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High-speed photometry of the eclipsing polar UZ Fornacis
摘要： We present 33 new mid-eclipse times spanning approximately eight years of the eclipsing polar UZ Fornacis. We have used our new observations to test the two-planet model previously proposed to explain the variations in its eclipse times measured over the past ～35 yr. We find that the proposed model does indeed follow the general trend of the new eclipse times, however, there are significant departures. In order to accommodate the new eclipse times, the two-planet model requires that one or both of the planets require highly eccentric orbits, that is, e ≥ 0.4. Such multiple planet orbits are considered to be unstable. Whilst our new observations are consistent with two cyclic variations as previously predicted, significant residuals remain. We conclude that either additional cyclic terms, possibly associated with more planets, or other mechanisms, such as the Applegate mechanism are contributing to the eclipse time variations. Further long-term monitoring is required.
关键词： planets and satellites: detection,planets and satellites: formation,stars: individual: UZ Fornacis,novae, cataclysmic variables,binaries: eclipsing
更新于2025-09-23 15:23:52
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Characterizing the Performance of the NIRC2 Vortex Coronagraph at W. M. Keck Observatory
摘要： The NIRC2 vortex coronagraph is an instrument on Keck II designed to directly image exoplanets and circumstellar disks at mid-infrared bands L′ (3.4–4.1 μm) and Ms (4.55–4.8 μm). We analyze imaging data and corresponding adaptive optics telemetry, observing conditions, and other metadata over a three-year time period to characterize the performance of the instrument and predict the detection limits of future observations. We systematically process images from 359 observations of 304 unique stars to subtract residual starlight (i.e., the coronagraphic point-spread function) of the target star using two methods: angular differential imaging (ADI) and reference star differential imaging (RDI). We ?nd that for the typical parallactic angle (PA) rotation of our data set (～10°), RDI provides gains over ADI for angular separations smaller than 0 25. Furthermore, we ?nd a power-law relation between the angular separation from the host star and the minimum PA rotation required for ADI to outperform RDI, with a power-law index of ?1.18 ± 0.08. Finally, we use random forest models to estimate ADI and RDI post-processed detection limits a priori. These models, which we provide publicly on a website, explain 70%–80% of the variance in ADI detection limits and 30%–50% of the variance in RDI detection limits. Averaged over a range of angular separations, our models predict both ADI and RDI contrast to within a factor of 2. These results illuminate important factors in high-contrast imaging observations with the NIRC2 vortex coronagraph, help improve observing strategies, and inform future upgrades to the hardware.
关键词： planets and satellites: detection,instrumentation: adaptive optics
更新于2025-09-23 15:22:29
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A Large Ground-based Observing Campaign of the Disintegrating Planet K2-22b
摘要： We present 45 ground-based photometric observations of the K2-22 system collected between 2016 December and 2017 May, which we use to investigate the evolution of the transit of the disintegrating planet K2-22b. Last observed in early 2015, in these new observations we recover the transit at multiple epochs and measure a typical depth of <1.5%. We ?nd that the distribution of our measured transit depths is comparable to the range of depths measured in observations from 2014 and 2015. These new observations also support ongoing variability in the K2-22b transit shape and time, although the overall shallowness of the transit makes a detailed analysis of these transit parameters dif?cult. We ?nd no strong evidence of wavelength-dependent transit depths for epochs where we have simultaneous coverage at multiple wavelengths, although our stacked Las Cumbres Observatory data collected over days-to-months timescales are suggestive of a deeper transit at blue wavelengths. We encourage continued high-precision photometric and spectroscopic monitoring of this system in order to further constrain the evolution timescale and to aid comparative studies with the other few known disintegrating planets.
关键词： planets and satellites: detection,planets and satellites: individual (K2-22 b),techniques: photometric
更新于2025-09-23 15:21:01
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Near-infrared scattered light properties of the HR?4796?A dust ring
摘要： Context. HR 4796 A is surrounded by a debris disc, observed in scattered light as an inclined ring with a high surface brightness. Past observations have raised several questions. First, a strong brightness asymmetry detected in polarised re?ected light has recently challenged our understanding of scattering by the dust particles in this system. Secondly, the morphology of the ring strongly suggests the presence of planets, although no planets have been detected to date. Aims. We aim here at measuring with high accuracy the morphology and photometry of the ring in scattered light, in order to derive the phase function of the dust and constrain its near-infrared spectral properties. We also want to constrain the presence of planets and set improved constraints on the origin of the observed ring morphology. Methods. We obtained high-angular resolution coronagraphic images of the circumstellar environment around HR 4796 A with VLT/SPHERE during the commissioning of the instrument in May 2014 and during guaranteed-time observations in February 2015. The observations reveal for the ?rst time the entire ring of dust, including the semi-minor axis that was previously hidden either behind the coronagraphic spot or in the speckle noise. Results. We determine empirically the scattering phase function of the dust in the H band from 13.6? to 166.6?. It shows a prominent peak of forward scattering, never detected before, for scattering angles below 30?. We analyse the re?ectance spectra of the disc from the 0.95 μm to 1.6 μm, con?rming the red colour of the dust, and derive detection limits on the presence of planetary mass objects. Conclusions. We con?rm which side of the disc is inclined towards the Earth. The analysis of the phase function, especially below 45?, suggests that the dust population is dominated by particles much larger than the observation wavelength, of about 20 μm. Compact Mie grains of this size are incompatible with the spectral energy distribution of the disc, however the observed rise in scattering e?ciency beyond 50? points towards aggregates which could reconcile both observables. We do not detect companions orbiting the star, but our high-contrast observations provide the most stringent constraints yet on the presence of planets responsible for the morphology of the dust.
关键词： planets and satellites: detection,planetary systems,scattering,instrumentation: high angular resolution,planet-disk interactions
更新于2025-09-23 15:21:01
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Circumbinary exoplanets and brown dwarfs with the Laser Interferometer Space Antenna
摘要： Aims. We explore the prospects for the detection of giant circumbinary exoplanets and brown dwarfs (BDs) orbiting Galactic double white dwarfs (DWDs) binaries with the Laser Interferometer Space Antenna (LISA). Methods. By assuming an occurrence rate of 50%, motivated by white dwarf pollution observations, we built a Galactic synthetic population of P-type giant exoplanets and BDs orbiting DWDs. We carried this out by injecting different sub-stellar populations, with various mass and orbital separation characteristics, into the DWD population used in the LISA mission proposal. We then performed a Fisher matrix analysis to measure how many of these three-body systems show a periodic Doppler-shifted gravitational wave perturbation detectable by LISA. Results. We report the number of circumbinary planets (CBPs) and BDs that can be detected by LISA for various combinations of mass and semi-major axis distributions. We identify pessimistic and optimistic scenarios corresponding, respectively, to 3 and 83 (14 and 2218) detections of CBPs (BDs), observed during the length of the nominal LISA mission. These detections are distributed all over the Galaxy following the underlying DWD distribution, and they are biased towards DWDs with higher LISA signal-to-noise ratio and shorter orbital period. Finally, we show that if LISA were to be extended for four more years, the number of systems detected will be more than doubled in both the optimistic and pessimistic scenarios. Conclusions. Our results present promising prospects for the detection of post-main sequence exoplanets and BDs, showing that gravitational waves can prove the existence of these populations over the totality of the Milky Way. Detections by LISA will deepen our knowledge on the life of exoplanets subsequent to the most extreme evolution phases of their hosts, clarifying whether new phases of planetary formation take place later in the life of the stars. Such a method is strongly complementary to electromagnetic studies within the solar region and opens a window into the investigation of planets and BDs everywhere in the entire Galaxy, and possibly even in nearby galaxies in the Local Group.
关键词： gravitational waves,planets and satellites: detection,white dwarfs,planets and satellites: gaseous planets,brown dwarfs
更新于2025-09-23 15:19:57
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Data Reduction Pipeline of the TOU Optical Very High Resolution Spectrograph and Its sub-m?s?1?Performance
摘要： TOU is an extremely high resolution optical spectrograph (R = 100 000, 380–900 nm), which is designed to detect low-mass exoplanets using the radial velocity technique. We describe an IDL-based radial velocity (RV) data reduction pipeline for the TOU spectrograph and its performance with stable stars. This pipeline uses a least-squares fitting algorithm to match observed stellar spectra to a high-signal-to-noise template created for each star. By carefully controlling all of the error contributions to RV measurements in both the hardware and data pipeline, we have achieved ～0.9 m s?1 long-term RV precision with one of the most RV-stable stars, Tau Ceti, similar to what has been achieved with HARPS. This paper presents steps and details in our data pipeline on how to reach the sub-m s?1 RV precision and also all major error sources that contribute to the final RV measurement uncertainties. The lessons learned in this pipeline development can be applied to other environmentally controlled, very high resolution optical spectrographs to improve RV precision.
关键词： techniques: radial velocities,planets and satellites: detection,instrumentation: spectrographs,techniques: spectroscopic
更新于2025-09-19 17:15:36
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Thermal Infrared Imaging of MWC 758 with the Large Binocular Telescope: Planetary-driven Spiral Arms?
摘要： Theoretical studies suggest that a giant planet around the young star MWC 758 could be responsible for driving the spiral features in its circumstellar disk. Here, we present a deep imaging campaign with the Large Binocular Telescope with the primary goal of imaging the predicted planet. We present images of the disk in two epochs in the L′ filter (3.8 μm) and a third epoch in the M′ filter (4.8 μm). The two prominent spiral arms are detected in each observation, which constitute the first images of the disk at M′, and the deepest yet in L′ (ΔL′ = 12.1 exterior to the disk at 5σ significance). We report the detection of an S/N ～ 3.9 source near the end of the Southern arm, and, from the source’s detection at a consistent position and brightness during multiple epochs, we establish a ～90% confidence-level that the source is of astrophysical origin. We discuss the possibilities that this feature may be (a) an unresolved disk feature, and (b) a giant planet responsible for the spiral arms, with several arguments pointing in favor of the latter scenario. We present additional detection limits on companions exterior to the spiral arms, which suggest that a ?4 MJup planet exterior to the spiral arms could have escaped detection. Finally, we do not detect the companion candidate interior to the spiral arms reported recently by Reggiani et al., although forward modeling suggests that such a source would have likely been detected.
关键词： planets and satellites: formation,stars: pre-main sequence,planets and satellites: detection,planet–disk interactions
更新于2025-09-19 17:13:59
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Mid-infrared characterization of the planetary-mass companion ROXs 42B b
摘要： We present new Keck/NIRC2 3–5 μm infrared photometry of the planetary-mass companion to ROXS 42B in L(cid:48), and for the ?rst time in Brackett-α (Brα) and in Ms-band. We combine our data with existing near-infrared photometry and K-band (2–2.4 μm) spectroscopy and compare these data with models and other directly imaged planetary-mass objects using forward modeling and retrieval methods in order to characterize the atmosphere of ROXS 42B b. The ROXS 42B b 1.25–5 μm spectral energy distribution most closely resembles that of GSC 06214 B and κ And b, although it has a slightly bluer Ks?Ms color than GSC 06214 B and thus currently lacks evidence of a circumplanetary disk. We cannot formally exclude the possibility that any of the tested dust-free/dusty/cloudy forward models describe the atmosphere of ROXS 42B b well. However, models with substantial atmospheric dust/clouds yield temperatures and gravities that are consistent when ?t to photometry and spectra separately, whereas dust-free model ?ts to photometry predict temperatures/gravities inconsistent with the ROXS 42B b K-band spectrum and vice-versa. Atmospheric retrieval on the 1–5 μm photometry places a limit on the fractional number density of CO2 of log(nCO2 ) < ?2.7, but provides no other constraints so far. We conclude that ROXS 42B b has mid-IR photometric features that are systematically di?erent from other previously observed planetary-mass and ?eld objects of similar temperature. It remains unclear whether this is in the range of the natural diversity of targets at the very young (～2 Myr) age of ROXS 42B b or unique to its early evolution and environment.
关键词： planets and satellites: detection,planets and satellites: individual: ROXS42Bb,stars: pre-main sequence
更新于2025-09-10 09:29:36
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Traces of exomoons in computed flux and polarization phase curves of starlight reflected by exoplanets
摘要： Context. Detecting moons around exoplanets is a major goal of current and future observatories. Moons are suspected to influence rocky exoplanet habitability, and gaseous exoplanets in stellar habitable zones could harbor abundant and diverse moons to target in the search for extraterrestrial habitats. Exomoons contribute to exoplanetary signals but are virtually undetectable with current methods. Aims. We identify and analyze traces of exomoons in the temporal variation of total and polarized fluxes of starlight reflected by an Earth-like exoplanet and its spatially unresolved moon across all phase angles, with both orbits viewed in an edge-on geometry. Methods. We compute the total and linearly polarized fluxes, and the degree of linear polarization P of starlight that is reflected by the exoplanet with its moon along their orbits, accounting for the temporal variation of the visibility of the planetary and lunar disks, and including the effects of mutual transits and mutual eclipses. Our computations pertain to a wavelength of 450 nm. Results. Total flux F shows regular dips due to planetary and lunar transits and eclipses. Polarization P shows regular peaks due to planetary transits and lunar eclipses, and P can increase and/or slightly decrease during lunar transits and planetary eclipses. Changes in F and P will depend on the radii of the planet and moon, on their reflective properties, and their orbits, and are about one magnitude smaller than the smooth background signals. The typical duration of a transit or an eclipse is a few hours. Conclusions. Traces of an exomoon due to planetary and lunar transits and eclipses show up in the F and P of sunlight reflected by planet–moon systems and could be searched for in exoplanet flux and/or polarization phase functions.
关键词： methods: numerical,planets and satellites: detection,planetary systems,polarization,radiative transfer
更新于2025-09-10 09:29:36
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Long-term radial-velocity variations of the Sun as a star: The HARPS view
摘要： Context. Stellar radial velocities play a fundamental role in the discovery of extrasolar planets and the measurement of their physical parameters as well as in the study of stellar physical properties. Aims. We investigate the impact of the solar activity on the radial velocity of the Sun using the HARPS spectrograph to obtain measurements that can be directly compared with those acquired in the extrasolar planet search programmes. Methods. We used the Moon, the Galilean satellites, and several asteroids as re?ectors to measure the radial velocity of the Sun as a star and correlated this velocity with disc-integrated chromospheric and magnetic indexes of solar activity that are similar to stellar activity indexes. We discuss in detail the systematic e?ects that a?ect our measurements and the methods to account for them. Results. We ?nd that the radial velocity of the Sun as a star is positively correlated with the level of its chromospheric activity at ～95 percent signi?cance level. The amplitude of the long-term variation measured in the 2006?2014 period is 4.98 ± 1.44 m/s, which is in good agreement with model predictions. The standard deviation of the residuals obtained by subtracting a linear best ?t is 2.82 m/s and is due to the rotation of the re?ecting bodies and the intrinsic variability of the Sun on timescales shorter than the activity cycle. A correlation with a lower signi?cance is detected between the radial velocity and the mean absolute value of the line-of-sight photospheric magnetic ?eld ?ux density. Conclusions. Our results con?rm similar correlations found in other late-type main-sequence stars and provide support to the predictions of radial velocity variations induced by stellar activity based on current models.
关键词： planets and satellites: detection,Sun: activity,techniques: radial velocities,stars: activity,Sun: magnetic ?elds
更新于2025-09-09 09:28:46