The Lockwood photometric system

Basic Reference

Lockwood G.W., 1972, ApJ. Suppl. 24, 375


A five-color narrow-band photometric system is described which has been used for determining magnitudes at 1.04 mu, near-infrared colors, and molecular band-strength indices for M stars. The system gives accurate spectral types from M4 to M10 and useful, though less accurate, spectral types from M0 to M4. Mean 1.04-mu magnitudes, near-infrared colors, and spectral-type indices are given for photometric and spectroscopic standard stars, and 1795 individual sets of five-color measurements are given for 292 M- and S-type Mira variables.

The Miras are shown to map out large loops in a diagram of molecular band strength as a function of color, and large differences of band strength can occur at a given color and phase in different stars or in the same stars during different cycles. The Miras with periods less than 300d are warmer by several hundred degrees at a given spectral type than either the normal giants used for calibration or the Miras with periods longer than 300d. The mean phase of earliest spectral type is ~0.03, while maximum light at 1.04 mu occurs at ~0.11. Minimum light at 1.04 mu and latest spectral type are reached almost simultaneously with minimum visual light.


Access to the data and references

Asiago Database on Photometric System (ADPS)

Indices and Parameters

78-87, 88-87, 87-104, 104, 105-104

Color-free Indices

TiO strength
T1 = (78-87) - 0.6 (87-104)
TiO absorption
T2 = (88-87) + 0.07 (87-104)
VO strength
V1 = (105-104) + 0.1 (87-104)
Composite index
D = 0.18 T1 + T2 + V1


78 :
Peak wavelength: 7818 Å ; Width : 90 Å
87 :
Peak wavelength: 8777 Å ; Width : 82 Å
88 :
Peak wavelength: 8884 Å ; Width : 114 Å
104 :
Peak wavelength: 10351 Å ; Width : 125 Å
105 :
Peak wavelength: 10506 Å ; Width : 100 Å


ITT FW-118
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Last update: 21 May 1996