Intrinsic Johnson-Cousins UBVI Colors of M Dwarf Standard Stars
Eric Mamajek (UR)
Last updated: 2 May 2010
Summary
Here I calculate robust mean Johnson-Cousins U-B,
B-V, and V-I colors for the M-type standard stars provided by Henry et
al. (2002).
Data
Henry et
al. (2002) published a comprehensive list of M-type standard stars
that builds upon previous spectral classification efforts by
Kirkpatrick et al. (1991, 1995, 1997),
Henry et al. (1994, 1997, 1999),
and McCarthy et
al. (1991). I cross-referenced Henry et al.'s list of M-type
standard stars against a few large photometric catalogs of
Johnson-Cousins photometry and colors: Mermilliod
(1991), Gliese & Jahreiss
(1991), and the Hipparcos catalog (Perryman
& ESA 1997). For some of the fainter, cooler targets, V-I colors
were found in Bessell
(1990) and Leggett
(1992). Here I list a robust "mean" (which is the mean of the
median, Chauvent-clipped mean, and probit mean), "standard error"
(which is the mean of the true median error and Chauvenet standard
error), and "standard deviation" (which is the mean of the 68%
confidence limits and the standard deviation estimated via the probit
method). These alternative methods of calculating these statistical
quantites were used as they are extremely resiliant to the effects of
outliers - and in the limit of large samples with no outliers, they
are virtually identical to the mean, standard error, and standard
deviation. For samples of 2 and 3, I simply calculated and list the
mean, standard error of the mean, and standard deviation.
Given the small number of standard stars available, I'm not
necessarily advocating using these mean colors as representative for
normal dwarf stars. However, they may be useful for spectral types
were there are few examples of stars with well-determined optical
colors. This exercise does demonstrate that there can be significant
scatter in the optical colors of M dwarf stars even among the
standard stars themselves.
Comments on the state of the various M-dwarf standard stars are
provided here. A plot of
B-V vs. V-I for nearby stars is shown on p. 378
of Bessell (1990). Useful color-color plots for M dwarfs are also
illustrated in Leggett
(1992) and at Neill Reid's website.
Spec.
Type |
< B-V > |
s.e.m.
< B-V > |
st.dev.
< B-V > |
N*s |
< V-I > |
s.e.m.
< V-I > |
st.dev.
< V-I > |
N*s |
< U-B > |
s.e.m.
< U-B > |
st.dev.
< U-B > |
N*s |
| K7V |
1.373 |
0.028 |
0.058 |
6 |
1.565 |
0.163 |
0.322 |
5 |
1.231 |
0.027 |
0.076 |
5 |
| M0V |
1.487 |
0.034 |
0.052 |
4 |
2.010 |
0.163 |
0.259 |
4 |
1.190 |
0.042 |
0.066 |
4 |
| M1V |
1.490 |
0.009 |
0.014 |
5 |
2.032 |
0.020 |
0.054 |
4 |
1.202 |
0.028 |
0.051 |
5 |
| M1.5V |
1.517 |
0.040 |
0.079 |
5 |
2.194 |
0.160 |
0.311 |
5 |
1.205 |
0.033 |
0.058 |
5 |
| M2V |
1.503 |
0.001 |
0.002 |
4 |
2.137 |
0.065 |
0.093 |
4 |
1.172 |
0.028 |
0.045 |
4 |
| M2.5V |
1.544 |
0.037 |
0.075 |
6 |
2.307 |
0.140 |
0.262 |
5 |
1.175 |
0.035 |
0.071 |
6 |
| M3V |
1.529 |
0.018 |
0.049 |
11 |
2.320 |
0.115 |
0.305 |
10 |
1.150 |
0.032 |
0.083 |
10 |
| M3.5V |
1.604 |
0.018 |
0.069 |
16 |
2.631 |
0.098 |
0.257 |
11 |
1.177 |
0.049 |
0.144 |
14 |
| M4V |
1.719 |
0.036 |
0.088 |
9 |
2.898 |
0.056 |
0.152 |
5 |
1.259 |
0.038 |
0.084 |
8 |
| M4.5V |
1.726 |
0.037 |
0.082 |
10 |
3.082 |
0.129 |
0.302 |
5 |
1.228 |
0.038 |
0.084 |
8 |
| M5.0V |
1.856 |
0.079 |
0.123 |
4 |
3.330 |
NA |
NA |
1 |
1.128 |
0.229 |
0.397 |
3 |
| M5.5V |
1.904 |
0.017 |
0.063 |
10 |
3.643 |
0.087 |
0.165 |
5 |
1.422 |
0.110 |
0.230 |
7 |
| M6V |
1.941 |
0.056 |
0.098 |
3 |
NA |
NA |
NA |
NA |
1.268 |
NA |
NA |
1 |
| M6.5V |
2.083 |
0.017 |
0.024 |
2 |
4.250 |
0.130 |
0.184 |
2 |
2.110 |
NA |
NA |
1 |
| M7V |
1.990 |
NA |
NA |
1 |
4.52 |
NA |
NA |
1 |
NA |
NA |
NA |
1 |
| M8V |
2.20 |
NA |
NA |
1 |
NA |
NA |
NA |
NA |
NA |
NA |
NA |
NA |