Kinematics of outer halo globular clusters: M 75 and NGC 6426
Globular clusters (GCs) and their dynamic interactions with the Galactic components provide an important insight into the structure and formation of the early Milky Way. We present a kinematic study of two outer halo GCs based on a combination of VLT/FORS2, VLT/FLAMES, and Magellan/MIKE low- and hig...
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| Main Authors: | , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
22 August 2018
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| In: |
Astronomy and astrophysics
Year: 2018, Volume: 616, Pages: A74 |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/201833110 |
| Online Access: | Verlag, Volltext: http://dx.doi.org/10.1051/0004-6361/201833110
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| Author Notes: | Andreas Koch, Michael Hanke, and Nikolay Kacharov |
| Summary: | Globular clusters (GCs) and their dynamic interactions with the Galactic components provide an important insight into the structure and formation of the early Milky Way. We present a kinematic study of two outer halo GCs based on a combination of VLT/FORS2, VLT/FLAMES, and Magellan/MIKE low- and high-resolution spectroscopy of 32 and 27 member stars, respectively. Although both clusters are located at Galactocentric distances of 15 kpc, they have otherwise very different properties. M 75 is a luminous and metal-rich system at [Fe/H] = 1.2 dex, which is a value that we confirm from the calcium triplet region. This GC shows mild evidence for rotation with an amplitude of 5 km s . One of the most metal-poor GCs in the Milky Way (at [Fe II/H] = dex), NGC 6426 exhibits marginal evidence of internal rotation at the 2 km s level. Both objects have velocity dispersions that are consistent with their luminosity. Although limited by small-number statistics, the resulting limits on their ratios suggest that M 75 is a slow rotator driven by internal dynamics rather than being affected by the weak Galactic tides at its large distances. In this work, M 75 ( ) is fully consistent with the properties of other, younger halo clusters. At , NGC 6426 appears to have a remarkably ordered internal motion for its low metallicity, but the large uncertainty does not allow for an unambiguous categorization as a fast rotator. An accretion origin of M 75 cannot be excluded, based on the eccentric orbit, which we derived from the recent data release 2 of <i>Gaia<i/>, and considering its younger age. |
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| Item Description: | Gesehen am 21.02.2019 |
| Physical Description: | Online Resource |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/201833110 |