Self-excited Pulsations and the Instability Strip of Long-period Variables: The Transition from Small-amplitude Red Giants to Semi-regular Variables
We use one-dimensional hydrodynamic calculations combined with synthetic stellar population models of the Magellanic Clouds to study the onset of self-excited pulsation in luminous red giants. By comparing the results with Optical Gravitational Lensing Experiment observations in the period–luminosit...
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IOP Publishing
2024-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/ad9475 |
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| author | Michele Trabucchi Giada Pastorelli |
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| description | We use one-dimensional hydrodynamic calculations combined with synthetic stellar population models of the Magellanic Clouds to study the onset of self-excited pulsation in luminous red giants. By comparing the results with Optical Gravitational Lensing Experiment observations in the period–luminosity (PL) diagram, we are able to link the transition from small-amplitude red giants to semi-regular variables with a shift from stochastic driving to self-excited pulsations. This is consistent with previous studies relating this transition with an increase in mass-loss rate, dust formation, and the appearance of long secondary periods. The luminosity and effective temperature at the onset of pulsation are found to depend on metallicity, hydrogen content, and the adopted mixing length parameter. This confirms the role of partial hydrogen ionization in driving the pulsation, supporting the idea of a heat mechanism similar to that of classical pulsators. We examine the impact of turbulent viscosity, and find clear evidence that it must be adjusted according to the stellar chemical and physical parameters to fully match observations. In order to improve the predictive power of pulsation models, the turbulent viscosity and the temperature scale of pulsating red giants must be jointly calibrated. This is critical for model-based studies of the PL relations of evolved stars and to exploit their potential as distance and age indicators, in particular given the sensitivity of the onset of pulsation to the envelope composition. The grid of models is made publicly available with a companion interpolation routine. |
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| spelling | doaj-art-c5fbfbbea0764ca5ba15198f94d716d92025-08-20T02:31:36ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-0197813010.3847/1538-4357/ad9475Self-excited Pulsations and the Instability Strip of Long-period Variables: The Transition from Small-amplitude Red Giants to Semi-regular VariablesMichele Trabucchi0https://orcid.org/0000-0002-1429-2388Giada Pastorelli1https://orcid.org/0000-0002-9300-7409Dipartimento di Fisica e Astronomia “Galileo Galilei,” Università di Padova , Vicolo dell’Osservatorio 3, I-35122 Padova, Italy ; michele.trabucchi@unipd.it, giada.pastorelli@unipd.it; INAF-Osservatorio Astronomico di Padova , Vicolo dell’Osservatorio 5, I-35122 Padova, ItalyDipartimento di Fisica e Astronomia “Galileo Galilei,” Università di Padova , Vicolo dell’Osservatorio 3, I-35122 Padova, Italy ; michele.trabucchi@unipd.it, giada.pastorelli@unipd.it; INAF-Osservatorio Astronomico di Padova , Vicolo dell’Osservatorio 5, I-35122 Padova, ItalyWe use one-dimensional hydrodynamic calculations combined with synthetic stellar population models of the Magellanic Clouds to study the onset of self-excited pulsation in luminous red giants. By comparing the results with Optical Gravitational Lensing Experiment observations in the period–luminosity (PL) diagram, we are able to link the transition from small-amplitude red giants to semi-regular variables with a shift from stochastic driving to self-excited pulsations. This is consistent with previous studies relating this transition with an increase in mass-loss rate, dust formation, and the appearance of long secondary periods. The luminosity and effective temperature at the onset of pulsation are found to depend on metallicity, hydrogen content, and the adopted mixing length parameter. This confirms the role of partial hydrogen ionization in driving the pulsation, supporting the idea of a heat mechanism similar to that of classical pulsators. We examine the impact of turbulent viscosity, and find clear evidence that it must be adjusted according to the stellar chemical and physical parameters to fully match observations. In order to improve the predictive power of pulsation models, the turbulent viscosity and the temperature scale of pulsating red giants must be jointly calibrated. This is critical for model-based studies of the PL relations of evolved stars and to exploit their potential as distance and age indicators, in particular given the sensitivity of the onset of pulsation to the envelope composition. The grid of models is made publicly available with a companion interpolation routine.https://doi.org/10.3847/1538-4357/ad9475Asymptotic giant branch starsMagellanic CloudsLong period variable starsOGLE small amplitude red giant starsRed giant starsSemi-regular variable stars |
| spellingShingle | Michele Trabucchi Giada Pastorelli Self-excited Pulsations and the Instability Strip of Long-period Variables: The Transition from Small-amplitude Red Giants to Semi-regular Variables The Astrophysical Journal Asymptotic giant branch stars Magellanic Clouds Long period variable stars OGLE small amplitude red giant stars Red giant stars Semi-regular variable stars |
| title | Self-excited Pulsations and the Instability Strip of Long-period Variables: The Transition from Small-amplitude Red Giants to Semi-regular Variables |
| title_full | Self-excited Pulsations and the Instability Strip of Long-period Variables: The Transition from Small-amplitude Red Giants to Semi-regular Variables |
| title_fullStr | Self-excited Pulsations and the Instability Strip of Long-period Variables: The Transition from Small-amplitude Red Giants to Semi-regular Variables |
| title_full_unstemmed | Self-excited Pulsations and the Instability Strip of Long-period Variables: The Transition from Small-amplitude Red Giants to Semi-regular Variables |
| title_short | Self-excited Pulsations and the Instability Strip of Long-period Variables: The Transition from Small-amplitude Red Giants to Semi-regular Variables |
| title_sort | self excited pulsations and the instability strip of long period variables the transition from small amplitude red giants to semi regular variables |
| topic | Asymptotic giant branch stars Magellanic Clouds Long period variable stars OGLE small amplitude red giant stars Red giant stars Semi-regular variable stars |
| url | https://doi.org/10.3847/1538-4357/ad9475 |
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