The 77-81 photometric system

Basic Reference

Cook K.H., Aaronson M. 1989, AJ 97, 923


This paper presents the definition of an intermediate-band photometric color system for the study of late-type stars. One of the intermediate passbands is centered on a region of TiO absorption at 7750Å (77), and the other is centered on a region of CN absorption at 8100Å (81). The 77 - 81 color of late-type stars clearly distinguishes carbon stars from M stars and is easily measured using modern area detectors such as CCDs. It has been used in a photometric technique where broadband, V and I images identify red stars and the 77 - 81 color is used to classify them as C or M type. The 77 - 81 color is also a single-sideband TiO band-strength measure and correlates well with M type and true band-strength measures. The 77 - 81, TiO band strength as a function of V - I color for a sample of nearby giants (Mould and Siegel 1982) is presented. The establishment of the 77 - 81 system extends the use of 77 - 81 data from identification and classification of late-type stars to the measurement of TiO band strengths in M stars, which it identifies.


Access to the data and references

Asiago Database on Photometric System (ADPS)


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77 :
central wavelength: 7752A
Full width at half-maximum transmission: 284A
81 :
central wavelength: 8104A
Full width at half-maximum transmission: 365A

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Last update: 21 May 1996