J/A+A/649/A49 Spectroscopic study of CEMP-(s and r/s) stars (Goswami+, 2021)
Spectroscopic study of CEMP-(s & r/s) stars. Revisiting classification criteria
and formation scenarios, highlighting i-process nucleosynthesis.
Goswami P.P., Rathour S.R., Goswami A.
<Astron. Astrophys. 649, A49 (2021)>
=2021A&A...649A..49G 2021A&A...649A..49G (SIMBAD/NED BibCode)
ADC_Keywords: Stars, carbon ; Stars, metal-deficient ; Abundances ;
Equivalent widths ; Spectroscopy
Keywords: stars: abundances - stars: carbon - stars: late-type
Abstract:
The origin of the enhanced abundances of both s- and r-process
elements observed in a subclass of Carbon-Enhanced Metal-Poor (CEMP)
stars, i.e., CEMP-r/s stars, still remains poorly understood. The
i-process nucleosynthesis has been suggested as one of the most
promising mechanisms for the origin of these stars.
To better understand the chemical signatures and formation
mechanism(s) of five previously claimed potential CH star candidates
HE 0017+0055, HE 2144-1832, HE 2339-0837, HD 145777 and CD-27 14351
through a detailed systematic follow-up spectroscopic study based on
high-resolution spectra.
The stellar atmospheric parameters, the effective temperature Teff,
the microturbulent velocity ζ, the surface gravity logg, and the
metallicity [Fe/H] are derived from local thermodynamic equilibrium
analyses using model atmospheres. Elemental abundances of C, N,
α-elements, iron-peak elements and several neutron-capture
elements are estimated using the equivalent width measurement
technique as well as spectrum synthesis calculations in some cases.
In the context of the double enhancement observed in four of the
programme stars, we have critically examined if the literature
i-process model yields ([X/Fe]) of heavy elements can explain the
observed abundance distribution. The estimated metallicity [Fe/H] of
the programme stars ranges from -1.63 to -2.74. All the five stars
show enhanced abundance for Ba and four of them exhibit enhanced
abundance for Eu. Based on our analysis, HE 0017+0055, HE 2144-1832
and HE 2339-0837 are found to be CEMP-r/s stars, whereas HD 145777 and
CD-27 14351 show characteristic properties of CEMP-s stars. From a
detailed analysis of different classifiers of CEMP stars, we have
identified the one which best describes the CEMP-s and CEMP-r/s stars.
We found that for both CEMP-s and CEMP-r/s stars, [Ba/Eu] and [La/Eu]
exhibit positive values and [Ba/Fe]≥1.0. However, CEMP-r/s stars
satisfy [Eu/Fe]≥1.0, 0.0≤[Ba/Eu]≤1.0 and/or 0.0≤[La/Eu]≤0.7.
CEMP-s stars normally show [Eu/Fe]<1.0 with [Ba/Eu]>0.0 and/or
[La/Eu]>0.5. If [Eu/Fe]~≥1.0, then the condition on [Ba/Eu] and/or
[La/Eu] for a star to be a CEMP-s star is [Ba/Eu]>1.0 and/or
[La/Eu]>0.7. Using a large sample of similar stars from the literature
we have examined if [hs/ls] alone can be used as a classifier, and if
there are any limiting values for [hs/ls] ratio that can be used to
distinguish CEMP-s and CEMP-r/s stars. In spite of peaking at
different values of [hs/ls], CEMP-s and CEMP-r/s stars show an overlap
in the range 0.0<[hs/ls]<1.5 ,and hence, this ratio cannot be used to
distinguish CEMP-s and CEMP-r/s stars. We have noticed a similar
overlap in the case of [Sr/Ba] ratio as well, in the range
-1.6<[Sr/Ba]←0.5 and hence, this ratio also cannot be used to
separate the two subclasses, CEMP-s and CEMP-r/s.
Description:
In this paper, we have carried out a detailed spectroscopic analysis
of HE 0017+0055, HE 2144-1832, HE 2339-0837, HD 145777 and CD-27
14351. In the Table 4 and Table 6, we have presented the measured
equivalent widths and abundances corresponding to several absorption
lines of Fe (I & II) and different species of light and heavy elements
respectively for each star. The atomic line information such as
excitation potential and log gf values are adopted from different
literature sources. References are given in the last column of each
Table.
Objects:
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RA (2000) DE Designation(s)
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16 13 13.87 -15 12 01.2 HD 145777 = BD-14 4371
19 53 08.00 -27 28 15.0 CD -27 14351 = HIP 97850
00 20 21.60 +01 12 06.8 HE 0017+0055 = TYC 3-708-1
21 46 54.66 -18 18 15.6 HE 2144-1832 = TYC 6367-819-1
23 41 59.93 -08 21 18.6 HE 2339-0837 = 2MASS J23415993-0821186
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table4.dat 83 60 Equivalent widths and atomic data information of
Fe I and Fe II lines used for deriving atmospheric
table6.dat 85 104 Equivalent widths and atomic data information of
different species of light and heavy elements of
the programme stars
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See also:
J/ApJ/788/180 : Very metal-poor stars in Milky Way's halo (Carollo+, 2014)
J/A+A/579/A28 : Abundances of 3 CEMP stars (Bonifacio+, 2015)
J/ApJ/812/109 : Bright CEMP-s stars HST & Keck spectroscopy (Placco+, 2015)
J/A+A/574/A129 : The First CEMP star in Sculptor dSph (Skuladottir+, 2015)
J/A+A/581/A22 : 67 CEMP-s stars model analysis (Abate+, 2015)
J/ApJ/814/121 : CASH project. III. The CEMP star HE0414-0343 (Hollek+, 2015)
J/ApJ/833/20 : Carbon-enhanced metal-poor star abundances (Yoon+, 2016)
J/A+A/586/A158 : Binary properties of CH and CEMP stars (Jorissen+, 2016)
J/A+A/606/A112 : Abundance analysis of ALW Carina 8 (Susmitha+, 2017)
J/A+A/606/A55 : Rotational mixing in CEMP-s stars (Matrozis+, 2017)
J/ApJS/228/19 : Exploring the SDSS dataset. EMP & CV stars (Carbon+, 2017)
J/ApJ/875/89 : Metal-poor stars with APF. LAMOST CEMP stars (Mardini+ 2019)
J/MNRAS/483/3196 : GALAH carbon-enhanced stars & CEMP candidates (Cotar+, 2019)
J/A+A/621/A108 : RV compilation for 45 CEMP-no stars (Arentsen+ 2019)
J/A+A/623/A128 : Galactic halo CEMP stars abund. & kinematics (Hansen+, 2019)
J/A+A/641/A135 : Sgr dSph CEMP-r/s star abundance analysis (Sbordone+, 2020)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 8 F8.3 0.1nm Lambda Wavelength (Å)
10- 11 A2 --- El [Fe] Element
13- 14 A2 --- Ion Ionised state
16- 19 F4.2 eV Elow Lower excitation potential
21- 26 F6.3 [-] loggf Oscillator strength
28- 32 F5.1 0.1pm EW1 ?=- Equivalent widths for HD 145777
34- 37 F4.2 --- Abund1 ?=- Abundance for HD 145777
39- 43 F5.1 0.1pm EW2 ?=- Equivalent widths for CD-27 14351
45- 48 F4.2 --- Abund2 ?=- Abundance for CD-27 14351
50- 54 F5.1 0.1pm EW3 ?=- Equivalent widths for HE 0017+0055
56- 59 F4.2 --- Abund3 ?=- Abundance for HE 0017+0055
61- 65 F5.1 0.1pm EW4 ?=- Equivalent widths for HE 2144-1832
67- 70 F4.2 --- Abund4 ?=- Abundance for HE 2144-1832
72- 76 F5.1 0.1pm EW5 ?=- Equivalent widths for HE 2339-0837
78- 81 F4.2 --- Abund5 ?=- Abundance for HE 2339-0837
83 I1 --- Ref [1/2] References (1)
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Note (1): References as follows:
1 = Fuhr J. R., Martin G. A., Wiese W. L., 1988, Journal of Physical and
Chemical Reference Data, 17, Cat. VI/72
2 = Bridges J. M., Kornblith R. L., 1974ApJ...192..793B 1974ApJ...192..793B
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 0.1nm Lambda Wavelength (Å)
10- 11 A2 --- El Elements
13- 14 A2 --- Ion Ionised state
16- 19 F4.2 eV Elow Lower Excitation Potential
21- 26 F6.3 [-] loggf Oscillator strength
28- 32 F5.1 0.1pm EW1 ?=- Equivalent widths for HD 145777
34- 37 F4.2 --- Abund1 ? Abundance for HD 145777
39- 43 F5.1 0.1pm EW2 ?=- Equivalent widths for CD-27 14351
45- 49 F5.2 --- Abund2 ? Abundance for CD-27 14351
51- 55 F5.1 0.1pm EW3 ?=- Equivalent widths for HE 0017+0055
57- 60 F4.2 --- Abund3 ? Abundance for HE 0017+0055
62- 66 F5.1 0.1pm EW4 ?=- Equivalent widths for HE 2144-1832
68- 71 F4.2 --- Abund4 ? Abundance for HE 2144-1832
73- 77 F5.1 0.1pm EW5 ?=- Equivalent widths for HE 2339-0837
79- 82 F4.2 --- Abund5 ? Abundance for HE 2339-0837
84- 85 I2 --- Ref [1/18] References (1)
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Note (1): Notes as follow:
1 = Kurucz R. L., Peytremann E., 1975, SAO Special Report
2 = Laughlin C., Victor G. A., 1974, ApJ, 192, 551
3 = Lincke R., Ziegenbein B., 1971, Zeitschrift fur Physik, 241, 369
4 = NBS in kurucz database
5 = K88 in kurucz database
6 = MFW in kurucz database
7 = Smith P. L., Kuehne M., 1978, Proceedings of the Royal Society of
London Series A, 362, 263
8 = Fuhr J. R., Martin G. A., Wiese W. L., 1988, Journal of Physical and
Chemical Reference Data, 17, Cat. VI/72
9 = Laurent J., Weniger S., 1970, J. Quant. Spectrosc. Radiative
Transfer, 10, 315
10 = Heise H., 1974A&A....34..275H 1974A&A....34..275H
11 = Warner B., 1968, MNRAS, 140, 53
12 = Hannaford P., Lowe R. M., Grevesse N., Biemont E., Whaling W.,
1982ApJ...261..736H 1982ApJ...261..736H
13 = Cowley C. R., Corliss C. H., 1983MNRAS.203..651C 1983MNRAS.203..651C
14 = Biemont E., Grevesse N., Hannaford P., Lowe R. M.,
1981ApJ...248..867B 1981ApJ...248..867B
15 = CB in kurucz database
16 = Saffman L., Whaling W., 1979, J. Quant. Spectrosc. Radiative
Transfer, 21, 93
17 = MC in kurucz database
18 = Ward L., Vogel O., Arnesen A., Hallin R., Wannstrom A.,
1985, Phys. Scr., 31, 161
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Acknowledgements:
Partha Goswami, partha.pg(at)iiap.res.in
Funding from DST SERB project No. EMR/2016/005283 is
gratefully acknowledged. RSR thank IISER-Pune and IIA-Bangalore for
providing the platform to do the research work and DST for INSPIRE
scholarship support during the project.
(End) Patricia Vannier [CDS] 15-Dec-2020