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HE 0107 5240 and HE 13272326: The most iron-deficient and carbon-rich stars known

HE 0107 5240 and HE 13272326: The most iron-deficient and carbon-rich stars known. Norbert Christlieb Hamburger Sternwarte. From 1 March 2006: Research Fellow @ Royal Swedish Academy of Sciences with duty station Uppsala University. Overview of the talk.

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HE 0107 5240 and HE 13272326: The most iron-deficient and carbon-rich stars known

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  1. HE 01075240 and HE 13272326: The most iron-deficient and carbon-rich stars known Norbert Christlieb Hamburger Sternwarte From 1 March 2006: Research Fellow @ Royal Swedish Academy of Sciences with duty station Uppsala University

  2. Overview of the talk • The most iron-deficient stars known • Basic properties • Some news on HE 01075240 • Overview of models for the origin of the abundance pattern • Outlook on metal-poor star surveys • Conclusions

  3. The most heavy-element deficient stars known HE 01075240 [Fe/H]NLTE = 5.2 HE 13272326 [Fe/H]NLTE = 5.4 Frebel et al. (2005), Nature 434, 871 Aoki et al. (2005), ApJ, in press Christlieb et al. (2002), Nature 419, 904 Christlieb et al. (2004), ApJ 603, 708 Bessell et al. (2004), ApJ 612, L61

  4. Basic facts of HE0107−5240 and HE1327−2326 HE0107−5240 HE1327−2326 Teff 5100 K 6180 K log g 2.2 dex 3.7 or 4.5 dex [Fe/H]NLTE −5.2 dex −5.4 dex  ? 0.0733 arcsec/yr B 15.86 mag 14.016 mag E(B−V) 0.013 mag 0.060–0.096 mag (B−V)0 0.68 mag 0.40 mag (V−K)0 1.90 mag 1.32 mag

  5. Selected abundances (1D) (Aoki et al. 2005) (For an update see Anna‘s talk, which is next) (Aoki et al. 2005) Solar abundances of Asplund et al. (2004) are used throughout this talk.

  6. „New“ data • Service Mode observations OctoberDecember 2002 with VLT UT2/UVES in dichroic mode • Settings:B346 (30553865Å) R=40,000 20h S/N= 30 @ 3100Å B437 (37604975Å) R=40,000 6h S/N=180 @ 4200ÅR580 (47606840Å) R=60,000 13h S/N=200 @ 5170ÅR860 (67208520Å) R=60,000 13h S/N=100 @ 8498Å • Publications:Bessell, Christlieb & Gustafsson (2004), ApJL 612, L61 (oxygen abundance)Bessell & Christlieb (2005), in Proceedings of IAU Symposium 228Bessell & Christlieb (2006), in preparation (UV spectrum)Korn et al. (2006), in preparation (re-determination of stellar parameters)Christlieb & Bessell (2006), in preparation (full re-analysis)

  7. 12C/13C ? ? ?

  8. [N/Fe] = [N/Fe] = [N/Fe] = Nitrogen abundance from NH Previous result were [N/Fe(5.3)]=+2.3 (CN, assuming [C/Fe]=4.0)[N/Fe(5.3)]=+2.6 (CN, assuming [C/Fe]=3.7) (Christlieb et al. 2004, ApJ 603, 708)

  9. Sr II 4077 [Sr/Fe(5.2)]=0.9 [Sr/Fe(5.2)]=0.7 Previous result was [Sr/Fe(5.3)] < 0.5 (Christlieb et al. 2004, ApJ 603, 708)

  10. Ba II 4554 [Ba/Fe(5.2)]=+0.2 [Ba/Fe(5.2)]=+0.4 Previous result was [Ba/Fe(5.3)] < +0.8 (Christlieb et al. 2004, ApJ 603, 708)

  11. Fe II 3255 [Fe/H]=5.2 [Fe/H]=5.0

  12. Fe II 3277 [Fe/H]=5.2 [Fe/H]=5.0

  13. 3D corrections for HE01075240 This is all from Collet et al. (2005, Proceedings of IAU Symposium 228, in press).

  14. Selected abundances

  15. What does all this mean for log g? • In order to correctly reproduce the strengths of Fe II lines with 1D models, we need to employ [Fe II/H] = 5.2  0.4  0.07 = 5.67assuming that • [Fe I/H]NLTE = 5.2 • 1D NLTE effects are the same as 3D NLTE effects • (1D and 3D) NLTE effects of Fe II are neglible. • That is, the Fe II lines are expected to be VERY weak and therefore in practice undetectable in HE 01075240. • Hence the constraints on log g from the Fe I /Fe II ionisation equilibrium are/will be very weak. • For better spectroscopic constraints see talk of Andreas later this morning.

  16. Scenarios for the originof the abundance patterns

  17. Application of 3D corrections Umeda & Nomoto (2004, priv. comm.)

  18. M=25M, Z=0 Mg-rich/poor HMP star Log X 56Fe He O 0 C H 58Ni －1 C Ne －2 Mg Mg O Ti －3 N －4 6 8 HE1327-2326 (Mg-rich) Mr (M) ejecta Mixing-Fallback (HE0107-1240, Mg-poor)

  19. Pre-enrichment by rotating, massive Pop. III stars? M = 60 MSun Meynet et al. (2005, A&A, in press) HE 01075240 (3D abundances)

  20. Scenarios for the originof the abundance patterns

  21. Pollution by a binary companion Suda et al. (2004), ApJ 611, 476: • Former primary had 1.2 to 3 Solar masses • Light element abundances of HE0107−5240 can well be reproduced • 12C/13C = 32 to 120

  22. Radial velocity monitoring HE 01075240 2001 2002 2004 2005 Data analysis done by Ulfert Wiesendahl (Hamburg) CD 38° 245

  23. Radial velocity monitoring 2001 2002 2004 2005 P = 25 yrs vorb = 7 km/s i = 90° • There is perhaps an indication that vrad is changing… But this is not yet significant at all. • Suda et al. (2004): P may be ~150 years, and orbital velocity ~ 7 km/s => further vrad monitoring needed.

  24. Self-enrichment Definitely excluded for HE13272326, because it is on the main-sequence or a subgiant. Detailed calculations for HE01075240 by • Weiss et al. (2004), A&A 422, 217 • Picardi et al. (2004), ApJ 609, 1035 Results: • C/N in HE01075240 much higher (~20, while ~1 predicted) • 12C/13C much higher (~60, while ~5 predicted) • [O/Fe] by at least 1 dex too low • Evolutionary status: HE0107-5240 is most likely on RGB, not AGB

  25. Metallicity distribution function issues • No stars known between −5.0 < [Fe/H] < −4.0 • Two stars with [Fe/H] < −5.0, and similar [Fe/H] • Both stars have similar abundance patterns; in particular, large overabundances of C and N. But there are also differences; e.g. Na, Mg. => Distinct enrichment histories!

  26. Outlookon metal-poor star surveys if (t < 5 min) goto Conclusions else continue

  27. How to find metal-poor stars • Candidate selection, based e.g. on wide-angle spectroscopic survey. HES data base: ~4,000,000 objects at 10 < B < 17.5 mag; ~10,000 candidates selected. • Moderate-resolution follow-up spectroscopy needed for confirmation of candidates. • High-resolution spectroscopy with largest telescopes => abundance analysis.

  28. Outlook: Hamburg/ESO Survey • Follow-up observations obtained for about 70% of the total of ~10,000 candidates. Strategy: • Observations of the best and brightest of the remaining candidates • Completion of observations in a subset of HES fields for statistical studies, such as determination of MDF. • 51 out of 380 HES fields until recently not included in stellar work. Search for metal-poor candidates in these fields is in progress; first follow-up was done in Oktober 2005. • High-resolution spectroscopy of the most interesting confirmed metal-poor stars will continue during the next few years.

  29. Identification of [Fe/H] < −5.0 stars From the discoveries of HE01075240 and HE13272326 we learned that [Fe/H] can be strongly overestimated in follow-up spectra, because: • Contamination of Ca K with CH (see HE0107−5240...) • Contamination of Ca K with interstellar absorption (see HE1327−2326...) • Overabundance of -element Ca higher than assumed in calibration of Ca K index (i.e., [Ca/Fe] > 0.5) Solution: Snapshot spectroscopy of all stars @ [Fe/H] <3.5

  30. Outlook: New surveys/Part I • Siding Spring Hamburg Survey (SSHS) • Slitless spectroscopy survey using the Siding Spring 1m telescope and a wide-field imager • Will focus on sky areas not covered by the HK and HE surveys • „Stellar extension“ of the Sloan Digital Sky Survey (SEGUE) • Imaging: SDSS + 3000 deg2 at low |b| and other directions • Spectroscopy: 250,000 stars; 14 mag < g < 20.3 mag • Stellar survey with the Chinese LAMOST telescope • 4m survey telescope; First Light planned for 2007 • Simultanious observation of 4000 objects in 5° x 5° • 16 fiber-fed two-arm spectrographs will allow to obtain R=1000−3000 spectra; i.e., quality corresponds to what has previously been used in follow-up observations • Performance aim: S/N = 10 for a V = 20 mag star at the highest resolution in a few hours

  31. www.lamost.org

  32. Fixed Spherical Mirror Corrector Mirror Focal Plane Fiber Optics Spectrographs LAMOST optical design

  33. The LAMOST survey for metal-poor stars LAMOST

  34. Conclusions • Metal-poor stars provide important constraints e.g. on the properties of the first generation of stars and SN, nucleosynthesis processes, and stellar evolution at low [Fe/H]. • 3D/NLTE needed to get abundances right! • So far, only two stars with [Fe/H] <−5.0 are known: HE0107−5240 and HE1327−2326. Both were found in the Hamburg/ESO survey. It can not yet be decided whether this are first or second generation stars. • New survey efforts are underway for identifying more stars with [Fe/H] < −5.0 and other interesting metal-poor stars.

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