Determining the Orientation of the Large Magellanic Cloud's Stellar Disk Using Gaia Parallaxes

Madison G. Kadrmas and David Nidever, Department of Physics, Montana State University, P.O. Box 173840, Bozeman, MT 59717-3840

Measurements of the Large Magellanic Cloud (LMC) indicate a slightly elliptical stellar disk set at an angle relative to the plane of the Milky Way described by line of nodes and inclination. All previous measurements of these parameters rely on our understanding of stellar evolution and stellar populations and often make assumptions about the distribution of ages and metallicities in the LMC stellar disk. However, utilizing parallax measurements removes the inherent biases and assumptions of these other methods by relying on purely geometrical information. We are able to measure the line of nodes position angle and inclination of the stellar disk directly from Gaia DR2 parallax measurements. While the uncertainty of a Gaia parallax measurement for a single LMC star is high, accurate distance information can be obtained by averaging over many stars. We used a spatial binning value such that each average contained information from thousands of LMC stars. A small systematic offset in the Gaia parallaxes dependent on apparent magnitude has been consistently reported. An offset of +0.0249 mas/yr to the Gaia parallaxes was needed to adjust our mean LMC distance to the known value of 50 kpc. This provides additional constraints on the Gaia parallax offset at the magnitudes of the LMC stars (G ~ 18-19 mag). Our best-fit LMC stellar disk distance model yields a line of nodes position angle of 145.3o ± 5.0o and an inclination angle of 52.7o ± 2.4o , with uncertainties derived from a Monte Carlo simulation. While this line of nodes orientation falls within the accepted range of 140o - 190o , our inclination falls above the accepted range of 20o - 30o . Our results show a central clump of stars behind the plane of the stellar disk (where crowding is a concern), which may be responsible for skewing inclination.

Additional Abstract Information

Presenter: Madison Kadrmas

Institution: Montana State University

Type: Poster

Subject: Physics/Astronomy

Status: Approved

Time and Location

Session: Poster 9
Date/Time: Wed 12:00pm-1:00pm
Session Number: 6139