Claire Davy, of Bryn Mawr College, worked with Jeff Mangum on

L1448IRS3: The Structure and Evolution of a Class 0 Protostar

The L1448 molecular cloud possesses all of the classic signposts of recent star formation: collimated and uncollimated molecular outflow, H2O masers, compact radio continuum sources, emission from dense gas tracers such as H2CO and NH3, strong IRAS point source emission, and intense millimeter-wavelength dust continuum emission originating from both compact and extended sources. The region is generally separated into two components, L1448C and L1448N. Both are classified as Class 0 "protostars" (Bontemps etal. 1996), are sources of molecular outflow, and are associated with compact IRAS emission. The northern source of this pair, L1448N, is associated with the brightest of the IRAS point sources in the region, IRS3 (L_(bol) ~ 10 L_(sun)). High resolution images of the 2 and 6 cm continuum emission from L1448N found that this source was composed of two components: L1448N(A) (NOTE: L1448N(A) and L1448N(B) are referred to as L1448 IRS3A and3B, respectively, by Looney, Mundy, & Welch, following IAU standard nomenclature. We will use the Looney, Mundy, & Welch designations.) and L1448N(B) (Curiel etal. 1990; Barsony etal. 1998; Looney, Mundy, & Welch 2000). Tereby & Padgett 1997 and Looney, Mundy, & Welch also identify a third dust continuum source, L1448NW (called L1448 IRS3C by Looney, Mundy, & Welch) located ~20 arcsec to the NW of the IRS3A/B cores.

High resolution millimeter continuum images of L1448N (Terebey, Chandler, & Andre 1993; Terebey & Padgett 1997; Looney, Mundy, & Welch 2000) indicate that even though L1448 IRS3A is the dominant source of centimeter-wave continuum emission, L1448 IRS3B contributes most of the millimeter continuum emission. The C18O J=1-0 measurements of the L1448 IRS3 region by Terebey & Padgett indicate that the three L1448 IRS3 subcores are rotating at a rate of 100 km/s pc^(-1). Their measurements also indicate that the L1448 IRS3A/B subcores are collapsing. All three subcores appear to be Class 0 sources in various stages of evolution.

L1448 may also be one of a handful of star formation regions which exhibit hints of triggered star formation. The blueshifted lobe of the highly-collimated molecular outflow from L1448C coincides with the L1448 IRS3 condensation. Measurements of the NH3 emission from this region by Curiel etal. (1999) indicate a potential interaction between this blueshifted lobe and L1448 IRS3, as evidenced by an increase in the local heating and velocity dispersion near IRS3. Curiel etal. cautioned that these physical affects could also be caused by heating from the young embedded source IRS3. High (<~ 9 arcsec, the spatial resolution of the Curiel etal. NH3 measurements) resolution measurements of the dense gas in the IRS3 region are needed to study the association between IRS3, the blueshifted lobe from L1448C, and the local heating and line broadening of the L1448 IRS3molecular core.

The Data

To provide the necessary information regarding the dense gas kinematic, spatial, and kinetic temperature structure within L1448 IRS3, we have imaged three lambda=1.4 mm transitions of H2CO with the BIMA millimeter-wave interferometer. These measurements will allow us to:
  1. Determine the association between the dense gas and the envelope, disk, and core structures observed in millimeter continuum measurements;
  2. Distinguish between local heating and kinematic structure due to IRS3 and that due to a suspected interaction with the L1448C outflow; and
  3. Probe the kinematic and kinetic temperature structure over the entire L1448 IRS3 region. Terebey & Padgett (1997) presented a model including infall and rotation, based on high resolution interferometric observations in the C18O 1-0 line. H2CO is a superior tracer of dense gas, and owing to its many transitions constrains models very well.

Two of the three transitions of H2CO we have imaged have been observed toward L1448 IRS3 using the IRAM 30m telescope. These data will be combined with the BIMA measurements to provide zero-spacings information to the analysis. As we will have information on the physical structure of the H2CO emission from L1448 IRS3, we intend to model the formaldehyde excitation using a non-uniform microturbulent analysis, extending our early uniform LVG model (Mangum & Wootten 1993; Wootten & Mangum 1998). These measurements will allow an analysis of the kinetic temperature structure on ~ 1000 AU size scales over the ~30 arcsec (~ 10,000 AU) extent of L1448 IRS3.

References

Barsony, M., Ward-Thompson, D., Andre, P., & O'Linger, J. 1998, ApJ, 509, 733

Bontemps, S., Andre, P., Tereby, S., & Cabrit, S. 1996, A&A, 311, 858

Curiel, S., Raymond, J. C., Rodriguez, L. F., Canto, J., & Moran, J. M. 1990, ApJ, 365, L85

Curiel, S., Torrelles, J. M., Rodriguez, L. F., Gomez, J. F., & Anglada, G. 1999, ApJ, 527, 310

Looney, L. W., Mundy, L. G., & Welch, W. J. 2000, ApJ, 529, 477

Mangum, J. G. & Wootten, A. 1993, ApJS, 89, 123

Terebey, S., Chandler, C. J., & Andre, P. 1993, ApJ, 414, 759

Terebey, S. & Padgett, D. L. 1997, in IAU Symposium 182, "Herbig-Haro Flows and the Birth of Low Mass Stars", ed. B. Reipurth & C. Bertout (Dordrecht: Kluwer), 507

Wootten, A. & Mangum, J. G. 1998, unpublished report.

-- JeffMangum - 28 Feb 2006
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