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Earlier this year, Representative Virginia Foxx (R-NC) introduced the College Cost Reduction Act (CCRA), a bill to reform higher education grant and loan programs and to establish new accountability rules for colleges. A key part of the bill would replace the myriad income-driven repayment (IDR) plans for federal student loans, including the Biden administration's Saving on a Valuable Education (SAVE) plan, with a new repayment plan. The bill features income-based payments, a cap on total payments, and monthly subsidies that waive unpaid interest and reduce principal balances for certain borrowers. In this brief, the authors compare the CCRA plan with the Biden administration's SAVE plan, the most generous IDR plan. The authors also compare the CCRA plan with another version of IDR, the Pay as You Earn (PAYE) plan.

Data showing what students earn after attending higher education institutions have become increasingly available, bolstering calls from policymakers and advocates that government financial aid programs should be tied to those outcomes. Often overlooked, however, is that these data and policies usually reflect the earnings of only students who graduate. A key rationale for using earnings data in accountability policies is that they help reveal whether the education generates a positive return on investment. Ignoring the earnings outcomes of noncompleters, therefore, may provide an incomplete assessment of that metric, especially for institutions with high dropout rates. This brief uses undergraduate earnings data from the College Scorecard to estimate how much earnings differ based on whether noncompleters are included. These findings help reveal where current quality assurance policies that focus only on completers' earnings may be misaligned with what a typical student is likely to earn when enrolling at a higher education institution.

Atmospheric and dynamical processes are thought to play a major role in shaping the distribution of close-in exoplanets. A striking feature of such distribution is the Neptunian desert, a dearth of Neptunes on the shortest-period orbits. We aimed to define the boundaries of the Neptunian desert and study its transition into the savanna, a moderately populated region at larger orbital distances. We built a sample of planets and candidates based on the Kepler DR25 catalogue and weighed it according to the transit and detection probabilities. We delimited the Neptunian desert as the close-in region of the period-radius space with no planets at a 3$\sigma$ level, and provide the community with simple, ready-to-use approximate boundaries. We identified an overdensity of planets separating the Neptunian desert from the savanna (3.2 days $ \lessapprox P_{\rm orb}$ $\lessapprox$ 5.7 days) that stands out at a 4.7$\sigma$ level above the desert and at a 3.5$\sigma$ level above the savanna, which we propose to call the Neptunian ridge. The period range of the ridge matches that of the hot Jupiter pileup ($\simeq$3-5 days), which suggests that similar evolutionary processes might act on both populations. We find that the occurrence fraction between the pileup and warm Jupiters is about twice that between the Neptunian ridge and savanna. Our revised landscape supports a previous hypothesis that a fraction of Neptunes were brought to the edge of the desert (i.e. the newly identified ridge) through high-eccentricity tidal migration (HEM) late in their life, surviving the evaporation that eroded Neptunes having arrived earlier in the desert. The ridge thus appears as a true physical feature illustrating the interplay between photoevaporation and HEM, providing further evidence of their role in shaping the distribution of close-in Neptunes., Comment: Accepted for publication in A&A

High-resolution spectrographs open a detailed window onto the atmospheres of stars and planets. As the number of systems observed with different instruments grows, it is crucial to develop a standard in analyzing spectral time series of exoplanet transits and occultations, for the benefit of reproducibility. Here, we introduce the ANTARESS workflow, a set of methods aimed at processing high-resolution spectroscopy datasets in a robust way and extracting accurate exoplanetary and stellar spectra. While a fast preliminary analysis can be run on order-merged 1D spectra and cross-correlation functions (CCFs), the workflow was optimally designed for extracted 2D echelle spectra to remain close to the original detector counts, limit the spectral resampling, and propagate the correlated noise. Input data from multiple instruments and epochs were corrected for relevant environmental and instrumental effects, processed homogeneously, and analyzed independently or jointly. In this first paper, we show how planet-occulted stellar spectra extracted along the transit chord and cleaned from planetary contamination provide a direct comparison with theoretical stellar models and enable a spectral and spatial mapping of the photosphere. We illustrate this application of the workflow to archival ESPRESSO data, using the Rossiter-McLaughlin effect Revolutions (RMR) technique to confirm the spin-orbit alignment of HD\,209458b and unveil biases in WASP-76b's published orbital architecture. Because the workflow is modular and its concepts are general, it can support new methods and be extended to additional spectrographs to find a range of applications beyond the proposed scope. In a companion paper, we will present how planet-occulted spectra can be processed further to extract and analyze planetary spectra decontaminated from the star, providing clean and direct measurements of atmospheric properties., Comment: 30 pages and 30 figures (plus Appendix). Accepted for publication in A&A

Rising college prices and student debt, the growth and collapse of online for-profit colleges, and expansions of federal grant, loan, and loan forgiveness policies have increased calls for more accountability in our higher education system. And there is significant consensus among lawmakers that the existing set of quality assurance policies for federal aid programs are not protecting students and taxpayers. But although these conditions have generated many proposals for policies to hold colleges accountable, none have won broad support among lawmakers. To help advance the reform debate, we review and compare recent proposed policies that address accountability and, drawing on interviews we conducted with former congressional staff members and higher education advocates, what factors have prevented policymakers from enacting reforms, and what conditions may be necessary to bring about policy changes. The report reveals that lawmakers, researchers, and advocates have put forth a wide range of reform proposals to strengthen quality assurance rules for federal aid programs. This variety implies that there is considerable disagreement over what reforms are needed and disagreement over the underlying problem. Some proposals focus on graduation rates, while others assess how colleges spend money. The most common approach among the proposals is to judge colleges on how their students fare in repaying their student loans, suggesting a possible place for consensus. The report also shows there are many political and design roadblocks to reform despite broad support for more accountability. The current political environment makes bipartisan policymaking difficult. Additionally, higher education is an open-access and diverse system of institutions, making policymakers reluctant to pass policies that might reduce access, particularly for low-income students and students from underrepresented ethnic and racial groups. Still, the individuals we interviewed all discussed several major design issues that will further frustrate reform efforts, such as whether students who do not receive federal aid should be included in the policies and whether some fields and institutions should be exempt. Regardless, many of the recent reform proposals illustrate the need to improve assurance for aid programs and should ultimately encourage lawmakers to work toward reforms that strengthen our higher education system and federal aid programs.

A systematic, population-level discrepancy exists between the densities of exoplanets whose masses have been measured with transit timing variations (TTVs) versus those measured with radial velocities (RVs). Since the TTV planets are predominantly nearly resonant, it is still unclear whether the discrepancy is attributed to detection biases or to astrophysical differences between the nearly resonant and non resonant planet populations. We defined a controlled, unbiased sample of 36 sub-Neptunes characterised by Kepler, TESS, HARPS, and ESPRESSO. We found that their density depends mostly on the resonant state of the system, with a low probability (of $0.002_{-0.001}^{+0.010}$) that the mass of (nearly) resonant planets is drawn from the same underlying population as the bulk of sub-Neptunes. Increasing the sample to 133 sub-Neptunes reveals finer details: the densities of resonant planets are similar and lower than non-resonant planets, and both the mean and spread in density increase for planets that are away from resonance. This trend is also present in RV-characterised planets alone. In addition, TTVs and RVs have consistent density distributions for a given distance to resonance. We also show that systems closer to resonances tend to be more co-planar than their spread-out counterparts. These observational trends are also found in synthetic populations, where planets that survived in their original resonant configuration retain a lower density; whereas less compact systems have undergone post-disc giant collisions that increased the planet's density, while expanding their orbits. Our findings reinforce the claim that resonant systems are archetypes of planetary systems at their birth.

Commercially impactful quantum algorithms such as quantum chemistry and Shor's algorithm require a number of qubits and gates far beyond the capacity of any existing quantum processor. Distributed architectures, which scale horizontally by networking modules, provide a route to commercial utility and will eventually surpass the capability of any single quantum computing module. Such processors consume remote entanglement distributed between modules to realize distributed quantum logic. Networked quantum computers will therefore require the capability to rapidly distribute high fidelity entanglement between modules. Here we present preliminary demonstrations of some key distributed quantum computing protocols on silicon T centres in isotopically-enriched silicon. We demonstrate the distribution of entanglement between modules and consume it to apply a teleported gate sequence, establishing a proof-of-concept for T centres as a distributed quantum computing and networking platform., Comment: 14 pages, 13 figures

The TOI-178 system consists of a nearby late K-dwarf transited by six planets in the super-Earth to mini-Neptune regime, with radii ranging from 1.2 to 2.9 earth radius and orbital periods between 1.9 and 20.7 days. All planets but the innermost one form a chain of Laplace resonances. The fine-tuning and fragility of such orbital configurations ensure that no significant scattering or collision event has taken place since the formation and migration of the planets in the protoplanetary disc, hence providing important anchors for planet formation models. We aim to improve the characterisation of the architecture of this key system, and in particular the masses and radii of its planets. In addition, since this system is one of the few resonant chains that can be characterised by both photometry and radial velocities, we aim to use it as a test bench for the robustness of the planetary mass determination with each technique. We perform a global analysis of all available photometry and radial velocity. We also try different sets of priors on the masses and eccentricity, as well as different stellar activity models, to study their effects on the masses estimated by each method. We show how stellar activity is preventing us from obtaining a robust mass estimation for the three outer planets using radial velocity data alone. We also show that our joint photo-dynamical and radial velocity analysis resulted in a robust mass determination for planets c to g, with precision of 12% for the mass of planet c, and better than 10% for planets d to g. The new precisions on the radii range from 2 to 3%. The understanding of this synergy between photometric and radial velocity measurements will be valuable during the PLATO mission. We also show that TOI-178 is indeed currently locked in the resonant configuration, librating around an equilibrium of the chain.

Gravitational waves from black-hole merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models - and also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are the remnants of massive metal-poor stars. Gaia astrometry is expected to uncover many Galactic wide-binary systems containing dormant BHs, which may not have been detected before. The study of this population will provide new information on the BH-mass distribution in binaries and shed light on their formation mechanisms and progenitors. As part of the validation efforts in preparation for the fourth Gaia data release (DR4), we analysed the preliminary astrometric binary solutions, obtained by the Gaia Non-Single Star pipeline, to verify their significance and to minimise false-detection rates in high-mass-function orbital solutions. The astrometric binary solution of one source, Gaia BH3, implies the presence of a 32.70 \pm 0.82 M\odot BH in a binary system with a period of 11.6 yr. Gaia radial velocities independently validate the astrometric orbit. Broad-band photometric and spectroscopic data show that the visible component is an old, very metal-poor giant of the Galactic halo, at a distance of 590 pc. The BH in the Gaia BH3 system is more massive than any other Galactic stellar-origin BH known thus far. The low metallicity of the star companion supports the scenario that metal-poor massive stars are progenitors of the high-mass BHs detected by gravitational-wave telescopes. The Galactic orbit of the system and its metallicity indicate that it might belong to the Sequoia halo substructure. Alternatively, and more plausibly, it could belong to the ED-2 stream, which likely originated from a globular cluster that had been disrupted by the Milky Way., Comment: 23 pages, accepted fro publication in A&A Letters. New version with small fixes

The Biden administration launched a new income-driven repayment (IDR) plan for federal student loans this year called Saving on a Valuable Education (SAVE). The plan cuts borrowers' monthly payments compared with current IDR plans, provides earlier loan forgiveness for smaller debts, and prevents unpaid interest from accumulating. To better understand how borrowers from different degree programs and higher education institutions will benefit from the new SAVE plan, this report uses College Scorecard data to examine loan repayment patterns for more than 25,000 postsecondary programs. Student loans--and loan forgiveness--will become a more central part of how the federal government finances higher education as a result of the SAVE plan. The findings suggest that in many cases, undergraduate students could be encouraged to take on federal student loans and err on the side of borrowing more.

The Biden administration is implementing a new income-driven repayment (IDR) plan for federal student loans called Saving on a Valuable Education (SAVE). The SAVE plan adds to existing IDR plans and reduces borrowers' monthly payments and shortens the time certain borrowers must repay before their debts are forgiven compared with current options. Borrowers who qualify for the Public Service Loan Forgiveness (PSLF) program--which forgives debt for borrowers working in a wide range of government and nonprofit jobs after 10 years--can also use the SAVE plan and are likely to receive some of the largest benefits from the new plan. The PSLF program has historically benefited graduate borrowers most, but the SAVE plan will now allow those with only undergraduate degrees to also qualify for large benefits. These changes are large enough to have ripple effects on other higher education policies and labor markets for certain credentials, especially those in education and social work. This brief examines how much borrowers from two large professions that are typically eligible for PSLF, teaching and social work, could benefit from the SAVE plan. The new plan is likely to subsidize a large share of the debt used to finance education and social work degrees in the coming years. The data show that borrowers with a bachelor's degree in education or social work with the typical loan balance of $32,000 would see their total loan payments drop to less than $7,000 under the SAVE plan and PSLF compared with $20,000 to $24,000 under current IDR options. Borrowers with master's degrees in teaching or social work will also see their total payments cut under the SAVE plan when using PSLF, but the reduction is largest for those with only undergraduate degrees. Larger PSLF benefits may influence students' decisions about whether to take on federal student loans and how much to borrow. For some graduate degrees, such as social work, the federal loan program could end up subsidizing the majority of the cost of obtaining these degrees. In response, policymakers may want to consider whether the current policy that allows graduate students to borrow for the full cost of their degree is optimal and whether new quality assurance rules are needed to guard against programs overcharging for graduate degrees leading to public service careers. Additionally, as PSLF is set to provide larger benefits to a broader set of borrowers because of the SAVE plan, policymakers must ensure that ongoing efforts to improve how the program is administered are successful.

Photoacoustic tomography (PAT) is a rapidly-evolving medical imaging modality that combines optical absorption contrast with ultrasound imaging depth. One challenge in PAT is image reconstruction with inadequate acoustic signals due to limited sensor coverage or due to the density of the transducer array. Such cases call for solving an ill-posed inverse reconstruction problem. In this work, we use score-based diffusion models to solve the inverse problem of reconstructing an image from limited PAT measurements. The proposed approach allows us to incorporate an expressive prior learned by a diffusion model on simulated vessel structures while still being robust to varying transducer sparsity conditions., Comment: 5 pages

The athletic achievements of African athletes in global running championships have long been subject to scientific and sociological inquiry. During the 1990s, a popular narrative emerged, suggesting that West African lineage conferred inherent sprinting advantages, and that North, South and East African's are specialized for longer distances. Part and parcel to this narrative was the enthusiastic belief that it would very soon be substantiated by a genotyping revolution that would enable prognostication of individual athletic potential. We revisit this hypothesis in the post-genomic era. First, we compare the global running records used to generate the racialist hypotheses with performances over the last twenty years (2004- 2023). Focusing on the 100m reveals intriguing trends, including the ascendancy of Jamaica as a sprint powerhouse and the elevation of South African and East Asian sprinters to the global stage, a direct challenge to the racialist paradigm. In line with an in-depth analysis of the influences on elite runners, we build a regression model to predict 100m performance based on environmental and psychological factors. Next, we direct our attention to 1500m, where the last two British champions have been part of a European resurgence that has not been seen in decades. Examining three different time periods, we identify a thirty year national slowdown (1989-2018). Adapting our model to this time period reveals striking evidence that racial perception has greater impact on performance than racial physiology. Synthesizing these findings, we introduce a psychocultural hypothesis, positing that interactions between racial perceptions and social dynamics shape the global distribution of running performance. We contrast this hypothesis with the racialist paradigm and propose extending it beyond sport where it offers insight across many domains., Comment: 12 Pages, 6 Figures

The new student loan repayment plan formally proposed by the Biden administration would let borrowers make lower payments and have remaining loans forgiven sooner than under current plans. Under the proposed income-driven repayment (IDR) plan, most undergraduate borrowers with typical debt levels--and nearly 90 percent of those with certificates and associate's degrees--would have at least some of their loans forgiven if they enroll in IDR. Under the newly announced plan, most undergraduates who take on typical debt loads would have at least some of their loans forgiven if they use the plan. Borrowers with certificates or associate's degrees would benefit the most, with 89 percent receiving some forgiveness and 38 percent paying nothing. The proposed IDR plan is the most generous yet, but it will make the student loan program significantly more expensive and risks encouraging students to take on more debt, which could have implications for their personal finances even if it is eventually forgiven.

The Biden administration is pursuing two higher education policies through a series of rulemaking processes that aim to make higher education more affordable and less risky for students. One policy focuses on the system's back end by helping students repay their loans, and the other focuses on the front end by cutting off access to federal aid for educational programs where graduate earnings are consistently low. The administration's new income-driven repayment (IDR) plan for student loans is the back-end policy, and the gainful employment (GE) rule is the front-end policy. In this brief, the authors estimate how much the Biden administration's GE and IDR policies might complement one another by estimating repayment rates for loans repaid in IDR before and after the GE rule goes into effect. This approach gauges how well the two policies align and can show how much the GE rule screens out programs where typical borrowers' debt and earnings profiles are likely to lead to loan forgiveness in IDR. The approach also can reveal how much debt will be left unpaid under the Biden IDR plan in programs that are currently exempt from GE. That information can help policymakers consider whether additional quality assurance policies may be necessary and whether loan forgiveness benefits in the Biden IDR plan should be targeted differently.

Context. The observed scarcity of brown dwarfs in close orbits (within 10 au) around solar-type stars poses significant questions about the origins of these substellar companions. These questions impact our broader understanding of planetary formation processes. However, to resolve these formation mechanisms, accurate observational constraints are essential. Most of the brown dwarfs have been discovered by radial velocity surveys, but this method introduces uncertainties due to its inability to determine the orbital inclination, leaving the true mass-and thus their true nature-unresolved. This highlights the crucial role of astrometric data, helping us distinguish between genuine brown dwarfs and stars. Aims. We aim to refine the mass estimates of massive companions to solar-type stars, mostly discovered through radial velocity measurements and subsequently validated using Gaia DR3 astrometry, to gain a clearer understanding of their true mass and occurrence rates. Methods. We selected a sample of 31 sources with substellar companion candidates validated by Gaia DR3 and with available radial velocities. Using the Gaia DR3 solutions as prior information, we performed an MCMC fit with the available radial velocity measurements to integrate these two sources of data and thus obtain an estimate of their true mass. Results. Combining radial velocity measurements with Gaia DR3 data led to more precise mass estimations, leading us to reclassify several systems initially labeled as brown dwarfs as low-mass stars. Out of the 32 analyzed companions, 13 are determined to be stars, 17 are sub-stellar, and 2 have inconclusive results with the current data. Importantly, using these updated masses, we reevaluated the occurrence rate of brown dwarf companions (13-80 M$_{jup}$ ) on close orbits (<10 au) in the CORALIE sample, determining a tentative occurrence rate of $0.8^{+0.3}_{-0.2}\%$, Comment: Accepted by A&A

Policymakers enacted a series of reforms in the mid-2000s that significantly expanded benefits in the federal student loan program for students pursuing graduate degrees. These reforms allow students to borrow up to the full cost of attendance for their degrees and use an Income-Driven Repayment (IDR) program that offers loan forgiveness after 20 years of payments or as early as 10 years for those who use the Public Service Loan Forgiveness Program. Despite virtually unlimited access to federal loans and the availability of a generous IDR program, policymakers have done little to prevent institutions from offering high-cost programs and those that consistently leave students with high debts relative to their incomes. To inform the future development of quality assurance policies, this report analyzes debt and earnings data in the Department of Education's College Scorecard for master's degree programs. Although federal loan policies increase access to graduate degrees and the economic payoff they provide, these policies also entail risks for both students and taxpayers. The College Scorecard provides a new source of information that policymakers can use to determine where those risks are greatest and gauge the potential effects of quality assurance policies that target programs where borrowers take on high debt relative to what they can expect to earn with their degrees.

When the Obama administration implemented the first gainful employment (GE) rule in 2014 to protect students from education credentials that lead to unaffordable debts, virtually all programs at public institutions passed the test. The Biden administration is developing its own GE rule after the Trump administration repealed the Obama-era rule. A discussion draft of the rule released earlier this year included a new minimum earnings test based on high school graduates' earnings. One in five certificate programs at public institutions could fail this requirement, causing them to fail the overall GE rule and lose eligibility for federal aid. This essay examines the undergraduate certificate programs at public institutions that fail this proposed high school earnings test. Understanding the characteristics of these programs and the students they enroll can inform the ongoing development of the GE rule. This information can help policymakers judge whether the GE rule effectively targets low-quality programs and whether these programs leave students worse off than if they had never enrolled, the commonly cited rationale for a high school earnings test. [Additional funding for this essay was provided by the Stand Together Trust.]

The Biden administration is developing regulations around gainful employment (GE) that would protect students from career-oriented college programs that don't adequately serve their students. A draft GE rule released earlier this year would require that graduates of certificate programs at public and nonprofit colleges and nearly all programs at for-profit colleges meet a debt-to-earnings test to be eligible for federal aid. Using debt to measure value involves major limitations, however, and programs with poor outcomes can pass a debt-to-earnings test if students finance their tuition with federal grant aid or out-of-pocket funds instead of loans. Using data to examine the effects of several thresholds, the authors analyze a tuition-to-earnings test for the GE rule and compare it with the effects of the Biden administration's proposed debt-to-earnings test. This test more directly measures what a program costs, is not affected by the share of students borrowing, and measures prices charged to all students regardless of the type or amount of federal aid they received. [Additional funding for this essay was provided by the Stand Together Trust.]

Recent work on the characterization of small exoplanets has allowed us to accumulate growing evidence that the sub-Neptunes with radii greater than $\sim2.5\,R_\oplus$ often host H$_2$/He-dominated atmospheres both from measurements of their low bulk densities and direct detections of their low mean-molecular-mass atmospheres. However, the smaller sub-Neptunes in the 1.5-2.2 R$_\oplus$ size regime are much less understood, and often have bulk densities that can be explained either by the H$_2$/He-rich scenario, or by a volatile-dominated composition known as the "water world" scenario. Here, we report the detection of water vapor in the transmission spectrum of the $1.96\pm0.08$ R$_\oplus$ sub-Neptune GJ9827d obtained with the Hubble Space Telescope. We observed 11 HST/WFC3 transits of GJ9827d and find an absorption feature at 1.4$\mu$m in its transit spectrum, which is best explained (at 3.39$\sigma$) by the presence of water in GJ9827d's atmosphere. We further show that this feature cannot be caused by unnoculted star spots during the transits by combining an analysis of the K2 photometry and transit light-source effect retrievals. We reveal that the water absorption feature can be similarly well explained by a small amount of water vapor in a cloudy H$_2$/He atmosphere, or by a water vapor envelope on GJ9827d. Given that recent studies have inferred an important mass-loss rate ($>0.5\,$M$_\oplus$/Gyr) for GJ9827d making it unlikely to retain a H-dominated envelope, our findings highlight GJ9827d as a promising water world candidate that could host a volatile-dominated atmosphere. This water detection also makes GJ9827d the smallest exoplanet with an atmospheric molecular detection to date., Comment: Published in ApJL, 11 pages, 6 figures

The Rocky Planet Search (RPS) program is dedicated to a blind radial velocity (RV) search of planets around bright stars in the Northern hemisphere, using the high-resolution echelle spectrograph HARPS-N installed on the Telescopio Nazionale Galileo (TNG). The goal of this work is to revise and update the properties of three planetary systems by analysing the HARPS-N data with state-of-the-art stellar activity mitigation tools. The stars considered are HD 99492 (83Leo B), HD 147379 (Gl617 A) and HD 190007. We employ a systematic process of data modelling, that we selected from the comparison of different approaches. We use YARARA to remove instrumental systematics from the RV, and then use SPLEAF to further mitigate the stellar noise with a multidimensional correlated noise model. We also search for transit features in the Transiting Exoplanets Survey Satellite (TESS) data of these stars. We report on the discovery of a new planet around HD 99492, namely HD 99492 c, with an orbital period of 95.2 days and a minimum mass of msin i = 17.9 M_Earth, and refine the parameters of HD 99492 b. We also update and refine the Keplerian solutions for the planets around HD 147379 and HD 190007, but do not detect additional planetary signals. We discard the transiting geometry for the planets, but stress that TESS did not exhaustively cover all the orbital phases. The addition of the HARPS-N data, and the use of advanced data analysis tools, has allowed us to present a more precise view of these three planetary systems. It demonstrates once again the importance of long observational efforts such as the RPS program. Added to the RV exoplanet sample, these planets populate two apparently distinct populations revealed by a bimodality in the planets minimum mass distribution. The separation is located between 30 and 50 M_Earth., Comment: 27 pages, 26 figures (13 in Appendix); Accepted for publication in A&A

This article presents a novel application of the Hirota bilinear formalism to the $N=2$ supersymmetric KdV and Burgers equations. This new approach avoids splitting N=2 equations into two $N=1$ equations. We use the super Bell polynomials to obtain bilinear representations and present multi-soliton solutions., Comment: 10 pages, 2 figures. arXiv admin note: text overlap with arXiv:1509.03137

The spin-orbit angle, or obliquity, is a powerful observational marker that allows us to access the dynamical history of exoplanetary systems. Here, we have examined the distribution of spin-orbit angles for close-in exoplanets and put it in a statistical context of tidal interactions between planets and their stars. We confirm the observed trends between the obliquity and physical quantities directly connected to tides, namely the stellar effective temperature, the planet-to-star mass ratio, and the scaled orbital distance. We further devised a tidal efficiency factor combining critical parameters that control the strength of tidal effects and used it to corroborate the strong link between the spin-orbit angle distribution and tidal interactions. In particular, we developed a readily usable formula to estimate the probability that a system is misaligned, which will prove useful in global population studies. By building a robust statistical framework, we reconstructed the distribution of the three-dimensional spin-orbit angles, allowing for a sample of nearly 200 true obliquities to be analyzed for the first time. This realistic distribution maintains the sky-projected trends, and additionally hints toward a striking pileup of truly aligned systems. The comparison between the full population and a pristine subsample unaffected by tidal interactions suggests that perpendicular architectures are resilient toward tidal realignment, providing evidence that orbital misalignments are sculpted by disruptive dynamical processes that preferentially lead to polar orbits. On the other hand, star-planet interactions seem to efficiently realign or quench the formation of any tilted configuration other than for polar orbits, and in particular for antialigned orbits., Comment: Accepted in A&A

The detection of terrestrial planets by radial velocity and photometry is hindered by the presence of stellar signals. Those are often modeled as stationary Gaussian processes, whose kernels are based on qualitative considerations, which do not fully leverage the existing physical understanding of stars. Our aim is to build a formalism which allows to transfer the knowledge of stellar activity into practical data analysis methods. In particular, we aim at obtaining kernels with physical parameters. This has two purposes: better modelling signals of stellar origin to find smaller exoplanets, and extracting information about the star from the statistical properties of the data. We consider several observational channels such as photometry, radial velocity, activity indicators, and build a model called FENRIR to represent their stochastic variations due to stellar surface inhomogeneities. We compute analytically the covariance of this multi-channel stochastic process, and implement it in the S+LEAF framework to reduce the cost of likelihood evaluations from $O(N^3)$ to $O(N)$. We also compute analytically higher order cumulants of our FENRIR model, which quantify its non-Gaussianity. We obtain a fast Gaussian process framework with physical parameters, which we apply to the HARPS-N and SORCE observations of the Sun, and constrain a solar inclination compatible with the viewing geometry. We then discuss the application of our formalism to granulation. We exhibit non-Gaussianity in solar HARPS radial velocities, and argue that information is lost when stellar activity signals are assumed to be Gaussian. We finally discuss the origin of phase shifts between RVs and indicators, and how to build relevant activity indicators. We provide an open-source implementation of the FENRIR Gaussian process model with a Python interface., Comment: Submitted to Astronomy \& Astrophysics

The federal government now offers a multitude of complicated income-driven repayment (IDR) plans that are difficult to understand, enroll in, and stay in. Many students who would benefit from IDR do not enroll, and others will have large amounts of debt forgiven despite earning high wages. The current problems with IDR are not an indictment of the basic approach, and IDR can be an important safety net for students whose earnings do not match the investment they made in their education. But the current version of IDR has problematic design details and implementation failures. This brief offers solutions to some of the biggest problems with IDR, drawing on the longer report, "Income-Driven Repayment of Student Loans: Logic, History, and the Need for Reform" (ED620805) which provides details on each of these solutions.