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See detailDynamical Evidence of a Spiral Arm-driving Planet in the MWC 758 Protoplanetary Disk
Ren, Bin; Dong, Ruobing; van Holstein, Rob G. et al

in Astrophysical Journal (2020), 898

More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses—companion-disk interaction and ... [more ▼]

More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses—companion-disk interaction and gravitational instability (GI)—predict distinct motion for spirals. By imaging the MWC 758 spiral arm system at two epochs spanning ∼5 yr using the SPHERE instrument on the Very Large Telescope, we test the two hypotheses for the first time. We find that the pattern speeds of the spirals are not consistent with the GI origin. Our measurements further evince the existence of a faint "missing planet" driving the disk arms. The average spiral pattern speed is 0°22 ± 0°03 yr[SUP]-1[/SUP], pointing to a driver at ${172}_{-14}^{+18}$ au around a 1.9 M[SUB]☉[/SUB] central star if it is on a circular orbit. In addition, we witness time-varying shadowing effects on a global scale that are likely originating from an inner disk. [less ▲]

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See detailA Deep Exposure in High Resolution X-Rays Reveals the Hottest Plasma in the ζ Puppis Wind
Huenemoerder, David P.; Ignace, Richard; Miller, Nathan A. et al

in Astrophysical Journal (2020), 893

We have obtained a very deep exposure (813 ks) of ζ Puppis (O4 supergiant) with the Chandra HETG Spectrometer. Here we report on analysis of the 1-9 Å region, especially well suited for Chandra, which has ... [more ▼]

We have obtained a very deep exposure (813 ks) of ζ Puppis (O4 supergiant) with the Chandra HETG Spectrometer. Here we report on analysis of the 1-9 Å region, especially well suited for Chandra, which has a significant contribution from continuum emission between well separated emission lines from high-ionization species. These data allow us to study the hottest plasma present through the continuum shape and emission line strengths. Assuming a power-law emission measure distribution that has a high-temperature cutoff, we find that the emission is consistent with a thermal spectrum having a maximum temperature of 12 MK as determined from the corresponding spectral cutoff. This implies an effective wind shock velocity of 900 km s[SUP]-1[/SUP], well below the wind terminal speed of 2250 km s[SUP]-1[/SUP]. For X-ray emission that forms close to the star, the speed and X-ray flux are larger than can be easily reconciled with strictly self-excited line-deshadowing-instability models, suggesting a need for a fraction of the wind to be accelerated extremely rapidly right from the base. This is not so much a dynamical instability as a nonlinear response to changing boundary conditions. [less ▲]

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See detailTESS Spots a Hot Jupiter with an Inner Transiting Neptune
Huang, Chelsea X.; Quinn, Samuel N.; Vanderburg, Andrew et al

in Astrophysical Journal (2020), 892

Hot Jupiters are rarely accompanied by other planets within a factor of a few in orbital distance. Previously, only two such systems have been found. Here, we report the discovery of a third system using ... [more ▼]

Hot Jupiters are rarely accompanied by other planets within a factor of a few in orbital distance. Previously, only two such systems have been found. Here, we report the discovery of a third system using data from the Transiting Exoplanet Survey Satellite (TESS). The host star, TOI-1130, is an eleventh magnitude K-dwarf in Gaia G-band. It has two transiting planets: a Neptune-sized planet (3.65 ± 0.10 R[SUB]\oplus[/SUB]) with a 4.1 days period, and a hot Jupiter (1.50[SUB]-0.22[/SUB][SUP]+0.27[/SUP] R[SUB]J[/SUB]) with an 8.4 days period. Precise radial-velocity observations show that the mass of the hot Jupiter is 0.974[SUB]-0.044[/SUB][SUP]+0.043[/SUP] M[SUB]J[/SUB]. For the inner Neptune, the data provide only an upper limit on the mass of 0.17 M[SUB]J[/SUB] (3σ). Nevertheless, we are confident that the inner planet is real, based on follow-up ground-based photometry and adaptive-optics imaging that rule out other plausible sources of the TESS transit signal. The unusual planetary architecture of and the brightness of the host star make TOI-1130 a good test case for planet formation theories, and an attractive target for future spectroscopic observations. [less ▲]

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See detailMining for Dark Matter Substructure: Inferring subhalo population properties from strong lenses with machine learning
Brehmer, Johann; Mishra-Sharma, Siddharth; Hermans, Joeri et al

in Astrophysical Journal (2019), 886(1),

The subtle and unique imprint of dark matter substructure on extended arcs in strong lensing systems contains a wealth of information about the properties and distribution of dark matter on small scales ... [more ▼]

The subtle and unique imprint of dark matter substructure on extended arcs in strong lensing systems contains a wealth of information about the properties and distribution of dark matter on small scales and, consequently, about the underlying particle physics. However, teasing out this effect poses a significant challenge since the likelihood function for realistic simulations of population-level parameters is intractable. We apply recently-developed simulation-based inference techniques to the problem of substructure inference in galaxy-galaxy strong lenses. By leveraging additional information extracted from the simulator, neural networks are efficiently trained to estimate likelihood ratios associated with population-level parameters characterizing substructure. Through proof-of-principle application to simulated data, we show that these methods can provide an efficient and principled way to simultaneously analyze an ensemble of strong lenses, and can be used to mine the large sample of lensing images deliverable by near-future surveys for signatures of dark matter substructure. [less ▲]

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See detailDetection of CN Gas in Interstellar Object 2I/Borisov
Fitzsimmons, Alan; Hainaut, Olivier; Meech, Karen J. et al

in Astrophysical Journal (2019), 885

The detection of interstellar objects passing through the solar system offers the promise of constraining the physical and chemical processes involved in planetary formation in other extrasolar systems ... [more ▼]

The detection of interstellar objects passing through the solar system offers the promise of constraining the physical and chemical processes involved in planetary formation in other extrasolar systems. While the effect of outgassing by 1I/2017 U1 (’Oumuamua) was dynamically observed, no direct detection of the ejected material was made. The discovery of the active interstellar comet 2I/Borisov means spectroscopic investigations of the sublimated ices is possible for this object. We report the first detection of gas emitted by an interstellar comet via the near-UV emission of CN from 2I/Borisov at a heliocentric distance of r = 2.7 au on 2019 September 20. The production rate was found to be Q(CN) = (3.7 ± 0.4) × 10[SUP]24[/SUP] s[SUP]−1[/SUP], using a simple Haser model with an outflow velocity of 0.5 km s[SUP]−1[/SUP]. No other emission was detected, with an upper limit to the production rate of C[SUB]2[/SUB] of 4 × 10[SUP]24[/SUP] s[SUP]−1[/SUP]. The spectral reflectance slope of the dust coma over 3900 Å < λ < 6000 Å is steeper than at longer wavelengths, as found for other comets. Broadband R [SUB] c [/SUB] photometry on 2019 September 19 gave a dust production rate of Afρ = 143 ± 10 cm. Modeling of the observed gas and dust production rates constrains the nuclear radius to 0.7─3.3 km assuming reasonable nuclear properties. Overall, we find the gas, dust, and nuclear properties for the first active interstellar object are similar to normal solar system comets. [less ▲]

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See detailAuroral Beads at Saturn and the Driving Mechanism: Cassini Proximal Orbits
Radioti, Aikaterini ULiege; Yao, Zhonghua ULiege; Grodent, Denis ULiege et al

in Astrophysical Journal (2019), 885

During the Grand Finale Phase of Cassini, the Ultraviolet Imaging Spectrograph on board the spacecraft detected repeated detached small- scale auroral structures. We describe these structures as auroral ... [more ▼]

During the Grand Finale Phase of Cassini, the Ultraviolet Imaging Spectrograph on board the spacecraft detected repeated detached small- scale auroral structures. We describe these structures as auroral beads, a term introduced in the terrestrial aurora. Those on DOY 232 2017 are observed to extend over a large range of local times, i.e., from 20 LT to 11 LT through midnight. We suggest that the auroral beads are related to plasma instabilities in the magnetosphere, which are often known to generate wavy auroral precipitations. Energetic neutral atom enhancements are observed simultaneously with auroral observations, which are indicative of a heated high pressure plasma region. During the same interval we observe conjugate periodic enhancements of energetic electrons, which are consistent with the hypothesis that a drifting interchange structure passed the spacecraft. Our study indicates that auroral bead structures are common phenomena at Earth and giant planets, which probably demonstrates the existence of similar fundamental magnetospheric processes at these planets. [less ▲]

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See detailTesting Seismic Models of Hot B Subdwarfs with Gaia Data
Fontaine, Gilles; Bergeron, P.; Brassard, Pierre et al

in Astrophysical Journal (2019), 880

We report the results of a study designed to test further the basic validity of the seismic models of hot pulsating B subdwarfs that have been developed over the last two decades. Given estimates of the ... [more ▼]

We report the results of a study designed to test further the basic validity of the seismic models of hot pulsating B subdwarfs that have been developed over the last two decades. Given estimates of the effective temperature, surface gravity, and mass as obtained from a seismic analysis, and given an estimate of the He/H ratio as available from independent spectroscopy, it is possible to compute a “seismic distance” that is suitably corrected for interstellar reddening from a model atmosphere calculation in conjunction with two-band photometry. The test consists of comparing such a distance with that obtained directly from the high-accuracy Gaia parallax measurements that have become available through Data Release 2. Using observed magnitudes in the Gaia G [SUB]BP[/SUB], G [SUB]RP[/SUB] bandpasses as well as ground- based photometry in the Johnson B, V, Strömgren b, y, and SDSS g, r filters, we find that all of our seismic estimates fall within 1σ of their parallax counterparts. In addition, the derived reddening for our target stars is shown to be generally consistent with Galactic dust reddening and extinction maps. These results apply to a sample of 14 pulsating hot B subdwarfs for which seismic models were published in the past. We also derive useful constraints on the distances to two more pulsators that belong to unresolved binary systems. The excellent agreement found between seismic and parallax distances for the bulk of the sample adds further credibility to the seismic models that have been calculated for pulsators of this type. [less ▲]

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See detailClues on the Origin and Evolution of Massive Contact Binaries: Atmosphere Analysis of VFTS 352
Abdul-Masih, Michael; Sana, Hugues; Sundqvist, Jon et al

in Astrophysical Journal (2019)

The massive O4.5 V + O5.5 V binary VFTS 352 in the Tarantula Nebula is one of the shortest-period and most massive overcontact binaries known. Recent theoretical studies indicate that some of these ... [more ▼]

The massive O4.5 V + O5.5 V binary VFTS 352 in the Tarantula Nebula is one of the shortest-period and most massive overcontact binaries known. Recent theoretical studies indicate that some of these systems could ultimately lead to the formation of gravitational waves via black hole binary mergers through the chemically homogeneous evolution pathway. By analyzing ultraviolet-optical phase resolved spectroscopic data, we aim to constrain atmospheric and wind properties that could be later used to confront theoretical predictions from binary evolution. In particular, surface abundances are powerful diagnostics of the evolutionary status, mass transfer, and internal mixing processes. From a set of 32 Very Large Telescope/FLAMES visual and eight Hubble Space Telescope/Cosmic Origins Spectrograph ultraviolet spectra, we used spectral disentangling to separate the primary and secondary components. Using a genetic algorithm wrapped around the NLTE model atmosphere and the spectral synthesis code FASTWIND, we perform an 11-parameter optimization to derive the atmospheric and wind parameters of both components, including the surface abundances of He, C, N, O, and Si. We find that both components are hotter than expected compared to single-star evolutionary models, indicating that additional mixing processes may be at play. However, the derived chemical abundances do not show significant indications of mixing when adopting baseline values typical of the system environment. [less ▲]

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See detailEvolutionary models for ultracool dwarfs
Silva Fernandes, Catarina ULiege; Van Grootel, Valérie ULiege; Salmon, Sébastien ULiege et al

in Astrophysical Journal (2019), 879(2),

Ultracool dwarfs (UCDs) have emerged as key targets for searches of transiting exoplanets. Precise estimates of the host parameters (including mass, age, and radius) are fundamental to constraining the ... [more ▼]

Ultracool dwarfs (UCDs) have emerged as key targets for searches of transiting exoplanets. Precise estimates of the host parameters (including mass, age, and radius) are fundamental to constraining the physical properties of orbiting exoplanets. We have extended our evolutionary code Code Liégeois d'Evolution Stellaire to the UCD regime. We include relevant equations of state (EOSs) for H, He, as well as C and O elements to cover the temperature–density regime of UCD interiors. For various metallicities, we couple the interior models to two sets of model atmospheres as surface boundary conditions. We show that including C and O in the EOS has a significant effect close to the H-burning limit mass. The typical systematic error associated with uncertainties in input physics in evolutionary models is ~0.0005 M⊙. We test model results against observations for objects whose parameters have been determined from independent techniques. We are able to reproduce dynamical mass measurements of LSPM J1314+1320AB within 1σ with the condition of varying the metallicity (determined from calibrations) up to 2.5σ. For GJ 65AB, a 2σ agreement is obtained between individual masses from differential astrometry and those from evolutionary models. We provide tables of UCD models for various masses and metallicities that can be used as reference when estimating parameters for ultracool objects. [less ▲]

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See detailA Changing Wind Collision
Nazé, Yaël ULiege; Koenigsberger, Gloria; Pittard, Julian M. et al

in Astrophysical Journal (2018), 853

We report on the first detection of a global change in the X-ray emitting properties of a wind–wind collision, thanks to XMM-Newton observations of the massive Small Magellenic Cloud (SMC) system HD 5980 ... [more ▼]

We report on the first detection of a global change in the X-ray emitting properties of a wind–wind collision, thanks to XMM-Newton observations of the massive Small Magellenic Cloud (SMC) system HD 5980. While its light curve had remained unchanged between 2000 and 2005, the X-ray flux has now increased by a factor of ∼2.5, and slightly hardened. The new observations also extend the observational coverage over the entire orbit, pinpointing the light-curve shape. It has not varied much despite the large overall brightening, and a tight correlation of fluxes with orbital separation is found without any hysteresis effect. Moreover, the absence of eclipses and of absorption effects related to orientation suggests a large size for the X-ray emitting region. Simple analytical models of the wind–wind collision, considering the varying wind properties of the eruptive component in HD 5980, are able to reproduce the recent hardening and the flux-separation relationship, at least qualitatively, but they predict a hardening at apastron and little change in mean flux, contrary to observations. The brightness change could then possibly be related to a recently theorized phenomenon linked to the varying strength of thin-shell instabilities in shocked wind regions. Based on XMM-Newton and Chandra data. [less ▲]

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See detailStellar parameters for TRAPPIST-1
Van Grootel, Valérie ULiege; Silva Fernandes, Catarina ULiege; Gillon, Michaël ULiege et al

in Astrophysical Journal (2018), 853

TRAPPIST-1 is an ultracool dwarf star transited by seven Earth-sized planets, for which thorough characterization of atmospheric properties, surface conditions encompassing habitability and internal ... [more ▼]

TRAPPIST-1 is an ultracool dwarf star transited by seven Earth-sized planets, for which thorough characterization of atmospheric properties, surface conditions encompassing habitability and internal compositions is possible with current and next generation telescopes. Accurate modeling of the star is essential to achieve this goal. We aim to obtain updated stellar parameters for TRAPPIST- 1 based on new measurements and evolutionary models, compared to those used in discovery studies. We present a new measurement for the parallax of TRAPPIST-1, 82.4 $\pm$ 0.8 mas, based on 188 epochs of observations with the TRAPPIST and Liverpool Telescopes from 2013 to 2016. This revised parallax yields an updated luminosity of $L_*=(5.22\pm0.19)\times 10^{-4} L_{\odot}$, very close to the previous estimate but almost twice more precise. We next present an updated estimate for TRAPPIST-1 stellar mass, based on two approaches: mass from stellar evolution modeling, and empirical mass derived from dynamical masses of equivalently classified ultracool dwarfs in astrometric binaries. We combine them through a Monte-Carlo approach to derive a semi-empirical estimate for the mass of TRAPPIST-1. We also derive estimate for the radius by combining this mass with stellar density inferred from transits, as well as estimate for the effective temperature from our revised luminosity and radius. Our final results are $M_*=0.089 \pm 0.006 M_{\odot}$, $R_* = 0.121 \pm 0.003 R_{\odot}$, and $T_{\rm eff} =$ 2516 $\pm$ 41 K. Considering the degree to which TRAPPIST-1 system will be scrutinized in coming years, these revised and more precise stellar parameters should be considered when assessing the properties of TRAPPIST-1 planets. [less ▲]

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See detailThe Circumstellar Disk HD 169142: Gas, Dust, and Planets Acting in Concert?
Pohl, A.; Benisty, M.; Pinilla, P. et al

in Astrophysical Journal (2017), 850

HD 169142 is an excellent target for investigating signs of planet-disk interaction due to previous evidence of gap structures. We perform J-band (̃1.2 μm) polarized intensity imaging of HD 169142 with ... [more ▼]

HD 169142 is an excellent target for investigating signs of planet-disk interaction due to previous evidence of gap structures. We perform J-band (̃1.2 μm) polarized intensity imaging of HD 169142 with VLT/SPHERE. We observe polarized scattered light down to 0.″16 (̃19 au) and find an inner gap with a significantly reduced scattered-light flux. We confirm the previously detected double-ring structure peaking at 0.″18 (̃21 au) and 0.″56 (̃66 au) and marginally detect a faint third gap at 0.″70-0.″73 (̃82-85 au). We explore dust evolution models in a disk perturbed by two giant planets, as well as models with a parameterized dust size distribution. The dust evolution model is able to reproduce the ring locations and gap widths in polarized intensity but fails to reproduce their depths. However, it gives a good match with the ALMA dust continuum image at 1.3 mm. Models with a parameterized dust size distribution better reproduce the gap depth in scattered light, suggesting that dust filtration at the outer edges of the gaps is less effective. The pileup of millimeter grains in a dust trap and the continuous distribution of small grains throughout the gap likely require more efficient dust fragmentation and dust diffusion in the dust trap. Alternatively, turbulence or charging effects might lead to a reservoir of small grains at the surface layer that is not affected by the dust growth and fragmentation cycle dominating the dense disk midplane. The exploration of models shows that extracting planet properties such as mass from observed gap profiles is highly degenerate. <P />Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 095.C-0273. [less ▲]

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See detailSearch for Gravitational Waves Associated with Gamma-Ray Bursts during the First Advanced LIGO Observing Run and Implications for the Origin of GRB 150906B
Abbott, B. P.; Collette, Christophe ULiege; others

in Astrophysical Journal (2017), 841(2),

We present the results of the search for gravitational waves (GWs) associated with γ-ray bursts detected during the first observing run of the Advanced Laser Interferometer Gravitational-Wave Observatory ... [more ▼]

We present the results of the search for gravitational waves (GWs) associated with γ-ray bursts detected during the first observing run of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO). We find no evidence of a GW signal for any of the 41 γ-ray bursts for which LIGO data are available with sufficient duration. For all γ-ray bursts, we place lower bounds on the distance to the source using the optimistic assumption that GWs with an energy of were emitted within the-Hz band, and we find a median 90 confidence limit of 71 Mpc at 150 Hz. For the subset of 19 short/hard γ-ray bursts, we place lower bounds on distance with a median 90 confidence limit of 90 Mpc for binary neutron star (BNS) coalescences, and 150 and 139 Mpc for neutron star-black hole coalescences with spins aligned to the orbital angular momentum and in a generic configuration, respectively. These are the highest distance limits ever achieved by GW searches. We also discuss in detail the results of the search for GWs associated with GRB 150906B, an event that was localized by the InterPlanetary Network near the local galaxy NGC 3313, which is at a luminosity distance of Mpc (z = 0.0124). Assuming the γ-ray emission is beamed with a jet half-opening angle, we exclude a BNS and a neutron star-black hole in NGC 3313 as the progenitor of this event with confidence >99\%. Further, we exclude such progenitors up to a distance of 102 Mpc and 170 Mpc, respectively. [less ▲]

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See detailFirst Search for Gravitational Waves from Known Pulsars with Advanced LIGO
Abbott, B. P.; Collette, Christophe ULiege; others

in Astrophysical Journal (2017), 839(1),

We present the result of searches for gravitational waves from 200 pulsars using data from the first observing run of the Advanced LIGO detectors. We find no significant evidence for a gravitational-wave ... [more ▼]

We present the result of searches for gravitational waves from 200 pulsars using data from the first observing run of the Advanced LIGO detectors. We find no significant evidence for a gravitational-wave signal from any of these pulsars, but we are able to set the most constraining upper limits yet on their gravitational-wave amplitudes and ellipticities. For eight of these pulsars, our upper limits give bounds that are improvements over the indirect spin-down limit values. For another 32, we are within a factor of 10 of the spin-down limit, and it is likely that some of these will be reachable in future runs of the advanced detector. Taken as a whole, these new results improve on previous limits by more than a factor of two. [less ▲]

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See detailUpper Limits on Gravitational Waves from Scorpius X-1 from a Model-based Cross-correlation Search in Advanced LIGO Data
Abbott, B. P.; Collette, Christophe ULiege; others

in Astrophysical Journal (2017), 847(1),

We present the results of a semicoherent search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1, using data from the first Advanced LIGO observing run. The search method ... [more ▼]

We present the results of a semicoherent search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1, using data from the first Advanced LIGO observing run. The search method uses details of the modeled, parametrized continuous signal to combine coherently data separated by less than a specified coherence time, which can be adjusted to trade off sensitivity against computational cost. A search was conducted over the frequency range 25-2000 Hz, spanning the current observationally constrained range of binary orbital parameters. No significant detection candidates were found, and frequency-dependent upper limits were set using a combination of sensitivity estimates and simulated signal injections. The most stringent upper limit was set at 175 Hz, with comparable limits set across the most sensitive frequency range from 100 to 200 Hz. At this frequency, the 95 upper limit on the signal amplitude h0 is 2.3 \?x 10-25 marginalized over the unknown inclination angle of the neutron star's spin, and 8.0 \?x 10-26 assuming the best orientation (which results in circularly polarized gravitational waves). These limits are a factor of 3-4 stronger than those set by other analyses of the same data, and a factor of ∼ 7 stronger than the best upper limits set using data from Initial LIGO science runs. In the vicinity of 100 Hz, the limits are a factor of between 1.2 and 3.5 above the predictions of the torque balance model, depending on the inclination angle; if the most likely inclination angle of 44° is assumed, they are within a factor of 1.7. [less ▲]

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See detailReturn of the King: Time-Series Photometry of FO Aquarii's Initial Recovery from its Unprecedented 2016 Low State
Littlefield, Colin; Garnavich, Peter; Kennedy, Mark et al

in Astrophysical Journal (2016), 883(93), 7

In 2016 May, the intermediate polar FO~Aqr was detected in a low state for the first time in its observational history. We report time-resolved photometry of the system during its initial recovery from ... [more ▼]

In 2016 May, the intermediate polar FO~Aqr was detected in a low state for the first time in its observational history. We report time-resolved photometry of the system during its initial recovery from this faint state. Our data, which includes high-speed photometry with cadences of just 2 sec, shows the existence of very strong periodicities at 22.5 min and 11.26 min, equivalent to the spin-orbit beat frequency and twice its value, respectively. A pulse at the spin frequency is also present but at a much lower amplitude than is normally observed in the bright state. By comparing our power spectra with theoretical models, we infer that a substantial amount of accretion was stream-fed during our observations, in contrast to the disk-fed accretion that dominates the bright state. In addition, we find that FO~Aqr's rate of recovery has been unusually slow in comparison to rates of recovery seen in other magnetic cataclysmic variables, with an e-folding time of 115±7 days. The recovery also shows irregular variations in the median brightness of as much as 0.2~mag over a 10-day span. Finally, we show that the arrival times of the spin pulses are dependent upon the system's overall brightness. [less ▲]

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See detailChandra View of Magnetically Confined Wind in HD191612: Theory Versus Observations
Nazé, Yaël ULiege; ud-Doula, Asif; Zhekov, Svetozar A.

in Astrophysical Journal (2016), 831(#138), 11

High-resolution spectra of the magnetic star HD 191612 were acquired using the Chandra X-ray Observatory at both maximum and minimum emission phases. We confirm the flux and hardness variations previously ... [more ▼]

High-resolution spectra of the magnetic star HD 191612 were acquired using the Chandra X-ray Observatory at both maximum and minimum emission phases. We confirm the flux and hardness variations previously reported with XMM-Newton, demonstrating the high repeatability of the behavior of HD 191612 over a decade. The line profiles appear typical for magnetic massive stars: no significant line shift, relatively narrow lines for high-Z elements, and formation radius at about 2 {R}[SUB]* [/SUB]. Line ratios confirm the softening of the X-ray spectrum at the minimum emission phase. Shift or width variations appear of limited amplitude at most (slightly lower velocity and slightly increased broadening at minimum emission phase, but within 1–2σ of values at maximum). In addition, a fully self-consistent 3D magnetohydrodynamic simulation of the confined wind in HD 191612 was performed. The simulation results were directly fitted to the data, leading to a remarkable agreement overall between them. [less ▲]

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See detailPolarization Measurements of Hot Dust Stars and the Local Interstellar Medium
Marshall, J. P.; Cotton, D. V.; Bott, K. et al

in Astrophysical Journal (2016), 825

Debris discs are typically revealed through the presence of excess emission at infrared wavelengths. Most discs exhibit excess at mid- and far-infrared wavelengths, analogous to the solar system’s ... [more ▼]

Debris discs are typically revealed through the presence of excess emission at infrared wavelengths. Most discs exhibit excess at mid- and far-infrared wavelengths, analogous to the solar system’s Asteroid and Edgeworth-Kuiper belts. Recently, stars with strong (˜1%) excess at near-infrared wavelengths were identified through interferometric measurements. Using the HIgh Precision Polarimetric Instrument, we examined a sub-sample of these hot dust stars (and appropriate controls) at parts-per-million sensitivity in SDSS g‧ (green) and r‧ (red) filters for evidence of scattered light. No detection of strongly polarized emission from the hot dust stars is seen. We, therefore, rule out scattered light from a normal debris disk as the origin of this emission. A wavelength-dependent contribution from multiple dust components for hot dust stars is inferred from the dispersion (the difference in polarization angle in red and green) of southern stars. Contributions of 17 ppm (green) and 30 ppm (red) are calculated, with strict 3-σ upper limits of 76 and 68 ppm, respectively. This suggests weak hot dust excesses consistent with thermal emission, although we cannot rule out contrived scenarios, e.g., dust in a spherical shell or face-on discs. We also report on the nature of the local interstellar medium (ISM), obtained as a byproduct of the control measurements. Highlights include the first measurements of the polarimetric color of the local ISM and the discovery of a southern sky region with a polarization per distance thrice the previous maximum. The data suggest that λ [SUB]max[/SUB], the wavelength of maximum polarization, is bluer than typical. [less ▲]

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See detailNulling Data Reduction and On-sky Performance of the Large Binocular Telescope Interferometer
Defrere, Denis ULiege; Hinz, P. M.; Mennesson, B. et al

in Astrophysical Journal (2016), 824

The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high angular resolution and high-contrast infrared imaging (1.5-13 μm). In this paper, we focus on the mid ... [more ▼]

The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high angular resolution and high-contrast infrared imaging (1.5-13 μm). In this paper, we focus on the mid-infrared (8-13 μm) nulling mode and present its theory of operation, data reduction, and on-sky performance as of the end of the commissioning phase in 2015 March. With an interferometric baseline of 14.4 m, the LBTI nuller is specifically tuned to resolve the habitable zone of nearby main-sequence stars, where warm exozodiacal dust emission peaks. Measuring the exozodi luminosity function of nearby main-sequence stars is a key milestone to prepare for future exo-Earth direct imaging instruments. Thanks to recent progress in wavefront control and phase stabilization, as well as in data reduction techniques, the LBTI demonstrated in 2015 February a calibrated null accuracy of 0.05% over a 3 hr long observing sequence on the bright nearby A3V star β Leo. This is equivalent to an exozodiacal disk density of 15-30 zodi for a Sun-like star located at 10 pc, depending on the adopted disk model. This result sets a new record for high-contrast mid-infrared interferometric imaging and opens a new window on the study of planetary systems. [less ▲]

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See detailThe LEECH Exoplanet Imaging Survey: Orbit and Component Masses of the Intermediate-age, Late-type Binary NO UMa
Schlieder, Joshua E.; Skemer, Andrew J.; Maire, Anne-Lise ULiege et al

in Astrophysical Journal (2016), 818

We present high-resolution Large Binocular Telescope LBTI/LMIRcam images of the spectroscopic and astrometric binary NO UMa obtained as part of the LBT Interferometer Exozodi Exoplanet Common Hunt ... [more ▼]

We present high-resolution Large Binocular Telescope LBTI/LMIRcam images of the spectroscopic and astrometric binary NO UMa obtained as part of the LBT Interferometer Exozodi Exoplanet Common Hunt exoplanet imaging survey. Our H-, K[SUB]s[/SUB]-, and L‧-band observations resolve the system at angular separations <0.″09. The components exhibit significant orbital motion over a span of ∼7 months. We combine our imaging data with archival images, published speckle interferometry measurements, and existing spectroscopic velocity data to solve the full orbital solution and estimate component masses. The masses of the K2.0 ± 0.5 primary and K6.5 ± 0.5 secondary are 0.83 ± 0.02 M[SUB]⊙[/SUB] and 0.64 ± 0.02 M[SUB]⊙[/SUB], respectively. We also derive a system distance of d = 25.87 ± 0.02 pc and revise the Galactic kinematics of NO UMa. Our revised Galactic kinematics confirm NO UMa as a nuclear member of the ∼500 Myr old Ursa Major moving group, and it is thus a mass and age benchmark. We compare the masses of the NO UMa binary components to those predicted by five sets of stellar evolution models at the age of the Ursa Major group. We find excellent agreement between our measured masses and model predictions with little systematic scatter between the models. NO UMa joins the short list of nearby, bright, late-type binaries having known ages and fully characterized orbits. Based on data obtained with the STELLA robotic telescope in Tenerife, an AIP facility jointly operated by AIP and IAC. [less ▲]

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