4 Results

   
4.1 Distribution of ammonia in L 1340

The ammonia cores defined by the integrated intensity distribution of the main-group of the (1,1) line are shown in the left panels of Figs. 3-5 for clumps A, B, and C, respectively. For comparison, we also plotted the C¹⁸O contours $\int\! T_A~{\rm d}v$ = 0.45 K km s^-1 and 0.75 K km s^-1. The ammonia cores are labelled in the figures.

In addition to the cores defined in Sect. 3.2 there is an extended region of weak NH₃(1,1) emission in the northern part of clump B, around the position of the C¹⁸O peak. The integrated intensity of the (1,1) line is below the 3$\sigma$ limit at most positions. The optically invisible source IRAS 02263+7251 lies in this area. Averaging 56 spectra around the position the C¹⁸O peak (bordered by a dotted polygon in Fig. 4) we obtained the spectrum displayed in Fig. 6. The weak line indicates low average column density for this region. Because the critical density of the excitation of NH₃(1,1) emission is about 10⁴ cm^-3, this part of the cloud probably contains high density regions much smaller than the angular resolution of our observations.

Column density maps are shown in the right panels of Figs. 3-5. IRAS point sources associated with the cores are labelled in these figures. Because of the effect of the optical depth, column densities are not directly proportional to the integrated intensities. Comparison of the two sets of maps shows the main structures to be largely similar, with the exception that core C3 splits into two parts, C3w and C3e, in the column density map.

Figure 3: Left: NH3(1,1) (solid contours) main group integrated intensity map of L 1340 A. The emission was integrated over the velocity interval between -17 km s-1 and -12 km s-1. The lowest contour is 0.40 K km s-1, and the increment is 0.15 K km s-1. The observed positions are shown by dots. Black circles mark the positions of optically invisible IRAS point sources, and asterisks indicate those associated with visible stars. Crosses show the positions of the C18O peaks. Dashed contours indicate the 0.45 K km s-1 level of the $\int\!{\rm C^{18}O}~{\rm d}v$ distribution. The HPBW of the ammonia observations is shown in the lower left corner. The HPBW of the C18O was $2\farcm7$. Coordinate offsets are given in arcmin with respect to RA(2000) = 2 $^{\rm h}29^{\rm m}41\hbox{$.\!\!^{\rm s}$ }64$ and Dec(2000) = +72$^\circ$43$^\prime$22 $.\!\!^{\prime\prime}$2. Right: Ammonia column density map of L 1340 A. The lowest contour is at 1.2 $\times$ 1014 cm-2, and the increment is 0.6 $\times$ 1014 cm-2.

Figure 4: Same as Fig. 3, but for L 1340 B. Left: contours start at 0.40 K km s-1, and the increment is 0.20 K km s-1. The polygon drawn by dotted line indicates an extended region where weak emission ( $T_{{\rm B}}(NH_3(1,1)) \leq 2~\sigma$) was detected. Right: the lowest contour is at 1.2 $\times$ 1014 cm-2, and the increment is 0.4 $\times$ 1014 cm-2.

Figure 5: Same as Fig. 3, for L 1340 C. Left: contours start at 0.45 K km s-1, and the increment is 0.20 K km s-1. Due to the larger velocity range observed in this clump the emission was integrated over the velocity interval of -19 km s-1--12 km s-1. Right: the lowest contour is at 1.2 $\times$ 1014 cm-2, and the increment is 0.8 $\times$ 1014 cm-2.

The physical properties of the cores, derived by the procedures described in Sect. 3.2, are displayed in Table 2. The following quantities are listed: Col. 1: name of the core. An asterisk following the name indicates that we associated the core with an embedded YSO; Col. 2: the half-maximum radius R_1/2, in parsecs; Col. 3: $T_{{\rm ex}}$ at the peak position where the S/N of the line allowed its determination; Col. 4: the mean kinetic temperature $T_{{\rm k}}$; Col. 5: the nonthermal component of the line width  $\Delta v_{{\rm NT}}$; Col. 6: the maximum column density $N_{{\rm max}}$(NH₃); Col. 7: volume density n(H₂) of the hydrogen derived from $T_{{\rm ex}}$; Col. 8: the mass of the core in solar masses. The Bonnor-Ebert mass is shown in Col. 9. Bolometric luminosity of the optically invisible IRAS point source associated with the core, calculated from the IRAS fluxes adding the long-wavelength bolometric correction (Myers et al. 1987) is shown in Col. 10. Where only flux upper limits were available, we estimated the fluxes from the infrared data sets (IRDS) obtained via the IRAS Software Telescope maintained at SRON (Assendorp et al. 1995).

The observed ammonia cores probably represent the densest regions of L 1340. B1 and B2, as well as C3w and C3e constitute twin core systems according to the definition by JMA. The cores are located close to the C¹⁸O peaks in clump A within the accuracy set by the different angular resolutions. In clumps B and C, however, the high density regions indicated by the ammonia emission are located far from the column density peaks of the C¹⁸O. These small dense regions might have been missed during the C¹⁸O survey because of their half-maximum sizes are smaller than the grid spacing (2$^\prime$). The total mass in the dense cores is 79 $M_{\odot}$, some 6% of the mass traced by C¹⁸O.

   
4.2 Velocity structure

While neither C¹⁸O nor NH₃ observations have indicated velocity gradients in L 1340 A and L 1340 B, C¹⁸O measurements of L 1340 C have shown a clear radial velocity gradient of 0.71 km s^-1 pc^-1 in the galactic longitude direction, which was interpreted as rotation of the clump in Paper I. The ammonia data, having higher angular resolution, suggest another possible scenario. Figure 3 shows that clump C contains two high density regions, separated by a lower density region between the right ascension offsets of about $9\farcm16$ and $10\farcm83$. The two subclumps have a velocity difference of about 1.2 km s^-1 (Table 2). The observed velocity gradient may result from the overlapping of the two clumps of different radial velocities. A similar situation was found in Orion KL by Wang et al. (1993).

 

 

Table 2: Derived physical parameters of the NH₃ cores of L 1340.

Core	R1/2	$T_{{\rm ex}}$	$T_{{\rm k}}$	$\Delta v_{{\rm NT}}$	$N_{{\rm max}}$(NH3)	$n{\rm (H_2)}$	$M{\rm (NH_3)}$	$M_{{\rm BE}}$	$L_{{\rm IRAS}}$
	(pc)	(K)		(km s-1)	(1014 cm-2)	(104 cm-3)	($M_{\odot}$)		($L_{\odot}$)
A1*	0.08	$\cdots$	15.2 (2.0)	0.61	2.34 (0.24)	$\cdots$	5.8	3.2	$\leq$9.6
A2	0.04	$\cdots$	$\leq$12.5	0.31	2.10 (0.50)	$\cdots$	1.5	0.4
A3	0.08	4.7	11.9 (2.3)	0.21	3.40 (0.33)	0.99 (0.08)	6.5	0.2
A4*	0.06	$\cdots$	13.5 (2.0)	0.97	2.53 (0.60)	$\cdots$	3.7	18.6	4.9
B1*	0.10	5.2	14.6 (3.1)	0.67	2.05 (0.27)	1.44 (0.10)	5.6	3.0	8.8
B2	0.08	$\cdots$	$\leq$15.0	0.24	1.45 (0.40)	$\cdots$	2.7	0.2
C1*	0.10	4.7	14.1 (1.7)	0.64	3.57 (0.46)	$\cdots$	12.0	3.9	2.8
C2*	0.10	4.6	16.7 (1.6)	0.81	4.61 (0.60)	1.07 (0.18)	10.2	9.7	$\cdots$
C3w*	0.15	5.2	13.6 (1.1)	0.95	4.89 (1.50)	1.82 (0.40)	15.6	17.2	1.5
C3e	0.11	6.0	12.5 (4.0)	0.36	3.73 (0.57)	1.29 (0.36)	15.4	0.5
Mean	0.08	5.1	14.0	0.58	3.07	1.32	7.9	5.7	5.4
Starless cores	0.07	5.1	12.2	0.28	2.67	1.14	6.5	0.3	$\cdots$
Cores with stars	0.09	5.0	14.6	0.78	3.33	1.44	8.8	9.3	5.4

Figure 7a displays $v_{{\rm LSR}}$ as a function of $\Delta\alpha$, at several $\delta$ offsets. The less negative velocity component at $\Delta \alpha < 11\hbox{$^\prime$ }$ shows a small velocity gradient. The velocity changes abruptly between the offsets $11\farcm33$ and $12\farcm00$, and is nearly constant (about -15.6 km s^-1) at larger offsets. Both components can be observed at $11\farcm33 \leq \Delta \alpha \leq 13\farcm33$. This overlapping shows up as an increase in the line widths in this $\Delta\alpha$ interval (Fig. 7b). The region of enhanced line widths coincides with the part of the clump where IRAS point sources are found. This morphology suggests that clump collision might have played role in triggering star formation in L 1340 C.