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Distances of absorbing features in the LDN 1622 direction. An application of Tycho-2 photometry and Michigan Classification
With Tycho-2 BT and VT photometry of Hipparcosstars with π > 8.0 mas, σπ/π < 15% andwith spectral type and luminosity classification from the MichiganCatalogues we have a presumably unreddened sample for establishing a(BT-VT_0- MV_T main sequence relationin the range from A0 to G5. We discuss the location of the median mainsequence relation relative to published ZAMS relations for the A0-G5range in some detail since the applications of this relation will haveto assume that the evolutionary status of the calibration sample isrepresentative of the local disk. If the ZAMS is defined as the lowerenvelope of the class V stars the published versions we discuss seem tobe too bright by about half a magnitude in the F0-G5 range. Theresulting intrinsic color and absolute magnitude estimates have errorsof the mean of 0.03m and 0.3m-0.4m respectively. From this relation anygiven star with Tycho-2 photometry, spectral classification andluminosity class V can have its color excess E(BT -VT) and distance modulus estimated. This means that the localinterstellar extinction may be estimated for the ~50% of the sky whereMichigan classification presently is available. The individual colorexcesses and distance moduli may not be particularly accurate but wepropose that they may be used to indicate extinction discontinuitiescaused by interstellar material at well defined distances. We haveapplied this new technique on stars from the Michigan Catalogue in thedirection of LDN 1622 (l, b) = (204.7dg, -11.8dg) supposed to beassociated to the Orion B region 400-500 pc away but color excessesE(BT - VT) exceeding 0.15m start appearing alreadyin the distance slot 160-200 pc. Presently we cannot decide whether thisnearby dust is related to LDN 1622 or whether this cloud is associatedto Orion B. In a final comparison we study the color excess -- distancevariation in a 4 deg region centered on LDN 1622 from Hipparcos --Tycho-1 -- Michigan data and the dust at ~160 pc is confirmed.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Five-channel photometry of cepheids and supergiants in the southern Milky Way.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976A&AS...24..413P&db_key=AST
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