Spectro-Photometric Study of Trumpler 11: Characterization of the Stellar Population and Cluster Properties

Open clusters serve as fundamental tracers of Galactic structure and stellar evolution, providing crucial insights into the history of the formation and dynamics of spiral arms. Recent studies have revealed significant open questions regarding the age gradient of clusters in the direction of arm rotation, with implications for understanding spiral density wave theory and star formation processes within the Galactic arms. The Carina-Sagittarius arm of the Milky Way Galaxy presents an interesting laboratory for investigating these phenomena, as it contains clusters spanning a wide range of ages and metallicity. However, many clusters in this outer Galactic region remain poorly characterized, limiting our ability to construct comprehensive models of spiral arm evolution and stellar population synthesis. This study aims to address these gaps by conducting a detailed spectroscopic and photometric analysis of the stellar populations in an open cluster located in the Carina region. Here, we present a comprehensive spectroscopic and photometric analysis of the open cluster Trumpler 11, located in the Carina-Sagittarius arm of the Milky Way Galaxy. Optical spectra (R = 1522) were obtained for 45 sources using the Gemini South GMOS spectroscopy in multi-object (MOS) mode. We successfully derived physical parameters for 24 cluster member stars through photospheric spectral model fitting. The stellar parameters include effective temperature (Teff), surface gravity (log(g)), microturbulent velocity (vmic), and projected rotational velocity (v sin i). Spectral classification reveals that the cluster population consists primarily of late B-type stars, with the identification of one new Be star. Complementary GMOS-S photometric observations were conducted using four broadband filters (u′, g′, r′, i′) and the Hα narrow-band filter. Aperture photometry was performed, and color-magnitude diagrams were used to derive the cluster parameters, color-excess, intrinsic distance module (13.12 ± 0.1 mag), and age (100 Myrs), along with independent distance estimates obtained through spectroscopic results and Gaia astrometric data. Preliminary analysis of TESS photometric time-series data revealed 8 eclipsing binary stars within the cluster, six of which had not been reported previously. All data analysis was performed using IRAF and custom Python codes developed for this study. This work contributes to our understanding of stellar populations and evolution in Galactic open clusters, particularly for B-type stars in the outer disk region. Moreover, by comparing properties of Trumpler 11 with those of the nearby open clusters, we discussed the large-scale structure of the Carina region.