J/A+A/703/A228 Theoretical predictions on Type II Cepheids (Marconi+, 2025)
New theoretical predictions on Type II Cepheids:
Towards a self-consistent Population II distance scale.
Marconi M., Molinaro R., Ripepi V., De Somma G., Sicignano T., Deka M.,
Di Criscienzo M., Luongo E., Musella I., Trentin E.
<Astron. Astrophys. 703, A228 (2025)>
=2025A&A...703A.228M 2025A&A...703A.228M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Parallaxes, trigonometric
Keywords: stars: distances - stars: oscillations - stars: variables: Cepheids
Abstract:
Type II Cepheids are pulsating stars that can be used as standard
candles for old stellar populations due to their characteristic
Period-Luminosity and Period-Luminosity-Colour relations. They are
traditionally divided in 3 sub-classes, namely BL Her, W Vir and RV
Tauri.In this paper we focus on the first two sub-classes, to provide
a new theoretical scenario and develop tools and relations to be
adopted in distance scale and old stellar populations studies.
We built new non-linear convective pulsation models of Type II
Cepheids, computed along selected stellar evolution tracks and
spanning a wide range of pulsation period and stellar parameters.
Three chemical compositions have been taken into account, namely
Z=0.0001 Y=0.245, Z=0.001 Y=0.245, and Z=0.01 Y=0.26. For each assumed
Z and Y, models were computed following stellar evolution predictions
for of-zero-age horizontal-branch evolution of stellar masses lower
than typical RR Lyrae stars, crossing the classical instability strip
as BL Her or W Vir pulsating stars.
A new theoretical prediction for the instability strip boundaries of
these classes of variable stars has been obtained together with their
dependence on metal abundance. The predicted light and radial-velocity
curves were computed along the evolution inside the strip, showing how
the amplitude and the morphology are affected by the position relative
to the edges and by the luminosity and mass values. The transformation
of bolometric light curves into various photometric systems allowed us
to provide new theoretical period-luminosity and period-Wesenheit
relations for BL Her and W Vir.
These relations are found to be consistent with previously published
RR Lyrae model results but with a smaller metallicity dependence.
Moreover, the application of the inferred theoretical relations to
Magellanic and Galactic Type II Cepheid data provides results in good
agreement with some independent distance estimates in the literature.
Description:
A new theoretical scenario was presented for BL Her and W Vir
pulsating stars with periods up to about ten days for three selected
metal abundances (Z=0.01, 0.001, and 0.0001).
Table 1 reports the stellar parameters of computed models that are
found to pulsate.
The resulting theoretical parallaxes, along with their associated
uncertainties, are reported in Table 4, together with the Gaia DR3
parallaxes and Lindegreen et al., 2021A&A...649A...4L 2021A&A...649A...4L correction
values.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 42 279 The structural parameters of all computed models
table4.dat 105 100 Adopted Galactic Type II Cepheids
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 F9.4 --- Z Metal content
11- 15 F5.3 --- Y Helium content
17- 21 F5.3 Msun Mass Mass
23- 27 F5.3 [Lsun] logL Luminosity
29- 32 I4 K Teff Effective temperature
34- 42 F9.6 d Per Pulsational period
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 28 A28 --- ID Variable name
30- 34 A5 --- Class Variable Class
36- 42 F7.4 d Per Period
44- 49 F6.3 --- plxcorr Parallax correction from
Lindegreen et al., 2021A&A...649A...4L 2021A&A...649A...4L
51- 56 F6.4 mas plxDR3 Gaia DR3 parallax
58- 63 F6.4 mas e_plxDR3 Gaia DR3 parallax error
65- 70 F6.4 mas plxteoZ0.0001 Theoretical parallax for Z=0.0001
72- 77 F6.4 mas e_plxteoZ0.0001 Theoretical parallax error for Z=0.0001
79- 84 F6.4 mas plxteoZ0.001 Theoretical parallax for Z=0.001
86- 91 F6.4 mas e_plxteoZ0.001 Theoretical parallax error for Z=0.001
93- 98 F6.4 mas plxteoZ0.01 Theoretical parallax for Z=0.01
100-105 F6.4 mas e_plxteoZ0.01 Theoretical parallax error for Z=0.01
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Acknowledgements:
Roberto Molinaro, roberto.molinaro(at)inaf.it
(End) Patricia Vannier [CDS] 17-Sep-2025