Bright-rimmed Clouds Research Articles

Bright-rimmed clouds in IC 1396

Aims. We investigate the dynamical and physical structures of bright-rimmed clouds (BRCs) in a nearby H II region. We focused on carbon- and oxygen-bearing species that trace photon-dominated regions (PDRs) and warm molecular cloud surfaces in order to understand the effect of UV radiation from the exciting stars on the cloud structure. Methods. We mapped four regions around the most prominent BRCs at scales of 4–10 arcmin in the H II region IC 1396 (IC 1396A, B, D, and E) in [C II] 158 µm with (up)GREAT on board SOFIA. IC 1396 is predominantly excited by an O6.5V star. Toward IC 1396A, we also observed [O I] 63 µm and 145 µm. We combined these observations with JCMT archive data, which provide the low-J transitions of CO, 13CO, and C18O. All spectra are velocity-resolved. Results. The line profiles in the four mapped regions show a variety of velocity structures, which we investigated in detail for all observed emission lines. IC 1396B and D show clearly distinct velocity components that overlap along the line of sight. We find no clear sign of photoevaporating flows in the [C II] spectra, although the uncertainty in the location of the BRCs along the line of sight makes this interpretation inconclusive. Our analysis of the [13C II] emission in IC1396 A, which has the best signal-to-noise ratio, suggests that the [C II] is likely mostly optically thin. The heating efficiency, measured by the ([C II]+[O I] 63 µm)/far-infrared intensity ratio, is higher in the northern part of IC 1396A than in the southern part, which may indicate a difference in the dust properties of the two areas. Conclusions. The complex velocity structures identified in the BRCs of IC 1396, which is apparently a relatively simple H II region, highlight the importance of velocity-resolved data for disentangling different components along the line of sight and thus facilitating a detailed study of the dynamics of the cloud. We also demonstrate that the optically thin [13C II] and [O I] 145 µm emission lines are essential for a conclusive interpretation of the [C II] 158 µm and [O I] 63 µm line profiles.

Optical polarimetry study of the Lambda-Orionis star-forming region

We present an optical polarimetry study of the nearby star-forming region Lambda-Orionis to map the plane-of-the-sky magnetic field geometry to understand the magnetized evolution of the HII region and the associated small molecular clouds. We made multiwavelength polarization observations of 34 bright stars distributed across the region. We also present the R-band polarization measurements that focused on the small molecular clouds, bright-rimmed clouds (BRC), BRC 17, and BRC 18, which are located at the periphery of the HII region. The magnetic field lines exhibit a large-scale ordered orientation consistent with the Planck submillimeter polarization measurements. The magnetic field lines in the two BRCs are found to be roughly in north-south directions. However, a larger dispersion is noted in the orientation for BRC 17 compared to BRC 18. Using a structure-function analysis, we estimate the strength of the plane-of-the-sky component of the magnetic field as ∼28 μG for BRC 17 and ∼40 μG for BRC 18. The average dust grain size and the mean value of the total-to-selective extinction ratio (RV) in the HII region are found to be ∼0.51 ± 0.05 μm and ∼2.9 ± 0.3, respectively. The distance of the whole HII region is estimated as ∼392 ± 8 pc by combining astrometry information from Global Astrometric Interferometer for Astrophysics (Gaia) early data release 3 (EDR3) for young stellar objects associated with BRCs and confirmed members of the central cluster Collinder 69.

Unveiling the Cosmic Cradle: clustering and massive star formation in the enigmatic Galactic bubble N59

ABSTRACT In this paper, we have conducted an investigation focused on a segment of the Spitzer mid-infrared bubble N59, specifically referred to as R1 within our study. Situated in the inner Galactic plane, this region stands out for its hosting of five 6.7 GHz methanol masers, as well as numerous compact $\mathrm{H}\, \rm {{\small II}}$ regions, massive clumps, filaments, and prominent bright rims. As 6.7 GHz masers are closely linked to the initial phases of high-mass star formation, exploring regions that exhibit a high abundance of these maser detections provides an opportunity to investigate relatively young massive star-forming sites. To characterize the R1 region comprehensively, we utilize multiwavelength (archival) data from optical to radio wavelengths, together with 13CO and C18O data. Utilizing the Gaia DR3 data, we estimate the distance towards the bubble to be 4.66 ± 0.70 kpc. By combining near-infrared (NIR) and mid-infrared (MIR) data, we identify 12 Class I and 8 Class II sources within R1. Furthermore, spectral energy distribution (SED) analysis of selected sources reveals the presence of four embedded high-mass sources with masses ranging from 8.70 to 14.20 M⊙. We also identified several O and B-type stars from radio continuum analysis. Our molecular study uncovers two distinct molecular clouds in the region, which, although spatially close, occupy different regions in velocity space. We also find indications of a potential hub-filament system fostering star formation within the confines of R1. Finally, we propose that the feedback from the $\mathrm{H}\, \rm {{\small II}}$ regions has led to the formation of prominent Bright Rimmed Clouds (BRCs) within our region of interest.

ATOMS: ALMA three-millimeter observations of massive star-forming regions – XIII. Ongoing triggered star formation within clump-fed scenario found in the massive (∼1500 M⨀) clump

ABSTRACT Whether ionization feedback triggers the formation of massive stars is highly debated. Using ALMA 3-mm observations with a spatial resolution of ∼0.05 pc and a mass sensitivity of 1.1 $\rm M_\odot$ per beam at 20 K, we investigate the star formation and gas flow structures within the ionizing feedback-driven structure, a clump-scale massive (≳ 1500 $\rm M_\odot$) bright-rimmed cloud (BRC) associated with IRAS 18290–0924. This BRC is bound only if external compression from ionized gas is considered. A small-scale (≲ 1 pc) age sequence along the direction of ionizing radiation is revealed for the embedded cores and protostars, which suggests triggered star formation via radiation-driven implosion (RDI). Furthermore, filamentary gas structures converge towards the cores located in the BRC’s centre, indicating that these filaments are fueling mass towards cores. The local core-scale mass infall rate derived from H13CO+ J = 1 − 0 blue profile is of the same order of magnitude as the filamentary mass inflow rate, approximately 1 $\rm M_\odot$ kyr−1. A photodissociation region (PDR) covering the irradiated clump surface is detected in several molecules, such as CCH, HCO+, and CS whereas the spatial distribution stratification of these molecules is indistinct. CCH spectra of the PDR possibly indicate a photoevaporation flow leaving the clump surface with a projected velocity of ∼2 km s−1. Our new observations show that RDI accompanied by a clump-fed process is operating in this massive BRC. Whether this combined process works in other massive BRCs is worth exploring with dedicated surveys.

NIR spectroscopic survey of protostellar jets in the star-forming region IC 1396N

Context. The bright-rimmed cloud IC 1396N, associated with an intermediate-mass star-forming region, hosts a number of CO, molecular hydrogen, and Herbig-Haro (HHs) outflows powered by a set of millimetre compact sources. Aims. The aim of this work is to characterise the kinematics and physical conditions of the H2 emission features spread throughout the IC 1396N region. The features appear as chains of knots with a jet-like morphology and trace different H2 outflows. We also obtain further information about (and an identification of) the driving sources. Methods. Low-resolution, long-slit near-infrared spectra were acquired with the NICS camera at the TNG telescope, using grisms KB (R ~ 1200), HK, and JH (R ~ 500). Several slit pointings and position angles were used throughout the IC 1396N region in order to sample a number of the H2 knots that were previously detected in deep H2 2.12 μm images. Results. The knots exhibit rich ro–vibrational spectra of H2, consistent with shock-excited excitation, from which radial velocities and relevant physical conditions of the IC 1396N H2 outflows were derived. These also allowed estimating extinction ranges towards several features. [Fe ii] emission was only detected towards a few knots that also display unusually high H2 1–0 S(3)/S(1) flux ratios. The obtained radial velocities confirm that most of the outflows are close to the plane of the sky. Nearby knots in the same chain often display different radial velocities, both blue–shifted and red–shifted, which we interpret as due to ubiquitous jet precession in the driving sources or the development of oblique shocks. One of the chains (strand A, i.e. knots A1 to A15) appears as a set of features trailing a leading bow-shock structure consistent with the results of 3D magneto-hydrodynamical models. The sides of the leading bow shock (A15) exhibit different radial velocities. We discuss possible explanations. Our data cannot confirm whether strands A and B have both originated in the intermediate mass young stellar object [BGE2002] BIMA 2 because a simple model of a precessing jet cannot account for their locations. Conclusions. Near-infrared spectroscopy has confirmed that most of the H2 ro-vibrational emission in IC 1396N is shock-excited rather than uv-excited in photon-dominated regions. It has shown a complex kinematical structure in most strands of emitting knots as well.

Collision of protostellar jets in the star-forming region IC 1396N

Context. The bright-rimmed cloud IC 1396N is believed to host one of the few known cases where two bipolar CO outflows driven by young stellar objects collide. The CO outflows are traced by chains of knots of H2 emission, with enhanced emission at the position of the possible collision. Aims. The aim of this work is to use the proper motions of the H2 knots to confirm the collision scenario. Methods. A second-epoch H2 image was obtained, and the proper motions of the knots were determined with a time baseline of ~11 yr. We also performed differential photometry on the images to check the flux variability of the knots. Results. For each outflow (N and S), we classified the knots as pre-collision or post-collision. The axes of the pre-collision knots, the position of the possible collision point, and the axes of the post-collision knots were estimated. The difference between the proper motion direction of the post-collision knots and the position angle from the collision point was also calculated. For some of the knots, we obtained the 3D velocity using the radial velocity derived from H2 spectra. Conclusions. The velocity pattern of the H2 knots in the area of interaction (post-collision knots) shows a deviation from that of the pre-collision knots, consistent with being a consequence of the interaction between the two outflows. This favours the interpretation of the IC 1396N outflows as a true collision between two protostellar jets instead of a projection effect.

Diagnosing Triggered Star Formation in the Galactic H ii region Sh 2-142

Abstract Stars are formed by gravitational collapse, spontaneously or, in some cases under the constructive influence of nearby massive stars, out of molecular cloud cores. Here we present an observational diagnosis of such triggered formation processes in the prominent H ii region Sh 2-142, which is associated with the young star cluster NGC 7380, and with some bright-rimmed clouds as the signpost of photoionization of molecular cloud surfaces. Using near- (2MASS) and mid-infrared (WISE) colors, we identified candidate young stars at different evolutionary stages, including embedded infrared sources having spectral energy distributions indicative of active accretion. We have also used data from our optical observations to be used in SEDs, and from Gaia EDR3 to study the kinematics of young objects. With this young stellar sample, together with the latest CO line emission data (spectral resolution ∼0.16 km s−1, sensitivity ∼0.5 K), a positional and aging sequence relative to the neighboring cloud complex, and to the bright-rimmed clouds, is inferred. The propagating stellar birth may be responsible, at least partially, for the formation of the cluster a few million years ago, and for the ongoing activity now witnessed in the cloud complex.

APEX CO observations towards the photodissociation region of RCW 120

Context. The edges of ionized (H II) regions are important sites for the formation of (high-mass) stars. Indeed, at least 30% of the Galactic high-mass-star formation is observed there. The radiative and compressive impact of the H II region could induce star formation at the border following different mechanisms such as the collect and collapse or the radiation-driven implosion (RDI) models and change their properties. Aims. We aim to study the properties of two zones located in the photo dissociation region (PDR) of the Galactic H II region RCW 120 and discuss them as a function of the physical conditions and young star contents found in both clumps. Methods. Using the APEX telescope, we mapped two regions of size 1.5′ × 1.5′ toward the most massive clump of RCW 120 hosting young massive sources and toward a clump showing a protrusion inside the H II region and hosting more evolved low-mass sources. The 12CO (J = 3−2), 13CO (J = 3−2) and C18O (J = 3−2) lines observed, together with Herschel data, are used to derive the properties and dynamics of these clumps. We discuss their relation with the hosted star formation. Results. Assuming local thermodynamic equilibrium, the increase of velocity dispersion and Tex are found toward the center of the maps, where star-formation is observed with Herschel. Furthermore, both regions show supersonic Mach numbers (7 and 17 in average). No substantial information has been gathered about the impact of far ultraviolet radiation on C18O photodissociation at the edges of RCW 120. The fragmentation time needed for CC to be at work is equivalent to the dynamical age of RCW 120 and the properties of region B are in agreement with bright-rimmed clouds. Conclusions. Although conclusions from this fragmentation model should be taken with caution, it strengthens the fact that, together with evidence of compression, CC might be at work at the edges of RCW 120. Additionally, the clump located at the eastern part of the PDR is a good candidate pre-existing clump where star-formation may be induced by the RDI mechanism.

Spectroscopic Survey of H<i>α</i> Emission Line Stars Associated with Bright Rimmed Clouds

The results of a spectroscopic survey of H alpha emission line stars associated with fourteen bright rimmed clouds are presented. Slit-less optical spectroscopy was carried out with the Inter University Centre for Astronomy and Astrophysics (IUCAA) 2m telescope and IUCAA Faint Object Spectrograph and Camera (IFOSC). H alpha emission line was detected from 173 objects. Among them 85 objects have a strong H alpha emission line with its equivalent width larger than 10 A. Those are classical T Tauri stars. 52 objects have a weak H alpha emission line with its equivalent width less than 10 A and do not show intrinsic near-infrared excess. Those are weak-line T Tauri stars. On the other hand, 36 objects have a weak H alpha emission line (<10 A), although they show intrinsic near-infrared excess. Such objects are not common in low-mass star forming regions. Those are misfits of the general concept on formation process of a low-mass star, in which it evolves from a classical T Tauri star to a weak-line T Tauri star. Those might be weak-line T Tauri stars with a flared disk in which gas is heated by ultraviolet radiation from a nearby early-type star. Alternatively, we propose pre-transitional disk objects as their evolutional stage.

FOREST Unbiased Galactic Plane Imaging Survey with the Nobeyama 45 m telescope (FUGIN). IV. Galactic shock wave and molecular bow shock in the 4 kpc arm of the Galaxy

AbstractThe FUGIN CO survey revealed the three-dimensional structure of a galactic shock wave in the tangential direction of the 4 kpc molecular arm. The shock front is located at G30.5+00.0 + 95 km s−1 on the upstream (lower longitude) side of the star-forming complex W 43 (G30.8−0.03), and comprises a molecular bow shock (MBS) concave to W 43, exhibiting an arc-shaped molecular ridge perpendicular to the galactic plane with width ∼0${^{\circ}_{.}}$1(10 pc) and vertical length ∼1° (100 pc). The MBS is coincident with the radio continuum bow of thermal origin, indicating association of ionized gas and similarity to a cometary bright-rimmed cloud. The upstream edge of the bow is sharp, with a growth width of ∼0.5 pc indicative of the shock front property. The velocity width is ∼10 km s−1, and the center velocity decreases by ∼15 km s−1 from the bottom to the top of the bow. The total mass of molecular gas in the MBS is estimated to be ∼1.2 × 106 M⊙, and ionized gas ∼2 × 104 M⊙. The vertical disk thickness has a step-like increase at the MBS by ∼2 times from lower to upper longitudes, which indicates hydraulic jump in the gaseous disk. We argue that the MBS was formed by the galactic shock compression of an accelerated flow in the spiral-arm potential encountering the W 43 molecular complex. A bow-shock theory can reproduce the bow morphology well. We argue that molecular bows are common in galactic shock waves, not only in the Galaxy but also in galaxies, where MBSs are associated with giant cometary H ii regions. We also analyzed the H i data in the same region to obtain a map of H i optical depth and molecular fraction. We found firm evidence of the H i to H2 transition in the galactic shock as revealed by a sharp molecular front at the MBS front.

Magnetic fields in multiple bright-rimmed clouds in different directions of H ii region IC 1396

Bright-rimmed clouds form on the edges of H II regions affected by the high energy radiation from a central ionizing source. The UV radiation from the ionizing source results in compression and ionization causing either cloud disruption or further star formation. In this work, we present R-band polarization measurements towards four bright-rimmed clouds, IC1396A, BRC 37, BRC 38, and BRC 39, located in the different directions of the H II region, Sh2-131, in order to map magnetic fields (B-fields) in the plane of the sky. These BRCs are illuminated by the O star HD206267 and present a range of projected on sky geometries. This provides an opportunity to understand the magnetized evolution of BRCs. The B-field geometries of the clouds deduced from the polarization data, after correction for foreground ISM contamination, are seen to be connected to the ambient B-fields on the large scale. They seem to play an important role in shaping the cloud IC1396A and BRC 37. BRCs 38 and 39 show a broader and snubber head morphology possibly due to the B-fields being aligned with incoming radiation as explained in the simulations. A good general agreement is noted on comparing our observational results with the simulations supporting the importance of B-fields in BRC evolution. This work is the first step towards systematic mapping the B-fields morphology in multiple BRCs in an expanding H II region, extending the work presented by Soam et al. (2017b).

A highly embedded protostar in SFO 18: IRAS 05417+0907

Bright-rimmed clouds, located at the periphery of relatively evolved HIT regions, are considered to be the sites of star formation possibly triggered by the implosion caused due to the ionizing radiation from nearby massive stars. SFO 18 is one such region showing a bright-rim on the side facing the 0-type star, A Ori. A point source, IRAS 05417+0907, is detected towards the high density region of the cloud. A molecular outflow has been found to be associated with the source. The outflow is directed towards a Herbig-Haro object, HH 175. From the Spitzer and WISE observations, we show evidence of a physical connection between the molecular outflow, IRAS 05417+0907 and the HH object. The spectral energy distribution constructed using multi-wavelength data shows that the point source is most likely a highly embedded protostar.

YSO Jets in the Galactic Plane from UWISH2. IV. Jets and Outflows in Cygnus-X

Abstract We have performed an unbiased search for outflows from young stars in Cygnus-X using 42 deg2 of data from the UKIRT Widefield Infrared Survey for H2 (UWISH2 Survey), to identify shock-excited near-IR H2 emission in the 1–0 S(1) 2.122 μm line. We uncovered 572 outflows, of which 465 are new discoveries, increasing the number of known objects by more than 430%. This large and unbiased sample allows us to statistically determine the typical properties of outflows from young stars. We found 261 bipolar outflows, and 16% of these are parsec scale. The typical bipolar outflow is 0.45 pc in length and has gaps of 0.025–0.1 pc between large knots. The median luminosity in the 1–0 S(1) line is 10−3 . The bipolar flows are typically asymmetrical, with the two lobes misaligned by 5°, one lobe 30% shorter than the other, and one lobe twice as bright as the other. Of the remaining outflows, 152 are single-sided and 159 are groups of extended, shock-excited H2 emission without identifiable driving sources. Half of all driving sources have sufficient WISE data to determine their evolutionary status as either protostars (80%) or classical T Tauri stars (20%). One-fifth of the driving sources are variable by more than 0.5 mag in the K-band continuum over several years. Several of the newly identified outflows provide excellent targets for follow-up studies. We particularly encourage the study of the outflows and young stars identified in a bright-rimmed cloud near IRAS 20294+4255, which seems to represent a textbook example of triggered star formation.

High-resolution Near-infrared Observations of a Small Cluster Associated with a Bright-rimmed Cloud in W5

Abstract We carried out near-infrared (IR) observations to examine star formation toward the bright-rimmed cloud SFO 12, of which the main exciting star is O7V star in W5-W. We found a small young stellar object (YSO) cluster of six members embedded in the head of SFO 12 facing its exciting star, aligned along the UV radiation incident direction from the exciting star. We carried out high-resolution near-IR observations with the Subaru adaptive optics (AO) system and revealed that three of the cluster members appear to have circumstellar envelopes, one of which shows an arm-like structure in its envelope. Our near-IR and -band photometry and Spitzer IRAC data suggest that formation of two members at the tip side occurred in advance of other members toward the central part, under our adopted assumptions. Our near-IR data and previous studies imply that more YSOs are distributed in the region just outside the cloud head on the side of the main exciting star, but there is little sign of star formation toward the opposite side. We infer that star formation has been sequentially occurring from the exciting star side to the central part. We examined archival data of far-infrared and CO ( ) which reveals that, unlike in the optical image, SFO 12 has a head–tail structure that is along the UV incident direction. This suggests that SFO 12 is affected by strong UV from the main exciting star. We discuss the formation of this head–tail structure and star formation there by comparing with a radiation-driven implosion (RDI) model.

A COMPREHENSIVE SEARCH FOR STELLAR BOWSHOCK NEBULAE IN THE MILKY WAY: A CATALOG OF 709 MID-INFRARED SELECTED CANDIDATES

ABSTRACT We identify 709 arc-shaped mid-infrared nebula in 24 μm Spitzer Space Telescope or 22 μm Wide Field Infrared Explorer surveys of the Galactic Plane as probable dusty interstellar bowshocks powered by early-type stars. About 20% are visible at 8 μm or at shorter mid-infrared wavelengths. The vast majority (660) have no previous identification in the literature. These extended infrared sources are strongly concentrated near the Galactic mid-plane, with an angular scale height of ∼0.°6. All host a symmetrically placed star implicated as the source of a stellar wind sweeping up interstellar material. These are candidate “runaway” stars potentially having high velocities in the reference frame of the local medium. Among the 286 objects with measured proper motions, we find an unambiguous excess with velocity vectors aligned with the infrared morphology—kinematic evidence that many of these are “runaway” stars with large peculiar motions responsible for the bowshock signature. We discuss a population of “in situ” bowshocks (∼103 objects) that face giant H ii regions where the relative motions between the star and ISM may be caused by bulk outflows from an overpressured bubble. We also identify ∼58 objects that face 8 μm bright-rimmed clouds and apparently constitute a sub-class of in situ bowshocks where the stellar wind interacts with a photoevaporative flow (PEF) from an eroding molecular cloud interface (i.e., “PEF bowshocks”). Orientations of the arcuate nebulae exhibit a correlation over small angular scales, indicating that external influences such as H ii regions are responsible for producing some bowshock nebulae. However, the vast majority of the nebulae in this sample appear to be isolated (499 objects) from obvious external influences.

Magnetic field structure of IC 63 and IC 59 associated with H ii region Sh 185

Bright-rimmed clouds (BRCs) are formed at the periphery of H$~$II regions as the radiation from the central star interacts with dense gas. The ionization and resulting compression of the clouds may lead to cloud disruption causing secondary star formation depending on the stellar and gas parameters. Here we use R-band polarimetry to probe the plane-of-the sky magnetic field in the two near-by BRCs IC\,59 and IC\,63. Both nebulae are illuminated by $\gamma$ Cas with the direction of ionizing radiation being orientated parallel or perpendicular to the local magnetic field, allowing us to probe the importance of magnetic field pressure in the evolution of BRCs. Because of the proximity of the system ($\sim$200pc) we have acquired a substantial sample of over 500 polarization measurements for stars background to the nebulae. On large scales, the magnetic field geometries of both clouds are anchored to the ambient magnetic field. For IC 63, the magnetic field is aligned parallel to the head-tail morphology of the main condensation, with convex morphology relative to the direction of the ionizing radiation. We estimate the plane of the sky magnetic field strength in IC\,63 to be $\sim90\mu$G. In IC\,59, the projected magnetic field follows the M shape morphology of the cloud. Here, field lines present a concave shape with respect to the direction of the ionizing radiation from $\gamma$ Cas. Comparing our observations to published theoretical models we find good general agreement, supporting the importance of magnetic fields in BRC evolution.

The JCMT Gould Belt Survey: evidence for radiative heating and contamination in the W40 complex

We present SCUBA-2 450{\mu}m and 850{\mu}m observations of the W40 complex in the Serpens-Aquila region as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) of nearby star-forming regions. We investigate radiative heating by constructing temperature maps from the ratio of SCUBA-2 fluxes using a fixed dust opacity spectral index, {\beta} = 1.8, and a beam convolution kernel to achieve a common 14.8" resolution. We identify 82 clumps ranging between 10 and 36K with a mean temperature of 20{\pm}3K. Clump temperature is strongly correlated with proximity to the external OB association and there is no evidence that the embedded protostars significantly heat the dust. We identify 31 clumps that have cores with densities greater than 105cm{^{-3}}. Thirteen of these cores contain embedded Class 0/I protostars. Many cores are associated with bright-rimmed clouds seen in Herschel 70 {\mu}m images. From JCMT HARP observations of the 12CO 3-2 line, we find contamination of the 850{\mu}m band of up to 20 per cent. We investigate the free-free contribution to SCUBA-2 bands from large-scale and ultracompact H ii regions using archival VLA data and find the contribution is limited to individual stars, accounting for 9 per cent of flux per beam at 450 {\mu}m or 12 per cent at 850 {\mu}m in these cases. We conclude that radiative heating has potentially influenced the formation of stars in the Dust Arc sub-region, favouring Jeans stable clouds in the warm east and fragmentation in the cool west.

STRUCTURAL STUDIES OF EIGHT BRIGHT RIMMED CLOUDS IN THE SOUTHERN HEMISPHERE

ABSTRACT We carried out deep- and wide-field near- and mid-infrared observations for a sample of eight bright-rimmed clouds (BRCs). Supplemented with the Spitzer archival data, we have identified and classified 44 to 433 young stellar objects (YSOs) associated with these BRCs. The Class I sources are generally located toward the places with higher extinction and are relatively closer to each other than the Class II sources, confirming that the young protostars are usually found in regions with denser molecular material. On the other hand the comparatively older population, Class II objects, are more randomly found throughout the regions, which can be due to their dynamical evolution. Using the minimal sampling tree analyses, we have extracted 13 stellar cores of eight or more members, which contain 60% of the total YSOs. The typical core is ∼0.6 pc in radii and somewhat elongated (aspect ratio of 1.45), of relatively low stellar density (surface density 60 pc−2), consisting of a small (35) number of YSOs of relatively young sources (66% Class I), and partially embedded (median A K = 1.1 mag). But the cores show a wide range in their mass distribution (∼20 to 2400 M ⊙), with a median value of around 130 M ⊙. We found the star-formation efficiencies in the cores to be between 3% and 30% with an average of ∼14%, which agrees with the efficiencies needed to link the core mass function to the initial mass function. We also found a linear relation between the density of the clouds and the number of YSOs. The peaked nearest neighbor spacing distributions of the YSOs and the ratio of Jeans lengths to the YSO separations indicates a significant degree of non-thermally driven fragmentation in these BRCs.

Study of a bright-rimmed cloud at the border of the infrared dust bubble CN20

Fil: Ortega, Martin Eduardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina

A Study of Magnetic Fields on Bright-Rimmed Clouds

AbstractWe have made near-infrared (JHKs) imaging polarimetry toward 24 bright-rimmed clouds in the southern hemisphere in order to reveal their magnetic field structures. The obtained polarization vector maps show that the magnetic field directions inside the bright rim are different from its ambient magnetic field direction, implying that magnetic field structures just inside the ionized front of the clouds are due to the gas compression by UV radiation from nearby massive star. Our investigation into the relation between the magnetic field configuration and the shape of the cloud suggests that the magnetic field configuration affects the evolution of the cloud shape.