IRS5 Research Articles

SOFIA observations of S106: dynamics of the warm gas

Context. The HII region/PDR/molecular cloud complex S106 is excited by a single O-star. The full extent of the warm and dense gas close to the star has not been mapped in spectrally resolved high-J CO or [CII] lines, so the kinematics of the warm, partially ionized gas, are unknown. Whether the prominent dark lane bisecting the hourglass-shaped nebula is due solely to the shadow cast by a small disk around the exciting star or also to extinction in high column foreground gas was an open question until now. Aims. To disentangle the morphology and kinematics of warm neutral and ionized gas close to the star, study their relation to the bulk of the molecular gas, and to investigate the nature of the dark lane. Methods. We use the heterodyne receiver GREAT on board SOFIA to observe velocity resolved spectral lines of [C II] and CO 11-10 in comparison with so far unpublished submm continuum data at 350 micron (SHARC-II) and complementary molecular line data. Results. The high angular and spectral resolution observations show a very complex morphology and kinematics of the inner S106 region, with many different components at different excitation conditions contributing to the observed emission. The [C II] lines are found to be bright and very broad, tracing high velocity gas close to the interface of molecular cloud and HII region. CO 11-10 emission is more confined, both spatially and in velocity, to the immediate surroundings of S106 IR showing the presence of warm, high density (clumpy) gas. Our high angular resolution submm continuum observations rule out the scenario where the dark lane separating the two lobes is due solely to the shadow cast by a small disk close to the star. The lane is clearly seen also as warm, high column density gas at the boundary of the molecular cloud and HII region.

MICROWAVE OBSERVATIONS OF EDGE-ON PROTOPLANETARY DISKS: PROGRAM OVERVIEW AND FIRST RESULTS

We are undertaking a multi-frequency Expanded Very Large Array (EVLA) survey of edge-on protoplanetary disks to probe the growth of solids in each disk, sedimentation of such material into the disk midplane, and the connection of these phenomena to the planet formation process. The projection of edge-on disk systems along our line of sight enables a study of the vertical stratification of large grains with fewer model dependencies than would be required for disks that are more face-on. Robust studies of the spatial distribution of grains up to ~1 cm in size are possible with the wavelength range and sensitivity of the EVLA. In this contribution we describe target selection and observational strategies. First results concerning the Class 0 source IRAS04368+2557 (L1527 IRS) are presented, including a study of this source's 8.46 GHz continuum variability over short and long time baselines and an indication that its protoplanetary disk may have a dearth of pebble-sized grains.

THE CIRCUMBINARY OUTFLOW: A PROTOSTELLAR OUTFLOW DRIVEN BY A CIRCUMBINARY DISK

The protostellar outflows have indispensable role in the formation of single stars, because they carry off the excess angular momentum from the centre of the shrinking gas cloud, and permits further collapse to form a star. On the other hand, a significant fraction of stars is supposed to be born as binaries with circumbinary disk that are frequently observed. Here, we investigate the evolution of a magnetized rotating cloud using three-dimensional resistive MHD nested-grid code, and show that the outflow is driven by the circumbinary disk and has an important role even in the binary formation. After the adiabatic core formation in the collapsing cloud core, the magnetic flux is significantly removed from the centre of the cloud by the Ohmic dissipation. Since this removal makes the magnetic braking ineffective, the adiabatic core continuously acquires the angular momentum to induce fragmentation and subsequent binary formation. The magnetic field accumulates in the circumbinary disk where the removal and accretion of magnetic field are balanced, and finally drives circumbinary outflow. This result explains the spectacular morphology of some specific young stellar objects such as L1551 IRS5. We can infer that most of the bipolar molecular outflows observed by low density tracers (i.e., CO) would correspond to circumbinary or circum-multiple outflows found in this report, since most of the young stellar objects are supposed to be binaries or multiples.

MULTIPLE BIPOLAR MOLECULAR OUTFLOWS FROM THE L1551 IRS5 PROTOSTELLAR SYSTEM

The multiple protostellar system L1551 IRS5 exhibits a large-scale bipolar molecular outflow. We have studied this outflow within ~4000 AU of its driving source(s) with the SubMillimeter Array. Our CO(2-1) image at ~4" (~560 AU) resolution reveals three distinct components: 1) an X-shaped structure spanning ~20" from center with a similar symmetry axis and velocity pattern as the large-scale outflow; 2) an S-shaped structure spanning ~10" from center also with an opposite velocity pattern to the large-scale outflow; and 3) a compact central component spanning ~1.4" from center again with a similar symmetry axis and velocity pattern as the large-scale outflow. The X-shaped component likely comprises the limb-brightened walls of a cone-shaped cavity excavated by the outflows from the two main protostellar components. The compact central component likely comprises material newly entrained by one or both outflows from the two main protostellar components. The S-shaped component mostly likely comprises a precessing outflow with its symmetry axis inclined in the opposite sense to the plane of the sky than the other two components. This outflow may be driven by a recently reported candidate third protostellar component in L1551 IRS5, whose circumstellar disk is misaligned relative to the two main protostellar components. Gravitational interactions between this protostellar component and its more massive northern neighbor may be causing the circumstellar disk and hence outflow of this component to precess.

GRAIN GROWTH AND DENSITY DISTRIBUTION OF THE YOUNGEST PROTOSTELLAR SYSTEMS

We present dust opacity spectral indexes (beta) of the youngest protostellar systems (so-called Class 0 sources), L1448 IRS 2, L1448 IRS 3, and L1157, obtained between 1.3 mm and 2.7 mm continua, using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The unprecedented compact configuration and image fidelity of CARMA allow a better detection of the dust continuum emission from Class 0 sources, with a less serious missing flux problem normally associated with interferometry. Through visibility-modeling at both 1.3 mm and 2.7 mm simultaneously, as well as image- and visibility-comparison, we show that beta of the three Class 0 sources are around or smaller than 1, indicating that dust grains have already significantly grown at the Class 0 stage. In addition, we find a radial dependence of beta, which implies faster grain growth in the denser central regions and/or dust segregation. Density distributions of the Class 0 sources are also addressed by visibility-modeling.

WIDE-FIELD NEAR-INFRARED IMAGING OF THE L1551 DARK CLOUD

We present wide-field near-infrared images of the densest part of the L1551 dark cloud taken with the narrow-band filters for [Fe II] λ 1.644 μm and H2 v = 1-0 S(1) lines, together with the broadband H and K s filters. Numerous [Fe II] and H2 emission features were detected from the regions around HL/XZ Tau, HH 30, HH 262, L1551 NE, and L1551 IRS 5. Most of the [Fe II] features are compact or jet-like, suggesting that the emission arises from fast shocks occurring in the ejecta of jets. The H2 features are more diffuse and widely distributed in outflow lobes, with none of the H2 features showing the well-collimated emission associated with jets. This implies that the H2 emission originates from slower shocks where the ejecta interacts with ambient material. The outflow structure in the vicinity of the deeply embedded object L1551 NE is revealed, featuring a well-collimated, spatially continuous [Fe II] jet penetrating a fan-shaped infrared reflection nebula. The tangential velocities of knots in the L1551 NE jet are estimated to be 140-190 km s–1 from their proper motions, implying an inclination of 45°-60° for the jet axis. A counter-jet from L1551 IRS 5 is detected for the first time in [Fe II]; this probably corresponds to the northern-most of the two jets on the blueshifted side. The relative brightness of the counter-jet suggests a visual extinction of 20-30 mag. The [Fe II] emissions from collimated jets are relatively strong toward L1551 NE and L1551 IRS 5 compared to those toward HL Tau and HH 30. This implies that the jets from the former objects, which are more embedded, have a higher shock velocity and/or a larger gas density than the latter, more revealed objects. The results presented here show that the near-infrared [Fe II] emission is a useful probe of well-collimated jets from deeply embedded sources, in much the same way that optical [S II] emission is used for relatively revealed objects.

NEAR-INFRARED IMAGING POLARIMETRY OF S106 CLUSTER-FORMING REGION WITH SIRPOL

We present the results of wide-field JHKS polarimetry toward the H ii region S106 using the Infrared Survey Facility telescope. Our polarimetry data revealed an extended (up to ∼5') polarized nebula over S106. We confirmed the position of the illuminating source of most of the nebula as consistent with S106 IRS 4 through an analysis of polarization vectors. The bright portion of the polarized intensity is consistent with the red wing component of the molecular gas. Diffuse polarized intensity emission is distributed along the north–south molecular gas lanes. We found the interaction region between the radiation from S106 IRS 4 and the dense gas. In addition, we also discovered two small polarization nebulae, SIRN 1 and SIRN 2, associated with a young stellar object (YSO). Aperture polarimetry of point-like sources in this region was carried out for the first time. The regional magnetic field structures were derived using point-like source aperture polarimetry, and the magnetic field structure position angle around the cluster region in S106 was found to be ∼120°. The magnetic fields in the cluster region, however, have three types of position angles: ∼20°, ∼80°, and ∼120°. The present magnetic field structures are consistent with results obtained by submillimeter continuum observations. We found that the magnetic field direction in the dense gas region is not consistent with that of the low-density gas region.

THE LOCAL ENVIRONMENT OF THE FU-ORIONIS-LIKE OBJECTS AR 6A AND 6B

We present new 12CO J = 3–2 and HCN J = 3–2 molecular line maps of the region surrounding the young star AR 6 using the 15 m James Clerk Maxwell Telescope (JCMT). AR 6 was previously found to be a double source with both components exhibiting several characteristics of FU Orionis (FUor) eruptive variable stars. The aims of this investigation were to determine if the AR 6 sources are associated with molecular outflows and if a significant reservoir of natal molecular gas and dust exists around the stars. These observations form a part of a large-scale study of the outflow and circumstellar environment characteristics of FUors and FUor-like objects to place constrains on the age and evolutionary state of sources exhibiting FUor-like tendencies. Our data indicate that AR 6, like FUor itself, does not possess a CO outflow and likewise, does not show evidence for large amounts of molecular gas in its circumstellar environment. In fact, AR 6 seems to lie in a local minimum of HCN emission. This is also found in 850 μm dust emission seen in JCMT archival data. We conclude that from the near-infrared to the sub-millimeter, AR 6 is similar to FUor in several respects. We interpret the lack of significant dust and molecular gas in the circumstellar environment of AR 6, together with the large near-infrared (NIR) thermal excess, as evidence that the sources have exhausted their natal envelopes, that they have at least small hot circumstellar disks, and that they are more evolved than Class I protostars. This, in itself, suggests that, since FUor eruptions have also been observed in stars with large dust mass envelopes (e.g., V346 Nor) and with CO outflows (e.g., L1551 IRS5), FUor events probably occur at many different stages in the early, formative phase of a star's life, and lends support to the idea that FUor outbursts are repetitive like their shorter-lived relatives occurring in EXor eruptive variables. Finally, we study the stellar environment around AR 6 using Two Micron All Sky Survey, Spitzer Infrared Array Camera, and Chandra ACIS images and show that, being part of the "Spokes" young stellar cluster, AR 6 is unlike many FUors which are typically located in more sparsely populated regions.

The nearest X-ray emitting protostellar jet (HH 154) observed with Hubble

Context. The jet coming from the YSO binary L1551 IRS5 is the closest astrophysical jet known. It is therefore a unique laboratory for studies of outflow mechanisms and of the shocks occurring when expanding material hits the ambient medium as well as of how the related processes influence the star- (and planet-) forming process. Aims. The optical data are related to other data covering the spectrum from the optical band to X-rays with goal of understanding the energetics of low-mass star jets, in general, and of this jet in particular. We study the time evolution of the jet, by measuring the proper motions of knots as they progress outwards from the originating source. Methods. The nebulosities associated with the jet(s) from the protostellar binary L1551 IRS5 were imaged in a number of spectral bands using the Hubble Space Telescope. This allows the proper motion to be measured and permits a simple characterization of the physical conditions in different structures. To this end we developed a reproducible method of data analysis, which allows us to define the position and shape of each substructure observed within the protostellar jet. Using this approach, we derive the proper motion of the knots in the jet, as well as their flux variability and shock emission. Results. The time base over which HST observations were carried out is now about ten years. The sub-structures within the jet undergo significant morphological variations: some knots seem to disappear in a few years and collision between different knots, ejected at different epochs and maybe with different speed, may occur. The velocities along the jet vary between ~100 km s -1 and over 400 km s -1 , with the highest speed corresponding to the knots at the base of the jet. Conclusions. There are indications that the HH 154 jet has been active relatively recently. Our results suggest the presence of a new shock front at the base of the jet identified with an internal working surface. From the analysis of the terminal and internal working surfaces within the jet, we find that the more likely scenario for the HH 154 jet is that of a jet traveling through a denser ambient medium (a “light jet”). These results are consistent with the Bonito et al. (2007) model predictions. Furthermore, there is strong evidence that the knots at the base of the northern jet correspond to the location where the highest velocity and the highest excitation component are measured along the jet. More important, this is the location where the X-ray source has been discovered.

Interacting jets from binary protostars

We investigate potential models that could explain why multiple proto-stellar systems predominantly show single jets. During their formation, stars most frequently produce energetic outflows and jets. However, binary jets have only been observed in a very small number of systems. We model numerically 3D binary jets for various outflow parameters. We also model the propagation of jets from a specific source, namely L1551 IRS 5, known to have two jets, using recent observations as constraints for simulations with a new MHD code. We examine their morphology and dynamics, and produce synthetic emission maps. We find that the two jets interfere up to the stage where one of them is almost destroyed or engulfed into the second one. We are able to reproduce some of the observational features of L1551 such as the bending of the secondary jet. While the effects of orbital motion are negligible over the jets dynamical timeline, their interaction has significant impact on their morphology. If the jets are not strictly parallel, as in most observed cases, we show that the magnetic field can help the collimation and refocusing of both of the two jets.

Imaging Scattered Light from the Youngest Protostars in L1448: Signatures of Outflows

We present deep IRAC images that highlight the scattered light emission around many of the youngest protostars, the so-called Class 0 sources, in L1448. By comparison of the data with a Monte Carlo radiative transfer code \citep{whitney2003a}, we demonstrate for the first time that the observed infrared light from these objects is consistent with scattered light from the central protostar. The scattered light escapes out the cavity, carved by molecular outflows, in the circumstellar envelope. In particular, we observe prominent scattered light nebulae associated with the Class 0 sources: L1448-mm, L1448 IRS 2, and 3B, as well as a Class I source: IRS 3A. We use a grid of models with probable protostellar properties to generate model spectral energy distributions (SEDs) and images for bands sensitive to this scattered light: J, H, Ks, and \textit{Spitzer} IRAC bands. By simultaneously fitting SEDs and images of the outflow cavities, we are able to model geometric parameters, i.e. inclination angle and opening angle, and loosely constrain physical parameters. The opening angle may be an important indicator of the evolutionary state of a source. We compare our results for Class 0 sources to similar studies of Class I sources. There may be a transition phase from Class 0 to Class I when a source has an opening angle between 20$^o$ to 30$^o$. It is important to note that while the best fit model image and SED do not fully describe the sources, the fits generally describe the circumstellar structure of Class 0 sources in L1448.

Properties and Formation of the Multiple Protostellar System L1551 IRS 5

We present an observation of L1551 IRS 5 at 7 mm with an angular resolution as high as ~004 (5 AU). Apart from the two main components oriented north-south with a projected separation of 47 AU, we discover a third component lying 13 AU to the southeast of the northern component, thereby making L1551 IRS 5 a triple protostellar system. The two main components comprise circumstellar dust disks with dimensions of ~17 AU, together with bipolar ionized jets collimated within a radial distance of 3 AU from their central protostars. The third component likely has an even smaller circumstellar dust disk with a dimension of ~9 AU. The relative proper motion of the two main components is consistent with a circular coplanar orbit with an orbital separation of ~50 AU, orbital period of ~380 yr, and total mass of ~0.9 M☉. Their measured disk sizes are smaller than the predicted gravitationally truncated sizes of ~26 AU. Together with the predicted minimum size for a circumbinary gap, noncircular coplanar orbits are constrained to an eccentricity 0.3. The disks of the two main components are accurately aligned with each other, as well as with a surrounding molecular pseudodisk. Furthermore, the clockwise orbital motion of these components coincides with the clockwise rotational motion of the pseudodisk. These attributes constitute a smoking gun for the formation of the two main components as a result of fragmentation within the inner regions of their parent pseudodisk. By contrast, the disk of the third component is significantly misaligned; measurements of its relative proper motion are required in order to help deduce its origin.

Methanol in the L1551 Circumbinary Torus

We report observations of gaseous methanol in an edge-on torus surrounding the young stellar object L1551 IRS 5. The peaks in the torus are separated by ~10,000 AU from L1551 IRS 5 and contain ~0.03 M⊕ of cold CH3OH. We infer that the CH3OH abundance increases in the outer part of the torus, probably as a result of methanol evaporation from dust grain surfaces heated by the shock luminosity associated with the shocks associated with the jets of an externally located X-ray source. Any methanol released in such a cold environment will rapidly freeze again, spreading CH3OH throughout the circumbinary torus to nascent dust grains, planetesimals, and primitive bodies. These observations probe the initial chemical conditions of matter infalling onto the disk.

An Equatorial Wind from the Massive Young Stellar Object S140 IRS 1

The discovery of the second equatorial ionized stellar wind from a massive young stellar object is reported. High-resolution radio continuum maps of S140 IRS 1 reveal a highly elongated source that is perpendicular to the larger scale bipolar molecular outflow. This picture is confirmed by location of a small-scale monopolar near-IR reflection nebula at the base of the blueshifted lobe. A second epoch of observations over a 5 yr baseline show little ordered outward proper motion of clumps as would have been expected for a jet. A third epoch, taken only 50 days after the second, did show significant changes in the radio morphology. These radio properties can all be understood in the context of an equatorial wind driven by radiation pressure from the central star and inner disk acting on the gas in the surface layers of the disk as proposed by Drew et al. This equatorial wind system is briefly compared with the one in S106 IR, and contrasted with other massive young stellar objects that drive ionized jets.

A Mid-Infrared Study of the Class 0 Cluster in LDN 1448

We present ground-based mid-infrared observations of Class 0 protostars in LDN 1448. Of the five known protostars in this cloud, we detected two, L1448N:A and L1448C, at 12.5, 17.9, 20.8, and 24.5 μm, and a third, L1448 IRS 2, at 24.5 μm. We present high-resolution images of the detected sources and photometry or upper limits for all five Class 0 sources in this cloud. With these data we are able to augment existing spectral energy distributions for all five objects and place them on an evolutionary status diagram.

A Cool Magnetized Shell Wrapped around the Hot HiiRegion S106: Geometry, Kinematics, Magnetic Vectors, and Pressure Balance

In the optical, the exciting star S106 IR resides in a conspicuous dust lane and it ionizes two bright, sharp gas lobes on both sides of the dust lane. Wrapped around this hot (10,000 K) ionized (H II) optical bipolar nebula (the two gas lobes), we see a cool shell in the millimeter-submillimeter radio. Outside the cool shell, there is an even colder (<22 K), large (20' = 4 pc), lower density molecular cloud. In this paper, we study the cool gas (spectroscopy in three lines), the cool dust (continuum imaging), and the magnetic field (polarimetry) in the shell, all made near a wavelength of 850 μm with the same angular resolution of 14'' using the James Clerk Maxwell Telescope (JCMT). Near a radial velocity of -1 km s-1, we used 12CO, 13CO, and C18O in the J = 3-2 lines to map the cool (32 K) gas in the shell peaks on both sides of the hot cavity walls, extending 2' (0.4 pc) in north-south length with a 100'' (0.3 pc) east-west diameter. Also, we used dust continuum emission and its linear polarization to map the cool shell. For the vertical cool shell, sandwiched between a hot region and a colder cloud, we find that the shell's combined pressure (made up mostly of turbulence and total magnetic field) can withstand the turbulent and thermal pressure of the hot ionized outflow, although the cool gas shell is slowly being eroded by the ionization process going on. The large-scale magnetic field appears roughly vertical along the roughly vertical gas shell. The magnetic field in the vertical shell (away from the central dust lane) has an estimated value near 400 μG. In the horizontal dust lane, the magnetic field appears roughly horizontal and parallel to the dust lane encompassing the IR and FIR components. Here the magnetic field derived from various methods has an estimated plane-of-sky median value near 570 μG, while the previously published Zeeman data indicated a line-of-sight strength near +240 μG.

X-Ray and Near-Infrared Studies of the Star-forming Cloud L1448

We present the results of X-ray and near-infrared (NIR) observations of L1448, a star-forming region in the Perseus cloud complex using the Chandra X-Ray Observatory and the 4 m telescope at the Kitt Peak National Observatory. We detect 72 X-ray sources in a ~17' × 17' region with a ~68 ks ACIS exposure down to the X-ray flux limit of ~ 10-15 ergs s-1 cm-2 (0.5–8 keV), for which we conduct follow-up NIR imaging observations in a concentric ~11' × 11' region with FLAMINGOS down to m ~ 17 mag. Twelve X-ray sources have NIR or optical counterparts. By plotting X-ray mean energy versus the NIR-to-X-ray flux ratio, the X-ray sources are clearly separated into two groups. The X-ray spectral and temporal features, as well as NIR magnitudes and colors, indicate that one group mainly consists of young stellar objects (YSOs) in the cloud and the other of background extragalactic sources. Ten X-ray-emitting YSO candidates are thus newly identified as low-mass or brown dwarf mass sources from their NIR magnitudes. In addition, a possible X-ray signal is found from a midinfrared protostar, L1448 IRS 3(A). The lack of detection of this source in our deep NIR images indicates that this source has a very steep spectral slope of 3.2 in the 2–10 μm wavelength range.

THE MULTIPLE PROTO STELLAR SYSTEM L1551 IRS5 AT 5 AU RESOLUTION

We present images of L1551 IRS5 at angular resolutions as high as <TEX>${\~}$</TEX>30 mas, corresponding to a spatial resolution of <TEX>${\~}$</TEX>5 AU, made at 7 mm with the VLA. Previously known to be a binary protostellar system, we show that L1551 IRS5 is likely a triple protostellar system. The primary and secondary components have a projected separation of <TEX>${\~}$</TEX>46 AU, whereas the tertiary component has a projected separation of <TEX>${\~}$</TEX>11 AU from the primary component. The circumstellar dust disks of the primary and secondary components have dimensions of <TEX>${\~}$</TEX>15 AU, whereas that of the tertiary component has a dimension of <TEX>${\~}$</TEX>10 AU. Their major axes are closely, but not perfectly, aligned with each other, as well as the major axis of the surrounding flattened, rotating, and contracting molecular condensation (pseudodisk). Furthermore, the orbital motion of the primary and secondary components is in the same direction as the rotational motion of this pseudodisk. We suggest that all three protostellar components formed as a result of the fragmentation of the central region of the molecular pseudo disk. The primary and secondary components, but apparently not the tertiary component, each exhibits a bipolar ionized jet that is centered on and which emergers perpendicular to its associated dust disk. Neither jets are resolved along their base, implying that they are driven within a radial distance of <TEX>${\~}$</TEX>2.5 AU from their central protostars. Finally, we show evidence for what may be dusty matter streams feeding the two main protostellar components.

HST and spectroscopic observations of the L1551 IRS5 jets (HH154)

We have carried out a thorough optical study of the closest star formation jet. The inner arcminute surrounding the class 0/I binary protostar L1551 IRS5 and its associated jet (HH154) have been observed using the Hubble Space Telescope with the WFPC2 camera, the ESO New Technology Telescope with the EMMI spectrograph and the Nordic Optical Telescope with the ALFOSC spectrograph. This data set is compared to earlier ground based imaging with the aim to study the evolution of this particular jet, and its possible interaction with the molecular material in the bipolar molecular outflow associated with this source. The velocity field of the jet is mapped out. The highest velocities are found in the vicinity of the recently discovered X-ray source emanating from a shock in this jet. The energy radiated by the X-ray source is compatible with these velocities. The Hα and Hβ emission from the jet is used to determine the extinction, which is found to increase inwards in the jet towards the protostar. The extinction towards the X-ray source is consistent with the one determined from the X-ray spectrum.

New results on the massive star-forming region S106 by BEAR spectro-imagery

As a typical example of interaction of a massive star with its parent cloud, the close environment of S106 IR in the star-forming region S106 was observed at high spectral resolution (~16 km s -1 ). Integral field spectroscopy with BEAR, an imaging Fourier Transform Spectrometer (FTS), on a field of ~40´´in diameter, in the H 2 1–0 S (1), 2–1 S (1), Br γ , $\ion{He}{i}$ and [$\ion{Fe}{iii}$] lines. From the data several maps were obtained: intensity, velocity and linewidth in the Br γ and the H 2 1–0 S (1) line, 1–0 S (1)/2–1 S (1) line ratio, and continuum emission at 2.1 μ m. From the latter, about twenty low-mass stars were detected with photometry in this band, and an estimate of their mass was made leading to the conclusion that S106 is a site of formation of mainly sub-solar mass stars. The intensity structure of the excited molecular gas H 2 was found to be clumpy while the velocity is almost uniformely at $v_{{\rm LSR}}$ $\simeq$ 1.5 km s -1 except to the south where the velocity reaches up to 15 km s -1 in a zone limited by the long edge of a rectangular hole in the emission. The H 2 line ratio map with values from 1 to 9 implies that UV-absorption and shocks are participating in the excitation process. A PDR model with a temperature of 3700 K for S106 IR was used to retrieve the H 2 gas density and temperature. The density was found to vary between 1 and 3.5 $\times$ 10 5 cm -3 with corresponding temperatures between 660 and 1240 K. The study of the linewidth distribution indicates for most of the gas a supersonic turbulence with a mean contribution to the observed profiles of ≥ 6 km s -1 . Turbulence is likely to be responsible for the observed clumpy structure of the excited gas. Point-like spots with a linewidth as high as 30 km s -1 in one position are detected, which may be vortices in the molecular gas. The $\ion{H}{ii}$ region probed by Br γ shows a broad range of velocity, from -45 to +80 km s -1 , organized in velocity structures that correspond to two pairs of large, bipolar outflows originating from the massive source, not directed along the axis of the $\ion{H}{ii}$ region. Emission lines of $\ion{He}{i}$ and [$\ion{Fe}{iii}$] are detected in a bright area to the southwest of S106 IR, with point-like structures suggesting photoevaporating clumps. From the velocity data, a 3-D model of the environment of S106 IR is proposed. S106 is an example of an evolved $\ion{H}{ii}$ region seen face-on. The central source located at the edge of its parent molecular cloud has carved an expanding cylinder of turbulent, atomic gas of $\simeq$0.1 pc in radius. This massive object was formed by an accretion disk process. The disk is still present and the bipolar outflows are remnants of the massive star activity. A time scale of 1400 yr is estimated for the most recent event. A thin and quiescent clumpy layer of warm H 2 marks the transition of the $\ion{H}{ii}$ region to the molecular cloud. From the data, there are locally no signs of ongoing star formation.