Hα fluxes and extinction distances for planetary nebulae in the IPHAS survey of the Northern Galactic Plane

We report Hα filter photometry for 197 northern hemisphere planetary nebulae (PNe) obtained using imaging data from the IPHAS survey. Hα+[N ii] fluxes were measured for 46 confirmed or possible PNe discovered by the IPHAS survey and for 151 previously catalogued PNe that fell within the area of the northern Galactic Plane surveyed by IPHAS. After correcting for [N ii] emission admitted by the IPHAS Hα filter, the resulting Hα fluxes were combined with published radio free-free fluxes and Hβ fluxes, in order to estimate mean optical extinctions to 143 PNe using ratios involving their integrated Balmer line fluxes and their extinction-free radio fluxes. Distances to the PNe were then estimated using three different 3D interstellar dust extinction mapping methods, including the IPHAS-based H-MEAD algorithm of Sale (2014). These methods were used to plot dust extinction versus distance relationships for the lines of sight to the PNe; the intercepts with the derived dust optical extinctions allowed distances to the PNe to be inferred. For 17 of the PNe in our sample reliable Gaia DR2 distances were available and these have been compared with the distances derived using three different extinction mapping algorithms as well as with distances from the nebular radius vs. Hα surface brightness relation of Frew et al. (2016). That relation and the H-MEAD extinction mapping algorithm yielded the closest agreement with the Gaia DR2 distances.

ISOPHOT observations of dust discs around main sequence stars

The photometer (ISOPHOT) on the ESA Infrared Space Observatory (ISO) satellite was used to study the four Vega-like prototypes (Vega, β Pic, α PsA, ɛ Eri) and a set of candidate stars believed to have similar dust/debris discs. Most of the candidate stars were main sequence stars, but probably younger than Vega and ɛ Eri since they showed residual emission in the cores of their stellar spectral lines. Low resolution spectra were combined with long wavelength multi-filter photometry (between 60/μm and 200/μm) to give the spectral energy distributions for the dust/debris discs. Models suggested that the masses of the discs were between 10−7 and 10−4 M⊙ (2–2000 times the mass of the moon). These were more massive than the discs around the four prototypes, but less massive than the discs around young stars such as T Tau stars.

The Galaxy Population of two Distant Galaxy Clusters: 0016+16 (z=0.54) and 0939+47 (z=0.41)

We analyzed the galaxy population of two distant clusters of galaxies by means of optimized multi filter photometry. To this purpose, broad and narrow band filters have been chosen to detect features characteristic of elliptical (4000 Å break and the Mg2 band) and E+A galaxies (Hβ, Hγ and Hδ in absorption). Cluster membership and morphological types of the galaxies have been obtained by fitting the low-resolution spectral energy distributions with template spectra. Ten templates for E+A galaxies have been built up using Bruzual & Chariot (1993, ApJ 405, 538) population synthesis models with the assumption that these galaxies result from a strong star formation episode occuring in an early-type galaxy.