J/ApJ/809/59 Ophiuchus stellar stream with PS1 data (Sesar+, 2015)
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.,
Wyse R.F.G.
<Astrophys. J., 809, 59 (2015)>
=2015ApJ...809...59S 2015ApJ...809...59S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Photometry, ugriz ; Proper motions ;
Equivalent widths
Keywords: Galaxy: halo; Galaxy: kinematics and dynamics; Galaxy: structure;
globular clusters: general
Abstract:
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∼290km/s), kinematically
cold group (σνlos≲1km/s) of α-enhanced and
metal-poor stars ([α/Fe]∼0.4dex, [Fe/H]~-2.0dex). 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 9kpc 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 ∼12Gyr old, and that its initial stellar
mass was ∼2x104M☉ (or at least ≳7x103M☉). 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 ∼350Myr,
and is on a fairly eccentric orbit (e∼0.66) with a pericenter of
∼3.5kpc and an apocenter of ∼17kpc. The phase-space structure and
stellar population of the stream show that its progenitor must have
been a globular cluster that was disrupted only ∼240Myr 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.
Description:
The Pan-STARRS1 (PS1) survey has observed the entire sky north of
declination -30° in five filters covering 400-1000nm (Tonry+,
2012, J/ApJ/750/99). The 1.8m PS1 telescope has a 7deg2 field of
view. In single-epoch images, the telescope can detect point sources
at a signal-to-noise ratio (S/N) of 5 at 22.0, 22.0, 21.9, 21.0, and
19.8mag in PS1 grizyP1 bands, respectively. The uncertainty in
photometric calibration of the survey is ≲0.01mag (Schlafly et al.
2012ApJ...756..158S 2012ApJ...756..158S), and the astrometric precision of single-epoch
detections is 10mas (Magnier et al. 2008IAUS..248..553M 2008IAUS..248..553M).
We observed the selected candidates using the DEIMOS spectrograph on
Keck II and using the Hectochelle fiber spectrograph on MMT over a
course of two nights. Seven candidate blue horizontal branch stars
were observed with DEIMOS on 2014 May 29th (project ID 2014A-C171D,
PI: J. Cohen). The remaining 163 Ophiuchus stream candidates were
observed with Hectochelle on 2014 June 6th (proposal ID 2014B-SAO-4,
PI: C. Johnson).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 127 15 Ophiuchus stream member stars
table2.dat 44 120 Lines used for abundance measurements
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See also:
J/ApJ/800/120 : Profiles of z<0.5 galaxies with Pan-STARRS1 (Zheng+, 2015)
J/A+A/559/A43 : Pan-STARRS1 (PS1) observations of the Hyades (Goldman+, 2013)
J/ApJ/776/26 : RRab stars in the Orphan stream distances (Sesar+, 2013)
J/ApJ/750/99 : The Pan-STARRS1 photometric system (Tonry+, 2012)
J/ApJ/736/146 : Radial velocities of stars in Bootes I (Koposov+, 2011)
J/ApJ/708/560 : Spectroscopy of UMa II and Coma Ber (Frebel+, 2010)
J/A+A/497/497 : Physical parameters from JHK flux (Gonzalez-Hernandez+, 2009)
J/AJ/137/94 : Star clusters in M31 (Caldwell+, 2009)
J/AJ/127/3034 : Proper-motion catalog combining USNO-B and SDSS (Munn+, 2004)
J/AJ/124/1144 : Orbits of single-lined spectroscopic binaries (Latham, 2002)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 A1 --- Inst Instrument code (D: DEIMOS or H: Hectochelle)
3- 7 A5 --- Name Star name (1)
9- 17 F9.5 deg RAdeg Right ascension in decimal degrees (J2000)
19- 26 F8.5 deg DEdeg Declination in decimal degrees (J2000)
28- 32 F5.2 mag gmag [15.6/19.3]? PS1 gP1 band magnitude (2)
34- 37 F4.2 mag e_gmag [0.01/0.02]? gmag uncertainty (2)
39- 43 F5.2 mag rmag [15.5/18.9]? PS1 rP1 band magnitude (2)
45- 48 F4.2 mag e_rmag [0.01/0.02]? rmag uncertainty (2)
50- 54 F5.2 mag imag [15.5/18.8]? PS1 iP1 band magnitude (2)
56- 59 F4.2 mag e_imag [0.01/0.02]? imag uncertainty (2)
61- 65 F5.2 mag zmag [15.5/18.7]? PS1 zP1 band magnitude (2)
67- 70 F4.2 mag e_zmag [0.02]? zmag uncertainty (2)
72- 76 F5.2 mag ymag [15.5/18.7]? PS1 yP1 band magnitude (2)
78- 81 F4.2 mag e_ymag [0.02/0.03]? ymag uncertainty (2)
83- 87 F5.1 km/s Vlos [285/292] Line-of-sight velocity
(νlos) (3)
89- 91 F3.1 km/s e_Vlos [0.5/3] Vlos uncertainty (4)
93- 97 F5.2 mag DM [14.4/14.8]? Distance modulus (5)
99-102 F4.2 mag e_DM [0.05/0.06]? Negative error on DM (5)
104-107 F4.2 mag E_DM [0.05/0.06]? Positive error on DM (5)
109-113 F5.1 mas/yr pml [-24/-3]? Proper motion along GLON (6)
115-117 F3.1 mas/yr e_pml [1/3]? pml uncertainty
119-123 F5.1 mas/yr pmb [-15/8]? Proper motion along GLAT (µb)
125-127 F3.1 mas/yr e_pmb [1/3]? pmb uncertainty
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Note (1): The name indicates the likely evolutionary stage inferred from
isochrone fitting (MSTO = main sequence turn-off;
SGB = subgiant branch; BHB = blue horizontal branch;
RGB = red giant branch).
Note (2): The PS1 photometry is not corrected for extinction.
Note (3): A comparison of velocities measured from DEIMOS and Hectochelle
spectra for star "bhb6", shows that the two velocity sets are
consistent within stated uncertainties. See section 2.2.
Note (4): The uncertainty in Vlos includes the uncertainty from
cross-correlation/fitting and the uncertainty in the zero-point of
wavelength calibration.
Note (5): The DM indicates the average DM of the stream at the position
of the star, and the uncertainties are 68% confidence intervals.
Note (6): The proper motion in the galactic longitude direction, µl,
includes the cosb term.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Name Star name (rgb1 to rgb5)
6- 13 F8.3 0.1nm lambda [5162.2/5284.1] Rest wavelength, Angstroms
15- 19 A5 --- Ion Element
21- 24 F4.2 eV ExPot [0/4.2] Excitation potential
26- 31 F6.3 [-] log(gf) [-5/0.02] Oscillator strength
33- 38 F6.2 0.0001nm EW [9.1/332.8] Equivalent width
40- 44 F5.2 --- rEW [-5.8/5.4] Reduced equivalent width
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Dec-2015