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Intrinsic colours as a function of spectral type

The following table aims to provide a guide to the unreddened colours expected for main sequence stars of spectral types B0 to M4. The data are taken from Fitzgerald (1970 - A&A 4, 234), who provides UBV data for spectral classes O5 to M8, and from Ducati et al. (2001 - ApJ, 558, 309), who cover B0 to M4. Both compilations also present data for giants and supergiants. Ducati et al. present photometry on the Johnson 11-colour system, and we have used the relations given by Bessell (1979 - PASP 91, 589) to transform the (V-R) and (V-I) colours to the Cousins system. The L (3.5 micron), M (4.8 micron) and N (10.5 micron) colours are essentially on the PbS-based system and give only a guide to the colours with modern photometers, detectors and filters.

Sp. Type U-B (B-V) (V-R)C (V-I)C (V-J) (V-H) (V-K) (V-L) (V-M) (V-N) (V-R)J (V-I)J
B0.0 -1.08 -0.30 -0.19 -0.31 -0.80 -0.92 -0.97 -1.13 -1.00 -9.99 -0.22 -0.44
B0.5 -1.00 -0.28 -0.18 -0.31 -0.77 -0.89 -0.95 -1.11 -0.99 -9.99 -0.20 -0.43
B1.0 -0.95 -0.26 -0.16 -0.30 -0.73 -0.85 -0.93 -1.08 -0.96 -9.99 -0.18 -0.42
B1.5 -0.88 -0.25 -0.15 -0.29 -0.70 -0.82 -0.91 -1.05 -0.94 -9.99 -0.17 -0.41
B2.0 -0.81 -0.24 -0.14 -0.29 -0.67 -0.79 -0.89 -1.02 -0.92 -9.99 -0.15 -0.40
B2.5 -0.72 -0.22 -0.13 -0.28 -0.64 -0.76 -0.86 -0.97 -0.88 -0.96 -0.14 -0.39
B3.0 -0.68 -0.20 -0.12 -0.27 -0.60 -0.72 -0.82 -0.92 -0.84 -0.91 -0.13 -0.38
B3.5 -0.65 -0.19 -0.12 -0.26 -0.58 -0.70 -0.80 -0.90 -0.82 -0.87 -0.12 -0.37
B4.0 -0.63 -0.18 -0.11 -0.25 -0.56 -0.68 -0.77 -0.86 -0.79 -0.84 -0.11 -0.35
B4.5 -0.61 -0.17 -0.11 -0.24 -0.54 -0.65 -0.74 -0.83 -0.76 -0.80 -0.11 -0.34
B5.0 -0.58 -0.16 -0.10 -0.24 -0.51 -0.62 -0.71 -0.78 -0.73 -0.75 -0.10 -0.33
B6.0 -0.49 -0.14 -0.10 -0.21 -0.46 -0.57 -0.64 -0.70 -0.65 -0.66 -0.09 -0.29
B7.0 -0.43 -0.13 -0.09 -0.19 -0.41 -0.51 -0.57 -0.61 -0.58 -0.58 -0.08 -0.26
B7.5 -0.40 -0.12 -0.09 -0.17 -0.39 -0.48 -0.54 -0.57 -0.54 -0.53 -0.08 -0.24
B8.0 -0.36 -0.11 -0.08 -0.16 -0.36 -0.45 -0.49 -0.52 -0.49 -0.48 -0.07 -0.22
B8.5 -0.27 -0.09 -0.08 -0.13 -0.31 -0.40 -0.43 -0.43 -0.42 -0.39 -0.07 -0.18
B9.0 -0.18 -0.07 -0.07 -0.10 -0.26 -0.34 -0.33 -0.34 -0.34 -0.30 -0.06 -0.14
B9.5 -0.10 -0.04 -0.05 -0.08 -0.22 -0.29 -0.26 -0.27 -0.26 -0.22 -0.03 -0.11
A0.0 -0.02 -0.01 -0.04 -0.04 -0.16 -0.19 -0.17 -0.18 -0.18 -0.14 -0.01 -0.05
A1.0 0.01 0.02 -0.02 -0.02 -0.11 -0.12 -0.11 -0.12 -0.13 -0.08 0.01 -0.03
A2.0 0.05 0.05 -0.01 0.00 -0.07 -0.04 -0.05 -0.07 -0.08 -0.02 0.03 0.00
A3.0 0.08 0.08 0.01 0.02 -0.02 0.03 0.01 -0.01 -0.02 0.03 0.05 0.02
A4.0 0.09 0.12 0.02 0.05 0.03 0.11 0.08 0.05 -0.04 0.09 0.07 0.07
A5.0 0.09 0.15 0.04 0.09 0.09 0.19 0.15 0.12 0.10 0.16 0.10 0.12
A6.0 0.10 0.17 0.05 0.12 0.13 0.30 0.21 0.17 0.15 0.21 0.11 0.16
A7.0 0.10 0.20 0.06 0.15 0.18 0.32 0.27 0.23 0.20 0.26 0.13 0.19
A8.0 0.09 0.27 0.09 0.20 0.25 0.42 0.36 0.33 0.29 0.34 0.16 0.26
A9.0 0.08 0.30 0.10 0.24 0.31 0.49 0.44 0.41 0.36 0.41 0.18 0.31
F0.0 0.03 0.32 0.12 0.28 0.37 0.57 0.52 0.49 0.43 0.48 0.21 0.36
F1.0 0.00 0.34 0.14 0.31 0.43 0.64 0.58 0.57 0.49 0.54 0.23 0.40
F2.0 0.00 0.35 0.15 0.35 0.48 0.71 0.66 0.66 0.56 0.60 0.25 0.45
F5.0 -0.02 0.45 0.21 0.44 0.67 0.93 0.89 0.90 0.77 0.80 0.33 0.57
F8.0 0.02 0.53 0.24 0.50 0.79 1.06 1.03 1.06 0.91 0.91 0.37 0.64
G0.0 0.06 0.60 0.27 0.54 0.87 1.15 1.14 1.18 1.01 1.01 0.41 0.70
G2.0 0.09 0.63 0.30 0.58 0.97 1.25 1.26 1.31 1.12 1.11 0.45 0.75
G3.0 0.12 0.65 0.30 0.59 0.98 1.27 1.28 1.33 1.14 1.13 0.45 0.76
G5.0 0.20 0.68 0.31 0.61 1.02 1.31 1.32 1.38 1.18 1.17 0.47 0.78
G8.0 0.30 0.74 0.35 0.66 1.14 1.44 1.47 1.55 1.34 1.30 0.52 0.85
K0.0 0.44 0.81 0.42 0.75 1.34 1.67 1.74 1.85 1.61 1.54 0.61 0.97
K1.0 0.48 0.86 0.46 0.82 1.46 1.80 1.89 2.02 1.78 1.68 0.67 1.05
K2.0 0.67 0.92 0.50 0.89 1.60 1.94 2.06 2.21 1.97 1.84 0.73 1.14
K3.0 0.73 0.95 0.55 0.97 1.73 2.09 2.23 2.40 2.17 2.01 0.80 1.25
K4.0 1.00 1.00 0.60 1.04 1.84 2.22 2.38 2.57 2.36 2.15 0.86 1.34
K5.0 1.06 1.15 0.68 1.20 2.04 2.46 2.66 2.87 2.71 2.44 0.97 1.54
K7.0 1.21 1.33 0.62 1.45 2.30 2.78 3.01 3.25 3.21 2.83 1.13 1.86
M0.0 1.23 1.37 0.70 1.67 2.49 3.04 3.29 3.54 3.65 3.16 1.26 2.15
M1.0 1.18 1.47 0.76 1.84 2.61 3.22 3.47 3.72 3.95 3.39 1.36 2.36
M2.0 1.15 1.47 0.83 2.06 2.74 3.42 3.67 3.92 4.31 3.66 1.46 2.62
M3.0 1.17 1.50 0.89 2.24 2.84 3.58 3.83 4.08 4.62 3.89 1.56 2.84
M4.0 1.07 1.52 0.94 2.43 2.93 3.74 3.98 4.22 4.93 4.11 1.65 3.07

Ascii versions of the above are linked below:

In both cases, the spectral types are coded numerically: B0 = 0; A0 = 10; F0 = 20; G0 = 30; K0 = 40; M0 = 47. Spectral type K extends only to K7, and there is not spectral type K6.

The mean relations given above are compared against observations of nearby stars in the following plots. Agreement is generally good in the UBV plane, but there are significant discrepancies with respect to the obsevations of redder stars (> K5) in most of the other colours. All of the spectral types for the latter are on the Kirkpatrick system (see the spectral classification pages ), primarily calibrated by TiO5 bandstrengths from PMSU observations.

  1. (B-V) and (U-B)
  2. (V-R) and (V-I)
  3. (I-J) and (J-K)
Green points indicate main-sequence stars from the 8-parsec and Hipparcos datasets; red triangles are ultracool M dwarfs with USNO data; magenta dots are USNO L dwarfs; cyan pentagons are T dwarfs. The following table gives the mean colour/spectral type relations derived from these observations:

Sp. Type (V-R)C rms n (V-I)C rms n (I-J)C rms n (J-H) rms n (H-K) rms n
A1.0 -0.010 - 1 -0.020 - 1 -0.010 - 0 -0.020 - 1 -0.030 - 1
A3.0 0.050 - 1 0.080 - 1 0.060 - 0 -0.010 - 1 0.040 - 1
A7.0 0.140 - 1 0.270 - 1 0.110 - 0 0.080 - 1 0.050 - 1
F5.0 0.250 - 1 0.490 - 1 0.290 - 0 0.180 - 1 0.060 - 1
F6.0 0.270 - 1 0.520 - 1 0.320 - 0 0.200 - 1 0.080 - 1
F8.0 0.330 - 1 0.660 - 1 0.450 - 0 0.290 - 1 0.090 - 1
F9.0 0.340 - 1 0.650 - 1 0.400 - 0 0.300 - 1 0.090 - 1
G0.0 0.335 0.005 2 0.655 0.025 2 0.375 0.045 0 0.835 0.595 2 0.060 0.010 2
G2.0 0.360 0.008 3 0.693 0.005 3 - - 0 - - 0 - - 0
G3.0 0.370 0.030 2 0.675 0.005 2 0.430 - 0 0.330 - 1 0.060 - 1
G5.0 0.380 0.020 5 0.744 0.036 5 0.510 0.025 0 0.328 0.031 4 0.090 0.024 4
G6.0 0.380 - 1 0.750 - 1 0.540 - 0 0.340 - 1 0.090 - 1
G8.0 0.422 0.026 5 0.808 0.069 5 0.512 0.040 0 0.328 0.022 4 0.120 0.014 4
G9.0 0.420 - 1 0.820 - 1 0.550 - 0 0.370 - 1 0.160 - 1
K0.0 0.468 0.027 5 0.888 0.040 5 0.567 0.056 0 0.440 0.014 3 0.133 0.009 3
K1.0 0.432 0.042 5 0.864 0.010 5 0.592 0.047 0 0.396 0.043 5 0.142 0.051 5
K2.0 0.590 0.140 5 1.118 0.268 5 0.692 0.168 0 0.522 0.089 5 0.108 0.013 5
K3.0 0.565 0.051 11 1.065 0.083 11 0.721 0.048 0 0.513 0.034 10 0.111 0.031 10
K3.5 0.665 0.015 2 1.215 0.045 2 0.785 0.045 0 0.540 0.060 2 0.140 0.010 2
K4.0 0.722 0.039 5 1.332 0.084 5 0.870 0.044 0 0.582 0.033 5 0.184 0.026 5
K4.5 0.750 - 1 1.390 - 1 0.950 - 0 0.610 - 1 0.140 - 1
K5.0 0.747 0.091 23 1.409 0.191 23 0.813 0.354 0 0.629 0.159 20 0.131 0.134 20
K7.0 0.860 0.055 23 1.677 0.203 24 1.028 0.182 0 0.615 0.045 24 0.189 0.028 24
M0.0 0.910 0.033 8 1.891 0.093 9 1.073 0.063 0 0.638 0.044 9 0.199 0.037 9
M0.5 0.939 0.035 10 1.976 0.061 10 1.135 0.082 0 0.630 0.033 10 0.194 0.014 10
M1.0 0.934 0.076 11 2.060 0.067 12 1.212 0.082 0 0.587 0.028 12 0.223 0.022 12
M1.5 0.968 0.030 12 2.123 0.054 12 1.227 0.055 0 0.584 0.047 12 0.220 0.020 12
M2.0 1.038 0.043 15 2.314 0.111 15 1.268 0.058 0 0.583 0.039 12 0.248 0.035 12
M2.5 1.044 0.034 10 2.335 0.111 10 1.201 0.193 0 0.561 0.064 10 0.255 0.034 10
M3.0 1.083 0.040 18 2.473 0.080 18 1.363 0.054 0 0.584 0.049 18 0.251 0.027 18
M3.5 1.157 0.073 18 2.647 0.200 18 1.437 0.103 0 0.564 0.037 17 0.256 0.028 17
M4.0 1.252 0.056 9 2.644 0.552 10 1.773 0.733 0 0.593 0.055 10 0.234 0.063 10
M4.5 1.336 0.064 10 3.062 0.117 10 1.607 0.048 0 0.521 0.052 7 0.303 0.056 7
M5.0 1.515 0.005 2 3.455 0.005 2 1.935 0.005 0 0.575 0.055 2 0.315 0.005 2
M5.5 1.558 0.086 4 3.515 0.171 4 1.963 0.160 0 0.580 0.024 3 0.317 0.026 3
M6.0 1.770 0.110 2 3.915 0.145 2 2.150 0.180 0 0.570 0.050 2 0.325 0.035 2
M6.5 2.110 0.078 3 4.393 0.106 3 2.410 0.135 0 0.587 0.009 3 0.373 0.019 3
M7.0 2.150 - 1 4.570 - 1 2.460 - 0 0.580 - 1 0.370 - 1
M7.5 2.290 - 1 4.690 - 1 2.580 - 0 0.500 - 1 0.380 - 1
M8.0 2.207 0.076 4 4.508 0.114 5 3.045 0.139 0 0.680 0.014 4 0.443 0.018 4
M8.5 2.295 0.045 2 4.645 0.065 2 3.200 - 0 0.685 0.035 2 0.520 0.020 2
M9.5 2.310 - 1 4.440 - 1 3.345 0.045 0 0.815 0.065 2 0.555 0.025 2
L0.0 2.410 - 1 4.650 - 1 3.440 - 0 0.760 - 1 0.540 - 1
L0.5 2.380 - 1 4.760 - 1 3.380 - 0 0.760 - 1 0.480 - 1
L1.0 2.520 - 1 4.920 - 1 3.405 0.035 0 0.740 0.030 2 0.545 0.075 2
L2.0 2.670 - 1 4.830 - 1 3.520 - 0 0.950 - 1 0.670 - 1
L3.0 2.510 - 1 4.800 - 1 3.730 - 0 0.910 - 1 0.620 - 1
L4.5 2.990 - 1 5.230 - 1 3.675 0.005 0 0.905 0.065 2 0.630 0.090 2
L5.0 3.860 - 1 6.250 - 1 3.940 0.142 0 0.997 0.084 3 0.627 0.085 3
L6.0 - - 0 - - 0 4.100 - 0 1.150 - 1 0.700 - 1
L7.0 - - 0 - - 0 4.040 0.190 0 1.070 0.100 2 0.680 0.120 2
L8.0 - - 0 - - 0 4.195 0.035 0 1.080 0.030 2 0.735 0.015 2
T2.0 - - 0 - - 0 4.860 - 0 0.840 - 1 0.150 - 1
T5.0 - - 0 - - 0 5.310 - 0 0.150 - 1 0.070 - 1
T6.0 - - 0 - - 0 6.335 0.655 0 -0.025 0.005 2 -0.035 0.035 2
T8.0 - - 0 - - 0 5.830 - 0 0.150 - 1 0.010 - 1

An ascii version of the above table is at the following link. Spectral type is coded as in the other tables.

SDSS calibrations

Suzanne Hawley et al. ( 2002 ) have sifted through the spectroscopic data in the Early Data Release from the Sloan survey, and identified over 700 M, L and T dwarfs. Based on that dataset, they have compiled mean relations between spectral type and the Sloan colours. Those datasets are listed here:

  1. template spectra from Figure 5 of the paper
  2. Readme file listing format of tables
  3. M0 to M8 dwarfs
  4. > M9 dwarfs
  5. Previously known dwarfs
See also Kevin Covey's page at University of Washington.

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page by Neill Reid, last updated 4/04/2002