IY Lyr: A Thick-Disk first-overtone RR Lyrae Star with a Possible Neutron Star Companion

Abstract

IY Lyr, historically misclassified as an eclipsing binary, has been previously identified as a first-overtone RR Lyrae star (RRc star). Using multiband photometry (All-Sky Automated Survey for Supernovae, Zwicky Transient Facility, TESS, and our BVRI data), Large Sky Area Multi-Object Fiber Spectroscopic Telescope spectroscopy, and Gaia astrometry, we investigate its pulsation, binarity, and Galactic population. From O-C analysis, we detect a long-term period decrease and a light-travel time effect with an orbital period of 3.94 $\pm$ 0.09 years, eccentricity of 0.46 $\pm$ 0.15, and a mass function of 0.65 $\pm$ 0.14 M${}_{\odot }$. The companion is independently supported by radial velocity residuals and Gaia proper motions. Combined constraints yield an orbital inclination of 94.2${}^{\circ }$ $\pm$ 1.1${}^{\circ }$ and a companion mass of 1.37 $\pm$ 0.19 M${}_{\odot }$. Chemical abundances ([Fe/H] $\simeq$ -1.0 $\pm$ 0.1, [$\alpha$/Fe] $\simeq$ +0.27 $\pm$ 0.03, Xiang et al. 2019) and dynamics ($L_{\mathrm{z}}$ $\simeq$ 1287 $\pm$ 35 kpc km s${}^{-1}$, $Z_{\max }$ $\simeq$ 1.17 $\pm$ 0.10 kpc) identify IY Lyr as likely an old, high-$\alpha$, thick-disk star. The companion mass lies at the peak of the neutron star mass distribution, and the system's age excludes a main-sequence star; we conclude the companion is most likely a typical neutron star, although a massive white dwarf near the Chandrasekhar limit cannot be ruled out. IY Lyr is among the few RRc binaries with a compact companion supported by multiple methods, and it has important implications for thick-disk binary evolution and neutron star formation.

20 pages, 6 figures, 5 tables

References in corpus (56)

• Gaia Data Release 2. Summary of the contents and survey properties
• Gaia Data Release 3: Summary of the content and survey properties
• The Transiting Exoplanet Survey Satellite
• Local Kinematics and the Local Standard of Rest
• The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
• galpy: A Python Library for Galactic Dynamics
• A statistical study of 233 pulsar proper motions
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood
• The mass distribution and gravitational potential of the Milky Way
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• A large stellar evolution database for population synthesis studies. II. Stellar models and isochrones for an alpha-enhanced metal distribution
• The ASAS-SN Catalog of Variable Stars I: The Serendipitous Survey
• Stellar and substellar companions of nearby stars from Gaia DR2 - Binarity from proper motion anomaly
• A First Catalog of Variable Stars Measured by the Asteroid Terrestrial-impact Last Alert System (ATLAS)
• The Zwicky Transient Facility Catalog of Periodic Variable Stars
• The Biggest Splash
• Pulsar Jets: Implications for Neutron Star Kicks and Initial Spins
• Stellar and substellar companions from Gaia EDR3 -- Proper motion anomaly and resolved common proper motion pairs
• A time-resolved picture of our Milky Way's early formation history
• On a new theoretical framework for RR Lyrae stars I: the metallicity dependence
• Abundance Estimates for 16 Elements in 6 Million Stars from LAMOST DR5 Low-Resolution Spectra
• The ASAS-SN Catalog of Variable Stars II: Uniform Classification of 412,000 Known Variables
• Machine-Learned Identification of RR Lyrae Stars from Sparse, Multi-band Data: the PS1 Sample
• The ASAS-SN Catalog of Variable Stars III: Variables in the Southern TESS Continuous Viewing Zone
• Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry
• Contamination in the Kepler Field. Identification of 685 KOIs as False Positives Via Ephemeris Matching Based On Q1-Q12 Data
• Deriving the stellar labels of LAMOST spectra with Stellar LAbel Machine (SLAM)
• RR-Lyrae-type pulsations from a 0.26-solar-mass star in a binary system
• The ASAS-SN Catalog of Variable Stars V: Variables in the Southern Hemisphere
• Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2 - I. Binarity from proper motion anomaly
• The ASAS-SN Catalog of Variable Stars IX: The Spectroscopic Properties of Galactic Variable Stars
• The ASAS-SN Catalog of Variable Stars X: Discovery of 116,000 New Variable Stars Using g-band Photometry
• New RR Lyrae variables in binary systems
• Pulsation models for the 0.26M_sun star mimicking RR Lyrae pulsator. Model survey for the new class of variable stars
• The RRC Stars: Chemical Abundances and Envelope Kinematics
• The Spectroscopic Binaries from LAMOST Medium-Resolution Survey (MRS). I. Searching for Double-lined Spectroscopic Binaries (SB2s) with Convolutional Neural Network
• Cyclic variations in O-C diagrams of field RR Lyrae stars as a result of LiTE
• RR Lyrae From Binary Evolution: Abundant, Young and Metal-Rich
• Local RR Lyrae Stars: native and alien
• Studies of RR Lyrae Variables in Binary Systems. I.: Evidence of a Trimodal Companion Mass Distribution
• KIC 2831097 - A 2-year orbital-period RR Lyrae binary candidate
• Stellar Parameters and Chemical Abundances Estimated from LAMOST-II DR8 MRS based on Cycle-StarNet
• On the Use of Field RR Lyrae as Galactic Probes. V. Optical and radial velocity curve templates
• Candidates for RR~Lyrae in binary systems from the OGLE Galactic bulge survey
• A first-overtone RR Lyrae star with cyclic period changes
• Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves: II. Period-Fourier-Metallicity Relations for First Overtone RR Lyrae
• The birth mass function of neutron stars
• The Identification of RR Lyrae and Delta Scuti Stars from Variable GALEX Ultraviolet Sources
• Four 'Peculiar' RRd Stars Observed by K2
• Neutron Stars: Formed, Spun and Kicked
• Reanalysis of c-type RR Lyrae Variable BE Dor, Period Modulations and Possible Mechanism
• Two Different Weak Modulations in ab-type RR Lyrae Variable V838 Cyg, and Potential Influence of Metal Abundance on Blazhko Modulation
• The elusive chase for the first RR Lyr star in a binary system: the case of KIC 2831097
• Connections between the cycle-to-cycle light curve and O-C variations of the non-Blazhko RR Lyrae stars
• Reconsidering The Bailey Diagrams of ab-type RR Lyrae Stars, Metallicity-Mediated Evolution as the Direct Cause of the Oosterhoff Phenomenon