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.
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