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Hierarquical Stellar Systems

Hierarquical Stellar Systems. Emilio J. Alfaro et al. “Group of Stellar Systems” Instituto de Astrofísica de Andalucía Consejo Superior de Investigaciones Científicas. La Galaxia en un Petabyte Mahón, October 2009. M33 Engargiola et al. (2004) LMC

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Hierarquical Stellar Systems

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  1. Hierarquical Stellar Systems Emilio J. Alfaro et al. “Group of Stellar Systems” Instituto de Astrofísica de Andalucía Consejo Superior de Investigaciones Científicas La Galaxia en un Petabyte Mahón, October 2009

  2. M33 Engargiola et al. (2004) LMC HI + CO Hα + U + V

  3. Scales of star formation Pattern recognition: Stellar Complexes

  4. 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

  5. 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

  6. 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)

  7. Motivation Initial conditions: GMCs, clouds, clumps ISM structure (environmental variables?) New born stars Star formation ??? Hierarchical structure, masses, sizes, … IMF, spatial distribution,… Objective/Systematic characterization/study

  8. 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)

  9. Df=2.6 Df=2.3 Df(ISM) ≈ 2.3 = universal !!!??? miprogramita.f well-defined Df miotroprogramita.f Dper , Dm , Dc , … • Proyection effects • Image resolution • Opacity • Noise Dper=1.35  Df = 2.6 +/- 0.1 !!! Sanchez et al. 2005

  10. Application to emission maps 13CO maps Ophiuchus, Perseus (COMPLETE, Ridge et al. 2006) Df=2.6-2.8 (Universal?)‏ Orion (Nobeyama, Tatematsu et al. 1993) Sanchez et al. 2007a

  11. Clump mass spectra: - 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? Simple random sampling through the fractal 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 = 1.0 For ε = 0.1 we get alpha_M ≈ 1.2 +/- 0.2 (Salpeter = 1.35) Sanchez et al. 2006

  12. Df=2.3 vs Df=2.6 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)

  13. HII regions in disk galaxies Dc=1.64 Dc=1.82 Dc=1.79 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

  14. New-born stars • Df(ISM)  Df (star distribution) • Application to the Gould Belt (closest star formation complex): GB LGD GB-early: Df = 2.68 +/- 0.04 GB-late: Df = 2.85 +/- 0.04 LGD-early: Df = 2.89 +/- 0.06 LGD-late: Df = 2.84 +/- 0.06 Blue = O-B3 Red = B4-B6 Sanchez et al. 2007b

  15. Stars in open clusters Minimum spanning tree (Q parameter) Sanchez et al. 2009

  16. Stars in open clusters Sanchez et al. 2009

  17. 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.

  18. 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)

  19. Some spectra

  20. 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)

  21. Corrección de completitud CG • 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 DGL

  22. Alfaro et al. 2009 Elias et al. 2009

  23. Gould Belt (??)

  24. NGC 6946 Sánchez Gil et al 2009

  25. Age maps of spiral galaxies

  26. Age maps of spiral galaxies Sánchez Gil et al. 2009 (in preparation)

  27. Velocity corrugations in face-on galaxies

  28. 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

  29. 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)

  30. PMS stars in open clusters • Two stellar populations

  31. Kinematics and mass of Sagittarius A* and the nuclear star cluster of the Milky Way

  32. 50 light days 14 light days The black hole at the Galactic center Mass of Sagittarius A*: 4.0±0.1 × 106 M Size of Sagittarius A* < 1 AU ➔ Sagittarius A* must be a black hole. MPE/ESO UCLA/Keck 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.

  33. Velocity dispersion at the Galactic Center Sgr A* would hardly be detectable if it 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

  34. 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)

  35. 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)

  36. ALHAMBRA & GAIA • Characterization of ALHAMBRA photometric system • Calibration strategy • Determination of stellar physical parameters from ALHAMBRA colors See poster by Teresa Aparicio (PhD)

  37. SSG & GAIA • Searching for new Galactic subsystems • Stellar Clusters (Galaxy dynamics, Membership studies, Internal structure and evolution with time) • Massive Stars (Binarity)

  38. The Crew • Cómplices Necesarios: • A.A Djupvik • N. Walborn • J. L. Yun Culpables: • E. J. Alfaro • T. Aparicio • A. J. Delgado • T. Gallego • J. Maíz-Apellániz • N. Sánchez • C. Sánchez-Gil • R. Schoedel • A. Sota • B. Vicente • Sospechos Habituales: • A. Eckart • Y. N. Efremov • R. Gamen • N. Morrell • S. Ocando • E. Pérez

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