On the Impact of Helium Content on the RR Lyrae Distance Scale

Journal
Date Issued
2018
Author(s)
•
Bono, G.
•
•
•
•
Stellingwerf, R. F.
DOI
Abstract
We constructed new sets of He-enhanced (Y = 0.30, Y = 0.40) nonlinear, time-dependent convective hydrodynamical models of RR Lyrae (RRL) stars covering a broad range in metal abundances (Z = 0.0001-0.02). The increase in He content from the canonical value (Y = 0.245) to Y = 0.30-0.40 causes a simultaneous increase in stellar luminosity and in pulsation period. To investigate the dependence of the RRL distance scale on the He abundance, we computed new optical (RI) and near-infrared (JHK) Period-luminosity-metallicity-helium relations. Interestingly enough, the increase in He content causes a minimal change in the coefficients of both period and metallicity terms, since canonical and He-enhanced models obey similar PLZ relations. On the contrary, the classical B- and V-band mean magnitude metallicity relations and the R-band PLZ relation display a significant dependence on the He content. The He-enhanced models are, at fixed metal content, 0.2-0.5 mag brighter than canonical ones. This variation is only marginally affected by evolutionary effects. The quoted distance diagnostics once calibrated with trigonometric parallaxes (Gaia) will provide the opportunity to estimate the He content of field and cluster RRLs. Moreover, the use of either spectroscopic or photometric metal abundances will pave the way to new empirical constraints on the universality of the helium-to-metal enrichment ratio in old (t ≳ 10 Gyr) stellar tracers.
Volume
864
Issue
1
Start page
L13
Uri
Url
Issn Identifier
2041-8205
Ads BibCode
2018ApJ...864L..13M
Rights
open.access
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