Optical images of MCLD123.5+24.9: a cloud illuminated by the North star?
F. Zagury, F. Boulanger, V. Banchet;
AaA, 1999, 352, 645
ABSTRACT:We present B R I images of a 1degr {x}1degr field centered on the molecular cloud (MCLD123.5+24.9) located in the large infrared cirrus known as
the Polaris Flare.
The optical images are compared with IRAS images and an
extinction map derived from stellar reddenings.
We analyse the possibility for
the North star (HD8890), only 1degr North of the field, to be the source of
MCLD123.5+24.9 optical emission.
For widely accepted values of the dust albedo
(omega = 0.6) and the assymetry parameter of the Henyey Greenstein phase
function (0.7<g_0), forward scattering of Polaris light explains the cloud
optical brightness, colors, and the surface brightness ratios derived from
comparison of optical and 100 mu m data.
The cloud colors are redder than what is
expected from diffusion of Polaris light by a low column density medium, but the
color difference may be explained by extinction with no need for red
luminescence.
Within this interpretation, the cloud is located between 105 and 125 pc from
the Sun and is 6 to 25 pc in front of Polaris.
Over this range of distances,
due to forward scattering, Polaris is the main source of the cloud optical
emission but a minor source of dust heating relative to the general Galactic
interstellar radiation field of the Solar neighborhood (ISRF).
KEYWORDS: ism: clouds, ism: dust, extinction, ism: individual objects: mcld123.5+24.9, stars: individual: polaris, scattering
PERSOKEY:dust, ,
CODE: zagury99