J/other/Nat/601.45 C-19 stream members (Martin+, 2022)
A stellar stream remnant of a globular cluster below the metallicity floor.
Martin N.F., Venn K.A., Aguado D.S., Starkenburg E.,
Gonzalez Hernandez J.I., Ibata R.A., Bonifacio P., Caffau E., Sestito F.,
Arentsen A., Allende Prieto C., Carlberg R.G., Fabbro S., Fouesneau M.,
Hill V., Jablonka P., Kordopatis G., Lardo C., Malhan K., Mashonkina L.I.,
McConnachie A.W., Navarro J.F., Sanchez-Janssen R., Thomas G.F., Yuan Z.,
Mucciarelli A.
<Nature, 601, 45-48 (2022)>
=2022Natur.601...45M 2022Natur.601...45M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, metal-deficient ; Spectroscopy ; Abundances ;
Equivalent widths
Abstract:
Stellar ejecta gradually enrich the gas out of which subsequent stars
form, making the least chemically enriched stellar systems direct
fossils of structures formed in the early Universe. Although a few
hundred stars with metal content below 1000th of the solar iron
content are known in the Galaxy, none of them inhabit globular
clusters, some of the oldest known stellar structures. These show
metal content of at least approximately 0.2% of the solar metallicity
([Fe/H]≳2.7). This metallicity floor appears universal, and it has
been proposed that protogalaxies that merged into the galaxies we
observe today were simply not massive enough to form clusters that
survived to the present day. Here we report observations of a stellar
stream, C-19, whose metallicity is less than 0.05% of the solar
metallicity ([Fe/H]=-3.38±0.06(statistical)±0.20(systematic)). The
low metallicity dispersion and the chemical abundances of the C-19
stars show that this stream is the tidal remnant of the most
metal-poor globular cluster ever discovered, and is significantly
below the purported metallicity floor: clusters with significantly
lower metallicities than observed today existed in the past and
contributed their stars to the Milky Way halo.
Description:
We performed spectroscopic observations of eight member stars with two
telescopes and two spectrographs (Gemini and the Gemini Remote Access
to CFHT ESPaDOnS Spectrograph (GRACES), and Gran Telescopio Canarias
(GTC) and the Optical System for Imaging and
low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS)) to
determine the nature of the C-19 progenitor and refine the orbit of
the stream.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 130 56 List of potential C-19 member from the
STREAMFINDER sample
table2.dat 125 11 Summary of observations for the
C-19 candidate stars
table3.dat 59 16 Spectroscopic parameters and 1DLTE chemical
abundances for the Gemini/GRACES spectra
table4.dat 52 54 Spectral lines and atomic data used for the
chemical abundances for the Gemini/GRACES
spectra
table5.dat 86 12 Stellar parameters and abundances of C-19 stars
observed with GTC/OSIRIS
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR2 Gaia DR2 ID
21- 31 F11.7 deg RAdeg Right ascension (ICRS) at Ep=2015.5
33- 42 F10.7 deg DEdeg Declination (ICRS) at Ep=2015.5
44- 49 F6.3 mag G0mag Deredenned G magnitude
51- 55 F5.3 mag e_G0mag Error on G magnitude
57- 61 F5.3 mag (BP-RP)0 Deredenned BP-RP colour index
63- 67 F5.3 mag e_(BP-RP)0 Error on BP-RP
69- 74 F6.3 arcsec Plx Parallax
76- 80 F5.3 arcsec e_Plx Parallax error
82- 86 F5.3 mas/yr pmRA* Proper motion along RA, pmRA*cosDE
88- 92 F5.3 mas/yr e_pmRA* Error on pmRA*
94- 99 F6.3 mas/yr pmDE Proper motion along DE
101-105 F5.3 mas/yr e_pmDE Error on pmDE
107-111 F5.2 [-] [Fe/H] ?=- Pristime metallicity (1)
113-130 A18 --- Note Note (2)
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Note (1): When available the photometric metallicities from the Pristine survey
are provided in this column. We note that, by construction, the Pristine
photometric metallicities do not go below [Fe/H]Pristine=-4.0 and that the
lessened sensitivity of the Pristine narrow-band in this regime means that,
although stars can be flagged quite successfully to have [Fe/H]←3:0,
the actual photometric metallicity value is less accurate in this regime
than for stars with [Fe/H]>-3:0.
Note (2): Notes:
HB: candidate horizontal branch star
non-member: considered a non-member based on the Pristine metallicity
([Fe/H]Pristine>-2:5) and not used in the analysis.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 21 A21 --- Name Name (Pristine LLL.ll+BB.bb)
23- 30 F8.4 deg RAdeg Right ascension (J2000)
32- 39 F8.4 deg DEdeg Declination (J2000)
41- 45 F5.2 mag Gmag G magnitude
47- 51 F5.2 [-] [Fe/H] Pristine metallicity
53- 58 A6 s Texp Exposure time
60- 62 I3 --- S/N Signal to noise at 600nm (Gemini/GRACES)
and 420nm (GTC/OSIRIS)
64- 69 F6.1 km/s RV Radial velocity
71- 74 F4.1 km/s e_RV ? Radial velocity error
76- 88 A13 --- Obs Observatory
90-125 A36 --- Com Comment
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Param Parameter
16 A1 --- l_P1 Limit flag on P1
18- 24 F7.2 --- P1 Value of Param for Pristine 354.77+30.25
26- 31 F6.2 --- e_P1 ? Error of Value of Param for
Pristine 354.77+30.25 (1)
33- 39 F7.2 --- P2 Value of Param for Pristine 355.13+27.98
40- 45 F6.2 --- e_P2 Error of Value of Param for
Pristine 355.13+27.98 (1)
46 A1 --- l_P3 Limit flag on P3
47- 53 F7.2 --- P3 Value of Param for Pristine 355.27+27.74
54- 59 F6.2 --- e_P3 ? Error of value of Param for
Pristine 355.27+27.74 (1)
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Note (1): The uncertainties of FeI measurements correspond to the line to
line scatter in the FeI abundances only, whereas uncertainties on [FeII/H]
and [X/Fe] combine the measurement uncertainties (where σ/SQRT(N))
and the uncertainties due to the stellar parameters, added in quadrature.
NLTE corrections are listed in Table 4; the averaged NLTE corrections are
applied here, other than Na I for which individual line calculations per
star were applied. We adopt the metallicities for these stars from [FeII/H].
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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
10- 13 A4 --- El Element
15- 18 F4.2 eV xi Energy
20- 24 F5.2 [-] loggf Oscillator strength
26- 28 I3 0.1pm EW1 ? Equivalent width for Pristine 355.1+27.9
29 A1 --- n_EW1 Note on EW1 (1)
30 A1 --- l_EW2 Limit flag on EW2
31- 33 I3 0.1pm EW2 ? Equivalent width for Pristine 354.7+30.2
34 A1 --- n_EW2 Note on EW2 (1)
36 A1 --- l_EW3 Limit flag on EW2
37- 39 I3 0.1pm EW3 ? Equivalent width for Pristine 355.2+27.7
40 A1 --- n_EW3 Note on EW3 (1)
42- 46 F5.2 0.1pm NLTEcorra ?=- NLTE correction estimates from the INSPECT
(http://www.inspect-stars.com) and/or MPIA
database (http://nlte.mpia.de) (2)
48- 52 F5.2 0.1pm NLTEcorrb ?=- NLTE corrections from the private
calculations of coauthor L. Mashonkina
(http://www.inasan.rssi.ru/~lima/pristine).
Only the NaI NLTE corrections show some star
to star variations due to the differences in
the line strengths (the average from the
three stars is reported here) (2)
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Note (1): Note that when lines could not be measured in all three stars,
they are noted as follows:
n = noisy
w = weak
b = blended
Note (2): As these three stars have very similar stellar parameters, a single
NLTE abundance correction estimate is shown per line from three sources
(where NLTE=log(X/H)NLTE-log(X/H)LTE).
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1 A1 --- Code [PW] Code (1)
3- 23 A21 --- Name Name (Pristine LLL.ll+BB.bb)
25- 28 I4 K Teff Effective temperature
30- 32 I3 K e_Teff Effective temperature error
34- 37 F4.2 [cm/s2] logg Surface gravity
38 A1 --- n_logg [lu] Note pn logg (2)
39- 42 F4.2 [cm/s2] e_logg ? Surface gravity error
44- 48 F5.2 [-] [M/H] Abundance [M/H]
50- 53 F4.2 [-] e_[M/H] Abundance [M/H]
55- 59 F5.2 [-] [Ca/H] ? Abundance [Ca/H]
61- 64 F4.2 [-] e_[Ca/H] ? Abundance [Ca/H] error
66- 70 F5.2 [-] [Fe/H] ? Abundance [Fe/H]
72- 75 F4.2 [-] e_[Fe/H] ? Abundance [FeM/H] error
77- 81 F5.2 [-] [C/Fe] ? Abundance [C/Fe]
83- 86 F4.2 [-] e_[C/Fe] ? Abundance [C/Fe] error
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Note (1): Code as follows:
W = With stellar parameters based on Gaia photometry (used in the paper)
P = Pure spectroscopic stellar parameters
Note (2): Note as follows:
l = lower limit for cases where FERRE reached the limit of the
spectral model grid
u = upper limit for cases where FERRE reached the limit of the
spectral model grid
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 20-Jun-2023