Open Clusters and Galactic Disk Observations with LAMOST

Li CHEN, Jinliang HOUShanghai Astronomical Observatory, CAS

chenli@shao.ac.cn

KIAA/PKU-IoA Workshop 1-5 Dec, 2008 Beijing, China

spatial distribution (Dgc ~ 20 kpc) ； reliable distanc

e & 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 ，…

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- 0.024

Older- 0.075

Chen et al (2003,2008) Overall: － 0.063 dex/kpc

8 10 12 14 16 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”, Vlim~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 2008.10.21

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~ 20deg2

3.4000 fibers4.Spectroscopy

most efficiently: ~ averagely 1 OC/per night

deep enough: V~15-16 to reach most of old OCs within d~5-7kpc

Vlim~16;30 - 40min. obs. S/N~30RV ~ 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?

4×102 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

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 prep

ared

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 sky2. ”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:

Vlim~16; bright nights obs.30min exp. suitable S/NRV ~ 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 /d2 （ AQ4 1999 ）

V b = 0 b = 5 b = 10 b = 20 b = 30 b = 60

12 56 56 55 46 35 17

13 188 185 165 122 86 40

14 510 494 414 281 190 84

15 1273 1216 966 603 389 161

16 3050 2880 2140 1227 750 287

SUM 4833 4590 3520 2111 750 287

Average number density ~ 3700/d2 for 0< |b| <20, 14< Vmag <16(model estimation) ~ 1600/d2 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 ~ 104d2 = 500 ×(1+ 10% overlapping) plates

40,240 GbGl

• one plate contains ~ 20 d2 ×3700(model Nr.) ~ 7.4×104 stars

need 3600 fibres×20 exp×0.5hour ~ 2 obs-nights per plate

~ 500 plates ×(1+ 10%) ×2 =1100 nights (4×107 spectra)

1. ”All field star survey” LAMOST Field Of View =20d2

(“LaFOV”=PLATE)

Density ~ 3700 stars/d2

(for Vlim ~15, 7-8 yrs)

OCs observable with LAMOST: total N ~ 720With distance ( > 200pc) information N ~ 400Aim: probe both OCS in Milky Way & statistical properties of the Disk

2. ”OC dominated survey” – LOCS project

LOCBaseDS sky area

40

21020230

Gb

Gl

Vlim~16;30 min. obs. RV ~ 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 & 740d2 (~2.7×106 stars)

40,5065115 GbGl

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

Rlim=18mag

Number of stars within 3” circle

Trivial !

NGC2323(L,B)=(221.84, -1.33), d=0.8kpc, age=0.13GyrCredit:

LIU Cao

maglim~18

Fibre aperture= 3arcsec

LOCBaseDS: ~ 4×37=148 plates ~ 300 nights

~ 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

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 !

40,210 GbGl

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, dij< 10mmStellar field overlapped with “fibre circle”

Fiber positioning for a single OC: one degree diameter

NGC2323

NGC2309