RR Lyrae stars: prime calibrators of the first rung of the distance ladder

Cacciari, C.

doi:10.1017/s1743921312021205

Proc. IAU

2012

DOI: 10.1017/s1743921312021205

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RR Lyrae stars: prime calibrators of the first rung of the distance ladder

C. Cacciari

Abstract: RR Lyrae variables are the primary standard candles for old stellar populations, and the traditional first step in the definition of the distance scale. Their properties are known on the basis of well-established physical concepts and their calibration is based on several empirical methods. Both aspects are critically reviewed, and their application as distance indicators within the Galaxy and the Local Group are discussed, also in view of the observing facilities that will be available in the near future.

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Cited by 3 publications

References 48 publications

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Carbon stars as standard candles – II. The median J magnitude as a distance indicator

Parada

Richer

Ripoche

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We introduce a new distance determination method using carbon-rich asymptotic giant branch stars (CS) as standard candles and the Large and Small Magellanic Clouds (LMC and SMC) as the fundamental calibrators. We select the samples of CS from the ((J − Ks)0, J0) colour–magnitude diagrams, as, in this combination of filters, CS are bright and easy to identify. We fit the CS J-band luminosity functions using a Lorentzian distribution modified to allow the distribution to be asymmetric. We use the parameters of the best-fitting distribution to determine if the CS luminosity function of a given galaxy resembles that of the LMC or SMC. Based on this resemblance, we use either the LMC or SMC as the calibrator and estimate the distance to the given galaxy using the median J magnitude ($\overline{J}$) of the CS samples. We apply this new method to the two Local Group galaxies NGC 6822 and IC 1613. We find that NGC 6822 has an ‘LMC-like’ CS luminosity function, while IC 1613 is more ‘SMC-like’. Using the values for the median absolute J magnitude for the LMC and SMC found in Paper I we find a distance modulus of μ0 = 23.54 ± 0.03 (stat) for NGC 6822 and μ0 = 24.34 ± 0.05 (stat) for IC 1613.

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Carbon stars as standard candles – II. The median J magnitude as a distance indicator

Parada

Richer

Ripoche

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Kinematics and multiband period–luminosity–metallicity relation of RR Lyrae stars via statistical parallax

Muhie

Дамбис

Бердников

et al. 2021

Monthly Notices of the Royal Astronomical Society

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This paper presents results from photometric and statistical-parallax analysis of a sample of 850 field RR Lyrae (RRL) variables. The photometric and spectroscopic data for our sample of RRLs are obtained from (1) our new spectroscopic observations (for 448 RRLs) carried out with the Southern African Large Telescope (SALT); (2) our photometric observations using the 1.0-m telescope of the South African Astronomical Observatory (SAAO), and (3) literature. These are combined with accurate proper motion data from the second data release of the Gaia mission (DR2). This study primarily determines the velocity distribution of solar neighborhood RRLs, and it also calibrates the zero points of the RRLs’ visual V-band luminosity-metallicity (LZ or MV −[Fe/H]) relation and their period-luminosity-metallicity (PLZ) relations in the WISE W1 − and 2MASS Ks −band. We find the bulk velocity of the halo RRLs relative to the Sun to be (U0, V0, W0)Halo =( − 16 ± 7, −219 ± 7, −6 ± 5) km s−1 in the direction of Galactic center, Galactic rotation, and North Galactic pole, respectively, with velocity-dispersion ellipsoids (σVR, σVφ, σVθ)Halo = (153 ± 7, 106 ± 4, 101 ± 4) km s−1. The corresponding parameters for the disk component are found to be (U0, V0, W0)Disk = ( − 19 ± 5, −46 ± 5, −14 ± 3) km s−1 and (σVR, σVφ, σVθ)Disk =(49 ± 4, 38 ± 4, 25 ± 3) km s−1. The calibrated PLZ in W1 −, Ks −band, and V-band LZ relations are 〈 MW1〉 = −0.824 + 0.124[Fe/H] − 2.381log PF, 〈MKs〉 = −0.804 + 0.101[Fe/H] − 2.33log PF and 〈 MV〉 = 1.041 + 0.232[Fe/H], respectively. The calibrated PLZ and LZ relations are used to estimate the Galactic Center distance and the distance modulus of the Large Magellanic Cloud (LMC), which are found to be 7.99±0.49 kpc and 18.46±0.09 mag, respectively. All our results are in excellent agreement with available literature based on statistical parallax analysis, but are considerably more accurate and precise. Moreover, the zero-points of our calibrated PLZ and LZ relations are quite consistent with current results found by other techniques and yield a LMC distance modulus that is within 0.04 mag of the current most precise estimate.

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Local RR Lyrae stars: native and alien

Zinn

Chen

Layden

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Measurements of [Fe/H] and radial velocity are presented for 89 RR Lyrae (RRL) candidates within 6 kpc of the Sun. After the removal of two suspected non-RRL, these stars were added to an existing database, which yielded 464 RRL with [Fe/H] on a homogeneous scale. Using data from the Gaia satellite (Data Release 2), we calculated the positions and space velocities for this sample. These data confirm the existence of a thin-disc of RRL with [α/Fe]∼ solar. The majority of the halo RRL with large total energies have near zero angular momenta about the Z axis. Kinematically these stars closely resemble the Gaia-Sausage/Gaia-Enceladus stars that others have proposed are debris from the merger of a large galaxy with the Milky Way. The metallicity and period distributions of the RRL and their positions in the period-amplitude diagram suggest that this disrupted galaxy was as massive as the Large Magellanic Cloud and possibly greater.

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RR Lyrae stars: prime calibrators of the first rung of the distance ladder

Cited by 3 publications

References 48 publications

Carbon stars as standard candles – II. The median J magnitude as a distance indicator

Carbon stars as standard candles – II. The median J magnitude as a distance indicator

Kinematics and multiband period–luminosity–metallicity relation of RR Lyrae stars via statistical parallax

Local RR Lyrae stars: native and alien

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