Context. The identification and characterisation of populations of young massive stars in (giant) H ii regions provides important constraints on i) the formation process of massive stars and their early feedback on the environment, and ii) the initial conditions for population synthesis models predicting the evolution of ensembles of stars. Aims. We identify and characterise the stellar populations of the following young giant H ii regions: M8, G333.6-0.2, and NGC 6357. Methods. We have acquired H-and K-band spectra of around 200 stars using The K-band Multi Object Spectrograph (KMOS) on the ESO Very Large Telescope. The targets for M8 and NGC 6357 were selected from the Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX), which combines X-ray observations with near-infrared and mid-infrared data. For G333.6-0.2, the sample selection is based on the near-infrared colours combined with X-ray data. We introduce an automatic spectral classification method in order to obtain temperatures and luminosities for the observed stars. We analysed the stellar populations using their photometric, astrometric, and spectroscopic properties and compared the position of the stars in the Hertzprung-Russell diagram with stellar evolution models to constrain their ages and mass ranges. Results. We confirm the presence of candidate ionising sources in the three regions and report new ones, including the first spectroscopically identified O stars in G333.6-0.2. In M8 and NGC 6357, two populations are identified: (i) OB main-sequence stars (M > 5 M ) and (ii) pre-main sequence stars (M ≈ 0.5 − 5 M ). The ages of the clusters are ∼1-3 Myr, < 3 Myr, and ∼0.5-3 Myr for M8, G333.6-0.2, and NGC 6357, respectively. We show that MYStIX selected targets have > 90% probability of being members of the H ii region, whereas a selection based on near infrared (NIR) colours leads to a membership probability of only ∼70%. Arias et al. (2007) performed intermediate resolution spectroscopy of PMS stars in M8. They identified 27 classical T Tauri stars, seven weak-lined T Tauri stars and three PMS emission objects with spectral type G. They identified the stars to be younger than 3 Myr and between 0.8 and 2.5 M . Prisinzano et al. (2007, 2019) identified 237 PMS stars as members including 53 binaries. Kumar & Anandarao (2010) identified 64 class 0/I and 168 class II objects using Spitzer near-infrared photometry. Article number, page 2 of 39 M.C. Ramírez-Tannus et al.: The young stellar content of M8, G333.6-0.2, and NGC 6357.
We present GalevNB (Galev for N-body simulations), an utility that converts fundamental stellar properties of N-body simulations into observational properties using the GALEV (GAlaxy EVolutionary synthesis models) package, and thus allowing direct comparisons between observations and N-body simulations. It works by converting fundamental stellar properties, such as stellar mass, temperature, luminosity and metallicity into observational magnitudes for a variety of filters of mainstream instruments/telescopes, such as HST, ESO, SDSS, 2MASS, etc.), and into spectra that spans from far-UV (90 Å) to near-IR (160 µm). As an application, we use GalevNB to investigate the secular evolution of spectral energy distribution (SED) and color-magnitude diagram (CMD) of a simulated star cluster over a few hundred million years. With the results given by GalevNB we discover an UV-excess in the SED of the cluster over the whole simulation time. We also identify four candidates that contribute to the FUV peak, core helium burning stars, thermal pulsing asymptotic giant branch (TPAGB) stars, white dwarfs and naked helium stars.
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