J/ApJ/840/30 HST/Gemini proper motions for Pyxis (Fritz+, 2017)
The proper motion of Pyxis: The first use of Adaptive Optics in tandem with HST
on a faint halo object.
Fritz T.K., Linden S.T., Zivick P., Kallivayalil N., Beaton R.L., Bovy J.,
Sales L.V., Sohn T., Angell D., Boylan-Kolchin M., Carrasco E.R., Damke G.,
Davies R., Majewski S., Neichel B., van der Marel R.
<Astrophys. J., 840, 30 (2017)>
=2017ApJ...840...30F 2017ApJ...840...30F
ADC_Keywords: Clusters, globular ; Proper motions ; Photometry, infrared ;
Photometry, HST
Keywords: globular clusters: individual (Pyxis) ; proper motions
Abstract:
We present a proper motion measurement for the halo globular cluster
Pyxis, using Hubble Space Telescope/ACS data as the first epoch and
GeMS/GSAOI Adaptive Optics data as the second, separated by a baseline
of ∼5 years. This is both the first measurement of the proper motion
of Pyxis and the first calibration and use of Multi-Conjugate Adaptive
Optics data to measure an absolute proper motion for a faint, distant
halo object. Consequently, we present our analysis of the Adaptive
Optics data in detail. We obtain a proper motion of
µαcos(δ)=1.09±0.31mas/yr and
µδ=0.68±0.29mas/yr. From the proper motion and
line-of-sight velocity, we find that the orbit of Pyxis is rather
eccentric, with its apocenter at more than 100kpc and its pericenter
at about 30kpc. We also investigate two literature-proposed
associations for Pyxis with the recently discovered ATLAS stream and
the Magellanic system. Combining our measurements with dynamical
modeling and cosmological numerical simulations, we find it unlikely
Pyxis is associated with either system. We examine other Milky Way
satellites for possible association using the orbit, eccentricity,
metallicity, and age as constraints and find no likely matches in
satellites down to the mass of Leo II. We propose that Pyxis probably
originated in an unknown galaxy, which today is fully disrupted.
Assuming that Pyxis is bound and not on a first approach, we derive a
68% lower limit on the mass of the Milky Way of 0.95x1012M☉.
Description:
The first epoch consists of archival HST ACS/WFC F606W and F814W data.
These images were obtained in 2009 (MJD=55115.7).
For the second epoch, we use the wide-field AO system GeMS/GSAOI at
Gemini South in K' band. The science data were obtained on 2015
January 7 (MJD=57030.3) under good conditions, giving a five-year
baseline between the first (HST) and second (AO) epoch of imaging. See
section 2.2 for further explanations.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 75 5 *Potential moving group members
table4.dat 80 349 Relative stellar proper motions
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Note on table2.dat: There is a cluster of three to five stars with proper
motions of ~-11mas/yr in R.A. and ∼7mas/yr in decl., visible in Figure 11.
Two of the stars (397 and 405) have motions that differ from the other three
by more than the measured errors, and therefore are likely only a chance
association, while the other three are consistent within 1σ/2σ
in R.A./decl. See section 4.3.1.
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See also:
VII/195 : Globular Clusters in the Milky Way (Harris, 1996)
J/AJ/118/1671 : Fornax cluster 4 VI photometry (Buonanno+, 1999)
J/MNRAS/360/185 : VI photometry of the Leo II galaxy (Bellazzini+, 2005)
J/A+A/459/423 : VI and [Fe/H] of Fornax dSph RGB stars (Battaglia+, 2006)
J/A+A/465/815 : Abundances of Sgr dSph stars (Sbordone+, 2007)
J/ApJ/684/1143 : BHB candidates in the Milky Way (Xue+, 2008)
J/ApJ/690/1236 : COSMOS photometric redshift catalog (Ilbert+, 2009)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/A+A/540/A27 : Spectroscopy in Galactic globular clusters (Saviane+, 2012)
J/ApJS/206/10 : CANDELS multiwavelength catalog (Galametz+, 2013)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/ApJ/797/115 : HSTPROMO I. Observations and NGC7078 results (Bellini+, 2014)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/ApJ/805/189 : Highly likely members of the Sgr stream (Hyde+, 2015)
J/AJ/149/42 : Proper motion of Draco dwarf galaxy from HST (Pryor+, 2015)
J/ApJ/809/59 : Ophiuchus stellar stream with PS1 data (Sesar+, 2015)
J/ApJ/830/17 : GC secondary IR astrometric standards (Boehle+, 2016)
J/A+A/595/L2 : Proper motions in NGC6681 globular cluster (Massari+, 2016)
J/ApJ/818/99 : Globular cluster populations in S4G gal. II. (Zaritsky+, 2016)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [33/405] Identifier
5-15 F11.7 deg RAdeg Right ascension in decimal degrees (J2000) (1)
17-27 F11.7 deg DEdeg Declination in decimal degrees (J2000) (1)
29-35 F7.3 arcsec delX Distance δX from star 33
37-42 F6.3 arcsec delY Distance δY from star 33
44-49 F6.2 mas/yr pmRA [-11.7/-10.4] Proper motion along RA
51-54 F4.2 mas/yr e_pmRA [0.08/0.2] Uncertainty in pmRA
56-59 F4.2 mas/yr pmDE [7/8] Proper motion along DE
61-64 F4.2 mas/yr e_pmDE [0.08/0.2] Uncertainty in pmDE
66-70 F5.2 --- Kmag [15.4/18.1] Gemini K' band magnitude
72-75 F4.2 --- C2 [1.7/2.2] The (F814W-K') color index
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Note (1): The uncertainty of the positions are about 7x10-6 degrees compared
to the absolute reference frame. This does not affect the relative positions.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [1/421] Identifier
5- 14 A10 --- Mm Member? ("Member": 218 occurrences,
"Non-Member": 129 occurrences or "Unclear")
16- 26 F11.7 deg RAdeg Right Ascension in decimal degrees (J2000)
28- 38 F11.7 deg DEdeg Declination in decimal degrees (J2000)
40- 45 F6.2 mas/yr pmRA [-14.5/2.7] Proper motion along RA
47- 50 F4.2 mas/yr e_pmRA [0.08/1.6] Uncertainty in pmRA
52- 56 F5.2 mas/yr pmDE [-5.5/8] Proper motion along DE
58- 61 F4.2 mas/yr e_pmDE [0.08/1.6] Uncertainty in pmDE
63- 67 F5.2 mag Kmag [15.4/22.6] Gemini K' band magnitude
69- 74 F6.2 mag C1 [-6/9.2]? HST (F606W-F814W) color index (1)
76- 80 F5.2 --- C2 [0.7/11] The (F814W-K') color index
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Note (1): Blank value when there is no useful measurement in F606W
(stars saturated).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 08-Dec-2017