A Search for Star Formation in the Translucent Cloud MBM 40

Details A Search for Star Formation in the Translucent Cloud MBM 40 A Search for Star Formation in the Translucent Cloud MBM 40

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...465..825m&link_type=abstract

Astrophysical Journal v.465, p.825

Astronomy and Astrophysics

Astronomy

11

Ism: Clouds, Ism: Individual Alphanumeric: Mbm 40, Ism: Molecules, Radio Lines: Ism, Stars: Formation, Stars: Pre-Main-Sequence, X-Rays: Stars

Scientific paper

The star formation status of the translucent high-latitude molecular cloud, MBM 40, is explored through analysis of radio, infrared, optical, and X-ray data. With a peak visual extinction of 1 to 2 mag, MBM 40 is an example of a high-latitude cloud near the diffuse/translucent demarcation. However, unlike most translucent clouds, MBM 40 exhibits a compact morphology and a kinetic energy-to- gravitational potential energy ratio near unity. Our radio data, encompassing the CO (J = 1-0), CS (J = 2-1), and H2CO 111-110 spectral line transitions, reveal that the cloud contains a ridge of molecular gas with n ≥ 103 cm-3. In addition, the molecular data, together with IRAS data, indicate that the mass of MBM 40 is ˜40 Msun. In light of the ever-increasing number of recently formed stars far from any dense molecular clouds or cores, we searched the environs of MBM 40 for any trace of recent star formation.
We used the ROSAT All-Sky Survey X-ray data and a ROSAT PSPC pointed observation toward MBM 40 to identify 33 stellar candidates with properties consistent with pre-main-sequence (PMS) stars. Follow-up optical spectroscopy of the candidates with V < 15.5 was conducted with the 1.5 m Fred Lawrence Whipple Observatory telescope in order to identify signatures of T Tauri or pre-mainsequence stars (such as the Li 6708 Å resonance line).
Since none of our optically observed candidates display standard PMS signatures, we conclude that MBM 40 displays no evidence of recent or ongoing star formation. The absence of high-density molecular cores in the cloud and the relatively low column density compared to star-forming interstellar clouds may be the principal reasons that MBM 40 is devoid of star formation. More detailed comparison between this cloud and other, higher extinction translucent and dark clouds may elucidate the necessary initial conditions for the onset of low-mass star formation.

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