An Orbit Fit to Likely Hermus Stream Stars

Abstract

We selected blue horizontal branch (BHB) stars within the expected distance range and sky position of the Hermus Stream from Data Release 10 of the Sloan Digital Sky Survey. We identify a moving group of $19$ BHB stars that are concentrated within two degrees of the Hermus Stream, between $10$ and $14$ kpc from the Sun. The concentration in velocity is inconsistent with a Gaussian distribution with 98% confidence (2.33 sigma).The stars in the moving group have line-of-sight velocities of v${}_{\mathrm{gsr}}\sim 50$ km s${}^{-1}$, a velocity dispersion of ${\sigma }_v\lesssim 11$ km s${}^{-1}$, a line-of-sight depth of $\sim 1$ kpc, and a metallicity of [Fe/H] $=-2.1\pm 0.4$. The best-fit orbit has a perigalacticon of $\sim 4$ kpc, apogalacticon of $\sim 17$ kpc, orbital period of $\sim 247$ Myr, eccentricity $e=0.62$, and inclination $i\sim 75^{\circ }$ from $b=90^{\circ }$. The BHB stars in the stream are estimated to be $12$ Gyr old. An N-body simulation of a mass-follows-light ultrafaint dwarf galaxy with mass $10^6{M}_{\odot }$ and radius $40$ pc is consistent with the observed properties. The properties of the identified moving group of 19 BHB stars are close enough to those of the Hermus Stream (which is traced predominantly in turnoff stars) that we find it likely that they are associated. If that is the case, then our orbit fit would imply that there is no relationship between the Hermus and Phoenix streams, as previously proposed.

arXiv comment18 pages, 7 figures, Published in MNRAS

References in corpus (82)

• The Sloan Digital Sky Survey: Technical Summary
• SEGUE: A Spectroscopic Survey of 240,000 stars with g=14-20
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of the Sagittarius Core and Tidal Arms
• The Tenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Apache Point Observatory Galactic Evolution Experiment
• The Field of Streams: Sagittarius and its Siblings
• The Ghost of Sagittarius and Lumps in the Halo of the Milky Way
• A Universal Mass Profile for Dwarf Spheroidal Galaxies?
• The Sagittarius Dwarf Galaxy: a Model for Evolution in a Triaxial Milky Way Halo
• Detection of massive tidal tails around the globular cluster Pal 5 with SDSS commissioning data
• Great Circle tidal streams: evidence for a nearly spherical massive dark halo around the Milky Way
• Building up the Stellar Halo of the Galaxy
• Constraining the Milky Way potential with a 6-D phase-space map of the GD-1 stellar stream
• Identification of A-colored Stars and Structure in the Halo of the Milky Way from SDSS Commissioning Data
• Discovery of an Unbound Hyper-Velocity Star in the Milky Way Halo
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: IV. Modeling the Sagittarius Tidal Tails
• Detection of a 63 Degree Cold Stellar Stream in the Sloan Digital Sky Survey
• The Milky Way stellar halo out to 40 kpc : Squashed, broken but smooth
• An Orphan in the "Field of Streams"
• The properties of Galactic globular cluster sub-systems
• Galactic Halo substructure in the Sloan Digital Sky Survey: the ancient tidal stream from the Sagittarius dwarf galaxy
• A Hierarchical O(N) Force Calculation Algorithm
• Four New Stellar Debris Streams in the Galactic Halo
• "Skinny Milky Way, Please", says Sagittarius
• Detection of a 60 Degree-Long Dwarf Galaxy Debris Stream
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: III. Constraints on the Flattening of the Galactic Halo
• Sagittarius II, Draco II and Laevens 3: three new Milky Way satellites discovered in the Pan-STARRS 1 3pi Survey
• A Very Fast and Momentum-Conserving Tree Code
• The QUEST RR Lyrae Survey: Confirmation of the Clump at 50 kpc and Other Over-Densities in the Outer Halo
• Comparing the properties of local globular cluster systems: implications for the formation of the Galactic halo
• The shape of the inner Milky Way halo from observations of the Pal 5 and GD-1 stellar streams
• The Hercules-Aquila Cloud
• The number and size of subhalo-induced gaps in stellar streams
• Detection of a 45 Degree Tidal Stream Associated with the Globular Cluster NGC 5466
• Spectroscopy of QUEST RR Lyrae Variables: the new Virgo Stellar Stream
• Constraints on the shape of the Milky Way dark matter halo from the Sagittarius stream
• Substructure in Tidal Streams; Tributaries in the Anticenter Ring
• Discovery of a New, Polar-Orbiting Debris Stream in the Milky Way Stellar Halo
• Ultra-Light Dark Matter in Ultra-Faint Dwarf Galaxies
• The Orbit of the Orphan Stream
• The Overdensity in Virgo, Sagittarius Debris, and the Asymmetric Spheroid
• A Synoptic Map of Halo Substructures from the Pan-STARRS1 3π Survey
• A box full of chocolates: The rich structure of the nearby stellar halo revealed by Gaia and RAVE
• Mapping the Galactic Halo VIII: Quantifying substructure
• Stream-orbit misalignment I: The dangers of orbit-fitting
• Stellar Streams and Clouds in the Galactic Halo
• Halo Star Streams in the Solar Neighborhood
• Galactic Archaeology. The dwarfs that survived and perished
• Star Stream Folding by Dark Galactic Sub-Halos
• The PAndAS Field of Streams: stellar structures in the Milky Way halo toward Andromeda and Triangulum
• Milky Way Mass and Potential Recovery Using Tidal Streams in a Realistic Halo
• A Cold Milky Way Stellar Stream in the Direction of Triangulum
• Discovery of a cold stellar stream in the ATLAS DR1 data
• Planet-disc evolution and the formation of Kozai-Lidov planets
• Gaps in the GD-1 Star Stream
• An Orbit Fit for the Grillmair Dionatos Cold Stellar Stream
• Serendipitous Discovery of a Thin Stellar Stream near the Galactic Bulge in the Pan-STARRS1 3Pi Survey
• Action-space clustering of tidal streams to infer the Galactic potential
• Tracing the Orphan Stream to 55 kpc with RR Lyrae Stars
• Kinematics and Chemistry of Stars Along the Sagittarius Trailing Tidal Tail and Constraints on the Milky Way Mass Distribution
• The Phoenix stream: a cold stream in the Southern hemisphere
• Triangulum II: Possibly a Very Dense Ultra-Faint Dwarf Galaxy
• Detecting the disruption of dark-matter halos with stellar streams
• The age structure of the Milky Way's halo
• Strong RR Lyrae excess in the Hercules-Aquila Cloud
• Discovery of a Stellar Overdensity in Eridanus-Phoenix in the Dark Energy Survey
• Upper Limit on the Milky Way Mass from the Orbit of the Sagittarius Dwarf Satellite
• A comprehensive view of the Virgo Stellar Stream
• The Origin of the Virgo Stellar Substructure
• Kinematic Discovery of a Stellar Stream located in Pisces
• Chronography of the Milky Way's Halo System with Field Blue Horizontal-Branch Stars
• Modeling the gravitational potential of a cosmological dark matter halo with stellar streams
• Halo Velocity Groups in the Pisces Overdensity
• Spectroscopic Confirmation of the Pisces Overdensity
• Detection of a Nearby Halo Debris Stream in the WISE and 2MASS Surveys
• Spitzer, Gaia, and the Potential of the Milky Way
• Update on the Cetus Polar Stream and its Progenitor
• Globular Clusters and Dwarf Spheroidal Galaxies
• Tails from the Orphanage
• Testing the Dark Matter Caustic Theory Against Observations in the Milky Way
• Discy dwarf disruption and the shape of the Galactic halo
• Resolved Stellar Populations as Tracers of Outskirts
• Theoretical lower limits on sizes of ultra faint dwarf galaxies from dynamical friction

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