J/AJ/149/42 Proper motion of Draco dwarf galaxy from HST (Pryor+, 2015)
Proper motion of the Draco dwarf galaxy based on Hubble Space Telescope imaging.
Pryor C., Piatek S., Olszewski E.W.
<Astron. J., 149, 42 (2015)>
=2015AJ....149...42P 2015AJ....149...42P
ADC_Keywords: Galaxies, nearby ; Proper motions
Keywords: astrometry - galaxies: dwarf - galaxies: individual: Draco -
proper motions
Abstract:
We have measured the proper motion of the Draco dwarf galaxy using
images at two epochs with a time baseline of about two years taken
with the Hubble Space Telescope Advanced Camera for Surveys. Wide
Field Channels 1 and 2 provide two adjacent fields, each containing a
known QSO. The zero point for the proper motion is determined using
both background galaxies and the QSOs and the two methods produce
consistent measurements within each field. Averaging the results from
the two fields gives a proper motion in the equatorial coordinate
system of
(µα,µδ)=(-17.7±6.3,-22.1±6.3)mas/century and
in the Galactic coordinate system of
(µl,µb)=(-23.1±6.3,-16.3±6.3)mas/century. Removing the
contributions of the motion of the Sun and of the LSR to the measured
proper motion yields a Galactic rest-frame proper motion of
(µαGrf,(µδGrf)=(51.4±6.3,-18.7±6.3)mas/century
and (µlGrf,(µbGrf)=(-21.8±6.3,-50.1±6.3)mas/century.
The implied space velocity with respect to the Galactic center is
(Π,Θ,Z)=27±14,89±25,-212±20)km/s. This velocity implies
that the orbital inclination is 70°, with a 95% confidence
interval of (59°,80°), and that the plane of the orbit is
consistent with that of the vast polar structure (VPOS) of Galactic
satellite galaxies.
Description:
We obtained first-epoch images for three distinct pointings in the
direction of Draco using the Advanced Camera for Surveys (ACS) and
Wide Field Channel (WFC) combination on HST in cycle 13 (based on
observations with the NASA/ESA Hubble Space Telescope, obtained at the
Space Telescope Science Institute, which is operated by the
Association of Universities for Research in Astronomy, Inc., under
NASA contract NAS 5-26555. The observations are associated with
programs 10229 and 10812). For each pointing, WFC1 is centered on a
spectroscopically-confirmed QSO. Ideally, second-epoch imaging would
be obtained with the same detector. However, only one pointing was
imaged in cycle 15 before the failure of ACS; the failure forced the
other two to be imaged with the WFPC2. Table 2 summarizes the
observations.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 95 3 Information about pointings and images
table4.dat 73 1938 Positions and proper motions in WFC1 field
table5.dat 73 2292 Positions and proper motions in WFC2 field
--------------------------------------------------------------------------------
See also:
J/MNRAS/435/1928 : Dwarf galaxy planes in Local Group (Pawlowski+, 2013)
J/AJ/136/1921 : Variable stars of Draco dSph (Kinemuchi+, 2008)
J/A+A/465/357 : Stroemgren photometry in Draco dSph galaxy (Faria+, 2007)
J/A+A/442/165 : Photometry of late-type stars in Draco dSph (Cioni+, 2005)
J/AJ/127/861 : RR Lyrae in Draco dSph (Bonanos+, 2004)
J/ApJS/145/245 : SDSS stars in Draco dwarf spheroidal galaxy (Rave+, 2003)
J/MNRAS/330/792 : Radial velocity in Draco (Kleyna+, 2002)
J/AJ/124/3222 : VI photometry of Draco and UMi galaxies (Bellazzini+, 2002)
J/AJ/123/2511 : Photometry of Draco dwarf spheroidal galaxy (Piatek+, 2002)
J/AJ/121/841 : RV photometry of Draco dwarf galaxy (Piatek+, 2001)
J/AJ/110/2131 : M/L for Draco and UMi. I. (Armandroff+ 1995)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Name Name of the pointing
7- 8 I2 h RAh Hour of Right Ascension (J2000) (1)
10- 11 I2 min RAm Minute of Right Ascension (J2000) (1)
13- 16 F4.1 s RAs Second of Right Ascension (J2000) (1)
18- 19 I2 deg DEd Degree of Declination (J2000) (1)
21- 22 I2 arcmin DEm Arcminute of Declination (J2000) (1)
24- 27 F4.1 arcsec DEs Arcsec of Declination (J2000) (1)
29- 39 A11 "Y:M:D" Date1 Date of the observation for the first epoch (2)
41- 47 A7 --- Det1 Detector for the first epoch (3)
49- 53 A5 --- Flt1 Filter for the first epoch (F555W or F606W)
55- 56 I2 --- N1 [19] Number of exposures for the first epoch
58- 60 I3 s Exp1 [430] Exposure time for the first epoch
62- 72 A11 "Y:M:D" Date2 Date of the observation for the second epoch (2)
74- 82 A9 --- Det2 Detector for the second epoch (3)
84- 88 A5 --- Flt2 Filter for the second epoch (F555W or F606W)
90- 91 I2 --- N2 [12/19] Number of exposures for the second epoch
93- 95 I3 s Exp2 [427/600] Exposure time for the second epoch
--------------------------------------------------------------------------------
Note (1): Celestial coordinates of the QSO.
Note (2): The difference between Date1 and Date2 is the time baseline. It is
about 3 years for Dra 1 and Dra 3 and about 2 years for Dra 2.
Note (3): The two detectors are:
ACS/WFC = Advanced Camera for Surveys/Wide Field Channel;
WFPC2/PC2 = Wide-Field Planetary Camera 2.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table[45].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Seq [1/2292] Running sequence number
6 I1 --- Type [0/2] Object type (0=QSO, 1=star, 2=galaxy)
8- 14 F7.2 pix Xpix [61.18/4084.9] The X pixel coordinate (1)
16- 22 F7.2 pix Ypix [-108.37/4218.09] The Y pixel coordinate (1)
24- 31 F8.3 arcsec oRA [-181/85] Right Ascension offset (2)
33- 40 F8.3 arcsec oDE [-173/112] Declination offset (2)
42- 44 I3 --- <S/N> [10/529] Average Signal-to-Noise at first epoch
46- 51 F6.1 10uas/yr pmRA [-953/1989] Measured proper motion along Right
Ascension (in mas/century)
53- 57 F5.1 10uas/yr e_pmRA [17/230] Uncertainty in pmRA (3)
59- 65 F7.1 10uas/yr pmDE [-1475/1012] Measured proper motion along
Declination (in mas/century)
67- 71 F5.1 10uas/yr e_pmDE [17/270] Uncertainty in pmDE (3)
73 I1 --- Mm [0/1] Member code (1=likely Draco member) (4)
--------------------------------------------------------------------------------
Note (1): From earliest, first epoch image.
Note (2): On the sky east and north from the QSO in the WFC1 field identified
by Kinemuchi et al. (2008AJ....136.1921K 2008AJ....136.1921K), source #264 ([KHS2008] 264 in
Simbad), located at J2000 position 17:20:52.31+57:55:13.4
Note (3): The quoted uncertainty is the sum in quadrature of the uncertainty in
the motion of an object in the standard coordinate system and the
uncertainty of the weighted mean proper motion of Draco.
Note (4): Indicates whether the object was included in the fit of the coordinate
transformation between epochs, one meaning yes and zero no. Objects with
this flag set to one are likely members of Draco.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 20-Feb-2015