The Astrophysical Journal, 834:61 (8pp), 2017 January 1 doi:10.3847/1538-4357/834/1/61
© 2017. The American Astronomical Society. All rights reserved.
CHEMICAL ANALYSIS OF A CARBON-ENHANCED VERY METAL-POOR STAR: CD-27 14351
Drisya Karinkuzhi1, Aruna Goswami1, and Thomas Masseron2
1 Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
2 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
Received 2016 September 19; revised 2016 October 31; accepted 2016 October 31; published 2017 January 3
ABSTRACT
We present, for the first time, an abundance analysis of a very metal-poor carbon-enhanced star CD-27 14351
based on a high-resolution (R∼48,000) FEROS spectrum. Our abundance analysis performed using local
thermodynamic equilibrium model atmospheres shows that the object is a cool star with stellar atmospheric
parameters, effective temperature T =4335 K, surface gravity log g=0.5, microturbulence ξ=2.42 km s−1eff ,
and metallicity [Fe/H]=−2.6. The star exhibits high carbon and nitrogen abundances with [C/Fe]=2.89 and
[N/Fe]=1.89. Overabundances of neutron-capture elements are evident in Ba, La, Ce, and Nd, with estimated
[X/Fe] > 1, the largest enhancement being seen in Ce with [Ce/Fe]=2.63. While the first peak s-process
elements Sr and Y are found to be enhanced with respect to Fe, ([Sr/Fe]=1.73 and [Y/Fe]=1.91), the third
peak s-process element Pb could not be detected in our spectrum at the given resolution. Europium, primarily an r-
process element also shows an enhancement with [Eu/Fe]=1.65. With [Ba/Eu]=0.12, the object CD-27 14351
satisfies the classification criterion for a CEMP-r/s star. The elemental abundance distributions observed in this star
are discussed in light of the chemical abundances observed in other CEMP stars in the literature.
Key words: stars: carbon – stars: chemically peculiar – stars: late-type – stars: low-mass
1. INTRODUCTION observed in this group of stars. While the enhancement in the
s-process elements is believed to be due to mass transfer in
The object CD-27 14351 drew our attention when a low- binary systems involving an asymptotic giant branch compa-
resolution spectrum of this object acquired on 2015 October 23, nion that underwent s-process nucleosynthesis, the origin of the
during the observing run of our observational program with
( enhanced abundance of the r-process element Eu remainsHCT Himalayan Chandra Telescope, at Indian Astronomical
( ) unexplained in this scenario. In a recent work, Hampel et al.Observatory IAO , Hanle; one of the objectives of this (2016) showed that the observed abundance patterns of CEMP-
program is to search for CH stars and carbon-enhanced metal- r/s stars could be convincingly reproduced through i-process
poor stars among field stars) on visual inspection was found to (intermediate neutron-capture process), which operates at
show significant resemblance to the low-resolution spectrum of neutron densities between those of the s-process and r-process.
HD5223, a well known classical CH star. From the known Except for one object, the abundance patterns of all the stars in
stellar parameters of HD5223, (Teff=4500 K, log g=1.0, their sample could be reproduced by this process. To place
and metallicity [Fe/H]=−2.06 (Goswami et al. 2006), a first observational constraints on the nucleosynthesis of s-, r-, and i-
guess was that the object CD-2714351 could be a cool metal- process elements at low metallicity, it is necessary to conduct
poor object similar to HD5223. Dominant carbon-bearing high-resolution spectroscopic analysis of stars with an excess
molecular bands in its spectrum also indicated that the object is of heavy elements, and CEMP stars undoubtedly form
likely carbon-enhanced. For an understanding of its elemental important targets. Such studies would help provide insight
abundance pattern and its origin, a detailed chemical composi- into the possible origin of this class of objects. Our detailed
tion study was undertaken based on a high-resolution FEROS high-resolution spectroscopic analysis of CD-27 14351 is
(Fiber-fed Extended Range Optical Spectrograph, connected to prompted by such motivation.
the 1.52 m telescope in Chile) spectrum. In Section 2, we describe the source of the low-resolution
Our analysis reveals that the object is indeed a carbon- and high-resolution spectra of the program star. In Section 3,
enhanced metal-poor star that also shows significant enhance- we present our estimates of effective temperatures based on
ment of nitrogen and neutron-capture elements. The heavy available BVJHK photometry of the object. The spectral
elements abundance estimates indicate that the surface analysis procedures and estimation of the stellar atmospheric
composition of the object has significant contributions that parameters are discussed in Section 4. The elemental
originated from both the r-process as well as the s-process abundance results and discussions are presented in Section 5.
nucleosynthesis. This is supported by our estimate of the Uncertainty in elemental abundances is discussed in Section 6.
abundance ratio [Ba/Eu] (=0.12), that qualifies the object to be Conclusions are provided in Section 7.
placed in the CEMP-r/s group (Beers & Christlieb 2005, for a
definition of CEMP-r/s stars and other CEMP stars). However,
the origin of CEMP-r/s stars is still far from being clearly 2. SPECTRA OF CD-27 14351
understood. Several proposed physical scenarios are available The low-resolution spectrum of CD-27 14351 was acquired
in the literature (Qian & Wasserburg 2003; Nomoto et al. 2004; on 2015 October 23, using HFOSC attached to the 2 m HCT
Zijlstra 2004; Barbuy et al. 2005; Wanajo et al. 2006). In spite (Himalayan Chandra Telescope) at the IAO, Mt Saraswati,
of considerable effort, no single mechanism has yet been Digpa-ratsa Ri, Hanle. The spectrograph used is HFOSC
identified that could explain satisfactorily the production of (Himalayan Faint Object Spectrograph Camera). The spectrum
enhanced carbon and heavy-element abundance patterns covers the wavelength range 3800–6800Å at a resolution of
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The Astrophysical Journal, 834:61 (8pp), 2017 January 1 Karinkuzhi, Goswami, & Masseron
Table 1
Basic Data for the Program Stars
Star Name R.A.(2000) Decl.(2000) B V J H K
CD-2714351 19 53 08.00 −27 28 14.96 11.82 9.70 7.022 6.296 6.135
Table 2
Temperatures from Photometry
Star Name Teff (J–K) Teff(J–H) Teff (V–K) Teff (B–V) Spectroscopic
K K K K K
CD-2714351 4067 4026 (−2.0) 3900 (−2.0) 2635(−2.0) 4335
3989(−2.5) 3900 (−2.5) 2528(−2.5)
3938(−3.0) 3904 (−3.0) 2438(−3.0)
Note. The numbers in parenthesis indicate the metallicity values at which the temperatures are calculated.
R∼1300. The high-resolution FEROS (FEROS: the Fiber-fed
Extended Range Optical Spectrograph, connected to the 1.52 m
telescope at ESO, Chile) spectrum of CD-27 14351 used in this
study was acquired on 2000 July 14, has a resolution of
R∼48,000, and covers the wavelength range spanning
3500–9000Å. The estimated radial velocity is ∼61.1 km s−1.
The basic data for this object are listed in Table 1.
3. TEMPERATURES FROM PHOTOMETRIC DATA
We have calculated the photometric temperatures of CD-
2714351 using the temperature calibrations of Alonso et al.
(1999, 2001) for the giants. The estimated values along with
the spectroscopic temperature estimate are given in Table 2. As
can be seen in the following section, the derived spectroscopic
temperatures are higher by ≈300 K from J–K and J–H
temperatures, and ≈400 K from the V–K temperatures. This
discrepancy is probably due to the high carbon enhancement
that significantly changes the colors; due to the severe blending
from the molecular lines, B–V temperatures could be much
lower than the spectroscopic temperature estimate.
4. SPECTRAL ANALYSIS Figure 1. A comparison of the low-resolution spectrum of CD-27 14351 withthe spectrum of CH star HD5223. Some prominent features are indicated in
In Figure 1, we show a comparison of the spectrum of CD- the figure.
2714351 with the spectrum of the classical CH star HD 5223 deriving the effective temperature Teff. The initial value is
(Goswami 2005) obtained from the same observational setup. assumed to be the photometric temperatures and the finally
The spectra of these two objects distinctly show a close adopted value is obtained by an iterative process until the slope
resemblance to each other. The high-resolution FEROS of the abundance versus excitation potential of Fe I lines is
spectrum is used for determination of stellar atmospheric found to be nearly zero (Figure 2, lower panel). The
parameters and elemental abundances. The stellar parameters microturbulent velocity is fixed at this temperature by
are determined by measuring the equivalent widths of clean demanding that there be no dependence of the derived Fe I
unblended Fe I and Fe II lines. The spectrum of CD-2714351 is abundance on the equivalent widths of the corresponding lines
severely blended with contributions from carbon molecular (Figure 2, upper panel). The surface gravity is fixed at a value
bands throughout the spectrum, making it difficult to find clean that makes the abundances of iron from the Fe I and Fe II lines
unblended lines of Fe I and Fe II. Only seventeen lines of Fe I equal. The adopted stellar parameters are listed in Table 4.
and two lines of Fe II are found usable for deriving the stellar
atmospheric parameters. Lines with excitation potential in the
range 0.0–5.0 eV and equivalent width 20–160Å are selected 5. RESULTS AND DISCUSSIONS: ELEMENTAL
ABUNDANCES
for this purpose. These lines, along with the abundances
derived from each line computed using the latest version of Elemental abundances are derived from the measured
MOOG (Sneden 1973), are listed in Table 3. We have used the equivalent widths of lines due to neutral and ionized elements
Kurucz grid of model atmospheres with no convective if clean unblended lines are present. We have also performed
overshooting (http://cfaku5.cfa.harvard.edu/) and assumed a spectral-synthesis calculations to derive the elemental abun-
local thermodynamic equilibrium (LTE) condition throughout dances for a few elements considering the hyperfine splitting
the analysis. The method of excitation equilibrium is used for effects. These elemental abundances along with the abundance
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The Astrophysical Journal, 834:61 (8pp), 2017 January 1 Karinkuzhi, Goswami, & Masseron
Table 3
Lines Used for the Analysis
Wavelength Element Elow log gf Equivalent log ò Reference
(Å) (ev) Width (mÅ) (dex)
5688.220 Na I 2.104 −0.45 58.3 4.89 (1)
4571.100 Mg I 0.000 −5.69 154.1 5.88 (2)
5528.405 4.350 −0.62 61.1 5.04 (3)
5172.680 2.710 −0.40 304.7 5.92 (4)
5261.710 Ca I 2.521 −0.73 27.1 4.39 (5)
6439.070 2.530 0.47 109.6 4.42 (5)
6499.650 2.523 −0.59 65.2 4.72 (5)
4999.500 Ti I 0.830 0.25 134.0 3.33 (6)
5210.390 0.048 −0.88 120.6 3.04 (6)
5192.970 0.020 −1.01 143.1 3.38 (6)
4443.790 Ti II 1.080 −0.70 178.7 3.29 (6)
4589.950 1.236 −1.79 94.9 3.02 (6)
5226.530 1.570 −1.30 131.9 3.30 (6)
5247.570 Cr I 0.961 −1.64 29.0 2.95 (6)
5348.312 1.003 −1.29 33.0 2.72 (6)
4476.019 Fe I 2.845 −0.57 108.1 4.98 (7)
4890.755 2.876 −0.43 121.2 4.68 (8)
4924.770 2.279 −2.22 79.4 5.16 (8)
4982.524 4.103 0.14 66.9 4.99 (9)
4994.130 0.915 −3.08 149.7 5.06 (8)
5171.600 1.485 −1.79 160.5 4.69 (8)
5194.941 1.557 −2.09 148.5 4.89 (8)
5198.711 2.223 −2.14 73.1 4.85 (8)
5202.340 2.180 −1.84 122.2 5.12 (8)
5217.389 3.211 −1.10 69.2 5.07 (9)
5247.050 0.087 −4.98 83.3 4.84 (8)
5307.370 1.610 −2.98 69.4 4.74 (8)
5339.928 3.266 −0.68 68.1 4.70 (8)
5415.192 4.386 0.50 60.9 4.73 (8)
6137.694 2.588 −1.40 98.0 4.77 (8)
6136.615 2.453 −1.40 114.4 4.78 (8)
6421.350 2.278 −2.03 92.8 4.90 (8)
5234.625 Fe II 3.22 −2.05 38.5 4.97 (8)
5276.002 3.199 −1.90 40.5 4.88 (8)
4607.327a Sr I 0.000 −0.57 43.9 2.02 (10)
5289.815a Y II 1.033 −1.85 70.4 1.52 (11)
5662.925 1.944 0.16 135.5 1.74 (12)
4934.076 Ba II 0.000 −0.15 414.6 1.38 (5)
6141.713a 0.704 −0.08 287.2 1.34 (5)
6496.897 0.604 −0.38 298.0 1.47 (5)
4526.111 La II 0.772 −0.77 60.1 0.49 (13)
4921.776a 0.244 −0.68 94.6 0.09 (14)
4460.207 Ce II 0.477 0.17 146.3 1.49 (15)
4527.348 0.320 −0.46 144.3 1.79 (15)
4451.981 Nd II 0.000 −1.34 38.3 0.10 (16)
4811.342 0.063 −1.14 50.9 0.07 (16)
5212.361a 0.204 −0.87 61.5 0.04 (16)
5293.163 0.823 −0.00 71.7 0.22 (17)
6645.064a Eu II 1.380 0.20 synth −0.40 (18)
Notes.
(1) Kurucz & Peytremann (1975), (2) Laughlin & Victor (1974), (3) Lincke & Ziegenbein (1971), (4) Anderson et al. (1967), (5) Miles & Wiese (1969), (6) Martin
et al. (1988), (7) Bridges & Kornblith (1974), (8) Führ et al. (1988), (9) Kurucz (1988), (10) Corliss & Bozman (1962b), (11) Hannaford et al. (1982), (12) Cowley &
Corliss (1983), (13) Andersen et al. (1975), (14) Corliss & Bozman (1962a) adjusted, (15) McEachran & Cohen (1971), (16) Meggers et al. (1975) adjusted, (17)
Ward et al. (1985), (18) Biemont et al. (1982).
a Abundances are also derived by spectral-synthesis calculations of these lines. The results are presented in Table 5.
ratios with respect to iron are presented in Table 5. We have 5.1. Carbon, Nitrogen, Oxygen
also calculated the [ls/Fe], [hs/Fe] and [hs/ls] values, where ls Several strong molecular features of carbon are clearly
represents light s-process elements Sr and Y, and hs represents noticeable throughout the spectrum of CD-2714351. We have
heavy s-process elements Ba, La, Ce, and Nd. These estimates calculated the carbon abundance from the spectral synthesis of
are presented in Table 6. the C2 band at 5635Å (Figure 3, middle panel). The C2 band at
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The Astrophysical Journal, 834:61 (8pp), 2017 January 1 Karinkuzhi, Goswami, & Masseron
Table 6
Abundance Ratios of Light and Heavy s-process Elements
Star Name [Fe/H] [ls/Fe] [hs/Fe] [hs/ls]
CD-27 14351 −2.62 1.82 1.77 −0.05
Note.[ls/Fe] and [hs/Fe] are calculated using the abundance values obtained
from spectral-synthesis calculations, as given in Table 5.
Figure 2. The iron abundance of CD-2714351 is shown for individual Fe I
(solid circles) and Fe II (solid triangles) lines as a function of excitation
potential (lower panel) and as a function of equivalent width (upper panel).
Table 4
Derived Atmospheric Parameters of CD-2714351
Star Name Teff log g ξ [Fe I/H] [Fe II/H]
(K) (km s−1)
CD-271435 4335 0.5 2.42 −2.62 −2.57 Figure 3. Lower panel: the spectral-synthesis fits of the CH feature around
4315 Å. Middle panel: the spectral synthesis of the C2 band around 5635 Å. In
both the panels, the dotted lines indicate the synthesized spectra and the solid
Table 5 lines indicate the observed line profiles. Two alternative synthetic spectra for
Elemental Abundances in CD-2714351 [C/Fe]=+0.3 (long-dashed line) and [C/Fe]=−0.3 (short-dashed line) are
shown to demonstrate the sensitivity of the line strength to the abundances. Top
Z Solar log òa log  [X/H] [X/Fe] panel: the spectral-synthesis fits of the CN features around 8005 Å obtained
with the adopted N abundance and 12C/13C∼10.1 (dotted curve). The
C I 6 8.43 8.70±0.20 0.27 2.89 observed spectrum is shown by a solid curve. Two alternative fits with
N I 7 7.83 7.10±0.20 −0.73 1.89 12C/13C∼25 (short-dashed line) and 5 (long-dashed line) are shown to
Na I 11 6.24 4.89±0.20 −1.35 1.27 illustrate the sensitivity of the line strengths to the isotopic carbon abundance
Mg I 12 7.60 5.61±0.40 −1.99 0.63 ratios.
Ca I 20 6.34 4.51±0.18 −1.83 0.79
Ti I 22 4.95 3.25±0.18 −1.70 0.92 5165Å is found to be saturated. Carbon shows a large
Ti II 22 4.95 3.21±0.16 −1.74 0.83 enhancement with [C/Fe] value of 2.89 as estimated from the
Cr I 24 5.64 2.84±0.17 −2.80 −0.18 C molecular band at 5635Å. The abundance of carbon derived
Fe I 26 7.50 4.87±0.15 −2.63 L 2
Fe II 26 7.50 4.93±0.09 −2.57 L from the CH band at 4300Å (Figure 3, lower panel) also shows
Sr I 38 2.87 2.02±0.20 −0.85 1.77 similar value with [C/Fe]=2.88. For the line lists of CH, C2,
Sr Ib 38 2.87 1.98±0.20 −0.89 1.73 CN, and 12C13C we have consulted Masseron et al. (2014),
Y II 39 2.21 1.63±0.12 −0.58 1.99 Brooke et al. (2013), Sneden et al. (2014), and Ram et al.
Y IIb 39 2.21 1.55±0.20 −0.66 1.91 (2014). Using the estimated carbon abundance, the nitrogen
Ba II 56 2.18 1.40±0.07 −0.78 1.79
b abundance was derived from the spectral-synthesis calculationBa II 56 2.18 1.38±0.20 −0.8 1.77
La II 57 1.10 0.29±0.18 −0.81 1.76 of the CN band with the band head at 4215Å (Figure 4). The
La IIb 57 1.10 0.10±0.20 −1.00 1.57 estimated nitrogen abundance ∼7.1 dex gives [C/N]=1.0 for
Ce II 58 1.58 1.43±0.30 −0.15 2.63 this object. We could not detect any oxygen lines in the
Nd II 60 1.42 0.11±0.08 −1.31 1.26 spectrum due to severe distortion in the spectrum. We have
Nd IIb 60 1.42 −0.05±0.20 −1.47 1.10 estimated the 12C/13C ratio from the 12CN and 13CN features
Eu IIb 63 0.52 −0.40±0.20 −0.92 1.65 near 8005Å (Figure 3, top panel). We have estimated
12
Notes. C/
13C=10.1 for this object. Such a low value is not
a Asplund et al. (2009). unreasonable as the estimated log g value of CD-2714351
b Abundance estimates are from spectral-synthesis calculation. indicates that the object is an evolved red giant star in which
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The Astrophysical Journal, 834:61 (8pp), 2017 January 1 Karinkuzhi, Goswami, & Masseron
Figure 4. Spectral-synthesis fits of the CN band around 4215 Å. The best fit Figure 6. Spectral-synthesis fits of the Ba II line at 6141.71 Å and Eu II line at
obtained with a carbon abundance of 8.7 dex and 12C/13C ∼10.1 returns a 6645 Å. In both the panels, the dotted lines indicate the synthesized spectra and
nitrogen abundance of 7.1 dex (dotted lines). The solid line corresponds to the the solid lines indicate the observed line profiles. Two alternative synthetic
observed spectrum. Two alternative plots with long-dash and short-dash are spectra for [X/Fe]=+0.3 (long-dashed line) and [X/Fe]=−0.3 (short-
shown with [N/Fe]=±0.3 from the adopted value. dashed line) from the adopted value are shown to demonstrate the sensitivity of
the line strength to the abundances.
= 1.27. Since this line is free from NLTE effects (Baumueller
& Gehren 1997), we have not applied NLTE correction to the
derived abundance. A few very metal-poor stars are also known
to show such high abundances of Na (Aoki et al. 2002a, 2002b,
2007, 2008). The abundance of Al could not be estimated in
CD-2714351.
5.3. Abundances of α-elements
We have estimated [Mg/Fe]∼0.64 from three Mg I lines at
4571.1, 5172.68, and 5528.41Å. This value is slightly higher
than the general trend of [α/Fe]=0.4 noticed in metal-poor
stars. We have measured three clean Ca I lines in the spectrum
of CD-2714351. Similar to Mg, Ca also shows large
enhancement with a [Ca/Fe] value of 0.79. Ti shows
enhancement with [Ti I/Fe] and [Ti II/Fe] values of 0.92 and
0.83, respectively. Johnson (2002) has also found that Ti I and
Ti II are discrepant in metal-poor stars, likely because of NLTE
effects. These estimates show that the object is a very metal-
poor star with high abundances of α elements.
Figure 5. Spectral-synthesis fits of the Sr I line at 4607.3 Å, Y II line at 5.4. Fe-peak Elements
5289.8 Å, and Nd II line at 5212.3 Å are shown. The dotted lines indicate the Two Cr I lines at 5247.57 and 5348.31Å are used to derive
synthesized spectra and the solid lines indicate the observed line profiles. Two
alternative synthetic spectra for [X/Fe] = +0.3 (long-dashed line) and [X/Fe] the Cr abundance. Cr shows underabundance with a [Cr/Fe]
= −0.3 (short-dashed line) from the adopted value are shown to demonstrate value −0.18. We have detected many Ni lines in the spectrum
the sensitivity of the line strength to the abundances. of CD-2714351. But none of them are usable for abundance
calculation due to distortion and severe line blending.
the CN cycled materials are expected to mix together into the
atmosphere, making the 12C/13C ratio low. 5.5. Abundances of Neutron-capture Elements
Abundances of neutron-capture elements are derived by the
5.2. Sodium (Na) and Aluminum (Al)
equivalent width measurements as well as spectral-synthesis
We have derived the Na abundance from the Na I line at calculations. We have accounted for any possible blending due
5688.22Å. The estimated Na abundance is high with [Na/Fe] to other elements in the line lists of the respective lines used for
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The Astrophysical Journal, 834:61 (8pp), 2017 January 1 Karinkuzhi, Goswami, & Masseron
Table 7
Abundance Uncertainties
Star Standard dTeff δ log g dx Total
Error ±100 K ±0.1 ±0.3 km s−1 Uncertainty
CD-2714351 0.15 0.08 0.01 0.09 0.17
Eu abundance gives [Eu/Fe]∼1.65. We could not detect Eu
lines at 4129 and 6437Å.
6. UNCERTAINTY IN ELEMENTAL ABUNDANCE
We have derived the uncertainties in elemental abundance
estimates by varying the stellar atmospheric parameters Teff,
log g, and microturbulence in the model atmosphere. We have
calculated the uncertainty due to temperature by varying the
temperatures by±100 K and recalculated the Fe abundance.
Similarly, by varying the log g value by±0.1 and micro-
turbulent velocity by±0.1 km s−1, we have calculated the
corresponding uncertainties in abundances due to these
changes. These values, along with the standard error are listed
in Table 7. The total uncertainty is calculated using the
standard equation of error calculations
E = E 2 + E 2 2 2r r1 r2 + Er3 + Er4 . (1)
We have assumed this value as the minimum error in the
derived abundances.
Figure 7. This figure shows a comparison of the [C/Fe] (lower panel) and [N/ 7. CONCLUSIONS
Fe] (upper panel) values observed in CD-2714351 (shown with a star symbol A detailed chemical composition study of CD-27 14351
in both the panels) with their counterparts (solid circles) in CEMP stars from
the literature (e.g., Masseron et al. 2010). based on a high-resolution FEROS spectrum revealed many
important features of this object. The object is characterized by
a large enhancement in carbon; a similar enhancement in
nitrogen is also evident from our analysis. Such high
spectral-synthesis calculation. The derived abundances along abundances of carbon and nitrogen are also seen in other
with the error estimates are listed in Table 5. The abundance of CEMP stars (Figure 7); these two elements, however, show a
Sr is derived from the Sr I line at 4607.7Å. Sr is found to be large scatter with respect to metallicity. The a-elements Mg,
enhanced with [Sr/Fe]∼1.75. Y also shows an enhancement Ca, Ti, and Fe-peak element Cr show similar abundances to
with [Y/Fe]∼1.95. The spectrum synthesis fits are shown in those generally noticed in CEMP stars; the high abundance of
Figure 5. We could not measure any Zr lines in the spectrum of Na is also a common feature of many CEMP stars (Figure 8). A
CD-2714351. Ba abundance calculated by measuring the comparison of our estimated abundance ratios of neutron-
equivalent widths of Ba II lines at 4934, 6141, and 6496Å give capture elements with those of Allen et al. (2012), 2016
a [Ba/Fe] value of 1.79. The spectrum synthesis of the Ba II Goswami et al. (2006; 2016 Goswami & Aoki 2010), and
line at 6141.713Å (Figure 6), considering the hyperfine Masseron et al. (2010), for CEMP stars, is shown in Figure 9.
splitting contributions from McWilliam (1998), gives [Ba/ A similar comparison of the neutron-capture elements
Fe]∼1.77. We have derived La abundance from the spectrum abundance ratios observed in CD-27 14351 with their
synthesis calculation of the La II line at 4921.77Å, considering counterparts observed in CEMP-s and CEMP-r/s stars alone
hyperfine components from Jonsell et al. (2006), which gives from Jonsell et al. (2006) clearly shows that Sr, Y, and Ce are
[La/Fe]∼1.57. Cerium abundance derived from two Ce II highly enhanced, whereas Ba, La, and Eu are similarly
lines at 4460.2 and 4527.3Å indicates a large enhancement of enhanced, as can be seen in the case of CEMP-r/s stars
Ce with [Ce/Fe]∼2.63. Nd abundance calculated by the (Figure 10). Large enhancement of s-process elements along
equivalent width measurement of four Nd lines gives [Nd/ with the enhancement in Mg indicates the operation of
22Ne(α,
II
n)25Mg as the main neutron source in CEMP-r/s stars
Fe]∼1.26. We have also derived the Nd abundance by (Masseron et al. 2010). As suggested by Gallino et al. (1998)
spectral-synthesis calculation of the Nd II line at 5212.3Å and Goriely & Mowlavi (2000), neutron density associated
(Figure 5); this gives a value of 1.1 for [Nd/Fe]. We have with this reaction favors the production of the s-process
derived Eu abundance from the Eu II line at 6645.130Å by element Ce and also the r-process element Eu. Highly
considering the hyperfine components from Worley et al. enhanced abundances of these two elements observed in this
(2013). Although the right wing of this Eu line is found to be star support this idea. However, Goriely & Siess (2005) suggest
blended with the Fe I line at 6645.36Å and a Tb I line at that a −ve value of [La/Ce] indicates the operation of 13C(α,
6645.37Å, we could get a proper fit for the left wing with the n)16O reaction, and, a value of [La/Ce] within the range
adopted Eu abundance of −0.40 dex (Figure 6). The adopted 0.2–0.4 indicates the operation of 22Ne(α, n)25Mg reaction. Our
6
The Astrophysical Journal, 834:61 (8pp), 2017 January 1 Karinkuzhi, Goswami, & Masseron
Figure 8. Comparison of the observed light-element abundances of CD-2714351 (indicated by a star symbol) with their counterparts in CEMP stars available in the
literature (i.e., Goswami et al. 2006, 2016; Goswami & Aoki 2010; Masseron et al. 2010, Allen et al. 2012).
Figure 9. Comparison of the observed heavy-element abundances in CD-27 Figure 10. Comparison of the observed heavy-element abundances in CD-27
14351 (indicated by a star symbol) with their counterparts in CEMP stars 14351 (indicated by a star symbol) with values from other CEMP-r/s (solid
available in the literature (i.e., Goswami et al. 2006, 2016; Goswami & Aoki circle) and CEMP-s stars (solid triangle) from Jonsell et al. (2006).
2010; Masseron et al. 2010, Allen et al. 2012).
estimated [La/Ce]=−1.06 would, therefore, imply the placed in the CEMP-r/s group. Although the binarity among
reaction 13C(α,n)16O to be the main source of neutrons. CEMP-s stars is well known, there are a very few studies (e.g.,
Estimated [Ba/Eu](=0.12) indicates that the object can be Abate et al. 2016) focused on the orbital properties of CEMP-r/
7
The Astrophysical Journal, 834:61 (8pp), 2017 January 1 Karinkuzhi, Goswami, & Masseron
s stars. In spite of several efforts in the literature, the origin of Brooke, J. S. A., Bernath, P. F., Schmidt, T. W., & Bacskay, G. B. 2013,
CEMP-r/s stars still remains far from being clearly understood. JQSRT, 124, 11
However, in future, it would be worthwhile to investigate if the Corliss, C. H., & Bozman, W. R. 1962a, NBS Monograph 53
Corliss, C. H., & Bozman, W. R. 1962b, NBS Monograph 53. adjusted
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