On the use of field RR Lyrae as Galactic probes: IV. New insights into and around the Oosterhoff dichotomy

Abstract

We discuss the largest and most homogeneous spectroscopic dataset of field RR Lyrae variables (RRLs) available to date. We estimated abundances using both high-resolution and low-resolution ({ΔS} method) spectra for fundamental (RRab) and first overtone (RRc) RRLs. The iron abundances for 7,941 RRLs were supplemented with similar literature estimates available, ending up with 9,015 RRLs (6,150 RRab, 2,865 RRc). The metallicity distribution shows a mean value of <[Fe/H]> = -1.51\pm0.01, and σ(standard deviation)= 0.41 dex with a long metal-poor tail approaching [Fe/H] = -3 and a sharp metal-rich tail approaching solar iron abundance. The RRab variables are more metal-rich (<[Fe/H]>ab = -1.48\pm0.01, σ = 0.41 dex) than RRc variables (<[Fe/H]>c = -1.58\pm0.01, σ = 0.40 dex). The relative fraction of RRab variables in the Bailey diagram (visual amplitude vs period) located along the short-period (more metal-rich) and the long-period (more metal-poor) sequences are 80% and 20\%, while RRc variables display an opposite trend, namely 30\% and 70\%. We found that the pulsation period of both RRab and RRc variables steadily decreases when moving from the metal-poor to the metal-rich regime. The visual amplitude shows the same trend, but RRc amplitudes are almost two times more sensitive than RRab amplitudes to metallicity. We also investigated the dependence of the population ratio (Nc/Ntot) of field RRLs on the metallicity and we found that the distribution is more complex than in globular clusters. The population ratio steadily increases from ~0.25 to ~0.36 in the metal-poor regime, it decreases from ~0.36 to ~0.18 for -1.8 < [Fe/H] < -0.9 and it increases to a value of ~0.3 approaching solar iron abundance.

arXiv comment22 pages, 13 figures, 3 tables. Accepted for publication in ApJ

References in corpus (51)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III
• SEGUE: A Spectroscopic Survey of 240,000 stars with g=14-20
• The Radial Velocity Experiment (RAVE): first data release
• The SEGUE Stellar Parameter Pipeline. I. Description and Initial Validation Tests
• NEOWISE Observations of Near-Earth Objects: Preliminary Results
• Variable Stars in Galactic Globular Clusters
• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• On the use of Gaia magnitudes and new tables of bolometric corrections
• On a new theoretical framework for RR Lyrae stars I: the metallicity dependence
• Machine-Learned Identification of RR Lyrae Stars from Sparse, Multi-band Data: the PS1 Sample
• Metal Abundances, Radial Velocities and other Physical Characteristics for the RR Lyrae Stars in the Kepler Field
• Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC 6388
• RR Lyrae variables: visual and infrared luminosities, intrinsic colours, and kinematics
• The Chemical Compositions of Variable Field Horizontal Branch Stars: RR Lyrae Stars
• Weak Galactic halo--dwarf spheroidal connection from RR Lyrae stars
• HST Snaphot Study of Variable Stars in Globular Clusters: Inner Region of NGC 6441
• Spectroscopic Comparison of Metal-Rich RRab Stars of the Galactic Field with Their Metal-Poor Counterparts
• Long time-scale behavior of the Blazhko effect from rectified Kepler data
• RR Lyrae variables in Galactic globular clusters: IV. Synthetic HB and RR Lyrae predictions
• Tracing the Orphan Stream to 55 kpc with RR Lyrae Stars
• On the RR Lyrae stars in globulars: IV. $\omega$ Centauri Optical UBVRI Photometry
• On the use of field RR Lyrae as Galactic probes: I. The Oosterhoff dichotomy based on fundamental variables
• On the Use of Field RR Lyrae as Galactic Probes. II. A new $\Delta$S calibration to estimate their metallicity
• The Topology of RR Lyrae Instability Strip and the Oosterhoff Dichotomy
• Chemical abundances of solar neighborhood RR Lyrae stars
• The RRC Stars: Chemical Abundances and Envelope Kinematics
• On the RR Lyrae stars in globulars: V. the complete Near-Infrared (JHKs) census of omega Centauri RR Lyrae variables
• Probing the galactic halo with RR Lyrae stars I: The catalog
• On the Impact of Helium Content on the RR Lyrae Distance Scale
• On the Use of Field RR Lyrae as Galactic Probes. III. The $\alpha$-element abundances
• A comprehensive view of the Virgo Stellar Stream
• Blazhko effect in the Galactic bulge fundamental mode RR~Lyrae stars I: Incidence rate and differences between modulated and non-modulated stars
• Local RR Lyrae Stars: native and alien
• Purveyors of fine halos. II. Chemodynamical association of halo stars with Milky Way globular clusters
• On a new method to estimate distance, reddening and metallicity of RR Lyrae stars using optical/near-infrared ($B$,$V$,$I$,$J$,$H$,$K$) mean magnitudes: $\omega$ Centauri as a first test case
• The mass fraction of halo stars contributed by the disruption of globular clusters in the E-MOSAICS simulations
• Long-term photometric monitoring of Messier 5 variables: II. Blazhko stars
• Chemical Compositions of Field and Globular Cluster RR~Lyrae Stars: II. omega Centauri
• Blazhko effect in the Galactic bulge fundamental mode RR Lyrae stars II: Modulation shapes, amplitudes and periods
• Identification of RR Lyrae stars in multiband, sparsely-sampled data from the Dark Energy Survey using template fitting and Random Forest classification
• On the Oosterhoff dichotomy in the Galactic bulge: I. spatial distribution
• An Oosterhoff Analysis of the Galactic Bulge Field RR Lyrae stars: Implications On Their Absolute Magnitudes
• Dynamical structure of the pulsating atmosphere of RR Lyr - I. A typical pulsation cycle
• Blazhko Effect in the first overtone RR Lyrae stars of the OGLE Galactic bulge collection
• On the Metamorphosis of the Bailey diagram for RR Lyrae stars
• Amplitude Fine-Structure in the Cepheid P-L Relation I: Amplitude Distribution Across the RR Lyrae Instability Strip Mapped Using the Accessibility Restriction Imposed by the Horizontal Branch
• Unveiling short period binaries in the inner VVV bulge
• Spectroscopic and photometric time series of the bright RRc star T Sex
• Possible evidence of hydrogen emission in the first-overtone and multi-mode RR Lyrae variables

Cited by in corpus (17)

• Milky Way archaeology using RR Lyrae and type II Cepheids II. High velocity RR Lyrae stars, and mass of the Milky Way
• The GALAH survey: Tracing the Milky Way's formation and evolution through RR Lyrae stars
• RR Lyrae mid-infrared Period-Luminosity-Metallicity and Period-Wesenheit-Metallicity relations based on Gaia DR3 parallaxes
• Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves: II. Period-Fourier-Metallicity Relations for First Overtone RR Lyrae
• On the Use of Field RR Lyrae as Galactic Probes. VI. Mixed mode RR Lyrae variables in Fornax and in nearby dwarf galaxies
• The Galactic Bulge exploration IV.: RR~Lyrae stars as traces of the Galactic bar -- 3D and 5D analysis, extinction variation
• RR Lyrae stars as probes of the outer Galactic halo: Chemical and kinematic analysis of a pilot sample
• A Very Metal-poor RR Lyrae Star with a Disk Orbit Found in the Solar Neighborhood
• Probing the Galactic halo with RR Lyrae stars -- IV. On the Oosterhoff dichotomy of RR Lyrae stars
• Two Different Weak Modulations in ab-type RR Lyrae Variable V838 Cyg, and Potential Influence of Metal Abundance on Blazhko Modulation
• On the Use of Field RR Lyrae as Galactic Probes -- VIII. Early Formation of the Galactic Spheroid
• Reconsidering The Bailey Diagrams of ab-type RR Lyrae Stars, Metallicity-Mediated Evolution as the Direct Cause of the Oosterhoff Phenomenon
• RRab variables with identical light-curve shapes at different pulsation periods
• Sparse logistic regression for RR Lyrae vs binaries classification
• Evaluating the V-band Photometric Metallicity with Fundamental Mode RR Lyrae in the Kepler Field
• A Multiband Photometric Study of RR Lyrae Stars in M53 (NGC 5024)
• RR Lyrae stars in the newly discovered ultra-faint dwarf galaxy Centaurus I