4 Echelle spectroscopy

High resolution spectral observations of the four brightest stars in NGC 6604 have been carried out on Oct. 10, 1998 with the Echelle spectrograph mounted at the Cassegrain focus of the 1.82 m telescope operated by Osservatorio Astronomico di Padova on top of Mt.Ekar in Asiago (Italy). The detector has been a THX31156 Thomson CCD 1024$\times$1024 pixels, 19 $\mu$m each and the slit was set to 2.2 arcsec. The whole $\lambda$ range 4550-8750 Åwas recorded on each frame, with a average dispersion of 0.173 Å/pix at NaI D. Stars #21 and #32 have been observed with a 2$\times$2 binning. The spectra have been extracted and calibrated in a standard fashion with IRAF running under Linux on a desk-top Pentium. The spectra are part of a long term investigation of the kinematics of young open clusters conducted in Asiago (see Munari & Tomasella 1999 for details).

The profiles of the Na I D (5890, 5896 Å) and KI (7699 Å) interstellar lines are presented in Fig. 4 and their equivalent widths are given in Table 4 together with the E_B-V derived from the Munari & Zwitter (1997) calibration.

The radial velocities of the same four cluster members are given in Table 5, together with their rotational velocities.

Figure 3: Colour-magnitude diagrams for the stars in Table 2. Solar abundance isochrones for 3, 4, 5, 6 and 7 106 yr areoverimposed

   

Table 3: Our and literature spectroscopic classifications. Stars with identification numbers greater than 27 lie outside the area covered by Fig. 1 and are identified in Fig. 3

star	V	B-V	spectral type		EB-V	V-MV
			ours	liter.
1	12.101	0.763	early B
2	12.201	0.800	B2V		1.04	14.65
7	12.227	0.807	mid B
12	11.658	0.772	late B
21	10.127	0.707	B0	B0V	1.01	14.13
23	9.681	0.729	O9.5	B1IV	1.04	13.93
24	10.426	0.735	B1V		1.00	13.63
26	7.524	0.812	O7	O8f	1.10	14.32
28	10.73	0.7	B3
29	12.27	0.7	late B
30	12.12	1.0	G4
31	11.06	1.0	M4III
32	9.26	0.7	O9.5	B1Ib
33	10.43	0.9	B4:	OB
34	10.82	0.9	B0.5	OB
35	12.06	1.1	early B
36	12.63	0.8	early F
37	12.72	0.9	K5:
38	12.77	1.6	late K
39	8.96	1.7	early G
40	12.41		K3
41	10.65		late B
42	10.90		early B
43	12.60		K3
44	12.66		A
45	12.83		early F
46	12.65		late A
47	12.04		A
48	12.24		K4
49	12.94		A
50	12.22		early G
51	12.90		F:

   

Table 4: Equivalent width and corresponding E_B-V (from the Munari & Zwitter 1997 calibration) of the interstellar NaI and KI lines in the Asiago Echelle+CCD spectra of some NGC 6604 stars

star	V	NaI (5890, 5896 Å)			KI (7699 Å)	EB-V
		EW (Å)	EW (Å)		EW (Å)
21	10.13	0.67	0.64		0.20	1.0
23	9.68	0.66	0.64		0.25	1.0
26	7.52	0.72	0.67		0.25	1.1
32	9.26	0.65	0.63		0.19	0.9

   

Table 5: Radial and rotational velocity for some NGC 6604 stars derived from Asiago Echelle+CCD spectra. EW, HIW = equivalent width and half intensity width of He I $\lambda$ 5876 Å; $V_{{\rm rot}}\sin i$ = projected rotational velocities derived from the HIW of the He I $\lambda$ 5876 Å line and the Munari & Tomasella (1999) calibration

star	JD$_{\odot}$	$RV_{\odot}$	$\sigma$	EW	HIW	$V_{{\rm rot}}\sin i$
		(km s-1)	(km s-1)	(Å)	(Å)	(km s-1)
21	2451097.277	+21	2	1.35	8.81	354 $\pm$ 6
23	2451097.253	+25	6	0.67	2.80	90 $\pm$ 5
26	2451097.234	+15	3	0.64	3.10	104 $\pm$ 5
32	2451097.291	+21	2	1.41	3.36	115 $\pm$ 6

Figure 4: Interstellar NaI (5889.951, 5895.924 Å) and KI (7698.979 Å) lines from Asiago Echelle+CCD spectra of four NGC 6604 stars