1 / 34

Timothy C. Beers National Optical Astronomy Observatory

Carbon-Enhanced Metal-Poor (CEMP) stars: probes of nucleosynthesis from the first generation of stars in the Universe. Timothy C. Beers National Optical Astronomy Observatory. SDSS. First-generation objects of high mass presumably formed from metal-free gas Lived short lives (Myrs)

pablor
Download Presentation

Timothy C. Beers National Optical Astronomy Observatory

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Carbon-Enhanced Metal-Poor (CEMP) stars: probes ofnucleosynthesis from the first generation of stars in the Universe Timothy C. Beers National Optical Astronomy Observatory SDSS

  2. First-generation objects of high mass presumably formed from metal-free gas • Lived short lives (Myrs) • Exploded • Distributed (pre or post explosion) their nucleosynthetic products • Next-generation objects formed from the gas polluted by first-generation objects • A wider range of masses allowed, perhaps including stars with main-sequence lifetimes > a Hubble time • Further star formation (Pop II) contributed additional material, and diluted the signatures of first/next-generation stars • We should look for a characteristic set of abundance signatures ONLY foundamong the lowest metallicity stars • Although alternatives have been suggested (e.g., “sawtooth pattern”), the odd-even effect associated with explosions of pair-instability SNe, I would like to advocate for CARBON and other light elements Expected Signatures

  3. HK Survey (Beers, Preston, & Shectman 1992) • Note that original selection criteria was carbon blind • Only based on perceived weaknessof CaII H and K lines on objective prism spectra The Discovery of Carbon-Enhanced Metal-Poor (CEMP) Stars

  4. Just How Common are These CEMP Stars ? • The HK Surveyof Beers and colleagues revealed that MANY low-[Fe/H] stars exhibit a large overabundance of carbon relative to iron (10s of CEMP stars) • This realization has inspired further searches for CEMP stars, both in the HK survey and the (then) newer Hamburg/ESO prism survey (100s of CEMP stars) • And by SDSS/SEGUE-1/SEGUE-2(1000s of CEMP stars)

  5. Carbon-Enhanced Metal-Poor (CEMP) stars have been recognized to be an important stellar component of the halo system • CEMP stars frequencies are: • 20% for [Fe/H] < —2.5 • 30% for [Fe/H] < —3.0 EMP • 40% for [Fe/H] < —3.5 • 75% for [Fe/H] < —4.0 UMP • But Why ? – Atmospheric/Progenitor or Population Driven ? • Carollo et al. (2012) suggest the latter Frequencies of CEMP Stars Based on Stellar Populations

  6. Exploration of Nature’s Laboratory for Neutron-Capture Processes Beers & Christlieb ARAA (2005)

  7. Aoki et al. (2007) • demonstrated that • the CEMP-no stars • occur preferentially • at lower [Fe/H] than • the CEMP-s stars • About 80% of CEMP • stars are CEMP-s • or CEMP-r/s, 20% are • CEMP-no • Global abundance • patterns of CEMP-no • stars incompatible • with AGB models • at low [Fe/H] The UMP/HMP Stars are (Almost) ALL CEMP-no Stars

  8. Carbon Enhancement Associated with s-process Patterns (Aoki et al. 2002) LP 625-44: [Fe/H] = -2.7; [C/Fe] = +2.0 LP 625-44 was the first s-process-rich MP star with Pb measured

  9. CS 22892-052: [Fe/H] = -3.1; [C/Fe] = +1.0 Carbon Enhancement Associated with r-process Patterns (CS 22892-052; McWilliam et al. 1995; Sneden et al. 2000) CS 22892-052 was the first highly r-process-rich MP star discovered

  10. CEMP-no Stars are Associated with UNIQUE Light-Element Abundance Patterns (Aoki et al. 2002) CS 29498-043: [Fe/H] = -3.8; [C/Fe] = +1.9 Harbingers of Things to Come!

  11. HE 0107-5240 [Fe/H] = -5.3 [C/Fe] = +3.9 Last but Definitely Least… (Christlieb et al. 2002; Frebel et al. 2005) It is the SAME pattern among the light elements !

  12. Ito et al. (2009) report on discovery that BD+44 is an [Fe/H] = —3.8, CEMP-no star • Light-element abundance patterns similar to those for other CEMP-no stars • Previous RV monitoring by Carney et al. indicate no variation at levels > 0.5 km/s over past 25 years • More detailed observations by Ito et al. (2013) BD+44:493 – A 9th Magnitude Messenger from the Early Universe

  13. Something You Don’t Often See An Object of COSMOLOGICAL Significance with Diffraction Spikes

  14. Abundance Pattern Compared to 25 Mo Mixing/Fallback Model Ito et al. (2013) : Note the low N, compared with some other CEMP-no stars with enhanced N

  15. Carney et al. (1986) + Ito et al. (2012) Radial Velocity Monitoring The rms variation over 25 years is 0.73 km/s !

  16. Follow-on of work from D. Carollo et al. (2007), demonstrating existence of inner/outer halo populations,based on 32,360 unique calibration stars from SDSS • Determination of velocity ellipsoids for thick disk, MWTD, inner, outer halos • Modeling of fractions of various components in local sample (d < 4 kpc) Inference of Inner/Outer Halo Structure (Carollo et al. 2010)

  17. Fractions of Components

  18. Velocity Ellipsoids

  19. Global CEMP Fraction and <[C/Fe]> vs [Fe/H](Carollo et al. 2012) analysis of SDSS/SEGUE Cal Stars Global variation shows smooth increase of f (CEMP) vs. [Fe/H] Clear increase of <[C/Fe]> vs. [Fe/H]

  20. Global CEMP Fraction vs. |Z| Clear increase of f (CEMP) with |Z| (not expected for single halo)

  21. Inner/Outer Halo CEMP Fractions f (CEMP)OH ~ 2 x f (CEMP) IH <[C/Fe]> roughly constant IH/OH (Carollo et al. 2012)

  22. The distribution of CEMP stars indicates that there is likely to be more than one source of C production at low metallicity, and that the difference can be associated with assignment to inner/outer halo • Modelers (e.g., Izzard, Pols, Stancliffe) have tried, without success, to reproduce the observed fractions of CEMP stars at low metallicity using AGB sources alone. Getting beyond 10% appears to be a real barrier • We speculate that the majority of CEMP stars associated with the inner halo will be CEMP-s, while those associated with the outer halo will be CEMP-no Interpretation

  23. CEMP stars in the Galaxy likely have had multiple sources of • carbon production • CEMP-s in AGB stars • CEMP-no in massive (50-100 Mo) rapidly rotating MMP stars • CEMP-no in intermediate (25-30 Mo) “faint” SNe • CEMP-no stars occur preferentially at the lowest metallicities, including the 3 of the 4 stars known with [Fe/H] < -4.5 • CEMP stars are found in great number in the ultra-faint SDSS dwarf galaxies, some of which have low n-capture abundances • High-z DLA systems exhibit similar abundance patterns as CEMP-no stars • We have observed (!) the nucleosynthesis products of first generation stars (Pop III) Bottom Line

  24. Fractions of CEMP-no and CEMP-s in the Inner/Outer halo • Carollo et al., in preparation • Sample of 183 stars with high-resolution spectroscopy obtained with Subaru and other sources (Aoki et al. 2013; Norris et al. 2013), including on the order of 50 CEMP stars • High resolution spectroscopy necessary to obtain the Barium signature of s-process

  25. IHP-OHP Memberships using Integrals of Motion Rapo > 15 kpc

  26. IHP-OHP Memberships using Integrals of Motion OHP IHP

  27. New CEMP + VMP Star Survey Summary • Placco, Beers, et al. have been using “bad weather” time on the Gemini N and S telescopes to search for NEW (formerly missed) • 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 CaII K 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 (~ 800 spectra / ~200 new CEMP stars) • VMP survey just getting underway • High-resolution work (AAT, Magellan, VLT/X-Shooter) – Just Starting

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

  29. Expansion of numbers of identified CEMP stars, in particular with [F/eH] < —2.5, which include both CEMP-s and CEMP-no stars • 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 and other light element abundances • 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 • An exciting time indeed ! The Path Forward

More Related