V440 Per: the longest period overtone Cepheid

TL;DR

V440 Per is confirmed as the longest period overtone Cepheid through high-precision radial velocity measurements and pulsation modeling, resolving previous uncertainties about its pulsation mode.

Contribution

The paper provides the first secure detection of the first harmonic in V440 Per, establishing its overtone pulsation at a long period, and demonstrates the effectiveness of pulsation models in reproducing observed Fourier parameters.

Findings

Detection of the 1st harmonic with A_2= 140+/- 15 m/s.

Velocity Fourier phase _21 inconsistent with fundamental mode.

Pulsation models successfully reproduce observed Fourier parameters.

Abstract

V440 Per is a Population I Cepheid with the period of 7.57 day and low amplitude, almost sinusoidal light and radial velocity curves. With no reliable data on the 1st harmonic, its pulsation mode identification remained controversial. We obtained a radial velocity curve of V440 Per with our new high precision and high throughput Poznan Spectroscopic Telescope. Our data reach the accuracy of 130 m/s per individual measurement and yield a secure detection of the 1st harmonic with the amplitude of A_2= 140+/- 15 m/s. The velocity Fourier phase \phi_21 of V440 Per is inconsistent at the 7.25 \sigma level with those of the fundamental mode Cepheids, implying that the star must be an overtone Cepheid, as originally proposed by Kienzle et al.(1999). Thus, V440 Per becomes the longest period Cepheid with the securely established overtone pulsations. We show, that the convective nonlinear pulsation hydrocode can reproduce the Fourier parameters of V440 Per very well. Requirement to match the observed properties of V440 Per constrains free parameters of the dynamical convection model used in the pulsation calculations, in particular the radiative losses parameter.