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Hierarquical Stellar Systems
La Galaxia en un PetabyteMahón, October 2009
Emilio J. Alfaro et al. “Group of Stellar Systems”
Instituto de Astrofísica de AndalucíaConsejo Superior de Investigaciones Científicas
M33 Engargiola et al. (2004) LMC HI + CO Hα + U + V
Scales of star formation
Pattern recognition:Stellar Complexes
A wider concept • Stellar Complexes represent the largest globular scale in the hierarquical
structure of star forming systems, going from double and trapezium systems to fragments of spiral arms in flocculent galaxies.
• Larger scales evolve slower than t ~ L0.5.
Efremov & Elmegreen 1998
The current scientific project• Three years ago we started a scientific project with the main
objective of studying:– The behaviour of the star forming processes at different spatial scales.
• In particular we focussed on four different scales showing different state equations and different physical mechanisms:– Molecular Clouds – Massive Stars (Binary and Trapezium systems)– Stellar Clusters
– Stellar Complexes
Geometry & Physics • The interstellar medium (ISM) shows a fractal structure
(Elmegreen & Falgarone 1996), with a fractal dimension wich appears to be nearly constant for different physical states of the gas and different chemical species. (Sánchez et al. 2005, 2007)
• How does the internal structure of the clouds induce or control the main properties of the emerging stellar population?
• Is the spatial pattern of the recent born stars a mimic of the internal structure of the parent cloud?
• How does the stellar spatial pattern evolve with time? • Is it scale invariant?Sandra Ocando (Grad thesis); Néstor Sánchez (Poster)
MotivationNew born stars
Initial conditions: GMCs, clouds, clumpsISM structure (environmental variables?)
Star formation
Hierarchical structure,masses, sizes, …
IMF, spatial distribution,…
Objective/Systematic characterization/study
???
Fractal ISM• Maps of nearby complexes show a
hierarchical and self-similar structure → underlying fractal structure
Taurus Molecular Cloud(IRAS 100μ emission)
Taurus complex: integrated emission in 12CO (Falgarone et al. 1991)
Df(ISM) ≈ 2.3 = universal !!!???
Df=2.3 Df=2.6
miprogramita.f
well-defined Df
miotroprogramita.fDper , Dm , Dc , …
• Proyection effects• Image resolution• Opacity• Noise
Dper=1.35 Dper=1.35 Df = 2.6 +/- 0.1 !!! Df = 2.6 +/- 0.1 !!!Sanchez et al. 2005
Application to emission maps
Ophiuchus, Perseus (COMPLETE, Ridge et al. 2006)
Orion (Nobeyama, Tatematsu et al. 1993)
13CO maps
Df=2.6-2.8 (Universal?)
Sanchez et al. 2007a
- What is the relationship between the physical properties of the interstellar clouds and their fractal structure?
- Are the observed properties in agreement with relatively high fractal dimension values?
Clump mass spectra:
Simple random sampling through thefractal yields alpha_M = 1.
Observations (as always, a problem!!):0.6 < alpha_M < 0.8 (E&F96)0.3 < alpha_M < 1.1 (others)
If Df = 2.6 then alpha_M ≈ 0.55 for ε = 1.0For ε = 0.1 we get alpha_M ≈ 1.2 +/- 0.2(Salpeter = 1.35)
Sanchez et al. 2006
Federrath et al. 2009:Stochastic forcing term f as source term in equations of hydrodynamics compressive modes (nabla x f = 0) and solenoidal (nabla · f = 0)
D 2.3 for compressive and D 2.6 for solenoidal forcing (M=5.5)∼ ∼
Df=2.3 vs Df=2.6
Dc=1.64 Dc=1.82 Dc=1.79
HII regions in disk galaxies
Dc,ave=1.81 Df(3D),ave=2.73
Significant Dc variations among galaxies!!!1.5 < Dc < 2.0 (2.4 < Df < 3.0)
Faintest galaxies smallest Dc values
Sanchez et al. 2008
New-born stars• Df(ISM) Df (star distribution)• Application to the Gould Belt
(closest star formation complex):
GB LGDBlue = O-B3Red = B4-B6
GB-early: Df = 2.68 +/- 0.04GB-late: Df = 2.85 +/- 0.04LGD-early: Df = 2.89 +/- 0.06LGD-late: Df = 2.84 +/- 0.06
Sanchez et al. 2007b
Stars in open clusters
Sanchez et al. 2009
Minimum spanning tree(Q parameter)
Stars in open clusters
Sanchez et al. 2009
Stars in open clusters
Sanchez et al. 2009
Dc = 1.74 Df ~ 2.0 << 2.6-2.7 ???
• Perhaps some clusters may develop some kind of substructure starting from an initially more homogeneous state (Goodwin & Whitworth 2004).• This difference could be a consequence of a more clustered distribution of the densest gas from which stars form at the smallest spatial scales in the molecular cloud complexes, according to a multifractal scenario (Chappell & Scalo 2001).• Another explanation is that the fractal dimension in the Galaxy does not have a universal value and therefore some regions form stars distributed following more clustered patterns.• Finally, maybe the star formation process itself modifies in some (unknown) way the underlying geometry generating distributions of stars that can be very different from the distribution of gas in the parental clouds.
Massive Stars & Low-Number Groupings
• Question:How do the massive stars form?
• Primary Objectives– Expand the Galactic O-star catalogue (Maíz-
Apellániz 2004) – Generate a catalogue of Galactic early-type stars
from Tycho-2 and 2MASS data bases
Alfredo Sota (PhD); J. Maíz-Apellániz (poster)
Some spectra
Some Special Stellar Complexes
• Gould Belt (supposed to be our closest stellar complex)
Federico Elias (PhD, 2006) • Super-bubble in NGC 6946 (contains a young
SSC with 106 solar masses and shows a diameter close to 700 pc)
Carmen Sánchez Gil (PhD)
Corrección de completitud
• fCG = 0.58 ± 0.06
• hCG = 31 ± 4 pc
• hDGL = 34 ± 5 pc
• Z0CG = -15 ± 12 pc
• Z0DGL = -12 ± 12 pc
• iCG = 14º ± 1º
• ΩCG = 287º ± 6º
• iDGL = 2º ± 2º
• ΩDGL = 352º ± 28º
-1000 -500 0 500 1000-1000
-500
0
500
1000
X (pc)
Y (
pc)
-1000 -500 0 500 1000-1000
-500
0
500
1000
X (pc)
Y (
pc)
DGL
CG
Alfaro et al. 2009Elias et al. 2009
Gould Belt (??)
NGC 6946
Sánchez Gil et al 2009
Age maps of spiral galaxies
Age maps of spiral galaxies
Sánchez Gil et al. 2009 (in preparation)
Velocity corrugations in face-on galaxies
PMS stars in open clusters
• Main Objective: Search and characterization of PMS members in young open clusters
– UBVRIJHK + Hα photometry + models– Mainly focussed on AF star
PMS stars in open clusters Colour
composite of 30’X30' from AAO/UKST-Hα survey image (blue) and Spitzer/IRAC/8microns image (red) (Sh-2 284)
Delgado et al. 2009 (referee)
PMS stars in open clusters
• Two stellar populations
Kinematics and mass of Sagittarius A* and the nuclear star cluster of the Milky Way
MPE/ESO
50 light days 14 light days
UCLA/Keck
Mass of Sagittarius A*: 4.0±0.1 106 M
Size of Sagittarius A* < 1 AU
➔ Sagittarius A* must be a black hole.
e.g. Eckart & Genzel (1996); Ghez et al. (1998, 2003,2008); Genzel et al. (2000); Eckart et al. (2002); Schödel et al. (2002, 2003, 2009); Reid et al. (2004); Eisenhauer et al. (2003, 2005); Gillessen et al. (2009); Doeleman et al. (2008) etc.
The black hole at the Galactic center
Velocity dispersion at the Galactic Center
Sgr A* would hardly be detectable ifit were located in another galaxy.
At R>0.5 pc the extended mass of the cluster becomes visible in the kinematics(deviation from Kepler law).
v~r-0.5
Modeling the enclosed mass
• Extended mass is detected for the first time unambiguously from the stellar dynamics in the central parsec.
• Cluster rotation confirmed
• Extended mass in central parsec: M★(r<1pc) = 1.5×106 M☉ for M/L = const. Consistent with normal stars.
Schödel, Merritt & Eckart (2009, A&A)
Searching for new stellar systems• Looking inside astrometric + photometric catalogues• Clusters, associations & streams• Development of new tools• Detailed studies for special systems
Starting point: Carte du Ciel (revisited), see poster by Belén Vicente
Sánchez et al. (2009) (referee)
ALHAMBRA & GAIA
• Characterization of ALHAMBRA photometric system
• Calibration strategy• Determination of stellar physical parameters
from ALHAMBRA colors
See poster by Teresa Aparicio (PhD)
SSG & GAIA
• Searching for new Galactic subsystems• Stellar Clusters (Galaxy dynamics,
Membership studies, Internal structure and evolution with time)
• Massive Stars (Binarity)
The CrewCulpables:
– E. J. Alfaro– T. Aparicio– A. J. Delgado– T. Gallego– J. Maíz-Apellániz– N. Sánchez– C. Sánchez-Gil– R. Schoedel– A. Sota– B. Vicente
Cómplices Necesarios: •A.A Djupvik•N. Walborn•J. L. Yun
Sospechos Habituales:• A. Eckart • Y. N. Efremov • R. Gamen• N. Morrell• S. Ocando• E. Pérez