The GALAH survey:
an overview
Sarah Martell
ARC DECRA Fellow, University of New South Wales GALAH Project Scientist
The GALAH survey
•
Large observational survey with HERMES @ AAT
•
Measuring radial velocity and 29 abundances for 1 million stars in the Milky Way @ R=30,000 in 4 optical bands
•
Galactic archaeology: exploring the history of
• Star formation
• Chemical evolution
• Dynamical evolution
• Minor mergers in the Milky Way
•
Near-field cosmology: use the local environment to get a
close-up view of universal processes
Introducing HERMES
•
4-channel high-resolution spectrograph
Blue
4718Å-4903Å
Green
5649Å-5873Å
Red
6481Å-6739Å IR
7590Å-7890Å
GA complementarity
•
Gaia-ESO Survey
• Halfway done with observing (300 n/5 years)
• 100,000 stars
• Fainter than GALAH
• R~20,000
• Targeted selection: thick disk, halo, star clusters
•
SDSS-III/APOGEE
• Observing complete (3 years) + APOGEE-2 to come
• 100,000 stars
• R~22,500, H-band (1.5-1.7μ)
• Targeted selection: red giants, very low latitude
Gaia (2014-19) will provide precision astrometry for about 10
9stars
For V < 14,
= 10 as,
= 10 as yr
-1-- Gaia at its best!
• 1% distance errors at 1 kpc, 0.7 km s-1 velocity errors at 15 kpc)
accurate transverse velocities for all stars in GALAH
accurate distances for same
therefore accurate color-(absolute magnitude) diagram:
independent check that chemically tagged groups have common age
• major implications for stellar astrophysics before
Galactic archaeology, e.g. correctness of 3D atmospheres, much improved abundance scale, seismic parameters,
ages…
Gaia is a major element of the GALAH survey
GALAH and Gaia
GA complementarity
•
GALAH’s goals are broad – De Silva et al. 2015
• High resolution
• R~28,000
• Large, diverse sample
• All stars 12<V<14, -80°<δ<+10°, |b|>10°, Σ>400/π deg2 are targets
• Galaxia prediction:
• 75% thin disk
• 24% thick disk
• 1% bulge
• 0.1% halo
• Relatively bright stars
• Comprehensive sample of the thin and thick disk
12<V<14, 10<|b|<45, Dec<10
0 5 10 15
Age (Gyr) 0.0
0.1 0.2 0.3
P(Age)
0 2 4 6 8 10
Distance d (kpc) 0.0
0.2 0.4 0.6 0.8 1.0
P(d)
-3 -2 -1 0 1
[Fe/H]
0.0 0.2 0.4 0.6 0.8 1.0
P([Fe/H])
Age (Gyr)
Distance (kpc)
Metallicity [Fe/H]
Probability Figure: S. Sharma
-135 -90
-45 0
45 90
135
-90
-60
-30 0 30 60
90
r < 2000 stars/(p deg2)
0. 500. 1000. 1500. 2000. 2500.
2MASS, 10<|b|>45, 12<V<14, Dec<10
-135 -90
-45 0
45 90
135
-90
-60
-30 0 30 60
90
Galactic archaeology
•
GALAH takes a new approach
• “Chemical tagging”: stars that form together will have the same abundance pattern
• Minimal abundance assumptions
• Phenomenological approach to data
• PCA, Manhattan distance metric
Ting et al. 2012
Mitschang et al. 2014
U (km/s) U (km/s) V (km/s) Teff (K)
V, W, W log(g)
Survey progress
•
Main survey: 78 nights Feb 2014 – Jan 2015, 140 more granted through Jan 2017
•
In 86 nights so far
• 108231 stars in 262 fields
• Of those, 5992 stars/17 fields are in the Kepler-2 campaign regions
Early analysis
Figure 6: HR diagram of 10000 st ars. Blue point s= [Fe\ H]< -1, black point s= [Fe\ H]> -0.5, red point s= -1< [Fe\ H]< -0.5. Mart in point ed out t hat t he artificial upturn in the lower main sequence is a common artefact in global-fits and is caused by the breakdown of Fe ionization balance at low t emperat ure and high log(g). Unsurprisingly for such a crude met hod, he st ruct ure is not * very* well defined.
8
UK/Germany National Astronomy Meeting Manchester UK
NAM 2012 28 March 2012
@galahsurvey
Number, mass of recovered clusters tells us about
• ICMF
• SFR vs time
• Radial mixing
Radial migration
GALAH: progress so far
•
Main survey: 78 nights Feb 2014 – Jan 2015, 140 more granted through Jan 2017
• Lose 28% to weather (plus a bit to seeing)
•
In 86 nights so far
• 108231 stars in 262 fields
• Of those, 5992 stars/17 fields are in the Kepler-2 campaign regions
Survey progress
•
Main survey, Feb 2014 –
•
36 nights in 2014A + 10 windfall, 31 nights in 2014B
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200 nights requested through 2016B
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In 2014A+B: 76,688 stars in 216 fields
•
