Nondetection of Helium in the Hot Jupiter WASP-48b

Bennett, Katherine A.; Redfield, Seth; Oklopčić, Antonija; Carleo, I.; Ninan, Joe P.; Endl, Michael

doi:10.3847/1538-3881/acd34b

“…Planets orbiting stars cooler than the Sun (Oklopčić 2019) are now routinely studied in He 10830 Å, allowing for population-level constraints on planetary massloss rates (Vissapragada et al 2022;Allart et al 2023;Guilluy et al 2023). Models suggest that planets orbiting late G stars like LTT 9779 should be favorable targets for helium outflow observations (Oklopčić 2019;Wang & Dai 2021;Biassoni et al 2023), but there have been relatively few He 10830 Å studies for planets orbiting G-type stars (Allart et al 2023;Bennett et al 2023;Guilluy et al 2023). Recently, Edwards et al (2023) attempted to constrain helium absorption in the upper atmosphere of LTT 9779b with the HST Wide-Field Camera 3 (WFC3) in the G102 grism, but resolving power was ultimately a limiting factor.…”

Section: Introductionmentioning

confidence: 99%

A High-resolution Non-detection of Escaping Helium in the Ultrahot Neptune LTT 9779b: Evidence for Weakened Evaporation

Vissapragada,

McCreery,

Dos Santos

et al. 2024

ApJL

1

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The recent discovery of “ultrahot” (P < 1 day) Neptunes has come as a surprise: some of these planets have managed to retain gaseous envelopes despite being close enough to their host stars to trigger strong photoevaporation and/or Roche lobe overflow. Here, we investigate atmospheric escape in LTT 9779b, an ultrahot Neptune with a volatile-rich envelope. We observed two transits of this planet using the newly commissioned WINERED spectrograph (R ∼ 68,000) on the 6.5 m Clay/Magellan II Telescope, aiming to detect an extended upper atmosphere in the He 10830 Å triplet. We found no detectable planetary absorption: in a 0.75 Å passband centered on the triplet, we set a 2σ upper limit of 0.12% (δ R p /H < 14) and a 3σ upper limit of 0.20% (δ R p /H < 22). Using a H/He isothermal Parker wind model, we found corresponding 95% and 99.7% upper limits on the planetary mass-loss rate of M ̇ < 10 10.03 g s−1 and M ̇ < 10 11.11 g s−1, respectively, smaller than predicted by outflow models even considering the weak stellar X-ray and ultraviolet emission. The low evaporation rate is plausibly explained by a metal-rich envelope, which would decrease the atmospheric scale height and increase the cooling rate of the outflow. This hypothesis is imminently testable: if metals commonly weaken planetary outflows, then we expect that JWST will find high atmospheric metallicities for small planets that have evaded detection in He 10830 Å.

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“…While both Hα and the metastable HeI triplet are observable from ground-based facilities and do not suffer from interstellar extinction, the former has only been detected in among the hottest, most irradiated giant planets (dos Santos 2023). The metastable HeI feature, in contrast, has been detected from a wider variety of planets; this latter probe has emerged as the most widely used over the past several years (e.g., Allart et al 2018Allart et al , 2019Allart et al , 2023Nortmann et al 2018;Salz et al 2018;dos Santos et al 2020;Kasper et al 2020;Spake et al 2021;Vissapragada et al 2022b;Kirk et al 2022;Bennett et al 2023;Guilluy et al 2023Guilluy et al , 2024Zhang et al 2023;Gully-Santiago et al 2024).…”

Section: Introductionmentioning

confidence: 99%

“…Extreme-ultraviolet (EUV) radiation is undetectable by current facilities, so X-ray fluxes are often used to infer total XUV outputs (Sanz-Forcada et al 2011;Chadney et al 2015;King et al 2018;Nortmann et al 2018). When X-ray data have been unavailable for systems with planetary metastable HeI measurements, previous studies have used proxy spectra from stars with similar masses and activity indices (Mansfield et al 2018;Vissapragada et al 2022a;Bennett et al 2023).…”

Section: Introductionmentioning

confidence: 99%

Exoplanet Aeronomy: A Case Study of WASP-69 b’s Variable Thermosphere

Levine,

Vissapragada,

Feinstein

et al. 2024

AJ

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Aeronomy, the study of Earth’s upper atmosphere and its interaction with the local space environment, has long traced changes in the thermospheres of Earth and other solar system planets to solar variability in the X-ray and extreme-ultraviolet (collectively, XUV) bands. Extending comparative aeronomy to the short-period extrasolar planets may illuminate whether stellar XUV irradiation powers atmospheric outflows that change planetary radii on astronomical timescales. In recent years, near-IR transit spectroscopy of metastable Hei has been a prolific tracer of high-altitude planetary gas. We present a case study of exoplanet aeronomy using metastable Hei transit observations from Palomar Observatory's Wide Field InfraRed Camera and follow-up high-energy data from the Neil Gehrels Swift Observatory that were taken within 1 month of the WASP-69 system, a K-type main-sequence star with a well-studied hot Jupiter companion. Supplemented by archival data, we find that WASP-69's X-ray flux in 2023 was less than 50% of what was recorded in 2016 and that the metastable Hei absorption from WASP-69 b was lower in 2023 versus past epochs from 2017 to 2019. Via atmospheric modeling, we show that this time-variable metastable Hei signal is in the expected direction given the observed change in stellar XUV, possibly stemming from WASP-69's magnetic activity cycle. Our results underscore the ability of multiepoch, multiwavelength observations to paint a cohesive picture of the interaction between an exoplanet’s atmosphere and its host star.

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“…Their proximity to their host stars could be responsible for the heating and expansion of their atmospheres (Batygin & Stevenson 2010;Pu & Valencia 2017;Thorngren & Fortney 2018), which contributes to their observed low density. For objects with equilibrium temperatures exceeding 1000 K, the inflated radius mechanism may be similar to hot Jupiter planets (Fortney et al 2021), i.e., (a) due to the thermal contraction of He/H atmospheres (Owen & Wu 2013;Lopez & Fortney 2014), (b) atmospheric winds driven by photoionization due to intense UV radiation from the host star (Murray-Clay et al 2009), which can be probed by observing the larger transit depths due to atmospheric expansion in the Lyα line at λ = 1215.6 Å signatures in a planet's spectrum (Kislyakova et al 2019;Owen et al 2023), Hα absorption at λ = 6562.8 Å (Jensen et al 2012;Christie et al 2013;Cauley et al 2017), or the Helium triplet in the near-infrared at λ = 10833 Å (Spake et al 2018;dos Santos et al 2020;Vissapragada et al 2020;Orell-Miquel et al 2022;Bennett et al 2023;Krolikowski et al 2024), and/or (c) photochemical hazes in the atmosphere responsible for a larger and puffier appearance (Gao & Zhang 2020; Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.…”

Section: Introductionmentioning

confidence: 99%

TOI-1173 A b: The First Inflated Super-Neptune in a Wide Binary System

Galarza,

Ferreira,

Lorenzo-Oliveira

et al. 2024

AJ

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Among Neptunian mass exoplanets (20−50 M ⊕), puffy hot Neptunes are extremely rare, and their unique combination of low mass and extended radii implies very low density (ρ < 0.3 g cm−3). Over the last decade, only a few puffy planets have been detected and precisely characterized with both transit and radial velocity observations, most notably including WASP-107 b, TOI-1420 b, and WASP-193 b. In this paper, we report the discovery of TOI-1173 A b, a low-density ( ρ = 0.195 − 0.017 + 0.018 g cm−3) super-Neptune with P = 7.06 days in a nearly circular orbit around the primary G-dwarf star in the wide binary system TOI-1173 A/B. Using radial velocity observations with the MAROON-X and HIRES spectrographs and transit photometry from TESS, we determine a planet mass of M p = 27.4 ± 1.7 M ⊕ and radius of R p = 9.19 ± 0.18 R ⊕. TOI-1173 A b is the first puffy super-Neptune planet detected in a wide binary system (projected separation ∼11,400 au). We explore several mechanisms to understand the puffy nature of TOI-1173 A b and show that tidal heating is the most promising explanation. Furthermore, we demonstrate that TOI-1173 A b likely has maintained its orbital stability over time and may have undergone von-Zeipel–Lidov–Kozai migration followed by tidal circularization, given its present-day architecture, with important implications for planet migration theory and induced engulfment into the host star. Further investigation of the atmosphere of TOI-1173 A b will shed light on the origin of close-in low-density Neptunian planets in field and binary systems, while spin–orbit analyses may elucidate the dynamical evolution of the system.

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Nondetection of Helium in the Hot Jupiter WASP-48b

Cited by 7 publications

References 136 publications

A High-resolution Non-detection of Escaping Helium in the Ultrahot Neptune LTT 9779b: Evidence for Weakened Evaporation

A High-resolution Non-detection of Escaping Helium in the Ultrahot Neptune LTT 9779b: Evidence for Weakened Evaporation

Exoplanet Aeronomy: A Case Study of WASP-69 b’s Variable Thermosphere

TOI-1173 A b: The First Inflated Super-Neptune in a Wide Binary System

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