Where do stars come from?

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

Transcript

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!
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
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
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
21. (Thanks to the person who put this panel up)
25. Russell Croman / 10 cm Takahashi / Filters: Halpha + S II + O III / 33x15 min exposure
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
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)
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.