The Hercules stream as seen by APOGEE-2 South

Abstract

The Hercules stream is a group of co-moving stars in the Solar neighbourhood, which can potentially be explained as a signature of either the outer Lindblad resonance (OLR) of a fast Galactic bar or the corotation resonance of a slower bar. In either case, the feature should be present over a large area of the disc. With the recent commissioning of the APOGEE-2 Southern spectrograph we can search for the Hercules stream at $(l,b)=(270^{\circ },0)$, a direction in which the Hercules stream, if caused by the bar's OLR, would be strong enough to be detected using only the line-of-sight velocities. We clearly detect a narrow, Hercules-like feature in the data that can be traced from the solar neighbourhood to a distance of about 4 kpc. The detected feature matches well the line-of-sight velocity distribution from the fast-bar (OLR) model. Confronting the data with a model where the Hercules stream is caused by the corotation resonance of a slower bar leads to a poorer match, as the corotation model does not predict clearly separated modes, possibly because the slow-bar model is too hot.

7 pages, 5 figures; Submitted to MNRAS 8th September 2017, accepted October 23rd

References in corpus (19)

• The Gaia mission
• The 2.5 m Telescope of the Sloan Digital Sky Survey
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• galpy: A Python Library for Galactic Dynamics
• The Radial Velocity Experiment (RAVE): first data release
• The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• The Structure of the Milky Way's Bar Outside the Bulge
• NMAGIC: Fast Parallel Implementation of a Chi-Squared-Made-to-Measure Algorithm for Modelling Observational Data
• Disentangling the Hercules stream
• New Constraints on the Galactic Bar
• The long Galactic bar as seen by UKIDSS Galactic Plane Survey
• The power spectrum of the Milky Way: Velocity fluctuations in the Galactic disk
• Tracing the Hercules stream with Gaia and LAMOST: new evidence for a fast bar in the Milky Way
• A Unified tool to estimate Distances, Ages and Masses (UniDAM) from spectrophotometric data
• The velocity distribution of nearby stars from Hipparcos data I. The significance of the moving groups
• Staying away from the bar: the local dynamical signature of slow and fast bars in the Milky Way
• Tracing the Hercules stream around the Galaxy
• A resonant feature near the Perseus arm revealed by red clump stars

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