spatial structure evolution of open star clusters
DESCRIPTION
Spatial Structure Evolution of Open Star Clusters. W. P. Chen and J. W. Chen Graduate Institute of Astronomy National Central University IAU-APRM2002.7.03 Tokyo. Open Clusters. What we have learned/taught in AST101: irregularly and sparsely shaped. How irregular are they anyway?. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/1.jpg)
Spatial Structure Evolution of Open Star Clusters
W. P. Chen and J. W. ChenGraduate Institute of Astronomy
National Central UniversityIAU-APRM2002.7.03 Tokyo
![Page 2: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/2.jpg)
Open Clusters
• What we have learned/taught in AST101: irregularly and sparsely shaped.
• How irregular are they anyway?
IC 348 by 2MASS
![Page 3: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/3.jpg)
Globular ClustersStars concentrate progressively toward the center. The King model (1962) is understood as a combination of an isothermal sphere; i.e., dynamically relaxed in the inner part of the cluster, and tidal truncation by the Milky Way in the outer part.
Surface brightness of M3 (Da Costa and Freeman, 1976)
![Page 4: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/4.jpg)
King Model (1962)
2
2/122/12 /1
1
/1
1
ctc rrrrkf
rc: core radius rt: tidal radius k central number density
![Page 5: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/5.jpg)
Structure of an Open Cluster• The initial stellar distribution in a star cluster is
dictated perhaps by the structure in the parental molecular cloud. (Initial)
• As the cluster evolves, the distribution is modified by gravitational interaction among member stars. (Internal)
• Eventually stellar evaporation and external disturbances --- Galactic tidal force, differential rotation, and collision with molecular clouds --- would dissolve the cluster. (External)
![Page 6: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/6.jpg)
Spatial Structure by Star Counting in 2MASS
• Stellar density within concentric annuli
• Center too crowded to resolve by 2MASS; outer part follows well a King model
• Background uniform out to large angular extents
• Klim (3-)=15.6 --- not deep enough to reach MS, for distant and old globular clusters Projected radial stellar
density of a GC, M55
![Page 7: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/7.jpg)
2MASS 3-sigma limit
![Page 8: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/8.jpg)
Open cluster NGC 2506 (1.9 Gyr; 3.3 kpc) mosaiced from 2MASS data
![Page 9: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/9.jpg)
Sources toward NGC2506 and the surface density
![Page 10: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/10.jpg)
![Page 11: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/11.jpg)
Locations of sample galactic open clusters. http://www.ipac.caltech.edu/2mass/
![Page 12: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/12.jpg)
Radial density profile of NGC 2506
![Page 13: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/13.jpg)
Cumulative stellar density profiles for NGC 2506 (1.9 Gyr; 3.3 kpc) shows apparent evidence of mass segregation
…… in contrast to that in M11 found by Mathieu (1984)
![Page 14: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/14.jpg)
Stars in the young (5 Myr) star cluster IC 348 are centrally concentrated, and seem to segregate star formation processes more than subsequent dynamic evolution
![Page 15: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/15.jpg)
The old (9 Gyr) open cluster Berkeley 17 shows no evidence of mass segregation.
![Page 16: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/16.jpg)
Cluster l,b (Myr)
N* M/M⊙ D (kpc)
Rs
(‘)
R (pc)
re
(Myr)
τ/τ re Segr.
YoungNGC1893 174, -02 4 498 309 4.4 6.5 8.9 291 0.01 ?
IC348 160, -18 5 322 200 0.32 16.5 1.6 14 0.2 Y
IntermediateNGC1817 186, -13 800 236 146 2.1 12.5 7.9 139 6 N?
NGC2506 231, +10 1,900 1,038 643 3.3 17.5 17.3 605 3 Y
NGC2420 198, +20 2,200 450 279 2.5 12.5 9.4 223 10 Y
OldNGC6791 070, +11 8,000 1,095 679 4.2 10.5 13.2 543 15 ?
Be17 176, -04 9,000 370 229 2.5 9.5 7.1 142 63 N
![Page 17: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/17.jpg)
Relaxation Time
τcross = R/V ; τrelax ~τcross.Ncross Ncross = 0.1 N / ln N
τevap ~ 100 τrelax
R: radius V: velocity dispersion
N: number of member stars
![Page 18: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/18.jpg)
NGC 1893 --- 4 Myr
![Page 19: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/19.jpg)
IC 348 --- 5 Myr
![Page 20: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/20.jpg)
NGC1817 --- 800 Myr
![Page 21: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/21.jpg)
NGC 6791 --- 8,000 Myr
![Page 22: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/22.jpg)
Be 17 --- 9,000 Myr
![Page 23: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/23.jpg)
Summary
• 2MASS good for study of open clusters - Full data release expected end of 2002 - Deep IR images to differentiate the MS (IR camera with Nagoya U & PMO)
• Stars in an open cluster, regardless of masses, are concentrated progressively toward the center.
• The youngest star clusters show evidence of luminosity (mass) segregation - cf. molecular cloud structure (SMA)
![Page 24: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/24.jpg)
Summary --- II
• By a few Gyr (several relaxation times), clusters become highly relaxed, until dynamical disruptions dominate.
• Tidal distortions (age, location, massive vs low-mass stars) Open clusters (scattering around the galactic disk) as probes of galactic mass distribution e.g., disk vs volume potential - galactic disk and (dark) halo models
![Page 25: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/25.jpg)
Our knowledge, or even recognition, of galactic open clusters is highly incomplete, most biased toward the ones that are nearby and with bright stars.
![Page 26: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/26.jpg)
Open clusters are distributed widely around the galactic disk.
![Page 27: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/27.jpg)
Open Cluster Study at NCU
• Luminosity Function Evolution age and star formation history (e.g., coeval vs periodic bursts) done
• Structural Evolution dynamics probing galactic mass distribution (e.g., disk vs volume potential) ½ done
• Variability and [rotation vs magnetic activity] doing
![Page 28: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/28.jpg)
Open Clusters/NCU --- cont.
• Lulin 1 m telescope (Taiwan) August 2002
• Maidanak Observatory (Uzbekistan) 1.5 m and 1 m
• Moletai Obs. 1.65 m (Lithuania)• YALO 1 m (Chile)• Imaging plus CORAVEL high-resolutio
n spectroscopy • Kentucky-Yunnan-Taiwan Telescope (K
YTT) to lift off by 2004-2005?
![Page 29: Spatial Structure Evolution of Open Star Clusters](https://reader035.vdocuments.us/reader035/viewer/2022062518/5681449f550346895db15ddb/html5/thumbnails/29.jpg)
Fast rotating stars P(rot) < 12 d (BLUE) are distinguished from slow rotators (RED) by their X-ray luminosity (normalized to solar – in yellow. The Rossby number gives the rotation period in units of the eddy's lifetime. (http://www.aip.de/groups/turbulence/star_t.html)