H2flows in the Corona Australis cloud and their driving sources

We present the results of a narrow-band near-infrared imaging survey for Molecular Hydrogen emission-line Objects (MHOs) toward 26 regions containing high-mass protostellar candidates and massive molecular outflows. We have detected a total of 236 MHOs, 156 of which are new detections, in 22 out of the 26 regions. We use H2 2.12 μm/H2 2.25 μm flux ratios, together with morphology, to separate the signatures of fluorescence associated with photo-dissociation regions (PDRs) from shocks associated with outflows in order to identify the MHOs. PDRs have typical low flux ratios of ∼1.5–3, while the vast majority of MHOs display flux ratios typical of C-type shocks (∼6–20). A few MHOs exhibit flux ratios consistent with expected values for J-type shocks (∼3–4), but these are located in regions that may be contaminated with fluorescent emission. Some previously reported MHOs have low flux ratios, and are likely parts of PDRs rather than shocks indicative of outflows. We identify a total of 36 outflows across the 22 target regions where MHOs were detected. In over half these regions, MHO arrangements and fluorescent structures trace features present in CO outflow maps, suggesting that the CO emission traces a combination of dynamical effects, which may include gas entrained in expanding PDRs as well as bipolar outflows. Where possible, we link MHO complexes to distinct outflows and identify candidate driving sources.

Context. Proper motion measurements provide unique and powerful means to identify the driving sources of mass outflows, which are of particular importance in regions with complex star formation activity and deeply embedded protostars. They also provide the necessary kinematic information to study the dynamics of mass outflows, the interaction between outflows and the ambient medium, and the evolution of outflows with the age of the driving sources. Aims. We aim to take a census of molecular hydrogen emission line objects (MHOs) in the Ophiuchi molecular cloud and to make the first systematic proper motion measurements of these objects in this region. The driving sources are identified based on the measured proper motions, and the outflow properties are characterized. The relationship between outflow properties and the evolutionary stages of the driving sources are also investigated. Methods. Deep H 2 near-infrared imaging is performed to search for molecular hydrogen emission line objects. Multi-epoch data are used to derive the proper motions of the features of these objects, and the lengths and opening angles of the molecular hydrogen outflows. Results. Our imaging covers an area of 0.11 deg 2 toward the L1688 core in the Ophiuchi molecular cloud. In total, six new MHOs are discovered, 32 previously known MHOs are detected, and the proper motions for 86 features of the MHOs are measured. The proper motions lie in the range of 14 to 247 mas/yr, corresponding to transversal velocities of 8 to 140 km s -1 with a median velocity of about 35 km s -1 . Based on morphology and proper motion measurements, 27 MHOs are ascribed to 21 driving sources. The molecular hydrogen outflows have a median length of 0.04 pc and random orientations. We find no obvious correlation between H 2 jet length, jet opening angle, and the evolutionary stage of the driving sources as defined by their spectral indices. We find that the fraction of protostars (23%) that drive molecular hydrogen outflows is similar to the one for Class II sources (15%). For most molecular hydrogen outflows, no obvious velocity variation along the outflow has been found. Conclusions. In Ophiuchus the frequency of occurrence of molecular hydrogen outflows has no strong dependency on the evolutionary stage of the driving source during the evolution from the protostellar stage to the classical T Tauri stage.

We have performed a census of the young stellar populations near the Corona Australis molecular cloud using photometric and kinematic data from several sources, particularly Gaia EDR3, and spectroscopy of hundreds of candidate members. We have compiled a catalog of 393 members of Corona Australis, (39 at >M6), 293 (36) of which are spectroscopically classified for the first time in this work. We find that Corona Australis can be described in terms of two stellar populations, a younger one (a few megayears) that is partially embedded in the cloud (the Coronet Cluster) and an older one (∼15 Myr) that surrounds and extends beyond the cloud (Upper Corona Australis). These populations exhibit similar space velocities, and we find no evidence for distinct kinematic populations in Corona Australis, in contrast to a recent study based on Gaia DR2. The distribution of spectral types in Corona Australis reaches a maximum at M5 (∼0.15 M ⊙), indicating that the initial mass function has a similar characteristic mass as other nearby star-forming regions. Finally, we have compiled mid-infrared photometry from the Wide-field Infrared Survey Explorer and the Spitzer Space Telescope for the members of Corona Australis, and we have used those data to identify and classify their circumstellar disks. Excesses are detected for 122 stars, one-third of which are reported for the first time in this work.

We present 450 and 850 $\mu$m James Clerk Maxwell Telescope (JCMT) observations of the Corona Australis (CrA) molecular cloud taken as part of the JCMT Gould Belt Legacy Survey (GBLS). We present a catalogue of 39 starless and protostellar sources, for which we determine source temperatures and masses using SCUBA-2 450 $\mu$m/850 $\mu$m flux density ratios for sources with reliable 450 $\mu$m detections, and compare these to values determined using temperatures measured by the Herschel Gould Belt Survey (HGBS). In keeping with previous studies, we find that SCUBA-2 preferentially detects high-volume-density starless cores, which are most likely to be prestellar (gravitationally bound). We do not observe any anticorrelation between temperature and volume density in the starless cores in our sample. Finally, we combine our SCUBA-2 and Herschel data to perform SED fitting from 160–850 $\mu$m across the central Coronet region, thereby measuring dust temperature T, dust emissivity index $\beta$, and column density $N({\rm H}_2)$ across the Coronet. We find that $\beta$ varies across the Coronet, particularly measuring $\beta = 1.55 \pm 0.35$ in the colder starless SMM-6 clump to the north of the B star R CrA. This relatively low value of $\beta$ is suggestive of the presence of large dust grains in SMM-6, even when considering the effects of $T\!-\!\beta$ fitting degeneracy and $^{12}$CO contamination of SCUBA-2 850 $\mu$m data on the measured $\beta$ values.

We present a catalogue of Molecular Hydrogen emission-line Objects (MHOs) in outflows from young stars, most of which are embedded. All objects are identified in the near-infrared lines of molecular hydrogen, all reside in the Milky Way, and all are associated with jets or molecular outflows from young stars. Objects in both low and high-mass star forming regions are included. This catalogue complements the existing database of Herbig-Haro objects; indeed, for completeness, HH objects that are detected in H2 emission are included in the MHO catalogue.

We have discovered 12 new molecular hydrogen emission-line objects (MHOs) in\nthe vicinity of the candidate massive young stellar object Mol 121, in addition\nto five that were previously known. H2 2.12-micron/H2 2.25-micron flux ratios\nindicate another region dominated by fluorescence from a photo-dissociation\nregion (PDR), and one region that displays an anomalously low H2 2.12-micron/H2\n2.25-micron flux ratio (<1) and coincides with a previously reported deeply\nembedded source (DES). Continuum observations at 3 mm reveal five dense cores;\nthe brightest core is coincident with the DES. The next brightest cores are\nboth associated with cm continuum emission. One of these is coincident with the\nIRAS source; the other lies at the centroid of a compact outflow defined by\nbipolar MHOs. The brighter of these bipolar MHOs exhibits [Fe II] emission and\nboth MHOs are associated with CH3OH maser emission observed at 95 GHz and 44\nGHz. Masses and column densities of all five cores are consistent with\ntheoretical predictions for massive star formation. Although it is impossible\nto associate all MHOs with driving sources in this region, it is evident that\nthere are several outflows along different position angles, and some\nunambiguous associations can be made. We discuss implications of observed H2\n2.12-micron/H2 2.25-micron and [Fe II] 1.64-micron/H2 2.12-micron flux ratios\nand compare the estimated total H2 luminosity with the bolometric luminosity of\nthe region. We conclude that the outflows are driven by massive young stellar\nobjects embedded in cores that are likely to be in different evolutionary\nstages.\n

Context. Jets from solar-type and low-mass stars are typical manifestations of stellar youth. Shocks along these jets produce visible, generally fast-moving Herbig-Haro objects whose proper motions are easily measured in nearby star-forming regions using images taken just a few years apart. Herbig-Haro objects have now been observed in association with objects close to the substellar boundary. Aims. We present second-epoch observations of the central area of the Lupus 3 star-forming region that include two of its most interesting Herbig-Haro systems. One is HH 228, produced by the classical T Tauri star Th 28 (=Sz 102), whereas the other is HH 600, which has its origin in the very low-mass star Par-Lup3-4. Methods. Narrow-band imaging through filters centered on the Hα and the [SII] lines was obtained with the FORS2 instrument at the Very Large Telescope (VLT) in mid-2010. The images obtained were compared to others obtained in early 2003, leading to the discovery of HH 600. Results. New Herbig-Haro objects are found at large distances from Th 28 and to be associated with it, representing an extension of the HH 228 jet to a projected distance of 0.32 pc from Th 28. The farthest Herbig-Haro object is HH 989, whose possible relationship with Th 28 had been already suggested in a previous study but is now kinematically confirmed. We find other likely Herbig-Haro objects whose proper motions are less indicative of a connection with Th 28, but which may be caused by oblique shocks near the outer walls of its jet. For the HH 600 jet, the knot discovered by ourselves in 2003 to the southeast of Par-Lup3-4 is found to have clearly moved and faded. Using high resolution spectroscopy obtained in 2003 and the proper motion that we can measure now, we determine a spatial velocity of 170 ± 30 km s −1 . The northwestern jet is found to have grown in prominence in the intervening years. The possible relationship of other Herbig-Haro objects in the region with Th 28, Par-Lup3-4, and other young stellar objects in the area is discussed.

Context. During the journey from the cloud to the disc, the chemical composition of the protostellar envelope material can be either preserved or processed to varying degrees depending on the surrounding physical environment. Aims. This works aims to constrain the interplay of solid (ice) and gaseous methanol (CH3OH) in the outer regions of protostellar envelopes located in the Coronet cluster in Corona Australis (CrA), and assess the importance of irradiation by the Herbig Ae/Be star R CrA. CH3OH is a prime test case as it predominantly forms as a consequence of the solid-gas interplay (hydrogenation of condensed CO molecules onto the grain surfaces) and it plays an important role in future complex molecular processing. Methods. We present 1.3 mm Submillimeter Array (SMA) and Atacama Pathfinder Experiment (APEX) observations towards the envelopes of four low-mass protostars in the Coronet cluster. Eighteen molecular transitions of seven species were identified. We calculated CH3OH gas-to-ice ratios in this strongly irradiated cluster and compared them with ratios determined towards protostars located in less irradiated regions such as Serpens SVS 4 in Serpens Main and the Barnard 35A cloud in the λ Orionis region. Results. The CH3OH gas-to-ice ratios in the Coronet cluster vary by one order of magnitude (from 1.2 × 10−4 to 3.1 × 10−3) which is similar to less irradiated regions as found in previous studies. We find that the CH3OH gas-to-ice ratios estimated in these three regions are remarkably similar despite the different UV radiation field intensities and formation histories. Conclusions. This result suggests that the overall CH3OH chemistry in the outer regions of low-mass envelopes is relatively independent of variations in the physical conditions and hence that it is set during the prestellar stage.

We aimed to map the jets and outflows from the Serpens South star forming region and find an empirical relationship between the magnetic field and outflow orientation. Near-infrared H2 v=1-0 S(1) 2.122{\mu}m -line imaging of the \sim 30'-long filamentary shaped Serpens South star forming region was carried out. K s broadband imaging of the same region was used for continuum subraction. Candidate driving sources of the mapped jets/outflows are identified from the list of known protostars and young stars in this region, which was derived from studies using recent Spitzer and Herschel telescope observations. 14 Molecular Hydrogen emission-line objects(MHOs) are identified using our continuum-subtracted images. They are found to constitute ten individual flows. Out of these, nine flows are located in the lower-half(southern) part of the Serpens South filament, and one flow is located at the northern tip of the filament. Four flows are driven by well-identified Class 0 protostars, while the remaining six flows are driven by candidate protostars mostly in the Class I stage, based on the Spitzer and Herschel observations. The orientation of the outflows is systematically perpendicular to the direction of the near-infrared polarization vector, recently published in the literature. No significant correlation was observed between the orientation of the flows and the axis of the filamentary cloud.

view Abstract Citations (84) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Structure and Proper Motions in Herbig-Haro Objects 1 and 2 Eisloffel, Jochen ; Mundt, Reinhard ; Bohm, Karl-Heinz Abstract We have carried out a detailed study on the structure and proper motions of the condensations in Herbig-Haro (HH) objects 1 and 2 and other HH objects in their immediate neighborhood. The presented proper motions are compatible with HH 1 being a bow shock, which is propagating into a moving medium ahead of it. They also reveal a very complex kinematical structure in HH 2. Proper motions for the nearby HH objects HH 144, HH 145, and the newly discoverd HH 147 are presented and the probable outflow sources for HH 144 and HH 147 are identified. Tangential velocities in the range of 100-250 km/s were measured for the condensations in HH 2, HH 144, and HH 147, while velocities of up to 380 km/s were found in the HH 1 bow shock and in the jet pointing from the VLA1 source towards HH 1 (VLA1 jet). These outflows appear not to be well aligned with respect to each other, nor with the local cloud magnetic field. Linear correlations between tangential velocities and excitation and radial velocity dispersion, respectively, were found for condensations in HH1 and 2. Surprisingly an anticorrelation between tangential velocity and radial velocity dispersion was found in the VLA1 jet. A deconvolved (S II) image of HH 1 (FWHM = 0.55 sec) shows a wealth of structural details in the bow shock and (just) resolves the knots in the VLA1 jet, whose diameter could be measured. The deconvolved (S II) image, as well as an H alpha image and the low tangential velocity suggest, that knot Gj might consist of two closely spaced components, one of which is excited by the entrainment of ambient material into the VLA1 jet. Photometric monitoring between 1987 and 1993 shows that many of the brighter condensation in HH 1 and 2 were variable in the (S II) lambda lambda 6716, 6731 lines. Most notable are the brightening of HH 2H by about 25%, the fading of HH 2C and G by about 20% and the strong variability of 10%-30% within only six years found for HH 1G, HH 2A', B, D, and G. Publication: The Astronomical Journal Pub Date: September 1994 DOI: 10.1086/117133 Bibcode: 1994AJ....108.1042E Keywords: Condensing; Herbig-Haro Objects; Kinematics; Shock Waves; Spectral Emission; Stellar Motions; Stellar Physics; Stellar Structure; Astronomical Photometry; Astronomical Spectroscopy; Correlation; Graphs (Charts); Line Spectra; Radial Velocity; Spectrum Analysis; Tables (Data); Astronomy; STARS: PRE-MAIN SEQUENCE full text sources ADS | data products SIMBAD (83)

We performed a deep search for Herbig–Haro (HH) objects toward the Lupus I and III clouds, covering a sky area of ∼ 1 and ∼ 0.5 deg2, respectively. In total, 11 new HH objects, HH 981--991, are discovered. The HH objects both in Lupus I and in Lupus III tend to be concentrated in small areas. The HH objects detected in Lupus I are located in a region of radius 0.26 pc near the young star Sz 68. The abundance of HH objects shows that this region of the cloud is active in on-going star formation. HH objects in the Lup III cloud are concentrated in the central part of the cloud around the Herbig Ae/Be stars HR 5999 and 6000. HH 981 and 982 in Lupus I are probably driven by the young brown dwarf SSTc2d J154457.9−342340 which has a mass of 50 MJ. HH 990 and 991 in Lup III align well with the HH 600 jet emanating from the low-mass star Par-Lup3-4, and are probably excited by this low-mass star of spectral type M5. High proper motions for HH 228 W, E, and E2 are measured, which confirms that they are excited by the young star Th 28. In contrast, HH 78 exhibits no measurable proper motion in the time span of 18 years, indicating that HH 78 is unlikely part of the HH 228 flow. The HH objects in Lup I and III are generally weak in terms of brightness and dimension in comparison to HH objects we detected with the same technique in the R CrA and Cha I clouds. Through a comparison with the survey results from the Spitzer c2d program, we find that our optical survey is more sensitive, in terms of detection rate, than the Spitzer IRAC survey to high-velocity outflows in the Lup I and III clouds.

We present optical and IR spectra of a set of low-mass stars and brown dwarfs in the Coronet cluster (aged ~1 Myr), obtained with the multifiber spectrograph FLAMES on the VLT and with the IRS instrument on Spitzer. Most of the objects had been selected via their X-ray emission in a deep Chandra survey. The optical spectra reveal spectral types between M1 and M7.5, confirm the youth of the objects (via Li λ6708 absorption), and show the presence of accretion (via Hα) and shocks (via forbidden line emission). The IRS spectra, together with IR photometry from the IRAC/MIPS instruments on Spitzer and 2MASS, confirm the presence of IR excesses characteristic of disks around ~70% of the objects. Half of the disks do not exhibit any silicate emission or present flat features characteristic of large grains (>6 μm). The rest of the disks show silicate emission with indications of amorphous and crystalline silicate grains a few microns in size. About 50% of the objects with disks do not show near-IR excess emission, corresponding to the presence of transitional disks, according to their classical definition. This is a very high fraction for such a young cluster. The large number of transitional disks suggests lifetimes comparable to the lifetimes of typical optically thick disks. Therefore, these disks may not be in a short-lived phase, intermediate between Class II and Class III objects. The median SED of the disks in the Coronet cluster is also closer to a flat disk than observed for the disks around solar-type stars in regions with similar age. The differences in the disk morphology and evolution in the Coronet cluster could be related to the fact that these objects have very late spectral types compared to the solar-type stars in other cluster studies. Finally, the optical spectroscopy reveals that one of the X-ray sources is produced by a Herbig-Haro object in the cloud.

We present a catalogue of prestellar and starless cores within the Corona Australis molecular cloud using photometric data from the Herschel Space Observatory. At a distance of d ~ 130 pc, Corona Australis is one of the closest star-forming regions. Herschel has taken multi-wavelength data of Corona Australis with both the Spectral and Photometric Imaging Receiver (SPIRE) and the Photodetector Array Camera and Spectrometer (PACS) photometric cameras in a parallel mode with wavelengths in the range 70–500 μm. A complete sample of starless and prestellar cores and embedded protostars is identified. Other results from the Herschel Gould Belt Survey have shown spatial correlation between the distribution of dense cores and the filamentary structure within the molecular clouds. We go further and show correlations between the properties of these cores and their spatial distribution within the clouds, with a particular focus on the mass distribution of the dense cores with respect to their filamentary proximity. We find that only lower-mass starless cores form away from filaments, while all of the higher-mass prestellar cores form in close proximity to or directly on the filamentary structure. This result supports the paradigm that prestellar cores mostly form on filaments. We analyse the mass distribution across the molecular cloud, finding evidence that the region around the Coronet appears to be at a more dynamically advanced evolutionary stage in comparison to the rest of the clumps within the cloud.

We present Spitzer Space Telescope IRAC and MIPS observations of a 0.85 deg^2 field including the Corona Australis (CrA) star-forming region. At a distance of 130 pc, CrA is one of the closest regions known to be actively forming stars, particularly within its embedded association, the Coronet. Using the Spitzer data, we identify 51 young stellar objects (YSOs) in CrA which include sources in the well-studied Coronet cluster as well as distributed throughout the molecular cloud. Twelve of the YSOs discussed are new candidates, one of which is located in the Coronet. Known YSOs retrieved from the literature are also added to the list, and a total of 116 candidate YSOs in CrA are compiled. Based on these YSO candidates, the star formation rate is computed to be 12 M_o Myr^-1, similar to that of the Lupus clouds. A clustering analysis was also performed, finding that the main cluster core, consisting of 68 members, is elongated (having an aspect ratio of 2.36), with a circular radius of 0.59 pc and mean surface density of 150 pc^-2. In addition, we analyze outflows and jets in CrA by means of new CO and H_2 data. We present 1.3 mm interferometric continuum observations made with the Submillimeter Array (SMA) covering R CrA, IRS 5, IRS 7, and IRAS 18595-3712 (IRAS 32). We also present multi-epoch H_2 maps and detect jets and outflows, study their proper motions, and identify exciting sources. The Spitzer and ISAAC/VLT observations of IRAS 32 show a bipolar precessing jet, which drives a CO (2-1) outflow detected in the SMA observations. There is also clear evidence for a parsec-scale precessing outflow, E-W oriented, and originating in the SMA 2 region, likely driven by SMA 2 or IRS 7A.

We present the results of a deep optical survey in the Corona Australis and Chamaeleon II star forming regions. Our optical photometry is combined with available near- and mid-infrared photometry to identify very low-mass candidate members in these dark clouds. In our Chamaeleon II field, only one object exhibits clear Hα emission, but the discrepancy between its optical and near-infrared colours suggests that it might be a foreground star. We also identify two objects without Hα emission that could be planetary mass members of Chamaeleon II. In Corona Australis, we find ten stars and three brown dwarf candidates in the Coronet cluster. Five of our new members are identified with ISOCAM sources. Only two of them have a mid-infrared excess, indicating the presence of an accretion disk. On the other hand, one brown dwarf candidate has a faint close companion, seen only in our deepest I-band image. For many of the candidates in both clouds, membership could not be inferred from their Hα emission or near-infrared colours; these objects need spectroscopic confirmation of their status.