What is the minimum caloric intake for a truly starving adult
A better example is the stories of tibetan monks who wrote accounts of their experience to survive for months or years on faith alone, and watch their hair and nails fall out in the search for wisdom. they could tell you how fast a coma arrives from eating just 300 calories per day.

There isn't a minimum amount though, because it's all subjective for time until, temperature, survival chores, time until coma, time until difficulty moving... you can probably keep someone in an emaciated coma with intravenous injections, or someone could stay awake with high exposure risk to illness, hair loss, nail loss. The question is vague, and there are 100 scientific studies about calorie restriction, so you are hoping someone will read 10-20 pages until they find some information for you.

It also depends how many watts the human needs to use in that situation to stay alive. 

In 30'C you probably need 30 watts to stay warm, and 20 degrees about 60 watts, so the value can double based on temperature, you must change your question a bit. 

60 watts basal metabolic rate body temperature would use 70 calories per hour, about a slice of bread, so 1400 calories per day without bedcovers. It depends a lot on ambient temperature and exercise, for example 1 mile of walking uses 100 calories. At less than 1000 calories per day, exercise becomes difficult and the person gets thin. Jogging uses about 250 watts. Extreme athletes and triathletes peak at about 650 watts for sprinting.

There are 100ds of citations on caloric defficiency and restriction, with values around 350 - 700 per day, which change metabolism considerably:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3014770/

https://www.ncbi.nlm.nih.gov/pubmed/2718912