My PhD thesis involved studying the role of protostellar outflows in star formation feedback. When young stars form, they accrete material from their parent molecular cloud. This material falls from the surrounding envelope onto an accretion disk and then is magnetically funneled onto the star. Due to a complex magneto hydrodynamic (MHD) process that is not yet fully understood, a portion of this material is launched from the poles of the star in a high speed (~100 - 500 km/s) collimated jet.
This high velocity jet slams into the surrounding molecular cloud,
depositing energy and momentum. These shocks excite the atoms and
molecules in the molecular material and are seen as emission line
nebulae also known as Herbig-Haro (HH) objects. I am using these HH
objects as a tracer of momentum deposition in the cloud.
The image at left is of NGC 1333, a virulent burst of star formation in the Perseus molecular cloud. The image was taken at Kitt Peak National Observatory using the Mosaic camera on the Mayall 4 meter telescope. The color coding is such that emission from ionized sulphur ([SII]) is red, emission from hydrogen (H-alpha) is green, and broadband emission (SDSS i') is blue. An alternate view of this object using infrared data from the Spitzer Space Telescope can be seen here. I have aligned the Spitzer image and our optical image, here is the resulting animated gif.
Star formation is a dynamic process whereby the outflows and radiation from young stars impact the dynamics of the parent cloud and affect the formation of subsequent generations of stars. In giant molecular clouds (GMCs) which form high mass stars, the interaction between the stars and the cloud is dominated by these high mass stars. Specifically the expansion of HII regions formed by the ionizing radiation from the massive stars and the shock waves from supernovae when they die are probably far more damaging to the cloud than protostellar outflows. In lower mass clouds, however, where no massive stars form, what generates the turbulence in the molecular material? Is that turbulence constantly driven or does it decay rapidly? If it is driven, then perhaps protostellar outflows are the driving force. The aim of my thesis is to determine the role of protostellar outflows in the driving of turbulence in molecular clouds.
Our primary tools in this study are large area imaging surveys of molecular clouds in narrowband filters which we use to identify and count the HH objects which trace the interaction between the protostellar jet and the cloud. By measuring the frequency and area covering factor of these shocks we can get a rough measure of the momentum injected by shocks.
Primarily
we've used the Mosaic cameras on the 4 meter Mayall telescope at Kitt Peak in Arizona and the 4
meter Blanco telescope at Cerro
Tololo in Chile with additional data collected at the WIYN 0.9
meter telescope at Kitt Peak and the 3.5 meter ARC telescope at Apache Point.
The image at right shows the L1451 region of Perseus. The outflow emerging from the cometary cloud at center was the subject of one of our papers.
The primary region which I've studied in detail is the Perseus Molecular Cloud. Perseus is relatively close (~300 pc or ~1000 light years distant) and is comparatively low mass (~10,000 solar masses). Perseus has no recently formed massive stars to produce large HII regions and so it is an ideal region to study the effect of protostellar outflows.
If you like, you can check out my Curriculum Vitae ... or my ADS entry.
You may be interested in downloading the actual data from our survey of Perseus. If so, the data is available here.
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Using optical (H-alpha, [SII], & i'), near-IR (H2, J, H, & KS), mid-IR (Spitzer IRAC 4.5 micron), and submillimeter (850 and 450 micron) data, we have examined the region surrounding the IC 348 cluster and the neighboring ``Flying Ghost Nebula'' and found a multitude of shocks from protostellar outflows including HH 211 which had previously not been detected in visible wavelength images. We have identified 13 protostars in the region which drive protostellar outflows. The region surrounding the FGN is rich in ongoing star formation with a number of outflows similar to those found in other sites of moderate star formation in Perseus (e.g. L1448, L1455, & Barnard 1). We have also found a candidate bent jet in this region. The axis defined by the bending angle suggests that this source may have been ejected from a multiple star system near the IC 348 IR source.
Using optical (H-alpha & [SII]), Near-IR (H2 & KS), and submillimeter (850 & 450 micron) data, we have examined the region surrounding the Barnard1 (B1) core and found a multitude of new shocks from protostellar outflows. We trace several flows, some of which are large, parsec scale outflows with dynamic ages of order 104 yr, indicating that star formation has been taking place in Barnard 1 for at least that long. We can confidently identify eight protostars which are driving outflows. Of those eight protostars, one source, SMM 2 (SMMJ 033330+31095) is a new class-0 source, giving B1 a total of 3 class-0 protostars. Based on the number of shocks and protostars in this region, B1 appears to be a much more active region of star formation than previously thought. The number of shocks is comparable to or greater than those of other active star forming regions in Perseus (e.g. IC 348, L1455, & L1448).
We present a catalog of 72 new Herbig-Haro (HH) objects discovered in the Perseus molecular cloud. There are 69 previously cataloged HH objects in this region, the new discoveries bring the total number of known HH objects in Perseus to 141. Individual outflows often contain several distinct HH objects. These observations demonstrate that the Perseus Molecular Cloud is one of the most active star forming regions in the solar vicinity. We explore different methods for probing the momentum injection rate of outflows and examine whether outflows can drive turbulence within the molecular cloud. On the scale of the entire Perseus cloud, the shocks produced by outflows from young stars may not inject momentum at a sufficient rate to counter the rate at which momentum decays. However, intense outflow activity within individual cloud cores with high star formation rates, such as NGC 1333, may be sufficient to locally support or even disrupt the core.
We report the discovery of a new giant Herbig-Haro flow near the L1451 region of the Perseus molecular cloud. The east-west oriented flow contains two known HH objects (HH 280 and HH 317), two new HH objects (HH 492 and HH 493), and is 2.1 pc long. The flow is driven by the Class I protostar IRAS 03235+3004 embedded in a bright-rimmed, sharp-edged cometary cloud facing northeast. The flow source is embedded in a west-facing conical reflection nebula. The cometary cloud appears to have been shaped by O and B stars in the Per OB2 association, including the B0.5 star 40 Per, located along the well-defined symmetry axis of the cloud and with a projected separation of 26 pc. A soft-UV induced photoablation model is proposed to explain the properties of the cometary cloud.
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Please send comments to Josh. All images Copyright © Josh Walawender unless otherwise noted.
