User`s guide

SECTION 6.0

WING FILTERS

With the cooperation of Dr. Robert F. Wing of Ohio State University, Optec has designed

three filters for the SSP-3 photometer which are useful in measuring the absorption of TiO

(titanium oxide), and the true color temperature of late type stars such as Miras. These

three filters labeled MA, MB and MI comprise a subset of the Wing 8-color system

. See

Table 6.1 for filter specifications.

It is widely known that the B-V color index of stars with spectral type K5 to M8 is nearly

constant although the surface temperature of stars in this range vary considerably. The cooler

the surface temperature of these stars the greater the TiO absorption in the visual band,

which prevents the color index from becoming redder. As a result, the common B and V

magnitude contain little useful information about these stars.

Used together, the MA and MB filters measure the amount of TiO absorption in the star's

outer atmosphere. The MA filter is centered on an absorption band at 712 nm and the MB

filter is centered just off the band and on the continuum at 754 nm. The ratio of readings

taken with these filters is proportional to the amount of TiO absorption.

The MI filter is centered on the continuum at 1025 nm. Readings taken with this filter and the

MB filter can be used together to measure the slope of blackbody curve between these two

points, and thus the temperature of the star may be calculated.

Because these stars radiate most of their energy in the infrared and the TC-211 CCD chip is

sensitive for part of this band, very good stellar images can be obtained with these filters

when only marginal images are obtained in the Johnson B and V bands. This is partially

true because the amount of background light from the atmosphere due to scatter from the

moon or ground lights is extremely low in the infrared wavelengths. Thus, good Wing

photometry can be performed even when B and V photometry is impossible because of bright

background sky noise.

FILTER CENTER BANDPASS PEAK

NAME WAVELENGTH 1/2T POINTS TRANSMISSION

MA 712 nm 10 nm 75 %

MB 754 nm 10 nm 75 %

MI 1025 nm 40 nm 55 %

Table 6-1. Specifications for Wing Filters.

Wing, R. F., 1971, Proceedings of the Conference on Late Type Stars,ed. G.W. Lockwood and H. M. Dyck

(KPNO Contribution No. 554), p. 145.