Abstract The surface abundances of the light elements lithium (Li) and beryllium (Be) reveal information about the physical processes taking place in stellar interiors. The investigation of the amount of these two elements in stars in open clusters shows the effect of age on those mechanisms. We have obtained spectra of both Li and Be in main-sequence stars in NGC 752 at high spectral resolution and high signal-to-noise ratios with HIRES on the Keck I telescope. In order to make meaningful comparisons with other clusters, we have determined the stellar parameters on a common scale. We have found abundances of Li and Be by spectral synthesis techniques. NGC 752 is twice the age of the well-studied Hyades. We find that (1) the Li dip centered near 6500 K is wider in NGC 752, having expanded toward cooler temperatures; (2) the Be dip is deeper in the older NGC 752; (3) the Li “peak” near 6200 K is lower by about 0.3 dex; (4) although there is little Be depletion in the cooler stars, it is possible that Be may be lower in NGC 752 than in the Hyades; and (5) the Li content in both clusters declines with decreasing temperature, but there is less Li in NGC 752 at a given temperature by ∼0.4 dex. These differences are consistent with the transport of the light-element nuclei below the surface convection zone as predicted by theory. That connection to rotational spin-down is indicated by the pattern of rotation with temperature in the two clusters.
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WIYN Open Cluster Study 89. M48 (NGC 2548) 2: Lithium Abundances in the 420 Myr Open Cluster M48 from Giants through K Dwarfs* †
We consider WIYN/Hydra spectra of 329 photometric candidate members of the 420 Myr old open cluster M48 and report lithium detections or upper limits for 234 members and likely members. The 171 single members define a number of notable Li-mass trends, some delineated even more clearly than in Hyades/Praesepe: the giants are consistent with subgiant Li dilution and prior MS Li depletion due to rotational mixing. A dwarfs (8600–7700 K) have upper limits higher than the presumed initial cluster Li abundance. Two of five late A dwarfs (7700–7200 K) are Li-rich, possibly due to diffusion, planetesimal accretion, and/or engulfment of hydrogen-poor planets. Early F dwarfs already show evidence of Li depletion seen in older clusters. The Li–
- Award ID(s):
- 1909456
- NSF-PAR ID:
- 10432911
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 952
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 71
- Size(s):
- ["Article No. 71"]
- Sponsoring Org:
- National Science Foundation
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Abstract Low-mass (≲1.2
M ⊙) main-sequence stars lose angular momentum over time, leading to a decrease in their magnetic activity. The details of this rotation–activity relation remain poorly understood, however. Using observations of members of the ≈700 Myr old Praesepe and Hyades open clusters, we aim to characterize the rotation–activity relation for different tracers of activity at this age. To complement published data, we obtained new optical spectra for 250 Praesepe stars, new X-ray detections for 10, and new rotation periods for 28. These numbers for Hyads are 131, 23, and 137, respectively. The latter increases the number of Hyads with periods by 50%. We used these data to measure the fractional Hα and X-ray luminosities,L Hα /L bolandL X/L bol, and to calculate Rossby numbersR o. We found that at ≈700 Myr almost all M dwarfs exhibit Hα emission, with binaries having the same overall color–Hα equivalent width distribution as single stars. In theR o–L Hα /L bolplane, unsaturated single stars follow a power law with indexβ = −5.9 ± 0.8 forR o> 0.3. In theR o–L X/L bolplane, we see evidence for supersaturation for single stars withR o≲ 0.01, following a power law with indexR ovalue at which activity saturates is smaller forL X/L bolthan forL Hα /L bol. Finally, we observed an almost 1:1 relation betweenL Hα /L bolandL X/L bol, suggesting that both the corona and the chromosphere experience similar magnetic heating. -
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Abstract X-ray observations of low-mass stars in open clusters are critical to understanding the dependence of magnetic activity on stellar properties and their evolution. Praesepe and the Hyades, two of the nearest, most-studied open clusters, are among the best available laboratories for examining the dependence of magnetic activity on rotation for stars with masses ≲1
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Abstract Precision CCD
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