Episodic mass-loss events such as giant eruptions in luminous blue variables or pre-supernova eruptions in red supergiants drastically alter the evolutionary path of a massive star, resulting in a rich and complex circumstellar environment and infrared excess. However, the incidence of these events, and hence their importance in massive star evolution, remains unknown. The ASSESS project (Episodic Mass Loss in Evolved Massive Stars: Key to Understanding the Explosive early Universe) aims to determine the role of episodic mass-loss in the evolution of massive stars. As a first step, we construct a catalog of spectroscopically identified dusty, evolved massive stars in ten southern galaxies for which Spitzer point-source catalogs are available. The resulting catalog will be used to identify stars which may have undergone an episodic mass-loss event. The target galaxies span a range of metallicities Z=0.06-1.6Z_{sun}_, allowing for the investigation of a potential metallicity dependence. We conducted multi-object spectroscopy of dusty massive star candidates in ten target galaxies using the Very Large Telescope (VLT). We obtained 763 spectra in WLM, NGC 55, NGC 247, NGC 253, NGC 300, NGC 1313, NGC 3109, Sextans A, M83 and NGC 7793. The targets were selected using their Spitzer photometry, by prioritizing targets with a strong infrared excess, which indicates the presence of hot dust.We determined a spectral classification for each target. Additionally, we used archival images from the Hubble Space Telescope (HST), available for 150 of our targets, to provide a visual classification for 80 targets, as a star, cluster, or galaxy. We provide a catalog of 541 spectroscopically classified sources including 185 massive stars, of which 154 are newly classified massive stars. The catalog contains 129 red supergiants, 27 blue supergiants, 10 yellow supergiants, four luminous blue variable candidates, seven supergiant B[e] stars and eight emission line objects. Evidence for circumstellar dust is found in 24% of these massive stars, based on their infrared colors. We report a success rate of 28% for identifying massive stars among our observed spectra, while the average success rate of our priority system in selecting evolved massive stars was 36%. Additionally, the catalog contains 21 background galaxies (including active galactic nuclei and quasars), 10 carbon stars and 99 HII regions. We measured the line ratios [NII]/H{alpha} and [SII]/H{alpha} for 76 HII regions and 36 other spectra with nebular emission-lines, thereby identifying eight sources with shocked emission. We present the largest catalog of evolved massive stars and in particular of red supergiants in nearby galaxies at low Z beyond the Local Group. The brightest and reddest of these are candidates for episodic mass loss. The fraction of dusty massive stars observed with respect to the initial selection is ~30%. We expect this catalog to trigger follow-up studies and to pave the way for a comprehensive study of the eruptive late stages of massive star evolution in the era of the James Webb Space Telescope and the new survey telescopes (e.g. Euclid mission, Nancy Grace Roman Space Telescope, and Vera C. Rubin Observatory).
Cone search capability for table J/A+A/686/A77/table7 (Spectral classifications for 541 sources)
