition, a flattening of the system qualitatively consistent with the rotation signal has been detected in the central region.

M dwarf stars in the b294 field from the VISTA Variables in the Vía Láctea (VVV)

ABSTRACT M dwarf stars are the dominant stellar population in the Milky Way, and they are important for a wide variety of astrophysical topics. The Gaia mission has delivered a superb collection of data, nevertheless, ground-based photometric surveys are still needed to study faint objects. Therefore, the present work aims to identify and characterize M dwarf stars in the direction of the Galactic bulge using photometric data and with the help of Virtual Observatory tools. Using parallax measurements and proper motions from Gaia Data Release 3, in addition to different colour-cuts based on VISTA filters, we identify and characterize 7 925 M dwarf stars in the b294 field from the Vista Variables in the Vía Láctea (VVV) survey. We performed a spectral energy distribution fitting to obtain the effective temperature for all objects using photometric information available at Virtual Observatory archives. The objects in our sample have temperatures varying from 2800–3900 K. We also search for periodic signals in VVV light curves with up to 300 epochs, approximately. As a secondary outcome, we obtain periods for 82 M dwarfs by applying two methods: the Lomb–Scargle and Phase Dispersion Minimization methods, independently. These objects, with periods ranging from 0.14–34 d, are good candidates for future ground-based follow up. Our sample has increased significantly the number of known M dwarfs in the direction of the Galactic bulge and within 500 pc, showing the importance of ground-based photometric surveys in the near-infrared.

Kepler K2Campaign 9 – II. First space-based discovery of an exoplanet using microlensing

ABSTRACTWe present K2-2016-BLG-0005Lb, a densely sampled, planetary binary caustic-crossing microlensing event found from a blind search of data gathered from Campaign 9 of the Kepler K2 mission (K2C9). K2-2016-BLG-0005Lb is the first bound microlensing exoplanet discovered from space-based data. The event has caustic entry and exit points that are resolved in the K2C9 data, enabling the lens-source relative proper motion to be measured. We have fitted a binary microlens model to the Kepler data and to simultaneous observations from multiple ground-based surveys. Whilst the ground-based data only sparsely sample the binary caustic, they provide a clear detection of parallax that allows us to break completely the microlensing mass-position-velocity degeneracy and measure the planet’s mass directly. We find a host mass of 0.58 ± 0.04 M⊙ and a planetary mass of 1.1 ± 0.1 MJ. The system lies at a distance of 5.2 ± 0.2 kpc from Earth towards the Galactic bulge, more than twice the distance of the previous most distant planet found by Kepler. The sky-projected separation of the planet from its host is found to be 4.2 ± 0.3 au which, for circular orbits, deprojects to a host separation $a = 4.4^{+1.9}_{-0.4}$ au and orbital period $P = 13^{+9}_{-2}$ yr. This makes K2-2016-BLG-0005Lb a close Jupiter analogue orbiting a low-mass host star. According to current planet formation models, this system is very close to the host mass threshold below which Jupiters are not expected to form. Upcoming space-based exoplanet microlensing surveys by NASA’s Nancy Grace Roman Space Telescope and, possibly, ESA’s Euclid mission, will provide demanding tests of current planet formation models.