2015ApJ...809...59S -
Astrophys. J., 809, 59 (2015/August-8)
The nature and orbit of the Ophiuchus stream.
SESAR B., BOVY J., BERNARD E.J., CALDWELL N., COHEN J.G., FOUESNEAU M., JOHNSON C.I., NESS M., FERGUSON A.M.N., MARTIN N.F., PRICE-WHELAN A.M., RIX H.-W., SCHLAFLY E.F., BURGETT W.S., CHAMBERS K.C., FLEWELLING H., HODAPP K.W., KAISER N., MAGNIER E.A., PLATAIS I., TONRY J.L., WATERS C. and WYSE R.F.G.
Abstract (from CDS):
The 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 (σvlos_ 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 x 104 M☉ (or at least >=7 x 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.
Abstract Copyright:
© 2015. The American Astronomical Society. All rights reserved.
Journal keyword(s):
Galaxy: halo - Galaxy: kinematics and dynamics - Galaxy: structure - globular clusters: general
VizieR on-line data:
<Available at CDS (J/ApJ/809/59): table1.dat table2.dat>
Nomenclature:
Table 1: [SBB2015] bhbN N=6 among (Nos bhb1-bhb7), [SBB2015] rgbN )Nos rgb1-rgb5), [SBB2015] sgbN (No sgb1), [SBB2015] mstoN (Nos msto1-msto2).
Simbad objects:
22
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