Testing the nonlinearity of the BVI_cJHK_s period-luminosity relations for the Large Magellanic Cloud Cepheids

¹ Department of Astronomy, University of Illinois, Urbana, IL 61801, USA e-mail: cngeow@astro.uiuc.edu
² Department of Physics, State University of New York at Oswego, Oswego, NY 13126, USA e-mail: kanbur@oswego.edu
³ Department of Mathematics, State University of New York at Oswego, Oswego, NY 13126, USA e-mail: nanthaku@oswego.edu

Received: 8 October 2007
Accepted: 24 October 2007

Abstract

Context.A number of recent works have suggested that the period-luminosity (PL) relation for the Large Magellanic Cloud (LMC) Cepheids exhibits a controversial nonlinear feature with a break period at 10 days.

Aims.We aim to test the linearity/nonlinearity of the PL relations in this Research Note for the LMC Cepheids in BVI_cJHK_s band, as well as in the Wesenheit functions.

Methods.We show that simply comparing the long and short period slopes, together with their associated standard deviations, leads to a strictly larger error rate than applying rigorous statistical tests such as the F-test. We applied various statistical tests to the current published LMC Cepheid data. These statistical tests include the F-test, the testimator test, and the Schwarz information criterion (SIC) method.

Results.The results from these statistical tests strongly suggest that the LMC PL relation is nonlinear in BVI_cJH band but linear in the K_s band and in the Wesenheit functions. Using the properties of period-color relations at maximum light and multi-phase relations, we believe that the nonlinear PL relation is not caused by extinction errors.