ABSTRACT
The class of ultra-hot Jupiters comprises giant exoplanets undergoing intense irradiation from their host stars. They have proved to be a particularly interesting population for their ...orbital and atmospheric properties. One such planet, WASP-121b, is in a highly misaligned orbit close to its Roche limit, and its atmosphere exhibits a thermal inversion. These properties make WASP-121b an interesting target for additional atmospheric characterization. In this paper, we present analyses of archival high-resolution optical spectra obtained during transits of WASP-121b. We model the Rossiter-McLaughlin effect and the Centre-to-Limb Variation and find that they do not significantly affect the transmission spectrum in this case. However, we discuss scenarios where these effects warrant more careful treatment by modelling the WASP-121 system and varying its properties. We report a new detection of atmospheric absorption from H α in the planet with a transit depth of $1.87\pm 0.11{{\ \rm per\ cent}}$. We further confirm a previous detection of the Na i doublet, and report a new detection of Fe i via cross-correlation with a model template. We attribute the H α absorption to an extended Hydrogen atmosphere, potentially undergoing escape, and the Fe i to equilibrium chemistry at the planetary photosphere. These detections help to constrain the composition and chemical processes in the atmosphere of WASP-121b.
Ultra-hot Jupiters (UHJs), giant exoplanets with equilibrium temperatures above 2000 K, are ideal laboratories for studying metal compositions of planetary atmospheres. At these temperatures the ...thermal dissociation of metal-rich molecules into their constituent elements makes these atmospheres conducive for elemental characterization. Several elements, mostly ionized metals, have been detected in UHJs recently using high-resolution transit spectroscopy. Even though a number of neutral transition metals (e.g., Fe, Ti, V, Cr) are expected to be strong sources of optical/near-ultraviolet (NUV) opacity and, hence, influence radiative processes in the lower atmospheres of UHJs, only Fe i has been detected to date. We conduct a systematic search for atomic species in the UHJ WASP-121 b. Using theoretical models we present a metric to predict the atomic species likely to be detectable in such planets with high-resolution transmission spectroscopy. We search for the predicted species in observations of WASP-121 b and report the first detections of neutral transition metals Cr i and V i in an exoplanet at 3.6 and 4.5 significance, respectively. We confirm previous detections of Fe i and Fe ii. Whereas Fe ii was detected previously in the NUV, we detect it in the optical. We infer that the neutral elements Fe i, V i, and Cr i are present in the lower atmosphere, as predicted by thermochemical equilibrium, while Fe ii is a result of photoionization in the upper atmosphere. Our study highlights the rich chemical diversity of UHJs.
Molecular species in planetary atmospheres provide key insights into their atmospheric processes and formation conditions. In recent years, high-resolution Doppler spectroscopy in the near-infrared ...has allowed detections of H2O and CO in the atmospheres of several hot Jupiters. This method involves monitoring the spectral lines of the planetary thermal emission Doppler-shifted due to the radial velocity of the planet over its orbit. However, aside from CO and H2O, which are the primary oxygen- and carbon-bearing species in hot H2-rich atmospheres, little else is known about the molecular compositions of hot Jupiters. Several recent studies have suggested the importance and detectability of nitrogen-bearing species in such atmospheres. In this Letter, we confirm potential detections of CO and H2O in the hot Jupiter HD 209458b using high-resolution spectroscopy. We also report a cross-correlation peak with a signal-to-noise ratio of 4.7 from a search for HCN. The results are obtained using high-resolution phase-resolved spectroscopy with the Very Large Telescope CRyogenic high-resolution InfraRed Echelle Spectrograph (VLT CRIRES) and standard analysis methods reported in the literature. A more robust treatment of telluric contamination and other residuals would improve confidence and enable unambiguous molecular detections. The presence of HCN could provide constraints on the C/O ratio of HD 209458b and its potential origins.
Abstract
The nondetection of a coma surrounding 1I/‘Oumuamua, the first discovered interstellar object (ISO), has prompted a variety of hypotheses to explain its nongravitational acceleration. Given ...that forthcoming surveys are poised to identify analogs of this enigmatic object, it is prudent to devise alternative approaches to characterization. In this study, we posit X-ray spectroscopy as a surprisingly effective probe of volatile ISO compositions. Heavily ionized metals in the solar wind interact with outgassed neutrals and emit high-energy photons in a process known as charge exchange, and charge-exchange-induced X-rays from comets and planetary bodies have been observed extensively in our solar system. We develop a model to predict the X-ray flux of an ISO based on its chemical inventory and ephemeris. We find that while standard cometary constituents, such as H
2
O, CO
2
, CO, and dust, are best probed via optical or infrared observations, we predict strong X-ray emission generated by charge exchange with extended comae of H
2
and N
2
—species that lack strong infrared fluorescence transitions. We find that XMM-Newton would have been sensitive to charge exchange emission from 1I/‘Oumuamua during the object’s close approach to Earth, and that constraints on composition may have been feasible. We argue for follow-up X-ray observations of newly discovered ISOs with close-in perihelia. Compositional constraints on the general ISO population could reconcile the apparently self-conflicting nature of 1I/‘Oumuamua and provide insight into the earliest stages of planet formation in extrasolar systems.
ABSTRACT
The alkali metal sodium (Na) is one of the most commonly detected chemical species in the upper atmospheres of giant exoplanets. In this work, we conducted a homogeneous survey of Na in a ...diverse sample of 10 highly irradiated giant exoplanets using high-resolution transmission spectroscopy. Our sample includes nine planets with previous Na detections and one new detection. We confirm previous detections and assess multiple approaches for deriving Na line properties from high-resolution transmission spectra. The homogeneously measured sodium line depths were used to constrain the atmospheric heights (HNa) with respect to the planetary radii (Rp). We assess an empirical trend describing the relative atmospheric height (HNa/Rp) as a function of planetary equilibrium temperature (Teq) and surface gravity (g), in which HNa/Rp decreases exponentially with ξ ∝ gTeq, approaching a constant at large ξ. We also report the sodium D2/D1 line ratios across our sample and find that seven targets have line ratios that are consistent with unity. Finally, we measured net blueshifted offsets of the sodium absorption lines from their rest frame wavelengths for all 10 planets, corresponding to day–night wind velocities of a few km s−1. This suggests that the broad sample of exoplanets share common underlying processes that govern atmospheric dynamics. Our study highlights a promising avenue for using high-resolution transmission spectroscopy to further our understanding of how atmospheric characteristics vary over a diverse sample of exoplanets.
Abstract
With an equilibrium temperature above 2500 K, the recently discovered HAT-P-70b belongs to a new class of exoplanets known as ultrahot Jupiters: extremely irradiated gas giants with day-side ...temperatures that resemble those found in stars. These ultrahot Jupiters are among the most amenable targets for follow-up atmospheric characterization through transmission spectroscopy. Here, we present the first analysis of the transmission spectrum of HAT-P-70b using high-resolution data from the HARPS-N spectrograph of a single-transit event. We use a cross-correlation analysis and transmission spectroscopy to look for atomic and molecular species in the planetary atmosphere. We detect absorption by Ca
ii
, Cr
i
, Cr
ii
, Fe
i
, Fe
ii
, H
i
, Mg
i
, Na
i,
and V
i
, and we find tentative evidence of Ca
i
and Ti
ii
. Overall, these signals appear blueshifted by a few km s
−1
, suggestive of winds flowing at high velocity from the day side to the night side. We individually resolve the Ca
ii
H and K lines, the Na
i
doublet, and the H
α
, H
β
, and H
γ
Balmer lines. The cores of the Ca
ii
and H
i
lines form well above the continuum, indicating the existence of an extended envelope. We refine the obliquity of this highly misaligned planet to
107.9
−
1.7
+
2.0
degrees by examining the Doppler shadow that the planet casts on its A-type host star. These results place HAT-P-70b as one of the exoplanets with the highest number of species detected in its atmosphere.
Abstract
Ongoing, extreme-precision Doppler radial-velocity (RV) surveys seek planets with masses less than several
M
⊕
; population-level studies to determine the distribution of planetary masses, ...however, remain difficult due to the required observational time investment, as well as challenges associated with robustly detecting the lowest-mass planets. We outline a novel approach that leverages extensive, existing RV data sets to constrain masses of exoplanet populations: stacking periodograms of RV time series across many targets. We show that an exoplanet population may be statistically identifiable in the stacked periodogram, even when individual planets do not pass the threshold of detection. We discuss analytical, statistical properties of the stacked periodogram, perform simulations to demonstrate the efficacy of the method, and investigate the influence of semistructured window functions and stellar activity. Analysis of the Lick–Carnegie Exoplanet Survey data set reveals a marginally significant (1.6
σ
) signal consistent with a population of exoplanets occupying 3–7 days periods with typical
K
between 1.6–5.1 m s
−1
. More detailed investigation of signals associated with stellar activity and yearly systematics may be necessary to confirm this result or detect other underlying Keplerian contributions.
Abstract
At present, there exists no consensus in the astronomical community regarding either the bulk composition or the formation mechanism for the interstellar object 1I/2017 U1 (‘Oumuamua). With ...the goal of assessing the merits of the various scenarios that have been suggested to explain ‘Oumuamua's appearance and observed properties, we report a number of new analyses and provide an up-to-date review of the current hypotheses. We consider the interpretations that can reconcile ‘Oumuamua's observed non-Keplerian trajectory with the nondetection of traditional cometary volatiles. We examine the ability of these proposed formation pathways to populate the galaxy with sufficient interstellar objects such that the detection of ‘Oumuamua by Pan-STARRS would be statistically favored. We consider two exotic ices, hydrogen and nitrogen, showing that the frigid temperature requirement for the former and the necessary formation efficiency of the latter pose serious difficulties for these interpretations. Via order-of-magnitude arguments and hydrodynamical cratering simulations, we show that impacts on extrasolar Kuiper Belt analogues are not expected to generate N
2
ice fragments as large as ‘Oumuamua. In addition, we discuss observational tests to confirm the presence of these ices in future interstellar objects. Next, we examine the explanations that attribute ‘Oumuamua's properties to other compositions: ultraporous dust aggregates and thin membranes powered by solar radiation pressure, among others. While none of these hypotheses are perfectly satisfactory, we make predictions that will be testable by the Vera Rubin Observatory to resolve the tension introduced by ‘Oumuamua.
Abstract
The first interstellar object, 1I/2017 U1 (‘Oumuamua), exhibited several unique properties, including an extreme aspect ratio, a lack of typical cometary volatiles, and a deviation from a ...Keplerian trajectory. Several authors have hypothesized that the non-gravitational acceleration was caused by either cometary outgassing or radiation pressure. Here, we investigate the spin dynamics of ‘Oumuamua under the action of high-surface-area fractional activity and radiation pressure. We demonstrate that a series of transient jets that migrate across the illuminated surface will not produce a secular increase in the spin rate. We produce 3D tumbling simulations that approximate the dynamics of a surface-covering jet and show that the resulting synthetic light curve and periodogram are reasonably consistent with the observations. Moreover, we demonstrate that radiation pressure also produces a steady spin state. While carbon monoxide (CO) has been dismissed as a possible accelerant because of its non-detection in emission by Spitzer, we show that outgassing from a surface characterized by a modest covering fraction of CO ice can satisfy the non-ballistic dynamics for a plausible range of assumed bulk densities and surface albedos. Spitzer upper limits on CO emission are, however, inconsistent with the CO production necessary to provide the acceleration. Nonetheless, an ad hoc but physically plausible explanation is that the activity level varied greatly during the time that the trajectory was monitored. We reproduce the astrometric analysis presented in Micheli et al., and verify that the non-gravitational acceleration was consistent with stochastic changes in outgassing.
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