2002ApJ...575..747O

Hickson Compact Group (HCG) 31, consisting of the Wolf-Rayet galaxy NGC 1741 and its irregular dwarf companions, was observed using the Infrared Space Observatory. The deconvolved ISOCAM maps of the galaxies using the 7.7 and 14.3 µm (LW6 and LW3) filters are presented, along with ISOPHOT spectrometry of the central starburst region of NGC 1741 and the nucleus of galaxy HCG 31A. Strong mid-IR emission was detected from the central burst in NGC 1741, along with strong polycyclic aromatic hydrocarbon (PAH) features and a blend of features, including [S IV] at 10.5 µm. The 14.3/6.75 µm flux ratio, for which the 6.75 µm flux was synthesized from the PHT-S spectrum, and 14.3/7.7 µm flux ratio suggest that the central burst within NGC 1741 may be moving toward the poststarburst phase. Diagnostic tools including the ratio of the integrated PAH luminosity to the 40-120 µm infrared luminosity and the far-infrared colors reveal that despite the high surface brightness of the nucleus, the properties of NGC 1741 can be explained in terms of a starburst and do not require the presence of an active galactic nucleus. The Tycho catalog star Tyc 04758 466 1, with m_V=11.3 and spectral type F6, was detected at 7.7 and 14.3 µm.