Nobeyama Radio Observatory Report: Number 375

Abstract

Galactic bulge IRAS (Infrared Astronomical Satellite) sources in the strips between - 15 deg less than one is less than 15 deg, and 4 deg less than absolute value of b less than 5 deg in the SiO J = 1 - 0 v = 1 and two transitions have been surveyed. The sources were selected from the IRAS Point Source Catalogue based on the IRAS 25/12 micrometer flux density ratio, extracting dust-enshrouded objects at a distance of about 8 kpc. The SiO masers were detected in 62 of 93 sources surveyed in these strips. The J, H, K, and L photometric data (1.2, 1.6, 2.2 and 3.4 micrometer) were also obtained for 85 sources. Because distances to the IRAS sources in these strips are not known, the distance based on the observed luminosity has been evaluated. The probability of the object being a bulge source is calculated assuming that the luminosity function of these infrared sources is the same as that of previously observed absolute value of b = 7 - 8 deg sources. The contamination due to foreground sources in the sample is minimized by excluding sources with the bulge probability less than 50 percent. The SiO maser properties of the absolute value of b = 4 - 5 deg sources are found to be very similar to those of absolute value of b = 7 - 8 deg sources. No systematic difference between bulge and disk sources is found for the SiO J = 1 - 0 v - 2/1 intensity ratio. If this shift is interpreted as due to a tilt of the bulge, the tilt angle of the bulge rotation axis to the Galactic circle would be 8 + 27 or - 31 deg, which is slightly smaller than the value obtained for the absolute value of b = 7 - 8 deg sources.

野辺山のミリ波アレイの4.4秒×3.8秒ビームサイズを用いて、惑星状星雲CRL2688のマッピング観測を(13)CO J=1-0線について行った結果を示した。(13)COの放出は約15秒まで拡散しているが、これは1台の皿型望遠鏡により観測されるCOエンベロープサイズの1/4に相当する。チャネル速度図は(13)CO放出が次の3つの成分から構成されていることを示している:すなわち、中心部が球対称の明るい核、それより幾分暗い塊状構造の拡散エンベロープ、ならびに中心近くの高速度成分である。明るい中心核は約10秒までが広がっており、球対称のように思われる。他の観測者が数種類の分子線に対して以前に観測した円盤ないしは円環状の構造は(13)CO図では見られなかった。このことは、エンベロープ中の気体密度は極軸に対して大きく変化しないことを示している。拡散成分は対称軸に沿って拡散していくように思われる。高速度成分の赤方および青方偏位に対するピーク位置は約3秒ほど離れているように見える。