WR 38/38a and the ratio of total-to-selective extinction in Carina
  A reanalysis of the (seemingly very distant) open cluster Shorlin 1, the
group of stars associated with WR 38 and WR 38a, is made on the basis of
existing UBV and JHKs observations for cluster members. The 2MASS observations,
in particular, imply a mean cluster reddening of E(B-V)=1.45+-0.07 and a
distance of 2.94+-0.12 kpc. The reddening agrees with the UBV results provided
that the local reddening slope is described by E(U-B)/E(B-V)=0.64+-0.01, but
the distance estimates in the 2MASS and UBV systems agree only if the ratio of
total-to-selective extinction for the associated dust is R=Av/E(B-V)=4.0+-0.1.
Both results are similar to what has been obtained for adjacent clusters in the
Eta Carinae region by similar analyses, which suggests that `anomalous' dust
extinction is widespread through the region, particularly for groups reddened
by relatively nearby dust. Dust associated with the Eta Carinae complex itself
appears to exhibit more `normal' qualities. The results have direct
implications for the interpretation of distances to optical spiral arm
indicators for the Galaxy at l=287-291 degrees, in particular the Carina arm
here is probably little more than ~2 kpc distant, rather than 2.5-3 kpc distant
as implied in previous studies. Newly-derived intrinsic parameters for the two
cluster Wolf-Rayet stars WR 38 (WC4) and WR 38a (WN5) are in good agreement
with what is found for other WR stars in Galactic open clusters, which was not
the case previously.
