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See detailAtomic data and spectral model for Fe II
Bautista, M A; Fivet, V; Ballance, C et al

in Astrophysical Journal (in press)

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See detailTests of the Planetary Hypothesis for PTFO 8-8695b
Yu, Liang; Winn, Joshua N.; Gillon, Michaël ULg et al

in Astrophysical Journal (2015), 812

The T Tauri star PTFO 8-8695 exhibits periodic fading events that have been interpreted as the transits of a giant planet on a precessing orbit. Here we present three tests of the planet hypothesis. First ... [more ▼]

The T Tauri star PTFO 8-8695 exhibits periodic fading events that have been interpreted as the transits of a giant planet on a precessing orbit. Here we present three tests of the planet hypothesis. First, we sought evidence for the secular changes in light-curve morphology that are predicted to be a consequence of orbital precession. We observed 28 fading events spread over several years and did not see the expected changes. Instead, we found that the fading events are not strictly periodic. Second, we attempted to detect the planet's radiation, based on infrared observations spanning the predicted times of occultations. We ruled out a signal of the expected amplitude. Third, we attempted to detect the Rossiter-McLaughlin effect by performing high-resolution spectroscopy throughout a fading event. No effect was seen at the expected level, ruling out most (but not all) possible orientations for the hypothetical planetary orbit. Our spectroscopy also revealed strong, time-variable, high-velocity Hα and Ca H & K emission features. All these observations cast doubt on the planetary hypothesis, and suggest instead that the fading events represent starspots, eclipses by circumstellar dust, or occultations of an accretion hotspot. [less ▲]

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See detailThe K2-ESPRINT Project I: Discovery of the Disintegrating Rocky Planet K2-22b with a Cometary Head and Leading Tail
Sanchis-Ojeda, R.; Rappaport, S.; Pallé, E. et al

in Astrophysical Journal (2015), 812(2), 112

We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hr: K2-22b. The highly variable transit depths, ranging from ∼0% to 1.3%, are suggestive of ... [more ▼]

We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hr: K2-22b. The highly variable transit depths, ranging from ∼0% to 1.3%, are suggestive of a planet that is disintegrating via the emission of dusty effluents. We characterize the host star as an M-dwarf with Teff ≃ 3800 K. We have obtained ground-based transit measurements with several 1-m class telescopes and with the GTC. These observations (1) improve the transit ephemeris; (2) confirm the variable nature of the transit depths; (3) indicate variations in the transit shapes; and (4) demonstrate clearly that at least on one occasion the transit depths were significantly wavelength dependent. The latter three effects tend to indicate extinction of starlight by dust rather than by any combination of solid bodies. The K2 observations yield a folded light curve with lower time resolution but with substantially better statistical precision compared with the ground-based observations. We detect a significant “bump” just after the transit egress, and a less significant bump just prior to transit ingress. We interpret these bumps in the context of a planet that is not only likely streaming a dust tail behind it, but also has a more prominent leading dust trail that precedes it. This effect is modeled in terms of dust grains that can escape to beyond the planet's Hill sphere and effectively undergo “Roche lobe overflow,” even though the planet's surface is likely underfilling its Roche lobe by a factor of 2. [less ▲]

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See detailImpact of ηEarth on the Capabilities of Affordable Space Missions to Detect Biosignatures on Extrasolar Planets
Léger, Alain; Defrère, Denis; Malbet, Fabien et al

in Astrophysical Journal (2015), 808

We present an analytic model to estimate the capabilities of space missions dedicated to the search for biosignatures in the atmosphere of rocky planets located in the habitable zone of nearby stars ... [more ▼]

We present an analytic model to estimate the capabilities of space missions dedicated to the search for biosignatures in the atmosphere of rocky planets located in the habitable zone of nearby stars. Relations between performance and mission parameters, such as mirror diameter, distance to targets, and radius of planets, are obtained. Two types of instruments are considered: coronagraphs observing in the visible, and nulling interferometers in the thermal infrared. Missions considered are: single-pupil coronagraphs with a 2.4 m primary mirror, and formation-flying interferometers with 4 × 0.75 m collecting mirrors. The numbers of accessible planets are calculated as a function of η[SUB]Earth[/SUB]. When Kepler gives its final estimation for η[SUB]Earth[/SUB], the model will permit a precise assessment of the potential of each instrument. Based on current estimations, η[SUB]Earth[/SUB] = 10% around FGK stars and 50% around M stars, the coronagraph could study in spectroscopy only ∼1.5 relevant planets, and the interferometer ∼14.0. These numbers are obtained under the major hypothesis that the exozodiacal light around the target stars is low enough for each instrument. In both cases, a prior detection of planets is assumed and a target list established. For the long-term future, building both types of spectroscopic instruments, and using them on the same targets, will be the optimal solution because they provide complementary information. But as a first affordable space mission, the interferometer looks the more promising in terms of biosignature harvest. [less ▲]

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See detailA Coordinated X-Ray and Optical Campaign of the Nearest Massive Eclipsing Binary, δ Orionis Aa. II. X-Ray Variability
Nichols, J.; Huenemoerder, D. P.; Corcoran, M. F. et al

in Astrophysical Journal (2015), 809

We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the δ Ori Aa binary system. The four observations, obtained with Chandra ACIS ... [more ▼]

We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the δ Ori Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of ≈ 479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range of 5–25 Å is confirmed, with a maximum amplitude of about ±15% within a single ≈ 125 ks observation. Periods of 4.76 and 2.04 days are found in the total X-ray flux, as well as an apparent overall increase in the flux level throughout the nine-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate the variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S xv, Si xiii, and Ne ix. For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at ϕ = 0.0 when the secondary δ Ori Aa2 is at the inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind–wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability. Based on data from the Chandra X-ray Observatory and the MOST satellite, a Canadian Space Agency mission, jointly operated by Dynacon Inc., the University of Toronto Institute of Aerospace Studies, and the University of British Columbia, with the assistance of the University of Vienna. [less ▲]

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See detailA Coordinated X-Ray and Optical Campaign of the Nearest Massive Eclipsing Binary, δ Orionis Aa. IV. A Multiwavelength, Non-LTE Spectroscopic Analysis
Shenar, T.; Oskinova, L.; Hamann, W.-R. et al

in Astrophysical Journal (2015), 809

Eclipsing systems of massive stars allow one to explore the properties of their components in great detail. We perform a multi-wavelength, non-LTE analysis of the three components of the massive multiple ... [more ▼]

Eclipsing systems of massive stars allow one to explore the properties of their components in great detail. We perform a multi-wavelength, non-LTE analysis of the three components of the massive multiple system δ Ori A, focusing on the fundamental stellar properties, stellar winds, and X-ray characteristics of the system. The primary’s distance-independent parameters turn out to be characteristic for its spectral type (O9.5 II), but usage of the Hipparcos parallax yields surprisingly low values for the mass, radius, and luminosity. Consistent values follow only if δ Ori lies at about twice the Hipparcos distance, in the vicinity of the σ-Orionis cluster. The primary and tertiary dominate the spectrum and leave the secondary only marginally detectable. We estimate the V-band magnitude difference between primary and secondary to be {{Δ }}V≈ 2\buildrel{{m}}\over{.} 8. The inferred parameters suggest that the secondary is an early B-type dwarf (≈B1 V), while the tertiary is an early B-type subgiant (≈B0 IV). We find evidence for rapid turbulent velocities (∼200 km s[SUP]‑1[/SUP]) and wind inhomogeneities, partially optically thick, in the primary’s wind. The bulk of the X-ray emission likely emerges from the primary’s stellar wind ({log}{L}[SUB]{{X[/SUB]}}/{L}[SUB]{Bol[/SUB]}≈ -6.85), initiating close to the stellar surface at {R}[SUB]0[/SUB]∼ 1.1 {R}[SUB]*[/SUB]. Accounting for clumping, the mass-loss rate of the primary is found to be {log}\dot{M}≈ -6.4 ({M}[SUB]ȯ [/SUB] {{yr}}[SUP]-1[/SUP]), which agrees with hydrodynamic predictions, and provides a consistent picture along the X-ray, UV, optical, and radio spectral domains. [less ▲]

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See detailPluto's atmosphere from stellar occultations in 2012 and 2013
Dias-Oliveira, A.; Sicardy, B.; Lellouch, E. et al

in Astrophysical Journal (2015), 1506

We analyze two multi-chord stellar occultations by Pluto observed on July 18th, 2012 and May 4th, 2013, and monitored respectively from five and six sites. They provide a total of fifteen light-curves ... [more ▼]

We analyze two multi-chord stellar occultations by Pluto observed on July 18th, 2012 and May 4th, 2013, and monitored respectively from five and six sites. They provide a total of fifteen light-curves, twelve of them being used for a simultaneous fit that uses a unique temperature profile, assuming a clear (no-haze) and pure N_2 atmosphere, but allowing for a possible pressure variation between the two dates. We find a solution that fits satisfactorily (i.e. within the noise level) all the twelve light-curves, providing atmospheric constraints between ~1,190 km (pressure ~ 11 \mubar) and ~ 1,450 km (pressure ~0.1 \mubar) from Pluto's center. Our main results are: (1) the best-fitting temperature profile shows a stratosphere with strong positive gradient between 1,190 km (at 36 K, 11 \mubar) and r = 1,215 km (6.0 \mubar), where a temperature maximum of 110 K is reached; above it is a mesosphere with negative thermal gradient of -0.2 K/km up to ~ 1,390 km (0.25 \mubar), where, the mesosphere connects itself to a more isothermal upper branch around 81 K; (2) the pressure shows a small (6 [less ▲]

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See detailFirst-light LBT Nulling Interferometric Observations: Warm Exozodiacal Dust Resolved within a Few AU of eta Crv
Defrere, D.; Hinz, P. M.; Skemer, A. J. et al

in Astrophysical Journal (2015), 799

We report on the first nulling interferometric observations with the Large Binocular Telescope Interferometer (LBTI), resolving the N' band (9.81-12.41 μm) emission around the nearby main-sequence star η ... [more ▼]

We report on the first nulling interferometric observations with the Large Binocular Telescope Interferometer (LBTI), resolving the N' band (9.81-12.41 μm) emission around the nearby main-sequence star η Crv (F2V, 1-2 Gyr). The measured source null depth amounts to 4.40% ± 0.35% over a field-of-view of 140 mas in radius (~2.6 AU for the distance of η Crv) and shows no significant variation over 35° of sky rotation. This relatively low null is unexpected given the total disk to star flux ratio measured by the Spitzer Infrared Spectrograph (IRS; ~23% across the N' band), suggesting that a significant fraction of the dust lies within the central nulled response of the LBTI (79 mas or 1.4 AU). Modeling of the warm disk shows that it cannot resemble a scaled version of the solar zodiacal cloud unless it is almost perpendicular to the outer disk imaged by Herschel. It is more likely that the inner and outer disks are coplanar and the warm dust is located at a distance of 0.5-1.0 AU, significantly closer than previously predicted by models of the IRS spectrum (~3 AU). The predicted disk sizes can be reconciled if the warm disk is not centrosymmetric, or if the dust particles are dominated by very small grains. Both possibilities hint that a recent collision has produced much of the dust. Finally, we discuss the implications for the presence of dust for the distance where the insolation is the same as Earth's (2.3 AU). [less ▲]

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See detailMonte Carlo Simulation of Metastable Oxygen Photochemistry in Cometary Atmospheres
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg et al

in Astrophysical Journal (2015), 798

Cometary atmospheres are produced by the outgassing of material, mainly H[SUB]2[/SUB]O, CO, and CO[SUB]2[/SUB] from the nucleus of the comet under the energy input from the Sun. Subsequent photochemical ... [more ▼]

Cometary atmospheres are produced by the outgassing of material, mainly H[SUB]2[/SUB]O, CO, and CO[SUB]2[/SUB] from the nucleus of the comet under the energy input from the Sun. Subsequent photochemical processes lead to the production of other species generally absent from the nucleus, such as OH. Although all comets are different, they all have a highly rarefied atmosphere, which is an ideal environment for nonthermal photochemical processes to take place and influence the detailed state of the atmosphere. We develop a Monte Carlo model of the coma photochemistry. We compute the energy distribution functions (EDF) of the metastable O([SUP]1[/SUP]D) and O([SUP]1[/SUP]S) species and obtain the red (630 nm) and green (557.7 nm) spectral line shapes of the full coma, consistent with the computed EDFs and the expansion velocity. We show that both species have a severely non-Maxwellian EDF, that results in broad spectral lines and the suprathermal broadening dominates due to the expansion motion. We apply our model to the atmosphere of comet C/1996 B2 (Hyakutake) and 103P/Hartley 2. The computed width of the green line, expressed in terms of speed, is lower than that of the red line. This result is comparable to previous theoretical analyses, but in disagreement with observations. We explain that the spectral line shape does not only depend on the exothermicity of the photochemical production mechanisms, but also on thermalization, due to elastic collisions, reducing the width of the emission line coming from the O([SUP]1[/SUP]D) level, which has a longer lifetime. [less ▲]

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See detailCO Gas Inside the Protoplanetary Disk Cavity in HD 142527: Disk Structure from ALMA
Perez, S.; Casassus, S.; Ménard, F. et al

in Astrophysical Journal (2014), 798

Inner cavities and annular gaps in circumstellar disks are possible signposts of giant planet formation. The young star HD 142527 hosts a massive protoplanetary disk with a large cavity that extends up to ... [more ▼]

Inner cavities and annular gaps in circumstellar disks are possible signposts of giant planet formation. The young star HD 142527 hosts a massive protoplanetary disk with a large cavity that extends up to 140 AU from the central star, as seen in continuum images at infrared and millimeter wavelengths. Estimates of the survival of gas inside disk cavities are needed to discriminate between clearing scenarios. We present a spatially and spectrally resolved carbon monoxide isotopologue 2-1 line of $^12$CO, $^13$CO, and C[SUP]18[/SUP]$O obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). We detect emission coming from inside the dust-depleted cavity in all three isotopologues. Based on our analysis of the gas in the dust cavity, the $^12$CO emission is optically thick, while $^13$CO and C[SUP]18[/SUP]$O emissions are both optically thin. The total mass of residual gas inside the cavity is \~1.5-2 M $_Jup$. We model the gas with an axisymmetric disk model. Our best-fit model shows that the cavity radius is much smaller in CO than it is in millimeter continuum and scattered light observations, with a gas cavity that does not extend beyond 105 AU (at 3$\sigma$). The gap wall at its outer edge is diffuse and smooth in the gas distribution, while in dust continuum it is manifestly sharper. The inclination angle, as estimated from the high velocity channel maps is 28 \plusmn 0.5 deg, higher than in previous estimates, assuming a fix central star mass of 2.2 M $_&sun;$. [less ▲]

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See detailConstraining the Exozodiacal Luminosity Function of Main-sequence Stars: Complete Results from the Keck Nuller Mid-infrared Surveys
Mennesson, B.; Millan-Gabet, R.; Serabyn, E. et al

in Astrophysical Journal (2014), 797

Forty-seven nearby main-sequence stars were surveyed with the Keck Interferometer mid-infrared Nulling instrument (KIN) between 2008 and 2011, searching for faint resolved emission from exozodiacal dust ... [more ▼]

Forty-seven nearby main-sequence stars were surveyed with the Keck Interferometer mid-infrared Nulling instrument (KIN) between 2008 and 2011, searching for faint resolved emission from exozodiacal dust. Observations of a subset of the sample have already been reported, focusing essentially on stars with no previously known dust. Here we extend this previous analysis to the whole KIN sample, including 22 more stars with known near- and/or far-infrared excesses. In addition to an analysis similar to that of the first paper of this series, which was restricted to the 8-9 mum spectral region, we present measurements obtained in all 10 spectral channels covering the 8-13 mum instrumental bandwidth. Based on the 8-9 mum data alone, which provide the highest signal-to-noise measurements, only one star shows a large excess imputable to dust emission (eta Crv), while four more show a significant (>3sigma) excess: beta Leo, beta UMa, zeta Lep, and gamma Oph. Overall, excesses detected by KIN are more frequent around A-type stars than later spectral types. A statistical analysis of the measurements further indicates that stars with known far-infrared (lambda >= 70 mum) excesses have higher exozodiacal emission levels than stars with no previous indication of a cold outer disk. This statistical trend is observed regardless of spectral type and points to a dynamical connection between the inner (zodi-like) and outer (Kuiper-Belt-like) dust populations. The measured levels for such stars are clustering close to the KIN detection limit of a few hundred zodis and are indeed consistent with those expected from a populat [less ▲]

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See detailFundamental Limitations of High Contrast Imaging Set by Small Sample Statistics
Mawet, D.; Milli, J.; Wahhaj, Z. et al

in Astrophysical Journal (2014), 792

In this paper, we review the impact of small sample statistics on detection thresholds and corresponding confidence levels (CLs) in high-contrast imaging at small angles. When looking close to the star ... [more ▼]

In this paper, we review the impact of small sample statistics on detection thresholds and corresponding confidence levels (CLs) in high-contrast imaging at small angles. When looking close to the star, the number of resolution elements decreases rapidly toward small angles. This reduction of the number of degrees of freedom dramatically affects CLs and false alarm probabilities. Naively using the same ideal hypothesis and methods as for larger separations, which are well understood and commonly assume Gaussian noise, can yield up to one order of magnitude error in contrast estimations at fixed CL. The statistical penalty exponentially increases toward very small inner working angles. Even at 5-10 resolution elements from the star, false alarm probabilities can be significantly higher than expected. Here we present a rigorous statistical analysis that ensures robustness of the CL, but also imposes a substantial limitation on corresponding achievable detection limits (thus contrast) at small angles. This unavoidable fundamental statistical effect has a significant impact on current coronagraphic and future high-contrast imagers. Finally, the paper concludes with practical recommendations to account for small number statistics when computing the sensitivity to companions at small angles and when exploiting the results of direct imaging planet surveys. [less ▲]

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See detailPrecision Asteroseismology of the Pulsating White Dwarf GD 1212 Using a Two-wheel-controlled Kepler Spacecraft
Hermes, J.J.; Charpinet, Stéphane; Barclay, Thomas et al

in Astrophysical Journal (2014), 789

We present a preliminary analysis of the cool pulsating white dwarf (WD) GD 1212, enabled by more than 11.5 days of space-based photometry obtained during an engineering test of the two-reaction-wheel ... [more ▼]

We present a preliminary analysis of the cool pulsating white dwarf (WD) GD 1212, enabled by more than 11.5 days of space-based photometry obtained during an engineering test of the two-reaction-wheel-controlled Kepler spacecraft. We detect at least 19 independent pulsation modes, ranging from 828.2-1220.8 s, and at least 17 nonlinear combination frequencies of those independent pulsations. Our longest uninterrupted light curve, 9.0 days in length, evidences coherent difference frequencies at periods inaccessible from the ground, up to 14.5 hr, the longest-period signals ever detected in a pulsating WD. These results mark some of the first science to come from a two-wheel-controlled Kepler spacecraft, proving the capability for unprecedented discoveries afforded by extending Kepler observations to the ecliptic. [less ▲]

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See detailExtremely Organic-rich Coma of Comet C/2010 G2 (Hill) during its Outburst in 2012
Kawakita, Hideyo; Dello Russo, Neil; Vervack, Ron et al

in Astrophysical Journal (2014), 788

We performed high-dispersion near-infrared spectroscopic observations of comet C/2010 G2 (Hill) at 2.5 AU from the Sun using NIRSPEC (R ≈ 25,000) at the Keck II Telescope on UT 2012 January 9 and 10 ... [more ▼]

We performed high-dispersion near-infrared spectroscopic observations of comet C/2010 G2 (Hill) at 2.5 AU from the Sun using NIRSPEC (R ≈ 25,000) at the Keck II Telescope on UT 2012 January 9 and 10, about a week after an outburst had occurred. Over the two nights of our observations, prominent emission lines of CH[SUB]4[/SUB] and C[SUB]2[/SUB]H[SUB]6[/SUB], along with weaker emission lines of H[SUB]2[/SUB]O, HCN, CH[SUB]3[/SUB]OH, and CO were detected. The gas production rate of CO was comparable to that of H[SUB]2[/SUB]O during the outburst. The mixing ratios of CO, HCN, CH[SUB]4[/SUB], C[SUB]2[/SUB]H[SUB]6[/SUB], and CH[SUB]3[/SUB]OH with respect to H[SUB]2[/SUB]O were higher than those for normal comets by a factor of five or more. The enrichment of CO and CH[SUB]4[/SUB] in comet Hill suggests that the sublimation of these hypervolatiles sustained the outburst of the comet. Some fraction of water in the inner coma might exist as icy grains that were likely ejected from nucleus by the sublimation of hypervolatiles. Mixing ratios of volatiles in comet Hill are indicative of the interstellar heritage without significant alteration in the solar nebula. [less ▲]

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See detailTransit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star
Van Grootel, Valérie ULg; Gillon, Michaël ULg; Valencia, D. et al

in Astrophysical Journal (2014), 786

Super-Earths transiting nearby bright stars are key objects that simultaneously allow for accurate measurements of both their mass and radius, providing essential constraints on their internal composition ... [more ▼]

Super-Earths transiting nearby bright stars are key objects that simultaneously allow for accurate measurements of both their mass and radius, providing essential constraints on their internal composition. We present here the confirmation, based on Spitzer transit observations, that the super-Earth HD 97658 b transits its host star. HD 97658 is a low-mass ($M_*=0.77\pm0.05\,M_{\odot}$) K1 dwarf, as determined from the Hipparcos parallax and stellar evolution modeling. To constrain the planet parameters, we carry out Bayesian global analyses of Keck-HIRES radial velocities, and MOST and Spitzer photometry. HD 97658 b is a massive ($M_P=7.55^{+0.83}_{-0.79} M_{\oplus}$) and large ($R_{P} = 2.247^{+0.098}_{-0.095} R_{\oplus}$ at 4.5 $\mu$m) super-Earth. We investigate the possible internal compositions for HD 97658 b. Our results indicate a large rocky component, by at least 60% by mass, and very little H-He components, at most 2% by mass. We also discuss how future asteroseismic observations can improve the knowledge of the HD 97658 system, in particular by constraining its age. Orbiting a bright host star, HD 97658 b will be a key target for coming space missions TESS, CHEOPS, PLATO, and also JWST, to characterize thoroughly its structure and atmosphere. [less ▲]

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See detailThe BANANA Project. V. Misaligned and Precessing Stellar Rotation Axes in CV Velorum
Albrecht, Simon; Winn, Joshua N.; Torres, Guillermo et al

in Astrophysical Journal (2014), 785

As part of the Binaries Are Not Always Neatly Aligned project (BANANA), we have found that the eclipsing binary CV Velorum has misaligned rotation axes. Based on our analysis of the Rossiter-McLaughlin ... [more ▼]

As part of the Binaries Are Not Always Neatly Aligned project (BANANA), we have found that the eclipsing binary CV Velorum has misaligned rotation axes. Based on our analysis of the Rossiter-McLaughlin effect, we find sky-projected spin-orbit angles of β[SUB]p[/SUB] = -52° ± 6° and β[SUB]s[/SUB] = 3° ± 7° for the primary and secondary stars (B2.5V + B2.5V, P = 6.9 days). We combine this information with several measurements of changing projected stellar rotation speeds (vsin i [SUB]sstarf[/SUB]) over the last 30 yr, leading to a model in which the primary star's obliquity is ≈65°, and its spin axis precesses around the total angular momentum vector with a period of about 140 yr. The geometry of the secondary star is less clear, although a significant obliquity is also implicated by the observed time variations in the vsin i [SUB]sstarf[/SUB]. By integrating the secular tidal evolution equations backward in time, we find that the system could have evolved from a state of even stronger misalignment similar to DI Herculis, a younger but otherwise comparable binary. Based on observations made with ESOs 2.2 m Telescopes at the La Silla Paranal Observatory under programme ID 084.C-1008 and under MPIA guaranteed time. [less ▲]

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See detailA Super-Jupiter orbiting a late-type star: A refined analysis of microlensing event OGLE-2012-BLG-0406
Tsapras, Y.; Choi, J.-Y.; Street, R. A. et al

in Astrophysical Journal (2014), 782

We present a detailed analysis of survey and follow-up observations of microlensing event OGLE-2012-BLG-0406 based on data obtained from 10 different observatories. Intensive coverage of the lightcurve ... [more ▼]

We present a detailed analysis of survey and follow-up observations of microlensing event OGLE-2012-BLG-0406 based on data obtained from 10 different observatories. Intensive coverage of the lightcurve, especially the perturbation part, allowed us to accurately measure the parallax effect and lens orbital motion. Combining our measurement of the lens parallax with the angular Einstein radius determined from finite-source effects, we estimate the physical parameters of the lens system. We find that the event was caused by a $2.73\pm 0.43\ M_{\rm J}$ planet orbiting a $0.44\pm 0.07\ M_{\odot}$ early M-type star. The distance to the lens is $4.97\pm 0.29$\ kpc and the projected separation between the host star and its planet at the time of the event is $3.45\pm 0.26$ AU. We find that the additional coverage provided by follow-up observations, especially during the planetary perturbation, leads to a more accurate determination of the physical parameters of the lens. [less ▲]

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See detailA Monitoring Campaign for Luhman 16AB. I. Detection of Resolved Near-Infrared Spectroscopic Variability
Burgasser, A. J.; Gillon, Michaël ULg; Faherty, J. K. et al

in Astrophysical Journal (2014), 785

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See detailThe Size, Shape, Albedo, Density, and Atmospheric Limit of Transneptunian Object (50000) Quaoar from Multi-chord Stellar Occultations
Braga-Ribas, F.; Sicardy, B.; Ortiz, J. L. et al

in Astrophysical Journal (2013), 773

We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation ... [more ▼]

We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation observed on 2012 October 15. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius R [SUB]equiv[/SUB] = 555 ± 2.5 km and geometric visual albedo p[SUB]V[/SUB] = 0.109 ± 0.007. Assuming that Quaoar is a Maclaurin spheroid with an indeterminate polar aspect angle, we derive a true oblateness of \epsilon = 0.087^{+0.0268}_{-0.0175}, an equatorial radius of 569^{+24}_{-17} km, and a density of 1.99 ± 0.46 g cm[SUP]–3[/SUP]. The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere. [less ▲]

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See detailHerschel's "Cold Debris Disks": Background Galaxies or Quiescent Rims of Planetary Systems?
Krivov, A. V.; Eiroa, C.; Löhne, T. et al

in Astrophysical Journal (2013), 772

(abridged) Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around ~100{\mu}m or shorter. However, six out of 31 excess sources in the Herschel OTKP DUNES have ... [more ▼]

(abridged) Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around ~100{\mu}m or shorter. However, six out of 31 excess sources in the Herschel OTKP DUNES have been seen to show significant - and in some cases extended - excess emission at 160{\mu}m, which is larger than the 100{\mu}m excess. This excess emission has been suggested to stem from debris disks colder than those known previously. Using several methods, we re-consider whether some or even all of the candidates may be associated with unrelated galactic or extragalactic emission and conclude that it is highly unlikely that none of the candidates represents a true circumstellar disk. For true disks, both the dust temperatures inferred from the SEDs and the disk radii estimated from the images suggest that the dust is nearly as cold as a blackbody. This requires the grains to be larger than ~100{\mu}m, regardless of their material composition. To explain the dearth of small grains, we explore several conceivable scenarios: transport-dominated disks, disks of low dynamical excitation, and disks of unstirred primordial macroscopic grains. Our qualitative analysis and collisional simulations rule out the first two of these scenarios, but show the feasibility of the third one. We show that such disks can survive for gigayears, largely preserving the primordial size distribution. They should be composed of macroscopic solids larger than millimeters, but smaller than kilometers in size. Thus planetesimal formation, at least in the outer regions of the systems, has stopped before "cometary" or "asteroidal" sizes were reached. [less ▲]

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