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

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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The ACS LCID project: Variable stars as tracers of population gradients

Proceedings of the International Astronomical Union ◽

10.1017/s174392130903172x ◽

2008 ◽

Vol 4 (S258) ◽

pp. 73-80

Author(s):

Edouard J. Bernard ◽

Keyword(s):

Theoretical Models ◽

Variable Stars ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Stellar Pulsation ◽

Short Period ◽

History Of ◽

Period Variable ◽

Star Formation Histories ◽

Lyrae Stars

AbstractWe present a few highlights concerning the search for short-period variable stars in four galaxies, namely IC 1613, LGS3, Cetus and Tucana, based on very deep, multi-epoch HST/ACS photometry. These are discussed in the context of the star formation histories obtained from our very deep color-magnitude diagrams. In particular, we show how the pulsational properties of the RR Lyrae stars, which represent the vast majority of the observed variables, can trace subtle differences in the age and metallicity of the old population. For example, in the dwarf spheroidal galaxy Tucana we find that the fainter RR Lyrae stars, having a shorter period, are more centrally concentrated than the more luminous, longer period RR Lyrae variables. Through comparison with the predictions of theoretical models of stellar evolution and stellar pulsation, we interpret the fainter RR Lyrae stars as a more metal-rich subsample. In addition, we show that they must be older than about 10 Gyr, indicating that the metallicity gradient must have appeared very early on in the history of this galaxy. We also compare the populations of Cepheids in the galaxies of our sample based on their period-Wesenheit diagram. We tentatively classify them as classical short-period Cepheids in the two gas-rich galaxies (IC 1613 & LGS3), and as anomalous Cepheids in the dwarf spheroidals.

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An Analysis of M31 and its Satellite Galaxies Using RR Lyrae Variables

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006270 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 147-150

Author(s):

Nahathai Tanakul ◽

Ata Sarajedini

Keyword(s):

Milky Way ◽

Local Group ◽

Hubble Space Telescope ◽

Common Type ◽

Published Data ◽

Host Galaxies ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

History Of ◽

Lyrae Stars

AbstractRR Lyrae stars are powerful tools to study their host populations. Information such as distance, metallicity, reddening, and age can be obtained from their pulsation properties. Dwarf spheroidal (dSph) galaxies are the most common type of galaxy in the Local Group. They are found around massive hosts such as the Milky Way (MW) and M31 and are suggested to be the present-day counterparts to systems from which spheroids and stellar halos of larger galaxies were assembled. By comparing RR Lyraes in these dSphs with their host galaxies, we hope to understand more about the formation of these galaxies. In order to achieve this goal, we have analyzed six fields in M31 using archival imaging from the Hubble Space Telescope. Published data for M31, M33, and several M31 dSphs are also included. The results are then compared with those in the MW to better constrain the early history of these systems.

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Galactic archaeology for amateur astronomers: RR Lyrae stars as tracers of the Milky Way formation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311003541 ◽

2009 ◽

Vol 5 (S260) ◽

Author(s):

Julio A. Carballo-Bello ◽

David Martínez-Delgado ◽

Jürgen Fliri

Keyword(s):

Milky Way ◽

Spiral Galaxies ◽

Variable Stars ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Stellar Streams ◽

Tidal Streams ◽

Galactic Astronomy ◽

Lyrae Stars ◽

Candidate Variable

AbstractCosmological models predict that large galaxies like the Milky Way formed from the accretion of smaller stellar systems. The most spectacular of these merger events are stellar tidal streams, rivers of stars and dark matter that envelop the discs of spiral galaxies. We present a research project for a collaboration with amateur astronomers in the study of the formation process of our Galaxy. The main objective is the search for RR Lyrae variable stars in the known stellar streams (Sagitarius, Monoceros, Orphan, etc) a project that can be carried out using small telescopes. The catalogue of candidate variable stars were selected from SDSS data based in colour criteria and it will be sent to interested amateur astronomers who wish to participate in scientific research in one of the most active and competitive topics in Galactic astronomy.

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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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Predicted properties of RR Lyrae stars in the Sloan Digital Sky Survey photometric system

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2006.10787.x ◽

2006 ◽

Vol 371 (3) ◽

pp. 1503-1512 ◽

Cited By ~ 11

Author(s):

M. Marconi ◽

M. Cignoni ◽

M. Di Criscienzo ◽

V. Ripepi ◽

F. Castelli ◽

...

Keyword(s):

Sloan Digital Sky Survey ◽

Photometric System ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Sky Survey ◽

Lyrae Stars

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Professional/Amateur Cooperation in the Study of Variable Stars as Illustrated by the Fourth Edition of the GCVS

International Astronomical Union Colloquium ◽

10.1017/s0252921100092800 ◽

1988 ◽

Vol 98 ◽

pp. 188-189

Author(s):

M.S. Frolov

Keyword(s):

Classical Group ◽

Cataclysmic Variables ◽

Variable Stars ◽

Eclipsing Binaries ◽

Fourth Edition ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Long Time ◽

Hand Involvement ◽

Lyrae Stars

Let us divide variable stars into two main groups: the first “classical” group, includes objects known for a long time, such as Cepheids, RR-Lyrae stars, Miras, cataclysmic variables, eclipsing binaries, etc. The second group includes micropulsating variables of δ Scuti and β Cephei types, magnetic variables, rotating variables of BY Draconis type, etc.Historically, the contribution of amateurs in investigating the first group was very significant, and it continues to increase. On the other hand, involvement in studying the second group of stars was practically equal to zero some years ago, but today one can see the beginnings of an expansion of amateur work on this second group of variables – among brighter objects, of course. One reason is the beginning of cooperation between amateurs and professional astronomers having powerful instruments.

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OGLE-ing the Magellanic System: Three-Dimensional Structure

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318007093 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 86-89

Author(s):

Anna M. Jacyszyn-Dobrzeniecka ◽

Keyword(s):

Three Dimensional ◽

Neutral Hydrogen ◽

Variable Stars ◽

Dimensional Structure ◽

Rr Lyrae Stars ◽

Three Dimensional Structure ◽

Rr Lyrae ◽

Classical Cepheids ◽

Lyrae Stars ◽

Magellanic System

AbstractWe present a three-dimensional structure of the Magellanic System using over 9 000 Classical Cepheids and almost 23 000 RR Lyrae stars from the OGLE Collection of Variable Stars. Given the vast coverage of the OGLE-IV data and very high completeness of the sample, we were able to study the Magellanic System in great details.We very carefully studied the distribution of both types of pulsators in the Magellanic Bridge area. We show that there is no evident physical connection between the Clouds in RR Lyrae stars distribution. We only see the two extended structures overlapping. There are few classical Cepheids in the Magellanic Bridge area that seem to form a genuine connection between the Clouds. Their on-sky locations match very well young stars and neutral hydrogen density contours. We also present three-dimensional distribution of classical pulsators in both Magellanic Clouds.

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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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Period-Luminosity-Metal Abundance Relations for Population II Variable Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100116896 ◽

1993 ◽

Vol 139 ◽

pp. 31-52 ◽

Cited By ~ 1

Author(s):

James M. Nemec ◽

Thomas E. Lutz

Keyword(s):

Variable Stars ◽

Clear Trend ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Short Period ◽

New Period ◽

Blue Straggler ◽

Metal Abundance ◽

Filter Type ◽

Lyrae Stars

AbstractNew period-luminosity-metallicity (P-L-[Fe/H]) relationships for Pop. II Cepheids, RR Lyrae stars, anomalous Cepheids and SX Phe (variable-blue straggler) stars are presented. These were computed by fitting regression lines to observed pulsation periods and mean B, V, K magnitudes for over 1200 stars in ∼40 stellar systems. The stars were assumed to be pulsating in either the fundamental (F) or first-overtone (H) modes (excluding double-mode and other multi-periodic variables). Eight P-L-[Fe/H] relationships (one for each of the two pulsation modes for the four kinds of stars) were simultaneously fitted for each filter. After accounting for the metal abundance differences, the slopes of the P-L relations were tested for departures from equality. The results are consistent with the assumption that, for each kind of star, the relations for the F and H stars are vertically offset, with a family of lines corresponding to the different metallicities. In the case of the globular cluster Cepheids, the available B, V data support Arp's 1955 contention that the Cepheids are oscillating in the F and H modes; moreover, the majority of the short-period Cepheids (BL Her stars) appear to be first-overtone pulsators, while most of the Cepheids with periods between 10 and 30 days (W Vir stars) appear to be fundamental-mode pulsators. For the RR Lyrae stars, the slopes of the P-L-[Fe/H] relations in B, V and K show a clear trend with filter type, namely, the absolute values of the slopes increase from B to K. Finally, for the SX Phe stars the differences between the P-L-[Fe/H] relations in B and V for the F and H stars are found to be consistent with the known period-ratio for the double-mode star SX Phe.

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