scholarly journals A stellar census in globular clusters with MUSE: Binaries in NGC 3201

2019 ◽  
Vol 632 ◽  
pp. A3 ◽  
Author(s):  
Benjamin Giesers ◽  
Sebastian Kamann ◽  
Stefan Dreizler ◽  
Tim-Oliver Husser ◽  
Abbas Askar ◽  
...  
Keyword(s):  
Black Hole ◽  
Binary System ◽  
Radial Velocity ◽  
Binary Stars ◽  
Globular Clusters ◽  
Spectroscopic Properties ◽  
Spectroscopic Studies ◽  
The Core ◽  
Blue Straggler ◽  
Mass Segregation

We utilise multi-epoch MUSE spectroscopy to study binary stars in the core of the Galactic globular cluster NGC 3201. Our sample consists of 3553 stars with 54 883 spectra in total comprising 3200 main-sequence stars up to 4 magnitudes below the turn-off. Each star in our sample has between 3 and 63 (with a median of 14) reliable radial velocity measurements within five years of observations. We introduce a statistical method to determine the probability of a star showing radial velocity variations based on the whole inhomogeneous radial velocity sample. Using HST photometry and an advanced dynamical MOCCA simulation of this specific cluster we overcome observational biases that previous spectroscopic studies had to deal with. This allows us to infer a binary frequency in the MUSE field of view and enables us to deduce the underlying true binary frequency of (6.75 ± 0.72)% in NGC 3201. The comparison of the MUSE observations with the MOCCA simulation suggests a large portion of primordial binaries. We can also confirm a radial increase in the binary fraction towards the cluster centre due to mass segregation. We discovered that in the core of NGC 3201 at least (57.5 ± 7.9)% of blue straggler stars are in a binary system. For the first time in a study of globular clusters, we were able to fit Keplerian orbits to a significant sample of 95 binaries. We present the binary system properties of eleven blue straggler stars and the connection to SX Phoenicis-type stars. We show evidence that two blue straggler formation scenarios, the mass transfer in binary (or triple) star systems and the coalescence due to binary-binary interactions, are present in our data. We also describe the binary and spectroscopic properties of four sub-subgiant (or red straggler) stars. Furthermore, we discovered two new black hole candidates with minimum masses (M sin i) of (7.68 ± 0.50) M⊙, (4.4 ± 2.8) M⊙, and refine the minimum mass estimate on the already published black hole to (4.53 ± 0.21) M⊙. These black holes are consistent with an extensive black hole subsystem hosted by NGC 3201.

scholarly journals Central Dynamics of Globular Clusters: the Case for a Black Hole in ω Centauri

2007 ◽  
Vol 3 (S246) ◽  
pp. 341-345
Author(s):  
Eva Noyola ◽  
Karl Gebhardt ◽  
Marcel Bergmann
Keyword(s):  
Black Hole ◽  
Relaxation Time ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Dwarf Galaxy ◽  
Kinematic Data ◽  
The Core ◽  
Galactic System ◽  
Interesting Candidate ◽  
Radial Anisotropy

AbstractThe globular cluster ω Centauri is one of the largest and most massive members of the Galactic system. Its classification as a globular cluster has been challenged making it a candidate for being the stripped core of an accreted dwarf galaxy; this and the fact that it has one of the largest velocity dispersions for star clusters in our galaxy makes it an interesting candidate for harboring an intermediate mass black hole. We measure the surface brightness profile from integrated light on an HST/ACS image, and find a central power-law cusp of logarithmic slope -0.08. We also analyze Gemini GMOS-IFU kinematic data for a 5”x5” field centered on the nucleus of the cluster, as well as for a field 14″ away. We detect a clear rise in the velocity dispersion from 18.6 kms−1 at 14″ to 23 kms−1 in the center. Given the very large core in ω Cen (2.58'), an increase in the dispersion in the central 10″ is difficult to attribute to stellar remnants, since it requires too many dark remnants and the implied configuration would dissolve quickly given the relaxation time in the core. However, the increase could be consistent with the existence of a central black hole. Assuming a constant M/L for the stars within the core, the dispersion profile from these data and data at larger radii implies a black hole mass of 4.0+0.75−1.0×104M⊙. We have also run flattened, orbit-based models and find a similar mass. In addition, the no black hole case for the orbit model requires an extreme amount of radial anisotropy, which is difficult to preserve given the short relaxation time of the cluster.

scholarly journals Slow decline and rise of the broad [O iii] emission line in globular cluster black hole candidate RZ2109

2019 ◽  
Vol 489 (4) ◽  
pp. 4783-4790 ◽  
Author(s):  
Kristen C Dage ◽  
Stephen E Zepf ◽  
Arash Bahramian ◽  
Jay Strader ◽  
Thomas J Maccarone ◽  
...  
Keyword(s):  
Black Hole ◽  
Emission Line ◽  
Globular Clusters ◽  
X Ray ◽  
Hydrogen Emission ◽  
Black Hole Candidate ◽  
The Core ◽  
Spectroscopic Monitoring ◽  
Slow Decline ◽  
Over Time

ABSTRACT RZ2109 is the first of several extragalactic globular clusters shown to host an ultraluminous X-ray source. RZ2109 is particularly notable because optical spectroscopy shows it has broad, luminous [O iii] λλ4959,5007 emission, while also having no detectable hydrogen emission. The X-ray and optical characteristics of the source in RZ2109 make it a good candidate for being a stellar mass black hole accreting from a white dwarf donor (i.e. an ultracompact black hole X-ray binary). In this paper we present optical spectroscopic monitoring of the [O iii]5007 emission line from 2007 to 2018. We find that the flux of the emission line is significantly lower in recent observations from 2016 to 2018 than it was in earlier observations in 2007–2011. We also explore the behaviour of the emission line shape over time. Both the core and the wings of the emission line decline over time, with some evidence that the core declines more rapidly than the wings. However, the most recent observations (in 2019) unexpectedly show the emission line core rebrightening

scholarly journals The Formation and Evolution of LMC Globular Clusters: The Database

1999 ◽  
Vol 190 ◽  
pp. 460-461 ◽  
Author(s):  
S. F. Beaulieu ◽  
R. Elson ◽  
G. Gilmore ◽  
R. A. Johnson ◽  
N. Tanvir ◽  
...  
Keyword(s):  
Binary Stars ◽  
Globular Clusters ◽  
Star Clusters ◽  
Data Set ◽  
Luminosity Functions ◽  
Formation And Evolution ◽  
Mass Segregation ◽  
Large Cycle

We present details of the database from a large Cycle 7 HST project to study the formation and evolution of rich star clusters in the LMC (see Elson et al., this volume). Our data set, which includes NICMOS, WFPC2 and STIS images of 8 clusters, will enable us to derive deep luminosity functions for the clusters and to investigate the universality of the stellar IMF. We will look for age spreads in the youngest clusters, quantify the population of binary stars in the cores of the clusters and at the half-mass radii, and follow the development of mass segregation.

scholarly journals Stellar Exotica in 47 Tucanae

2007 ◽  
Vol 3 (S246) ◽  
pp. 321-325
Author(s):  
C. Knigge ◽  
A. Dieball ◽  
J. Maíz-Apellániz ◽  
K. S. Long ◽  
D. R. Zurek ◽  
...  
Keyword(s):  
Binary System ◽  
White Dwarf ◽  
Broad Band ◽  
Cataclysmic Variables ◽  
Ultraviolet Spectroscopy ◽  
The Core ◽  
Blue Straggler ◽  
Far Ultraviolet

AbstractWe have used far-ultraviolet spectroscopy and broad-band photometry to identify and study dynamically-formed stellar exotica in the core of 47 Tucanane. Here, we present a subset of our main results, including: (i) the spectroscopic confirmation of three cataclysmic variables; (ii) the discovery of stripped sub-giant core in a binary system with a dark primary; (iii) the discovery of a Helium white dwarf; (iv) the discovery of a blue straggler with a white dwarf companion.

scholarly journals Discovery of a nitrogen-enhanced mildly metal-poor binary system: Possible evidence for pollution from an extinct AGB star

2019 ◽  
Vol 631 ◽  
pp. A97 ◽  
Author(s):  
José G. Fernández-Trincado ◽  
Ronald Mennickent ◽  
Mauricio Cabezas ◽  
Olga Zamora ◽  
Sarah L. Martell ◽  
...  
Keyword(s):  
Binary System ◽  
Radial Velocity ◽  
Globular Clusters ◽  
Near Infrared ◽  
Asymptotic Giant Branch ◽  
Main Element ◽  
Large Variability ◽  
Asymptotic Giant Branch Star ◽  
Red Giant ◽  
Branch Star

We report the serendipitous discovery of a nitrogen-rich, mildly metal-poor ([Fe/H] = −1.08) giant star in a single-lined spectroscopic binary system found in the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) survey, Data Release 14 (DR14). Previous work has assumed that two percent of halo giants with unusual elemental abundances have been evaporated from globular clusters, but other origins for their abundance signatures, including binary mass transfer, must also be explored. We present the results of an abundance reanalysis of the APOGEE-2 high-resolution near-infrared spectrum of 2M12451043+1217401 with the Brussels Automatic Stellar Parameter (BACCHUS) automated spectral analysis code. We manually re-derive the main element families, namely light elements (C, N), elements (O, Mg, Si), the iron-peak element (Fe), s-process element (Ce), and light odd-Z element (Al). Our analysis confirms the N-rich nature of 2M12451043+1217401, which has a [N/Fe] ratio of +0.69, and shows that the abundances of C and Al are slightly discrepant from those of a typical mildly metal-poor red giant branch star, but exhibit Mg, Si, O and s-process abundances (Ce) of typical field stars. We also detect a particularly large variability in the radial velocity of this star over the period of the APOGEE-2 observations; the most likely orbit fit to the radial velocity data has a period of 730.89  ±  106.86 days, a velocity semi-amplitude of 9.92  ±  0.14 km s−1, and an eccentricity of ∼0.1276  ±  0.1174. These data support the hypothesis of a binary companion, which has probably been polluted by a now-extinct asymptotic giant branch star.

scholarly journals The black hole retention fraction in star clusters

2018 ◽  
Vol 617 ◽  
pp. A69 ◽  
Author(s):  
Václav Pavlík ◽  
Tereza Jeřábková ◽  
Pavel Kroupa ◽  
Holger Baumgardt
Keyword(s):  
Binary Stars ◽  
Globular Clusters ◽  
Dwarf Galaxies ◽  
Star Clusters ◽  
One Dimensional ◽  
Mass Segregation ◽  
The One ◽  
Good Agreement ◽  
Effective Distribution ◽  
Retention Fraction

Context. Recent research has been constraining the retention fraction of black holes (BHs) in globular clusters by comparing the degree of mass segregation with N-body simulations. They are consistent with an upper limit of the retention fraction being 50% or less. Aims. In this work, we focus on direct simulations of the dynamics of BHs in star clusters. We aim to constrain the effective distribution of natal kicks that BHs receive during supernova (SN) explosions and to estimate the BH retention fraction.Methods. We used the collisional N-body code nbody6 to measure the retention fraction of BHs for a given set of parameters, which are: the initial mass of a star cluster, the initial half-mass radius, and σBH, which sets the effective Maxwellian BH velocity kick distribution. We compare these direct N-body models with our analytic estimates and newest observational constraints. Results. The numerical simulations show that for the one-dimensional velocity kick dispersion σBH < 50 km s−1, clusters with radii of 2 pc and that are initially more massive than 5 × 103 M⊙ retain more than 20% of BHs within their half-mass radii. Our simple analytic model yields a number of retained BHs that is in good agreement with the N-body models. Furthermore, the analytic estimates show that ultra-compact dwarf galaxies should have retained more than 80% of their BHs for σBH ≤ 190 km s−1. Although our models do not contain primordial binaries, in the most compact clusters with 103 stars, we have found evidence of delayed SN explosions producing a surplus of BHs compared to the IMF due to dynamically formed binary stars. These cases do not occur in the more populous or expanded clusters.

scholarly journals The correlation between blue straggler and binary fractions in the core of Galactic globular clusters

2008 ◽  
Vol 481 (3) ◽  
pp. 701-704 ◽  
Author(s):  
A. Sollima ◽  
B. Lanzoni ◽  
G. Beccari ◽  
F. R. Ferraro ◽  
F. Fusi Pecci
Keyword(s):  
Globular Clusters ◽  
The Core ◽  
Blue Straggler ◽  
Galactic Globular Clusters

scholarly journals Features of globular cluster’s dynamics with an intermediate-mass black hole

2018 ◽  
Vol 27 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Marina V. Ryabova ◽  
Alena S. Gorban ◽  
Yuri A. Shchekinov ◽  
Evgenii O. Vasiliev
Keyword(s):  
Black Hole ◽  
Binary System ◽  
Globular Cluster ◽  
Binary Stars ◽  
Stellar Mass ◽  
Core Collapse ◽  
Intermediate Mass

Abstract In this paper, we address the question of how a central intermediate-mass black hole (IMBH) in a globular cluster (GC) affects dynamics, core collapse, and formation of the binary population. It is shown that the central IMBH forms a binary system that affects dynamics of stars in the cluster significantly. The presence of an intermediate-mass black hole with mass ≥ 1.0-1.7%of the total stellar mass in the cluster inhibits the formation of binary stars population.

scholarly journals Blue straggler populations of seven open clusters with Gaia DR2

2020 ◽  
Vol 496 (2) ◽  
pp. 2402-2421
Author(s):  
Kaushar Vaidya ◽  
Khushboo K Rao ◽  
Manan Agarwal ◽  
Souradeep Bhattacharya
Keyword(s):  
Relaxation Time ◽  
Systematic Study ◽  
Globular Clusters ◽  
Open Clusters ◽  
Core Radius ◽  
The Core ◽  
Blue Straggler ◽  
Cluster Age ◽  
Gaia Dr2 ◽  
Cluster Correlation

ABSTRACT Blue straggler stars (BSS) are well studied in globular clusters but their systematic study with secure membership determination is lacking in open clusters. We use Gaia DR2 data to determine accurate stellar membership for four intermediate-age open clusters, namely Melotte 66, NGC 2158, NGC 2506, and NGC 6819, and three old open clusters, namely, Berkeley 39, NGC 188, and NGC 6791, to subsequently study their BSS populations. The BSS radial distributions of five clusters, namely Melotte 66, NGC 188, NGC 2158, NGC 2506, and NGC 6791, show bimodal distributions, placing them with Family II globular clusters that are of intermediate dynamical ages. The location of minima, rmin, in the bimodal BSS radial distributions, varies from 1.5rc to 4.0rc, where rc is the core radius of the clusters. We find a positive correlation between rmin and Nrelax, the ratio of cluster age to the current central relaxation time of the cluster. We further report that this correlation is consistent in its slope, within the errors, with the slope of the globular cluster correlation between the same quantities, but with a slightly higher intercept. This is the first example in open clusters that shows BSS radial distributions as efficient probes of dynamical age. The BSS radial distributions of the remaining two clusters, Berkeley 39 and NGC 6819, are flat. The estimated Nrelax values of these two clusters, however, indicate that they are dynamically evolved. Berkeley 39 especially has its entire BSS population completely segregated to the inner regions of the cluster.

scholarly journals Binaries in Globular Clusters

1998 ◽  
Vol 11 (2) ◽  
pp. 616-621 ◽  
Author(s):  
S. L. W. Mcmillan ◽  
C. Pryor ◽  
E. S. Phinney
Keyword(s):  
Kinetic Energy ◽  
Globular Cluster ◽  
Binary Stars ◽  
Formation Process ◽  
Globular Clusters ◽  
The Other ◽  
Energy Distributions ◽  
Other Hand ◽  
Mass Segregation ◽  
Three Body

Binary stars in a globular cluster (hereafter, GC) may be primordial (i.e. formed along with the cluster), or the result of cluster dynamics. “Dynamical” binaries can result from conservative three-body encounters (e.g. Spitzer, 1987) if a third star can carry away enough kinetic energy to leave two others bound, or from dissipative two-body encounters, if two stars happen to pass within a few stellar radii of one other (Fabian, Pringle, & Rees, 1975). Such non-primordial systems are likely to be found primarily in evolved GC cores, both because conditions are more favorable for making them there, and because of mass segregation. Knowledge of the formation process allows reasonable estimates to be made of their mass and energy distributions. The initial spatial, mass, and energy distributions of primordial binaries, on the other hand, are largely unknown.

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