• Title, Summary, Keyword: stars: outflows

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LINEAR POLARIZATION OF CLASS I METHANOL MASERS IN MASSIVE STAR-FORMING REGIONS

  • Kang, Ji-hyun;Byun, Do-Young;Kim, Kee-Tae;Kim, Jongsoo;Lyo, A-Ran;Kim, Mi-Kyung;Vlemmings, W.H.T.
    • The Bulletin of The Korean Astronomical Society
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    • v.42 no.1
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    • pp.46.1-46.1
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    • 2017
  • Class I methanol masers are found to be good tracers of the interaction between outflows from massive young stellar objects with their surrounding media. Although polarization observations of Class II methanol masers have been able to provide information about magnetic fi elds close to the central (proto)stars, polarization observations of Class I methanol masers are rare, especially at 44 and 95GHz. We present the results of linear polarization observations of 39 Class I methanol maser sources at 44 and 95GHz. These two lines are observed simultaneously with one of the 21m Korean VLBI Network telescopes in single-dish mode. Approximately 60% of the observed sources have fractional polarizations of a few percent in at least one transition. This is the fi rst reported detection of linear polarization of the 44GHz methanol maser. We also observed 7 targets with the KVN in VLBI mode. We will present its preliminary results, too.

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CHEMICAL EVOLUTION IN VeLLOs

  • Lee, Jeong-Eun
    • Journal of The Korean Astronomical Society
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    • v.40 no.4
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    • pp.83-89
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    • 2007
  • A new type of object called "Very Low Luminosity Objects (VeLLOs)" has been discovered by the Spitzer Space Telescope. VeLLOs might be substellar objects forming by accretion. However, some VeLLOs are associated with strong outflows, indicating the previous existence of massive accretion. The thermal history, which significantly affects the chemistry, between substellar objects with a continuous low accretion rate and objects in a quiescent phase after massive accretion (outburst) must be greatly different. In this study, the chemical evolution has been calculated in an episodic accretion model to show that CO and $N_2H^+$ have a relation different from starless cores or Class 0/I objects. Furthermore, the $CO_2$ ice feature at $15.2{\mu}m$ will be a good tracer of the thermal process in VeLLOs.

Optical Long-slit Spectroscopy of Parsec-scale Jets

  • Oh, Heeyoung;Pyo, Tae-Soo;Yuk, In-Soo;Kim, Kang-Min;Lee, Sungho;Park, Byeong-Gon
    • The Bulletin of The Korean Astronomical Society
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    • v.38 no.1
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    • pp.55.2-55.2
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    • 2013
  • We present the observational study of parsec-scale jets from YSOs reaching lengths of several arc-minutes. The medium-resolution spectroscopic data were obtained between 6000 - $7000{\AA}$ with BOAO long-slit spectrograph. By performing multi-position observation, we investigated the physical variation of the jets and the ambient gas along the whole path of the jets. The flux, electron density, ionization fraction, and electron temperature are discussed with the estimated line ratios between from [OI], [NII], $H{\alpha}$ and [SII] emission lines. This study carried out with more than 8 jets of YSOs including low- to intermediate-mass stars. We also briefly discuss the kinematics of the outflows using spatial and spectroscopic data.

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HIGH ANGULAR RESOLUTION [Fe II] λ1.644 μ SPECTROSCOPY OF YSOS WITH SUBARU TELESCOPE

  • PYO TAE-SOO;HAYASHI MASAHIKO;NAOTO KOBAYASHI;TERADA HIROSHI;TOKUNAGA ALAN T.
    • Journal of The Korean Astronomical Society
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    • v.38 no.2
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    • pp.249-252
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    • 2005
  • We present results of the velocity-resolved spectroscopy of the [Fe II] $\lambda$1.644${\mu}m$ emission toward outflow sources with the Subaru Telescope at the angular resolution of 0.apos;16 ${\~}$ 0.apos;5 arcseconds. The observed sources are L1551 IRS 5, DG Tau, HL Tau and RW Aur, which are located in the Taurus-Aurigae Molecular Cloud, one of the closest star forming regions (0.apos;1 = 14 AU). We were able to resolve outflow structure in the vicinity of the sources at a scale of a few tens of AU. The position-velocity diagram of each object shows two velocity components: the high velocity component (HVC: 200 - 400 km $s^{-l}$) and the low velocity component (LVC: 50 - 150 km $s^{-l}$), which are clearly distinct in space and velocity. The HVC may be a highly collimated jet presumed from its narrow velocity width and high velocity. The LVC, on the other hand, may be a widely opened disk wind inferred from its broad velocity width and low velocity. The spectrum taken perpendicular to the L1551 IRS 5 outflow at its base shows that the LVC has a spatially wide subcomponent, supporting the above interpretation. We demonstrated that the [Fe II] 1.644 $\mu$ spectroscopy is a very powerful tool for the studies of fast jets and winds that directly emanate from star-disk systems.

FOLLOW-UP OBSERVATIONS TOWARD PLANCK COLD CLUMPS WITH GROUND-BASED RADIO TELESCOPES

  • LIU, TIE;WU, YUEFANG;MARDONES, DIEGO;KIM, KEE-TAE;MENTEN, KARL M.;TATEMATSU, KEN;CUNNINGHAM, MARIA;JUVELA, MIKA;ZHANG, QIZHOU;GOLDSMITH, PAUL F;LIU, SHENG-YUAN;ZHANG, HUA-WEI;MENG, FANYI;LI, DI;LO, NADIA;GUAN, XIN;YUAN, JINGHUA;BELLOCHE, ARNAUD;HENKEL, CHRISTIAN;WYROWSKI, FRIEDRICH;GARAY, GUIDO;RISTORCELLI, ISABELLE;LEE, JEONG-EUN;WANG, KE;BRONFMAN, LEONARDO;TOTH, L. VIKTOR;SCHNEE, SCOTT;QIN, SHENGLI;AKHTER, SHAILA
    • Publications of The Korean Astronomical Society
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    • v.30 no.2
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    • pp.79-82
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    • 2015
  • The physical and chemical properties of prestellar cores, especially massive ones, are still far from being well understood due to the lack of a large sample. The low dust temperature (< 14 K) of Planck cold clumps makes them promising candidates for prestellar objects or for sources at the very initial stages of protostellar collapse. We have been conducting a series of observations toward Planck cold clumps (PCCs) with ground-based radio telescopes. In general, when compared with other star forming samples (e.g. infrared dark clouds), PCCs are more quiescent, suggesting that most of them may be in the earliest phase of star formation. However, some PCCs are associated with protostars and molecular outflows, indicating that not all PCCs are in a prestellar phase. We have identified hundreds of starless dense clumps from a mapping survey with the Purple Mountain Observatory (PMO) 13.7-m telescope. Follow-up observations suggest that these dense clumps are ideal targets to search for prestellar objects.

Constraining the Mass Loss Geometry of Beta Lyrae

  • Lomax, Jamie R.
    • Journal of Astronomy and Space Sciences
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    • v.29 no.1
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    • pp.47-49
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    • 2012
  • Massive binary stars lose mass by two mechanisms: jet-driven mass loss during periods of active mass transfer and by wind-driven mass loss. Beta Lyrae is an eclipsing, semi-detached binary whose state of active mass transfer provides a unique opportunity to study how the evolution of binary systems is affected by jet-driven mass loss. Roche lobe overflow from the primary star feeds the thick accretion disk which almost completely obscures the mass-gaining star. A hot spot predicted to be on the edge of the accretion disk may be the source of beta Lyrae's bipolar outflows. I present results from spectropolarimetric data taken with the University of Wisconsin's Half-Wave Spectropolarimeter and the Flower and Cook Observatory's photoelastic modulating polarimeter instrument which have implications for our current understanding of the system's disk geometry. Using broadband polarimetric analysis, I derive new information about the structure of the disk and the presence and location of a hot spot. These results place constraints on the geometrical distribution of material in beta Lyrae and can help quantify the amount of mass lost from massive interacting binary systems during phases of mass transfer and jet-driven mass loss.

WATER MASERS FROM THE PROTOSTELLAR DISK AND OUTFLOW IN THE NGC 1333 IRAS 4 REGION

  • Park, Geum-Sook;Choi, Min-Ho
    • Journal of The Korean Astronomical Society
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    • v.40 no.4
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    • pp.123-125
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    • 2007
  • NGC 1333 is a nearby star forming region, and IRAS 4A and IRAS 4BI are low-mass Class 0 protostars. IRAS 4A is a protobinary system. The NGC 1333 IRAS 4 region was observed in the 22 GHz water maser with a high resolution (0.08") using the Very Large Array. Two groups of masers were detected: one near A2 and the other near BI. Most of the masers associated with A2 are located very close (< 100 AU) to the radio continuum source. They may be associated with the circumstellar disk. Since no maser was detected near AI, the A2 disk is relatively more active than the Al disk. Most of the masers in the BI region are distributed along a straight line, and they are probably related with the outflow. As in many other water maser sources, the IRAS 4 water masers seem to trace selectively either the disk or the outflow. Considering the outflow lifetimes, the disk-outflow dichotomy is probably unrelated with the evolutionary stage of protostars. A possible explanation may be that both the outflow-maser and the disk-maser are rare phenomena and that detecting both kinds of maser around a single protostar may be even rarer.

MOLECULAR LINE STUDY OF L1014 WITH SRAO 6M TELESCOPE (L1014 분자운 핵에 대한 SRAO 6m 망원경을 이용한 분자선 관측연구)

  • Lee, Chang-Won
    • Publications of The Korean Astronomical Society
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    • v.20 no.1
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    • pp.1-5
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    • 2005
  • We report molecular line observations of CO(1-0), $^{13}CO(1-0)$, CS(2-1), and HCN(1-0) with SRAO 6m telescope toward L1014-IRS which is thought to be a very faint infrared source embedded in previously known 'starless' core L1014. The CO(1-0) observations find several components with different velocities along the line of sight of L1014, $4km\;s^{-1}$ and between $40{\sim}50km\;s^{-1}$. We find a parsec scale CO molecular outflow at the $4km\;s^{-1}$ component for the first time the direction of which is coincident with that of the small scale (${\sim}500pc$) outflow previously found. Although the observation is not covered for whole area of the outflow, the size of the molecular outflow seems not very inconsistent with the expected age of L1014-IRS. More accurate size and shape of the molecular outflow from L1014-IRS will be determined from the full coverage mapping in CO over the outflow region in very near future.