A new titanium oxide index in the visual band

Abstract

We introduce a new color index consisting of two spectral band width to measure TiO absorption band strength centered at 567 nm. Based on the most up-to-date line list for TiO we regenerate a grid of synthesized spectra and investigate the temperature sensitivity of the index. The new index behave similar to older Wing TiO-index where it decrease monotonically from coolest atmosphere with T ef f = 2800 up to T ef f = 4000 where the TiO molecules disassociate. To further examine the feasibility of the new index we reproduce the calibration using a list of observed high resolution spectra and found similar results. This index extend TiO absorption band capability to measure effective temperature of late K to M stars to visual spectrum where it is more accessible to small telescopes for long term dedicated observation.

Hiding in plain sight: observing planet-starspot crossings with the James Webb Space Telescope

“…While the TiO spectral lines at 567, 705.5 and 886 nm are also known as robust temperature indicators (e.g. Wing et al 1967;Vogt 1979Vogt , 1981Ramsey & Nations 1980;Neff et al 1995;Mirtorabi et al 2003;O'Neal et al 2004;Bidaran et al 2016), a spectral resolution larger than ∼ 10000 would be needed to achieve significant constraints. Moreover, such lines were only observed in very active stars, where starspots occupy a significant fraction of the visible stellar disc, but which are usually excluded from exoplanet searches.…”

A survey of TiOλ567 nm absorption in solar-type stars

“…Filter B (FWHM = 11 nm) with central wavelength at 754 nm and filter C (FWHM = 42 nm) with central wavelength of 1024 nm both are located in continuum region. is compared with the nearby continuum with the second filter (E) at 610 nm with FWHM equal to 10 nm (Bidaran, Mirtorabi & Azizi 2016). The continuum filter was appropriately chosen to be free from molecular absorption.…”

“…The fourth and fifth columns of Table 1 shows the mean and standard deviation of B-index for all stars, respectively. The coolest star in the sample has a effective temperature of 4600 K which according to Bidaran, Mirtorabi & Azizi (2016) calibration is associated with a photospheric B-index of less than 0.05. Figure 1 clearly shows that all of the stars in the sample exhibit high level of TiO absorption in the photospheres which are too hot too sustain TiO molecules.…”

“…We previously introduced a new color index (B-index) to measure the TiO absorption band strength centered at 567 nm (Bidaran, Mirtorabi & Azizi 2016). In that paper we showed that there is a clear correlation between the Bindex and surface temperature of cool M giants where cooler atmospheres exhibits higher B-index.…”

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

“…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.…”