Abajo vs. Debajo
"Abajo", formed with the directional preposition "a", can indicate motion towards a lower position, but also a position that it is relatively lower to any other reference.
"Debajo", formed with de- plus bajo, indicates a position that it is immediately below another. In most cases, it is followed by "de" to indicate below which thing or person we are referring to (eg. debajo de la mesa).
For example, "Están abajo" means "They are down there", but "Están debajo", we are saying that "They are below (something)", where this "something" can be implicitly stated. With "debajo", they are RIGHT below some given reference point, such as a floor.
"Vamos abajo" means "We're going down" (we don't know how deep), but "Vamos debajo" would make you wonder: "Under... what?" (debajo de... ¿qué?)
Hi MIke, good question, as I just found this I was not aware of:
abajo de. 1. loc. prepos. desus. Debajo de, al pie de. En muchos lugares de América, u. c. coloq.
Which means this is everyday use in American countries, however in Spain it would be considerred incorrect. Abajo is an adverb of place.
Debajo de is a preposition, so in your sentence this is the one to use.
Is it below the table or beneath (underneath) the table? Which would you pick?
[abajo=under as in below (lower than) abajo=downstairs (lower than where I am now)]
In some contexts they are interchangeable.