Sesar, BranimirBovy, JoBernard, Edouard J.Caldwell, NelsonCohen, Judith G.Fouesneau, MorganJohnson, Christian I.Ness, MelissaFerguson, Annette M. N.Martin, Nicolas F.Price-Whelan, Adrian M.Rix, Hans-WalterSchlafly, Edward F.Burgett, William S.Chambers, Kenneth C.Flewelling, HeatherHodapp, Klaus W.Kaiser, NickMagnier, Eugene A.Platais, ImantsTonry, John L.Waters, ChristopherWyse, Rosemary F. G.2025-06-022025-06-020004-637XRIS:urn:DD06F4C89EFEAE9DE9D1C1A2EDBAAB3AORCID:/0000-0001-5082-6693/work/163624309https://hdl.handle.net/1885/733756387The Ophiuchus stream is a recently discovered stellar tidal stream in the Milky Way. We present high-quality spectroscopic data for 14 stream member stars obtained using the Keck and MMT telescopes. We confirm the stream as a fast moving (vlos ∼ 290 km s-1), kinematically cold group ({σ }{v{los}}≲ 1 km s-1) of α-enhanced and metal-poor stars ([α/Fe] ∼ 0.4 dex, [Fe/H] ∼ -2.0 dex). Using a probabilistic technique, we model the stream simultaneously in line-of-sight velocity, color-magnitude, coordinate, and proper motion space, and so determine its distribution in 6D phase-space. We find that the stream extends in distance from 7.5 to 9 kpc from the Sun; it is 50 times longer than wide, merely appearing highly foreshortened in projection. The analysis of the stellar population contained in the stream suggests that it is ∼12 Gyr old, and that its initial stellar mass was ∼2 × 104 M⊙ (or at least ≳7 × 103 M⊙). Assuming a fiducial Milky Way potential, we fit an orbit to the stream that matches the observed phase-space distribution, except for some tension in the proper motions: the stream has an orbital period of ∼350 Myr, and is on a fairly eccentric orbit (e ∼ 0.66) with a pericenter of ∼3.5 kpc and an apocenter of ∼17 kpc. The phase-space structure and stellar population of the stream show that its progenitor must have been a globular cluster that was disrupted only ∼240 Myr ago. We do not detect any significant overdensity of stars along the stream that would indicate the presence of a progenitor, and conclude that the stream is all that is left of the progenitor.enGalaxy: haloGalaxy: kinematics and dynamicsGalaxy: structureglobular clusters: generalAstrophysics - Astrophysics of Galaxies2015-08-0110.1088/0004-637X/809/1/5984945300396