• 천문학회보
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• 제42권1호
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• pp.46.3-47
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• 2017

We performed simultaneous VLBI observations of H2O 616-523 (22.2 GHz) and SiO v=1, 2, J=1-0 (43.1, 42.8 GHz) and v=1, J=2-1, J=3-2 (86.2, 129.3 GHz) masers toward VX Sagittarius using the Korean VLBI Network (KVN). The astrometrically registered maps of the 22.2 GHz H2O and 43.1, 42.8, 86.2 SiO masers were successfully obtained at two epochs of 2016 February 27 and 2016 March 27 by adopting the Source Frequency Phase Referencing (SFPR) method. In addition we detected 129.3 Ghz SiO maser at second epoch. These results make it possible to determine the accurate position of central star as a dynamical center of 22.2 GHz H2O maser and relative locations of 43.1, 42.8, 86.2, 129.3 GHz SiO masers. In addition, it is possible to investigate the morphological and kinematic variations of clumpy structures from SiO maser to H2O maser regions in future together with the development of asymmetric structure of H2O maser region.

• 천문학회보
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• 제37권2호
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• pp.237.1-237.1
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• 2012

We report extensive statistical analyses based on the simultaneous observational results of SiO and $H_2O$ masers toward 166 known both SiO and $H_2O$ maser sources (Kim et al. 2010), 83 known SiO maser sources (Cho & Kim 2012 submitted), and 152 known $H_2O$ maser sources (Kim et al. 2012 in preparation). We investigate mutual relations between SiO and $H_2O$ maser properties (peak and total flux density ratios, full line width ratios, and velocity structures etc.) according to stellar pulsation phases and type of evolved stars. These statistical results are compared with monitoring observational results of some individual stars. In addition, a relation between the full line width of SiO/$H_2O$ masers and stellar mass loss rates is examined. For 401 observed stars, we also investigate characteristics of SiO and $H_2O$ maser properties related with evolutionary stages in the IRAS two-color diagram.

• 천문학회지
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• 제43권2호
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• pp.41-54
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• 2010

We report relative proper motion measurements of $H_{2}O$ masers in massive star-forming region W51 Main, based on data sets of VLBI observations for $H_{2}O$ masers at 22 GHz with Japanese VERA telescopes from 2003 to 2006. Data reductions and single-beam imaging analysis are to measure internal kinematics of maser spots and eventually to estimate the three-dimensional kinematics of $H_{2}O$ masers in W51 Main. Average space motions and proper motion measurements of $H_{2}O$ masers are given both graphical and in table formats. We find in this study that W51 Main appears to be associated with hyper-compact H II region with multiple massive proto-stars whose spectral types are of late O.

• 천문학회지
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• 제48권6호
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• pp.357-364
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• 2015

We observe ten known 22GHz H₂O maser galaxies during February 19-22, 2011 using the 21 m Tamna telescope of the Korean VLBI Network and a new wide-band digital spectrometer. Simultaneously we searched for 43GHz SiO v = 1, 2, J = 1-0 maser emission. We detect H₂O maser emission towards five sources (M 33, NGC 1052, NGC 1068, NGC 4258, M 82), with non-detections towards the remaining sources (UGC 3193, UGC 3789, Antennae H₂O-West, M 51, NGC 6323) likely due to sensitivity. Our 22GHz spectra are consistent with earlier findings. Our simultaneous 43GHz SiO maser search produced non-detections, yielding - for the first time - upper limits on the 43GHz SiO maser emission in these sources at a 3 σ sensitivity level of 0.018K-0.033K (0.24 Jy-0.44 Jy) in a 1.75 km s⁻¹ velocity resolution. Our findings suggest that any 43GHz SiO masers in these sources (some having starburst-associated H₂O kilomasers) must be faint compared to the 22GHz H₂O maser emission.

• 천문학회보
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• 제37권2호
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• pp.240.1-240.1
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• 2012

We performed simultaneous observations of SiO v=1, 2, $^{29}SiO$ v=0, J=1-0 and $H_2O$ $6_{16}-5_{23}$ maser lines toward 252 OH/IR stars using the Korean VLBI Network 21m telescopes. The observations were carried out from 2011 November to 2012 July for studying SiO and $H_2O$ maser properties associated with the evolutionary stages of OH/IR stars. Both $H_2O$ and SiO masers were detected from 49 sources, one-side maser of SiO and $H_2O$ was detected from 109 and 11 sources, respectively. Mutual relations between SiO and $H_2O$ maser properties are investigated based on statistical analyses. We also investigate these maser properties in the IRAS two-color diagram related with stellar evolutionary sequence.

• 천문학회보
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• 제38권2호
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• pp.63.1-63.1
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• 2013

We present the results of time monitoring observations of $^{28}SiO$ v = 1, 2, J = 1-0, $^{29}SiO$ v = 0, J = 1-0 and $H_2O$ $6_{16}-5_{23}$ maser lines toward radio Source I in Orion KL. The observations have been performed from 2009 June to 2013 April using the 21m single dish radio telescopes of the Korean VLBI Network. Both SiO and $H_2O$ maser lines were simultaneously obtained at 20 epochs. In particular, the third outburst of $H_2O$ maser emission (the first: 1985, the second: 1998) was detected and the flux density variation curve was obtained. The maximum flux density flared up to an order of $10^5$ Jy during 2012 May-July at peak velocity of 7.33 km $s^{-1}$. Hirota et al. (2011) reported that the bursting maser features are located at 8" from Source I and coincident with the interacting region between the outflow from Source I and a dense ambient gas, Orion Compact Ridge. In the case of SiO masers arising from close to the Source I, the peak emission of the v = 1, J = 1-0 maser line appeared in 2010 April. We are investigating the possible relation between this SiO maser peak emission and the third $H_2O$ maser flaring.

• 천문학회보
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• 제36권2호
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• pp.109.2-109.2
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• 2011

We have carried out a multi-epoch, simultaneous 22GHz $H_2O$ and 44GHz class I $CH_3OH$ maser survey of 109 low-mass protostars. $H_2O$ maser emission was detected in 23 sources, while $CH_3OH$ maser emission in 12 sources. Eight of the $CH_3OH$ detected sources are new detections. For comparison, only four low-mass protostars have been previously found to emit the maser emisison. We investigate difference between the properties of the two masers, such as relative velocity with respect to molecular gas and variability. We also compare the isotropic luminosities of both masers with the bolometric luminosity of the central star.

• 천문학회보
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• 제40권2호
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• pp.58.4-59
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• 2015

We have performed single dish and VLBI monitoring observations of $H_2O$ and SiO masers toward the semi-regular variable star R Crateris using the Korean VLBI Network(KVN) 4 band receiving system. In the case of VLBI observations at 3 epochs, successful superposed maps of $H_2O$ and SiO masers were obtained on 2015 May by adopting the Source Frequency Phase Referencing(SFPR) method. These results enable us to investigate the development of outflow and asymmetric motions from SiO maser to $H_2O$ maser regions according to stellar pulsation which are closely related with a mass-loss process. Single dish monitoring observations were carried out from 2009 June to 2015 May. Intensity variations between $H_2O$ and SiO masers were investigated according to stellar phases together with peak velocity variations. We will compare the VLBI results with those of single dish.

• 천문학회지
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• 제50권6호
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• pp.157-165
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• 2017

$H_2O$ maser emission at 22 GHz in the circumstellar envelope is one of the good tracers of detailed physics and kinematics in the mass loss process of asymptotic giant branch stars. Long-term monitoring of an $H_2O$ maser spectrum with high time resolution enables us to clarify acceleration processes of the expanding shell in the stellar atmosphere. We monitored the $H_2O$ maser emission of the semi-regular variable R Crt with the Kagoshima 6-m telescope, and obtained a large data set of over 180 maser spectra over a period of 1.3 years with an observational span of a few days. Using an automatic peak detection method based on least-squares fitting, we exhaustively detected peaks as significant velocity components with the radial velocity on a $0.1kms^{-1}$ scale. This analysis result shows that the radial velocity of red-shifted and blue-shifted components exhibits a change between acceleration and deceleration on the time scale of a few hundred days. These velocity variations are likely to correlate with intensity variations, in particular during flaring state of $H_2O$ masers. It seems reasonable to consider that the velocity variation of the maser source is caused by shock propagation in the envelope due to stellar pulsation. However, it is difficult to explain the relationship between the velocity variation and the intensity variation only from shock propagation effects. We found that a time delay of the integrated maser intensity with respect to the optical light curve is about 150 days.

• 천문학회보
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• 제36권2호
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• pp.145.2-145.2
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• 2011

We present the results of simultaneous observations of SiO v = 1, 2, J = 1-0, $^{29}SiO$ v = 0, J = 1-0, and $H_2O$ $6_{16}-5_{23}$ maser lines toward 152 known $H_2O$-only maser sources (the sources which are previously detected only in the 22 GHz $H_2O$ maser emission) using Yonsei and Tamna 21-m radio telescopes of the Korean VLBI Network from 2009 June to 2011 January. Both SiO and $H_2O$ maser emission were detected from 62 sources giving a detection rate of 40.8 %. SiO-only maser emission was detected from 27 sources, while $H_2O$-only maser was detected from 22 sources. We have identified 19 new detections of SiO maser emission for previous non-detection sources and 51 new detections of SiO maser for previously not observed sources. Characteristics of all observed sources in the IRAS two-color diagram is investigated including their evolutionary sequence and mutual relations between SiO and $H_2O$ maser emission. These observational results will be useful for statistical study of asymptotic giant branch (AGB) stars and future VLBI observation.