The Pulsation Properties of $\lambda$ Bootis Stars I. The Southern TESS Sample

Abstract

We analyse TESS light curves for 70 southern $\lambda$ Boo stars to identify binaries and to determine which of them pulsate as $\delta$ Scuti stars. We find two heartbeat stars and two eclipsing binaries among the sample. We calculate that 81 percent of $\lambda$ Boo stars pulsate as $\delta$ Sct variables, which is about twice that of normal stars over the same parameter space. We determine the temperatures and luminosities of the $\lambda$ Boo stars from photometry and Gaia DR2 parallaxes. A subset of 40 $\lambda$ Boo stars have 2-min TESS data, reliable temperatures and luminosities, and $\delta$ Sct pulsation. We use Petersen diagrams (period ratios), échelle diagrams and the period--luminosity relation to identify the fundamental mode in 20 of those 40 stars and conclude that a further 8 stars are not pulsating in this mode. For the remaining 12, the fundamental mode cannot be unambiguously identified. Further mode identification is possible for 12 of the fundamental mode pulsators that have regular sequences of pulsation overtones in their échelle diagrams. We use stellar evolution models to determine statistically that the $\lambda$ Boo stars are only superficially metal weak. Simple pulsation models also better fit the observations at a metallicity of $Z=0.01$ than at $Z=0.001$. The TESS observations reveal the great potential of asteroseismology on $\lambda$ Boo stars, for determining precise stellar ages and shedding light on the origin(s) of the $\lambda$ Boo phenomenon.

Accepted to MNRAS. 25 pages (main text 16 pages), including data tables and figures. Figures use colour liberally

References in corpus (27)

• Modules for Experiments in Stellar Astrophysics (MESA)
• The Transiting Exoplanet Survey Satellite
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open cluster
• Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes
• The interior rotation of a sample of gamma Doradus stars from ensemble modelling of their gravity mode period spacings
• {\em Gaia}-derived luminosities of {\em Kepler} A/F stars and the pulsator fraction across the δ Scuti instability strip
• A unifying explanation of complex frequency spectra of gamma Dor, SPB and Be stars: combination frequencies and highly non-sinusoidal light curves
• Theory and evidence of global Rossby waves in upper main-sequence stars: r-mode oscillations in many Kepler stars
• The first view of $\delta$ Scuti and $\gamma$ Doradus stars with the TESS mission
• Very regular high-frequency pulsation modes in young intermediate-mass stars
• The role of turbulent pressure as a coherent pulsational driving mechanism: the case of the delta Scuti star HD 187547
• Diverse Variability of O and B Stars Revealed from 2-minute Cadence Light Curves in Sectors 1 and 2 of the TESS Mission: Selection of an Asteroseismic Sample
• Investigation of the inner structures around HD169142 with VLT/SPHERE
• Period spacings of $\gamma$ Doradus pulsators in the \textit{Kepler} field: Rossby and gravity modes in 82 stars
• Gravity-mode period spacings and near-core rotation rates of 611 $\gamma$ Doradus stars with \textit{Kepler}
• The period-luminosity relation for delta Scuti stars using Gaia DR2 parallaxes
• MOBSTER - II. Identification of rotationally variable A stars observed with \emph{TESS} in Sectors 1 to 4
• Blobs, spiral arms, and a possible planet around HD 169142
• Rotation and pulsation in Ap stars: first light results from TESS sectors 1 and 2
• Gaia's view of the $\lambda$ Boo star puzzle
• Characterization of the inner disk around HD 141569 A from Keck/NIRC2 L-band vortex coronagraphy
• TESS first look at evolved compact pulsators : Discovery and asteroseismic probing of the g-mode hot B subdwarf pulsator EC 21494-7018
• The role of rotation on Petersen Diagrams. II The influence of near-degeneracy
• Pulsation of the Lambda Bootis star HD 210111
• Imaging the 44 AU Kuiper Belt-analogue debris ring around HD 141569A with GPI polarimetry

Cited by in corpus (10)

• A precise asteroseismic age and metallicity for HD 139614: a pre-main-sequence star with a protoplanetary disc in Upper-Centaurus Lupus
• Revisiting bright delta Scuti stars and their period-luminosity relation with TESS and Gaia DR3
• TESS observations of the Pleiades cluster: a nursery for delta Scuti stars
• Pulsational instability of pre-main sequence models from accreting protostars. I. Constraining the input physics for accretion with spectroscopic parameters and stellar pulsations
• The Discovery of lambda Bootis Stars -- The Southern Survey II
• The Effects of Metallicity on Convective Overshoot Behaviour in Models of delta Scuti Variable Stars
• Variability and stellar pulsation incidence in Am/Fm stars using TESS and Gaia data
• Modelling $\delta$ Scuti pulsations: A new grid of p, g, and f modes across pre-main-sequence to post-main-sequence evolution
• Searching for lambda Boo stars in binary systems
• Characterizing bright $\delta$ Scuti pulsators using TESS lightcurves