Precise CCD positions of Himalia using Gaia DR1 in 2015-2016

0.73 MB·

by  H. W. Peng

MNRAS000,1–9(2016) Preprint26January2017 CompiledusingMNRASLATEXstylefilev3.0
Precise CCD positions of Himalia using Gaia DR1 in
2015-2016
H. W. Peng,1,2,3,4 Q. Y. Peng1,4⋆ and N. Wang1,4
1Department of Computer Science, Jinan University,Guangzhou 510632, China
2Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, China
3Universityof Chinese Academy of Sciences,Beijing 100049, China
7 4Sino-French Joint Laboratory for Astrometry, Dynamicsand Space Science, Jinan University,Guangzhou 510632, China
1
0
2
Accepted2017January24.Received2017January19;inoriginalform2016October17

n
a
J ABSTRACT

5 Inorderto obtainhighprecisionCCD positions ofHimalia,the sixthJoviansatellite,
2
a total of 598 CCD observations have been obtained during the years 2015-2016.The

observationsweremadebyusingthe2.4mand1mtelescopesadministeredbyYunnan
]
P Observatories over 27 nights. Several factors which would influence the positional
E precision of Himalia were analyzed, including the reference star catalogue used, the
. geometric distortion and the phase effect. By taking advantage of its unprecedented
h
positional precision, the recently released catalogue Gaia DR1 was chosen to match
p
reference stars in the CCD frames of both Himalia and open clusters which were
-
o observed for deriving the geometric distortion. The latest version of SOFA library
r was used to calculate the positions of reference stars. The theoretical positions of
t
s Himalia were retrieved from the Jet Propulsion Laboratory Horizons System which
a includes the satellite ephemeris JUP300, while the positions of Jupiter were based
[
on the planetary ephemeris DE431. Our results showed that the means of observed

1 minus computed (O-C) residuals are 0.071 and -0.001 arcsec in right ascension and
v declination,respectively.Theirstandarddeviationsareestimatedatabout0.03arcsec
2 in each direction.
4
Key words: astrometry – planets and satellites: individual: Himalia – methods:
1
observational– techniques: image processing
7
0
.
1
0
7 1 INTRODUCTION servationsofirregularsatellitescanalsobeusedforimprov-
1 ingthe ephemeridesof their host planets.
The irregular satellites in our solar system have been stud-
:
v ied for many years. Parts of them may be formed follow- Himaliaisthelargest memberofJovianirregularsatel-
i
X ing with their host giant planets. However, some of these lites (Grav et al. 2015). It has been discovered by Perrine
objects are widely believed to have been heliocentric as- at Lick Observatory in 1904 (Perrine 1905). The astromet-
r
a teroids before being captured by a giant planet’s gravity ricobservationsofHimaliawereobtainedcontinuouslysince
(Colombo & Franklin 1971; Heppenheimer & Porco 1977; then.TheprecisionofpositionsofHimaliawasalsoimproved
Pollacketal.1979;Sheppard&Jewitt2003;Agnor&Hamil- steadily with the time after larger diameter telescopes and
ton2006;Nesvorny´etal.2007,2014).Thismeanstheirreg- newastrometricdataprocessingtechniqueswereused.Thus
ular satellites may have close relationship with the forma- two medium size telescopes which are the 2.4 m telescope
tionofearlysolarsystem.Theyaresmallerandfarther,and (Fan et al. 2015) and 1 m telescope (Zhou et al. 2001) ad-
havinghighly eccentricand inclined orbitsthan theregular ministeredbyYunnanObservatorieswereusedforobtaining
satellites (Nicholson 2008; Grav et al. 2015).The astromet- our CCD observations. For the data processing, in order to
ric observationsof irregular satellites are also more difficult obtainhighprecisionresults,severalfactorsweretakeninto
tobeobtainedwithhighprecision.Untilnow,thoughmany account. Specifically, the reference star catalogue used, the
space missions have had close flyby, observations made by geometricdistortion(calledGDhereafter)andthephaseef-
ground-based telescopes could still be the primary way to fect, etc. The latest version of software routines from the
studyirregularsatellites.Thehighprecisionastrometricob- IAU-SOFA(InternationalAstronomicalUnion-Standardsof
FundamentalAstronomy)collection(Hohenkerk2015)were
used for calculating the topocentric apparent positions of
⋆ E-mail:[email protected] referencestars.OurpreviouslyproposedGDsolution(Peng
(cid:13)c 2016TheAuthors
2 H. W. Peng et al.
etal.2012)wasusedforderivingtheGDpatterns.TheGD
Table 1.Specifications of the 2.4 m and 1 m telescopes admin-
effects of the 2.4 m and 1 m telescopes have been proved istered by Yunnan Observatories and the corresponding CCD
in our previous works (Peng et al. 2012, 2015; Zhang et detectors. Column 1 shows the parameters and the following
al. 2012; Wang et al. 2015; Peng et al. 2016). In consid- columnslisttheirvaluesforthetwotelescopes.
eration of the fewer numberof reference stars in each CCD
frame of Himalia, the high-order plate model can’t be ap- Parameters 2.4m 1m
plied. In some cases, there are only several reference stars
Approximatefocallength 1920cm 1330cm
available in the CCD field of view, and a plate model with
F-Ratio 8 13
four constants becomes the most reasonable choice. Under
Diameterofprimarymirror 240cm 100cm
this circumstance, the GD effects should be corrected ac- CCDfieldofview(effective) 9′×9′ 7′×7′
curately. Furthermore, the phase effect of Himalia was also SizeofCCDarray(effective) 1900×1900 2048×2048
analyzed (Lindegren 1977). Sizeofpixel 13.5m ×13.5m 13.5m ×13.5m
Asiswell known,theprecision ofareferencestarcata- Approximatescalefactor 0.286′′/pixel 0.209′′/pixel
logueisessentialtothemeasurementsofirregularsatellites.
Furthermore, the zonal errors of a star catalogue also have
direct influence on the positional precision. The astrome-
try satellite Gaia (Gaia Collaboration et al. 2016a) which
Table 2.CCD observations of Himaliaand calibrationfields by
is fully funded by the European Space Agency (ESA) has
using the 2.4 m and 1 m telescopes administered by Yunnan
been launched on December 19, 2013. After less than three Observatories. Column 1 lists the observational dates. Column
years, the first catalogue Gaia Data Release 1 (Gaia DR1) 2showstheopenclustersobserved.Column3andColumn4list
(GaiaCollaboration etal.2016b)waspublishedonSeptem- thenumberofobservationsforopenclustersandHimalia,respec-
ber14,2016. TheprecisestarpositionsderivedbytheGaia tively.TheJohnson-I filterwasusedinallobservations.Column
could render better predictions with the primary source of 5showswhichtelescopewasused.
errorbeingtheephemerides(deBruijne2012;Gomes-Ju´nior
et al. 2015). Though the final mission products are waiting Obsdates Calibrationfields Himalia Tel
to be released in the future, the results of Gaia DR1 still openclusters No. No.
represent a huge improvementin theavailable fundamental
2015-01-31 NGC1664 44 21 2.4m
stellar data and practical definition of the optical reference
2015-02-07 NGC2324 44 25 2.4m
frame (Lindegren et al. 2016). We believe that the higher
2015-02-08 NGC2324 44 14 2.4m
positional precision of targets will be achieved. 2015-02-09 NGC2324 44 18 2.4m
The contents of this paper are arranged as follows. 2015-02-10 NGC1664 44 18 2.4m
In Section 2, the CCD observations are described. Section 2015-02-11 19 2.4m
3 presents the reduction details. In Section 4, results are 2015-02-12 17 2.4m
showed. In Section 5, discussions are made. Finally, in Sec- 2015-02-13 19 2.4m
tion 6, conclusions are drawn. 2015-02-12 M35 60 14 1m
2015-02-14 20 1m
2016-03-01 M35 49 36 1m
2016-03-02 M35 49 30 1m
2 CCD OBSERVATIONS 2016-03-03 M35 49 41 1m
2016-03-04 M35 49 51 1m
Atotalof27nightsofCCDobservationsofHimaliawereob- 2016-03-06 20 2.4m
tained from two telescopes administered by YunnanObser- 2016-03-08 18 2.4m
vatoriesduringtheyears2015-2016.Theobservationaldates 2016-03-09 20 2.4m
werechosenaccordingtotheepochswhenJupiterisnearits 2016-03-10 3 2.4m
2016-03-11 NGC6633 44 23 2.4m
opposition.Specifically,19nightsofCCDobservationswere
2016-03-12 21 2.4m
made by the YunnanFaint Object Spectrograph and Cam-
2016-03-13 21 2.4m
era (YFOSC) instrument attached to the 2.4 m telescope
2016-03-14 24 2.4m
(longitude E 100◦1′51′′, latitude N 26◦42′32′′, height 3193
2016-03-15 23 2.4m
m above sea level), and 9 nights of CCD observations were 2016-03-16 22 2.4m
madebythe1mtelescope(longitudeE102◦47′18′′,latitude 2016-03-17 20 2.4m
N 25◦1′46′′,height 2000 m abovesealevel). It isnoted that 2016-04-07 14 1m
observations were obtained from both the 2.4 m and 1 m 2016-04-09 M67 35 11 1m
telescopes on February 12, 2015. The specifications of the 2016-04-10 M67 44 15 1m
two telescopes and corresponding CCD detectors are listed
Total 599 598
in Table 1.
A total of 598 CCD observations of Himalia have been
obtained, as well as 599 CCD frames of calibration fields
which are open clusters. Distributions of the observations
withrespecttotheobservationaldatesarelistedinTable2. 120secondsdependingonthetelescopesandmeteorological
It can be seen that 366 CCD observations of Himalia were conditions. Calibration fields were observed following with
obtained from the 2.4 m telescope, and 232 CCD observa- Himalia,exceptforthosenightsthatobservationsweresub-
tionsofHimalia wereobtainedfrom the1mtelescope. The jected to rapidly changing weather conditions and limited
exposure time for each CCD frame is ranged from 20 to telescope time.
MNRAS000,1–9(2016)
Precise CCD positions of Himalia using Gaia DR1 3
2015-01-31 Med =0.29 Max=2.08 2015-02-10 Med =0.31 Max=2.06 2016-03-11 Med =0.33 Max=2.23
2000 2000 2000
1500 1500 1500
el el el
x1000 x1000 x1000
pi pi pi
Y/ Y/ Y/
500 500 500
0 0 0
0 500 1000 1500 2000 0 500 1000 1500 2000 0 500 1000 1500 2000
X/pixel X/pixel X/pixel
2015-02-12 Med =0.21 Max=0.45 2016-03-01 Med =0.20 Max=0.46 2016-04-10 Med =0.21 Max=0.51
2000 2000 2000
1500 1500 1500
el el el
x x x
pi1000 pi1000 pi1000
Y/ Y/ Y/
500 500 500
0 0 0
0 500 1000 1500 2000 0 500 1000 1500 2000 0 500 1000 1500 2000
X/pixel X/pixel X/pixel
Figure 1. GD patterns for the 2.4 m and 1 m telescopes administered by Yunnan Observatories using catalogue Gaia DR1. Only six
typicalGDpatternsareshowed.TheupperthreepanelsshowtheGDpatternsderivedfromtheCCDobservationsofthe2.4mtelescope.
Thelower threepanels show the GD patterns derivedfromthe CCDobservations of the1m telescope. Allobservations wereobtained
with the Johnson-I filter. In each panel, the observational date, the median and maximum GD values are listed on the top in units of
pixels.Afactorof200isusedtoexaggeratethemagnitudeofeachGDvector.
3 ASTROMETRIC REDUCTION cataloguewaschosentomatchreferencestarsinalltheCCD
frames.
Thereductionprocedureswerecarried outaccordingtoour InordertoobtaintheobservationalpositionsofHimalia
previouswork(Pengetal.2012).Firstly,alltheCCDframes andalsotoderivetheGDpatterns,thetopocentricapparent
wereprocessedtoobtainthepixelpositionsofbothHimalia positionsofreferencestarsinalltheCCDframesneedtobe
andreferencestars.Secondly,theGDpatternswerederived calculated. In this work, the latest version of software rou-
fromtheCCDframesofopenclusters.Thirdly,theGDcor- tinesfromtheIAU-SOFAcollection (Hohenkerk2015)were
rections were applied for both Himalia and reference stars. used to compute the topocentric apparent positions. How-
Atlast,thetopocentricapparentpositionsofHimaliacould ever, the catalogue Gaia DR1 does provide parallaxes only
be obtained with respect to the reference stars in the same forTychostars.Thusonlythesereferencestarswereapplied
CCD field of view. More description follows. withbothparallaxesandaberration correctionsintopocen-
tric correction. The other reference stars were applied with
Before the data reduction, there are several preprocess
aberration correction, only.
steps need to be accomplished. As showed in Section 2,
several open clusters were observed for the purpose of de- After the positional computations of reference stars in
riving GD patterns. These CCD frames together with the theCCDframesofopenclusterswerefinished,theGDpat-
CCDframesofHimaliawerefirstlyprocessedwithbiasand terns could be derived according to the solution presented
flat-field corrections. Then the CCD frames obtained from in our previous work (Peng et al. 2012). For the purpose
the 2.4 m telescope were clipped into 1900×1900 square of derivingGD patternsaccurately, theatmospheric refrac-
pixels because they have ineffective boundaries which have tion effect should be added to the positional computations
non-exposure pixels. Next, the pixel positions of both Hi- ofreferencestars. Astandardatmosphericrefraction model
malia and reference stars were obtained by using the two- should be precise enough (Peng et al. 2012). According to
dimensional Gaussian fit algorithm. Lastly, a reference star thestudypresentedinStone(2002),thefiltersusedandob-
MNRAS000,1–9(2016)
4 H. W. Peng et al.
servationalzenithdistanceareimportantforcomputingthe
Table 3. Statistics on the (O-C) residuals of positions of Hi-
differentialcolor refraction (DCR).In ourobservations, the malia.ThecatalogueGaiaDR1wasused.Column1andcolumn
Johnson-I filter was used, and the average of observational 2 show the observational dates and GD corrections. The follow-
zenithdistancesisabout25degrees.Undersuchconditions, ingcolumnslistthemeansof(O-C)residualsandtheirstandard
theDCRisinsomedegreenegligibleaccordingtothestudy deviations (SDs)inrightascensionanddeclination, respectively.
presented in Stone (2002). Thus the DCR for our observa- Allunitsareinarcseconds.
tions was not taken into account in the refraction model.
Fig. 1 shows six typical GD patterns derived by using the Obsdates GDC hO-Ci SD hO-Ci SD
andTel RA DEC
star catalogue Gaia DR1. It can be seen that the GD ef-
fects of the 1 m telescope are much smaller than the 2.4 m 2015-01-31 Before 0.064 0.065 -0.032 0.059
telescope. (2.4m) After 0.061 0.021 0.003 0.019
TheGDcorrectionswereappliedforthepixelpositions 2015-02-07 Before 0.044 0.037 -0.003 0.055
ofbothHimaliaandreferencestarsinthesameCCDfieldof (2.4m) After 0.036 0.011 0.020 0.016
view.Inpractice,GDcorrectionswereappliedoneachnight 2015-02-08 Before -0.012 0.076 -0.032 0.028
(2.4m) After 0.054 0.020 0.021 0.030
if the GD pattern is available, otherwise the GD pattern of
2015-02-09 Before -0.002 0.050 -0.042 0.058
nearest night is used(Penget al. 2016).More details about
(2.4m) After 0.057 0.013 0.012 0.014
the different GD correction schemes are presented in our
2015-02-10 Before 0.050 0.078 -0.016 0.033
previouswork(Wangetal.2015).AftertheGDcorrections
(2.4m) After 0.041 0.014 0.024 0.021
werefinished,thetopocentricapparentpositionsofreference 2015-02-11 Before 0.000 0.064 -0.014 0.036
starswerecalculated.TheobservationalpositionsofHimalia (2.4m) After 0.050 0.016 0.024 0.021
were computed relative to these reference stars in the same 2015-02-12 Before 0.014 0.071 0.009 0.075
CCD field of view. A plate model with four constants was (2.4m) After 0.061 0.012 0.020 0.023
used for the computations. However, this is accurate only 2015-02-13 Before 0.022 0.081 -0.047 0.063
after all the astrometric effects, including the GD effects, (2.4m) After 0.068 0.012 0.012 0.017
2015-02-12 Before 0.040 0.046 -0.029 0.012
are taken intoaccount (Penget al. 2012).
(1m) After 0.063 0.045 -0.003 0.011
According to the illustration presented in Linde-
2015-02-14 Before 0.054 0.027 0.014 0.035
gren (1977), the phase effect has a direct influence on posi-
(1m) After 0.075 0.028 0.013 0.034
tionalmeasurementsofplanetsandnaturalsatellites in our
2016-03-01 Before 0.051 0.053 -0.092 0.045
solar system. Phase corrections should be considered and (1m) After 0.054 0.026 -0.024 0.043
applied for these objects. Though our observational dates 2016-03-02 Before 0.071 0.014 0.023 0.011
were selected near Jupiter’s opposition, the phase effect of (1m) After 0.067 0.014 -0.013 0.010
Himalia isstill calculated. Asan irregular satellite, Himalia 2016-03-03 Before 0.082 0.034 0.030 0.026
maybefarfrom beingasphere,whilethisisan implicitas- (1m) After 0.074 0.031 0.002 0.026
sumption in Lindegren (1977). Under the assumption that 2016-03-04 Before 0.070 0.017 -0.038 0.013
(1m) After 0.077 0.012 -0.014 0.011
Himalia is a sphere, the phase effect of Himalia was calcu-
2016-03-06 Before 0.000 0.010 0.056 0.019
lated byusingequation(14) presentedinLindegren(1977).
(2.4m) After 0.074 0.010 -0.006 0.019
Severaltypicalobservationaltimewereselected tocompute
2016-03-08 Before 0.064 0.019 -0.116 0.039
thephaseeffects.Ourresultsshowthatthemaximumvalue
(2.4m) After 0.066 0.018 0.006 0.039
of phase effects according to the observational time is as 2016-03-09 Before 0.155 0.049 -0.058 0.042
smallas∼0.002′′,andmostofthephaseeffectsarelessthan (2.4m) After 0.061 0.051 0.007 0.044
0.001′′. These values are beyond our measurable precision 2016-03-10 Before 0.129 0.023 -0.154 0.061
limitation. It means the phase effect of Himalia for our ob- (2.4m) After 0.095 0.003 -0.021 0.058
servations is negligible. 2015-03-11 Before -0.036 0.038 0.036 0.019
(2.4m) After 0.089 0.038 -0.015 0.016
2016-03-12 Before 0.090 0.012 -0.097 0.018
(2.4m) After 0.072 0.010 -0.003 0.018
4 RESULTS 2016-03-13 Before -0.006 0.033 -0.078 0.035
(2.4m) After 0.078 0.037 0.000 0.034
In this work, the reference star catalogue Gaia DR1 (Gaia 2016-03-14 Before 0.128 0.042 -0.041 0.038
Collaboration et al. 2016b) was used in the astrometric (2.4m) After 0.085 0.037 -0.024 0.043
data reduction. The observed positions of Himalia were 2016-03-15 Before 0.204 0.040 -0.042 0.042
compared to the ephemeris retrieved from Jet Propulsion (2.4m) After 0.100 0.040 -0.014 0.039
Laboratory (JPL) Horizons ephemeris service (Giorgini et 2016-03-16 Before 0.056 0.015 -0.010 0.021
(2.4m) After 0.091 0.015 0.013 0.021
al.1996)whichincludesthesatelliteephemerisJUP300(Ja-
2016-03-17 Before 0.092 0.009 -0.072 0.009
cobson 2013) and planetary ephemeris DE431 (Folkner et
(2.4m) After 0.054 0.008 0.000 0.010
al. 2014). Fig. 2 shows the (O-C) residuals of positions of
2016-04-07 Before 0.106 0.037 0.004 0.032
Himalia with respect to the Julian Dates. Table 3 lists the
(1m) After 0.111 0.029 -0.009 0.034
statisticsonthe(O-C)residualsforHimaliabeforeandafter 2016-04-09 Before 0.078 0.006 -0.055 0.012
GD corrections. It can be seen that the internal agreement (1m) After 0.083 0.006 -0.030 0.012
orprecisionforanindividualnighthasbeensignificantlyim- 2016-04-10 Before 0.072 0.008 -0.022 0.011
provedafterGDcorrectionsforthe2.4mtelescope,butthe (1m) After 0.084 0.008 -0.018 0.010
results slightly improved for the 1 m telescope. This is due Total Before 0.060 0.066 -0.028 0.056
to the GD effects associated with the 1 m telescope being After 0.071 0.029 -0.001 0.030
MNRAS000,1–9(2016)
Precise CCD positions of Himalia using Gaia DR1 5

0.3 0.3
0.2 0.2
A A
R 0.1 R 0.1
n n
c) i c) i
se 0.0 se 0.0
c c
ar ar
C ( C (
O- -0.1 O- -0.1
Before GDC (2.4 m) Before GDC (2.4 m)
After GDC (2.4 m) After GDC (2.4 m)
-0.2 -0.2
Before GDC (1 m) Before GDC (1 m)
After GDC (1 m) After GDC (1 m)
-0.3 -0.3
52 54 56 58 60 62 64 66 68 70 445 450 455 460 465 470 475 480 485 490 495
JD-24 57000 JD-24 57000
0.3 0.3
Before GDC (2.4 m) Before GDC (2.4 m)
0.2 After GDC (2.4 m) 0.2 After GDC (2.4 m)
Before GDC (1 m) Before GDC (1 m)
C After GDC (1 m) C After GDC (1 m)
E 0.1 E 0.1
D D
n n
c) i c) i
se 0.0 se 0.0
c c
ar ar
O-C ( -0.1 O-C ( -0.1
-0.2 -0.2
-0.3 -0.3
52 54 56 58 60 62 64 66 68 70 445 450 455 460 465 470 475 480 485 490 495
JD-2457000 JD-2457000
Figure 2. (O-C) residuals of the positions of Himalia in comparison with the ephemeris retrieved from JPL, including the satellite
ephemeris JUP300 and planetary ephemeris DE431, with respect to the Julian Dates. The catalogue Gaia DR1 was used for data
reduction. The upper two panels show the (O-C) residuals in right ascension in the year 2015 and 2016, respectively. The lower two
panelsshowthe(O-C)residualsindeclinationinthetwoyears.Thedarkandredpointsrepresentthe(O-C)residualsforobservations
obtainedfromthe2.4mtelescopebeforeandafterGDcorrections,respectively.Theblueandgreenpointsrepresentthe(O-C)residuals
forobservationsobtainedfromthe1mtelescopebeforeandafterGDcorrections,respectively.Ineachpanel,thedarkdashlineandred
dash line represent the means of (O-C) residuals before and after GD corrections on right ascension and declination for the two years
separately.
quitesmallerthanthe2.4mtelescope.Themeansof(O-C) sion using Gaia DR1 has been improved by a factor of two
residuals for all data sets after GD corrections are 0.071′′ thantheresultsusingUCAC4.Thisismainlyresultingfrom
and -0.001′′ in right ascension and declination, respectively. the unprecedent precision of reference star catalogue Gaia
Their standard deviations are estimated at about 0.03′′ in DR1. Our results give proof that the tremendous potential
each direction. We can see that this precision is improved in improving astrometric precision of CCD observations of
bya factor of two than theresults before GD corrections. irregular satellites byusing Gaia DR1.
In order to analyze the effects on positional precision
madebythereferencestarcatalogue,thecatalogueUCAC4
(Zacharias et al. 2013) was also used for astrometric reduc- 5 DISCUSSIONS
tion.Fig.3showsthe(O-C)residualsofpositionsofHimalia
using UCAC4 and Gaia DR1. The same ephemeris which In order to analyze the dispersion of (O-C) residuals of Hi-
was retrieved from JPL was used.Itcan beseen larger sys- malia, the (O-C) residuals of Himalia by using both cat-
tematic errors appearing in the (O-C) residuals of Himalia alogue Gaia DR1 and UCAC4 are drawn together. Fig. 4
byusingUCAC4thantheresultsbyusingGaiaDR1,bothin shows the details. It can been seen that the dispersion of
rightascensionanddeclination.Thismaybemainlycaused (O-C) residuals for Gaia DR1 is much more compact than
by the existence of zonal errors in the reference star cata- UCAC4.Thesystematicerrorsappearinginthe(O-C)resid-
logueUCAC4.However,thesystematicerrorsbyusingGaia ualsofHimaliabyusingGaiaDR1aresignificantlyreduced.
DR1 are significantly reduced. Table 4 shows the statistics This is because the zonal errors existing in catalogue Gaia
on the (O-C) residuals for Himalia for UCAC4 and Gaia DR1 are quite subtle. We can also see from Fig. 2 that the
DR1, respectively. It can be seen that the positional preci- dispersion of (O-C) residuals for Himalia after GD correc-
MNRAS000,1–9(2016)
6 H. W. Peng et al.

0.4 0.4
UCAC4 UCAC4
0.3 Gaia DR1 0.3 Gaia DR1
A 0.2 A 0.2
R R
n n
c) i 0.1 c) i 0.1
e e
s s
c c
ar 0.0 ar 0.0
C ( C (
O- O-
-0.1 -0.1
-0.2 -0.2
-0.3 -0.3
52 54 56 58 60 62 64 66 68 70 445 450 455 460 465 470 475 480 485 490 495
JD-24 57000 JD-24 57000
0.4 0.4
UCAC4 UCAC4
0.3 Gaia DR1 0.3 Gaia DR1
C 0.2 C 0.2
E E
D D
n n
c) i 0.1 c) i 0.1
se se
arc 0.0 arc 0.0
C ( C (
O- -0.1 O- -0.1
-0.2 -0.2
-0.3 -0.3
52 54 56 58 60 62 64 66 68 70 445 450 455 460 465 470 475 480 485 490 495
JD-2457000 JD-2457000
Figure3.(O-C)residualsofthepositionsofHimaliaincomparisonwiththeephemerisretrievedfromJPLwhichincludesthesatellite
ephemerisJUP300andplanetary ephemerisDE431, withrespecttothe JulianDates. Thecatalogue UCAC4andGaiaDR1wereboth
used. The upper two panels show the (O-C) residuals in right ascension in the year 2015 and 2016, respectively. The lower two panels
showthe(O-C)residualsindeclinationinthetwoyears.Thedarkpointsrepresentthe(O-C)residualsafterGDcorrectionsforUCAC4
and the redones represent the (O-C)residualsafter GD corrections forGaia DR1.In each panel, the darkdash lineand reddash line
representthemeansof(O-C)residualsafterGDcorrectionsonrightascensionanddeclinationforthetwoyearsseparately.
DE431. Fig. 5 shows the (O-C) residuals of topocentric as-
Table4.Statisticsonthe(O-C)residualsofpositionsofHimalia
forGaiaDR1andUCAC4.Column1showsthenumberofCCD trometric positions of Himalia in comparison with the two
observations. Column 2 shows the catalogue used. The follow- different ephemerides. Table 5 shows the statistics on the
ingcolumnslistthemeansof(O-C)residualsandtheirstandard (O-C)residualsforHimaliaafterGDcorrectionsforthetwo
deviations in right ascension and declination, respectively. The ephemerides.Themeansof(O-C)residualsforephemerisre-
ephemerides wereretrievedfromJPLwhich includethe satellite trievedfromIMCCEare0.062′′and0.011′′inrightascension
ephemerisJUP300andplanetaryephemerisDE431.Allunitsare and declination, respectively. Their corresponding standard
inarcseconds. deviationsare0.040′′ and0.030′′.Themeansof(O-C)resid-
ualsforalldatasetsbetweenthetwoephemeridesarenearly
N Catalogue hO-Ci SD hO-Ci SD
equal.Wecanalso see from Table5thattheirstandardde-
RA DEC
viationsbetweenthetwoephemeridesforthetwoyearssep-
598 UCAC4 0.118 0.058 -0.019 0.055 aratelyareingoodagreement.However,adifferenceforthe
GaiaDR1 0.071 0.029 -0.001 0.030 meansof(O-C)residualsinrightascensionbetweenthetwo
ephemeridesin2015couldbefound.Inconsiderationofthe
same planetary ephemeris DE431 was used, this difference
tionsintheyear2016issomewhatworsethantheresultsin should befrom thedifferent satellite ephemeridesused.
the year 2015. This is mainly due to the seeing of observa-
tions in 2016 is worse than theseeing in 2015. To compare our CCD observations with previous ones,
For comparison, the ephemerides retrieved from Insti- some major observational statistics of Himalia are listed in
tute de M´echanique C´eleste et de Calcul des E´ph´em´erides Table6.ThedataareretrievedfromtheMinorPlanetCen-
(IMCCE) were also obtained, including the satellite ter (MPC). The ephemeris used for our observations was
ephemeris by Emelyanov (2005) and planetary ephemeris retrieved from JPL which includes the satellite ephemeris
MNRAS000,1–9(2016)
Precise CCD positions of Himalia using Gaia DR1 7
Table 6. Comparisons made with other observations retrieved
from the MPC. Column 1 shows the IAU code of observatory.

Column 2 lists the number of CCD observations. The following
0.4
columns show the mean (O-C) residuals and its standard devi-
ation (SD) in right ascension and declination, respectively. All
0.3 positions of Himalia are observed topocentric astrometric posi-
tions.Allunitsareinarcseconds.
C 0.2
DE IAU No. hO-Ci SD hO-Ci SD Time(yr)
n code RA DEC
c) i 0.1
e 689 277 -0.013 0.163 -0.013 0.160 2000-2007
s
arc 0.0 415 24 -0.008 0.106 0.065 0.088 2008
C ( 809 23 -0.051 0.092 0.014 0.045 2007-2009
O--0.1 511 357 -0.021 0.049 -0.008 0.061 1997-2008
874 56 -0.039 0.112 -0.026 0.070 1992-2014
874 238 -0.077 0.175 -0.009 0.034 1992-2014
UCAC4
-0.2 874 560 0.001 0.069 -0.018 0.053 1992-2014
Gaia DR1
Our 598 0.071 0.029 -0.001 0.030 2015-2016
-0.3
-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4
O-C (arcsec) in RA
Table7.Extractexampleoftheobservedtopocentricastromet-
ric positions of Himalia. These positions are comparable to the
Figure4.(O-C)residualsofHimaliaindeclinationwithrespect astrometric positions of stars at the same pixel locations with
to right ascension. The dark points represent the (O-C) residu- Himalia.According to Urban & Seidelmann (2013), only proper
als after GD corrections for catalogue UCAC4 and the red ones motionandannualparallaxesaretakenintoaccountintheastro-
represent the (O-C) residualsafter GD corrections forcatalogue metricplacecomputationofstars.Thustheaberrationisignored.
GaiaDR1.TheephemeriswasretrievedfromJPLwhichincludes TheobservedtopocentricastrometricpositionsofHimaliainthis
thesatelliteephemerisJUP300andplanetaryephemerisDE431. paper can also be directly compared to the positions in its as-
Thetwodarkdashlinesrepresentzerolinesineachdirection. trometric ephemeris. Column 1 shows the exposure middle time
ofeachCCDobservationinformofJulianDate(UTC).RAand
DEC are the observed topocentric astrometric positions inright
ascensionanddeclination,respectively.
Table 5. Statistics on the (O-C) residuals for Himalia in com-
parisonwiththetwodifferentephemerides. Column1showsthe
Date RA DEC
number of CCD observations. Column 2 shows the ephemeris
JD hms ◦ ′ ′′
used. The following columns list the means of (O-C) residuals
andtheirstandarddeviationsinrightascensionanddeclination, 2457054.134398 092228.8650 164524.733
respectively. The ephemerides retrieved from IMCCE and JPL 2457054.136921 092228.8028 164525.122
are Emelyanov (2005)/DE431 and JUP300/DE431, respectively. 2457054.138322 092228.7675 164525.338
Allunitsareinarcseconds. ...... ...... ......
2457489.135787 110312.1353 071608.834
Year N Ephemeris hO-Ci SD hO-Ci SD 2457489.136609 110312.1150 071608.979
RA DEC 2457489.137488 110312.0936 071609.134
2015 185 IMCCE 0.017 0.023 0.026 0.023
JPL 0.056 0.023 0.015 0.022
2016 413 IMCCE 0.082 0.029 0.004 0.030 6 CONCLUSIONS
JPL 0.078 0.029 -0.009 0.030
Inthispaper,atotalof598CCDobservationsobtainedfrom
Total 598 IMCCE 0.062 0.040 0.011 0.030 the 2.4 m and 1 m telescopes administered by YunnanOb-
JPL 0.071 0.029 -0.001 0.030 servatories were processed. Several factors were analyzed,
including the reference star catalogue used, the geometric
distortionandthephaseeffect.Thereferencestarcatalogue
JUP300andplanetaryephemerisDE431.Table6showsthe GaiaDR1andUCAC4werebothusedforastrometricreduc-
statistics on the (O-C) residuals. The positions of Himalia tion and havebeen made with comparisons. Positional pre-
are observed topocentric astrometric positions. It can be cision of Himalia has been significantly improved after GD
seen that our positional precision has significant improve- corrections. The systematic errors existingin theresultsby
ments. usingUCAC4 aresignificantly reducedafter Gaia DR1was
Table 7 lists the extract example of the observed used. Comparisons between the two different ephemerides
topocentric astrometric positions of Himalia. The positions whichretrievedfromJPLandIMCCEhavebeenmade.Our
are listed with respect to Julian Date (UTC). RA which results show that the means of (O-C) residuals of Himalia
expressed in hours, minutes and seconds are the observed are 0.071′′ and -0.001′′ by using ephemeris retrieved from
topocentric astrometric positions of Himalia in right ascen- JPL in right ascension and declination, respectively. Their
sion. DEC are the observed topocentric astrometric posi- standarddeviationsareestimatedatabout0.03′′ ineachdi-
tionsofHimaliaindeclination,expressedindegrees,arcmin- rection. This positional precision of Himalia is significantly
utesand arcseconds. improved by taking advantage of the unprecedent precision
MNRAS000,1–9(2016)
8 H. W. Peng et al.

0.3 0.3
JPL JPL
IMCCE IMCCE
0.2 0.2
A A
R 0.1 R 0.1
n n
c) i c) i
se 0.0 se 0.0
c c
ar ar
C ( C (
O- -0.1 O- -0.1
-0.2 -0.2
-0.3 -0.3
52 54 56 58 60 62 64 66 68 70 445 450 455 460 465 470 475 480 485 490 495
JD-24 57000 JD-24 57000
0.3 0.3
JPL JPL
IMCCE IMCCE
0.2 0.2
C C
E 0.1 E 0.1
D D
n n
c) i c) i
se 0.0 se 0.0
c c
ar ar
O-C ( -0.1 O-C ( -0.1
-0.2 -0.2
-0.3 -0.3
52 54 56 58 60 62 64 66 68 70 445 450 455 460 465 470 475 480 485 490 495
JD-2457000 JD-2457000
Figure5.(O-C)residualsofthepositionsofHimaliaincomparisonwiththetwodifferentephemerides.Theuppertwopanelsshowthe
(O-C)residualsinrightascensionintheyear2015and2016,respectively.Thelowertwopanelsshowthe(O-C)residualsindeclination
in the two years. The dark points represent the (O-C) residuals after GD corrections for the ephemeris retrieved from IMCCE which
includesthesatelliteephemerisbyEmelyanov(2005)andplanetaryephemerisDE431.Theredpointsrepresentthe(O-C)residualsafter
GD corrections for the ephemeris retrieved from JPL which includes the satellite ephemeris JUP300 and planetary ephemeris DE431.
Ineach panel,the darkdashlineandreddashlinerepresentthemeans of(O-C)residualsafterGD corrections onrightascension and
declinationforthetwoyearsseparately.
of star catalogue Gaia DR1 in comparison with previous REFERENCES
works.
AgnorC.B.,HamiltonD.P.,2006,Nature,441,192
ColomboG.,FranklinF.A.,1971, Icarus,15,186
deBruijneJ.H.J.,2012,Ap&SS,341,31
ACKNOWLEDGEMENTS EmelyanovN.V.,2005,A&A,435,1173
FanY.F.,BaiJ.M.,ZhangJ.J.,WangC.J.,ChangL.,XinY.X.,
This research work is financially supported by the Na- ZhangR.L.,2015,ResearchinAstronomyandAstrophysics,
tional Natural Science Foundation of China (grant nos. 15,918
U1431227,11273014). We acknowledge the support of FolknerW.M.,WilliamsJ.G.,BoggsD.H.,ParkR.S.,Kuchynka
the staff of the Lijiang 2.4 m telescope. Funding for the P.,2014,IPNProgressReport,196,1
telescope has been provided by CAS and the People’s GaiaCollaboration,PrustiT.etal.,2016a,A&A,595,A1
Government of Yunnan Province. We also acknowledge GaiaCollaboration,BrownA.G.A.etal.,2016b,A&A,595,A2
GiorginiJ.D.etal.,1996,DPS,28,2504
the support of the staff of the 1 m telescope at Yun-
Gomes-Ju´niorA.R.etal.,2015,A&A,580,76
nan Observatories. This work has made use of data
from the European Space Agency (ESA) mission Gaia Grav T., Bauer J. M., Mainzer A. K., MasieroJ. R., Nugent C.
R.,CutriR.M.,SonnettS.,KramerE.,2015,ApJ,809,3
(http://www.cosmos.esa.int/gaia), processed by the
HeppenheimerT.A.,PorcoC.,1977,Icarus,30,385
Gaia Data Processing and Analysis Consortium (DPAC,
HohenkerkC.,2015,jsrs.conf,256
http://www.cosmos.esa.int/web/gaia/dpac/consortium).
Jacobson R. A., 2013, American Astronomical Society, DDA
FundingfortheDPAChasbeenprovidedbynational insti- meeting#44,402,04
tutions, in particular the institutions participating in the LindegrenL.,1977,A&A,57,55
Gaia Multilateral Agreement. LindegrenL.etal.,2016,A&A,595,A4
MNRAS000,1–9(2016)
Precise CCD positions of Himalia using Gaia DR1 9
Nesvorny´D.,Vokrouhlicky´D.,MorbidelliA.,2007,AJ,133,1962
Nesvorny´D.,Vokrouhlicky´D.,DeiennoR.,2014,ApJ,784,22
Nicholson P. D., 2008, The Solar System Beyond Neptune, eds.,
BarucciM.A.,Tucson:Univ.ArizonaPress,411
PengQ.Y.,VienneA.,ZhangQ.F.,DesmarsJ.,YangC.Y.,He
H.F.,2012,AJ,144,170
Peng Q. Y., Wang N., Vienne A., Zhang Q. F., Li Z., Meng X.
H.,2015,MNRAS,449,2638
PengH.W.,WangN.,PengQ.Y.,2016,ResearchinAstronomy
andAstrophysics,16,186
PerrineC.D.,1905,LickObservatoryBulletin,3,129
PollackJ.B.,BurnsJ.A.,TauberM.E.,1979,Icarus,37,587
SheppardS.S.,JewittD.C.,2003,Nature,423,261
StoneR.C.,2002, PASP,114,1070
UrbanS.E.,SeidelmannP.K.,2013,ExplanatorySupplementto
theAstronomicalAlmanac-3rdEdition,LibraryofCongress
Cataloging-in-PublicationData,page281
WangN.,PengQ.Y.,ZhangX.L.,ZhangQ.F.,LiZ.,MengX.
H.,2015,MNRAS,454,3805
Zacharias N.,FinchC.T.,GirardT.M.,Henden A.,Bartlett J.
L.,MonetD.G.,ZachariasM.I.,2013,AJ,145,44
Zhang Q. F., Peng Q. Y., Zhu Z., 2012, Research in Astronomy
andAstrophysics,12,1451
ZhouJ.G.,LiZ.L.,WangB.,2001PYunO,86,42
Thispaper has been typeset fromaTEX/LATEXfile preparedby
theauthor.
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