1. Columbia Univ. (Simons Fellow)
Red Clump Stars, Stellar Twins, and the Prospects of Chemical Cartography with Gaia
Ignace Gaston Pardies, Star Map Plate 2: Cetus, Aquarius, Andromeda. etc, Paris, 1693
Keith Hawkins
Columbia Univ. (Simons Fellow)
1 Feb. 2017

2. A Vision of Chemical Cartography
[Mg/Fe] as a function of spatial position in Gaia-ESO
Adapted from Greg Stinson and Maria Bergemann.
Ingredients : chemical abundances, Distances, sky positions, ages?

3. What can cartography tell us
chemical history across the galaxy
chemical substructure
Radial migration
Hayden+2015

4. Ingredient 1: chemical abundances
credit: commons.wikimedia.org

5. Role of chemistry in Galactic structure
Hawkins+ 2015b
α-elements = Ca, Ti, Si, Mg, [O, S..]

6. The Era of Large Surveys
N ~ 100,000
N ~ 10,000,000
25+ elements
N ~ 1,000,000
18+? elements
15+ elements ?
N ~ 100,000
15 (20+) elements
N ~ 483,000
8+ elements
2008-Present

7. The Era of Large Surveys
Venn+2004
Holtzman+2015

8. Improvements in APOGEE
Line-list (w/ T. Masseron), line-by-line differential analysis, Line-selection,
local dwarfs
APOGEE+Kepler DR12
APOGEE+Kepler Hawkins
Hawkins+ 2016b

9. Improvements in APOGEE
Bensby+2014
Caffau+2011
Battistini+2015
Hawkins+ 2016b

10. Chemical ‘Labeling’
Galactic components ‘cluster’ in chemical space! (cartography is the next step —> need distances)
Hawkins+ 2015b

11. Ingredient 2: Distances
Red clump stars (Stanek+1998) stellar twins (Jofre+2016)

12. Distances: Red Clump Use Gaia parallaxes to assess:
Is the red clump a good standard candle? (2) Update magnitude of RC in JHK, G, W1?, W2?, …

13. Red Clump Datasets
G-K
Parallax cut at 30% (prior v.s. data dominated posterior)
N ~ 950 (30%); 130 (10%)
-1.62 (Laney+2012) MK
APOKASC (Elsworth+2016), APOGEE-RC (Bovy+2014), Laney+2012, APO1m (Feuillet+ in prep)

14. Distances: Red Clump The Model
M, σM — RC
Mc=M, σMc=1.0 mag — cont.
fout — fraction of contamination
Other important parameter(s):
L — scale-length of exponentially decreasing space density prior (Bailer-Jones 2015, Astraatmadja+2016) RC N
Contaminates M

15. Red Clump K(JHG)-Magnitude
M = abs mag
sigma_M = dispersion of abs mag
L = scale-length of exponential decreasing space density prior
f_out = contamination fraction
Red Clump K(JHG)-Magnitude
Mk = / ; σMK = 0.22+/- 0.03; fout ~ 2%
M = abs mag
σM = dispersion of abs mag
L = scale-length of exponential decreasing space density prior
fout = contamination fraction

16. Stellar Twins
credit: IoA, Cambridge

17. Distances: Stellar Twins
Jofre et al. 2016

18. Distances: Stellar Twins
Twins used to help ‘settle’ Pleiades debate
Mädler et al. (incl. KH) 2016
Figure taken from Gaia collab. et al. 2016

19. Stellar Twins in APOGEE
Alternative ways to find stellar twins:
K-S test? χ2? Other probabilistic ways?
APOGEE-TGAS
for stars with σῶ/ῶ < 0.3
~ 45%
PKS = 0.91

20. What are the Prospects for chemical cartography?
[Mg/Fe] as a function of spatial position in Gaia-ESO
Adapted from Greg Stinson and Maria Bergemann.
Great! with RC stars, Gaia, stellar twins and a ton of large surveys for chemistry.