GD-1: the relic of an old metal-poor globular cluster

Abstract

Combining data from Gaia DR2, SDSS DR14 and LAMOST DR6, we update the fit to model of the properties of the stellar stream GD-1 and find that it has an age of $\sim 13$ Gyr, [Fe/H] of $-2.2\pm 0.12$, and a distance from the sun of $\sim 8$ kpc. We tabulate 6D phase-space fiducial points along the GD-1 stream orbit over a 90$^\circ$ arc. The fitted orbit shows that the stream has an eccentricity $e \sim 0.3$, perigalacticon of 14.2 kpc, apogalacticon of 27.0 kpc and inclination $i \sim 40^{\circ}$. There is evidence along the arc for 4 candidate stellar overdensities, one candidate gap, two candidate stellar underdensities and is cut off at $\phi_1 \sim 2^{\circ}$ (in the stream-aligned $(\phi_1,\phi_2)$ coordinate system of \citet{kop10}). The spur originating at $\phi_1 \sim -40^{\circ}$ implies stars were pulled away from the stream trace by an encounter (potentially a dark matter subhalo). The narrowest place ( FWHM $\sim 44.6$ pc) of the GD-1 trace is at $(\phi_1, \phi_2^c) \sim (-14^{\circ}, 0.15^{\circ})$, which is $\sim (178.18^{\circ}, 52.19^{\circ})$ in (R. A., Decl.), where the progenitor is possibly located. We also find six BHB and 10 BS spectroscopic stars in the GD-1 stream.