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1. 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)

   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 themore »age of M67, in conflict with the predictions of the latest spin-down models.

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2. The Gaia -ESO Survey: a new approach to chemically characterising young open clusters: II. Abundances of the neutron-capture elements Cu, Sr, Y, Zr, Ba, La, and Ce

   https://doi.org/10.1051/0004-6361/202141069  

   Baratella, M. ; D’Orazi, V. ; Sheminova, V. ; Spina, L. ; Carraro, G. ; Gratton, R. ; Magrini, L. ; Randich, S. ; Lugaro, M. ; Pignatari, M. ; et al ( September 2021 , Astronomy & Astrophysics)

   Context. Young open clusters (ages of less than 200 Myr) have been observed to exhibit several peculiarities in their chemical compositions. These anomalies include a slightly sub-solar iron content, super-solar abundances of some atomic species (e.g. ionised chromium), and atypical enhancements of [Ba/Fe], with values up to ~0.7 dex. Regarding the behaviour of the other s -process elements like yttrium, zirconium, lanthanum, and cerium, there is general disagreement in the literature: some authors claim that they follow the same trend as barium, while others find solar abundances at all ages. Aims. In this work we expand upon our previous analysis of a sample of five young open clusters (IC 2391, IC 2602, IC 4665, NGC 2516, and NGC 2547) and one star-forming region (NGC 2264), with the aim of determining abundances of different neutron-capture elements, mainly Cu  I , Sr  I , Sr  II , Y  II , Zr  II , Ba  II , La  II , and Ce  II . For NGC 2264 and NGC 2547 we present the measurements of these elements for the first time. Methods. We analysed high-resolution, high signal-to-noise spectra of 23 solar-type stars observed within the Gaia -ESO survey. After a careful selection, wemore »derived abundances of isolated and clean lines via spectral synthesis computations and in a strictly differential way with respect to the Sun. Results. We find that our clusters have solar [Cu/Fe] within the uncertainties, while we confirm that [Ba/Fe] is super-solar, with values ranging from +0.22 to +0.64 dex. Our analysis also points to a mild enhancement of Y, with [Y/Fe] ratios covering values between 0 and +0.3 dex. For the other s -process elements we find that [X/Fe] ratios are solar at all ages. Conclusions. It is not possible to reconcile the anomalous behaviour of Ba and Y at young ages with standard stellar yields and Galactic chemical evolution model predictions. We explore different possible scenarios related to the behaviour of spectral lines, from the dependence on the different ionisation stages and the sensitivity to the presence of magnetic fields (through the Landé factor) to the first ionisation potential effect. We also investigate the possibility that they may arise from alterations of the structure of the stellar photosphere due to the increased levels of stellar activity that affect the spectral line formation, and consequently the derived abundances. These effects seem to be stronger in stars at ages of less than ~ 100 Myr. However, we are still unable to explain these enhancements, and the Ba puzzle remains unsolved. With the present study we suggest that other elements, for example Sr, Zr, La, and Ce, might be more reliable tracer of the s -process at young ages, and we strongly encourage further critical observations.« less
3. Detections of solar-like oscillations in dwarfs and subgiants with Kepler DR25 short-cadence data

   https://doi.org/10.1051/0004-6361/202141168  

   Mathur, S. ; García, R. A. ; Breton, S. ; Santos, A. R. ; Mosser, B. ; Huber, D. ; Sayeed, M. ; Bugnet, L. ; Chontos, A. ( January 2022 , Astronomy & Astrophysics)

   During the survey phase of the Kepler mission, several thousand stars were observed in short cadence, allowing for the detection of solar-like oscillations in more than 500 main-sequence and subgiant stars. These detections showed the power of asteroseismology in determining fundamental stellar parameters. However, the Kepler Science Office discovered an issue in the calibration that affected half of the store of short-cadence data, leading to a new data release (DR25) with corrections on the light curves. In this work, we re-analyzed the one-month time series of the Kepler survey phase to search for solar-like oscillations that might have been missed when using the previous data release. We studied the seismic parameters of 99 stars, among which there are 46 targets with new reported solar-like oscillations, increasing, by around 8%, the known sample of solar-like stars with an asteroseismic analysis of the short-cadence data from this mission. The majority of these stars have mid- to high-resolution spectroscopy publicly available with the LAMOST and APOGEE surveys, respectively, as well as precise Gaia parallaxes. We computed the masses and radii using seismic scaling relations and we find that this new sample features massive stars (above 1.2  M ⊙ and up to 2  Mmore »⊙ ) and subgiants. We determined the granulation parameters and amplitude of the modes, which agree with the scaling relations derived for dwarfs and subgiants. The stars studied here are slightly fainter than the previously known sample of main-sequence and subgiants with asteroseismic detections. We also studied the surface rotation and magnetic activity levels of those stars. Our sample of 99 stars has similar levels of activity compared to the previously known sample and is in the same range as the Sun between the minimum and maximum of its activity cycle. We find that for seven stars, a possible blend could be the reason for the non-detection with the early data release. Finally, we compared the radii obtained from the scaling relations with the Gaia ones and we find that the Gaia radii are overestimated by 4.4%, on average, compared to the seismic radii, with a scatter of 12.3% and a decreasing trend according to the evolutionary stage. In addition, for homogeneity purposes, we re-analyzed the DR25 of the main-sequence and subgiant stars with solar-like oscillations that were previously detected and, as a result, we provide the global seismic parameters for a total of 525 stars.« less
4. Magnetic and Rotational Evolution of ρ CrB from Asteroseismology with TESS

   Metcalfe, Travis S. ; van Saders, Jennifer L. ; Basu, Sarbani ; Buzasi, Derek ; Drake, Jeremy J. ; Egeland, Ricky ; Huber, Daniel ; Saar, Steven H. ; Stassun, Keivan G. ; Ball, Warrick H. ; et al ( October 2021 , The Astrophysical journal)

   During the first half of main-sequence lifetimes, the evolution of rotation and magnetic activity in solar-type stars appears to be strongly coupled. Recent observations suggest that rotation rates evolve much more slowly beyond middle-age, while stellar activity continues to decline. We aim to characterize this mid-life transition by combining archival stellar activity data from the Mount Wilson Observatory with asteroseismology from the Transiting Exoplanet Survey Satellite (TESS). For two stars on opposite sides of the transition (88 Leo and ρ CrB), we independently assess the mean activity levels and rotation periods previously reported in the literature. For the less active star (ρ CrB), we detect solar-like oscillations from TESS photometry, and we obtain precise stellar properties from asteroseismic modeling. We derive updated X-ray luminosities for both stars to estimate their mass-loss rates, and we use previously published constraints on magnetic morphology to model the evolutionary change in magnetic braking torque. We then attempt to match the observations with rotational evolution models, assuming either standard spin-down or weakened magnetic braking. We conclude that the asteroseismic age of ρ CrB is consistent with the expected evolution of its mean activity level, and that weakened braking models can more readily explain its relativelymore »fast rotation rate. Future spectropolarimetric observations across a range of spectral types promise to further characterize the shift in magnetic morphology that apparently drives this mid-life transition in solar-type stars.« less
5. LoVoCCS. I. Survey Introduction, Data Processing Pipeline, and Early Science Results

   https://doi.org/10.3847/1538-4357/ac68e8  

   Fu, Shenming ; Dell’Antonio, Ian ; Chary, Ranga-Ram ; Clowe, Douglas ; Cooper, M. C. ; Donahue, Megan ; Evrard, August ; Lacy, Mark ; Lauer, Tod ; Liu, Binyang ; et al ( July 2022 , The Astrophysical Journal)

   We present the Local Volume Complete Cluster Survey (LoVoCCS; we pronounce it as “low-vox” or “law-vox,” with stress on the second syllable), an NSF’s National Optical-Infrared Astronomy Research Laboratory survey program that uses the Dark Energy Camera to map the dark matter distribution and galaxy population in 107 nearby (0.03 <z< 0.12) X-ray luminous ([0.1–2.4 keV]L_X500> 10⁴⁴erg s⁻¹) galaxy clusters that are not obscured by the Milky Way. The survey will reach Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) Year 1–2 depth (for galaxiesr= 24.5,i= 24.0, signal-to-noise ratio (S/N) > 20;u= 24.7,g= 25.3,z= 23.8, S/N > 10) and conclude in ∼2023 (coincident with the beginning of LSST science operations), and will serve as a zeroth-year template for LSST transient studies. We process the data using the LSST Science Pipelines that include state-of-the-art algorithms and analyze the results using our own pipelines, and therefore the catalogs and analysis tools will be compatible with the LSST. We demonstrate the use and performance of our pipeline using three X-ray luminous and observation-time complete LoVoCCS clusters: A3911, A3921, and A85. A3911 and A3921 have not been well studied previously by weak lensing, and we obtain similar lensing analysis resultsmore »for A85 to previous studies. (We mainly use A3911 to show our pipeline and give more examples in the Appendix.)

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