arXiv subjects

G. Anglada

Publications and source records attributed to G. Anglada.

At least 19 recordsLinked to original sources

arXiv2025

Bowshocks driven by the pole-on molecular jet of outbursting protostar SVS 13

Outflows play a key role in the star and planet formation processes. Some outflows show discrete clumps of cold molecular gas moving at extremely high velocities (EHVs) of $\sim$100 km s$^{-1}$, known as ''molecular bullets'', that are likely closely associated with their primary driving agent. Here we present ALMA CO(J=3-2) observations of a bright EHV molecular bullet that reveal its morphology in detail down to scales of 30 au and its kinematic structure across the entire intermediate velocity range ($\sim$30-100 km s$^{-1}$). These provide important new insights into how outflows transfer mass and momentum to the surrounding medium. The observed channel maps display several sequences of ring-like features whose velocity increases and size decreases with projected distance from the driving source, each sequence tracing a thin, bow-shaped shell culminating on-axis in a bright EHV head. The shape, kinematics, and mass of each shell all agree remarkably well with the simplest textbook models of momentum-conserving bowshocks produced by a time-variable EHV jet. The dynamical timescale between consecutive shells is of a few decades, with the latest ejection event coinciding with the protostar optical/IR outburst observed in $\sim$1990. The very strong evidence for bowshock-driven entrainment induced by jet variability revealed by this work suggests that accretion bursts, and therefore variations in the disk snowlines, should occur on decade timescales, which could substantially impact grain growth and planet formation.

astro-ph.GA↗

arXiv2025

Diverse stages of star formation in the IRAS 18162-2048 region. Emergence of UV Feedback

Methods: We obtained adaptive optics-assisted integral field spectroscopy in the near-infrared (IR) $K$ band ($1.93-2.47 \mathrm{\mu m}$) with VLT/SINFONI, complemented by VLA X and C bands (3$-$6 cm) and ALMA band 3 ($\sim$3.3 mm) observations. Results: The near-IR continuum reveals two infrared sources, IRS 2 and IRS 7, while the main protostellar core IRAS 18162-2048 remains undetected up to $2.47 \mathrm{\mu m}$. IRS 7 shows a peculiar Hydrogen Recombination Line Br$\gamma$ profile with a narrow emission component superimposed on a broad absorption feature, consistent with a B2/B3 zero-age main-sequence star. Extended H$_2$ emission exhibits a `sawtooth' pattern in the excitation diagram, characteristic of UV radiation in a PDR rather than shock excitation. The radiative transfer model Cloudy reproduces the H$_2$ ro-vibrational populations for $T_\mathrm{gas}=600$ K and $n_\mathrm{H}=7.9\times10^3 \mathrm{cm^{-3}}$. VLA X and C bands observations reveal a compact radio source previously reported as a stationary condensation (SC) and coincident with IRS 7. For the first time, we detect IRS 7/SC in mm wavelengths. The spectral index in the 3$-$6 cm and 3.3 mm regime is consistent with optically thin free-free emission. Conclusions: Our near-IR and radio observations reveal that IRS 7/SC is a B2/B3 ZAMS star that has begun to photoionise its environment, giving rise to an extended PDR and a compact \ion{H}{ii} region. The coexistence of this source with the deeply embedded protostar IRAS 18162-2048 and other bubble-like structures in the field, suggests a multigenerational star-forming environment. Future \textit{James Webb Space Telescope} observations targeting the H$_2$ pure rotational lines ($3-28 \mathrm{\mu m}$) and other HRLs less affected by extinction will be essential to characterise the cooler molecular and ionised gas to fully disclose the formation history of the region.

astro-ph.GA↗

arXiv2025

A compact Keplerian-like disc and H30$\alpha$ emission towards the radio jet in the massive protostar W75N(B)-VLA3

Studying young, high-mass stellar objects is challenging for testing models of massive star formation due to their great distances, often kiloparsecs away. This requires extremely high-angular resolution to resolve features like accretion discs around massive protostars. Consequently, while powerful, collimated outflows are evident in massive protostars, the compact accretion discs anticipated at their centres are still proving difficult to pinpoint. This study presents ALMA continuum and molecular line observations at 1.3 mm of the massive protostar W75N(B)-VLA3. The observations achieve an angular resolution of $\sim$0.12$^{\prime\prime}$ ($\sim$156 au). Dense gas tracers reveal a circumstellar disc of $\sim$450 au in radius surrounding VLA3, with an orientation perpendicular to its associated thermal radio jet. From the millimetre continuum, a total mass of $\approx$0.43-1.74 $M_\odot$ is estimated for the disc. The disc's velocity profile is consistent with Keplerian rotation around a protostar of $\approx$16 $M_\odot$. This adds VLA3 to the small number of massive disc-protostar-jet systems documented in the literature with a centrifugally supported disc with a radius less than 500 au. Additionally, we detected H30$\alpha$ recombination line emission towards the radio jet powered by VLA3. Despite limitations in the spatial and spectral resolution, our data reveal a very broad line, indicative of high-velocity motions, as well as a tentative velocity gradient in the jet's direction, thus favouring the H30$\alpha$ emission to originate from the radio jet. Should this interpretation be confirmed with new observations, W75N(B)-VLA3 could represent the first protostellar radio jet for which a thermal radio recombination line has been detected.

astro-ph.GA↗

arXiv2025

Helical Magnetic Field in a Massive Protostellar Jet

Highly collimated outflows (jets) are observed across a wide range of astrophysical systems involving the accretion of material onto central objects, from supermassive black holes in active galaxies to proto-brown dwarfs and stellar-mass black holes. Despite the diversity of their driving sources, it is believed that all jets are different manifestations of a single universal phenomenon. However, a unified explanation for their ejection and collimation remains elusive. In this study we present the first rotation measure analysis of the polarized synchrotron emission ever performed in a protostellar radio jet, which allows us to reveal its true 3D magnetic structure. Unlike extragalactic radio jets, which often exhibit faint counterjets, protostellar radio jets allow both the jet and the counterjet to be analyzed. This exceptional circumstance allows us to unveil the magnetic field structure of both components. Our findings provide the first solid evidence for a helical magnetic field within a protostellar jet, supporting the universality of the jet collimation mechanism.

astro-ph.GA↗

arXiv2024

Searching for star-planet interactions in GJ 486 at radio wavelengths with the uGMRT

We search for radio emission from star-planet interactions in the M-dwarf system GJ~486, which hosts an Earth-like planet. We observed the GJ~486 system with the upgraded Giant Metrewave Radio Telescope (uGMRT) from 550 to 750 MHz in nine different epochs, between October 2021 and February 2022, covering almost all orbital phases of GJ~486 b from different orbital cycles. We obtained radio images and dynamic spectra of the total and circularly polarized intensity for each individual epoch We do not detect any quiescent radio emission in any epoch above 3$\sigma$. Similarly, we do not detect any bursty emission in our dynamic spectra. While we cannot completely rule out that the absence of a radio detection is due to time variability of the radio emission, or to the maximum electron-cyclotron maser emission being below our observing range, this seems unlikely. We discuss two possible scenarios: an intrinsic dim radio signal, or alternatively, that the anisotropic beamed emission pointed away from the observer. If the non-detection of radio emission from star-planet interaction in GJ~486 is due to an intrinsically dim signal, this implies that, independently of whether the planet is magnetized or not, the mass-loss rate is small (\dot{M}_\star $\lesssim$ 0.3 \dot{M}_\sun) and that, concomitantly, the efficiency of the conversion of Poynting flux into radio emission must be low ($\beta \lesssim 10^{-3}$). Free-free absorption effects are negligible, given the high value of the coronal temperature. Finally, if the anisotropic beaming pointed away from us, this would imply that GJ~486 has very low values of its magnetic obliquity and inclination.

astro-ph.EP↗

arXiv2024

Characterisation of the TOI-421 planetary system using CHEOPS, TESS, and archival radial velocity data

The TOI-421 planetary system contains two sub-Neptune-type planets and is a prime target to study the formation and evolution of planets and their atmospheres. The inner planet is especially interesting as the existence of a hydrogen-dominated atmosphere at its orbital separation cannot be explained by current formation models without previous orbital migration. We jointly analysed photometric data of three TESS sectors and six CHEOPS visits as well as 156 radial velocity data points to retrieve improved planetary parameters. We also searched for TTVs and modelled the interior structure of the planets. Finally, we simulated the evolution of the primordial H-He atmospheres of the planets using two different modelling frameworks. We determine the planetary radii and masses of TOI-421 b and c to be $R_{\rm b} = 2.64 \pm 0.08 \, R_{\oplus}$, $M_{\rm b} = 6.7 \pm 0.6 \, M_{\oplus}$, $R_{\rm c} = 5.09 \pm 0.07 \, R_{\oplus}$, and $M_{\rm c} = 14.1 \pm 1.4 \, M_{\oplus}$. We do not detect any statistically significant TTV signals. Assuming the presence of a hydrogen-dominated atmosphere, the interior structure modelling results in both planets having extensive envelopes. While the modelling of the atmospheric evolution predicts for TOI-421 b to have lost any primordial atmosphere that it could have accreted at its current orbital position, TOI-421 c could have started out with an initial atmospheric mass fraction somewhere between 10 and 35%. We conclude that the low observed mean density of TOI-421 b can only be explained by either a bias in the measured planetary parameters (e.g. driven by high-altitude clouds) and/or in the context of orbital migration. We also find that the results of atmospheric evolution models are strongly dependent on the employed planetary structure model.

astro-ph.EP↗

arXiv2024

Self-similarity of the magnetic field at different scales: the case of G31.41+0.31

Context. Dust polarization observations of the massive protocluster G31.41+0.31 carried out at ~1'' (~3750 au) resolution with the SMA at 870 microm have revealed one of the clearest examples to date of an hourglass-shaped magnetic field morphology in the high-massregime. Additionally, ~0.24'' (~900 au) resolution observations with ALMA at 1.3 mm have confirmed these results. The next step is to investigate whether the magnetic field maintains its hourglass-shaped morphology down to circumstellar scales. Aims. To study the magnetic field morphology toward the four (proto)stars A, B, C, and D contained in G31.41+0.31 and examine whether the self-similarity observed at core scales (1'' and 0.24'' resolution) still holds at circumstellar scales, we carried out ALMA observations of the polarized dust continuum emission at 1.3 mm and 3.1 mm at an angular resolution of ~0.068'' (~250 au), sufficient to resolve the envelope emission of the embedded protostars. Methods. We used ALMA to perform full polarization observations at 233 GHz (Band 6) and 97.5 GHz (Band 3) with a synthesized beam of 0.072'' x 0.064''. We carried out polarization observations at two different wavelengths to confirm that the polarization traces magnetically aligned dust grains and is not due to dust self-scattering. Results. The polarized emission and the direction of the magnetic field obtained at the two wavelengths are basically the same, except for an area between the embedded sources C and B. In such an area, the emission at 1.3 mm could be optically thick and affected by dichroic extinction. ...

astro-ph.GA↗

arXiv2024

Precise characterisation of HD 15337 with CHEOPS: a laboratory for planet formation and evolution

We aim to constrain the internal structure and composition of HD 15337 b and c, two short-period planets situated on opposite sides of the radius valley, using new transit photometry and radial velocity data. We acquire 6 new transit visits with the CHaracterising ExOPlanet Satellite (CHEOPS) and 32 new radial velocity measurements from the High Accuracy Radial Velocity Planet Searcher (HARPS) to improve the accuracy of the mass and radius estimates for both planets. We reanalyse light curves from TESS sectors 3 and 4 and analyse new data from sector 30, correcting for long-term stellar activity. Subsequently, we perform a joint fit of the TESS and CHEOPS light curves, and all available RV data from HARPS and the Planet Finder Spectrograph (PFS). Our model fits the planetary signals, the stellar activity signal and the instrumental decorrelation model for the CHEOPS data simultaneously. The stellar activity was modelled using a Gaussian-process regression on both the RV and activity indicators. We finally employ a Bayesian retrieval code to determine the internal composition and structure of the planets. We derive updated and highly precise parameters for the HD 15337 system. Our improved precision on the planetary parameters makes HD 15337 b one of the most precisely characterised rocky exoplanets, with radius and mass measurements achieving a precision better than 2\% and 7\%, respectively. We are able to improve the precision of the radius measurement of HD 15337 c to 3\%. Our results imply that the composition of HD 15337 b is predominantly rocky, while HD 15337 c exhibits a gas envelope with a mass of at least $0.01\ M_\oplus$.Our results lay the groundwork for future studies, which can further unravel the atmospheric evolution of these exoplanets and give new insights into their composition and formation history and the causes behind the radius gap.

astro-ph.EP↗

arXiv2024

Hunt for complex cyanides in protostellar ices with JWST: Tentative detection of CH$_3$CN and C$_2$H$_5$CN

Nitrogen-bearing complex organic molecules have been commonly detected in the gas phase but not yet in interstellar ices. This has led to the long-standing question of whether these molecules form in the gas phase or in ices. $\textit{James Webb}$ Space Telescope ($\textit{JWST}$) offers the sensitivity, spectral resolution, and wavelength coverage needed to detect them in ices and investigate whether their abundance ratios are similar in gas and ice. We report the first tentative detection of CH$_3$CN, C$_2$H$_5$CN, and the simple molecule, N$_2$O, based on the CN-stretch band in interstellar ices toward three (HOPS 153, HOPS 370, and IRAS 20126+4104) out of the five protostellar systems observed as part of the Investigating Protostellar Accretion (IPA) GO program with $\textit{JWST}$-NIRSpec. We also provide upper limits for the two other sources with smaller luminosities in the sample. We detect OCN$^-$ in the ices of all sources with typical CH$_3$CN/OCN$^-$ ratios of around 1. Ice and gas column density ratios of the nitrogen-bearing species with respect to each other are better matched than those with respect to methanol, which are a factor of ${\sim}5$ larger in the ices than the gas. We attribute the elevated ice column densities with respect to methanol to the difference in snowline locations of nitrogen-bearing molecules and of methanol, biasing the gas-phase observations toward fewer nitrogen-bearing molecules. Moreover, we find tentative evidence for enhancement of OCN$^-$, CH$_3$CN, and C$_2$H$_5$CN in warmer ices, although formation of these molecules likely starts along with methanol in the cold prestellar phase. Future surveys combining NIRSpec and MIRI, and additional laboratory spectroscopic measurements of C$_2$H$_5$CN ice, are necessary for robust detection and conclusions on the formation history of complex cyanides.

astro-ph.GA↗

arXiv2023

The EBLM Project XI. Mass, radius and effective temperature measurements for 23 M-dwarf companions to solar-type stars observed with CHEOPS

Observations of low-mass stars have frequently shown a disagreement between observed stellar radii and radii predicted by theoretical stellar structure models. This ``radius inflation'' problem could have an impact on both stellar and exoplanetary science. We present the final results of our observation programme with the CHEOPS satellite to obtain high-precision light curves of eclipsing binaries with low mass stellar companions (EBLMs). Combined with the spectroscopic orbits of the solar-type companion, we can derive the masses, radii and effective temperatures of 23 M-dwarf stars. We use the PYCHEOPS data analysis software to analyse their primary and secondary occultations. For all but one target, we also perform analyses with TESS light curves for comparison. We have assessed the impact of starspot-induced variation on our derived parameters and account for this in our radius and effective temperature uncertainties using simulated light curves. We observe trends for inflation with both metallicity and orbital separation. We also observe a strong trend in the difference between theoretical and observational effective temperatures with metallicity. There is no such trend with orbital separation. These results are not consistent with the idea that observed inflation in stellar radius combines with lower effective temperature to preserve the luminosity predicted by low-mass stellar models. Our EBLM systems are high-quality and homogeneous measurements that can be used in further studies into radius inflation.

astro-ph.SR↗

arXiv2023

No random transits in CHEOPS observations of HD 139139

HD 139139 (a.k.a. 'The Random Transiter') is a star that exhibited enigmatic transit-like features with no apparent periodicity in K2 data. The shallow depth of the events ($\sim$200 ppm -- equivalent to transiting objects with radii of $\sim$1.5 R$_\oplus$ in front of a Sun-like star), and their non-periodicity, constitutes a challenge for the photometric follow-up of this star. The goal of this study is to confirm with independent measurements the presence of shallow, non-periodic transit-like features on this object. We performed observations with CHEOPS, for a total accumulated time of 12.75 d, distributed in visits of roughly 20 h in two observing campaigns in years 2021 and 2022. The precision of the data is sufficient to detect 150 ppm features with durations longer than 1.5 h. We use the duration and times of the events seen in the K2 curve to estimate how many should have been detected in our campaigns, under the assumption that their behaviour during the CHEOPS observations would be the same as in the K2 data of 2017. We do not detect events with depths larger than 150 ppm in our data set. If the frequency, depth, and duration of the events were the same as in the K2 campaign, we estimate the probability of having missed all events due to our limited observing window would be 4.8 %. We suggest three different scenarios to explain our results: 1) Our observing window was not long enough, and the events were missed with the estimated 4.8 % probability. 2) The events recorded in the K2 observations were time critical, and the mechanism producing them was either not active in the 2021 and 2022 campaigns or created shallower events under our detectability level. 3) The enigmatic events in the K2 data are the result of an unidentified and infrequent instrumental noise in the original data set or its data treatment.

astro-ph.EP↗

arXiv2023

Constraining the reflective properties of WASP-178b using Cheops photometry

Multiwavelength photometry of the secondary eclipses of extrasolar planets is able to disentangle the reflected and thermally emitted light radiated from the planetary dayside. This leads to the measurement of the planetary geometric albedo $A_g$, which is an indicator of the presence of clouds in the atmosphere, and the recirculation efficiency $\epsilon$, which quantifies the energy transport within the atmosphere. In this work we aim to measure $A_g$ and $\epsilon$ for the planet WASP-178 b, a highly irradiated giant planet with an estimated equilibrium temperature of 2450 K.} We analyzed archival spectra and the light curves collected by Cheops and Tess to characterize the host WASP-178, refine the ephemeris of the system and measure the eclipse depth in the passbands of the two respective telescopes. We measured a marginally significant eclipse depth of 70$\pm$40 ppm in the Tess passband and statistically significant depth of 70$\pm$20 ppm in the Cheops passband. Combining the eclipse depth measurement in the Cheops (lambda_eff=6300 AA) and Tess (lambda_eff=8000 AA) passbands we constrained the dayside brightness temperature of WASP-178 b in the 2250-2800 K interval. The geometric albedo 0.1<$\rm A_g$<0.35 is in general agreement with the picture of poorly reflective giant planets, while the recirculation efficiency $\epsilon>$0.7 makes WASP-178 b an interesting laboratory to test the current heat recirculation models.

astro-ph.EP↗

arXiv2023

Refining the properties of the TOI-178 system with CHEOPS and TESS

The TOI-178 system consists of a nearby late K-dwarf transited by six planets in the super-Earth to mini-Neptune regime, with orbital periods between 1.9 and 20.7 days. All planets but the innermost one form a chain of Laplace resonances. Mass estimates derived from a preliminary radial velocity (RV) dataset suggest that the planetary densities do not decrease in a monotonic way with the orbital distance to the star, contrary to what one would expect based on simple formation and evolution models. To improve the characterisation of this key system and prepare for future studies (in particular with JWST), we perform a detailed photometric study based on 40 new CHEOPS visits, one new TESS sector, as well as previously published CHEOPS, TESS, and NGTS data. First we perform a global analysis of the 100 transits contained in our data to refine the transit parameters of the six planets and study their transit timing variations (TTVs). We then use our extensive dataset to place constraints on the radii and orbital periods of potential additional transiting planets in the system. Our analysis significantly refines the transit parameters of the six planets, most notably their radii, for which we now obtain relative precisions $\lesssim$3%, with the exception of the smallest planet $b$ for which the precision is 5.1%. Combined with the RV mass estimates, the measured TTVs allow us to constrain the eccentricities of planets $c$ to $g$, which are found to be all below 0.02, as expected from stability requirements. Taken alone, the TTVs also suggest a higher mass for planet $d$ than the one estimated from the RVs, which had been found to yield a surprisingly low density for this planet. However, the masses derived from the current TTV dataset are very prior-dependent and further observations, over a longer temporal baseline, are needed to deepen our understanding of this iconic planetary system.

astro-ph.EP↗

arXiv2023

CHEOPS and TESS view of the ultra-short period super-Earth TOI-561 b

Ultra-short period planets (USPs) are a unique class of super-Earths with an orbital period of less than a day and hence subject to intense radiation from their host star. While most of them are consistent with bare rocks, some show evidence of a heavyweight envelope, which could be a water layer or a secondary metal-rich atmosphere sustained by an outgassing surface. Much remains to be learned about the nature of USPs. The prime goal of the present work is to study the bulk planetary properties and atmosphere of TOI-561b, through the study of its transits and occultations. We obtained ultra-precise transit photometry of TOI-561b with CHEOPS and performed a joint analysis of this data with four TESS sectors. Our analysis of TOI-561b transit photometry put strong constraints on its properties, especially on its radius, Rp=1.42 +/- 0.02 R_Earth (at ~2% error). The internal structure modelling of the planet shows that the observations are consistent with negligible H/He atmosphere, however requiring other lighter materials, in addition to pure iron core and silicate mantle to explain the observed density. We find that this can be explained by the inclusion of a water layer in our model. We searched for variability in the measured Rp/R* over time to trace changes in the structure of the planetary envelope but none found within the data precision. In addition to the transit event, we tentatively detect occultation signal in the TESS data with an eclipse depth of ~27 +/- 11 ppm. Using the models of outgassed atmospheres from the literature we find that the thermal emission from the planet can mostly explain the observation. Based on this, we predict that NIR/MIR observations with JWST should be able to detect silicate species in the atmosphere of the planet. This could also reveal important clues about the planetary interior and help disentangle planet formation and evolution models.

astro-ph.EP↗

arXiv2023

Investigating the visible phase-curve variability of 55 Cnc e

55 Cnc e is an ultra-short period super-Earth transiting a Sun-like star. Previous observations in the optical range detected a time-variable flux modulation that is phased with the planetary orbital period, whose amplitude is too large to be explained by reflected light and thermal emission alone. The goal of the study is to investigate the origin of the variability and timescale of the phase-curve modulation in 55 Cnc e. To this end, we used the CHaracterising ExOPlanet Satellite (CHEOPS), whose exquisite photometric precision provides an opportunity to characterise minute changes in the phase curve from one orbit to the next. CHEOPS observed 29 individual visits of 55 Cnc e between March 2020 and February 2022. Based on these observations, we investigated the different processes that could be at the origin of the observed modulation. In particular, we built a toy model to assess whether a circumstellar torus of dust driven by radiation pressure and gravity might match the observed flux variability timescale. We find that the phase-curve amplitude and peak offset of 55 Cnc e do vary between visits. The sublimation timescales of selected dust species reveal that silicates expected in an Earth-like mantle would not survive long enough to explain the observed phase-curve modulation. We find that silicon carbide, quartz, and graphite are plausible candidates for the circumstellar torus composition because their sublimation timescales are long. The extensive CHEOPS observations confirm that the phase-curve amplitude and offset vary in time.We find that dust could provide the grey opacity source required to match the observations. However, the data at hand do not provide evidence that circumstellar material with a variable grain mass per unit area causes the observed variability. Future observations with the James Webb Space Telescope promise exciting insights into this iconic super-Earth.

astro-ph.EP↗

arXiv2023

TOI-5678 b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS

A large sample of long-period giant planets has been discovered thanks to long-term radial velocity surveys, but only a few dozen of these planets have a precise radius measurement. Transiting gas giants are crucial targets for the study of atmospheric composition across a wide range of equilibrium temperatures and for shedding light on the formation and evolution of planetary systems. Indeed, compared to hot Jupiters, the atmospheric properties and orbital parameters of cooler gas giants are unaltered by intense stellar irradiation and tidal effects. We identify long-period planets in the Transiting Exoplanet Survey Satellite (TESS) data as duo-transit events. To solve the orbital periods of TESS duo-transit candidates, we use the CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability period aliases in order to discard or confirm a transit event at a given period. We also collect spectroscopic observations with CORALIE and HARPS in order to confirm the planetary nature and measure the mass of the candidates. We report the discovery of a warm transiting Neptune-mass planet orbiting TOI-5678. After four non-detections corresponding to possible periods, CHEOPS detected a transit event matching a unique period alias. Joint modeling reveals that TOI-5678 hosts a 47.73 day period planet. TOI-5678 b has a mass of 20 (+-4) Me and a radius of 4.91 (+-0.08 Re) . Using interior structure modeling, we find that TOI-5678 b is composed of a low-mass core surrounded by a large H/He layer with a mass of 3.2 (+1.7, -1.3) Me. TOI-5678 b is part of a growing sample of well-characterized transiting gas giants receiving moderate amounts of stellar insolation (11 Se). Precise density measurement gives us insight into their interior composition, and the objects orbiting bright stars are suitable targets to study the atmospheric composition of cooler gas giants.

astro-ph.EP↗

arXiv2023

Refined parameters of the HD 22946 planetary system and the true orbital period of planet d

Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period planets in these systems often escape detection. HD 22946 is a bright star around which 3 transiting planets were identified via TESS photometry, but the true orbital period of the outermost planet d was unknown until now. We aim to use CHEOPS to uncover the true orbital period of HD 22946d and to refine the orbital and planetary properties of the system, especially the radii of the planets. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS. We identified 2 transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO radial velocity data. Finally, a combined model was fitted to the entire dataset. We successfully determined the true orbital period of the planet d to be 47.42489 $\pm$ 0.00011 d, and derived precise radii of the planets in the system, namely 1.362 $\pm$ 0.040 R$_\oplus$, 2.328 $\pm$ 0.039 R$_\oplus$, and 2.607 $\pm$ 0.060 R$_\oplus$ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3$\sigma$ upper limits for these respective planet masses, which are 13.71 M$_\oplus$, 9.72 M$_\oplus$, and 26.57 M$_\oplus$. We estimated that another 48 ESPRESSO radial velocities are needed to measure the predicted masses of all planets in HD 22946. Planet c appears to be a promising target for future atmospheric characterisation. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and internal structure.

astro-ph.EP↗

arXiv2023

TOI-1055 b: Neptunian planet characterised with HARPS, TESS, and CHEOPS

TOI-1055 is a Sun-like star known to host a transiting Neptune-sized planet on a 17.5-day orbit (TOI-1055 b). Radial velocity (RV) analyses carried out by two independent groups using nearly the same set of HARPS spectra have provided measurements of planetary masses that differ by $\sim$ 2$\sigma$. Our aim in this work is to solve the inconsistency in the published planetary masses by significantly extending the set of HARPS RV measurements and employing a new analysis tool that is able to account and correct for stellar activity. Our further aim was to improve the precision on measurements of the planetary radius by observing two transits of the planet with the CHEOPS space telescope. We fit a skew normal (SN) function to each cross correlation function extracted from the HARPS spectra to obtain RV measurements and hyperparameters to be used for the detrending. We evaluated the correlation changes of the hyperparameters along the RV time series using the breakpoint technique. We performed a joint photometric and RV analysis using a Markov chain Monte Carlo (MCMC) scheme to simultaneously detrend the light curves and the RV time series. We firmly detected the Keplerian signal of TOI-1055 b, deriving a planetary mass of $M_b=20.4_{-2.5}^{+2.6} M_{\oplus}$ ($\sim$12%). This value is in agreement with one of the two estimates in the literature, but it is significantly more precise. Thanks to the TESS transit light curves combined with exquisite CHEOPS photometry, we also derived a planetary radius of $R_b=3.490_{-0.064}^{+0.070} R_{\oplus}$ ($\sim$1.9%). Our mass and radius measurements imply a mean density of $\rho_b=2.65_{-0.35}^{+0.37}$ g cm$^{-3}$ ($\sim$14%). We further inferred the planetary structure and found that TOI-1055 b is very likely to host a substantial gas envelope with a mass of $0.41^{+0.34}_{-0.20}$ M$_\oplus$ and a thickness of $1.05^{+0.30}_{-0.29}$ R$_\oplus$.

astro-ph.EP↗