We analyzed the light curves of 1376 early-to-late, nearby M dwarfs to search for white-light flares using photometry from the All-Sky Automated Survey for Supernovae (ASAS-SN). We identified 480 M ...dwarfs with at least one potential flare employing a simple statistical algorithm that searches for sudden increases in \(V\)-band flux. After more detailed evaluation, we identified 62 individual flares on 62 stars. The event amplitudes range from \(0.12 <\Delta V < 2.04\) mag. Using classical-flare models, we place lower limits on the flare energies and obtain \(V\)-band energies spanning \(2.0\times10^{30} \lesssim E_{V} \lesssim 6.9\times10^{35}\) erg. The fraction of flaring stars increases with spectral type, and most flaring stars show moderate to strong H\(\alpha\) emission. Additionally, we find that 14 of the 62 flaring stars are rotational variables, and they have shorter rotation periods and stronger H\(\alpha\) emission than non-flaring rotational variable M dwarfs.
We present the discoveries of KELT-25b (TIC 65412605, TOI-626.01) and KELT-26b (TIC 160708862, TOI-1337.01), two transiting companions orbiting relatively bright, early A-stars. The transit signals ...were initially detected by the KELT survey, and subsequently confirmed by \textit{TESS} photometry. KELT-25b is on a 4.40-day orbit around the V = 9.66 star CD-24 5016 (\(T_{\rm eff} = 8280^{+440}_{-180}\) K, \(M_{\star}\) = \(2.18^{+0.12}_{-0.11}\) \(M_{\odot}\)), while KELT-26b is on a 3.34-day orbit around the V = 9.95 star HD 134004 (\(T_{\rm eff}\) =\(8640^{+500}_{-240}\) K, \(M_{\star}\) = \(1.93^{+0.14}_{-0.16}\) \(M_{\odot}\)), which is likely an Am star. We have confirmed the sub-stellar nature of both companions through detailed characterization of each system using ground-based and \textit{TESS} photometry, radial velocity measurements, Doppler Tomography, and high-resolution imaging. For KELT-25, we determine a companion radius of \(R_{\rm P}\) = \(1.64^{+0.039}_{-0.043}\) \(R_{\rm J}\), and a 3-sigma upper limit on the companion's mass of \(\sim64~M_{\rm J}\). For KELT-26b, we infer a planetary mass and radius of \(M_{\rm P}\) = \(1.41^{+0.43}_{-0.51}\) \(M_{\rm J}\) and \(R_{\rm P}\) = \(1.940^{+0.060}_{-0.058}\) \(R_{\rm J}\). From Doppler Tomographic observations, we find KELT-26b to reside in a highly misaligned orbit. This conclusion is weakly corroborated by a subtle asymmetry in the transit light curve from the \textit{TESS} data. KELT-25b appears to be in a well-aligned, prograde orbit, and the system is likely a member of a cluster or moving group.
A gold standard for the study of M dwarfs is the eclipsing binary CM Draconis. It is rare because it is bright (\(J_{\rm mag}=8.5\)) and contains twin fully convective stars on an almost perfectly ...edge-on orbit. Both masses and radii were previously measured to better than \(1\%\) precision, amongst the best known. We use 15 sectors of data from the Transiting Exoplanet Survey Satellite (TESS) to show that CM Draconis is the gift that keeps on giving. Our paper has three main components. First, we present updated parameters, with radii and masses constrained to previously unheard of precisions of \(\approx 0.06\%\) and \(\approx 0.12\%\), respectively. Second, we discover strong and variable spot modulation, suggestive of spot clustering and an activity cycle on the order of \(\approx 4\) years. Third, we discover 163 flares. We find a relationship between the spot modulation and flare rate, with flares more likely to occur when the stars appear brighter. This may be due to a positive correlation between flares and the occurrence of bright spots (plages). The flare rate is surprisingly not reduced during eclipse, but one flare may show evidence of being occulted. We suggest the flares may be preferentially polar, which has positive implications for the habitability of planets orbiting M dwarfs.
We explore the prospects for Twinkle to determine the atmospheric composition of the nearby terrestrial-like planet LTT 1445 Ab, including the possibility of detecting the potential biosignature ...ammonia (NH\(_{3}\)). At a distance of 6.9 pc, this system is the second closest known transiting system and will be observed through transmission spectroscopy with the upcoming Twinkle mission. Twinkle is equipped with a 0.45 m telescope, covers a spectral wavelength range of 0.5 - 4.5 \(\mu\)m simultaneously with a resolving power between 50 - 70, and is designed to study exoplanets, bright stars, and solar system objects. We investigate the mission's potential to study LTT 1445 Ab and find that Twinkle data can distinguish between a cold Haber World (N\(_2\)-H\(_2\)-dominated atmosphere) and a Hycean World with a H\(_2\)O-H\(_2\)-dominated atmosphere, with a \(\chi_{\nu}^{2}\) = 3.01. Interior composition analysis favors a Haber World scenario for LTT 1445 Ab, which suggests that the planet probably lacks a substantial water layer. We use petitRADTRANS and a Twinkle simulator to simulate transmission spectra for the more likely scenario of a cold Haber World for which NH\(_{3}\) is considered to be a biosignature. We study the detectability under different scenarios: varying hydrogen fraction, concentration of ammonia, and cloud coverage. We find that ammonia can be detected at a \(\sim\) 3\(\sigma\) level for optimal (non-cloudy) conditions with 25 transits and a volume mixing ration of 4.0 ppm of NH\(_{3}\). We provide examples of retrieval analysis to constrain potential NH\(_{3}\) and H\(_{2}\)O in the atmosphere. Our study illustrates the potential of Twinkle to characterize atmospheres of potentially habitable exoplanets.
TOI-1259 consists of a transiting exoplanet orbiting a main sequence star, with a bound outer white dwarf companion. Less than a dozen systems with this architecture are known. We conduct follow-up ...spectroscopy on the white dwarf TOI-1259B using the Large Binocular Telescope (LBT) to better characterise it. We observe only strong hydrogen lines, making TOI-1259B a DA white dwarf. We see no evidence of heavy element pollution, which would have been evidence of planetary material around the white dwarf. Such pollution is seen in ~ 25 - 50% of white dwarfs, but it is unknown if this rate is higher or lower in TOI-1259-like systems that contain a known planet. Our spectroscopy permits an improved white dwarf age measurement of 4.05 (+1.00 -0.42) Gyrs, which matches gyrochronology of the main sequence star. This is the first of an expanded sample of similar binaries that will allow us to calibrate these dating methods and provide a new perspective on planets in binaries.
We present analytic estimates of the fractional uncertainties on the mass, radius, surface gravity, and density of a transiting planet, using only empirical or semi-empirical measurements. We first ...express these parameters in terms of transit photometry and radial velocity (RV) observables, as well as the stellar radius \(R_{\star}\), if required. In agreement with previous results, we find that, assuming a circular orbit, the surface gravity of the planet (\(g_p\)) depends only on empirical transit and RV parameters; namely, the planet period \(P\), the transit depth \(\delta\), the RV semi-amplitude \(K_{\star}\), the transit duration \(T\), and the ingress/egress duration \(\tau\). However, the planet mass and density depend on all these quantities, plus \(R_{\star}\). Thus, an inference about the planet mass, radius, and density must rely upon an external constraint such as the stellar radius. For bright stars, stellar radii can now be measured nearly empirically by using measurements of the stellar bolometric flux, the effective temperature, and the distance to the star via its parallax, with the extinction \(A_V\) being the only free parameter. For any given system, there is a hierarchy of achievable precisions on the planetary parameters, such that the planetary surface gravity is more accurately measured than the density, which in turn is more accurately measured than the mass. We find that surface gravity provides a strong constraint on the core mass fraction of terrestrial planets. This is useful, given that the surface gravity may be one of the best measured properties of a terrestrial planet.
Given their location on the Hertzsprung-Russell (HR) diagram, thoroughly characterized subgiant stars can place stringent constraints on a wide range of astrophysical problems. Accordingly, they are ...prime asteroseismic targets for the Transiting Exoplanet Survey Satellite (TESS) mission. In this work, we infer stellar properties for a sample of 347 subgiants located in the TESS Continuous Viewing Zones (CVZs), which we select based on their likelihood of showing asteroseismic oscillations. We investigate how well they can be characterized using classical constraints (photometry, astrometry), and validate our results using spectroscopic values. We derive luminosities, effective temperatures, and radii with mean 1\(\sigma\) random (systematic) uncertainties of 4.5% (2%), 33 K (60 K), and 2.2% (2%), as well as more model-dependent quantities such as surface gravities, masses, and ages. We use our sample to demonstrate that subgiants are ideal targets for mass and age determination based on HR diagram location alone, discuss the advantages of stellar parameters derived from a detailed characterization over widely available catalogs, show that the generally used 3D extinction maps tend to overestimate the extinction for nearby stars (distance \(\lesssim\) 500 pc), and find a correlation that supports the rotation-activity connection in post main sequence stars. The complementary roles played by classical and asteroseismic data sets will open a window to unprecedented astrophysical studies using subgiant stars.
We measure abundances of 12 elements (Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni) in a sample of 86 metal-poor (\(-2 \lesssim \text{Fe/H} \lesssim -1\)) subgiant stars in the solar neighborhood. ...Abundances are derived from high-resolution spectra taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope, modeled using iSpec and MOOG. By carefully quantifying the impact of photon-noise (\(< 0.05\) dex for all elements) we robustly measure the intrinsic scatter of abundance ratios. At fixed Fe/H the RMS intrinsic scatter in X/Fe ranges from 0.04 dex (Cr) to 0.16 dex (Na), with a median of 0.08 dex. Scatter in X/Mg is similar, and accounting for \(\alpha\)/Fe only reduces the overall scatter moderately. We consider several possible origins of the intrinsic scatter with particular attention to fluctuations in the relative enrichment by core-collapse supernovae (CCSN) and Type Ia supernovae (SNIa) and stochastic sampling of the CCSN progenitor mass distribution. The stochastic sampling scenario provides a good quantitative explanation of our data if the effective number of CCSN contributing to the enrichment of a typical sample star is \(N \sim 50\). At the median metallicity of our sample, this interpretation implies that the CCSN ejecta are mixed over a gas mass \(\sim 10^5 M_{\odot}\) before forming stars. The scatter of elemental abundance ratios is a powerful diagnostic test for simulations of star formation, feedback, and gas mixing in the early phases of the Galaxy.
Lava worlds are a potential emerging population of Super-Earths that are on close-in orbits around their host stars with likely partially molten mantles. To date, few studies address the impact of ...magma on the observed properties of a planet. At ambient conditions magma is less dense than solid rock; however, it is also more compressible with increasing pressure. Therefore, it is unclear how large-scale magma oceans affect planet observables, such as bulk density. We update ExoPlex, a thermodynamically self-consistent planet interior software, to include anhydrous, hydrous (2.2 wt \% H_2O), and carbonated magmas (5.2 wt\% CO_2). We find that Earth-like planets with magma oceans larger than \sim 1.5 R_{\oplus} and \sim 3.2 M_{\oplus} are modestly denser than an equivalent mass solid planet. From our model, three classes of mantle structures emerge for magma ocean planets: (1) mantle magma ocean, (2) surface magma ocean, and (3) one consisting of a surface magma ocean, solid rock layer, and a basal magma ocean. The class of planets in which a basal magma ocean is present may sequester dissolved volatiles on billion-year timescales, in which a 4 M_{\oplus} mass planet can trap more than 130 times the mass of water than in Earth's present-day oceans and 1000 times the carbon in the Earth's surface and crust.
RESUMEN Objetivo: Determinar las características clínicas y epidemiológicas de la maculopatía diabética en adultos de 50 años y más en Cuba. Métodos: Se realizó una investigación epidemiológica, ...descriptiva transversal, que tomó la Encuesta Rápida de Ceguera Evitable realizada en Cuba en el año 2016, la cual incluyó la retinopatía diabética validada por la Organización Mundial de la Salud. Resultados: La prevalencia de cualquier grado de maculopatía fue de 8,5 % (6,1 a 10,8) y la maculopatía observable y remitible fue de 4,2 % (2,2 a 6,0). El riesgo de desarrollar maculopatía resultó mayor en el sexo femenino, con el 9,3 % (6,6-12,9), y en los diabéticos que tenían entre 60 y 69 años de edad, de 9,2 % (5,7-14,0). Este riesgo se incrementaba si existía descontrol de la glicemia y si la enfermedad tenía 15 años y más de evolución. La asociación con la retinopatía observable fue de 2,5 %. La discapacidad visual moderada por maculopatía fue de 1,4 % y la grave junto con la ceguera de 0,8 %. La cobertura de tratamiento fue baja (28,6 % por personas). Conclusiones: El diabético de 50 años y más en Cuba tiene baja prevalencia de maculopatía diabética, la cual se comporta de manera similar para la forma observable y para la remitible. La retinopatía no proliferativa moderada tiene mayor riesgo de afectación macular. La discapacidad visual por afectación macular en el diabético es baja, aunque la estrategia de atención oftalmológica en el diabético no alcanza los estándares necesarios de efectividad, relacionados con la cobertura del tratamiento con láser.
