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Neutral sodium (Na I) is an alkali metal with a favorable absorption cross section such that tenuous gases are easily illuminated at select transiting exoplanet systems. We examine both the time-averaged and time-series alkali spectral flux individually, over 4 nights at a hot Saturn system on a $\sim$ 2.8 day orbit about a Sun-like star WASP-49 A. Very Large Telescope/ESPRESSO observations are analyzed, providing new constraints. We recover the previously confirmed residual sodium flux uniquely when averaged, whereas night-to-night Na I varies by more than an order of magnitude. On HARPS/3.6-m Epoch II, we report a Doppler redshift at $v_{ \Gamma, \mathrm{NaD}} =$ +9.7 $\pm$ 1.6 km/s with respect to the planet's rest frame. Upon examining the lightcurves, we confirm night-to-night variability, on the order of $\sim$ 1-4 % in NaD rarely coinciding with exoplanet transit, not readily explained by stellar activity, starspots, tellurics, or the interstellar medium. Coincident with the $\sim$+10 km/s Doppler redshift, we detect a transient sodium absorption event dF$_{\mathrm{NaD}}$/F$_{\star}$ = 3.6 $\pm$ 1 % at a relative difference of $\Delta F_{\mathrm{NaD}} (t) \sim$ 4.4 $\pm$ 1 %, enduring $\Delta t_{\mathrm{NaD}} \gtrsim$ 40 minutes. Since exoplanetary alkali signatures are blueshifted due to the natural vector of radiation pressure, estimated here at roughly $\sim$ -5.7 km/s, the radial velocity is rather at +15.4 km/s, far larger than any known exoplanet system. Given that the redshift magnitude v$_{\Gamma}$ is in between the Roche limit and dynamically stable satellite orbits, the transient sodium may be a putative indication of a natural satellite orbiting WASP-49 A b., Comment: Accepted to ApJ Letters (2024 August 2)

Warm Jupiters are ideal laboratories for testing the limitations of current tools for atmospheric studies. The cross-correlation technique is a commonly used method to investigate the atmospheres of close-in planets, leveraging their large orbital velocities to separate the spectrum of the planet from that of the star. Warm Jupiter atmospheres predominantly consist of molecular species, notably water, methane and carbon monoxide, often accompanied by clouds and hazes muting their atmospheric features. In this study, we investigate the atmospheres of six warm Jupiters K2-139 b, K2-329 b, TOI- 3362 b, WASP-130 b, WASP-106 b, and TOI-677 b to search for water absorption using the ESPRESSO spectrograph, reporting non-detections for all targets. These non-detections are partially attributed to planets having in-transit radial velocity changes that are typically too small to distinguish between the different components (star, planet, Rossiter-McLaughlin effect and telluric contamination), as well as the relatively weak planetary absorption lines as compared to the S/N of the spectra. We simulate observations for the upcoming high-resolution spectrograph ANDES at the Extremely Large Telescope for the two favourable planets on eccentric orbits, TOI-3362b and TOI-677 b, searching for water, carbon monoxide, and methane. We predict a significant detection of water and CO, if ANDES indeed covers the K-band, in the atmospheres of TOI-677 b and a tentative detection of water in the atmosphere of TOI-3362b. This suggests that planets on highly eccentric orbits with favourable orbital configurations present a unique opportunity to access cooler atmospheres., Comment: 20 pages, 11 figures, accepted for publication in AJ

The Near-InfraRed Planet Searcher or NIRPS is a precision radial velocity spectrograph developed through collaborative efforts among laboratories in Switzerland, Canada, Brazil, France, Portugal and Spain. NIRPS extends to the 0.98-1.8 $\mu$m domain of the pioneering HARPS instrument at the La Silla 3.6-m telescope in Chile and it has achieved unparalleled precision, measuring stellar radial velocities in the infrared with accuracy better than 1 m/s. NIRPS can be used either stand-alone or simultaneously with HARPS. Commissioned in late 2022 and early 2023, NIRPS embarked on a 5-year Guaranteed Time Observation (GTO) program in April 2023, spanning 720 observing nights. This program focuses on planetary systems around M dwarfs, encompassing both the immediate solar vicinity and transit follow-ups, alongside transit and emission spectroscopy observations. We highlight NIRPS's current performances and the insights gained during its deployment at the telescope. The lessons learned and successes achieved contribute to the ongoing advancement of precision radial velocity measurements and high spectral fidelity, further solidifying NIRPS' role in the forefront of the field of exoplanets., Comment: Proceeding at the SPIE Astronomical Telescopes + Instrumentation conference [Yokohama,Japan; June 2024]

We search for excess in-transit absorption of neutral helium at 1.083 $\mu$m in the atmospheres of the young (<800 Myr) sub-Jovian (0.2-0.5 $\rm R_{J}$) planets HD 63433b, K2-100b, and V1298 Tau c using high-resolution (R~25,000) transit observations taken with Keck II/NIRSPEC. Our observations do not show evidence of helium absorption for any of the planets in our sample. We calculate 3$\sigma$ upper limits on the planets' excess helium absorption of <0.47% for HD 63433b, <0.56% for K2-100b, and <1.13% for V1298 Tau c. In terms of equivalent width, we constrain these to <2.52, <4.44, and <8.49 mA for HD 63433b, K2-100b, and V1298 Tau c, respectively. We fit our transmission spectra with one-dimensional Parker wind models to determine upper limits on the planets' mass-loss rates of <7.9$\times10^{10}$, <1.25$\times10^{11}$, and <$7.9\times10^{11}$g s$^{-1}$. Our non-detections align with expectations from one-dimensional hydrodynamic escape models, magnetic fields, and stellar wind confinement. The upper limits we measure for these planets are consistent with predicted trends in system age and He equivalent width from 1D hydrodynamic models., Comment: 24 pages, 14 figures, accepted for publication in The Astronomical Journal

The Atacama desert stands as the most arid, non-polar, region on Earth and has accommodated a considerable portion of the world's ground-based astronomical observatories for an extended period. The comprehension of factors important for observational conditions in this region, and the potential alterations induced by the escalating impact of climate change, are, therefore, of the utmost significance. In this study, we conduct an analysis of the surface-level air temperature, water vapour density, and astronomical seeing at the European Southern Observatory (commonly known by its acronym, ESO) telescope sites in northern Chile. Our findings reveal a discernible rise in temperature across all sites during the last decade. Moreover, we establish a correlation between the air temperature and water vapour density with the El Ni\~no Southern Oscillation (ENSO) phases, wherein, the warm anomaly known as El Ni\~no (EN) corresponds to drier observing conditions, coupled with higher maximum daily temperatures favouring more challenging near-infrared observations. The outcomes of this investigation have potential implications for the enhancement of the long-term scheduling of observations at telescope sites in northern Chile, thereby aiding in better planning and allocation of resources for the astronomy community., Comment: Accepted for publication in Atmospheres (ISSN: 2073-4433) on Sept 17, 2023, 19 pages, 2 appendices, 7 Figures, 3 Tables

The Hunga Tonga-Hunga Ha'apai volcano erupted on 15 January 2022 with an energy equivalent to around 61 megatons of TNT. The explosion was bigger than any other volcanic eruption so far in the 21st century. Huge quantities of particles, including dust and water vapour, were released into the atmosphere. We present the results of a preliminary study of the effects of the explosion on observations taken at Paranal Observatory using a range of instruments. These effects were not immediately transitory in nature, and a year later stunning sunsets are still being seen at Paranal., Comment: 4 pages, 5 figures, published in ESO Messenger vol. 190

KELT-11b is an inflated sub-Saturn with a hot atmosphere and that orbits a bright evolved subgiant star, making it a prime choice for atmospheric characterization, but that transits its host star for more than seven hours. We observed this system in series of three consecutive nights with the HARPS spectrograph and report on the analysis of the transmission spectrum obtained from this dataset. Our results highlight the potential for independent observations of a long-transiting planet over consecutive nights. Our study reveals a sodium excess absorption of $0.28 \pm 0.05 \%$ and $0.50 \pm 0.06 \%$ in the Na D1 and D2 lines, respectively. This corresponds to 1.44 and 1.69 times the white-light planet radius in the line cores. Wind pattern modeling tends to prefer day-to-night side winds with no vertical winds, which is surprising considering the planet bloatedness. The modeling of the Rossiter-Mclaughlin effect yields a significantly misaligned orbit, with a projected spin-orbit angle of ${\lambda} = -77.86^{+2.36}_{-2.26}{}^\circ$. The characteristics of KELT-11 b, notably its extreme scale height and long transit, make it an ideal and unique target for next-generation telescopes. Our results as well as recent findings from HST, TESS, and CHEOPS observations could make KELT-11 b a benchmark exoplanet in atmospheric characterization., Comment: 19 pages, 18 figures, 8 tables. Accepted for publication in Astronomy & Astrophysics

Ultra-hot Jupiters (UHJs), rendering the hottest planetary atmospheres, offer great opportunities of detailed characterisation with high-resolution spectroscopy. MASCARA-4 b is a recently discovered close-in gas giant belonging to this category. In order to refine system and planet parameters, we carried out radial velocity measurements and transit photometry with the CORALIE spectrograph and EulerCam at the Swiss 1.2m Euler telescope. We observed two transits of MASCARA-4 b with the high-resolution spectrograph ESPRESSO at ESO's Very Large Telescope. We searched for atomic, ionic, and molecular species via individual absorption lines and cross-correlation techniques. These results are compared to literature studies on UHJs characterised to date. With CORALIE and EulerCam observations, we updated the mass of MASCARA-4 b (1.675 +/- 0.241 Jupiter masses) as well as other system and planet parameters. In the transmission spectrum derived from ESPRESSO observations, we resolve excess absorption by H$\alpha$, H$\beta$, Na D1 & D2, Ca+ H & K, and a few strong individual lines of Mg, Fe and Fe+. We also present the cross-correlation detection of Mg, Ca, Cr, Fe and Fe+. The absorption strength of Fe+ significantly exceeds the prediction from a hydrostatic atmospheric model, as commonly observed in other UHJs. We attribute this to the presence of Fe+ in the exosphere due to hydrodynamic outflows. This is further supported by the positive correlation of absorption strengths of Fe+ with the H$\alpha$ line. Comparing transmission signatures of various species in the UHJ population allows us to disentangle the hydrostatic regime (as traced via the absorption by Mg and Fe) from the exospheres (as probed by H$\alpha$ and Fe+) of the strongly irradiated atmospheres., Comment: 13 pages, 9 figures, accepted to A&A

The ESPRESSO spectrograph at ESO's Very Large Telescope (VLT) has, since it began science operations in October 2018, revolutionised exoplanet science. The combination of the large VLT mirrors and the high resolution and stability of the spectrograph is enabling the detection of small, low-mass planets as well as detailed studies of the planets' atmospheres. In this article, we present a brief overview of the first results from ESPRESSO and a hopeful glimpse towards the ultimate goal of reaching the radial velocity precision of 10 cm/s needed to detect an Earth-like planet., Comment: Published in the ESO messenger #187: https://www.eso.org/sci/publications/messenger/archive/no.187-jun22/messenger-no187-8-11.pdf

The temperature of an atmosphere decreases with increasing altitude, unless a shortwave absorber exists that causes a temperature inversion. Ozone plays this role in the Earth`s atmosphere. In the atmospheres of highly irradiated exoplanets, shortwave absorbers are predicted to be titanium oxide (TiO) and vanadium oxide (VO). Detections of TiO and VO have been claimed using both low and high spectral resolution observations, but later observations have failed to confirm these claims or overturned them. Here we report the unambiguous detection of TiO in the ultra-hot Jupiter WASP-189b using high-resolution transmission spectroscopy. This detection is based on applying the cross-correlation technique to many spectral lines of TiO from 460 to 690 nm. Moreover, we report detections of metals, including neutral and singly ionised iron and titanium, as well as chromium, magnesium, vanadium and manganese (Fe, Fe+, Ti, Ti+, Cr, Mg, V, Mn). The line positions of the detected species differ, which we interpret as a consequence of spatial gradients in their chemical abundances, such that they exist in different regions or dynamical regimes. This is direct observational evidence for the three-dimensional thermo-chemical stratification of an exoplanet atmosphere derived from high-resolution ground-based spectroscopy., Comment: Published in Nature Astronomy on 27 January 2022, accepted on 1 December 2021 (32 pages, 21 figures, 3 tables)

Atmospheric escape is considered to be one of the main channels for evolution in sub-Jovian planets, particularly in their early lives. While there are several hypotheses proposed to explain escape in exoplanets, testing them with atmospheric observations remains a challenge. In this context, high-resolution transmission spectroscopy of transiting exoplanets for the metastable helium triplet (He 2$^3$S) at $1\,083$ nm has emerged as a reliable technique to observe and measure escape. To aid in the prediction and interpretation of metastable He transmission spectroscopy observations, we developed the code p-winds. This is an open-source, fully documented, scalable Python implementation of the one-dimensional, purely H+He Parker wind model for upper atmospheres coupled with ionization balance, ray-tracing, and radiative transfer routines. We demonstrate an atmospheric retrieval by fitting p-winds models to the observed metastable He transmission spectrum of the warm Neptune HAT-P-11 b, and take into account the variation of the in-transit absorption caused by transit geometry. For this planet, our best fit yields a total atmospheric escape rate of approximately $2.5 \times 10^{10}$ g s$^{-1}$ and wind temperature of $7200$ K. The range of retrieved mass loss rates increases significantly when we let the H atom fraction be a free parameter, but the posterior distribution of the latter remains unconstrained by He observations alone. The stellar host limb darkening does not have a significant impact in the retrieved escape rate or outflow temperature for HAT-P-11 b. Based on the non-detection of escaping He for GJ 436 b, we are able to rule out total escape rates higher than $3.4 \times 10^{10}$ g s$^{-1}$ at 99.7% (3$\sigma$) confidence., Comment: 13 pages, 12 figures. Accepted for publication in Astronomy & Astrophysics. We encourage the community to send comments and test the code, which is openly available at https://github.com/ladsantos/p-winds

We report the discovery of the massive hot Jupiter NGTS-13b by the Next Generation Transit Survey (NGTS). The V = 12.7 host star is likely in the subgiant evolutionary phase with log g$_{*}$ = 4.04 $\pm$ 0.05, T$_{eff}$ = 5819 $\pm$ 73 K, M$_{*}$ = 1.30$^{+0.11}_{-0.18}$ M$_{\odot}$, and R$_{*}$ = 1.79 $\pm$ 0.06 R$_{\odot}$. NGTS detected a transiting planet with a period of P = 4.12 days around the star, which was later validated with the Transiting Exoplanet Survey Satellite (TESS; TIC 454069765). We confirm the planet using radial velocities from the CORALIE spectrograph. Using NGTS and TESS full-frame image photometry combined with CORALIE radial velocities we determine NGTS-13b to have a radius of R$_{P}$ = 1.142 $\pm$ 0.046 R$_{Jup}$, mass of M$_{P}$ = 4.84 $\pm$ 0.44 M$_{Jup}$ and eccentricity e = 0.086 $\pm$ 0.034. Some previous studies suggest that $\sim$4 M$_{Jup}$ may be a border between two separate formation scenarios (e.g., core accretion and disk instability) and that massive giant planets share similar formation mechanisms as lower-mass brown dwarfs. NGTS-13b is just above 4 M$_{Jup}$ making it an important addition to the statistical sample needed to understand the differences between various classes of substellar companions. The high metallicity, [Fe/H] = 0.25 $\pm$ 0.17, of NGTS-13 does not support previous suggestions that massive giants are found preferentially around lower metallicity host stars, but NGTS-13b does support findings that more massive and evolved hosts may have a higher occurrence of close-in massive planets than lower-mass unevolved stars., Comment: 11 pages, 9 figures, 4 tables, accepted by Astronomy & Astrophysics

We present the discovery and characterization of five hot and warm Jupiters -- TOI-628 b (TIC 281408474; HD 288842), TOI-640 b (TIC 147977348), TOI-1333 b (TIC 395171208, BD+47 3521A), TOI-1478 b (TIC 409794137), and TOI-1601 b (TIC 139375960) -- based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The five planets were identified from the full frame images and were confirmed through a series of photometric and spectroscopic follow-up observations by the $TESS$ Follow-up Observing Program (TFOP) Working Group. The planets are all Jovian size (R$_{\rm P}$ = 1.01-1.77 R$_{\rm J}$) and have masses that range from 0.85 to 6.33 M$_{\rm J}$. The host stars of these systems have F and G spectral types (5595 $\le$ T$_{\rm eff}$ $\le$ 6460 K) and are all relatively bright (9 $ 1.7R$_{\rm J}$, possibly a result of its host star's evolution) and resides on an orbit with a period longer than 5 days. TOI-628 b is the most massive hot Jupiter discovered to date by $TESS$ with a measured mass of $6.31^{+0.28}_{-0.30}$ M$_{\rm J}$ and a statistically significant, non-zero orbital eccentricity of e = $0.074^{+0.021}_{-0.022}$. This planet would not have had enough time to circularize through tidal forces from our analysis, suggesting that it might be remnant eccentricity from its migration. The longest period planet in this sample, TOI-1478 b (P = 10.18 days), is a warm Jupiter in a circular orbit around a near-Solar analogue. NASA's $TESS$ mission is continuing to increase the sample of well-characterized hot and warm Jupiters, complementing its primary mission goals., Comment: 25 Pages, 7 Figures, 5 Tables, Accepted to The Astronomical Journal

We report the detection of a transiting hot Neptune exoplanet orbiting TOI-824 (SCR J1448-5735), a nearby (d = 64 pc) K4V star, using data from the \textit{Transiting Exoplanet Survey Satellite} (TESS). The newly discovered planet has a radius, $R_{\rm{p}}$ = 2.93 $\pm$ 0.20 R$_{\oplus}$, and an orbital period of 1.393 days. Radial velocity measurements using the Planet Finder Spectrograph (PFS) and the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph confirm the existence of the planet and we estimate its mass to be $M_{\rm{p}}$ = 18.47 $\pm$ 1.84 M$_{\oplus}$. The planet's mean density is $\rho_{\rm{p}}$ = 4.03$^{+0.98}_{-0.78}$ g cm$^{-3}$ making it more than twice as dense as Neptune. TOI-824 b's high equilibrium temperature makes the planet likely to have a cloud free atmosphere, and thus an excellent candidate for follow up atmospheric studies. The detectability of TOI-824 b's atmosphere from both ground and space is promising and could lead to the detailed characterization of the most irradiated, small planet at the edge of the hot Neptune desert that has retained its atmosphere to date., Comment: 22 pages, 10 figures. Accepted for publication in the Astronomical Journal

The Transiting Exoplanet Survey Satellite mission was designed to find transiting planets around bright, nearby stars. Here we present the detection and mass measurement of a small, short-period ($\approx\,4$\,days) transiting planet around the bright ($V=7.9$), solar-type star HD 86226 (TOI-652, TIC 22221375), previously known to host a long-period ($\sim$1600 days) giant planet. HD 86226c (TOI-652.01) has a radius of $2.16\pm0.08$ $R_{\oplus}$ and a mass of 7.25$^{+1.19}_{-1.12}$ $M_{\oplus}$ based on archival and new radial velocity data. We also update the parameters of the longer-period, not-known-to-transit planet, and find it to be less eccentric and less massive than previously reported. The density of the transiting planet is $3.97$ g cm$^{-3}$, which is low enough to suggest that the planet has at least a small volatile envelope, but the mass fractions of rock, iron, and water are not well-constrained. Given the host star brightness, planet period, and location of the planet near both the ``radius gap'' and the ``hot Neptune desert'', HD 86226c is an interesting candidate for transmission spectroscopy to further refine its composition., Comment: Accepted in AJ on 22 June 2020

Large-scale exoplanet search surveys have shown evidence that atmospheric escape is a ubiquitous process that shapes the evolution and demographics of planets. However, we lack a detailed understanding of this process because very few exoplanets discovered to date could be probed for signatures of atmospheric escape. Recently, the metastable helium triplet at 1.083 $\mu$m has been shown to be a viable window for the presence of He-rich escaping envelopes around short-period exoplanets. Our objective is to use, for the first time, the Phoenix spectrograph to search for helium in the upper atmosphere of the inflated hot Jupiter WASP-127 b. We observed one transit and reduced the data manually since there is no pipeline available. We did not find a significant in-transit absorption signal indicative of the presence of helium around WASP-127 b, and set a 90% confidence upper limit for excess absorption at 0.87% in a 0.075 nm passband covering the He triplet. Given the large scale height of this planet, the lack of a detectable feature is likely due to unfavorable photoionization conditions to populate the metastable He triplet. This conclusion is supported by the inferred low coronal and chromospheric activity of the host star and the old age of the system, which result in a relatively mild high-energy environment around the planet., Comment: 5 pages, 5 figures, accepted for publication in Astronomy & Astrophysics, v2 with editorial revision

Ultra-hot giant exoplanets receive thousands of times Earth's insolation. Their high-temperature atmospheres (>2,000 K) are ideal laboratories for studying extreme planetary climates and chemistry. Daysides are predicted to be cloud-free, dominated by atomic species and substantially hotter than nightsides. Atoms are expected to recombine into molecules over the nightside, resulting in different day-night chemistry. While metallic elements and a large temperature contrast have been observed, no chemical gradient has been measured across the surface of such an exoplanet. Different atmospheric chemistry between the day-to-night ("evening") and night-to-day ("morning") terminators could, however, be revealed as an asymmetric absorption signature during transit. Here, we report the detection of an asymmetric atmospheric signature in the ultra-hot exoplanet WASP-76b. We spectrally and temporally resolve this signature thanks to the combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by -11+/-0.7 km s-1 on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside. In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. Iron must thus condense during its journey across the nightside., Comment: Published in Nature (Accepted on 24 January 2020.) 33 pages, 11 figures, 3 tables

We report the discovery of two intermediate-mass brown dwarfs (BDs), TOI-569b and TOI-1406b, from NASA's Transiting Exoplanet Survey Satellite mission. TOI-569b has an orbital period of $P = 6.55604 \pm 0.00016$ days, a mass of $M_b = 64.1 \pm 1.9 M_J$, and a radius of $R_b = 0.75 \pm 0.02 R_J$. Its host star, TOI-569, has a mass of $M_\star = 1.21 \pm 0.03 M_\odot$, a radius of $R_\star = 1.47 \pm 0.03 R_\odot$, $\rm [Fe/H] = +0.29 \pm 0.09$ dex, and an effective temperature of $T_{\rm eff} = 5768 \pm 110K$. TOI-1406b has an orbital period of $P = 10.57415 \pm 0.00063$ days, a mass of $M_b =46.0 \pm 2.7 M_J$, and a radius of $R_b = 0.86 \pm 0.03 R_J$. The host star for this BD has a mass of $M_\star =1 .18 \pm 0.09 M_\odot$, a radius of $R_\star = 1.35 \pm 0.03 R_\odot$, $ \rm [Fe/H] = -0.08 \pm 0.09$ dex and an effective temperature of $T_{\rm eff} = 6290 \pm 100K$. Both BDs are in circular orbits around their host stars and are older than 3 Gyr based on stellar isochrone models of the stars. TOI-569 is one of two slightly evolved stars known to host a transiting BD (the other being KOI-415). TOI-1406b is one of three known transiting BDs to occupy the mass range of $40-50 M_J$ and one of two to have a circular orbit at a period near 10 days (with the first being KOI-205b).Both BDs have reliable ages from stellar isochrones in addition to their well-constrained masses and radii, making them particularly valuable as tests for substellar isochrones in the BD mass-radius diagram., Comment: 18 pages, 10 figures, 8 tables, accepted for publication in AJ