Gwanjeong Kim

How do stars gain their mass? : A JCMT/SCUBA-2 Transient Survey of Protostars in Nearby Star Forming Regions

Most protostars have luminosities that are fainter than expected from steady accretion over the protostellar lifetime. The solution to this problem may lie in episodic mass accretion—prolonged periods of very low accretion punctuated by short bursts of rapid accretion. However, the timescale and amplitude for variability at the protostellar phase is almost entirely unconstrained. In A James Clerk Maxwell Telescope/SCUBA-2 Transient Survey of Protostars in Nearby Star-forming Regions, we are monitoring monthly with SCUBA-2 the submillimeter emission in eight fields within nearby (<500 pc) star-forming regions to measure the accretion variability of protostars. The total survey area of ~1.6 deg^2 includes ~105 peaks with peaks brighter than 0.5 Jy/beam (43 associated with embedded protostars or disks) and 237 peaks of 0.125–0.5 Jy/beam (50 with embedded protostars or disks). Each field has enough bright peaks for flux calibration relative to other peaks in the same field, which improves upon the nominal flux calibration uncertainties of submillimeter observations to reach a precision of ~2%–3% rms, and also provides quantified confidence in any measured variability. The timescales and amplitudes of any submillimeter variation will then be converted into variations in accretion rate and subsequently used to infer the physical causes of the variability. This survey is the first dedicated survey for submillimeter variability and complements other transient surveys at optical and near-IR wavelengths, which are not sensitive to accretion variability of deeply embedded protostars.

ASSOCIATION OF INFRARED DARK CLOUD CORES WITH YSOS: STARLESS OR STARRED IRDC CORES

In this paper we examined theassociation of InfraRed Dark Cloud (IRDC) cores with YSOs and the geometric properties of the IRDC cores. For this studya total of 13,650 IRDC cores were collected mainly from the catalogs of the IRDC cores published from other studies andpartially from our catalog of IRDC cores containing new 789 IRDC core candidates. The YSO candidates were searched for usingthe GLIMPSE, MSX, and IRAS point sources by the shape of their SED or using activity of water or methanol maser. The associationof the IRDC cores with these YSOs was checked by their line- of-sight coincidence within the dimension of the IRDC core.This work found that a total of 4,110 IRDC cores have YSO candidates while 9,540 IRDC cores have no indication of the existenceof YSOs. Considering the 12,200 IRDC cores within the GLIMPSE survey region for which the YSO candidates were determinedwith better sensitivity, we found that 4,098 IRDC cores (34%) have at least one YSO candidate and 1,072 cores among themseem to have embedded YSOs, while the rest 8,102 (66%) have no YSO candidate. Therefore, the ratio of [N(IRDC core with protostars)]/[N(IRDCcore without YSO)] for 12,200 IRDC cores is about 0.13. Taking into account this ratio and typical lifetime of high-massembedded YSOs, we suggest that the IRDC cores would spend about 104 ~ 105 years to form high-mass stars.However, we should note that the GLIMPSE point sources have a minimum detectable luminosity of about 1.2 Lq at a typical IRDC cores distanceof ~4 kpc. Therefore, the ratio given here should be a lower limit and the estimated lifetime of starless IRDC cores canbe an upper limit. The physical parameters of the IRDC cores somewhat vary depending on how many YSO candidates the IRDCcores contain. The IRDC cores with more YSOs tend to be larger, more elongated, and have better darkness contrast than theIRDC cores with fewer or no YSOs.

Probing the magnetic fields in L1415 and L1389

We present the R-band polarimetric results towards two nebulae L1415 and L1389 containing low luminosity stars. Aim of this study is to understand the role played by magnetic fields in formation of low luminosity objects. Linear polarization arise due to dichroism of the background starlight projected on the cloud providing the plane-of-the sky magnetic field orientation. The offsets between mean magnetic field directions obtained towards L1415 and L1389 and the projected outflow axes are found to be 35

Dense Molecular Cores Being Externally Heated

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High-resolution ALMA Study of the Proto-brown-dwarf Candidate L328-IRS

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Planck Cold Clumps in the λ Orionis Complex. II. Environmental Effects on Core Formation

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A SEARCH FOR VERY LOW-LUMINOSITY OBJECTS IN GOULD BELT CLOUDS

, respectively. The offset between cloud minor axes and mean envelope magnetic field direction in L1415 and L1389 are 50

A Holistic Perspective on the Dynamics of G035.39-00.33: The Interplay between Gas and Magnetic Fields

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Survey for CO Outflow Activities in 68 VeLLOs

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Chemical Differentiation of CS and N₂H + in Starless Cores

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