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Where do stars come from?

Where do stars come from?

Outreach talk presented at the "Cosmos Star Party" in Tullamore, Ireland, on 2 Apr 2011.


Geert Barentsen

April 02, 2011


  1. Geert Barentsen Armagh Observatory gba@arm.ac.uk Where do stars form? Where

    did the Solar System form? ... and how do we know?
  2. Stars form when clouds of interstellar material collapse under their

    gravity... Tends to produce clusters!
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  6. End: stellar wind+radiation destroys disk Optical 'T Tauri stars': Infrared

    'young stellar objects':
  7. Artist impression ... Disk Strong magnetic field Large spots Accretion

    How young? How massive? How fast is it growing? => Answers in the light emitted
  8. = Hydrogen alpha emission Proton Electron Elements absorp/emit light at

    specific frequencies Photon (freq = 656.3 nm)
  9. The Sun ...

  10. Temp too low: no excitation Temp too high: electron no

    longer bound (ionized)
  11. Hot Less hot (video)

  12. Spectra tell more than just temperature ...

  13. ~0.1 AU ~100 AU Viscous evolution Magnetospheric accretion flows Shock

    Infrared + radio emission (warm dust) Optical emission (hot gas) UV emission (very hot gas) ... variable ... 'T Tauri' stars
  14. UV emission (Herczeg et al. 2008) Hydrogen emission

  15. None
  16. H-alpha emission line strength Mass accretion rate We can estimate

    how fast a star is growing, simply by looking at one emission line !
  17. (Drew et al. 2005) Spectra are expensive and limited in

    distance... let's use images in filtered light! r' - i' = Temperature r' - Ha = Line strength
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  19. IPHAS: „INT Photometric H-Alpha Survey“ - 20 000 images taken

    between 2004 - 2009 - covering 180 x 10 degrees of galactic plane - public data: www.iphas.org
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  21. (Thanks to the person who put this panel up)

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  25. Russell Croman / 10 cm Takahashi / Filters: Halpha +

    S II + O III / 33x15 min exposure
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  27. Nick Wright - www.iphas.org

  28. Halpha r' i' Photometry 1) Compute sum of pixel values

    in circle 2) Subtract sky annulus 3) Divide by pixel value of Vega = magnitude 9.8 9.6 8.4
  29. Spectral type (temperature) Halpha emission 'synthetic' stars

  30. Young stars previously discovered using spectroscopy (Sicilia-Aguilar et al.)

  31. Previous work (spectroscopy) IPHAS photometry

  32. Result: 158 newly discovered growing stars Halpha emission (Barentsen et

    al. 2011) Spectral type (temperature) 1 million „normal“ stars 158 emission-line stars
  33. None
  34. Temperature (r'-i') Luminosity (r'; corrected for distance) Mass Age Hertszprung-Russel

    Diagram + predictions by theoretical model (dashed lines)
  35. Age Grow rate 10 Myr 0.1 Myr

  36. Hot star Result: stars further away from the hot star

    appear younger
  37. Many Sun-like stars may be triggered by massive hot stars?

  38. d ~ 3000 - 5000 pc GLIMPSE/Spitzer 8 um (Watson

    et al. 2010)
  39. www.milkywayproject.org

  40. So where did the Solar System form? Taurus ~200 stars

    IC1396 ~2000 stars Tarantula ~millions? Was it similar to ...
  41. (Hurt 2008)

  42. None
  43. (Carter Roberts) IC1396

  44. Cluster most likely dispersed - model:

  45. Test: nearby stars with matching motion? Motion Distance Hipparcos data

    (Brown et al. 2010) Black dots: good candidates, but have different composition :-(
  46. So what do we know? We can constrain the size

    of the Solar cluster by considering the influence siblings might have had: 1) Dynamical interactions 2) Radiation from hot stars 3) Supernova chemistry
  47. Dynamical interactions - upper limit Solar cluster < ~3000 stars

    Solar System Known exoplanets: Orbit size Eccentricity
  48. Dynamical interactions - lower limit Sedna: aphelion at 960 AU!

    Kuiper Belt: edge at ~50 AU?! (~1500 km) Stellar encounter within ~200-800 AU ? (e.g. Morbidelli & Levison 2004) Solar cluster > ~1000 stars
  49. Limited UV radiation - upper limit (Hubble - Orion proplyds)

    Solar cluster < ~5000 stars Planets will not form when radiation too high
  50. Supernova chemisty - lower limit Solar cluster > ~500 stars

    Meteorites show signs of 26 Aluminium (cf. Mike Simms talk) Can only be produced by supernova explosion + decays in few million years (half-life: 700 kyr) Solar System formed near a massive star (i.e. supernova)
  51. Number of stars in cluster Probability Supernova Sedna Circular planet

    orbits FUV radiation (Adams 2010) Tarantula Taurus IC1396
  52. Conclusions • We can understand star-forming regions (i.e. estimate 'grow

    rates' + ages + masses) simply by taking images with 3 filters! • IC1396 contains hundreds of new stars, many triggered by the central hot star. • Solar System most likely formed in an environment similar to IC1396.