Broad-band JHK(L′) photometry of a sample of giants with 0.5>[Fe/H]>-3

We present the results of a three-year campaign of broad-band photometry in the near-infrared J, H, K and L' bands for a sample of approximately 250 giant stars carried out at the Observatorio del Teide (Tenerife, Spain). Transformations of the Telescopio Carlos Sanchez system into/from several currently used infrared systems are extended to the redward part of the colour axis. The linearity of our photometric system in the range -3 mag < K < 10.5 mag is inferred from the intercomparison of data of stars common to this and other photometric systems. A preliminary assessment of the photometric extinction profile of the Observatorio del Teide in JHKL' is also provided. These observations are a continuation of a programme aimed towards the progressive completion of a whole grid of T-eff-[Fe/H]- log(g)-colour relations for population I and II stars. The analysis of optical and IR colour-colour diagrams reveals that the range F0III-K5III is well sampled for 0.5 > [Fe/H] > -3. Data of comparable quality previously published have been added to the sample in order to increase the reliability of the relations to be obtained. We also provide mean IR colours for giant stars according to spectral type(1).