Astron. Astrophys. Suppl. Ser. 144, 123-140

Multiline CO observations of MBM 32

J.G.A. Wouterloot ^1,2 - A. Heithausen ¹ - W. Schreiber ² - G. Winnewisser ²

Send offprint request: J.G.A. Wouterloot,
e-mail: wouterloot@astro.uni-bonn.de

1 - Radioastronomisches Institut, Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
2 - I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, D-50937 Köln, Germany

Received October 5, 1999; accepted February 2, 2000

Abstract:

We present a detailed study of the high latitude cloud MBM 32. Observations were made in the J=(1-0), (2-1), and (3-2) transitions of ¹²CO and in ¹³CO(1-0) and (2-1). These data were complemented by 21 cm H I data and by IRAS 60 and 100 $\mu$m data.

Our data show that MBM 32 consists of a main cloud component at $V_{\rm {lsr}}>2$ km$\,$s^-1 (mass about 16.9 $M_\odot$), and a smaller component at $V_{\rm {lsr}}<0$ km$\,$s^-1 (4.1 $M_\odot$), in addition to some emission in between those two velocities (<0.5 $M_\odot$).

We study the gas distribution and the CO line ratios within MBM 32, the latter also along a cut through both cloud components. We find that the ratios of different rotational transitions are constant within each cloud part. Only the ratio ¹²CO( 1-0)/¹³CO(1-0) is lower in the cloud center. This suggests equal excitation conditions through MBM32 and line temperatures determined through clump filling factors.

All CO components show associated H I emission, but small velocity differences of typically 1 km$\,$s^-1 exist between the H I and CO gas. The mass of associated H I gas is similar to the molecular mass for all components.

There is a good correlation between FIR, CO, and H I emission. The dust mass is about 0.073 $M_\odot$, and the ratio of gas and dust mass (280) is lower than found from similar (IRAS) data for denser clouds, suggesting that the amount of dust colder than 20 K is relatively small.

We subdivide the CO data cubes in Gaussian shaped clumps; 40-50% of the CO emission can be assigned to the larger clumps. The remaining emission comes from either more extended clumps or from overlapping unresolved clumps.

Key words: ISM: clouds -- ISM: individual objects: MBM 32 -- ISM: molecules -- radio lines: ISM