Separation between RR Lyrae and type II Cepheids and their importance for a distance determination: the case of omega Cen
Journal
Date Issued
2020
Author(s)
•
Bono, G.
•
•
Stetson, P. B.
•
Dall’Ora, M.
•
Salaris, M.
•
da Silva, R.
•
•
•
Marrese, M. P.
•
Mateo, M.
•
Matsunaga, N.
•
Monelli, M.
•
Wallerstein, G.
Abstract
The separation between RR Lyrae (RRLs) and Type II Cepheid (T2Cs) variables
based on their period is debated. Both types of variable stars are distance
indicators and we aim to promote the use of T2Cs as distance indicators in
synergy with RRLs. We adopted new and existing optical and Near-Infrared (NIR)
photometry of \wcen~to investigate several diagnostics (colour-magnitude
diagram, Bailey diagram, Fourier decomposition of the light curve, amplitude
ratios) for their empirical separation. We found that the classical period
threshold at 1 day is not universal and does not dictate the evolutionary
stage: V92 has a period of 1.3 days but is likely to be still in its core
Helium-burning phase, typical of RRLs. We also derived NIR Period-Luminosity
relations and found a distance modulus of 13.65$\pm$0.07 (err.)$\pm$0.01
($\sigma$) mag, in agreement with the recent literature. We also found that
RRLs and T2Cs obey the same PL relations in the NIR. This equivalence gives the
opportunity to adopt RRLs+T2Cs as an alternative to classical Cepheids to
calibrate the extragalactic distance scale.
Volume
644
Start page
A95
Issn Identifier
0004-6361
Rights
open.access
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