Journal
ASTRONOMICAL JOURNAL
Volume 156, Issue 6, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/1538-3881/aaee6d
Keywords
Galaxy: halo; globular clusters: general; stars: variables: Cepheids
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Funding
- Kennilworth Fund of the New York Community Trust
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In a step toward understanding the origin of the Galactic Halo, we have reexamined Type II Cepheids (T2C) in the field with new input from the second data release (DR2) of Gaia. For 45 T2C with periods from 1 to 20 days, parallaxes, proper motions, and [Fe/H] values are available for 25 stars. Only five show [Fe/H] < -1.5, while the remaining stars show thick disk kinematics and [Fe/H] > -0.90. We have compared the T2C stars of the field with their cousins in the globular clusters of the Halo and found that the globular clusters with T2C stars show metallicities and kinematics of a pure Halo population. The globular cluster may have formed during the overall collapse of the Galaxy, while the individual thick disk T2C stars may have been captured from small systems that self-enriched prior to capture. The relationship of these two populations to the microgalaxies currently recognized as surrounding the Galaxy is unclear.
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