ABSTRACT
We study the population of Herbig–Haro (HH) flows and jets in an area of Cygnus OB7 designated the Braid Nebula star formation region. This complex forms part of the L 1003 dark cloud, and hosts two FU Orionis (FUor)-like objects as well as several other active young stars. To trace outflow activity and to relate both known and newly discovered flows to young star hosts we intercompare new, deep, narrowband Hα and [S ii] optical images taken on the Subaru 8 m Telescope on Mauna Kea, Hawaii. Our images show that there is considerable outflow and jet activity in this region suggesting the presence of an extensive young star population. We confirm that both of the FUor-like objects drive extensive HH flows and document further members of the flows in both objects. The L 1003 star formation complex is a highly kinematically active region with young stars in several different stages of evolution. We trace collimated outflows from numerous young stars although the origin of some HH objects remains elusive.
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1. INTRODUCTION
The constellation of Cygnus contains numerous regions of active star formation and many have been the subject of previous studies. The activity in the region as a whole is well summarized in the review article by Reipurth & Schneider (2008). These star-forming regions are typically located at larger distances than the more popular complexes such as Taurus–Auriga and Orion, and galactic structure makes both segregating regions and deriving precise distances somewhat problematic. In Cygnus, nine OB associations have been found (Uyaniker et al. 2001) with Cygnus OB7 being one of the lesser studied, yet likely one of the nearest. There have been several estimates of distance to Cygnus OB7 starting with Hiltner (1956) and Schmidt (1958), both of whom derived a distance of 740 pc. The Hipparcos study of this region (de Zeeuw et al. 1999) gave similar results and it is generally accepted that the distance to this association is ∼800 pc. It is this distance that we assume for all subsequent analysis.
Within Cygnus OB7 there is a large dark cloud complex (around 7° × 10° in size) designated Kh 141 by Khavtassi (1960) and TGU 541 by Dobashi et al. (2005). It is also sometimes referred to as "the Northern Coalsack." Within its somewhat filamentary structure (see, for example, Figure 28 of the review by Reipurth & Schneider 2008 taken from the extinction maps of Dobashi et al. 2005) there are several smaller dark clouds, some with Lynds (1962) classifications. One of these, L 1003, also known as TGU 541 P1 (Dobashi et al. 2005), is one of the two regions of high-extinction in Kh 141 and was first surveyed by Cohen (1980) who cataloged a red nebulous object (RNO). This object was designated RNO 127 and later was discovered to be a Herbig–Haro (HH) object, HH 448, rather than a red reflection nebula (Melikian & Karapetian 2001, 2003).
Our attention was drawn to L 1003 when it was found to contain not one, but numerous HH objects and cometary nebulae (Movsessian et al. 2003). In addition, several Hα emission-line stars had also been found, e.g., Cyg 19 (Melikian et al. 1996), which were potentially part of a larger pre-main-sequence (PMS) population. Especially interesting was the discovery of a new FU Orionis eruptive variable star (termed FUors after the progenitor of the group, FU Ori; Ambartsumian 1971) by Movsessian et al. (2006). This source awaits a variable star designation (N. Samus 2009, private communication, GCVS Newsletter 80) and hence, below we refer to it as "the Braid Nebula star" due to the twisting double-spiral morphology of its associated reflection nebula (Movsessian et al. 2003, 2006). The Braid Nebula star was also found to be the driving source of an extensive bipolar HH flow (Movsessian et al. 2006).
The area to the west of the Braid Nebula had previously been found to contain several interesting HH objects, including HH 381 and 382 (Devine et al. 1997). They are located close to a double fan-shaped reflection nebula which, in turn, is associated with an IRAS source (IRAS 20568+5217). It is, however, still unclear if the HH objects are physically related to the IRAS source. An NIR K-band spectrum of the point source at the center of the fan-shaped nebula (currently designated HH 381 Infrared Source (IRS)) by Reipurth & Aspin (1997) showed it to exhibit a relatively featureless spectrum except for deep CO overtone absorption bands longward of 2.294 μm. The spectrum was noted as being extremely similar to that of many known FUors. Further, NIR spectroscopy by Aspin et al. (2009) showed that HH 381 IRS also possesses strong water vapor absorption features, again a common feature of other FUors. Greene et al. (2008) discovered that HH 381 IRS showed significant velocity broadening of its 2 μm spectral features, a characteristic they found in a number of FUors. Finally, Magakian et al. (2007) showed that HH 381 IRS and its associated reflection nebula had brightened considerably over the last few decades. HH 381 IRS therefore also seems to be in an elevated FUor state, and it is interesting to note that it is located within 30' of the Braid Nebula star. Hence, two FUor-like objects are located in this one dark cloud.
In order to better understand the environment around the two FUor-like objects and study the outflows and jets present and their relationship with the young stellar objects, we initiated a multi-wavelength (optical to submillimeter/millimeter) study of a region of L 1003 approximately 60'×30' in size which includes both the Braid Nebula star and HH 381 IRS. In this paper, we describe the results of our optical survey and present deep narrowband images centered on the emission lines of Hα (λ6563 Å) and [S ii] (λ6717 and 6732 Å). In low-mass star-forming regions, nebulosities showing these lines in emission are the result of shock excitation as found in HH objects and flows. Here, we concentrate on defining the extent of the outflow population and the inherent morphological structures observed. In Section 2, we present details of the observations and data reduction/analysis. In Section 3, we briefly discuss the determination of the distance to L 1003, while in Section 4 we present the results of the survey, detailing the new HH objects/flows. In Section 5, we discuss the morphology of the shock-excited features, their inter-association, and their possible originating stellar sources.
2. OBSERVATIONS AND DATA REDUCTION
We obtained the images presented below on UT 2006 September 22–24 using the Subaru Prime Focus Camera (Suprime-Cam; Miyazaki et al. 2002) mounted on the prime focus of 8.2 m Subaru Telescope atop Mauna Kea, Hawaii. The Suprime-Cam is a mosaic CCD camera with 10 2K×4K Hamamatsu Photonics CCDs arranged in a 5 × 2 pattern. The field of view is about 34'×27' with a pixel scale of 0
2 per pixel. We used two narrowband filters, Hα (N-A-L659, λc = 6607 Å, ΔλFWHM = 101 Å; Okamura et al. 2002), [S ii] (N-A-L671, λc = 6712 Å, ΔλFWHM = 120 Å; Yagi et al. 2007), and two broadband filters, RC (λc = 6500 Å, ΔλFWHM = 1500 Å), IC (λc = 8000 Å, ΔλFWHM = 1500 Å). We use the broadband filter images for direct comparison with the narrowband filter images to provide good discrimination between HH objects emitting line emission and reflection nebulosity in continuum emission. The area observed is ∼60'×30', which was acquired by combining the images dithered with Δα = Δδ = 1' dithering width to fill the small gaps of 14''–16'' between the CCDs at the Braid Nebula (α = 21:00:25.0, δ = +52:30:15.2 J2000) and IRAS 20568+5217 (α = 20:58:21.4, δ = +52:29:27 J2000). The total on-source exposure time for each band is 60 minutes for Hα, 35 minutes for [S ii], 230 s for IC, and 190 s for the RC band. The seeing (FWHM of stars) was variable from 045 to 08 during the observations.
The imaging data were reduced by using IDL and the Suprime-cam Deep Field REDuction package (SDFRED, Yagi et al. 2002; Ouchi et al. 2004) which consists of C-shell scripts using IRAF and SEXtractor. We performed bias subtraction, overscan, flat-fielding, bad pixel masking, image distortion correction, sky subtraction, and mosaicking.
Coordinate calibration was performed during the data reduction with the SDFRED package. During the measurements and making of figures we adjusted the coordinates in various filters to each other and to the coordinate system of DSS-2. Taking into account that many of HH knots are non-stellar or have irregular shape, we estimate that absolute errors of coordinates are about 1''.
3. THE HERBIG–HARO OBJECTS IN THE BRAID NEBULA STAR FORMATION REGION
Figure 1 presents the optical Hα image of the full region observed. Overlaid on this image are dashed-line boxes indicating regions or "zones" of the full image that are studied in more detail below. Large numbers inside each of the 11 dashed-line boxes indicate the identification number of the zone, which were assigned approximately in order of right ascension. The locations of numerous compact nebulae (CNs), HH objects, and IRAS sources also are shown. The Braid Nebula star is not optically visible but is located close to the bottom-left corner of the letter "B" in the word "Braid." In order to identify shock-excited features in our images, we have made a direct comparison of the narrowband Hα and [S ii] images to a broadband IC filter image which does not include these emission lines. By this visual comparison, we have discovered a significant number of new nebulous features in the region as well as structural details in previously known objects. Some of these HH objects form distinct flows from optical or NIR sources, while others have no obvious originating object. We list all newly discovered HH objects in Table 1. Coordinates of previously detected HH objects can be found in the paper of Movsessian et al. (2003). The 11 zones shown in Figure 1 have been defined to include objects and flows that are likely related. Below we discuss each zone separately. To remain consistent with other papers based on this region, below, in any discussion of previously known objects, we use their previously assigned HH numbers, adding new capital letters for newly discovered knots, where appropriate. Usually, we show objects in both Hα and [S ii] images, except in cases when their appearance in these filters is nearly the same. Such cases are described below.
Figure 1. Image of the region studied in this paper. This mosaic image was taken in Hα and shows the 11 zones discussed below (the dashed-line boxes). Many of the interesting stars and nebulous features present are labeled.
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Standard image High-resolution imageTable 1. The Catalog of New HH Objects
| HH Object | α (J2000) | δ (J2000) |
|---|---|---|
| (h m s) | (○ ' '') | |
| HH 965 SW bow | 20 58 05 | 52 24 23 |
| HH 965 SW knot | 20 58 11.3 | 52 25 23 |
| HH 965 NE knot | 20 58 12.0 | 52 25 32 |
| HH 965 NE bow | 20 58 19 | 52 26 22 |
| HH 381 jet | 20 58 21.2 | 52 29 32 |
| HH 381 C | 20 58 21.9 | 52 28 54 |
| HH 382 G | 20 58 21.9 | 52 28 10 |
| HH 382 F | 20 58 21.9 | 52 27 56 |
| HH 382 E | 20 58 21.9 | 52 27 36 |
| HH 382 D | 20 58 27.1 | 52 18 32 |
| HH 966 A | 20 58 13.9 | 52 41 00 |
| HH 966 B | 20 58 15.1 | 52 40 48 |
| HH 966 C | 20 58 15.3 | 52 40 24 |
| HH 966 D | 20 58 13.6 | 52 40 18 |
| HH 967 | 20 58 08.8 | 52 44 59 |
| HH 968 G | 20 58 41.6 | 52 31 56 |
| HH 968 F | 20 58 44.8 | 52 32 10 |
| HH 968 E | 20 58 45.5 | 52 32 11 |
| HH 968 D | 20 58 47.0 | 52 32 17 |
| HH 968 C | 20 58 48.0 | 52 32 26 |
| HH 968 B | 20 58 48.5 | 52 32 32 |
| HH 968 A | 20 58 49.2 | 52 32 37 |
| HH 380 F | 20 58 55.1 | 52 34 56 |
| HH 380 C | 20 59 08.2 | 52 36 32 |
| HH 380 D | 20 59 09.1 | 52 36 14 |
| HH 380 E | 20 59 15 | 52 35 06 |
| HH 973 | 20 59 09.0 | 52 21 13 |
| HH 974 A | 20 59 10.3 | 52 22 39 |
| HH 974 B | 20 59 11.6 | 52 22 34 |
| HH 975 | 20 59 50.4 | 52 40 37 |
| HH 627 D | 20 59 42.4 | 52 32 46 |
| HH 627 C | 20 59 46.2 | 52 32 55 |
| HH 627 B | 20 59 46.6 | 52 33 17 |
| HH 628 B | 21 00 05.0 | 52 33 26 |
| HH 628 C | 21 00 05.0 | 52 32 52 |
| HH 632 A | 21 00 35.0 | 52 34 18 |
| HH 629 H | 21 00 07.7 | 52 29 13 |
| HH 629 I | 21 00 08.7 | 52 29 18 |
| HH 629 D | 21 00 11.0 | 52 29 02 |
| HH 629 J | 21 00 11.2 | 52 29 42 |
| HH 629 E | 21 00 11.6 | 52 29 13 |
| HH 629 F | 21 00 11.7 | 52 29 07 |
| HH 629 G | 21 00 12.5 | 52 29 08 |
| HH 629 X | 21 00 14.4 | 52 29 29 |
| HH 635 D | 21 00 31.1 | 52 30 44 |
| HH 635 E | 21 00 36.9 | 52 31 10 |
| HH 635 F | 21 00 40.5 | 52 31 30 |
| HH 635 G | 21 00 44.1 | 52 31 51 |
| HH 635 H | 21 00 54.7 | 52 33 15 |
| HH 631 F | 21 00 15.2 | 52 28 23 |
| HH 976 knot | 21 00 17.2 | 52 26 30 |
| HH 631 E | 21 00 18.4 | 52 28 09 |
| HH 630 A | 21 00 18.9 | 52 25 58 |
| HH 631 D | 21 00 19.4 | 52 27 54 |
| HH 631 C | 21 00 20.2 | 52 28 01 |
| HH 977 north | 21 00 22.8 | 52 26 32 |
| HH 977 south | 21 00 23.1 | 52 26 24 |
| HH 631 B | 21 00 23.5 | 52 28 08 |
| HH 634 E | 21 00 39.4 | 52 27 38 |
| HH 634 F | 21 00 40.8 | 52 27 16 |
| HH 969 | 20 58 57.2 | 52 29 32 |
| HH 970 | 20 59 07.2 | 52 29 50 |
| HH 971 | 20 59 08.2 | 52 24 51 |
| HH 972 | 20 59 09.5 | 52 24 09 |
| HH 978 | 21 02 11.6 | 52 35 59 |
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In addition to HH objects/flows, we have also found several reflection nebulae, mainly of cometary shape. The majority of these have not been previously described, though some were mentioned in Movsessian et al. (2003). For completeness, all such objects are listed in Table 2 as CN (cometary and/or compact nebulae) objects, continuing our numeration in the papers of Movsessian et al. (2003, 2006). Also in Table 2, we show IRAS, Two Micron All Sky Survey (2MASS), and Hα emission-line catalog identifications if the association is unambiguous. To date, no Chandra X-ray nor Spitzer infrared observations of this region exist.
Table 2. List of the Reflection and Cometary Nebulae
| Object | α (J2000) | δ (J2000) | IRAS | 2MASS | Hα Emission |
|---|---|---|---|---|---|
| (h m s) | (○ ' '') | ID | ID | Star | |
| HH 965 source | 20 58 11.8 | 52 25 29 | ... | ... | ... |
| IRAS 20568+5217 Nebula | 20 58 21.1 | 52 29 28 | 20568+5217 | 2058211+5229277 | ... |
| CN 9 | 20 58 50.2 | 52 32 50 | 20573+5221 | 2058501+5228254 | ... |
| CN 5 | 20 59 04.7 | 52 21 41 | ... | 2059042+5221448 | ... |
| CN 4 | 20 59 09.5 | 52 22 44 | ... | 2059089+5222388 | ... |
| CN 6 | 20 59 40.7 | 52 34 13 | ... | 2059407+5234136 | ... |
| CN 10 | 20 59 51.7 | 52 40 20 | 20583+5228 | 2059518+5240206 | ... |
| CN 3 | 21 00 03.8 | 52 34 29 | 20585+5222 | 2100038+5234290 | ... |
| Cyg 19 | 21 00 11.5 | 52 18 18 | ... | 2100116+5218172 | yes |
| CN 2 | 21 00 16.7 | 52 26 24 | ... | 2100166+5226311 | yes |
| CN 7 | 21 00 17.4 | 52 28 27 | ... | 2100173+5228354 | yes |
| CN 8 | 21 00 19.2 | 52 27 29 | ... | 2100190+5227282 | yes |
| GLMP 1017 | 21 00 21.6 | 52 27 09 | 20588+5215 | 2100214+5227095 | yes |
| CN 1 | 21 00 35.3 | 52 33 26 | 20590+5221 | 2100352+5233244 | ... |
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3.1. Zone 1: the HH 965 Flow
The detailed image of this newly discovered chain of emission knots is presented in Figure 2. The stellar object that is the probable source of this flow is a red star, labeled "source" in Figure 2. Due to its relative brightness in our Hα and broadband RC images (see insets), it probably possess strong Hα emission. It is embedded in the CN detectable also only in Hα. A nearby star, <2'' in a NE direction, may be physically related but could also be a foreground/background object. There are two faint emission knots, marked as NE and SW, which are located on opposite sides of the Hα emission star, but at different radial distances. Farther away, two diffuse radially symmetric bow shocks can be seen (also marked in Figure 2), though the southern one is extremely faint. The total length of this flow (end to end) is ∼0.7 pc. All nebulous features are visible only in Hα emission (i.e., not in [S ii]), which speaks of high excitation of this flow.
Figure 2. Region immediately surrounding the HH 965 outflow in Hα. The main features in this image are labeled. The two insets (≈13'' in size) show close-ups of the proposed exciting source for the HH flow in Hα and RC. We note that the south–west bow shock is certainly present but due to its extremely faint nature it is difficult to reproduce in a gray-scale image.
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Standard image High-resolution image3.2. Zone 2: the HH 381 IRS (IRAS 20568+5217) Flow
Several different groups of HH objects, including HH 381 and 382, have been found in the vicinities of the IRAS 20568+5217 double fan-shaped nebula (Devine et al. 1997). HH 382 was suggested to be related to the above IRAS source and part of a probable N–S outflow from the central star, HH 381 IRS. As we related above, this object appears to be FUor like in nature (Reipurth & Aspin 1997) and will be our focus in two further papers (T. Yu Magakian et al. 2010, in preparation; T.-S. Pyo et al. 2010, in preparation).
The optical images presented here show that within this zone there are a number of new HH objects. In particular, we confirmed the existence of an extended bipolar outflow from the HH 381 IRS which is oriented roughly in a north–south direction and passes symmetrically though both fan-shaped nebula lobes. The total length of this HH flow is around 6 pc. We present the images of the HH objects in zone 2 in Figures 3–7. Below, we consider individual components of the flows in this region in more detail.
Figure 3. Micro-jet extending from HH 381 IRS. The left image shows the region in [S ii], the middle in Hα, and the right in IC. The size of each image is about 20''. The IRAS detection error ellipse is shown by a dashed line.
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Figure 4. HH 381 A–C and HH 382 E–G in Hα (left) and [S ii] (right). Note that the right panel contains several linear artifacts. Also, the inclined dark streak on the left panel passing through the region containing the HH 382 E and F knots is likely the trace of a meteor or artificial satellite.
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Figure 5. HH 382 A–D in Hα (left) and [S ii] (right). The white streak on the right panel is an artifact.
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Figure 6. HH 966 in Hα (left) and [S ii] (right).
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Figure 7. HH 967 object in Hα. Dark streak is likely a trace of a meteor or an artificial satellite.
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Standard image High-resolution imageJet. Detailed inspection of the images of HH 381 IRS shows that it possesses a 22 long (1200 AU at 800 pc) emission jet marked as "jet" in Figure 3. The feature appears strongly in both our [S ii] (left) and Hα (middle) images but not in IC (right). The beginning of a counterjet also is traceable (see Figure 3). It is likely that the northern flow lobe is inclined toward the observer, so that the southern component is mainly obscured by circumstellar material in a flattened disk.
HH 381 A and B. These two knots (Figure 4) were described previously by Devine et al. (1997). Even though the provisional identification for the central star is HH 381 IRS, no strong evidence exists that HH 381 A and B are indeed physically related to it. We note that the stellar jet presented above is oriented in a totally different direction to the axis implied by the HH 381 A and B knots. To produce a second flow, HH 381 IRS would have to be a close binary system; however, to date there is no evidence for such multiplicity. There are also other possibilities (see our description of zone 3 below). In any case, HH 381 A and B may be physically related since they seem to be connected by emission filaments. These are best seen in Figure 4 where they appear to curve from the southern lobe of the double fan-shaped nebula and end in knots A and B.
HH 381 C. Knot C (Figure 4) is a compact patch of emission strongest in Hα but visible also in [S ii]. It is located slightly to the south of the southern fan-shaped reflection lobe and appears to be connected to it by one, or possibly two, emission filaments. In Hα, a bright, star-like knot is the most prominent feature while in [S ii] the knot appears more linear in nature. HH 381 C may well belong to the HH 381 IRS north–south flow since it lies relatively close to the linear axis formed by HH 381 IRS and HH 382 E–G.
HH 382 E–G. These knots form a chain of extremely faint, barely detectable, nebulous features (see Figure 4). They lie to the south of HH 381 B and C, on a line pointing back to HH 381 IRS. Due to their faintness and diffuse appearance it is difficult to isolate individual knots along the flow. The knots bear some resemblance to small bow shocks, especially in [S ii]. They are close to an area of very high extinction, which could certainly effect their shape and brightness. The HH nature of these knots is supported by the detection of at least two of them in NIR molecular hydrogen (H2) emission (T. Khanzadyan et al. 2010, in preparation). This flow appears to be around 2' in length corresponding to ∼0.5 pc, measured from the central star to HH 382 E, and it appears to be colinear with the northern micro-jet shown in Figure 3.
HH 382 A–D. These knots (see Figure 5) appear to be continuation of the linear jet-like flow extending from HH 381 IRS and containing HH 382 E–G. They are the southernmost objects we have detected in this flow, although they are located close to the southern boundary of our optical images (see Figure 1) and so it is possible that the flow could extend further still. Knots A–C were described in the work of Devine et al. (1997), and we have added one additional member to this group, HH 382 D. The morphology of the knots is somewhat different in [S ii] and Hα. The overall structure of this group suggests that it may be a disrupted giant bow shock with HH 382 A in its head.
HH 966. In this grouping there are four emission knots labeled HH 966 A–D in Figure 6. Contrary to diffuse knots A–C, knot D is rather compact. Faint knot B is projected on a field star. This grouping is both located along a linear axis passing through HH 381 IRS and HH 382, and at approximately the same distance (to the north) from the HH 381 IRS as HH 382 A–D is (to the south). It may therefore be the northern counterpart to HH 382. Note that the HH 966 group also possesses a disrupted appearance.
HH 967. This is the very diffuse object of low surface brightness, projected on the stellar background (see Figure 7). Unfortunately, our [S ii] images did not cover this region being at the north–west corner of the survey area. However, we note that HH 967 is also located on the axis passing through HH 966 and HH381 IRS and may be an outer shock-excited knot and member of this outflow.
Thus, all knots forming HH 382 seem to comprise the southern jet-like outflow from HH 381 IRS (IRAS 20568+5217), and HH 966 and probably HH 967, located north of the double fan-shaped nebula, form the northern counterpart to this flow.
3.3. Zone 3: Flows Near IRAS 20573+5221
This zone includes several known HH objects (Devine et al. 1997) and a few new ones found in our survey.
CN 9 and HH 968. On the IC continuum image presented in Figure 8, we see a faint fan-shaped nebula extending in a southeastern direction from a star that is coincident with IRAS 20573+5221. This reflection nebula is also discernible on the DSS-2 R-band image and we designate it CN 9. HH 968 is formed by a chain of small and faint bow shocks extending away from CN 9 and strongest in Hα. We labeled them with the letters "A–G" in Figure 8 and in Table 1. Another interesting feature is the very narrow jet-like streak, extending away from IRAS 20573+5221, which is seen virtually only in [S ii] and can be traced from knot A to knot F (see Figure 8, middle panel, where its position is shown by two lines).
Figure 8. HH 968 object in Hα (top), [S ii] (middle), and IC (bottom). The IRAS detection error ellipse is shown by a dashed line.
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Standard image High-resolution imageThis chain of emission knots is probably the same object which is mentioned by Devine et al. (1997) as "faint smudges of HH emission between HH 380 and IRAS 20568+5217."
HH 380. We have found several new faint HH objects in the vicinity of HH 380, whose A and B components were discovered by Devine et al. (1997). The new emission features are named HH 380 C–F and can be seen in Figure 9. Two relatively bright elongated objects, HH 380 C and D are located north–east of HH 380 B, and comprise of several compact knots. HH 380 E and F are seen as very faint diffuse knots. The relationship of knots C–F to the brighter knots A and B is unclear. HH 380 B–D, and F seem to be arranged on an almost direct line passing through IRAS 20573+5221 and the HH 968 flow. Moreover, as was already mentioned by Devine et al. (1997), HH 381 A and B also are located on the same line. They are also at approximately the same distance from IRAS 20573+5221 as HH 380 C and D are, but on the opposite side of the IRAS source. The internal structure of the bright knots HH 380 A and B is well documented in our images, but their essentially irregular shape makes estimating the direction of their motion difficult with respect to any stellar source. We note that the coordinates of HH 380 C and D given in Table 1 correspond to their brightest emission peaks.
Figure 9. HH 380 group in [S ii].
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Standard image High-resolution image3.4. Zone 4: HH Objects Near CN 4 and CN 5
CN 4 and HH 974. The area immediately surrounding CN 4 is shown in Figure 10. CN 4 appears as a compact nebula with an approximately spherical morphology centered on a bright star. HH 974 comprises a jet-like emission feature (knot A) and, further to south–east, another object, knot B. Knot B consists of several emission condensations with the brightest of them being nearly star like. Both knots are fainter in [S ii] than in Hα. We consider that the star in the CN 4 is the most probable source of this collimated flow.
Figure 10. HH 974 in Hα.
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Standard image High-resolution imageCN 5 and HH 973. CN 5 is a compact cometary nebula extending from a red star to the south–east (see Figure 11). In the same direction, we also find a star-like emission object that we designate HH 973. It is brighter in [S ii] than in Hα and not present at all in IC. In the same field we found a very red, nebulous object directly to the east of CN 5. In Figure 11, it is labeled as "IR knot." We note that this easterly object is well detected in NIR images (T. Khanzadyan et al. 2010, in preparation). Both CN 5 and the "IR knot" should be considered as possible sources for HH 973.
Figure 11. HH 973 in [S ii] (top) and IC (bottom).
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Standard image High-resolution image3.5. Zone 5: CN 10 and HH 975
HH 975 is a group of emission objects divided into two relatively bright parts, labeled A and B in Figure 12. They are surrounded by diffuse emission which contains compact star-like emission knots. There are no distinct differences between the morphology of HH 975 in Hα and [S ii], and hence only the latter image is shown. The coordinates in Table 1 refer to the center of the group. About 30'' south–east of the HH 975 knots lies IRAS 20583+5228. It is coincident with the stellar object embedded in a faint reflection nebulous bubble-like structure. We designate this bubble-like nebula as CN 10. It is probable that IRAS 20583+5228 is the source of HH 975, a fact supported by NIR data (T. Khanzadyan et al. 2010, in preparation).
Figure 12. HH 975 in Hα (left) and IC (right). The IRAS detection error ellipse is shown by a dashed line.
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Standard image High-resolution image3.6. Zone 6: CN 6 and HH 627
HH 627 was described in a previous paper (Movsessian et al. 2003) as the conspicuous emission knot, located near a rather bright star which was shown to be a foreground late G to early K main-sequence star by Aspin et al. (2009). In Figure 13, this knot is marked as A. Several new faint emission nebulae are also present. B is a very small spot with emission filament, probably connecting it to HH 627 A. C is a very faint and relatively compact emission knot, and D has the appearance of an elongated bow shock, visible only in [S ii]. There are also diffuse nebular wisps in this area, seen in the IC image. A new compact reflection nebula with a conical shape is also seen to the north–west of the foreground star and is labeled as CN 6.
Figure 13. HH 627 group in [S ii] (left) and IC (right). The bright star in the center is a foreground object.
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Standard image High-resolution image3.7. Zone 7: CN 3 and HH 628
The cometary nebula CN 3 is associated with IRAS 20585+5222. Three emission knots are visible in Figure 14, which are designated HH 628 A–C. Knot A was previously known (Movsessian et al. 2003), and we have found two new faint emission features (B and C). The new knots appear to have a bow-like morphology and are possibly intermediate bow shocks in the HH 628 flow.
Figure 14. HH 628 flow in Hα+[S ii].
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Standard image High-resolution image3.8. Zone 8: CN 1 and HH 632
This cometary reflection nebula, described by Movsessian et al. (2003), is illuminated by an Hα emission star (Melikian et al. 2006) and is associated with IRAS 20590+5221. It is found to possess a small-scale emission jet named HH 632. In our new images, especially in [S ii], the knotty structure of this jet is clearly evident. In Figure 15, one can see three virtually star-like knots of emission. In addition, a faint bow shock is seen ∼53'' north of the star (labeled A). At 800 pc, this corresponds to a projected distance of ∼0.2 pc. Note that a narrow nebulous appendage to the southern side of the CN 1 star is probably not a counterjet because it is well seen in the IC continuum image. Some details can be better seen in the color representation of the CN 1 field which is shown in Figure 16.
Figure 15. HH 632 flow in [S ii] (left) and IC (right). The IRAS detection error ellipse is shown by a dashed line.
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Figure 16. Three-color representation of CN 1 as shown in gray-scale in Figures 4 and 15. In this image, blue is Hα, green is [S ii], and red is IC.
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Standard image High-resolution image3.9. Zone 9: the Braid Nebula Flow
In the work of Movsessian et al. (2006), it was suggested that the central star of the Braid Nebula is the source of the bipolar outflow which includes HH 629 A–C, and HH 635 A–C. Our new images have both improved sensitivity and spatial resolution and we have found a number of new knots which likely belong to the same outflow. All new HH knots are marked on Figures 17 and 18 and are included in Table 1.
Figure 17. HH 629 flows in Hα (top) and [S ii] (bottom).
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Figure 18. HH 635 flow in Hα (top) and [S ii] (bottom).
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Standard image High-resolution imageIt appears that the southwestern part of the flow, which includes HH 629 A and B, also contains four new knots designated D–G. All these knots are very compact and have a star-like appearance. HH 635A is bright in our IC images implying it probably contains significant dust and is therefore also partly a refection nebula.
The emission complex labeled HH 629 C (which itself contains at least four very compact knots) is probably part of a different outflow. This flow comprises several other newly discovered knots (labeled H–J in Figure 17) and is nearly parallel to the Braid Nebula flow. The J knot is extended, with an arc-like shape, and could mark the termination of the flow. It is interesting that this flow is brighter in [S ii] than in Hα, in contrast to the HH 629 A–G flow which has nearly the same brightness in both lines. The difference in physical parameters also argues for the presence of two separate parallel flows.
Yet another diffuse HH condensation is present in this area; it is labeled HH 629 X in Figure 17 and lies between the two outflows we have described above. Again, it is brighter and more well defined in [S ii] than in Hα.
As was mentioned above, a counter-flow from the Braid Nebula star, extended to the north–east, contains HH 635 A–C emission knots. Here we also find several new components which are labeled D–H in Figure 18. Knots D–F are seen only in Hα while knot H is visible only in [S ii]. The morphology of the knots in this flow varies strongly. HH 635 A is compact (although its shape is somewhat unusual) while HH 635 C and H are very diffuse. In fact, knots B, C and H together give the impression of the large broken bow shock. On the other hand, it is also interesting that knots D, E, and G are shaped like small bow shocks and are separated from each other by approximately the same distance, i.e., ∼0
5–1'.
We see that the NE lobe of the outflow from the Braid Nebula star appears to be more than twice the length of the SW lobe (1.4 pc compared to 0.6 pc).
3.10. Zone 10: South of the Braid Nebula
Zone 10 is located to the south of the Braid Nebula and to the west of bright RNO 127 (HH 448). It is a complex region rich in HH objects. The area is shown in Figure 19 in both Hα and [S ii].
Figure 19. Zone 10 with multiple HH flows and knots in Hα (left) and [S ii] (right).
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Standard image High-resolution imageCN 2, HH 630, and HH 670. The narrow jet HH 630 (Movsessian et al. 2003) extends to the southeast and is excited by an Hα emission-line star (Melikian & Karapetian 2001) which in turn illuminates a fan-shaped reflection nebula designated CN 2. Figure 19 shows that the HH 630 flow is significantly longer than previously thought; it consists of a number of emission knots, well detected in both Hα and [S ii]. The flow terminates in a small bow-shock-like feature. Close to the CN 2, but on the opposite side of HH 630, there is another bow-shock-like object visible mainly in Hα. Both features are marked in Figure 19 as "bow shock." This bow shock points to the north–west and a faint narrow filament, also only seen in Hα, can be traced between it up to the compact and bright HH 670 knot. HH 670 is located at the same distance from CN 2 as the last knot in HH 630 flow. Thus, HH 670, previously described as a separate HH object (Movsessian et al. 2003), in fact terminates the counterjet from the CN 2 star. The HH 630 and HH 670 flows are not colinear and both appear slightly curved.
It is also important to note the knot designated HH 630 A, which is a faint structure only visible in [S ii] (see Figure 19), slightly aside from the main HH 630 flow. It was previously detected in the NIR in H2 line emission (the NIR2 IR source, mentioned in Movsessian et al. 2003), but, as we see, it also has an optical counterpart.
HH 976. This is another structure near CN 2, which extends perpendicularly to the HH 630 flow and is detected in both Hα and [S ii]. It starts from a star-like knot (marked as HH 976 in Figure 19), which is brighter in [S ii] and has an emission filament, oriented in the northeast direction. The coordinates in Table 1 correspond to this knot. Several other very faint emission spots can be traced further in the approximately same north–east direction, creating the appearance of an elongated flow. Its relation to CN 2 is not obvious; but, in any case, the compact knot is likely not a stellar source since nothing is visible at its location in our IC image.
In this area, we also have found three other faint, nearly linear features or filaments, all of which are seen mostly in Hα although two of them are also presenting [S ii]. They are marked in Figure 19 with the letters "LF." One is parallel to the HH 670 jet, the second is seen to cross the HH 670 jet in an approximately north–south direction, while the third is close to parallel to HH 976 lying to the northwest of the CN 8. In principle, they can be emission fragments of flows. However, since at least two are visible in IC, they may just be cloud edges or dusty filaments illuminated by one or more emission stars in the region.
HH 977. This object is located to the east of CN 2. It consists of two knots that show more structure in [S ii] (see Figure 19). The southern knot is visible also in our IC image and is probably the optical counterpart of the NIR3 H2 emission knot from Movsessian et al. (2003).
CN 7, CN 8, HH 631. Both compact reflection nebulae, CN 7 and CN 8, are illuminated by Hα emission-line stars (Melikian et al. 1996; Melikian & Karapetian 2001) and, as is evident from their morphology, both have conic cavities, the walls of which are especially well pronounced in CN 8 (Figure 19). The previously found HH 631 lies to the east of CN 7 and is seen as an oblong diffuse spot (knot A on Figure 19) with some inner structure. Several HH knots are detected between it, CN 7, and CN 8. We marked them as HH 631 B–F, although their association with one flow is to be proved. All these HH objects have nearly similar brightness in both the Hα and [S ii] images. The relatively bright knot F, which coincides with the NIR H2 emission knot NIR1, was actually detected before (Movsessian et al. 2003). For the originating source of these HH knots, in addition to CN 7 and CN 8, one should also consider the double T Tauri star GLMP 1017 (Garcia-Lario et al. 1997). This star is also nebulous (see Figure 19) and is probably embedded in the same cloud.
The color representation of this field, where many of above-mentioned details can be seen more clearly, is shown in Figure 20.
Figure 20. Three-color representation of CN 7 as shown in gray-scale in Figure 19. In this image, blue is Hα, green is [S ii], and red is IC.
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Standard image High-resolution image3.11. Zone 11: RNO 127, HH 633, and HH 634
These bright HH objects and flows were described in detail in a previous work (Movsessian et al. 2003). Our new images, however, show some interesting features.
HH 448 (RNO 127). This is the brightest HH object in our survey area. In previous work, it was described as consisting of the four major condensations. As can be seen from Figure 21, this description is, in principle, true, but the complete picture is much more complex. First, the general appearance of HH 448 in [S ii] is much more "knotty," with many fine details. Hα, however, is much smoother. Also, in Hα the structure of HH 448 appears more like the superposition of a number of arc-like features. One such small, faint arc, which was not described previously, is marked in Figure 21 at the top right of the Hα image. These new data are therefore consistent with the suggestion made by Movsessian et al. (2003) that HH 448 is made up of several interacting or spatially superimposed outflows.
Figure 21. RNO 127 and HH 634 flows in Hα (left) and [S ii] (right).
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Standard image High-resolution imageHH 634 flow. New images confirm that this chain of HH objects belongs to one outflow, directed to the southeast with no pronounced structural differences between Hα and [S ii] (see Figure 21). Knots HH 634 B and C with two faint smudges to the west (which can also be seen in the previously published images of Movsessian et al. 2003 and are labeled here as HH 634 E and F), actually form one large emission patch. Again one should note the rich structure inside the main knots of this flow.
HH 633. This object has a similar appearance in our new images to that shown in previous images (Movsessian et al. 2003), and has the same morphology in both Hα and [S ii] (Figure 22). Its relation to IRAS 20591+5214 (barely visible in the optical range; see Figure 22), which was proposed in the previous paper, seems still probable.
Figure 22. HH 633 in [S ii]. The IRAS detection error ellipse is shown by a dashed line.
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Standard image High-resolution imageFinally, in Figure 23, the full picture of the region around the Braid Nebula and HH 448 is presented in color.
Figure 23. Three-color representation of the Braid Nebula region as shown in gray-scale in Figures 17 and 18. In this image, blue is Hα, green is [S ii], and red is IC.
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Standard image High-resolution image3.12. HH Objects With No Clear Association
Here we describe several HH objects found in the studied field, which cannot be associated with certainty to any stellar source or even to one of the zones discussed above.
HH 969 and HH 970. This is a pair of faint emission features located south of HH 380 A (see Figure 24). HH 970 consists of two knots while HH 969 has a bow-like shape. Both objects are brighter in Hα than in [S ii].
Figure 24. HH 969 and HH 970 in Hα.
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Standard image High-resolution imageHH 971 and HH 972. This is a pair of faint emission features brighter in Hα (Figure 25) than in [S ii]. Both are relatively diffuse in nature.
Figure 25. HH 971 and 972 in Hα.
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Standard image High-resolution imageHH 978. This is the easternmost of all HH objects in our survey field. It is shown in Figure 26 and appears as two faint curving structures, possibly bow shocks, visible only in [S ii]. It is located far from the main groups of HH objects and cometary nebulae.
Figure 26. HH 978 object in [S ii].
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4. DISCUSSION
4.1. HH Flows: Origins and Sizes
In Table 3, we list the HH flows present in the survey region that have identifiable originating/exciting sources. Also shown are the projected sizes of the flows (in parsecs) and the minimum ejection timescale (in years, assuming a typical ejection velocity of 200 km s−1). At least 12 optical flows can be identified in the field with some confidence, including two parsec-scale flows. Interestingly, both parsec-scale flows are related to FUor-like objects. We discuss these flows in the following section. One more parsec-size outflow can be added if future observations prove the association of HH 380 and HH 381 to IRAS 20573+5221. Another obvious candidate for a giant flow is represented by the HH 634 knots, which almost certainly belong to one outflow and which cover ∼0.5 pc even without knowing the location of the driving source. Yet another rather extensive flow, visible only in H2 IR emission, was found in this field and will be described in detail in T. Khanzadyan et al. (2010, in preparation). Obviously, as the significant number of HH knots in the studied field remains without identifiable driving sources, further multi-wavelength observational data will very probably increase the number of outflows.
Table 3. Parameters of the HH Flows
| Source | Components of HH Outflow | Projected Length | Ejection Timescale | Comments |
|---|---|---|---|---|
| (pc)a | (yr)b | |||
| HH 965 source | NE part: NE knot, NE bow; SW part: SW knot, SW bow | 0.35 0.33 | 1700 1600 | Bipolar |
| IRAS 20568+5217 | N part: jet, HH 966 A–D, HH 967; S part: HH 382 E–G, HH 382 A–D | 3.6 3.6 | 17600 17600 | Bipolar; HH 381 B–D also can be related |
| CN9 (IRAS 20573+5221) | HH 968 A–G | 0.37 | 1800 | The knots HH 380 and HH 381 also can be related, making this |
| outflow bipolar | ||||
| CN4 | HH 974 A–B | 0.08 | 400 | |
| CN5 | HH 973 | 0.19 | 900 | |
| CN10 (IRAS 20568+5228) | HH 975 A–B | 0.08 | 400 | |
| CN6 | HH 627 A–D | 0.36 | 1800 | The relation between CN6 and HH 627 is not obvious and needs |
| further confirmation | ||||
| CN3 (IRAS 20585+5222) | HH 628 A–C | 0.47 | 2300 | |
| CN1 (IRAS 20590+5221) | HH 632 jet and A knot | 0.2 | 1000 | |
| Braid Nebula | NE part: HH 635 A-H; SW part: HH 629 A, B, E–G, X(?) | 1.42 0.60 | 7000 3000 | Bipolar |
| CN2 | NW part: HH 670; SE part: HH 630 | 0.26 0.33 | 1300 1600 | Bipolar |
| IRAS 20591+5214 | HH 633 |
Notes. aThe distance used is 800 pc. bThe mean velocity assumed for HH objects is 200 km s−1.
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When comparing the Cyg OB7 field studied here with other more well-known star-forming regions, we conclude that although there are numerous outflows, their number density is not as high as found in the Perseus (at least 26 outflows) and L1641 (over 50 outflows) star-forming regions which are of comparable size and also without young high-mass stars (Davis et al. 2008, 2009). This, perhaps, can be related to differences in age and/or star formation efficiency. However, the Braid Nebula field is clearly very interesting if only due to its preponderance of parsec-scale flows, i.e., these number, at least 20% of the flows observed. This is a significantly higher value than the 10%, typically found in other such surveys, e.g., Davis et al. (2007, 2008, 2009).
4.2. HH Flows from FUors
The probable existence of an extended bipolar outflow from the optically invisible Braid Nebula star was suggested by Movsessian et al. (2003) and supported by further observation in Movsessian et al. (2006). Our new images allow us to analyze this flow in more detail where we find two notable features. First, is the existence of several small quasi-periodic bow shocks in the NE region of the flow (see above). This is suggestive of multiple ejections with similar occurrence timescales. Assuming a distance of 800 pc, a typical HH flow velocity of 200 km s−1, and a 20° flow inclination with respect to the plane of the sky (Movsessian et al. 2006), we derive a kinematic inter-ejection timescale of about 1000 years. This value is in accord with previous estimate (Reipurth & Bally 2001) for the time interval between internal working surfaces in HH flows. Second, the Braid Nebula flow is asymmetrical. We find that its NE component consists mainly of arcuate clumps (which we interpret as bow shock on various stages of disruption) while the SW counterpart is over a factor of 2 shorter and is represented mostly by compact knots. This discordance probably can be ascribed to differences in the density structure of local interstellar medium between the two sides of the flow.
As we have seen, the other FUor-like object in the survey area, HH 381 IRS, is also the source of an extended bipolar flow. Contrary to the Braid Nebula outflow, the HH 381 IRS flow is much more symmetric and contains large groupings of HH knots. We interpret the structure seen here as being the result of the disruption of several bow shocks. Here again, the southern part of the flow closer to the exciting star shows evidence for several structures (e.g., HH 382 E–G) that can be interpreted as evidence for multiple ejections.
To conclude, at least nine FUors and FUor-like objects (namely V346 Nor, Z CMa, L1551 IRS5, Pars 21, the Braid Nebula star, V883 Ori, Haro 5a IRS, HH 364 IRS, and HH 381 IRS) are considered to be the exciting sources of HH flows. Comparing this number to the list presented in Hartmann & Kenyon (1996) suggests that the percentage of FUors (including FUor-like objects) with HH flows is larger than previously thought. This supports the argument that multiple ejection events, common in HH flows, are intimately related (in some manner) to FUor outbursts.
4.3. Morphology of the Flows
As can be seen from the figures presented above, the variety of outflows and associated structures seen in the region of Cyg OB7 studied here is diverse. We find examples of short, micro-jet-like flows, giant parsec-scale flows, elongated curved collimated flows, and multiple bow shock structures some of which are probably dissipating after exiting the associated molecular cloud. In the HH 635–HH 629 flow, we observe pronounced morphologic asymmetry between the flow and counterflow. As another example of such asymmetry is the HH 630–HH 670 which has inclined axes of flow and counterflow. Several other examples of unusual morphology should be mentioned. The HH 634 flow gives the impression that it takes the form of a wide, curved ribbon with bow-shock-like structures embedded within. Also, the isolated group HH 975 seems to be encapsulated in a nebulous bubble with its brightest emission knots located at the location of maximum extinction. The HH 968 group shows some similarity to HH 975 and its defining feature is the coexistence of a straight, narrow [S ii] streak and a curved chain of Hα knots likely forming a curved flow. Alternatively, the [S ii] streak may be an HH jet and Hα knots could then be oblique secondary shocks delineating the wall of an outflow cavity produced by the jet. Such a morphology is somewhat reminiscent of the HH 34S flow (Bührke et al. 1988).
The most complex object in the field is HH 448 (RNO 127) with its intricate structure of intersecting arcs, bows, and streaks. As mentioned above, these fine details are best observed in [S ii] emission. Other nebulous objects in our survey region do not show such pronounced differences in morphology between [S ii] and Hα although some examples are seen, specifically HH 382A and HH 631A. Such a dichotomy is probably related to the predilection of [S ii] emission to occur close to jet axes, denser knots, and heads of bow shocks. This feature can perhaps aid in better understanding the nature of HH 448 in further investigations.
5. CONCLUSION
To conclude, this survey has been aimed at cataloging the outflow structure present in this specific region of the L 1003 molecular cloud in the Cyg OB7 star formation complex. It has been driven by our desire to understand the general properties of the outflows from young stars present in the region, and the environment harboring two FUor-like objects. In future papers, we will present and discuss the results of complimentary near-IR narrowband and submillimeter/millimeter line and continuum surveys and investigate such important parameters as star formation efficiency, cloud mass, and the age and age spread of star formation.
We are grateful to Bo Reipurth for providing new HH numbers in advance and for helpful discussions. We also thank the entire staff of the Subaru Telescope for their dedicated support to the telescope and observatory operations. T.Y.M., E.H.N., and T.A.M. were partly supported by ANSEF 08-1142 grant. T.K.'s research was supported through a Science Foundation Ireland (SFI) Research Frontiers award. The Two Micron All Sky Survey is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by NASA and the NSF. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166.
Footnotes
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Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.