219 Million Stars: A New Atlas of our Milky Way

Outreach talk for the Cambridge Astronomical Association, presented on 21 November 2014.

1. 219 Million Stars:
 A New Atlas of our Milky Way
 a talk by Geert Barentsen for the Cambridge Astronomical Association, 21 Nov 2014
3. Ceci n`est pas La Voie Lactee Credit: Robert Hurt
4. The Whirlpool Galaxy Credit: Hubble Space Telescope
5. The Milky Way Credit: Nick Risinger (www.skysurvey.org)
6. Credit: Ben Benjamin, Dame et al. The evidence that our Galaxy has a spiral structure:
7. Emission
8. Credit: Sven De Deyne Orion Nebula
9. Credit: Peter Van den Eijnde North America Nebula (Cygnus)
10. Credit: Koen van Gorp Rosette Nebula (Orion)
11. Credit: Koen van Gorp IC 1396 (Cepheus)
12. How do astronomers go about studying their own Galaxy?
13. 300 billion stars Where did they form? When do they die? How are they distributed? Credit: ESO
14. Stars form when giant clouds of gas and dust collapse under their own gravity Credit: Matthew Bate
15. A realistic computer simulation
 showing the formation of stars: Credit: Matthew Bate
16. Credit: Axel Mellinger 100 million
 years old 600 million
 years old < 2 million
 years old
17. Credit: Planck (ESA)
18. Credit: Axel Mellinger
19. T Tauri Credit: Don Goldman
 (16” RC + SBIG CCD)
20. Star
 (optical radiation) Hot dust (near-IR radiation) Warm dust & gas (IR & radio) Hot gas
 (optical radiation) “T Tauri objects” are young stars, which are still growing by accreting material from a disc around the star
21. Hubble’s view towards the dark clouds in Taurus
23. Credit: ESO/ALMA HL Tauri
24. T Tauri stars in the Orion nebula Photo: Hubble
25. Our knowledge is inferred from electromagnetic radiation
26. wavelength intensity
27. wavelength intensity
28. wavelength intensity
29. Electron Photon Atoms emit and absorb light at specific wavelengths => Hydrogen-alpha
 (“H-alpha”) spectral line e.g. Hydrogen:
30. The strength of a spectral line radiated by a gas depends on the temperature of the gas Temperature
31. And spectral lines can reveal more than temperature alone observer em ission emission absorption Markova et al. wavelength intensity
32. (Herczeg et al. 2008) Young stars are easy to identify because they show well-defined emission lines This star 
 is growing!
33. 300 billion stars It is impossible to collect spectra for all the objects in our Galaxy
34. The “GIRAFFE” spectrograph at ESO’s Very Large Telescope (VLT) can observe 132 spectra simultaneously Credit: ESO
35. Ceci n`est pas La Voie Lactee
36. g r u i Hα Solution: one can obtain
 wavelength-filtered images to 
 obtain “poor man’s spectra” wavelength throughput
37. For example: the H-alpha filter
 of a 2.5-meter telescope
38. NGC 3293 in H-alpha
39. NGC 3293 in a UV filter
40. Filters allow stars to be measured at different wavelengths; this is called photometry H-alpha Red light Infrared light +12.8 +12.6 +11.9
42. red vs infrared light ratio red light
 intensity
43. red light
 intensity red vs infrared light ratio
44. Diagrams of the photometric measurements allow interesting objects to be discovered H-alpha vs red
 light ratio
 red vs infrared light ratio
45. IC 1396 (Cepheus) Area studied using spectra Area studied
 using photometry
46. Spatial distribution of young stars:
47. How to obtain photometry
 across the Galaxy?
48. At the University of Hertfordshire we carry out several “photometric surveys” of the Milky Way
49. INT (La Palma) VST (Chile) UKIRT (Hawaii) VISTA (Chile) JCMT (Hawaii) Herschel Prof Janet Drew Dr Phil Lucas Dr Mark Thompson
50. INT Photometric H-Alpha Survey (IPHAS) www.iphas.org ! 
 ! ! VST Photometric H-Alpha Survey (VPHAS) www.vphasplus.org Two projects that pay my salary …
51. Credit: Nick Risinger (www.skysurvey.org)
53. La Palma Credit: Google
55. Roque de los Muchachos Observatory
 La Palma, Canary Islands (2.4 km altitude) INT
57. Isaac Newton Telescope
 2.5-meter Cassegrain (f/3.3) Credit: Max Alexander
60. => “moved” to La Palma in 1984 (with new dome, new mirror & new mount) Herstmonceux Castle The Isaac Newton Telescope was originally located 
 at the Royal Greenwich Observatory (1967-1979)
62. 32-megapixel camera
65. Credit: Nick Risinger (www.skysurvey.org)
67. The data already led to the discovery of 159 new planetary nebulae, e.g. the“Necklace Nebula”: Credit: Nick Wright
68. Also, the discovery of new young stars, e.g. in Cygnus: Credit: Hubble
69. And many pretty pictures of star-forming regions …
73. The images comprise 3 TB of “FITS” files
 (268 000 CCD frames; 8 megapixel each) You can download them from www.iphas.org
75. The images have been converted into a catalogue,
 which details the position and brightness for each 
 of 219 million detected objects
76. The spatial density of objects 
 detected near Cygnus: Credit: Hywel Farnhill
77. The catalogue has many applications, e.g. it has already been used to infer the 3D distribution of dust in the Galaxy: Credit: Stuart Sale
78. Credit: Nick Risinger (www.skysurvey.org)
79. Credit: Nick Risinger (www.skysurvey.org)
80. We have started completing the work using the VLT Survey Telescope (VST) in Chile
81. VLT Survey Telescope (VST) European Southern Observatory (ESO)
 Atacama Desert, Chile (2.6 km altitude)
 Credit: ESO
82. 256 megapixel camera The VLT Survey Telescope (VST) Credit: ESO
83. 300 310 320 330 340 350 0 10 20 30 40 10 5 0 5 10 u,g,r and H↵,r,i observed u,g,r observed H↵,r,i observed Awaiting observation 200 210 220 230 240 250 260 270 280 290 300 Galactic longitude (l) 10 5 0 5 10 Galactic latitude (b)
84. Modern ESO telescopes are largely automated; observations are scheduled remotely
85. Lagoon Nebula (~1.5º wide) Credit: ESO/VPHAS+
86. NGC 3293 Credit: Hywel Farnhill
87. IC 2944 (Hα, 40’ wide)
88. IC 2944 (Hα, 3’ wide)
89. IC 2944 (Hα, 1’ wide)
90. NGC 6611 (Hα, 20’ wide)
91. NGC 6611 (Hα, 2’ wide)
92. The recent discovery of a nebula around a famous red supergiant: Credit: Nick Wright
93. Project status Northern Hemisphere Isaac Newton Telescope 94% done Southern Hemisphere VLT Survey Telescope 30% done
94. Next important step: the ESA Gaia mission Launched 19 Dec 2013
 Measuring the distance to most objects in our images Credit: ESA
95. Credit: ESA
96. Credit: Astrium
97. In combination with the data observed from Earth, we will obtain an extensive picture of our cosmic backyard
98. Ceci est La Voie Lactee
99. Thank you