Globular clusters in the inner Galaxy classified from dynamical orbital criteria

Abstract Globular clusters (GCs) are the most ancient stellar systems in the Milky Way. Therefore, they play a key role in the understanding of the early chemical and dynamical evolution of our Galaxy. Around 40% of them are placed within ∼4 kpc from the Galactic center. In that region, all Galactic components overlap, making their disentanglement a challenging task. With Gaia DR2, we have accurate absolute proper motions for the entire sample of known GCs that have been associated with the bulge/bar region. Combining them with distances, from RR Lyrae when available, as well as radial velocities from spectroscopy, we can perform an orbital analysis of the sample, employing a steady Galactic potential with a bar. We applied a clustering algorithm to the orbital parameters apogalactic distance and the maximum vertical excursion from the plane, in order to identify the clusters that have high probability to belong to the bulge/bar, thick disk, inner halo, or outer halo component. We found that $\sim 30\%$ of the clusters classified as bulge GCs based on their location are just passing by the inner Galaxy, they appear to belong to the inner halo or thick disk component, instead. Most of GCs that are confirmed to be bulge GCs are not following the bar structure and are older than the epoch of the bar formation.

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Detailed study of the Milky Way globular cluster Laevens 3

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2592 ◽

2019 ◽

Vol 490 (2) ◽

pp. 1498-1508

Author(s):

Nicolas Longeard ◽

Nicolas Martin ◽

Rodrigo A Ibata ◽

Michelle L M Collins ◽

Benjamin P M Laevens ◽

...

Keyword(s):

Globular Cluster ◽

Globular Clusters ◽

Milky Way ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Magnitude Diagram ◽

Mass Segregation ◽

Stellar Properties ◽

Lyrae Stars ◽

Gaia Dr2

ABSTRACT We present a photometric and spectroscopic study of the Milky Way satellite Laevens 3. Using MegaCam/Canada–France–Hawaii Telescope $g$ and $i$ photometry and Keck II/DEIMOS multi-object spectroscopy, we refine the structural and stellar properties of the system. The Laevens 3 colour–magnitude diagram shows that it is quite metal-poor, old ($13.0 \pm 1.0$ Gyr), and at a distance of $61.4 \pm 1.0$ kpc, partly based on two RR Lyrae stars. The system is faint ($M_V = -2.8^{+0.2}_{-0.3}$ mag) and compact ($r_h = 11.4 \pm 1.0$ pc). From the spectroscopy, we constrain the systemic metallicity (${\rm [Fe/H]}_\mathrm{spectro} = -1.8 \pm 0.1$ dex) but the metallicity and velocity dispersions are both unresolved. Using Gaia DR2, we infer a mean proper motion of $(\mu _\alpha ^*,\mu _\delta)=(0.51 \pm 0.28,-0.83 \pm 0.27)$ mas yr−1, which, combined with the system’s radial velocity ($\langle v_r\rangle = -70.2 \pm 0.5 {\rm \, km \,\, s^{-1}}$), translates into a halo orbit with a pericenter and apocenter of $40.7 ^{+5.6}_{-14.7}$ and $85.6^{+17.2}_{-5.9}$ kpc, respectively. Overall, Laevens 3 shares the typical properties of the Milky Way’s outer halo globular clusters. Furthermore, we find that this system shows signs of mass segregation that strengthens our conclusion that Laevens 3 is a globular cluster.

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Search for variable stars in globular clusters

Symposium - International Astronomical Union ◽

10.1017/s0074180900151538 ◽

1986 ◽

Vol 118 ◽

pp. 287-288

Author(s):

M. L. Hazen-Liller

Keyword(s):

Globular Clusters ◽

Galactic Center ◽

Variable Stars ◽

Galactic Bulge ◽

Rr Lyrae ◽

High Metallicity

A program to search poorly studied southern globular clusters for variable stars is being carried out on the 1-m Yale telescope at CTIO. Recently two galactic bulge clusters of moderately high metallicity have been found to contain RR Lyrae variables; a cluster of similar metallicity a little farther from the galactic center apparently has none.

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Radial velocities with CORAVEL: results on stellar variability and duplicity

Symposium - International Astronomical Union ◽

10.1017/s0074180900151770 ◽

1986 ◽

Vol 118 ◽

pp. 385-400

Author(s):

G. Burki ◽

M. Mayor

Keyword(s):

Dynamical Evolution ◽

Distribution Functions ◽

Open Clusters ◽

Formation Mechanisms ◽

Radial Velocity Curve ◽

Stellar Radius ◽

Orbital Parameters ◽

Pulsating Stars ◽

Rr Lyrae ◽

The Galaxy

The complete radial velocity curve has been determined with CORAVEL for many pulsating stars of various classes: cepheid stars in the Galaxy and in the Magellanic Clouds, RR Lyrae, δ Scuti and SX Phoenicis stars. These measurements allow the determination of the radius variation and of the surface acceleration of these stars. In addition, the mean stellar radius of many of these stars has been determined by applying the Baade-Wesselink method.Systematic surveys of definite groups of binary or multiple stars are in progress with CORAVEL in order to determine the distribution functions of the orbital parameters. The eccentricity distributions for the binaries in the open clusters Pleiades, Praesepe, Coma Ber and Hyades are presented and their dependence on the physical processes (star formation mechanisms, mass exchange, tidal circularization, dynamical evolution) is briefly discussed.

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MOCCA Survey Database: Extra Galactic Globular Clusters. I. Method and first results

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa4027 ◽

2021 ◽

Author(s):

A Leveque ◽

M Giersz ◽

M Paolillo

Keyword(s):

Globular Clusters ◽

Surface Brightness ◽

Velocity Dispersion ◽

Structural Parameters ◽

Dynamical Evolution ◽

Central Surface ◽

First Results ◽

Preliminary Study ◽

Galactic Globular Clusters ◽

Gaia Dr2

Abstract Over the last few decades, exhaustive surveys of extra Galactic globular clusters (EGGCs) have become feasible. Only recently, limited kinematical information of globular clusters (GCs) were available through Gaia DR2 spectroscopy and also proper motions. On the other hand, simulations of GCs can provide detailed information about the dynamical evolution of the system. We present a preliminary study of EGGCs- properties for different dynamical evolutionary stages. We apply this study to 12 Gyr-old GCs simulated as part of the MOCCA Survey Database. Mimicking observational limits, we consider only a subssample of the models in the database, showing that it is possible to represent observed Milky Way GCs. In order to distinguish between different dynamical states of EGGCs, at least three structural parameters are necessary. The best distinction is achieved by considering the central parameters, those being observational core radius, central surface brightness, ratio between central and half-mass velocity dispersion, or similarly considering the central color, the central V magnitude and the ratio between central and half-mass radius velocity dispersion, although such properties could be prohibitive with current technologies. A similar but less solid result is obtained considering the average properties at the half-light radius, perhaps accessible presently in the Local Group. Additionally, we mention that the color spread in EGGCs due to internal dynamical models, at fixed metallcity, could be just as important due to the spread in metallicity.

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The circular velocity at the sun

Symposium - International Astronomical Union ◽

10.1017/s0074180900014510 ◽

1979 ◽

Vol 84 ◽

pp. 225-230

Author(s):

G. R. Knapp

Keyword(s):

Globular Clusters ◽

Galactic Center ◽

Solar Rotation ◽

Center Of Mass ◽

Rotation Velocity ◽

Current Evidence ◽

Galactic Rotation ◽

The Sun ◽

Galactocentric Distance ◽

Rr Lyrae

The galactic rotation velocity at the Sun, , can be derived several ways, none of them direct and unambiguous - (1) the solar velocity can be found relative to the halo population (the RR Lyrae stars, globular clusters etc.), but may contain an unknown contribution from possible systematic rotation of the halo system (2) the product Ro ω(Ro) = Ro (A-B) can be calculated but is uncertain because of large uncertainties in each of these three quantities (3) the motion of the Sun with respect to the center of the Local Group can be found but includes the motion of the galactic center of mass and (4) the velocity-longitude dependence of the outer HI boundary can be examined to deduce the most likely value of . The incorporation of new data into analyses using methods (1) and (3) gives essentially the same answers as older studies. Examination of the accumulated current evidence suggests that the best values for the solar rotation velocity and the galactocentric distance Ro are 220 km s−1 and 8.5 kpc respectively.

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The Luminosity-Metallicity Relation for RR Lyrae Stars and its Implications for the Astronomical Distance Scale

International Astronomical Union Colloquium ◽

10.1017/s0252921100011635 ◽

1989 ◽

Vol 111 ◽

pp. 255-255

Author(s):

G. Clementini ◽

C. Cacciari

Keyword(s):

Globular Clusters ◽

Galactic Center ◽

Absolute Magnitude ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Visual Magnitude ◽

Phase Range ◽

The Absolute ◽

Lyrae Stars ◽

Magnitude Difference

AbstractThe surface brightness version of the Baade-Wesselink method, has been applied to 7 field RR Lyrae stars with metallicity ranging from [Fe/H]= −0.2 to −1.5. V magnitudes, V-R and V-I colors and CORAVEL radial velocities were used, and the analysis was performed over a restricted phase range in order to avoid the complications caused by the pulsating atmospheres. The combination with previous results of the B-W method, which used comparable criteria (Jones, Carney, & Latham, 1988, preprint; Jameson, Fernley, & Longmore 1987, in press M.N.R.A.S; Cohen & Gordon 1987, Ap.J., 318, 215) leads to the following relation between the absolute luminosity and metallicity:Mv = (1.0 ± 0.05) + (0.17 ± 0.05) [Fe/H]This relation is in very good agreement with the preliminary results found by Liu and Janes (this volume). The application of the above relation to the RR Lyraes in M31 and the Magellanic Clouds leads to distance moduli of (m–M)o= 24.21 ± 0.20 for M31, (m–M)o = 18.26 ± 0.20 for the LMC, and (m–M)o =18.85 ± 0.20 for the SMC, and the distance to the galactic center turns out to be approximately 7.2 kpc. From the absolute magnitude of the RR Lyraes and adopting a constant visual magnitude difference between the RR Lyraes and the turn-off ΔV = 3.55 (Buonanno 1986, Mem.S.A.It., 57, 333), we estimate ages of 18.8 and 15.7 Gyr for globular clusters of metallicity [Fe/H] = −2.2 (e.g. M92) and [Fe/H] = −0.8 (e.g. 47 Tuc) respectively, using the age-turnoff luminosity relation derived by Sandage (1982, Ap.J., 252, 553) or 20.9 and 16.9 Gyr using Buonanno’s relation.

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Mapping the Stellar Distribution in Globular Clusters: An Application to NGC 6809 = M55

Symposium - International Astronomical Union ◽

10.1017/s007418090010926x ◽

1995 ◽

Vol 164 ◽

pp. 409-409

Author(s):

S. R. Zaggia ◽

G. Piotto ◽

M. Capaccioli

Keyword(s):

Globular Clusters ◽

Galactic Center ◽

Galactic Disk ◽

Dynamical Evolution ◽

Mass Function ◽

Blue Stragglers ◽

Set Constraints ◽

Central Regions ◽

Single Mass ◽

The Rich

The principal aim of this work is to map the stellar distribution of a large sample of galactic globular clusters from the central regions to the outer envelope (beyond the tidal radius for an estimate of the foreground/background contamination) with a good statistical sampling of stars in the different branches of the color-magnitude diagram and with different masses. These new data will be used to investigate the dynamical evolution of stellar systems embedded in the gravitational field of our Galaxy, and, eventually, to set constraints on the mass distribution of the Milky Way. In this context, star counts have been carried out on V and I CCD frames of the rich, low concentration galactic globular cluster M55. The frames cover 35% of the cluster, from the center to 1.3 times the tidal radius (with total coverage inside 1rc). From V=14 (i.e. the horizontal branch level) to a limiting magnitude V=22 (MV = 7.9), a total of 36800 stars have been measured. A population of blue stragglers (BS) has been identified, but, at variance with other clusters of similar core concentration, the BS of M55 are only marginally more concentrated toward the center. No population gradient has been identified in M55. A luminosity function down to V = 21.3 has been obtained, after applying completeness and field star contamination correction to the star counts. The mass function is very flat (xglobal ≤ −0.5), as it was expected for this cluster located close to the galactic center and to the galactic disk. A single mass King model fitted to the radial star counts gives a core radius rc = 143″ and a tidal radius rt = 970″, ~ 10% greater than previously estimated.

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Fourier Coefficients of OGLE Variables

International Astronomical Union Colloquium ◽

10.1017/s0252921100057869 ◽

2000 ◽

Vol 176 ◽

pp. 275-275

Author(s):

Siobahn Morgan ◽

Melanie Simet ◽

Stephanie Bargenquast ◽

Chris Dickerson

Keyword(s):

Globular Clusters ◽

Fourier Coefficients ◽

Galactic Center ◽

Variable Stars ◽

Physical Characteristics ◽

Rr Lyrae ◽

Made In

AbstractFourier coefficients for the variable stars in the OGLE survey of the Galactic Center and several globular clusters are presented. The characteristics of the RR Lyrae, δ Scuti and SX Phe stars are presented and a comparison to those observed in other studies is made. In some cases the coefficients of the stars can be used to determine distances and the physical characteristics of the variables.

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Another relic bulge globular cluster: ESO 456-SC38 (Djorgovski 2)

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935726 ◽

2019 ◽

Vol 627 ◽

pp. A145 ◽

Cited By ~ 6

Author(s):

S. Ortolani ◽

E. V. Held ◽

D. Nardiello ◽

S. O. Souza ◽

B. Barbuy ◽

...

Keyword(s):

Globular Clusters ◽

Stellar Population ◽

Milky Way ◽

Galactic Center ◽

Horizontal Branch ◽

Very Old ◽

Orbital Parameters ◽

Data Release ◽

Best Fitting ◽

Bulge Formation

Context. The object ESO 456-SC38 (Djorgovski 2) is one of the globular clusters that is closest to the Galactic center. It is on the blue horizontal branch and has a moderate metallicity of [Fe/H] ∼ −1.0. It is thus similar to the very old inner bulge globular clusters NGC 6522, NGC 6558, and HP 1, and therefore appears to be part of the primeval formation stages of the Milky Way. Aims. The aim of this work is to determine an accurate distance and metallicity for ESO 456-SC38, as well as orbital parameters, in order to check similarities with other clusters in the inner bulge that have previously been well studied in terms of spectroscopy and photometry. This is a considerably fainter cluster that is contaminated by a rich stellar field; it is also quite absorbed by the dusty foreground. Methods. We analyzed ESO 456-SC38 based on HST photometry, with the filters F606W from ACS, F110W and F160W from WFC3, and photometry in V and I from FORS2 at the VLT. We combined this with identified stars that are covered by Gaia Data Release 2. Results. The isochrone fitting was carried out with the statistical Markov chain Monte Carlo method. We derive an accurate distance of d⊙ = 8.75 ± 0.12 kpc and a reddening of E(B−V) = 0.81+0.02−0.02. The best-fitting BaSTI isochrones correspond to an age of 12.70+0.72−0.69 Gyr and a metallicity of [Fe/H] = −1.11+0.03−0.03. Conclusions. ESO 456-SC38 adds to the list of moderately metal-poor globular clusters located in the inner bulge. It has a blue horizontal branch and is very old. The cluster is confined to the bulge and bar region, but it does not support the Galactic bar structure. The old stellar population represented by clusters like this has to be taken into account in models of Galactic bulge formation. Studying them also provides indications on the formation times of the globular clusters themselves.

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Identifying stellar streams in Gaia DR2 with data mining techniques

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3479 ◽

2019 ◽

Vol 492 (1) ◽

pp. 1370-1384 ◽

Cited By ~ 5

Author(s):

Nicholas W Borsato ◽

Sarah L Martell ◽

Jeffrey D Simpson

Keyword(s):

Data Mining ◽

Globular Clusters ◽

Dwarf Galaxy ◽

Large Data ◽

Data Sets ◽

Integral Of Motion ◽

Data Mining Techniques ◽

Orbital Parameters ◽

Stellar Streams ◽

Gaia Dr2

ABSTRACT Streams of stars from captured dwarf galaxies and dissolved globular clusters are identifiable through the similarity of their orbital parameters, a fact that remains true long after the streams have dispersed spatially. We calculate the integrals of motion for 31 234 stars, to a distance of 4 kpc from the Sun, which have full and accurate 6D phase space positions in the Gaia DR2 catalogue. We then apply a novel combination of data mining, numerical, and statistical techniques to search for stellar streams. This process returns five high confidence streams (including one which was previously undiscovered), all of which display tight clustering in the integral of motion space. Colour–magnitude diagrams indicate that these streams are relatively simple, old, metal-poor populations. One of these resolved streams shares very similar kinematics and metallicity characteristics with the Gaia-Enceladus dwarf galaxy remnant, but with a slightly younger age. The success of this project demonstrates the usefulness of data mining techniques in exploring large data sets.

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