Browsing by Subject "planets and satellites: formation"

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Asteroseismic Determination Of Obliquities Of The Exoplanet Systems Kepler-50 And Kepler-65
(2013-04) Chaplin, W. J.; Sanchis-Ojeda, R.; Campante, T. L.; Handberg, R.; Stello, D.; Winn, Joshua N.; Basu, S.; Christensen-Dalsgaard, J.; Davies, G. R.; Metcalfe, T. S.; Buchhave, Lars A.; Fischer, Debra A.; Bedding, T. R.; Cochran, William D.; Elsworth, Y.; Gilliland, R. L.; Hekker, S.; Huber, Daniel; Isaacson, Howard; Karoff, C.; Kawaler, Steven D.; Kjeldsen, H.; Latham, D. W.; Lund, M. N.; Lundkvist, M.; Marcy, Geoffrey W.; Miglio, A.; Barclay, Thomas; Lissauer, J. J.; Cochran, William D.
Results on the obliquity of exoplanet host stars-the angle between the stellar spin axis and the planetary orbital axis-provide important diagnostic information for theories describing planetary formation. Here we present the first application of asteroseismology to the problem of stellar obliquity determination in systems with transiting planets and Sun-like host stars. We consider two systems observed by the NASA Kepler mission which have multiple transiting small (super-Earth sized) planets: the previously reported Kepler-50 and a new system, Kepler-65, whose planets we validate in this paper. Both stars show rich spectra of solar-like oscillations. From the asteroseismic analysis we find that each host has its rotation axis nearly perpendicular to the line of sight with the sines of the angles constrained at the 1 sigma level to lie above 0.97 and 0.91, respectively. We use statistical arguments to show that coplanar orbits are favored in both systems, and that the orientations of the planetary orbits and the stellar rotation axis are correlated.
First Detection Of Near-Infrared Line Emission From Organics In Young Circumstellar Disks
(2012-03) Mandell, Avi M.; Bast, Jeanette; van Dishoeck, Ewine F.; Blake, Geoffrey A.; Salyk, Colette; Mumma, Michael J.; Villanueva, Geronimo; Salyk, Colette
We present an analysis of high-resolution spectroscopy of several bright T Tauri stars using the CRIRES spectrograph on the Very Large Telescope and NIRSPEC spectrograph on the Keck Telescope, revealing the first detections of emission from HCN and C2H2 in circumstellar disks at near-infrared wavelengths. Using advanced data reduction techniques, we achieve a dynamic range with respect to the disk continuum of similar to 500 at 3 mu m, revealing multiple emission features of H2O, OH, HCN, and C2H2. We also present stringent upper limits for two other molecules thought to be abundant in the inner disk, CH4 and NH3. Line profiles for the different detected molecules are broad but centrally peaked in most cases, even for disks with previously determined inclinations of greater than 20 degrees, suggesting that the emission has both a Keplerian and non-Keplerian component as observed previously for CO emission. We apply two different modeling strategies to constrain the molecular abundances and temperatures: we use a simplified single-temperature local thermal equilibrium (LTE) slab model with a Gaussian line profile to make line identifications and determine a best-fit temperature and initial abundance ratios, and we compare these values with constraints derived from a detailed disk radiative transfer model assuming LTE excitation but utilizing a realistic temperature and density structure. Abundance ratios from both sets of models are consistent with each other and consistent with expected values from theoretical chemical models, and analysis of the line shapes suggests that the molecular emission originates from within a narrow region in the inner disk (R < 1 AU).
The Giant Planet Orbiting The Cataclysmic Binary DP Leonis
(2011-02) Beuermann, K.; Buhlmann, J.; Diese, J.; Dreizler, S.; Hessman, F. V.; Husser, T. O.; Miller, G. F.; Nickol, N.; Pons, R.; Ruhr, D.; Schmulling, H.; Schwope, A. D.; Sorge, T.; Ulrichs, L.; Winget, D. E.; Winget, K. I.; Winget, D. E.; Winget, K. I.
Planets orbiting post-common envelope binaries provide fundamental information on planet formation and evolution, especially for the yet nearly unexplored class of circumbinary planets. We searched for such planets in DP Leo, an eclipsing short-period binary, which shows long-term eclipse-time variations. Using published, reanalysed, and new mid-eclipse times of the white dwarf in DP Leo, obtained between 1979 and 2010, we find agreement with the light-travel-time effect produced by a third body in an elliptical orbit. In particular, the measured binary period in 2009/2010 and the implied radial velocity coincide with the values predicted for the motion of the binary and the third body around the common center of mass. The orbital period, semi-major axis, and eccentricity of the third body are P-c = 28.0 +/- 2.0 yrs, a(c) = 8.2 +/- 0.4 AU, and e(c) = 0.39 +/- 0.13. Its mass of sin i(c) M-c = 6.1 +/- 0.5 M-Jup qualifies it as a giant planet. It formed either as a first generation object in a protoplanetary disk around the original binary or as a second generation object in a disk formed in the common envelope shed by the progenitor of the white dwarf. Even a third generation origin in matter lost from the present accreting binary can not be entirely excluded. We searched for, but found no evidence for a fourth body.
High-Dispersion Infrared Spectroscopic Observations Of Comet 8P/Tuttle With VLT/CRIRES
(2010-01) Kobayashi, H.; Bockelee-Morvan, D.; Kawakita, H.; Dello Russo, N.; Jehin, E.; Manfroid, J.; Smette, A.; Hutsemekers, D.; Stuwe, J.; Weiler, M.; Arpigny, C.; Biver, N.; Cochran, A.; Crovisier, J.; Magain, P.; Sana, H.; Schulz, R.; Vervack, R. J.; Weaver, H.; Zucconi, J. M.; Cochran, A.
We report on the composition of the Halley-family comet (HFC) 8P/Tuttle investigated with high-dispersion near-infrared spectroscopic observations. The observations were carried out at the ESO VLT (Very Large Telescope) with the CRIRES instrument as part of a multi-wavelength observation campaign of 8P/Tuttle performed in late January and early February 2008. Radar observations suggested that 8P/Tuttle is a contact binary, and it was proposed that these components might be heterogeneous in chemistry. We determined mixing ratios of organic volatiles with respect to H(2)O and found that mixing ratios were consistent with previous near infrared spectroscopic observations obtained in late December 2007 and in late January 2008. It has been suggested that because 8P/Tuttle is a contact binary, it might be chemically heterogeneous. However, we find no evidence for chemical heterogeneity within the nucleus of 8P/Tuttle. We also compared the mixing ratios of organic molecules in 8P/Tuttle with those of both other HFCs and long period comets (LPCs) and found that HCN, C(2)H(2), and C(2)H(6) are depleted whereas CH(4) and CH(3)OH have normal abundances. This may indicate that 8P/Tuttle was formed in a different region of the early solar nebula than other HFCs and LPCs. We estimated the conversion efficiency from C(2)H(2) to C(2)H(6) by hydrogen addition reactions on cold grains by employing the C(2)H(6)/(C(2)H(6)+C(2)H(2)) ratio. The C(2)H(6)/(C(2)H(6)+C(2)H(2)) ratio in 8P/Tuttle is consistent with the ratios found in other HFCs and LPCs within the error bars. We also discuss the source of C(2) and CN based on our observations and conclude that the abundances in the comet, so at least one additional parent is needed for each species, as pointed out in previous study.
M Dwarf Metallicities And Giant Planet Occurrence: Ironing Out Uncertainties And Systematics
(2014-08) Gaidos, Eric; Mann, Andrew W.; Mann, Andrew W.
Comparisons between the planet populations around solar-type stars and those orbiting M dwarfs shed light on the possible dependence of planet formation and evolution on stellar mass. However, such analyses must control for other factors, i.e., metallicity, a stellar parameter that strongly influences the occurrence of gas giant planets. We obtained infrared spectra of 121 M dwarfs stars monitored by the California Planet Search and determined metallicities with an accuracy of 0.08 dex. The mean and standard deviation of the sample are -0.05 and 0.20 dex, respectively. We parameterized the metallicity dependence of the occurrence of giant planets on orbits with a period less than two years around solar-type stars and applied this to our M dwarf sample to estimate the expected number of giant planets. The number of detected planets (3) is lower than the predicted number (6.4), but the difference is not very significant (12% probability of finding as many or fewer planets). The three M dwarf planet hosts are not especially metal rich and the most likely value of the power-law index relating planet occurrence to metallicity is 1.06 dex per dex for M dwarfs compared to 1.80 for solar-type stars; this difference, however, is comparable to uncertainties. Giant planet occurrence around both types of stars allows, but does not necessarily require, a mass dependence of similar to 1 dex per dex. The actual planet-mass-metallicity relation may be complex, and elucidating it will require larger surveys like those to be conducted by ground-based infrared spectrographs and the Gaia space astrometry mission.
Photophoresis Boosts Giant Planet Formation
(2013-07) Teiser, J.; Dodson-Robinson, S. E.; Dodson-Robinson, S. E.
In the core accretion model of giant planet formation, a solid protoplanetary core begins to accrete gas directly from the nebula when its mass reaches similar to 5 M-circle plus. The protoplanet has at most a few million years to reach runaway gas accretion, as young stars lose their gas disks after 10 million years at the latest. Yet gas accretion also brings small dust grains entrained in the gas into the planetary atmosphere. Dust accretion creates an optically thick protoplanetary atmosphere that cannot efficiently radiate away the kinetic energy deposited by incoming planetesimals. A dust-rich atmosphere severely slows down atmospheric cooling, contraction, and inflow of new gas, in contradiction to the observed timescales of planet formation. Here we show that photophoresis is a strong mechanism for pushing dust out of the planetary atmosphere due to the momentum exchange between gas and dust grains. The thermal radiation from the heated inner atmosphere and core is sufficient to levitate dust grains and to push them outward. Photophoresis can significantly accelerate the formation of giant planets.
Silicon And Oxygen Abundances In Planet-Host Stars
(2011-09) Brugamyer, Erik; Dodson-Robinson, Sarah E.; Cochran, William D.; Sneden, Christopher; Brugamyer, Erik; Dodson-Robinson, Sarah E.; Cochran, William D.; Sneden, Christopher
The positive correlation between planet detection rate and host star iron abundance lends strong support to the core accretion theory of planet formation. However, iron is not the most significant mass contributor to the cores of giant planets. Since giant planet cores are thought to grow from silicate grains with icy mantles, the likelihood of gas giant formation should depend heavily on the oxygen and silicon abundance of the planet formation environment. Here we compare the silicon and oxygen abundances of a set of 76 planet hosts and a control sample of 80 metal-rich stars without any known giant planets. Our new, independent analysis was conducted using high resolution, high signal-to-noise data obtained at McDonald Observatory. Because we do not wish to simply reproduce the known planet-metallicity correlation, we have devised a statistical method for matching the underlying [Fe/H] distributions of our two sets of stars. We find a 99% probability that planet detection rate depends on the silicon abundance of the host star, over and above the observed planet-metallicity correlation. We do not detect any such correlation for oxygen. Our results would thus seem to suggest that grain nucleation, rather than subsequent icy mantle growth, is the important limiting factor in forming giant planets via core accretion. Based on our results and interpretation, we predict that planet detection should correlate with host star abundance for refractory elements responsible for grain nucleation and that no such trends should exist for the most abundant volatile elements responsible for icy mantle growth.
A Spitzer Infrared Spectrograph Study Of Debris Disks Around Planet-Host Stars
(2011-01) Dodson-Robinson, Sarah E.; Beichman, C. A.; Carpenter, John M.; Bryden, Geoffrey; Dodson-Robinson, Sarah E.
Since giant planets scatter planetesimals within a few tidal radii of their orbits, the locations of existing planetesimal belts indicate regions where giant planet formation failed in bygone protostellar disks. Infrared observations of circumstellar dust produced by colliding planetesimals are therefore powerful probes of the formation histories of known planets. Here we present new Spitzer infrared spectrograph (IRS) spectrophotometry of 111 solar-type stars, including 105 planet hosts. Our observations reveal 11 debris disks, including two previously undetected debris disks orbiting HD 108874 and HD 130322. Combining the 32 mu m spectrophotometry with previously published MIPS photometry, we find that the majority of debris disks around solar-type stars have temperatures in the range 60 less than or similar to T-dust less than or similar to 100 K. Assuming a dust temperature T-dust = 70 K, which is representative of the nine debris disks detected by both IRS and MIPS, debris rings surrounding Sun-like stars orbit between 15 and 240 AU depending on the mean particle size. Our observations imply that the planets detected by radial-velocity searches formed within 240 AU of their parent stars. If any of the debris disks studied here have mostly large, blackbody emitting grains, their companion giant planets must have formed in a narrow region between the ice line and 15 AU.
Three Wide Planetary-Mass Companions To fw Tau, ROXs 12, And ROXs 42B
(2014-01) Kraus, Adam L.; Ireland, Michael J.; Cieza, Lucas A.; Hinkley, Sasha; Dupuy, Trent J.; Bowler, Brendan P.; Liu, Michael C.; Kraus, Adam L.
We report the discovery of three planetary-mass companions (M = 6-20 M-Jup) in wide orbits (rho similar to 150-300 AU) around the young stars FW Tau (Taurus-Auriga), ROXs 12 (Ophiuchus), and ROXs 42B (Ophiuchus). All three wide planetary-mass companions (PMCs) were reported as candidate companions in previous binary survey programs, but then were neglected for > 10 yr. We therefore obtained followup observations that demonstrate that each candidate is comoving with its host star. Based on the absolute M-K' magnitudes, we infer masses (from hot-start evolutionary models) and projected separations of 10 +/- 4 M-Jup and 330 +/- 30 AU for FW Tau b, 16 +/- 4 M-Jup and 210 +/- 20 AU for ROXs 12, and 10 +/- 4 M-Jup and 140 +/- 10 AU for ROXs 42B b. We also present similar observations for 10 other candidates that show that they are unassociated field stars, as well as multicolor JHK'L' near-infrared photometry for our new PMCs and for five previously identified substellar or planetary-mass companions. The near-infrared photometry for our sample of eight known and new companions generally parallels the properties of free-floating, low-mass brown dwarfs in these star-forming regions. However, five of the seven objects with M < 30 M-Jup are redder in K' - L' than the distribution of young free-floating counterparts of similar J - K' color. We speculate that this distinction could indicate a structural difference in circumplanetary disks, perhaps tied to higher disk mass since at least two of the objects in our sample are known to be accreting more vigorously than typical free-floating counterparts.
Transitional Disks As Signposts Of Young, Multiplanet Systems
(2011-09) Dodson-Robinson, Sarah E.; Salyk, Colette; Dodson-Robinson, Sarah E.; Salyk, Colette
Although there has yet been no undisputed discovery of a still-forming planet embedded in a gaseous protoplanetary disk, the cleared inner holes of transitional disks may be signposts of young planets. Here, we show that the subset of accreting transitional disks with wide, optically thin inner holes of 15 AU or more can only be sculpted by multiple planets orbiting inside each hole. Multiplanet systems provide two key ingredients for explaining the origins of transitional disks. First, multiple planets can clear wide inner holes where single planets open only narrow gaps. Second, the confined, non-axisymmetric accretion flows produced by multiple planets provide a way for an arbitrary amount of mass transfer to occur through an apparently optically thin hole without overproducing infrared excess flux. Rather than assuming that the gas and dust in the hole are evenly and axisymmetrically distributed, one can construct an inner hole with apparently optically thin infrared fluxes by covering a macroscopic fraction of the hole's surface area with locally optically thick tidal tails. We also establish that other clearing mechanisms, such as photoevaporation, cannot explain our subset of accreting transitional disks with wide holes. Transitional disks are therefore high-value targets for observational searches for young planetary systems.
Turbulence-Induced Relative Velocity Of Dust Particles. II. The Bidisperse Case
(2014-08) Pan, Lubin B.; Padoan, Paolo; Scalo, John; Scalo, John
We extend our earlier work on turbulence-induced relative velocity between equal-size particles ( Paper I, in this series) to particles of arbitrarily different sizes. The Pan & Padoan (PP10) model shows that the relative velocity between different particles has two contributions, named the generalized shear and acceleration terms, respectively. The generalized shear term represents the particles' memory of the spatial flow velocity difference across the particle distance in the past, while the acceleration term is associated with the temporal flow velocity difference on individual particle trajectories. Using the simulation of Paper I, we compute the root-mean-square relative velocity, < w(2)>(1/2), as a function of the friction times, tau(p1) and tau(p2), of the two particles and show that the PP10 prediction is in satisfactory agreement with the data, confirming its physical picture. For a given tau(p1) below the Lagrangian correlation time of the flow, T-L, < w(2)>(1/2) as a function of tau(p2) shows a dip at tau(p2) similar or equal to tau(p1), indicating tighter velocity correlation between similar particles. Defining a ratio f equivalent to tau(p,1)/tau(p,h), with tau(p,1) and tau(p,h) the friction times of the smaller and larger particles, we find that < w(2)>(1/2) increases with decreasing f due to the generalized acceleration contribution, which dominates at f less than or similar to 1/4. At a fixed f, our model predicts that < w(2)>(1/2) scales as tau(1/2)(p,h) tau(p,h) for in the inertial range of the flow, stays roughly constant for T-L less than or similar to tau(p,h) less than or similar to T-L/f, and finally decreases as tau(-1/2)(p,h) p, h for tau(p,h) >> T-L/f. The acceleration term is independent of the particle distance, r, and reduces the r dependence of < w(2)>(1/2) in the bidisperse case.
Turbulence-Induced Relative Velocity Of Dust Particles. III. The Probability Distribution
(2014-09) Pan, Lubin B.; Padoan, Paolo; Scalo, John; Scalo, John
Motivated by its important role in the collisional growth of dust particles in protoplanetary disks, we investigate the probability distribution function (PDF) of the relative velocity of inertial particles suspended in turbulent flows. Using the simulation from our previous work, we compute the relative velocity PDF as a function of the friction timescales, tau(p1) and tau(p2), of two particles of arbitrary sizes. The friction time of the particles included in the simulation ranges from 0.1 tau(eta) to 54T(L), where tau(eta) and T-L are the Kolmogorov time and the Lagrangian correlation time of the flow, respectively. The relative velocity PDF is generically non-Gaussian, exhibiting fat tails. For a fixed value of tau(p1), the PDF shape is the fattest for equal-size particles (tau(p2) = tau(p1)), and becomes thinner at both tau(p2) < tau(p1) and tau(p2) > tau(p1). Defining f as the friction time ratio of the smaller particle to the larger one, we find that, at a given f in (1/2) less than or similar to f less than or similar to 1, the PDF fatness first increases with the friction time tau(p,h) of the larger particle, peaks at tau(p,h) similar or equal to tau(eta), and then decreases as tp, h increases further. For 0 <= f less than or similar to (1/4), the PDF becomes continuously thinner with increasing tau(p,h). The PDF is nearly Gaussian only if tau(p,h) is sufficiently large (>> T-L). These features are successfully explained by the Pan & Padoan model. Using our simulation data and some simplifying assumptions, we estimated the fractions of collisions resulting in sticking, bouncing, and fragmentation as a function of the dust size in protoplanetary disks, and argued that accounting for non-Gaussianity of the collision velocity may help further alleviate the bouncing barrier problem.
Turbulent Clustering Of Protoplanetary Dust And Planetesimal Formation
(2011-10) Pan, Lubin B.; Padoan, Paolo; Scalo, John; Kritsuk, Alexei G.; Norman, Michael L.; Scalo, John
We study the clustering of inertial particles in turbulent flows and discuss its applications to dust particles in protoplanetary disks. Using numerical simulations, we compute the radial distribution function (RDF), which measures the probability of finding particle pairs at given distances, and the probability density function of the particle concentration. The clustering statistics depend on the Stokes number, St, defined as the ratio of the particle friction timescale, tau(p), to the Kolmogorov timescale in the flow. In agreement with previous studies, we find that, in the dissipation range, the clustering intensity strongly peaks at St similar or equal to 1, and the RDF for St similar to 1 shows a fast power-law increase toward small scales, suggesting that turbulent clustering may considerably enhance the particle collision rate. Clustering at inertial-range scales is of particular interest to the problem of planetesimal formation. At these large scales, the strongest clustering is from particles with tau(p) in the inertial range. Clustering of these particles occurs primarily around a scale where the eddy turnover time is similar to tau(p). We find that particles of different sizes tend to cluster at different locations, leading to flat RDFs between different particles at small scales. In the presence of multiple particle sizes, the overall clustering strength decreases as the particle size distribution broadens. We discuss particle clustering in two recent models for planetesimal formation. We argue that, in the model based on turbulent clustering of chondrule-size particles, the probability of finding strong clusters that can seed planetesimals may have been significantly overestimated. We discuss various clustering mechanisms in simulations of planetesimal formation by gravitational collapse of dense clumps of meter-size particles, in particular the contribution from turbulent clustering due to the limited numerical resolution.
Two Planets Orbiting The Recently Formed Post-Common Envelope Binary NN Serpentis
(2010-10) Beuermann, K.; Hessman, F. V.; Dreizler, S.; Marsh, T. R.; Parsons, S. G.; Winget, D. E.; Miller, G. F.; Schreiber, M. R.; Kley, W.; Dhillon, V. S.; Littlefair, S. P.; Copperwheat, C. M.; Hermes, J. J.; Winget, D. E.; Miller, G. F.
Planets orbiting post-common envelope binaries provide fundamental information on planet formation and evolution. We searched for such planets in NN Ser ab, an eclipsing short-period binary that shows long-term eclipse time variations. Using published, reanalysed, and new mid-eclipse times of NN Ser ab obtained between 1988 and 2010, we find excellent agreement with the light-travel-time effect produced by two additional bodies superposed on the linear ephemeris of the binary. Our multi-parameter fits accompanied by N-body simulations yield a best fit for the objects NN Ser (ab)c and d locked in the 2:1 mean motion resonance, with orbital periods P-c similar or equal to 15.5 yrs and P-d similar or equal to 7.7 yrs, masses M-c sin i(c) similar or equal to 6.9 M-Jup and M-d sin i(d) similar or equal to 2.2 M-Jup, and eccentricities e(c) similar or equal to 0 and e(d) similar or equal to 0.20. A secondary chi(2) minimum corresponds to an alternative solution with a period ratio of 5:2. We estimate that the progenitor binary consisted of an A star with similar or equal to 2 M-circle dot and the present M dwarf secondary at an orbital separation of similar to 1.5 AU. The survival of two planets through the common-envelope phase that created the present white dwarf requires fine tuning between the gravitational force and the drag force experienced by them in the expanding envelope. The alternative is a second-generation origin in a circumbinary disk created at the end of this phase. In that case, the planets would be extremely young with ages not exceeding the cooling age of the white dwarf of 10(6) yrs.