Orwell Astronomical Society (Ipswich)
Variable Stars, July 1980 - December 2015
This page records observations of variable stars by members of OASI, August 1980 - December 2015. Except where noted to the contrary, observations are by Mike Nicholls.
S Cassiopeiae is a member of the long period class of variables, with a lengthy period of 612 days (compared with the more usual 300-400 days).
The observations below were made with a 200 mm reflector.
The following estimated light curve shows S Cas from August to December 1980. The BAA predictions for the star show it reaching maximum on 12 August. In the event, it appears to have been late, with maximum occurring around the end of September. Astronomical literature shows that it is common for long period variables to have a variability of up to a few weeks in their periodicity. Observations had to cease once the star reached magnitude 13, because I could barely glimpse, on a very clear night, a comparison star of magnitude 13.2.
Mira (ο Ceti) is the most famous long period variable star and was the first of the class to be discovered. David Fabricius noticed it in 1596; he saw it increase in brightness and then fade away and assumed that it was a nova, never to be seen again, until he spotted it once more 15 years later. Johannes Holwarda studied it systematically in 1638, attributing a period of 11 months. Johannes Hevelius, arguably the last astronomer to do significant work without the aid of a telescope, named it Mira in a publication of 1662. In recognition of the historical importance of Mira, members of the class of stars displaying similar characteristics are sometimes referred to as Mira stars.
Mira is located at a distance of approximately 300 light years. It is a binary system, an old red giant named Mira A has in orbit about it a white dwarf, Mira B, with a period of approximately 400 years. Mira B is steadily accreting material from Mira A. The system is an example of a symbiotic star. Mira averages a variation in brightness of approximately six magnitudes in a period of 331 days. Around 100 days in each cycle, it is brighter than magnitude 5. Its peak brightness averages magnitude 3.5, with historical limits of 2.0 and 4.9. At faintest, it ranges from magnitude 8.6 to 10.1. During a typical cycle, brightness increases at twice the rate that it falls. Mira is a convenient star for beginners to observe because it has a large amplitude and is relatively bright for much of its period.
The predicted date of maximum in 1980 was early September. The estimated light curve below suggests that the star may have been a little later than predicted, but this is not unusual. The termination of estimates in early February 1981 was due not to the disappearance of Cetus into the sunset but to the poor weather throughout February and March.
The observations below were made with 10x50 binoculars, a 200 mm reflector and the 26 cm Orwell Park Refractor.
The following estimated light curve shows Mira from September 1980 to February 1981.
The following observations, by Joe Startin, show estimates of the magnitude of Mira during the three-month period 18 August - 18 November 2012. Attempts at earlier observations were thwarted by bad weather. All observations were made with binoculars; attempts to continue observation after the star had become fainter than magnitude 7, and thus was difficult to see in the binoculars, were unsuccessful.
SS Herculis is a member of the long period class of variables, but has an unusually short average period (for this class of variable) of 107 days.
The observations below were made with a 200 mm reflector.
The following estimated light curve shows SS Her from May to August 1981. It shows a period of the star.
X Aurigae is a member of the long period class of variables with an average period of 164 days.
The observations below were made with a 200 mm reflector.
The following estimated light curve shows X Aur from September 1980 to May 1981. It shows approximately 1.5 periods of the star.
The following estimated light curve shows X Aur from October 1981 to May 1982. It shoes two consecutive maxima of the star, spanning slightly more than a whole period.
R Leonis is a member of the long period class of variables. It is a favourite amongst beginners to variable star observing because it is easy to locate and can be followed with binoculars for much of its cycle.
R Leo has a period of 313 days, so its maxima and minima tend to occur slightly earlier each year - this can be seen in the following light curves. The star has a magnitude range of approximately 5.4-10.5.
An interesting feature of the estimated light curves below is the irregularity at circa magnitude 7. It is evident in all three light curves, indicating that it is a real feature rather than an artefact or observing error. Some long period variables are known to exhibit this type of behaviour.
All the observations below were made with 10x50 binoculars, a 200 mm reflector and the Orwell Park Observatory 26 cm refractor.
The following estimated light curve shows R Leo from January to early June 1981. The light curve shows a minimum at the end of February but there is no sign of a maximum.
The following estimated light curve shows R Leo from March to May 1982.
The following estimated light curve shows R Leo from February to May 1983. The star exhibits a maximum magnitude of 5.7 during mid-April.
W Cygni is a member of the semi-regular class of variables, with a period quoted officially as approximately 127 days and a brightness range of 5.0-7.6. Most semi-regular variables have magnitude ranges of two or less. Like most semi-regular variables, W Cyg is an old red giant and it is thought that variations in brightness are associated with pulsations in the shell of the star, with several modes combining to produce the semi-regular nature of the variation. In the case of W Cyg, there are believed to be at least three modes of oscillation, with periods 1000, 227 and 127 days although there is some disagreement among experts as to these values. The latter periodicity defines the main mode. W Cyg has been observed by astronomers almost continuously since 1927.
Examination of the AAVSO website will reveal a large variation in magnitude estimates of W Cyg between different observers. Bright red variables are notorious for this phenomenon. The trend in variation, however, is easily seen.
The observations below were made with 10x50 binoculars.
The following star chart shows stars in the comparison field of W Cyg, with magnitudes marked in red. W Cyg is approximately 0.25° distant from the fourth magnitude star Rho Cyg, so is easily located.
The following estimated light curve shows W Cyg from August 1980 to February 1981. It suggests the presence of a short period variability with a period of approximately 20 days. I can find no mention of such a variability in the literature. However, another member of OASI, E H Collinson, also observed the star during this period and did not record such a variability.
The following light curve shows W Cyg from April to December 1981. It shows a minimum of the star. The estimates show some low amplitude fluctuations to start with, becoming more steady in July and August. Again, E H Collinson also observed the star during this period and did not record these fluctuations.
The following light curve shows W Cyg from June to November 1982.
The following light curve shows W Cyg from June to November 1983. It shows what appears to be slightly more than a full cycle of variation, with a period agreeing with the official figure - however this is the first occasion in three years of observation that I have seen such agreement! Of course the relatively brief observational period is much too short to show evidence of the longer periodicity of 3100 days.
The following light curve shows W Cyg from May 1985 to January 1986. It suggests a periodicity of 60-70 days, which does not agree with any of the accepted periodicities of the star.
The following light curve shows W Cyg from June to November 1986. During this period, there is not much variation in the magnitude of the star.
The following light curve shows W Cyg from June to November 1987.
The following light curve shows W Cyg from May to December 1989. The period of 130 days is clearly visible.
The following light curve shows W Cyg during the last five months of 2015.
SS Cygni is the best known member of a class of stars known as dwarf novae or U Geminorum variables. Such stars remain at minimum brightness for most of the time, but suddenly and unpredictably rise to maximum brightness, which may be up to six magnitudes greater, within a day or two. They stay at maximum for a few days and then fall back more slowly to minimum magnitude.
The observed behaviour is caused by the interaction of components of a binary system, one component of which is a main sequence star and the other a white dwarf. The components are close, generally hardly a star diameter between them, and orbit one another in the space of a few hours. The gravity of the white dwarf draws material from the other star into an accretion disk around the former, from where it gradually spirals down on to the surface. The outbursts are thought to be caused by occasional instabilities in the accretion disc due to changes in temperature and viscosity, allowing sudden increases in the rate at which material descends to the surface of the white dwarf.
The outbursts of SS Cyg are not regular, but the average periodicity is generally between seven and eight weeks. The light range of the star is generally between magnitudes 8.2 and 12.4 (that is, outbursts cause the star to brighten by approximately four magnitudes).
Most of the observations below were made with a 200 mm reflector while a few were made using the Orwell Park 26 cm refractor. In the following light curves, the triangular symbols indicate the magnitude of the faintest star in the comparison field when the variable itself is too faint to be visible.
The following light curve shows SS Cyg from August 1980 to January 1981.
The following light curve shows SS Cyg from May 1981 to January 1982. This shows maxima approximately three months apart; however there is only a single estimate after December 1981 so it is not possible to rule out an earlier maximum.
The following light curve shows SS Cyg from June to December 1983. It shows four maxima. The maximum at the end of July and the maximum in September/October are of different duration. Note the longer minimum following the longer maximum - this is a normal occurrence for dwarf novae.
The following light curve shows SS Cyg from July 1985 to January 1986. It confirms the average periodicity of approximately 52 days (bearing in mind that the curve captures only the start of the rise to maximum occurring in mid-September).
The following light curve shows SS Cyg from June 1986 to January 1987. It shows three maxima.
The following light curve shows SS Cyg from June 1987 to February 1988. It shows more frequent outbursts than the average rate (one per 140 days approximately).
The following light curve shows SS Cyg from August to December 2015. The empirical period just about fits the accepted period of seven-eight weeks.
BU Persei is a member of the class of semi-regular variables. Although it has been known to reach as bright as magnitude 7.9, it generally has a small magnitude range and indeed this is typical of semi-regular variables. BU Per is an old red giant star and it is thought that variations in its brightness are caused by pulsations in its atmosphere. The official period of BU Per is 365 days, but this is only indicative as individual cycles can differ considerably from this figure.
The observations below were made with a 200 mm reflector.
The following light curve shows BU Per from October 1983 to April 1984. As can be seen, the magnitude range is small.
The following light curve shows BU Per from November 1985 to April 1986. Again, it confirms the small magnitude range.
BU Per lies close to the Sword Handle cluster (indeed, it may be a member of the cluster). The following image illustrates the two objects. By James Appleton, 27 October 1997 (35 mm telephoto lens, 2 minute exposure at f2.8, SLR camera driven on equatorial mount).
RS Persei belongs to the class of old red giants which are semi-regular pulsating variables. As the light curves below show, the magnitude of the star does not vary much, a characteristic of this class of variables. The astronomy literature indicates that the star has a magnitude range from 7.9 to 10.2 with an average period of 152 days. However, my own observations have not shown the magnitude of the star to vary significantly from 8.5. RS Per is a member of the Sword Handle cluster: being located in a region of space with so many other stars makes it a difficult star to observe (see image above).
The observations below were made with a 200 mm reflector.
The following light curve shows RS Persei from October 1983 to April 1984.
The following light curve shows RS Persei from September 1986 to May 1987.
The following light curve shows RS Persei from September 1987 to May 1988.
S Persei is an old red supergiant and is usually considered a member of the class of semi-regular variable stars. The official light range for the star is magnitudes 8.6-12.0, with a period of approximately 826 days, although it is thought in fact that there are two distinct periodicities controlling the visual brightness. However, the average period of S Per is rather long for a semi-regular variable and the magnitude range is greater than the two magnitudes that is typical for that class of star, thus some astronomers class S Per as a long period variable.
Although S Per is located close to the Sword Handle cluster it is not a member of the cluster. (See image above.)
The observations below were made with a 200 mm reflector.
The following light curve shows S Per from December 1981 - April 1982. As can be seen, the magnitude of the star does not vary much over this period.
The following light curve shows S Per from November 1982 - April 1983, covering only some 20% of a period. Although the variations are rather erratic, the general trend is of a decrease in brightness. This is broadly similar to the curve above where the star appeared to be declining from maximum.
The following light curve shows S Per from October 1983 - March 1984. It shows what appears to be a maximum and, as the periodicity is long compared with the window of observations, there is only limited evidence of variability. However, the periodicity of semi-regular variables can alter considerably from cycle to cycle.
The following light curve shows S Per from September 1984 - March 1985. It appears to show a minimum around Christmas 1984, indicating a shorter period than the official 826 days, as my records show the previous minimum in May 1983, only some 580 days earlier.
The following light curve shows S Per from September 1986 - April 1987. It shows the effect of long period variations in the visual magnitude of the star, evidenced by the long term trend of reducing magnitude during the latter part of the seven month interval shown.
The following light curve shows S Per from July 1987 - January 1988. It shows the star on the rising portion of its cycle and near to maximum at the end.
The following light curve shows S Per from August 1988 - April 1989. It shows the star fading from maximum to minimum.
The following light curve shows S Per from August 1989 - March 1990. It shows the star beginning to brighten after a long fade.
V Coronae Borealis is a long period variable with a range officially recorded as magnitudes 8.5-12.8 and a period of 358 days. The star is very red, which tends to produce more observational errors than other colours.
The observations below were made with a 200 mm reflector.
The following light curve is that of V CrB from April to early September 1983. The curve shows a rather erratic rise towards maximum: this may be real or or may be due to the inherent variability of observations by a single observer (note the comment above about the red colour of the star). The curve shows a significant proportion of the rising phase but it is not possible to say whether the star has reached maximum until it begins to fade and there is evidence of a sustained downturn. The predicted maximum was on 06 August.
The following light curve shows V CrB from April to September 1984. The light curve may have captured both a minimum and a maximum: if this is indeed the case, the fade from maximum back to minimum will be much longer than the rising portion of the curve in order to give a period of about one year. Such behaviour is quite normal for a long period variable.
The following light curve shows V CrB from April to October 1986. The light curve shows a typical maximum for a long period variable, with the rise to maximum much steeper than the fall to minimum.
The following light curve shows V CrB from April to October 1987. The light curve shows a typical maximum for the star.
The following light curve shows V CrB from April to October 1988. It shows a steep rise to maximum followed by a more gentle fade towards minimum: even though the ratio of rise time to fall time can vary considerably for a long period variable it is usual for the rise to be shorter than the fall.
R Coronae Borealis is the archetypal and best known star of the class of the same name. Normally, it stays at a magnitude of about 6.1 (marked in the light curves below by a dotted line). However, occasionally and quite irregularly, it fades quickly to around magnitude 15 and remains at this magnitude for an unpredictable period, which can be years, before rising to maximum again. The rise is usually slower and more erratic than the fade. R CrB is an old, giant star with a high proportion of carbon in its atmosphere, and it is thought that the rapid fading is caused by carbon condensing to form a veil of soot. In early 1986, R CrB featured in astronomy news articles following analysis of IRAS (Infra red Astronomy Satellite) data which showed a vast cloud of dust, approximately 26 light years across, centred on the star. (If the Sun had a similar cloud, it would engulf not only the solar system but the 50 nearest stars!) There remains a mystery as to why the cloud shines so brightly in the infra red: R CrB cannot supply sufficient energy, and neither does it appear to come from the surrounding stars.
The variability of R CrB was discovered in 1795, and it has been studied ever since. Since 1795, there has been one period of ten years when R CrB remained continuously at maximum and a period of approximately nine years when the star never settled at maximum at all. No signs of regularity have ever been detected.
The observations below were made with 10x50 binoculars and a 200 mm reflector.
The following star chart shows the comparison field of R CrB, with magnitudes marked in red. Normally, R CrB is the brightest star within the crown of Corona Borealis and easily visible with binoculars.
During the 1981 observing season and up until summer 1982, R CrB remained constant at magnitude 6.1 (±0.1). During the summer, however, it suddenly dropped in brightness and then rose again. Unfortunately, I was unable to observe the star after October. The following light curve covers the three month period August - October 1982.
The following light curve shows R CrB from April to October 1983. The star has been at maximum for at least the previous three years apart from occasional short, shallow decreases of a magnitude or so (as above). However, in August of 1983 it dropped suddenly by several magnitudes. Its magnitude from this point onwards is unpredictable: it could return to its normal magnitude quickly, it could remain at minimum magnitude for an extended period or it could vary in magnitude erratically for several years.
The following light curve shows R CrB from April to November 1984. It shows a portion of the rise towards maximum following a fall to magnitude 15 in Autumn 1983. By November 1984, the star had not quite attained its maximum magnitude.
The following light curve shows R CrB from April to November 1985. It shows a dip in brightness of circa four magnitudes from which the star appears to be recovering rapidly.
The following unimposing light curve shows R CrB from April to October 1986. It shows the star at its normal, maximum brightness.
The following light curve shows R CrB from April to September 1988. It shows the star fading from its normal magnitude (6.1) to a minimum around magnitude 12 and then starting to recover again.
The following light curve shows R CrB from April to November 1989. It captures one of the irregular fades of the star.
R Scuti is a member of the RV Tauri group of variables, regarded as a sub-class of the semi-regular type, of which the main characteristic is alternate deep and shallow minima. RV Tauri stars are thought to oscillate in at least two different modes, accounting for the two different depths of minima. They are among the most massive variable stars known. In the case of R Sct, in fact, it is common for two shallow minima to occur in succession, and every fourth or fifth minimum tends to be extra deep. The maxima of the star are not identical and have no regular pattern associated with them. The officially quoted period for R Sct is 144 days.
The observations below were made with 10x50 binoculars and a 200 mm reflector for magnitudes less than 7. The ability to observe this star with binoculars for most of its magnitude range makes it an easy observing target.
The following estimated light curve shows R Sct from July to November 1980. It shows a shallow minimum of the star. Unfortunately, Scutum moved into the twilight before R Sct went into what looked like a deeper minimum.
The following light curve shows R Sct from June to November 1981. It shows a deep minimum of the star.
The following light curve shows R Sct from July to October 1983. It shows two maxima and one minimum which may or may not be an extra deep one; it appears to fit in between the accepted magnitude of approximately 6.0 for normal minima and approximately 8.0 for deep minima. Whether or not the slight dip in mid-October is real is impossible to say from only one observer's results.
The following light curve shows R Sct from July to October 1984. It shows a rise from a deep minimum, followed by a shallow minimum in September. The magnitude is falling towards another minimum at the end of October, but it is impossible to predict whether this will be shallow or deep.
The following light curve shows R Sct from June to October 1986. The main features are the deep minima at the start and end of the light curve. There is some evidence of a shallow minima occurring in early August, but lack of data means that this is not very convincing.
The following light curve shows R Sct from June to October 1987. It shows two maxima separated by a deep minimum.
R Andromedae is a member of the class of long period, or Mira-type, variables. It has a period of 409 days (which can vary slightly), a maximum magnitude of approximately 6.9 (but it has been known to reach naked eye visibility) and a minimum usually around magnitude 14. Long period variables typically exhibit a rise to maximum magnitude that is steeper than the fall to minimum, although some do have equal rise and fall rates. The light curves below exhibit typical asymmetric behaviour.
The observations below were made with 10x50 binoculars and a 200 mm reflector. In the following light curves, estimates marked by triangular symbols indicate the magnitude of the faintest star in the comparison field when R And is fainter than this star.
The following light curve shows R And from August 1982 to February 1983. The curve shows the large magnitude range of the star, typical of the class of long period variables.
The following light curve shows R And from August 1983 to January 1984. It shows a maximum occurring at the end of October (predicted time 20 October).
The following light curve shows R And from September 1984 to March 1985. The actual magnitude at minimum was probably near the nominal value of 14, indicating a brightness range of some seven magnitudes.
The following light curve shows R And from August 1985 to March 1986. It shows a typical maximum, with the rise steeper than the fall.
The following light curve shows R And from September 1986 to March 1987. The maximum on this cycle looks as though it will peak at somewhat less than the typical value of magnitude 6.9.
V Vulpeculae is a member of the RV Tauri class of variable stars which in turn is a sub-group of the class of semi-regular variables. RV Tauri stars are characterised by alternate deep and shallow minima. The magnitude range of V Vul is 8.0-9.7 and the period between deep minima is 76 days. Shallow minima typically have a magnitude of 8.5-9.0 and deep minima typically circa 9.5. However, the period and other characteristics of the light curve of RV Tauri stars can vary from cycle to cycle. RV Tauri stars are giants, among some of the most massive known. The light variation is associated with pulsations of the envelope of the star, however little is known about the mechanisms responsible. Another RV Tauri star, R Scuti, is featured above.
The observations below were made with a 200 mm reflector.
The following light curve shows V Vul from July 1983 - January 1984. Maxima and minima are not easy to distinguish, largely because there are too few observations. However, it is likely that the three faintest points below represent the deep minima.
The following light curve shows V Vul from June - December 1984. The curve shows the variations in characteristics of the light curve from cycle to cycle.
The following light curve shows V Vul from July - December 1985. The curve certainly illustrates two deep minima but it is difficult to be convinced about the presence of any shallow minima. The accepted period of deep minima is 76 days so it appears that one of the latter has been missed. However, the paucity of observations means that it is difficult to identify definitively the key characteristics of the star.
The star NSV14466 (New Suspected Variable #14466) was, until early 1984, only a suspected variable. It was discovered on a photographic plate early in 1984 with position corresponding to that of a suspected long period variable captured on a photographic plate taken at Mount Palomar in 1933 but apparently not observed since. Examination of other photographic plates reveals a suspected variable in this position with a magnitude range 13-15.5.
The observations below were made with a 200 mm reflector.
The following light curve shows NSV14466 from shortly after its (re-)discovery until late March 1985. The star faded during summer 1984 but I, together with several other variable star observers, recovered it in spring 1985. Our observations confirmed the star as a true variable in the long period class, and it was renamed V362 Cephei. The period appears to be about 11 months from the curve shown below and the next maximum is anticipated circa February 1986. I believe that the observations shown below for 1985 represent the sum total of the observations made during that year.
The following light curve shows V362 Cep from October 1985 to April 1986. The first seven points and last four points on the graph, marked by triangular symbols, indicate the magnitude of the faintest star in the comparison field when V362 Cep is fainter than this star. This light curve captures a maximum of V362 Cep, probably only the third maximum ever to be observed visually. Several more years of observations will be needed to establish the period accurately. The minima of V362 Cep must be at least magnitude 15 or 16 and I do not know whether the star has ever been observed at minimum.
RS Cancri is a member of the class of semi-regular variables, with a period of approximately 120 days and a magnitude range 5.5-7.0.
RS Cnc is easy to locate because of its proximity to bright stars in Cancer (see e.g. Norton's Star Atlas) and can be followed throughout its light range using binoculars. It is unfortunate that the star can only be observed for a short period each year as, following the winter months, Cancer moves rapidly into the twilight during May.
The observations below were made with 10x50 binoculars.
The following light curve shows RS Cnc from February to May 1984. The curve shows what appears to be a distinct minimum. Unfortunately, I was unable to make observations over a sufficiently lengthy interval to detect the following maximum.
The following light curve shows RS Cnc from February to May 1985. During this period, the star does not exhibit much variability - a comparison with the light curve above indicates that this may be an example of the star altering the characteristics of its light curve on successive cycles.
T Ursa Majoris is a long period or Mira-type variable. The normal brightness range of the star is magnitude 7.7-13.0 with a period of 257 days. The rise to maximum of the star is typically steeper than the fall to minimum, and the light curve usually is flattish around peak brightness. The star field close to T UMa is a sparse, difficult one and it is possible to miss the star when it is fainter than circa magnitude 12.
The observations below were made with a 200 mm reflector. In the following light curves, the triangular symbols indicate the magnitude of the faintest star in the comparison field when T UMa is fainter than this star.
The following light curve shows T UMa from March to July 1982. The curve shows the characteristic shape, with a steeper rise than fall.
The following light curve shows T UMa from February to July 1983. The star fades over the first part of this period and then becomes too faint to locate. At the end of July, it reappeared again, presumably marking the start of an increase in magnitude.
The following light curve shows T UMa from February to August 1984. The curve shows a maximum around the end of June, which agrees with the predicted time. I have previously observed brighter maxima of this star.
The following light curve shows T UMa from February to August 1985. It shows a maximum lasting for around two months: based on my previous observations, this appears normal for the star. Following maximum, the star is expected to fade to a minimum of circa magnitude 13.
The following light curve shows T UMa from January to August 1986. This curve covers almost a whole cycle of the star. It can be seen that the minimum lasts slightly longer than the maximum, although this is not necessarily the case on every cycle.
The following light curve shows T UMa from February to August 1987. The curve exhibits a characteristic well-defined, flattish maximum with rise to maximum steeper than fall towards minimum.
The following light curve shows T UMa from January to September 1988. It shows a descent to minimum magnitude followed by a rise to maximum.
The following light curve shows T UMa from April to November 1989. It shows virtually an entire period of the star, with the slopes of the rise to maximum and subsequent fall to minimum being practically equal.
The following light curve shows T UMa from March to September 1990 - it shows a typical minimum in brightness.
U Boötis is a semi-regular variable.
The observations below were made with a 200 mm reflector.
The following light curve shows U Boo from April to August 1988. It shows the star increasing to maximum brightness and then fading.
The following light curve shows U Boo from April to September 1989 and again shows the star increasing to maximum brightness and then fading.
V Boötis is a red giant star in the later stages of its life. It is a member of the semi-regular class of variable stars. The officially quoted light range for the star is 7.6-10.4 (within the expected range for a semi-regular variable) and the period is approximately 258 days, although both light range and period may vary. Some star catalogues put V Boo into the class of long period variables, illustrating the close relationship and overlap between the two classes.
The observations below were made with a 200 mm reflector.
The following light curve shows V Boo from April to October 1984. It exhibits a magnitude range between 7.9 and 9.3 with a maximum in July.
The following light curve shows V Boo from April to October 1985. It exhibits a magnitude range between 8.5 and 9.15 with a minimum in June.
The following light curve shows V Boo from April to August 1986, with a maximum in June.
The following light curve shows V Boo from April to September 1987. This light curve appears to suggest a shorter period and smaller amplitude range than the normally accepted values for the star.
RU Herculis is a long period variable. The average period of the star is 485 days (approximately 16 months) with a variability of a few days and the usual brightness range is magnitudes 8.0-13.7.
The observations below were made with a 200 mm reflector. In the following light curves, the triangular symbol indicates the magnitude of the faintest star in the comparison field when RU Her is fainter than this star.
The following light curve shows RU Her from April to September 1984. It shows a typical maximum for the star, with peak magnitude on or about 01 June. As the average period of the star is some 16 months, the star typically spends more of a period at fainter magnitudes than the curve indicates. Note that the rising portion of the curve is considerably steeper than the falling portion: this is normal for a long period variable.
The following light curve shows RU Her from July to October 1985. It shows the magnitude rising to maximum and then starting to decline again.
The following light curve shows RU Her from April to November 1988. It shows a steep rise to maximum followed by a slower fade.
The following light curve shows RU Her from June to December 1989. Note the steep rise to maximum.
AG Draconis derives its variability from being a binary star system rather than a single star. It belongs to a rather rare group of binary stars known as Z Andromedae or symbiotic stars. The binary pair consists of a white dwarf and a red giant star. The gravity of the white dwarf attracts gas, mostly hydrogen, from the surface of the red giant onto its surface. At intervals of several years the hydrogen on the surface of the white dwarf undergoes a nuclear reaction causing brightening of the star.
AG Dra has not undergone an outburst for several years. It normally exhibits a brightness of circa magnitude 10.0 but occasionally brightens to a maximum which can be as high as magnitude 8.2. It is erratic and no periodicity has been identified. The following light curve shows AG Dra from March to December 1985. It shows the star reaching a peak brightness of circa magnitude 9.0.
The observations below were made with a 200 mm reflector.
T Draconis is a long period variable, with a period of about 421 days. Its light range, magnitude 9.6 to 12.3, is rather small for this class of variable. It is not an easy star to observe: it is close to ξ Draconis, which is easily located, but it is a close double star with a 10th magnitude companion only 15" distant. It is difficult to judge the brightness of the star accurately in the presence of such a close neighbour - it is necessary to use a high-power eyepiece to separate the two components but this tends to move the comparison stars out of the field of view!
The observations below were made with a 200 mm reflector.
The following light curve shows T Dra from June to November 1982. It shows the brightness of the star rise to a rather flat maximum at circa magnitude 10 then begin to decline again.
The following light curve shows T Dra from May to November 1987. It shows the star fading from a maximum to a minimum.
RV Tauri is the prototype and best known member of the class of variable stars which is characterised by alternate deep and shallow minima. However, my own observations of the star indicate that it can be difficult to discern, from a relatively short sequence of observations, the alternating deep and shallow minima. My observations suggest a period of approximately 79 days, in agreement with the official figure. However, the variations are semi-regular, both in terms of periodicity and magnitude.
RV Tau is a pulsating super-giant star, but the precise cause of the pulsations is not known. In fact, the star is thought to pulsate in several modes simultaneously, and in particular the major period of 79 days is superimposed on a much longer term period of approximately 1300 days (circa 3.5 years).
The observations below were made with a 200 mm reflector.
The following light curve shows RV Tau from mid-November 1982 to March 1983.
The following light curve shows RV Tau from October 1986 to March 1987.
W Andromedae is a long period variable, with a period of about 396 days. Typically it shows a steep rise and more gentle fade, with the rise taking on average 42% of a period and the fade 58%.
The observations below were made with a 200 mm reflector.
The following light curve shows W And from September 1987 - March 1988. It shows the star fading from maximum. Triangular symbols indicate the magnitude of the faintest star in the comparison field when the variable itself is too faint to be visible.
The following light curve shows W And from July 1989 - January 1990. It shows the steep rise and more gentle fade of a typical maximum.
BM Geminorum is unclassified because so little about it is understood. It is rich in carbon but does not behave as other carbon-rich stars. Astronomers at Imperial College, London, are studying the star and I will pass these observations to them.
The following light curve shows BM Gem from December 1988 to May 1989.
V778 Cygni is another poorly understood carbon star which is, at the time of writing (early 1989), under investigation by Imperial College, London. (See also BM Gem immediately above.) I will pass the following observations to Imperial College.
The following light curve shows V778 Cyg from December 1988 to June 1989.
The following light curve shows Nova Vulpeculae 1984 No 1 from August to December 1984. The nova is an example of a slow nova. It was discovered at the end of July 1984 and exhibited a maximum at around magnitude 6.8 early in August (not recorded below). The light curve below indicates two or three maxima in August and early September following the main peak in early August. Following the maxima, the general trend is for the star to fade slowly although there are numerous erratic variations (this is normal for a nova!) Attempts to identify the precursor star from photographs of the star field prior to the nova have proved inconclusive.
The observations below were made with a 200 mm reflector.
The following light curve shows Nova Andromedae 1986 during December 1986 and January 1987. The nova was discovered in early December, a few days before maximum. Maximum magnitude was 6.4. The following curve begins shortly after maximum and shows a rapid decline from 7th to 11th magnitude in less than two months. There are three classes of novae: fast, medium and slow. To qualify as fast, a nova must fade by three magnitudes from maximum in less than 110 days: Nova And 1986 easily falls into this class. Although the rise to maximum magnitude took only a day or two, it could take years for the star to return to its original brightness, known as the postnova stage.
The amplitudes of novae generally lie between magnitudes 7-16. There is a star of magnitude 17.8 on Palomar Sky Survey plates at the position of Nova And 1986; however, it remains to be confirmed that this was, indeed, the precursor star.
The observations below were made with a 200 mm reflector.
Mike Nicholls, Joe Startin