J/A+A/637/A98 Globular cluster escapees in the Galactic halo (Hanke+, 2020)
Purveyors of fine halos.
II. Chemodynamical association of halo stars with Milky Way globular clusters.
Hanke M., Koch A., Prudil Z., Grebel E. K., Bastian U.
<Astron. Astrophys. 637, A98 (2020)>
=2020A&A...637A..98H 2020A&A...637A..98H (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Associations, stellar ; Radial velocities ;
Abundances
Keywords: stars: carbon - stars: statistics - Galaxy: formation -
globular clusters: general - Galaxy: halo -
Galaxy: kinematics and dynamics
Abstract:
A long-lasting open question in the field of Galactic archeology
refers to the size of the contribution from former globular cluster
(GC) stars to the formation of the stellar halo of the Milky Way. We
contribute to answering this important question by establishing
observational links between the present-day halo field star population
and GCs. To this end, we combined astrometric information such as
space motions and parallaxes from the second data release of the Gaia
mission (Gaia DR2) with spectroscopic radial velocities and
metallicities ([Fe/H]) from the Sloan Digital Sky Survey (SDSS-IV,
DR14) to end up with a seven-dimensional chemodynamical information
space for more than 3x105 stars. Moreover, from our previous study,
we incorporated the sample of halo giant stars with a distinct
chemical signature (strong CN bandheads) that resembles the
light-elements anomaly otherwise only seen in the second generation of
globular cluster stellar populations. Using three different tagging
techniques -- among which is the exploration of conservative integrals
of motion -- we are able to establish unique associations between 151
extratidal stars in the neighborhood of eight GCs, which coincide with
earlier findings of stellar envelopes beyond the tidal radius and even
beyond (out to several tens of tidal radii). In addition, we trace the
possible origin of about 62% of the sample of CN-strong giants to
their potential host clusters. We find a connection between several of
the involved GCs and the Gaia-Enceladus and Sequoia merger events. By
establishing kinematic and chemical connections between 17 CN-strong
stars and their surrounding fields, we identify co- moving groups of
stars at the same [Fe/H] with a possible cluster origin. Some of these
associations contain RR Lyrae variables, which allows meaningful
distance inferences to be made. From these, we find strong evidence
that four CN-strong stars and their associates are connected to the
Sagittarius stream whilst their tightly confined [Fe/H] may hint to a
birth site in M 54, the massive cluster in Sagittarius' core remnant.
Finally, by employing the counts of CN-strong and bona-fide CN-normal
giants from our novel sample, we provide tentative estimates for the
fraction of first-generation cluster stars among all stars lost to the
halo. In the immediate cluster vicinity, this value amounts to
50.0±16.7% while the associations in the halo field rather imply
80.2-5.2+4.9%. We speculate that -- if proven real by spectroscopic
follow-up -- the disparity between these numbers could indicate a
major contribution of low- mass clusters to the overall number of
stars escaped to the halo or could alternatively suggest strong mass
loss from the first generation during early cluster dissolution.
Description:
Chemodynamical associations of stars in the vicinity of globular
clusters with those very globular clusters are presented. Moreover, we
provide possible associations of Galactic halo field stars with
bona-fide second- generation (showing strong CN-bands) globular
cluster escapees in the halo.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 127 151 *Information about star-cluster associations
tablec3.dat 144 777 Information about associations among field stars
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Note on tablec1.dat: clusters are NGC 4147, NGC 5024, NGC 5053, NGC 5272,
NGC 6205, NGC 6341, NGC 7078 and NGC 7089.
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/ApJ/813/89 : Radial velocities of Milky Way inner halo stars (King+, 2015)
Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Cluster Potential host cluster
17- 35 I19 --- GaiaDR2 Gaia DR2 source ID
37- 43 F7.3 deg RAdeg Right Ascension (ICRS) at Ep=2015.5
45- 50 F6.3 deg DEdeg Declination (ICRS) at Ep=2015.5
52- 56 F5.1 [-] r Separation from cluster (in tidal radii)
58- 62 F5.2 mas Plx Trigonometric parallax
64- 67 F4.2 mas e_Plx Trigonometric parallax error
69- 72 F4.1 mas/yr pmRAcosDE Proper motion in RA, pmRA*cosDE
74- 76 F3.1 mas/yr e_pmRAcosDE Proper motion in RA error
78- 81 F4.1 mas/yr pmDE Proper motion in DE
83- 85 F3.1 mas/yr e_pmDE Proper motion in DE error
87- 92 F6.1 km/s RV Line-of-sight radial velocity
94- 97 F4.1 km/s e_RV Line-of-sight radial velocity error
99-103 F5.2 [-] [Fe/H] Metallicity
105-108 F4.2 [-] e_[Fe/H] Metallicity error
110-113 F4.2 [-] P(A/B) Association probability
115-119 F5.2 mag Gmag Gaia DR2 G-band magnitude
121-125 F5.2 mag BP-RP Gaia DR2 BP-RP color index
127 I1 [-] Note [1/2]? Special note flag (1)
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Note (1): Special notes as follows:
1 = Classified as being a CN-strong giant
2 = Identified as RR Lyrae star
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Byte-by-byte Description of file: tablec3.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- CNSid Gaia DR2 source ID of CN-strong star
21- 39 I19 --- GaiaDR2 Gaia DR2 source ID of associated star
41- 47 F7.3 deg RAdeg Right Ascension (ICRS) at Ep=2015.5
49- 55 F7.3 deg DEdeg Declination (ICRS) at Ep=2015.5
57- 60 F4.1 deg r Separation from CN-strong star
62- 66 F5.2 mas Plx Trigonometric parallax
68- 71 F4.2 mas e_Plx Trigonometric parallax error
73- 76 F4.1 mas/yr pmRAcosDE Proper motion in RA, pmRA*cosDE
78- 80 F3.1 mas/yr e_pmRAcosDE Proper motion in RA error
82- 85 F4.1 mas/yr pmDE Proper motion in Dec
87- 89 F3.1 mas/yr e_pmDE Proper motion in Dec error
91- 96 F6.1 km/s RV Line-of-sight radial velocity
98-101 F4.1 km/s e_RV Line-of-sight radial velocity error
103-107 F5.2 [-] [Fe/H] Metallicity
109-112 F4.2 [-] e_[Fe/H] Metallicity error
114-117 F4.2 [-] P(A/B) Association probability
119-123 F5.2 mag Gmag Gaia DR2 G-band magnitude
125-128 F4.2 mag BP-RP Gaia DR2 BP-RP color index
130-133 A4 [-] RRtype ? RR Lyrae type
135 I1 [-] Ref [1,5]? Reference flag (1)
137-140 F4.1 kpc d ? Distance
142-144 F3.1 kpc e_d ? Distance error
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Note (1): References as follows:
1 = Drake et al., 2013ApJ...763...32D 2013ApJ...763...32D, Cat. J/ApJ/763/32
2 = Drake et al., 2013ApJ...765..154D 2013ApJ...765..154D, Cat. J/ApJ/765/154
3 = Drake et al., 2014ApJS..213....9D 2014ApJS..213....9D, Cat. J/ApJS/213/9
4 = Abbas et al., 2014MNRAS.441.1186D 2014MNRAS.441.1186D, Cat. J/MNRAS/441/1186
5 = This study
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Acknowledgements:
Michael Hanke, mhanke(at)ari.uni-heidelberg.de
References:
Koch et al., Paper I 2019A&A...625A..75K 2019A&A...625A..75K
(End) Michael Hanke [ARI, Germany], Patricia Vannier [CDS] 10-May-2020