Evolutionary and pulsation properties of Type II Cepheids

Bono, G.; Braga, V. F.; Fiorentino, G.; Salaris, M.; Pietrinferni, A.; Castellani, M.; Di Criscienzo, M.; Fabrizio, M.; Martínez-Vázquez, C. E.; Monelli, M.
Referencia bibliográfica

Astronomy and Astrophysics

Fecha de publicación:
12
2020
Número de autores
10
Número de autores del IAC
1
Número de citas
18
Número de citas referidas
17
Descripción
We discuss the observed pulsation properties of Type II Cepheids (TIICs) in the Galaxy and in the Magellanic Clouds. We found that period (P) distributions, luminosity amplitudes, and population ratios of the three different sub-groups (BL Herculis [BLH, P < 5 days], W Virginis [WV, 5 ≤ P < 20 days], RV Tauri [RVT, P > 20 days]) are quite similar in different stellar systems, suggesting a common evolutionary channel and a mild dependence on both metallicity and environment. We present a homogeneous theoretical framework based on horizontal branch (HB) evolutionary models, showing that TIICs are mainly old (t ≥ 10 Gyr) low-mass stars. The BLH stars (BLHs) are predicted to be post-early asymptotic giant branch (PEAGB) stars (double shell burning) on the verge of reaching their AGB track (first crossing of the instability strip), while WV stars (WVs) are a mix of PEAGB and post-AGB stars (hydrogen shell burning) moving from the cool to the hot side (second crossing) of the Hertzsprung-Russell Diagram. This suggests that they are a single group of variable stars. The RVT stars (RVTs) are predicted to be a mix of post-AGB stars along their second crossing (short-period tail) and thermally pulsing AGB stars (long-period tail) evolving towards their white dwarf cooling sequence. We also present several sets of synthetic HB models by assuming a bi-modal mass distribution along the HB. Theory suggests, in agreement with observations, that TIIC pulsation properties marginally depend on metallicity. Predicted period distributions and population ratios for BLHs agree quite well with observations, while those for WVs and RVTs are almost a factor of two smaller and higher than observed, respectively. Moreover, the predicted period distributions for WVs peak at periods shorter than observed, while those for RVTs display a long-period tail not supported by observations. We investigate several avenues to explain these differences, but more detailed calculations are required to address these discrepancies.
Proyectos relacionados
Una vista de nuestra galaxia, la Vía Láctea, con sus vecinos cercanos,  las Nubes de Magallanes
Evolución Galáctica en el Grupo Local
La formación y evolución de galaxias es un problema fundamental en Astrofísica. Su estudio requiere “viajar atrás en el tiempo”, para lo cual hay dos enfoques complementarios. El mas extendido consiste en analizar las propiedades de las galaxias a diferentes distancias cosmológicas. Nuestro equipo se concentra en el otro enfoque, denominado
Matteo
Monelli