Twelve years of spectroscopic monitoring in the galactic center: The closest look at S-stars near the black hole
مریم حبیبی (Max Planck institute for extraterrestrial physics in Garching/Munich)
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Abstract: We study the young S-stars within a distance of 0.04 pc from the supermassive black hole in the center of our Galaxy. Given how inhospitable the region is for star formation, their presence is more puzzling the younger we estimate their ages. In this study, we analyse the result of 12 years (2004- 2016) of high resolution spectroscopy within the central arc-second of the Galactic Center (GC). By co-adding between 55 and 105 hours of spectra we have obtained high signal to noise (S/N ∼ ۵۰-۴۰۰) H- and K-band spectra of eight stars orbiting the central supermassive black hole. Using deep H-band spectra, we show that these stars must be high surface gravity (dwarf) stars. We compare these deep spectra to detailed model atmospheres to infer the stellar parameters. All the available observables from spectroscopy and photometry are then compared to stellar evolution models to constrain the final stellar parameters of the stars including their evolutionary stages and masses. Our analysis reveals an effective temperature of 21000–۲۸۵۰۰ K, a rotational velocity of 60-170 km/s, and a surface gravity of 4.1–۴٫۲٫ These parameters imply a spectral type of B0-B3V for these stars. The inferred masses lie within 8–۱۴M . We derive an age of 6.6 +3.4 −۴٫۷ Myr for the star S2, which is compatible with the age of the clockwise rotating young stellar disk in the GC. We estimate the age of all other studied S-stars to be less than 15 Myr, which are compatible with the age of S2 within the uncertainties. The relatively low ages for all S-stars we have investigated favor a scenario in which the stars formed in a local disk rather than the field-binary-disruption scenario throughout a longer period of time.
یکشنبه ۲۵ تیر ماه ۱۳۹۶، ساعت ۱۰:۰۰
دانشکده فیزیک، طبقه اول، کلاس فیزیک ۳