TV Geminorum

TV Geminorum is a red supergiant star and possible VV Cephei binary in the constellation of Gemini.

TV Gem has a spectral type of M0-M1.5Iab, and has been classified as a semiregular variable star of type SRc. It varies in apparent visual magnitude from between 6.3 at maximum to 7.4 at minimum with a period of $426$ days. A longer secondary period of $2,550$ days has also been detected.

The effective temperature, luminosity, and radius of TV Gem are pulsating between 3,500–3,850 K,, and respectively over a long-term cycle lasting for 3,137 days. TV Gem can be occulted by the moon, allowing for a direct measurement of the star's angular diameter. The angular diameter of the star has thus been measured in the K-band to be $4.8 mas$, corresponding to a linear radius of at their adopted distance of $623$ pc.

Like many other red supergiants, TV Gem is surrounded by circumstellar dust. By analyzing the light curve obtained from the lunar occultation, the presence of a circumstellar dust shell about 20 times the size of the star is revealed. Additionally a cooler dust shell about 500 times the size of the star was needed for an explanation of the [[w:Photometry (astronomy)
 * photometric data]] from IRAS.

Companion
The star appears to have a hot companion with spectral type B4. Although the companion's spectrum resembles that of a giant, it is more likely to be a main-sequence star with the stellar wind being the cause of its classification as a giant. The absolute magnitude of this companion has been estimated to be around -1.4. By integrating the flux from 1200 Å to 5500 Å a temperature of 17,700 K for the companion was determined. The same paper calculated a radius of assuming a distance of 1,200 pc to the system and an angular diameter of 0.04 mas.