The period-luminosity and period-radius relations of Type II and anomalous Cepheids in the Large and Small Magellanic Clouds

Abstract

Context. Type II Cepheids (T2Cs) and anomalous Cepheids (ACs) are pulsating stars that follow separate period-luminosity relations. Aims. We study the period-luminosity (PL) and period-radius (PR) relations for T2Cs and ACs in the Magellanic Clouds. Methods. In an accompanying paper we determined luminosity and effective temperature for the 335 T2Cs and ACs in the LMC and SMC discovered in the OGLE-III survey, by constructing the spectral energy distribution (SED) and fitting this with model atmospheres and a dust radiative transfer model (in the case of dust excess). Building on these results we study the PL-and PR relations. Using existing pulsation models for RR Lyrae and classical Cepheids we derive the period-luminosity-mass-temperaturemetallicity relations, and then estimate the pulsation mass. Results. The PL relation for the T2Cs does not appear to depend on metallicity, and, excluding the dusty RV Tau stars, is M bol = +0.12 − 1.78 log P (for P < 50 days). Relations for fundamental and first overtone LMC ACs are also presented. The PR relation for T2C also shows little or no dependence on metallicity or period. Our preferred relation combines SMC and LMC stars and all T2C subclasses, and is log R = 0.846 + 0.521 log P. Relations for fundamental and first overtone LMC ACs are also presented. The pulsation masses from the RR Lyrae and classical Cepheid pulsation models agree well for the short period T2Cs, the BL Her subtype, and ACs, and are consistent with estimates in the literature, i.e. M BLH ∼ 0.49 M ⊙ and M AC ∼ 1.3 M ⊙ , respectively. The masses of the W Vir appear similar to the BL Her. The situation for the pWVir and RV Tau stars is less clear. For many RV Tau the masses are in conflict with the standard picture of (single-star) post-AGB evolution, the masses being either too large ( 1 M ⊙ ) or too small ( 0.4 M ⊙ ).

OGLE-ing the Magellanic System: Cepheids in the Bridge*

“…9 and are consistent with those of Iwanek et al (2018). There is slight discrepancy between our results and those of Groenewegen and Jurkovic (2017) and Ripepi et al (2014) that is probably caused by the latter being based on less numerous samples.…”

Luminosities and mass-loss rates of Local Group AGB stars and red supergiants

“…Only some examples are shown here for guidance regarding its form and content. Groenewegen et al (2017), VMC K-band data combined with literature data, 3= Kamath et al (2010); Amplitude estimated from their figures, 4= Whitelock et al (2003), 5= ALLWISE + NEOWISE + SAGE + SAGE-VAR, 6= MACHO, 7= EROS, 9= redetermined combining Whitelock et al (2003) and Wood (1998), 10= Wood, Bessell & Paltoglou (1985), 11= Menzies et al (2011) Identifier T eff / log g grain size and type…”

OGLE-GAL-ACEP-091: The First Known Multi-mode Anomalous Cepheid

“…On the PL plane, ACs populate the region between the PL relations delineated by classical Cepheids and the PL sequences defined by type II Cepheids and RR Lyr stars (e.g., Soszyński et al 2015;Groenewegen & Jurkovic 2017b). The F-mode ACs in the LMC are about 0.7mag fainter than F-mode classical Cepheids with the same periods.…”

“…At the linear level we cannot constrain the physical parameters of OGLE-GAL-ACEP-091 further. We can, however, compare the resulting luminosity with the observed one, estimated using the period-luminosity relation for F-mode ACs published by Groenewegen & Jurkovic (2017b). This way we can estimate the luminosity of OGLE-GAL-ACEP-091 to ≈110 L  .…”