Table 4:

Coefficients and range of applicability of the colour-temperature-metallicity relations.

Colour	range	Colour range	a0	a1	a2	a3	a4	a5	N
B-V	[-5.0,0.4]	[0.18,1.29]	0.5665	0.4809	-0.0060	-0.0613	-0.0042	-0.0055	400	73
	[-5.0,0.3]	[0.24,0.80]	0.4386	1.4614	-0.7014	-0.0807	0.0142	-0.0015	201	62
	[-5.0,0.3]	[0.23,0.68]	0.3296	1.9716	-1.0225	-0.0298	0.0329	0.0035	211	82
	[-5.0,0.3]	[0.46,1.47]	0.4033	0.8171	-0.1987	-0.0409	0.0319	0.0012	208	59
V-J	[-5.0,0.4]	[0.61,2.44]	0.4669	0.3849	-0.0350	-0.0140	0.0225	0.0011	401	42
V-H	[-5.0,0.4]	[0.67,3.01]	0.5251	0.2553	-0.0119	-0.0187	0.0410	0.0025	401	33
	[-5.0,0.4]	[0.78,3.15]	0.5057	0.2600	-0.0146	-0.0131	0.0288	0.0016	401	25
	[-5.0,0.4]	[0.07,0.80]	0.6393	0.6104	0.0920	-0.0330	0.0291	0.0020	412	132
	[-2.7,0.4]	[0.19,1.49]	0.5839	0.4000	-0.0067	-0.0282	-0.0346	-0.0087	251	79
	[-2.7,0.4]	[0.77,2.56]	0.4525	0.3797	-0.0357	-0.0082	0.0123	-0.0009	272	43
	[-2.7,0.4]	[0.77,3.16]	0.5286	0.2354	-0.0073	-0.0182	0.0401	0.0021	263	26
	[-2.4,0.4]	[0.99,3.29]	0.4892	0.2634	-0.0165	-0.0121	0.0249	-0.0001	258	18
b-y	[-3.7,0.5]	[0.18,0.72]	0.5796	0.4812	0.5747	-0.0633	0.0042	-0.0055	1120	62

Notes. The photometric systems are Johnson-Cousins , 2MASS , Tycho2 and Strömgren by. For the latter, additional corrections as function of and (b-y) apply, as discussed in Sect. 6.1.1. For some indices the calibrations are given down to , meaning that the effective temperatures of such a metal-poor star can be recovered using in Eq. (3). Notice that only two hyper metal-poor stars are currently known and caution should be used, as discussed in the text. Especially for metal-poor stars, please refer to Fig. 13 to check that the calibration is not extrapolated outside its range. N is the number of stars employed for the fit after the clipping and is the standard deviation (in Kelvin) of the proposed calibrations. Notice that the standard deviation does not account for the uncertainty in the zero point of the temperature scale, which is of order 15-20 K (Sects. 3.2 and 4.1).