Search

Observing exoplanets through transmission spectroscopy supplies detailed information on their atmospheric composition, physics, and chemistry. Prior to JWST, these observations were limited to a narrow wavelength range across the near-ultraviolet to near-infrared, alongside broadband photometry at longer wavelengths. To understand more complex properties of exoplanet atmospheres, improved wavelength coverage and resolution are necessary to robustly quantify the influence of a broader range of absorbing molecular species. Here we present a combined analysis of JWST transmission spectroscopy across four different instrumental modes spanning 0.5-5.2 micron using Early Release Science observations of the Saturn-mass exoplanet WASP-39b. Our uniform analysis constrains the orbital and stellar parameters within sub-percent precision, including matching the precision obtained by the most precise asteroseismology measurements of stellar density to-date, and further confirms the presence of Na, K, H$_2$O, CO, CO$_2$, and SO$_2$ atmospheric absorbers. Through this process, we also improve the agreement between the transmission spectra of all modes, except for the NIRSpec PRISM, which is affected by partial saturation of the detector. This work provides strong evidence that uniform light curve analysis is an important aspect to ensuring reliability when comparing the high-precision transmission spectra provided by JWST., Comment: 34 pages, 11 figures, 3 tables. Nat Astron (2024)

We validate the Transiting Exoplanet Survey Satellite (TESS) object of interest TOI-2266.01 (TIC 348911) as a small transiting planet (most likely a super-Earth) orbiting a faint M5 dwarf ($V=16.54$) on a 2.33~d orbit. The validation is based on an approach where multicolour transit light curves are used to robustly estimate the upper limit of the transiting object's radius. Our analysis uses SPOC-pipeline TESS light curves from Sectors 24, 25, 51, and 52, simultaneous multicolour transit photometry observed with MuSCAT2, MuSCAT3, and HiPERCAM, and additional transit photometry observed with the LCOGT telescopes. TOI-2266 b is found to be a planet with a radius of $1.54\pm\0.09\,R_\oplus$, which locates it at the edge of the transition zone between rocky planets, water-rich planets, and sub-Neptunes (the so-called M~dwarf radius valley). The planet is amenable to ground-based radial velocity mass measurement with red-sensitive spectrographs installed in large telescopes, such as MAROON-X and Keck Planet Finder (KPF), which makes it a valuable addition to a relatively small population of planets that can be used to probe the physics of the transition zone. Further, the planet's orbital period of 2.33 days places it inside a `keystone planet' wedge in the period-radius plane where competing planet formation scenarios make conflicting predictions on how the radius valley depends on the orbital period. This makes the planet also a welcome addition to the small population of planets that can be used to test small-planet formation scenarios around M~dwarfs., Comment: Accepted to A&A

Icy grain mantles are the main reservoir of the volatile elements that link chemical processes in dark, interstellar clouds with the formation of planets and composition of their atmospheres. The initial ice composition is set in the cold, dense parts of molecular clouds, prior to the onset of star formation. With the exquisite sensitivity of JWST, this critical stage of ice evolution is now accessible for detailed study. Here we show the first results of the Early Release Science program "Ice Age" that reveal the rich composition of these dense cloud ices. Weak ices, including, $^{13}$CO$_2$, OCN$^-$, $^{13}$CO, OCS, and COMs functional groups are now detected along two pre-stellar lines of sight. The $^{12}$CO$_2$ ice profile indicates modest growth of the icy grains. Column densities of the major and minor ice species indicate that ices contribute between 2 and 19% of the bulk budgets of the key C, O, N, and S elements. Our results suggest that the formation of simple and complex molecules could begin early in a water-ice rich environment., Comment: To appear in Nature Astronomy on January 23rd, 2023. 33 pages, 16 figures, 3 tables; includes extended and supplemental data sections. Part of the JWST Ice Age Early Release Science program's science enabling products. Enhanced spectra downloadable on Zenodo at the following DOI: 10.5281/zenodo.7501239

Transmission spectroscopy of exoplanets has revealed signatures of water vapor, aerosols, and alkali metals in a few dozen exoplanet atmospheres. However, these previous inferences with the Hubble and Spitzer Space Telescopes were hindered by the observations' relatively narrow wavelength range and spectral resolving power, which precluded the unambiguous identification of other chemical species$-$in particular the primary carbon-bearing molecules. Here we report a broad-wavelength 0.5-5.5 $\mu$m atmospheric transmission spectrum of WASP-39 b, a 1200 K, roughly Saturn-mass, Jupiter-radius exoplanet, measured with JWST NIRSpec's PRISM mode as part of the JWST Transiting Exoplanet Community Early Release Science Team program. We robustly detect multiple chemical species at high significance, including Na (19$\sigma$), H$_2$O (33$\sigma$), CO$_2$ (28$\sigma$), and CO (7$\sigma$). The non-detection of CH$_4$, combined with a strong CO$_2$ feature, favours atmospheric models with a super-solar atmospheric metallicity. An unanticipated absorption feature at 4$\mu$m is best explained by SO$_2$ (2.7$\sigma$), which could be a tracer of atmospheric photochemistry. These observations demonstrate JWST's sensitivity to a rich diversity of exoplanet compositions and chemical processes., Comment: 41 pages, 4 main figures, 10 extended data figures, 4 tables. Under review in Nature

The ExoClock project has been created with the aim of increasing the efficiency of the Ariel mission. It will achieve this by continuously monitoring and updating the ephemerides of Ariel candidates over an extended period, in order to produce a consistent catalogue of reliable and precise ephemerides. This work presents a homogenous catalogue of updated ephemerides for 450 planets, generated by the integration of $\sim$18000 data points from multiple sources. These sources include observations from ground-based telescopes (ExoClock network and ETD), mid-time values from the literature and light-curves from space telescopes (Kepler/K2 and TESS). With all the above, we manage to collect observations for half of the post-discovery years (median), with data that have a median uncertainty less than one minute. In comparison with literature, the ephemerides generated by the project are more precise and less biased. More than 40\% of the initial literature ephemerides had to be updated to reach the goals of the project, as they were either of low precision or drifting. Moreover, the integrated approach of the project enables both the monitoring of the majority of the Ariel candidates (95\%), and also the identification of missing data. The dedicated ExoClock network effectively supports this task by contributing additional observations when a gap in the data is identified. These results highlight the need for continuous monitoring to increase the observing coverage of the candidate planets. Finally, the extended observing coverage of planets allows us to detect trends (TTVs - Transit Timing Variations) for a sample of 19 planets. All products, data, and codes used in this work are open and accessible to the wider scientific community., Comment: Recommended for publication to ApJS (reviewer's comments implemented). Main body: 13 pages, total: 77 pages, 7 figures, 7 tables. Data available at http://doi.org/10.17605/OSF.IO/P298N

We report the discovery and validation of two TESS exoplanets orbiting faint M dwarfs: TOI-4479b and TOI-2081b. We have jointly analyzed space (TESS mission) and ground based (MuSCAT2, MuSCAT3 and SINISTRO instruments) lightcurves using our multi-color photometry transit analysis pipeline. This allowed us to compute contamination limits for both candidates and validate them as planet-sized companions. We found TOI-4479b to be a sub-Neptune-sized planet ($R_{p}=2.82^{+0.65}_{-0.63}~\rm R_{\oplus}$) and TOI-2081b to be a super-Earth-sized planet ($R_{p}=2.04^{+0.50}_{-0.54}~\rm R_{\oplus}$). Furthermore, we obtained that TOI-4479b, with a short orbital period of $1.15890^{+0.00002}_{-0.00001}~\rm days$, lies within the Neptune desert and is in fact the largest nearly ultra-short period planet around an M dwarf known to date. These results make TOI-4479b rare among the currently known exoplanet population around M dwarf stars, and an especially interesting target for spectroscopic follow-up and future studies of planet formation and evolution., Comment: Accepted for publication in Astronomy&Astrophysics

The NASA space telescope $TESS$ is currently in the extended mission of its all-sky search for new transiting planets. Of the thousands of candidates that TESS is expected to deliver, transiting planets orbiting nearby M dwarfs are particularly interesting targets since they provide a great opportunity to characterize their atmospheres by transmission spectroscopy. We aim to validate and characterize the new sub-Neptune-sized planet candidate TOI-2136.01 orbiting a nearby M dwarf ($d = 33.36 \pm 0.02$ pc, $T_{eff} = 3373 \pm 108$ K) with an orbital period of 7.852 days. We use TESS data, ground-based multicolor photometry, and radial velocity measurements with the InfraRed Doppler (IRD) instrument on the Subaru Telescope to validate the planetary nature of TOI-2136.01 and estimate the stellar and planetary parameters. We also conduct high-resolution transmission spectroscopy to search for helium in its atmosphere. We confirmed that TOI-2136.01 (now named as TOI-2136b) is a bona fide planet with a planetary radius of $R_p = 2.2 \pm 0.07$ $R_{Earth}$ and a mass of $M_p = 4.7^{+3.1}_{-2.6}$ $M_{Earth}$. We also search for helium 10830 \r{A} absorption lines and place an upper limit on the equivalent width of $<$ 7.8 m\r{A} and on the absorption signal of $<$ 1.44 % with 95 % confidence. TOI-2136b is a sub-Neptune transiting a nearby and bright star (J=10.8) and is a potentially hycean planet, which is a new class of habitable planets with large oceans under a H$_2$-rich atmosphere, making it an excellent target for atmospheric studies to understand the formation, evolution, and habitability of the small planets., Comment: 19 pages, 16 figures, accepted for publication in Astronomy & Astrophysics

Context. Exoplanets with orbital periods of less than one day are known as ultra-short period (USP) planets. They are relatively rare products of planetary formation and evolution processes, but especially favourable for characterisation with current planet detection methods. At the time of writing, 125 USP planets have already been confirmed. Aims. Our aim is to validate the planetary nature of two new transiting planet candidates around M dwarfs announced by the NASA Transiting Exoplanet Survey Satellite (TESS), registered as TESS Objects of Interest (TOIs) TOI-1442.01 and TOI-2445.01. Methods. We used TESS data, ground-based photometric light curves, and Subaru/IRD spectrograph radial velocity (RV) measurements to validate both planetary candidates and to establish their physical properties. Results. TOI-1442 b is a validated exoplanet with an orbital period of $P$=0.4090682+/-0.0000004 d, a radius of $R_p$=1.15+/-0.06$R_{\oplus}$, and equilibrium temperature of $T_{p,eq}$=1357$_{-42}^{+49}$K. TOI-2445 b is also validated with an orbital period of $P$=0.3711286+/-0.0000004 d, a radius of $R_p$= 1.33+/-0.09$R_{\oplus}$, and equilibrium temperature of $T_{p,eq}$=1330$_{-56}^{+61}$K. Their physical properties align with current empirical trends and formation theories of USP planets. Based on the RV measurements, we set 3$\sigma$ upper mass limits of 8$M_{\oplus}$ and 20$M_{\oplus}$, thus confirming the non-stellar, sub-Jovian nature of both transiting objects. More RV measurements will be needed to constrain the planetary masses and mean densities, and the predicted presence of outer planetary companions. These targets extend the small sample of USP planets orbiting around M dwarfs up to 21 members. They are also among the 20 most suitable terrestrial planets for atmospheric characterisation via secondary eclipse with the JWST, according to a widespread emission spectroscopy metric., Comment: Published in A&A, 18 pages, 6 tables, 8 figures

We present the discovery and characterisation of two transiting planets observed by \textit{TESS} in the light curves of the young and bright (V=9.67) star HD73583 (TOI-560). We perform an intensive spectroscopic and photometric space- and ground-based follow-up in order to confirm and characterise the system. We found that HD73583 is a young ($\sim 500$~Myr) active star with a rotational period of $12.08 \pm 0.11 $\,d, and a mass and radius of $ 0.73 \pm 0.02 M_\odot$ and $0.65 \pm 0.02 R_\odot$, respectively. HD73583 b ($P_b=6.3980420 _{ - 0.0000062 }^{+0.0000067}$ d) has a mass and radius of $10.2 _{-3.1}^{+3.4} M_\oplus$ and$2.79 \pm 0.10 R_\oplus$, respectively, that gives a density of $2.58 _{-0.81}^{ 0.95} {\rm g\,cm^{-3}}$. HD73583 c ($P_c= 18.87974 _{-0.00074 }^{+0.00086}$) has a mass and radius of $9.7_{-1.7} ^ {+1.8} M_\oplus$ and $2.39_{-0.09}^{+0.10} R_\oplus$, respectively, this translates to a density of $3.88 _{-0.80}^{+0.91} {\rm g\,cm^{-3}}$. Both planets are consistent with worlds made of a solid core surrounded by a volatile envelope. Because of their youth and host star brightness, they both are excellent candidates to perform transmission spectroscopy studies. We expect ongoing atmospheric mass-loss for both planets caused by stellar irradiation. We estimate that the detection of evaporating signatures on H and He would be challenging, but doable with present and future instruments., Comment: Accepted for publication in MNRAS

Up to now, WASP-12b is the only hot Jupiter confirmed to have a decaying orbit. The case of WASP-43b is still under debate. Recent studies preferred or ruled out the orbital decay scenario, but further precise transit timing observations are needed to definitively confirm or refute the period change of WASP-43b. This possibility is given by the Transiting Exoplanet Survey Satellite (TESS) space telescope. In this work we used the available TESS data, multi-color photometry data obtained with the Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets 2 (MuSCAT2) and literature data to calculate the period change rate of WASP-43b and to improve its precision, and to refine the parameters of the WASP-43 planetary system. Based on the observed-minus-calculated data of 129 mid-transit times in total, covering a time baseline of about 10 years, we obtained an improved period change rate of $\dot{P} = -0.6 \pm 1.2$ ms yr$^{-1}$ that is consistent with a constant period well within $1\sigma$. We conclude that new TESS and MuSCAT2 observations confirm no detection of WASP-43b orbital decay., Comment: 10 pages, 6 figures, accepted for publication in MNRAS

We report the discovery of one super-Earth- (TOI-1749b) and two sub-Neptune-sized planets (TOI-1749c and TOI-1749d) transiting an early M dwarf at a distance of 100~pc, which were first identified as planetary candidates using data from the TESS photometric survey. We have followed up this system from the ground by means of multiband transit photometry, adaptive-optics imaging, and low-resolution spectroscopy, from which we have validated the planetary nature of the candidates. We find that TOI-1749b, c, and d have orbital periods of 2.39, 4.49, and 9.05 days, and radii of 1.4, 2.1, and 2.5 $R_\oplus$, respectively. We also place 95\% confidence upper limits on the masses of 57, 14, and 15 $M_\oplus$ for TOI-1749b, c, and d, respectively, from transit timing variations. The periods, sizes, and tentative masses of these planets are in line with a scenario in which all three planets initially had a hydrogen envelope on top of a rocky core, and only the envelope of the innermost planet has been stripped away by photoevaporation and/or core-powered mass loss mechanisms. These planets are similar to other planetary trios found around M dwarfs, such as TOI-175b,c,d and TOI-270b,c,d, in the sense that the outer pair has a period ratio within 1\% of 2. Such a characteristic orbital configuration, in which an additional planet is located interior to a near 2:1 period-ratio pair, is relatively rare around FGK dwarfs., Comment: 30 pages, 19 figures, published in AJ

Photometric monitoring of Beta Pictoris in 1981 showed anomalous fluctuations of up to 4% over several days, consistent with foreground material transiting the stellar disk. The subsequent discovery of the gas giant planet Beta Pictoris b and the predicted transit of its Hill sphere to within 0.1 au projected distance of the planet provided an opportunity to search for the transit of a circumplanetary disk in this $21\pm 4$ Myr-old planetary system. Continuous broadband photometric monitoring of Beta Pictoris requires ground-based observatories at multiple longitudes to provide redundancy and to provide triggers for rapid spectroscopic followup. These observatories include the dedicated Beta Pictoris monitoring observatory bRing at Sutherland and Siding Springs, the ASTEP400 telescope at Concordia, and observations from the space observatories BRITE and Hubble Space Telescope. We search the combined light curves for evidence of short period transient events caused by rings and for longer term photometric variability due to diffuse circumplanetary material. We find no photometric event that matches with the event seen in November 1981, and there is no systematic photometric dimming of the star as a function of the Hill sphere radius. We conclude that the 1981 event was not caused by the transit of a circumplanetary disk around Beta Pictoris b. The upper limit on the long term variability of Beta Pictoris places an upper limit of $1.8\times 10^{22}$ g of dust within the Hill sphere. Circumplanetary material is either condensed into a non-transiting disk, is condensed into a disk with moons that has a small obliquity, or is below our detection threshold. This is the first time that a dedicated international campaign has mapped the Hill sphere transit of a gas giant extrasolar planet at 10 au., Comment: 12 pages, 9 figures, 1 table, accepted for publication in A&A. Reduced data and reduction scripts on GitHub at https://github.com/mkenworthy/beta_pic_b_hill_sphere_transit

Context: We report the discovery of TOI-519 b (TIC 218795833), a transiting substellar object (R = 1.07 RJup) orbiting a faint M dwarf (V = 17.35) on a 1.26 d orbit. Brown dwarfs and massive planets orbiting M dwarfs on short-period orbits are rare, but more have already been discovered than expected from planet formation models. TOI-519 is a valuable addition into this group of unlikely systems, and adds towards our understanding of the boundaries of planet formation. Aims: We set out to determine the nature of the Transiting Exoplanet Survey Satellite (TESS ) object of interest TOI-519 b. Methods: Our analysis uses a SPOC-pipeline TESS light curve from Sector 7, multicolour transit photometry observed with MuSCAT2 and MuSCAT, and transit photometry observed with the LCOGT telescopes. We estimate the radius of the transiting object using multicolour transit modelling, and set upper limits for its mass, effective temperature, and Bond albedo using a phase curve model that includes Doppler boosting, ellipsoidal variations, thermal emission, and reflected light components. Results: TOI-519 b is a substellar object with a radius posterior median of 1.07 RJup and 5th and 95th percentiles of 0.66 and 1.20 RJup, respectively, where most of the uncertainty comes from the uncertainty in the stellar radius. The phase curve analysis sets an upper effective temperature limit of 1800 K, an upper Bond albedo limit of 0.49, and a companion mass upper limit of 14 MJup. The companion radius estimate combined with the Teff and mass limits suggests that the companion is more likely a planet than a brown dwarf, but a brown-dwarf scenario is more likely a priori given the lack of known massive planets in 1 day orbits around M dwarfs with Teff < 3800 K, and the existence of some (but few) brown dwarfs., Comment: Accepted to A&A

We present the optical transmission spectrum of the hot Jupiter WASP-104b based on one transit observed by the blue and red channels of the DBSP spectrograph at the Palomar 200-inch telescope and 14 transits observed by the MuSCAT2 four-channel imager at the 1.52 m Telescopio Carlos Sanchez. We also analyse 45 additional K2 transits, after correcting for the flux contamination from a companion star. Together with the transit light curves acquired by DBSP and MuSCAT2, we are able to revise the system parameters and orbital ephemeris, confirming that no transit timing variations exist. Our DBSP and MuSCAT2 combined transmission spectrum reveals an enhanced slope at wavelengths shorter than 630 nm and suggests the presence of a cloud deck at longer wavelengths. While the Bayesian spectral retrieval analyses favour a hazy atmosphere, stellar spot contamination cannot be completely ruled out. Further evidence, from transmission spectroscopy and detailed characterisation of the host star's activity, is required to distinguish the physical origin of the enhanced slope., Comment: 17 pages, 14 figures, accepted for publication in MNRAS

We present the confirmation and characterisation of GJ 3473 b (G 50--16, TOI-488.01), a hot Earth-sized planet orbiting an M4 dwarf star, whose transiting signal ($P=1.1980035\pm0.0000018\mathrm{\,d}$) was first detected by the Transiting Exoplanet Survey Satellite (TESS). Through a joint modelling of follow-up radial velocity observations with CARMENES, IRD, and HARPS together with extensive ground-based photometric follow-up observations with LCOGT, MuSCAT, and MuSCAT2, we determined a precise planetary mass, $M_b = 1.86\pm0.30\,\mathrm{M_\oplus},$ and radius, $R_b = {1.264\pm0.050}\,\mathrm{R_\oplus}$. Additionally, we report the discovery of a second, temperate, non-transiting planet in the system, GJ 3473 c, which has a minimum mass, $M_c \sin{i} = {7.41\pm0.91}\,\mathrm{M_\oplus,}$ and orbital period, $P_c={15.509\pm0.033}\,\mathrm{d}$. The inner planet of the system, GJ 3473 b, is one of the hottest transiting Earth-sized planets known thus far, accompanied by a dynamical mass measurement, which makes it a particularly attractive target for thermal emission spectroscopy., Comment: 21 pages; accepted for publication in A&A

We report the discovery of TOI 837b and its validation as a transiting planet. We characterize the system using data from the NASA TESS mission, the ESA Gaia mission, ground-based photometry from El Sauce and ASTEP400, and spectroscopy from CHIRON, FEROS, and Veloce. We find that TOI 837 is a $T=9.9$ mag G0/F9 dwarf in the southern open cluster IC 2602. The star and planet are therefore $35^{+11}_{-5}$ million years old. Combining the transit photometry with a prior on the stellar parameters derived from the cluster color-magnitude diagram, we find that the planet has an orbital period of $8.3\,{\rm d}$ and is slightly smaller than Jupiter ($R_{\rm p} = 0.77^{+0.09}_{-0.07} \,R_{\rm Jup}$). From radial velocity monitoring, we limit $M_{\rm p}\sin i$ to less than 1.20 $M_{\rm Jup}$ (3-$\sigma$). The transits either graze or nearly graze the stellar limb. Grazing transits are a cause for concern, as they are often indicative of astrophysical false positive scenarios. Our follow-up data show that such scenarios are unlikely. Our combined multi-color photometry, high-resolution imaging, and radial velocities rule out hierarchical eclipsing binary scenarios. Background eclipsing binary scenarios, though limited by speckle imaging, remain a 0.2% possibility. TOI 837b is therefore a validated adolescent exoplanet. The planetary nature of the system can be confirmed or refuted through observations of the stellar obliquity and the planetary mass. Such observations may also improve our understanding of how the physical and orbital properties of exoplanets change in time., Comment: AJ accepted. Figure 11 is my favorite. Comments welcome!

We present new transit observations of the hot Jupiter WASP-74 b ($T_\mathrm{eq} \sim$ 1860 K) using the high-resolution spectrograph HARPS-N and the multi-colour simultaneous imager MuSCAT2. We refine the orbital properties of the planet and its host star, and measure its obliquity for the first time. The measured sky-projected angle between the stellar spin-axis and the planet's orbital axis is compatible with an orbit well-aligned with the equator of the host star ($\lambda = 0.77\pm0.99 \mathrm{deg}$). We are not able to detect any absorption feature of H$\alpha$, or any other atomic spectral features, in its high-resolution transmission spectra due to low S/N at the line cores. Despite previous claims regarding the presence of strong optical absorbers such TiO and VO gases in the atmosphere of WASP-74 b, the new ground-based photometry combined with a reanalysis of previously reported observations from the literature shows a slope in the low-resolution transmission spectrum steeper than expected from Rayleigh scattering alone., Comment: Accepted for publication in Astronomy & Astrophysics. 12 pages, 8 figures, 5 tables

We report the discovery of TOI 263.01 (TIC 120916706), a transiting substellar object (R = 0.87 RJup) orbiting a faint M3.5~V dwarf (V=18.97) on a 0.56~d orbit. We set out to determine the nature of the TESS planet candidate TOI 263.01 using ground-based multicolour transit photometry. The host star is faint, which makes RV confirmation challenging, but the large transit depth makes the candidate suitable for validation through multicolour photometry. Our analysis combines three transits observed simultaneously in r', i', and z_s bands using the MuSCAT2 multicolour imager, three LCOGT-observed transit light curves in g, r', and i' bands, a TESS light curve from Sector 3, and a low-resolution spectrum for stellar characterisation observed with the ALFOSC spectrograph. We model the light curves with PyTransit using a transit model that includes a physics-based light contamination component that allows us to estimate the contamination from unresolved sources from the multicolour photometry. This allows us to derive the true planet-star radius ratio marginalised over the contamination allowed by the photometry, and, combined with the stellar radius, gives us a reliable estimate of the object's absolute radius. The ground-based photometry excludes contamination from unresolved sources with a significant colour difference to TOI 263. Further, contamination from sources of same stellar type as the host is constrained to levels where the true radius ratio posterior has a median of 0.217. The median radius ratio corresponds to an absolute planet radius of 0.87 RJup, which confirms the substellar nature of the planet candidate. The object is either a giant planet or a brown dwarf (BD) located deep inside the so-called "brown dwarf desert". Both possibilities offer a challenge to current planet/BD formation models and makes 263.01 an object deserving of in-depth follow-up studies., Comment: Accepted to A&A

We report the analysis of additional multiband photometry and spectroscopy and new adaptive optics (AO) imaging of the nearby planetary microlensing event TCP J05074264+2447555 (Kojima-1), which was discovered toward the Galactic anticenter in 2017 (Nucita et al.). We confirm the planetary nature of the light-curve anomaly around the peak while finding no additional planetary feature in this event. We also confirm the presence of apparent blending flux and the absence of significant parallax signal reported in the literature. The AO image reveals no contaminating sources, making it most likely that the blending flux comes from the lens star. The measured multiband lens flux, combined with a constraint from the microlensing model, allows us to narrow down the previously unresolved mass and distance of the lens system. We find that the primary lens is a dwarf on the K/M boundary (0.581 \pm 0.033 M_sun) located at 505 \pm 47 pc and the companion (Kojima-1Lb) is a Neptune-mass planet (20.0 \pm 2.0 M_earth) with a semi-major axis of 1.08 ^{+0.62}_{-0.18} au. This orbit is a few times smaller than those of typical microlensing planets and is comparable to the snow-line location at young ages. We calculate that the a priori detection probability of Kojima-1Lb is only \sim 35%, which may imply that Neptunes are common around the snow line, as recently suggested by the transit and radial velocity techniques. The host star is the brightest among the microlensing planetary systems (Ks = 13.7), offering a great opportunity to spectroscopically characterize this system, even with current facilities., Comment: 27 pages, 12 figures, published in Astronomical Journal

Dome C in Antarctica is a promising site for photometric observations thanks to the continuous night during the Antarctic winter and favorable weather conditions. We developed instruments to assess the quality of this site for photometry in the visible and to detect and characterize variable objects through the Antarctic Search for Transiting ExoPlanets (ASTEP) project. We present the full analysis of four winters of data collected with ASTEP South, a 10 cm refractor pointing continuously toward the celestial south pole. We improved the instrument over the years and developed specific data reduction methods. We achieved nearly continuous observations over the winters. We measure an average sky background of 20 mag arcsec$^{-2}$ in the 579-642 nm bandpass. We built the lightcurves of 6000 stars and developed a model to infer the photometric quality of Dome C from the lightcurves themselves. The weather is photometric $67.1\pm4.2$ % of the time and veiled $21.8\pm2.0$ % of the time. The remaining time corresponds to poor quality data or winter storms. We analyzed the lightcurves of $\sigma$ Oct and HD 184465 and find that the amplitude of their main frequency varies by a factor of 3.5 and 6.7 over the four years, respectively. We also identify 34 new variable stars and eight new eclipsing binaries with periods ranging from 0.17 to 81 days. The phase coverage that we achieved with ASTEP South is exceptional for a ground-based instrument and the data quality enables the detection and study of variable objects. These results demonstrate the high quality of Dome C for photometry in the visible and for time series observations in general., Comment: 23 pages, 23 figures, A&A in press

Exoplanets with relatively clear atmospheres are prime targets for detailed studies of chemical compositions and abundances in their atmospheres. Alkali metals have long been suggested to exhibit broad wings due to pressure broadening, but most of the alkali detections only show very narrow absorption cores, probably because of the presence of clouds. We report the strong detection of the pressure-broadened spectral profiles of Na, K, and Li absorption in the atmosphere of the super-Neptune WASP-127b, at 4.1$\sigma$, 5.0$\sigma$, and 3.4$\sigma$, respectively. We performed a spectral retrieval modeling on the high-quality optical transmission spectrum newly acquired with the 10.4 m Gran Telescopio Canarias (GTC), in combination with the re-analyzed optical transmission spectrum obtained with the 2.5 m Nordic Optical Telescope (NOT). By assuming a patchy cloudy model, we retrieved the abundances of Na, K, and Li, which are super-solar at 3.7$\sigma$ for K and 5.1$\sigma$ for Li (and only 1.8$\sigma$ for Na). We constrained the presence of haze coverage to be around 52%. We also found a hint of water absorption, but cannot constrain it with the global retrieval owing to larger uncertainties in the probed wavelengths. WASP-127b will be extremely valuable for atmospheric characterization in the era of James Webb Space Telescope., Comment: 14 pages, 11 figures, accepted for publication in A&A on May 18, 2018

The Antartica Search for Transiting Extrasolar Planets (ASTEP), an automatized 400 mm telescope located at Concordia station in Antarctica, monitored beta Pictoris continuously to detect any variability linked to the transit of the Hill sphere of its planet beta Pictoris b. The long observation sequence, from March to September 2017, combined with the quality and high level duty cycle of our data, enables us to detect and analyse the delta Scuti pulsations of the star. Time series photometric data were obtained using aperture photometry by telescope defocussing. The 66 418 data points were analysed using the software package Period04. We only selected frequencies with amplitudes that exceed four times the local noise level in the amplitude spectrum. We detect 31 delta Scuti pulsation frequencies, 28 of which are new detections. All the frequencies detected are in the interval 34.76-75.68 d-1 . We also find that beta Pictoris exhibits at least one pulsation mode that varies in amplitude over our monitoring duration of seven months., Comment: 4 pages, 4 figures

The NASA TESS mission will deliver hundreds of transiting exoplanet candidates orbiting bright stars. The spectrometers SOPHIE at OHP and SPIRou at CFHT will be ideal to obtain radial velocities of these candidates, confirm their nature, and derive the planets' masses. These measurements will be crucial to deliver the best targets for atmospheric characterization with JWST. Here, we calculate the required observing time with SOPHIE, SPIRou, and JWST for each of the TESS targets in order to prepare follow-up observations. To infer their potential for JWST, we restrict the calculations to the case of transmission spectroscopy with NIRISS. The radial velocity follow-up of the giant planets ($R_p > 4 \rm \, R_E$) could be achieved with SOPHIE, with a median observing time of 3.47 hours per target, and a total observing time of 305 hours that includes the 80% most favorable cases. Several small planets ($R_p < 4 \rm \, R_E$) could also be confirmed, but most of them would require an unrealistic time investment. On the other hand, SPIRou is ideally suited to the follow-up of the small planets, with a median observing time of 2.65 hours per target, and a median observing time of 4.70 hours for the terrestrial planets in the habitable zone ($R_p < 2 \rm \, R_E$, $S < 2 \rm \, S_E$). With JWST, the 10% most favorable small planets (184 planets) have a median observing time of 16.2 hours, and the 10% most favorable habitable zone terrestrial planets (7 planets) have a median observing time of 59.7 hours. Overall, this study will help define a follow-up strategy and prepare observation programs with SOPHIE and SPIRou before the first planet candidates are delivered by TESS., Comment: 5 pages, 3 figures, Proceedings of the Soci\'et\'e Fran\c{c}aise d'Astronomie et d'Astrophysique (SF2A) 2016

Only a few hot Jupiters are known to orbit around fast rotating stars. These exoplanets are harder to detect and characterize and may be less common than around slow rotators. Here, we report the discovery of the transiting hot Jupiter XO-6b, which orbits a bright, hot, and fast rotating star: V = 10.25, Teff = 6720 +/- 100 K, v sin i = 48 +/- 3 km/s. We detected the planet from its transits using the XO instruments and conducted a follow-up campaign. Because of the fast stellar rotation, radial velocities taken along the orbit do not yield the planet's mass with a high confidence level, but we secure a 3-sigma upper limit Mp < 4.4 MJup. We also obtain high resolution spectroscopic observations of the transit with the SOPHIE spectrograph at the 193-cm telescope of the Observatoire de Haute-Provence and analyze the stellar lines profile by Doppler tomography. The transit is clearly detected in the spectra. The radii measured independently from the tomographic analysis and from the photometric lightcurves are consistent, showing that the object detected by both methods is the same and indeed transits in front of XO-6. We find that XO-6b lies on a prograde and misaligned orbit with a sky-projected obliquity lambda = -20.7 +/- 2.3 deg. The rotation period of the star is shorter than the orbital period of the planet: Prot < 2.12 days, Porb = 3.77 days. Thus, this system stands in a largely unexplored regime of dynamical interactions between close-in giant planets and their host stars., Comment: 12 pages, 11 figures, Accepted for publication in AJ

ASTEP (Antarctica Search for Transiting ExoPlanets) is a pilot project that aims at searching and characterizing transiting exoplanets from Dome C in Antarctica and to qualify this site for photometry in the visible. Two instruments were installed at Dome C and ran for six winters in total. The analysis of the collected data is nearly complete. We present the operation of the instruments, and the technical challenges, limitations, and possible solutions in light of the data quality. The instruments performed continuous observations during the winters. Human interventions are required mainly for regular inspection and ice dust removal. A defrosting system is efficient at preventing and removing ice on the mirrors. The PSF FWHM is 4.5 arcsec on average which is 2.5 times larger than the specification, and is highly variable; the causes are the poor ground-level seeing, the turbulent plumes generated by the heating system, and to a lower extent the imperfect optical alignment and focusing, and some astigmatism. We propose solutions for each of these aspects that would largely increase the PSF stability. The astrometric and guiding precisions are satisfactory and would deserve only minor improvements. Major issues are encountered with the camera shutter which did not close properly after two winters; we minimized this issue by heating the shutter and by developing specific image calibration algorithms. Finally, we summarize the site testing and science results obtained with ASTEP. Overall, the ASTEP experiment will serve as a basis to design and operate future optical and near-infrared telescopes in Antarctica., Comment: 10 pages, 6 figures, SPIE conference proceedings, Ground-based and Airborne Instrumentation for Astronomy VI, 2016

We report near-infrared spectroscopy of the gas giant planet HD 189733b in transit. We used the Hubble Space Telescope Wide Field Camera 3 (HST WFC3) with its G141 grism covering 1.1 um to 1.7 um and spatially scanned the image across the detector at 2\arcsec$s^{-1}$. When smoothed to 75 nm bins, the local maxima of the transit depths in the 1.15 um and 1.4 um water vapor features respectively are 83+/-53 ppm and 200+/-47 ppm greater than the local minimum at 1.3 um. We compare the WFC3 spectrum with the composite transit spectrum of HD 189733b assembled by Pont et al. (2013), extending from 0.3 um to 24 um. Although the water vapor features in the WFC3 spectrum are compatible with the model of non-absorbing, Rayleigh-scattering dust in the planetary atmosphere (Pont et al. 2013), we also re-interpret the available data with a clear planetary atmosphere. In the latter interpretation, the slope of increasing transit depth with shorter wavelengths from the near infrared, through the visible and into the ultraviolet is caused by unocculted star spots, with a smaller contribution of Rayleigh scattering by molecular hydrogen in the planet's atmosphere. At relevant pressures along the terminator, our model planetary atmosphere's temperature is ~700 K, which is below the condensation temperatures of sodium- and potassium-bearing molecules, causing the broad wings of the spectral lines of Na I and K I at 0.589 um and 0.769 um to be weak., Comment: 14 pages, 5 figures, Accepted to ApJ

Observing sites at the East-Antarctic plateau are considered to provide exceptional conditions for astronomy. The aim of this work is to assess its potential for detecting transiting extrasolar planets through a comparison and combination of photometric data from Antarctica with time series from a midlatitude site. During 2010, the two small aperture telescopes ASTEP 400 (Dome C) and BEST II (Chile) together performed an observing campaign of two target fields and the transiting planet WASP-18b. For the latter, a bright star, Dome C appears to yield an advantageous signal-to-noise ratio. For field surveys, both Dome C and Chile appear to be of comparable photometric quality. However, within two weeks, observations at Dome C yield a transit detection efficiency that typically requires a whole observing season in Chile. For the first time, data from Antarctica and Chile have been combined to extent the observational duty cycle. This approach is both feasible in practice and favorable for transit search, as it increases the detection yield by 12-18%., Comment: 22 pages, 12 figures, accepted for publication in PASP (in press)

The ASTEP (Antarctica Search for Transiting ExoPlanets) program was originally aimed at probing the quality of the Dome C, Antarctica for the discovery and characterization of exoplanets by photometry. In the first year of operation of the 40 cm ASTEP 400 telescope (austral winter 2010), we targeted the known transiting planet WASP-19b in order to try to detect its secondary transits in the visible. This is made possible by the excellent sub-millimagnitude precision of the binned data. The WASP-19 system was observed during 24 nights in May 2010. The photometric variability level due to starspots is about 1.8% (peak-to-peak), in line with the SuperWASP data from 2007 (1.4%) and larger than in 2008 (0.07%). We find a rotation period of WASP-19 of 10.7 +/- 0.5 days, in agreement with the SuperWASP determination of 10.5 +/- 0.2 days. Theoretical models show that this can only be explained if tidal dissipation in the star is weak, i.e. the tidal dissipation factor Q'star > 3.10^7. Separately, we find evidence for a secondary eclipse of depth 390 +/- 190 ppm with a 2.0 sigma significance, a phase consistent with a circular orbit and a 3% false positive probability. Given the wavelength range of the observations (420 to 950 nm), the secondary transit depth translates into a day side brightness temperature of 2690(-220/+150) K, in line with measurements in the z' and K bands. The day side emission observed in the visible could be due either to thermal emission of an extremely hot day side with very little redistribution of heat to the night side, or to direct reflection of stellar light with a maximum geometrical albedo Ag=0.27 +/- 0.13. We also report a low-frequency oscillation well in phase at the planet orbital period, but with a lower-limit amplitude that could not be attributed to the planet phase alone, and possibly contaminated with residual lightcurve trends., Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 13 figures

The ASTEP project aims at detecting and characterizing transiting planets from Dome C, Antarctica, and qualifying this site for photometry in the visible. The first phase of the project, ASTEP South, is a fixed 10 cm diameter instrument pointing continuously towards the celestial South pole. Observations were made almost continuously during 4 winters, from 2008 to 2011. The point-to-point RMS of 1-day photometric lightcurves can be explained by a combination of expected statistical noises, dominated by the photon noise up to magnitude 14. This RMS is large, from 2.5 mmag at R=8 to 6% at R=14, because of the small size of ASTEP South and the short exposure time (30 s). Statistical noises should be considerably reduced using the large amount of collected data. A 9.9-day period eclipsing binary is detected, with a magnitude R=9.85. The 2-season lightcurve folded in phase and binned into 1000 points has a RMS of 1.09 mmag, for an expected photon noise of 0.29 mmag. The use of the 4 seasons of data with a better detrending algorithm should yield a sub-millimagnitude precision for this folded lightcurve. Radial velocity follow-up observations are conducted and reveal a F-M binary system. The detection of this 9.9-day period system with a small instrument such as ASTEP South and the precision of the folded lightcurve show the quality of Dome C for continuous photometric observations, and its potential for the detection of planets with orbital period longer than those usually detected from the ground., Comment: 5 pages, 3 figures, IAUS 288 conference proceedings

Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form according to the core accretion theory of planet formation. In this paper, we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA-2010-BLG-477. The measured planet-star mass ratio is $q=(2.181\pm0.004)\times 10^{-3}$ and the projected separation is $s=1.1228\pm0.0006$ in units of the Einstein radius. The angular Einstein radius is unusually large $\theta_{\rm E}=1.38\pm 0.11$ mas. Combining this measurement with constraints on the "microlens parallax" and the lens flux, we can only limit the host mass to the range $0.13