Open Clusters and Galactic Disk Observations with LAMOST

1. KIAA/PKU-IoA Workshop 1-5 Dec, 2008   Beijing, China Open Clusters and Galactic Disk Observations with LAMOST Li CHEN, Jinliang HOU Shanghai Astronomical Observatory, CAS chenli@shao.ac.cn

2. The importance of open clusters Main characteristics of Galactic OC system： • spatial distribution (Dgc ~ 20 kpc)；reliable distance & less radial mixing  tracer of disk structure • wide range of age (106－ 109 yr) & mass  evolution effects；IMF，… • [M/H]: -0.8 ~ +0.7, coeval, more reliable  chemical evolution of disk，AMR，…

3. Updated OC sample:( up to 2007 ) • Number of clusters: 1696 • Clusters with Distances: 1022 (60%) • Clusters with Ages: 993 (59%) • Clusters with Proper motions: 848 (50%) • Clusters with Radial velocities: 385 (23%) • Clusters with P.Motions + RVs: 369 (22%) • Clusters with Abundances: 144 ( 8%) (Ref: Dias 2003; Kharchenko et al. 2005; WEBDA)

4. Age distribution of open clusters

5. OCs results: gradient vs. age Young - 0.024 Older - 0.075 • 10 12 14 16 • Rgc(kpc) Overall: －0.063 dex/kpc Chen et al (2003,2008)

6. Present status & needs for the OCs data • Global disk dynamical/chemical evolution  lack of samples with both [Fe/H] & motion data • Abundance gradient/evolution  need more outer-disk OCs [Fe/H] data

7. Present status & needs for the OCs data (cont.) • Most Open Clusters: only a few stars observed spectroscopically  mean OC [Fe/H] & Vr parameters not very reliable • Many Open Clusters: no kinematic data  lack of reliable membership information • No homogeneous database

8. Some recent Open Cluster survey projects • WOCS(The WIYN Open Cluster Study) 14 “fundamental OCs”, Vlim~25mag, high-precision PM, Vr, [Fe/H] and 5color photometry; • BOCCE(BolognaOpen Cluster Chemical Evolution) photometry+HRS ~30 OCs, age,distance,abundance Mathieu 2000 Bragaglia & Tosi 2006 …… and

9. LOCS– LAMOST Open Cluster Survey

10. LAMOST at present 2008.10.21

11. The mirrors Inside the telescope

12. The 4k fibres

13. LAMOST wide field and large sample astronomy One of major scientific tasks – Stellar Spectroscopic Survey -- mainly for Galactic structure & stellar physics For disk spectroscopic obs., of great interests: 1. A survey for the properties of Galactic open clusters; and the structure, dynamics and evolution of the thin disk as probed by open clusters; 2. The chemical abundance pattern and evolution of the disk;

14. LOCS: Why LAMOST ? -- Within the framework of Stellar Spectroscopic Survey -- == low latitude regions == • LAMOST, 4m Schmidt telescope • Large aperture, • Large FOV~ 20deg2 • 4000 fibers • Spectroscopy Vlim~16; 30 - 40min. obs.  S/N~30 RV~ 5 km/s [Fe/H]~ 0.2 dex • most efficiently: ~ averagely 1 OC/per night • deep enough: V~15-16 to reach most of old OCs within d~5-7kpc

15. LOCS: What will be the output? • 4×102 OCs surveyed, each FOV ~ 1d×1d • RV and [Fe/H], homogeneous dataset • V ~ 15 -16 limit Scientific goals: With OCs dynamical & chemical information (large, homogeneous dataset)  Structure & evolution of the Galactic disk

16. much reliable(kinematic)membership for cluster fields -- fundamental base for cluster studies • Structure/dynamical • Young OCs • spiral structure of the disk / differential rotation; • Very young OCs • best targets for IMF study; • Age-Metallicity-Velocity relation based on OCs • crucial constrainsto modelingevolution of the disk • Chemical evolution • radial abundance gradients/time evolution • more distant OCs with kinematics and metallicity • conclusive results for Galactic chemical evolution ……

17. LOCS: Clusters selection and input catalogue • Observation site: δ> －10d  N ~ 400 OCs • Important targets Dgc ~ 9－16 kpc • Age ~ 0.1 － 3.0 Gyr  154 OCs • Comparing sample：13 “standard” OCs. • Input catalogue for all stars in the cluster regions prepared • Membership determination for candidate clusters

18. Some properties of the selected OC sample: most Glat. <5 d; half with E(B-V)<0.3 extinction ~ 1mag

19. LOCS: • A large and homogenous spectroscopic database for open clusters is necessary for further understanding the disk structure and evolution • LAMOST could be very efficient in spectroscopic OC survey. LOCS project aims to produce a homogeneous Rv & metallicity dataset for about 400 OCs. This dataset would be of great importance for future researches on Galactic structure and evolution -- Within the framework of Stellar Spectroscopic Survey – == low latitude regions == >>>>>>>>>>>>>>>>>>>

20. LOCBaseDS – LAMOST Open Cluster Based Disk Survey Galactic disk survey strategy: 1. ”All field star survey” -- all sky 2. ”OC dominated survey” – selective,“LOCBaseDS” Balance: scientific goals vs. observation efficiency

21. Galactic disk survey scientific goals • Large Sample of Disk Stars with Spectral Classification • Significant Improvements in Obtaining Reliable Essential Parameters of OCs • Probing Spatial and Dynamical Structure of the Galactic Disk with OCs • The Spectroscopic Study of the Galactic Thick Disk Stars • Chemical Evolution of the Galactic Disk • IMF Studies in Young Open Clusters and Association • Stellar Candidates with Special Astrophysical Interests (in OCs)

22. Observation efficiency Premise: Vlim~16; bright nights obs. 30min exp.  suitable S/N RV~ 5 km/s [Fe/H]~ 0.3 dex R=5k/10k ? -- Rv~1 km/s, [Fe/H]~0.1dex R=1k/2k -- SEGUE claimed precisions

23. Model star count /d2（AQ4 1999） Average number density ~ 3700/d2 for 0< |b| <20, 14< Vmag <16 (model estimation) ~ 1600/d2 for 0 < |b| < 20, 13< Vmag <15

24. LAMOST Field Of View =20d2 (“LaFOV”=PLATE) 1. ”All field star survey” LAMOST observable area: Total ~ 104d2 = 500 ×(1+ 10% overlapping) plates Density ~ 3700 stars/d2 • one plate contains ~ 20 d2 ×3700(modelNr.)~ 7.4×104 stars • need 3600 fibres×20 exp×0.5hour  ~ 2 obs-nights perplate ~ 500 plates ×(1+ 10%)×2 =1100nights (4×107 spectra) • Observable nights (spectra) for LAMOST：~200/yr • If 1/3 assigned to Galactic survey ~ 65/yr  totally need >17 yrs • [(2/3)*(8bright/month)*12months] (for Vlim ~15,  7-8 yrs)

25. 2. ”OC dominated survey” – LOCS project Vlim~16; 30 min. obs. RV~ 5 km/s [Fe/H]~ 0.2 dex Aim: probe both OCS in Milky Way & statistical properties of the Disk OCs observable with LAMOST: total N ~ 720 With distance ( > 200pc) information N ~ 400 LOCBaseDS sky area

26. A Subsample of LOCS:122OCs Total of ~37 plates ~74 nights -- about one year of observation  122 OCs & 740d2(~2.7×106 stars)

27. Credits: LIU Cao (NAOC) And the bright nights

28. Crowding effect to a fibre ?…… Trivial ! Fibre aperture= 3arcsec maglim~18 Ngc2309: (L,B)=(219.84, -2.25), d=2.5kpc, age=0.25Gyr Rlim=18mag Number of stars within 3” circle NGC2323 (L,B)=(221.84, -1.33), d=0.8kpc, age=0.13Gyr Credit: LIU Cao

29. LOCBaseDS: ~ 4×37=148 plates ~ 300nights • ~ 3000d2 (|b|<20) ,107 stars thin (outer) disk survey, incl.400OCs  ~ 5 yrs to complete the survey (for Vlim~15,  2.5 yrs) • Comparison: • SDSS-III, ~ 6 yrs: • SEGUE-2, (|b|> 20)thick disk, 3.5×105 spectra • APOGEE, HR, emphasis on inner disk, 105 spectra • GAIA, 2018? • matching GAIA & LOCBaseDS 107 star [Fe/H] in GAIA catalog Complementary

30. LOCBaseDS: • 400 OCs (spectroscopic database) to probe disk properties; • a representative sample of the disk stars： • spectra for 107 stars distributed in this 2-D sky area (Rv & [Fe/H]) Within 5 years ! • And, for ~ 150 first priority OC subsample (statistically significant) • LAMOST may output an important obs. dataset for disk study within 2 yrs

31. Thanks !

32. Take into account the weather condition (distribution), May add ~1/3 extra time to above obs.time estimations. Observable at zenith (+-2h) Local time: 22h-2h (2008)

33. The LOCS sample: ~440 OCs Wikimedia

34. CMD of OCs

35. Fiber positioning for a single OC: one degree diameter Example: Praesepe ( l＝205.9°，b＝32.5°) Stellar field overlapped with “fibre circle” Number histogram, dij< 10mm

36. NGC2323 NGC2309