J/A+A/623/A128 Galactic halo CEMP stars abundances & kinematics (Hansen+, 2019)
Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic
halo. A new classification scheme based on Sr and Ba.
Hansen C.J., Hansen T.T., Koch A., Beers T.C., Nordstroem B., Placco V.M.,
Andersen J.
<Astron. Astrophys. 623, A128 (2019)>
=2019A&A...623A.128H 2019A&A...623A.128H (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, metal-deficient ; Abundances ;
Proper motions ; Stars, distances
Keywords: stars: abundances - stars: carbon - stars: kinematics and dynamics -
stars: Population II - Galaxy: halo -
nuclear reactions, nucleosynthesis, abundances
Abstract:
Carbon-enhanced metal-poor (CEMP) stars span a wide range of stellar
populations, from bona fide second-generation stars to later-forming
stars that provide excellent probes of binary mass transfer and
stellar evolution. Here we analyse 11 metal-poor stars (8 of which are
new to the literature), and demonstrate that 10 are CEMP stars. Based
on high signal-to-noise ratio (S/N) X-Shooter spectra, we derive
abundances of 20 elements (C, N, O, Na, Mg, Ca, Sc, Ti, Cr, Mn, Fe,
Ni, Sr, Y, Ba, La, Ce, Pr, Nd, and Eu). From the high-S/N spectra, we
were able to trace the chemical contribution of the rare earth
elements (REE) from various possible production sites, finding a
preference for metal-poor low-mass asymptotic giant branch (AGB) stars
of 1.5M☉ in CEMP-s stars, while CEMP-r/s stars may indicate a
more massive AGB contribution (2-5M☉). A contribution from the
r-process -- possibly from neutron star--neutron star mergers (NSM) --
is also detectable in the REE stellar abundances, especially in the
CEMP-r/s sub-group rich in both slow(s) and rapid(r) neutron-capture
elements. Combining spectroscopic data with Gaia DR2 astrometric data
provides a powerful chemodynamical tool for placing CEMP stars in the
various Galactic components, and classifying CEMP stars into the four
major elemental-abundance sub-groups, which are dictated by their
neutron-capture element content. The derived orbital parameters
indicate that all but one star in our sample (and the majority of the
selected literature stars) belong to the Galactic halo. These stars
exhibit a median orbital eccentricity of 0.7, and are found on both
prograde and retrograde orbits. We find that the orbital parameters of
CEMP-no and CEMP-s stars are remarkably similar in the 98 stars we
study. A special case is the CEMP-no star HE 0020-1741, with
very low Sr and Ba content, which possesses the most eccentric orbit
among the stars in our sample, passing close to the Galactic centre.
Finally, we propose an improved scheme to sub-classify the CEMP stars,
making use of the Sr/Ba ratio, which can also be used to separate very
metal-poor stars from CEMP stars. We explore the use of [Sr/Ba] versus
[Ba/Fe] in 93 stars in the metallicity range -4.2≲[Fe/H]←2. We show
that the Sr/Ba ratio can also be successfully used for distinguishing
CEMP-s, CEMP-r/s, and CEMP-no stars. Additionally, the Sr/Ba ratio is
found to be a powerful astro-nuclear indicator, since the metal-poor
AGB stars exhibit very different Sr/Ba ratios compared to
fast-rotating massive stars and NSM, and is also reasonably unbiased
by NLTE and 3D corrections.
Description:
Our programme sample was selected from the "Catalogue of carbon stars
found in the Hamburg-ESO survey" (Christlieb et al., 2001, Cat.
J/A+A/375/366) and the later studies by Placco et al. (2010, Cat.
J/AJ/139/1051, 2011, Cat. J/AJ/142/188); the likely most metal-poor
stars (based on line indices calculated directly from the
objective-prism spectra) were targeted.
The 11 sample stars were observed, between October 2012 and January
2013, with X-Shooter/VLT using a nodding technique.
Table A1: Lines used for abundance derivation of neutral and ionised
atoms/species in the 11 CEMP stars.
Line list containing wavelength, species (Z.mult), excitation
potential, oscillator strength (loggf), and references. The
bibliography is given in the notes below.
Table A2: Star name, proper motion, distance, and the orbital
parameters based on Gaia DR2 for 98 CEMP and metal-poor C-normal
stars.
Kinematics information including stellar ID, proper motion, distance,
and orbital parameters such as apo- and pericentric distances, maximum
height above the plane, and eccentricity. CEMP subclass where mp
refers to c-normal, metal-poor stars and references are listed as
well.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 37 166 Atomic data for 19 elements (linelist)
tablea2.dat 81 98 Kinematics of 98 stars
--------------------------------------------------------------------------------
See also:
J/A+A/375/366 : Carbon stars from the Hamburg/ESO survey (Christlieb+ 2001)
J/AJ/139/1051 : Carbon-enhanced metal-poor stars in the Galaxy (Placco+, 2010)
J/AJ/142/188 : Metal-poor stars from the HES using CH G-band (Placco+, 2011)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 0.1nm Line Wavelength of absorption line in Angstroem
10- 16 F7.4 -- Z.mult Element with multiplicity (level of ionisation)
and isotope (if hyperfine splitting is adopted)
18- 22 F5.3 eV chi Excitation potential
24- 29 F6.3 [-] loggf Oscillator strength
31- 37 A7 -- Ref Reference for atomic data listed (1)
--------------------------------------------------------------------------------
Note (1): References as follows:
PR17 = Pehlivan Rhodin et al. (2017A&A...598A.102P 2017A&A...598A.102P)
B12 = Bergemann et al. (2012A&A...546A..90B 2012A&A...546A..90B)
G12 = Gallagher et al. (2012A&A...538A.118G 2012A&A...538A.118G)
S09 = Sneden et al. (2009ApJS..182...80S 2009ApJS..182...80S)
L01 = Lawler et al. (2001ApJ...563.1075L 2001ApJ...563.1075L)
I06 = Ivans et al. (2006ApJ...645..613I 2006ApJ...645..613I) and
http://kurucz.harvard.edu/linelists.html.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Star Stellar ID
13- 17 F5.2 mas/yr pmRA* Proper motion in right ascension
(mu_α*cosδ)
19 A1 --- --- [+]
20- 23 F4.2 mas/yr E_pmRA* Positive uncertainty in right ascension
proper motion
25 A1 --- --- [-]
26- 29 F4.2 mas/yr e_pmRA* Negative uncertainty in right ascension
proper motion
31- 37 F7.2 mas/yr pmDE Proper motion in declination (mu_δ)
39- 42 F4.2 mas/yr e_pmDE Symmetric uncertainty in declination
proper motion
44- 50 F7.2 kpc D Distance (if negative the star is below the
plane)
52- 55 F4.2 kpc e_D Uncertainty in distance
57- 60 F4.1 kpc Rapo Apocentric distance
62- 66 F5.1 kpc Rperi Pericentric distance
68- 71 F4.1 kpc Zmax Maximum height above the plane
73- 76 F4.2 --- e Eccentricity of orbit
78- 79 A2 --- Class CEMP subclassification, mp indicates C-normal
81 I1 --- Ref Reference (1)
--------------------------------------------------------------------------------
Note (1): References as follows:
1 = Hansen et al. (2015ApJ...807..173H 2015ApJ...807..173H)
2 = Hansen et al. (2016A&A...586A.160H 2016A&A...586A.160H)
3 = Hansen et al. (2016A&A...588A...3H 2016A&A...588A...3H)
4 = Hansen et al. (2016A&A...588A..37H 2016A&A...588A..37H)
5 = This work
--------------------------------------------------------------------------------
Acknowledgements:
Camilla Juul Hansen, camillajuul(at)gmail.com
(End) Camilla Juul Hansen [MPIA, Heidelberg], Patricia Vannier [CDS] 15-Mar-2019