• 천문학회보
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• 제40권2호
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• pp.35.2-35.2
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• 2015

We present the results of simultaneous observations of the H2O and SiO masers emitted from the circumstellar envelopes (CSEs) of the late-type stars. These observations have been carried out at the four frequency bands (K, Q, W and D bands) using KVN to apply the source frequency phase referencing (SFPR) analysis to the maser lines. We obtain the relative positions between the H2O and the SiO maser spots by using the SFPR method, which are very important to study the physical links between the inner and the outer parts of the CSEs of the late-type stars. The relative positions between the SiO maser spots of the different transitions are also obtained very accurately, which are very crucial to investigate the pumping mechanism of the SiO maser lines. From our results, the capability of the simultaneous multi-band observation of KVN is proved to be powerful to study the complicated physical environments of the CSEs and the stellar evolution of the late-type stars.

• 천문학회지
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• 제29권spc1호
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• pp.261-262
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• 1996

Nearly simultaneous observations for $^{28}SiO$ v=0, 1, 2, J =3-2 transitions in 39 late-type stars have been carried out in February 1995 and 1996 with the 14 m radio telescope at Taeduk Radio Astronomy Observatory (TRAO). Observations for $^{28}SiO$ v=0, 1, 2, J=2-1 lines in the same objects have been also carried out in March 1995 and March-April 1996. The detection rate of $^{28}SiO$ v=l, J=3-2 line for the $^{28}SiO$ v=l, J=2-1 sources was $59\%$. Seventeen new detections in the $^{28}SiO$ v=l, J=3-2 transition and 4 new detections in the $^{28}SiO$ v=2, J=3-2 transition have been reported including the intensity ratios within the vibrational ladders and rotational states.

• 천문학회보
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• 제46권2호
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• pp.49.2-49.2
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• 2021

We present the results of long-term simultaneous monitoring observations (~ 12 years) of H²O (22 GHz) maser and several vibrationally excited lines of SiO J = 1-0, 2-1, 3-2 masers (43, 86, 129 GHz) carried out with the 21-m antennas of the Korean VLBI Network (KVN) toward a sample of three AGB stars (RT Vir, RR Aql, IRC-10151) that are believed to be semiregular variable star, Mira variable star, and OH/IR star, respectively, according to a sequential evolutionary phase of AGB star. A total 10 transitions were observed, of which we detected H²O, SiO 𝝊 = 1 and 2, J = 1-0, SiO 𝝊 = 1, J = 2-1 and J = 3-2 maser lines in all three target objects, depending on the observational epochs. In this study, we scrutinize the evolutionary traits of each target object based on the maser line profiles, flux/velocity variations, and phase lags with the optical light curves. The IRAS two color diagram and the infrared spectral energy distributions (SEDs) in the wavelength range from 1.2 to 240 ㎛ of three observed sources were also analyzed.

• 천문학회보
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• 제35권2호
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• pp.79.2-79.2
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• 2010

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 performed with the KVN Yonsei 21 m radio telescope from 2009 Nov. to 2010 Jan (ApJ, 719, 126, 2010). We searched for these masers in 47 symbiotic stars and detected maser emission from 21 stars, giving the first time detection from 19 stars. Both SiO and $H_2O$ masers were detected from seven stars of which six stars are D-type symbiotic and one is an S-type star, WRAY 15-1470. In the SiO maser emission, the $^{28}SiO$ v=1 maser was detected from 10 stars, while the v=2 maser detected from 15 stars. In particular, the $^{28}SiO$ v=2 maser emission without the v=1 maser detection was detected from nine stars with its detection rate of 60 %, which is much higher than that of isolated Miras/red giants. The $^{29}SiO$ v=0 maser emission was also detected from two stars, H 2-38 and BF Cyg, together with the $^{28}SiO$ v=2 maser. We conclude that these different observational results between isolated Miras/red giants and symbiotic stars may be related with the presence of hot companions in a symbiotic binary system.

• 천문학논총
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• 제7권1호
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• pp.155-166
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• 1992

We observed a total of 14 Mira variables as well as 4 late type variable stars for their SiO ${\nu}= 1$, J = 2 - 1 maser lines from April 1989 to November 1990 with the 13.7 m radio telescope at Daeduk Radio Astronomy Observatory. The maser intensity variations were the prime objective of the observations which well covered the periods of the variations. The origion of the variations were studied by comparing wi th those previousely measured in optical and infrared(IR) wavelengths and we confirmed that the intensity variations were in good correlation with those in V magnitude and IR intensity as previousely found in former investigators in general. However, for a few sources, we could find the missing maxima. The intensities themselves also were in good correlation with SiO ${\nu}\;=\;1$, J = 1 - 0 maser intensities observed in Yebes as expected. The good correlations indicate that the pumping source of the SiO maser is likely to be the IR emission in the masing regions and the "missing maxima" that are apparent in two particular sources are considered to relate wi th the strength of shocks arising from the eruptive mass-loss from central stars.

• 천문학회지
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• 제34권3호
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• pp.167-179
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• 2001

A molecular line survey towards the UC H II region G34.3+0.15 from 155.3 to 165.3GHz has been conducted with the TRAO 14-m radio telescope. Combined with our previous observations from 84.7 to 115.6GHz and 123.5 to 155.3GHz (Paper I), the spectral coverage of this survey in G34.3+0.15 now runs from 85 to 165 GHz. From these latest observations, a total of 18 lines from 6 species were detected. These include four new lines corresponding to ${\Delta}$J = 0, ${\Delta}$K = 1 transitions of the $CH_3OH$ E-type species, and two new lines corresponding to transitions from $SO_2$ and $HC_3N$. These 6 new lines are $CH_3OH$[1(1) - 1(0)E], $CH_3OH$[2(1) - 2(0)E], $CH_3OH$[3(1) - 3(0)E], $CH_3OH$[4(1) - 4(0)E], $SO_2$[14(1, 13) -14(0, 14)] and $HC_3N$[18 -17]. We applied a rotation diagram analysis to derive rotation temperatures and column densities from the methanol transitions detected, and combined with NRAO 12-m data from Slysh et al. 1999. Applying a two-component fit, we find a cold component with temperature 13-16K and column density $3.3-3.4 {\times} 10^{14} cm^{-2}$, and a hot component with temperature 64 - 83K and column density $9.3{\times}10^{14} - 9.7 {\times} 10^{14} cm^{-2}$. On the other hand, applying just a one-component fit yields temperatures in the 47 -62 K range and column densities from $7.5-1.1 {\times} 10^{15} cm^{-2}$.

• 천문학회지
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• 제47권6호
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• pp.259-277
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• 2014

G192.8-1.1 has been known as one of the faintest supernova remnants (SNRs) in the Galax until the radio continuum of G192.8-1.1 is proved to be thermal by Gao et al. (2011). Yet, the nature of G192.8-1.1 has not been fully investigated. Here, we report the possible discovery of faint non-thermal radio continuum components with a spectral index ${\alpha}{\sim}0.56(S_{\nu}{\propto}{\nu}^{-{\alpha}})$ around G192.8-1.1, while of the radio continuum emission is thermal. Also, our Arecibo $H_I$ data reveal an $H_I$ shell, expanding with an expansion velocity of $20-60km\;s^{-1}$, that has an excellent morphological correlation with the radio continuum emission. The estimated physical parameters of the $H_I$ shell and the possible association of non-thermal radio continuum emission with it suggest G192.8-1.1 to be an~0.3 Myr-old SNR. However, the presence of thermal radio continuum implies the presence of early-type stars in the same region. One possibility is that a massive star is ionizing the interior of an old SNR. If it is the case, the electron distribution assumed by the centrally-peaked surface brightness of thermal emission implies that G192.8-1.1 is a "thermal-composite" SNR, rather than a typical shell-type SNR, where the central hot gas that used to be bright in X-rays has cooled down. Therefore, we propose that G192.8-1.1 is an old evolved thermal-composite SNR showing recurring emission in the radio continuum due to a nearby massive star. The infrared image supports that the $H_I$ shell of G192.8-1.1 is currently encountering a nearby star forming region that possibly contains an early type star(s).

• 천문학회보
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• 제37권2호
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• pp.237.2-237.2
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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 132 AGB and 183 post-AGB stars in order to investigate how evolutionary characteristics from AGB to post-AGB stars appear in these two maser emissions. The observations were carried out from 2011 February to 2012 March using the Korean VLBI Network 21-m radio telescopes. We have detected SiO and/or $H_2O$ maser emission from 29 sources out of 183 post-AGB stars including 19 new detections. Of 132 AGB stars which are mainly selected based on the IRAS Point Source Catalog, we detected SiO and/or $H_2O$ maser emission from 38 stars including 18 newly detected sources. An evolutionary characteristic from AGB to post-AGB stars is discussed in IRAS two-color diagram. It is found that SiO v=2, J=1-0 maser emission without SiO v=1 maser detections was detected from 8 sources among 21 SiO detected post-AGB stars and the intensity of SiO v=2, J=1-0 maser tends to be much stronger than that of SiO v=1. We also found that for the post-AGB stars the maser detection rate of blue group sources (which have higher outflow velocities than red group) are higher than that of red group. Especially, only $H_2O$ maser emission was detected from 7 sources among 94 red group sources without SiO maser detections.

• 천문학회지
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• 제48권5호
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• pp.267-275
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• 2015

Simultaneous time monitoring observations of H₂O and SiO maser lines were performed toward the D-type symbiotic binary system V407 Cyg with the Korean VLBI Network single dish radio telescope. These monitoring observations were carried out from March 2, 2010 (optical phase ϕ = 0.0), 8 days before the nova outburst on March 10, 2010 to June 5, 2014 (ϕ = 2.13). Eight days before the nova outburst, we detected the SiO v = 1, 2, J = 1–0 maser lines which exhibited values of 0.51 K (∼ 6.70 Jy) and 0.71 K (∼ 9.30 Jy), respectively, while after the outburst we could not detect them on April 2 (ϕ = 0.04), May 5 (ϕ = 0.09), May 8 (ϕ = 0.09), or on June 5, 2010 (ϕ = 0.13) within the upper limits of our KVN observations. After restarting our monitoring observations, we detected SiO v = 2, J = 1–0 masers starting on October 20, 2011 (ϕ = 0.83) and detected SiO v = 1, J = 1–0 masers starting on December 22, 2011 (ϕ = 0.92). These results provide clear evidence of the interaction between the shock from the nova outburst and the SiO maser regions of the Mira envelope. The peak emission of SiO v = 1, 2, J = 1–0 masers always occurred at blueshifted velocities with respect to the stellar velocity except for that of SiO v = 1 at one epoch. These phenomena may be related to the redistribution of SiO maser regions after the outburst. The peak velocity variations of SiO masers associated with stellar pulsation phases show an increasing blueshifted trend during our monitoring interval after the outburst.

• 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.