An Orbit Fit for the Grillmair Dionatos Cold Stellar Stream

TL;DR

This paper models the orbit of the Grillmair Dionatos stellar stream using spectroscopic data, revealing its retrograde orbit, metallicity, and velocity, but cannot determine the dark matter halo shape.

Contribution

It provides a detailed orbit fit for the Grillmair Dionatos stream using velocity and metallicity data, offering new insights into its properties and constraints on the Milky Way's dark matter halo.

Findings

Stream has a retrograde orbit with eccentricity 0.33

Metallicity of the stream is [Fe/H] = -2.1

Stream stars move at about 276 km/s at perigalacticon

Abstract

We use velocity and metallicity information from SDSS and SEGUE stellar spectroscopy to fit an orbit to the narrow $63^\circ$ stellar stream of Grillmair and Dionatos. The stars in the stream have a retrograde orbit with eccentricity $e = 0.33$ (perigalacticon of 14.4 kpc and apogalacticon of 28.7 kpc) and inclination approximately $i \sim 35^\circ$. In the region of the orbit which is detected, it has a distance of about 7 to 11 kpc from the Sun. Assuming a standard disk plus bulge and logarithmic halo potential for the Milky Way stars plus dark matter, the stream stars are moving with a large space velocity of approximately $276 \rm km s^{-1}$ at perigalacticon. Using this stream alone, we are unable to determine if the dark matter halo is oblate or prolate. The metallicity of the stream is [Fe/H] $= -2.1\pm0.1$. Observed proper motions for individual stream members above the main sequence turnoff are consistent with the derived orbit. None of the known globular clusters in the Milky Way have positions, radial velocities, and metallicities that are consistent with being the progenitor of the GD-1 stream.