S316p.97 — GalevNB: a conversion from N-BODY simulations to observations—its application on the study of UV-excess in star clusters

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Aug 10th at 6:00 PM until 7:30 PM




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Author(s): Xiaoying Pang2, Christoph Olczak1, Difeng Guo1, Rainer Spurzem1

Institution(s): 1. National Astronomical Observatories of China, 2. Shanghai Institute of Technology

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. The model cluster in this work is evolved using the most recent version of NBODY6++ utilizing many GPU cores in parallel to accelerate multi-node multi-core simulations (Wang et al. 2015), which is the MPI parallel version based on the state-of-the-art direct N-body integrator NBODY6GPU. With the results given by GalevNB, we discover an UV-excess in the integrated 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. Among them, TAGB is a favorable candidate from theoretical point of view (O’connell 1999). On the contrary, white dwarf’s candidate position is controversial (Magris & Bruzual 1993, Landsman et al. 1998) because of low luminosity. The life time of massive star descendants: core helium burning stars and naked helium stars, is very short. Though both of they are very bright at the UV at the early age, their short-term emission makes them become insignificant candidates.