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 |