While on the lateral track of the STAR, maintain the last published speed. When ATC issues you a vector off the STAR, absent a speed restriction as part of the vector, or an approach clearance without a speed restriction, speed is now your discretion.
AIM: 4-4-12.a:
ATC will issue speed adjustments to pilots of radar controlled aircraft to achieve or maintain appropriate spacing. If necessary, ATC will assign a speed when approving deviations or radar vectoring off procedures that include published speed restrictions or a chart note used to transition from Mach to IAS. If no speed is assigned, speed becomes pilot's discretion.
However, when the aircraft reaches the end of the STAR, the last published speed on the STAR must be maintained until ATC deletes it, assigns a new speed, issues a vector, assigns a direct route, or issues an approach clearance.
This also matches what ATC is expecting.
7110.65: 5-7-1-e:
A speed restriction published as part of a
SID/
STAR is canceled when an aircraft is vectored off, or a deviation from the
SID/
STAR is approved. If necessary, assign a speed in conjunction with the vector or approval to deviate.
NOTE-
The last published speed on a
STAR will be maintained by the aircraft until ATC deletes it, assigns a new speed, issues a vector, assigns a direct route or issues an approach clearance.