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Open Clusters and Galactic Disk Observations with LAMOST
Li CHEN, Jinliang HOUShanghai Astronomical Observatory, CAS
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