On the metallicity dependence of classical Cepheid light amplitudes

Abstract

Classical Cepheids remain a cornerstone of the cosmic distance scale, and thus characterizing the dependence of their light amplitude on metallicity is important. Period-amplitude diagrams constructed for longer-period classical Cepheids in IC 1613, NGC 3109, SMC, NGC 6822, LMC, and the Milky Way imply that very metal-poor Cepheids typically exhibit smaller V -band amplitudes than their metal-rich counterparts. The results provide an alternate interpretation relative to arguments for a null and converse metallicity dependence. The empirical results can be employed to check predictions from theoretical models, to approximate mean abundances for target populations hosting numerous long-period Cepheids, and to facilitate the identification of potentially blended or peculiar objects.

Evidence for photometric contamination in key observations of Cepheids in the benchmark galaxy IC 1613

“…The former assertion is supported by observations indicating that longperiod Cepheids in NGC 6822 exhibit larger V-band amplitudes than metal-poor SMC Cepheids, and marginally smaller amplitudes than LMC Cepheids (Majaess et al 2013b). The trend agrees with certain models that produce 10 d −30 d metal-poor Cepheids which feature smaller amplitudes than their metal-rich counterparts (Bono et al 2000, for an alternate interpretation see Szabados & Klagyivik 2012).…”

“…Cepheids in NGC 6822 could exhibit a mean abundance between SMC and LMC Cepheids (Venn et al 2001;Majaess et al 2013b, and references therein), and may thus bolster efforts to constrain the impact of metallicity on the distance scale. The former assertion is supported by observations indicating that longperiod Cepheids in NGC 6822 exhibit larger V-band amplitudes than metal-poor SMC Cepheids, and marginally smaller amplitudes than LMC Cepheids (Majaess et al 2013b).…”

“…Applying functions is inadvisable until the underlying form is known in order to mitigate misleading reduced χ 2 values. HST photometry 5 indicates that several short-period Cepheids tabulated in the OGLE survey display unresolved companions (Majaess et al 2013b). HST features superior resolution relative to ground-based surveys (e.g., OGLE, Prša et al 2008, their Fig.…”

TESS Observations of Cepheid Stars: First Light Results

“…Such a clear relation between the light curve shape and the metallicity is not known for Cepheid stars. Although there are indications that metallicity affects the pulsation amplitudes of Cepheids, the nature of the dependence has been debated (Szabados & Klagyivik 2012;Majaess et al 2013). Recent efforts to estimate fundamental parameters such as mass, radius, luminosity, and effective temperature from photometry also demonstrated that light curve structure is statistically important both in RR Lyrae and Cepheid types (Bellinger et al 2020).…”

Anchors for the cosmic distance scale: the Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae

“…The discrepancy is sufficient to hinder efforts to constrain the nature of dark energy (for which σ w ∼ 2σ H 0 , ), and could be linked to a systematic offset in the Cepheid calibration, or unreliable photometry for remote extragalactic Cepheids owing to crowding effects (Mochejska et al 2004;Majaess 2010Majaess , 2011a, see also Table 2 in Riess et al 2011). Research continues on the aforementioned topics irrespective of the discrepancy, namely to resolve the putative degeneracy between the impact of crowding and metallicity on Cepheid parameters (Majaess et al 2011a(Majaess et al , 2013aChavez et al 2012, and references therein), and to strengthen the Galactic Cepheid calibration (e.g., Majaess et al 2012a;Anderson et al 2013). That calibration is likewise important for defining the metallicity gradient of the Milky Way (Luck et al 2011), benchmarking standard candles (Matsunaga 2012;Kudritzki et al 2012), and constraining the behavior of intermediate mass stars (Neilson et al 2012;Bono et al 2013, and references therein).…”