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HD 21777


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Reddening and the Extinction Law at High Galactic Latitude
We present near-infrared (JHKL) photometry of 103 southern stars locatedbehind translucent interstellar clouds at high Galactic latitude. Ourdata are combined with visual photometry and spectral type informationfrom the literature in a detailed analysis of the wavelength dependenceof interstellar extinction by dust in these high-latitude clouds. Weinvestigate the shape of the near-infrared extinction curve and evaluatethe total line-of-sight extinction (AV) and ratio oftotal-to-selective extinction (RV) in each line of sight.Sources of uncertainty in RV arising from photometric errorsand spectral classification errors are carefully assessed and quantifiedas functions of the line-of-sight reddening. We detect appreciabledifferences in our results compared with the average extinction curvefor dust in the diffuse interstellar medium (ISM) close to the Galacticplane. Assuming a power-law form in the near-infrared, we find the meanfor high-latitude clouds to be well described by~λ-2.3, somewhat steeperthan that for the diffuse ISM(~λ-1.8). Our sampleincludes a substantial number of lines of sight with low RVvalues (47% with RV<2.8) relative to the diffuse ISMaverage of 3.05+/-0.15. We conclude that many high-latitude clouds haveenhanced abundances of relatively small grains.

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Observation and Astrometry data

Constellation:Stier
Right ascension:03h30m44.74s
Declination:+05°30'47.1"
Apparent magnitude:7.684
Distance:241.546 parsecs
Proper motion RA:6.9
Proper motion Dec:-2.5
B-T magnitude:7.906
V-T magnitude:7.703

Catalogs and designations:
Proper Names
HD 1989HD 21777
TYCHO-2 2000TYC 70-204-1
USNO-A2.0USNO-A2 0900-00807458
HIPHIP 16356

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