VLTI-GRAVITY measurements of cool evolved stars: II. Pulsation properties and mass-loss process of the Mira star R Car and the red supergiant VX Sgr

Abstract

The mass-loss process of red supergiant (RSG) and asymptotic giant branch (AGB) stars and its relation to variability are poorly constrained. We study two evolved stars, the Mira-type AGB star R Car and the extreme RSG VX Sgr. Our sample comprises 54 VLTI-GRAVITY snapshots taken over 7 years, being the largest VLTI time-series dataset to date. We determine the angular diameter as a function of time. The radii of the photosphere ($R_{\star }$) and atomic atmospheric layers are variable and relate to the light curve with phase shifts, showing a maximum radius near visual brightness minima. The more extended CO layers show longer, irregular periods and maximum extensions of $\sim 1.3-1.7R_{\star }$ for R Car, and of $\sim 1.5-2.2R_{\star }$ for VX Sgr. Comparison with CO5BOLD simulations revealed a similar behavior. Furthermore, during 2020-2021, VX Sgr exhibited an extreme mass-loss event similar to that of Betelgeuse, preceded by two strong shocks and culminating with the extreme expansion of H${}_2$O and CO layers, both up to $\sim 2.2R_{\star }$. During this event, we detected Brackett $\gamma$ and Balmer emission lines, both of which are signatures of a shock propagating through the atmosphere. The Mira R Car showed a photospheric radius $R_{\star }=280\pm 25{\mathrm{R}}_{\odot }$, with a fundamental mode (FM) pulsation amplitude $\sim 13\%$ of $R_{\star }$. During its active cycle, the RSG VX Sgr showed $R_{\star }=1556\pm 110{\mathrm{R}}_{\odot }$ with FM amplitude $\sim 13\%$ of $R_{\star }$, the same as R Car. During its quiescent cycle, it showed $R_{\star }=1456\pm 108{\mathrm{R}}_{\odot }$ and low-amplitude pulsations near the first overtone, only $\sim 4\%$ of $R_{\star }$. This supports a steady mass loss for Miras related to stable, large-amplitude FM pulsation, whereas the mass-loss process for RSGs may be dominated by extreme events connected to changes in the pulsation mode.

Accepted for publication in A&A, a language-corrected version

References in corpus (42)

• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The Athena++ Adaptive Mesh Refinement Framework: Design and Magnetohydrodynamic Solvers
• Variability in red supergiant stars: pulsations, long secondary periods and convection noise
• Atmospheric dynamics and the mass loss process in red supergiant stars
• Final Moments I: Precursor Emission, Envelope Inflation, and Enhanced Mass loss Preceding the Luminous Type II Supernova 2020tlf
• 2D Models for Dust-driven AGB Star Winds
• A dusty veil shading Betelgeuse during its Great Dimming
• What causes the large extensions of red-supergiant atmospheres? Comparisons of interferometric observations with 1-D hydrostatic, 3-D convection, and 1-D pulsating model atmospheres
• Numerical Simulations of Convective 3-Dimensional Red Supergiant Envelopes
• Near-IR Spectra of Red Supergiants and Giants. I- Models with Solar and with Mixing-Induced Surface Abundance Ratios
• Dynamical Opacity-Sampling Models of Mira Variables. I: Modelling Description and Analysis of Approximations
• An extensive grid of DARWIN models for M-type AGB stars I. Mass-loss rates and other properties of dust-driven winds
• The evolution of DARWIN: current status of wind models for AGB stars
• The molecular and dusty composition of Betelgeuse's inner circumstellar environment
• Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse
• The Great Dimming of Betelgeuse: a Surface Mass Ejection (SME) and its Consequences
• Atmosphere of Betelgeuse before and during the Great Dimming event revealed by tomography
• Exploring the origin of clumpy dust clouds around cool giants. A global 3D RHD model of a dust-forming M-type AGB star
• Global 3D radiation-hydrodynamical models of AGB stars with dust-driven winds
• Episodic Gaseous Outflows and Mass Loss from Red Supergiants
• Tomography of cool giant and supergiant star atmospheres II. Signature of convection in the atmosphere of the red supergiant star $\mu$ Cep
• Betelgeuse fainter in the sub-millimetre too: an analysis of JCMT and APEX monitoring during the recent optical minimum
• The Great Dimming of Betelgeuse seen by the Himawari-8 meteorological satellite
• Properties of self-excited pulsations in 3D simulations of AGB stars and red supergiants
• Dynamic atmospheres and winds of cool luminous giants, II. Gradual Fe enrichment of wind-driving silicate grains
• The impact of winds on the spectral appearance of Red Supergiants
• VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A), sigma Oph, BM Sco, and HD 206859
• Determination of pulsation periods and other parameters of 2875 stars classified as MIRA in the All Sky Automated Survey (ASAS)
• The extended atmosphere and circumstellar environment of the cool evolved star VX Sagittarii as seen by MATISSE
• The Great Dimming of Betelgeuse: the photosphere as revealed by tomography over the past 15 years
• One month convection timescale on the surface of a giant evolved star
• The effect of winds on atmospheric layers of red supergiants I. Modelling for interferometric observations
• A new dimension in the variability of AGB stars: convection patterns size changes with pulsation
• The effect of winds on atmospheric layers of red supergiants II. Modelling VLTI/GRAVITY and MATISSE observations of AH Sco, KW Sgr, V602 Car, CK Car and V460 Car
• Eppur si eclissa: Eccentric low-mass companions and time-in-dust selection explain long secondary periods
• The K-band highest-resolution images of the Mira star R Car with GRAVITY-VLTI
• The dramatic transition of the extreme Red Supergiant WOH G64 to a Yellow Hypergiant
• MOLsphere and pulsations of the Galactic Center's red supergiant GCIRS 7 from VLTI/GRAVITY
• Pulsations change the structures of massive stars before explosion: interpreting SN 2023ixf and SN 2024ggi
• Multi-mode Pulsations in AGB Stars: Insights from 3D RHD CO5BOLD Simulations
• Thorne-Żytkow Objects