Interactions of the Infrared bubble N4 with the surroundings
  The physical mechanisms that induce the transformation of a certain mass of
gas in new stars are far from being well understood. Infrared bubbles
associated with HII regions have been considered to be good samples of
investigating triggered star formation. In this paper we report on the
investigation of the dust properties of the infrared bubble N4 around the HII
region G11.898+0.747, analyzing its interaction with its surroundings and star
formation histories therein, with the aim of determining the possibility of
star formation triggered by the expansion of the bubble. Using Herschel PACS
and SPIRE images with a wide wavelength coverage, we reveal the dust properties
over the entire bubble. Meanwhile, we are able to identify six dust clumps
surrounding the bubble, with a mean size of 0.50 pc, temperature of about 22 K,
mean column density of 1.7 $\times10^{22}$ cm$^{-2}$, mean volume density of
about 4.4 $\times10^{4}$ cm$^{-3}$, and a mean mass of 320 $M_{\odot}$. In
addition, from PAH emission seen at 8 $\mu$m, free-free emission detected at 20
cm and a probability density function in special regions, we could identify
clear signatures of the influence of the HII region on the surroundings. There
are hints of star formation, though further investigation is required to
demonstrate that N4 is the triggering source.
