The VVV Survey: Globular Clusters and more

AbstractIn the efforts to map the Milky Way structure, the central regions have remained very difficult to probe. The VISTA Variables in the Vía Láctea Survey (VVV) is a near-IR variability Survey that scans 560 sq.deg. across the Milky Way bulge and an adjacent section of the southern mid-plane. The main goal of the VVV Survey is to build a 3D map of the structure of the inner Galaxy and characterize its stellar populations. This survey has discovered different kinds of objects, such as globular clusters, Microlensing events, RR Lyrae stars, Cepheids, WITs, among others. The extension of the Survey (VVVX) is observing until 2020, tripling the areal coverage, and complementing the variability studies done by the VVV Survey.

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Search for extra-tidal RR Lyrae stars in Milky Way globular clusters fromGaiaDR2

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sty3239 ◽

2018 ◽

Vol 483 (2) ◽

pp. 1737-1743 ◽

Cited By ~ 12

Author(s):

Richa Kundu ◽

Dante Minniti ◽

Harinder P Singh

Keyword(s):

Globular Clusters ◽

Milky Way ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Lyrae Stars

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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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New Views From Galactoseismology: Rethinking the Galactic Disk-Halo Connection

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317006639 ◽

2017 ◽

Vol 13 (S334) ◽

pp. 185-188

Author(s):

Allyson A. Sheffield ◽

Kathryn V. Johnston ◽

Adrian M. Price-Whelan ◽

Anastasios Tzanidakis ◽

Chervin F. P. Laporte ◽

...

Keyword(s):

Formation Mechanism ◽

Milky Way ◽

Galactic Disk ◽

External Perturbation ◽

Stellar Populations ◽

Preliminary Evidence ◽

Low Latitude ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Lyrae Stars

AbstractWe present preliminary results from a study exploring the origin of Milky Way substructures, and show initial evidence of a common “kicked-out” formation mechanism for two low-latitude substructures. In this scenario, stars in these substructures formed in the disk and were subsequently “kicked-out” by an external perturbation, such as the merger of an accreted satellite, which created an oscillation in the Galactic disk. To test this origin scenario, we found the fraction of different stellar populations – M giants and RR Lyrae stars – in the Monoceros Ring (also known as GASS) and A13, supplementing a study of stellar populations in the Triangulum-Andromeda cloud. This work provides: (1) the first analysis of the GASS and A13 features based upon their stellar populations; and (2) preliminary evidence of disk stars in the Milky Way that have been relocated to the disk-halo interface due to vertical oscillations of the Milky Way’s disk.

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RR Lyrae Stars in Globular Clusters

International Astronomical Union Colloquium ◽

10.1017/s025292110005747x ◽

2000 ◽

Vol 176 ◽

pp. 165-171

Author(s):

Alistair R. Walker

Keyword(s):

Globular Clusters ◽

Stellar Populations ◽

Variable Stars ◽

Rr Lyrae Stars ◽

Technical Aspects ◽

Rr Lyrae ◽

Lyrae Stars

AbstractOf the several types of variable stars that occur in globular clusters, RR Lyrae stars have deservedly received the most attention. These stars are ideally suited for comparisons between evolution and pulsation theory, they play a prominent role in distance determinations, and are valuable tracers of the oldest stellar populations. After a brief discussion of technical aspects, we review some of the recent observational work.

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Looking for building blocks of the Galactic halo: variable stars in the Fornax, Bootes I, Canes Venatici II dwarfs and in NGC 2419

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309991530 ◽

2009 ◽

Vol 5 (S266) ◽

pp. 411-411

Author(s):

Claudia Greco ◽

Gisella Clementini ◽

E. V. Held ◽

E. Poretti ◽

M. Catelan ◽

...

Keyword(s):

Galaxy Formation ◽

Globular Clusters ◽

Galactic Halo ◽

Stellar Populations ◽

Variable Stars ◽

Star Formation History ◽

Image Subtraction ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Lyrae Stars

AbstractΛ cold-dark-matter hierarchical models of galaxy formation suggest that the halo of the Milky Way (MW) has been assembled, at least in part, through accretion of protogalactic fragments partially resembling the present-day dwarf spheroidal (dSph) satellites of the MW. Investigation of the stellar populations of the MW's globular clusters (GCs) and dSph companions can thus provide excellent tests to infer the dominant Galaxy-formation scenario, whether merger/accretion or cloud collapse. Pulsating variable stars offer a very powerful tool in this context, since variables of different types allow tracing the different stellar generations in a galaxy and to reconstruct the galaxy's star-formation history and assembly back to the first epochs of galaxy formation. In particular, the RR Lyrae stars, belonging to the old population (t > 10 Gyr), witnessed the epoch of halo formation, and thus hold a crucial role to identify the MW satellites that may have contributed to build up the Galactic halo. In the MW, most GCs with an RR Lyrae population sharply divide into two distinct groups (Oosterhoff types I and II) based on the mean periods and relative proportion of fundamental-mode (RRab) and first-overtone (RRc) RR Lyrae stars. On the other hand, the Galactic-halo field RR Lyrae stars show a dominance of Oosterhoff I properties. Here, we investigate the Oosterhoff properties of a number of different stellar systems, starting from relatively undisturbed dwarf galaxies (the Fornax dSph and its globular clusters), through distorted and tidally disrupting ones (the Bootes and Canes Venatici II dSphs), to possible final relics of the disruption process (the Galactic globular cluster NGC 2419). We are addressing the crucial question of whether the RR Lyrae pulsation properties in these systems conform to the Oosterhoff dichotomy characterizing the MW variables. If they do not, the Galaxy's halo cannot have been assembled by dSph-like protogalactic fragments resembling the present-day dSph companions of the MW. We have reduced and combined long time series from different telescopes, both ground- and space-based. Variable stars have been detected with image-subtraction techniques using the package isis2.1. Periods, amplitudes and Oosterhoff type for all variable stars, as well as color–magnitude diagrams of the stellar populations are discussed for each stellar cluster analyzed.

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General Properties of the Two Groups of Globular Clusters and Their Variable Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900010743 ◽

1975 ◽

Vol 67 ◽

pp. 541-543

Author(s):

A. V. Mironov ◽

N. N. Samus'

Keyword(s):

Chemical Composition ◽

Globular Clusters ◽

Variable Stars ◽

Rr Lyrae Stars ◽

General Properties ◽

Rr Lyrae ◽

Lyrae Stars

The dependences of the numbers of variable stars in globular clusters on the chemical composition are studied. For given metallicity the numbers of RR Lyrae stars reduced to some definite total number of stars in the cluster are different for the two groups of globular clusters introduced by Mironov.

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The Milky Way Revealed by Variable Stars. I. Sample Selection of RR Lyrae Stars and Evidence for Merger History

The Astrophysical Journal Supplement Series ◽

10.3847/1538-4365/ac347f ◽

2022 ◽

Vol 258 (1) ◽

pp. 20

Author(s):

Iminhaji Ablimit ◽

Gang Zhao ◽

Uy. Teklimakan ◽

Jian-Rong Shi ◽

Kunduz Abdusalam

Keyword(s):

Milky Way ◽

Sample Selection ◽

Variable Stars ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Sky Survey ◽

Spectroscopic Information ◽

History Of ◽

Dual Origin ◽

Lyrae Stars

Abstract In order to study the Milky Way, RR Lyrae (RRL) variable stars identified by Gaia, ASAS-SN, and ZTF sky survey projects have been analyzed as tracers in this work. Photometric and spectroscopic information of 3417 RRLs including proper motions, radial velocity, and metallcity are obtained from observational data of Gaia, LAMOST, GALAH, APOGEE, and RAVE. Precise distances of RRLs with typical uncertainties less than 3% are derived by using a recent comprehensive period–luminosity–metallicity relation. Our results from kinematical and chemical analysis provide important clues for the assembly history of the Milky Way, especially for the Gaia–Sausage ancient merger. The kinematical and chemical trends found in this work are consistent with those of recent simulations that indicated that the Gaia–Sausage merger had a dual origin in the Galactic thick disk and halo. As recent similar works have found, the halo RRL sample in this work contains a subset of radially biased orbits besides a more isotropic component. This higher orbital anisotropy component amounts to β ≃ 0.8, and it contributes between 42% and 83% of the halo RRLs at 4 < R( kpc) < 20.

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On the Two Oosterhoff Groups of Globular Clusters

International Astronomical Union Colloquium ◽

10.1017/s0252921100033522 ◽

1973 ◽

Vol 21 ◽

pp. 196-196

Author(s):

T. S. Van Albada ◽

Norman Baker

Keyword(s):

Stellar Evolution ◽

Globular Clusters ◽

Transition Point ◽

Transition Period ◽

Observational Evidence ◽

Horizontal Branch ◽

Average Difference ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Lyrae Stars

AbstractThe observational evidence leading to the classification, following Oosterhoff, of globular clusters containing RR Lyrae stars into two distinct groups, is summarized and discussed in the light of results of stellar evolution theory and pulsation theory. The dichotomy is caused, at least in part, by a dichotomy in the ‘transition period’ between the type-ab and type-c stars which reflects a difference in effective temperature at the transition point. When this difference is accounted for, there remains a smaller average difference between the groups, though no longer a clear dichotomy, that is probably a mass and luminosity effect. If this remaining difference is interpreted as a luminosity effect the average difference in luminosity between the two Oosterhoff groups is at most 0.1 mag. It is suggested that Christy’s theoretical relationship between transition period and luminosity cannot be valid, at least not for clusters of different Oosterhoff groups. It is conjectured that the transition-temperature dichotomy may be a reflection of different predominant directions of evolution along the horizontal branch, accompanied by a hysteresis effect in the pulsations.

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Search for Variables in the Galactic Globular Clusters NGC 6544 and NGC 6642

International Astronomical Union Colloquium ◽

10.1017/s0252921100117774 ◽

1993 ◽

Vol 139 ◽

pp. 337-337

Author(s):

Martha L. Hazen

Keyword(s):

Globular Clusters ◽

Slow Variable ◽

Variable Stars ◽

Horizontal Branch ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

A Value ◽

Short Period ◽

Period Variable ◽

Lyrae Stars

A search for variable stars in the globular cluster NGC 6544 has revealed only one possible short period variable within the tidal radius of the cluster. A search in NGC 6642 yielded 16 new RR Lyrae stars within the tidal radius and 5 new field RRs. The previously discovered (Hoffleit 1972) V1 is a slow variable, and V2 is an RR Lyrae star. Photometry of the variables within the tidal radius gives a mean B for the horizontal branch of < B > = 17.0 mag. With E(B – V) = 0.37 mag and (B – V) = 0.35 mag for RR Lyraes, a value for V(HB) = 16.3 mag is derived. This is about one mag fainter than previous estimates (Webbink 1985), and places NGC 6642 at a distance of approximately 7.9 kpc.

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