PASJ: Publ. Astron. So. Japan 62 No.2 in press, 1{??,

2010. Astronomial Soiety of Japan.SiO and H2O Maser Observations of Red Supergiants in Star ClustersEmbedded in the Galati DiskShuji Deguhi1, Jun-ihi Nakashima2Yong Zhang2, Selina S. N. Chong2, Kazutaka Koike1andSun Kwok21Nobeyama Radio Observatory, National Astronomial Observatory,and Graduate University for Advaned Studies,Minamimaki, Minamisaku, Nagano 384-13052Department of Physis, University of Hong Kong, Pokfulam Rd, Hong Kong, China(PASJ 62, No. 2, the April 25 2010 issue in press)(Reeived 2009 Otober 9; a

epted 2010 February 1)AbstratWe present the result of radio observations of red supergiants in the star luster, Stephenson's #2, andandidates for red supergiants in the star lusters, Merer et al. (2005)'s #4, #8, and #13, in the SiO andH2O maser lines. The Stephenson's #2 luster and nearby aggregation at the South-West ontain morethan 15 red supergiants. We deteted one at the enter of Stephenson's #2 and three in the south-westaggregation in the SiO maser line, and three of these 4 were also deteted in the H2O maser line. Theaverage radial veloity of the 4 deteted objets is 96 km s�1, giving a kinemati distane of 5.5 kp, whihloates this luster near the base of the Sutum-Crux spiral arm. We also deteted 6 SiO emitting objetsassoiated with the other star lusters. In addition, mapping observations in the CO J = 1{0 line towardthese lusters revealed that an appreiable amount of moleular gas still remains around Stephenson's #2luster in ontrast to the prototypial red-supergiant luster, Bia et al.'s #122. It indiates that a timesale of gas expulsion di�ers onsiderably in individual lusters.Key words: Galaxy: open lusters and assoiations: individual (Merer et al.'s #4, #8, #13,Stephenson #2), | masers | stars: mass-loss | stars: supergiants1. IntrodutionMassive young star lusters o

asionally harbor a num-ber of red supergiants with an initial mass of � 10{15M�(Shild 1970), whih are destined for a supernova ex-plosion leaving behind a neutron star as a �nal produt(Heger et al. 2003). Sine red supergiants exhibit high lu-minosity, they are easily identi�ed at infrared wavelengthseven if large interstellar extintion is assumed. They anbe used as an indiator of age and mass of star lustersembedded in the Galati disk (Lada & Lada 2003; Figeret al. 2006). A red supergiant with L = 105 L� has aprogenitor mass of about 15 M� (Salasnih et al. 1999),whih is likely the upper limit of the initial masses of redsupergiants in star lusters.Figer et al. (2006) measured the equivalent widths ofthe CO �rst overtone bands, and identi�ed 14 M super-giants in a luster in Sutum [#122 of Bia et al. (2003)=RSGC1℄. They inferred the initial mass of this lus-ter to be � 2{4� 104M� and the age between 7 and12 Myr, based on the olor-luminosity diagram assum-ing the Salpeter's initial mass funtion. Nakashima &Deguhi (2006) deteted SiO masers from 4 of these redsupergiants. They found that the veloity dispersion ofthe maser soures is equivalent to that of a luster with amass of � 104M�, and that the average radial veloity ofmaser soures indiates a kinemati distane of 6.5 kp tothe luster. This example demonstrated that SiO masersare a useful tool for studying kinematis of star lustersas well as mass-losing proess of massive stars at the �nalstage of stellar evolution.In this paper, we present the results of SiO and H2Omaser searhes for red supergiants in #2 of Stephenson(1990), and andidates for red supergiants in the otherstar lusters in the Merer et al. (2005)'s atalog. Theformer luster ontains more than 10 red supergiants(Stephenson 1990). A later near-infrared (NIR) studyfound more supergiants and early type stars in theStephenson #2 luster (Nakaya et al. 2001). More re-ently, Davies et al. (2008) spetrosopially identi�ed 15red supergiants in the Stephenson #2 luster and nearbyaggregation 50 south-west from the Stephenson #2 luster.Merer et al. (2005) ataloged about 200 infrared star lus-ters lying in the Galati disk using the Spitzer/GLIMPSEsurvey. Some of them inlude nearby bright middle-infrared (MIR) soures, whih are likely red supergiantsshowing a typial olor of SiO maser soures. However,sine the olor ranges of evolved stars in the NIR and MIR

2 Deguhi et al. [Vol. ,-06°08'

-06°04'

-06°00'

-05°56'

18h39m00s39m20s18h39m40sRA (J2000)

DE

C (

J200

0)

29

14 18

26

28

20

23

271517

21

13

25

11

84

Fig. 1. a. Positions of the observed soures overlaid onthe Spitzer/GLIMPSE image of Stephenson #2. The largetwo ellipses indiate approximate positions of the lusters,Stephenson #2 (left) and #2 SW (right).bands are somewhat overlapped with those of young stel-lar objets, it is not easy to disriminate young stars fromevolved stars solely by the infrared olors. Detetions ofSiO masers are ruial for on�rming the supergiant sta-tus of andidate stars in embedded lusters. We seletedthree star lusters (#4, #8 and #13) as observing tar-gets from Merer et al. (2005)'s atalog: eah seletedlusters inludes multiple andidates for red supergiants.The luster #13 of Merer et al. (2005), whih is loatedabout 6Æ north of Stephenson #2, is interesting beauseof an assoiated bright IR objet (144 Jy at 12 �m).We have also mapped CO emission of Stephenson #2and several other lusters seleted from the Merer etal.'s atalog. In addition, we mapped CO emissiontoward the prototypial red-supergiant star luster inSutum (RSGC1) for omparison. Massive star lustersare formed in giant moleular louds (Lada & Lada 2003),but the gas omponents of the lusters are eventually ex-pelled and dissoiated by radiation of massive stars whilethe stars are at the main sequene of stellar evolution,and at the later phase by supernova explosion (Lada etal. 1984). Dynamial evolution and dissolution of starlusters depend strongly on gas expulsion proess (see forexample, Boily & Kroupa 2003). Therefore, it is inter-esting to know how muh amount of CO gas does remainin the star lusters with red supergiants.2. Observations and resultsThe observations were made with the 45m radio tele-sope at Nobeyama in 2006 April and 2008 April in theH2O JKK = 616{523 transition at 22.235 GHz, the SiO

1 52

4 3

8

20m20s 18h20m10s

-16°00'

-16°02'

-16°04'

-16°06'

-16°08'

20m40s 20m30s18h20m50sRA (J2000)

DE

C (

J200

0)Fig. 1. b. Positions of the observed soures overlaid on theSpitzer/GLIMPSE image of Merer et al.'s #4 (shown byellipse).

1

2

3

4

5

6

18h29m10s 29m00s 28m50s 28m40s

-10°58'

-10°54'

-10°56'

18h28m30sRA (J2000)

DE

C (

J200

0)Fig. 1. . Positions of the observed soures overlaid on theSpitzer/GLIMPSE image of Merer et al.'s #8 (shown byellipse).56 3

2

4 1

18h54m10s 54m00s 53m50s

00°36'

00°40'

00°38'

00°44'

00°42'

53m40s 18h53m30sRA (J2000)

DE

C (

J200

0)

Fig. 1. d. Positions of the observed soures overlaid on theSpitzer/GLIMPSE of Merer et al.'s #13 (shown by ellipse).

No. ℄ Red Supergiants in Embedded Star Clusters 3J =1{0 v= 1 and 2 transitions at 43.122 and 42.821 GHz,respetively, and the CO J = 1{0 transition at 115.271GHz. Cooled HEMT reeivers (H22 and H40) were usedfor the 22 and 43 GHz observations with aousto-opt spe-trometer arrays with 40 and 250 MHz bandwidths (velo-ity resolution of about 0.3 and 1.8 km s�1 at 43 GHz, and0.6 and 3.6 km s�1 at 22 GHz, respetively). The overallsystem temperature was about 140 K for 22 GHz H2Oobservations, and between 180 and 250 K for the 43 GHzSiO observations. The half-power telesope beam width(HPBW) was about 9000 at 22 GHz and 4000 at 43 GHz.The onversion fator of the antenna temperature to theux density was about 3.0 Jy K�1 at 22 GHz, and 2.9 JyK�1 at 43 GHz, respetively. All of the observations weremade by the position-swithingmode. Sine the soures inthe lusters are onentrated in a small region less thana 150 � 150 area, we employed the position-swithing se-quene like O�{On1{On2{On3, where the o� position wastaken 70 west of the �rst on-soure position. It saves the50% of integration time ompared with a usual O�{Onsequene (Deguhi et al. 2004). The 5� 5 beam foal-plane array reeiver system (BEARS) was used for the115 GHz CO observation (i.e., Sunada et al. 2000). Thesystem temperatures of the array reeivers were between400 and 600 K (DSB). The grid spaing of the array re-eiver was 4100 and the individual beam size was about 1500(HPBW). The 1024 hannel digital autoorrelator spe-trometer (Sorai et al. 2000) with a band width of 32 MHzwas used for the 115 GHz observations, giving an e�etiveveloity resolution of 0.16 km s�1 in a two-hannel bind-ing mode. Further details of observations using the NRO45-m telesope have been desribed elsewhere1, and arenot repeated here.The data redutions were made using the NEWSTARsoftware pakage developed by Nobeyama radio observa-tory. The BEARS data were �rst multiplied by the or-retion fators of antenna temperature for eah beam dis-plaement, and were integrated over time. Then the best�t quadrati urve was subtrated to determine the base-line of eah spetrum. Channel maps were reated usingthe "MAP" task of NEWSTAR, with a 2 km s�1 separa-tion and a 5 km s�1 taper for hannel smoothing. Theresulting CO hannel maps were shown in Figures 5a{5f.Targets for SiO searhes were hosen as follows. We �rstseleted MIR objets brighter than 1 Jy in the MSX bandC (12 �m) (Egan et al. 2003) toward the Stephenson#2 and the Merer et al.'s lusters. Sine we notiedan aggregation of bright MIR objets 50 south-west ofStephenson #2, we seleted objets from a relatively largearea (100000�100000) overing both Stephenson #2 and thesouth-west aggregation, though some of them were possi-bly not a member of the luster. We all the SW aggrega-tion as Stephenson #2 SW, hereafter. Then, we hekedto see if the seleted MIR objets have a NIR ounterpartin a partiular olor range of the 2MASS olors (Cutri etal. 2003) (i.e., K < 9, and H �K > 0:9), whih has beenused as riteria for target seletions for our previous SiO1 see http://www.nro.nao.a.jp/ nro45mrt/obs/bears

maser surveys (Deguhi et al. 2004). Finally, we seleted18 infrared objets in the Stephenson #2 and #2 SW lus-ters. The positions of the seleted objets were shown inFigure 1a.The star lusters with red supergiants other than theStephenson #2 were hosen from the table of new starlusters disovered in the GLIMPSE survey data [Table1 of Merer et al. (2005)℄. We seleted the MIR objetsusing the riteria similar to the above. Then, we elimi-nated several young stellar objets from this list by eyeinspetion of 2MASS images. For example, those assoi-ated with large extended nebulosity (e.g., Merer et al.'s#40) were disarded. We seleted 3 star lusters inlud-ing 15 andidates for red supergiants. In ase of Merer#4, we added three red stars (J18202853�1602159,J18204070�1603412, 18203850�1604163), whih do not�ll the riteria, but failitate our observing method usinga three-on-points sequene. Table 1 summarizes the in-frared properties of the observed soures. Figure 1 showsthe Spitzer/GLIMPSE images of the lusters and posi-tions of the observed objets. The star lusters, Mereret al.'s #4 and #8, are a bit hard to reognize on theGLIMPSE images shown in �gures 1b and 1, respe-tively, beause of the sales, but they an be seen learlyon enlarged 2MASS images whih are not shown here. Foronveniene, we assigned a short name to eah star, suhas the abbreviated luster name and the star number sep-arated by a hyphen as St2-01. Here, the Stephenson #2is presented by St2 (inluding St #2 SW), and Merer etal.'s #4, #8, #13 lusters are presented by M4, M8,and M13, respetively. Table 4 summarizes the alterna-tive naming of these objets.Table 2 summarizes the observational results for SiOmasers, and Table 3 for H2O masers. Figures 2a and 2bshow the SiO and H2O maser spetra of deteted soures,respetively. Figure 3 shows the K-magnitude versus NIRolor and 12�m ux density versus MIR olor diagrams,where the detetions and no detetions are presented by�lled and open irles, respetively. Note that the beamsize of the telesope in the 22 GHz H2O maser observationis 9000 (HPBW), approximately twie larger than the beamsize in the 43 GHz SiO observation. Sine a mean separa-tion between red supergiants in lusters is roughly 40{5000,we o

asionally deteted nearby H2O maser soures whihare ontaminated from the Gaussian tail of the telesopebeam. However, suh ontamination ould be identi�edin the present observations, beause we observed multi-ple, lose positions within one luster. The data gives uspositional information on ontaminating soures.2.1. Stephenson #2Several bright objets are identi�ed with IRAS soures:the brightest two soures are IRAS 18366�0603 (St2-03) and 18363�0607 (St2-18) with FC = 19:9 and 56.9Jy, respetively, and three others are IRAS 18364�0605(St2-08), 18368�0610 (St2-20), 18370�0602 (St2-23).However, the other fainter soures have no IRAS oun-terpart. Though St2-26 is a faint objet with FC = 1:8 Jy,we deteted SiO maser emission. The broad line pro�le of

4 Deguhi et al. [Vol. ,-0.2

0

0.2

0.4

0.6

0.8

-40 -20 0 20 40 60 80

Ta

(K)

J18203644080428.2 v=2

v=1

0

0.5

1

1.5

2

0 20 40 60 80 100 120 140

Ta

(K)

v=2

v=1

J18283530080428.2

-0.2

0

0.2

0.4

0.6

0.8

40 60 80 100 120 140 160

Ta

(K)

J18285207080427.2 v=2

v=1

-0.2

0

0.2

0.4

0.6

0.8

40 60 80 100 120 140 160

Ta

(K)

J18285844080427.2 v=2

v=1

-0.4

0

0.4

0.8

1.2

1.6

2

0 20 40 60 80 100 120 140

Ta

(K)

J18535249080427.1 v=2

v=1

-0.2

0

0.2

0.4

0.6

0.8

0 20 40 60 80 100 120 140

Ta

(K)

J18540749080427.2 v=2

v=1

Vlsr

(km s-1)

-0.20

0.20.40.60.8

11.2

20 40 60 80 100 120 140 160

Ta

(K)

J18385699060415.3 v=2

v=1

-0.20

0.20.40.60.8

11.2

20 40 60 80 100 120 140 160

Ta

(K)

J18390238060412.3 v=2

v=1

0

1

2

3

4

20 40 60 80 100 120 140 160

Ta

(K)

J18390558060412.3 v=2

v=1

-0.20

0.20.40.60.8

11.2

40 60 80 100 120 140 160

Ta

(K)

J18391961060413.3 v=2

v=1

-0.20

0.20.40.60.8

11.2

-20 0 20 40 60 80 100 120T

a (K

)

J18392891060415.3 v=2

v=1

Vlsr

(km s-1)

Vlsr

(km s-1)

Mc4-02 Mc8-01 Mc8-03

Mc8-05 St2-26 St2-18

St2-11

Mc13-6Mc13-5

St2-17St2-03

Fig. 2. a. SiO J = 1-0 v = 1 and 2 spetra. The star name, abbreviation of 2MASS name (Jhhmmssss format), and the observeddate (yymmdd.d format) are shown at the upper left of eah panel.St2-18 suggests that this is a typial red supergiant [forexample, Cerniharo et al. (1997)℄.The radial veloity of St2-17 is shifted by more than 40km s�1 from the veloities of the other stars. Therefore,we onlude that St2-17 is not a member of Stephenson#2. We infer from this fat that some stars at the north-ern part of Stephenson #2 (i.e, St2-15, St2-21, St2-23,St2-27, and St2-29), whih are loated far from the lus-ter enter, are not physially assoiated with Stephenson#2.What is interesting is whether Stephenson #2 SW isphysially assoiated with the Stephenson #2. Notethat Stephenson #2 inludes St2-01 up to St2-05, andStephenson #2 SW inludes St2-08, St2-11, St2-14, St2-18 and St2-26. The angular size of Stephenson #2 sug-gested by Bia et al. (2003) is 3:50� 30, and Stephenson#2 SW is out of this area. The average radial veloity andveloity dispersion for the SiO soures in Stephenson #2SW are 94.5 km s�1 and 3.5 km s�1, respetively, whih isshifted from the veloity of St2-3 in the Stephenson #2 by7.7 km s�1. This di�erene is not large enough to rule outthe assoiation of Stephenson #2 SW to Stephenson #2.For onveniene, we presume that Stephenson #2 SW isassoiated with Stephenson #2.2.2. Merer et al.'s #4This luster is loated at the northern boundaryof M17. SiO masers were deteted only in M4-02(J18203644�1602589) at Vlsr = 18 km s�1. Water maserswere deteted at several loations. The radial veloity ofM4-02 determined from the present SiO observation islose to that of the CO omponent of M17 at Vlsr = 20{23km s�1 (Lada 1976). In fat, a strong CO emission isseen in the north-west parts of the hannel maps in therange between Vlsr = 20 and 23 km s�1. The H2O maseremission was deteted toward three objets M4-01, M4-03 and M4-08. Beause of the large beam size at 22GHz, H2O emission of nearby objets ould be deteted

No. ℄ Red Supergiants in Embedded Star Clusters 5-0.5

0

0.5

1

1.5

2

2.5

-40 -20 0 20 40 60 80

Ta

(K)

J18202853080430.1

H2O

-0.10

0.10.20.30.40.50.60.7

-80 -60 -40 -20 0 20 40 60

Ta

(K)

J18203460080430.1

H2O

-0.1

0

0.1

0.2

-40 -20 0 20 40 60 80

Ta

(K)

J18203850080430.1

H2O

-0.1

0

0.1

0.2

0.3

20 40 60 80 100 120 140 160

Ta

(K)

J18390776080430.1

H2O

-0.50

0.51

1.52

2.53

20 40 60 80 100 120 140

Ta

(K)

J18390558080430.1

H2O

-0.50

0.51

1.52

2.53

-20 0 20 40 60 80 100

Ta

(K)

J18534227080430.0

H2O

Vlsr

(km s-1

)

Vlsr

(km s-1

) Vlsr

(km s-1

)

-0.1

-0.05

0

0.05

0.1

0.15

0.2

40 60 80 100 120 140 160

Ta

(K)

J18391961080430.1 H2O

-0.4

0

0.4

0.8

1.2

1.6

2

0 20 40 60 80 100 120 140

Ta

(K)

J18535249080430.0

H2O

-0.2

0

0.2

0.4

0.6

0.8

-20 0 20 40 60 80 100

Ta

(K)

J18535240080430.0

H2O

-0.2-0.1

00.10.20.30.40.50.6

20 40 60 80 100 120 140

Ta

(K)

J18390238080430.1

H2O

Mc4-01 Mc4-08 Mc4-03

St2-18

St2-03

St2-11 St2-08

Mc13-4

Mc13-5

Mc13-1

Fig. 2. b. H2O 616{523 spetra. The star name, abbreviation of 2MASS name (Jhhmmssss format), and the observed date(yymmdd.d format) are shown at the upper left of eah panel. The arrows indiate the emission ontaminated from the other objetdeteted at the Gaussian tail of the beam.at the tail of a Gaussian beam. The veloity of H2O emis-sion toward M4-03 is 20.5 km s�1. This is lose to theveloity 19.4 km s�1 of the seondary (redshifted) ompo-nent of H2O emission of M4-08. The angular separationbetween these two objets is 14300, indiating that the in-tensity should be redued to 0.1% level if the 19.4 km s�1emission from M4-08 is deteted at the Gaussian tail ofthe beam pattern at the position of M4-03. The observedratio of the integrated intensity of M4-03 to that of M4-08 is 29%, whih is too large for a side-lobe detetion,indiating that the 20.5 km s�1 emission of M4-03 is nota ontamination from M4-08 (though we annot rule outthe possibility that the emission omes from an unknownH2O soure loated near the middle between M4-03 andM4-08). Two water maser soures (possibly of a youngstar origin) have been deteted in M17 north (Cesarsky etal. 1978; Braz & Ephtein 1983): G15.18�0.62 (+21 kms�1), and G15.20�0.63 (+47 km s�1). They are loatedat 2000 and 9200 away from M4-01 (Vlsr = 24 km s�1).Therefore, G15.18�0.62 ould be the same H2O masersoure as M4-01, but G15.20�0.63 is di�erent from M4-01. The di�erene of 3 km s�1 between peak veloitiesof M4-01 and G15.18�0.62 ould be explained by a timevariation of a line pro�le. Thus, we onlude that twoof the three H2O maser soures deteted in the presentobservation are new.2.3. Merer et al.'s #8In M8-01, SiO maser emission is deteted at Vlsr = 74km s�1, whih is onsiderably di�erent from the averageveloity of M8-03 and M8-04 (105.5 km s�1). Thereforeit is possible that the objet M8-01 is a foreground soure.Sine no water maser was deteted toward this star luster(Table 3), dense moleular gas of a young star origin (asseen toward Merer et al.'s #4) does not remain inside thisstar luster. In fat, CO hannel maps shown in Figure 5d

6 Deguhi et al. [Vol. ,indiate that CO emission is quite weak toward this lus-ter, exept the 106 km s�1 omponent, whih is extendedto the north-east of the star luster toward M8-05. Apulsar, PSR J1828�1057, exists 10 south-east of M8-0,and three X-ray soures (XGPS-I J182844�105428 andXGPS-I J182851�105539, GPSR5 20.722-0.075) exist inthis diretion. The presene of these high-energy souresseems onsistent with the interpretation that CO gas waswiped out by supernova explosions.2.4. Merer et al.'s #13M13-5 in this star luster is a bright IR soure (FC =145 Jy), but a searh for SiO maser in this objet wasnegative in a previous observation (Hall et al. 1990). Wedeteted the SiO masers for the �rst time in this objet.Water maser was deteted toward M13-1, M13-3, M13-4, and M13-5. However, sine the angular separation be-tween M13-3 and M13-5 is only 4100, the H2O emissionat 70.2 km s�1 deteted at the position of M13-3 omesfrom M13-5. Similarly, the angular separation betweenM13-4 and M13-5 is 4600, the emission at the position ofM13-4 is also a ontamination from M13-05. The emis-sion at 21.4 km s�1 deteted toward M13-4 is strongerthan that deteted at the position of M13-05. Therefore,we onlude that the emission at 21.4 km s�1 is assoiatedwith M13-04. A ompat CO emission at Vlsr = 75 kms�1 was found at the position between M13-5 and M13-6 (see Figure 5e), indiating that the moleular gas stillremains in this luster.2.5. Bia et al.'s #122 =RSGC1In addition to the star lusters mentioned above, weobserved CO emission toward Bia et al. (2003)'s #122(=RSGC1 in Davies et al. 2007), whih involves 14 redsupergiants (Figer et al. 2006). SiO masers have been de-teted in four of them (Nakashima & Deguhi 2006); theaverage radial veloity and veloity dispersion are 120 kms�1 and 3 km s�1, respetively. The lower right panel ofFigure 4 shows the CO J = 1{0 spetra of Bia et al.'s#122 taken at 5 di�erent positions aligning in the north{south diretion (entered toward the star F13; Nakashima& Deguhi 2006). CO emission was seen in the veloityrange between 85 and 110 km s�1. However, no CO emis-sion stronger than Ta = 0:2 K was deteted at veloitiesabove 110 km s�1 toward this luster in this work. Thisfat suggests that almost no moleular gas remains in thisluster.3. DisussionWe observed 36 andidates for red supergiants in 4 starlusters in the SiO and H2O maser lines, and obtaineda

urate radial veloities. The membership of stars toeah luster was on�rmed by the veloity information ob-tained in the present observation, sine veloities of on-taminated bakground stars are generally di�erent fromthat of member stars. With the veloity information ob-tained by the present maser observations, we an assesswhether or not the CO emission is assoiated with the star

2

4

6

8

10

120 0.5 1 1.5 2 2.5 3 3.5

SiOno SiO

K

H-K

1

10

100

-0.1 0 0.1 0.2 0.3 0.4 0.5

Fc

(Jy)

CACFig. 3. K magnitude versus H �K olor and 12 �m uxdensity versus CAC diagrams for the observed objets. Filledand un�lled irles indiate SiO maser detetions and no de-tetions, respetively.luster in terms of radial veloities.3.1. Cluster kinematis of Stephenson #2The age and distane of the luster Stephenson #2 weresomewhat unertain. Nakaya et al. (2001) estimated theage and distane to be 50 Myr and 1.5 kp, respetively,from a magnitude-olor diagram. However, Ortolani etal. (2002) suggested the age of 20 Myr and a distane of6 kp for this luster, based on the V IJH-band photom-etry and model alulations. The average radial veloityobtained in the present observation is 96.5 km s�1, givinga kinemati distane of 5.5 kp. This distane is onsis-tent with the estimation given by Ortolani et al. (2002).Here we assumed a at rotation urve with a onstant ve-loity of 220 km s�1 and a distane to the Galati enterof 8 kp.The standard deviation of radial veloities is 4.4 kms�1 (for 4 stars). To obtain this value, we assumed theunertainty of 2 km s�1 in the veloity measurement ofthe SiO maser observation [see, Setion 3.2 in Nakashima& Deguhi (2006)℄. The veloity dispersion gives a virialmass of the luster (� 6�r�v2r=G ; Eigenbrod et al. 2004) of1:3� 105M� under the assumption that the radius of theluster (inluding both Stephenson #2 and Stephenson#2 SW) is 3.10 (� 5:5 p). The obtained virial massis larger than the mass of the Bia et al.'s #122 (2{4�104 M�; Figer et al. 2006). The virial mass only forStephenson #2 SW is 3:7�104 M� for a radius of 20 (3.5p). This value is lose to the mass of Bia et al.'s #122,

No. ℄ Red Supergiants in Embedded Star Clusters 7and seems to be reasonable for a single massive luster.Davies et al. (2007) obtained the K-band spetra ofabout 70 stars in Stephenson #2 and Stephenson #2 SWwith Kitt Peak National Observatory 4m telesope. Theymeasured equivalent widths of the CO band-head featuresand obtained the radial veloities by ross-orrelating theband head features with that of Arturus. We omparedthe radial veloities obtained in the present radio observa-tion with the veloities obtained by above infrared obser-vations [see Figure 4 of Davies et al. (2007)℄. The radioand infrared radial veloities of St2-18 [No 1 of Davies etal. (2007)℄ oinide within about 2 km s�1, but otherthree stars do not show a good math in veloity, and thedi�erene is roughly 8{10 km s�1. On average, the radialveloities obtained from the CO band head are systemat-ially redshifted by about 10 km s�1. It has been knownthat the radial veloities obtained from infrared line pro-�les are systematially shifted from the true veloity of astar beause of the sattering by dust grains in outow-ing irumstellar envelopes (Reid & Dikinson 1976; VanBlerkom et al. 1982). Therefore, if we take into a

ountthe unertainty in the radial veloity obtained by the in-frared observation, we an say that the veloities obtainedin the present observation is onsistent with those givenby Davies et al. (2007).3.2. CO emission toward Stephenson #2The CO hannel maps in the veloity range Vlsr = 101{105 km s�1 (Figure 5a) show an emission enhanementnear the enter of the map (though the peak position doesnot oinide with the map enter). The radial veloity ofthis loud is approximately equal to the SiO radial veloityof St2-03 (102.7 km s�1). Therefore it is likely that thisloud is assoiated with the star luster Stephenson #2.In ontrast, the CO hannel maps of Stephenson #2 SW(Figure 5b) exhibit no strong enhanement of emissionaround the map enter, but emission features are seen nearthe south edge of the map. Additionally, weak emissionpeak is notieable at the north-east part of the hannelmaps [(RA, De) � (18h39m05s, �06Æ0403000)℄ in the Vlsrrange between 93 and 103 km s�1. The oordinates andveloity of this omponent roughly oinide with thoseof St2-11. However, we attribute this CO emission to afragment of the loud toward this diretion, whih is notrelated to the irumstellar envelope of the red supergiantSt2-11, beause the CO intensity is too strong for a redsupergiant 5 kp away.Jakson et al. (2006) mapped the region of l = 18Æ {58Æ and jbj< 1Æ in the 13CO J = 1{0 radio line with the2200 beam of on-the-y sampling. Their hannel map atVlsr = 95 { 115 km s�1 exhibits an emission peak nearStephenson #2 at (l; b)� (26:15Æ;�0:08Æ). This position,possibly the densest part of the moleular loud in thisomplex, is a few arminutes south of Stephenson #2 anda few arminutes east of Stephenson #2 SW, but it isout of overage of Figures 1a and 1b. If we assume thatthe kinemati distane is reliable, the Stephenson #2 SWluster (Vlsr � 94 km s�1 ) is loated at near side, and thethik CO louds with the spetral peak showing an inten-

sity peak at Vlsr�100{105 km s�1 is loated at the far sideof the Stephenson #2 omplex. Furthermore, Stephenson#2 (Vlsr � 102 km s�1) is lose to the thik CO loud.This onjeture is onsistent with the on�guration of theSutum-Crux arm, whih has a tangeny at distane of 7kp from the Sun in the diretion of l� 35Æ. The Sutum-Crux arm rosses the tip of the Bulge bar at distaneD � 6 kp in the diretion of l � 30Æ, approahing to-ward the Sun with dereasing l (see, e.g., Benjamin 2008).Therefore, the di�erene of the radial veloities betweenStephenson #2 and Stephenson #2 SW an be under-standable in terms of the struture and kinematis of theSutum-Crux arm.3.3. CO toward the Bia et al.'s #122 and omparisonwith Stephenson #2The red-supergiant star luster, Bia et al.'s #122(RSGC1), is loated very lose to Stephenson #2 witha separation of about 1.0Æ. No CO emission is seen to-ward Bia et al.'s #122 at the veloities above 110 kms�1 in lower right panel of Figure 4 and in Figure 5f.This fat suggests that almost no moleular gas is leftbehind Bia et al.'s #122. This is a sharp ontrast withthe ase of Stephenson #2 (RSGC2). The ages of redsupergiants of Bia et al.'s #122 and Stephenson #2were estimated to be 8 and 17 Myr, respetively, fromisohrone �ttings using the "fast-rotating" Geneva mod-els. Davies et al. (2007) found that ages of red super-giants in Stephenson #2 show a relatively large dispersion(several Myr), and therefore they onluded that the redsupergiants in Stephenson #2 and #2 SW are not o-eval. For the ase of Stephenson #2, the radial veloityobtained by the present SiO maser observation is slightlydi�erent from that obtained by the NIR observation. Thisfat suggests that the distane to Stephenson #2 and #2SW lusters is loser than the previous expetation. It issafely onluded that Stephenson #2 and #2 SW is lo-ated in front of the base of the Sutum-Crux arm (e.g.,Russeil 2003), and that Bia et al.'s #122 is muh fartherthan Stephenson #2; i.e., Bia et al.'s #122 is loated nearthe tangent point of this diretion, possibly inside the ir-le of the Galati bulge tip. The aged luster Stephenson#2 appears to hold more CO gases than the younger lus-ter Bia et al.'s #122 does. This fat seems to indiatethat the gas expulsion from a star luster is not a simplefuntion of time, and it depends on the environment of theluster, possibly on a mass and spheriity of the originalmoleular loud, a distribution of birth dates of massivestars, and a positioning of sequene of loud formation ina spiral arm.Note that the radial veloity of Stephenson #2 (� 96km s�1) falls on the "Moleular Ring" feature in thelongitude-veloity map of the Galati disk CO emission[see, Dame et al. (2001)℄, but the veloity of Bia et al.'s#122 (120 km s�1) exeeds the moleular ring veloityat l = 26Æ. This fat suggests that Bia et al.'s #122 isformed under strong inuene of the Galati bulge un-like majority of usual star lusters formed in the Galatispiral arms.

8 Deguhi et al. [Vol. ,0

10

20

30

40

50

60

-10 0 10 20 30 40 50

M4-02

(0, +82)

(0, +41)

(0, 0)

(0, -41)

(0, -82)

0

4

8

12

16

80 90 100 110 120 130 140Vlsr

(0, +82)

(0, +41)

(0, 0)

(0, -41)

(0, -82)

B112-13

0

2

4

6

8

10

40 50 60 70 80 90 100

Vlsr

M13-5

(0, +82)

(0, +41)

(0, 0)

(0, -41)

(0, -82)0

2

4

6

8

10

70 80 90 100 110 120 130Vlsr

M8-03

(0, +82)

(0, +41)

(0, 0)

(0, -41)

(0, -82)

Ta

(K)

0

5

10

15

20

25

70 80 90 100 110 120

(0, +82)

(0, +41)

(0, 0)

(0, -41)

(0, -82)

S2-18

0

5

10

15

70 80 90 100 110 120

Ta

(K)

(0, +82)

(0, +41)

(0, 0)

(0, -41)

(0, -82)

S2-03

Fig. 4. CO J = 1{0 spetra towards star lusters harboring observed targets. The (0,0) positions orrespond to the diretionsto St2-18, St2-03, M4-02, M8-03, M13-5. The (0,0) position in the last panel is toward 2MASS J18375890�0652321, F13 ofNakashima & Deguhi 2006 in Bia et al.'s #122. The o�set positions were shown between the parentheses in arseond. The thiklight blue bar in eah panel indiates the possible veloity range of star lusters.4. SummaryWe deteted SiO maser emission (J = 1{0 v = 1 and2) toward 11 of 36 observed targets inluding red super-giants and andidates for red supergiants in star lustersembedded in the Galati disk. We also deteted H2Omaser emission (JKK=616{523) toward 10 of these 36 tar-gets, in whih both SiO and H2O lines were deteted in4. A

urate radial veloities of the deteted objets wereobtained from veloities of SiO maser lines. The esti-mated kinemati distane indiates that the distane ofStephenson #2 is signi�antly smaller than that of Biaet al.'s #122. The radial veloity obtained by the presentobservation was used to hek the assoiation of CO gasto these lusters. We found that a plenty of moleulargas still remains in Stephenson #2, whereas almost nomoleular gas remains in Bia et al.'s #122. We onludethat the SiO and H2O masers are useful tools for inves-tigating the massive stars in star lusters and kinematisof star lusters, as well as proesses of mass loss of redsupergiants. At the end, these studies will larify detailedproesses of disruption mehanisms of massive star lus-ters in the Galaxy.This work is supported in part by Grant-in-Aid forSienti� Researh from Japan Soiety for Promotionof Sienes (20540234), and by a grant awarded toJN, YZ, and SK from the Researh Grants Counilof Hong Kong (projet ode: HKU 703308P) andthe Seed Funding Program for Basi Researh of theUniversity of Hong Kong [projet ode: 200802159006(JN) and 200909159007 (YZ)℄, and by a grant from theResearh 359 Grants Counil of the Hong Kong SpeialAdministrative 360 Region, China (Projet No.HKU7020/08P). This researh made use of the SIMBAD andVizieR databases operated at CDS, Strasbourg, Frane,and as well as use of data produts from Two MironAll Sky Survey, whih is a joint projet of the Universityof Massahusetts and Infrared Proessing and AnalysisCenter/California Institute of Tehnology, funded bythe National Aeronautis and Spae Administration andNational Siene foundation, and from the MidourseSpae Experiment at NASA/ IPAC Infrared SieneArhive, whih is operated by the Jet PropulsionLaboratory, California Institute of Tehnology, underontrat with the National Aeronautis and SpaeAdministration.

No. ℄ Red Supergiants in Embedded Star Clusters 9-05°59'00"

30

-06°00'00"

30

01'00"

30

02'00"

-05°59'00"

30

-06°00'00"

30

01'00"

30

02'00"

-05°59'00"

30

-06°00'00"

30

01'00"

30

02'00"

RIGHT ASCENSION (J2000)18h39m26s 24 22 20 18 16 14

-05°59'00"

30

-06°00'00"

30

01'00"

30

02'00"

109 km s-1

107 km s-1103 km s-1 105 km s-1

101 km s-197 km s-1 99 km s-1

95 km s-193 km s-191 km s-1

RIGHT ASCENSION (J2000)39m26s 24 22 20 18 16 14

RIGHT ASCENSION (J2000)39m26s 24 22 20 18 16 14

Declination

Declination

Declination

DeclinationFig. 5. a. CO J =1{0 hannel maps toward Stephenson#2. Cross marks are observed positions by the array reeiver. The ontourlevels are drawn by every 0.3 K from the lowest one (0.3 K)Appendix. Individually interesting objets� M4-02 (=M17WF 26): This star is loated near thenorth boundary of M17. Ando et al. (2002) studiedthe infrared objets around M17 and reorded thisstar as #26 in their Table 2 (also see their Figure3). We deteted SiO maser emission at Vlsr = 18 kms�1. Correted K magnitude of this star is K=5.45.If this objet is at the same distane as that of M17(2.4) kp (Lada 1976), the luminosity is estimatedto be � 103 L�, whih is too small as a supergiant.The Ks magnitude of this star was measured in thepast as 7:98� 0:02 (2MASS), 8:15� 0:05 (DENIS),and 8:2� 0:2 (Ando et al. 2002). This star is possi-bly a distant bulge population, whih has no diretrelation to Merer #4.� M8-01 (=IRAS 18258�1058): The SiO maserswere deteted in this star by Izumiura et al. (1999)in their SiO maser survey of Galati bulge stars.Deguhi et al. (1998) suggested a questionable NIRounterpart loated 800 south of the IRAS position.However, the 2MASS star, J18283530�105636,whih is identi�ed in the present work, is muhbrighter, and is spatially loser to the MSX oun-terpart (G020.6034+00.0234). The SiO radial ve-

loity (� 74 km s�1) suggests that this objet is notthe member of Merer et al.'s #8, and is possiblyassoiated with the Galati bulge.� M13-1 (=IRAS 18511+0038): This objet is anultra-ompat HII region (Giveon et al. 2007).In fat, CS J = 7{6 emission was deteted to-ward this soure at Vlsr = 46 km s�1 (Plume etal. 1992), though a searh for the CS J = 1-0 andNH3 (1,1) lines was negative (Anglada et al. 1996).Water maser emission has been deteted by Braz &Ephtein (1983) at Vlsr = 38 km s�1, whih is loseto the peak veloity of 45.4 km s�1 obtained in thiswork. Sine the large di�erene is found in the radialveloities, this objet is not assoiated with Mereret al.'s #13 whih exhibits a radial veloity of � 72km s�1. No SiO maser was deteted in this star.� St2-03 (=IRAS 18366�0603) exhibits a relativelyat IRAS LRS spetrum with a small hump around10 �m (Kwok et al. 1997). SiO and H2Omaser emis-sions were deteted at Vlsr = 103 and 106 km s�1,respetively, in the present observation. A searh forthe OH 1612 MHz maser was negative in a previousobservation [IRC �10447; Wilson & Barrett 1972℄.� St2-18 (=J18390238�0605106): This is an enig-mati objet showing a K magnitude of 1.03 (or-

10 Deguhi et al. [Vol. ,

RIGHT ASCENSION (J2000)18h39m08s 06 04 02 00 58 56

-06°03'30"

04'00"

30

05'00"

30

06'00"

30

109 km s-1

107 km s-1103 km s-1 105 km s-1

101 km s-197 km s-1 99 km s-1

95 km s-193 km s-191 km s-1

-06°03'30"

04'00"

30

05'00"

30

06'00"

30

-06°03'30"

04'00"

30

05'00"

30

06'00"

30

-06°03'30"

04'00"

30

05'00"

30

06'00"

30

RIGHT ASCENSION (J2000)39m08s 06 04 02 00 58 56

RIGHT ASCENSION (J2000)39m08s 06 04 02 00 58 56

Declination

Declination

Declination

Declination

Fig. 5. b. CO J = 1{0 hannel map toward Stephenson #2 SW. Cross marks are observed positions by the array reeiver. Theontour levels are drawn by every 0.5 K from the lowest one (0.5 K)RIGHT ASCENSION (J2000)

18h20m42s 40 38 36 34 32 30

-16°01'30"

02'00"

30

03'00"

30

04'00"

30

RIGHT ASCENSION (J2000)20m42s 40 38 36 34 32 30

RIGHT ASCENSION (J2000)20m42s 40 38 36 34 32 30

13 km s-1

29 km s-127 km s-125 km s-1

23 km s-121 km s-119 km s-1

17 km s-115 km s-1

Declination

-16°01'30"

02'00"

30

03'00"

30

04'00"

30

Declination

-16°01'30"

02'00"

30

03'00"

30

04'00"

30

Declination

Fig. 5. . CO J = 1{0 hannel map toward Merer et al.'s #4. Cross marks are observed positions by the array reeiver. Theontour levels are drawn by every 1.0 K from the lowest one (1.0 K)

No. ℄ Red Supergiants in Embedded Star Clusters 11-10°56'30"

57'00"

30

58'00"

30

59'00"

30

RIGHT ASCENSION (J2000)18h28m58s 56 54 52 50 48 46

-10°56'30"

57'00"

30

58'00"

30

59'00"

30

RIGHT ASCENSION (J2000)18h28m58s 56 54 52 50 48 46

108 km s-1106 km s-1

102 km s-1 104 km s-1

Declination

Declination

Fig. 5. d. CO J = 1{0 hannel map toward Merer et al.'s #8. Cross marks are observed positions by the array reeiver. Theontour levels are drawn by every 0.2 K from the lowest one (0.2 K)18h54m10s 05 00 53m55s 50 45

18h54m10s 05 00 53m55s 50 45

00°41'

40

39

38

37

36

35

71 km s-1 73 km s-1

75 km s-1 77 km s-1

79 km s-1

00°41'

40

39

38

37

36

35

00°41'

40

39

38

37

36

35

RIGHT ASCENSION (J2000)

RIGHT ASCENSION (J2000)

Declination

Declination

Declination

Fig. 5. e. CO J = 1{0 hannel map toward Merer et al.'s #13. Cross marks are observed positions by the array reeiver. Theontour levels are drawn by every 0.2 K from the lowest one (0.2 K). from the left to the right.

12 Deguhi et al. [Vol. ,-06°51'00"

30

52'00"

30

53'00"

30

54'00"

RIGHT ASCENSION (J2000)18h38m04s 02 00 37m58s 56 54 52

-06°51'00"

30

52'00"

30

53'00"

30

54'00"

RIGHT ASCENSION (J2000)18h38m04s 02 00 37m58s 56 54 52

106 km s-1

112 km s-1110 km s-1

108 km s-1

Declination

DeclinationFig. 5. f. CO J = 1{0 hannel map toward Bia et al.'s #112 (=RSGC1). Cross marks are observed positions by the array reeiver.The ontour levels are drawn by every 0.2 K from the lowest one (0.2 K). No CO emission stronger than Ta = 0:2 K was found inhannels of Vlsr > 112 km s�1, .reted for interstellar extintion). IRAS LRS spe-trum (IRAS 18363�0607) exhibits strong 10 and 18�m siliate emission (Volk & Cohen 1989). Notethat the typial K magnitude of SiO soures (AGBstars) in the Galati bulge is about 5.5 (Fujii etal. 2006). It indiates the luminosity of St2-18 is 30times the luminosity of average bulge SiO soures atthe K bands. An estimation of luminosity using theIRAS 12 and 25 �m ux densities (Jiang et al. 1996)gives the luminosity of 9�104 L� at the distane of5.5 kp.ReferenesAndo, M., Nagata, T., Sato, S., Mizuno, N., Mizuno, A.,Kawai, T., Nakaya, H., & Glass, I. S. 2002, ApJ, 574, 187Anglada, G., Estalella, R., Pastor, J., Rodriguez, Luis F., &Hashik, A. D. 1996, ApJ, 463, 205Benjamin, R. A. 2008, ASPC, 387, 375Bia, E., Dutra, C. M., Soares, J., & Barbuy, B. 2003, A&A,404, 223Boily, C. M.& Kroupa, P. 2003, MNRAS, 338, 673Braz, M. A. & Ephtein, N. 1983, A&AS, 54, 167Cerniharo, J., Alolea, J., Baudry, A. & Gonzalez-Alfonso, E.1997, A&A, 319, 607Cesarsky, C. J., Cesarsky, D. A., Lequeux, J., & Churhwell,E. 1978, A&A, 68, 33Cutri, R.M., et al. 2003, 2MASS All Sky Catalog of PointSoures2Dame, T. M., Hartmann, D., & Thaddeus, P. 2001, ApJ, 547,792Davies, B., Figer, D. F., Law, C. J., Kudritzki, R.-P., Najarro,F., Herrero, A., MaKenty, J. W. 2008, ApJ, 676, 1016Davies, B., Figer, D. F., Kudritzki, R.-P. MaKenty, J.,Najarro, F., Herrero, A. 2007, ApJ, 671, 7812 http://irsa.ipa.alteh.edu/appliations/Gator/

Deguhi, S., Matsumoto, S. & Wood, P. R. 1998, PASJ, 50,597Deguhi, S., Imai, H., Fujii, T., Glass, I., Ita, Y., Izumiura,H., Kameya, O., Miyazaki, A., Nakada, Y., Nakashima, J.2004, PASJ, 56, 261Deguhi, S., et al. 2004, PASJ, 56, 261Dutra, C. M., & Bia, E. 2000, A&A, 359, L9Egan M.P., Prie S.D., Kraemer K.E., Mizuno D.R., CareyS.J., Wright C.O., Engelke C.W., Cohen M., Gugliotti G.M. 2003, Air Fore Researh Laboratory Tehnial ReportAFRL-VS-TR-2003-15893Eigenbrod, A.,Mermilliod, J.-C., Clari, J. J., Andersen, J., &Mayor, M. 2004, A&A, 423, 189Figer, D. F., MaKenty, J., Robberto, M., Smith, K., Najarro,F, Kudritzki, R. P., Herrero, A. 2006, ApJ, 643, 1166Fujii, T., Deguhi, S., Ita, Y., Izumiura, H., Kameya, O.,Miyazaki, A., & Nakada, Y. 2006, PASJ 58, 529Giveon, U., Rihter, M. J., Beker, R. H., & White, R. L. 2007,AJ, 133, 639Hall, P. J., Allen, D. A., Troup, E. R., Wark, R. M., & Wright,A. E., 1990, MNRAS, 243, 480Heger, A., Fryer, C. L., Woosley, S. E., Langer, N., Hartmann,D. H. 2003, ApJ, 591, 288Izumiura, H., Deguhi, S., Fujii, T., Kameya, O., Matsumoto,S., Nakada, Y., Ootsubo, T., Ukita, N. 1999, ApJS, 125,257Jakson, J. M., et al. 2006, ApJS, 163, 145Jiang, B. W., Deguhi, S., Yamamura, I., Nakada, Y., Cho, S.H., & Yamagata, T. 1996, ApJS, 106, 463Kwok, S., Volk, K., & Bidelman, W. P. 1997, ApJS, 112, 557Lada, C. J. 1976, ApJS, 32, 603Lada, C. J., Margulis, M., & Dearborn, D. 1984, ApJ, 285, 141Lada, C. J., & Lada, E. A. 2003, ARA&A, 41, 57Merer, E. P. et al., 2005, ApJ, 635, 560Nakajima, Y. Kato, D., Nagata, T., Tamura, M., Sato, S. etal. 2005, AJ, 129, 7763 http://vizier.nao.a.jp/viz-bin/VizieR?-soure=V/114

No. ℄ Red Supergiants in Embedded Star Clusters 13Nakashima, J., & Deguhi, S. 2003b, PASJ, 56, 229Nakashima, J., & Deguhi, S. 2006, ApJ, 647, L139Nakaya, H., Watanabe, M., Ando, M., Nagata, T. & Sato, S.2001, AJ, 122, 876Ortolani, S., Bia, E., Barbuy, B., & Momany, Y. 2002, A&A,390, 931Plume, R., Ja�e, D. T., & Evans, N. J., II, 1992, ApJS78, 505Reid, M. J.& Dikinson, D. F. 1976, ApJ, 209, 505Russeil, D. 2003, A&A, 397, 133Salasnih, B., Bressan, A., & Chiosi, C. 1999, A&A, 342, 131Shild, R. E. 1970, ApJ, 161, 855Sorai, K., Sunada, K., Okumura, S. K. Iwasa, T., Tanaka, A.,Natori, K., Onuki, H. 2000, SPIE, 4015, 86Stephenson, C. B. 1990, AJ, 99, 1867Sunada, K., Yamaguhi, C., Nakai, N., Sorai, K., Okumura, S.K. & Ukita, N. 2000, SPIE, 4015, 237van Blerkom, D. & Mao, X. 1982, ApJL, 252, L73Volk, K., & Cohen, M. 1989, AJ, 98, 931Wilson, W. J. & Barrett, A. H. 1972, A&A, 17, 385

14 Deguhi et al. [Vol. ,Table 1. Properties of observed objets in Stephenson and embedded lusters.2MASS name No� K J �H H �K MSX name sep F CAC CCE V SiOlsr(00) (Jy) (km s�1)18201544�1602142 M4-05 8.23 4.19 2.32 G015.1542�00.5707 0.8 2.2 0.408 0.034 |18202853�1602159 M4-01 7.38 3.50 1.86 | | | | | |18203460�1606282 M4-08 8.89 2.35 1.63 G015.1288�00.6717 3.0 10.9 0.150 0.917 |18203644�1602589 M4-02 7.98 4.04 2.26 G015.1831�00.6482 8.6 2.4 0.407 -0.247 18.318203850�1604163 M4-03 7.85 2.58 1.27 | | | | | |18204070�1603412 M4-04 7.70 2.86 1.39 | | | | | |18283530�1056364 M8-01 4.88 1.92 1.10 G020.6034+00.0234 0.4 5.6 0.081 -0.184 74.118283912�1055526 M8-02 4.97 1.89 0.89 G020.6214+00.0151 1.1 1.0 -0.091 -0.154 |18285207�1057576 M8-03 6.23 2.23 1.32 G020.6156�00.0476 1.7 4.1 0.085 -0.105 102.418285402�1056453 M8-04 5.59 2.40 1.32 G020.6367�00.0452 0.3 3.6 0.055 -0.250 |18285844�1056069 M8-05 5.57 2.08 1.23 G020.6545�00.0562 0.9 2.2 0.179 -0.329 108.618290303�1053153 M8-06 4.49 1.59 0.76 G020.7053�00.0511 1.0 2.3 -0.035 -0.482 |18385699�0606459 St2-26 6.95 3.51 1.57 G026.0708�00.0208 7.6 1.8 0.124 | 92.318390238�0605106 St2-18 2.90 2.45 1.80 G026.1044�00.0283 5.6 56.9 0.260 �0.202 92.718390558�0604265 St2-11 7.32 4.31 2.60 G026.1215�00.0345 4.5 16.6 0.354 �0.067 98.618390776�0603203 St2-08 5.23 2.26 1.08 G026.1431�00.0343 3.4 1.5 0.049 | |18390805�0605244 St2-14 4.82 2.48 1.23 G026.1120�00.0510 4.7 4.9 0.159 �0.219 |18391223�0553586 St2-29 6.47 3.53 1.77 G026.2891+00.0206 7.9 1.6 0.153 0.047 |18391470�0601366 St2-05 5.24 2.00 0.97 G026.1806�00.0465 1.4 1.5 �0.051 | |18391489�0609272 St2-28 5.60 3.07 1.61 G026.0649�00.1076 7.8 3.4 0.121 �0.289 |18391825�0602142 St2-02 5.26 2.15 0.95 G026.1782�00.0641 0.7 1.5 �0.042 | |18391961�0600408 St2-03 4.12 1.85 0.93 G026.2038�00.0574 1.0 19.9 0.180 �0.179 102.718391989�0601481 St2-01 5.11 1.80 0.91 G026.1886�00.0679 0.0 1.9 �0.021 | |18392161�0555197 St2-21 8.86 1.99 2.76 G026.2868�00.0240 6.3 2.7 0.158 �0.152 |18392461�0602138 St2-04 4.50 1.82 0.96 G026.1903�00.0876 1.1 6.6 0.088 �0.401 |18392736�0607408 St2-20 5.45 2.85 1.50 G026.1150�00.1395 6.2 3.4 0.223 �0.210 |18392891�0556435 St2-17 5.82 2.07 1.25 G026.2800�00.0617 5.4 5.5 0.053 �0.209 50.218392947�0557165 St2-15 4.65 2.20 1.06 G026.2732�00.0679 4.9 5.4 0.135 �0.206 |18394340�0556290 St2-27 5.88 1.95 0.90 G026.3112�00.1130 7.7 3.1 0.716 | |18394635�0559473 St2-23 4.51 1.71 0.83 G026.2678�00.1492 6.7 5.9 0.115 �0.126 |18534227+0041459 M13-1 9.51 4.21 3.29 G033.8104�00.1869 2.5 18.8 0.348 0.470 |18534913+0038021 M13-2 6.13 2.81 1.46 G033.7671�00.2406 1.3 | | | |18535060+0039015 M13-3 6.01 2.68 1.27 | | | | | |18535240+0040172 M13-4 5.89 3.67 1.95 G033.8071�00.2351 1.5 3.6 0.103 -0.216 |18535249+0039313 M13-5 2.67 3.03 1.62 G033.7963�00.2417 1.6 144.9 0.184 -0.257 72.318540749+0039039 M13-6 7.28 2.87 1.66 G033.8179�00.3008 1.0 3.2 0.079 -0.101 73.3� the star number in �gure 1.

No. ℄ Red Supergiants in Embedded Star Clusters 15Table 2. Observational results of the SiO maser searh.SiO J = 1{0 v = 1 SiO J = 1{0 v = 22MASS name No� Ta Vlsr L.F. rms Ta Vlsr L.F. rms obs. date(K) (km s�1) (K km s�1) (K) (K) (km s�1) (K km s�1 ) (K) (yymmdd.d)18201544�1602142 M4-05 | | | 0.049 | | | 0.052 080427.218202853�1602159 M4-01 | | | 0.038 | | | 0.036 080428.218203460�1606282 M4-08 | | | 0.051 | | | 0.055 080427.218203644�1602589 M4-02 0.210 18.3 0.542 0.037 | | | 0.035 080428.218203850�1604163 M4-03 | | | 0.051 | | | 0.056 080427.218204070�1603412 M4-04 | | | 0.037 | | | 0.035 080428.218283530�1056364 M8-01 0.932 74.6 3.285 0.051 0.673 73.7 2.601 0.053 080427.218283912�1055526 M8-02 | | | 0.046 | | | 0.048 080427.218285207�1057576 M8-03 0.312 101.9 0.826 0.052 0.311 102.9 0.927 0.050 080427.218285402�1056453 M8-04 | | | 0.048 | | | 0.050 080427.218285844�1056069 M8-05 0.221 108.6 0.374 0.050 0.273 108.6 0.846 0.054 080427.218290303�1053153 M8-06 | | | 0.046 | | | 0.050 080427.218385699�0606459 St2-26 0.258 94.2 0.589 0.065 0.330 90.4 0.582 0.068 060415.318390238�0605106 St2-18 0.367 92.7 4.199 0.062 |- | |{ 0.065 060412.318390558�0604265 St2-11 1.963 100.9 16.398 0.072 1.378 96.3 8.621 0.066 060412.318390776�0603203 St2-08 | | | 0.075 | | | 0.074 060413.318390805�0605244 St2-14 | | | 0.064 | | | 0.067 060412.318391223�0553586 St2-29 | | | 0.068 | | | 0.067 060415.318391470�0601366 St2-05 | | | 0.070 | | | 0.075 060413.318391489�0609272 St2-28 | | | 0.068 | | | 0.068 060415.318391825�0602142 St2-02 | | | 0.072 | | | 0.072 060413.318391961�0600408 St2-03 0.435 102.7 0.726 0.074 | | | 0.074 060413.318391989�0601481 St2-01 | | | 0.071 | | | 0.071 060413.318392161�0555197 St2-21 | | | 0.083 | | | 0.087 060416.318392461�0602138 St2-04 | | | 0.074 | | | 0.075 060413.318392736�0607408 St2-20 | | | 0.066 | | | 0.068 060415.318392891�0556435 St2-17 0.345 49.1 0.979 0.070 0.193 51.3 0.809 0.069 060415.318392947�0557165 St2-15 | | | 0.085 | | | 0.085 060416.318394340�0556290 St2-27 | | | 0.070 | | | 0.068 060415.318394635�0559473 St2-23 | | | 0.086 | | | 0.087 060416.318534227+0041459 M13-1 | | | 0.042 | | | 0.044 080427.118534913+0038021 M13-2 | | | 0.033 | | | 0.042 080427.218535060+0039015 M13-3 | | | 0.045 | | | 0.044 080427.118535240+0040172 M13-4 | | | 0.040 | | | 0.042 080427.218535249+0039313 M13-5 0.993 69.4 10.487 0.080 | | | 0.077 060413.4M13-5 0.941 72.3 7.148 0.043 | | | 0.045 080427.118540749+0039039 M13-6 0.278 74.9 1.053 0.041 0.184 71.6 0.697 0.042 080427.2� the star number in �gure 1.

16 Deguhi et al. [Vol. ,Table 3. Observational results of the H2O maser searh.H2O 616{523 Seond Peak2MASS name No� Ta Vlsr L.F. rms Ta Vlsr L.F. rms obs. date(K) (km s�1) (K km s�1) (K) (K) (km s�1 ) (K km s�1) (K) (yymmdd.d)18201544�1602142 M4-05 | | | 0.027 | | | | 080430.118202853�1602159 M4-01 2.232 24.0 6.119 0.032 | | | | 080430.118203460�1606282 M4-08 0.428 -44.5 0.803 0.028 0.209 19.4 0.684 | 080430.118203644�1602589 M4-02 | | | 0.031 | | | | 080430.118203850�1604163 M4-03 0.101 20.5 0.201 0.027 | | | | 080430.118204070�1603412 M4-04 | | | 0.035 | | | | 080430.118283530�1056364 M8-01 | | | 0.033 | | | | 080430.218283912�1055526 M8-02 | | | 0.071 | | | | 080430.218285207�1057576 M8-03 | | | 0.034 | | | | 080430.218285402�1056453 M8-04 | | | 0.074 | | | | 080430.218285844�1056069 M8-05 | | | 0.039 | | | | 080430.218290303�1053153 M8-06 | | | 0.099 | | | | 080430.218385699�0606459 St2-26 | | | 0.035 | | | | 080430.218390238�0605106 St2-18 0.519 95.6 7.368 0.031 | | | | 080430.118390558�0604265 St2-11 2.610 87.2 28.605 0.032 | | | | 080430.118390776�0603203 St2-08 0.167 86.7 1.583 0.031 | | | | 080430.118390805�0605244 St2-14 | | | 0.032 | | | | 080430.118391223�0553586 St2-29 | | | 0.033 | | | | 080430.218391470�0601366 St2-05 | | | 0.031 | | | | 080430.118391489�0609272 St2-28 | | | 0.033 | | | | 080430.218391825�0602142 St2-02 | | | 0.030 | | | | 080430.118391961�0600408 St2-03 0.112 106.8 0.336 0.034 | | | | 080430.118391989�0601481 St2-01 | | | 0.032 | | | | 080430.118392161�0555197 St2-21 | | | 0.033 | | | | 080430.218392461�0602138 St2-04 | | | 0.035 | | | | 080430.118392736�0607408 St2-20 | | | 0.042 | | | | 080430.218392891�0556435 St2-17 | | | 0.033 | | | | 080430.218392947�0557165 St2-15 | | | 0.034 | | | | 080430.218394340�0556290 St2-27 | | | 0.037 | | | | 080430.218394635�0559473 St2-23 | | | 0.035 | | | | 080430.218534227+0041459 M13-1 2.476 45.4 5.225 0.032 | | | | 080430.018534913+0038021 M13-2 | | | 0.032 | | | | 080430.018535060+0039015 M13-3 0.717y 70.2y 2.163y 0.034 | | | | 080430.018535240+0040172 M13-4 0.445 21.4 0.950 0.031 0.635y 70.2y 1.858y | 080430.018535249+0039313 M13-5 1.495 70.2 5.011 0.036 0.197[ 20.4[ 0.404[ | 080430.018540749+0039039 M13-6 | | | 0.033 | | | | 080430.0� the star number shown in �gure 1.[ ontamination from M13-04.y ontamination from M13-05.

No. ℄ Red Supergiants in Embedded Star Clusters 17Table 4. Other names for observed objets.2MASS name No� D071 MSX name other names & note18201544�1602142 M4-05 G015.1542�00.570718202853�1602159 M4-01 | H2O G15.18�0.6218203460�1606282 M4-08 G015.1288�00.6717 M17WF 24218203644�1602589 M4-02 G015.1831�00.6482 M17WF 26218203850�1604163 M4-03 | M17WF 29218204070�1603412 M4-04 |18283530�1056364 M8-01 G020.6034+00.0234 IRAS 18258�105818283912�1055526 M8-02 G020.6214+00.015118285207�1057576 M8-03 G020.6156�00.047618285402�1056453 M8-04 G020.6367�00.045218285844�1056069 M8-05 G020.6545�00.056218290303�1053153 M8-06 G020.7053�00.0511 StRS 20218385699�0606459 St2-26 G026.0708�00.020818390238�0605106 St2-18 1 G026.1044�00.0283 IRAS 18363�0607 (1700)18390558�0604265 St2-11 49 G026.1215�00.0345 K418390776�0603203 St2-08 9 G026.1431�00.0343 M5 IRAS 18364�0605 (2600)18390805�0605244 St2-14 5 G026.1120�00.0510 M418391223�0553586 St2-29 G026.2891+00.020618391470�0601366 St2-05 10 G026.1806�00.0465 M518391489�0609272 St2-28 G026.0649�00.107618391825�0602142 St2-02 11 G026.1782�00.0641 M418391961�0600408 St2-03 2 G026.2038�00.0574 M3 Cl Stephenson 2 2 IRC �1044718391989�0601481 St2-01 8 G026.1886�00.0679 K5 Cl Stephenson 2 418392161�0555197 St2-21 G026.2868�00.024018392461�0602138 St2-04 3 G026.1903�00.0876 M4 Cl Stephenson 2 1018392736�0607408 St2-20 G026.1150�00.139518392891�0556435 St2-17 22 G026.2800�00.061718392947�0557165 St2-15 4 G026.2732�00.067918394340�0556290 St2-27 G026.3112�00.113018394635�0559473 St2-23 G026.2678�00.1492 IRAS 18370-0602 StRS 23918534227+0041459 M13-1 G033.8104�00.1869 IRAS 18511+003818534913+0038021 M13-2 G033.7671�00.240618535060+0039015 M13-3 |18535240+0040172 M13-4 G033.8071�00.235118535249+0039313 M13-5 G033.7963�00.2417 IRAS 18513+0035 NSV 1148518540749+0039039 M13-6 G033.8179�00.3008� the star number in �gure 1.1 Davies et al. 2007.2 Ando et al. 2002.