Context. Young, nearby stars are ideal targets for direct imaging searches for giant planets and brown dwarf companions. After the first-imaged planet discoveries, vast efforts have been devoted to ...the statistical analysis of the occurence and orbital distributions of giant planets and brown dwarf companions at wide (≥5–6 AU) orbits. Aims. In anticipation of the VLT/SPHERE planet-imager, guaranteed-time programs, we have conducted a preparatory survey of 86 stars between 2009 and 2013 to identify new faint comoving companions to ultimately analyze the occurence of giant planets and brown dwarf companions at wide (10–2000 AU) orbits around young, solar-type stars. Methods. We used NaCo at VLT to explore the occurrence rate of giant planets and brown dwarfs between typically 0.1 and 8′′. Diffraction-limited observations in H-band combined with angular differential imaging enabled us to reach primary star-companion brightness ratios as small as 10-6 at 1.5′′. Repeated observations at several epochs enabled us to discriminate comoving companions from background objects. Results. During our survey, twelve systems were resolved as new binaries, including the discovery of a new white dwarf companion to the star HD 8049. Around 34 stars, at least one companion candidate was detected in the observed field of view. More than 400 faint sources were detected; 90% of them were in four crowded fields. With the exception of HD 8049 B, we did not identify any new comoving companions. The survey also led to spatially resolved images of the thin debris disk around HD 61005 that have been published earlier. Finally, considering the survey detection limits, we derive a preliminary upper limit on the frequency of giant planets for the semi-major axes of 10, 2000 AU: typically less than 15% between 100 and 500 AU and less than 10% between 50 and 500 AU for exoplanets that are more massive than 5 MJup and 10 MJup respectively, if we consider a uniform input distribution and a confidence level of 95%. Conclusions. The results from this survey agree with earlier programs emphasizing that massive, gas giant companions on wide orbits around solar-type stars are rare. These results will be part of a broader analysis of a total of ~210 young, solar-type stars to bring further statistical constraints for theoretical models of planetary formation and evolution.
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On 2020 February 24, during their third observing run ("O3"), the Laser Interferometer Gravitational-wave Observatory and Virgo Collaboration detected S200224ca: a candidate gravitational wave (GW) ...event produced by a binary black hole (BBH) merger. This event was one of the best-localized compact binary coalescences detected in O3 (with 50%/90% error regions of 13/72 deg2), and so the Neil Gehrels Swift Observatory performed rapid near-UV/X-ray follow-up observations. Swift-XRT and UVOT covered approximately 79.2% and 62.4% (respectively) of the GW error region, making S200224ca the BBH event most thoroughly followed-up in near-UV (u-band) and X-ray to date. No likely EM counterparts to the GW event were found by the Swift BAT, XRT, or UVOT, nor by other observatories. Here, we report on the results of our searches for an EM counterpart, both in the BAT data near the time of the merger, and in follow-up UVOT/XRT observations. We also discuss the upper limits we can place on EM radiation from S200224ca, as well as the implications these limits have on the physics of BBH mergers. Namely, we place a shallow upper limit on the dimensionless BH charge, , and an upper limit on the isotropic-equivalent energy of a blast wave E < 4.1 × 1051 erg (assuming typical GRB parameters).
Context. Young, close stars are ideal targets for searching planets using the direct imaging technique. The determination of stellar parameters is crucial for the interpretation of imaging survey ...results, particularly since the luminosity of substellar objects has a strong dependence on system age. Aims. We have conducted a large program with NaCo at the VLT to search for planets and brown dwarfs in wide orbits around 86 stars. A large fraction of the targets observed with NaCo were poorly investigated in the literature. We performed a study to characterize the fundamental properties (age, distance, and mass) of the stars in our sample. To improve target age determinations, we compiled and analyzed a complete set of age diagnostics. Methods. We measured spectroscopic parameters and age diagnostics using dedicated observations acquired with FEROS and CORALIE spectrographs at La Silla Observatory. We also made extensive use of archival spectroscopic data and the results that are available in the literature. Additionally, we exploited photometric time-series, which are available in ASAS and Super-WASP archives, to derive a rotational period for a large fraction of our program stars. Results. We provided updated characterization of all the targets observed in the VLT NaCo Large program, a survey designed to probe the occurrence of exoplanets and brown dwarfs in wide orbits. The median distance and age of our program stars are 64 pc and 100 Myr, respectively. Nearly all the stars have masses between 0.70 and 1.50 M⊙, with a median value of 1.01 M⊙. The typical metallicity is close to solar with a dispersion that is smaller than that of samples usually observed in radial velocity surveys. Several stars are confirmed or proposed here to be members of close young moving groups. Eight spectroscopic binaries are identified.
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ABSTRACT
We analysed the photometry of 20 038 cool stars from campaigns 12, 13, 14, and 15 of the K2 mission in order to detect, characterize, and validate new planetary candidates transiting ...low-mass stars. We present a catalogue of 25 new periodic transit-like signals in 22 stars, of which we computed the parameters of the stellar host for 19 stars and the planetary parameters for 21 signals. We acquired speckle and AO images, and also inspected archival Pan-STARRS1 images and Gaia DR2 to discard the presence of close stellar companions and to check possible transit dilutions due to nearby stars. False positive probability (FPP) was computed for 22 signals, obtaining FPP < $1{{\ \rm per\ cent}}$ for 17. We consider 12 of them as statistically validated planets. One signal is a false positive and the remaining 12 signals are considered as planet candidates. 20 signals have an orbital period of P$_{\rm orb} \lt 10\,\mathrm{ d}$, 2 have $10\, \mathrm{ d} \lt $ P$_{\rm orb} \lt 20\, \mathrm{ d}$, and 3 have P$_{\rm orb} \gt 20\, \mathrm{ d}$. Regarding radii, 11 candidates and validated planets have computed radius R < 2R⊕, 9 have 2R⊕ < R < 4R⊕, and 1 has R > 4R⊕. Two validated planets and two candidates are located in moderately bright stars ($\rm \mathit{ m}_{kep}\lt 13$) and two validated planets and three candidates have derived orbital radius within the habitable zone according to optimistic models. Of special interest is the validated warm super-Earth K2-323 b (EPIC 248616368 b) with T$_{\rm eq} = 318^{+24}_{-43} \, \mathrm{ K}$, S$_{\rm p} = 1.7\pm 0.2 \, \mathrm{ S}_{\oplus }$, and R$_{\rm p} = 2.1\pm 0.1 \, \mathrm{ R}_{\oplus }$, located in an m$\rm _{kep}$ = 14.13 star.
Theories of the formation and early evolution of planetary systems postulate that planets are born in circumstellar disks, and undergo radial migration during and after dissipation of the dust and ...gas disk from which they formed. The precise ages of meteorites indicate that planetesimals—the building blocks of planets—are produced within the first million years of a star’s life. Fully formed planets are frequently detected on short orbital periods around mature stars. Some theories suggest that the in situ formation of planets close to their host stars is unlikely and that the existence of such planets is therefore evidence of large-scale migration. Other theories posit that planet assembly at small orbital separations may be common. Here we report a newly born, transiting planet orbiting its star with a period of 5.4 days. The planet is 50 per cent larger than Neptune, and its mass is less than 3.6 times that of Jupiter (at 99.7 per cent confidence), with a true mass likely to be similar to that of Neptune. The star is 5–10 million years old and has a tenuous dust disk extending outward from about twice the Earth–Sun separation, in addition to the fully formed planet located at less than one-twentieth of the Earth–Sun separation.
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We present Spitzer Space Telescope variability monitoring observations of three low-gravity L dwarfs with previous detections of variability in the near-IR: 2MASS J0045+16, 2MASS J0501−00, and 2MASS ...J1425−36. We detect significant periodic variability in two of our targets, 2MASS J0045+16 and 2MASS J0501−00. We do not detect variability in 2MASS J1425−36. Combining our new rotation periods with rotational velocities, we calculate inclination angles of 22° 1°, , and for 2MASS J0045+16, 2MASS J0501−00, and 2MASS J1425−36, respectively. Our three new objects are consistent with the tentative relations between inclination, amplitude, and color anomaly previously reported. Objects with the highest variability amplitudes are inclined equator on, while the maximum observed amplitude decreases as the inclination angle decreases. We also find a correlation between the inclination angle and color anomaly for the sample of objects with measured inclinations. Compiling the entire sample of brown dwarfs with Spitzer variability detections, we find no enhancement in amplitude for young, early-L dwarfs compared to the field dwarf population. We find a possible enhancement in amplitude of low-gravity late-L dwarfs at 4.5 m. We do not find a correlation between amplitude ratio and spectral type for field dwarfs or for the young population. Finally, we compile the rotation periods of a large sample of brown dwarfs with ages 1 Myr-1 Gyr and compare the rotation rates predicted by evolutionary models assuming angular momentum conservation. We find that the rotation rates of the current sample of brown dwarfs fall within the expected range set by evolutionary models and breakup limits.
Substellar companions at wide separation around stars hosting planets or brown dwarfs (BDs) yet close enough for their formation in the circumstellar disc are of special interest. In this Letter we ...report the discovery of a wide (projected separation ~16".0, or 2400AU, and position angle 114.61°) companion of the GQLup A-B system, most likely gravitationally bound to it. A VLT/X-shooter spectrum shows that this star, 2MASS J15491331-3539118, is a bonafide low-mass (~0.15 M(ʘ) ) young stellar object (YSO) with stellar and accretion/ejection properties typical of Lupus YSOs of similar mass, and with kinematics consistent with that of the GQLup A-B system. A possible scenario for the formation of the triple system is that GQ Lup A and 2MASS J15491331-3539118 formed by fragmentation of a turbulent core in the Lup I filament, while GQ Lup B, the BD companion of GQ Lup A at 0".7, formed in situ by the fragmentation of the circumprimary disc. The recent discoveries that stars form along cloud filaments would favour the scenario of turbulent fragmentation for the formation of GQ Lup A and 2MASS J15491331-3539118.
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We present a uniform transiting exoplanet candidate list for Campaign 5 of the K2 mission. This catalog contains 75 planets with seven multi-planet systems (five double, one triple, and one quadruple ...planet system). Within the range of our search, we find eight previously undetected candidates, with the remaining 67 candidates overlapping 51% of the study of Kruse et al. that manually vets candidates from Campaign 5. In order to vet our potential transit signals, we introduce the Exoplanet Detection Identification Vetter (EDI-Vetter), which is a fully automated program able to determine whether a transit signal should be labeled as a false positive or a planet candidate. This automation allows us to create a statistically uniform catalog, ideal for measurements of planet occurrence rate. When tested, the vetting software is able to ensure that our sample is 94.2% reliable against systematic false positives. Additionally, we inject artificial transits at the light-curve level of the raw K2 data and find that the maximum completeness of our pipeline is 70% before vetting and 60% after vetting. For convenience of future studies of occurrence rate, we include measurements of stellar noise (CDPP) and the three-transit window function for each target. This study is part of a larger survey of the K2 data set and the methodology that will be applied to the entirety of that set.
Context. Evolutionary models are widely used to infer the mass of stars, brown dwarfs, and giant planets. Their predictions are thought to be less reliable at young ages (< 200 Myr) and in the ...low-mass regime (< 1 M⊙). GJ 2060 AB and TWA 22 AB are two rare astrometric M-dwarf binaries, respectively members of the AB Doradus (AB Dor) and Beta Pictoris (β Pic) moving groups. As their dynamical mass can be measured to within a few years, they can be used to calibrate the evolutionary tracks and set new constraints on the age of young moving groups. Aims. We provide the first dynamical mass measurement of GJ 2060 and a refined measurement of the total mass of TWA 22. We also characterize the atmospheric properties of the individual components of GJ 2060 that can be used as inputs to the evolutionary models. Methods. We used NaCo and SPHERE observations at VLT and archival Keck/NIRC2 data to complement the astrometric monitoring of the binaries. We combined the astrometry with new HARPS radial velocities (RVs) and FEROS RVs of GJ 2060. We used a Markov chain Monte-Carlo (MCMC) module to estimate posteriors on the orbital parameters and dynamical masses of GJ 2060 AB and TWA 22 AB from the astrometry and RVs. Complementary data obtained with the integral field spectrograph VLT/SINFONI were gathered to extract the individual near-infrared (1.1–2.5 μm) medium-resolution (R ∼ 1500 − 2000) spectra of GJ 2060 A and B. We compared the spectra to those of known objects and to grids of BT-SETTL model spectra to infer the spectral type, bolometric luminosities, and temperatures of those objects. Results. We find a total mass of 0.18 ± 0.02 M⊙ for TWA 22, which is in good agreement with model predictions at the age of the β Pic moving group. We obtain a total mass of 1.09 ± 0.10 M⊙ for GJ 2060. We estimate a spectral type of M1 ± 0.5, L/L⊙ = −1.20 ± 0.05 dex, and Teff = 3700 ± 100 K for GJ 2060 A. The B component is a M3 ± 0.5 dwarf with L/L⊙ = −1.63 ± 0.05 dex and Teff = 3400 ± 100 K. The dynamical mass of GJ 2060 AB is inconsistent with the most recent models predictions (BCAH15, PARSEC) for an AB Dor age in the range 50–150 Myr. It is 10%–20% (1–2σ, depending on the assumed age) above the model’s predictions, corresponding to an underestimation of 0.10–0.20 M⊙. Coevality suggests a young age for the system (∼50 Myr) according to most evolutionary models. Conclusions. TWA 22 validates the predictions of recent evolutionary tracks at ∼20 Myr. On the other hand, we evidence a 1–2σ mismatch between the predicted and observed mass of GJ 2060 AB. This slight departure may indicate that one of the stars hosts a tight companion. Alternatively, this would confirm the model’s tendency to underestimate the mass of young low-mass stars.
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Abstract
We provide the first full K2 transiting exoplanet sample, using photometry from Campaigns 1–8 and 10–18, derived through an entirely automated procedure. This homogeneous planet candidate ...catalog is crucial to perform a robust demographic analysis of transiting exoplanets with K2. We identify 747 unique planet candidates and 57 multiplanet systems. Of these candidates, 366 have not been previously identified, including one resonant multiplanet system and one system with two short-period gas giants. By automating the construction of this list, measurements of sample biases (completeness and reliability) can be quantified. We carried out a light-curve-level injection/recovery test of artificial transit signals and found a maximum completeness of 61%, a consequence of the significant detrending required for K2 data analysis. Through this operation we attained measurements of the detection efficiency as a function of signal strength, enabling future population analysis using this sample. We assessed the reliability of our planet sample by testing our vetting software
EDI-Vetter
against inverted transit-free light curves. We estimate that 91% of our planet candidates are real astrophysical signals, increasing up to 94% when limited to the FGKM dwarf stellar population. We also constrain the contamination rate from background eclipsing binaries to less than 5%. The presented catalog, along with the completeness and reliability measurements, enable robust exoplanet demographic studies to be carried out across the fields observed by the K2 mission for the first time.
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