More Like this

1. Acoustic modes in M67 cluster stars trace deepening convective envelopes

   https://doi.org/10.1038/s41586-025-08760-2  

   Reyes, Claudia; Stello, Dennis; Ong, Joel; Lindsay, Christopher; Hon, Marc; Bedding, Timothy R (April 2025, Nature)

   Abstract Acoustic oscillations in stars are sensitive to stellar interiors¹. Frequency differences between overtone modes—large separations—probe stellar density², whereas differences between low-degree modes—small separations—probe the sound-speed gradient in the energy-generating core of main-sequence Sun-like stars³, and hence their ages. At later phases of stellar evolution, characterized by inert cores, small separations are believed to lose much of their power to probe deep interiors and become proportional to large separations^4,5. Here we present evidence of a rapidly evolving convective zone as stars evolve from the subgiant phase into red giants. By measuring acoustic oscillations in 27 stars from the open cluster M67, we observe deviations of proportionality between small and large separations, which are caused by the influence of the bottom of the convective envelope. These deviations become apparent as the convective envelope penetrates deep into the star during subgiant and red giant evolutions, eventually entering an ultradeep regime that leads to the red-giant-branch luminosity bump. The tight sequence of cluster stars, free of large spreads in ages and fundamental properties, is essential for revealing the connection between the observed small separations and the chemical discontinuities occurring at the bottom of the convective envelope. We use this sequence to show that combining large and small separations can improve estimations of the masses and ages of field stars well after the main sequence. 

   more » « less
2. Stellar Radial Velocities in the Old Open Cluster M67 (NGC 2682). II. The Spectroscopic Binary Population

   https://doi.org/10.3847/1538-3881/abdd23  

   Geller, Aaron M.; Mathieu, Robert D.; Latham, David W.; Pollack, Maxwell; Torres, Guillermo; Leiner, Emily M. (March 2021, The Astronomical Journal)

   null (Ed.)
3. A 4 Gyr M-dwarf Gyrochrone from CFHT/MegaPrime Monitoring of the Open Cluster M67

   https://doi.org/10.3847/1538-4357/ac90be  

   Dungee, Ryan; van Saders, Jennifer; Gaidos, Eric; Chun, Mark; García, Rafael A.; Magnier, Eugene A.; Mathur, Savita; Santos, Ângela R. G. (October 2022, The Astrophysical Journal)

   Abstract We present stellar rotation periods for late K- and early M-dwarf members of the 4 Gyr old open cluster M67 as calibrators for gyrochronology and tests of stellar spin-down models. Using Gaia EDR3 astrometry for cluster membership and Pan-STARRS (PS1) photometry for binary identification, we build this set of rotation periods from a campaign of monitoring M67 with the Canada–France–Hawaii Telescope’s MegaPrime wide-field imager. We identify 1807 members of M67, of which 294 are candidate single members with significant rotation period detections. Moreover, we fit a polynomial to the period versus color-derived effective temperature sequence observed in our data. We find that the rotation of very cool dwarfs can be explained by simple solid-body spin-down between 2.7 and 4 Gyr. We compare this rotational sequence to the predictions of gyrochronological models and find that the best match is Skumanich-like spin-down,P_rot∝t^0.62, applied to the sequence of Ruprecht 147. This suggests that, for spectral types K7–M0 with near-solar metallicity, once a star resumes spinning down, a simple Skumanich-like relation is sufficient to describe their rotation evolution, at least through the age of M67. Additionally, for stars in the range M1–M3, our data show that spin-down must have resumed prior to the age of M67, in conflict with the predictions of the latest spin-down models. 

   more » « less
4. A uvbyCaHβ CCD Analysis of the Open Cluster Standard, M67, and Its Relation to NGC 752

   https://doi.org/10.3847/1538-3881/acb0ce  

   Twarog, Bruce A.; Anthony-Twarog, Barbara J.; Deliyannis, Constantine P. (February 2023, The Astronomical Journal)

   Abstract Precision CCDuvbyCaHβphotometry is presented of the old cluster, M67, covering one square degree with typical internal precision at the 0.005–0.020 mag level toV∼ 17. The photometry is calibrated using standards over a wide range in luminosity and temperature from NGC 752 and zeroed to the standard system via published photoelectric observations. Relative to NGC 752, differential offsets in reddening and metallicity are derived using astrometric members, supplemented by radial velocity information. From single-star members, offsets in the sense (M67−NGC 752) areδE(b−y) = −0.005 ± 0.001 (sem) mag from 327 F/G dwarfs andδ[Fe/H] = 0.062 ± 0.006 (sem) dex from the combinedm₁andhkindices of 249 F dwarfs, leading toE(b−y) = 0.021 ± 0.004 (sem) and [Fe/H]_M67= +0.030 ± 0.016 (sem) assuming [Fe/H]_Hyades= +0.12. With probable binaries eliminated usingc₁, (b−y) indices, 83 members with (π/σ_π) > 50 generate (m−M)₀= 8.220 ± 0.005 (sem) for NGC 752 and an isochronal age of 1.45 ± 0.05 Gyr. Using the same parallax restriction for 312 stars, M67 has (m−M) = 9.77 ± 0.02 (sem), leading to an age tied solely to the luminosity of the subgiant branch of 3.70 ± 0.03 Gyr. The turnoff color spread implies ±0.1 Gyr, but the turnoff morphology defines a younger age/higher mass for the stars, consistent with recent binary analysis and broadband photometry indicating possible missing physics in the isochrones. Anomalous stars positioned blueward of the turnoff are discussed. 

   more » « less
5. Correlated Depletion and Dilution of Lithium and Beryllium Revealed by Subgiants in M67

   https://doi.org/10.3847/1538-4357/ab4fdb  

   Boesgaard, Ann Merchant; Lum, Michael G.; Deliyannis, Constantine P. (January 2020, The Astrophysical Journal)