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Photometric Investigation of the MBM 12 Molecular Cloud Area in ARIES. III. CCD Photometry
Magnitudes and color indices of 138 stars down to l V = 15 mag in theseven-color Vilnius photometric system are determined in the area of theAries molecular cloud MBM 12. Spectral types, color excesses,interstellar extinctions and distances of stars are determined from thephotometric data. For some stars classification is verified fromspectrograms. The plot of extinction vs. distance exhibits a steep riseof the extinction up to 4 mag at 300 pc which corresponds to thedistance of the dust cloud at 375 pc. However, this distance may beoverestimated if the heavily reddened stars found in the present studyare not inside the cloud, but behind it. Additionally, a small bump ofthe extinction is present at 100--140 pc which can be related to theextension of the Taurus-Auriga dark cloud complex. Four known T Tauritype stars were measured and classified, and their variabilityconfirmed. Two new T Tauri stars are suspected. More young objects maybe present among the stars with peculiar color indices. Some of them canalso be unresolved binaries. Some new heavily reddened stars areidentified and discussed.
| 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).
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| The optical counterpart of the X-ray source H0253+193 - A distant, high-luminosity RS Canum Venaticorum system
Optical and near-infrared photometry in the VRIJHK and CO (2.35 microns)bands and optical spectroscopy and polarimetry reveal that the opticalcounterpart of the X-ray source H0253+193 is most likely a RS CVn binarysystem. The results show a visual extinction of 11.3 mag to the star,with an IR excess possibly due a cooler binary companion orcircumstellar material. It is suggested that the I-band polarization of8.1 + or - 1.8 may be induced in the starlight by passage through themolecular cloud. The lack of strong H-alpha emission in the opticalspectrum argues against the possibility of a classical T Tauri star, andthe IR excess argues against a naked T Tauri star. The wide energyspectrum found in the dereddened optical and near-infrared photometrysupports the binary star model.
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