New results on HE and future surveys for metal-poor stars

Transcription

1 New results on HE and future surveys for metal-poor stars Norbert Christlieb Department of Astronomy and Space Physics, Uppsala University

2 HE [Fe I/H] NLTE = 5.3 The most heavy-element deficient stars known HE [Fe I/H] NLTE = 5.4 Frebel et al. (2005), Nature 434, 871 Frebel et al. (2006), ApJ 638, L17 Aoki et al. (2006), ApJ 639, 897 Christlieb et al. (2002), Nature 419, 904 Christlieb et al. (2004), ApJ 603, 708 Bessell et al. (2004), ApJ 612, L61 First Stars/Seatlle/July 06 2

3 Basic facts of HE and HE HE HE T eff 5100 K 6180 K log g 2.2 dex 3.7 or 4.5 dex [Fe I/H] NLTE 5.3 dex 5.4 dex µ? arcsec/yr B mag mag E(B V) mag mag (B V) mag 0.40 mag (V K) mag 1.32 mag First Stars/Seatlle/July 06 3

4 The data Service Mode observations with VLT UT2/UVES in dichroic mode Settings: B346 ( Å) R=40,000 20h S/N= 3100Å B437 ( Å) R=40,000 6h 4200Å R580 ( Å) R=60,000 13h 5170Å R860 ( Å) R=60,000 13h 8498Å Publications: Bessell, Christlieb & Gustafsson (2004), ApJL 612, L61 (oxygen abundance) Bessell & Christlieb (2005), in Proceedings of IAU Symposium 228 Christlieb, Bessell & Eriksson (2006), in preparation (UV spectrum) Korn et al. (2006), in preparation (re-determination of stellar parameters) Christlieb & Bessell (2006), in preparation (analysis of blue and red spectra) First Stars/Seatlle/July 06 4

5 12 C/ 13 C 12 C/ 13 C 60? This is consistent with previous result of Christlieb et al. (2004), i.e., 12 C/ 13 C > 50.?? First Stars/Seatlle/July 06 5

6 Nitrogen abundance from NH [N/Fe( 5.3)]=+1.5, +2.2, Best fit: 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) First Stars/Seatlle/July 06 6

7 Sc II Å First Stars/Seatlle/July 06 7

8 Sc II Å First Stars/Seatlle/July 06 8

9 Sr II 4077 [Sr/Fe( 5.3)]= 0.8 [Sr/Fe( 5.3)]= 0.6 Previous result was [Sr/Fe( 5.3)] < 0.5 (Christlieb et al. 2004, ApJ 603, 708) First Stars/Seatlle/July 06 9

10 Ba II 4554 [Ba/Fe( 5.3)]=+0.3 [Ba/Fe( 5.3)]=+0.5 Previous result was [Ba/Fe( 5.3)] < +0.8 (Christlieb et al. 2004, ApJ 603, 708) First Stars/Seatlle/July 06 10

11 Iron

12 Summary of previous results 25 lines of Fe I detected, yielding [Fe/H] LTE = 5.4 (Christlieb et al. 2002, 2004). NLTE correction of Fe I is +0.1 dex, according to calculations of A. Korn No lines of Fe II detected; upper limit derived from Fe II Å was [Fe II/H] < 4.5 (Christlieb et al. 2004) First Stars/Seatlle/July 06 12

13 Detection of Fe II Å First Stars/Seatlle/July 06 13

14 Detection of Fe II Å Continuum is a bit low here, hence we adopt result of equivalent width-based analysis, i.e., log ε = 1.7±0.2 [Fe II/H] = 5.7±0.2 First Stars/Seatlle/July 06 14

15 Fe II Å detected? First Stars/Seatlle/July 06 15

16 Fe II 3255 [Fe/H]= 5.2 [Fe/H]= 5.0 First Stars/Seatlle/July 06 16

17 Fe II 3277 [Fe/H]= 5.2 [Fe/H]= 5.0 First Stars/Seatlle/July 06 17

18 3D corrections for HE Species 3D Collet et al. (2005, Proceedings of IAU Symposium 228). CH 1.09 NH OH Mg I Sc II 0.13 Fe I 0.23 Fe II Co I Ni I Collet et al. (2006, ApJ 644, L121) First Stars/Seatlle/July 06 18

19 Selected abundances of HE D 3D σ [C/Fe] C/ 13 C [N/Fe] [O/Fe] [Mg/Fe] [Sc/Fe] [FeI/H] LTE [FeII/H] [Co/Fe] [Ni/Fe] Remarks: Solar abundances are from Asplund, Grevesse & Sauval (2005) 3D corrections from Collet, Asplund & Trampedach (2006, ApJ 644, L121) Adopted [Fe/H] is 5.7. This value has been used when computing [X/Fe]. Note the good agreement between Fe I and Fe II abundances, which constraints the maximum possible NLTE effect of Fe I (assuming log g derived from isochrone is correct). First Stars/Seatlle/July 06 19

20 Scenarios for the origin of the abundance patterns First Stars/Seatlle/July 06 20

21 The abundance pattern of HE Umeda & Nomoto (2004, priv. comm.) First Stars/Seatlle/July 06 21

22 Sc in other metal-poor stars Cayrel et al. (2004) HE : [Sc/Fe] 1D = +0.2 First Stars/Seatlle/July 06 22

23 Co in other metal-poor stars Cayrel et al. (2004) HE : [Co/Fe] 1D = +0.7 First Stars/Seatlle/July 06 23

24 Scenarios for the origin of the abundance patterns First Stars/Seatlle/July 06 24

25 Radial velocity monitoring HE CD Data analysis done by Ulfert Wiesendahl (Hamburg) First Stars/Seatlle/July 06 25

26 Radial velocity monitoring P = 25 yrs v orb = 7 km/s i = 90 Thereisperhaps an indication that v rad 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 v rad monitoring needed. First Stars/Seatlle/July 06 26

27 Future surveys for metal-poor stars

28 Siding Spring Hamburg Survey (SSHS) Slitless spectroscopy survey using the Siding Spring 1m telescope and its wide-field imager Will focus on sky areas not covered by the HK and HE surveys λ 10Å, survey limit perhaps B = 18mag, sky coverage a few hundred square degrees First Stars/Seatlle/July 06 28

29 LAMOST A stellar survey will be conducted with the Chinese Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) 4m survey telescope; located at Xinglong Station (about 100km northeast of Beijing) First Light with a few mirror segments planned for spring 2007; fully operational in 2008 Simultanious observation of 4000 objects in 5 x 5 16 fiber-fed two-arm spectrographs will allow to obtain R= 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 in a few hours P.I.s of stellar survey: G. Zhao & N.C. First Stars/Seatlle/July 06 29

30 First Stars/Seatlle/July 06 30

31 LAMOST optical design Fixed Spherical Mirror Focal Plane Corrector Mirror Fiber Optics Spectrographs First Stars/Seatlle/July 06 31

32 The LAMOST survey for metal-poor stars LAMOST First Stars/Seatlle/July 06 32

33 SkyMapper Fully automated 1.35m telescope currently being built at Siding Spring Observatory. Camera will have 32 CCDs of 4k x 2k each, 0.5" pixels. Sky coverage in single shot will hence be 5.7 deg 2. First light planned for early Will conduct a multi-colour (ugriz + Strömgren-like v), multi-epoch survey of the southern hemisphere known as the Stromlo Southern Sky Survey (SSSS). Will provide accurate, uniformally standardized photometry between 8 and 22 mag for the whole of the southern hemisphere. Web page: First Stars/Seatlle/July 06 33

34 Synthetic photometry SkyMapper Filter Set Ex-atmosphere Sky Mapper SDSS Research School of Astronomy & Astrophysics Slide 34

35 Synthetic photometry Metal-poor Stars in the SSSS Change of flux when changing [Fe/H] from 0.0 to 1.0. flux u vs wavelength F G K Stefan Keller, Mike Bessell, et al. F stars: vs filter captures Ca H+K G+K stars: u + vs capture magnitude of metal line blanketing Search for very metal poor stars in the halo and thick disk Research School of Astronomy & Astrophysics Slide 35

36 Synthetic photometry Expected survey limits u vs g r i z 1 epoch expt. time epochs Sloan Digital Sky Survey comparison 22.0 n/a Research School of Astronomy & Astrophysics Slide 36

37 Approximate numbers of EMP and HMP stars to be found Survey Effective sky coverage Effective mag limit HES 6400 deg 2 B < N < 3.0 N < 5.0 SEGUE 1000 deg 2 B < SSHS 500 deg 2 B < 17 LAMOST 10,000 deg 2 B < 19 SSSS 20,000 deg 2 B < , Number of stars to be found in SEGUE will mainly be limited by number of fibers allocated for follow-up. Only about 10% of all candidates down to B = 19 can be observed. SSHS and SSSS follow-up will be done with SSO 2.3m, hence faint stars can not be observed (now). First Stars/Seatlle/July 06 37

38 Summary/conclusions A new, more robust estimate of the iron abundance of HE , based on Fe II lines, yields [Fe/H] 3D = 5.7. Weak odd-even effect is seen, as in other metal-poor stars (see e.g. Cayrel et al. sample). There are possible indications that the radial velocity of HE is changing; however, this is not yet significant. Further monitoring is in progress with the VLT. Upcoming deeper surveys for metal-poor stars: Siding-Spring Hamburg Survey (SSHS) LAMOST Stromlo Southern Sky Survey (SSSS) It is expected that in these surveys significant numbers of new stars with [Fe/H] < 5.0 will be found in the next few years. First Stars/Seatlle/July 06 38

39 Acknowledgements Analysis of HE done in collaboration with Mike Bessell (ANU) and Kjell Eriksson (Uppsala). Financial support: Df JINA, INT Wallenberg Foundation via Royal Swedish Academy of Sciences Deutsche Forschungsgemeinschaft Picturs of probes of elements: Thomas Seilnacht, SkyMapper transparencies kindly provided by M. Bessell First Stars/Seatlle/July 06 39