Kinematics of an Anticenter Stream Tributary in Kapteyn’s Selected Area 76

¹ Department of Astronomy, University of Virginia, PO Box 400325, Charlottesville, VA 22904-4325, USA
² Astronomy Department, Yale University, PO Box 208101, New Haven, CT 06520-8101, USA
³ Spitzer Science Center, 1200 E. California Blvd., Pasadena, CA 91125, USA
⁴ Department of Astronomy, University of Virginia, USA

e-mail: jcarlin@virginia.edu

Abstract

We have measured 3-D kinematics of stars in Kapteyn’s Selected Area (SA) 76 that were selected to be Anticenter Stream (ACS) members on the basis of their kinematics and CMD positions. Mean stream kinematics from the 31 identified ACS members produce an orbit inclined by ~30° to the well-defined spatial distribution of the stream. We have explored possible explanations for this, and suggest that our data in SA 76 are measuring the motion of a kinematically cold sub-stream among the ACS debris, which was likely a fragment of the same infalling structure that created the larger ACS system.