DEEP IR IMAGING OF GLOBULAR CLUSTERS. III. M13
Journal Articles
Overview
Research
View All
Overview
abstract
We have used the CFHT REDEYE infrared camera to obtain deep J and K' images
of four fields in the globular cluster M13. The composite K, J-K
color-magnitude diagram (CMD) extends from the upper red giant branch (RGB) to
2 magnitudes below the main sequence turn-off (MSTO). Selected [Fe/H]~ -1.6
isochrones from Bergbusch & VandenBerg (1992, ApJS, 81, 163) and Straniero &
Chieffi (1991, ApJS, 76, 525) are transformed onto the near-infrared
observational plane, and these suggest an age for M13 in the range 14-16 Gyr.
We emphasize that any effort to estimate ages should be considered as tentative
given uncertainties in the input physics; however, these uncertainties
notwithstanding, comparisons between the near-infrared isochrones indicate that
age differences of order +/-2 Gyr should be detectable among metal-poor
clusters on the K, J-K plane. Building on this result, we find that the
difference in J-K color between the MSTO and the base of the RGB in M13 is the
same as in M4, and conclude that these clusters have similar ages. This
conclusion is verified by comparing (1) the K brightnesses of the MSTO, and (2)
the morphologies of optical CMDs. Finally, we investigate the mass function of
main sequence stars in M13 with distances between 3 and 6 core radii from the
cluster center. The mass functions in the interval 0.55 and 0.8 solar masses
are relatively flat, independent of radius. Optical studies at larger radii
have found non-zero mass function indices in this same mass interval, and we
attribute this radial variation in mass function morphology to dynamical
evolution.
