THE FIRST VERY LONG BASELINE INTERFEROMETRY IMAGE OF A 44 GHz METHANOL MASER WITH THE KVN AND VERA ARRAY (KaVA)
- Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
- Graduate School of Science and Engineering, Yamaguchi University, 1677-1 Yoshida, Yamaguchi, Yamaguchi 753-8512 (Japan)
- Korea Astronomy and Space Science Institute, Daedeokdae-ro 776, Yuseong-gu, Daejeon 305-348 (Korea, Republic of)
- East Asian ALMA Regional Center, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
- Department of Astronomical Science, The Graduate University of Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
We have carried out the first very long baseline interferometry (VLBI) imaging of a 44 GHz class I methanol maser (7{sub 0}-6{sub 1} A {sup +}) associated with a millimeter core MM2 in a massive star-forming region IRAS 18151–1208 with KaVA (KVN and VERA Array), which is a newly combined array of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We have succeeded in imaging compact maser features with a synthesized beam size of 2.7 milliarcseconds × 1.5 milliarcseconds (mas). These features are detected at a limited number of baselines within the length of shorter than ≈ 650 km corresponding to 100 Mλ in the uv-coverage. The central velocity and the velocity width of the 44 GHz methanol maser are consistent with those of the quiescent gas rather than the outflow traced by the SiO thermal line. The minimum component size among the maser features is ∼5 mas × 2 mas, which corresponds to the linear size of ∼15 AU × 6 AU assuming a distance of 3 kpc. The brightness temperatures of these features range from ∼3.5 × 10{sup 8} to 1.0 × 10{sup 10} K, which are higher than the estimated lower limit from a previous Very Large Array observation with the highest spatial resolution of ∼50 mas. The 44 GHz class I methanol maser in IRAS 18151–1208 is found to be associated with the MM2 core, which is thought to be less evolved than another millimeter core MM1 associated with the 6.7 GHz class II methanol maser.
- OSTI ID:
- 22365760
- Journal Information:
- Astrophysical Journal Letters, Vol. 789, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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