A preprint of my short paper on V538 Cas, accepted for publication in JAAVSO, is now available at arxiv.
1000 observations and counting
I just passed the 1 000 mark of observations reported to SVO, the Swedish variable star database. Two thirds are CCD observations, remotely controlled, and one third visual observations mostly using 15×70 binoculars, a 6 cm refractor and a 20 cm Newton reflector. I enjoy both types of observation equally.
Having observed regularly for some time now, a number of individual stars and types of stars have come across as special. I like miras, and gladly observe a set of classical miras – T Cep, R And, R Ari, R Leo, S and T UMa and so on.
But I also like to think that important work could be done by exploring some of the miras that are not very well observed. Hans Bengtsson has put together a list of 50 miras that are not very well observed, and a programme of observation of these is perhaps about to take form in the Swedish variable star community. To start with, we need to get some sequences, and a number of requests for sequences have been made to the AAVSO sequence team. So far, two stars have been observed.
I also like R CrB stars provided they show some action which has been the case with ample opportunity to follow changes these last months in R CrB, Z UMi, and SU Tau. Among the semiregulars, I often like to observe stars like BQ Ori, Z UMa and RY UMa.
I also like to combine my observations with literature study. Some of that has been posted here on the blog as an irregularly appearing series of biographies of variable stars. Another result is my first paper for the JAAVSO, which just got accepted. It is a combined literature and observation-based study of V538 Cas, using data collected with the AAVSO Bright Star Monitor.
Meeting of variable star observers in Gothenburg
There will be a meeting of Swedish variable star observers in Gothenburg in mid-April. I really look forward to it!
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Two eyes are better than one
Just before Christmas, I bought a telescope. (Statistically, telescope sales must be going up in December.) A 20 cm Newtonian with 120 cm focal length on a Dobsonian mount. I really like the scope, and observing with it is a joy.
This recent addition to my optical resources is something of a dream come true. As a teenager in the 1980’s, the telescope I regularly used was a 6 cm refractor. It was a versatile instrument, with which I made hundreds of observations of sunspots and quite a few of variable stars, but still, only a 6 cm refractor. I never got round to getting a bigger instrument, and then, around 1990 drifted out of amateur astronomy. Other things occupied my mind.
Now, some 20+ years later, I have a much larger instrument at my hands – but I still like to observe with my binoculars as well.
I think the reason for this is a kind of pragmatic observational style that is possible with a small instrument. It takes no time at all to start observing with the binoculars, which is important given the slightly unsteady weather here in southern Sweden. Sometimes, I even observe variable stars with it through (open) windows. It is a quick instrument, suitable for a set of rapid variable star estimates.
No perfect instrument exists. Every instrument has its pros and cons.
The fading of SU Tau
SU Tau has put on a remarkable show this last month, dropping from 10.5-11 in late November to 16.5. I caught most of it using the 61 cm Sierra Cassegrain telescope:
Mike Simonsen recently wrote an interesting blog post about R Coronae Borealis stars, including SU Tau.
Lunar eclipse
The Moon in partial eclipse after the clouds close to the horizon had drifted away.
Here in Lund in southern Sweden, the Moon rose totally eclipsed last Saturday. Because of clouds close to the horizon, I couldn’t see the Moon while in totality. However, the clouds soon cleared and the Moon became visible. The partial phase was a nice sight in 15×70 binoculars, parts of the umbra had a slightly red tinge.
Observing the lunar eclipse on December 10 2011.
I observed together with my 8-year old son – it was his first eclipse – and we also met another stargazer with whom we shared the experience. It turned out she was an experienced bird-watcher (285 species observed from Sweden) who also was interested in observing the night sky.
V538 Cas revisited
V538 Cas has a diverse history. It was discovered to have variations of about 0.6 magnitude, but more recent observations showed very small variations.
In order to throw some further light on this object, I thought it would be interesting to make observations to see whether the star is a variable star after all. The star is around 7.6V and is therefore rather too bright for many telescopes and surveys, but the AAVSOnet Bright Star Monitor is a suitable instrument.
I submitted a proposal for time on the BSM for monitoring of V538 Cas and it got accepted. The first observations have been made. Preliminary analysis of a couple of weeks’ data show not much variability in this star. It will be interesting to see whether that holds over longer time spans.
The companion of W Aurigae
Looking up W Aurigae in the Simbad database, we find that it is a double star, Cou 1725. Paul Couteau discovered the double star nature of W Aur in 1979, when he measured the star on three nights. The stars both had magnitude 9.7 and lay at a distance of 0.”16.1
How come, then, that W Aur doesn’t have a flat minimum at 9.7? Are both stars variables?
Update: Thomas Karlsson pointed out that the entry for W Aur was mixed up in Simbad with another star that is Cou 1725.
Simbad no longer identify W Aur with Cou 1725.
- P. Couteau, “New Double Stars Discovered at Nice – Part Sixteen,” Astronomy and Astrophysics Supplement Series 43 (January 1, 1981): 79. [↩]
W Aur
Lydia Ceraski discovered 219 variable stars (or 180 – the literature disagrees somewhat). Among them are important ones such as SU UMa, RV Tauri and T UMi. Despite that, not much is known about her. She graduated from the Petersburg Teachers’ Institute and was married to the astronomer Witold Ceraski.1
Witold Ceraski (1849-1925) became an astronomer at a time when the introduction of photography and photometers were changing the way astronomers aqcuire photometric data. Coming into astronomy in the 1870’s, he began his career by photographing the sun and doing stellar photometry with a Zöllner photometer, the topic for his doctoral dissertation. Stellar photometry would remain his main interest. His observations spanned some 36 magnitudes, since he even measured the magnitude of the sun.2
In 1890, he was appointed director of Moscow observatory. During his reign, the observatory was rebuilt, the photographic capabilities were expanded, and new instruments were added, among them a 15 inch astrograph. A type of astronomical team work developed. Plates were exposed by assistant astronomers, and then analyzed by Lydia Ceraski, and discoveries were published by the director, Witold Ceraski who oversaw operations. That was how the astronomical division of labour was set up back then; observatory directors often reported the results of assistant astronomers and similar staff. This does not mean that Lydia Ceraski was uncredited by other astronomers for her discoveries, quite the opposite:
Photographic technologies changed the everyday work-life at the observatory, not only in Moscow but throughout the world. Data became more mobile and could be analyzed during the daytime by other staff than the ones that manned the telescopes at night; this led to an increase in astronomical data and discoveries. New types of staff emerged that worked with analysis of plates rather than at the telescope; Lydia Ceraski was one of them.
In 1898, Lydia Ceraski found a variable in Auriga on plates taken by Blažko. In March and April of 1898, it was 8.9 mag, but half a year later it was invisible even in a quite big telescope, Witold Ceraski wrote in a paper dated 16/28 October 1898 (Russia was still using the Julian calendar).3
Astronomers at the Yerkes observatory were following variables, especially those that were suspected of having deep minima, and they put Lydia Ceraski’s find on their programme. In the winter of 1899-1900, using the Yerkes 12 and 40 inch refractors, Edward Emerson Barnard and J.A. Parkhurst could follow it as it reached a minimum of around 15th magnitude early in March.4 Parkhurst continued to observe the star at Yerkes with a wedge photometer, and used his observations together with those in the literature to determine the period to be 276 days; the star was now called W Aur.5
Later on, W Aurigae was found on objective prism survey plates to have an emission line spectrum. Also, it was discovered to be a tight visual double by Paul Couteau; in 1979 he measured the separation between the two components with the Nice 20 inch refractor to be 0.”16.6
W Aurigae is presently at or near a minimum. Nowadays you don’t need to be Edward Emerson Barnard or J.A. Parkhurst and observe with a 40 inch refractor to follow this mira through its minimum; a moderate size amateur telescope with a ccd camera will do.
Update: W Aur is not identical with Cou 1725; Simbad has changed the identification; Cou 1725 is, instead, identical with HD 281114.
- Variable Star of the Season: XZ Cyg; Dorrit Hoffleit, Women in the history of variable star astronomy (AAVSO, 1993), p. 9. [↩]
- S. Blažko, “Anzeige des Todes von Witold Ceraski,” Astronomische Nachrichten 225 (July 1, 1925): 111; A. Mironov and I. Pustylnik, “Vitold Ceraski and Vladimir Nikonov – founders of stellar photometry in Russia,” Astronomische Nachrichten 323 (July 1, 2002): 562-566. [↩]
- W. Ceraski, “Découverte d’une nouvelle étoile variable,” Astronomische Nachrichten 148 (November 1, 1898): 15. [↩]
- G. E. Hale, “Variable star observations with the 12-inch and 40-inch refractors.,” The Astrophysical Journal 12 (July 1, 1900): 52-54 – another observatory director reporting the work of his astronomers. [↩]
- J. A. Parkhurst, “The variable star 1921 W Aurigae.,” The Astrophysical Journal 18 (December 1, 1903): 309-323. [↩]
- L. Kohoutek and R. Wehmeyer, “Catalogue of H-alpha emission stars in the Northern Milky Way,” Astronomy and Astrophysics Supplement Series 134, no. 2 (1999): 2. P. Couteau, “New Double Stars Discovered at Nice – Part Sixteen,” Astronomy and Astrophysics Supplement Series 43 (January 1, 1981): 79. [↩]
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Tagged Aur, Edward Emerson Barnard, J.A. Parkhurst, Lydia Ceraski, Miras, W Aur, Witold Ceraski
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V370 And
The discovery and observation of variables are sometimes the byproducts of astronomical projects and instruments doing other things. Current examples include the Kepler and CoRot missions.
Hipparcos, the very successful European space astrometry telescope, also measured photometry, and it found many variables, 11 597 to be precise, of which more than 8000 were new discoveries.
One of the variables measured by Hipparcos was V370 And. It is a rather bright star, and therefore it was early on recommended that amateur astronomers take up the star on their observing programmes and astronomers check the platestacks at observatories with histories of sky patrol programmes. This star merited further observations.1
Said and done. After Hoffleit’s and Lee’s plea for more observations of V370 And, the AAVSO data archive contains a number of observations, and German amateurs observing visually found variations between 7.4-7.8 with periods around 120 and/or 240 days, about similar to what the Hipparcos data showed.2 Photoelectric measurements in the winter of 1992-1993 do not, it seems, support a period around 230-240 days.3
Analysis of historical photographical archives found variations with an amplitude of 0.5.4
The Hipparcos data shows an excursion, making the total amplitude in the available data, so far, 6.85-8.05 V. Not only is the excursion event present in several Hipparcos measurements around 2448600, but a similar bright excursion is found in the photographic material as well.5
The star was recently placed in the highest priority category in a paper recommending which semiregulars to observe.6 The last two years, only few observations were, however, recorded in the AAVSO archive, but maybe Percy’s and Terziev’s recommendation might change that:
Observations of V370 And since the beginning of 2010 in AAVSO:s database
Long term monitoring of this bright variable could be a worthwhile observing project, well within the reach of small-scale equipment.
- Dorrit Hoffleit and J. T. Lee, “More Observations Needed for V370 And, an Hipparcos Discovery,” Information Bulletin on Variable Stars 4630 (September 1, 1998): 1; Dorrit Hoffleit, “Hipparcos Versus GCVS Amplitudes of Non-Mira M-Type Giants,” Journal of the American Association of Variable Star Observers (JAAVSO) 27 (Oktober 1999): 131-140. [↩]
- G.-U. Flechsig, “BAV-Beobachter-Treffen 2005 in Hartha.,” BAV Rundbrief – Mitteilungsblatt der Berliner Arbeits-gemeinschaft fuer Veraenderliche Sterne 54 (2005): 156-158. [↩]
- Tinggao Yang, Ming Cao, and Shiyang Jiang, “UBV Photometry for Three New Variable Stars,” Information Bulletin on Variable Stars 3956 (November 1, 1993): 1; note and diagram added to VSX by Otero 2011-07-13. Otero also writes that Tinggao et al are the discoverers of the variable, not Hipparcos. [↩]
- C. Lloyd, R. D. Pickard, and R. H. Chambers, “The periods of the semiregular variable V370 And,” Information Bulletin on Variable Stars 5217 (January 1, 2002): 1; T. Berthold, “V370 And – ein neuer halbregelmäßiger Veränderlicher.,” BAV Rundbrief 48 (1999): 59-61. [↩]
- C. Lloyd, R. D. Pickard, and R. H. Chambers, “The periods of the semiregular variable V370 And,” Information Bulletin on Variable Stars 5217 (January 1, 2002): 1. [↩]
- J. R. Percy and E. Terziev, “Studies of ‘Irregularity’ in Pulsating Red Giants. III. Many More Stars, an Overview, and Some Conclusions,” Journal of the American Association of Variable Star Observers (JAAVSO) 39 (June 1, 2011): 1. [↩]
