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

spatial distribution (Dgc ~ 20 kpc) ； reliable distance & less radial mixing  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 ：

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)

Age distribution of open clusters

OCs results: gradient vs. age Young Older Chen et al (2003,2008) Overall: － dex/kpc Rgc(kpc)

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

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

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

LOCS – LAMOST Open Cluster Survey

LAMOST at present

The mirrors Inside the telescope

The 4k fibres

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; One of major scientific tasks – Stellar Spectroscopic Survey -- mainly for Galactic structure & stellar physics LAMOST  wide field and large sample astronomy

LAMOST, 4m Schmidt telescope 1.Large aperture, 2.Large FOV~ 20deg fibers 4.Spectroscopy most efficiently: ~ averagely 1 OC/per night deep enough: V~15-16 to reach most of old OCs within d~5-7kpc V lim ~16; min. obs.  S/N~30 R V ~ 5 km/s [Fe/H] ~ 0.2 dex LOCS: Why LAMOST ? -- Within the framework of Stellar Spectroscopic Survey -- == low latitude regions ==

LOCS: What will be the output? 4×10 2 OCs surveyed, each FOV ~ 1d×1d R V and [Fe/H], homogeneous dataset V ~ limit Scientific goals: With OCs dynamical & chemical information (large, homogeneous dataset)  Structure & evolution of the Galactic disk

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 constrains to modeling evolution of the disk Chemical evolution radial abundance gradients/time evolution  more distant OCs with kinematics and metallicity  conclusive results for Galactic chemical evolution ……  much reliable (kinematic) membership for cluster fields -- fundamental base for cluster studies

LOCS: Clusters selection and input catalogue  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 Observation site: δ> － 10d  N ~ 400 OCs

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

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 == >>>>>>>>>>>>>>>>>>>

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

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)

Premise: V lim ~16; bright nights obs. 30min exp.  suitable S/N R V ~ 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 Observation efficiency

Model star count /d 2 （ AQ ） Vb = 0b = 5b = 10b = 20b = 30b = SUM Average number density ~ 3700/d 2 for 0< |b| <20, 14< V mag <16 (model estimation) ~ 1600/d 2 for 0 < |b| < 20, 13< Vmag <15

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] LAMOST observable area:  Total ~ 10 4 d 2 = 500 ×(1+ 10% overlapping) plates one plate contains ~ 20 d 2 ×3700 (model Nr.) ~ 7.4×10 4 stars  need 3600 fibres×20 exp×0.5hour  ~ 2 obs-nights per plate  ~ 500 plates ×(1+ 10%) ×2 =1100 nights (4×10 7 spectra) 1. ”All field star survey” LAMOST Field Of View =20d 2 (“LaFOV”=PLATE) Density ~ 3700 stars/d 2 (for V lim ~15,  7-8 yrs)

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

A Subsample of LOCS:122OCs Total of ~37 plates ~74 nights -- about one year of observation  122 OCs & 740d 2 (~2.7×10 6 stars)

And the bright nights Credits: LIU Cao (NAOC)

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= 3arcsec

LOCBaseDS: ~ 4×37=148 plates ~ 300 nights  ~ 3000d 2 (|b|<20),10 7 stars thin (outer) disk survey, incl. 400OCs  ~ 5 yrs to complete the survey (for V lim ~15,  2.5 yrs) 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 & LOCBaseDS  10 7 star [Fe/H] in GAIA catalog Complementary

LOCBaseDS: 400 OCs (spectroscopic database) to probe disk properties; a representative sample of the disk stars ：  spectra for 10 7 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

Thanks !

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)

The LOCS sample: ~440 OCs Wikimedia

CMD of OCs

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

NGC2323 NGC2309