Red Horizontal Branch stars: an asteroseismic perspective

Abstract

Robust age estimates of red giant stars are now possible thanks to the precise inference of their mass based on asteroseismic constraints. However, there are cases where such age estimates can be highly precise yet very inaccurate. An example is giants that have undergone mass loss or mass transfer events that have significantly altered their mass. In this context, stars with "apparent" ages significantly higher than the age of the Universe are candidates as stripped stars, or stars that have lost more mass than expected, most likely via interaction with a companion star, or because of the poorly understood mass-loss mechanism along the red-giant branch. In this work we identify examples of such objects among red giants observed by $\text{Kepler}$, both at low ([Fe/H] $\lesssim -0.5$) and solar metallicity. By modelling their structure and pulsation spectra, we find a consistent picture confirming that these are indeed low-mass objects consisting of a He core of $\approx 0.5M_{\odot }$ and an envelope of $\approx 0.1-0.2M_{\odot }$. Moreover, we find that these stars are characterised by a rather extreme coupling ($q\gtrsim 0.4$) between the pressure-mode and gravity-mode cavities, i.e. much higher than the typical value for red clump stars, providing thus a direct seismic signature of their peculiar structure. The complex pulsation spectra of these objects, if observed with sufficient frequency resolution, hold detailed information about the structural properties of likely products of mass stripping, hence can potentially shed light on their formation mechanism. On the other hand, our tests highlight the difficulties associated with measuring reliably the large frequency separation, especially in shorter datasets, with impact on the reliability of the inferred masses and ages of low-mass Red Clump stars with e.g. K2 or TESS data.

arXiv commentAccepted for publication in A&A Letters

References in corpus (59)

• The chemical composition of the Sun
• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• Modules for Experiments in Stellar Astrophysics (MESA): Binaries, Pulsations, and Explosions
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• The K2 Mission: Characterization and Early results
• The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
• A 3D Dust Map Based on Gaia, Pan-STARRS 1 and 2MASS
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• Asteroseismology of Solar-Type and Red-Giant Stars
• GYRE: An open-source stellar oscillation code based on a new Magnus Multiple Shooting Scheme
• Testing Scaling Relations for Solar-Like Oscillations from the Main Sequence to Red Giants using Kepler Data
• Asteroseismology of old open clusters with Kepler: direct estimate of the integrated RGB mass loss in NGC6791 and NGC6819
• 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
• Calculating asteroseismic diagrams for solar-like oscillations
• Synthetic Stellar Photometry - I. General considerations and new transformations for broad-band systems
• Asteroseismology of 16000 Kepler Red Giants: Global Oscillation Parameters, Masses, and Radii
• The second and third parameters of the Horizontal Branch in Globular Clusters
• Theoretical amplitudes and lifetimes of non-radial solar-like oscillations in red giants
• On a new theoretical framework for RR Lyrae stars I: the metallicity dependence
• Angular momentum transport by heat-driven g-modes in slowly pulsating B stars
• Age dissection of the Milky Way discs: red giants in the Kepler field
• Period spacings in red giants II. Automated measurement
• The universal red-giant oscillation pattern; an automated determination with CoRoT data
• The SDSS-III APOGEE Spectral Line List for H-band Spectroscopy
• Gaia Data Release 3: Catalogue Validation
• The APOGEE Data Release 16 Spectral Line List
• An in-depth study of grid-based asteroseismic analysis
• Gaia Data Release 3. Astrometric binary star processing
• NGC 6819: testing the asteroseismic mass scale, mass loss, and evidence for products of non-standard evolution
• Uncertainties on near-core mixing in red-clump stars: effects on the period spacing and on the luminosity of the AGB bump
• Mode lifetimes of stellar oscillations - Implications for asteroseismology
• The Contour Method: a new approach to finding modes of non-adiabatic stellar pulsations
• Period spacings in red giants IV: Toward a complete description of the mixed-mode pattern
• Mass loss along the red giant branch in 46 Globular Clusters and their multiple populations
• Period spacings in red giants; III. Coupling factors of mixed modes
• Kepler red-clump stars in the field and in open clusters: constraints on core mixing
• The Red-Giant Branch Bump Revisited: Constraints on Envelope Overshooting in a Wide Range of Masses and Metallicities
• Discovery of post-mass-transfer helium-burning red giants using asteroseismology
• Amplitude and lifetime of radial modes in red giant star spectra observed by Kepler
• Asteroseismology of red giants: from analysing light curves to estimating ages
• Semi-analytic Expressions for the Isolation and Coupling of Mixed Modes
• The Metallicity Gradient of the Thick Disk Based on Red Horizontal Branch Stars From SDSS DR8
• Integrated Mass Loss of Evolved Stars in M4 using Asteroseismology
• Chemical compositions of thin-disk, high-metallicity red horizontal-branch field stars
• Asteroseismology of the multiple stellar populations in the Globular Cluster M4
• Probing the mid-layer structure of red giants I. Mixed-mode coupling factor as a seismic diagnosis
• Kinematics of RHB stars to trace the structure of the galaxy
• A Semi-Empirical Study of the Mass Distribution of Horizontal Branch Stars in M3 (NGC 5272)
• A synthetic sample of short-cadence solar-like oscillators for TESS
• Asteroseismology of overmassive, undermassive, and potential past members of the open cluster NGC6791
• Variations of the mixing character of dipolar mixed modes in red giant stars
• A Spectroscopic Survey of Field Red Horizontal-Branch Stars
• A Search for Variable Stars in the Globular Cluster M4 with K2
• Metallicity and Kinematic distributions of Red Horizontal-Branch Stars from the SDSS Survey
• Multi-cavity gravito-acoustic modes in stars: A general analytical resonance condition

Cited by in corpus (11)

• Investigating Gaia EDR3 parallax systematics using asteroseismology of Cool Giant Stars observed by Kepler, K2, and TESS II. Deciphering Gaia parallax systematics using red clump stars
• Evidence that Mass Loss on the Red Giant Branch Decreases with Metallicity
• Connecting integrated RGB mass loss from asteroseismology and globular clusters
• Advancing accuracy in age determinations of old-disk stars using an oscillating red giant in an eclipsing binary
• DUETS: Setting expectations for asteroseismic binaries and binary products with synthetic populations
• Anomalously low-mass core-He-burning star in NGC 6819 as a post-common-envelope phase product
• Mixed-mode coupling in the Red Clump I. Standard single star models
• Power density spectra morphologies of seismically unresolved red-giant asteroseismic binaries
• Parametric models of core-helium-burning stars: structural glitches near the core
• Where are the binaries? -- Searching for blue horizontal-branch stars in binary systems in the inner Galactic Halo
• Matching seismic masses for RR Lyrae-type and oscillating red horizontal-branch stars in M4