Far-infrared dust opacity and visible extinction in the Polaris Flare
L. Cambrésy, F. Boulanger, G. Lagache, B. Stepnik;
AaA, 2001, 375, 999
ABSTRACT:We present an extinction map of the Polaris molecular cirrus cloud derived from star counts and compare it with the Schlegel et
al.
(\cite{SFD98}) extinction map derived from the far-infrared dust opacity.
We find
that, within the Polaris cloud, the Schlegel et al.
(\cite{SFD98})
AV values are a factor 2 to 3 higher than the star count values.
We propose
that this discrepancy results from a difference in
tauFIR/AV between the diffuse atomic medium and the Polaris cloud.
We use the
difference in spectral energy distribution, warm for the diffuse atomic medium,
cold for the Polaris cloud, to separate their respective contribution to
the line of sight integrated infrared emission and find that the
tauFIR/AV of cold dust in Polaris is on average 4 times higher than the Schlegel et
al.
(\cite{SFD98}) value for dust in atomic cirrus.
This change in dust property could be
interpreted by a growth of fluffy particles within low opacity molecular cirrus
clouds such as Polaris.
Our work suggests that variations in dust emissivity
must be taken into account to estimate AV from dust emission
wherever cold infrared emission is present (i.e.
molecular clouds).
KEYWORDS: ism: clouds, ism: dust, extinction, ism: individual object: polaris flare, infrared: ism: continuum
PERSOKEY:dust, fir, extinction, optical, iras, ,
CODE: cambresy2001