The Nature of Faint Blue Stars in the PHL and Ton Catalogues based on Digital Sky Surveys

TL;DR

This study refines positions for 3000 faint blue stars from historical catalogs using digital sky surveys, revealing many are quasars and estimating at least 15% are extragalactic objects, despite challenges in identifying all original objects.

Contribution

The paper provides accurate positions for faint blue stars from PHL and Ton catalogues using digital sky surveys, updating their identifications and revealing a significant extragalactic component.

Findings

At least 15% of the catalogued objects are extragalactic.

Accurate subarcsecond positions were derived for 3000 objects.

Many objects are now known quasars, but original catalog identifiers are often missing.

Abstract

We determined accurate positions for 3000 of the "faint blue stars" in the PHL (Palomar-Haro-Luyten) and Ton/TonS catalogues. These were published from 1957 to 1962, and, aimed at finding new white dwarfs, provide approximate positions for about 10750 blue stellar objects. Some of these "stars" had become known as quasars, a type of objects unheard-of before 1963. We derived subarcsec positions from a comparison of published finding charts with images from the first-epoch Digitized Sky Survey. Numerous objects are now well known, but unfortunately neither their PHL or Ton numbers, nor their discoverers, are recognized in current databases. A comparison with modern radio, IR, UV and X-ray surveys leads us to suggest that the fraction of extragalactic objects in the PHL and Ton catalogues is at least 15 per cent. However, because we failed to locate the original PHL plates or finding charts, it may be impossible to correctly identify the remaining 7726 PHL objects.