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Abstract Ground-based high-resolution cross-correlation spectroscopy (HRCCS;R ≳ 15,000) is a powerful complement to space-based studies of exoplanet atmospheres. By resolving individual spectral lines, HRCCS can precisely measure chemical abundance ratios, directly constrain atmospheric dynamics, and robustly probe multidimensional physics. But the subtleties of HRCCS data sets—e.g., the lack of exoplanetary spectra visible by eye and the statistically complex process of telluric removal—can make interpreting them difficult. In this work, we seek to clarify the uncertainty budget of HRCCS with a forward-modeling approach. We present an HRCCS observation simulator,scope,⁵⁵https://github.com/arjunsavel/scopethat incorporates spectral contributions from the exoplanet, star, tellurics, and instrument. This tool allows us to control the underlying data set, enabling controlled experimentation with complex HRCCS methods. Simulating a fiducial hot Jupiter data set (WASP-77Ab emission with IGRINS), we first confirm via multiple tests that the commonly used principal component analysis does not bias the planetary signal when few components are used. Furthermore, we demonstrate that mildly varying tellurics and moderate wavelength solution errors induce only mild decreases in HRCCS detection significance. However, limiting-case, strongly varying tellurics can bias the retrieved velocities and gas abundances. Additionally, in the low signal-to-noise ratio limit, constraints on gas abundances become highly non-Gaussian. Our investigation of the uncertainties and potential biases inherent in HRCCS data analysis enables greater confidence in scientific results from this maturing method. 

Abstract A primary goal of exoplanet science is to measure the atmospheric composition of gas giants in order to infer their formation and migration histories. Common diagnostics for planet formation are the atmospheric metallicity ([M/H]) and the carbon-to-oxygen (C/O) ratio as measured through transit or emission spectroscopy. The C/O ratio in particular can be used to approximately place a planet’s initial formation radius from the stellar host, but a given C/O ratio may not be unique to formation location. This degeneracy can be broken by combining measurements of both the C/O ratio and the atmospheric refractory-to-volatile ratio. We report the measurement of both quantities for the atmosphere of the canonical ultrahot Jupiter WASP-121 b using the high-resolution (R= 45,000) IGRINS instrument on Gemini South. Probing the planet’s direct thermal emission in both pre- and post-secondary eclipse orbital phases, we infer that WASP-121 b has a significantly superstellar C/O ratio of ${0.70}_{-0.10}^{+0.07}$and a moderately superstellar refractory-to-volatile ratio at ${3.83}_{-1.67}^{+3.62}\times$stellar. This combination is most consistent with formation between the soot line and H₂O snow line, but we cannot rule out formation between the H₂O and CO snow lines or beyond the CO snow line. We also measure velocity offsets between H₂O, CO, and OH, potentially an effect of chemical inhomogeneity on the planet dayside. This study highlights the ability to measure both C/O and refractory-to-volatile ratios via high-resolution spectroscopy in the near-IRHandKbands. 

Abstract We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy atz≥ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift ofz= 5.043, placing it shortly after the end of the “Epoch of Reionization,” and an AB magnitudez_AB= 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of thez= 1.001 cluster lens is $M(<5.″77)={1.079}_{-0.007}^{+0.023}\times {10}^{13}{M}_{☉}$, significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is 〈μ_arc〉 = ${76}_{-20}^{+40}$, a factor of ${2.4}_{-0.7}^{+1.4}$greater than previously estimated from ground-based data; the flux-weighted average magnification is 〈μ_arc〉 = ${92}_{-31}^{+37}$. We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to $\log \left(M_{\star }/M_{\odot }\right)=$9.7 ± 0.3 and SFR = ${10.3}_{-4.4}^{+7.0}$M_⊙yr⁻¹, respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy.