David Devine

A Burst of Herbig-Haro Flows in NGC 1333

We report the discovery of over 20 groups of new Herbig-Haro (HH) objects in the NGC 1333 region of the Perseus molecular cloud, including some highly collimated jets. Our images contain over 30 groups of HH objects driven by over a dozen active outflow sources. Several of the new jets appear to be driven by optically visible stars, including HH 333, HH 334, and possibly HH 335 and HH 336. A spectacular jet, HH 333, lies nearly in the plane of the sky and has a length-to-width ratio exceeding 100 and may exhibit S-shaped point symmetry about a faint Hα emission-line star. HH 336 is located toward the cloud edge and is also centered on a visible star. A large number of new HH objects lie to the south of the concentration of known young stellar objects near SVS 13. We use published millimeter-wavelength CO and near-infrared H2 maps and images to associate HH objects, H2 emitting shocks, and CO outflows with more than a dozen potential driving sources. The high density of objects results in source confusion that limits the extent to which this can be done. Some HH objects are seen toward low-extinction regions far from the opaque cloud cores and may trace parts of parsec scale outflows from embedded sources. The large number of collisionally excited nebulae in this young stellar cluster requires a nearly coeval microburst of star formation.

Protostellar jets irradiated by massive stars

The formation of solar-type stars is a gradual process during which they accrete mass from the dense disks and cloud cores that surround them. This accretion requires the release of angular momentum, and an important mechanism for achieving this seems to be the production of jets along the polar axes of the young stars,. But the presence of massive, luminous stars within the same star-forming region can affect the forming stars by stripping away their circumstellar envelopes with ultraviolet radiation, thereby removing the reservoir of gas from which the stars are built up and exposing the disks to photoerosion. Here we present observations of four highly collimated jets from young stars that appear to have been stripped of their circumstellar molecular cloud cores in this way. The production of jets seemstohave been largely unaffected. If these jets are also photoionized, their mass loss rates can be determined from observations with much greater accuracy than for normal shock-excited jets.

New Herbig-Haro Flows in L1448 and L1455

We present a deep narrowband Hα and [S II] optical survey of a roughly 1 deg2 region containing L1448 and L1455 in the southwestern region of the Perseus molecular cloud. We report the detection of 13 new groups of Herbig-Haro (HH) objects in this region. The L1448 core contains eight groups of Herbig-Haro objects (HH 193, HH 194, HH 195, HH 196, HH 197, HH 267, HH 268, and HH 277). Many of the new HH objects near L1448 have orientations similar to the L1448C molecular jet and L1448 IRS3 outflow. All four known infrared sources in L1448 power Herbig-Haro objects. L1448 IRS 1 is the likely source of HH 194, HH 195E, and possibly HH 268. L1448 IRS 2 drives HH 195, and L1448 IRS 3 may power HH 196 and possibly HH 193. HH 267 and HH 277 lie close to the axes of the IRS 2 and IRS 3 flows and may also be powered by one of these sources. Finally, the class 0 source L1448C powers HH 197. The L1455 core contains five new groups of HH objects (HH 278, HH 279, HH 280, HH 317, and HH 318). L1455 IRS 1 and L1455 IRS 2 are likely to power HH objects, but a unique association between each IRAS source and a specific HH object is difficult to make. Both clouds contain some HH objects whose driving sources cannot be conclusively identified. Most of the new HH objects are located near the cloud edges while some are in the interclump medium (ICM) more than 1 pc from the nearest cloud core or known young stellar object. These observations provide further evidence that HH flows can extend far beyond the cloud cores containing their sources, and in some cases extend over greater distances than associated high-velocity millimeter-wavelength CO emission. Herbig-Haro objects associated with the terminal working surfaces of outflows located in the ICM can be used to probe the nature of the interclump gas in molecular clouds. The large number of HH objects found in relatively inactive star forming regions such as L1448 and L1455 indicates that shock heating and acceleration by protostellar outflows plays an important role in determining the ionization state and energetics of the ICM that surrounds low-mass star forming regions.

L1551 NE or L1551 IRS 5: Which Source Drives HH 28/29?

We have obtained deep high-resolution interference filter images of the HH objects in the L1551 molecular cloud in 1990 and 1997, and we suggest that the well-known and well-studied objects HH 28 and 29 are driven by the deeply embedded class 0 source L1551 NE, not by the well-known IRS 5 source. We find a new, small bipolar HH flow, HH 454, surrounding L1551 NE. This new HH flow is aligned along the axis of a highly collimated infrared jet from this source, is blueshifted by 110 km s-1 southwest of the source, and is redshifted by 100–130 km s-1 northeast of L1551 NE. A line through the L1551 NE source and along this well-defined flow axis passes straight through HH 29 and within parts of the more distant HH 259 and HH 28. The proper motion of HH 29 exhibits a complex flow pattern with some knots appearing to move away from the nearby source IRS 5 while other parts are moving away from L1551 NE. The HH 29 object encompasses several bright, stationary knots that have faded between the two epoch images. When these stationary knots are excluded from the proper-motion analysis, the resulting overall flow vector points away from L1551 NE, not from IRS 5. Most components of HH 259 and some parts of HH 28 also appear to be moving in a direction pointing away from L1551 NE rather than from IRS 5. In the opposite, redshifted lobe, we find a new, distant HH object, HH 286, but it is unclear whether L1551 NE or IRS 5 is the driving source. Altogether, it appears that L1551 NE plays a much more prominent role than hitherto anticipated in the outflow activity of this highly complex and confused region.

Kinematics of Herbig-Haro Objects in the Protostellar Outflow L1551 as Mapped by Fabry-Perot Spectroscopy

We present new velocity-resolved Fabry-Perot images in [S II] λ6731 and Hα of the blueshifted portion of the protostellar outflow L1551. These new data isolate the line emission from the reflected continuum and make it possible to visualize the kinematics of the shock waves in the outflow clearly for the first time on large scales with subarcsecond spatial resolution. Velocity images of the L1551 jet confirm that a fainter, slower jet lies a few arcseconds below the main jet. Emission from the main jet decreases sharply in radial velocity and the emission-line width increases suddenly as the jet encounters bright knot 3, in agreement with bow shock models. This knot must move into previously ejected material to account for the observed radial velocities, supporting the idea that shocks in Herbig-Haro (HH) flows form as the result of variable velocity ejections from the embedded protostar. However, a velocity gradient observed along the entire edge of the bow shock is spatially larger than expected if the bow shock alone were responsible for all the line emission. Deviations from the simple model are most easily explained if a Mach disk alters the emission and kinematics within the bow shock region, though a precursor to the bow shock is an alternate possibility. The spatial distribution of radial velocities and emission-line widths across HH 29 implies that this object is a slower portion of the outflow currently being overtaken by faster material. New proper-motion images of HH 29 independently confirm this result. The large-scale velocity structure of the L1551 outflow is complex but can generally be understood if faster material drives shock waves into slower material around the edge of a cavity. A striking circular feature whose center lies near the intersection of the axis of the bright jet and the cavity resembles similar structures in the Orion Nebula and could define a hole through which a fast jet has penetrated. The velocity structure along a string of HH objects to the southwest of HH 29 is consistent with the recent result of Devine et al. that L1551 NE drives this portion of the outflow. Linear features that cross the L1551 flow may be associated with separate, unrelated jets from the HH 30 region or elsewhere within L1551.

Herbig-Haro Flows from the L1641-N Embedded Infrared Cluster

We have discovered a large number of Herbig-Haro (HH) flows associated with the embedded infrared cluster surrounding the IRAS source 05338-0624, the driving source of the L1641-N molecular outflow. The best collimated HH flow in the region, HH 303, stretches in two groups of knots along a well-defined axis from the VLA source that coincides with the IRAS source. This HH flow is coaxial with the blue northern lobe of the molecular flow. To the north-northwest of the cluster we find a long series of very large and finely shaped bow shocks, which stretch on a well-defined axis away from the cluster. The most distant HH object, HH 310, is 6.3 pc in projection from the center of the cluster, making it the largest HH lobe known from a low-mass star. We identify the counterlobe with an already known chain of infrared H2 emission knots. Additionally, we find two very large fragmented bow shocks, HH 403 and 404, to the northeast of and facing away from the cluster. They lie on an axis that passes through the cluster at projected distances of 4.2 and 5.4 pc. In the opposite direction, to the southwest we identify the previously known object HH 127 at a projected distance of 5.2 pc from the cluster and within an angle of 10° of the HH 403/404 axis. HH 127 consists of three faint knots also on a line through the cluster. Precisely south of the VLA source and on the axis of the HH 303 jet, we find a large bow shock, HH 61, which is 5.9 pc in projection from the cluster, and which we believe is part of the counterflow to the HH 303 jet. Our CCD images and 13CO maps clearly show that HH 61 and HH 127 are located just beyond the well-defined edge of the L1641 cloud, which explains why they are optically visible. Our extensive C18O map of the region shows that the cluster is associated with a prominent cloud core. Our 12CO map reveals, in addition to the known L1641-N outflow, a large pair of compact low-velocity outflow lobes, a southeastern blueshifted lobe, and a northwestern redshifted lobe, separated by 2.7 pc and centered on the infrared cluster. The numerous outflows in the region provide evidence that a large number of the young stars in the loose cluster are presently in active mass-losing phases. The L1641-N cluster is clearly the presently most active site of low-mass star formation in the L1641 molecular cloud.

Molecular hydrogen in the IRAS 03282+3035 stellar jet

We detected shock-excited 2.122 μm molecular hydrogen from the blueshifted lobe of the highly collimated CO outflow associated with the young stellar object IRAS 03282+3035 in the Perseus molecular cloud. The H 2 emission has a peak surface brightness of 5×10 -4 ergs s -1 cm -2 sr -1 , making this one of the brightest shock-excited molecular hydrogen sources associated with a low-mass young stellar object. The emission has knotty structure with faint tails lying parallel to the mean outflow axis. These knots coincide with molecular bullets B3 and B4 located near the end of the highest velocity CO-emitting component and may be bow shocks where a fast jet interacts with the surrounding medium. The bulk of the lower velocity CO emission is located downwind from the H 2 emission zone

Hubble Space Telescope Planetary Camera Imaging of HH 29

We present Hubble Space Telescope Hα and [S II] images of HH 29. The proximity of HH 29 (140 pc) and the high resolution of the Planetary Camera has resulted in the most detailed images obtained so far of any Herbig-Haro object. The most prominent feature is a linear Hα ridge leading the working surface of a bow shock with a chaotic trailing [S II] bright region. The high-excitation ridge is perpendicular to a line extending toward the class 0 protostar L1551-NE, supporting its recent identification as the driving source. Previous studies have identified several low-velocity features within the working surface. Our images reveal them to be miniature bow shocks facing upstream. Evidently a cluster of dense quasi-stationary clumps have been overrun by a faster, lower density flow. The shock front impacted the front of the largest clump several decades ago, and during the 1990s, a prominent gap appeared in the advancing bow shock in the wake of the obstacle. The Hubble Space Telescope images show that by 1998 the shock front had wrapped around the back of the clump, closing the shock shadow it produced.

Molecular Hydrogen in IRAS03282+3035

We detected shock excited 2.122 µm molecular hydrogen emission from the blueshifted lobe of the highly collimated CO flow associated with the young stellar object IRAS03282 in the Perseus molecular cloud. The emission has a knotty structure with faint tails lying parallel to the mean outflow axis. The knots coincide with clumps of high velocity ( 50 km/s) CO and may be bow shocks where a fast jet interacts with the surrounding medium. IRAS03282+3035 has the highest ratio ( 10 % ) of molecular hydrogen luminosity to total bolometric luminosity of any presently known young stellar object.