Expanding Asteroseismic Studies in Star Clusters Using NASA's TESS and ESA's Gaia Missions

Abstract

Star clusters have long been central to the study of stellar evolution due to their chemically and chronologically homogeneous populations. Asteroseismology, the analysis of stellar oscillations and pulsations, provides precise information about properties such as masses, radii, and ages of stars in the field. However, these stars lack calibration to an absolute scale, and so this project seeks to utilize the data from NASA's TESS mission and ESA's Gaia mission to identify additional cluster stars suitable for asteroseismic analysis and calibration. In this work we analyze 14 stars belonging to 3 well-populated clusters, 5 additional stars that are the only detected oscillators in their respective clusters, and 3 detected oscillators of unknown cluster membership. By significantly expanding the number of clusters with measured oscillating giants, this project increases the opportunity for cross-validation between classical stellar models and asteroseismic methods, allowing for improvements in both calibration techniques and age estimations across the galaxy.

Figures (22)

• Figure 1: Global HR diagram using (Gaia) absolute magnitude vs BP-RP color. Main sequence stars are shown in blue, potential red-giants in red, seismic detections marked as green stars, and the main sequence approximated by the black dashed line.
• Figure 2: Cluster HR diagrams for the three clusters in our study with more than one seismic detection in a giant. Panels (a)-(c) show individual clusters with main sequence stars in blue, potential red-giants in orange, and seismic detections marked as orange stars. Panel (d) overlays all three clusters: Theia 6046 in teal, NGC 752 in orange, Casado Alessi-1 in magenta, with potential red-giants shown as stars, seismic detections circled in red, and the main sequence approximated by the black dashed line.
• Figure 3: Nine-panel grid of TESS targets across various bleeding (grouped horizontally) and crowding (grouped vertically) ratings.
• Figure 4: Example of the background modeling and $\nu_{\max}$ measurement process for TIC 306955660. Panel (a) shows the detrended time series. Panel (b) displays the initial background fit to the power spectrum. Panel (c) presents the background-corrected power spectrum, where the oscillation signal emerges. Panel (d) shows the smoothed spectrum with a Gaussian fit to the oscillation envelope; the vertical dashed line indicates the measured $\nu_{\max}$. This workflow shows how we extract global asteroseismic parameters from TESS data for our cluster sample.
• Figure 5: Échelle diagnostics for TIC 306552813 with adopted large separation $\Delta\nu=6.479~\mu\mathrm{Hz}$. Panel (a) shows the collapsed/overlay representation: the power spectrum is folded by $\Delta\nu$ (x-axis: frequency modulo $\Delta\nu$) and collapsed across the displayed $\pm2\Delta\nu$ window; the collapse is replicated in y for visualization. Panel (b) shows the 2D échelle: x is frequency modulo $\Delta\nu$ and y is an order index spanning the $\pm2\Delta\nu$ window around nu_max. Mode ridges appear as near-vertical bands of enhanced power in the 2D échelle; for this target the most prominent vertical bands are concentrated near $\nu \bmod \Delta\nu \approx 0.5~\mu\mathrm{Hz}$, $\nu \bmod \approx 3.2$--$3.6~\mu\mathrm{Hz}$, and $\nu \bmod \approx 5.3$--$5.4~\mu\mathrm{Hz}$. These same x-locations correspond to the strongest columns in the collapsed/overlay panel.