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A Spectroscopic and Photometric Survey of Stars in the Field of L1457: A New Distance Determination
We present a spectroscopic and photometric survey of a sample of fieldstars in the region of the molecular cloud L1457. High-qualitycoudé feed spectra, together with five-band photometry in theSloan Digital Sky Survey system and near-infrared archival data from theTwo Micron All Sky Survey, are used to derive color excesses anddistances for the stars. Based on these data, a new distance estimate of360+/-30 pc is derived for the cloud, supporting recent results by K. L.Luhman. The data further indicate that the north-south velocity gradientseen in the millimeter-wave CO data is mirrored in a distance gradient,with the northern part of the cloud being closer to us. A second, lessopaque, layer of extinction is detected at ~80 pc. This distance isconsistent with the earlier distance estimates to the cloud, based on NaI absorption. We identify this layer with the wall of the hot LocalBubble. Hence, the dense cloud is not, as previously thought, associatedwith the Local Bubble.
| Photometric Investigation of the MBM 12 Molecular Cloud Area in Aries. II. Cloud Distance
Photoelectric magnitudes and color indices in the Vilnius seven-colorsystem for 152 stars are used to investigate the interstellar extinctionin the area of the Aries molecular cloud MBM 12, coinciding with theL1454 and L1457 dust clouds. Spectral types, absolute magnitudes, colorexcesses, interstellar extinctions and distances of the stars aredetermined. The plot of interstellar extinction A_V versus distanceshows that the dust cloud is situated at a distance of 325 pc, at 180 pcfrom the Galactic plane, and its true diameter is about 11 pc. Theinterstellar extinction law in the area is found to be normal, typicalfor the diffuse dust. Ten peculiar or unresolved binary stars and someheavily reddened stars are detected.
| Photometric Investigation of the MBM 12 Molecular Cloud Area in Aries. I. Photoelectric Photometry
The results of photoelectric photometry in the Vilnius seven-colorsystem are given for 152 stars down to 12.2 mag in the area of themolecular cloud MBM 12 and the dust clouds L1454 and L1457 in Aries. Theresults of photometric classification of stars are also given. Theinvestigation of interstellar extinction in the area is described in thenext paper.
| On the MBM 12 Young Association
I present a comprehensive study of the MBM 12 young association (MBM12A). By combining infrared (IR) photometry from the Two-Micron All-SkySurvey (2MASS) survey with new optical imaging and spectroscopy, I haveperformed a census of the MBM 12A membership that is complete to 0.03Msolar (H~15) for a 1.75d×1.4d field encompassing theMBM 12 cloud. I find five new members with masses of 0.1-0.4Msolar and a few additional candidates that have not beenobserved spectroscopically. From an analysis of optical and IRphotometry for stars in the direction of MBM 12, I identify M dwarfs inthe foreground and background of the cloud. By comparing the magnitudesof these stars to those of local field dwarfs, I arrive at a distancemodulus 7.2+/-0.5 (275 pc) to the MBM 12 cloud; it is not the nearestmolecular cloud and is not inside the local bubble of hot ionized gas ashad been implied by previous distance estimates of 50-100 pc. I havealso used Li strengths and H-R diagrams to constrain the absolute andrelative ages of MBM 12A and other young populations; these dataindicate ages of 2+3-1 Myr for MBM 12A and ~10 Myrfor the TW Hya and η Cha associations. MBM 12A may be a slightlyevolved version of the aggregates of young stars within the Taurus darkclouds (~1 Myr) near the age of the IC 348 cluster (~2 Myr).
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