Although the J and K filters used in this study are similar to those employed in the original infrared photometric system as described by H. L. Johnson and others, the need for a high degree of internal accuracy required the determination of a new set of standard magnitudes. Twenty-one stars, selected so that a reasonably large range of brightness and color could be spanned were set up as standards.
Individual standards were typically observed on 10-20 different nights with between one and three observations per night. The system was closed once around the sky, and no systematic closure errors were found. We estimate that the internal accuracy of the system is ± 0.01 mag at H, K, and in the CO index; and ± 0.03 mag at J. A combination of the transmission characteristics of the J filter, the atmosphere, and the field lens, and the rounded nature of the beam profile, causes the J measurements to have the largest uncertainty.
Table Al contains the J - H and H - K colors, K-magnitudes, and CO indices for our grid of standards. The zero-point of this system is set by defining the magnitudes and colors of Lyr to be 0.00 at all wavelengths. If allowance is made for the fact that Johnson (1966b and references therein) takes K( Lyr) = + 0.02, there is no systematic difference between the magnitude scales of Johnson and of Table Al based on a comparison of 16 stars. Thus, except for the zero-point shift, the V - K values in this paper are on the system of Johnson. Because the effective wavelength of our J-filter is different from that of Johnson, a small transformation exists between the two systems. To transform the J-magnitudes of this paper to the Johnson (1966b) system, the following equation is adequate
JJ = 1.09(J - H) + H | (A1) |
i. e., the J - K colors in this paper are systematically blue compared with Johnson's. We caution other observers using the photometric system defined by these stars to check carefully for the presence of a color equation, particularly at 1.2 µm.
Name | Sp. Type | V | K | J-H | H-K | CO |
BS 117 | MO III | 5.71 | 1.87 | 0.74 | 0.16 | 0.155 |
BS 134 | KO III | 6.30 | 4.07 | 0.45 | 0.08 | 0.04 |
BS 718 | B9 III | 4.28 | 4.38 | -0.05 | -0.02 | 0.00 |
BS 923 | KO III | 5.99 | 3.74 | 0.49 | 0.08 | 0.05 |
BS 1552 | B2 III | 3.69 | 4.14 | -0.04 | -0.05 | 0.00 |
BS 1698 | K3 III | 4.46 | 1.84 | 0.53 | 0.10 | 0.095 |
BS 3304 | KS III | 5.63 | 2.37 | 0.66 | 0.13 | 0.15 |
BS 3403 | K2 III | 4.59 | 1.88 | 0.54 | 0.06 | 0.08 |
BS 3427 | KO III | 6.39 | 4.25 | 0.48 | 0.07 | 0.04 |
BS 4039 | dF5 | 5.82 | 4.49 | 0.28 | 0.03 | -0.005 |
BS 4550 | G8 VI | 6.45 | 4.42 | 0.44 | 0.06 | 0.005 |
BS 4608 | G8 III | 4.13 | 1.89 | 0.47 | 0.05 | 0.05 |
BS 4689 | A2 V | 3.88 | 3.77 | -0.05 | -0.01 | -0.005 |
HD 107906 | K | - | 7.04 | 0.39 | 0.05 | 0.035 |
HD 132950 | K | - | 6.33 | 0.51 | 0.07 | 0.04 |
BS 5634 | F5 V | 4.92 | 3.88 | 0.22 | 0.02 | 0.00 |
BS 6092 | B5 IV | 3.89 | 4.30 | -0.06 | -0.05 | 0.01 |
BS 6136 | K4 III | 5.39 | 2.02 | 0.66 | 0.14 | 0.145 |
BS 6228 | K5 III | 5.16 | 1.44 | 0.72 | 0.15 | 0.165 |
BS 7001 | AO V | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
BS 8498 | K3 II-III | 4.12 | 0.99 | 0.62 | 0.13 | 0.15 |
BS 8551 | KO III-IV | 4.80 | 2.29 | 0.53 | 0.09 | 0.07 |
Table A2 contains measurements of selected high luminosity late-type stars. These data were used to define mean relationships between colors, CO index, and spectral type, and can be employed to establish transformations from the present photometric system to any other system. The three supergiants in Cygnus, plus the stars identified with BD numbers, are heavily reddened (Lee 1970).
Name | Sp. Type | K | J-H | H-K | CO |
BS 3027 | M2 II-III | 2.01 | 0.83 | 0.20 | 0.20 |
BS 3705 | M0 III | -0.61 | 0.84 | 0.16 | 0.17 |
BS 4008 | MO III | 2.10 | 0.80 | 0.17 | 0.20 |
BS 4069 | MO III | -0.84 | 0.79 | 0.15 | 0.18 |
BS 4336 | M2 III | 1.44 | 0.79 | 0.18 | 0.20 |
BS 4902 | M3 III | 0.14 | 0.82 | 0.20 | 0.20 |
BS 4910 | M3 III | -1.25 | 0.80 | 0.18 | 0.21 |
BS 5879 | gMl | 0.05 | 0.82 | 0.17 | 0.19 |
BS 7139 | M4 II | -1.17 | 0.85 | 0.21 | 0.26 |
BS 7157 | M5 III | -2.06 | 0.83 | 0.26 | 0.25 |
BK Vir | M7 III | -0.91 | 0.89 | 0.33 | 0.25 |
SW Vir | M7 III | -1.88 | 0.91 | 0.34 | 0.27 |
RT Vir | M8 III | -1.18 | 0.90 | 0.36 | 0.24 |
BC Cyg | M4 Ia | 0.25 | 1.17 | 0.54 | 0.33 |
AZ Cyg | M2 Ia | 1.31 | 0.97 | 0.38 | 0.34 |
KY Cyg | M4 Ia | 1.54 | 1.27 | 0.59 | 0.30 |
+9° 3920 | M2 III | 4.37 | 0.85 | 0.22 | 0.21 |
+29° 3730 | M4 III | 1.95 | 0.85 | 0.24 | 0.21 |
+35° 4138 | M3 III | 3.89 | 0.86 | 0.23 | 0.20 |
+59° 2541 | M2.5 III | 4.46 | 0.85 | 0.26 | 0.18 |
+64° 1842 | M2 II | 3.11 | 1.03 | 0.33 | 0.19 |
+42° 1065 | MO III | 5.66 | 0.83 | 0.20 | 0.14 |
Table A3 gives the adopted mean relationships based on the system of Tables Al and A2. The V - K and J - K colors as functions of spectral type for the giants are transformed from Johnson (1966b) for stars earlier than M0 and from Lee (1970) for MO-M6. The H - K colors and CO indices of the giants are from the data of Tables Al and A2 and from additional unpublished measurements. All of the mean values for the dwarf's are based on our own infrared measurements plus V-magnitudes from the literature. The agreement with most of the recently published infrared photometry of dwarfs (e.g., Mould and Hyland 1976) is generally better than ± 0.02 mag at all wavelengths. A complete discussion of our observations of late-type dwarfs will be presented elsewhere.
Giants |
Dwarfs |
|||||||
Sp. Type | V-K | J-H | H-K | CO | V-K | J-H | H-K | CO |
G5 | 2.08 | 0.47 | 0.05 | 0.03 | 1.25 | 0.26 | 0.04 | 0.01 |
G8 | 2.16 | 0.49 | 0.06 | 0.04 | 1.50 | 0.32 | 0.05 | 0.02 |
KO | 2.35 | 0.51 | 0.08 | 0.07 | 1.75 | 0.37 | 0.06 | 0.02 |
K1 | 2.48 | 0.54 | 0.09 | 0.09 | 2.00 | 0.42 | 0.07 | 0.03 |
K2 | 2.59 | 0.56 | 0.10 | 0.11 | 2.25 | 0.47 | 0.08 | 0.04 |
K3 | 2.92 | 0.62 | 0.12 | 0.12 | 2.50 | 0.52 | 0.09 | 0.04 |
K4 | 3.24 | 0.68 | 0.13 | 0.14 | 2.75 | 0.56 | 0.10 | 0.04 |
K5 | 3.67 | 0.73 | 0.15 | 0.15 | 3.00 | 0.59 | 0.11 | 0.04 |
MO | 3.74 | 0.74 | 0.16 | 0.17 | 3.25 | 0.63 | 0.13 | 0.04 |
M1 | 3.90 | 0.76 | 0.17 | 0.18 | 3.50 | 0.65 | 0.14 | 0.04 |
M2 | 4.16 | 0.77 | 0.18 | 0.19 | 3.75 | 0.65 | 0.16 | 0.03 |
M3 | 4.63 | 0.79 | 0.20 | 0.21 | 4.00 | 0.63 | 0.21 | 0.02 |
M4 | 5.34 | 0.81 | 0.23 | 0.22 | 4.25 | 0.60 | 0.22 | 0.00 |
M5 | 6.20 | 0.86 | 0.26 | 0.23 | 4.50 | 0.57 | 0.24 | -0.02 |
M6 | 7.20 | 0.89 | 0.30 | 0.24 | 4.75 | 0.54 | 0.25 | -0.03 |
M7 | - | 0.91: | 0.33: | 0.25: | 5.00 | 0.53 | 0.26 | -0.04 |
M8 | - | 0.89: | 0.37: | 0.26: | 5.25 | 0.52 | 0.28 | -0.05 |
5.50 | 0.53 | 0.29 | -0.05 | |||||
5.75 | 0.54 | 0.31 | -0.04 | |||||
6.00 | 0.55 | 0.32 | -0.04 | |||||
6.25 | 0.57 | 0.33 | -0.03 | |||||
6.50 | 0.59 | 0.35 | -0.03 | |||||
6.75 | 0.61 | 0.36 | -0.02 | |||||
7.00 | 0.62 | 0.37 | -0.02 | |||||
7.25 | 0.63 | 0.38 | -0.01 | |||||
7.50 | 0.65 | 0.39 | -0.01 | |||||