The Mira discovery problem -- Observations by David Fabricius in 1596 and 1609 (and by others before?): Positional accuracy, brightness, color index, and period

TL;DR

This paper reviews historical observations of Mira by Fabricius and others, analyzing positional accuracy, brightness, color index, and period, revealing insights into early variable star detection and measurement accuracy over centuries.

Contribution

It provides a detailed analysis of Fabricius's 1596 and 1609 observations of Mira, including brightness, color, and period, contextualized within historical and observational biases.

Findings

Fabricius measured Mira's position with b1 1.6-1.7' accuracy.

Mira's brightness around 1.9 mag and color index b1 1.3-1.4 mag in 1596.

The Mira period is consistent at 330.2 days over centuries, with no evidence of secular shifts.

Abstract

The pulsating variable star Mira (omikron Ceti) was observed by David Fabricius (Frisia) in 1596 and 1609. We review suggested previous detections (e.g. China, Hipparchos). We analyze all Mira records from Fabricius in their historical context. Fabricius measured the separation of Mira to other stars to \pm 1.6-1.7'. From his texts, we derive a brightness (slightly brighter than Hamal) of ca. 1.9 \pm 0.1 mag and a color index B-V \simeq 1.3-1.4 mag (`like Mars') for 1596 Aug 3 (jul.). Mira started to fainten 19 days later and was observed until mid/late Oct. We show why such a red star cannot be followed by the naked eye until ca. 6 mag: For Mira's color at disappearance and altitude from Frisia, the limit is reduced by ca. 1.0 mag. Since Fabricius connected the Mira brightening with the close-by prograde Jupiter, he re-detected it only 12 years later, probably shortly before a relatively bright maximum - discoveries are strongly affected by biases. A Mira period of 330.2 days is consistent with both the oldest data (from Fabricius 1596 to Hevelius 1660) and the most current data (VSX 2004-2023), so that we see no evidence for secular period or phase shifts. (We also present Fabricius' observations of P Cygni in 1602.)