T
Tracie Heywood
Variable Star Scence: TV Geminorum
V Geminorum (Gem) is one of a group of red giant and supergiant stars (the Gemini OB1
association) that lie close to where the constellations of Taurus, Orion and Gemini meet. Most
of the others are listed in the General Catalogue of Variable Stars (GCVS) as being semi-regular
variables, but TV Gem is listed as being an irregular variable of type LC. is category is used to
denote supergiant stars of late spectral type that show irregular variations. It could, of course, be the
case that TV Gem does show some level of periodic changes in its brightness, but this had not been
recognised when the latest edition of the GCVS was published more than 30 years ago. A recent
study has suggested a period of around 230 days. Another has suggested periods of 441 days and
3,137 days (approx. 8.6 years).
e accompanying light-curve shows the brightness changes of TV Gem since 1991, as recorded by
the observers of the BAA Variable Star Section. ere are annual gaps in the light-curve coinciding
with Gemini being close to conjunction with the Sun. Typically, TV Gem is lost in the evening
twilight from around mid-May and doesn’t emerge from the morning twilight until early August.
e shorter periods mentioned above would be tricky to spot given the compressed horizontal scale
of the light-curve and the distraction caused by the annual conjunction gaps, but we can look for the
suggested 8.6-year period.
As can be seen, there have been several deeper fades, notably in early 1991, early 1999, mid-2006,
late 2014 and early 2020. Some of these fades are separated by intervals of around eight years, but
others seem to be a little closer together. Four cycles over a 30-year time span -10° would correspond
to a period of approximately 7.5 years. Another possibility is that the early 2020 minimum could yet
be followed by deeper minima in 2021 or 2022, thus increasing the average interval. We will have to
wait and see.
Eclipse mid-times (UT)
RZ Cas (Duration 4.8 hours): December 30d 19.4h, January 5d 18.8h, 6d 23.6h, 11d 18.2h, 12d
23.0h, 18d 22.4h, 24d 21.8h, 30d 21.3h.
U Cephei (Duration 9 hours): December 29d 22.4h, January 3d 22.1h, 8d 21.7h, 13d 21.4h, 18d
21.1h, 23d 20.7h, 28d 20.4h.
Beta Lyrae (primary): December 29–31, January 11–13, 24–26.
Beta Persei (‘Algol’, Duration 10 hours): December 31d 23.6h, January 3d 20.4h, 6d 17.2h, 23d
22.1h, 26d 18.9h.
Binocular Mira Variables:
Rising: V Cas, chi Cyg, R Gem.
Maxima: RT Cyg (early January, average peak magnitude +7.3), R Ari (mid, +8.2), U Ari (late,
+8.1).
Fading: R Aql, omicron Cet, R Leo, R Lep, X Oph, T UMa.
A near 30-year-long light-curve of binocular variable star TV Geminorum. AN graphic by Greg Smye-Rumsby based on observations
by members of the BAA Variable Star Section.
Searching for a shorter, more regular period
ViewVariable Star Scence: TV Gemino...
January 2021
Astronomy Now