Bochum 15, a new young stellar aggregate in Puppis.

Summary. Bochum 15 (centred at 1= 248?0, b= - 5?5) is found to be a loose aggregate of about 30 OB stars located 4.4 kpc from the sun and 420 pc below the galactic plane. It is very young on the basis of its earliest member (spectral type 07). The aggregate has a mean colour excess EB V = 0W5 with considerable differential reddening which tends to decrease away from the galactic plane. Its young age makes it a good spiral arm indicator and it is associated with 6 other young spiral tracers located at this distance in Puppis. Key words: photometry - stellar aggregate galactic structure