ESO 442-04: A dissolving open cluster

MAIA, F.F.S.; SANTOS, J.F.C.; CORRADI, W.; PIATTI, ANDRÉS E.

Congreso; XXXVI Reunión de la Sociedade Astronomica Brasileira; 2011

  We present a conclusive analysis on the true nature of the controversial objectESO442-04, which initially has been listed as a possible open cluster remnantand later on considered a random stellar alignment. We have derived radial ve-locity, spectral type, surface gravity and metallicity for 17 stars from their spectra.Tentative age and structural parameters were estimated from near-infrared anddeep optical photometry. The kinematics was studied by complementing derivedradial velocities with available proper motion data. Although colour-magnitude di-agram analyses suggest a single stellar population 2.5 Gyr old, the inspection ofthe colour-colour diagram (U-B) x (B-V) seems more akin to a Galactic disc fieldpopulation. Spectroscopic parallaxes also place the stars at significantly differentdistances. Taken all together the analyses indicate that the stellar aggregate is notan open cluster remnant, but an unbound concentration of bright stars contrastingwith the surrounding Galactic thick disc field.