TRANSFORMATIONS BETWEEN THE JHK IR SYSTEMS OF THE OBSERVATORIO-ASTRONOMICO-NACIONAL (OAN) AND THE SOUTH-AFRICAN-ASTRONOMICAL-OBSERVATORY (SAAO)

A set of infrared standard stars for the South African Astronomical Ob servatory (SAAO) (Carter 1990) are observed from the Observatorio Astr onomico Nacional (OAN) located at San Pedro Martir (SPM) in northern M exico. A number of linear transformation equations is obtained; in the m, there is a slight need for a colour term which implies that both se ts of filters have slightly different values for their effective wavel engths. Values for the OAN mean extinction coefficients are calculated . They are larger than the values reported in Carrasco et al. (1991); this might, however, be due to the ash and debris deposited on the atm osphere by recent volcanic eruptions. We also calculate a set of colou r transformations to the homogeneous IR photometric system proposed by Bessell & Brett (1988).