Gaia and Hubble unveil the kinematics of stellar populations in the Type II globular clusters ω Centauri and M 22
G. Cordoni, A. P. Milone, A. F. Marino, G. S. Da Costa, E. Dondoglio, H. Jerjen, E. P. Lagioia, A. Mastrobuono-Battisti, J. E. Norris, M. Tailo, D. Yong
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24 pages, 13 figures, accepted for publication in ApJ
The origin of multiple stellar populations in Globular Clusters (GCs) is one of the greatest mysteries of modern stellar astrophysics. N-body simulations suggest that the present-day dynamics of GC stars can constrain the events that occurred at high redshift and led to the formation of multiple populations. Here, we combine multi-band photometry from the Hubble Space Telescope (HST) and ground-based facilities with HST and Gaia Data Release 2 proper motions to investigate the spatial distributions and the motions in the plane of the sky of multiple populations in the type II GCs NGC 5139 ($ω\,$Centauri) and NGC 6656 (M 22). We first analyzed stellar populations with different metallicities. Fe-poor and Fe-rich stars in M 22 share similar spatial distributions and rotation patterns and exhibit similar isotropic motions. Similarly, the two main populations with different iron abundance in $ω\,$Centauri share similar ellipticities and rotation patterns. When analyzing different radial regions, we find that the rotation amplitude decreases from the center towards the external regions. Fe-poor and Fe-rich stars of $ω\,$Centauri are radially anisotropic in the central region and show similar degrees of anisotropy. We also investigate the stellar populations with different light-element abundances and find that their N-rich stars exhibit higher ellipticity than N-poor stars. In $ω\,$Centauri Centauri both stellar groups are radially anisotropic. Interestingly, N-rich, Fe-rich stars exhibit different rotation patterns than N-poor stars with similar metallicities. The stellar populations with different nitrogen of M 22 exhibit similar rotation patterns and isotropic motions. We discuss these findings in the context of the formation of multiple populations.
The galactic globular cluster Omega Centauri is the most massive of its kind, with a complex mix of multiple stellar populations and several kinematic and dynamical peculiarities. Different mean proper motions have been detected among the three main sub-populations, implying that the most metal-rich one is of accreted origin. This particular piece of evidence has been a matter of debate because the available data have either not been sufficiently precise or limited to a small region of the cluster to ultimately confirm or refute the result. Using astrometry from the second Gaia data release an…
Historically, photometry has been largely used to identify stellar populations (MPs) in Globular Clusters (GCs) by using diagrams that are based on colours and magnitudes that are mostly sensitive to stars with different metallicities or different abundances of helium, carbon, nitrogen and oxygen. In particular, the pseudo two-colour diagram called chromosome map (ChM), allowed the identification and the characterization of MPs in about 70 GCs by using appropriate filters of the Hubble Space Telescope (HST) that are sensitive to the stellar content of He, C, N, O and Fe. We use here high-preci…
Spatial Property of Multiple Metallic Populations in the Tidal Stream of ω Centauri
Sun Yat-sen University（中山大学）；CSST Science Center for the Guangdong-Hong Kong-Macau Greater Bay Area（CSST粤港澳大湾区科学中心）；Instituto de Astronomía, Universidad Católica del Norte（北方天主教大学天文学研究所）
The series of events, which occurred at high redshift and originated multiple stellar populations in Globular Clusters (GCs) are still poorly understood. Theoretical work suggests that the present-day dynamics of stars in nearby GCs, including the rotation and velocity dispersion, may retain important clues on the formation of multiple populations. So far, the dynamics of multiple populations have been investigated either from radial velocities of a relatively-small sample of stars, or from relative proper motions of stars in the small field of view provided by the Hubble Space Telescope. In t…
We report 1,656 new star clusters found in the Galactic disk (|b|<20 degrees) beyond 1.2 kpc, using Gaia EDR3 data. Based on an unsupervised machine learning algorithm, DBSCAN, and followed our previous studies, we utilized a unique method to do the data preparation and obtained the clustering coefficients, which proved to be an effective way to search blindly for star clusters. We tabulated the physical parameters and member stars of the new clusters, and presented some interesting examples, including a globular cluster candidate. The cluster parameters and member stars are available at CDS v…
For more than a decade, Alpha Centauri AB (G2V+K1V) has been observed by Chandra, in a long-term program to follow coronal (T~1MK) activity cycles of the two sunlike stars. Over 2008.4-2017.8, nineteen HRC-I exposures were taken, each about 10 ks in duration, and spaced about six months apart. Beyond monitoring the AB X-ray luminosities, the HRC-I sequence represents a unique decadal record of the dozen, or so, serendipitous X-ray sources in the Alpha Cen field, which is at low Galactic latitude and thus dominated by nearby stars. For the present study, the ten brightest candidates were consid…
We use Gaia DR2 data to isolate the pre-main sequence population corresponding to the Scorpius-Lupus-Centaurus-Crux area on the sky making use the Hertzsprung-Russell diagram. A sample of $120\,911$ sources was selected with galactic coordinates $285^\circ\leq\ell\leq360^\circ$ and $-10^\circ\leq b\leq+32^\circ$, and parallaxes between $5$ and $12$~mas where the relative uncertainty in parallax was restricted to be $<10\%$. The pre-main sequence sources were isolated due to a clear separation between the pre-main and main sequences, well above the expected $0.75$ magnitude from a possible obse…
oMEGACat. X. Shedding light on the disrupted dwarf galaxy of Omega Centauri
Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；University of Utah（犹他大学）；European Southern Observatory（欧洲南方天文台）；Universität Heidelberg（海德堡大学）；Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg（海德堡大学天体物理计算研究所）；Zentrum für Astronomie der Universität Heidelberg, Landessternwarte（海德堡大学天文学中心，州立天文台）
The most massive and complex globular clusters in the Galaxy are thought to have originated as the nuclear cores of now tidally disrupted dwarf galaxies, but the connection between globular clusters and dwarf galaxies is tenuous with the M54/Sagittarius system representing the only unambiguous link. The globular cluster Omega Centauri (w Cen) is more massive and chemically diverse than M 54, and is thought to have been the nuclear star cluster of either the Sequoia or Gaia-Enceladus galaxy. Local Group dwarf galaxies with masses equivalent to these systems often host significant populations of…
With an unprecedented astrometric and photometric data precision, Gaia EDR3 gives us, for the first time, the opportunity to systematically detect and map in the optical bands, the low mass populations of the star forming regions (SFRs) in the Milky Way. We provide a catalogue of the Gaia EDR3 data (photometry, proper motions and parallaxes) of the young stellar objects (YSOs) identified in the Galactic Plane (|b|<30 deg) within about 1.5 kpc. The catalogue of the SFRs to which they belong is also provided to study the properties of the very young clusters and put them in the context of the Ga…
The Stellar "Snake"-III: Co-evolution of Stars and Molecular Clouds Unveiled by Gaia, MWISP, and LAMOST
School of sciences, HangZhou Dianzi University（杭州电子科技大学理学院）；Zhejiang Branch of National Astronomical Data Center（国家天文台浙江分中心）；Institute of Astronomy and Information, Dali University（大理大学天文与信息学院）；School of Physics and Astronomy, China West Normal University（西华师范大学物理与天文学院）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）
Unveiling the Milky Way with a Gaia DR3 census of OB-type stars within 2 kpc. I. Tracing local Galactic structure, massive star-forming regions and core-collapse supernova progenitors
Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台，巴黎文理研究大学，索邦大学，巴黎西岱大学，CY塞吉-蓬图瓦兹大学，法国国家科学研究中心）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；INAF – Osservatorio Astrofisico di Torino（意大利国家天体物理研究所都灵天文台）；University of Vienna（维也纳大学）；Keele University（基尔大学）；Instituto de Astrofísica de Canarias（加那利天体物理学研究所）；Universidad de La Laguna（拉古纳大学）；European Southern Observatory（欧洲南方天文台）
Unveiling the Sagittarius Dwarf Spheroidal Galaxy Core with Gaia DR3: A Red Clump Distance Precise to 2%
The University of Texas at Austin（德克萨斯大学奥斯汀分校）；Whitman College（惠特曼学院）；Institute for Astronomy, University of Hawai‘i（夏威夷大学天体物理研究所）；Texas Christian University（得克萨斯基督教大学）；Maunakea Spectroscopic Explorer, Canada-France-Hawaii-Telescope（莫纳克亚光谱巡天项目，加拿大法国夏威夷望远镜）
In this paper we report a new estimate of the absolute proper motion (PM) of the globular cluster NGC 5139 ($ω$ Cen) as part of the HST large program GO-14118+14662. We analyzed a field 17 arcmin South-West of the center of $ω$ Cen and computed PMs with an epoch span of $\sim$15.1 years. We employed 45 background galaxies to link our relative PMs to an absolute reference-frame system. The absolute PM of the cluster in our field is: $(μ_α\cosδ, μ_δ) = (-3.341 \pm 0.028 , -6.557 \pm 0.043)$ mas yr$^{-1}$. Upon correction for the effects of viewing perspective and the known cluster rotation, this…
Abbreviated. We aim to identify new low-mass companions to young stars using the astrometric measurements provided by the Gaia space mission and complementary VLT/SPHERE data. We identify companion candidates from a sample of K-type, pre-main sequence stars in the Scorpius Centaurus association using the early version of the third data release of the Gaia space mission. Based on the provided positions, proper motions, and magnitudes, we identify all objects within a predefined radius whose differential proper motions are consistent with a gravitationally bound system. We derive companion masse…
We use Gaia DR2 data to survey the classic Monoceros OB1 region and look for the existence of a dispersed young population, co-moving with the cloud complex. An analysis of the distribution of proper motions reveals a 20-30 Myr association of young stars, about 300-400 pc away from the far side of the Mon OB1 complex, along the same general line-of-sight. We characterize the new association, Monoceros OB4, and estimate it contains between 1400 and 2500 stars, assuming a standard IMF, putting it on par in size with NGC\,2264. We find from the internal proper motions that Mon OB4 is unbound and …
Chromospheres and coronae are common phenomena on solar-type stars. Understanding the energy transfer to these heated atmospheric layers requires direct access to the relevant empirical data. Study of these structures has, by and large, been limited to the Sun thus far. The region of the temperature reversal can be directly observed only in the far infrared and submm. We aim at the determination of the characteristics of the atmosphere in the region of the temperature minimum of the solar sister star alpha Cen A. For the nearby binary system alpha Centauri, stellar parameters are known with hi…
Unveiling $δ$ Scuti and $γ$ Doradus Hybrid Pulsation of HD 53166 and HD 53349 Plus Rich Frequencies in HD 52788 -- Catalogs of 70552 $δ$ Sct and 8080 $γ$ Dor
We investigate the star formation history of the IC1396 region by studying its kinematics and completing the population census. We use multiwavelength data, combining optical spectroscopy (to identify and classify new members), near-infrared photometry (to trace shocks, jets, and outflows and the interactions between the cluster members and the cloud), along with Gaia EDR3 to identify new potential members in the multidimensional proper motion/parallax space. The revised Gaia EDR3 distance is 925$\pm$73 pc, slightly closer than previously obtained with DR2. The Gaia data reveal four distinct s…
We introduce a new kinematic method to investigate the structure of open star clusters. We adopt a hierarchical clustering algorithm that uses the celestial coordinates and the proper motions of the stars in the field of view of the cluster to estimate a proxy of the pairwise binding energy of the stars and arrange them in a binary tree. The cluster substructures and their members are identified by trimming the tree at two thresholds, according to the $σ$-plateau method. Testing the algorithm on 100 mock catalogs shows that, on average, the membership of the identified clusters is $(91.5\pm 3.…
The Gaia-ESO Survey has recently unveiled the complex kinematic signature of the Gamma Velorum cluster: this cluster is composed of two kinematically distinct populations (hereafter, population A and B), showing two different velocity dispersions and a relative ~2 km s^-1 radial velocity (RV) shift. In this paper, we propose that the two populations of the Gamma Velorum cluster originate from two different sub-clusters, born from the same parent molecular cloud. We investigate this possibility by means of direct-summation N-body simulations. Our scenario is able to reproduce not only the RV sh…
Stellar associations can be discerned as overdensities of sources not only in the physical space but also in the velocity space. The common motion of their members, gradually eroded by the galactic tidal field, is partially reminiscent of the initial kinematic structure. Using recent data from Gaia EDR3, combined with radial velocities from GALAH and APOGEE, we traced back the present positions of stars belonging to Upper Scorpius, a subgroup of Scorpius-Centaurus, the nearest OB association. About one half of the subgroup (the "clustered" population) appears composed of many smaller entities,…
The Gaia Sausage is the major accretion event that built the stellar halo of the Milky Way galaxy. Here, we provide dynamical and chemical evidence for a second substantial accretion episode, distinct from the Gaia Sausage. The Sequoia Event provided the bulk of the high energy retrograde stars in the stellar halo, as well as the recently discovered globular cluster FSR 1758. There are up to 6 further globular clusters, including $ω$~Centauri, as well as many of the retrograde substructures in Myeong et al. (2018), associated with the progenitor dwarf galaxy, named the Sequoia. The stellar mas…
We present the methods devised to identify the BY Dra variables candidates in Gaia DR2 and infer their variability parameters. BY Dra candidates are pre-selected from their position in the HR diagram, built from Gaia parallaxes, $G$ magnitudes, and $(G_{BP} - G_{RP})$ colours. Since the time evolution of the stellar active region can disrupt the coherence of the signal, segments not much longer than their expected evolution timescale are extracted from the entire photometric time-series and period search algorithms are applied to each segment. For the Gaia DR2, we select sources having similar…
By exploiting the exceptional high-resolution capabilities of the near-IR camera GSAOI combined with the multi-conjugate adaptive optics system GeMS at the GEMINI South Telescope, we investigated the structural and physical properties of the heavily obscured globular cluster Liller 1 in the Galactic bulge. We have obtained the deepest and most accurate color-magnitude diagram published so far for this cluster, reaching Ks ~ 19 (below the main sequence turn-off level). We used these data to re-determine the center of gravity of the system, finding that it is located about 2.2" south-east from t…
A small fraction of the halo field is made up of stars that share the light element (Z<=13) anomalies characteristic of second generation globular cluster (GC) stars. The ejected stars shed light on the formation of the Galactic halo by tracing the dynamical history of the clusters, which are believed to have once been more massive. Some of these ejected stars are expected to show strong Al enhancement at the expense of shortage of Mg, but until now no such star has been found. We search for outliers in the Mg and Al abundances of the few hundreds of halo field stars observed in the first eigh…
Obscuration and confusion conspire to limit our knowledge of the inner Milky Way. Even at moderate distances, the identification of stellar systems becomes compounded by the extremely high density of background sources. Here we provide a very revealing example of these complications by unveiling a large, massive, young cluster in the Sagittarius arm that has escaped detection until now despite containing more than 30 stars brighter than $G=13$. By combining Gaia DR2 astrometry, Gaia and 2MASS photometry and optical spectroscopy, we find that the new cluster, which we name Valparaiso~1, located…
Nearby stellar streams carry unique information on the dynamical evolution and disruption of stellar systems in the Galaxy, the mass distribution in the disk, and provide unique targets for planet formation and evolution studies. We revisit the stream discovered in Meingast et al (2019) to search for new members, using Gaia DR2 data and a machine learning approach. We use a bagging classifier of one-class Support Vector Machines to perform a search in positions and proper motions for new stream members. We use the variable prediction frequency resulting from the multitude of classifiers to est…
The second Gaia data release contains the identification of 147 535 low-mass ($\le 1.4 M_{\odot}$) rotational modulation variable candidates on (or close to) the main sequence, together with their rotation period and modulation amplitude. The richness, the period and amplitude range, and the photometric precision of this sample make it possible to unveil, for the first time, signatures of different surface inhomogeneity regimes in the amplitude-period density diagram. The modulation amplitude distribution shows a clear bimodality, with an evident gap at periods $P \le 2$ d. The low amplitude b…
Although a large number of Galactic open clusters (OCs) have been identified, the internal kinematic properties (e.g., rotation) of almost all the known OCs are still far from clear. With the high-precision astrometric data of Gaia EDR3, we have developed a methodology to unveil the rotational properties of the Praesepe cluster. Statistics of the three-dimensional residual motions of the member stars reveal the presence of Praesepe's rotation and determine its spatial rotation axis. The mean rotation velocity of the Praesepe cluster within its tidal radius is estimated to be 0.2 $\pm$ 0.05 km …
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…
Gyrochronology is one of the methods currently used to estimate the age of stellar open clusters. Hundreds of new clusters, associations, and moving groups unveiled by Gaia and complemented by accurate rotation period measurements provided by recent space missions such as Kepler and TESS are allowing us to significantly improve the reliability of this method. We use gyrochronology, that is, the calibrated age-mass-rotation relation valid for low-mass stars, to measure the age of the recently discovered moving group Group X. We extracted the light curves of all candidate members from the TESS f…
The binary properties of open clusters place crucial constraints on star formation theory and clusters' dynamical evolution. We develop a comprehensive approach that models the color-magnitude diagram (CMD) of the cluster members as the mixture of single stars and photometric unresolved binaries. This method enables us to infer the binary properties, including the binary fraction $f_\mathrm{b}$ and binary mass-ratio distribution index $γ_q$ when a power-law is assumed, with high accuracy and precision, which were unfeasible in conventional methods. We employ a modified Gaussian process to dete…
Unresolved triple systems in the aged open cluster Trumpler 19: Discovery, confirmation, and implications
Universidad Andres Bello（安德斯贝洛大学）；Vatican Observatory（梵蒂冈天文台）；Universidade Federal de Santa Catarina（圣卡塔琳娜联邦大学）；European Southern Observatory（欧洲南方天文台）；University of Hertfordshire（赫特福德大学）；Universidad Bernardo O’Higgins（贝尔纳多·奥希金斯大学）；Universidad de Antofagasta（安托法加斯塔大学）
