I have not found any reference in any of my texts that mention Hesperus having any artifacts of any kind.
What I did find was that Hesperus, being the evening star or the planet Venus was hailed as being symbolic of anything that represents evening, twilight, or things westward.
There is also the Hesperides, which were nymphs who tend a blissful garden in a far western corner of the world, located near the Atlas mountains in North Africa at the edge of the encircling Oceanus, the world-ocean. (again referencing west.) It was here that Hercules stole the golden apples and confronted Atlas.
There is no reference to any amulet or necklace, or really ANY artifacts related to Hesperus.
Keep in mind, Hesperus Denotes the evening star, and is related to the PLANET Venus, not the roman goddess, who's counterpart is Aphrodite. Hesperus is male and a Demigod.
If you want other references such as "The Wreck of the Hesperus" BY Longfellow, there is no references to any amulets or jewelry either.
Hesperus is also used in philosophy as the antithesis of Phosphorus, or Lucifer, the "Son of the morning" and used to show that both are really the same, and that seeming opposites really are just mirrors of themselves and hold equal importance.
I know this doesn't help you in your quest to understand the powers of such an artifact, but that's all the information I have on Hesperus. It would seem that the writers of this show simply made up an artifact and gave it a cool sounding name, IMHO.