Reflected Light from Sand Grains in the Terrestrial Zone of a Protoplanetary Disk

We show that grains have grown to ~mm size (sand sized) or larger in the terrestrial zone (within ~3 AU) of the protoplanetary disk surrounding the 3 Myr old binary star KH 15D. We also argue that the reflected light in the system reaches us by back scattering off the far side of the same ring whose near side causes the obscuration.Comment: 22 pages, 5 figures. To be published in Nature, March 13, 2008. Contains a Supplemen

Refined parameters and spectroscopic transit of the super-massive planet HD147506b

In this paper, we report a refined determination of the orbital parameters and the detection of the Rossiter-McLaughlin effect of the recently discovered transiting exoplanet HD147506b (HAT-P-2b). The large orbital eccentricity at the short orbital period of this exoplanet is unexpected and is distinguishing from other known transiting exoplanets. We performed high-precision radial velocity spectroscopic observations of HD147506 (HAT-P-2) with the new spectrograph SOPHIE, mounted on the 1.93 m telescope at the Haute-Provence observatory (OHP). We obtained 63 new measurements, including 35 on May 14 and 20 on June 11, when the planet was transiting its parent star. The radial velocity (RV) anomaly observed illustrates that HAT-P-2b orbital motion is set in the same direction as its parent star spin. The sky-projected angle between the normal of the orbital plane and the stellar spin axis, \lambda = 0.2 +12.2 -12.5 deg, is consistent with zero. The planetary and stellar radii were re-determined, yielding R_p = 0.951 +0.039 -0.053 R_Jup, R_s = 1.416 +0.040 -0.062 R_Sun. The mass M_p = 8.62 +0.39 -0.55 M_Jup and radius of HAT-P-2b indicate a density of 12.5 +2.6 -3.6 g cm^{-3}, suggesting an object in between the known close-in planets with typical density of the order of 1 g cm^{-3}, and the very low-mass stars, with density greater than 50 g cm^{-3}.Comment: Submitted to A&A; V2: Replaced by accepted versio

Elodie metallicity-biased search for transiting Hot Jupiters IV. Intermediate period planets orbiting the stars HD43691 and HD132406

We report here the discovery of two planet candidates as a result of our planet-search programme biased in favour of high-metallicity stars, using the ELODIE spectrograph at the Observatoire de Haute Provence. One of them has a minimum mass m_2\sin{i} = 2.5 M_Jup and is orbiting the metal-rich star HD43691 with period P = 40 days and eccentricity e = 0.14. The other planet has a minimum mass m_2\sin{i} = 5.6 M_Jup and orbits the slightly metal-rich star HD132406 with period P = 974 days and eccentricity e = 0.34. Both stars were followed up with additional observations using the new SOPHIE spectrograph that replaces the ELODIE instrument, allowing an improved orbital solution for the systems.Comment: 6 pages, 4 figures, to be published in A&

On the Eccentricity Distribution of Short-Period Single-Planet Systems

We apply standard Markov chain Monte Carlo (MCMC) analysis techniques for 50 short- period, single-planet systems discovered with radial velocity technique. We develop a new method for accessing the significance of a non-zero orbital eccentricity, namely {\Gamma} analysis, which combines frequentist bootstrap approach with Bayesian analysis of each simulated data set. We find the eccentricity estimations from {\Gamma} analysis are generally consistent with results from both standard MCMC analysis and previous references. The {\Gamma} method is particular useful for assessing the significance of small eccentricities. Our results suggest that the current sample size is insufficient to draw robust conclusions about the roles of tidal interaction and perturbations in shaping the eccentricity distribution of short-period single-planet systems. We use a Bayesian population analysis to show that a mixture of analytical distributions is a good approximation of the underlying eccentricity distribution. For short-period planets, we find the most probable values of parameters in the analytical functions given the observed eccentricities. These analytical functions can be used in theoretical investigations or as priors for the eccentricity distribution when analyzing short-period planets. As the measurement precision improves and sample size increases, the method can be applied to more complex parametrizations for the underlying distribution of eccentricity for extrasolar planetary systems.Comment: 13 pages, 11 figures, 4 tables, accepted by MNRA

Time-Series Photometry of Stars in and around the Lagoon Nebula. I. Rotation Periods of 290 Low-Mass Pre-Main-Sequence Stars in NGC 6530

We have conducted a long-term, wide-field, high-cadence photometric monitoring survey of ~50,000 stars in the Lagoon Nebula \ion{H}{2} region. This first paper presents rotation periods for 290 low-mass stars in NGC 6530, the young cluster illuminating the nebula, and for which we assemble a catalog of infrared and spectroscopic disk indicators, estimated masses and ages, and X-ray luminosities. The distribution of rotation periods we measure is broadly uniform for 0.5 < P < 10 d; the short-period cutoff corresponds to breakup. We observe no obvious bimodality in the period distribution, but we do find that stars with disk signatures rotate more slowly on average. The stars' X-ray luminosities are roughly flat with rotation period, at the saturation level ($\log L_X / L_{\rm bol} \approx -3.3$). However, we find a significant positive correlation between $L_X / L_{\rm bol}$ and co-rotation radius, suggesting that the observed X-ray luminosities are regulated by centrifugal stripping of the stellar coronae. The period-mass relationship in NGC 6530 is broadly similar to that of the Orion Nebula Cluster (ONC), but the slope of the relationship among the slowest rotators differs from that in the ONC and other young clusters. We show that the slope of the period-mass relationship for the slowest rotators can be used as a proxy for the age of a young cluster, and we argue that NGC 6530 may be slightly younger than the ONC, making it a particularly important touchstone for models of angular momentum evolution in young, low-mass stars.Comment: 28 pages, 18 figures, Accepted for publication in ApJ. For a brief video explaining the key results of this paper, see http://www.youtube.com/user/OSUAstronomy#p/u/1/WarGh6GiWu

The HARPS search for southern extra-solar planets XXXV. Super-Earths around the M-dwarf neighbors Gl433 and Gl667C

M dwarfs have been found to often have super-Earth planets with short orbital periods. Such stars are thus preferential targets in searches for rocky or ocean planets in the solar neighbourhood. In a recent paper (Bonfils et al. 2011), we announced the discovery of respectively 1 and 2 low mass planets around the M1.5V stars Gl433 and Gl667C. We found those planets with the HARPS spectrograph on the ESO~3.6-m telescope at La Silla Observatory, from observations obtained during the Guaranteed Time Observing program of that instrument. We have obtained additional HARPS observations of those two stars, for a total of respectively 67 and 179 Radial Velocity measurements for Gl433 and Gl667C, and present here an orbital analysis of those extended data sets and our main conclusion about both planetary systems. One of the three planets, Gl667Cc, has a mass of only M2.sin(i)~4.25 M_earth and orbits in the central habitable zone of its host star. It receives just 10% less stellar energy from Gl667C than the Earth receives from the Sun. However planet evolution in habitable zone can be very different if the host star is a M dwarf or a solar-like star, without necessarily questioning the presence of water. The two other planets, Gl433b and Gl667Cb, both have M2.sin(i) of ~5.5 M_earth and periods of ~7 days. The Radial Velocity measurements of both stars contain longer time scale signals, which we fit as longer period Keplerians. For Gl433 that signal probably originates in a Magnetic Cycle, while a longer time span will be needed to conclude for Gl667C. The metallicity of Gl433 is close to solar, while Gl667C is metal poor with [Fe/H] ~ -0.6. This reinforces the recent conclusion that the occurence of Super-Earth planets does not strongly correlate with stellar metallicity.Comment: 14 pages, 8 figures, submitted to A&

The debris disk host star HD 61005: a member of the Argus Association?

HD 61005 is a nearby young solar type star that shows a large infrared excess due to a debris disk. The disk has been recently imaged from ground and space, with indications of several components. Some characteristics of the disk suggest the presence of planetary companions around the star, that remain undetected in deep adaptive optics imaging. For a better understanding of the system we aim to refine the determination of the stellar parameters, with emphasis on the stellar age and system orientation. We used ASAS and Hipparcos photometry and FEROS spectra to determine the rotation period, radial and rotational velocity, chromospheric emission, effective temperature, and chemical composition. We find no indication of any misalignment between the star rotation axis and the disk. The standard age calibrations applied to several indicators yield an age close to that of the Pleiades (120 Myr); however the kinematic properties strongly support its membership in the younger (40 Myr) Argus association, which also includes the IC 2391 open cluster. Detailed comparison of the properties of HD 61005 and IC 2391 members shows that the characteristics of HD 61005 are compatible with membership to the Argus association, once its rather slow rotation is taken into account, because lithium and other age indicators are somewhat correlated with stellar rotation at a fixed age. We also identify systematic differences between the field and cluster population of the Argus association, which are probably selection effects, so we suggest that additional members with slower rotation and lower activity level are waiting to be identified.Comment: A&A, in press, 13 pages, 11 figure

Excitations in the field-induced quantum spin liquid state of α-RuCl3

The celebrated Kitaev quantum spin liquid (QSL) is the paradigmatic example of a topological magnet with emergent excitations in the form of Majorana Fermions and gauge fluxes. Upon breaking of time-reversal symmetry, for example in an external magnetic field, these fractionalized quasiparticles acquire non-Abelian exchange statistics, an important ingredient for topologically protected quantum computing. Consequently, there has been enormous interest in exploring possible material realizations of Kitaev physics and several candidate materials have been put forward, recently including α-RuCl3. In the absence of a magnetic field this material orders at a finite temperature and exhibits low-energy spin wave excitations. However, at moderate energies, the spectrum is unconventional and the response shows evidence for fractional excitations. Here we use time-of-flight inelastic neutron scattering to show that the application of a sufficiently large magnetic field in the honeycomb plane suppresses the magnetic order and the spin waves, leaving a gapped continuum spectrum of magnetic excitations. Our comparisons of the scattering to the available calculations for a Kitaev QSL show that they are consistent with the magnetic field induced QSL phase.The work at ORNL’s Spallation Neutron Source and the High Flux Isotope Reactor was supported by the United States Department of Energy (US-DOE), Office of Science - Basic Energy Sciences (BES), Scientific User Facilities Division. Part of the research was supported by the US-DOE, Office of Science - BES, Materials Sciences and Engineering Division (P.K., C.A.B. and J-Q.Y.). D.M. and P.K. acknowledge support from the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant GBMF4416. The work at Dresden was in part supported by DFG grant SFB 1143 (J.K. and R.M.). J.K. is supported by the Marie Curie Programme under EC Grant agreements No.703697

The pedunculopontine tegmental nucleus and the nucleus basalis magnocellularis: Do both have a role in sustained attention?

It is well established that nucleus basalis magnocellularis (NbM) lesions impair performance on tests of sustained attention. Previous work from this laboratory has also demonstrated that pedunculopontine tegmental nucleus (PPTg) lesioned rats make more omissions on a test of sustained attention, suggesting that it might also play a role in mediating this function. However, the results of the PPTg study were open to alternative interpretation. We aimed to resolve this by conducting a detailed analysis of the effects of damage to each brain region in the same sustained attention task used in our previous work. Rats were trained in the task before surgery and post-surgical testing examined performance in response to unpredictable light signals of 1500 ms and 4000 ms duration. Data for PPTg lesioned rats were compared to control rats, and rats with 192 IgG saporin infusions centred on the NbM. In addition to operant data, video data of rats' performance during the task were also analysed

Stellar evolution and modelling stars

In this chapter I give an overall description of the structure and evolution of stars of different masses, and review the main ingredients included in state-of-the-art calculations aiming at reproducing observational features. I give particular emphasis to processes where large uncertainties still exist as they have strong impact on stellar properties derived from large compilations of tracks and isochrones, and are therefore of fundamental importance in many fields of astrophysics.Comment: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201