The distance to the nearest star-forming clouds: MBM12 and MBM20

Hearty, T., Fernández, M., Alcalá, J. M., Covino, E., and Neuhäuser, R.
Astronomy and Astrophysics, v.357, p.681-685 (2000)


We present high-resolution spectra (R ~ 49,000) of stars that have parallax measurements from the Hipparcos satellite and are projected along the line of sight to the two nearest known star forming clouds to the Sun: MBM12 and MBM20. The spectra were obtained with the FOCES Echelle Spectrograph at the 2.2 meter telescope in Calar Alto, Spain and the wavelength range was chosen to include the interstellar Na I D lines at lambda 5889.950 Ä and lambda 5895.924 Ä. Since the stars are at a range of distances, we use their spectra along with their parallaxes from Hipparcos to determine the distance to the molecular gas. The stars in front of the cloud do not show interstellar Na I D absorption features while the stars behind the cloud do show interstellar absorption features. We find that both clouds are somewhat more distant than previously estimated. The revised distance to MBM12 is 58+/-5 pc < d < 90+/-12 pc and the distance to MBM20 is 112+/-15 pc < d < 161+/-21 pc.