VLBA15B-010

A trigonometric parallax for a globular cluster

Abstract

We propose an astrometric campaign on the radio pulsar in the globular cluster M4 as a pilot program aimed at an eventual trigonometric parallax. M4 is one of the nearest and best studied globular clusters, but still has a distance uncertainty of about 20%, which impacts progress in many areas of stellar astrophysics. Traditional distance indicators give a distance of about 2.2 kpc for M4, so a parallax is clearly feasible, especially given that the pulsar is moderately bright; that the VLBA DiFX correlator provides advanced pulsar processing (gating) which recovers the mximum S/N; and that there is a high quality nearby calibrator. Direct and precise distance estimates for globular clusters are fundamental for using them to provide strong constraints on stellar evolution and on Galactic structure. A parallax on M4 will provide such a measurement several years in advance of when Gaia will provide such a measurement, and will also serve as an important check on the level of uncertainty of Gaia's measurements in moderately crowded regions such as the outskirts of globular clusters.

Investigators

Name	Institution
Dana Casetti	Yale University
Andrew Lyne	Manchester, University of
Scott Ransom	National Radio Astronomy Observatory; Virginia, University of
Ben Stappers	Manchester, University of
Laura Chomiuk	Michigan State University
Jay Strader	Michigan State University
James Miller-Jones	Curtin University of Technology
Walter Brisken	National Radio Astronomy Observatory
Adam Deller	Swinburne University of Technology
Tom Maccarone *	Texas Tech University
GBT Operator	Green Bank Observatory
vlbaops vlbaops	National Radio Astronomy Observatory
vlbiobs vlbiobs	National Radio Astronomy Observatory

* indicates the PI