Open AccessOn the second‐overtone stability among Small Magellanic Cloud Cepheids
Author(s) -
Bono G.,
Caputo F.,
Marconi M.
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.1365-8711.2001.04464.x
Subject(s) - cepheid variable , overtone , physics , astrophysics , amplitude , large magellanic cloud , small magellanic cloud , range (aeronautics) , galaxy , astronomy , stars , spectral line , optics , materials science , composite material
We present a new set of Cepheid, full amplitude, non‐linear, convective models which are pulsationally unstable in the second overtone (SO). Hydrodynamical models were constructed by adopting a chemical composition typical of Cepheids in the Small Magellanic Cloud (SMC) and for stellar masses ranging from 3.25 to 4 M ⊙ . Predicted φ 21 Fourier parameters agree, within current uncertainties, with empirical data for pure first‐ and second‐overtone variables as well as for first‐/second‐overtone (FO/SO) double‐mode Cepheids collected by Udalski et al. in the SMC. On the other hand, predicted I ‐band amplitudes are systematically larger than the observed ones in the short‐period range, but attain values that are closer to the empirical ones for log P SO ≥−0.12 and log P FO ≥0.1 . We also find, in agreement with empirical evidence, that the region within which both second and first overtones attain a stable limit cycle widens when moving towards lower luminosities. Moreover, predicted P SO / P FO and P FO / P F period ratios agree quite well with empirical period ratios for FO/SO and fundamental/FO double‐mode SMC Cepheids. Interestingly enough, current models support the evidence that pure SO Cepheids and SO components in FO/SO Cepheids are good distance indicators. In fact, we find that the fit of the predicted period–luminosity–colour ( V , V – I ) relation to empirical SMC data supplies a distance modulus ( DM ) of 19.11±0.08 mag . The same outcome applies to pure FO Cepheids and FO components in FO/SO Cepheids, and indeed we find DM=19.16±0.19 mag . Current distance estimates do not account for, within current uncertainties on photometry and reddening, the so‐called short distance scale.