We present a homogeneous catalogue for blue straggler, red giant branch, horizontal branch and main-sequence turn-off stars in a sample of 35 clusters taken from the ACS Survey for Globular Clusters. As a result of the superior photometry and relatively large field of view offered by the ACS data, this new catalogue is a significant improvement upon the one presented in Leigh, Sills & knigge (2007). Using our catalogue, we study and compare the radial distributions of the different stellar populations.
We have confirmed our previous result (Knigge, Leigh & Sills 2009) that there is a clear, but sub-linear, correlation between the number of blue stragglers found in the cluster core and the total stellar mass contained within it. By considering a larger spatial extent than just the core, our results suggest that mass segregation is not the dominant effect contributing to the observed sub-linearity. We also investigate the radial distributions of the different stellar populations in our sample of clusters. Our results are consistent with a linear relationship between the number of stars in these populations and the total mass enclosed within the same radius. Therefore, we conclude that the cluster dynamics does not significantly affect the relative distributions of these populations in our sample.
In this paper we present the astro-photometric catalogues of 56 globular clusters and one open cluster. Astrometry and photometry are mainly based on images collected within the "HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation" (GO-13297, PI:~Piotto), and the "ACS Survey of Galactic Globular Clusters" (GO-10775, PI:~Sarajedini). For each source in the catalogues for which we have reliable proper motion we also publish a membership probability for separation of field and cluster stars. These new catalogues, which we make public in Mikulski A…
Globular clusters produce many exotic stars due to a much higher frequency of dynamical interactions in their dense stellar environments. Some of these objects were observed together with several hundred thousands other stars in our MUSE survey of 26 Galactic globular clusters. Assuming that at least a few exotic stars have exotic spectra, that means spectra that contain emission lines, we can use this large spectroscopic data set of over a million stellar spectra as a blind survey to detect stellar exotica in globular clusters. To detect emission lines in each spectrum, we model the expected …
Aims. We demonstrate the high multiplex advantage of crowded field 3D spectroscopy using the new integral field spectrograph MUSE by means of a spectroscopic analysis of more than 12,000 individual stars in the globular cluster NGC 6397. Methods. The stars are deblended with a PSF fitting technique, using a photometric reference catalogue from HST as prior, including relative positions and brightnesses. This catalogue is also used for a first analysis of the extracted spectra, followed by an automatic in-depth analysis using a full-spectrum fitting method based on a large grid of PHOENIX spect…
A Homogenized Catalogue of Variable Stars in the Globular Cluster M22: Membership, Physical Parameters, and Distance
Instituto Nacional de Astrofísica, Óptica y Electrónica（国家天体物理学、光学和电子学研究所）；Benemérita Universidad Autónoma de Puebla, Facultad de Ciencias Físico Matemáticas（普埃布拉自治大学物理数学科学学院）；Universidad de Guadalajara, Departamento de Física（瓜达拉哈拉大学物理系）；Universidad Nacional Autónoma de México, Instituto de Astronomía（墨西哥国立自治大学天文学研究所）
Using an image subtraction method we have searched for variable stars in the globular cluster M14. We confirmed 62 previously known catalogued variables. In addition to the previoulsy known variables we have identified 71 new variables. We have confirmed the periods of most of the cataloged variables with just a few exceptions. Of the the total number of confirmed variables, we found a total of 112 RR Lyrae stars, several of which exhibited the Blazhko Effect. Of the total we classified 55 RR0, 57 RR1, 19 variables with periods greater than 2 days, a W UMa contact binary, and an SX Phe star. W…
We combined Chandra ACIS observations of the globular cluster 47 Tucanae (hereafter, 47 Tuc) from 2000, 2002, and 2014-15 to create a deeper X-ray source list, and study some of the faint radio millisecond pulsars (MSPs) present in this cluster. We have detected 370 X-ray sources within the half-mass radius (2$'$.79) of the cluster, 81 of which are newly identified, by including new data and using improved source detection techniques. The majority of the newly identified sources are in the crowded core region, indicating cluster membership. We associate five of the new X-ray sources with chrom…
With a high value of heliocentric radial velocity, a retrograde orbit, and being suspected to have an extragalactic origin, NGC 3201 is an interesting globular cluster for kinematical studies. Our purpose is to calculate the relative proper motions (PMs) and membership probability for the stars in the wide region of globular cluster NGC 3201. Proper motion based membership probabilities are used to isolate the cluster sample from the field stars. The membership catalogue will help address the question of chemical inhomogeneity in the cluster. Archive CCD data taken with a wide-field imager (WF…
Context. RR Lyrae stars are useful standard candles allowing one to derive accurate distances for old star clusters. Based on the recent catalogues from OGLE-IV and Gaia Early Data Release 3 (EDR3), the distances can be improved for a few bulge globular clusters. Aims. The aim of this work is to derive an accurate distance for the following six moderately metal-poor, relatively high-reddening bulge globular clusters: NGC 6266, NGC 6441, NGC 6626, NGC 6638, NGC 6642, and NGC 6717. Methods. We combined newly available OGLE-IV catalogues of variable stars containing mean I magnitudes, with Clemen…
NGC 6809 is a luminous metal-poor halo globular cluster that is relatively easy to study due to its proximity and low concentration. Because of its high Galactic latitude (b = -23deg), interstellar reddening and contamination is not very high. We aim to determine the relative proper motion and membership probability of the stars in the wide area of globular cluster NGC 6809. To target cluster members reliably during spectroscopic surveys and both spatial and radial distributions in the cluster outskirts without including field stars, a good proper motion and membership probability catalogue of…
We present the first results from the GeMS/GSAOI Galactic Globular Cluster Survey (G4CS) of the Milky-Way globular clusters (GCs) NGC 3201 and NGC 2298. Using the Gemini South Adaptive Optics Imager (GSAOI), in tandem with the Gemini Multi-conjugate adaptive optics System (GeMS) on the 8.1-meter Gemini-South telescope, we collected deep near-IR observations of both clusters, resolving their constituent stellar populations down to $K_s\simeq21$ Vega mag. Point spread function (PSF) photometry was performed on the data using spatially-variable PSFs to generate $JHK_{s}$ photometric catalogues fo…
Proper motions (PMs) are crucial to fully understand the internal dynamics of globular clusters (GCs). To that end, the Hubble Space Telescope (HST) Proper Motion (HSTPROMO) collaboration has constructed large, high-quality PM catalogues for 22 Galactic GCs. We highlight some of our exciting recent results: the first directly-measured radial anisotropy profiles for a large sample of GCs; the first dynamical distance and mass-to-light (M/L) ratio estimates for a large sample of GCs; and the first dynamically-determined masses for hundreds of blue-straggler stars (BSSs) across a large GC sample.
We derive relative proper motions of stars in the fields of the globular clusters M12, NGC 6362, M4, M55, M22, NGC 6752, NGC 3201, M30, M10, NGC 362, M5, and 47 Tucanae based on data collected between 1997 and 2015 with the 1-m Swope telescope of Las Campanas Observatory. We determine membership class and membership probability for over 446 000 objects, and show that these are efficient methods for separating field stars from members of the cluster. In particular, membership probabilities of variable stars and blue/yellow/red stragglers are determined. Finally, we find absolute proper motions …
We use Hubble Space Telescope multicolour photometry of the globular cluster 47 Tucanae to uncover a population of 24 objects with no previous classification that are outliers from the single-star model tracks in the colour-magnitude diagram and yet are likely cluster members. By comparing those sources with evolutionary models and X-ray source catalogues, we were able to show that the majority of those sources are likely binary systems that do not have any X-ray source detected nearby, most possibly formed by a white dwarf and a main-sequence star and a small number of possible double-degener…
We present an analytic model for blue straggler formation in globular clusters. We assume that blue stragglers are formed only through stellar collisions and binary star evolution, and compare our predictions to observed blue straggler numbers taken from the catalogue of Leigh, Sills & Knigge (2011). We can summarize our key results as follows: (1) Binary star evolution consistently dominates blue straggler production in all our best-fitting models. (2) In order to account for the observed sub-linear dependence of blue straggler numbers on the core masses (Knigge, Leigh & Sills 2009), the core…
We have derived the absolute proper motion (PM) of the globular cluster M55 using a large set of CCD images collected with the du Pont telescope between 1997 and 2008. We find (PM_RA*cos(DEC), PM_DEC) = (-3.31 +/- 0.10, -9.14 +/- 0.15) mas/yr relative to background galaxies. Membership status was determined for 16 945 stars with 14<V<21 from the central part of the cluster. The PM catalogue includes 52 variables of which 43 are probable members of M55. This sample is dominated by pulsating blue straggler stars but also includes 5 eclipsing binaries, three of which are main sequence objects. Th…
We present a far-ultraviolet (FUV) study of the globular cluster M30 (NGC 7099). The images were obtained using the Advanced Camera for Surveys (ACS/SBC, F150LP, FUV) and the Wide Field Planetary Camera 2 (WFPC2, F300W, UV) on board the Hubble Space Telescope (HST). We compare the catalogue of FUV objects to ten known X-ray sources and find six confident matches of two cataclysmic variables (CVs), one RS CVn, one red giant with strong FUV emission and two sources only detected in the FUV. We also searched for variable sources in our dataset and found a total of seven blue stragglers (BSs), fou…
We present wide-field, ground-based Johnson-Cousins UBVRI photometry for 48 Galactic globular clusters based on almost 90000 public and proprietary images. The photometry is calibrated with the latest transformations obtained in the framework of our secondary standard project, with typical internal and external uncertainties of order a few millimagnitudes. These data provide a bridge between existing small-area, high-precision HST photometry and all sky-catalogues from large surveys like Gaia, SDSS, or LSST. For many clusters, we present the first publicly available photometry in some of the f…
We present the first results of eight Globular Clusters (GCs) from the AstroSat/UVIT Legacy Survey program GlobULeS based on the observations carried out in two FUV filters (F148W and F169M). The FUV-optical and FUV-FUV color-magnitude diagrams (CMDs) of GCs with the proper motion membership were constructed by combining the UVIT data with HST UV Globular Cluster Survey (HUGS) data for inner regions and Gaia Early Data Release (EDR3) for regions outside the HST's field. We detect sources as faint as F148W $\sim$ 23.5~mag which are classified based on their locations in CMDs by overlaying stell…
We have collected spectra of about 2000 red giant branch (RGB) stars in 19 Galactic globular clusters (GC) using FLAMES@VLT (about 100 star with GIRAFFE and about 10 with UVES, respectively, in each GC). These observations provide an unprecedented, precise, and homogeneous data-set of Fe abundances in GCs. We use it to study the cosmic scatter of iron and find that, as far as Fe is concerned, most GCs can still be considered mono-metallic, since the upper limit to the scatter in iron is less than 0.05 dex, meaning that the degree of homogeneity is better than 12%. The scatter in Fe we find see…
Three-body interactions can eject stars from the core of a globular cluster, causing them to enter the Galactic halo as extra-tidal stars. While finding extra-tidal stars is imperative for understanding cluster evolution, connecting isolated extra-tidal field stars back to their birth cluster is extremely difficult. In this work, we present a new methodology consisting of high-dimensional data analysis and a particle spray code to identify extra-tidal stars of any Galactic globular cluster using M3 as a case study. Using the t-Stochastic Neighbour Embedding (t-SNE) and Uniform Manifold Approxi…
The latest edition of the APOGEE-2/DR14 survey catalogue and the first \texttt{Payne} data release of APOGEE abundance determinations by Ting et al. are examined. We identify 31 previously unremarked metal-poor giant stars with anomalously high levels of nitrogen in the chemical space defined by [Fe/H] and [N/Fe]. The APOGEE chemical abundance patterns of such objects revealed that these are chemically distinct from the Milky Way (MW) in most chemical elements. We have found all these objects have a [N/Fe]$>+0.5$, and are thus identified here as nitrogen-rich stars. An orbital analysis of thes…
Spectroscopy from the final internal data release of the Gaia-ESO Survey (GES) has been combined with Gaia EDR3 to assign membership probabilities to targets observed towards 63 Galactic open clusters and 7 globular clusters. The membership probabilities are based chiefly on maximum likelihood modelling of the 3D kinematics of the targets, separating them into cluster and field populations. From 43211 observed targets, 13985 are identified as highly probable cluster members ($P>0.9$), with an average membership probability of 0.993. The addition of GES radial velocities successfully drives dow…
[ABRIDGED] $ω$ Centauri (NGC 5139) contains large numbers of variable stars of different types and, in particular, more than a hundred RR Lyrae stars. We have conducted a variability survey of $ω$ Cen in the NIR, using ESO's 4.1m Visible and Infrared Survey Telescope for Astronomy (VISTA). This is the first paper of a series describing our results. $ω$ Cen was observed using VIRCAM mounted on VISTA. A total of 42 and 100 epochs in $J$ and $K_{\rm S}$, respectively, were obtained, distributed over a total timespan of 352 days. PSF photometry was performed, and periods of the known variable star…
Most Globular Clusters so far examined host (at least) two stellar populations. This feature requires a two--step process, in which the nuclearly processed matter from a first generation (FG) of stars gives birth to a second generation (SG) bearing the fingerprint of a fully CNO-cycled matter. Since the present population of most globular clusters is made up largely of SG stars, a substantial fraction of the FG (>~90%) must be lost. Nevertheless, two types of clusters dominated by a simple stellar population (FG clusters) should exist: either clusters initially too small to be able to retain a…
We present a pilot study of Galactic globular cluster (GC) proper motion (PM) determinations using Gaia data. We search for GC stars in the Tycho-Gaia Astrometric Solution (TGAS) catalogue from Gaia Data Release 1 (DR1), and identify five members of NGC104 (47 Tucanae), one member of NGC5272 (M3), five members of NGC6121 (M4), seven members of NGC6397, and two members of NGC6656 (M22). By taking a weighted average of member stars, fully accounting for the correlations between parameters, we estimate the parallax (and, hence, distance) and PM of the GCs. This provides a homogeneous PM study of …
We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this cluster and refine the periods of known variables; we then used our variable star light curves to derive values for the cluster's parameters. We used difference image analysis to reduce our data to obtain high-precision light curves of variable stars. We then estimated the cluster parameters by performing a Fourier decomposition of the light curves of RR Lyrae stars for which a good period estimate was possibl…
Context. The APOGEE survey has obtained high-resolution infrared spectra of more than 100,000 stars. Deriving chemical abundances patterns of these stars is paramount to piecing together the structure of the Milky Way. While the derived chemical abundances have been shown to be precise for most stars, some calibration problems have been reported, in particular for more metal- poor stars. Aims. In this paper, we aim to (1) re-determine the chemical abundances of the APOGEE+Kepler stellar sample (APOKASC) with an independent procedure, line list and line selection, and high quality surface gravi…
The number of stars with a measured value of [Fe/H] is considerably increasing thanks to spectroscopic surveys. However different methodologies, inputs and assumptions used in spectral analyses lead to different precisions in [Fe/H] and possibly to systematic differences that need to be evaluated. It is essential to understand the characteristics of each survey to fully exploit their potential, in particular if the surveys are combined. The purpose of this study is to compare [Fe/H] determinations from the largest spectroscopic surveys (APOGEE, GALAH, the Gaia ESO survey, RAVE, LAMOST, SEGUE )…
Recent wide-area surveys have enabled us to study the Milky Way with unprecedented detail. Its inner regions, hidden behind dust and gas, have been partially unveiled with the arrival of near-IR photometric and spectroscopic datasets. Among recent discoveries, there is a population of low-mass globular clusters, known to be missing, especially towards the Galactic bulge. In this work, five new low-luminosity globular clusters located towards the bulge area are presented. They were discovered by searching for groups in the multi-dimensional space of coordinates, colours, and proper motions from…
Theory and observations indicate that the distribution of stars along the horizontal branch of Galactic globular clusters mainly depends on the metal content. However, the existence of globular clusters with similar metal content and absolute age but different horizontal branch morphologies, suggests the presence of another parameter affecting the star distribution along the branch. To investigate the variation of the horizontal branch morphology in Galactic globular clusters, we define a new photometric horizontal branch morphology index, overcoming some of the limitations and degeneracies af…
Phase-Space Crystallization in Galactic Globular Clusters: A Gaia-Based Metric and Implications for Technosignature Searches
Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究所）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）；College of Computer and Information Engineering, Dezhou University（德州学院计算机与信息工程学院）
Gaia Data Release 3 provides novel flux-calibrated low-resolution spectrophotometry for about 220 million sources in the wavelength range 330nm - 1050nm (XP spectra). Synthetic photometry directly tied to a flux in physical units can be obtained from these spectra for any passband fully enclosed in this wavelength range. We describe how synthetic photometry can be obtained from XP spectra, illustrating the performance that can be achieved under a range of different conditions - for example passband width and wavelength range - as well as the limits and the problems affecting it. Existing top-q…
