Ralph Neuhaeuser

We present new radial velocity measurements of 13 selected intermediate mass stars (2–6 M _⊙ ). The measurements were performed between 29 April and 6 September 2024 at the University Observatory Jena using the échelle spectrograph FLECHAS. The radial velocity of eight stars was found to be constant during our spectroscopic monitoring, namely: 17 Dra A, HD 148374, HD 169487 A, 57 Cnc, And, HD 11031, And, and Cas. In contrast, the radial velocity of five stars showed significant variability throughout or spectroscopic observation, namely: 7 CrB A, 7 CrB B, HD 214007, Her, and HD 201433 A. In all these cases, Keplerian orbital solutions were fitted to the observational data and the orbital elements of these spectroscopic binary systems were determined. In addition, we searched for wide companions of our targets using the third data release from ESA's Gaia mission, in order to determine the multiplicity status of these stars and contribute to the census of bright, nearby multiple stars.

The remnant of the historical supernova SN 1181 is under discussion: While the previously suggested G130.7+3.1 (3C58) appears too old (3000–5000 year), the unusual star IRAS00500+6713 with a surrounding nebula (Pa‐30) has an expansion age not inconsistent with a SN Iax explosion in ad 1181 under the assumption that neither acceleration nor deceleration occurred. Previously, only reports from China and Japan were known, pointing to an event near the northern circumpolar region. Any further reports from other cultures can therefore be highly relevant. We present here an Arabic poem in praise of Saladin by the contemporaneous author Ibn Sanā' al‐Mulk (Cairo, Egypt). We re‐date its composition to between Dec 1181 and May 1182. It contains a new bright star, which can be identified as SN 1181. The poem also provides new and independent information on the object type (called ‘najm’ for ‘star’), location on sky in or near the Arabic constellation al‐Kaff al‐Khaḍīb (lit. the henna‐dyed hand, five bright stars in Cassiopeia), and brightness (brighter than Cas, 2.25 mag). In addition, we present another Arabic text on SN 1006, also from Cairo, by the historian al‐Maqrīzī, probably based on the contemporaneous al‐Musabbiḥī.

The pulsating variable star Mira (o 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 ±1.6−1.7′. From his texts, we derive a brightness (slightly brighter than Hamal) of ca. 1.9±0.1 mag and a color index B‐V1.3−1.4 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.)

After core hydrogen burning, massive stars evolve from blue-white dwarfs to red supergiants by expanding, brightening, and cooling within few millennia. We discuss a previously neglected constraint on mass, age, and evolutionary state of Betelgeuse and Antares, namely their observed colour evolution over historical times: We place all 236 stars bright enough for their colour to be discerned by the unaided eye (V ≤ 3.3 mag) on the colour-magnitude-diagram (CMD), and focus on those in the Hertzsprung gap. We study pre-telescopic records on star colour with historically critical methods to find stars that have evolved noticeably in colour within the last millennia. Our main result is that Betelgeuse was recorded with a colour significantly different (non-red) than today (red, B − V = 1.78 ± 0.05 mag). Hyginus (Rome) and Sima Qian (China) independently report it two millennia ago as appearing like Saturn (B − V = 1.09 ± 0.16 mag) in colour and ‘yellow’ (quantifiable as B − V = 0.95 ± 0.35 mag), respectively (together, 5.1σ different from today). The colour change of Betelgeuse is a new, tight constraint for single-star theoretical evolutionary models (or merger models). It is most likely located less than one millennium past the bottom of the red giant branch, before which rapid colour evolution is expected. Evolutionary tracks from MIST consistent with both its colour evolution and its location on the CMD suggest a mass of ∼14 M_⊙ at ∼14 Myr. The (roughly) constant colour of Antares for the last three millennia also constrains its mass and age. Wezen was reported white historically, but is now yellow.

In a recent discussion of the Maunder Minimum, two sunspot observations by Chinese court astronomers on February 15, 1900 and January 30, 1911 (±1 day) – presumably made with the unaided eye – were considered false detections because the spot areas of the largest spot on those days (±1 day) as recorded by the Royal Greenwich Observatory, would be too small for naked‐eye detection, namely 11 and 13 millionths of a solar disk (msd), respectively (Usoskin et al. 2015). We revisit this issue here. First, we review theoretical and empirical considerations of the lower limit for the sunspot area detectable by the naked eye: under optimal conditions, very good observers can detect spots as small as ∼100 msd (and we present one example, where an observer reported a spot, when the largest spot on that day was only 65 msd, but being part of a longish group facilitating the detection). Then, we review all known sunspot observations on and around February 15, 1900 and January 30, 1911, including full‐disk drawings. For February 15, 1900, Kalocsa observatory, Hungary, shows a feature close to the western limb with an area of 134 msd, but it is not clear whether it was a spot or faculae or pores (as spot, it could have been detectable even by naked‐eye). The two spot groups detected in Kodaikanal, India, on January 31, 1911 and February 1 with 18.5 to 33.0 msd area would be too small for detection by the naked eye. However, the Chinese records for February 15, 1900 and January 30, 1911 do not even mention whether the observations were performed with a telescope or by the unaided eye. We conclude that there is no convincing evidence that these two – or even all – Chinese sunspot records are unreliable.

We present reconstructed sunspot positions based on observations reported in letters between Gottfried Kirch and other contemporary astronomers from AD 1680 to 1709, that is in the last decades of the Maunder minimum. The letters to and from Gottfried Kirch in Latin and German language were compiled and edited by Herbst (). The letters (and observations) from Kirch are mostly by Gottfried Kirch, but some also by his second wife Maria M. Kirch (married 1692) and their son Christfried Kirch (born 1694). Using excerpts from the letters, some with drawings, we found some 35 sunspot groups (often for several days in a row or with interruptions) by Kirch and/or his letter partners (in three cases, only the month is given: 1704 January, February, 1707 March, otherwise always the exact dates)—usually one group at a time. We also found 17 explicit spotless days, several of them new (previously without any known observations). We could constrain the heliographic latitude by Bayesian inference for 19 sunspot groups—five of them completely new (one group 1680 May 20–22 from Kirch and Ihle, one to two groups 1680 June 15–23 for Kirch, one group 1684 May 6 from Ihle, and one group 1688 December 14–15 from Kirch), while the others mostly agree (within 2σ) with previously published values for those dates by others. With these data, we then amend the butterfly diagram for the Maunder minimum. By comparison of our data with the sunspot group catalogue in Hoyt & Schatten (), we noticed a number of discrepancies, for examaple, that dates for British observers in the Maunder minimum (Flamsteed, Caswell, Derham, Stannyan, Gray, and Sharp) as listed in Hoyt & Schatten () are their original Julian dates, not converted to the Gregorian calendar (10–11 day offset in Hoyt and Schatten). Most of these modifications also apply to the modified sunspot group catalogue in Vaquero et al. (). We also present two aurorae observed by the Kirchs in 1707 and 1716.

We review some applications of the method of electronic searching for historical observations of sunspots and aurorae in the Chinese text corpus by Hayakawa et al. (,,,), Kawamura et al. (), and Tamazawa et al. (). However, we show strong shortcomings in the digital search technique as applied by them: almost all likely true sunspot and aurora records were presented earlier (e.g., Xu et al.), which are not mentioned in those papers; the remaining records are dubious and often refer to other phenomena, neither spots nor aurorae (this also applies to Hayakawa et al.). The alleged aurorae in Hayakawa et al. () and Kawamura et al. () show a broad peak around full moon, not expected for aurorae. Hayakawa et al. () use the Korean reportAt night, the gate of heaven was opened(between AD 992 Dec 6 and AD 993 Jan 25, i.e., close to the¹⁴C variation AD 993/994) to estimate the Dst index of solar activity, even though the text does not fulfill any discriminative aurora criteria (except night‐time). Most of the above publications include very few Chinese texts and translations, and their tables with abbreviated keywords do not allow the reader to consider alternative interpretations (the tables also do not specify which records mention night‐time). We have compared some of their event tables with previously published catalogues and found various discrepancies. There are also intrinsic inconsistencies, misleading information (lunar phase for day‐time events), and dating errors. We present Chinese texts and translations for some of their presumable new aurorae: only one can be considered a likely true aurora (AD 604 Jan); some others were selected on the sole basis of the use of the wordlightorrainbow. Several alleged new aurorae present observations beside the Sun during day‐time. There are well‐known comets among their presumable aurorae. We also discuss (a) whetherheiqi ri pangcan stand for black spot(s)on one side oforbesidethe sun, (b) the aurora color confusion in Hayakawa et al. (,), and (c) whetherwhiteandunusual rainbowscan be aurorae.

We present here an Arabic report about supernova 1006 (SN 1006) written by the famous Persian scholar Ibn Sīnā (Lat. Avicenna, AD 980–1037), which has not been discussed in astronomical literature before. The short observational report about a new star is part of Ibn Sīnā's book called al‐Shifā', a work on philosophy including physics, astronomy, and meteorology. We present the Arabic text and our English translation. After a detailed discussion of the dating of the observation, we show that the text specifies that the transient celestial object was stationary and/or tail‐less (a star among the stars), that it remained for close to 3 months getting fainter and fainter until it disappeared, that it threw out sparks, that is, it was scintillating and very bright, and that the colour changed with time. The information content is consistent with the other Arabic and non‐Arabic reports about SN 1006. Hence, it is quite clear that Ibn Sīnā refers to SN 1006 in his report, given as an example for transient celestial objects in a discussion of Aristotle's Meteorology. Given the wording and the description, for example, for the colour evolution, this report is independent of other reports known so far.

The recently published Yemeni observation report about SN 1006 from al‐Yamānī clearly gives AD 1006 April 17 ± 2 (mid‐Rajab 396h) as the first observation date. Since this is ∼1.5 weeks earlier than the otherwise earliest reports (April 28 or 30) as discussed so far, we were motivated to investigate an early sighting in more depth. We searched for additional evidences from other areas like East Asia and Europe. We found that the date given by al‐Yamānī is fully consistent with other evidence, including the following: (a) SN 1006 rose several times half an hour after sunset (al‐Yamānī), which is correct for the location of Ṣan^cā' in Yemen for the time around April 17, but it would not be correct for late April or early May. (b) The date (third year, third lunar month, 28th day wuzi, Ichidai Yoki) for an observation of a guest star in Japan is inconsistent (there is no day wuzi in that lunar month), but may be dated to April 16 by reading a wuwu date rather than a wuzi date. (c) There is observational evidence that SN 1006 was observed in East Asia in early or mid‐April; for the second half of April, a bad weather (early monsoon) period is not unlikely— there is a lack of night reports. (d) The observer in St. Gallen reported to have seen SN 1006 for 3 months, which must have ended at the very latest on AD 1006 July 10, given his northern location, so that his observations probably started in April. We conclude that the correctly reported details give quite high confidence in the fully self‐consistent report of al‐Yamānī, so that the early discovery date should be considered seriously.