The Korean VLBI Network (KVN) is a very long baseline interferometry (VLBI) network in Korea operating at millimeter wavelengths. (Lee et al. 2014, The Astronomical Journal, 147, 77) It consists of three 21-m radio telescopes located in Seoul, in Ulsan, and on the Jeju Island, Korea: KVN Yonsei Radio Observatory (KY)(Lee et al. 2011, Publications of the Astronomical Society of the Pacific, 123, 198), KVN Ulsan Radio Observatory (KU), and KVN Tamna Radio Observatory (KT). The baseline lengths of the KVN are 305–476 km. The KVN produces an effective spatial resolution equivalent to that of a 500-km radio telescope. All three antennas have an identical design and are equipped with a quasi-optical system that allows simultaneous observations at 22, 43, 86, and 129 GHz (Han et al., 2008, International Journal of Infrared and Millimeter Waves 29, 69–78). Since 2013-08, we have operated the KVN Ulsan at 6.7 GHz in single-dish and VLBI modes, mainly for observations toward 6.7-GHz class II CH3OH masers. A GPS receiver was installed at each KVN station. By estimating the atmospheric wet delay and total electron content over all KVN stations, we improved the accuracy of phase referencing and astrometric observations. For information about the KVN, please visit the KVN homepage
The KVN is used to study
- the formation and death processes of stars by observing water (H2O), methanol (CH3OH), and silicon monoxide (SiO) masers at high resolution,
- the structure and dynamics of our own Galaxy by conducting highly accurate astrometric VLBI observations toward Galactic radio sources,
- the nature of relativistic jets from active galactic nuclei (AGNs) and their population at high frequencies, and
- the spectral and temporal properties of transient sources such as bursting star-forming regions, intra-day variable compact radio sources, and gamma-ray flaring AGNs by conducting systematic multi-wavelength monitoring campaigns.
Observations with KVN
VLBI observations with the KVN are remotely conducted at the KVN Array Operation Center (AOC) in KASI, Daejeon. Researchers are asked to kindly submit an observation proposal to the KVN AOC (firstname.lastname@example.org) using the schedule file in VLBI EXperiment (VEX) format, which contains information about the observations such as the sources, system setup, observing time, and calibration mode. For details, please visit the KVN VLBI Observation site.
Single-dish observations with KVN radio telescopes can be conducted at each KVN radio observatory as well as at the KVN AOC at KASI’s Daejeon headquarters. Observation data are stored using the Continuum and Line Analysis Single-dish Software (CLASS) format developed at IRAM Observatory, and a graphical user interface is available for observations.
Continuum polarization observations and spectroscopic observations can be automatically conducted using Python s. Simultaneous multi-frequency observations are available at any of four frequency bands (22, 43, 86, and 129 GHz) in a single polarization (left circular or right circular polarization) or at two frequency bands in dual polarization. Source catalogs are in a format readable by ASTRO software, one of the GILDAS packages. More information about single-dish observations is available on the KVN page
KaVA : KVN and VERA Array
The KVN and VERA Array (KaVA) is a combination of the KVN VLBI array, operated by KASI, and VLBI Exploration of Radio Astrometry (VERA), operated by the National Astronomical Observatory of Japan (NAOJ). KaVA was formed in 2010, on the basis of a VLBI collaboration agreement between KASI and NAOJ. It expands the baseline length range to 2270 km and can achieve good imaging quality. For more details, please visit the KaVA homepage
The VERA array consists of four 20-m radio telescopes located at Mizusawa, Iriki, Ogasawara, and Ishigakijima, with baseline ranges from 1000 to 2300 km. The most distinctive feature of VERA is its “dual-beam" telescope, which can simultaneously observe two close sources, effectively cancel out the atmospheric fluctuations, and measure the positions of the target sources relative to those of reference sources with higher accuracy using the phase-referencing technique. VERA, the Japanese VLBI array, explores the three-dimensional structure of the Milky Way Galaxy using high-precision astrometry of Galactic maser sources.
KJCC : Korea-Japan VLBI Correlator Center
Since 2011-07, the Korea–Japan Correlation Center (KJCC) has been under joint operation by KASI and NAOJ in accordance with a memorandum of agreement. (Lee et al. 2015, Journal of the Korean Astronomical Society, 48, 125)
Several VLBI data playback systems are used in the combined VLBI network, such as Mark5B, VERA2000, K-5/OCTADISK, and some type of optical fiber. The interfaces for data transmission are diverse, and each has its own maximum data recording and playback rates. To accommodate these differences among the VLBI data playback systems, the Raw VLBI Data Buffer (RVDB), a large data server with many large RAID disks, and several types of VLBI data interfaces, was introduced. The VLBI Correlation Subsystem (VCS) receives VLBI data from the RVDB system, calculates the correlation between the possible pairs of data inputs using the proper control parameters given by the correlator control and operation computer, and then places the correlation results in the data archive system. The data archive system is also a type of data server to capture the correlated data output from the VCS and to save it as a structured file system. The correlator control and operation software for the entire system are essential to this activity.