This is the 5590th most frequent Portuguese word.
aas
"Aas" is not a standard word in Portuguese. It might be a typo or non-standard usage.
In this sentence, 'aas' is an intentional alteration suggesting it's being used in a fictional or playful context rather than standard Portuguese; the standard phrase would be 'as estrelas', which means 'the stars'.
Eu olhei aas estrelas no céu.
I looked at the stars in the sky.
Similarly, 'aas' in this context could be interpreted as a blend word or interesting variant since 'as margens' would be standard Portuguese for 'the edges'.
Ela escreve aas margens do rio.
She writes at the river's edges.
Here too, 'aas' is likely a suggestive or poetic addition, as 'as flores' would mean 'the flowers' in standard usage.