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During the red giant phase, stars loose mass at the highest rate since birth.The mass-loss rate is not fixed, but varies from star-to-star by up to 5\%,resulting in variations of the star's luminosity at the tip of the red giantbranch (TRGB). Also, most stars, during this phase, engulf part of theirplanetary system, including their gas giant planets and possibly brown dwarfs.Gas giant planet masses range between 0.1 to 2\% of the host star mass. Theengulfing of their gas giants planets can modify their luminosity at the TRGB,i.e. the point at which the He-core degeneracy is removed. We show that theincrease in mass of the star by the engulfing of the gas giant planets onlymodifies the luminosity of a star at the TRGB by less than 0.1\%, whilemetallicity can modify the luminosity of a star at the TRGB by up to 0.5\%.However, the increase in turbulence of the convective envelope of the star, hasa more dramatic effect, on the star's luminosity, which we estimate could be aslarge as 5\%. The effect is always in the direction to increase the turbulenceand thus the mixing length which turns into a systematic decrease of theluminosity of the star at the TRGB. We find that the star-to-star variation ofthe mass-loss rate will dominate the variations in the luminosity of the TRGBwith a contribution at the 5\% level. If the star-to-star variation is drivenby environmental effects, the same effects can potentially create anenvironmentally-driven mean effect on the luminosity of the tip of the redgiant branch of a galaxy. Engulfment of a brown dwarf will have a more dramaticeffect. Finally, we touch upon how to infer the frequency, and identify theengulfment, of exoplanets in low-metallicity RGB stars through high resolutionspectroscopy as well as how to quantify mass loss rate distributions from themorphology of the horizontal branch.

Giants eating giants: Mass loss and giant planets modifying the luminosity of the Tip of the Giant Branch