IRC-10443: a multi-periodic SRa variable and the nature of long secondary periods in AGB stars

TL;DR

This study characterizes IRC-10443 as a multi-periodic SRa variable AGB star with two main sinusoidal periods, revealing that its long secondary periods are likely due to pulsation, supported by detailed photometric and spectroscopic data.

Contribution

First detailed analysis of IRC-10443 revealing dual periodicities and their physical implications, especially supporting pulsation as the cause of long secondary periods in AGB stars.

Findings

IRC-10443 is an SRa variable with two main periods: 85.5 and 620 days.

The star shows color variations consistent with pulsation-driven changes.

Long secondary periods are likely caused by pulsation, not other mechanisms.

Abstract

We obtained BVIc photometry of IRC-10443 on 85 different nights distributed over two years, and in addition low resolution absolute spectro- photometry and high resolution Echelle spectroscopy. Our data show that IRC-10443, which was never studied before in any detail, is a SRa variable, characterized by Delta(B)=1.27, Delta(V)=1.14 and Delta(I)=0.70 mag amplitudes and mean values <B>=13.75, <V>=11.33 and <Ic>=6.18 mag. Two strong periodicities are simultaneously present: a principal one of 85.5 (+/-0.2) days, and a secondary one of 620 (+/-15) days, both sinusoidal in shape, and with semi-amplitudes Delta(V)=0.41 and 0.20 mag, respectively. IRC-10443 turns out to be a M7III star, with a mean heliocentric radial velocity -28 km/s and reddened by E(B-V)=0.87, a third of which of circumstellar origin. The same 0.5 kpc distance is derived from application of the appropriate period-luminosity relations to both the principal and the secondary periods. The long secondary period causes a sinusoidal variation in color of 0.13 mag semi-amplitude in V-Ic, with IRC-10443 being bluest at maximum and reddest at minimum, and with associated changes in effective temperature and radius of 85 K and 6%, respectively. This behavior of colors argues in favor of a pulsation nature for the still mysterious long secondary periods in AGB stars.