Radial velocities of RR Lyrae stars in and around NGC 6441

• Verfasst von: Kunder, Andrea [VerfasserIn]
• Verfasst von: Koch-Hansen, Andreas [VerfasserIn]
• Titel: Radial velocities of RR Lyrae stars in and around NGC 6441
• Verf.angabe: Andrea Kunder, Arthur Mills, Joseph Edgecomb, Mathew Thomas, Levi Schilter, Craig Boyle, Stephen Parker, Gordon Bellevue, R. Michael Rich, Andreas Koch, Christian I. Johnson, and David M. Nataf
• E-Jahr: 2018
• Jahr: 2018 March 28
• Umfang: 9 S.
• Fussnoten: Gesehen am 15.03.2019
• Titel Quelle: Enthalten in: The astronomical journal
• Ort Quelle: London : Institute of Physics Publ., 1998
• Jahr Quelle: 2018
• Band/Heft Quelle: 155(2018,4) Artikel-Nummer 171, 9 Seiten
• ISSN Quelle: 1538-3881
• DOI: doi:10.3847/1538-3881/aab42d
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1590333772

Abstract

Detailed elemental abundance patterns of metal-poor ([Fe/H] ∼ −1 dex) stars in the Galactic bulge indicate that a number of them are consistent with globular cluster (GC) stars and may be former members of dissolved GCs. This would indicate that a few per cent of the Galactic bulge was built up from destruction and/or evaporation of GCs. Here, an attempt is made to identify such presumptive stripped stars originating from the massive, inner Galaxy GC NGC 6441 using its rich RR Lyrae variable star (RRL) population. We present radial velocities of 40 RRLs centered on the GC NGC 6441. All 13 of the RRLs observed within the cluster tidal radius have velocities consistent with cluster membership, with an average radial velocity of 24 ± 5 km s−1 and a star-to-star scatter of 11 km s−1. This includes two new RRLs that were previously not associated with the cluster. Eight RRLs with radial velocities consistent with cluster membership but up to three time the distance from the tidal radius are also reported. These potential extra-tidal RRLs also have exceptionally long periods, which is a curious characteristic of the NGC 6441 RRL population that hosts RRLs with periods longer than seen anywhere else in the Milky Way. As expected of stripped cluster stars, most are inline with the cluster’s orbit. Therefore, either the tidal radius of NGC 6441 is underestimated and/or we are seeing dissolving cluster stars stemming from NGC 6441 that are building up the old spheroidal bulge.