Short answers, pulled from the story.
A solar analog requires stricter photometric criteria than the broader solar-type group. Temperature must stay within 500 Kelvin of the Sun's value, creating a range from 5278 to 6278 Kelvin. Metallicity levels must also match closely with values between 50% and 200% of solar metallicity.
Solar twins require candidates to fall within 50 Kelvin of the Sun's surface temperature, extending from 5728 to 5828 Kelvin. Some definitions tighten this further to just 10 Kelvin, creating a range between 5768 and 5788 Kelvin. No exact solar twin matching all criteria has been discovered to date.
HD 19373 measures 5750 Kelvin with a metallicity of -0.04 dex and sits 88 light-years away at 6.2 billion years old. HD 104067 reaches 5760 Kelvin but carries a metallicity of -0.04 dex while lying 98 light-years distant and dating back 2.9 billion years. Mamajek and Hillenbrand calculated ages for 108 solar-type stars within 52 light-years in 2008.
Astronomers define habitable stars as those capable of hosting life-bearing planets that must remain on the main sequence for at least 0.5 to 1 billion years. This requirement sets an upper mass limit of approximately 2.2 to 3.4 solar masses. Variability plays a crucial role requiring less than 1% variation though practical limits allow up to 3%.
Magnetic braking causes these stars to spin down during their main-sequence lifetimes allowing astronomers to estimate ages based on observed correlations. Researchers used calcium, hydrogen, and potassium emission lines to derive these figures for 108 solar-type stars within 52 light-years in 2008. The resulting list includes stars like HD 19373 at 10.4 billion years old and HD 104067 at 11.9 billion years.