Integrated spectroscopy is an observational technique based on the concept of stellar population sinthesis. Applied in combination with medium size aperture telescopes (d > 2 m), it enables to infer fundamental astrophysical properties of compact, faint, and distant objects. Using this technique, we determine age, interstellar reddening and metallicity of 3 southern open clusters, namely Hogg 15, Mel 105 and NGC 2849. The integrated spectra obatined at CASLEO (San Juan, Argentina) in the spectral range 3500-9200Å with a typical dispersion of 3.4 Å/pixel, were calibrated in units of wavelength and flux. A first reddening-independent age was obtained using the equivalent widths of the Balmer lines. This first estimate allows us to choise in each case the spectral template whose features most resemble those of the observed spectra. The interstellar reddening of each cluster was then varied to get the best match of continuum and spectral lines. Hogg 15 and NGC 2849 are both very young open clusters with ages between 3 and 6 million years and E(B-V) colour excesses of 1.05 ± 0.03 and 0.53 ± 0.05, respectively. Mel 105 appears to be much older with an age of nearly 108 years and a reddening of E(B-V) = 0.31 ± 0.02. Using the near infrared spectral region, a rough estimate of the metallicity of Hogg 15 and Mel 105 was determined, but not that of NGC 2849 due to the low signal-to-noise ratio of the corresponding spectrum. The equivalent widths of spectral windows including NaI and CaII triplet lines in the infrared allow us to conclude that Mel 105 and Hogg 15 are metal-rich and metal-poor clusters as compared to the Sun, respectively.
Boletin de la Asociacion Argentina de Astronomia La Plata Argentina
- Pub Date: