Intrinsic Johnson-Cousins B-V and V-Ic Colors of B8V-M3V Nearby Field Dwarf Stars

Intrinsic Johnson-Cousins B-V and V-Ic Colors of A0V-M3V Nearby Field Dwarf Stars

Eric Mamajek (U. Rochester)

Last updated: 4 October 2009

Approximately 2300 nearby stars have recently been accurately spectrally classified on the MK system by Gray, Corbally, and collaborators via the NStars project (Gray et al. 2001, 2003, 2006). Nearly all of the stars are in the Hipparcos catalog (ESA 1997), and have accurate Johnson B-V and Johnson-Cousins V-Ic colors. The Hipparcos catalog itself contains spectral types from the literature for the majority of its ~120k entries. 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).

I measured the median colors for the dwarf (luminosity class V only) temperature subclasses for nearby star samples using both the Gray et al. ("NStars") spectral types and the Hipparcos literature spectral types ("HIP"). Spectral flags regarding rotation, activity, metallicity, and other peculiarities were ignored in the selection. Only stars with parallaxes greater than 13.33 mas were included (d < 75 pc), to select those stars ostensibly within the "Local Bubble" which should negligible reddening. I only list colors for subtypes with >=2 stars with B-V and V-I colors in Hipparcos.

For the NStars spectral type stars, the listed color is the mean of the median, Chauvenet-clipped mean (Bevington & Robinson 2003), and probit mean (Lutz & Upgren 1980). The standard error "s.e.m." is the mean of the standard error of the median (Gott et al. 2001) and the standard error of the clipped mean (using Chauvenet's criterion; Bevington & Robinson 2003). The value "st.dev" is the mean of the 68% confidence interval and the standard deviation as estimated using the probit method (Lutz & Upgren 1980). All of the estimators are extremely insensitive to the presense of outliers, which is why they were used in assessing the statistical moments. Subtype median colors whose standard error is >0.05 mag are flagged with "*", denoting that it is not recommended to adopt the values listed (better median colors are probably found elsewhere in the literature).

In the last columns, I list the median subtype B-V and V-Ic colors using stars in the Hipparcos catalog within 75 pc using the spectral classifications in the Hipparcos catalog. The more sophisticated estimation of median, standard error, and standard deviation was not calculated as this was from an earlier, preliminary analysis.

Where significant differences exist between the median intrinsic colors calculated using the NStars and Hipparcos samples, these differences probably reflect differences in the choice of standards among spectroscopists (as there is obviously intrinsic scatter among the colors of stars of the same classified subtype). The differences at G2V (the spectral type of the Sun) are significant: the NStars G2V stars have median B-V = 0.65, while the Hipparcos G2V stars have median B-V = 0.62.

Spec. Type	NStars < B-V >	s.e.m. < B-V >	st.dev. < B-V >	NStars < V-Ic >	s.e.m. < V-Ic >	st.dev. < V-Ic >	Nstars N*s	HIP < B-V >	HIP < V-Ic >	HIP N*s
B8V	...	...	...	...	...	...	1	-0.099	-0.08	9
B9V	...	...	...	...	...	...	0	-0.067	-0.05	8
B9.5V	...	...	...	...	...	...	0	-0.067	-0.05	3
A0V	-0.015	0.009	0.015	-0.021	0.011	0.010	3	0.013	0.03	44
A1V	0.056	0.013	0.020	0.071	0.016	0.023	4	0.035	0.055	38
A2V	0.075	0.019	0.036	0.048	0.028	0.055	5	0.063	0.08	47
A3V	0.087	0.002	0.004	0.083	0.013	0.023	5	0.114	0.13	57
A4V	0.145	...	...	0.160	...	...	1	0.160	0.18	17
A5V	0.175	0.016	0.023	0.195	0.015	0.021	2	0.189	0.21	39
A6V	0.170	0.001	0.001	0.185	0.005	0.007	2	0.200	0.22	9
A7V	0.204	0.010	0.029	0.226	0.015	0.043	12	0.202	0.22	32
A8V	0.230	0.016	0.038	0.261	0.015	0.038	5	0.243	0.27	15
A9V	...	...	...	...	...	...	0	0.305	0.35	23
F0V	0.296	0.005	0.006	0.345	0.005	0.007	2	0.316	0.37	88
F1V	0.313	0.005	0.015	0.368	0.008	0.026	14	0.355	0.415	14
F2V	0.374	0.005	0.027	0.437	0.005	0.033	31	0.374	0.44	91
F3V	0.375	0.007	0.021	0.434	0.006	0.022	14	0.419	0.49	138
F4V	0.412	0.003	0.015	0.481	0.005	0.019	17	0.427	0.49	45
F5V	0.443	0.004	0.027	0.512	0.004	0.027	54	0.465	0.53	307
F6V	0.482	0.003	0.024	0.557	0.004	0.024	41	0.496	0.57	268
F7V	0.511	0.003	0.012	0.579	0.004	0.022	20	0.524	0.60	262
F8V	0.530	0.003	0.020	0.601	0.004	0.028	50	0.544	0.62	248
F9V	0.552	0.005	0.036	0.623	0.005	0.032	57	0.578	0.65	52
G0V	0.599	0.001	0.018	0.669	0.001	0.024	81	0.587	0.66	293
G1V	0.627	0.003	0.019	0.692	0.001	0.015	66	0.604	0.67	176
G2V	0.647	0.003	0.035	0.706	0.005	0.024	48	0.618	0.69	271
G3V	0.667	0.004	0.014	0.724	0.007	0.020	17	0.639	0.70	285
G4V	0.684	0.006	0.022	0.740	0.005	0.018	16	0.658	0.725	18
G5V	0.669	0.005	0.037	0.728	0.004	0.030	55	0.678	0.74	415
G6V	0.693	0.005	0.024	0.748	0.005	0.023	22	0.712	0.76	143
G7V	0.709	0.005	0.030	0.758	0.007	0.026	33	0.729	0.79	8
G8V	0.726	0.004	0.027	0.777	0.004	0.023	54	0.750	0.80	253
G9V	0.777	0.005	0.031	0.821	0.007	0.030	77	0.796	0.83	16
K0V	0.818	0.009	0.057	0.857	0.006	0.038	40	0.821	0.85	260
K1V	0.842	0.005	0.034	0.880	0.003	0.028	44	0.856	0.89	153
K2V	0.878	0.006	0.033	0.923	0.005	0.039	69	0.923	0.97	193
K3V	0.997	0.006	0.038	1.038	0.008	0.041	63	0.990	1.02	183
K4V	1.101	0.006	0.042	1.172	0.012	0.065	46	1.115	1.18	67
K5V	1.156	0.009	0.070	1.259	0.014	0.113	40	1.130	1.21	145
K6V	1.242	0.008	0.059	1.391	0.018	0.114	50	...	...	0
K7V	1.341	0.017	0.063	1.571	0.032	0.105	30	1.289	1.41	101
K8V	1.382	0.009	0.048	1.608	0.035	0.179	23	...	...	0
K9V	1.418	0.016	0.040	1.735	0.039	0.103	11	...	...	0
M0V	1.421	0.011	0.065	1.735	0.029	0.158	27	1.368	1.60	61
M1V	1.438	0.011	0.035	1.841	0.032	0.117	18	1.460	1.825	26
M2V	1.489	0.023	0.052	2.078*	0.122*	0.291*	8	1.484	1.975	32
M3V	1.557	0.021	0.070	2.449*	0.128*	0.399*	8	...	...	...