Search

The recent inference of sulphur dioxide (SO$_2$) in the atmosphere of the hot ($\sim$1100 K), Saturn-mass exoplanet WASP-39b from near-infrared JWST observations suggests that photochemistry is a key process in high temperature exoplanet atmospheres. This is due to the low ($<$1 ppb) abundance of SO$_2$ under thermochemical equilibrium, compared to that produced from the photochemistry of H$_2$O and H$_2$S (1-10 ppm). However, the SO$_2$ inference was made from a single, small molecular feature in the transmission spectrum of WASP-39b at 4.05 $\mu$m, and therefore the detection of other SO$_2$ absorption bands at different wavelengths is needed to better constrain the SO$_2$ abundance. Here we report the detection of SO$_2$ spectral features at 7.7 and 8.5 $\mu$m in the 5-12 $\mu$m transmission spectrum of WASP-39b measured by the JWST Mid-Infrared Instrument (MIRI) Low Resolution Spectrometer (LRS). Our observations suggest an abundance of SO$_2$ of 0.5-25 ppm (1$\sigma$ range), consistent with previous findings. In addition to SO$_2$, we find broad water vapour absorption features, as well as an unexplained decrease in the transit depth at wavelengths longer than 10 $\mu$m. Fitting the spectrum with a grid of atmospheric forward models, we derive an atmospheric heavy element content (metallicity) for WASP-39b of $\sim$7.1-8.0 $\times$ solar and demonstrate that photochemistry shapes the spectra of WASP-39b across a broad wavelength range., Comment: Published in Nature

Our understanding of how exoplanets form and evolve relies on analyses of both the mineralogy of protoplanetary disks and their detailed structures; however, these key complementary aspects of disks are usually studied separately. We present initial results from a hybrid model that combines the empirical characterization of the mineralogy of a disk, as determined from its mid-infrared spectral features, with the MCFOST radiative transfer disk model, a combination we call the EaRTH Disk Model. With the results of the mineralogy detection serving as input to the radiative transfer model, we generate mid-infrared spectral energy distributions (SEDs) that reflect both the mineralogical and structural parameters of the corresponding disk. Initial fits of the SED output by the resulting integrated model to Spitzer Space T elescope mid-infrared (IRS) spectra of the protoplanetary disk orbiting the nearby T Tauri star MP Mus demonstrate the potential advantages of this approach by revealing details like the dominance of micron-sized olivine and micron-sized forsterite in this dusty disk. The simultaneous insight into disk composition and structure provided by the EaRTH Disk methodology should be directly applicable to the interpretation of mid-infrared spectra of protoplanetary disks that will be produced by the James Webb Space Telescope., Comment: Accepted for publication in ApJ, 38 pages, 11 figures, 6 tables

Hot Jupiters are among the best-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5-12 $\mu$m with JWST's Mid-Infrared Instrument (MIRI). The spectra reveal a large day-night temperature contrast (with average brightness temperatures of 1524$\pm$35 and 863$\pm$23 Kelvin, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase curve shape and emission spectra strongly suggest the presence of nightside clouds which become optically thick to thermal emission at pressures greater than ~100 mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Contrary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2$\sigma$ upper limit of 1-6 parts per million, depending on model assumptions)., Comment: 61 pages, 13 figures, 4 tables. This preprint has been submitted to and accepted in principle for publication in Nature Astronomy without significant changes

We present the discovery and multi-wavelength characterisation of VVV J1438-6158 AB, a new field wide-binary system consisting of a 4.6(+5.5-2.4) Gyr and Teff = 9500+/-125 K DA white dwarf (WD) and a Teff = 2400+/-50 K M8 ultracool dwarf (UCD). The projected separation of the system is a = 1236.73 au (~13.8"), and although along the line-of-sight towards the Scorpius-Centaurus (Sco-Cen) stellar association, VVV J1438-6158 AB is likely to be a field star, from a kinematic 6D probabilistic analysis. We estimated the physical, and dynamical parameters of both components via interpolations with theoretical models and evolutionary tracks, which allowed us to retrieve a mass of 0.62+/-0.18 MSun for the WD, and a mass of 98.5+/-6.2 MJup (~0.094+/-0.006 MSun) for the UCD. The radii of the two components were also estimated at 0.01309+/-0.0003 RSun and 1.22+/-0.05 RJup, respectively. VVV J1438-6158 AB stands out as a benchmark system for comprehending the evolution of WDs and low-mass companions given its status as one of the most widely separated WD+UCD systems known to date, which likely indicates that both components may have evolved independently of each other, and also being characterised by a large mass-ratio (q = 0.15+/-0.04), which likely indicates a formation pathway similar to that of stellar binary systems., Comment: Accepted for publication in MNRAS, 11 pages, 6 figures

Close-in giant exoplanets with temperatures greater than 2,000 K (''ultra-hot Jupiters'') have been the subject of extensive efforts to determine their atmospheric properties using thermal emission measurements from the Hubble and Spitzer Space Telescopes. However, previous studies have yielded inconsistent results because the small sizes of the spectral features and the limited information content of the data resulted in high sensitivity to the varying assumptions made in the treatment of instrument systematics and the atmospheric retrieval analysis. Here we present a dayside thermal emission spectrum of the ultra-hot Jupiter WASP-18b obtained with the NIRISS instrument on JWST. The data span 0.85 to 2.85 $\mu$m in wavelength at an average resolving power of 400 and exhibit minimal systematics. The spectrum shows three water emission features (at $>$6$\sigma$ confidence) and evidence for optical opacity, possibly due to H$^-$, TiO, and VO (combined significance of 3.8$\sigma$). Models that fit the data require a thermal inversion, molecular dissociation as predicted by chemical equilibrium, a solar heavy element abundance (''metallicity'', M/H = 1.03$_{-0.51}^{+1.11}$ $\times$ solar), and a carbon-to-oxygen (C/O) ratio less than unity. The data also yield a dayside brightness temperature map, which shows a peak in temperature near the sub-stellar point that decreases steeply and symmetrically with longitude toward the terminators., Comment: JWST ERS bright star observations. Uploaded to inform JWST Cycle 2 proposals. Manuscript under review. 50 pages, 14 figures, 2 tables

Transmission spectroscopy provides insight into the atmospheric properties and consequently the formation history, physics, and chemistry of transiting exoplanets. However, obtaining precise inferences of atmospheric properties from transmission spectra requires simultaneously measuring the strength and shape of multiple spectral absorption features from a wide range of chemical species. This has been challenging given the precision and wavelength coverage of previous observatories. Here, we present the transmission spectrum of the Saturn-mass exoplanet WASP-39b obtained using the SOSS mode of the NIRISS instrument on the JWST. This spectrum spans $0.6 - 2.8 \mu$m in wavelength and reveals multiple water absorption bands, the potassium resonance doublet, as well as signatures of clouds. The precision and broad wavelength coverage of NIRISS-SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favoring a heavy element enhancement ("metallicity") of $\sim 10 - 30 \times$ the solar value, a sub-solar carbon-to-oxygen (C/O) ratio, and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are best explained by wavelength-dependent, non-gray clouds with inhomogeneous coverage of the planet's terminator., Comment: 48 pages, 12 figures, 2 tables. Under review at Nature

Photometric observations of occultations of transiting exoplanets can place important constraints on the thermal emission and albedos of their atmospheres. We analyse photometric measurements and derive geometric albedo ($A_\mathrm{g}$) constraints for five hot Jupiters observed with TESS in the optical: WASP-18 b, WASP-36 b, WASP-43 b, WASP-50 b and WASP-51 b. For WASP-43 b, our results are complemented by a VLT/HAWK-I observation in the near-infrared at $2.09~\mu$m. We derive the first geometric albedo constraints for WASP-50 b and WASP-51 b: $A_\mathrm{g}<0.445$ and $A_\mathrm{g}<0.368$, respectively. We find that WASP-43 b and WASP-18 b are both consistent with low geometric albedos ($A_\mathrm{g}<0.16$) even though they lie at opposite ends of the hot Jupiter temperature range with equilibrium temperatures of $\sim1400$ K and $\sim2500$ K, respectively. We report self-consistent atmospheric models which explain broadband observations for both planets from TESS, \HST, \Spitzer and VLT/HAWK-I. We find that the data of both hot Jupiters can be explained by thermal emission alone and inefficient day-night energy redistribution. The data do not require optical scattering from clouds/hazes, consistent with the low geometric albedos observed., Comment: 21 pages, 7 figures

One of the most important questions in the field of planet formation is how mm-cm sized dust particles overcome the radial drift and fragmentation barriers to form kilometer-sized planetesimals. ALMA observations of protoplanetary disks, in particular transition disks or disks with clear signs of substructures, can provide new constraints on theories of grain growth and planetesimal formation and therefore represent one possibility to progress on this issue. We here present ALMA band 4 (2.1 mm) observations of the transition disk system Sz 91 and combine them with previously obtained band 6 (1.3 mm) and 7 (0.9 mm) observations. Sz 91 with its well defined mm-ring, more extended gas disk, and evidence of smaller dust particles close to the star, is a clear case of dust filtering and the accumulation of mm sized particles in a gas pressure bump. We computed the spectral index (nearly constant at $\sim$3.34), optical depth (marginally optically thick), and maximum grain size ($\sim\,0.61$ mm) in the dust ring from the multi-wavelength ALMA observations and compared the results with recently published simulations of grain growth in disk substructures. Our observational results are in very good agreement with the predictions of models for grain growth in dust rings that include fragmentation and planetesimal formation through the streaming instability., Comment: Accepted for publication in the ApJ 19 pages, 13 figures

Abridged: The interest towards searches for extraterrestrial civilizations (ETCs) was boosted by the discovery of thousands of exoplanets. We turn to the classification of ETCs for new considerations that may help to design better strategies for ETCs searches. We take a basic taxonomic approach to ETCs and investigate the implications of the new classification on ETCs observational patterns. We use as a counter-example to our qualitative classification the quantitative scheme of Kardashev. We propose a classification based on the abilities of ETCs to modify their environment and to integrate with it: Class 0 uses the environment as it is, Class 1 modifies the it to fit its needs, Class 2 modifies itself to fit the environment and Class 3 ETC is fully integrated with the environment. Combined with the classical Kardashev's scale our scheme forms a 2d scheme for interpreting ETC properties. The new framework makes it obvious that the available energy is not an unique measure of ETCs, it may not even correlate with how well that energy is used. The possibility for progress without increased energy consumption implies lower detectability, so the existence of a Kardashev Type III ETC in the Milky Way cannot be ruled out. This reasoning weakens the Fermi paradox, allowing the existence of advanced, yet not energy hungry, low detectability ETCs. The integration of ETCs with environment makes it impossible to tell apart technosignatures from natural phenomena. Thus, the most likely opportunity for SETI searches is to look for beacons, specifically set up by them for young civilizations like us (if they want to do that is a matter of speculation). The other SETI window is to search for ETCs at technological level close to ours. To rephrase the saying of A. Clarke, sufficiently advanced civilizations are indistinguishable from nature., Comment: accepted in A&A; 7 pages, 1 figure; the acknowledgements were updated in the new version

We present polarized light observations of the transitional disk around Sz 91 acquired with VLT/NaCo at $H$ (1.7$\mu$m) and $K_s$ (2.2$\mu$m) bands. We resolve the disk and detect polarized emission up to $\sim$0."5 ($\sim$80 au) along with a central cavity at both bands. We computed a radiative transfer model that accounts for the main characteristics of the polarized observations. We found that the emission is best explained by small, porous grains distributed in a disk with a $\sim$45 au cavity. Previous ALMA observations have revealed a large sub-mm cavity ($\sim$83 au) and extended gas emission from the innermost (<16 au) regions up to almost 400 au from the star. Dynamical clearing by multiple low-mass planets arises as the most probable mechanism for the origin of Sz 91's peculiar structure. Using new $L'$ band ADI observations we can rule out companions more massive than $M_p$ $\geq$ 8 $M_\mathrm{Jup}$ beyond 45 au assuming hot-start models. The disk is clearly asymmetric in polarized light along the minor axis, with the north side brighter than the south side. Differences in position angle between the disk observed at sub-mm wavelengths with ALMA and our NaCo observations were found. This suggests that the disk around Sz 91 could be highly structured. Higher signal-to-noise near-IR and sub-mm observations are needed to confirm the existence of such structures and to improve the current understanding in the origin of transitional disks., Comment: 14 pages, 8 figures, accepted for publication in MNRAS

Two studies utilizing sparse aperture masking (SAM) interferometry and $H_{\rm \alpha}$ differential imaging have reported multiple jovian companions around the young solar-mass star, LkCa 15 (LkCa 15 bcd): the first claimed direct detection of infant, newly-formed planets ("protoplanets"). We present new near-infrared direct imaging/spectroscopy from the SCExAO system coupled with the CHARIS integral field spectrograph and multi-epoch thermal infrared imaging from Keck/NIRC2 of LkCa 15 at high Strehl ratios. These data provide the first direct imaging look at the same wavelengths and in the same locations where previous studies identified the LkCa 15 protoplanets and thus offer the first decisive test of their existence. The data do not reveal these planets. Instead, we resolve extended emission tracing a dust disk with a brightness and location comparable to that claimed for LkCa 15 bcd. Forward-models attributing this signal to orbiting planets are inconsistent with the combined SCExAO/CHARIS and Keck/NIRC2 data. An inner disk provides a more compelling explanation for the SAM detections and perhaps also the claimed $H_{\alpha}$ detection of LkCa 15 b. We conclude that there is currently no clear, direct evidence for multiple protoplanets orbiting LkCa 15, although the system likely contains at least one unseen jovian companion. To identify jovian companions around LkCa 15 from future observations, the inner disk should be detected and its effect modeled, removed, and shown to be distinguishable from planets. Protoplanet candidates identified from similar systems should likewise be clearly distinguished from disk emission through modeling., Comment: 12 pages, 4 figures, 1 table; Astrophysical Journal Letters in press

We report the discovery of VVV-WIT-07, an unique and intriguing variable source presenting a sequence of recurrent dips with a likely deep eclipse in July 2012. The object was found serendipitously in the near-IR data obtained by the VISTA Variables in the V\'ia L\'actea (VVV) ESO Public Survey. Our analysis is based on VVV variability, multicolor, and proper motion (PM) data. Complementary data from the VVV eXtended survey (VVVX) as well as archive data and spectroscopic follow-up observations aided in the analysis and interpretation of VVV-WIT-07. A search for periodicity in the VVV Ks-band light curve of VVV-WIT-07 results in two tentative periods at P~322 days and P~170 days. Colors and PM are consistent either with a reddened MS star or a pre-MS star in the foreground disk. The near-IR spectra of VVV-WIT-07 appear featureless, having no prominent lines in emission or absorption. Features found in the light curve of VVV-WIT-07 are similar to those seen in J1407 (Mamajek's object), a pre-MS K5 dwarf with a ring system eclipsing the star or, alternatively, to KIC 8462852 (Boyajian's star), an F3 IV/V star showing irregular and aperiodic dips in its light curve. Alternative scenarios, none of which is fully consistent with the available data, are also briefly discussed, including a young stellar object, a T Tauri star surrounded by clumpy dust structure, a main sequence star eclipsed by a nearby extended object, a self-eclipsing R CrB variable star, and even a long-period, high-inclination X-ray binary., Comment: 7 pages, 5 figures. Accepted for publication in MNRAS

We present the first part of our DARTTS-S (Disks ARound TTauri Stars with SPHERE) survey: Observations of 8 TTauri stars which were selected based on their strong (sub-)mm excesses using SPHERE / IRDIS polarimetric differential imaging (PDI) in the J and H bands. All observations successfully detect the disks, which appear vastly different in size, from $\approx$80 au in scattered light to $>$400 au, and display total polarized disk fluxes between 0.06% and 0.89% of the stellar flux. For five of these disks, we are able to determine the three-dimensional structure and the flaring of the disk surface, which appears to be relatively consistent across the different disks, with flaring exponents $\alpha$ between $\approx$1.1 and $\approx$1.6. We also confirm literature results w.r.t. the inclination and position angle of several of our disk, and are able to determine which side is the near side of the disk in most cases. While there is a clear trend of disk mass with stellar ages ($\approx$1 Myr to $>$10 Myr), no correlations of disk structures with age were found. There are also no correlations with either stellar mass or sub-mm flux. We do not detect significant differences between the J and H bands. However, we note that while a high fraction (7/8) of the disks in our sample show ring-shaped sub-structures, none of them display spirals, in contrast to the disks around more massive Herbig Ae/Be stars, where spiral features are common., Comment: 31 pages, 12 figures

About a dozen substellar companions orbiting young stellar objects or pre-main sequence stars at several hundred au have been identified in the last decade. These objects are interesting both due to the uncertainties surrounding their formation, and because their large separation from the host star offers the potential to study the atmospheres of young giant planets and brown dwarfs. Here, we present X-shooter spectroscopy of SR 12 C, a $\sim\,2\,$Myrs young brown dwarf orbiting SR 12 at an orbital separation of 1083 au. We determine the spectral type, gravity, and effective temperature via comparison with models and observational templates of young brown dwarfs. In addition, we detect and characterize accretion using several accretion tracers. We find SR 12 C to be a brown dwarf of spectral type L0 $\pm$ 1, $\log$ g = 4 $\pm$ 0.5, an effective temperature of 2600 $\pm$ 100 K. Our spectra provide clear evidence for accretion at a rate of $\sim$ $10^{-10}$ $M_{\odot}yr^{-1}$. This makes SR 12 one of the few sub-stellar companions with a reliable estimate for its accretion rate. A comparison of the ages and accretion rates of sub-stellar companions with young isolated brown dwarfs does not reveal any significant differences. If further accretion rate measurements of a large number of substellar companions can confirm this trend, this would hint towards a similar formation mechanism for substellar companions at large separations and isolated brown dwarfs.

DH Tau is a young ($\sim$1 Myr) classical T Tauri star. It is one of the few young PMS stars known to be associated with a planetary mass companion, DH Tau b, orbiting at large separation and detected by direct imaging. DH Tau b is thought to be accreting based on copious H${\alpha}$ emission and exhibits variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place constraints on the disk dust mass for both DH Tau b and the primary in a regime where the disks will appear optically thin. We estimate a disk dust mass for the primary, DH Tau A of $17.2\pm1.7\,M_{\oplus}$, which gives a disk-to-star mass ratio of 0.014 (assuming the usual Gas-to-Dust mass ratio of 100 in the disk). We find a conservative disk dust mass upper limit of 0.42$M_{\oplus}$ for DH Tau b, assuming that the disk temperature is dominated by irradiation from DH Tau b itself. Given the environment of the circumplanetary disk, variable illumination from the primary or the equilibrium temperature of the surrounding cloud would lead to even lower disk mass estimates. A MCFOST radiative transfer model including heating of the circumplanetary disk by DH Tau b and DH Tau A suggests that a mass averaged disk temperature of 22 K is more realistic, resulting in a dust disk mass upper limit of 0.09$M_{\oplus}$ for DH Tau b. We place DH Tau b in context with similar objects and discuss the consequences for planet formation models., Comment: accepted for publication in AJ

A snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. Snow-lines play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains. Signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged in the disks surrounding the pre-main-sequence stars TW Hydra and HD163296, at distances of about 30 astronomical units (au) from the star. But the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 au away for solar-type stars). Water-ice is important because it regulates the efficiency of dust and planetesimal coagulation, and the formation of comets, ice giants and the cores of gas giants. Here we report ALMA images at 0.03-arcsec resolution (12 au) of the protoplanetary disk around V883 Ori, a protostar of 1.3 solar masses that is undergoing an outburst in luminosity arising from a temporary increase in the accretion rate. We find an intensity break corresponding to an abrupt change in the optical depth at about 42 au, where the elevated disk temperature approaches the condensation point of water, from which we conclude that the outburst has moved the water snow-line. The spectral behaviour across the snow-line confirms recent model predictions: dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. As most planetary systems are expected to experience outbursts caused by accretion during their formation our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation., Comment: Published in the July 14th, 2016 issue of Nature. Version 2 includes a minor word change in the abstract

Eclipse timing variations observed from the post common-envelope binary (PCEB) NN Ser offer strong evidence in favour of circumbinary planets existing around PCEBs. If real, these planets may be accompanied by a disc of dust. We here present the ALMA detection of flux at 1.3 mm from NN Ser, which is likely due to thermal emission from a dust disc of mass $\sim0.8\pm0.2\,M_{\oplus}$. We performed simulations of the history of NN Ser to determine possible origins of this dust, and conclude that the most likely origin is, in fact, common-envelope material which was not expelled from the system and instead formed a circumbinary disc. These discs have been predicted by theory but previously remained undetected. While the presence of this dust does not prove the existence of planets around NN Ser, it adds credibility to the possibility of planets forming from common-envelope material in a 'second-generation' scenario., Comment: resubmitted after minor revision to MNRAS

It is thought that planetary mass companions may form through gravitational disk instabilities or core accretion. Identifying such objects in the process of formation would provide the most direct test for the competing formation theories. One of the most promising candidates for a planetary mass object still in formation is the third object in the FW Tau system. We here present ALMA cycle 1 observations confirming the recently published 1.3 mm detection of a dust disk around this third object and present for the first time a clear detection of a single peak $^{12}$CO (2-1) line, providing direct evidence for the simultaneous existence of a gas disk. We perform radiative transfer modeling of the third object in FW Tau and find that current observations are consistent with either a brown dwarf embedded in an edge-on disk or a planet embedded in a low inclination disk, which is externally irradiated by the binary companion. Further observations with ALMA, aiming for high SNR detections of non contaminated gas lines, are required to conclusively unveil the nature of the third object in FW Tau., Comment: Accepted for publication in ApJL

GJ 1214b is one of the few known transiting super-Earth-sized exoplanets with a measured mass and radius. It orbits an M-dwarf, only 14.55 pc away, making it a favorable candidate for follow-up studies. However, the composition of GJ 1214b's mysterious atmosphere has yet to be fully unveiled. Our goal is to distinguish between the various proposed atmospheric models to explain the properties of GJ 1214b: hydrogen-rich or hydrogen-He mix, or a heavy molecular weight atmosphere with reflecting high clouds, as latest studies have suggested. Wavelength-dependent planetary radii measurements from the transit depths in the optical/NIR are the best tool to investigate the atmosphere of GJ 1214b. We present here (i) photometric transit observations with a narrow-band filter centered on 2.14 microns and a broad-band I-Bessel filter centered on 0.8665 microns, and (ii) transmission spectroscopy in the H and K atmospheric windows that cover three transits. The obtained photometric and spectrophotometric time series were analyzed with MCMC simulations to measure the planetary radii as a function of wavelength. We determined radii ratios of 0.1173 for I-Bessel and 0.11735 at 2.14 microns. Our measurements indicate a flat transmission spectrum, in agreement with last atmospheric models that favor featureless spectra with clouds and high molecular weight compositions., Comment: 10 pages, 13 figures. Accepted for publication in A&A