Thin stellar streams , formed from the tidal disruption of globular clusters , are important gravitational tools , sensitive to both global and small-scale properties of dark matter .
The Palomar 5 stellar stream ( Pal 5 ) is an exemplar stream within the Milky Way : Its \sim 20 \degr tidal tails connect back to the progenitor cluster , and the stream has been used to study the shape , total mass , and substructure fraction of the dark matter distribution of the Galaxy .
However , most details of the phase-space distribution of the stream are not fully explained , and dynamical models that use the stream for other inferences are therefore incomplete .
Here we aim to measure distance and kinematic properties along the Pal 5 stream in order to motivate improved models of the system .
We use a large catalog of RR Lyrae-type stars ( RRLs ) with astrometric data from the Gaia mission to probabilistically identify RRLs in the Pal 5 stream .
RRLs are useful because they are intrinsically-luminous standard candles and their distances can be inferred with small relative precision ( \sim 3 \% ) .
By building a probabilistic model of the Pal 5 cluster and stream in proper motion and distance , we find 27 RRLs consistent with being members of the cluster ( 10 ) and stream ( 17 ) .
Using these RRLs , we detect gradients in distance and proper motion along the stream , and provide an updated measurement of the distance to the Pal 5 cluster using the RRLs , d = 20.6 \pm 0.2 ~ { } \mathrm { kpc } .
We provide a catalog of Pal 5 RRLs with inferred membership probabilities for future modeling work .