Versatile light curve templates of Cepheids

Multi-band fitting of photometric time series

¹ LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 5 place Jules Janssen, 92195 Meudon, France
² French-Chilean Laboratory for Astronomy, IRL 3386, CNRS and U. de Chile, Casilla 36-D, Santiago, Chile
³ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁴ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warszawa, Poland
⁵ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
⁶ Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile

^⋆ Corresponding author: garance.bras@obspm.fr

Received: 16 January 2025
Accepted: 27 March 2025

Abstract

Context. To use the period–luminosity relations of Cepheids to derive distances of extragalactic Cepheids, it is crucial to have reliable estimations of the luminosity of such stars. However, the light curves (LCs) of extragalactic Cepheids are sparsely sampled, which makes the interpolation difficult.

Aims. Our purpose is to create general templates of Cepheid LCs that can be efficiently applied with only a few parameters, while ensuring they are reliable in terms of resulting mean magnitudes. We have also aimed to provide adaptable templates for the large variety of photometric bands to enlarge their possible applications.

Methods. We performed a principal component analysis (PCA) on LCs in different bands from the optical to the mid-infrared (MIR) fitted by atmosphere models along the pulsation cycle for 75 galactic Cepheids. All the photometric bands were treated together to incorporate the results of the effective temperature variation. To link the different shapes of LCs, we also derived the relations between the period and the coefficients associated to the PCA.

Results. We present our templates and a further analysis to validate their reliability. We also offer an example of their application to one Cepheid in the galaxy NGC 5584. We find a good agreement with previous estimations of mean magnitudes in the HST filters. We show examples of a template fitting for Cepheids in various environments to demonstrate the variety of applications of these templates.

Conclusions. The templates we propose here can be used in a number of different situations (good phase coverage in many filters, poor phase coverage in one specific filter, but good phase coverage in some others, or noisy and sparse data), thereby mobilising the adapted fitting strategies. Moreover, the broad adaptability of this LC prediction tool is provided by the multiple photometric bands in which they can be inferred.