Pismis 23 y BH 222: dos cúmulos abiertos altamente enrojecidos ubicados más allá del brazo espiral de Sagitario

PIATTI, ANDRÉS E.; CLARIA OLMEDO, JUAN JOSÉ

Buenos Aires

Congreso; Reunión Anual de la Asoc. Argentina de Astronomía; 2002

We present CCD BVI photometry of the two open cluster candidates Pismis 23 and BH 222, both projected close to the direction towards the Galactic centre. Both the analysis of the colour-magnitude diagrams (CMDs), and star counts in the regions of the two objects, support their physical reality. Pismis 23 presents a main sequence and other clearly visible features in the CMDs. For this cluster we derive colour excesses E(B-V) = 2.0 ± 0.1 and E(V-I) = 2.6 ± 0.1, a distance from the Sun d = (2.5 ± 0.6) kpc and an age of (300 ± 100) Myr. BH 222 is a young stellar aggregate formed by a main sequence and a conspicuous group of luminous stars, typically supergiants. For this cluster we derive E(V-I) = 2.4 ± 0.2, d = (6.0 ± 2.7) kpc and an age of (60 ± 30) Myr. Both objects, located beyond Sagittarius arm and projected close to the direction towards the Galactic centre, are among the most distant and reddened known open clusters.