The MIRI Exoplanets Orbiting White Dwarfs (MEOW) Survey: Mid-Infrared Excess Reveals a Giant Planet Candidate around a Nearby White Dwarf (2408.16813v1)

Abstract: The MIRI Exoplanets Orbiting White dwarfs (MEOW) Survey is a cycle 2 JWST program to search for exoplanets around dozens of nearby white dwarfs via infrared excess and direct imaging. In this paper, we present the detection of mid-infrared excess at 18 and 21 microns towards the bright (V = 11.4) metal-polluted white dwarf WD 0310-688. The source of the IR excess is almost certainly within the system; the probability of background contamination is $<0.1\%$. While the IR excess could be due to an unprecedentedly small and cold debris disk, it is best explained by a $3.0^{+5.5}_{-1.9}$ M${\rm Jup}$ cold (248$^{+84}{-61}$ K) giant planet orbiting the white dwarf within the forbidden zone (the region where planets are expected to be destroyed during the star's red giant phase). We constrain the source of the IR excess to an orbital separation of 0.1-2 AU, marking the first discovery of a white dwarf planet candidate within this range of separations. WD 0310-688 is a young remnant of an A or late B-type star, and at just 10.4 pc it is now the closest white dwarf with a known planet candidate. Future JWST observations could distinguish the two scenarios by either detecting or ruling out spectral features indicative of a planet atmosphere.

• The paper reports the discovery of a giant planet candidate orbiting the white dwarf WD 0310-688 using JWST's MIRI instrument to detect mid-infrared excess.
• Key findings include the candidate planet's estimated mass (3.0 M D:up: :sup:`+5.5` :down: :sub:`-1.9` :sup:`Jup`), temperature (248 K), and orbit (0.1-2 AU), placing it within the previously thought-to-be-empty "forbidden zone."
• This detection suggests planets can survive or migrate into close orbits around white dwarfs and opens new avenues for studying planetary system evolution and potential habitability in post-main-sequence systems.

Detection of a Giant Planet Candidate Orbiting a White Dwarf

The paper discusses the discovery of a giant planet candidate orbiting the white dwarf WD 0310-688, as part of the MIRI Exoplanets Orbiting White dwarfs (MEOW) Survey under the James Webb Space Telescope (JWST) cycle 2 observations. The primary method of detection involved identifying excess mid-infrared (IR) radiation at wavelengths of 18 and 21 microns, indicating a potential planetary body whose probability of being a background source was calculated as less than 0.1%.

Key Observational Findings

The presence of an IR excess was attributed to a planetary-mass object with a mass of 3.0^{+5.5}{-1.9}M{Jup} and a temperature of 248^{+84}_{-61} K, orbiting within 0.1-2 AU from the white dwarf. This sets a precedent for identifying exoplanets around white dwarfs within this specific range of separation, termed the "forbidden zone," where planets are customarily destroyed during the host star's red giant phase. This represents the first detection of such a candidate planet within these separations, marking a significant milestone in white dwarf planetary science.

Methodological Approach

The paper utilized JWST's advanced sensing capabilities to capture infrared excess, allowing for a significant enhancement in the search for exoplanets compared to previous methods. The apparatus's sensitivity permits the detection of exoplanets with lower temperatures and masses than those detectable by earlier space telescopes, such as Spitzer. The research team conducted aperture photometry followed by detailed IR excess evaluation, affirming the planet hypothesis.

Analysis and Constraints

The infrared readings and photometric analysis facilitated an estimation of the planet's properties, framing it as a cold, giant planet with specific characteristics mimicking a planetary atmosphere rather than a circumstellar debris disk, albeit acknowledging that further characterization is necessary.

Implications and Future Directions

The detection has several notable implications:

1. Expanding the demography of known exoplanetary systems by including those around white dwarfs, particularly within previously considered unviable separations.
2. Suggesting possible surviving mechanisms or migration scenarios for planets in such forbidden zones, including common envelope scenarios or planet-planet scattering during stellar evolution.
3. Opening new avenues for habitability research, given the potential for white dwarf planets to host life, especially since giant planets in close orbits could harbor moons or subsidiary environments conducive to life.

Future research includes potential follow-up observations using JWST’s Mid-Infrared Instrument (MIRI) for direct atmospheric characterization, which may distinguish planetary atmospheres from dust disk phenomena. This will elucidate the chemical compositions and physical structures within these systems.

Conclusion

This analysis profoundly enhances our understanding of planetary system evolution in post-main-sequence stellar environments. The methodologies and results from the MEOW survey contribute significantly to the paper of planetary dynamics around stellar remnants, offering a framework for future detections and theoretical models of planet survival and migration. This research indicates that planets orbiting close to white dwarfs, previously thought to be uncommon, may be detectable and more prevalent than anticipated, particularly with advances in observational astronomy.