A High-Cadence UV-Optical Telescope Suite On The Lunar South Pole
Scott W. Fleming, Thomas Barclay, Keaton J. Bell, Luciana Bianchi, C. E. Brasseur, JJ Hermes, R. O. Parke Loyd, Chase Million, Rachel Osten, Armin Rest, Ryan Ridden-Harper, Joshua Schlieder, Evgenya L. Shkolnik, Paula Szkody, Brad E. Tucker, Michael A. Tucker, Allison Youngblood
aa r X i v : . [ a s t r o - ph . I M ] S e p A High-Cadence UV-Optical Telescope Suite On The Lunar South Pole
Scott W. Fleming, Thomas Barclay, Keaton J. Bell, Luciana Bianchi, C. E. Brasseur, JJ Hermes, R. O. Parke Loyd, Chase Million, Rachel Osten, Armin Rest, Ryan Ridden-Harper, Joshua Schlieder, Evgenya L. Shkolnik, Paula Szkody, Brad E. Tucker, Michael A. Tucker, and Allison Youngblood Space Telescope Science Institute Goddard Space Flight Center University of Washington Johns Hopkins University Boston University Arizona State University Million Concepts LLC Mt Stromlo Observatory, the Australian National University University of Hawaii University of Colorado
ABSTRACTWe propose a suite of telescopes be deployed as part of the Artemis III human-crewed expeditionto the lunar south pole, able to collect wide-field simultaneous far-ultraviolet (UV), near-UV, andoptical band images with a fast cadence (10 seconds) of a single part of the sky for several hourscontinuously. Wide-field, high-cadence monitoring in the optical regime has provided new scientificbreakthroughs in the fields of exoplanets, stellar astrophysics, and astronomical transients. Similarobservations cannot be made in the UV from within Earth’s atmosphere, but are possible from theMoon’s surface. The proposed observations will enable studies of atmospheric escape from close-ingiant exoplanets, exoplanet magnetospheres, the physics of stellar flare formation, the impact of stellarflares on exoplanet habitability, the internal stellar structure of hot, compact stars, and the early-timeevolution of supernovae and novae to better understand their progenitors and formation mechanisms. INTRODUCTIONSpace-based telescopes and ground-based surveys using a combination of high-cadence, high-precision photometrywith wide fields-of-view have advanced, and in some cases created, many sub-disciplines within astronomy.
The sameprinciple of wide-field, high-cadence surveys, conducted in the UV, pushes the boundaries of discovery within these sameastronomical sub-disciplines in unique ways.
Such a survey can be achieved using existing technologies: e.g., a modestaperture telescope (30 cm) equipped with CMOS detectors and appropriate protection for lunar dust. Tracking is notnecessary given the slow rotation of the Moon, thus the telescopes can be constructed without moving parts. Thisproject serves as a scientific and technological pathfinder for larger astronomical facilities in a future with increasedand sustained human presence on the Moon. TRANSITING EXOPLANETSA transiting exoplanet is one that crosses the face of its host star relative to our line of sight. Their atmo-spheres (and thus chemical compositions and bulk densities) can be studied via transmission and emission photom-etry and spectroscopy. In the UV, the depth of the exoplanet transit can be a tracer of atmospheric mass loss(Vidal-Madjar et al. 2003) or bowshocks generated by the interaction of the stellar wind and the exoplanet’s magne-tosphere (Alexander et al. 2016). These transit depths can be significantly larger in the UV compared to the optical(Ehrenreich et al. 2015). Transits for typical close-in gas and ice giants last a few hours, but the ingress and egress lastfor only tens of minutes. High cadence sampling allows for detailed modeling of both the ingress/egress of the transit,and a check for additional variability that may be present from the star’s atmosphere itself. The far ultraviolet (FUV)and near ultraviolet (NUV) ranges contain absorption lines from different species (Hydrogen’s Ly α , O I, C II in FUV;Mg II in NUV), while simultaneous observations in the optical of the same transit event serves as a crucial benchmarkfor transit start/stop times and shape comparison. High-cadence UV observations are also ideal for detecting deeptransits of planets orbiting white dwarfs, which last only minutes (Agol 2011). White dwarfs are the final remnants ofthe majority of planet hosting stars, and this difficult-to-detect population will reveal the ultimate fate of planets likethe Earth. STELLAR FLARES
Fleming et al.
The formation mechanisms of flares on stars other than the Sun are still poorly constrained from observational data.Because flare timing is random, a long baseline of observation is required to capture a representative sample of flares.The UV is an ideal wavelength regime to study flares because the contrast between a flare and the star’s atmosphereis large. Observing a flare in multiple bands simultaneously provides the best constraints on the flare physics, butcoordinating multiple telescopes in space and on the ground is difficult for large numbers of targets. Space-based opticaltelescopes like Kepler and TESS have not been able to resolve short-duration flares. Archival GALEX data allowsfor sampling at the seconds level, uncovering a population of flares that last 1-5 minutes, but did not continuouslyobserve any single target longer than 30 minutes (Brasseur et al. 2019). The wide field and high sampling of thelunar telescopes will detect thousands of flares, comparable to the first results from TESS (G¨unther et al. 2020), whilethe multi-band observations enable studies of the temperature evolution. The 10-second cadence is fast enough todetect quasi-periodic pulsations that can occur during flares, while the multi-band data will be able to characterizethe formation mechanisms of these enigmatic pulsations. HOT STAR PULSATIONSThe field of asteroseismology studies the gravity-mode and/or pressure-mode pulsations found in certain types ofstars. These pulsations can be used to place tight constraints on fundamental stellar parameters and internal structure.Precision asteroseismology requires a combination of high quality photometry, a fast sampling rate compared topulsation periods, and a long baseline of observations to resolve the beat cycles between closely spaced frequencies.Hot, compact objects like subdwarf B (sdB, Jeffery & Ramsay 2014; Sahoo et al. 2020) stars and white dwarfs (WD,Hermes et al. 2017; Bell et al. 2019) have been studied with optical space telescopes. But their true interiors can bemore fully explored using the UV, where the pulsation amplitudes can be an order of magnitude higher. Some work hasbeen done to extract pulsations from archival GALEX UV data (Boudreaux et al. 2017; Tucker et al. 2018; Rowan et al.2019), but these efforts have been limited by the 30-minute maximum continuous baseline of the space telescope. UVobservations are also crucial for tracking rapid evolution of pulsating WDs through rare dwarf novae outbursts incataclysmic variables, where the accretion disk dominates in the optical (Szkody et al. 2012). The uninterrupted,long baseline afforded by the lunar telescopes will result in clean power spectra to identify pulsation frequencies. Thesimultaneous, multi-band observations can identify the specific geometry of individual pulsation modes. TRANSIENTSAstrophysical transients are objects experiencing drastic changes in brightness over a short timespan, includingnovae, supernovae (SNe), tidal disruption events (TDEs) from black holes, and kilonova counterparts to gravitationalwave events. These are hot objects with blackbody temperatures peaking at &
10 000 K, so UV observations are crucialwhen constraining the temperature and radius evolution. The changes in brightness within the first few minutes ofthese events place strong constraints on the underlying physics, but are challenging to acquire. For Type Ia SNe,the nature of the progenitor can be constrained with high cadence sampling of the light curve (Olling et al. 2015;Fausnaugh et al. 2019). The sample of known TDEs has increased greatly in the past decade, but many questionsremain about their formation and evolution. While rare, a 24x24 deg. field results in ∼
12 transients over a ∼ Agol, E. 2011, ApJL, 731, L31Alexander, R. D., Wynn, G. A., Mohammed, H., et al. 2016,MNRAS, 456, 2766Bell, K. J., C´orsico, A. H., Bischoff-Kim, A., et al. 2019, A&A,632, A42Boudreaux, T. M., Barlow, B. N., Fleming, S. W., et al. 2017,ApJ, 845, 171Brasseur, C. E., Osten, R. A., & Fleming, S. W. 2019, ApJ,883, 88 Ehrenreich, D., Bourrier, V., Wheatley, P. J., et al. 2015,Nature, 522, 459Fausnaugh, M. M., Vallely, P. J., Kochanek, C. S., et al. 2019,arXiv:1904.02171G¨unther, M. N., Zhan, Z., Seager, S., et al. 2020, AJ, 159, 60Hermes, J. J., G¨ansicke, B. T., Kawaler, S. D., et al. 2017,ApJS, 232, 23Jeffery, C. S. & Ramsay, G. 2014, MNRAS, 442, L61Olling, R. P., Mushotzky, R., Shaya, E. J., et al. 2015, Nature,521, 332
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