Relationship between the Elemental Abundances and the Kinematics of Galactic-Field RR Lyrae Stars

Марсаков, В. А.; Gozha, M. L.; Koval, V. V.

doi:10.1134/s1063772918010055

Cited by 19 publications

(33 citation statements)

References 30 publications

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“…Thus, we find the traditional procedure of distinguishing thick-disk clusters from halo clusters according to their metallicity to be more acceptable. (Note that a similar discrepancy between criteria for membership in the thick-disk and halo subsystems based on chemical and kinematic properties is also observed for field RR Lyrae stars; see, in particular, [52].) Recall that the probabilities of cluster membership in the Galactic subsystems were calculated from the clusters' residual velocities at the Galactocentric distances corresponding to their current positions.…”

Section: Discussionmentioning

confidence: 66%

The Chemical Composition of Globular Clusters of Different Nature in Our Galaxy

2019

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A catalog of Galactic globular clusters has been compiled and used to analyze relations between the chemical and kinematic parameters of the clusters. The catalog contains positions, distances, luminosities, metallicites, and horizontal-branch morphology indices for 157 globular clusters, as well as space velocities for 72 globular clusters. For 69 globular clusters, these data are suppleented with the relative abundances of 28 chemical elements produced in various nuclearsynthesis processes, taken from 101 papers published between 1986 and 2018. The tendency for redder horizontal branches in low-metallicity accreted globular clusters is discussed. The discrepancy between the criteria for cluster membership in the thick-disk and halo subsystems based on chemical and kinematic properties is considered. This is manifest through the fact that all metalrich ([Fe/H] > −1.0) clusters are located close to the center and plane of the Galaxy, regardless of their kinematic membership in particular Galaxy subsystems. An exception is three accreted clusters lost by a dwarf galaxy in Sagittarius. At the same time, the fraction of more distant clusters is high among metal-poorer clusters in any kinematically selected Galactic subsystem. In addition, all metal-rich clusters whose origins are related to the same protogalactic cloud are located in the [Fe/H][α/Fe] diagram considerably higher than the strip populated with field stars. All metal-poor clusters (most of them accreted) populate the entire width of the strip formed by high-velocity (i. e., presumably accreted) field stars. Stars of dwarf satellite galaxies (all of them being metal-poor) are located in this diagram much lower than accreted field stars. These facts suggest that all stellar objects in the accreted halo are remnants of galaxies with higher masses than those in the current environment of the Galaxy. Differences in the relative abundances of α-process elements among stellar objects of the Galaxy and surrounding dwarf satellite galaxies confirm that the latter have left no appreciable stellar traces in the Galaxy, with the possible exception of the low-metallicity cluster Rup 106, which has low relative abundances of α-process elements.

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Section: Discussionmentioning

confidence: 66%

The Chemical Composition of Globular Clusters of Different Nature in Our Galaxy

2019

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“…The pericenter peak RR Lyrae stars then possibly belong to the chemical and kinematical distribution of the thick disc overlapping the region occupied by the thin disc stars. However, their [Fe/H] and [α/Fe] values are consistent with young thin disc stars, which remains a conundrum (see also the discussion in Marsakov et al 2018Marsakov et al , 2019a.…”

Section: Discussionmentioning

confidence: 94%

Evidence for Galactic disc RR Lyrae stars in the solar neighbourhood

Prudil

Dékány

Grebel

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present a kinematical study of 314 RR Lyrae stars in the solar neighbourhood using the publicly available photometric, spectroscopic, and Gaia DR2 astrometric data to explore their distribution in the Milky Way. We report an overdensity of 22 RR Lyrae stars in the solar neighbourhood at a pericenter distance of between 5-9 kpc from the Galactic center. Their orbital parameters and their chemistry indicate that these 22 variables share the kinematics and the [Fe/H] values of the Galactic disc, with an average metallicity and tangential velocity of [Fe/H]=−0.60 dex and v θ = 241 km s −1 , respectively. From the distribution of the Galactocentric spherical velocity components, we find that these 22 disc-like RR Lyrae variables are not consistent with the Gaia Sausage (Gaia-Enceladus), unlike almost half of the local RR Lyrae stars. Chemical information from the literature shows that the majority of the selected pericenter peak RR Lyrae variables are α-poor, a property shared by typically much younger stars in the thin disc. Using the available photometry we rule out a possible misclassification with the known classical and anomalous Cepheids. The similar kinematic, chemical, and pulsation properties of these disc RR Lyrae stars suggest they share a common origin. In contrast, we find the RR Lyrae stars associated with the Gaia-Enceladus based on their kinematics and chemical composition show a considerable metallicity spread in the old population (∼ 1 dex).

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“…This paper continues our studies of RR Lyrae variables in the Galactic field initiated in [1,2,3]. These papers describe a catalog we have compiled containing the positions, velocities, and metal abundances of 415 field RR Lyrae stars, along with the relative abundances [el/Fe] of 12 elements for 100 RR Lyrae stars, including four α-process elements (Mg, Ca, Si, and Ti).…”

Section: Introductionmentioning

confidence: 82%

“…Such Cepheids have already been discovered in the Large and Small Magellanic Clouds through the OGLE project. Therefore, we suggested in [1,3] that we should look for the origins of the kinematic and chemical youth of metal-rich RR Lyrae stars in their classification as variable stars. In this case, however, their masses should be even higher than for lower-temperature RR Lyrae stars, in contradiction with the general trend for the masses of horizontal-branch star to increase with decreasing temperature.…”

Section: Introductionmentioning

confidence: 99%

Masses of RR Lyrae Stars with Different Chemical Abundances in the Galactic Field

2019

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The surface gravities and effective temperatures have been added to a compilative catalog published earlier, which includes the relative abundances of several chemical elements for 100 field RR Lyrae stars. These atmoshperic parameters and evolutionary tracks from the Dartmouth database are used to determine the masses of the stars and perform a comparative analysis of the properties of RR Lyrae stars with different chemical compositions. The masses of metal-rich ([Fe/H] > −0.5) RR Lyrae stars with thin disk kinematics are in the range (0.51 − 0.60)M ⊙ . Only stars with initial masses exceeding 1M ⊙ can reach the horizontal branch during the life time of this subsystem. To become an RR Lyrae variable, a star must have lost approximately half of its mass during the red-giant phase. The appearance of such young, metal-rich RR Lyrae stars is possibly due to high initial helium abundances of their progenitors. According to the Dartmouth evolutionary tracks for Y = 0.4, a star with an initial mass as low as 0.8M ⊙ could evolve to become an RR Lyrae variable during this time. Such stars should have lost (0.2 − 0.3)M ⊙ in the red-giant phase, which seems quite realistic. Populations of red giants and RR Lyrae stars with such high helium abundances have already been discovered in the bulge; some of these could easily be transported to the solar neighborhood as a consequence of perturbations due to inhomogeneities of the Galaxys gravitational potential.

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Relationship between the Elemental Abundances and the Kinematics of Galactic-Field RR Lyrae Stars

Cited by 19 publications

References 30 publications

The Chemical Composition of Globular Clusters of Different Nature in Our Galaxy

The Chemical Composition of Globular Clusters of Different Nature in Our Galaxy

Evidence for Galactic disc RR Lyrae stars in the solar neighbourhood

Masses of RR Lyrae Stars with Different Chemical Abundances in the Galactic Field

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