1. Open Clusters and Galactic Disk Observations with LAMOST Li CHEN Shanghai Astronomical Observatory, CAS CHEMISTRY, DYNAMICS AND STRUCTURE OF THE MILKY WAY 19-23 July, 2010 KIAA, Beijing

2. Three subsets: (1)Spheroid (|b|>20°) portion will survey at least 2.5 million objects at R=2000, with 90 minute exposures, during dark/grey time, reaching g 0 =20 with S/N=10. (2)Anticenter (|b|<30°, 150°<l<210°) portion will survey about 3 million objects at R=2000 with 40 minute exposures, during bright time (and some dark/grey time), reaching J=15.8 with S/N=20. (3) Disk (|b|<20°, 20°<l<230°) and will survey about 3 million objects at R=2000 and R=5000, with 10 and 30 minute exposures, respectively, during bright time, reaching g 0 =16 with S/N=20 Survey Strategy (five years) LAMOST_LEGUE -- LAMOST Experiment for Galactic Understanding and Exploration

3. 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 HII & Young Open Clusters regions Stellar Candidates with Special Astrophysical Interests

4. spatial distribution (Dgc ~ 20 kpc) ； reliable distance  tracer of disk structure wide range of age (10 6 － 10 9 yr) & mass  evolution effects ； IMF ， … [M/H]: -0.8 ~ +0.7, coeval, more reliable  chemical evolution of disk ， AMR ， … The importance of open clusters Main characteristics of Galactic OC system ：

5. LOCS: What will be the output? ~300 OCs surveyed, each FOV ~ 1d×1d R V and [Fe/H], homogeneous dataset V ~ 16 limit Scientific goals: With OCs dynamical & chemical information (large, homogeneous dataset)  Structure & evolution of the Galactic disk

6. LAMOST Open Cluster Dominated Disk Survey

7. ”OC dominated survey” – most surveying regions including OCs Galactic disk survey strategy: Balance: scientific goals vs. observation efficiency LAMOST Open Cluster Dominated Disk Survey  300 OCs (spectroscopic database) to probe disk properties;  a nearly continuous ， representative sample of the disk stars

8. Premise: V lim ~16; bright nights obs. 30 min exp.  suitable S/N ~30 R V ~ 5-10 km/s [Fe/H] ~ 0.3 dex R=2k -- SEGUE claimed precisions Observation efficiency I - instrument

9. Telescope observable region : 1.5 hours to upper transit; Disk crossing meridian – continuously  applicable obs.time/night ~ 5 hours (estimating) δ> -10 deg.  disk unobservable : the April (whole month) and for June,July,August : rarely applicable (bad weather)  most obs.-nights distributed in the other 7-8 months Observation efficiency II – conditions (site, weather,……)

10. Feasibility analysis I - survey sample Disk: suitable region ~ 300OCs Disk: observable region ~ 400 OCs

11. Feasibility analysis I – survey sample (cont.) 100 plates, covering ~ 300 OCs M67

12. Feasibility analysis II – input catalog UCAC : US NAVAL OBSERVATORY CCD ASTROGRAPH CATALOG 2MASS ： J,H,Ks photometric information Sky coverage: whole sky Completeness: R (579-642 nm) ~8-16mag, final ver. (UCAC3) ~ 99% Position accuracy: 15-70 mas Proper motion accuracy: ~7 mas/yr for R~16 mag Total of 100 plates Total Nr. of stars: ~ 4×10 6 Average Nr./plate: ~ 4×10 4 Average density ： ~ 2000/deg 2

13. Feasibility analysis III – time budget Observation --conditions: telescope observable region : within 1.5 hours to upper transit; disk ( |b| -10 deg.) observation BJ time: 19:00—5:00 ；  in each obs.night, average disk observable time ~ 6.3 hours(>5hrs)  each obs.~ 1 hr. (0.5expo + 0.5trans)  ~ 5 exposures/obs.-night begin_t: disk begin upper transit end_t: disk end upper transit obs_t: disk observable period

14. Feasibility analysis IV – time budget (cont.) Observable nights for LAMOST ： ~200 day/yr (weather) 1200day － 20day(April)=180day 1/4 assigned to disk survey (bright nights)  45 nights/yr density ~ 2500 stars/d 2  one plate ~ 20 d 2 ×2500 ~ 5×10 4 stars  need 3400 fibres(“3S” result)×15 exp  3 obs.-nights  100 plates ~ 300 obs.-nights  6-7 yrs

15. A sample plate field NGC 2236 Collinder 97 NGC 2252 NGC 2244 NGC 2254 Collinder 111 Collinder 106 Collinder 104 Collinder 107 Yellow circle: rad=2.5deg, 9 OCs covered L=205d, B=-1.2d Density~ 2600/d 2

16. mag lim ~18 Ngc2309: (L,B)=(219.84, -2.25), d=2.5kpc, age=0.25Gyr NGC2323 (L,B)=(221.84, -1.33), d=0.8kpc, age=0.13Gyr A “diluted” sampling:

17. Sampling Priorities: OC members (if available); special targets; randomly distributed in coord./mag./color ranges need more considerations; based on Xuyi disk obs. photometry ?

18. Crowding effect to a fibre ?…… Ngc2309: (L,B)=(219.84, -2.25), d=2.5kpc, age=0.25Gyr R lim =18mag Number of stars within 3” circle Trivial ! NGC2323 (L,B)=(221.84, -1.33), d=0.8kpc, age=0.13Gyr Credit: LIU Cao mag lim ~18 Fibre aperture= 3 arcsec 5”

19. OC dominated survey: ~ 100 plates ~ 300 nights  ~ 2000d 2 (|b|<10), 4×10 6 stars thin (outer) disk survey, incl. 300OCs  ~ 6 yrs to complete the survey Comparison: SDSS-III, ~ 6 yrs: SEGUE-2, (|b|> 20) thick disk, 3.5×10 5 spectra APOGEE, HR, emphasis on inner disk, 10 5 spectra GAIA, 2018 matching GAIA & LOCS  10 6 star [Fe/H] in GAIA catalog Complementary Discussion II – comparison

20. Thanks !

21. The LOCS sample: ~300 OCs Wikimedia

22. Model star count /d 2 （ AQ4 1999 ） Vb = 0b = 5b = 10b = 20b = 30b = 60 1256 55463517 131881851651228640 1451049441428119084 1512731216966603389161 163050288021401227750287 SUM4833459035202111750287 Average number density: for 0< |b| <10, 14< V mag <16 model estimation ~ 4300/d 2 (upper limit) Observationally ~ 2500/d 2

23. CMD of OCs