Follow-up Observations of Candidate White Dwarf Planets with MIRI

Abstract

We report on second-epoch imaging of two candidate planet-hosting white dwarfs stars, WD2105-82 and WD1202-232. Both stars showed evidence of resolved, planet-mass candidate companions in observations using the MIRI mid-infrared imager on JWST. WD2105-82 also showed evidence of an infrared excess consistent with an unresolved 1.4 Jupiter mass companion with an orbital separation of <4 au. Our second epoch observations confirm that the source of the excess shares common proper motion with the star. The excess is almost certainly due to a companion planet or debris disk. However, neither of the two resolved sources with projected separations of >1" in the first epoch of JWST observations show measurable proper motion and are thus likely faint, unresolved background galaxies. We also search for common proper motion companions out to hundreds of au, but find no evidence of widely separated companions.

Figures (3)

• Figure 1: Discovery (left) and follow-up (right) images of WD 2105$-$82 (top) and WD 1202$-$232 (bottom). The images are centered on the location of the candidate companions, which are marked with red cross-hairs. The WDs, marked with a green triangle in each image, show significant proper motion relative to the candidates demonstrating that they are not physically bound. The other stationary objects are all background sources.
• Figure 2: Top: 5$\sigma$ detection limits for resolved companions around WD 1202$-$232 in units of limiting flux and contrast. The solid blue line indicates expected flux from 1.0 $\mathrm{M_J}$ 6.1 Gyr model from Linder19. The grey dashed lines show expected flux extrapolated beyond the lower limit of the model grid. Bottom: Detection limits for WD 2105$-$82. Mass limits assume an age of 2.4 Gyr.
• Figure 3: Schematic of the detection limits for the four stars in our survey. Details of varying detection limits with orbital separation shown in Figure \ref{['detectionlimits']} have been simplified, and detection limits below 0.3 $\mathrm{M_J}$ are extrapolated beyond the limits of the available model grid (see text for details). Solid lines (WD 2105$-$82 and WD 1202$-$232) indicate the two stars in this work with two epochs of data, while the dashed lines indicate two stars with a single epoch Mullally24. The hexagons to the left of the plot indicate the inferred masses of the unresolved candidate companions. The small grey points are known radial-velocity planets, while the larger purple points indicate directly imaged planets around young A-stars from Nielsen2019GPI. The triangles indicate the locations where Jupiter and Saturn would appear after adiabatic outward migration of WD 1202$-$232 (expansion factor of 2.2, the left triangle) and WD 2105$-$82 (expansion factor of 3.6, right triangle) during the mass-loss phase of their parent stars.