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3. Results for individual sources

3.1. RNO 43

RNO 43 (Cohen 1980) is the brightest spot of a chain of Herbig-Haro knots (Jones et al. 1984; Ray 1987; Mundt et al. 1987) extending tex2html_wrap_inline3917 to the northeast of the source IRAS 05295+1247. This chain is designated as HH 243 in the new catalog of Herbig-Haro objects of Reipurth (1994). Another long (tex2html_wrap_inline3921), well collimated chain of Herbig-Haro knots (HH 245) extends to the north of RNO 43. Reipurth (1991) found a large fragmented counter bow-shock (HH 244) to the southwest of the IRAS source, suggesting that HH 243 and HH 244 constitute a bipolar HH flow. Anglada et al. (1992) found several radio continuum sources that could be related to the HH 243, HH 244 and HH 245 chains. The high-velocity CO emission in the region has been mapped by Edwards & Snell (1984), Cabrit et al.\ (1988), and Bence et al. (1996). The CO outflow exhibits a complex distribution with several overlapping red and blueshifted lobes, extending on both sides of the IRAS source, and aligned roughly in the north-south direction. The CO lobes located to the north of the IRAS source were initially proposed to constitute two separate outflows (Edwards & Snell 1984). However, no exciting sources have been found for these proposed outflows. Also, no tex2html_wrap_inline3923 emission associated with these northern lobes has been detected (Anglada et al. 1989). On the other hand, Cabrit et al.\ (1988) proposed that the overall high-velocity structure constitutes a single bipolar CO outflow powered by IRAS 05295+1247. A CS clump (Cabrit et al. 1988) is associated with the IRAS source. However, the nominal position of the IRAS source appears to be displaced tex2html_wrap_inline3927 east from the center of the clump. Anglada et al. (1992) found a 3.6 cm VLA source (also detected at 1.3 mm by Reipurth et al. 1993) which is better centered on the CS cloud. Anglada et al. (1992) suggest that the IRAS catalog position is in error by tex2html_wrap_inline3929 in right ascension, and that the IRAS and the radio continuum sources are tracing the same embedded object, which is the powering source of both the molecular and the HH outflows.

In Fig. 3.1 (click here), we show our tex2html_wrap_inline3931 map of this region. We have detected a weak tex2html_wrap_inline3933 condensation centered tex2html_wrap_inline3935 to the west of the IRAS source, similar to the CS condensation observed by Cabrit et al. (1988). As the exciting sources of outflows are usually deeply embedded objects, the fact that the high-density gas (traced by the CS and tex2html_wrap_inline3937 emission; Cabrit et al. 1988; this paper) is found associated only with the cm-mm-IRAS source, and that no tex2html_wrap_inline3939 emission was found associated with the northern CO lobes near RNO 43 (Anglada et al. 1989), further supports that the radio continuum source represents a deeply embedded young stellar object, and is the most plausible powering source for the molecular and HH outflows observed in this region, as suggested by Anglada et al. (1992).

  figure488
Figure 4: Contour map of the peak antenna temperature of the main line of the ammonia (J,K)=(1,1) inversion transition (thick line) in the RNO 43 region. The lowest contour level is 0.1 K, and the increment is 0.02 K. The observed positions are indicated with small crosses. The half power beam width of the telescope is shown as a circle. The positions of several relevant objects in the region are indicated. The central part of the CO bipolar outflow mapped by Cabrit et al. (1988) is shown with thin lines (solid contours indicate blueshifted gas, and dashed contours indicate redshifted gas)

3.2. HH 83

This HH object lies at the western edge of the L1641 molecular cloud. The optical structure consists of a jet (at least 32'' long), apparently emanating from the embedded infrared source HH83 IRS (IRAS 05311-0631; Reipurth 1989), which is associated with a reflection nebula and ending with a bow-shock. The jet is highly collimated, and presents large variations in velocity and physical conditions along its length (Reipurth 1989). There is a faint nebulosity tex2html_wrap_inline3949 southeast of the central infrared source that could be part of the counter bow-shock (Reipurth 1989; Ogura & Walsch 1991). The estimated bolometric luminosity of HH83 IRS is 8 tex2html_wrap_inline3951 (Reipurth et al. 1993). This source does not present detectable radio continuum emission at 3.6 and 2 cm (Rodríguez & Reipurth 1994). Recently, Bally et al. (1994) have mapped a very low velocity, poorly collimated asymmetric molecular outflow (with the redshifted lobe much larger than the blueshifted one) associated with HH83 IRS. These authors suggest that the outflow from HH83 IRS has ``blown out'' of the molecular cloud and that it may be in a late stage of evolution. Interferometric CS observations (angular resolution tex2html_wrap_inline3953) of the cloud core associated with HH83 IRS (Nakano et al. 1994) reveal a high-density structure consisting of a bar (tex2html_wrap_inline3955 long, centered on HH83 IRS and nearly perpendicular to the HH jet) and two ridges surrounding the base of the jet. These authors interpret the CS bar as a rotating circumstellar disk and the two ridges as tracing a small elongated hollow that may be playing an important role in focusing the HH jet.

We have detected a weak tex2html_wrap_inline3957 clump with the emission peak close to the proposed exciting source of HH 83 (see Fig. 3.2 (click here)). The tex2html_wrap_inline3959 clump appears unresolved with our beam of tex2html_wrap_inline3961, and we cannot study the small scale structure observed in CS by Nakano et al. (1994). At a larger scale, the weakest tex2html_wrap_inline3963 emission seems to extend further to the north and to the west, outside our mapped area. The region we mapped in tex2html_wrap_inline3965\ corresponds to the core of the molecular clump studied in tex2html_wrap_inline3967 by Bally et al. (1987, 1994), which also shows a clear northern extension.

  figure506
Figure 5: Same as Fig. 4, for the HH 83 region. The ammonia lowest contour level is 0.08 K, and the increment is 0.02 K. The map of the CO bipolar outflow is from Bally et al. (1994). The position of IRAS 05311-0631 is indicated

3.3. HH 84

This HH object was identified and studied by Reipurth (1985, 1989). HH 84 is a long (tex2html_wrap_inline3973) chain of HH knots outlining a well-collimated optical flow with a position angle of tex2html_wrap_inline3975tex2html_wrap_inline3977. Unlike the large majority of the optical jets, this HH outflow is redshifted with respect to the ambient cloud. Morgan et al. (1991) found evidence for red wing emission in CO profiles, but could not confirm whether this is a molecular outflow. Up to now, no good candidate for the HH flow excitation has been proposed. IRAS 05317-0638 (identified with SW Ori, an tex2html_wrap_inline3981 star and X-ray source; Strom et al. 1989a) lies tex2html_wrap_inline3983 south along the jet axis (see Fig. 3.3 (click here)). However, based on the morphology of the knots, Reipurth (1989) argues that the flow exciting source should most probably be an embedded source (still undetected) located to the north of the jet.

We found weak ammonia emission associated with the HH knots. Our tex2html_wrap_inline3985 map is presented in Fig. 3.3 (click here). The ammonia emission maximum is close to the northern edge of the jet, and may be tracing the location of a possible embedded exciting source, then supporting the suggestion of Reipurth (1989). However, we only mapped a small region and, in particular, our map does not reach the position of the IRAS source. The tex2html_wrap_inline3987 emission appears to extend further to the northeast, roughly following the distribution of the emission of the molecular cloud mapped in tex2html_wrap_inline3989 by Bally et al. (1987; see detail in Reipurth 1989).

  figure521
Figure 6: Same as Fig. 4, for the HH 84 region. The ammonia lowest contour level is 0.08 K, and the increment is 0.02 K. The position of IRAS 05317-0638 (identified as SW Ori) is indicated

3.4. HH 86/87/88

The Herbig-Haro objects HH 86, HH 87 and HH 88 appear to be closely associated, and probably originate in the same flow (Reipurth 1985, 1989). The three objects are roughly aligned, but they exhibit a rather complex substructure and no local exciting source has been found. The knots in HH 86 appear to cluster around a faint star, but this star is probably not related to the flow, as discussed by Reipurth (1989). The T Tauri star V573 Ori (possibly associated with IRAS 05332-0637; Weintraub 1990) is also close by, but it does not lie on the line traced by the HH jet. Bally & Devine (1994) suggest that these HH objects are the southern end of a 3 pc long ``superjet'' emanating from the exciting source of HH 34.

Our tex2html_wrap_inline3997 map is shown in Fig. 3.4 (click here). As it can be seen in the figure, the tex2html_wrap_inline3999 emission is faint and displaced to the east of the HH 86/87/88 complex. As the HH 86/87/88 complex lies along a ridge with increasing column density to the east (as mapped in tex2html_wrap_inline4001 by Bally et al. 1987), it is plausible that the tex2html_wrap_inline4003 emission continues further to the east of the region we have mapped. Since no tex2html_wrap_inline4005\ emission is seen towards the HH complex, this lack of high-density gas associated with the HH objects seems to exclude that their exciting source could be an undetected deeply embedded object in this region, then favoring a non local origin for the HH excitation, as suggested by Bally & Devine (1994).

  figure534
Figure 7: Same as Fig. 4, for the HH 86/87/88 region. The ammonia lowest contour level is 0.12 K, and the increment is 0.04 K. The position of IRAS 05332-0637 (possibly associated with V573 Ori) is indicated

L1641-N

A bipolar CO outflow, L1641-N (Fukui et al. 1986, 1988; Wilking et al.\ 1990), has been mapped in the northern part of the L1641 cloud. The outflow is centered on IRAS 05338-0624, which is proposed as the outflow exciting source. Although optically invisible, this source is one of the most luminous (tex2html_wrap_inline4013 tex2html_wrap_inline4015) IRAS sources in this region. Near-IR images (Strom et al. 1989c; Chen et al. 1993) reveal a dense stellar concentration centered on the IRAS position. The IRAS counterpart has been identified in the near-IR (Chen et al. 1993), millimeter (Wilking et al. 1989; Chen et al. 1995) and centimeter (Mundy et al.\ 1993; Anglada et al. 1996; Chen et al. 1995) ranges. Recently, tex2html_wrap_inline4017\ maser emission has been found in association with IRAS 05338-0624 (Xiang & Turner 1995). In addition, several faint red nebulous objects of unknown nature have been found in a CCD image of the region (Reipurth 1985). A centimeter continuum source (Morgan et al. 1990; Anglada et al.\ 1996), also visible in the CCD image by Reipurth (1985), is found tex2html_wrap_inline4021 to the NE of the IRAS source, approximately midway between the red nebulous objects Re 35 and Re 43.

About 3' to the SW of the center of the L1641-N molecular outflow, lies the source IRAS 05339-0626. This source (tex2html_wrap_inline4027 tex2html_wrap_inline4029) is a typical Class I source (Strom et al. 1989a). Several near-IR sources (Chen et al. 1993) and a centimeter continuum source (Morgan et al.\ 1990 Anglada et al. 1996) are found near the IRAS position. Red wing CO emission has been observed towards this position, although it is unclear whether this high-velocity emission originates from IRAS 05339-0626 or it is just extended high-velocity emission from the L1641-N outflow (Morgan et al. 1991).

We have mapped in tex2html_wrap_inline4033 a region that includes both IRAS sources. The map we have obtained is shown in Fig. 8. The tex2html_wrap_inline4035 structure consists of two subcondensations, peaking near the positions of the IRAS sources. This result suggests that both IRAS sources are embedded in dense gas. The condensation around IRAS 05338-0624 has been mapped in several molecular species (Fukui et al. 1988; Chen et al. 1992; Harju et al.\ 1991; McMullin et al. 1994) with the emission peaking close to the IRAS position as in our tex2html_wrap_inline4039 map. In particular, the tex2html_wrap_inline4041 map obtained by Harju et al. (1991) with higher angular resolution (40''), is in good agreement with our results. The whole region encompassing both IRAS sources was mapped previously only in HCN (Takaba et al. 1986) and with lower (tex2html_wrap_inline4045) angular resolution. CS emission was detected but not mapped, towards the two IRAS sources (Morgan & Bally 1991).

  figure569
Figure 8: Same as Fig. 4, for the L1641-N region. The ammonia lowest contour level is 0.15 K, and the increment is 0.15 K. The IRAS source associated with the northern ammonia peak is IRAS 05338-0624 and the one associated with the southern ammonia peak is IRAS 05339-0626. The map of the CO outflow is from Fukui et al. (1986)

3.6. L100

L100 (Barnard 62) is a large, very opaque Bok globule in Ophiuchus, surrounded by bright rims. Reipurth & Gee (1986), based on a photometric study, estimate a distance of tex2html_wrap_inline4053 pc. These authors found several tex2html_wrap_inline4055 emission stars associated with L100 and conclude that IRAS 17130-2053 (0.25 tex2html_wrap_inline4059 tex2html_wrap_inline4061 tex2html_wrap_inline4063), an IRAS source with no optical counterpart, represents the envelope of an embedded PMS object, more evolved than a protostar. Parker et al. (1988) detected a bipolar molecular outflow elongated in the NE-SW direction and centered at the position of IRAS 17130-2053, which was proposed as the outflow exciting source.

We have mapped in tex2html_wrap_inline4067 the region around IRAS 17130-2053. We have detected faint and unresolved tex2html_wrap_inline4071(1,1) emission peaking near the position of the IRAS source. Our map is shown in Fig. 3.6 (click here). The IRAS position is near the maximum of the ammonia map, in agreement with the idea that it is an object embedded in high-density gas. However, the weakness of the ammonia emission suggests that it is associated with only a small amount of high-density gas and that the size of the ammonia clump could be much smaller than our beam.

  figure579
Figure 9: Same as Fig. 4, for the L100 region. The ammonia lowest contour level is 0.08 K, and the increment is 0.02 K. The map of the CO outflow is from Parker et al. (1988)

3.7. L483

Parker et al. (1988, 1991) and Fuller et al. (1995) have mapped in CO a compact bipolar molecular outflow in the L483 dark cloud. The outflow is clearly elongated along the E-W direction and it is centered on the low-luminosity infrared source IRAS 18148-0440 (L=14 tex2html_wrap_inline4079, assuming a distance of 200 pc; Ladd et al. 1991a), which is proposed as the outflow exciting source. This source has neither optical nor near-infrared counterpart (Parker 1991). The source has been detected with the VLA at 3.6 cm (Anglada et al. 1996). From the far-IR data and from submillimeter observations (Ladd et al. 1991b; Fuller et al. 1995), Fuller et al. (1995) conclude that the IRAS source is a very young object similar to the so-called Class 0 sources. The source is surrounded by a bipolar near-IR nebula, and a jet-like region of tex2html_wrap_inline4081 emission, ending in a bright knot, extends along the blue lobe of the CO outflow (Fuller et al. 1995). An tex2html_wrap_inline4083 maser near the IRAS position has been detected by Xiang & Turner (1995) through single-dish observations.

In Fig. 3.7 (click here) we show the ammonia map obtained from our observations. The tex2html_wrap_inline4085 emission peaks very close to the IRAS source position. This fact, together with the infrared results (Fuller et al. 1995), suggest that the IRAS source is deeply embedded in the dense core, giving support to its identification as the powering source of the molecular outflow. Our ammonia map is in good agreement with the ammonia map shown by Fuller & Myers (1993). Fuller & Myers (1993) found two velocity components separated by 0.28 tex2html_wrap_inline4087 in an tex2html_wrap_inline4089 spectrum obtained towards the peak of the core, and discuss on their relationship with the overall distribution of dense gas. The velocity resolution of our observations (tex2html_wrap_inline4091 tex2html_wrap_inline4093) does not allow us to separate these components in the spectra. Goodman et al. (1993) report a velocity gradient (tex2html_wrap_inline4095 tex2html_wrap_inline4097, PA = 52tex2html_wrap_inline4099) in the region. From our data, we estimate a velocity gradient of 2-3 tex2html_wrap_inline4103 approximately in the SW-NE direction, which is consistent with the result of Goodman et al. (1993).

  figure601
Figure 10: Same as Fig. 4, for the L483 region. The ammonia lowest contour level is 0.20 K, and the increment is 0.15 K. The map of the CO outflow is from Parker et al. (1988)

3.8. L673

The distance to the L673 dark cloud is not well established. Estimates by different authors range between 150 pc and 400 pc. We will adopt a distance of 300 pc, based on proper motions studies (Herbig & Jones 1983). Armstrong & Winnewisser (1989) discovered a very extended (tex2html_wrap_inline4107) bipolar molecular outflow in the northern part of L673. There are four IRAS point sources within five arcmin of the center of the outflow. From an analysis of the IRAS colors, Armstrong & Winnewisser conclude that IRAS 19184+1118 is probably a visible main-sequence star, while the IRAS colors of the other three sources (IRAS 19180+1116, 19180+1114, 19181+1112) are consistent with those of embedded stars. In particular, the source IRAS 19180+1116, which coincides with RNO 109 (Cohen 1980), is proposed by Armstrong & Winnewisser (1989) as the most likely candidate to be the outflow exciting source. Ladd et al. (1991a, b) obtained far-infrared photometry and images of IRAS 19180+1116 and IRAS 19180+1114, showing that a large fraction of the luminosity of these objects is radiated at long wavelengths (tex2html_wrap_inline4123 60 tex2html_wrap_inline4125), indicating that they are very young.

Our ammonia map is shown in Fig. 3.8 (click here). The ammonia structure consists of three subcondensations, peaking near the position of the sources IRAS 19180+1116 (RNO 109), IRAS 19180+1114 and IRAS 19181+1112. This result suggests that the three sources are embedded in dense gas. The source IRAS 19180+1114 is located very close to the strongest emission maximum, suggesting that this source is associated with the largest amount of high-density gas, being probably the most deeply embedded of these three objects. The spectral energy distribution of this source (Armstrong & Winnewisser 1989; Ladd et al. 1991a) is also consistent with this suggestion. The source IRAS 19180+1114 is also well centered in between the two outflow lobes, despite of the irregular geometry of the molecular outflow (see Fig. 3.8 (click here)). Taking into account the ammonia results, the spectral energy distribution, and the location with respect to the CO outflow, we favor IRAS 19180+1114 (rather than IRAS tex2html_wrap_inline4139 109) as the best candidate for the excitation of the molecular outflow in the region.

Although our observations do not reach the position of IRAS 19184+1118, from the region we have mapped it seems clear that the tex2html_wrap_inline4143 emission decreases as one moves to the NE, towards the position of this IRAS source. Thus, this source does not appear to be associated with a significant amount of dense molecular gas. This result is confirmed by the CS (tex2html_wrap_inline4145) observations of Morata et al. (1996). Even though the CS emission appears to be more extended than the tex2html_wrap_inline4147 emission, the CS map shows that IRAS 19184+1118 lies at the outer edge of the CS distribution, suggesting that this source is not embedded in high density gas. These results are in agreement with those of Armstrong & Winnewisser (1989), which concluded that the IRAS colors of this source are typical of a visible main-sequence star.

  figure620
Figure 11: Same as Fig. 4, for the L673 region. The ammonia lowest contour level is 0.15 K, and the increment is 0.1 K. The IRAS sources associated with the ammonia structure are (from north to south) IRAS 19180+1116 (RNO 109), IRAS 19180+1114 and IRAS 19181+1112. The IRAS source outside the ammonia structure is IRAS 19184+1118. The map of the CO outflow is from Armstrong & Winnewisser (1989)

3.9. IRAS 20188+3928

IRAS 20188+3928 (tex2html_wrap_inline4163 tex2html_wrap_inline4165; Odenwald & Schwartz 1993) is associated with a compact molecular cloud located in the Cygnus region. The distance to this source is very uncertain (0.4 kpc tex2html_wrap_inline4167 kpc; Little et al. 1988). We adopt in this paper its largest value (4 kpc); thus, most of the physical parameters obtained for this region will be upper limits. Little et al. (1988) mapped in tex2html_wrap_inline4169\ and tex2html_wrap_inline4171 a bipolar molecular outflow associated with this IRAS source, concluding that the outflowing gas has a dense and clumpy nature.

We have detected a compact ammonia condensation (Fig. 3.9 (click here)), with the emission peaking very close to the IRAS 20188+3928 position. This result suggests that the IRAS source is deeply embedded in the high density gas, as usually are the exciting sources of molecular outflows. The ammonia lines in this condensation are significantly wider (tex2html_wrap_inline4175 tex2html_wrap_inline4177) than in the other regions of our sample (see Table 2 (click here)). Moreover, there is a north-south velocity gradient in the tex2html_wrap_inline4179\ condensation, with the line velocity in the northern part being redshifted (by tex2html_wrap_inline4181 tex2html_wrap_inline4183) with respect to the southern part, i.e., roughly in the same direction as the outflow. These results suggest that the dense gas around IRAS 20188+3928 is perturbed by the outflow from this star and is entrained into the high velocity gas, in agreement with the tex2html_wrap_inline4187\ results obtained by Little et al. (1988).

Palla et al. (1991) detected tex2html_wrap_inline4189 maser emission on January 30, 1989 in a single observation towards the position of the IRAS source, obtaining a peak line flux tex2html_wrap_inline4191 Jy and a radial velocity tex2html_wrap_inline4193 tex2html_wrap_inline4195. We detected this tex2html_wrap_inline4197 maser on February 10, 1990. From a seven-point map centered on the IRAS position, we found that the maximum of emission was displaced tex2html_wrap_inline4199 to the NW of the IRAS source. In Fig. 2 (click here), we show the spectrum of the tex2html_wrap_inline4201 maser towards this position. The single feature we observed can be fitted with a Gaussian profile having peak line flux tex2html_wrap_inline4203 Jy, half-power full width tex2html_wrap_inline4205 tex2html_wrap_inline4207, and radial velocity with respect to the local standard of rest, tex2html_wrap_inline4209 tex2html_wrap_inline4211. Thus, this tex2html_wrap_inline4213 maser feature shows high variability on a time scale of one year. Several new maser features, at different velocities appeared also in observations carried out in 1990 and 1991 (Xiang & Turner 1995). One of these features coincides within 4'' with the position of the IRAS source.

  figure640
Figure 12: Same as Fig. 4, for the IRAS 20188+3928 region. The ammonia lowest contour level is 0.20 K, and the increment is 0.1 K. The map of the CO outflow is from Little et al. (1988)

3.10. L1228

L1228 is a high galactic latitude dark cloud, whose distance is poorly known. Haikala et al. (1991) estimate a distance between 100 and 200 pc, while Bally et al. (1995) argue that a better value is 300 pc. In this paper we have adopted this last value. Haikala & Laureijs (1989) discovered a large (tex2html_wrap_inline4221, for the assumed distance of 300 pc) and well-collimated bipolar CO outflow, with its axis in the NE-SW direction. The outflow is centered on the low luminosity object IRAS 20582+7724 (tex2html_wrap_inline4225 tex2html_wrap_inline4227), which was proposed as the outflow exciting source. Anglada et al. (1996) have detected this source in the radio continuum at 3.6 cm with the VLA. Very recently, Bally et al. (1995) have obtained a new CO map of the outflow and detected several HH objects along the axis of the molecular outflow. Moreover, these authors detected an tex2html_wrap_inline4229 jet emerging from IRAS 20582+7724, but the jet axis differs from that of the molecular outflow by tex2html_wrap_inline4233tex2html_wrap_inline4235, suggesting that the jet ejection direction varies over time. Bally et al. (1995) also detected a long highly collimated HH jet (HH 200), which may be associated with a very low velocity and faint blueshifted CO lobe, and whose exciting source appears to be an embedded T Tauri star located tex2html_wrap_inline4237 of the IRAS source.

Tafalla et al. (1994) have observed the dense gas around the IRAS source as traced by tex2html_wrap_inline4239 and HCN. These authors found sudden shifts in the line velocity of these molecules, with a systematic velocity pattern that agrees in direction and velocity sense with the CO outflow. Tafalla et al. identified three distinct velocity components in the core, and interpreted these results as evidence for the disruption of the dense core by the bipolar outflow from the IRAS source.

Our ammonia map of this region (Fig. 3.10 (click here)) shows a condensation of tex2html_wrap_inline4241 in size, elongated in the N-S direction. The ammonia emission peaks very close to the position of the IRAS and radio continuum source, suggesting that this source is deeply embedded in the high density gas, as it is expected for the exciting source of the outflow. For positions with good signal-to-noise ratio, our data show a velocity shift in the ammonia line velocity, consistent with the direction and sense of the bipolar molecular outflow. In Fig. 3.10 (click here) we show the spectra of the tex2html_wrap_inline4243(1,1) main line observed towards the position of the IRAS source, as well as towards two additional positions displaced tex2html_wrap_inline4245 to the east and tex2html_wrap_inline4247 to the west, respectively. As it can be seen in the figure, the central velocity of the lines are clearly displaced, with a velocity shift between the extreme positions of tex2html_wrap_inline4249 tex2html_wrap_inline4251, corresponding to a velocity gradient of tex2html_wrap_inline4253 tex2html_wrap_inline4255. Tafalla et al.\ (1994), from their higher angular resolution data, obtained velocity gradients of up to 10 tex2html_wrap_inline4257 on a scale of 20''. Our lower angular resolution data do not allow us to detect these sudden shifts in velocity but, in any case, they provide evidence that the dense gas is perturbed and accelerated by the molecular outflow.

  figure656
Figure 13: Same as Fig. 4, for the L1228 region. The ammonia lowest contour level is 0.20 K, and the increment is 0.15 K. The map of the CO bipolar outflow is from Haikala & Laureijs (1989)

  figure661
Figure 14: Spectra of the tex2html_wrap_inline4261(1,1) main line towards three selected positions in L1228. The offsets are in arc minutes with respect to the IRAS position. To make easiest the comparison, the main beam brightness temperature of the (0,0) spectrum has been divided by 3

3.11. HHL 73

HHL 73 is an Herbig-Haro like object, whose position coincides, within observational errors, with an tex2html_wrap_inline4267 maser (Gyulbudaghian et al. 1987) and with the source IRAS 21432+4719. A region of tex2html_wrap_inline4271 around HHL 73 was mapped in ammonia by Verdes-Montenegro et al. (1989), using also the Haystack radio telescope. Their observations revealed a condensation with an angular size of tex2html_wrap_inline4273, elongated in the NW-SE direction, and with the HHL 73 object located very close to the ammonia emission peak. Verdes-Montenegro et al. (1989) detected also a weaker ammonia condensation, located tex2html_wrap_inline4275 northeast of the main condensation. No signs of star formation associated with this second clump are known at present.

The region was mapped in CS by Pastor et al. (1991). The CS emitting region is elongated in the E-W direction and it is more extended (tex2html_wrap_inline4277) than the region mapped in ammonia by Verdes-Montenegro et al. (1989). The CS structure presents several emission peaks, three of them coinciding with IRAS 21429+4726, IRAS 21432+4719 and IRAS 21441+4722. These IRAS sources have faint optical counterparts on the Palomar Sky Survey red print and were classified as ``protostar type'' by Dobashi et al. 1992. Recently, Dobashi et al. (1993) have detected three highly asymmetric molecular outflows associated with these IRAS sources.

To complete the study in tex2html_wrap_inline4285 of this region, we carried out new observations, completing those of Verdes-Montenegro et al. (1989), in order to cover the overall region observed in CS. In Fig. 3.11 (click here) we show the complete tex2html_wrap_inline4287 map of the region (including the data of Verdes-Montenegro et al. 1989). Four ammonia clumps, coinciding with emission peaks in the CS map of Pastor et al. (1991), are observed in the figure. Three of the ammonia clumps are associated with an IRAS source, located very close to the emission peak, thus suggesting that these clumps contain a young embedded object. The mean separation between these clumps (tex2html_wrap_inline4289) is of the order of the typical distance between stars. Therefore, this region appears to be an example of simultaneous formation of several stars in the same cloud, as it was suggested by Pastor et al. (1991).

  figure679
Figure 15: Same as Fig. 4, for the HHL 73 region. The ammonia lowest contour level is 0.12 K, and the increment is 0.1 K. The tex2html_wrap_inline4291 map obtained by Verdes-Montenegro et al. (1989) is also included. The maps of the CO outflows are from Dobashi et al. (1993)

  figure684
Figure 16: Same as Fig. 4, for the IRAS 22343+7501 region in L1251. The ammonia lowest contour level is 0.1 K, and the increment is 0.1 K

3.12. L1251

L1251 is an elongated dark cloud (Lynds 1962) apparently belonging to the ``Cepheus Flare" giant molecular cloud complex (Lebrun 1986). The estimated distance of this cloud is between 200 pc to 500 pc. We have adopted a distance of 300 pc, estimated from a photometric study by Kun & Prusti (1993). Several indications of low-mass star formation have been found in L1251, with several tex2html_wrap_inline4303 emission stars and infrared point sources detected in the cloud (see Kun & Prusti 1993 and references therein). Our following study of this region focuses on two IRAS sources, IRAS 22343+7501 and IRAS 22376+7455, which are the most luminous sources in L1251 and appear to be the powering sources of bipolar CO outflows.

3.12.1. IRAS 22343+7501

IRAS 22343+7501 is the driving source of an extended and poorly collimated outflow, L1251-A (Schwartz et al. 1988; Sato & Fukui 1989). The outflow map differs from one study to the other. The outflow map obtained by Sato & Fukui (1989) represents molecular gas with relatively low velocity (tex2html_wrap_inline4313 tex2html_wrap_inline4315) and is extended (tex2html_wrap_inline4317), with the axis approximately in the NE-SW direction. On the other hand, the map obtained by Schwartz et al. (1988), with higher angular resolution, includes higher velocity gas (tex2html_wrap_inline4319 tex2html_wrap_inline4321), is more compact and shows a clear asymmetry in the intensity the two lobes.

Balázs et al. (1992) detected several Herbig-Haro objects (apparently forming an optical jet with its axis coincident with that of the CO outflow), and propose that the exciting source of these objects is also IRAS 22343+7501. Anglada et al. (1996) have detected this source in the radio continuum at 3.6 cm. Xiang & Turner (1995) have detected an tex2html_wrap_inline4325\ maser within tex2html_wrap_inline4327 of the IRAS position.

The source IRAS 22350+7502 (probably a T Tauri star; Kun & Prusti 1993) lies about 2' to the north-east of IRAS 22343+7501.

  figure703
Figure 17: Same as Fig. 4, for the IRAS 22376+7455 region in L1251. The lowest contour level is 0.15 K, and the increment is 0.1 K

  figure708
Figure 18: Position-velocity diagram of the tex2html_wrap_inline4337(1,1) main line along the major axis (tex2html_wrap_inline4339tex2html_wrap_inline4341) of the condensation associated with IRAS 22376+7455, in L1251. The lowest contour level is 0.2 K and the increment is 0.05 K. Right ascension offsets are from the position of IRAS 22376+7455

In Fig. 3.11 (click here), we show our ammonia map. The two IRAS sources lie at the edge of the tex2html_wrap_inline4347 condensation, being displaced by tex2html_wrap_inline4349 (tex2html_wrap_inline4351) from the emission peak. At present, no source coincident with the ammonia emission peak has been found. As the emission peak is displaced from the outflow center, it is not likely that the outflow exciting source coincides with this ammonia maximum. The fact that the source proposed as the exciting source of the outflow, IRAS 22343+7501, is displaced tex2html_wrap_inline4355 in projection from the ammonia emission peak may be due either because the outflow has disrupted part of the cloud core, or because the source was formed in the dense cloud but has escaped out of the clump (for a velocity of the star with respect to the cloud of tex2html_wrap_inline4357 tex2html_wrap_inline4359, a time of tex2html_wrap_inline4361, which is similar to the time-scale of the outflow, is required to cover the observed displacement). We note that Morata et al.\ (1996) have mapped this region in CS, obtaining that the CS extends over a region larger than the tex2html_wrap_inline4363 with IRAS 22343+7501 near a CS emission peak.

3.12.2. IRAS 22376+7455

CO observations in the region associated with this source (Sato & Fukui 1989; Sato et al. 1994) have revealed a well collimated and very compact bipolar outflow, L1251-B, extending over 4' in the NW-SE direction. IRAS 22376+7455 (tex2html_wrap_inline4377 tex2html_wrap_inline4379; Sato et al. 1994) lies near the center of the two lobes, suggesting that is driving the bipolar outflow. IRAS 22376+7455, apparently without optical counterpart (Kun & Prusti 1993; Eiroa et al.\ 1994b), is detected in the radio continuum at 3.6 cm by Anglada et al. (1996), and is likely to be a protostar embedded in a dense molecular cloud core (Sato et al. 1994). Eiroa et al.\ (1994b) found several Herbig-Haro objects (HH 189A, B and C) that may be associated with IRAS 22376+7455 or with a nearby nebulous star. Kun & Prusti (1993) and Eiroa et al. (1994b) also found several infrared sources and tex2html_wrap_inline4385 emission stars in this region.

In Fig. 3.12.1 (click here) we show our ammonia map. The observed tex2html_wrap_inline4387 condensation appears to be very elongated (tex2html_wrap_inline4389) in the east-west direction. IRAS 22376+7455 is located in the midst of the high density gas, confirming that it is an embedded source. However, this source is displaced tex2html_wrap_inline4393 (tex2html_wrap_inline4395) from the tex2html_wrap_inline4397 emission peak. Several other infrared sources are observed towards the tex2html_wrap_inline4399 condensation, suggesting that they represent embedded sources. One of these sources coincides positionally with the tex2html_wrap_inline4401 emission peak. There is a secondary emission peak (located tex2html_wrap_inline4403 to the west of the main one) that appears not to be associated with any known infrared source. The source IRAS 22385+7457 is located tex2html_wrap_inline4407 to the northeast of IRAS 22376+7455, at the edge of the tex2html_wrap_inline4411 structure, suggesting that it is not deeply embedded in the dense cloud. This source is associated positionally with an tex2html_wrap_inline4413\ emission star, and it is proposed to be a T Tauri star (Kun & Prusti 1993), in agreement with the suggestion that this source is more evolved than the sources still deeply embedded in dense gas.

From our tex2html_wrap_inline4415 data, we found a velocity gradient of tex2html_wrap_inline4417 tex2html_wrap_inline4419 in the NE-SW direction, with sudden velocity shifts of up to 1 tex2html_wrap_inline4421\ (corresponding to gradients of 8 tex2html_wrap_inline4423) along the region. In Fig. 3.12.1 (click here) we show a position-velocity diagram along the major axis of the clump. The velocity gradient does not follows the tex2html_wrap_inline4425 condensation axis, but it has a complex bidimensional structure, so that we do not think that it is due to a global rotational motion of the dense condensation. Goodman et al.\ (1993) from tex2html_wrap_inline4427 observations, Morata et al. (1996) from CS observations, and Sato & Fukui (1989) from tex2html_wrap_inline4429, also found the existence of a velocity gradient in this region.

In Fig. 3.13 (click here), we show the overall L1251 region, enclosing the two ammonia condensations we have mapped and their associated molecular outflows. Note that these two condensations coincide with the two brightest spots in the tex2html_wrap_inline4431 map by Sato et al. (1994).

3.13. L1262

L1262 is an isolated Bok globule with a very high visual extinction (Lynds 1962) located at a distance of 200 pc (Parker et al. 1991). Parker et al. (1988, 1991) discovered a well-collimated bipolar molecular outflow approximately tex2html_wrap_inline4433 in extent along its axis. Interferometric tex2html_wrap_inline4435\ observations (Terebey et al. 1989) show a more compact (tex2html_wrap_inline4437) outflow. The outflow is elongated in the northeast-southwest direction and is centered at the position of the source IRAS 23238+7401, which is proposed as the exciting source of the outflow. This IRAS source has been classified as a Class I embedded source without optical counterpart (Parker 1991). The velocity of the outflow decreases gradually as one moves away from the source (Parker et al. 1988). Anglada et al.\ (1996) found two radio continuum sources at 3.6 cm, one of them being associated with the IRAS source.

  figure743
Figure 19: Region enclosing the two ammonia dense cores observed in L1251 (Figs. 16 and 17). Superposed are shown the two associated CO outflows, L1251-A and L1251-B (Sato et al. 1994)

Our tex2html_wrap_inline4441 map is shown in Fig. 3.13 (click here). The tex2html_wrap_inline4443 condensation presents two emission peaks, one of them coinciding with the source IRAS 23238+7401. Our map is similar to the map obtained by Benson et al. (1984) using the same ammonia inversion line, but our sensitivity is slightly better and we are able to distinguish two emission peaks. Zhou et al. (1989) observed this region in CS, tex2html_wrap_inline4447 and tex2html_wrap_inline4449, obtaining that the CS emission is more extended than the tex2html_wrap_inline4451 one, as it is usually found in other regions.

  figure751
Figure 20: Same as Fig. 4, for the L1262 region. The ammonia lowest contour level is 0.15 K, and the increment is 0.1 K. The map of the CO outflow is from Yun & Clemens (1994)


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