Contamination of RR Lyrae stars from Binary Evolution Pulsators

A Binary Evolution Pulsator (BEP) is a low-mass (0.26 𝔐☉) member of a binary system, which pulsates as a result of a former mass transfer to its companion. The BEP mimics RR Lyrae-type pulsations, but has completely different internal structure and evolution history. Although there is only one known BEP (OGLE-BLG-RRLYR-02792), it has been estimated that approximately 0.2% of objects classified as RR Lyrae stars can be undetected Binary Evolution Pulsators. In the present work, this contamination value is re-evaluated using the population synthesis method. The output falls inside a range of values dependent on tuning the parameters in the StarTrack code, and varies from 0.06% to 0.43%.

Download Full-text

The age of the Milky Way inner stellar spheroid from RR Lyrae population synthesis

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038305 ◽

2020 ◽

Vol 641 ◽

pp. A96 ◽

Cited By ~ 4

Author(s):

A. Savino ◽

A. Koch ◽

Z. Prudil ◽

A. Kunder ◽

R. Smolec

Keyword(s):

Stellar Population ◽

Milky Way ◽

Population Synthesis ◽

Milky Way Galaxy ◽

First Stars ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

The Galaxy ◽

Stellar Halo ◽

Lyrae Stars

The central kiloparsecs of the Milky Way are known to host an old, spheroidal stellar population, whose spatial and kinematical properties set it apart from the boxy-peanut structure that constitutes most of the central stellar mass. The nature of this spheroidal population, whether it is a small classical bulge, the innermost stellar halo, or a population of disk stars with large initial velocity dispersion, remains unclear. This structure is also a promising candidate to play host to some of the oldest stars in the Galaxy. Here we address the topic of the inner stellar spheroid age, using spectroscopic and photometric metallicities for a sample of 935 RR Lyrae stars that are constituents of this component. By means of stellar population synthesis, we derive an age-metallicity relation for RR Lyrae populations. We infer, for the RR Lyrae stars in the bulge spheroid, an extremely ancient age of 13.41 ± 0.54 Gyr and conclude they were among the first stars to form in what is now the Milky Way galaxy. Our age estimate for the central spheroid shows a remarkable agreement with the age profile that has been inferred for the Milky Way stellar halo, suggesting a connection between the two structures. However, we find mild evidence for a transition in the halo properties at rGC ∼ 5 kpc. We also investigate formation scenarios for metal-rich RR Lyrae stars, such as binarity and helium variations, and consider whether they can provide alternative explanations for the properties of our sample. We conclude that within our framework, the only viable alternative is to have younger, slightly helium-rich, RR Lyrae stars. This is a hypothesis that would open intriguing questions for the formation of the inner stellar spheroid.

Download Full-text

A DECam view of the diffuse dwarf galaxy Crater II – Variable stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3393 ◽

2019 ◽

Vol 492 (1) ◽

pp. 1061-1077 ◽

Cited By ~ 1

Author(s):

A Katherina Vivas ◽

Alistair R Walker ◽

Clara E Martínez-Vázquez ◽

Matteo Monelli ◽

Giuseppe Bono ◽

...

Keyword(s):

Time Series ◽

Dwarf Galaxy ◽

Position Angle ◽

Variable Stars ◽

Distance Modulus ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

The Galaxy ◽

Binary Evolution ◽

Lyrae Stars

ABSTRACT Time series observations of a single dithered field centred on the diffuse dwarf satellite galaxy Crater II were obtained with the Dark Energy Camera (DECam) at the 4m Blanco Telescope at Cerro Tololo Inter-American Observatory, Chile, uniformly covering up to two half-light radii. Analysis of the g and i time series results in the identification and characterization of 130 periodic variable stars, including 98 RR Lyrae stars, 7 anomalous Cepheids, and 1 SX Phoenicis star belonging to the Crater II population, and 24 foreground variables of different types. Using the large number of ab-type RR Lyrae stars present in the galaxy, we obtained a distance modulus to Crater II of (m − M)0 = 20.333 ± 0.004 (stat) ±0.07 (sys). The distribution of the RR Lyrae stars suggests an elliptical shape for Crater II, with an ellipticity of 0.24 and a position angle of 153°. From the RR Lyrae stars, we infer a small metallicity dispersion for the old population of Crater II of only 0.17 dex. There are hints that the most metal-poor stars in that narrow distribution have a wider distribution across the galaxy, while the slightly more metal-rich part of the population is more centrally concentrated. Given the features in the colour–magnitude diagram of Crater II, the anomalous Cepheids in this galaxy must have formed through a binary evolution channel of an old population.

Download Full-text

Galactic calibration of the tip of the red giant branch

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2018.46 ◽

2019 ◽

Vol 36 ◽

Cited By ~ 4

Author(s):

Jeremy Mould ◽

Gisella Clementini ◽

Gary Da Costa

Keyword(s):

Globular Clusters ◽

Photometric System ◽

Low Mass Stars ◽

Rr Lyrae Stars ◽

Geometric Calibration ◽

Rr Lyrae ◽

Low Mass ◽

Red Giant ◽

Extragalactic Distance Scale ◽

Lyrae Stars

AbstractIndications from Gaia data release 2 are that the tip of the red giant branch (a population II standard candle related to the helium flash in low mass stars) is close to –4 in absolute I magnitude in the Cousins photometric system. Our sample is high-latitude southern stars from the thick disk and inner halo, and our result is consistent with longstanding findings from globular clusters, whose distances were calibrated with RR Lyrae stars. As the Gaia mission proceeds, there is every reason to think an accurate Galactic geometric calibration of tip of the red giant branch will be a significant outcome for the extragalactic distance scale.

Download Full-text

Low-Mass Evolution from He Ignition to Beyond the Horizontal Branch

International Astronomical Union Colloquium ◽

10.1017/s0252921100081951 ◽

1980 ◽

Vol 58 ◽

pp. 483-489

Author(s):

Keith Despain

Keyword(s):

Stellar Model ◽

Horizontal Branch ◽

Helium Burning ◽

Rr Lyrae Stars ◽

The Core ◽

Rr Lyrae ◽

Low Mass ◽

Red Giant ◽

Lyrae Stars

AbstractThe evolution of an 0.6 M⊙ stellar model during core helium burning is presented. Following the off-center ignition of helium in the “core” flash, the star remains on the red giant branch for > 106 years, undergoing twelve additional flashes. After leaving the giant branch, the star evolves on the horizontal branch for 8.15×107 years before returning to the giant branch and undergoing strong helium-shell flashes. The implications for horizontal branch and RR Lyrae stars are discussed.

Download Full-text

Evolutionary Models of RR Lyrae Stars

International Astronomical Union Colloquium ◽

10.1017/s025292110011766x ◽

1993 ◽

Vol 139 ◽

pp. 294-303

Author(s):

Young-Wook Lee

Keyword(s):

Variable Stars ◽

Mass Star ◽

Supporting Evidence ◽

Evolutionary Models ◽

Rr Lyrae Stars ◽

Cosmological Distance Scale ◽

Rr Lyrae ◽

Low Mass ◽

Lyrae Stars ◽

Distance Indicators

As tracers of old stellar populations and as primary Population II standard candles, RR Lyrae stars have played an important role in the development of modern astronomy. Our knowledge of stellar evolution has identified these variable stars in a core helium burning phase of low-mass star evolution, the hoiizontal-branch (HB) phase. Consequently, not only to understand fully the nature of RR Lyrae stars, but also to apply them correctly as population probes and distance indicators, we must understand the underlying evolutionary effect of HB stars.In this paper, I briefly review the most important properties of RR Lyrae stars predicted from the HB evolutionary models, and present many pieces of supporting evidence for these models. For the implications of these models on the chronology of the Galactic formation and on the cosmological distance scale, the reader is referred to several recent publications by Lee (1992a,b,c,d).

Download Full-text

Mass-Loss During the RR Lyrae Phase of the HB: Mass Dispersion on the HB and RR Lyrae Period Changes

International Astronomical Union Colloquium ◽

10.1017/s0252921100117713 ◽

1993 ◽

Vol 139 ◽

pp. 312-312

Author(s):

Rebecca A. Koopmann ◽

Young-Wook Lee ◽

Pierre Demarque ◽

Jamie M. Howard

Keyword(s):

Mass Loss ◽

Horizontal Branch ◽

Constant Mass ◽

Instability Strip ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Mass Dispersion ◽

Low Mass ◽

Lyrae Stars ◽

Loss Rates

Horizontal branch (HB) models were evolved using the Yale stellar evolution code, YREC, to test the possibility that mass loss during the RR Lyrae phase is able to produce the observed color (mass) dispersion on the HB (Willson and Bowen 1984) and the anomalous period changes in RR Lyrae stars (Laskarides 1974). Models of total mass 0.64, 0.66, 0.68, 0.70, and 0.72 M⊙ (YMS = 0.23, Z = 0.001) were evolved with constant mass loss rates of 0, 10-10, and 10-9 M⊙ yr-1. Mass loss was assumed to occur only in the RR Lyrae phase, and the instability strip was defined by 3.800 < log Teff < 3.875.HB stars which lose mass evolve further to the blue. Low mass loss rates do not affect the shape of the tracks significantly. Stars, which without mass loss could not become blue HB stars, were able to emerge from the instability strip on the blue side.

Download Full-text

The Unusual Period Distribution of the RR Lyrae Variables in NGC 5897

International Astronomical Union Colloquium ◽

10.1017/s0252921100011957 ◽

1989 ◽

Vol 111 ◽

pp. 287-287

Author(s):

Amelia Wehlau

Keyword(s):

Light Curves ◽

Instability Strip ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Period Distribution ◽

Unusual Distribution ◽

Photoelectric Observations ◽

Lyrae Stars ◽

Branch Star ◽

Central Concentration

AbstractAttention is called to the rather unusual distribution of the periods of the RR Lyrae variables in NGC 5897, a metal-poor halo globular cluster with a very low central concentration. Of the seven RR Lyrae stars known in the cluster, three have periods between 0.797 and 0.856 day and two have periods of 0.45 and 0.42 day. The other two have periods of 0.34 and 0.35 day with much lower amplitudes of variation. Due to the lack of crowding in this cluster photoelectric observations and Fourier decompositions of the resulting light curves should be possible for at least six of the RR Lyrae variables. In addition, the cluster appears to contain a non-variable horizontal branch star, SK 120, lying within the instability strip. As this is the only well documented case of such a star, photoelectric observations of this star would also be desirable.

Download Full-text

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.

Download Full-text