R Ari

One of the great visual surveys of the northen sky was done at Bonn by Friedrich Wilhelm Argelander with the aid of his asistants Eduard Schönfeld and Adalbert Krüger. They observed the sky north of -2 degrees declination during the 1850’s and the results were published as the Atlas des nördlichen gestirnten Himmels für den Anfang des Jahres 1855, commonly referred to as the Bonner Durchmusterung, in 1863. It quickly became a standard reference work for stellar astronomy. One of the things that made BD so useful was the precision and care with which the work was carried out. Argelander would not enter a star into the catalogue unless it had been observed twice. Also, inconsistencies were straightened out using larger instruments as a check.¹

One effect of this continuous re-checking of results during the production of the BD was the discovery of new variable stars, one of which is visible in the November evening sky presently shining at magnitude 8.5 (at least when I observed it on November 5 using 15×70 binoculars): R Arietis. It was discovered by Argelander during the BD work; while Bessel had observed it in 1828 and 1832 as a star of magnitude 8 and 8.9, respectively, the Bonn observers found nothing in January, September, and October of 1855, despite a limiting magnitude of 9.1 (the Bonner Durchmusterung was observed with a 78 mm comet seeker – this must be one of the records in the history of astronomy if you’re looking for a high publication impact to instrument cost ratio). However, in November of 1857 it was visible right at the limit of 9.1, and the following months saw the star brighten to a maximum in January of 1858. It was announced to the world in a paper by Argelander dated February 14, together with his discoveries of S Aqr and an 8.9 m star with a proper motion of 2.”3.²

As we move forward through the decades, the avaliable data on R Ari is, at first, scarce, but increases towards the end of the 19th century. An 1890 review of published and unpublished observations of variable stars made since 1840 tabulated 198 observations of R Ari, almost all of them made in the 1880’s. This trend of an increase of variable star observing during the 1880’s is visible in the statistics of other variables as well. One reason is that Harvard observatory is moving in to this field of astronomy, another is an increase in amateur observation.

For R Arietis we find observations made by professional astronomers such as Argelander, the Harvard observers (EC Pickering, O.C. Wendell and Arthur Searle) using the meridian photometer and the 15 inch refractor, J.G. Hagen, then at the College of the Sacred Heart in Wisconsin, and Vojtech Safarik in Prague. Amateurs contributing observations of R Arietis in the 1880s include Henry Parkhurst, a prominent amateur who invented photometric equipment and whose observations were published by the Harvard observatory. He also formed collaborations with other amateur astronomers such as John Eadie and Arthur Perry, who with their smaller telescopes observed the brighter parts of the variables, leaving the fainter parts to Parkhurst and his 9 inch Fitz telescope.³ In 1884-1887, Parkhurst alone made 37 observations of R Arietis, compared to the 48 observations made at the Harvard College Observatory.

Other amateurs observing R Arietis in the 1880’s were Joseph Baxendell, father and son. Pickering, writing in 1890, knew of only a few observations by the Baxendells, but later on a batch of observations in manuscript surfaced that showed that Baxendell sr had placed R Arietis on his observing programme soon after it was discovered, in November 1858, and then made many observations of it right up until his death: his last observation of R Arietis was March 3 1887, at magnitude 8.5; he died half a year later, on October 7.⁴

Seth Chandler straddles the pro-am border, having made his observations of R Arietis in his own observatory in 1883-1884 using a 6 inch telescope, while he was employed by the Harvard observatory. Knowledge about R Arietis thus came about through a mixture of rather advanced amateurs such as Parkhurst and Baxendell collaborating with professional astronomers. By 1890, that knowledge included the period, given as 186.7 days, a range from 7.6 to 13.0 and a classification of it as what was then called “class II”, a Mira variable.⁵

That data is practically valid 120 years later; the AAVSO Variable Star Index gives 185.67 days and 7.1-14.3 V. It is a maser source.⁶

This Mira has shown some irregularities. A.A. Nijland at Utrecht had the star on his extensive programme of observation and observed the star with 3 and 10 inch telescopes. During the autumn of 1917, the star’s rise to maximum seemed to halt at about magnitude 9.4, where it lay more or less constant for two months; it was, Nijland noted, the lowest maximum for twelve years.⁷ According to one study, the extremes in maximum light are 7.6 and 9.4, so Nijland’s observations were of a more or less unique maximum.⁸ Material for further studies in the behaviour of the light curve of R Arietis is available: it is a quite well-observed Mira star, with 21 543 observations in the AAVSO archive.

1. “How the BD was made”, Joseph Ashbrook, The Astronomical Scrapbook: Skywatchers, Pioneers, and Seekers in Astronomy, Cambridge University Press & Sky Publishing Corporation, 1984, chapter 80 (also in S&T, April 1980. [↩]
2. Friedrich Wilhelm August Argelander, “Aus einem Schreiben des Herrn Prof. Argelander, Directors der Bonner Sternwarte, an den Herausgeber,” Astronomische Nachrichten 48 (March 1, 1858): 13. [↩]
3. J. A. Parkhurst, “Henry M. Parkhurst,” Popular Astronomy 16 (April 1, 1908): 231-239. [↩]
4. H. H. Turner, “Baxendell’s observations of variable stars, edited by,” Monthly Notices of the Royal Astronomical Society 73 (December 1, 1912): 124. More on the work of this very able amateur astronomer is in H. H. Turner, “U. Geminorum, Baxendell’s observations of, edited,” Monthly Notices of the Royal Astronomical Society 67 (March 1, 1907): 316 and “Obituary: List of Fellows and Associates deceased Baxendell, Joseph,” Monthly Notices of the Royal Astronomical Society 48 (February 1, 1888): 157. He is today sometimes remembered for his “unphotographable nebula”. [↩]
5. Edward Charles Pickering, “Index to observations of variable stars,” Annals of Harvard College Observatory 18 (1890): 215-257. [↩]
6. Priscilla J. Benson and Irene R. Little-Marenin, “Water Masers Associated with Circumstellar Shells,” The Astrophysical Journal Supplement Series 106 (Oktober 1996): 579. [↩]
7. Albert Antonie Nijland, “Beobachtungen von langperiodischen Variablen (1917),” Astronomische Nachrichten 206 (Maj 1918): 173. [↩]
8. J. E. Isles and D. R. B. Saw, “Mira stars – I: R Ari, R Aur, R Boo and S Boo,” Journal of the British Astronomical Association 97 (February 1, 1987): 106-116. [↩]