A survey of TiOλ567 nm absorption in solar-type stars

Abstract

Molecular absorption bands are estimators of stellar activity and spot cycles on magnetically active stars. We have previously introduced a new color index that compare absorption strength of the titanium oxide (TiO) at 567 nm with nearby continuum. In this paper we implement this index to measure long-term activity variations and the statistical properties of the index in a sample of 302 solar-type stars from the HARPS planet search program. The results indicate a pattern of change in star's activity, covers a range of periods from 2 years up to 17 years.

The Effect of Magnetic Variability on Stellar Angular Momentum Loss. I. The Solar Wind Torque during Sunspot Cycles 23 and 24

“…Stellar mass and radius remain essentially constant throughout the main sequence. However, in addition to the long-time secular changes of the magnetic field due to rotation, magnetic activity is also observed to vary significantly over timescales of years to decades (Baliunas et al 1995;Azizi & Mirtorabi 2017). This is routinely observed for the Sun which is known to have a magnetic activity cycle (Babcock 1961;Wilcox & Scherrer 1972;Willson & Hudson 1991;Guedel et al 1997;Güdel 2007;Schrijver & Liu 2008), moving from an activity maximum through minimum and back to maximum in roughly 11 years.…”

B-Index as activity proxy for Proxima Centauri star ; HARPS survey

“…Potential evidence of active regions on solar-type stars has been found through studies using molecular bands of TiO [2,20]. The aim of our research is to identify significant long-term periodicities in the light curve of Proxima Centauri by analyzing the variation in absorption of T iO at a wavelength of 567 nm.…”

“…This photometric system has recently been updated by Azizi & Mirtorabi [3] by a slight shift in continuum bands of Wing system in order to make it less contaminated from the weak absorption of V O bands. In our previous paper [4] a new TiO index was introduced which examines the absorption at visual bands around 567 nm and then applied it to investigation for stellar activity in sample of solar-type stars [2]. In this work, using HARPS, high-resolution spectra at the ESO La Silla 3.6m telescope, we attempted to determine possible long-term activity cycles of the closest star to the Sun, P roxima Centauri, during a period of 13 years.…”

A Jovian planet in an eccentric 11.5 day orbit around HD 1397 discovered by TESS

“…To constrain the rotation period and overall stellar variability of the star we computed the time series of several spectroscopic line indicators from the CORALIE spectra. We based our analysis on the Mount Wilson Ca II H&K S-index (Noyes et al 1984;Lovis et al 2011), the Hα index (Gomes da Silva et al 2011), He I index (Boisse et al 2009), NA I index (Díaz et al 2007) and TiO index (Azizi & Mirtorabi 2018). We compute the power spectrum of the different time series using a generalised Lomb-Scargle periodogram (Zechmeister & Kürster 2009).…”