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 ${\varphi }_1\sim 2^{\circ }$ (in the stream-aligned $({\varphi }_1,{\varphi }_2)$ coordinate system of \citet{kop10}). The spur originating at ${\varphi }_1\sim -40^{\circ }$ 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 $({\varphi }_1,{\varphi }_2^c)\sim (-14^{\circ },0.15^{\circ })$, 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.

21 pages, 16 figures, 8 tables