Open AccessThe field of NGC 6397 as a test for Galactic models
Author(s) -
Castellani V.,
Degl'Innocenti S.,
Petroni S.,
Piotto G.
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04283.x
Subject(s) - physics , globular cluster , astrophysics , magnitude (astronomy) , stars , luminosity , luminosity function , absolute magnitude , star cluster , apparent magnitude , horizontal branch , astronomy , astrometry , galaxy
Taking advantage of recent Hubble Space Telescope ( HST ) data for field stars in the region of the Galactic globular cluster NGC 6397, we tested the predictions of several Galactic models with star counts reaching a largely unexplored range of magnitudes, down to V∼26.5. After updating the input stellar (V−I) colours, we found that the two‐component Bahcall–Soneira (B&S) model can be put into satisfactory agreement with observations for suitable choices of disc/spheroid luminosity functions (LFs). However, if one assumes the disc LF of Gould, Bahcall and Flynn together with the spheroid LF of Gould, Flynn and Bahcall, there is no way to reconcile the predicted and observed V ‐magnitude distribution. We also analysed the agreement between observed and predicted magnitude and colour distributions for two selected models with a thick disc component. Even in this case there are suitable combinations of model parameters and faint‐magnitude LFs that can give a reasonable agreement with observational star counts in both magnitude and colour. However, the above‐quoted combination of Gould et al. LFs again gives predictions in clear disagreement with observations.