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219 Million Stars: A New Atlas of our Milky Way
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Geert Barentsen
November 21, 2014
Science
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120
219 Million Stars: A New Atlas of our Milky Way
Outreach talk for the Cambridge Astronomical Association, presented on 21 November 2014.
Geert Barentsen
November 21, 2014
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Transcript
219 Million Stars: A New Atlas of our Milky Way
a talk by Geert Barentsen for the Cambridge Astronomical Association, 21 Nov 2014
None
Ceci n`est pas La Voie Lactee Credit: Robert Hurt
The Whirlpool Galaxy Credit: Hubble Space Telescope
The Milky Way Credit: Nick Risinger (www.skysurvey.org)
Credit: Ben Benjamin, Dame et al. The evidence that our
Galaxy has a spiral structure:
Emission
Credit: Sven De Deyne Orion Nebula
Credit: Peter Van den Eijnde North America Nebula (Cygnus)
Credit: Koen van Gorp Rosette Nebula (Orion)
Credit: Koen van Gorp IC 1396 (Cepheus)
How do astronomers go about studying their own Galaxy?
300 billion stars Where did they form? When do they
die? How are they distributed? Credit: ESO
Stars form when giant clouds of gas and dust collapse
under their own gravity Credit: Matthew Bate
A realistic computer simulation showing the formation of stars: Credit:
Matthew Bate
Credit: Axel Mellinger 100 million years old 600 million years
old < 2 million years old
Credit: Planck (ESA)
Credit: Axel Mellinger
T Tauri Credit: Don Goldman (16” RC + SBIG CCD)
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
Hubble’s view towards the dark clouds in Taurus
None
Credit: ESO/ALMA HL Tauri
T Tauri stars in the Orion nebula Photo: Hubble
Our knowledge is inferred from electromagnetic radiation
wavelength intensity
wavelength intensity
wavelength intensity
Electron Photon Atoms emit and absorb light at specific wavelengths
=> Hydrogen-alpha (“H-alpha”) spectral line e.g. Hydrogen:
The strength of a spectral line radiated by a gas
depends on the temperature of the gas Temperature
And spectral lines can reveal more than temperature alone observer
em ission emission absorption Markova et al. wavelength intensity
(Herczeg et al. 2008) Young stars are easy to identify
because they show well-defined emission lines This star is growing!
300 billion stars It is impossible to collect spectra for
all the objects in our Galaxy
The “GIRAFFE” spectrograph at ESO’s Very Large Telescope (VLT) can
observe 132 spectra simultaneously Credit: ESO
Ceci n`est pas La Voie Lactee
g r u i Hα Solution: one can obtain wavelength-filtered
images to obtain “poor man’s spectra” wavelength throughput
For example: the H-alpha filter of a 2.5-meter telescope
NGC 3293 in H-alpha
NGC 3293 in a UV filter
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
None
red vs infrared light ratio red light intensity
red light intensity red vs infrared light ratio
Diagrams of the photometric measurements allow interesting objects to be
discovered H-alpha vs red light ratio red vs infrared light ratio
IC 1396 (Cepheus) Area studied using spectra Area studied using
photometry
Spatial distribution of young stars:
How to obtain photometry across the Galaxy?
At the University of Hertfordshire we carry out several “photometric
surveys” of the Milky Way
INT (La Palma) VST (Chile) UKIRT (Hawaii) VISTA (Chile) JCMT
(Hawaii) Herschel Prof Janet Drew Dr Phil Lucas Dr Mark Thompson
INT Photometric H-Alpha Survey (IPHAS) www.iphas.org ! ! !
VST Photometric H-Alpha Survey (VPHAS) www.vphasplus.org Two projects that pay my salary …
Credit: Nick Risinger (www.skysurvey.org)
None
La Palma Credit: Google
None
Roque de los Muchachos Observatory La Palma, Canary Islands (2.4
km altitude) INT
None
Isaac Newton Telescope 2.5-meter Cassegrain (f/3.3) Credit: Max Alexander
None
None
=> “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)
None
32-megapixel camera
None
None
Credit: Nick Risinger (www.skysurvey.org)
None
The data already led to the discovery of 159 new
planetary nebulae, e.g. the“Necklace Nebula”: Credit: Nick Wright
Also, the discovery of new young stars, e.g. in Cygnus:
Credit: Hubble
And many pretty pictures of star-forming regions …
None
None
None
The images comprise 3 TB of “FITS” files (268 000
CCD frames; 8 megapixel each) You can download them from www.iphas.org
None
The images have been converted into a catalogue, which details
the position and brightness for each of 219 million detected objects
The spatial density of objects detected near Cygnus: Credit:
Hywel Farnhill
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
Credit: Nick Risinger (www.skysurvey.org)
Credit: Nick Risinger (www.skysurvey.org)
We have started completing the work using the VLT Survey
Telescope (VST) in Chile
VLT Survey Telescope (VST) European Southern Observatory (ESO) Atacama Desert,
Chile (2.6 km altitude) Credit: ESO
256 megapixel camera The VLT Survey Telescope (VST) Credit: ESO
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)
Modern ESO telescopes are largely automated; observations are scheduled remotely
Lagoon Nebula (~1.5º wide) Credit: ESO/VPHAS+
NGC 3293 Credit: Hywel Farnhill
IC 2944 (Hα, 40’ wide)
IC 2944 (Hα, 3’ wide)
IC 2944 (Hα, 1’ wide)
NGC 6611 (Hα, 20’ wide)
NGC 6611 (Hα, 2’ wide)
The recent discovery of a nebula around a famous red
supergiant: Credit: Nick Wright
Project status Northern Hemisphere Isaac Newton Telescope 94% done Southern
Hemisphere VLT Survey Telescope 30% done
Next important step: the ESA Gaia mission Launched 19 Dec
2013 Measuring the distance to most objects in our images Credit: ESA
Credit: ESA
Credit: Astrium
In combination with the data observed from Earth, we will
obtain an extensive picture of our cosmic backyard
Ceci est La Voie Lactee
Thank you