Green Bank Observatory/SOFIA Joint Observations

The SMO has made an agreement for joint proposals with the Green Bank Observatory (GBO). This agreement allows users to apply for time with the Green Bank Telescope via the SOFIA proposal process or for time with SOFIA via the Green Bank Telescope (GBT) proposal process. Up to 5% of the total open-skies time on the GBT will be reserved for proposals received via this call, and up to 3% of the total US GO time on SOFIA will be reserved for proposals received by the GBO. More information on the Green Bank Observatory website.

SOFIA Green Bank Telescope Programs

Proposal ID: 09_0089

Principal Investigator: Jonathan Tan (University of Virginia)

Instrument: GREAT

Title: The Inception of Star Cluster Formation: [CII] Emission from IRDCs Massive Protoclusters and GMC Collisions

Abstract: Most stars are born in clusters. Thus, the processes that may initiate star cluster formation are of fundamental importance throughout astrophysics, from the evolution of stellar populations in galaxies to the formation of planets in protoplanetary disks in these environments. Infrared Dark Clouds (IRDCs) are now recognized as the likely precursors of star clusters. Thus it is important to understand the kinematics, dynamics & formation environments of IRDCs. We propose to utilize the efficient OTF mapping capabilities of upGREAT to map [CII] and [OI] emission in a sample of 3 IRDCs that have been extremely well studied over the last decade with numerous facilities, including Spitzer, IRAM 30m, IRAM PdBI, Herschel, Chandra & ALMA. [CII] probes the photodissociation region around the IRDC. Thus it provides crucial information on the kinematics of the gas that is becoming molecular and joining the IRDC. Different theoretical models of IRDC formation are expected to have different signatures of [CII] kinematics. For example, simulations of dense gas formation via either decaying turbulence or triggering by cloud-cloud collisions make specific distinguishing predictions for [CII] spatial and kinematic structures. These will be tested against upGREAT observations to deduce the processes that initiate star cluster formation. We also request GBT-ARGUS time to map 13CO(1-0) and C18O(1-0) at high angular and velocity resolution to obtain the best maps of molecular gas kinematics to compare to those of [CII] and further test models of IRDC dynamics and formation.

Proposal ID: 09_0104

Principal Investigator: Jonathan Tan (University of Virginia)

Instrument: HAWC+

Title: Magnetic Fields at the Onset of Star Formation: Polarization Mapping of Infrared Dark Clouds

Abstract: Most stars are born in clusters, so the processes that initiate star cluster formation are of fundamental importance throughout astrophysics. Infrared Dark Clouds (IRDCs) are now recognized as the likely precursors of star clusters. Thus it is important to understand the physical processes that control IRDC formation and evolution. We propose to observe 214 micron polarized emission from dust in a sample of nine well-studied IRDCs. These clouds have been mapped extensively with many other facilities, including IRAM 30m and ALMA to study the kinematics of the molecular gas that reveals properties of the turbulent motions. However, the B-field morphology and strength in these IRDCs are currently very poorly explored, thus motivating this SOFIA-HAWC+ proposal. Polarized emission is expected to be well-detected in many independent positions over the clouds. Sophisticated numerical simulations of magnetized clouds will also be used to help interpret the observations. We also request GBT-Argus time to map 13CO(1-0) and C18O(1-0) at high angular and velocity resolution to obtain the highest spatial dynamic range maps of molecular gas kinematics. Analysis of these maps will yield independent estimates of B-field properties, which will be compared with those derived from the HAWC+ observations. This will provide important tests of the fidelity of polarized dust emission methods of magnetic field estimation. Using all these methods, this project will enable a much improved understanding of the importance of B-fields in IRDCs and thus for the onset of star cluster formation. 

Proposal ID: 09_0155

Principal Investigator: Samantha Scibelli (University of Arizona)

Instrument: HAWC+

Title: Far-IR Dust and Magnetic Field Alignment Study of the Collapse Candidate Starless Core L63

Abstract: Modeling the internal structure and dynamics of prestellar cores is crucial for understanding their evolution up to the initial stages of disk and protostar formation. An evolved core, especially one on the brink of collapse, will reflect the primordial conditions of star formation without contamination from protostar outflows. L63 is a unique prestellar core in that it has prominent infall or collapse signatures, yet it was not targeted by Herschel due to its remote location in the Ophiuchus molecular cloud. We propose to utilize the SOFIA HAWC+ instrument to take polarimetry and total intensity measurements of L63. We will 1) measure relative magnetic field alignment to compare to modeled infall structure and 2) constrain from total intensity measurements at 154micron and 214micron the peak of L63's SED. We also ask for time, as part of the joint proposal process, to obtain high resolution (11'') HCN 1-0 observations with ARGUS on the GBT to study this cores' infall profile at high spatial resolution. These observations will be an integral piece of thesis work, which will include multi-dimensional continuum and line radiative transfer modeling on prestellar core L63, exploring both physical and chemical conditions.

Proposal ID: 09_0164

Principal Investigator: Chi Yan Law (Chalmers University of Technology)

Instrument: HAWC+

Title: Giant growing under still water: Polarized emissions from isolated massive protostar G28.20-0.05

Abstract: Massive stars are believed to play a crucial role in galaxy evolution, chemical enrichment of the interstellar medium, and the formation of black holes. Gravity, supersonic turbulence, magnetic fields, and feedback processes are main stakeholders in the formation of massive stars. Recent studies have shown that magnetic fields can play a dynamically important role in massive star formation. Magnetic fields may regulate the fragmentation of the parental cloud and the orientation of disks and outflows. The proposed observation aims to map the polarized dust continuum emission of an extremely isolated massive protostar G28.2-0.05 at four different wavelengths (53, 89, 154 & 214 um) with HAWC+. The derived polarization vector orientations will be studied, along with complementary molecular line data from the GBT, to infer magnetic field properties and their relation to gas density structures from the large scale IRDC filament to protostellar core and outflow scales. One way to explain isolated massive star formation is via the presence of very strong magnetic fields, i.e., to limit fragmentation, and this observation will test such a prediction.

Proposal ID: 09_0231

Principal Investigator: Alexandre Lazarian (University of Wisconsin Madison)

Instrument: HAWC+

Title: Testing a new method for identifying regions of gravitational collapse within a magnetized molecular cloud using HAWC+ and GBT/ARGUS

Abstract: Understanding how star formation is regulated requires studying the energy balance between turbulence, magnetic fields, feedback and gravity within molecular clouds. Here we propose to use HAWC+ to test a promising new method for both (a) identifying regions within clouds that are gravitationally collapsing, and (b) characterizing the relative importance of magnetic fields, turbulence and self-gravity within clouds. This method is based on predictions from the Velocity Gradient Technique (VGT), that in collapsing regions of molecular clouds the spatial velocity gradients will rotate by 90deg to align parallel to the magnetic field. Such rotations mark the transition from a magnetic field and turbulence dominated regime at low densities, to higher density regions that are collapsing under gravity. VGT rotations towards high density clumps have been observed in simulations and in low resolution (10' FWHM) comparisons between Planck inferred magnetic field maps and velocity gradients derived from molecular line observations. However Planck cannot resolve magnetic fields within dense gas clumps and filaments. Here we propose to make high resolution (19'' FWHM) HAWC+ Band E polarization observations of the nearby dense clump L1551 that shows a change in velocity gradient orientation with respect to the magnetic field at Planck resolution. We also request GBT/ARGUS spectral line observations of HCN and HCO+ to make VGT maps at the same resolution as our HAWC+ data. With these data we will (1) determine whether the rotations of velocity gradients to align parallel with the magnetic field predicted by the VGT method do exist, (2) use the VGT to identify the boundary of the self-gravitating region within L1551, and (3) determine the transition density, which will allow us to estimate the magnetic field strength of L1551. Validation of this VGT technique with HAWC+ observations would provide a powerful new tool for studying gas dynamics in star formation.

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