Luisa F. Zamudio-Ruvalcaba, Catherine C. Espaillat, Álvaro Ribas
et al.
Protoplanetary disks are an essential component of the planet-formation process. The amount of dust and gas in the disk constrains the number and size of planets that can form in a system. We analyze 178 T-Tauri stars, 18 in Serpens and 160 in L1641/L1647, and measure their disk dust masses using spectral energy distribution (SED) modeling and multiwavelength data, including 1.3 mm (ALMA band 6) fluxes from the literature. The disk masses calculated in this work are up to $\sim$2 times higher than those previously reported. We conclude that this is because disks may be partially optically thick at millimeter wavelengths while most calculations of the disk mass assume that the disk is optically thin at 1.3 mm. We calculate optical depths at 1.3 and 7 mm for a subset of the Serpens and L1641/L1647 disk sample and show that the vast majority of disks become optically thin at longer millimeter wavelengths; thus, observations at 7 mm (i.e., ALMA band 1) are vital to better characterize disk dust masses.
In his 1856 Adams Prize essay, James Clark Maxwell demonstrated that Saturn's rings cannot be comprised of a uniform rigid body. This is a consequence of the two-body gravitational interaction between a ring and planet resulting in instability. Similarly, it is also known that a so-called Dyson sphere encompassing a single star would be unstable due to Newton's shell theorem. A surprising finding is reported here that both a ring and a sphere (shell) can be stable in the restricted three-body problem. First, if two primary masses are considered in orbit about their common centre of mass, a large, uniform, infinitesimal ring enclosing the smaller of the masses can in principle be stable under certain conditions. Similarly, a Dyson sphere can, be stable, if the sphere encloses the smaller of the two primary masses, again under certain conditions. These findings extend Maxwell's results on the dynamics of rings and have an interesting bearing on so-called Ringworlds and Dyson spheres from fiction. Moreover, the existence of passively stable orbits for such large-scale structures may have implications for so-called techno-signatures in search for extra-terrestrial intelligence studies.
Convection is a fundamental mechanism for energy transport in stars and planets, playing a pivotal role in shaping their structures and evolution. The Mixing-Length Theory, a monomodal approach to convection, is widely adopted and implemented in 1D stellar structure and evolution codes. However, it overlooks the combined effects of rotation and magnetic fields, which are ubiquitous across a wide range of stars and planets. To address this limitation, we extend the Mixing-Length Theory including both rotation and magnetic fields within a Cartesian set-up. Building on the work by Stevenson 1979, we use a heat-flux maximisation principle, which amounts to selecting the convective mode that carries the most heat. Our findings show that both rotation and magnetic fields individually tend to suppress convection. However, when combined, they can enhance convection strength under certain conditions. We derive expressions for the root-mean-square (rms) velocity, characteristic length scale, and degree of superadiabaticity as functions of the rotation rate and magnetic field strength. These results offer new insights for more accurately modeling convection and its impact on stellar and planetary structures in one-dimensional and forthcoming multi-dimensional evolution models.
Sebastián Zúñiga-Fernández, Michael Gillon, SPECULOOS consortium
The SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) project aims to detect temperate terrestrial planets transiting nearby ultracool dwarfs, including late M-dwarf stars and brown dwarfs, which are well-suited for atmospheric characterization using the James Webb Space Telescope (JWST) and upcoming giant telescopes like the European Extremely Large Telescope (ELT). Led by the University of Liège, SPECULOOS is conducted in partnership with the University of Cambridge, the University of Birmingham, the Massachusetts Institute of Technology, the University of Bern, and ETH Zurich. The project operates a network of robotic telescopes at two main observatories: SPECULOOS-South in Chile, with four telescopes, and SPECULOOS-North in Tenerife, currently with one telescope (soon to be two). This network is complemented by the SAINT-EX telescope located in San Pedro Mártir, Mexico. In this paper, we review the status of our facilities after five years of operations, the current challenges and development plans, and our latest scientific results.
Ignas Snellen, Sebastiaan Haffert, Matthew Kenworthy
et al.
Transmission and eclipse spectroscopy have been invaluable tools for the characterisation of extrasolar planet atmospheres. While they will continue to provide many new insights and discoveries in the decade(s) to come, these methods are running up against sources of stellar noise from stellar surface inhomogeneities and variability. In this white paper we discuss how the next steps in the characterisation of small, temperate rocky planets requires high-contrast imaging, making the planetary systems around our closest neighbouring stars the new frontier in exoplanet science. The Extremely Large Telescopes (ELTs) will be at the forefront of this quest. The Planetary Camera and Spectrograph (PCS) on ESO's ELT and GmagAO-X on the GMT are planned to become operational in the 2035-2040 time-frame, allowing the characterisation of up to dozen(s) of rocky planets around nearby red dwarf stars. We discuss what role there will be still to play for ground-based exoplanet characterisation in the era of the space-borne Habitable Worlds Observatory and LIFE missions.
Tidal torques can alter the spins of tidally interacting stars and planets, usually over shorter timescales than the tidal damping of orbital separations or eccentricities. Simple tidal models predict that, in eccentric binary or planetary systems, rotation periods will evolve toward a "pseudosynchronous" ratio with the orbital period. However, this prediction does not account for "inertial" waves that are present in stars or gaseous planets with (i) convective envelopes and (ii) even very slow rotation. We demonstrate that tidal driving of inertial oscillations in eccentric systems generically produces a network of stable "synchronization traps" at ratios of orbital to rotation period that are simple to predict but can deviate significantly from pseudosynchronization. The mechanism underlying spin synchronization trapping is similar to tidal resonance locking, involving a balance between torques that is maintained automatically by the scaling of inertial mode frequencies with the rotation rate. In contrast with many resonance locking scenarios, however, the torque balance required for synchronization trapping need not drive mode amplitudes to nonlinearity. Synchronization traps may provide an explanation for low-mass stars and hot Jupiters with observed rotation rates that deviate from pseudosynchronous or synchronous expectations.
Directly imaging Earth-like exoplanets within habitable zones is challenging because faint signals can be obscured by exozodiacal dust, analogous to our solar system's zodiacal dust. This dust scatters starlight, creating a bright background noise. This paper introduces Toy Coronagraph, a Python package designed to quantify the impact of this dust on exoplanet detection. It takes circularly symmetric disk images point spread functions (PSFs), and exoplanet orbital parameters as input, generating key metrics like contrast curves, signal-to-noise ratios, and dynamic visualizations of exoplanet motion under the dust background. The package also provides tools for generating vortex coronagraph PSFs and includes example disk images. Toy Coronagraph empowers researchers to understand exozodiacal dust, develop mitigation strategies, and optimize future telescope designs and mission time, ultimately advancing the search for potentially habitable worlds. Future work will focus on handling non-circularly symmetric inputs, incorporating realistic noise models, and estimating exoplanet yield rates for future space telescope missions.
The presence of cubic PuH2 and PuH3, the products of hydrogen corrosion of Pu, during long-term storage is of concern because of the materials’ pyrophoricity and ability to catalyse the oxidation reaction of Pu to form PuO2. Here, we modelled cubic PuH2 and PuH3 using Density Functional Theory (DFT) and assessed the performance of the PBEsol+U+SOC (0 ≤ U ≤ 7 eV) including van der Waals dispersion using the Grimme D3 method and the hybrid HSE06sol+SOC. We investigated the structural, magnetic and electronic properties of the cubic hydride phases. We considered spin–orbit coupling (SOC) and non-collinear magnetism to study ferromagnetic (FM), longitudinal and transverse antiferromagnetic (AFM) orders aligned in the <100>, <110> and <111> directions. The hybrid DFT confirmed that FM orders in the <110> and <111> directions were the most stable for cubic PuH2 and PuH3, respectively. For the standard DFT, the most stable magnetic order is dependent on the value of U used, with transitions in the magnetic order at higher U values (U > 5 eV) seen for both PuH2 and PuH3.
The electron density profile on a plasma surface has a decisive influence on the mechanism and characteristics of the plasma high-order harmonic generation. When the pre-pulse has a similar spatial and temporal distribution as the main laser pulse, the plasma surface on the target will expand to form a convex profile of the similar size as the focal spot of the main pulse. We experimentally observed that the divergence of the harmonics generated by the relativistic laser light incident on a silica target has a saddle-shaped structure. The two-dimensional particle-in-cell simulation with convex plasma surfaces explains the experimental results very well and infers a 0.12λL plasma scale length around the center of the convex profile. Further, we qualitatively explained that the asymmetry of the saddle-shaped harmonic divergence is caused by oblique incidence.
Galáxias desempenharam e seguem desempenhando um relevante papel na determinação da matéria escura e suas propriedades. Apresentamos uma introdução sobre a dinâmica interna de galáxias, em particular sobre a rotação de galáxias de disco, e sobre como seus dados indicam a presença de matéria escura. Este texto é destinado a qualquer leitor interessado no assunto, ainda que sem experiência prévia em astrofísica.
Observations of the main sequence F3 V star KIC 8462852 (also known as Boyajian's star) revealed extreme aperiodic dips in flux up to 20% during the four years of the Kepler mission. Smaller dips (< 2%) were also observed with ground-based telescopes between May and September 2017. We investigated possible correlation between recent dips and the major dips in the last 100 days of the Kepler mission. We compared Kepler light curve data, 2017 data from two observatories (TFN, OGG) which are part of the Las Cumbres Observatory (LCO) network and Sternberg observatory archival data, and determined that observations are consistent with a 1,574-day (4.31 year) periodicity of a transit (or group of transits) orbiting Boyajian's star within the habitable zone. It is unknown if transits that have produced other major dips as observed during the Kepler mission (e.g. D792) share the same orbital period. Nevertheless, the proposed periodicity is a step forward in guiding future observation efforts.
By monitoring a large number of stars in the Local Group galaxies, we can detect nanolensing events by sub-lunar mass compact objects (SULCOs) such as primordial black holes (PBHs) and rogue (free-floating) dwarf planets in the Milky Way halo. In contarst to microlensing by stellar-mass objects, the finite-source size effect becomes important and the lensing time duration becomes shorter ($\sim 10^{1-4}\,\textrm{s}$). Using stars with $V<26$ in M33 as sources, for one-night observation, we would be able to detect $10^{3-4}$ nanolensing events caused by SULCOs in the Milky Way halo with a mass of $10^{-9}M_{\odot}$ to $10^{-7}M_{\odot}$ for sources with S/N$>5$ if SULCOs constitute all the dark matter components. Moreover, we expect $10^{1-2}$ events in which bright blue stars with S/N$>100$ are weakly amplified due to lensing by SULCOs with a mass range of $10^{-11}M_{\odot}$ to $10^{-9}M_{\odot}$. Thus the method would open a new window on SULCOs in the Milky Way halo that would otherwise not be observable.
We present the FARGO3D code, recently publicly released. It is a magnetohydrodynamics code developed with special emphasis on protoplanetary disks physics and planet-disk interactions, and parallelized with MPI. The hydrodynamics algorithms are based on finite difference upwind, dimensionally split methods. The magnetohydrodynamics algorithms consist of the constrained transport method to preserve the divergence-free property of the magnetic field to machine accuracy, coupled to a method of characteristics for the evaluation of electromotive forces and Lorentz forces. Orbital advection is implemented, and an N-body solver is included to simulate planets or stars interacting with the gas. We present our implementation in detail and present a number of widely known tests for comparison purposes. One strength of FARGO3D is that it can run on both "Graphical Processing Units" (GPUs) or "Central Processing unit" (CPUs), achieving large speed up with respect to CPU cores. We describe our implementation choices, which allow a user with no prior knowledge of GPU programming to develop new routines for the CPU, and have them translated automatically for the GPU.
We investigate the effect that the turbulent mixing strength parameter $α_{\rm{turb}}$ plays on near-infrared polarimetric and sub-millimetre interferometric imaging observations of transitional discs (TDs) with a gap carved by a planet. We generate synthetic observations of these objects with ALMA and VLT/SPHERE-ZIMPOL by combining hydrodynamical, dust evolution, radiative transfer and instrument models for values of $α_{\rm{turb}}=[10^{-4}, 10^{-3}, 10^{-2}]$. We find that, through a combination of effects on the viscosity of the gas, the turbulent mixing and dust evolution processes, $α_{\rm{turb}}$ strongly affects the morphology of the dust distribution that can be traced with these observations. We constrain the value of $α_{\rm{turb}}$ to be within an order of magnitude of $10^{-3}$ in TD sources that show cavities in sub-mm continuum images while featuring continuous distribution of dust or smaller cavities in NIR-polarimetric images.
[Abridged] Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability, and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability, supplemented with a survey of numerical simulations that aim to capture the non-linear evolution. We emphasize the role of thermodynamics and large scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analytic predictions and numerical results. We highlight open questions related to (1) the development of a turbulent cascade in thin disks, and (2) the role of mode-mode coupling in setting the maximum angular momentum transport rate in thick disks.
David H. Kasper, Tyler G. Ellis, Rex R. Yeigh
et al.
We have implemented upgrades to the University of Wyoming's Red Buttes Observatory (RBO) to allow remote and autonomous operations using the 0.6 m telescope. Detailed descriptions of hardware and software components provide sufficient information to guide upgrading similarly designed telescopes. We also give a thorough description of the automated and remote operation modes with intent to inform the construction of routines elsewhere. Because the upgrades were largely driven by the intent to perform exoplanet transit photometry, we discuss how this science informed the automation process. A sample exoplanet transit observation serves to demonstrate RBO's capability to perform precision photometry. The successful upgrades have equipped a legacy observatory for a new generation of automated and rapid-response observations.
We describe our second installment of the 4.75 GHz survey of ultracool dwarfs (UCDs) conducted with the Arecibo radio telescope, which has observed 27 such objects and resulted in the detection of sporadic flaring from the T6 dwarf, WISEPC J112254.73+255021.5. We also present follow up observations of the first radio-emitting T dwarf, 2MASS J10475385+2124234, a tentatively identified radio emitting L1 dwarf, 2MASS J1439284+192915, and the known radio-flaring source, 2MASS J13142039+132011 AB. Our new data indicate that 2MASS J1439284+192915 is not a radio flaring source. The overall detection rate of our unbiased survey for radio-flaring UCDs is ~5% for new sources, with a detection rate for each spectral class of ~5-10%. Evidently, radio luminosity of the UCDs does not appear to monotonically decline with spectral type from M7 dwarfs to giant planets, in contradiction to theories of the magnetic field generation and internal structure of these objects. Along with other, recently published results, our data exemplify the unique value of using radio surveys to reveal and study properties of substellar magnetic activity.
Abstract We use the Apparent Motion Parameters (AMP) method for the determination of orbits of visual double stars (Kiselev & Kiyaeva 1980). The quality of AMP orbits is completely dependent on the precision of parameters of relative positions and motions at the same instant. They are calculated on the basis of a short arc of observations. To determine these parameters, we use recent high precision observations obtained with the best modern techniques. New orbits of three stars are presented.