Scattered H-alpha emission from a large translucent cloud G294-24
  We study an undocumented large translucent cloud, detected by means of its
enhanced radiation on the SHASSA (Southern H-Alpha Sky Survey Atlas) survey. We
consider whether its excess surface brightness can be explained by light
scattered off the dust grains in the cloud, or whether emission from in situ
ionized gas is required. In addition, we aim to determine the temperature of
dust, the mass of the cloud, and its possible star formation activity. We
compare the observed H-alpha surface brightness of the cloud with predictions
of a radiative transfer model. We use the WHAM (Wisconsin H-Alpha Mapper)
survey as a source for the Galactic H-alpha interstellar radiation field
illuminating the cloud. Visual extinction through the cloud is derived using
2MASS J, H, and K band photometry. We use far-IR ISOSS (ISO Serendipitous
Survey), IRAS, and DIRBE data to study the thermal emission of dust. The LAB
(The Leiden/Argentine/Bonn Galactic HI Survey) is used to study 21cm HI
emission associated with the cloud. Radiative transfer calculations of the
Galactic diffuse H-alpha radiation indicate that the surface brightness of the
cloud can be explained solely by radiation scattered off dust particles in the
cloud. The maximum visual extinction through the cloud is about 1.2mag. The
cloud is found to be associated with 21cm HI emission at a velocity of about -9
km/s. The total mass of the cloud is about 550-1000 solar masses. There is no
sign of star formation in this cloud. The distance of the cloud is estimated
from the Hipparcos data to be about 100 pc.
