V1820 Orionis : an RR Lyrae star with strong and irregular Blazhko effect

TL;DR

This study presents four years of detailed observations of V1820 Orionis, revealing its strong, irregular Blazhko effect, multiple modulation periods, and complex frequency structures, advancing understanding of RR Lyrae star variability.

Contribution

It provides the first detailed analysis of V1820 Orionis's Blazhko effect, identifying multiple modulation periods and complex frequency structures not previously documented.

Findings

Blazhko period of 27.917 days was determined.

Detected a second, weaker Blazhko modulation at 34.72 days.

Identified triplet and quintuplet frequency structures in the star's spectrum.

Abstract

The Blazhko effect in V1820 Orionis and its period were reported for the first time by Wils et al. (2006) from a data analysis of the Northern Sky Variability Survey. The results of additional V1820 Orionis observations over a time span of 4 years are presented herein. From the observed light curves, 73 pulsation maxima have been measured. The times of light maxima have been compared to ephemerides to obtain the (O-C) values. The Blazhko period (27.917 +/- 0.002 d) has been derived from light curve Fourier analysis and from ANOVA analyses of the (O-C) values and of magnitudes at maximum light (Mmax). During one Blazhko cycle, a hump in the ascending branch of the light curve was clearly identified and has also created a double maximum in the light curve. The frequency spectrum of the light curve, from a Fourier analysis with Period04, has revealed triplet, quintuplet structures, and a second Blazhko weak modulation (period = 34.72 +/-0.01 d). V1820 Orionis can be ranked as a strongly modulated star based on its observed amplitude and phase variations. The amplitude ratio of the largest triplet component to main pulsation component is quite large: 0.34.