Published in the AAVSO Newsletter – April 2010
Enjoying the Unexpected
ROD STUBBINGS (SRX)
TETOORA ROAD, VICTORIA, AUSTRALIA
Having made my first observation of a variable star in 1993 I could not have imagined it would lead to such a rewarding hobby. The involvement with professionals and observers all around the world brings many observing experiences.
In the first few years of observing variable stars I developed a very obsessive passion with these crazy stars. I would observe for two nights in succession without sleep, check the night sky on cloudy nights every half hour searching for breaks in clouds, stay in the observatory and observe in between rain and storms and set the alarm each night when the Moon was present to avoid it. Back then, contact with headquarters (RASNZ) was through letters, fax or, if important, by phone. There was a special program on the SU UMa-type eclipsing star OY Car which required satellite observations. I still remember detecting an outburst of OY Car at 2:00am one morning. Having never rang anyone outside of Australia before and at that time of the night I was a bit hesitant, and also I was about to alert the Director of the Variable star Section of New Zealand. I decided to make the call and to my surprise, the director, Dr. Frank Bateson answered instantly! Just a quick “Okay Rod,” was the reply, but it was a great feeling knowing the satellite observations took place. This communication situation changed with the availability of the Internet and became much easier.
One time I received an email from Frank Bateson in regards to the SU UMa stars. When one went into outburst he wanted me to observe the star every minute. I replied that I usually get through my list in under two hours, went inside for a cup of tea, then back outside to observe some more, so I will endeavor to make these estimates every minute when a SU UMa star goes into outburst. Frank wrote back and commented that it is just as well that we no longer observe flare stars since there would be no dashing in for cups of tea. He well understood the problems of making observations at minute intervals: “Flare stars involved making a visual estimate every 30 seconds for unbroken spells of at least four hours. I was the only ‘nut’ ever to do this with temperatures well below freezing at Mt. John. It did bring rewards as when major flares occurred I got the entire flares whereas a German graduate who was recording photoelectrically lost the major part of the flares when his recorder ran off scale. Mind you, I was younger then and even crazier than I am today.”
Well, two SU UMa stars went off one night and after a couple of night’s observations, I sent a note to Frank. “I thought this would happen, as there were two SU UMa stars up the other night I decided to stay on TU Men. I have watched for 2 hours the past two nights, having found the second night a little easier to look at the same field for so long. I started to see a variation of 0.1 magnitude every 3 to 4 minutes, if that’s possible. On the first night I [had] also seen this and thought maybe my eyes [were] playing tricks but I came up with the same result on the second night. Do stars in outburst behave like this?” Frank replied that, “… in SU UMa stars you can observe both the orbital period and in the case of super maxima the superhump period. The former will show a small variation in a few minutes which remains constant for any particular star but differs in both period and amplitude from one star to another. The superhump amplitude varies slightly as the superoutburst progresses and the period may also change slightly. I was glad that you kept with TU Men.”
I once commented to Albert Jones that in the early years of his variable star observing that he had all the southern sky to himself. Albert mentioned that, looking back, he realized how lucky he was to be “in at the start” of monitoring CVs. He read that VW Hyi was the brightest star of that class in the southern sky, but there did not seem to be any charts for it, although a French bulletin showed a finder chart showing only the brighter stars. Evidently VW Hyi had been discovered on Harvard patrol plates but had not been observed visually. Albert had been able to purchase an old set of CPD catalogues and had a go at plotting a chart showing the CPD stars. The very next night was clear and when he looked, VW Hyi was at maximum and faded over the following days. He later told Frank Bateson what he had been up to and started sending him observations of VW Hyi. Around that time Albert was corresponding with some French amateurs, two of them Brun and Petit, were compiling an Atlas of UG stars (which was published later in a Russian variable star journal), and Monsiener Brun asked him to plot a number of southern fields because he did not have catalogs for southern regions. Some were known UGs while others were only suspected and had only “temporary” numbers from Sonneberg Observatory. Hoffmeister had gone to South Africa, taken lots of photos, then took them back to Sonneberg to study them. On some fields he found one image, so he suspected those might be U Gem stars “short maxima”. Albert kept a watch on these, then Z Cha showed up and later EK TrA. He had the whole sky to himself at first, and then others became interested and looked for outbursts. VW Hyi, and Z cha are two of the most observed stars in the southern sky and today still attract a lot of attention by professionals.
I was observing a lot of unstudied CV’s in star fields which had no decent charts until Bruce Sumner offered to produce the charts. I was sky checking the fields for Bruce. This obsession lead to a number of stars being caught in outburst for the very first time. One in particular, CG CMa, was discovered by Verlooy on Franklin-Adams plates taken in 1934. CG CMa was considered to be a possible classical nova one of most distant in our Galaxy. Duerbeck (1987) identified the possible quiescent counterpart, a star around magnitude 16.4. The cataclysmic classification, however, became less likely when Zwitter and Munari (1995) took the spectrum of the suggested quiescent counterpart, which showed an isolated white dwarf. After observing this star for only two months I caught an outburst in 1999, the first recorded outburst since its discovery in 1934 on photographic plates. CCD observations showed that the outbursting object was slightly offset from the suggested quiescent counterpart and the true CG CMa was a 20th magnitude star. The outburst lasted for 22 days, and CG CMa was reclassified as a new SU UMa-type dwarf nova. CG CMa has had no further outbursts to date.
Still in my memory is the outburst of V4641 Sgr, a black hole binary system 1,600 lights years away. On September 15th 1999, I went outside to make a few observations in between clouds. First up was V4641 Sgr. I found the star had exploded to magnitude 8.8, so I sent off an alert. CCD images at the Kyoto University, Japan, confirmed the outburst. Astronomers at the MIT diverted an X-ray satellite to take a look and it showed a rapid rise and fall in X-ray brightness. Within 24 hours radio telescopes around the world were observing V4641 Sgr. Optically this outburst lasted less than 8 hours. V4641 Sgr still exhibits X-ray outbursts and flares each year and is a great target for the visual observer (it has been brightening to visual magnitude 11 ). To this day I am still the only person to visually see and record the outburst at magnitude 8.8. This emphasizes the scientific value of visual observations in variable star astronomy.
In 1997 the planetary nebula V651 Mon, which is a spectroscopic binary with an orbital period of almost 16 days, began to show fading episodes. As the star was too low for northern observers, Rafael Costero from Mexico contacted me to see if I could get some observations from the southern hemisphere before the Sun ended the show in late June. I observed V651 Mon for the first time on May 30th and it was fainter than 14.4. My next observations were on June 2nd and 3rd around magnitude 11, and I sent these on to Rafael. Apparently I was the first and only observer that had reported data on V651 Mon in the preceding three weeks and observed the exiting of the star behind the cloud on or about June 2nd. V651 Mon was now predicted to re-enter behind the cloud again, stay quite weak for a few days, and then once again re-brighten. I only had a short window of opportunity to observe this star, and I wasn’t going to let the usual cloud, rain and haze beat me. I did observe the next fading around June 15th, and again I was able to follow the star’s brightening right up to June 22nd, when it was only 10 degrees above the horizon. The next challenge was to follow the object as soon as it became observable again, July 22nd, to see if the fading episodes were still ongoing. V651 Mon was bright and remained bright, so the occultations were clearly over. It was great exchanging emails with Rafael on the antics of V651 Mon and I also learned a lot more about the star.
The polar star EF Eri was added to my list in June 1997 after a request from Dr. Frank Bateson. Apparently professionals in the U.K. and U.S.A. had Target of Opportunity (TOO) observations on two satellites for observations. My observations showed that EF Eri was not in an active state and fainter than magnitude 15.0. Three months later, observations were still required now that EF Eri had emerged from conjunction with the sun. Frank received a message from the controllers of the EUVE and XTE satellites. “These birds were positioned to observe EF Eri as soon as we can report it is brightening.” EF Eri was still fainter than magnitude 15.0. Eight months on, the program was still running but no outbursts. After two years of observing EF Eri with no outbursts or activity, the satellite people in U.K. and U.S.A. still had TOOs on two satellites and assured us that the star does rise to 13th magnitude. I never heard much about the program on EF Eri after this and assumed it had ended but still keep it on my list. Well after 9 years of negative observations I got the biggest shock when I caught EF Eri bright in June 2006 at magnitude 15.6. The next night it rose to 14.2. I still wonder if the satellite observations ever took place.* This star was supposed to have died but came back to life!
I continue to observe these crazy stars at every opportunity and still get a rush of blood every time an outburst is detected. *