Semi Regular Variable Star Survey - First Data Release

TARGET STARS BY CONSTELLATION - 100 DAY SURVEY

Semiregular variable stars are giants or supergiants of intermediate and late spectral type showing considerable periodicity in their light changes, accompanied or sometimes interrupted by various irregularities. Periods lie in the range from 20 to more than 2000 days, while the shapes of the light curves may be rather different and variable with each cycle. The amplitudes may be from several hundredths to several magnitudes (usually 1-2 magnitudes in the V filter).

Semiregular variables are classified into several subtypes:

• SRA: Late spectral-type (M, C, S or Me, Ce, Se) giants displaying persistent periodicity and usually small amplitude, less than 2.5 magnitudes in V. Amplitudes and light-curve shapes generally vary and periods are in the range of 35-1200 days. Many of these stars differ from Mira variables only by showing smaller light amplitudes. S AQL, RS CRB, RU CRB, GN CYG, WW SGE, BV VUL
• SRB: Late spectral-type (M, C, S or Me, Ce, Se) giants with poorly defined periodicity (mean cycles in the range of 20 to 2300 days) or with alternating intervals of periodic and slow irregular changes. Some may occasionally cease varying at all for a time. In a number of cases, the simultaneous presence of two or more periods of light variation exists. LS AQL, LU AQL, RR CRB, Y CRB, AA CYG, TT CYG, AQ DEL, CZ DEL, BU LYR, CV LYR, EG LYR, EK LYR, SY LYR, HH SGE, T SGE, W VUL
• SRC: Late spectral-type (M, C, S or Me, Ce, Se) supergiants with amplitudes of about 1 mag and periods of light variation from 30 days to several thousand days. AZ CYG, RW CYG
• SRD: Giants and supergiants of F, G, or K spectral types, sometimes with emission lines in their spectra. Amplitudes of light variation are in the range from 0.1 to 4 mag, and the range of periods is from 30 to 1100 days. KK AQL, TW AQL, TX AQL, AV CYG, MX VUL

Classified as semi-regular but with no further subdivision - DN AQL, CH CYG, FY CYG, AE LYR

Classified as irregular - ST CRB, SY CRB

THE FOUR GROUPS

Although some of these stars have extensive records going back over many year (S AQL 10 year curve) the number of observers obtaining filtered CCD images of even these stars is surprisingly small.

LS AQL is typical of the next group (LS AQL 10 year curve) where, although there are a reasonable number of visual observations, there is too little data for the lightcurve to be fully characterised.

The third group contains stars such as RY CRB (10 year curve). There are a few observations scattered through the years but far too few to say much, or anything, about the lightcurve.

Poor old LU AQL (10 year curve) with virtually no observations in the last ten years.

ARCHIVE RESULTS AND ANALYSIS

The maximum brightness of RS CRB has fallen steadily of the last ten years. There is a similar trend with Y CRB.

AZ CYG shows an increase followed by a decrease in the peak magnitude reached.

CH CYG shows a sudden drop in the peak magnitude in the last couple of years.

FIRST DATA RELEASE - RESULTS AND ANALYSIS

One amusing feature of this survey was the series of emails from an observer who, although doing no practical CCD work himself, has very strong (and in my view wrong) views on how the rest of the astronomical world should do their work. Im my opinion to do a short trial run to check on all aspects of target selection the targets was a sensible precaution - he thought differently!

WHAT WOULD I DO DIFFERENTLY - OR THE SAME?

1. CHARTS - I use these to find the variable star on the image and to make certain that I use the same comparison stars with the same magnitudes each time I do the photometry. This time round I did a screen dump from SkyMap Pro 10 and then annotated it with the magnitudes. This worked providing I did the map at scale 9 (rather than 8) and only chose Tycho stars that were close enough to be in the field of view. However it was sometimes rather difficult to match crowded fields with the SkyMap Pro image so I suspect that an annotated screen dump of an actual image, easily obtained from the AAVSO, would be easier for matching purposes.
2. TARGETS (1) - If I am taking images every 5 to 7 days then I am bound to coincide with the period around full moon about one image in four. Targets should be chosen to allow for this rather than having a gap in the lightcurve every month.
3. TARGETS (2) - Imaging fewer stars in more detail (BVRI) is an option, as is concentrating on shorter period SR stars. In any event there are so many bright SR stars that are hardly ever measured by AAVSO members I don't need to go to the unlisted ones.
4. TARGETS (3) - Some fields have large numbers of suitable targets so by imaging them I can get more science done per image. An example of this would be the Double Cluster in Perseus. Somewhat trickier would be the masses of faint (not SR) variables in Monoceros, Orion and Taurus (unfiltered differential photometry perhaps, once or twice a month).

In collaboration with the Remote Astronomical Society Observatory

Martin Nicholson - Daventry, United Kingdom.

This page was last updated on October 4th 2008.