The ratio of total to selective absorption in the Rho Ophiuchi cloud.
Abstract
The ratio of total to selective absorption, R = Av/ , is determined for the p Oph dust cloud by the variable extinction method, using published data for stars in the Sco OB2 association. The calibration of absolute magnitude in terms of spectral type is discussed and compared with results from H and Hfl photometry. A least squares fit to the /(VMv) plot gives an overall result of R = 3.7 . The stars associated with nebulosity give R = jo5, while a normal' value of R = 33+03 is found for the remainder. The mean distance modulus of the association is deduced to be 61 +0.1 which agrees well with the kinematical value.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 August 1974
 DOI:
 10.1093/mnras/168.2.371
 Bibcode:
 1974MNRAS.168..371W