Halo

Dwarf Galaxies

Surveysr-process enhanced stars in the Milky Way haloand its satellites
Terese Hansen
Carnegie Observatories
Hirschegg 2017

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

Surveysr-process enhanced stars
Metal-poor ([Fe/H] < −1) stars showing an enhancement inr-process elements.

r-I : 0.3 < [Eu/Fe] < 1.0 and [Ba/Eu] < 0

r-II : [Eu/Fe] > 1.0 and [Ba/Eu] < 0Reminder of bracket
 notation: NXX
[X/Y] = log N−logNYNY∗

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

HaloDwarf Galaxies

Surveys

The first r-process enhanced star
CS 22892−052 with [Fe/H] = −3.10 and [Eu/Fe] = 1.64
(Sneden+ 1994).

CS 22892−052 (blue) and HD 122563 (red), Sneden+ 2008

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

HaloDwarf Galaxies

Surveys

The first r-process enhanced starCowan+ 1995

Sneden+ 2003

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

SurveysAbundance pattern of r-process enhanced stars
r-I stars

r-II stars

Siqueira Mello+ 2014
Sneden+ 2008
Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

SurveysAbundance pattern of r-process enhanced stars
r-I stars

r-II stars

Roederer+ 2014

Siqueira Mello+ 2014

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

HaloDwarf Galaxies

Surveys

Actinide boost stars
One r-I and five r-II stars are enhanced in Th (and U wheredetected) relative to second and third peak r-process elements.
CS 31082−001[U/Fe] = 1.49

normal r-II
CS 22892−052: [Eu/Th] = 0.28
actinide boost stars:
CS 30315−029: [Eu/Th] = −0.23
CS 30306−132: [Eu/Th] = −0.36
CS 31078−018: [Eu/Th] = −0.24
CS 31082−001: [Eu/Th] = −0.20
HE 1219−0312: [Eu/Th] = −0.30
HE 2252−4225: [Eu/Th] = −0.11(Sneden+2003, Siqueira Mello+2014, Lai+2008,Hill+2002, Honda+2004, Mashonkina+ 2014,Roederer+ 2009)

Hill+ 2002
Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

SurveysDwarf Galaxies

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

Surveys

1.1

1.0

1.0

0.9

0.9

0.8
0.7
0.6

0.8

0.6
0.5

0.40.4EuII

412.90412.95413.00
Wavelength (nm)

1.0

SmII

0.7

0.5

0.3

1.1

0.9
0.8
0.7
PrII

0.6

0.3
413.05

Normalised Flux

1.1

Normalised Flux

Normalised Fluxr-I star in Tucana III with [Eu/Fe] = 0.6

446.65 446.70 446.75 446.80 446.85
Wavelength (nm)0.5
417.80417.85417.90 417.95 418.00
Wavelength (nm)418.05

Hansen+ submitted

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

Surveysr-process enhanced stars in other dwarf galaxies
Dwarf galaxy
Ursa Minor
Draco
Sculptor
FornaxCarinaReticulum II

r-I
641620

r-II
11040
7

Total stars with Eu and Ba
1717
21
147
149

Image credit: Andrew Colvin
Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

SurveysAbundance pattern of r-process enhanced stars in dwarfgalaxies
1918

Sr Zr
YBa Ce Nd SmGd Dy Er
La PrEu171615
1413

Relative log ε1211109876543210∆ε10-1
354045505560
Atomic number

6570

Hansen+ submitted
Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

SurveysSurveysTerese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

Surveys

Dedicated search for r-process enhanced stars in the haloFirst search:
Barklem+ 2005 took snapshot of 253 stars and discovered 8r-II and 35 r-I stars → r-II stars are very rare!
Today:
Halo: 25 r-II and ∼125 r-I stars.
Dwarf galaxies: 13 r-II and 20 r-I stars.

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

HaloDwarf Galaxies

Surveys

New survey for r-process enhanced stars

Obtain high resolution spectra for ∼2000 stars to find ∼75 new r-IIstars plus a large number of r-I stars.

Selection:
Bright V > 13.5 → can observe many stars in short time
Cool 4000 < Teff < 5500 → Get Eu abundance or good upperlimits
Metal poor [Fe/H] < −2 → Only few nucleosynthesis events

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

Surveys

Pilot runSix nights on du Pont at Las Campanas Observatory in August
2016, obtained spectra of 110 stars.

Hansen+ in prep.

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

SurveysMore data to comeLarge sample with fullabundance pattern
More stars with Th and U
detections, possible actinideboost
HST observations

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017

Halo

Dwarf Galaxies

Surveys

Summary

Abundance pattern same for r-I and r-II stars in halo anddwarf galaxies.
r-process element enrichment is not coupled to light element
abundances, but small number show additional enhancementin actinides
New survey to find more r-process enhanced stars

Terese Hansen Carnegie Observatories
r-process enhanced stars in the Milky Way halo and its satellites

Hirschegg 2017