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Open Clusters and Galactic Disk Observations with LAMOST

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

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Open Clusters and Galactic Disk Observations with LAMOST

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

  2. LAMOST_LEGUE -- LAMOST Experiment for Galactic Understanding and Exploration Survey Strategy (five years) Three subsets: • Spheroid (|b|>20°) portion will survey at least 2.5 million objects at R=2000, with 90 minute exposures, during dark/grey time, reaching g0=20 with S/N=10. • 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 g0=16 with S/N=20

  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. The importance of open clusters Main characteristics of Galactic OC system： • spatial distribution (Dgc ~ 20 kpc)；reliable distance  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，…

  5. LOCS: What will be the output? • ~300 OCs surveyed, each FOV ~ 1d×1d • RV 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. LAMOST Open Cluster Dominated Disk Survey Galactic disk survey strategy: Balance: scientific goals vs. observation efficiency ”OC dominated survey” – most surveying regions including OCs • 300 OCs (spectroscopic database) to probe disk properties; • a nearly continuous，representative sample of the disk stars

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

  9. Observation efficiency II – conditions (site, weather,……) • 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

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

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

  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: ~ 4×106 Average Nr./plate: ~ 4×104 Average density：~ 2000/deg2

  13. Feasibility analysis III– time budget • Observation --conditions: • telescopeobservable region : within 1.5 hours to upper transit; • disk ( |b| <= 10 deg.) observable (δ> -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/d2 one plate ~ 20 d2 ×2500 ~ 5×104 stars •  need 3400 fibres(“3S” result)×15 exp 3 obs.-nights • 100 plates ~ 300 obs.-nights  6-7yrs

  15. A sample plate field Yellow circle: rad=2.5deg, 9 OCs covered L=205d, B=-1.2d Density~ 2600/d2 NGC 2254 Collinder 111 Collinder 106 Collinder 104 Collinder 107 NGC 2236 Collinder 97 NGC 2252 NGC 2244

  16. A “diluted” sampling: maglim~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

  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 ?…… Trivial ! Fibre aperture= 3 arcsec 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 5”

  19. Discussion II – comparison • OC dominated survey: ~ 100 plates ~ 300nights • ~ 2000d2 (|b|<10), 4×106 stars thin (outer) disk survey, incl.300OCs  ~ 6 yrs to complete the survey • Comparison: • SDSS-III, ~ 6 yrs: • SEGUE-2, (|b|> 20)thick disk, 3.5×105 spectra • APOGEE, HR, emphasis on inner disk, 105 spectra • GAIA, 2018 • matching GAIA & LOCS 106star [Fe/H] in GAIA catalog Complementary

  20. Thanks !

  21. The LOCS sample: ~300 OCs Wikimedia

  22. Model star count /d2（AQ4 1999） Averagenumber density: for 0< |b| <10, 14< Vmag <16 model estimation ~ 4300/d2 (upper limit) Observationally ~ 2500/d2

  23. CMD of OCs

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