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J/A+A/608/A145      What is the Milky Way outer halo made of? (Battaglia+, 2017)

What is the Milky Way outer halo made of? High resolution spectroscopy of distant red giants. Battaglia G., North P.L., Jablonka P., Shetrone M., Minniti D., Diaz M., Starkenburg E., Savoy M. <Astron. Astrophys. 608, A145 (2017)> =2017A&A...608A.145B (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, nearby ; Stars, giant ; Abundances Keywords: stars: abundances - Galaxy: halo - Galaxy: structure - Galaxy: formation - galaxies: interactions Abstract: In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in-situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this work we focus on the outer regions of the Milky Way stellar halo, by determining chemical abundances of halo stars with large present-day Galactocentric distances, >15 kpc. The data-set we acquired consists of high resolution HET/HRS, Magellan/MIKE and VLT/UVES spectra for 28 red giant branch stars covering a wide metallicity range, -3.1<[Fe/H]←0.6. We show that the ratio of alpha-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H]>-1.5 when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples. Description: High resolution spectra have been taken of 28 red giant stars members of the Galactic outer halo. Three spectrographs were used: HRS@HET (stars #1 to #7), MIKE@Magellan (stars #8 to #18), and UVES@VLT (stars #19 to #28). Stars #21, #26, and #28 were also observed with Element abundances were determined using the equivalent width method. The tables 5 to 11 presented here contain the spectral line parameters, observed equivalent widths and corresponding abundances for all lines adopted for the abundance determination in the 28 stars of the sample. Table 5 contains this data for stars #1, #2, #3, #4, and #21 all observed with Table 6 contains the same for stars #26, #5, #6, #7, and #28 observed with HRS@HET (note that stars #21, #26, and #28 were also observed with UVES@VLT, and we display in Tables 5 and 6 their equivalent widths and abundances based on their HRS spectra for comparison purpose). Table 7 contains the same data, but for stars #8, #9, #10, #11, and #12 observed with MIKE@Magellan; Tables 8 and 9 contain the same for stars #13, #14, #15, #16, #17 and for star #18 respectively, all observed with Tables 10 and 11 contain the same data for stars #19, #20, #21, #22, #23 and for stars #24, #25, #26, #27, #28 respectively, all observed with File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 180 31 Coordinates, magnitude, distance and velocity of the stars in the sample table5.dat 111 215 Lines parameters, observed equivalent widths and abundances of stars #1, #2, #3, #4, and #21 observed with HRS table6.dat 111 214 Lines parameters, observed equivalent widths and abundances of stars #26, #5, #6, #7, and #28 observed with HRS table7.dat 111 374 Lines parameters, observed equivalent widths and abundances of stars #8, #9, #10, #11, and #12 observed with MIKE table8.dat 111 283 Lines parameters, observed equivalent widths and abundances of stars #13, #14, #15, #16, and #17 observed with MIKE table9.dat 43 104 Lines parameters, observed equivalent widths and abundances of star #18 observed with MIKE table10.dat 111 312 Lines parameters, observed equivalent widths and abundances of stars #19, #20, #21, #22, and #23 observed with UVES table11.dat 111 297 Lines parameters, observed equivalent widths and abundances of stars #24, #25, #26, #27, and #28 observed with UVES
See also: I/337 : Gaia DR1 (Gaia Collaboration, 2016) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 2 I02 --- Seq [1/28] Star sequential number 4- 11 A8 --- Name Star name 13- 31 I19 --- Source Gaia source ID 33- 45 F13.9 deg RAdeg Gaia right ascension (ICRS) at epoch 2015.0 46- 58 F13.9 deg DEdeg Gaia declination (ICRS) at epoch 2015.0 60- 72 F13.9 deg GLON Gaia Galactic longitude at epoch 2015.0 73- 85 F13.9 deg GLAT Gaia Galactic latitude at epoch 2015.0 87- 92 F6.3 mag Gmag Gaia G-band mean magnitude 94- 97 F4.1 kpc dH ? Heliocentric distance 99-102 F4.1 kpc Rgal ? Galactocentric distance 104-109 F6.1 km/s VGSR ? Galactic Standard of Rest velocity 111-118 F8.4 deg Lambda ? Longitude in a system aligned with the Sag stream 120-127 F8.4 deg B ? Latitude in a system aligned with the Sag stream 129-135 A7 --- Sub Substructure 137-168 A32 --- Com Comments 170-180 A11 --- File Name of the table with abundances
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
1- 2 A2 --- El Element designation 4 I1 --- Ion Ionization state (1: neutral, 2: once ionized) 6- 13 F8.3 0.1nm lambda Laboratory line wavelength 15- 18 F4.2 eV Chiex Excitation potential 20- 26 F7.3 --- log(gf) Statistical weight times oscillator strength 28- 32 F5.1 0.1pm EW01 ? Observed equivalent width of star #01 34- 37 F4.1 0.1pm e_EW01 ? Error on EW01 39- 43 F5.2 --- Abund01 ? log of the abundance (H abundance = 12.00) 45- 49 F5.1 0.1pm EW02 ? Observed equivalent width of star #02 51- 54 F4.1 0.1pm e_EW02 ? Error on EW02 56- 60 F5.2 --- Abund02 ? log of the abundance (H abundance = 12.00) 62- 66 F5.1 0.1pm EW03 ? Observed equivalent width of star #03 68- 71 F4.1 0.1pm e_EW03 ? Error on EW03 73- 77 F5.2 --- Abund03 ? log of the abundance (H abundance = 12.00) 79- 83 F5.1 0.1pm EW04 ? Observed equivalent width of star #04 85- 88 F4.1 0.1pm e_EW04 ? Error on EW04 90- 94 F5.2 --- Abund04 ? log of the abundance (H abundance = 12.00) 96-100 F5.1 0.1pm EW21 ? Observed equivalent width of star #21 102-105 F4.1 0.1pm e_EW21 ? Error on EW21 107-111 F5.2 --- Abund21 ? log of the abundance (H abundance = 12.00)
Byte-by-byte Description of file: table6.dat
Bytes Format Units Label Explanations
1- 2 A2 --- Element Element designation 4 I1 --- Ion Ionization state (1: neutral, 2: once ionized) 6- 13 F8.3 0.1nm lambda Laboratory line wavelength 15- 18 F4.2 eV Chiex Excitation potential 20- 26 F7.3 --- log(gf) Statistical weight times oscillator strength 28- 32 F5.1 0.1pm EW26 ? Observed equivalent width of star #26 34- 37 F4.1 0.1pm e_EW26 ? Error on EW26 39- 43 F5.2 --- Abund26 ? log of the abundance (H abundance = 12.00) 45- 49 F5.1 0.1pm EW05 ? Observed equivalent width of star #05 51- 54 F4.1 0.1pm e_EW05 ? Error on EW05 56- 60 F5.2 --- Abund05 ? log of the abundance (H abundance = 12.00) 62- 66 F5.1 0.1pm EW06 ? Observed equivalent width of star #06 68- 71 F4.1 0.1pm e_EW06 ? Error on EW06 73- 77 F5.2 --- Abund06 ? log of the abundance (H abundance = 12.00) 79- 83 F5.1 0.1pm EW07 ? Observed equivalent width of star #07 85- 88 F4.1 0.1pm e_EW07 ? Error on EW07 90- 94 F5.2 --- Abund07 ? log of the abundance (H abundance = 12.00) 96-100 F5.1 0.1pm EW28 ? Observed equivalent width of star #28 102-105 F4.1 0.1pm e_EW28 ? Error on EW28 107-111 F5.2 --- Abund28 ? log of the abundance (H abundance = 12.00)
Byte-by-byte Description of file: table7.dat
Bytes Format Units Label Explanations
1- 2 A2 --- El Element designation 4 I1 --- Ion Ionization state (1: neutral, 2: once ionized) 6- 13 F8.3 0.1nm Lambda Laboratory line wavelength 15- 18 F4.2 eV Chiex Excitation potential 20- 26 F7.3 --- log(gf) Statistical weight times oscillator strength 28- 32 F5.1 0.1pm EW08 ? Observed equivalent width of star #08 34- 37 F4.1 0.1pm e_EW08 ? Error on EW08 39- 43 F5.2 --- Abund08 ? log of the abundance (H abundance = 12.00) 45- 49 F5.1 0.1pm EW09 ? Observed equivalent width of star #09 51- 54 F4.1 0.1pm e_EW09 ? Error on EW09 56- 60 F5.2 --- Abund09 ? log of the abundance (H abundance = 12.00) 62- 66 F5.1 0.1pm EW10 ? Observed equivalent width of star #10 68- 71 F4.1 0.1pm e_EW10 ? Error on EW10 72 A1 --- l_Abund10 Limit flag on Abund10 73- 77 F5.2 --- Abund10 ? log of the abundance (H abundance = 12.00) 79- 83 F5.1 0.1pm EW11 ? Observed equivalent width of star #11 85- 88 F4.1 0.1pm e_EW11 ? Error on EW11 90- 94 F5.2 --- Abund11 ? log of the abundance (H abundance = 12.00) 96-100 F5.1 0.1pm EW12 ? Observed equivalent width of star #12 102-105 F4.1 0.1pm e_EW12 ? Error on EW12 106 A1 --- l_Abund12 Limit flag on Abund12 107-111 F5.2 --- Abund12 ? log of the abundance (H abundance = 12.00)
Byte-by-byte Description of file: table8.dat
Bytes Format Units Label Explanations
1- 2 A2 --- El Element designation 4 I1 --- Ion Ionization state (1: neutral, 2: once ionized) 6- 13 F8.3 0.1nm lambda Laboratory line wavelength 15- 18 F4.2 eV Chiex Excitation potential 20- 26 F7.3 --- log(gf) Statistical weight times oscillator strength 28- 32 F5.1 0.1pm EW13 ? Observed equivalent width of star #13 34- 37 F4.1 0.1pm e_EW13 ? Error on EW13 39- 43 F5.2 --- Abund13 ? log of the abundance (H abundance = 12.00) 45- 49 F5.1 0.1pm EW14 ? Observed equivalent width of star #14 51- 54 F4.1 0.1pm e_EW14 ? Error on EW14 56- 60 F5.2 --- Abund14 ? log of the abundance (H abundance = 12.00) 62- 66 F5.1 0.1pm EW15 ? Observed equivalent width of star #15 68- 71 F4.1 0.1pm e_EW15 ? Error on EW15 73- 77 F5.2 --- Abund15 ? log of the abundance (H abundance = 12.00) 79- 83 F5.1 0.1pm EW16 ? Observed equivalent width of star #16 85- 88 F4.1 0.1pm e_EW16 ? Error on EW16 90- 94 F5.2 --- Abund16 ? log of the abundance (H abundance = 12.00) 96-100 F5.1 0.1pm EW17 ? Observed equivalent width of star #17 102-105 F4.1 0.1pm e_EW17 ? Error on EW17 107-111 F5.2 --- Abund17 ? log of the abundance (H abundance = 12.00)
Byte-by-byte Description of file: table9.dat
Bytes Format Units Label Explanations
1- 2 A2 --- El Element designation 4 I1 --- Ion Ionization state (1: neutral, 2: once ionized) 6- 13 F8.3 0.1nm lambda Laboratory line wavelength 15- 18 F4.2 eV Chiex Excitation potential 20- 26 F7.3 --- log(gf) Statistical weight times oscillator strength 28- 32 F5.1 0.1pm EW18 Observed equivalent width of star #18 34- 37 F4.1 0.1pm e_EW18 Error on EW18 39- 43 F5.2 --- Abund18 log of the abundance (H abundance = 12.00)
Byte-by-byte Description of file: table10.dat
Bytes Format Units Label Explanations
1- 2 A2 --- El Element designation 4 I1 --- Ion Ionization state (1: neutral, 2: once ionized) 6- 13 F8.3 0.1nm lambda Laboratory line wavelength 15- 18 F4.2 eV Chiex Excitation potential 20- 26 F7.3 --- log(gf) Statistical weight times oscillator strength 28- 32 F5.1 0.1pm EW19 ? Observed equivalent width of star #19 34- 37 F4.1 0.1pm e_EW19 ? Error on EW19 39- 43 F5.2 --- Abund19 ? log of the abundance (H abundance = 12.00) 45- 49 F5.1 0.1pm EW20 ? Observed equivalent width of star #20 51- 54 F4.1 0.1pm e_EW20 ? Error on EW20 56- 60 F5.2 --- Abund20 ? log of the abundance (H abundance = 12.00) 62- 66 F5.1 0.1pm EW21 ? Observed equivalent width of star #21 68- 71 F4.1 0.1pm e_EW21 ? Error on EW21 73- 77 F5.2 --- Abund21 ? log of the abundance (H abundance = 12.00) 79- 83 F5.1 0.1pm EW22 ? Observed equivalent width of star #22 85- 88 F4.1 0.1pm e_EW22 ? Error on EW22 90- 94 F5.2 --- Abund22 ? log of the abundance (H abundance = 12.00) 96-100 F5.1 0.1pm EW23 ? Observed equivalent width of star #23 102-105 F4.1 0.1pm e_EW23 ? Error on EW23 106 A1 --- l_Abund23 Limit flag on Abund23 107-111 F5.2 --- Abund23 ? log of the abundance (H abundance = 12.00)
Byte-by-byte Description of file: table11.dat
Bytes Format Units Label Explanations
1- 2 A2 --- El Element designation 4 I1 --- Ion Ionization state (1: neutral, 2: once ionized) 6- 13 F8.3 0.1nm lambda Laboratory line wavelength 15- 18 F4.2 eV Chiex Excitation potential 20- 26 F7.3 --- log(gf) Statistical weight times oscillator strength 28- 32 F5.1 0.1pm EW24 ? Observed equivalent width of star #24 34- 37 F4.1 0.1pm e_EW24 ? Error on EW24 39- 43 F5.2 --- Abund24 ? log of the abundance (H abundance = 12.00) 45- 49 F5.1 0.1pm EW25 ? Observed equivalent width of star #25 51- 54 F4.1 0.1pm e_EW25 ? Error on EW25 56- 60 F5.2 --- Abund25 ? log of the abundance (H abundance = 12.00) 62- 66 F5.1 0.1pm EW26 ? Observed equivalent width of star #26 68- 71 F4.1 0.1pm e_EW26 ? Error on EW26 73- 77 F5.2 --- Abund26 ? log of the abundance (H abundance = 12.00) 79- 83 F5.1 0.1pm EW27 ? Observed equivalent width of star #27 85- 88 F4.1 0.1pm e_EW27 ? Error on EW27 90- 94 F5.2 --- Abund27 ? log of the abundance (H abundance = 12.00) 96-100 F5.1 0.1pm EW28 ? Observed equivalent width of star #28 102-105 F4.1 0.1pm e_EW28 ? Error on EW28 107-111 F5.2 --- Abund28 ? log of the abundance (H abundance = 12.00)
Acknowledgements: Giuseppina Battaglia, gbattaglia(at)iac.es
(End) Giuseppina Battaglia [IAC, Spain], Patricia Vannier [CDS] 17-Oct-2017
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