Faculae are a dominant source of stellar activity noise in radial velocity measurements, yet their low contrast and broad surface distribution make them difficult to track in disc-integrated observations. We apply Spectral Ratio Analysis (SRA) to HARPS-N Sun-as-a-star observations to isolate and characterize the spectral imprint of facular regions over rotational timescales. The resulting SRA spectra show coherent, line-dependent variability sensitive to surface magnetic activity, with the Fe I 4377 Angstrom line exhibiting a particularly strong diagnostic response to facular coverage. We interpret the observed signatures using two complementary synthetic frameworks: composite PHOENIX spectra, from which we derive best-fit facular temperature contrasts in the range 200-400 K, and MPS-ATLAS spectra synthesized using MURaM simulations of the quiet Sun including a small-scale dynamo and magnetically-enhanced facular analogues with initial mean vertical magnetic fields of 100G, 200G, and 300G. Both approaches are benchmarked against facular filling factors measured from Solar Dynamics Observatory (SDO) disc-resolved images. We find good agreement between SDO-measured and SRA-inferred filling factors using the Fe I 4377 Angstrom line, with Pearson R coefficients of 0.587-0.927 across models and timescales. The estimated filling factors track the solar activity cycle, rising from 1.5

We present the discovery of TIC-65910228 b / NGTS-38 b, a giant exoplanet with a radius of 1 . 081 +/- 0 . 047 R-J and a mass of 4 . 77(-0.37)(+0 . 39) M-J on a long-period ( 180 . 52797 +/- 0 . 00036 d), moderately eccentric ( e = 0 . 3086 +/- 0 . 010 ) orbit transiting a bright (V=10 . 230 +/- 0 . 020 mag) metal rich ([Fe/H] =0 . 33 +/- 0 . 09 'dex') F6V-F7V type host star. The planet was initially detected from a single transit in TESS Sector 33. A photometric monitoring campaign of 228 nights with NGTS detected a transit egress of the planet, which together with spectroscopic radial velocity monitoring with CORALIE and HARPS identified an orbital period of 180.5 d. These radial velocity measurements also showed the mass of the companion to be planetary. Additional transit observations coordinated by the TESS follow-up observing program allowed further confirmation and refinement of this period. With its relatively cool equilibrium temperature of 457 +/- 11 K, NGTS-38 b joins a small but growing population of well characterized transiting warm-Jupiters and has one of the longest periods of any discovered to date. The target is situated in the LOPS2 field of the upcoming PLATO mission which will allow for greater refinement of the system parameters and potential for the discovery of additional companions too small and/or too long-period to be seen by TESS or NGTS. NGTS-38 b's bright host star and wide orbital separation make it an attractive target for further study, including potential measurement of its spin-orbit alignment or targeted exomoon/ring searches.

We present the first transmission spectroscopy study of an exoplanet atmosphere with the high-resolution mode of the new Gemini High-resolution Optical SpecTrograph (GHOST) instrument at the Gemini South Observatory. We observed one transit of HAT-P-70 b—an ultra-hot Jupiter with an inflated radius—and made a new detection of the infrared Ca ii triplet in its transmission spectrum. The depth of the strongest line implies that a substantial amount of Ca ii extends to at least 47% above the bulk planetary radius. The triplet lines are blueshifted between ∼3 to 5 km s ^−1 , indicative of strong dayside-to-nightside winds common on highly irradiated gas giants. Comparing the transmission spectrum with atmospheric models that incorporate non–local thermodynamic equilibrium effects suggests that the planetary mass is likely between 1 and 2 M _J , much lighter than the upper limit previously derived from radial velocity measurements. Importantly, thanks to the high signal-to-noise ratio achieved by GHOST/Gemini South, we are able to measure the temporal variation of these signals. Absorption depths and velocity offsets of the individual Ca ii lines remain mostly consistent across the transit, except for the egress phases, where weaker absorption and stronger blueshifts are observed, highlighting the atmospheric processes within the trailing limb alone. Our study demonstrates the ability of GHOST to make time-resolved detections of individual spectral lines, providing valuable insights into the 3D nature of exoplanet atmospheres by probing different planetary longitudes as the tidally locked planet rotates during the transit.

Aims. We model the atmosphere of the ultra-hot Jupiter (UHJ) WASP-178b while accounting for non-local thermodynamical equilibrium (NLTE) effects and compare synthetic transmission spectra with near-ultraviolet (NUV) and optical observations. Methods. We used the HELIOS code (LTE) in the lower atmosphere and the ClOUDY code (LTE or NLTE) in the middle and upper atmosphere to compute the temperature-pressure (TP) and abundance profiles. We further used CLOUDY to compute the theoretical planetary transmission spectrum both in LTE and NLTE for comparison with observations. Results. We find an isothermal TP profile at pressures higher than 10 mbar and lower than 10(-8) bar, with an almost linear increase from similar to 2200 K to similar to 8100 K in between. The temperature structure is driven by NLTE effects, particularly in the form of increased heating resulting from the overpopulation of long-lived FeII levels with strong transitions in the NUV band, where the stellar emission is strong, and of decreased cooling due to the underpopulation of MgI and MgII levels that dominate the cooling. The planetary atmosphere is hydrostatic up to pressures of similar to 1 nbar, and thus accurately modelling spectral lines forming at pressures lower than similar to 1 nbar requires accounting for both hydrodynamics and NLTE effects. The NLTE synthetic transmission spectrum overestimates the observed H alpha and H beta absorption, while the LTE model is in good agreement, which is surprising because the opposite has been found for the other UHJs for which NLTE modelling has been performed. In the NUV, we find an excellent match between the NLTE transmission spectrum and the HST/UVIS data, contrary to the LTE model. This contrasts with previous LTE results requiring SiO absorption to fit the observations. Conclusions. The accurate characterisation of the atmosphere of UHJs is possible only when accounting for NLTE effects and particularly for the level population of Fe and Mg, which respectively dominate heating and cooling.

With high equilibrium temperatures and tidally locked rotation, ultra-hot Jupiters (UHJs) are unique laboratories within which to probe extreme atmospheric physics and chemistry. In this paper, we present high-resolution dayside spectroscopy of the UHJ WASP-189 b obtained with the new Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South Observatory. The observations, which cover 3 hr of post-eclipse orbital phases, were obtained during the instrument’s System Verification run. We detect the planet’s atmosphere via the Doppler cross-correlation technique, and recover a detection of neutral iron in the planet’s dayside atmosphere at a significance of 7.5 σ in the red arm of the data, verifying the presence of a thermal inversion. We also investigate the presence of other species in the atmosphere and discuss the implications of model injection/recovery tests. These results represent the first atmospheric characterization of an exoplanet with GHOST’s high-resolution mode, and demonstrate the potential of this new instrument in detecting and studying ultra-hot exoplanet atmospheres.

ABSTRACT High-resolution cross-correlation spectroscopy (HRCCS) combined with adaptive optics has been enormously successful in advancing our knowledge of exoplanet atmospheres, from chemistry to rotation and atmospheric dynamics. This powerful technique now drives major science cases for ELT instrumentation including METIS/ELT, GMTNIRS/GMT, and MICHI/TMT, targeting biosignatures on rocky planets at 3–5 μm, but remains untested beyond 3.5 μm where the sky thermal background begins to provide the dominant contribution to the noise. We present 3.51–5.21 μm M-band CRIRES+/VLT observations of the archetypal young directly imaged gas giant β Pictoris b, detecting CO absorption at S/N = 6.6 at 4.73 μm and H2O at S/N = 5.7, and thus extending the use of HRCCS into the thermal background noise dominated infrared. Using this novel spectral range to search for more diverse chemistry, we report marginal evidence of SiO at S/N = 4.3, potentially indicative that previously proposed magnesium–silicate clouds in the atmosphere are either patchy, transparent at M-band wavelengths, or possibly absent on the planetary hemisphere observed. The molecular detections are rotationally broadened by the spin of β Pic b, and we infer a planetary rotation velocity of vsin(i) = 22 ± 2 km s−1 from the cross-correlation with the H2O model template, consistent with previous K-band studies. We discuss the observational challenges posed by the thermal background and telluric contamination in the M-band, the custom analysis procedures required to mitigate these issues, and the opportunities to exploit this new infrared window for HRCCS using existing and next-generation instrumentation.

ABSTRACT Ultrahot Jupiters (UHJs) undergo intense irradiation by their host stars and are expected to experience non-local thermodynamic equilibrium (NLTE) effects in their atmospheres. Such effects are computationally intensive to model but, at the low pressures probed by high-resolution cross-correlation spectroscopy (HRCCS), can significantly impact the formation of spectral lines. The UHJ WASP-121 b exhibits a highly inflated atmosphere, making it ideal for investigating the impact of NLTE effects on its transmission spectrum. Here, we formally introduce cloudy for exoplanets, a cloudy-based modelling code, and use it to generate 1D LTE and NLTE atmospheric models and spectra to analyse archival HARPS WASP-121 b transmission spectra. We assessed the models using two HRCCS methods: (i) Pearson cross-correlation, and (ii) a method that aims to match the average observed line depth for given atmospheric species. All models result in strong detections of Fe i (7.5 < S/N < 10.5). However, the highest S/N model (LTE) does not agree with the best-matching model of the average line depth (NLTE). We also find degeneracy, such that increasing the isothermal temperature and metallicity of the LTE models can produce average line depths similar to cooler, less metal rich NLTE models. Thus, we are unable to conclusively remark on the presence of NLTE effects in the atmosphere of WASP-121 b. We instead highlight the need for standardized metrics in HRCCS that enable robust statistical assessment of complex physical models, e.g. NLTE or 3D effects, that are currently too computationally intensive to include in HRCCS atmospheric retrievals.

We aim at extracting the transmission spectrum of the HI Balmer lines of the ultra-hot Jupiter (UHJ) KELT-20b/MASCARA-2b from observations and to further compare the results with what obtained through forward modelling accounting for non-local thermodynamic equilibrium (NLTE) effects. We extract the line profiles from six transits obtained with the HARPS-N high-resolution spectrograph attached to the Telescopio Nazionale Galileo telescope. We compute the temperature-pressure (TP) profile employing the helios code in the lower atmosphere and the Cloudy NLTE code in the middle and upper atmosphere. We further use Cloudy to compute the theoretical planetary transmission spectrum in LTE and NLTE for comparison with observations. We detected the Halpha (0.79+/-0.03%; 1.25 Rp), Hbeta (0.52+/-0.03%; 1.17 Rp), and Hgamma (0.39+/-0.06%; 1.13 Rp) lines, while we detected the Hdelta line at almost 4 sigma (0.27+/-0.07%; 1.09 Rp). The models predict an isothermal temperature of about2200 K at pressures >10^-2 bar and of about 7700 K at pressures <10^-8 bar, with a roughly linear temperature rise in between. In the middle and upper atmosphere, the NLTE TP profile is up to about 3000 K hotter than in LTE. The synthetic transmission spectrum derived from the NLTE TP profile is in good agreement with the observed HI Balmer line profiles, validating our obtained atmospheric structure. Instead, the synthetic transmission spectrum derived from the LTE TP profile leads to significantly weaker absorption compared to the observations. Metals appear to be the primary agents leading to the temperature inversion in UHJs and the impact of NLTE effects on them increases the magnitude of the inversion. We find that the impact of NLTE effects on the TP profile of KELT-20b/MASCARA-2b is larger than for the hotter UHJ KELT-9b, and thus NLTE effects might be relevant also for planets cooler than KELT-20b/MASCARA-2b.

We explore atmospheric escape from close-in exoplanets with the highest mass-loss rates. First, we locate the transition from stellar X-ray and UV-driven escape to rapid Roche lobe overflow, which occurs once the 10–100 nbar pressure level in the atmosphere reaches the Roche lobe. Planets enter this regime when the ratio of the substellar radius to the polar radius along the visible surface pressure level, which aligns with a surface of constant Roche potential, is X/Z ≳ 1.2 for Jovian planets ( M p ≳ 100 M ⊕ ) and X/Z ≳ 1.02 for sub-Jovian planets ( M p ≈ 10–100 M ⊕ ). Around a Sun-like star, this regime applies to orbital periods of less than two days for planets with radii of about 3–14R ⊕ . Our results agree with the properties of known transiting planets and can explain parts of the sub-Jovian desert in the population of known exoplanets. Second, we present detailed numerical simulations of atmospheric escape from a planet like Uranus or Neptune orbiting close to a Sun-like star that support the results above and point to interesting qualitative differences between hot Jupiters and sub-Jovian planets. We find that hot Neptunes with solar-metallicity hydrogen and helium envelopes have relatively more extended upper atmospheres than typical hot Jupiters, with a lower ionization fraction and higher abundances of escaping molecules. This is consistent with existing ultraviolet transit observations of warm Neptunes, and it might provide a way to use future observations and models to distinguish solar-metallicity atmospheres from higher-metallicity atmospheres.

The extreme contrast ratios between stars and their planets at optical wavelengths make it challenging to isolate the light reflected by exoplanet atmospheres. Yet, these reflective properties reveal key processes occurring in the atmospheres, and they also span wavelengths that include the potential O$_2$ biosignature. High resolution cross-correlation spectroscopy (HRCCS) offers a robust avenue for developing techniques to extract exoplanet reflection spectra. We aimed to extract the optical reflected light spectrum of the non-transiting hot Jupiter 51 Peg b by adapting techniques designed to remove tellurics in infrared HRCCS to instead remove optical stellar lines. Importantly, we investigated the so far neglected impact of the broadening of the reflected host star spectrum due to the difference between the stellar rotation and the planet's orbital velocity. We used 484, R=115000 optical spectra of 51 Peg b from HARPS-N and HARPS, which we aligned to the exact stellar rest frame in order to effectively remove the contaminating host star. However, some stellar residuals remained, likely due to stellar activity. We cross-correlated with an appropriately broadened synthetic stellar model to search for the planet's Doppler-shifting spectrum. We detect no significant reflected light from 51 Peg b and report a S/N=3 upper limit on the contrast ratio of 76.0 ppm (7.60x10$^{-5}$) when including broadening, and 24.0 ppm (2.40x10$^{-5}$) without. These upper limits rule out radius and albedo combinations of previously claimed detections. Broadening can significantly impact the ability of HRCCS to extract reflected light spectra and must be considered when determining the contrast ratio, radius, and albedo of the planet. Asynchronous systems (Prot,$_{\star}\ne$ Porb) are most affected, including most hot Jupiters as well as Earth-size planets in the traditional habitable zones of some M-dwarfs.

Oxygen is a constituent of many of the most abundant molecules detected in exoplanetary atmospheres and a key ingredient for tracking how and where a planet formed. In particular, the OI 777.4 nm triplet is used to probe airglow and aurora on the Earth and the oxygen abundance in stellar atmospheres, but has not been detected in an exoplanet atmosphere before. We present a definite ground-based detection of the neutral oxygen 777.4 nm triplet lines in the transmission spectrum of the ultra-hot Jupiter KELT-9b, the hottest known giant planet. The synthetic spectrum computed employing novel non-local thermodynamic equilibrium (NLTE) radiative transfer calculations matches the data significantly better compared to the one computed assuming local thermodynamic equilibrium. These NLTE radiative transfer calculations imply a mass-loss rate of 10^8-10^9 kg s-1, which exceeds the lower limit of 10^7-10^8 kg s-1 required to facilitate the escape of oxygen and iron from the atmosphere. Assuming a solar oxygen abundance, the NLTE model points towards the need of microturbulence and macroturbulence broadening of 3.0pm0.7 km s-1 and 13pm5 km s-1, respectively, indicative of the presence of fast winds in the middle and upper atmosphere. Present and upcoming high-resolution spectrographs will allow the detection in other exoplanets of the 777.4 nm OI triplet, which is a powerful tool to constrain the key characteristics of exoplanetary atmospheres when coupled with forward modelling accounting for NLTE effects.

Context. Several observational and theoretical results indicate that the atmospheric temperature of the ultra-hot Jupiter KELT-9b in the main line formation region is a few thousand degrees higher than predicted by self-consistent models. Aims. Our aim was to test whether non-local thermodynamic equilibrium (NLTE) effects are responsible for the presumably higher temperature. Methods. We employed the Cloudy NLTE radiative transfer code to self-consistently compute the upper atmospheric temperature-pressure (TP) profile of KELT-9b, assuming solar metallicity and accounting for Roche potential. In the lower atmosphere, we used an updated version of the HELIOS radiative-convective equilibrium code to constrain the Cloudy model. Results. The Cloudy NLTE TP profile is ≈2000 K hotter than that obtained with previous models assuming LTE. In particular, in the 1–10 −7 bar range the temperature increases from ≈4000 to ≈8500 K, remaining roughly constant at lower pressures. We find that the high temperature in the upper atmosphere of KELT-9b is driven principally by NLTE effects modifying the Fe and Mg level populations, which strongly influence the atmospheric thermal balance. We employed Cloudy to compute LTE and NLTE synthetic transmission spectra on the basis of the TP profiles computed in LTE and NLTE, respectively, finding that the NLTE model generally produces stronger absorption lines, particularly in the ultraviolet, than the LTE model (up to 30%). We compared the NLTE synthetic transmission spectrum with the observed H α and H β line profiles obtaining an excellent match, thus supporting our results. Conclusions. The NLTE synthetic transmission spectrum can be used to guide future observations aiming at detecting features in the KELT-9b transmission spectrum. Metals, such as Mg and Fe, and NLTE effects shape the upper atmospheric temperature structure of KELT-9b, and thus affect the mass-loss rates derived from it. Finally, our results call for checking whether this is the case also for cooler planets.

With a dayside temperature in excess of 4500 K, comparable to a mid-K-type star, KELT-9b is the hottest planet known. Its extreme temperature makes KELT-9b a particularly interesting test bed for investigating the nature and diversity of gas giant planets. We observed the transit of KELT-9b at high spectral resolution (R similar to 94,600) with the CARMENES instrument on the Calar Alto 3.5 m telescope. Using these data, we detect for the first time ionized calcium (Ca ii triplet) absorption in the atmosphere of KELT-9b; this is the second time that Ca ii has been observed in a hot Jupiter. Our observations also reveal prominent H alpha absorption, confirming the presence of an extended hydrogen envelope around KELT-9b. We compare our detections with an atmospheric model and find that all four lines form between atmospheric temperatures of 6100 and 8000 K and that the Ca ii lines form at pressures between 50 and 100 nbar while the H alpha line forms at a lower pressure (similar to 10 nbar), higher up in the atmosphere. The altitude that the core of H alpha line forms is found to be similar to 1.4 R-p, well within the planetary Roche lobe (similar to 1.9 R-p). Therefore, rather than probing the escaping upper atmosphere directly, the H alpha line and the other observed Balmer and metal lines serve as atmospheric thermometers enabling us to probe the planet's temperature profile, thus the energy budget.

The inflated transiting hot Jupiter HD 209458b is one of the best studied objects since the beginning of exoplanet characterization. Transmission observations of this system between the mid infrared and the far ultraviolet have revealed the signature of atomic, molecular, and possibly aerosol species in the lower atmosphere of the planet, as well as escaping hydrogen and metals in the upper atmosphere. From a re-analysis of near-ultraviolet (NUV) transmission observations of HD 209458b, we detect ionized iron (Fe II) absorption in a 100 A-wide range around 2370 A, lying beyond the planetary Roche lobe. However, we do not detect absorption of equally strong Fe II lines expected to be around 2600 A. Further, we find no evidence for absorption by neutral magnesium (Mg I), ionized magnesium (Mg II), nor neutral iron (Fe I). These results avoid the conflict with theoretical models previously found by Vidal-Madjar et al. (2013), which detected Mg I but did not detect Mg II from this same data set. Our results indicate that hydrodynamic escape is strong enough to carry atoms as heavy as iron beyond the planetary Roche lobe, even for planets less irradiated than the extreme ultra-hot-Jupiters such as WASP-12b and KELT-9b. The detection of iron and non-detection of magnesium in the upper atmosphere of HD 209458b can be explained by a model in which the lower atmosphere forms (hence, sequesters) primarily magnesium-bearing condensates, rather than iron condensates. This is suggested by current microphysical models. The inextricable synergy between upper- and lower-atmosphere properties highlights the value of combining observations that probe both regions.

Context. Observationally constraining the atmospheric temperature-pressure (TP) profile of exoplanets is an important step forward for improving planetary atmosphere models, thus further enabling one to place the detection of spectral features and the measurement of atomic and molecular abundances through transmission and emission spectroscopy on solid ground. Aims. The aim is to constrain the TP profile of the ultra-hot Jupiter KELT-9b by fitting synthetic spectra to the observed Hα and Hβ lines and identify why self-consistent planetary TP models are unable to fit the observations. Methods. We constructed 126 one-dimensional TP profiles varying the lower and upper atmospheric temperatures, as well as the location and gradient of the temperature rise. For each TP profile, we computed the transmission spectra of the Hα and Hβ lines employing the Cloudy radiative transfer code, which self-consistently accounts for non-local thermodynamic equilibrium (NLTE) effects. Results. The TP profiles, leading to best fit the observations, are characterised by an upper atmospheric temperature of 10 000–11 000 K and by an inverted temperature profile at pressures higher than 10−4 bar. We find that the assumption of local thermodynamic equilibrium (LTE) leads one to overestimate the level population of excited hydrogen by several orders of magnitude and hence to significantly overestimate the strength of the Balmer lines. The chemical composition of the best fitting models indicate that the high upper atmospheric temperature is most likely driven by metal photoionisation and that FeII and FeIII have comparable abundances at pressures lower than 10−6 bar, possibly making the latter detectable. Conclusions. Modelling the atmospheres of ultra-hot Jupiters requires one to account for metal photoionisation. The high atmospheric mass-loss rate (>1011 g s−1), caused by the high temperature, may have consequences on the planetary atmospheric evolution. Other ultra-hot Jupiters orbiting early-type stars may be characterised by similarly high upper atmospheric temperatures and hence high mass-loss rates. This may have consequences on the basic properties of the observed planets orbiting hot stars.

Context. Exoplanetary upper atmospheres are low density environments where radiative processes can compete with collisional ones and introduce non-local thermodynamic equilibrium (NLTE) effects into transmission spectra.Aims. We develop a NLTE radiative transfer framework capable of modelling exoplanetary transmission spectra over a wide range of planetary properties.Methods. We adapted the NLTE spectral synthesis code Cloudy to produce an atmospheric structure and atomic transmission spectrum in both NLTE and local thermodynamic equilibrium (LTE) for the hot Jupiter HD 209458b, given a published T-P profile and assuming solar metallicity. Selected spectral features, including H alpha, NaI D, HeI lambda 10 830, FeI andII ultra-violet (UV) bands, and C, O, and Si UV lines, are compared with literature observations and models where available. The strength of NLTE effects are measured for individual spectral lines to identify which features are most strongly affected.Results. The developed modelling framework that computes NLTE synthetic spectra reproduces literature results for the HeI lambda 10 830 triplet, the NaI D lines, and the forest of FeI lines in the optical. Individual spectral lines in the NLTE spectrum exhibit up to 40% stronger absorption relative to the LTE spectrum.

Nitrogen is a biosignature gas that cannot be maintained in its Earth‐like ratio with CO 2 under abiotic conditions. It has also been proven to be notoriously hard to detect at optical and infrared wavelengths. Fortunately, the ultraviolet region, which has only recently started being explored for terrestrial exoplanets, may provide new opportunities to characterize exoplanetary atmospheric nitrogen. In this work, the future prospects for detecting atomic nitrogen absorption lines in the transmission spectrum of an Earth‐like planet orbiting in the habitable zone of a Sun‐like star with LUVOIR are explored. Using the nonlocal thermodynamic equilibrium spectral synthesis code Cloudy, we produce a far‐ultraviolet atomic transmission spectrum for an Earth–Sun‐like system and identify several nitrogen features, including both Ni and Nii lines. We calculate the number of transits required for 1 σ and 3 σ detections of the planetary Ni λ 1200 triplet signal with the G120M grating of the LUMOS spectrograph designed for LUVOIR as a function of distance to the system and stellar ultraviolet emission. The minimum number of transit observations necessary for 1 σ and 3 σ detections of atomic N are 188 and 1,685, respectively, for a system located at a distance of 1 pc with 100 times the solar ultraviolet flux. Given that the orbital period of an Earth–Sun system is 1 year, it is not feasible to detect atomic N in the transmission spectrum for these systems. Future studies in this direction should therefore focus on Earth‐like planets orbiting in the habitable zone of M dwarfs.

Extremely irradiated, close-in planets to early-type stars might be prone to strong atmospheric escape. We review the literature showing that X-ray-to-optical measurements indicate that for intermediate-mass stars (IMSs) cooler than ≈8250 K, the X-ray and extreme-ultraviolet (XUV) fluxes are on average significantly higher than those of solar-like stars, while for hotter IMSs, because of the lack of surface convection, it is the opposite. We construct spectral energy distributions for prototypical IMSs, comparing them to solar. The XUV fluxes relevant for upper-planet atmospheric heating are highest for the cooler IMSs and lowest for the hotter IMSs, while the ultraviolet (UV) fluxes increase with increasing stellar temperature. We quantify the influence of this characteristic of the stellar fluxes on the mass loss of close-in planets by simulating the atmospheres of planets orbiting EUV-bright (WASP-33) and EUV-faint (KELT-9) A-type stars. For KELT-9b, we find that atmospheric expansion caused by heating due to absorption of the stellar UV and optical light drives mass-loss rates of ≈10 11 g s −1 , while heating caused by absorption of the stellar XUV radiation leads to mass-loss rates of ≈10 10 g s −1 , thus underestimating mass loss. For WASP-33b, the high XUV stellar fluxes lead to mass-loss rates of ≈10 11 g s −1 . Even higher mass-loss rates are possible for less massive planets orbiting EUV-bright IMSs. We argue that it is the weak XUV stellar emission, combined with a relatively high planetary mass, which limit planetary mass-loss rates, to allow the prolonged existence of KELT-9-like systems.