Hot Stuff for One Year (HSOY) - A 583 million star proper motion catalogue derived from Gaia DR1 and PPMXL

0.84 MB·

by  Martin Altmann

Astronomy&Astrophysicsmanuscriptno.paper161˙arxiv (cid:13)c ESO2017
February23,2017
LettertotheEditor
Hot Stuff for One Year (HSOY)
A 580 million star proper motion catalog derived from Gaia DR1 and PPMXL
M.Altmann1,S.Roeser1,2,M.Demleitner1,U.Bastian1,andE.Schilbach1,2
1 Zentrum fu¨r Astronomie der Universita¨t Heidelberg, Astronomisches Rechen-Institut, Mo¨nchhofstr. 12-14, 69120 Heidelberg,
Germanye-mail:[email protected]
2 Zentrumfu¨rAstronomiederUniversita¨tHeidelberg,LandessternwarteKo¨nigsstuhl,Ko¨nigsstuhl12,69117Heidelberg,Germany
ReceivedJanuary04,2017,acceptedxxx
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ABSTRACT
0
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Context.Recently,thefirstinstallmentofdatafromESA’sGaiaastrometricsatellitemission(GaiaDR1)wasreleased,containing

b positions of more than 1 billion stars with unprecedented precision, as well as proper motions and parallaxes, however only for a
e subsetof2millionobjects.Thesecondreleasewillincludethosequantitiesformostobjects.
F Aims.InordertoprovideadatasetthatbridgesthetimegapbetweentheGaiaDR1andGaiaDR2releasesandpartlyremediesthelack
ofpropermotionsintheformer,HSOY(”HotStuffforOneYear”)wascreatedasahybridcatalogbetweenGaiaandground-based
2
astrometry,featuringpropermotions(butnoparallaxes)foralargefractionoftheDR1objects.Whilenotattemptingtocompetewith
2
futureGaiareleasesintermsofdataqualityornumberofobjects,theaimofHSOYistoprovideimprovedpropermotionspartly

basedonGaiadata,allowingstudiestobecarriedoutjustnoworaspilotstudiesforlaterprojectsrequiringhigher-precisiondata.
]
A Methods.TheHSOYcatalogwascompiledusingthepositionstakenfromGaiaDR1combinedwiththeinputdatafromthePPMXL
catalog,employingthesameweightedleast-squarestechniquethatwasusedtoassemblethePPMXLcatalogitself.
G Results.Thiseffortresultedinafour-parameterastrometriccatalogcontaining583millionstars,withGaiaDR1qualitypositions
. andpropermotionswithprecisionsfromfarlessthan1mas/yrto5mas/yr,dependingonobjectbrightnessandlocationonthesky.
h
p Keywords.astrometry–catalogs–Galaxy:kinematicsanddynamics–propermotions
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o
r
t 1. Introduction
s
a
1e8
[ Gaia, ESA’s 1-billion star astrometric space mission (Gaia

2 Collaboration , 2016a) set out in late 2013 to revolutionise
v (among many other fields of astronomy) our understanding of
9 the kinematics, the structure and evolution of our Galaxy. On 1e6
2 September 14, 2016, the Gaia consortium published the first
6 GaiaDatarelease,GaiaDR1(GaiaCollaboration,2016b),con-
2 taining the positions and broad-band photometry for 1.143 bil- n
1e4
0 lionobjects. Giventheshorttimespanofthemeasurementsin-
.
1 corporatedintothisrelease(lessthan15months),theseparation
0 of parallaxes and proper motions was not possible. Therefore
7 Gaia DR1 in general does not include these quantities, with 100
1 the exception of a small subset of those 2 million stars already
: presentintheHipparcos(ESA,1997)orTycho2catalogs(Høg
v
i et al., 2000). Using this data as a first epoch, proper motions
X 1
and parallaxes could be disentangled, yielding the Tycho Gaia
5 10 15 20 25
r AstrometricSolution(TGAS,Michaliketal.,2015).Thusmost
a Gmag[mag]
astrometry-related projects within the astronomical community
might focus on the TGAS data, as well as on preparing for the Fig.1. Distribution of object counts in HSOY over the Gaia G
nextGaiarelease. magnitude(red filled circles). As comparison, the object counts
forGaiaDR1arealsoshown(blueopentriangles).
Inthemeantime,wepresentaveryshort-livedyetpowerful
astrometriccatalog,addingvalueandscientificusecasestoGaia
DR1.Itprovidespropermotionsfor583millionobjects,i.e.for
more than half of the objects for which Gaia DR1 only gives
positions.ThisisachievedbycombiningdatafromthePPMXL precise positions of DR1 and the ultra-precise full 5 parameter
catalog (Roeser et al., 2010) and Gaia DR1 positions. Named astrometryofDR2.
”HSOY” (Hot Stuff for One Year), highlighting its short-lived UntilHSOYwillbesupersededbyGaiaDR2,itpresentsthe
nature,weintendtopartlyfillthegapintimebetweentheultra- best set of proper motions in existence in the magnitude range
1
M.Altmannetal.:HotStuffforOneYear(HSOY)
6
¢¹®cos±(±>¡30±)
5 ¢¹±(±>¡30±)
¢¹®cos±(±<¡30±)
¢¹±(±<¡30±)
4
yr]
=
as
m 3
[
¹avg
¢
2
1
0
4 6 8 10 12 14 16 18 20
Gmag[mag]
Fig.2.MeanstandarderrorsinpropermotionsoftheHSOYcat-
alognorthandsouthofδ=−30◦.Theerrorsaregiveninbinsof
onemagnitudecenteredonfullGaiaGmagnitudes.Thesymbols
aredefinedinthelegendboxwithintheplot
fainter than TGAS to G = 20 mag, and is a valuable base for
studiesofstellarkinematics.
Sect. 2 describes the assembly of this catalog and its input
data,aswellasgivingtheoverallcharacteristicsofthiscatalog.
In Sect. 3 we demonstrate the improvement of the precision of
propermotionsofHSOYwithrespecttocurrententirelyground-
basedvalueswithtwosciencecaseexamples.
2. PresentingHSOY
2.1. ConstructionandstellarcontentofHSOY
HSOYhasbeenconstructedusingthemethodpreviouslyusedto
assemblethePPMXLcatalog(Roeseretal.,2010),whichitself
nowformsoneoftheinputdatasetsforHSOY.ForPPMXLthe
inputdatawerethe2MASS(Skrutskieetal.,2006)andUSNO-
B1.0 catalogs (Monet et al., 2003), for HSOY, accordingly,
PPMXL and Gaia DR1. The procedure of construction, de- Fig.3. The upper two panels show the global variation of the
scribedindetailinRoeseretal.(2010),involvescross-matches r.m.s. errors in proper motion (upper panel, right ascension,
between the datasets, and a weighted least-squares fit to derive middle panel, declination) in equatorial coordinates. Darker
positionsandpropermotions. shades/colours indicate higher errors. The bottom panel shows
PPMXL contains about 900 million, and Gaia DR1 1.1 thedensityofHSOYinstarspersquaredegreesovertheentire
billion sources. Yet HSOY only contains 583,001,653 entries, skyingalacticcoordinateshighlightingtheoveralluniformityof
i.e. about 50-60% of the object numbers of the input catalogs. thecatalog.
Fig. 1 shows the object counts for both HSOY and Gaia DR1.
Of course, HSOY can only contain objects which are in both
PPMXLandGaiaDR1.Objectsthatdidnotmakeitintothefinal ject for each pair member and the observations had sufficient
HSOYareveryprobablynon-stellarobjectsandfailedmatches precision, they will form a close, common proper motion pair
originatingintheUSNO-B1.However,theinhomogeneoussky inPPMXLandwillconsequentlybematchedtothesameGaia
coverageofGaiaDR1(GaiaCollaboration,2016b)mostlikely DR1 object. Such objects (and a few other cases where two or
alsoplaysarole. morePPMXLobjectsarematchedtothesameGaiaDR1object)
On the other hand, there still is a significant fraction of en- aremarkedwithanon-NULLcloneflag(0.7%oftheentirecat-
triesprobablynotrelatedtophysicalobjectsinHSOY.Themost alog).PPMXLcontainedabout24.5millionobjectswithproper
commonformofthesearespuriouspairs.Thesemayarisefrom motions larger than 150 mas/yr on the northern hemisphere,
observations that have not been matched in USNO-B, either alone against an expectation of about 105 as discussed in the
from different epochs or from different plates. As long as the PPMXLpaper.Theprocedureoutlinedabovebringsthenumber
originalUSNO-Bmatcheduptwoobservationsofthesameob- ofhigh-PMobjectsinHSOYdownto2.5millionontheentire
2
M.Altmannetal.:HotStuffforOneYear(HSOY)
Table1.ContentoftheHSOYcatalog. determinedbytheprecisionofthepropermotions.Theseareat
maximum 5 mas/yr (see below), so the positional rms-errors at
Name Unit description J2000.0arewellbelow0.1arcsec,andarenotindividuallygiven
1 ipix – PPMXLobjectidentifier in the catalog. Since for the HSOY-proper motions, PPMXL’s
2 comp – flagindicatingmultipleGaiamatches positions are necessary, the vastly higher precision of the Gaia
toonePPMXLobject DR1-positions does not dominate as in the case of the mean-
3 raj2000 degrees RAatJ2000.0,epoch2000.0 epochpositionsintheHSOYcatalog.Thisalsomeansthatthey
4 dej2000 degrees Decl.J2000.0,epoch2000.0
reflectsomeofthesystematicerrorsinthePPMXL,suchasthe
5 e ra degrees Meanerror:αcosδatmeanepoch
zonalerrorspresentinallground-basedcatalogsofsimilartype
6 e de degrees Meanerror:δatmeanepoch
7 pmra deg/yr Propermotioninαcosδ (Roeser et al., 2010). This is to be kept in mind, when using
8 pmde deg/yr Propermotioninδ HSOY proper motions. Due to the addition of Gaia DR1 these
9 e pmra deg/yr Meanerrorinµ cosδ systematics are reduced to a certain extent, but do not vanish
α
10 e pmde deg/yr Meanerrorinµ altogether1. Given the much smaller positional errors of Gaia
δ
11 epra yr MeanEpochinRA(α) DR1,thecorrelationsbetweentheerrorsinRAanddeclination
11 epde yr MeanEpochinDec.(δ) in Gaia DR1 can here be neglected. Generally the average for-
13 jmag mag 2MASSJmagnitude mal errors for HSOY proper motions range from < 0.2 mas/yr
14 e jmag mag errorof2MASSJmag. forstarsbrighterthan8mag,upto4or5mas/yrnearthefaint
15 hmag mag 2MASSHmagnitude
magnitudelimit,seeFig.2.
16 e hmag mag errorof2MASSHmag.
Fig.3exhibitsmuchlargererrorsinbothpropermotioncom-
17 kmag mag 2MASSKmagnitude
ponents at declinations south of −30◦- the mean formal errors
18 e kmag mag errorof2MASSKmag.
there are slightly less than double of those in the rest of the
19 b1mag mag Bmag:USNO-B,1stepoch
20 b2mag mag Bmag:USNO-B,2ndepoch sky, as shown in Fig. 2. This is inherited from the underlying
21 r1mag mag Rmag:USNO-B,1stepoch plate surveys: the first all-sky Schmidt plate surveys started in
22 r2mag mag Rmag:USNO-B,2ndepoch thenorthernhemisphereinthe1950sandwereextendedtothe
23 imag mag Imag:USNO-B south only much later in the 1970s. Therefore the baseline for
24 surveys – OriginofUSNO-Bmags proper motions in the southern quarter of the sky is shorter by
25 nobs – total number of astrometric observa- 20 years, with the corresponding consequences for the formal
tions(n +1)
PPMXL proper motion uncertainties. Apart from this issue the errors in
26 gaiaid – Gaiauniquesourceidentifier
propermotionoverthewholeskyareremarkablyhomogeneous,
27 Gmag mag meanGaiaG-bandmagnitude
beingjustalittlehighernearthedenseareasoftheMilkyWay.
28 e Gmag mag estimatederrorofGaiaG-mag
Note that we used the original PPMXL proper motions rather
29 clone – >1PPMXLmatchtoGaiaobject
30 no sc – objectnotinSuperCOSMOS than the possibly more inertial ones given by (Vickers et al.,
2016)sincethelatterareonlyavailableforobjectswith2MASS
photometryandhencelessthanhalfthePPMXL.
sky(2.5·105 inthenorth).Hence,therearestillmanyspurious HSOY is not a dedicated photometric catalog; therefore it
high PM objects in HSOY accidentally matching a (real) Gaia utilises all photometry that its input catalogs supply. From its
DR1objectatJ2015.Anotherreductionofthespurioussources PPMXL parent, it retains the photographic magnitudes taken
can be effected by matching PPMXL against SuperCOSMOS fromtheUSNO-B1catalogandtheNIR2MASSvalues.Added
(Hambly et al., 2001), an independent source extraction from tothisistheGaiaDR1G-magnitude.Therefore,formoreinfor-
the plate collections underlying USNO-B at J2000. Where no mation regarding the quality of the photometry, we refer to the
suchmatchcanbefoundwithin3(cid:48)(cid:48),HSOYsettheno sccolumn originalsources,i.e.GaiaDR1,USNO-B1,and2MASS.
to 1. On the northern sky, only using objects with matches in As for Gaia DR1 itself, the primary access mode to HSOY
SuperCOSMOS,only168206objectswithµ > 150mas/yr are is the Virtual Observatory protocol TAP through the service at
left,withinafactoroftwooftheleveltobeexpectedfromLPSM http://dc.g-vo.org/tap. Further access options are discussed at
(Le´pine & Shara, 2005). All-sky, including the very crowded http:///dc.g-vo.org/hsoy(Demleitneretal.,2015).Table1shows
fields on the southern sky, there are about 1.38·106 high-PM thedatacontentofHSOY.
objectswithmatchesinSuperCOSMOSinHSOY.
Conversely, sometimes more than one Gaia DR1 object is
withinonePPMXLobjects’matchradius.Whileincomecases, 3. ThepropermotionsofM4andM67asscience
thismaybeduetotruebinariesalreadyresolvedbyGaia,more caseexamples
typically they willbe due to failedobservation matching in the
InordertodemonstratetheincreasedcapabilitiesofHSOY,es-
constructionofGaiaDR1andshouldthereforegenerallybecon-
pecially with respect to earlier, entirely ground-based catalogs,
sideredspuriouspairs,too.Theyaremarkedwithanon-NULL
e.g. PPMXL, we present the proper motion distributions in the
comp flag (1.5% of the entire catalog). In both catalogs, there
fieldsoftheglobularclusterM4(NGC6121)andtherich,old
areacoupleofhundredsourcesfainterthan21mag,seeFig.1.
openclusterM67(NGC2682).Theseobjectsareespeciallyin-
Thesehavetobeconsideredspurioussources.
structive,giventheirlargepropermotionandhighstellardensity.
ForM4wedownloadedacircularfieldwitharadiusof0.5◦,
2.2. TheastrometricprecisionofHSOY whichwasfoundtoshowboththeclusterandthefieldstarsbest,
frombothcatalogs.ThefieldofviewisshowninFig.4.There-
For the positions, the overwhelming precision of Gaia DR1 re-
sultingvectorpointdiagrams(VPD)arealsoshowninFig.4.A
sults in mean epochs close to that of Gaia DR1 of 2015.0; the
meanepochofmostobjectsinHSOYisnear2014.8.InHSOY, 1 Itwouldinprinciplebepossibletoreducetheseerrorsevenfurther
the positions are given for epoch J2000.0 by applying proper by re-constructing the PPMXL itself using Gaia DR1, but this is not
motions.Also,theformalprecisionofthesepositionsisentirely worthwhileonthetimescaleoftheusefullifeofHSOY
3
M.Altmannetal.:HotStuffforOneYear(HSOY)
50 50
PPMXL HSOY
40 120 40 120
¡26:2 30 110100 30 110100
20 90 20 90
(J20000)[deg]±:¡¡2266::64 [masyr]¹=±¡1210000 4567800000 Density[starspixel]= [masyr]¹=±¡1210000 4567800000 Density[starspixel]=
¡ ¡
¡26:8 30 30 30 30
¡ 20 ¡ 20
40 40
¡ 10 ¡ 10
27:0
¡ 50 0 50 0
246:4 246:2 ®24(J62:0000:002[4d5e:g8] 245:6 245:4 ¡¡50 ¡40 ¡30 ¡20 ¡¹1®0cos±0[mas=1y0r] 20 30 40 50 ¡¡50 ¡40 ¡30 ¡20 ¡¹1®0cos±0[mas=y1r0] 20 30 40 50
Fig.4. left panel: plot of the field with a radius of 30’ taken from the HSOY catalog centered around M 4 . The center and right
panelsshowthevectorpointdiagramsoftheM4region,withpropermotionstakenfromthePPMXL(centre)andHSOY(right).
TheholeinthemiddleoftheplotiscausedbythestrongcrowdinginthecentralpartofM4,thefewpointsinsidethisholecanbe
consideredasbeingspurious,whichmeanstheyhavetobysuppressedinanykindofanalysis.
50 50
PPMXL HSOY
40 120 40 120
12:5 110 110
30 30
100 100
20 90 20 90
(J20000)[deg]±:1112::50 [masyr]¹=±¡1210000 4567800000 Density[starspixel]= [masyr]¹=±¡1210000 4567800000 Density[starspixel]=
¡ ¡
30 30 30 30
¡ 20 ¡ 20
11:0 40 40
¡ 10 ¡ 10
50 0 50 0
133:5 ®13(J32:0000:00[deg1]32:5 132:0 ¡¡50 ¡40 ¡30 ¡20 ¡¹1®0cos±0[mas=1y0r] 20 30 40 50 ¡¡50 ¡40 ¡30 ¡20 ¡¹1®0cos±0[mas=y1r0] 20 30 40 50
Fig.5.leftpanel:plotofthefieldwitharadiusof1degreesaroundM67takenfromtheHSOYcatalog.Thecenterandrightpanels
showthevectorpointdiagramsoftheM67region,withpropermotionstakenfromthePPMXL(centre)andHSOY(right).
comparisonoftheVPDmadefromthePPMXLpropermotions than either the current catalogs or Gaia, and will continue the
(centrepanel)withthatmadefromHSOYdataclearlyshowsthe traditionofspace-calibratedground-basedastrometriccatalogs.
dramatic improvement. Although the PPMXL has significantly
morestarsinthisfieldthanHSOY(42,000vs. 30,000),theM4 Acknowledgements. S. Roeser and E. Schilbach were supported by
SonderforschungsbereichSFB881TheMilkyWaySystem(subprojectsB5)of
propermotionpeakismuchmoreandthefieldpeaksomewhat
theGermanResearchFoundation(DFG).Itisagreatpleasuretoacknowledge
morepronouncedinthelattercase.
Mark Taylor from the Astrophysics Group of the School of Physics at the
The open cluster, M 67, one of the oldest of its kind and UniversityofBristolforhiswonderfulworkonTOPCAT,ToolforOPerations
rather populous, is our second demonstration object. Fig. 5 onCataloguesAndTablesandSTILTS,StarlinkTablesInfrastructureLibrary
showsthefieldandthevectorpointdiagramsforbothPPMXL Tool Set. This research has made use of the resources of CDS, Strasbourg,
France. Technical and publication support was provided by GAVO under
(centre) and HSOY (right), this time, given the less dense en-
BMBFgrant05A14VHA.ThisworkhasmadeuseofdatafromtheEuropean
vironment, using a field with a radius of 1◦. Again the clear Space Agency (ESA) mission Gaia (http://www.cosmos.esa.int/gaia),
improvement is seen by comparing the centre and right panels processed by the Gaia Data Processing and Analysis Consortium (DPAC,
in Fig. 5. While the PPMXL only shows hints of the cluster, it http://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding
for the DPAC has been provided by national institutions, in particular the
clearlystandsoutintheVPDgeneratedusingHSOY.
institutionsparticipatingintheGaiaMultilateralAgreement.
Both demonstration cases, i.e. M 4 and M 67 highlight the
scientific potential of this catalog. The improvement is clearly
shown.Therearecertainlymanyothersciencecaseswhichwill References
profitfromtheexistenceofHSOY.
Demleitner,M.,Roeser,S.,Proft,S.,2015,”HsoyObjectCatalog”,http://
dc.zah.uni-heidelberg.de/tableinfo/hsoy.main
ESA1997,ESASpecialPublication,1200
4. Outlook
GaiaCollaboration,Brown,A.G.A.,Vallenari,A.,etal.2016b,A&A,595,A2
GaiaCollaboration,Prusti,T.,deBruijne,J.H.J.,etal.2016a,A&A,595,A1
Inalittlemorethanayearfromnow,GaiaDR2willbereleased
Hambly,N.C.,MacGillivray,H.T.,Read,M.A.,etal.2001,MNRAS,326,1279
and will thus make HSOY obsolete. However, we believe that Høg,E.,Fabricius,C.,Makarov,V.V.,etal.2000,A&A,355,L27
thiscatalogwillbeputtogooduseuntilthen.Inawayitisthe Le´pine,S.,&Shara,M.M.2005,AJ,129,1483
finalversionofthesecond-generationground-basedastrometric Michalik,D.,Lindegren,L.,&Hobbs,D.2015,A&A,574,A115
Monet,D.G.,Levine,S.E.,Canzian,B.,etal.2003,AJ,125,984
catalogs,i.e.,thosedonebeforeoratthebeginningoftheCCD
Roeser,S.,Demleitner,M.,&Schilbach,E.2010,AJ,139,2440
age, but with old photographic plates as the long time-baseline
Skrutskie,M.F.,Cutri,R.M.,Stiening,R.,etal.2006,AJ,131,1163
basis.Ontheotherhanditpresentsabridgetoanewgeneration Vickers,J.J.,Ro¨ser,S.,&Grebel,E.K.2016,AJ,151,99
of ground-based astrometric surveys, now based on Gaia data,
suchaswhatwillcomeoutofLSST.Thesewillgomuchfainter
4