**Table 1:** Candidate stars associated with HII regions.
Radio source	RA (2000)	Dec (2000)	J	H	Ks	J-H	$H-K{\rm s}$	Inferred mass ( $M_{\odot}$ )
CC	19:10:11.60	9:07:06.5	$19.09\pm0.02$	$15.78\pm0.02$	$13.92\pm0.04$	3.31	1.86	56
F	19:10:13.42	9:06:22.0	-	$15.80\pm0.01$	$11.94\pm0.02$	-	3.86	>120?
J2	19:10:14.22	9:06:27.4	-	$17.36\pm0.01$	$15.45\pm0.02$	-	1.91	25
O3	19:10:16.92	9:06:10.9	$18.61\pm0.02$	$15.54\pm0.02$	$13.90\pm0.03$	3.07	1.64	46
RQ	19:10:10.76	9:05:18.2	-	$19.18\pm0.03$	$15.87\pm0.03$	-	3.31	78
RQ	19:10:10.93	9:05:15.9	-	$17.33\pm0.02$	$15.63\pm0.02$	-	1.70	18
RQ	19:10:10.96	9:05:17.7	-	$18.57\pm0.03$	$12.94\pm0.02$	-	5.64	>120?
RQ	19:10:11.16	9:05:11.6	$17.84\pm0.01$	$15.51\pm0.02$	$14.36\pm0.02$	2.34	1.14	21
S	19:10:11.66	9:05:27.5	$16.48\pm0.02$	$14.16\pm0.02$	$13.02\pm0.04$	2.32	1.14	46
S	19:10:11.80	9:05:27.1	-	$18.19\pm0.04$	$15.23\pm0.05$	-	2.96	80
S	19:10:11.83	9:05:28.3	-	$17.21\pm0.03$	$14.57\pm0.04$	-	2.64	84
S	19:10:11.88	9:05:28.2	-	$16.73\pm0.01$	$14.40\pm0.02$	-	2.33	68
South	19:10:21.90	9:04:57.1	-	$17.60\pm0.02$	$14.96\pm0.04$	-	2.64	68
South	19:10:22.08	9:05:00.0	-	$17.43\pm0.02$	$14.54\pm0.03$	-	2.89	111
South	19:10:22.09	9:05:01.5	-	$19.02\pm0.04$	$16.29\pm0.02$	-	2.73	36
South	19:10:21.97	9:05:04.2	-	$16.61\pm0.02$	$14.54\pm0.03$	-	2.07	49
South	19:10:22.20	9:05:04.2	-	$18.23\pm0.03$	$16.19\pm0.02$	-	2.05	19
South	19:10:21.90	9:04:58.1	-	$16.78\pm0.05$	$14.74\pm0.04$	-	2.04	42
South	19:10:22.20	9:05:01.5	-	$18.06\pm0.03$	$15.84\pm0.04$	-	2.22	28
South	19:10:21.80	9:05:03.3	-	$18.33\pm0.03$	$14.34\pm0.05$	-	3.99	>120?
South	19:10:21.88	9:05:04.3	$20.07\pm0.04$	$15.36\pm0.01$	$12.74\pm0.03$	4.71	2.62	>120?
South	19:10:21.75	9:05:04.3	-	$18.61\pm0.03$	$14.88\pm0.05$	-	3.73	>120?
South	19:10:22.24	9:05:00.3	-	$18.46\pm0.01$	$16.29\pm0.03$	-	2.17	20
South	19:10:22.02	9:05:00.3	-	$18.27\pm0.03$	$16.11\pm0.05$	-	2.16	22
South	19:10:22.00	9:05:06.5	-	$18.56\pm0.03$	$16.36\pm0.04$	-	2.20	20

Notes: names are from De Pree et al. (1997). Sources associated with RQ, S, and W49 South are likely to be multiple unresolved objects; nebular emission near these sources complicates the determination of the background and likely makes the errors in the photometry larger than the quoted formal photometric errors. Masses are inferred from the extinction-corrected K magnitudes, a distance of 11.4 kpc, and $4\times 10^{5}$ yr stellar tracks from Lejeune & Schaerer (2002) with solar metallicity and enhanced mass loss. Objects with only H & Ks magnitudes may have an unknown Ks excess which could severely affect the inferred mass. Five objects have inferred masses above $120~M_{\odot}$ , which is likely due to a Ks excess and/or multiplicity. Errors of 10-20% in the mass estimate are expected simply from the uncertainty in the distance.

Source LaTeX | All tables | In the text

	1 Introduction
	2 Stages of massive star formation
	3 Observations and data reduction
	4 Results
	5 Discussion
	6 Conclusions
	References