Revised distances of Northern HII regions

27 Pages·2007·5.3 MB·English

A&A470,161–171(2007) Astronomy
DOI:10.1051/0004-6361:20066051 &
(cid:1)c ESO2007 Astrophysics
(cid:1),(cid:1)(cid:1)
Revised distances of Northern HII regions
D.Russeil1,C.Adami2,andY.M.Georgelin1
1 LAM,2PlaceLeVerrier,13248MarseilleCedex04,France
e-mail:[email protected]
2 LAM,TraverseduSiphon-LestroisLucs,BP8,13376MarseilleCedex12,France
Received17July2006/Accepted19April2007
ABSTRACT
Aims.OuraimistodeterminethedistanceofouterGalaxystar-formingcomplexesinordertomodelthekinematicstructureofour
Galaxy.
Methods.Wesearched for exciting star(s) of HII regions, with poor or unknown stellar distance, inthe second and third galactic
quadrants.Wecarriedoutspectroscopicandphotometric(whennecessary)observationsinordertoestablishtheirspectraltypeand
theirU,BandV magnitudes.Fromthesedata,complementedwithliteraturedata,wedeterminethespectro-photometricdistanceof
theirassociatedcomplexes.
Results.We (re)established the stellar distance of 23 star forming complexes. Reinvestigating the kinematics of the Perseus and
Cygnusarms,wedeterminedthevelocitydeparturesfromcircularrotationandweinterpretedthemasstreamingmotionsinthespiral
arms. Indeed, in addition to the Perseus arm where such departures were known for a long time, we added evidence for velocity
deviationsintheCygnusarm.MostsignificantisthatwefoundtheoppositesignforthesedeparturesinthePerseusandCygnusarms,
whichsuggeststhattheco-rotationradiusislocatedbetweenthesetwoarmsat∼13kpcfromthegalacticcenter.
Keywords.Galaxy:general–Galaxy:kinematicsanddynamics–Galaxy:structure–ISM:HIIregions
1. Introduction We havefocussedourstudyonthese galacticquadrantsfor
tworeasons:
The study of the kinematics and spiral structure of the
– In these quadrants the Perseus spiral arm is the dominant
MilkyWayrequirestheestablishmentofthedistanceofthestar-
structuralfeatureforwhich we wantto determinethe kine-
formingcomplexesdistributedinto the arms. This can be done
matics. Velocity anomalies in the Perseus arm have been
viakinematicorstellardistancedeterminations.
known for a long time (Rickard 1968; Humphreys 1970,
1976;Brand&Blitz1993).Morerecently,Heyer&Terebey
– The kinematic distance determination is based on the rota-
(1998) show evidence that expanding motions are present
tioncurveofourGalaxyassumingtheobjectsareincircular
withinthePerseusarm.
rotation.Butdeparturesfromcircularrotationarecommonly
– Inthesecondandthirdquadrantswecandeterminethestel-
noted inducing sometimes significant errors. In addition,
lardistanceoftheCygnusarmcomplexes(thisisimpossible
these distances are unreliable toward center and anticenter
in the inner galactic directions because of their larger dis-
directions. Finally, they depend on the solar parameters R
0
andθ whichweregraduallyrevisedtolowervalues(Vallée tance and significant extinction). We want to confirm and
0 specify the design of the Cygnus arm (=External arm =
2005).Thisshortensthededucedkinematicdistances.
Outer arm) as well as its velocity departure we suspected
– Itisthenessentialtoestablishthestellardistanceofthestar-
in the previous paper (Russeil 2003). Indeed, it was noted
forming complexes. This is done from the stellar distance
that beyond the Perseus arm there are complexes which
of their constitutive HII regions. But, still today, numerous
are very sparsely distributed. Several authors demonstrated
HII regions have a very uncertain distance. This is mainly
the presence of far-outer Galaxy molecular material: e.g.
duetouncertaintyin,orabsenceof,thespectraltypedeter-
Kutner&Mead(1981),Digeletal.(1994,1994),Wouterloot
minationaswellastomisidentificationoftheexcitingstars.
& Brand (1989), Brand & Wouterloot (1994), May et al.
(1997), Heyer et al. (1998), Brunt et al. (2003), Nakagawa
In this framework, we have selected from the catalogue of
etal.(2005).Kaltcheva&Hilditch(2000),fromthedistribu-
Russeil (2003), the complexesof the second and third galactic
tionofbrightOBstarstowardslongitudes225◦and245◦and
quadrantswhichhaveuncertainornodistancedeterminationin
Kimeswenger&Weinberger(2004),fromthedistributionof
orderto(re)establishtheirstellardistance.
opticaltracersinthesecondgalacticquadrant,suggestedthe
presenceofanexternalarmbeyondthePerseusarm.
(cid:2) BasedonobservationscollectedattheHaute-Provence
Observatory. Complexesin the far-outerGalaxyare importantto specifythe
(cid:2)(cid:2) AppendixAisonlyavailableinelectronicformat presenceanddesignoftheCygnusarm,inadditiontotracethe
http://www.aanda.org rotationcurveatlargegalactocentricdistance.
Article published by EDP Sciences and available at http://www.aanda.orgor http://dx.doi.org/10.1051/0004-6361:20066051
162 D.Russeiletal.:ReviseddistancesofNorthernHIIregions
2. Observationsandspectralclassification Table1.Spectralclassificationofknownstars.
WehaveselectedfromthecatalogueofRusseil(2003),thecom-
Star Spectraltype Spectraltype
plexes of the second and third galactic quadrants, observable
(literature) (found)
from OHP (Observatoire de Haute-Provence), which have un-
GammaOri. B2III B2.5V
certainornodistancedetermination.Toexcludelocalarmcom- EtaHyade B3V B2V
plexeswefocusourstudyoncomplexeswithkinematicdistance HD214680 O9V O9V
fartherthan1kpcandgalacticlatitudewithin±6◦.Forthecom- UpsilonOri. B0V B0V
plexes selected we excluded HII regionsthat are very extented HD215835 O6V O5V
or withveryunclearmorphologyand/orwithoutMSX orradio HD225160 O8Ib O7.5Ia
counterpart. For these HII regions the exciting star(s) are very
diffulttoidentify.
The selected HII regions can be divided into three groups:
wecorrectedfortheflat-field(tungstenlamp),biasandskycon-
HII regionswith photometricand spectroscopic data in the lit-
tribution.Thewavelengthcalibrationwas madeusinganargon
erature,HIIregionswithonlyphotometricdataintheliterature
lamp.
andHIIregionswithnodataatallorveryunreliabledatainthe
literature. For the first group we directly deduced the spectro-
photometric distance, for the second group we complemented
2.3.Thespectralclassification
thephotometricdatawithspectroscopicobservationsoftheex-
citing star candidatesandfinally forthe third groupwe carried Amid the observedspectra we selectthe hotstar candidateson
outphotometricandspectroscopicobservationsandsearchedfor the basis of the following criterion. For hot (O and B) stars
theexcitingstarscandidates.Inthisway32HIIregionsbelong- the primary criteria is the presence of HeII and/orHeI absorp-
ingto23complexesrequiredobservations. tion lines. The colder stars are characterised by the absence of
Concerningthe exciting stars themselves, we based our se- He lines but the presence of the G band, CaII (H and K) and
lection on the location of the star(s) regarding the HII region CaI linesandnumerousmetallic linesupto TiO bands(forthe
morphology(theexcitingstar(s)candidate(s)areexpectedtobe cooleststars).Thefactthattheselectedstarsarehotisconfirmed
strategicallypositionedintheHIIregionsseeninoptical,radio bytheequivalentwidthoftheHγline.FollowingtheTables8.1
andmid-IR)andfromU,BandV photometricdata(weselected and9.1ofJaschek&Jaschek(1987)thisequivalentwidthgives
thebluestcandidatesofthefields,fromB−VversusU−Bplots). usaroughestimateofthespectraltype.
We limited our selection to stars brighter than V magni- Toassess the spectraltypewecomparespectratothe spec-
tude 17 because we cannot observe in a reasonable exposure tralatlasofWalborn&Fitzpatrick(1990)whichprovideslow-
timethespectraoffainterstars.We thenobtainedthespectrum
resolution spectra in the 4000–4700 Å range. We then re-
forallthesecandidatestodeducetheirspectraltype.
sized, rebined and cross-correlated (the cross-correlation was
performedwithIDL)theobservedspectraofhotstarcandidates
tothereferencespectraallowingforpossiblevelocityshiftsbe-
2.1.Photometry
tweenthem.
U, B and V images have been obtained in 2005 (1–5 Sep.) at TheresultingdataarelistedinTable2.Inthistableforevery
the 1.20-m telescope at the Observatoire de Haute Provence HIIregion(listedinCol.1)wehavedeterminedthecoordinates
(OHP,France).Thef/61.20-mOHPtelescopeisequippedwith (Cols. 3 and 4) for each observed stars from their identifica-
a thinned TK 1024 × 1024 pixels CCD detector, with a pixel tiononDSSimagesusingAladin(Bonnareletal.2000).Aladin
size of 0.69 arcsec and a field of view of 11.8 × 11.8 arcmin. (http://aladin.u-strasbg.fr/aladin.gml)isaninterac-
At the adopted gain, the conversion is 3.5 e-/adu, with a read- tive software sky atlas allowing the user to visualize digitized
outnoiseof8.5e-.Theobservationswerecalibratedandtrans- imagesofanypartofthesky,tosuperimposeentriesfromastro-
formed into the Johnson UBV system using standard stars in nomicalcatalogsorpersonaluserdatafiles,andtointeractively
the catalogue of Landolt (1983). The instrumental magnitudes accessrelateddataandinformationfromarchivesforallknown
on the images have been measured using the Sextractor pack- objects in the field. In Col. 5, we give the determined spectral
age(Bertin&Arnouts1996).Standardstarmeasurementsgave typeforhotstarsonly.Forcoldstarsweonlyindicatethemajor
meandifferencesof0.11mag,thatweassumeasthetypicalun- featureswhichallowustorejectthem.Thelastcolumngivesthe
certainty of the photometricresult. This impliesan uncertainty alternativenameofthestarwhenavailable.Theasteriskfollow-
inthedistanceof2.2%. ingsomestarsnumbermeanstheyhavebeenobservedwiththe
lowerresolutionspectroscopicconfiguration.
2.2.Spectroscopy To estimate the quality of our spectral type determination
we observeda few starswith knownspectraltype in the litera-
TheobservationswerecarriedoutwiththeCARELECspectro- ture.We passedthemthroughourclassificationprocessandre-
graph (Lemaitre et al. 1990), mounted at the Cassegrain focus sults are given in Table 1. Despite the small sample, we note
ofthe193-cmtelescopeoftheOHP.Theobservationswerecar- that main sequencestars are well identified while the luminos-
ried out in three runs (16–21 Sep. 1998, 26–28 Oct. 2005 and ityclassislesswelldeterminedfor(super)giantsstars.Wethen
31Jan.–3Feb.2006)usingtwodifferentgratings.Thegratings adoptastypicalspectraltypeuncertaintythemaximaldifference
used give spectra with dispersion of 33 Å/mm and 133 Å/mm wefound(oneunity)andfor(super)giantsstarsatypicaldiffer-
andaspectralrangeof4055–4978Åand3800–6856Årespec- encefortheluminosityclassoftwo.Onthisbasis,theabsolute
tively.Theslitis5.5arcminlongandhasawidthof2.1arcsec. magnitudeuncertaintyisthendeducedadoptingtheMv-spectral
Theintegrationtimerangedfrom1200sto10800sdepending typecalibrationofRusseil(2003).Thisuncertaintydependson
onthestar’smagnitudeandtheinstrumentalconfiguration.The the actual spectral type and luminosity class found and varies
datareductionwascarriedoutusingMIDAS.Foreachspectrum between 0.24 mag that is to say 0.07 in relative distance
D.Russeiletal.:ReviseddistancesofNorthernHIIregions 163
uncertainty(foraO8V)and2.61magthatistosay0.55inrela-
tivedistanceuncertainty(foraB2IV).
Let us note that we took advantage of CARELEC capabil-
ities to arrange the slit orientation to observe at all times at
least two stars in each exposure, even if the second star is not
acandidate.
3. Thedistanceofstar-formingcomplexes
ThestellardistanceofindividualHIIregionsiscalculatedcom-
biningUBVphotometryandspectraltypeoftheexcitingstarsas
describedinSect.2.2ofRusseil(2003).Theresultsarelistedin
Table3,whiletheidentificationfieldsandspectraoftheexciting
starsarepresentedintheonlineappendix.
On the basis on the new distance determinationfor HII re-
gions we (re)established the distance of the star-forming com-
plexestheybelongto.AcomplexisthegroupingofHIIregions
basedontheirkinematicandspatialnearness.Thedetermination
ofthecomplexesandtheirconstitutingHIIregionswithveloci-
tiesarelistedanddiscussedinRusseil(2003,Table1).
We also re-establishedthe distanceto theotherHII regions
ofthecomplexesusingspectroscopicandphotometricdatafrom
theliterature(usingCDS/Simbadfacilities).Forstarswithonly
photometricdataweadoptanerroronthedistanceof40%.For
othercasesthedistanceerrorisestimatedinthesamewayasfor
ourdata.ThedistanceofHIIregionsandcomplexesarealways
determinedfromtheusualleastsquaredmethod(Meyer1975).
We discuss below the new distance determination for the
complexes(summarizedinTable4andFig.2).Letusnotethat Fig.1.Top:colordiagramofstarsinthefieldofBFS6.Thecurverep-
IAUnotationforSharplessregionsis“Sh2-”butforconvenience resentstheunreddened mainsequence whilethelineisthereddening
inthispaperweabbreviateto“S”.ForexampleSh2-128willbe vector for a B3 star up to Av = 5 mag. Bottom: distribution of stars
abovethereddeningvectorversusthedistance.
notedS128.
The complex 96.0+2.0: This complexgathersthe HII regions that DA 568 is the most prominentpart of a much larger star-
BFS6, BFS7 and S128. Chini & Wink (1984) established the forming complex that includes the optical HII region BFS 10
spectral type (O7V) and UBV photometry of the exciting star (considered as a blister HII region) and numerous associated
ofS128givingadistanceof7.91kpc.Recently,Bohigas&Tapia IRAS sources tracing the last generation of star formation oc-
(2003)reevaluatedthedistance(adoptingthesamespectraltype curinginthecomplex.Thisstar-formingcomplexappearsquite
forthestar)to9.4±0.4kpcusingJandV bandphotometry. evolved,with mostof the parentalgiantmolecularcloudbeing
We observedBFS6 but, unfortunately,no exciting star was severelydisruptedbyDA568.
found from spectroscopy. BFS6 has a quasi-circular (17.7(cid:4) × ItwassuspectedthatthestarALS12050,whichliesnearthe
16.5(cid:4))radiocounterpart,whileitisadiffuseopticalnebula.From center of the radio emission, is a probable exciting star which
ourUBVimages(coveringalargepartoftheradioemissionex- we confirmfromourdata.We determinea distanceforDA568
tension),wemadetheU−BversusB−Vplotofthefieldobjects of4.99±0.32kpcfromthetwostarsidentified.
(Fig. 1, top). We then selected and determinedthe photometric Thedistanceofthecomplexisthen5.25±0.29kpc.
distance (assuming they are main sequence stars) of the bluest
stars (28 stars) brighterthan 17 mag. Plotting the histogram of
The complex 105.6+0.4: This complex is composed of S138
thedistance(Fig.1,bottom)themainfeatureappearsasapeak
and S139. No stellar distance is available for S139. The spec-
at10kpc.Thisfavours9.4kpcforthedistanceofS128.
Wethenadoptforthecomplexadistanceof9.4±0.4kpc. trumofS138stellarcandidateshowsemissionlines,whichpre-
ventsanyspectralclassification.Ourstarcandidatecorresponds
tostar183inDeharvengetal.(1999).FromaspectrumnearHα
The complex 96.3−0.2: This complex consists of BFS8 only. and8600ÅtheyshowthatthestarisprobablyaHerbigBestar.
BSF8isafaintnebulawithadiameterofabout12(cid:4)(Fich1993). The photometric distance of the star has been evaluated in the
We find an O5V star as exciting star for which we established samewayasfornormalstarsandassumingitisamainsequence
adistanceof8.8±0.61kpc. star. Indeed, Wegner (1994) shows there is no significant dif-
ference between the intrinsic flux distribution of normalB and
Bestars.Weevaluateadistanceof2.91±1.4kpc.Weadoptthis
Thecomplex101.4+2.7: ThiscomplexconsistsonlyoftheHII
distanceforthiscomplex.
region BFS10 for which we find a stellar distance of 6.39 ±
0.67 kpc. We now add the HII region DA568. Kerton et al.
(2004) carried out a multiwavelength study of DA568. They The complex106.8+3.3: ThiscomplexconsistsofS141only,
estimate a mean molecular velocity of −64 kms−1 and show forwhichweestablishedadistanceof8.34±0.6kpc.Star1is
164 D.Russeiletal.:ReviseddistancesofNorthernHIIregions
Table2.Coordinatesandspectraltypeofexcitingstarcandidates.
HIIregion Starnumber α δ Spectraltype Notes
J2000 J2000
hms ◦(cid:4)(cid:4)(cid:4)
BFS6 1 213622.1 +522816.2 TiObands
2 213621.9 +522720.0 BandG
3 213641.7 +522759.6 DominantHlines
BFS8 1 214114.2 +523434.9 Numerouslines
2 214104.6 +523552.0 NoHelines
3 214103.2 +523605.0 DominantHlines
4* 214125.1 +523721.6 CaIIH,Klines+BandG
5* 214117.6 +523832.3 O5V
DA568 1* 215515.4 +573945.3 O5V ALS12050
2* 215511.4 +573749.8 B2V
BFS10 1 215630.5 +580140.5 O9V
S138 1 223245.5 +582821.3 Emissionlines
2 223245.6 +582737.9 BandG+CaI
3* 223247.7 +582854.2 CaIIH,Klines+BandG
S141 1 222838.8 +613745.3 O8V
S144 1 224459.5 +595554.3 BandG+CaI
2 224453.9 +595104.3 TiObands
S152 1 225914.1 +584431.1 BandG+CaI,faintHlines
2 225915.3 +584321.2 DominantHlines
3 225916.9 +584243.4 BandG+CaI
4 225841.6 +584656.6 O8.5V
S153 1 225913.6 +584442.3 O9V/O9.5V ALS12719
S156 1 230510.3 +601442.0 O8
S158 1 231334.3 +613014.3 O9V
2 231330.3 +613011.6 O3V
3 231321.9 +613001.7 NoHelines
S159 1 231549.1 +610758.2 O9V
S163 1 233222.9 +604005.1 B1III ALS13004
2 233230.0 +603949.3 BandG+CaI+FeI
3 233205.7 +604041.7 DominantHlines
4 233208.8 +604035.0 BandG+CaI
5* 233336.9 +604506.8 O9V
6* 233332.7 +604732.1 O8V
7* 233349.6 +605107.0 B1V
S170 1 000146.6 +643528.7 B1V ALS13376
2* 000134.9 +643724.8 O9V ALS13370
3* 000133.5 +643715.6 B2V
4* 000113.6 +643519.0 B2V ALS13365
5* 000108.3 +643721.1 B3V ALS13362
6* 000106.2 +643724.0 CaIIH,Klines+BandG
S173 1 002152.1 +614527.0 B2IV ALS6150
2 002226.5 +614939.8 B1V ALS6158
3 002219.8 +613909.2 B2IV ALS6157
4 002224.3 +613923.4 NumerousFeIlines
S175 1 002717.1 +644218.0 B1.5V ALS6200
2 002721.0 +644238.1 BandG
S182 1 005006.0 +644533.5 EmissionPCygnilines
2 005005.6 +644558.2 BandG+CaI
3 005009.6 +644528.1 BandG+CaI+FeI
4 005003.9 +644600.4 BandG
S187 1 012307.3 +615153.2 B2.5V
2 012308.4 +615134.0 DominantHlines
3 012312.5 +615033.1 Emissionlines
S192 1 024724.4 +615448.0 B2.5V
2 024718.2 +615740.1 BandG+CaI+FeI
S193 1 024742.0 +615828.1 B2.5V
2 024746.8 +615817.6 DominantHlines
3 024740.0 +615832.7 B1.5V
4 024734.4 +615840.4 FaintHlines,NoHelines
wellcenteredontheopticalemissionaswellasonthering-like The MSX (mid-infrared Midcourse Space Experiment)
featurestracedbyMSX-bandAemissionsupportingouridenti- bandA(λ=8.28µmand20arcsecresolution)data(Priceetal.
ficationoftheexcitingstar. 2001)spanawavelengthrangeof6.8–10.8µm,whichincludes
D.Russeiletal.:ReviseddistancesofNorthernHIIregions 165
Table2.continued.
HIIregion Starnumber α δ Spectraltype Notes
J2000 J2000
hms ◦(cid:4)(cid:4)(cid:4)
G137.8+1.0 1 024922.3 +582643.7 O9V GSC03712-01870
S196 1 025132.2 +621321.9 BandG+CaI
2 025132.1 +621225.7 IntenseCaI,faintHlines
3 025130.8 +621107.0 BandG+CaI
4* 025132.0 +621319.7 O9.5V
S203 1 032303.0 +544716.1 BandG+CaI
2 032249.4 +544532.9 BandG+CaI
3* 032037.2 +545408.3 (B2Vphot)
BFS31 1* 032451.2 +545705.0 B2V
S204 1 035641.0 +571529.0 O9V ALS7811
S217 1 045851.5 +475919.6 CaIIH,Klines+BandG
2 045845.1 +475954.0 O9.5V ALS8107
3 045832.8 +480104.8 CaIIH,Klines+BandG
S219 1 045607.1 +472303.1 B2.5V
2 045600.3 +472242.0 Noisy
3 045620.2 +472343.0 BandG+CaI
4 045610.2 +472332.2 B1V ALS8094
5 045608.9 +472353.9 BandG+CaI+FeI
6 045608.1 +472401.8 BandG+CaI
7 045607.4 +472355.3 B2.5V
S256 1* 061236.6 +175625.3 CaIIH,Klines
2* 061236.6 +175653.4 B2.5V
3* 061236.6 +175752.8 CaIIH,Klines+BandG
S258 1* 061327.6 +175431.6 CaIIH,Klines
2* 061327.6 +175520.9 B3V
S283 1* 063812.4 +004400.9 B3V
2* 063813.6 +004409.9 O7V
3* 063815.6 +004418.5 CaIIH,Klines+BandG+CaI
4* 063828.1 +004440.6 Noisy,RefilledHlines
5* 063827.3 +004438.1 B1V
BFS53 1* 064436.4 +010754.6 B2V
S294 1* 071633.2 −092525.6 B1.5V
2* 071634.5 −092700.4 FeI+numerouslines
Note:theasteriskfollowingsomestar’snumber meanstheyhavebeenobserved withthelowerresolutionspectroscopic configuration. ALSis
acronymforAlmaLuminousStar(Reed1998).
emissionbandsattributedtoPolycyclicAromaticHydrocarbons note a large discrepancy between the distance determination
(PAHs) and thermal emission of dust (Cohen & Green 2001). of these two HII regions while Crampton et al. (1988) found
In the star-forming regions PAHs emission is a good tracer of thematsimilardistancesof3.6and4kpcrespectivelyforS152
the photon-dominatedregions(Leger& Puget1984).The pho- and S153.However,kinematicstudies(Mirzoyan1994;Pismis
ton dominated region allows us to establish the location of the 1990; Pismis & Hasse 1980) suggest that the two nebulae are
parentalmolecularcloud.ThiscomplementstheHIIregionex- physicallylinkedinthewaytheywereformedwithinthesame
tensionhelpingustolocatetheexcitingstar(s). cloud;butthey are at differentevolutionarystages, S152being
theyoungest.TheyoungageofS152isconfirmedbyitsintense
Inaddition,weselectedfromcolor–colorplottheblueststars
(31 stars) and determined their photometric distance assuming MSX-BandAcounterpart.
theyaremain-sequencestars.Themeanvalueofthedistribution For the distance determination of the complex, we favour
gives a distance of 9.45 kpc. This supports the distance found the distance of star 4. Indeed, star 4 is obviouslyembedded in
forS141. the optical emission of S152 while we can not rule out, due to
thefaintopticalemissionofS153,thepossibilitythatALS12719
is a field star and thepossibility thatS153couldbeinterpreted
The complex 107.7+0.8: This complex consists of S144 asaflowofionizedmatterfromS152.
only. We do not identify the exciting star. The DSS image
shows only a faint emission with a filament-like structure. The
identification is also difficult because there is no detectable Thecomplex110.1+0.0: ThiscomplexgathersseveralHIIre-
gions:BFS14,BFS15,BFS16,BFS17,BFS18andS156.
MSX-BandAcounterpart.
ThespectraltypeoftheexcitingstarofS156wasnotdeter-
mined fromthe cross-correlationmethodbecauseof the strong
The complex 108.8−1.0: This complex is composed of S152 refilling in the hydrogen lines. The presence of HeII lines is
and S153. S152 is a bright and compact HII region excited characteristicofO typestar.We estimatedaO8Vspectraltype
by star 4 (distance 2.39 ± 0.21 kpc) while S153 is a diffuse fromthe criteria(developedbyConti& Underhill1988) based
region excited by ALS12719 (distance 4.73 ± 0.6 kpc). We on the equivalent widths of HeI4471 and HeII4541. Then, we
166 D.Russeiletal.:ReviseddistancesofNorthernHIIregions
Table3.Photometry,distanceandextinctionoftheexcitingstars.
HIIregion Starnumber V B−V U−B d(kpc) Av Notes
BFS8 5 13.582 1.035 −0.088 8.88±0.61 4.32
DA568 1 11.898 0.900 −0.182 5.04±0.35 3.86
2 14.037 0.755 −0.037 4.74±0.86 3.13
BFS10 1 15.031 1.419 0.311 6.39±0.67 5.48
S138 1 15.014 1.578 0.547 2.91±1.4 5.89 photometric
S141 1 14.282 0.969 −0.488 8.34±0.6 4.46
S152 4 11.925 1.002 −0.537 2.39±0.21 4.65
S153 1 11.38 0.466 −0.427 4.73±0.6 2.43
S156 1 11.234 0.979 0.257 2.87±0.75 3.73
S158 1 11.762 1.288 0.05 1.60±0.17 5.21
2 12.093 1.321 0.647 4.24±0.29 4.72
S159 1 11.919 0.921 −0.261 2.97±0.31 4.03
S163 1 11.51 0.83 −0.14 2.93±1.3 3.52
5 12.803 1.127 −0.029 3.38±0.35 4.63
6 14.054 1.485 0.3785 4.28±0.3 5.68
7 14.040 0.833 −0.079 5.63±0.93 3.48
S170 1 11.353 0.313 −0.477 3.55±0.58 1.80
2 9.786 0.439 −0.358 2.60±0.27 2.18
3 13.406 0.370 −0.258 6.52±1.19 1.80
4 12.401 0.396 −0.329 3.78±0.68 1.98
5 10.935 0.303 −0.457 1.43±0.28 1.74
S173 1 11.820 0.38 −0.45 3.78±2.06 2.02
2 11.220 0.17 −0.64 4.02±0.66 1.39
3 9.974 0.183 −0.502 2.27±1.23 1.29
S175 1 11.301 0.906 −0.196 1.09±0.21 3.90
S182 1 11.739 0.984 0.435 – –
S187 1 13.570 1.236 0.254 1.44±0.26 4.78
3 14.711 0.85 0.159 – –
S192 1 13.743 0.751 −0.315 2.96±0.54 3.39
S193 1 12.368 0.565 −0.42 2.11±0.39 2.75
3 14.598 0.615 −0.317 8.12±1.56 2.84
G137.8−1.0 1* 13.01 0.71 −0.41 6.78±0.59 3.32 Muzzio&Rydgren(1974)
S196 4 12.183 0.530 −0.458 5.67±0.59 2.65
S203 3 15.439 1.0843 0.212 5.51±2.65 4.21 B2Vphotometric
BFS31 1 12.670 1.018 0.175 1.71±0.31 3.97
S204 1 10.844 0.419 −0.57 3.98±0.42 2.32
S217 2* 11.32 0.42 −0.6 4.37±0.37 2.35 Georgelinetal.(1973)
S219 1 14.387 0.726 −0.088 4.64±0.85 3.06
4 12.06 0.498 −0.33 3.74±0.62 2.39
7* 14.43 0.84 −0.04 3.90±0.65 3.47 Lahulla(1987)
S256 2* 14.37 1.15 −0.03 2.14±0.39 4.73 Moffatetal.(1979)
S258 2* 15.28 1.22 0.4 2.90±0.51 4.57 Moffatetal.(1979)
S283 1* 13.12 1.30 1.01 1.24±0.22 4.26 Moffatetal.(1979)
2* 12.19 0.52 −0.52 8.11±0.31 2.67 Turbide&Moffat(1993)
5* 14.22 0.65 −0.4 7.39±1.21 3.08 Moffatetal.(1979)
BFS53 1* 13.93 0.85 −0.23 4.01±0.73 3.71 Moffatetal.(1979)
S294 1* 13.99 1.03 −0.03 3.24±0.56 4.23 Moffatetal.(1979)
Notes:Theasteriskfollowingsomestar’snumbermeansthatthephotometryiscomingfromtheliteraturewhithreferenceinCol.8.InCol.6,the
distanceanditsuncertainty(calculatedfromerrorsonthephotometry,spectraltypeandluminosityclassdetermination)isgiven.
determine the distance of 2.87 ± 0.75 kpc assuming the star is The complex 114.0−0.7: Thiscomplexis composedofS163,
amainsequencestar. S164 and S166. For S166 Foster & MacWilliams (2006) give
From CDS/ALADIN facilities we can identify the a spectrophotometric stellar distance of 2.57 ± 0.6 kpc for the
star WRAM17 (Wramdemark 1981) as a probable excit- excitingstarBD+602607.
ing star of BFS17. From their photometric data (Wramdemark S164 is excited by the B0.2III star (Negueruela & Marco
1981) and assuming it is a main sequence star, we estimate 2003)ALS13056.UsingSIMBADwecollectitsphotometryand
B1.5Vasthespectraltypeandadistanceof3.66±1.7kpc. calculateadistanceof2.87±0.26kpc.
Wethenadoptforthecomplexthedistance3±0.7kpc. For S163 we observed four hot stars. Star 1 is outside the
optical and MSX emissions while star 7 is in the direction of
thePDR.Stars6and5aretheclosesttothecenteroftheradio
Thecomplex111.5−0.8: ThiscomplexiscomposedoftheHII source GB6B2331+6031.Then, we establish a distance of 4 ±
regionsS158andS159.Weestablishedadistanceof2.27±0.15 0.22kpcforS163basedonstar5,6and7.
forS158and2.97±0.31kpcforS159andthenforthecomplex We then determine a distance of 3.53 ± 0.17 kpc for the
adistanceof2.40±0.14kpc. complex.
D.Russeiletal.:ReviseddistancesofNorthernHIIregions 167
Table4.Revisedstellardistanceofthestar-formingcomplexes.
Complex Velocity Old New
V distance distance
lsr
kms−1 kpc kpc
96.00+2.00 −74.0 7.8±2.3 9.40±0.4
96.30−0.20 −54.2 – 8.88±0.61
101.40+2.70 −62.0 – 5.25±0.29
105.60+0.40 −52.0 4±1.2 2.91±1.4
106.80+3.30 −64.4 – 8.34±0.6
108.80−1.00 −51.0 3.7±0.8 2.39±0.21
110.10+0.00 −52.0 4.2±0.9 3±0.7 Fig.2.Newstellardistanceofthecomplexes(filledsymbols)versusold
111.50−0.80 −55.3 4.1±0.9 2.4±0.14 distance.Theolddistanceiseithertheoldstellardistance(squares)or
114.00−0.70 −44.3 2.4±0.4 3.53±0.17 thekinematicdistance(circles).TheSunisrepresentedbythelargestar
117.60+2.30 −43.7 2.8±0.6 2.6±0.27 symbolandthearmsbythecontinuouslines.Thecurvesarethefitted
119.00−1.10 −36.6 2.4±0.5 3.12±0.34 spiralarmsfromRusseil(2003).
120.40+2.00 −49.0 2.3±0.7 1.09±0.21
126.70−1.00 −13.0 – 1.44±0.26
136.10+2.10 −46.3 – 2.40±0.32
137.80−1.00 −102.0 – 6.78±0.59
143.60−1.80 −34.4 – 1.71±0.31
145.80+3.00 −26.0 4±1.2 3.83±0.26 classified as O9.5V (Georgelin et al. 1973). This placed it at
159.50+2.50 −23.9 6.1±0.7 4.19±0.27 2.13 kpc. Now, we find a spectral type for this star of B1.5V
192.50−0.10 7.6 2.3±0.3 2.46±0.16 givingadistanceof1.09±0.21kpc.
210.60−1.40 22.0 1.9±0.4 1.17±0.29
211.14−1.01 37.1 – 4.01±0.73
213.00−1.00 47.4 6.6±0.25 7.89±0.27 The complex 122.7+2.1: This complex consists of S181 and
224.20+1.20 33.6 5.4±1.6 3.24±0.56
S182.NodistanceisavailableforS181whichisanextendedand
Note:theadoptederrorbaronthevelocity(±5kms−1),thevelocityof diffuse HII region.The exciting star of S182 exhibits emission
thecomplexesandtheolddistancearefromRusseil(2003). lines which prevent any classification. Indeed, the lines, espe-
ciallythehydrogenones,exhibitPcygniprofilesorareemission
lines. S182 is associated with the source IRAS 00470+6429.
The complex 117.6+2.3: This complex is S170. S170 has a Thissourceisclassifiedasaproto-planetarynebulaandthespec-
round(diameter∼17(cid:4))andwelldefinedmorphology.Alltheob- tral type is Ae (Kelly & Hrivnak 2005). S182 is then removed
servedstarsarelocatedinthecentralpartoftheregionbelong- fromthecomplex.
ingcertainlytotheclusterStock18.Unfortunately,nodistance
is available in the literature for this cluster. We found 5 stellar
candidates with distance ranging from 1.4 to 6.5 kpc. Four of Thecomplex126.7−1.0: Thiscomplexpreviouslygatheredthe
themareBtypestarswhilestar2 isanOtypestar. Inaddition HIIregionsS183,S187andS188.
star 2 is located at the center of the HII region.We then adopt
S183mustberemovedfromthiscomplex.Landeckeretal.
thedistanceofstar2(2.6±0.27kpc)forthecomplex.
(1992)showthatS183correspondstoabrightrimofradioemis-
sion on the western edge of a much larger object apparently
The complex 119.0−1.1: Thiscomplexis composedofS172, hidden by extensive obscuring material. The region is seen as
S173 and S177. No stellar distance is available for S172. a bubble blown by the stellar winds of the star(s) which excite
For S177, Foster & MacWilliams (2006) propose HD2421 the HII region. In addition, Landecker et al. (1992) obtained
(a B0.5IV star with distance 2.04 ± 0.47 kpc) as exciting star from the radio recombination line observations a velocity of
while accordingto Felli & Perinotto (1974) the excitingstar is −63.5 kms−1 which is very different from the velocity of the
ALS6240(aO9Vstarwithdistance2.42±0.55kpc).AsS177is complex(−13kms−1).Fich&Blitz(1984)measuredaCOve-
an extended(diameterabout40 arcmin)anddiffuse HII region locityat−10.3kms−1 inthedirectionofS183whileFichetal.
with no clear MSX and radio counterpart, it is not possible to (1990)giveaHαvelocityof−62.6kms−1.Similarly,Dameetal.
confirmtheexcitingstaridentification. (1987)presentedmapsshowingcloudsofCOaroundthisveloc-
In the field of S173, using ALADIN we identified seven ity. Wouterloot & Brand (1989) list three CO velocity compo-
hot stars. From data extracted from the literature (Haug 1970; nentsat−66.4kms−1(thestrongest,4.2K)−12.6kms−1(2.4K)
Nicolet 1978) we establish the distance of the stars: ALS6151 and−5kms−1(2.8K).Bruntetal.(2003)findmolecularclouds
(O9V, d = 2.57 ± 0.5 kpc), ALS6156 (photometric spectral inthedirectionofS183distributedaroundtwomainvelocities:
typeB2V,d=4.41±1.77kpc),ALS6145(photometricspectral −62.4and−12kms−1.TheyalsoshowthattheHIprofilepeaks
type B0.5V, d = 3.17 ± 1.27 kpc) and ALS6155 (photometric at−63.5kms−1.Theseobservationsindicatethatthemolecular
spectral type B0.5V, d = 3.36 ± 1.34 kpc). From our observa- materialaround−13kms−1 isprobablyassociatedwithabsorb-
tions we establish the distance of the stars: ALS6150 (3.78 ± ing materialinfrontofS183.S183nowformsa newcomplex,
1.89 kpc), ALS6158 (4.02 ± 0.66 kpc) and ALS6157 (2.27 ± 123.28+3.03,withvelocity−63kms−1.
1.14 kpc). The distance of S173 is then 3.12 ± 0.34 kpc. We S188isaplanetarynebulaewithadistancebetween600pc
adoptthisdistanceforthecomplex. (Harris et al. 1997) and 1000 pc (Napiwotzki 2001). It is
removedfromthecomplex.
The complex 120.4+2.0: This complex is S175. The star Thenthedistanceofthecomplexisbasedonthedistanceof
centered on the nebula is ALS6206. This star was previously S187onlywhichis1.44±0.26kpc.
168 D.Russeiletal.:ReviseddistancesofNorthernHIIregions
The complex 136.1+2.1: We included in this complex the counterpart while no MSX counterpart is noted. We identify
HII regions S192, S193 and S196 on the basis of their veloci- a hot star close to the radio source GB6 B0316+5439 but its
tiesonly. spectral classification is not possible due to the refilling of the
The HII regions S192 and S193 clearly define a subgroup. lines.InparticulartheHαlineisinemissionwhiletheotherhy-
Indeed the MSX-band A emission appears elongated encom- drogenlinesareclearlyrefilled.TheHeIlinesat4390Å,4471Å
passing these 2 HII regions. Near the middle of these HII re- and4924ÅareclearlynotedsuggestingitisaBstar.Thenwe
gions,correspondingtoanMSXemissionpeak(02h47m26.47s estimated only the photometric distance. However, due to the
+61◦56(cid:4)49.2(cid:4)(cid:4)),thereistheIRASsourceIRAS02435+6144and largeextentandthemorphologyofS203,theassociationofthis
the near infrared star clusters [BDS2003]57 (Bica et al. 2003) starwithS203isveryuncertain.
possibly inducedby the HII regions. This consolidatesthe fact BFS31isontheborderofS203.ItexhibitsMSXandradio
thattheyarephysicallylinked. counterpartssuggestingitisarecentHIIregion.Theidentifica-
Weestablishadistanceof2.96±0.54kpcforS192forwhich tion of its exciting star is unambiguous, contrary to S203. We
the quasi-circular morphologymakes easy the identification of thenadoptthedistanceofBFS31(1.71kpc)forthedistanceof
thestar.ForS193theobservedstar3exhibitsverydifferentdis- thecomplex.
tance. Itslargedistance (8.12kpc),suggestsit is a background
star.TheadopteddistanceforS193(2.11±0.39kpc)isthenthe
distanceofthestar1. Thecomplex145.8+3.0: ThiscomplexistheHIIregionS204.
The case of S196 is more complex. On the one hand, S204 is a faint and diffuse arc-like nebula extended on about
the ionized (−48.1 kms−1, Fich et al. 1990) and molecular 48arcminwithoutMSXbandAcounterpart.
(−45.1kms−1,Blitzetal.1982)gasvelocitiesofS196aresim- FromCDS/ALADINwefindintheareatworadiosources:
ilar to that of S192 and S193 suggesting they are linked. On RRF1509andGB6B0355+5658inthedirectionofwhichthere
the other hand, the stellar distance assigned to S196 is 5.67 ± are respectively the stars ALS7833 (O7.5, Hiltner & Johnson
0.59kpc(star4).Thisdistanceisdifferentfromthedistanceof 1956;Nicolet1978,d=4.21±1.77kpc)andBD+56◦866(O9V,
other HII regions of this complex. Already Hunter & Massey Hiltner & Johnson 1956; Haug 1970, d = 3.63 ± 0.38 kpc).
(1990) found a large and unreliable distance (9 kpc) for the In addition, three hot stars, with photometric data only (Haug
identified star leading them to adopt the kinematic distance. 1970),areidentifiedinthefield:ALS7816(photometricspectral
Moreover, in Digel et al. (1994), the molecular cloud associ- typeB0V,d=4.49±1.35kpc),ALS7815(photometricspectral
ated to S192 and S193 is clearly noted (cloud 28) while S196 typeB1V,d=4.33±1.3kpc)andALS7829(photometricspec-
appearsassociatedtoadistinctfaintermolecularfeaturemaking traltypeB1V,d =3.63±1.09kpc).Fromourobservationswe
itsbelongingtothecomplexnotclear. establishaspectraltypeanddistanceforALS7811ofO9Vand
We choosearbitrarilyto calculatethe distanceforthecom- 3.98±0.42kpc.
plex(2.4±0.32kpc)basedonthedistancesofS192andS193 ThedistanceoftheHIIregionisthen3.83±0.26kpc.
butwenotethatthecaseofS196isnotclosed.
Thecomplex159.5+2.5: ThiscomplexgathersS219,S217and
BFS44.ForBFS44nostellardistanceisavailable.
The complex 137.8−1.0: This complex corresponds to the
The spectral type of the main exciting star (ALS8107) of
molecular cloud denoted as Cloud 2 in the list by Digel et al.
S217 is O9.5V, B0V or O8V according to Georgelin et al.
(1994). (1973), Moffat et al. (1979) and Chini & Wink (1984) respec-
De Geus et al. (1993) reported an extended Hα emission
tively. Deharveng et al. (2003), from the analysis of the nebu-
withthesameradialvelocityasCloud2(VLSR=−103kms−1).
lar emission lines, show that S217 and S219 appearto be low-
TheyconcludedthatthisHαemissiontracesanHIIregionasso-
excitation regionssuggesting a B0V spectral type for the main
ciatedwithCloud2,andtheyproposedanearlyB-typestarnear
excitatingstarofS219andaO9.5VorO9Vfortheexcitingstar
Cloud2(“MR1“:Muzzio&Rydgren1974)asthephotoioniz-
ofS217.
ingsource.
We confirm the O9.5V spectral type of Georgelin et al.
Smarttet al. (1996), observedand analysedhigh resolution
(1973) for the exciting star of S217 for which we determine
spectraofMR1usingLTEatmospheremodelisation.Theyesti- a distance of 4.37 ± 0.37 kpc. For S219 we establish a dis-
mate a distance between 8.2 kpc and 12 kpc and a LSR veloc- tance of 3.99 ± 0.39 kpc. The distance of the complex is then
ityforthestarof−90±13kms−1.Fromourspectraweestab- 4.19±0.27kpc.
lishedavelocityforthestarof−102.7±12kms−1inagreement
with thenebularandmolecularcloudconfirmingtheirphysical
Thecomplex192.5−0.1: Thiscomplexiscomposedofthere-
link. In addition, the geometry of ionized gas, IRAS sources,
gions S254, S255, S256, S257 and S258. Moffat et al. (1979)
NIRsources,andmolecularcloudsuggeststhatMR1hastrig-
identifiedtheexcitingstarsoftheseHIIregionsgivingthespec-
gered the star formation activity in the cloud (Kobayashi &
traltypeandphotometry(fromwhichweestablishthedistance:
Tokunaga2000)confirmingthelinkbetweenthestar,theHIIre-
S254 (HD253247, O9V, d = 2.49 ± 0.26 kpc), S255 (ALS19,
gionandthemolecularcloud.
B0V, d = 2.36 ± 0.37 kpc) and S257 (HD253327, B0V, d =
We established a distance of 6.78 kpc. In agreement with
2.53±0.37)andgiveonlyphotometricinformationfortheex-
Smartt et al. (1996) we confirm the large discrepancybetween
citingstarofS256andS258.
the stellar distance and the kinematic distance (23 kpc) which
The spectral type found for the exciting star of S258 is in
underlinesthepresenceofnon-circularmotions.
good agreementwith the photometricspectral type and its dis-
tanceis2.9±0.51kpc.ThereviseddistanceofS256,whichis
The complex 143.6−1.8: This complex gathers S203 and 2.14±0.39kpc,isinbetteragreementwiththedistanceofthe
BFS31. S203 is an extended quite diffuse HII region (1.23◦ × otherHII regions.Indeed,the photometricdistancewas unreli-
1◦) as seen in Hα in the VTSS survey (Dennison et al. 1997). able(6.8kpc).
Only the northern part of S203 exhibits a radio (5 GHz) Thedistancetothiscomplexisthen2.46±0.16kpc.
D.Russeiletal.:ReviseddistancesofNorthernHIIregions 169
Fig.3.Computedrotationcurve(dashedline)comparedwiththeBrand
&Blitz(1993)curve(solidline).
The complex 210.8−1.3: This complex is composed of the Fig.4. Fitted spiral structure. The symbol size is proportional to the
regionsBFS53,S282andBFS54. excitationparameter(seeRusseil2003).TheSunpositionisgivenby
thelargestarsymbol.1:Sagittarius-Carinaarm,2:Scutum-Cruxarm,
ThedistanceofBFS54isestimatedfromthedistanceofthe 1(cid:4):Norma-Cygnusarmand2(cid:4):Perseusarm.Thelocalarmfeature(long
starHD289120.ThisstarclassifiedasB3(Nesterovetal.1995) dashedline),thebar(dashed-dot-dot line,fromEnglmaier&Gerhard
hasadistanceof1.13±0.34kpcassumingitisamainsequence 1999),theexpecteddeparturefromthelogarithmicspiralobservedfor
star.TheexcitingstarofS282isHD47432(Carrasco-Gonzalez the Sagittarius-Carina arm (short dashed line) and a feature probably
etal.2006),itsspectraltypeisO9.5II(Karchenko2001)andits linkedtothe3-kpcarm(solidline)aresketched.
distanceis1.3±0.55kpc.
BFS53wasplacedinthiscomplexduetoitsionisedgasve-
locity (23.5 kms−1). But its CO velocity is 37.1 kms−1 while 4. Kinematicimplications
the velocity of S282 and BFS54 is 22 kms−1. From the stellar
We take advantage of the new distance determinationsto rein-
distance we can now put BFS53 aside. Indeed, for BFS53 we
vestigate the kinematic of our Galaxy. Indeed, in the Perseus
determineadistanceof4.01±0.73kpcverydifferentfromthe
arm,velocitydepartureshavebeenobservedforalongtime(e.g.
others.
Miller 1968; Rickard 1968; Roberts 1972; Humphreys 1976;
On this basis we can split the complex into two com- Brand&Blitz1993).Inthepresentdiscussionwehaveadopted
plexes: complex 210.6−1.4 (BFS54 and S282) with a distance fortheSunagalactocentricdistanceof8.5kpcandforthesolar
of 1.17± 0.29kpcand BFS 53(complex211.14−1.01)placed circularvelocityavalueof220kms−1.
at4.01±0.73kpc. For the following kinematic study of the Galaxy, we adopt
the analytical expression of the Brand & Blitz (1993) rotation
curve. Indeed,refitting the rotation curve (Fig. 3), we still find
Thecomplex213.0−1.0: Thiscomplexiscomposedofthefol- aresultsimilartothatofBrand&Blitz (1993).Duetothefact
lowing HII regions: S283, S284, S285 and S286. For S286 no thatmostobjectsinthispaperareatgalactocentricdistancesbe-
distance is available. Turbide & Moffat (1993) obtained CCD tween 10 and 12 kpc, where there are already lots of objects
UBVmagnitudesofstarstowardsS283,S284andS285.Based tracingtherotationcurve,thenewdistancedeterminationswere
on isochrones fits (assuming solar abundance) they determine expectedtohavenegligibleeffectonthisrotationcurve.
distance of 7.3, 5.6 and 6.9 kpc respectively for S283, S284
To investigate the velocity departuresof star-forming com-
andS285.
plexesinthePerseusandCygnusarmswefirstidentifythecom-
WedetermineforS283adistancea8.06±0.30kpcfromour plexes location respectively to each of these arms. We then fit
stars 2 and 5. We determine distance for S284 and S285 from the fourarmmodel(Russeil2003) takingintoaccountthe new
thephotometricandspectroscopicresultsofMoffatetal.(1979) stellardistances(Fig.4).Asexpected,thelargescalestructureis
andTurbide&Moffat(1993).Adistanceof6.03±1.16kpcis notmodifiedbythefewnewdistances.Plottingthearmsandthe
deducedfor S284fromstar 1, 9 and 12 of Moffatet al. (1979) complexesinagalactocentricdistanceversuslongitudediagram
andadistanceof7.69±0.68kpcisdeducedforS285fromstar1 (Fig. 5) we determine the complexes association to every arm
and6ofMoffatetal.(1979). assuming that a complexbelongsto an arm if its position is in
Wewillfavourtheselastdistanceestimatesforhomogeneity. thearmorifitserrorbarreachesthearm.Toquantifytheveloc-
Thedistanceforthecomplexisthen7.89±0.27kpc. itydepartureswecalculatethevelocitydifferencededucedfrom
themeasuredradialvelocityandthestellardistance(Fig.6),re-
spectively.
The complex 224.2+1.2: The distance of this complex is the The Perseus arm exhibitsmean Vlsr departuresof −14.9±
distance of S294. We find a new distance of 3.24 ± 0.56 kpc. 8.9 kms−1 in the second Galactic quadrant and +5.17 ±
Theolddistance(5.4kpc)wasdeterminedfromthesamephoto- 9.14 kms−1 in the third Galactic quadrant. The Cygnus arm
metricdata(Moffatetal.1979)butwithaphotometricspectral exhibits mean Vlsr departures +8.06 ± 9.95 kms−1 in the sec-
typeB0V. ondGalacticquadrantand−8.34±6.95kms−1 inthethird.
170 D.Russeiletal.:ReviseddistancesofNorthernHIIregions
Fig.5.Positionofthecomplexesrespectivelytothefittedarms.Every
arm is represented by three curves (central position and and width, Fig.6.VelocitydifferenceversuslongitudeforthePerseusarm(circular
±0.7 kpc, extension of the arm). Up is the cygnus arm, down is the symbol)andtheCygnusarm(squaresymbols).
Perseus arm. The triangle symbols are the complexes with kinematic
distanceonly.
Thesevaluesconfirmourpreviousresults(Russeil2003)and
are in agreement with the typical values observed in external
galaxies. In addition, these velocity departures imply that the
kinematicdistanceofthePerseuscomplexesareover-estimated
whilethekinematicdistancetotheCygnuscomplexesareunder-
estimated.
Inexternalgalaxiessuchmotionsareobservedonlargeparts
ofarms(e.g.inNGC300,Marcelinetal.1985;inM31,Ryden
& Stark 1986; in M 81, Adler & Westpfahl 1996; in M 83,
Tilanus & Allen 1993; in NGC 1530, Zurita et al. 2004) from
atomic,molecularandionizedgasvelocitydata.Theamplitudes
ofthesemotionsaretypicallybetween10and40kms−1.
In addition, we note that the velocity departures we obtain Fig.7. Circular velocity difference versus galactocentric distance (the
haveoppositesignforthetwoarms.FromHIdataBurton(1973) symbolsarethesameasinFig.6).Thelinearregressiongivesaslope
and Burton & Bania (1974) previouslyfoundnegativevelocity of8.74±1.10andaconstanttermof−111.09±13.34.
difference(forthesecondquadrant)atthelocationofthePerseus
arm and positive difference at the location of the external arm this way we find the co-rotation radius to be 12.7 kpc (Fig. 7)
(see e.g.Fig. 7 of Burton1973). He showedthatalonga given fromthefittedlineexpression.
lineofsightthestreamingmotionhasaperiodicvariation.Such This is higher than the usual value which places the co-
a behaviourwasmodeledbyFeitzinger&Spicker(1987)from rotation radius close to the Sun’s location at a galactocentric
modelsoftheradialvelocityfieldofourGalaxytakingintoac- distance ∼9 kpc. In the classical Lin et al. (1969) theory, the
countstreamingmotionsduetospiraldensitywave. co-rotation resonance in our Galaxy is situated at the very end
Then, the velocity departures we obtain and their signs of the Galactic disc. However,Marochniket al. (1972) and in-
are well explained by the streaming motion along the arms. dependentlyCrézé&Mennessier(1973)cametotheconclusion
According to the density-wave theory, the perturbationsof the that the co-rotation is located close to the Solar position. This
gravitationalpotentialinarotatinggalaxyandtheresultingspi- resulthasbeensupportedbylaterwork(e.g.Nelson&Matsuda
ralshocksgiverisetostreamingmotionofyoungstarsandgas 1977;Amaral& Lépine1997; Mishurovetal. 1997;Mishurov
(Lin et al. 1969; Roberts 1969). These streaming motions pro- &Zenina1999;Fernandezetal.2001;Lépineetal.2001;Luna
duceradialandazimuthalresidualvelocities.Sitniketal.(2001) etal.2006;Diasetal.2005).Recently,Popova&Loktin(2005)
showedthatinside theco-rotationradiustheresidualvelocities founda co-rotationradiusofabout10.5kpcfromkinematicof
should be maximumnear the inner edge of the arm, where the openstarclustersandOBstars.
shock front occurs. The radial and azimuthal residual veloci-
ties are directed toward the Galactic center and oppositeto the
Galacticrotationrespectively.Themagnitudeoftheresidualve- 5. Conclusion
locity decreases with the distance to the edge of the arm. At
Basedonspectro-photometricobservationsweestablishedorre-
the outer edge of the arm the radial residual velocity is close
finedthestellardistanceofHIIregions,andthenoftheirassoci-
tozeroandtheazimuthalresidualvelocityisinthedirectionof
atedcomplex,oftheouterGalaxy.
the Galactic rotation. Outside the co-rotation radius the radial
Wereachthefollowingmainconclusions:
component of the streaming motion is directed away from the
Galacticcenterandtheazimuthalcomponentisinthedirection – Therotationcurveisunchangedandstillinagreementwith
oftheGalacticrotation(Mel’niketal.2001). theBrand&Blitz(1993)rotationcurve.
In this frameworkwe can interpretthe opposite sign of the – We confirm the presence of departures from circular rota-
velocitydeparturesasindicatingthatthePerseusarmliesinside tion in the Perseus arm and quantifysuch departuresin the
the co-rotation radius while the Cygnus arm lies outside it. In Cygnusarm.