Using the characteristics of the KVN 4 band receiving system, we set up following scientific goals. (1) We aim at investigating spatial structures and dynamical effects from SiO to 22 GHz H2O maser regions (i. e., atmosphere to circumstellar envelope) according to stellar pulsation through simultaneous monitoring observations of KVN 4 bands using both KVN single dish and VLBI network. The SiO maser lines, due to their high excitation temperature and density, are suitable for investigating nearby regions of central star which are under accelerating and decelerating by the influence of a stellar pulsation. On the other hand, 22 GHz H2O maser traces the region above dust forming layer in which outflow velocities approach to a terminal velocity of mass-loss. Therefore, both masers are good probes for investigating the development of outflow motion and asymmetry from the atmosphere to the circumstellar envelope. Furthermore, we can investigate the shock propagation effect from SiO to H2O maser regions because both masers are affected by shock waves. These works will lead us to understand how the mass-loss process is connected to stellar pulsation.
(2) Mutual association and difference between SiO and H2O maser properties are also investigated based on combined studies of SiO and H2O masers for a basis. In the last analysis, SiO and H2O maser models coupled to hydrodynamical model of circumstellar envelope should be established.
(3) We trace correlation and difference of SiO maser properties including spatio-kinematic properties among SiO J = 1-0, J = 2-1, and J = 3-2 transition masers according to different type of stars (for example, H2O strong, weak and non-detected sources, SiO v = 2, J = 2-1 rare maser detected sources). Our goal is to constrain SiO maser pumping models which are still under debate between collisional and radiative pumping models including the effects of line overlap between the ro-vibrational transitions of SiO and H2O.
(4) Through the development of outflow motion and asymmetry from SiO to H2O maser regions in individual stars at different evolutionary stages, we want to find a clue to the dynamical evolution from AGB to post-AGB stars connected to the development process of asymmetric mass-loss, for example, bipolar outflow and water fountain jet motions. In parallel, we make an effort to examine the cause of large detection rates of SiO v= 2, J = 1-0 only maser emission at late AGB evolutionary stage and different detection rates between SiO and H2O masers in post-AGB RI and LI regions which are obtained from the KVN single dish results.
Using both KVN single dish and VLBI network, we perform regular monitoring of H2O 22 GHz / SiO 43/86/129 GHz bands toward 15 objects of KSP (every one-two months according to their periods). Three years as the first term of KSP are required for covering at least 2 pulsation periods of 15 sources. Single dish monitoring observations at 4 bands go on being performed toward 15 objects for grasping the global features of SiO and H2O masers and for reciprocally complemented researches with VLBI. Total integration time for each target source is required for about 5 hours in order to obtain a sufficient (u, v) coverage for a good quality imaging. Therefore, we need ~350 hrs per year for VLBI monitoring and ~100 hrs for single dish monitoring. Source Frequency Phase Referencing (SFPR) technique will be adopted for registering both H2O and SiO masers using the KVN 4-bands receiving system for simultaneous observations at different bands.
Note: These sources were selected from KVN single dish and VLBI feasibility test observations. R Cas is a spare candidate source. S.A. is the angular separations from maser sources. 1Detected in the KVN calibrator survey (private communication with J. A. Lee). 2Detected in the source frequency phase referencing test observations (n14sc01g, n14sc01h). 3Detected in the calibrator survey in 2014B pilot KSP observations (p14sc01d, p14sc01k and p14sc01o).
|Se-Hyung Cho (P.I)||firstname.lastname@example.org||Korea Astronomy & Space Science Institute (KASI)|
|Yoon Kyung Choiemail@example.com||KASI|
|Dong-Hwan Yoonfirstname.lastname@example.org||SNU/KASI (Doctor course)|
|Dong-Jin Kimemail@example.com||Yonsei Univ/KASI (Master course)|
|Richard Dodsonfirstname.lastname@example.org||ICRAR (Australia)|
|Maria Riojaemail@example.com||OAN (Spain)|
|Hiroshi Imaifirstname.lastname@example.org||Kagoshima Univ.(Japan)|
Welcome to join KVN Evolved Star KSP. The fields are observations, pipeline post-correlation data processing (~AIPS/ParselTongue scripts), database for calibration visibilities and image cubes, scientific analyses, theoretical model fit for KVN H2O and SiO maser data etc. Please contact P. I. Se-Hyung Cho (email@example.com).
At the first stage of KVN single dish operation, we have carried out simultaneous surveys of SiO and H2O masers toward 166 evolved stars which are known as both SiO and H2O maser sources. We detected both SiO and H2O masers from 112 stars at one epoch (Kim et al. 2010, Paper I). As the second and third surveys, we have carried out those observations toward previous 83 SiO-only detected sources and 152 H2O-only detected sources, respectively (Cho & Kim 2012: Paper II, Kim, Cho, & Kim 2013: Paper III). We insured a large number of new both SiO and H2O maser sources. We also performed statistical studies based on these homogeneous data (Kim, Cho, & Kim 2014: Paper IV). Simultaneous observations of SiO and H2O masers toward 252 OH/IR stars (Cho et al. 2013), 164 post-AGB and 132 AGB stars (Yoon et al. 2014), and 47 symbiotic stars (Cho et al. 2010) were added. Based on these surveys, we have also performed monitoring observations toward about 60 relatively strong SiO and H2O maser sources for single dish researches and future KVN and KaVA (KVN+VERA) VLBI observations. They are composed of semi-regular variables, Mira variables, OH/IR stars, and several post-AGB stars including water fountain sources at different evolutionary stages. From 2014A observing season, we selected 16 KVN KSP candidate sources and performed regular intensive monitoring of 22 GHz H2O and 43/86/129 GHz SiO maser lines.
A simultaneous fringe survey at 22/43/86/129 GHz bands was performed toward 41 sources in 2013 April (Yun et al. 2015 in prep.). The objects were selected from KVN single dish monitoring sources including 7 water fountain sources and post-AGB stars. Five frequencies of H2O: 22.235 GHz, SiO v = 1, J = 1-0: 43.122 GHz, SiO v = 2, J = 1-0: 42.821 GHz, SiO v = 1, J = 2-1: 86.243 GHz, and SiO v = 1, J = 3-2: 129.363 GHz were observed simultaneously. On source integration time was from 30 to 70 minutes depending on sources. The correlation was done with the DiFX correlator. As a result, both SiO and H2O maser fringes were detected from 15 sources among 30 both H2O and SiO maser sources (50%) at one epoch. The fringe of 129 GHz SiO maser was detected from 6 sources (17%) and fringes at all 4 bands were detected from 4 sources. The fringe detection rates of 22, 43, 86 GHz bands were 62, 83, 54 %, respectively. We also performed 4 band snapshot imaging observations toward 14 sources in 2013 May. On source integration time of snapshot was from 40 to 160 minutes. The sample snapshot images of VY CMa simultaneously obtained at 4 bands are shown in Figure 4. These results of the fringe survey and the snapshot imaging inform a promising future of simultaneous observations at four bands of KVN. We also carried out full track imaging at 4 bands toward several stars via Open Use and pilot project of KSP. All four-band images including 129 GHz were obtained from VY CMa, IK Tau (Cho et al. 2015 in prep.). For registering these different maser lines, Multi-Frequency Phase Referencing (MFPR) was highly required together with astrometry. Therefore, SFPR technique for KSP with the astrometric alignment of the SiO masers with respect to H2O maser emission are under testing like R LMi by Dodson et al. (2014).
|Figure: Snapshot image of maser spots observed from supergiant VY CMa. All maser lines were observed simultaneously at 4 bands for 1 hour. From the very left panel, each image corresponds to 22 GHz H2O, 43 GHz SiO, 42 GHz SiO, 86 GHz SiO, and 129 GHz SiO, respectively. The color bar of 22 GHz H2O maser map represents the velocity along the line of sight, and the color bar of SiO maser maps represents the integrated intensity. The contour of 129 GHz SiO maser map also represents the integrated intensity.|
Jaeheon Kim, Se-Hyung Cho, Chung Sik Oh, & Do-Young Byun, “Simultaneous Observations of SiO and H2O Masers toward Known Stellar SiO and H2O Maser Sources. I.”, ApJS, 188, 209 (Paper I), 2010 April
Se-Hyung Cho & Jaeheon Kim, “Simultaneous Observations of SiO and H2O Masers toward Symbiotic Stars”, ApJ, 719, 126, 2010 August
Se-Hyung Cho & Jaeheon Kim, “Simultaneous Observations of SiO and H2O Masers toward Known Stellar SiO Maser Sources”, AJ, 144, 129 (Paper II), 2012 November
Jaeheon Kim, Se-Hyung Cho, & Sang Joon Kim, “Simultaneous Observations of SiO and H2O Masers toward Known Stellar H2O Maser Sources”, AJ, 145, 22 (Paper III), 2013 January
Jaeheon Kim, Se-Hyung Cho, & Sang Joon Kim, “Statistical Study Based on Simultaneous SiO and H2O Maser Surveys toward Evolved Stars”, AJ, 147, 22 (Paper IV), 2014 January
Dong-Hwan Yoon, Se-Hyung Cho, Jaeheon Kim, Young Joo Yun, & Yong-Sun Park, “SiO and H2O Maser Survey toward Post-AGB and AGB Stars”, ApJS, 211, 15, 2014 March
Dodson, Richard, Rioja, María, Jung, Tae-Hyun et al., “Astrometrically Registered Simultaneous Observations of the 22 GHz H2O and 43 GHz SiO Masers toward R Leonis Minoris Using KVN and Source/Frequency Phase Referencing” AJ, 148, 97, 2014 November
Se-Hyung Cho, Jaeheon Kim, & Youngjoo Yun, “First Detection of 22 GHz H2O Masers in TX Camelopardalis”, JKAS, 47, 293, 2014 December
Chi-Young Cho, Se-Hyung Cho et al., “SiO and H2O Maser Survey toward OH/IR Stars” 2013 MS Thesis (Sejong Univ.), 2015 ApJS in prep