Asteroseismology of luminous red giants with Kepler I: Long Period Variables with radial and non-radial modes

Abstract

While long period variables (LPVs) have been extensively investigated, especially with MACHO and OGLE data for the Magellanic Clouds, there still exist open questions in their pulsations regarding the excitation mechanisms, radial order and angular degree assignment. Here, we perform asteroseismic analyses on LPVs observed by the 4-year Kepler mission. Using a cross-correlation method, we detect unambiguous pulsation ridges associated with radial fundamental modes ($n=1$) and overtones ($n⩾2$), where the radial order assignment is made by using theoretical frequencies and observed frequencies. Our results confirm that the amplitude variability seen in semiregulars is consistent with oscillations being solar-like. We identify that the dipole modes, $l=1$, are dominant in the radial orders of $3\le n\le 6$, and that quadrupole modes, $l=2$, are dominant in the first overtone $n=2$. A test of seismic scaling relations using Gaia DR2 parallaxes reveals the possibility that the relations break down when ${\nu }_{\max }$ $\lesssim$ 3 $\mu$Hz (R $\gtrsim$ 40 R${}_{\odot }$, or log $L/{\mathrm{L}}_{\odot }$ $\gtrsim$ 2.6). Our homogeneous measurements of pulsation amplitude and period for 3213 LPVs will be very valuable for probing effects of pulsation on mass loss, in particular in those stars with periods around 60 days, which has been argued as a threshold of substantial pulsation-triggered mass loss.

17 pages, 13 figures, 1 table. Accepted for publication in MNRAS. Table 1 is available for download as an ancillary file

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• The Stars Kepler Missed: Investigating the Kepler Target Selection Function Using Gaia DR2
• Asteroseismology of luminous red giants with Kepler. II. Dependence of mass loss on pulsations and radiation
• The far side of the Galactic bar/bulge revealed through semi-regular variables
• Kepler meets Gaia DR3: homogeneous extinction-corrected color-magnitude diagram and binary classification
• Astroconformer: The Prospects of Analyzing Stellar Light Curves with Transformer-Based Deep Learning Models
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• Measuring frequency and period separations in red-giant stars using machine learning
• Automated Extended Aperture Photometry of K2 variable stars
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• Self-Excited Pulsations and the Instability Strip of Long-Period Variables: the Transition from Small-Amplitude Red Giants to Semi-Regular Variables
• Tracking Advanced Planetary Systems (TAPAS) with HARPS-N VII. Elder suns with low-mass companions
• FALCO: a Foundation model of Astronomical Light Curves for time dOmain astronomy
• Beyond MESA Defaults: The Impact of Structural Resolution Uncertainty in p-mode Asteroseismology
• Asteroseismology of red giants in the globular cluster 47 Tuc using the HST
• Halo Photometry and Asteroseismology for 98 of the Brightest Stars Observed by TESS
• Physical interpretation of the oscillation spectrum on the RGB and AGB