NEAR-IR IMAGING PHOTOMETRY OF NGC-1333 .1. THE EMBEDDED PMS STELLAR POPULATION

We present near-IR (NIR) J, H and K mosaic images of the active star forming region associated with the optical reflection nebula NGC 1333. These observations cover an area of 10' x 10' and are centered on the energetic outflow source SSV 13. From these data, we have obtained NIR photometry of 134 objects down to a 5sigma limiting K magnitude Of m(K)=16.2 and a conservative survey completeness limit of m(K)=16.0. With the addition of new optical R and I band CCD photometry, and both (sub)mm line and continuum maps, we analyse and discuss the region's morphology and spatial source distribution with additional reference to existing multi-wavelength data. Within the survey field, NGC 1333-S, we find a significant population of young, PMS stars. Specifically, we consider 55 sources or approximately 41% of the total stellar population are likely in a PMS evolutionary state. These sources exhibiting clustering in the vicinity of SSV 13 although SSV 13 is not at the cluster centre. The implied stellar PMS population has a range of M(K) of 0-9 magnitudes and J-K colours of approximately 1-5. We interpret the data as evidence that i) the embedded population is dominated by relatively low-mass stars i.e. <0.3 M. (approximately 55%), and ii) there exists smaller populations of objects consistent with standard young star classes namely, classical T Tauri stars (approximately 25%), Herbig Ae/Be stars (<10%) and Class I sources (<10%). We demonstrate that an apparent turn-over in the m(K) luminosity function for all sources in the survey field can be modelled by the combined effect of the survey detection limit and spatially variable extinction over the survey region. This suggests that a combination of a de-reddened sample of PMS star, and a detection limit several magnitudes below the expected faintest m(K) for those sources is required before inferences can be drawn on the luminosity/mass function. We additionally present the discovery of several new compact nebulous features in the region. Two such objects are possibly associated with SSV 13 and HH 7-11. Almost all of these features are associated with blue-shifted CO in the outflows from IRAS sources in the region. We consider in some detail the usage of NIR photometry and colours in a region of significant extinction, e.g. within the boundaries of molecular clouds, to both determine the evolutionary state of an observed sample of stars and subsequently to characterize them into mass, luminosity, activity and age classes. We discuss and apply several methods to separate a population of embedded young pre-main sequence (PMS) stars from the generally larger population of reddened background galactic sources.