Volume 502, Number 2, August I 2009
|Page(s)||579 - 597|
|Section||Interstellar and circumstellar matter|
|Published online||04 June 2009|
Our high resolution images allow us to disentangle the structure of the studied HH objects. Figures 4 (right panel) and A.1 show the HH 52 and 53 region in the three different filters. In H and [S II] HH 52 exhibits a roughly bow shape, where knots labelled A can be identified as the head of the shock (nucleus). The brightest knot (A1) is surrounded by several smaller structures, with knots A3 and A4 placed behind, while A5 and A6 are in front, elongated towards a group of separated knots (D1-D3) roughly E-W aligned. A faint emission (knot D4) is placed just in front of the nucleus. Groups of knots B and C constitute the right and left wings of the bow, respectively. The right wing appears particularly fragmented with knots B1-B3 representing a first condensation close to the nucleus. B4-B9 are located behind.
The H2 emission (Fig. A.1, bottom) shows a more amorphous shape. A semi-ring shaped region, roughly coincident with knots A2-A4, is located just behind the nucleus. Three more bright spots identify the two wings. The first emission coincides with C1 on the left wing, the second, on the right wing, extends to an area corresponding to B2 and B3 in the optical, and the third to B5 and B6 on the right wing as well. Finally, fainter and diffuse emission is detected on the D1-D3 knots.
In addition to the three HH 53 knots already known (A-C), we detect several more emissions coming from this region. Three more knots, mainly emitting in the H line (Fig. 4), are found along the main flow, forming an elongated S-shape chain of E-W knots. We label C1 the emission between C and A, and B1 and B2 those close to B. These objects are not detected in our H2 images and two of them (knots C1 and B1) are just barely visible on the [S II] images. More diffuse emission, detected in all three filters, appears superimposed on the HH 53 main flow, connected to the HH 52 streamer. HH 53 I lies SW, towards HH 52, while H and E are situated NE in the opposite direction. Two brighter structures are located farther NE along the streamer. Group F, with a jet-like appearance in the optical filters, is approximately elongated towards NE, also visible in H2. Knot G, only visible in the optical, is approximatively located at the origin of the continuous emission of the streamer.
In Figs. 4 (left panel) and A.2 we show the HH 54 images and contours in H, [S II] (left panel of Fig. A.2) and H2 (right panel of Fig. A.2). The morphology of the object appears extremely complex. Our images reveal several substructures. For the sake of simplicity, we divide the description of the region in two parts, the streamer, composed of groups X, Y, and Z, and the main body of HH 54, made up of the remaining knots.
HH 54 streamer shows an uncommon shape of a double helix, clearly visible in H. The brightest helix is also well delineated in [S II], appearing as a wiggling jet fragmented in several knots. The morphology of the streamer closely resembles that of the HH 46/47 outflow (see e.g. Eislöffel & Mundt 1994b; Heathcote et al. 1996), except for the presence of a second faint helix. The base of the streamer is X0, with knots X2 and X3 delineating the first bend of the bright helix. The path follows with X4. Y1 and Y2 delineate the second bend of the jet, that continues with Y4. The faint helix is delineated by X1, Y3, Y8, Y7 and Y6. Both the bright and faint structures end in two shocks (Z and Z1, respectively), that barely appear as a bow shock feature in H2 (Fig. A.2, right panel). Molecular hydrogen emission is also detected in knots X0, X2, Y1, and Y2. A further knot (T) complementary to the ionic emission is observed along the jet. Finally, some filaments (X4 A, Y5, R), detected at optical wavelengths, are located aside, detached from the main flow.
The morphology of the main body appears even more complicated than the streamer. In addition to the original knots (from A to K), observed in previous papers (Schwartz 1977; Schwartz & Dopita 1980; Sandell et al. 1987), we detect more features (labelled L to S). Moreover, several knots present sub-structures, labelled here with numbers.
Group A at the bottom appears as bow-shaped in the optical, with a PA of about 75 . In H2 the group exhibits emission only in the northern part of the structure, only partially overlapping the atomic emission. A fainter arc-shaped emission (group Q), mainly visible in H, is located east. Knots P (detected in the optical) and S (detected in H2) are located west, and together with knots O (farther north, visible in the optical) form the farthest point of the HH 52 streamer.
Towards north, more groups are detected. From east to west, almost coincident in all three wavelengths, we detect groups K and E, slightly elongated northward, then group B, and, finally group F, detected only in the optical. Farther NE an arc-like structure is identified by groups J and M in both optical and NIR.
In the north-eastern region, knot I and group H appear as optical jets with PAs of 45 and 20 , respectively. An arc emission in H2 is delineated ahead of I.
In the north-western region, we detect group G, composed of five subsequent knots only detected in the optical (mainly in the H filter, see also Fig. 4), with a PA of 55 . At the end of this flow another group of knots (C) is observed, with C1 and C2 already known, and the new knot C3 located on a straight line connecting knots G and C2.
It is worth to note that the identification in the NIR of knots C accomplished by Gredel (1994) (and then used in Caratti o Garatti et al. 2006; and in Giannini et al. 2006) is erroneous. Indeed the knots that were labelled in H2 as C1 and C2 have a similar appearance in the optical, but are situated about 6 SW. As a consequence, the knot previously known as C1 in the NIR coincides with knot H2 in the optical, while C2 roughly corresponds to C1 in the optical (see Figs. 4 and A.2). In this paper we use this nomenclature to avoid further confusion.
Knot position angles along HH 52 flow have a quite wide spread in their values (30 -80 ). The bulk of HH 52 and other knots, as HH 53 C1, I, and H, have a PA of 50 . On the other hand HH 52 A3, A4 and a few more knots as HH 53 F and G, proceed towards HH 54 with different PAs between 60 and 80 . A completely different behaviour is found for the features located on HH 52 wings in the rear of the flow. Although following the bulk of the flow, they show a high degree of variability during the 20 years of observations, as reported in Appendix C. Such a variability, both due to local instabilities inside the flow and fast moving shocks overtaking HH 52 from behind, makes their identification in different epochs and a correct evaluation of the PMs and PAs sometimes difficult (see also Figs. 5 and 6).
In Fig. B.1 H2 proper motions are reported (see also Tables B.3 and B.4). Significant measurements in HH 52 were possible only for the three bright spots located in the wings. B2-B3 and C1 follow the flow as in the optical, with similar tangential velocities and position angles.
HH 53 A, B and C, in the HH 53 outflow, exhibit small PMs with PAs around 270 also in the NIR. Here, however, the measurements are less significant due to the larger errors.
Proper motions in the HH 54 streamer range between 0.01 and 0.07 yr-1(i.e. 8 and 61 km s-1), where the highest velocities (between 30 and 60 km s-1) are detected in the inner part of the flow and exhibit alternating PAs (322 -69 ), likely due to precession, with directions that oscillate around an average value of 20 .
Some features, located on the edge of the streamer, are not collimated and are drifting apart (PA 90 ) at a lower velocity. At the tip of the streamer group Z appears almost stationary in H ( 10 km s-1), while in [S II] has a higher value of 30 km s-1.
Moving towards NE we observe a decrease in the tangential velocities from groups Q (40 km s-1) to K and E (20 and 15 km s-1, respectively). From the PAs and inclinations (see Sect. 4.6) we can reasonably associate these knots with the HH 54 flow.
Group A appears as an expanding bow shock, towards ENE with an average direction of about 80 and a mean of 30 km s-1. Knots A1, A2, A6 and A8 exhibit some variability, as reported in Appendix C. Because of the morphology, the direction, and the average inclination (see Sect. 4.6), the structure appears to be connected to knot P and to the HH 52 flow. Indeed part of the flow along the HH 52 streamer curves and shocks this region, producing group O as well (see also Fig. 1). H2 emission in HH 54 A (Fig. A.2) appears as an expanding arc, and its motion ( 30 km s-1) has a different orientation depending on the position along the structure (Fig. B.1). Proceeding from east to west, we separately measured four regions, indicated in Table B.4 as A1, A2, A3, and A4. The directions of the motions have different PAs with respect to the optical counterparts and it is not clear if the molecular emission comes from material swept up by the bow shock on one side (see e.g. HH 219, Caratti o Garatti et al. 2004) or from the HH 54 streamer.
The faintest component of the HH 52 streamer follows a straight trajectory (of 55 ) and impacts ahead, producing groups HH 54 G and then C. We observe a sudden deceleration of the flow along the HH 52 streamer (from 65 to 30 km s-1) as it collides with the leading material, that is partially deflected sideways (PA 80 ). G0 is part of such a fast flow, that shocks at the end of a slow moving component (knot G), changing its direction (see also Sect. 4.4). This dynamic is also visible in knots G1 and G3, that are not aligned with the flow, moving with a PA of 80 and 65 , respectively. Group C ahead of G is proceeding in the same direction at similar tangential velocities (25-30 km s-1). Surprisingly, knot C3, at the tip of the flow, slightly moves in the opposite direction in both optical and NIR filters (PA 250 and 15 km s-1). This behaviour is observed also in knot K1, on the opposite side of the HH object, showing nearly a reverse motion with respect to the main flows.
Velocities of knots M are quite low (about 20 km s-1) with a position angle around 80 . The direction and the velocities suggest that they could be part of the same outflow, generated by the same deflection mechanism.
Groups H, I and J, on the northeast side, are moving NE (PA 45 ) with a between 10 and 50 km s-1.
Group N, in the central region of the main body, could be part of the HH 54 flow, with a 20-25 km s-1 and a PA 320 .
It is difficult to determine the membership of several knots (as B or F groups) in the central part of the HH object. The bulk of knot B possibly moves slightly towards ESE, while B1, few arcseconds north, seems to proceed in the opposite direction. Also F and F1 show a similar behaviour.
The molecular component of knot B presents distinct internal motions. We detect three components, reported in Table B.4 (B1, B2, B3, from north to south). B1 appears as a bright arc in the high spatial resolution ISAAC images and it is moving towards NNE (20 ). B2 and B3 are proceeding towards ESE (130 -140 ) as in the optical. In this case we are possibly observing the motion of the two different outflows.
Table B.1: Proper Motions in HH 52 and HH 53 - H and [S II] - parameters derived from the linear fit.
Flow charts with error bars of HH 54 ( left panel), HH 52 and 53 ( right panel) in H2 filter. Proper motions and their error bars are indicated by arrows and ellipses, respectively.
Table B.2: Proper Motions in HH 54 - H and [S II] - parameters derived from the linear fit.
Table B.3: Proper Motions in HH 52 and HH 53 - H2.
Table B.4: Proper Motions in HH 54 - H2.
Table C.1: Accelerated Motions in HH 52, HH 53, and HH 54 - H, [S II] and H2 - parameters derived from the quadratic fit.
Variability in morphology and flux of HH 52. Left panel: close up of HH 52 from 1993 H calibrated image (labels refer to 2006 image). Right panel: close up of HH 52 from 2006 H calibrated image. Both images have the same contour levels.
Both wings of HH 52 bow-shock show a high degree of variability. As an example of such a variability, we show in Fig. C.1 a close up of HH 52 in 1993 and 2006 H calibrated images. Changes in morphology and flux are easy to recognise, especially for the knots of group B.
HH 52 B1 and B2 come from the fragmentation of a single structure around 1987. The first knot is moving ESE with a PA 110 , while the second is moving northward (PA 5 ). A third knot B3, clearly visible from 1989, likely causes the break, proceeding from SE to NE and pushing forward the structure. The direction of the feature considerably changes with time in both optical filters, accordingly, from 55 in 1989 to 85 in 1993. Also B1 and B2 show variability (see Figs. C.1, 8, and C.2), exhibiting evidence of deceleration and acceleration, respectively.
Knots HH 52 B4-B9, in the outskirts of the wing, exhibit large variability and complicated motions as well. The presence of such a high variability and the large gap between the second to last (1993 for [S II] and 1995 for H) and the last epoch image (2006) produce uncertainties in the identification of the knots and in the PM derivation. A large structure, B5, appears in 1989 (see Fig. 7, top panel and also Fig. C.1), rapidly increasing its brightness and then almost vanishing in 2006, apparently fragmented in several knots (B4-B6, and B8), that move in different directions. The flux variation of the object has different timing in the three filters, with a delay of some years between the flux variations of [S II] and H, and then between H and H2 (Fig. 7, top panel). In [S II] it slightly varies its brightness, reaching a maximum possibly around 1991-1993. In H and H2 the variations are more considerable, especially in the molecular component, where the flux increases an order of magnitude during six years.
Knots C in the left wing of HH 52 present a peculiar behaviour as well. C1 (see Fig. 7, central panel and Fig. C.3) shows a large variability similar to B5, with a large brightness increase in H, due to the presence of a fast shock colliding against the target. This is clearly visible in 1993 and 1995 H images (Fig. C.1), where a high velocity knot (C6) appears behind C1. In the 2006 image the bullet is not visible anymore, but an increase in C1 brightness is detected, in both atomic emissions. As in B5, also the molecular emission increases with time. Here the increment is not so pronounced as in the previous knot. HH 52 C2, located behind HH 52 nucleus, starts forming in 1989 as a [S II] emission (Fig. 7, bottom panel) and increases its luminosity until 2006. On the other hand the H emission is visible above a 3 limit only in the 2006 image.
Figure C.4 (bottom panel) displays the peculiar kinematics of HH 54 Y2, located in the middle of the streamer. The proper motion measurements reveal an apparent acceleration of the knot, detected in all three filters. However, due to the faint emission, errors in H2 appear remarkably larger. Here, the PM measurements are referred to epoch 2002, since in H2 2005 image Y2 is out of the FoV. We measure an acceleration of 0.006 0.0002 yr-2 and 0.01 0.004 yr-2 in H and H2, respectively (see Table C.1). The average value obtained including both optical (H and [S II]) and molecular PMs is 0.0031 0.0008 yr-2. Thus a mechanism must exist there that is accelerating the streamer or, conversely, the observed motion could be a reminiscence of the original acceleration experienced by the flow. The upper panel of Fig. C.4 reports the measured flux for the three filters. For this object, all the emissions appear almost constant with time (inside the error bars). This is indeed due to the high degree of ionisation along the HH 54 streamer.
Also along the streamer it is possible to observe the formation of new condensations. A new H knot is forming 1 6 ENE of HH 54 Y3. This is probably an instability in the flow created by the material compressed and pushed ahead of Y3.
Figure C.5 illustrates flux variability in HH 54 A group. Here, at variance with other knots, the measured velocities are constant (inside the error bars) in all the three filters. The brightest feature (knot A1, bottom panel) doubles its H luminosity, after 1990. Variability is, however, not observed in [S II], which appears constant during the considered period. The molecular emission, that does not spatially coincide with the atomic one but it is located about 1 6 forward, from 1993 shows an increase with time. Knot A8, next to A1 along the flow, appears in H images in 1989 (Fig. C.5, top panel), and increases its brightness in all the three filters, and it is extremely luminous in the molecular component. In both [S II] and H2 it has a diffuse emission, probably originating from moving gas cooling behind the H emission. The feature has a different direction (PA 35 ) with respect to the bulk of the flow (PA 80 ). This deflection could be generated in the interaction with knot A6 (see also Fig. A.2), a faint emission following the group, that seems to push aside A8, or, conversely, it could indicate that the knot is not part of the same flow.
Measured fluxes (uncorrected for the extinction) in knots HH 54 A1 ( bottom panel), and A8 ( top panel) in [S II] (circles), H (triangles), and H2 (squares) filters.
Group HH 54 H is a very active and fast variable region of the flow.
Between 1987 and 1993 H1 has decreased the speed in the optical bands from 40 to 20 km s-1with a PM deceleration of 0.02 0.01 yr-2 in H (see Table C.1), and a value of 0.0025 0.0012 yr-2, or 0.0063 0.0005 yr-2 without considering 1993 data, combining all the optical PMs (see upper Fig. C.8, bottom panel). During this period the H and [S II] fluxes gradually increase from 4.9 10-15 erg s-1 cm-2 to 7.2 10-15 erg s-1 cm-2, and 1.8 10-15 erg s-1 cm-2 to 2.8 10-15 erg s-1 cm-2, respectively (top panel).
Knot H2 (see lower Fig. C.8, bottom panel) apparently drops in velocity between 1987 and 1989 H, changing the PM value from 0.08 to 0.04 yr-1 (decelerating of 0.022 0.002 yr-2 in H, see Table C.1). The knot has also a relevant flux variability at least in the H and H2 emissions, that have a constant increase of the flux from 2.7 10-15 erg s-1 cm-2 (1987) to 8.5 10-15 erg s-1 cm-2 (2006) in H, and from 7.6 10-15 erg s-1 cm-2 (1993) to 16 10-15 erg s-1 cm-2 (2005) in H2. On the other hand the measured flux in the three [S II] images is constant.
Finally H3 emission appears only in 2006 optical images, whereas in H2 it appears as a faint featureless emission and no significant motion is detectable. Again, the gap between the second to last and the last optical images makes it hard to derive the initial position of the condensation. We have tried to correlate it with a feature close to H2 in 1993, but the interpretation is not certain.
Along the HH 52 flow, knots have radial velocities from about -70 to -90 km s-1, with lower values detected at the end of the flow, in HH 54, where the velocity decreases moving from G to C, indicating that the flow has been decelerated. The lowest value is detected in HH 54 C2 (-18 4 km s-1) at the very end of the flow. C3 is following C2 at a higher velocity (-45 4 km s-1) (see Table D.3). Along the jet, in knots G1-G3, we observe two distinct velocity components of -87 and -21 km s-1. In the EMMI spectral image the emissions are well separated, delineating two distinct lines of similar intensities for each detected species (see Table D.3). At the base of the jet, where G0 and G are located, the fast component, extending a few arcseconds from the HH 52 streamer to G0, shows an abrupt deceleration (from -78 to -18 km s-1) and then ahead, along the flow, a second slower velocity component is detected. Also in consideration of the proper motion analysis, where a portion of the flow appears to be deflected in this region, the two velocities could be ascribed to the two flow components, rather than a bow shock structure. Moreover, due to the profile of the observed emission lines, a hypothetical bow shock would lie close the plane of the sky (see e.g. Hartigan et al. 1987), but, as the inclination angle suggests (see also Sect. 4.6), this is not the case.
Two velocities components, not completely separated, are also detected in HH 52 knots located in front (D4) and behind (A3-A4) the nucleus (A1, = -79 6 km s-1) (see Table D.1). Velocities in A3-A4 are slightly higher (-98 5 km s-1 and -35 6 km s-1), with respect to D4 (-85 3 km s-1 and -30 3 km s-1). Line fluxes of the low velocity component are considerably fainter than the other component. The velocity profiles of the H line in both structures closely match the theoretical profile of a bow shock with an inclination angle of 60 with respect to the plane of the sky (see Hartigan et al. 1987) and a shock velocity of 70-80 km s-1 (observed from the full width zero intensity - FWZI, measured on the spectrum where the flux reaches a 2 background noise level, see e.g. Davis et al. 2001).
The highest values are observed in the three knots of HH 53 (see Table D.2) outflow, A (-110 10 km s-1), B (-113 9 km s-1), and C (-96 14 km s-1), derived averaging the radial velocities of the different species from B&C slit 1 and 2. In the EMMI spectrum (Table D.2) it is not possible to spatially disentangle the emission coming from knots C and C1. Here, however, we measure two different velocities of -104 7 km s-1 and -55 18 km s-1. Considering that the two knots are from two separate flows, the higher velocity should be ascribed to knot C and the lower to C1.
Along the portion of the HH 54 streamer encompassed by our B&C slits, we measure an increase in the velocity moving towards the main body of HH 54 (see also Table D.3). The values rise from about -50 km s-1, roughly at the base of the streamer (X1A-X3), up to -100 km s-1, close to the middle (X4A-X4B). Such a behaviour was also observed by Graham & Hartigan (1988), but the value measured in the middle (considering also the errors) is lower than ours of 10-20 km s-1. Such a difference in their values could be due to a not perfect positioning of the slit, due to the sinuous geometry of the HH 54 streamer.
Table D.1: Radial velocities and line intensities for different optical lines of individual knots in HH 52 from EMMI and B&C spectra. Radial velocities are corrected for the cloud speed with respect to the LSR ( = 2 km s-1, Knee 1992). When detected, two velocity components are reported.
Table D.2: Radial velocities and line intensities for different optical lines of individual knots in HH 53 from EMMI and B&C spectra. Radial velocities are corrected for the cloud speed with respect to the LSR ( = 2 km s-1, Knee 1992). When detected, two velocity components are reported.
Table D.3: Radial velocities and line intensities for different optical lines of individual knots in HH 54 from EMMI and B&C spectra. Radial velocities are corrected for the cloud speed with respect to the LSR ( = 2 km s-1, Knee 1992). When detected, two velocity components are reported.
Table D.4: [Fe II] radial velocities of the individual knots of HH 54 obtained from ISAAC high resolution spectroscopy, corrected for the cloud speed with respect to the LSR ( = 2 km s-1, Knee 1992). When detected, two velocities components are reported.
In HH 52 bow shock we obtain an average inclination with respect to the sky plane of 58 3 , excluding D2-D3 measurement, that shows a value of 67 4 . HH 53 E1 and F2, as already deduced from the PM analysis, are part of the same outflow with inclinations of 57 3 and 63 4 , respectively. The association of groups HH 54 G and C to the HH 52 outflow is also confirmed. HH 54 G0 has an inclination of 55 3 , at the end of the streamer. Moreover, if we assume that along HH 54 G1-G3 the high and low radial velocities are associated with the high and low tangential velocities observed along the jet, we obtain inclinations ranging between 50 4 and 56 5 , respectively. Values in HH 54 C2 and C3 are 61 3 and 52 8 , respectively. Spatial velocity along the flow are around 100 km s-1 (see Table E.1) and decreases in group G and C (20-50 km s-1).
HH 53 A, B, and C have similar inclinations (83 2 ) and spatial velocities (around 110 km s-1). HH 53 C1 is superimposed on the second flow and is moving accordingly with the HH 52 streamer, with an inclination angle of 49 9 ,considering the low velocity component measured in HH 53 C-C1 spectrum (see Table D.2).
In the HH 54 streamer we measure an average inclination angle of 67 3 , but the errors of the single data points are too large to derive variations of inclination along the wiggling jet.
Table E.1: Inclination and spatial velocities of individual knots of HH 52, 53, and 54 inferred from the kinematical analysis.
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