Intrinsic Johnson-2MASS V-Ks Colors of B9V-M6V Field Stars

Eric Mamajek (U. Rochester)

Last updated: 8 April 2010

I cross-referenced the Hipparcos catalog (Perryman & ESA 1997) with the 2MASS catalog (Cutri et al. 2003). Many, if not most, of the spectral types in the Hipparcos catalogs are from the first four volumes of the Michigan Spectral Survey (e.g. Houk & Cowley 1975).

In order to extract unreddened V-Ks colors from the Hipparcos-2MASS catalog, only stars with parallaxes greater than 13.33 mas and relative parallax error less than 12.5% were included (d < 75 pc), to select those stars ostensibly within the "Local Bubble" which should have negligible reddening.

As Hipparcos contains very few M dwarfs, an auxillary sample of cool stars (K5-M6) was compiled with Johnson V and 2MASS Ks magnitudes drawn from Neill Reid's photometry table for nearby CNS3 stars. There are systematic differences between the mean V-Ks colors for the Hipparcos and Reid samples for subtype K4 and later. As there are more cool stars in Reid's CNS3 sample, and most are typed on Kirkpatrick's modern system of M standards, I adopt the mean V-Ks colors for the Reid sample over that of the Hipparcos sample. In all cases the Hipparcos mean is bluer than the Reid CNS3 mean, perhaps attributable to the more pronounced magnitude-limited nature of the Hipparcos sample (where the CNS3 sample is a volume-limited sample constructed from a plethora of samples with a multitude of biases).

The listed V-Ks color for the "HIP" and "CNS3" samples is the mean of the median, Chauvenet-clipped mean, and probit mean. The standard error is the mean of the standard error of the median and the standard error of the Chauvenet-clipped mean. The standard deviation is the mean of the standard deviation calculated using the Chauvenet-clipped sample, and using the probit method. These estimators are very resistant to the effects of outlier points. I only list statistical moments of V-Ks when there are either more than 2 stars/measurements, and the standard error is >0.1 mag.

I have also added colors (or medians of colors) for the M-type spectral standards discussed at http://www.pas.rochester.edu/~emamajek/spt/. These are labeled as e.g. "M5V(stan)", and the median, standard error, and standard deviation are listed, along with the number of standard stars considered.

For the spectral types where I have calculated multiple median colors, the one that I consider "best" is shaded darker. For many of the K and M standards, I side with the CNS3 sample as it is volume-limited and not magnitude-limited (the HIP colors seem systematically bluer). For M5V through M9V, I have relied upon a few well-studied standard stars.

SpT V-Ks s.e.m.st.dev. N*s
B8V -0.189 0.033 0.055 4
B9V -0.103 0.010 0.018 3
A0V 0.074 0.018 0.095 27
A1V 0.176 0.022 0.094 21
A2V 0.213 0.021 0.120 26
A3V 0.336 0.023 0.153 35
A4V 0.401 0.038 0.099 11
A5V 0.487 0.018 0.099 22
A7V 0.529 0.045 0.135 18
A8V 0.567 0.034 0.063 5
A9V 0.775 0.038 0.143 14
F0V 0.799 0.020 0.142 64
F1V 0.845 0.072 0.217 9
F2V 0.958 0.015 0.102 85
F3V 1.035 0.007 0.083 142
F4V 1.102 0.019 0.106 33
F5V 1.156 0.006 0.085 314
F6V 1.228 0.007 0.094 240
F7V 1.287 0.006 0.082 241
F8V 1.327 0.007 0.094 224
F9V 1.421 0.014 0.083 41
G0V 1.423 0.007 0.085 255
G1V 1.449 0.008 0.088 170
G2V 1.506 0.006 0.094 255
G3V 1.540 0.004 0.074 279
G4V 1.572 0.033 0.094 15
G5V 1.631 0.004 0.092 404
G6V 1.712 0.008 0.083 151
G7V 1.776 0.039 0.107 8
G8V 1.782 0.010 0.107 221
G9V 2.034 0.079 0.227 17
K0V 1.969 0.012 0.140 208
K1V 2.062 0.011 0.138 128
K2V 2.227 0.010 0.147 175
K3V(stan) 2.34 ... ... 3
K3V(CNS3)* 2.365 0.037 0.155 17
K3V(HIP) 2.411 0.017 0.187 158
K4V(stan) 2.65 ... ... 1
K4V(HIP) 2.720 0.034 0.245 56
K4V(CNS3)* 2.825 0.090 0.308 17
K5V(stan) 2.770 ... ... 1
K5V(HIP) 2.815 0.023 0.248 129
K5V(CNS3)* 3.086 0.058 0.335 66
K7V(CNS3)* 3.502 0.040 0.312 70
K7V(HIP) 3.218 0.040 0.249 67
M0V(HIP) 3.468 0.045 0.213 25
M0V(CNS3)* 3.675 0.043 0.331 48
M0V(stan) 3.950 0.116 0.173 4
M1V(CNS3)* 4.053 0.025 0.109 33
M1V(stan) 4.105 0.073 0.127 3
M2V(CNS3) 4.311 0.046 0.301 39
M2V(stan)* 4.206 0.038 0.066 3
M2V(HIP) 3.897 0.059 0.169 10
M3V(CNS3)* 4.643 0.023 0.133 27
M3V(stan) 4.447 ... ... 1
M4V(CNS3)* 5.223 0.084 0.201 10
M4V(stan) 5.242 0.072 0.167 7
M5V(stan)* 6.086 0.144 0.204 2
M6V(stan)* 7.129 0.187 0.375 4
M7V(stan)* 8.053 0.067 0.098 2
M8V(stan)* 8.714 0.077 0.133 3
M9V(stan)* 8.847 0.011 0.016 2