Timothy C. Beers National Optical Astronomy Observatory

1. The AEGIS Survey (and more …) Timothy C. Beers National Optical Astronomy Observatory SDSS

2. The AAOmegaEvolution of Galactic Structure (AEGIS) program aims: • Constrain the chemodynamical evolution of the Milky Way through the study of the halo and the outer thick disk • Determine the metal content, kinematics, and chemical abundance ratios for 70,000 stars over 4,900 deg2 using the AAOmegamulti-object spectrograph on the 3.9m Australian Astronomical Telescope • Has been underway at the AAT for the past ~2.5 years, completed its intended acquisition of stars, targeted from SkyMapper • Determination of stellar atmospheric parameters (Teff, logg, [Fe/H]), as well as [C/Fe] and [α/Fe], and accurate radial velocities, making use of a modified version of the SEGUE Stellar Parameter Pipeline (a-SSPP) AEGIS

3. Targeted Fields Target fields circa 1 year ago, about 60,000 stars / now have ~ 70,000

4. AEGIS – Typical Spectra

5. AEGIS – Typical Spectra

6. AEGIS – Comparison with SkyMapper Estimate of [Fe/H]

7. AEGIS – Distribution of Radial Velocities

8. AEGIS – Distribution of log g vs. Teff

9. AEGIS – Distribution of [Fe/H]

10. AEGIS – Distribution of V_GSR vs. [Fe/H]

11. AEGIS – Distribution of [C/Fe] vs. [Fe/H]

12. Complete visual inspection of AEGIS spectra, kicking out problematic parameter estimates, optimize metallicities • Proper motions from UCAC4, SPM 4, PPMXL have been gathered (about 80-90% of stars) • Combine PMs, RVs, and distance estimates in order to obtain full space motions • Examination of full space motions, in combination with chemistry ([Fe/H], [C/Fe], [/Fe]) in order to deduce properties of the various Galactic components • High-resolution follow-up of most interesting EMP and CEMP stars AEGIS -- The Path Forward

13. New CEMP + VMP Star Survey Summary • Placco, Beers, Kennedy et al. have been using “bad weather” time on the Gemini N and S telescopes to search for NEW examples of CEMP and VMP stars chosen from the HK and HES candidates • Numerous examples of new CEMP stars found by targeting on the G-band strength of scanned HES stars • By taking advantage of the apparently strong correlation between large C over-abundances and declining [Fe/H], rather than on the weakness • of the CaIIK line for metal weakness, and obtaining C information later • from medium-res spectroscopic follow-up • Numerous examples of new VMP stars found by targeting on previously unobserved HK and HES candidates • CEMP survey recently completed (~ 900 spectra / ~300 new CEMP stars) • VMP survey just getting underway • High-resolution work (AAT, Magellan, VLT/X-Shooter) – Just Starting

19. [C/Fe] vs. [Fe/H] (Medium-Res Results)

20. Expansion of numbers of identified CEMP stars, in particular with [Fe/H] < —2.5, which include both CEMP-s and CEMP-no stars, both from HK/HES and the ~ 5-10 million medium-res spectra coming from LAMOST • High-resolution follow-up spectroscopy of a core sample of 100-200 CEMP stars, in order to assign classifications based on heavy elements, and to determine CNO, alpha elements, and other light element abundances, in particular Be and Li • Radial velocity monitoring of CEMP stars, in order to determine binary nature, as well as characterize correlations between chemical patterns and nature of the detected binary -- already begun (Hansen et al., 2013, and in preparation) CEMP Stars -- The Path Forward

21. A Chemical Signature of First-Generation Very-Massive Stars W. Aoki, N. Tominaga, T. C. Beers, S. Honda, Y. S. Lee Abstract: Numerical simulations of structure formation in the early Universe predict the formation of some fraction of stars with masses several hundred times the solar mass. No clear evidence of supernovae from such super-massive stars has, however, yet been found in the chemical compositions of Milky Way stars. Here we report on an analysis of a very metal-poor star, SDSS J001820.5−093939.2, which possesses elemental-abundance ratios that differ significantly from any previously known star. This star exhibits low [α-element/Fe] ratios and large contrasts between the abundances of odd and even element pairs, such as Sc/Ti and Co/Ni. Such features have been predicted by model calculations of the nucleosynthesis associated with a pair-instability supernova of a 130-260 solar-mass star, or a core-collapse supernova of an even more massive star. The result suggests that the mass distribution of first-generation stars might extend to 100 solar masses or larger. Aoki et al. (Science, in press)

22. SDSS J0018-0939 is a cool (Teff ~ 4600) main-sequence star with [Fe/H] = -2.5, NOT carbon-enhanced, and with elemental-abundance ratios unlike any previously studied very low-metallicity star. Abundance ratios between adjacent odd- and even-element pairs are very low: [Na/Mg] = -0.56, [Sc/Ti] < -0.99, [Co/Ni] = -0.77. In addition, the n-capture elements are quite low compared to other VMP stars: [Sr/Fe] < -1.8, [Ba/Fe] < -1.3. Frequency (~ 1/500) similar to frequency of high-mass progenitors predicted by Karlsson et al. (2008) Abundance Patterns Like No Other

23.  Core-collapse SN, M = 25 Mo • Type Ia SN + core-collapse SN, • M = 25 Mo • PISN, M = 130 Mo (black) • Super-massive star, • M = 1000 Mo (purple) Alternative Supernova Models

25. Establishment of the frequency of such objects as SDSS J0018-0939, based on high-resolution spectroscopic surveys of the many thousands of stars known with [Fe/H] < -2.5 • Refinement of model-based SN abundance patterns for PISN and very-massive stars • Full numerical GCE models, taking into account the effects of local mixing, in order to match frequencies of CEMP stars and C-normal stars, as well as Li-depletion phenomenon for very metal-poor stars VMS Progenitors -- The Path Forward