Research

    B-FROST: B-Fields and staR fOrmation across Scales with TRAO


    ABSTRACT
    Understanding star formation requires to untangle the roles of gravity, turbulence, and magnetic fields (B-fields) in the formation and evolution of molecular clouds across all scales from cores (0.1 pc) to clouds (tens of pc). We compiled a sample of six clouds representative of various environments, evolutionary stages, and mass ranges. We propose large-scale mapping of their extended emission in 12CO and 13CO(J=1-0), to characterize (i) their environment, in terms of X-factor and impinging radiation field, (ii) their multi-scale dynamics, using coherent velocity structures, dendrogram analysis and the spectral correlation function, and (iii) their magnetic fields. For point (iii), TRAO data will be combined with Planck polarization data to study the large scale B-fields, and the velocity gradient technique (VGT) will enable us to study the B-field morphology and intensity at smaller scales with TRAO data alone. This project will provide a unique dataset in terms of cloud diversity and of scale range (up to ~800 beams), which we plan to make public after we have completed the main analyses.

No Key Science Program in this season

We would like to announce the selection results of TRAO KSP (Key Science Program) proposals; Five proposals were submitted from KASI and two domestic universities in South Korea. KSP proposals were evaluated by six referees from domestic/foreign institutes and universities. TRAO KSP selection committee decided three proposals as TRAO KSPs based on the referees’ evaluation and comments

  1. C. W. Lee (FUNS: Filaments, the Universal Nursery of Stars)
  2. J. E. Lee (TIMES: mapping Turbulent properties In star-forming MolEcular clouds down to the Sonic scale)
  3. T. Liu (TOP: TRAO Observations of Planck cold clumps)

About 400 hours of telescope time per year will be allocated to the TRAO KSPs for three years. KSP summary and information of their publication plan, management and data reduction etc. will be updated later when they are ready.


Abstracts of TRAO KSPs

FUNS: Filaments, the Universal Nursery of Stars (TRAO Multi-beam Legacy Survey of Nearby Filamentary Molecular Clouds)

How dense cores and filaments in molecular clouds form is a central issue in star formation. TRAO 14m telescope equipped with a new multi-beam receiver array, TRAO-SEQUOIA, will allow us to challenge this issue with its capability of high speed mapping in the supreme sensitivity. With this new system we will make a systematic mapping survey of nearby molecular clouds in various environments with high (N2H+, HCN 1-0, CS 2-1, SO 32-21, and NH2D ν=1-0 lines) and low (C18O 1-0) density tracers to dynamically and chemically understand how filaments, dense cores, and stars form under different environments.

The specific goals for this survey are (1) to obtain the velocity distribution of low dense filaments and their dense cores for the study of their origin of the formation, (2) to understand whether the dense cores form from any radial accretion or inward motions toward dense cores from their surrounding filaments, and (3) to study the chemical differentiation of the filaments and the dense cores.

Our observing targets as the filamentary clouds are nearby (within 500 pc) and categorized into five different environments (1) quiescent non-star-forming cloud, (2) quiescent low-mass star-forming cloud, (3) turbulent low-mass star-forming cloud, (4) star cluster forming cloud, and (5) high-mass star forming cloud. Targets selected are Polaris, IC5146, Perseus, Auriga, Taurus, Orion-B, Scorpius, Aquila, and Cepheus cloud. We expect to complete the survey in 3 years with observations of 400 hours per year. Our survey will shed light on the mysteries of star formation in filamentary clouds.

TIMES: mapping Turbulent properties In star-forming MolEcular clouds down to the Sonic scale

This program will provide the first full high-resolution maps of three star-forming clouds (L1251, Ophiuchus, and Orion A), which have distinct star formation environments, in C18O, HCO+, HCN, and N2H+ (J = 1 – 0). The main goal of this program is to study the properties of turbulence in nearby star-forming molecular clouds and follow the turbulent cascade over two orders of magnitude by mapping three sets of molecular lines that trace different densities (13CO and C18O; HCN and HCO+; and N2H+ and CS). These data will be combined with existing large maps of 12CO to recover additional extended cloud structure. We will employ statistical methods such as the spectral correlation function (SCF) and principal component analysis (PCA), which have been shown to be sensitive to underlying turbulent properties, to quantitatively characterize and compare cloud structure. The comparison of the complete emission maps to hydrodynamic astrochemical models will provide a fundamental opportunity to understand (1) the influence of turbulence on the conditions of molecular clouds, (2) the turbulent cascade and transition from supersonic to subsonic turbulence, and (3) the relation between turbulent properties and star formation efficiency.

In addition to the studies listed above, these complete maps will provide a unique database that can be combined with follow-up high-resolution observations with ground-based mm/submm telescopes and interferometers such as ALMA to study a variety of additional star formation problems. For example, ALMA will allow a more comprehensive study of astrochemistry on small scales and allow the extension of this work to smaller scales. Our data in combination with polarization studies (e.g., Planck, SCUBA-2, and possibly ALMA) will shed light on how magnetic field correlates with structure in molecular emission. Detailed studies of embedded sources will be able to address how feedback influences dense gas and excitation conditions. Therefore, in conjunction with follow-up observations, this program will provide an important new legacy database for the study of astrochemistry, turbulent properties and cloud conditions over various scales of molecular clouds with different star formation environments.

TOP: TRAO Observations of Planck cold clumps

Stars form in the densest parts of molecular clouds, so–called prestellar cores. However, the formation and spatial distribution of prestellar cores in different kinds of molecular clouds is far from being understood due to the lack of an “all-sky” census. The important connection between core formation and the hierarchical fragmentation of molecular clouds remains obscure. Now, the Planck telescope has provided us with an unprecedented sample of “all-sky” pre-stellar object candidates. Planck cold clumps correspond to the coldest portion of the ISM where stars form, and can be used to characterize the earliest stages of star formation. In order to make significant progress in understanding the early evolution of molecular clouds and dense cores in a wide range of Galactic environments, we are carrying out an unbiased “all-sky” CO/13CO survey of 2000 Planck cold clumps with the TRAO 13.7-m telescope. Through this extensive survey, we will study:

  • the structure of the Miky Way especially the solar neighborhood,
  • hierarchical structure of molecular clouds,
  • the universality of filaments in the cold ISM and their roles in generating dense cores,
  • the roles of magnetic field, turbulence and gravity in structure formation,
  • the chemical and dynamical evolution of molecular clouds,
  • how dense cores form and how star formation varies as a function of environment,
  • the existence of a density threshold for dense core formation,
  • the variation of CO abundance in different galactic environments,
  • Kinematics of molecular clumps (e.g., rotation, outflow, infall),...

We have being performed related parallel surveys at other mm and radio telescopes (e.g., JCMT, SMT, KVN...) and we will actively develop follow-up observations (e.g., NRO 45-m, SMA) for this legacy survey, which will allow us to deepen the investigation of the dense core or star formation in a widely different environments at their earliest evolutionary phases. These joint surveys (TRAO, JCMT, PMO, KVN, NRO 45-m, ...) will also provide a unique legacy database for such studies with other instruments, especially with ALMA.