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 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
tablea1.dat 208 31 Atmospheric stellar parameters and details of
observations for the sample stars
tablea2.dat 181 31 Coordinates, magnitude, distance and velocity
of the stars in the sample
tablea5.dat 111 215 Lines parameters, observed equivalent widths and
abundances of stars #1, #2, #3, #4, and #21
observed with HRS
tablea6.dat 111 214 Lines parameters, observed equivalent widths and
abundances of stars #26, #5, #6, #7, and #28
observed with HRS
tablea7.dat 111 374 Lines parameters, observed equivalent widths and
abundances of stars #8, #9, #10, #11, and #12
observed with MIKE
tablea8.dat 111 283 Lines parameters, observed equivalent widths and
abundances of stars #13, #14, #15, #16, and #17
observed with MIKE
tablea9.dat 43 104 Lines parameters, observed equivalent widths and
abundances of star #18 observed with MIKE
tablea10.dat 111 312 Lines parameters, observed equivalent widths and
abundances of stars #19, #20, #21, #22, and #23
observed with UVES
tablea11.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: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I02 --- Seq [1/28] Star sequential number (1)
4- 7 I4 K Teff Spectroscopic effective temperature
9- 11 F3.1 [-] [Fe/H] Metallicity of the atmosphere model
13- 17 F5.2 [cm/s2] logg Spectroscopic surface gravity
19- 22 F4.2 km/s vturb Microturbulence velocity
24- 26 F3.1 [cm/s2] loggph Photometric surface gravity
28- 30 F3.1 [cm/s2] e_loggph rms uncertainty on loggph (2)
32- 40 A9 --- JDInt Days of the first and last exposures
42- 46 I5 s texp Total exposure time
48- 54 F7.2 km/s RVavg Average radial velocity of all exposures
56- 59 F4.2 km/s e_RVavg rms uncertainty on RVavg
61- 63 I3 --- S/N4000 ?=- Signal-to-noise ratios at ∼4000Å
65- 66 I2 --- S/N4900 Signal-to-noise ratios at ∼4900Å
68- 70 I3 --- S/N6700 Signal-to-noise ratios at ∼6700Å
72- 99 A28 --- Inst Instrument
100-107 F8.3 d JD1 Julian day for the middle of the exposure
109-115 F7.2 km/s RV1 Radial velocity of JD1 exposure
117-120 F4.2 km/s e_RV1 rms uncertainty on RV1
122-129 F8.3 d JD2 ? Julian day for the middle of the exposure
131-137 F7.2 km/s RV2 ? Radial velocity of JD2 exposure
139-142 F4.2 km/s e_RV2 ? rms uncertainty on RV2
144-151 F8.3 d JD3 ? Julian day for the middle of the exposure
153-159 F7.2 km/s RV3 ? Radial velocity of JD3 exposure
161-164 F4.2 km/s e_RV3 ? rms uncertainty on RV3
166-173 F8.3 d JD4 ? Julian day for the middle of the exposure
175-181 F7.2 km/s RV4 ? Radial velocity of JD4 exposure
183-186 F4.2 km/s e_RV4 ? rms uncertainty on RV4
188-195 F8.3 d JD5 ? Julian day for the middle of the exposure
197-203 F7.2 km/s RV5 ? Radial velocity of JD5 exposure
205-208 F4.2 km/s e_RV5 ? rms uncertainty on RV5
--------------------------------------------------------------------------------
Note (1): Sources: all stars observed with HRS and UVES, and stars #8-12 with
MIKE, were selected from the Spaghetti survey, as listed in
(Starkenburg, 2011, Ph.D. Thesis, Kapteyn Astronomical Institute,
University of Groningen); star #11 comes from the APOGEE survey;
stars from #13-18 were drawn from the Xue et al. (2014, Cat. J/ApJ/784/170)
catalog.
Note (2): The photometric logg of most HRS stars had asymmetric error bars;
the error quoted here is the larger one of the upper and lower errors.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea2.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
170-181 A12 --- File Name of the table with abundances
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea5.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: tablea6.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: tablea7.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: tablea8.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: tablea9.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: tablea10.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: tablea11.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