Visual minima timings of eclipsing binaries: To use or not to use?

TL;DR

Visual eclipse timings, often used in period analysis, are heavily subjective and biased, making them unreliable for precise orbital studies without careful verification.

Contribution

This study demonstrates that visual eclipse timings are biased and unsuitable for accurate period analysis without prior validation.

Findings

Visual timings from 1979-2003 were biased towards existing ephemeris.

Subjective nature of visual observations disqualifies them for precise period analysis.

Careful verification is necessary before using visual timings in orbital studies.

Abstract

Plenty of mid-eclipse timings of short-periodic eclipsing binaries derived from series of visual observations appear to be an acceptable source of information for orbital period analyses, namely if they were done in time-intervals not covered by other types of observations. However, our thorough period analysis of the nearly contact eclipsing binary BS Vulpeculae proves that visually determined timings done in 1979--2003 were undoubtedly biased to accommodate the existing linear ephemeris. The heavily subjective character of visual observations disqualifies them as a source of true phase information apt for fine eclipsing binary period analyses. Consequently we warn against the use of visual timings without a preceding careful verification.