SPECTROSCOPY IN OPEN CLUSTER REMNANTS

G.R. SOLIVELLA; E.E. GIORG; G. BAUME; R.A. VÁZQUEZ

Isla Margarita (Venezuela)

Congreso; XII Reunión Regional Latinoamericana de Astronomía; 2007

The nature of NGC 1557, NGC 1963 y NGC 2017, catalogued as posssible clusters remnants (Bica et al. 2001) has been investigated combining infrared photometry and spectral classification. Another object, NGC 1520, an open cluster candidate (Dias et al.2002), was also investigated. The four objects are located in poorly populated fields at galactic latitudes |b| > 15◦. Spectra were obtained at CASLEO (Argentina), using a REOSC-DS spectrograph, along many observation runs from 2004 to 2006. They cover a range from 3900 A to 5500 A. These observations were complemented with JHK photometry and proper motions from 2MASS and UCAC 2 (Zacharias et al. 2003) catalogues respectively. Weobtained spectral classification for 36 stars in the four fields. It allow us to clarify the nature of these objects in the sense that no one of them is a real open cluster remnants. The available proper motion data and infrared color-magnitude diagrams analysis are not enough to give another interpretation when are both combined with spectral classification. In fact, the spectrophotometric distances derived for the bright stars in each regions suggest we are lookingat just a handful of evolved stars superimposed along the line of the sight. This is revealing that the simple strategy of superimposing isochrones to apparent main sequences and ilusory red giant branches can lead to wrong conclutions in the computation ofsurvival rates of open clusters.