An empirical isochrone for the Hyades

The isochrone here is described in Pinsonneault et al. 2004, "The Distances to Open Clusters as Derived from Main-Sequence Fitting. II. Construction of Empirically Calibrated Isochrones," ApJ, 600, 946.  

We began with the latest YREC evolutionary tracks (Sills, Pinsonneault & Terndrup 2000), and generated an isochrone at [Fe/H] = +0.13, the Hyades metallicity from Paulson, Sneden, & Cochran (2003).  Then we generated corrections to the isochrone colors to better match photometry in the Hyades.  That paper showed that other widely available color-temperature relations, such as those in Alonso et al. (1995, 1996) or Lejeune et al. (1998), did not precisely match multicolor photometry in the Hyades.  We then described a method of generating adjustments to the broadband colors to bring the isochrone and the photometry into better agreement.  These adjustments are applied to isochrones with several metallicities on this page.

The isochrone is given in the file hyadesiso.txt, a tab-separated file.  The columns are:

  1. Effective temperature (Kelvins)
  2. Mass (solar units)
  3. Absolute visual magnitude
  4. B-V color
  5. Cousins V-I color
  6. V-K color, where K is on the 2MASS system
  7. color correction from the Lejeune (1998) color-temperature relation applied in B-V
  8. color correction in V-I
  9. color correction in V-K

The photometric data used to calibrate the isochrone is given in the file hyadesphot.txt.  The columns are:

  1. Hipparcos star number
  2. V magnitude
  3. adopted error in V
  4. absolute visual magnitude MV, determined from the Hipparcos parallaxes as described in Pinsonneault et al. (2004)
  5. error in MV
  6. B-V
  7. error in B-V
  8. Cousins V-I
  9. error in V-I
  10. Ks ("short" K) magnitude from 2MASS
  11. error in Ks
  12. V-Ks color
  13. error in V-Ks

Missing data are listed as 99999 or .9999 in an obvious fashion.

The agreement between the Hyades photometry and the empirical isochrone can be judged in three CMDs in postscript format: bvcmd.ps, vicmd.ps, and vkcmd.ps.

See Taylor & Joner (2005), who disagreed with some details of the assembly of the photometry.

References:

Alonso, A., Arribas, S., & Martínez-Roger, C. 1995, A&A, 297, 197
Alonso, A., Arribas, S., & Martínez-Roger, C. 1996, A&AS, 117, 227
Lejeune, T., Cuisinier, F., & Buser, R. 1998, A&AS, 130, 65
Paulson, D. B., Sneden, C., & Cochran, D. W. 2003, AJ, 125, 3185
Sills, A., Pinsonneault, M. H., & Terndrup, D. 2000, ApJ, 534, 335 
Taylor, B. J., & Joner, M. D. 2005, ApJS, 159, 100

Return to: YREC isochrones and tracks | Department of Astronomy | Ohio State University

Last modified:  August 9, 2005 (dmt)