arXiv subjects

Ryan Cloutier

Publications and source records attributed to Ryan Cloutier.

102 records · Page 6Linked to original sources

arXiv2018

Quantifying the Observational Effort Required for the Radial Velocity Characterization of TESS Planets

The Transiting Exoplanet Survey Satellite will conduct a 2-year long wide-field survey searching for transiting planets around bright stars. Many TESS discoveries will be amenable to mass characterization via ground-based radial velocity measurements with any of a growing suite of existing and anticipated velocimeters in the optical and near-infrared. In this study we present an analytical formalism to compute the number of radial velocity measurements---and hence the total observing time---required to characterize RV planet masses with the inclusion of either a white or correlated noise activity model. We use our model to calculate the total observing time required to measure all TESS planet masses from the expected TESS planet yield while relying on our current understanding of the targeted stars, stellar activity, and populations of unseen planets which inform the expected radial velocity precision. We also present specialized calculations applicable to a variety of interesting TESS planet subsets including the characterization of 50 planets smaller than 4 Earth radii which is expected to take as little as 60 nights of observation. Although, the efficient RV characterization of such planets requires a-priori knowledge of the `best' targets which we argue can be identified prior to the conclusion of the TESS planet search based on our calculations. Our results highlight the comparable performance of optical and near-IR spectrographs for most planet populations except for Earths and temperate TESS planets which are more efficiently characterized in the near-IR. Lastly, we present an online tool to the community to compute the total observing times required to detect any transiting planet using a user-defined spectrograph.

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arXiv2017

Predictions of planet detections with near infrared radial velocities in the up-coming SPIRou Legacy Survey-Planet Search

The SPIRou near infrared spectro-polarimeter is destined to begin science operations at the Canada-France-Hawaii Telescope in mid-2018. One of the instrument's primary science goals is to discover the closest exoplanets to the Solar System by conducting a 3-5 year long radial velocity survey of nearby M dwarfs at an expected precision of $\sim 1$ m s$^{-1}$; the SPIRou Legacy Survey-Planet Search (SLS-PS). In this study we conduct a detailed Monte-Carlo simulation of the SLS-PS using our current understanding of the occurrence rate of M dwarf planetary systems and physical models of stellar activity. From simultaneous modelling of planetary signals and activity, we predict the population of planets detected in the SLS-PS. With our fiducial survey strategy and expected instrument performance over a nominal survey length of $\sim 3$ years, we expect SPIRou to detect $85.3^{+29.3}_{-12.4}$ planets including $20.0^{+16.8}_{-7.2}$ habitable zone planets and $8.1^{+7.6}_{-3.2}$ Earth-like planets from a sample of 100 M1-M8.5 dwarfs out to 11 pc. By studying mid-to-late M dwarfs previously inaccessible to existing optical velocimeters, SPIRou will put meaningful constraints on the occurrence rate of planets around those stars including the value of $η_{\oplus}$ at an expected level of precision of $\lesssim 45$%. We also predict a subset of $46.7^{+16.0}_{-6.0}$ planets may be accessible with dedicated high-contrast imagers on the next generation of ELTs including $4.9^{+4.7}_{-2.0}$ potentially imagable Earth-like planets. Lastly, we compare the results of our fiducial survey strategy to other foreseeable survey versions to quantify which strategy is optimized to reach the SLS-PS science goals. The results of our simulations are made available to the community on github.

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arXiv2016

On the radial velocity detection of additional planets in transiting, slowly rotating M-dwarf systems: the case of GJ 1132

M-dwarfs are known to commonly host high-multiplicity planetary systems. Therefore M-dwarf planetary systems with a known transiting planet are expected to contain additional small planets ($r_p \le 4$ R$_{\oplus}$, $m_p \lesssim 20$ M$_{\oplus}$) that are not seen in transit. In this study we investigate the effort required to detect such planets using precision velocimetry around the sizable subset of M-dwarfs which are slowly rotating ($P_{\mathrm{rot}} \gtrsim 40$ days) and hence more likely to be inactive. We focus on the test case of GJ 1132. Specifically, we perform a suite of Monte-Carlo simulations of the star's radial velocity signal featuring astrophysical contributions from stellar jitter due to rotationally modulated active regions and keplarian signals from the known transiting planet and hypothetical additional planets not seen in transit. We then compute the detection completeness of non-transiting planets around GJ 1132 and consequently estimate the number of RV measurements required to detect those planets. We show that with 1 m s$^{-1}$ RV precision per measurement, only $\sim 50$ measurements are required to achieve a 50\% detection completeness to all non-transiting planets in the system and to planets which are potentially habitable. Throughout we advocate the use of Gaussian process regression as an effective tool for mitigating the effects of stellar jitter including stars with high activity. Given that GJ 1132 is representative of a large population of slowly rotating M-dwarfs, we conclude with a discussion of how our results may be extended to other systems with known transiting planets such as those which will be discovered with TESS.

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arXiv2016

Prospects for detecting the Rossiter-McLaughlin effect of Earth-like planets: the test case of TRAPPIST-1b and c

The Rossiter-McLaughlin effect is the principal method of determining the sky-projected spin--orbit angle ($β$) of transiting planets. Taking the example of the recently discovered TRAPPIST-1 system, we explore how ultracool dwarfs facilitate the measurement of the spin--orbit angle for Earth-sized planets by creating an effect that can be an order of magnitude more ample than the Doppler reflex motion caused by the planet if the star is undergoing rapid rotation. In TRAPPIST-1's case we expect the semi-amplitudes of the Rossiter-McLaughlin effect to be $40-50$ m/s for the known transiting planets. Accounting for stellar jitter expected for ultracool dwarfs, instrumental noise, and assuming radial velocity precisions both demonstrated and anticipated for upcoming near-infrared spectrographs, we quantify the observational effort required to measure the planets' masses and spin--orbit angles. We conclude that if the planetary system is well-aligned then $β$ can be measured to a precision of $\lesssim 10^{\circ}$ if the spectrograph is stable at the level of 2 m/s. We also investigate the measure of $Δβ$, the mutual inclination, when multiple transiting planets are present in the system. Lastly, we note that the rapid rotation rate of many late M-dwarfs will amplify the Rossiter-McLaughlin signal to the point where variations in the chromatic Rossiter-McLaughlin effect from atmospheric absorbers should be detectable.

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arXiv2016

The Matryoshka Disk: Keck/NIRC2 Discovery of a Solar System-Scale, Radially Segregated Residual Protoplanetary Disk Around HD 141569A

Using Keck/NIRC2 $L^\prime$ (3.78 $μm$) data, we report the direct imaging discovery of a scattered light-resolved, solar system-scale residual protoplanetary disk around the young A-type star HD 141569A, interior to and concentric with the two ring-like structures at wider separations. The disk is resolved down to $\sim$ 0\farcs{}25 and appears as an arc-like rim with attached hook-like features. It is located at an angular separation intermediate between that of warm CO gas identified from spatially-resolved mid-infrared spectroscopy and diffuse dust emission recently discovered with the \textit{Hubble Space Telescope}. The inner disk has a radius of $\sim$ 39 AU, a position angle consistent with north-up, an inclination of $i$ $\sim$ 56$^{o}$, and has a center offset from the star. Forward-modeling of the disk favors a thick torus-like emission sharply truncated at separations beyond the torus' photocenter and heavily depleted at smaller separations. In particular, the best-fit density power law for the dust suggests that the inner disk dust and gas (as probed by CO) are radially segregated, a feature consistent with the dust trapping mechanism inferred from observations of "canonical" transitional disks. However, the inner disk component may instead be explained by radiation pressure-induced migration in optically-thin conditions, in contrast to the two stellar companion/planet-influenced ring-like structures at wider separations. HD 141569A's circumstellar environment --- with three nested, gapped, concentric dust populations --- is an excellent laboratory for understanding the relationship between planet formation and the evolution of both dust grains and disk architecture.

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arXiv2015

Resolving the HD 100546 Protoplanetary System with the Gemini Planet Imager: Evidence for Multiple Forming, Accreting Planets

We report Gemini Planet Imager H band high-contrast imaging/integral field spectroscopy and polarimetry of the HD 100546, a 10 $Myr$-old early-type star recently confirmed to host a thermal infrared bright (super)jovian protoplanet at wide separation, HD 100546 b. We resolve the inner disk cavity in polarized light, recover the thermal-infrared (IR) bright arm, and identify one additional spiral arm. We easily recover HD 100546 b and show that much of its emission originates an unresolved, point source. HD 100546 b likely has extremely red infrared colors compared to field brown dwarfs, qualitatively similar to young cloudy superjovian planets, however, these colors may instead indicate that HD 100546 b is still accreting material from a circumplanetary disk. Additionally, we identify a second point source-like peak at $r_{proj}$ $\sim$ 14 AU, located just interior to or at inner disk wall consistent with being a 10--20 $M_{J}$ candidate second protoplanet-- "HD 100546 c" -- and lying within a weakly polarized region of the disk but along an extension of the thermal IR bright spiral arm. Alternatively, it is equally plausible that this feature is a weakly polarized but locally bright region of the inner disk wall. Astrometric monitoring of this feature over the next 2 years and emission line measurements could confirm its status as a protoplanet, rotating disk hot spot that is possibly a signpost of a protoplanet, or a stationary emission source from within the disk.

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arXiv2015

Could Jupiter or Saturn Have Ejected a Fifth Giant Planet?

Models of the dynamical evolution of the early solar system following the dispersal of the gaseous protoplanetary disk have been widely successful in reconstructing the current orbital configuration of the giant planets. Statistically, some of the most successful dynamical evolution simulations have initially included a hypothetical fifth giant planet, of ice giant mass, which gets ejected by a gas giant during the early solar system's proposed instability phase. We investigate the likelihood of an ice giant ejection event by either Jupiter or Saturn through constraints imposed by the current orbits of their wide-separation regular satellites Callisto and Iapetus respectively. We show that planetary encounters that are sufficient to eject an ice giant, often provide excessive perturbations to the orbits of Callisto and Iapetus making it difficult to reconcile a planet ejection event with the current orbit of either satellite. Quantitatively, we compute the likelihood of reconciling a regular Jovian satellite orbit with the current orbit of Callisto following an ice giant ejection by Jupiter of ~ 42% and conclude that such a large likelihood supports the hypothesis of a fifth giant planet's existence. A similar calculation for Iapetus reveals that it is much more difficult for Saturn to have ejected an ice giant and reconcile a Kronian satellite orbit with that of Iapetus (likelihood ~ 1%), although uncertainties regarding the formation of Iapetus, on its unusual orbit, complicates the interpretation of this result.

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arXiv2014

Deep Thermal Infrared Imaging of HR 8799 bcde: New Atmospheric Constraints and Limits on a Fifth Planet

We present new $L^\prime$ (3.8 $μm$) and Br-$α$ (4.05 $μm$) data and reprocessed archival $L^\prime$ data for the young, planet-hosting star HR 8799 obtained with Keck/NIRC2, VLT/NaCo and Subaru/IRCS. We detect all four HR 8799 planets in each dataset at a moderate to high signal-to-noise (SNR $\gtrsim$ 6-15). We fail to identify a fifth planet, "HR 8799 f", at $r$ $<$ 15 $AU$ at a 5-$σ$ confidence level: one suggestive, marginally significant residual at 0.2" is most likely a PSF artifact. Assuming companion ages of 30 $Myr$ and the Baraffe (Spiegel \& Burrows) planet cooling models, we rule out an HR 8799 f with mass of 5 $M_{J}$ (7 $M_{J}$), 7 $M_{J}$ (10 $M_{J}$), and 12 $M_{J}$ (13 $M_{J}$) at $r_{proj}$ $\sim$ 12 $AU$, 9 $AU$, and 5 $AU$, respectively. All four HR 8799 planets have red early T dwarf-like $L^\prime$ - [4.05] colors, suggesting that their SEDs peak in between the $L^\prime$ and $M^\prime$ broadband filters. We find no statistically significant difference in HR 8799 cde's colors. Atmosphere models assuming thick, patchy clouds appear to better match HR 8799 bcde's photometry than models assuming a uniform cloud layer. While non-equilibrium carbon chemistry is required to explain HR 8799 bc's photometry/spectra, evidence for it from HR 8799 de's photometry is weaker. Future, deep IR spectroscopy/spectrophotometry with the Gemini Planet Imager, SCExAO/CHARIS, and other facilities may clarify whether the planets are chemically similar or heterogeneous.

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arXiv2014

A Deep Spitzer Survey of Circumstellar Disks in the Young Double Cluster, h and chi Persei

We analyze very deep IRAC and MIPS photometry of $\sim$ 12,500 members of the 14 Myr old Double Cluster, h and $χ$ Persei, building upon on our earlier, shallower Spitzer studies (Currie et al. 2007a, 2008a). Numerous likely members show infrared (IR) excesses at 8 μm and 24 $μ$m indicative of circumstellar dust. The frequency of stars with 8 $μ$m excess is at least 2% for our entire sample, slightly lower (higher) for B/A stars (later type, lower-mass stars). Optical spectroscopy also identifies gas in about 2% of systems but with no clear trend between the presence of dust and gas. Spectral energy distribution (SED) modeling of 18 sources with detections at optical wavelengths through MIPS 24 $μm$ reveals a diverse set of disk evolutionary states, including a high fraction of transitional disks, although similar data for all disk-bearing members would provide better constraints. We combine our results with those for other young clusters to study the global evolution of dust/gas disks. For nominal cluster ages, the e-folding times ($τ_{o}$) for the frequency of warm dust and gas are 2.75 Myr and 1.75 Myr respectively. Assuming a revised set of ages for some clusters (e.g. Bell et al. 2013), these timescales increase to 5.75 and 3.75 Myr, respectively, implying a significantly longer typical protoplanetary disk lifetime. The transitional disk duration, averaged over multiple evolutionary pathways, is $\sim$ 1 Myr. Finally, 24 $μ$m excess frequencies for 4-6 M$_{\odot}$ stars appear lower than for 1-2.5 M$_{\odot}$ stars in other 10-30 Myr old clusters.

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arXiv2014

Gravitational instability of planetary gaps and its effect on orbital migration

Gap formation by giant planets in self-gravitating disks may lead to a gravitational edge instability (GEI). We demonstrate this GEI with global 3D and 2D self-gravitating disk-planet simulations using the ZEUS, PLUTO and FARGO hydrodynamic codes. High resolution 2D simulations show that an unstable outer gap edge can lead to outwards orbital migration. Our results have important implications for theories of giant planet formation in massive disks.

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arXiv2013

A Deep Keck/NIRC2 Search for Thermal Emission from Planetary Companions Orbiting Fomalhaut

We present deep Keck/NIRC2 1.6 and 3.8 $μm$ imaging of Fomalhaut to constrain the near-infrared (IR) brightness of Fomalhaut b, recently confirmed as a likely planet (Currie et al. 2012a), and search for additional planets at r_proj = 15--150 AU. Using advanced/novel PSF subtraction techniques, we identify seven candidate substellar companions at projected separations comparable to Fomalhaut b. However, multi-epoch data shows them to be background objects. We set a new 3-$σ$ upper limit for Fomalhaut b's H-band brightness of m(H) $\sim$ 23.15 or 1.5 to 4.5 M_J, depending on the system age and planet cooling models used. We do not recover the possible point source reported from Spitzer/IRAC data: at its location detection limits are similar to those for Fomalhaut b. Our data when combined with other recent work rule out planets with masses and projected separations comparable to HR 8799 bcde and planets with masses M $>$ 3 M_{J} at r_proj $>$ 45 AU. The James Webb Space Telescope will likely be required to shed substantial further light on Fomalhaut's planetary system.

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arXiv2013

Orbital migration of giant planets induced by gravitationally unstable gaps: the effect of planet mass

It has been suggested that long-period giant planets, such as HD 95086b and HR 8799bcde, may have formed through gravitational instability of protoplanetary discs. However, self-gravitating disc-satellite interaction can lead to the formation of a gravitationally unstable gap. Such an instability significantly affects the orbital migration of gap-opening perturbers in massive discs. We use 2D hydrodynamical simulations to examine the role of planet mass on the gravitational stability of gaps and its impact on orbital migration. We consider giant planets with planet-to-star mass ratio q=0.0003 to q=0.003, in a self-gravitating disc with disc-to-star mass ratio M_d/M_*=0.08, aspect ratio h=0.05, and Keplerian Toomre parameter Q = 1.5 at 2.5 times the planet's initial orbital radius. Fixed-orbit simulations show that all planet masses we consider open gravitationally unstable gaps, but the instability is stronger and develops sooner with increasing planet mass. The disc-on-planet torques typically become more positive with increasing planet mass. In freely-migrating simulations, we observe faster outward migration with increasing planet mass, but only for planet masses capable of opening unstable gaps early on. For q=0.0003, the planet undergoes rapid inward type III migration before it can open a gap. For q=0.0013 we find it is possible to balance the tendency for inward migration by the positive torques due to an unstable gap, but only for a few 10's of orbital periods. We find the unstable outer gap edge can trigger outward type III migration, sending the planet to twice its initial orbital radius on dynamical timescales. This triggered type III migration may be a way of bringing giant planets to large orbital distances. On the other hand, our results also imply gap-opening is not a sufficient condition for the in situ formation of giant planets on wide orbits through disc fragmentation.

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