TY - JOUR
T1 - Red giant branch bump star counts in data and stellar models
AU - Nataf, David M.
N1 - Publisher Copyright:
© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2014/9/29
Y1 - 2014/9/29
N2 - We compare model predictions to observations of star counts in the red giant branch bump (RGBB) relative to the number density of first-ascent red giant branch at the magnitude of the RGBB, EWRGBB. The predictions are shown to exceed the data by (5.2 ± 4.3) per cent for the BaSTI models and by (17.1 ± 4.3) per cent for the Dartmouth models, where the listed errors are purely statistical. These two offsets are brought to zero if the Galactic globular cluster metallicity scale is assumed to be overestimated by a linear shift of ~0.11 and ~0.36 dex, respectively. This inference based on RGBB star counts goes in the opposite direction to the increase in metallicities of Δ[M/H] ≈ 0.20 dex that would be required to fix the offset between predicted and observed RGBB luminosities. This comparison is a constraint on 'deepmixing' models of stellar interiors, which predict decreased RGBB star counts. We tabulate the predictions for RGBB star counts as a function of [Fe/H], [α/Fe], CNONa, initial helium abundance, and age. Though our study suggests a small zero-point calibration issue, RGBB star counts should nonetheless be an actionable parameter with which to constrain stellar populations in the differential sense. The most significant outliers are towards the clusters NGC 5024 (M53), NGC 6723, and NGC 7089 (M2), each of which shows a ~2σ deficit in their RGBB star counts.
AB - We compare model predictions to observations of star counts in the red giant branch bump (RGBB) relative to the number density of first-ascent red giant branch at the magnitude of the RGBB, EWRGBB. The predictions are shown to exceed the data by (5.2 ± 4.3) per cent for the BaSTI models and by (17.1 ± 4.3) per cent for the Dartmouth models, where the listed errors are purely statistical. These two offsets are brought to zero if the Galactic globular cluster metallicity scale is assumed to be overestimated by a linear shift of ~0.11 and ~0.36 dex, respectively. This inference based on RGBB star counts goes in the opposite direction to the increase in metallicities of Δ[M/H] ≈ 0.20 dex that would be required to fix the offset between predicted and observed RGBB luminosities. This comparison is a constraint on 'deepmixing' models of stellar interiors, which predict decreased RGBB star counts. We tabulate the predictions for RGBB star counts as a function of [Fe/H], [α/Fe], CNONa, initial helium abundance, and age. Though our study suggests a small zero-point calibration issue, RGBB star counts should nonetheless be an actionable parameter with which to constrain stellar populations in the differential sense. The most significant outliers are towards the clusters NGC 5024 (M53), NGC 6723, and NGC 7089 (M2), each of which shows a ~2σ deficit in their RGBB star counts.
KW - Hertzsprung
KW - Magnitude diagrams
KW - Mass function
KW - Russell and colour
KW - Stars: evolution
KW - Stars: luminosity function
UR - http://www.scopus.com/inward/record.url?scp=84923011064&partnerID=8YFLogxK
U2 - 10.1093/mnras/stu1974
DO - 10.1093/mnras/stu1974
M3 - Article
SN - 0035-8711
VL - 445
SP - 3839
EP - 3847
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -