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Title: The factory and the beehive. II. Activity and rotation in Praesepe and the Hyades

Open clusters are collections of stars with a single, well-determined age, and can be used to investigate the connections between angular-momentum evolution and magnetic activity over a star's lifetime. We present the results of a comparative study of the relationship between stellar rotation and activity in two benchmark open clusters: Praesepe and the Hyades. As they have the same age and roughly solar metallicity, these clusters serve as an ideal laboratory for testing the agreement between theoretical and empirical rotation-activity relations at ≈600 Myr. We have compiled a sample of 720 spectra—more than half of which are new observations—for 516 high-confidence members of Praesepe; we have also obtained 139 new spectra for 130 high-confidence Hyads. We have also collected rotation periods (P {sub rot}) for 135 Praesepe members and 87 Hyads. To compare Hα emission, an indicator of chromospheric activity, as a function of color, mass, and Rossby number R{sub o} , we first calculate an expanded set of χ values, with which we can obtain the Hα to bolometric luminosity ratio, L {sub Hα}/L {sub bol}, even when spectra are not flux-calibrated and/or stars lack reliable distances. Our χ values cover a broader range of stellar masses and colorsmore » (roughly equivalent to spectral types from K0 to M9), and exhibit better agreement between independent calculations, than existing values. Unlike previous authors, we find no difference between the two clusters in their Hα equivalent width or L {sub Hα}/L {sub bol} distributions, and therefore take the merged Hα and P {sub rot} data to be representative of 600 Myr old stars. Our analysis shows that Hα activity in these stars is saturated for R{sub o}≤0.11{sub −0.03}{sup +0.02}. Above that value activity declines as a power-law with slope β=−0.73{sub −0.12}{sup +0.16}, before dropping off rapidly at R{sub o} ≈ 0.4. These data provide a useful anchor for calibrating the age-activity-rotation relation beyond 600 Myr.« less
Authors:
; ; ; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8]
  1. Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)
  2. Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)
  3. Haverford College, 370 Lancaster Avenue, Haverford, PA 19041 (United States)
  4. Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States)
  5. Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712 (United States)
  6. Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599 (United States)
  7. Department of Astronomy, Yale University, New Haven, CT 06520 (United States)
  8. Department of Astronomy, University of Wisconsin-Madison, 2535 Sterling Hall, 475 North Charter Street, Madison, WI 53706 (United States)
Publication Date:
OSTI Identifier:
22370001
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 795; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANGULAR MOMENTUM; BOLOMETERS; COLOR; DISTRIBUTION; EMISSION; LIFETIME; LUMINOSITY; MASS; METALLICITY; ROTATION; SPECTRA; STAR EVOLUTION; STARS