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 ?m (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 ?m. The 14.3/6.75 ?m flux ratio, for which the 6.75 ?m flux was synthesized from the PHT-S spectrum, and 14.3/7.7 ?m 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 ?m 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 mV = 11.3 and spectral type F6, was detected at 7.7 and 14.3 ?m.

Infrared Space Observatory Observations of Hickson Compact Group 31 with the Central Wolf-Rayet Galaxy NGC 1741

We studied the Class I protostar 2MASS 22352345+7517076 whose dramatic brightening between the IRAS, Akari, and WISE surveys was reported by Onozato et al. (2015). 2MASS 22352345+7517076 is a member of a small group of low-mass young stellar objects, associated with IRAS 22343+7501 in the molecular cloud Lynds 1251. The IRAS, ISO, Spitzer, Akari, Herschel, and WISE missions observed different stages of its outburst. Supplemented these data with archival and our own near-infrared observations, and considering the contributions of neighbouring sources to the mid-infrared fluxes we studied the nature and environment of the outbursting object, and its photometric variations from 1983 to 2017. The low-state bolometric luminosity Lbol ~ 32 Lsun is indicative of a 100000-200000 years old protostar of 1.6-1.8 solar masses. Its 2-micron brightness started rising between 1993 and 1998, reached a peak in 2009-2011, and started declining in 2015. Changes in the spectral energy distribution suggest that the outburst was preceded by a decade-long, slow brightening in the near-infrared. The actual accretion burst occurred between 2004 and 2007. We fitted the spectral energy distribution in the bright phases with simple accretion disc models. The modelling suggested an increase of the disc accretion rate from some 3.5\times 10^{-7} Msun yr^{-1} to 1.1 \times 10^{-4} Msun yr^{-1}. The central star accreted nearly 10^{-3} solar masses, about a Jupiter mass during the ten years of the outburst. We observed H_2 emission lines in the K-band spectrum during the fading phase in 2017. The associated optical nebulosity RNO 144 and the Herbig-Haro object HH 149 have not exhibited significant variation in shape and brightness during the outburst.

The outbursting protostar 2MASS 22352345 + 7517076 and its environment

The European Large Area ISO Survey (ELAIS) was the largest Open Time survey on the Infrared Space Observatory (ISO). It was designed to explore obscured galaxies and hence quantify the recent star-formation history of the Universe. The final reanalysis of the data has been completed and a band-merged catalogue with associations across many wavelengths compiled and released the data to the global astronomical community (http://astro.imperial.ac.uk/Elais/). This paper summarises some of the key results.

The European Large Area ISO Survey

A large fraction of ISO observing time was used to study the late stages of stellar evolution. Many molecular and solid state features, including crystalline silicates and the rotational lines of water vapour, were detected for the first time in the spectra of (post-)Asymptotic Giant Branch (AGB) stars. Their analysis has greatly improved our knowledge of stellar atmospheres and circumstellar environments. A surprising number of objects, particularly young planetary nebulae with Wolf-Rayet (WR) central stars, were found to exhibit emission features in their ISO spectra that are characteristic of both oxygen-rich and carbon-rich dust species, while far-IR observations of the PDR around NGC 7027 led to the first detections of the rotational line spectra of CH and CH + . © 2005 Springer.

Late stages of stellar evolution

Dans ce papier, nous presentons les resultats d'une analyse systematique de l'emissivite dans l'infrarouge lointain des nuages interstellaires observes avec ISOPHOT. Deux domaines de temperature ont ete etudies 12 K< T d <14 K et 14 K< T d < 16 K. Les interpretations possibles des resultats sont discutees dans le papier.

Constraints on the nature of dust particles by infrared observations

PHT - The imaging photo-polarimeter

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PHT - The imaging photo-polarimeter