Transmission spectroscopy and Rossiter-McLaughlin measurements of the young Neptune orbiting AU Mic

AU Mic b is a Neptune-sized planet on an 8.47-day orbit around the nearest pre-main sequence (~20 Myr) star to the Sun, the bright (V = 8.81) M dwarf AU Mic. The planet was preliminary detected in Doppler radial velocity time series and recently confirmed to be transiting with data from the TESS mission. AU Mic b is likely to be cooling and contracting and might be accompanied by a second, more massive planet, in an outer orbit. Here, we present the observations of the transit of AU Mic b using ESPRESSO on the Very Large Telescope. We obtained a high-resolution time series of spectra to measure the Rossiter-McLaughlin effect, to constrain the spin-orbit alignment of the star and planet, and to simultaneously attempt to retrieve the planet’s atmospheric transmission spectrum. These observations allowed us to study, for the first time, the early phases of the dynamical evolution of young systems. We applied different methodologies to derive the spin-orbit angle of AU Mic b, and all of them retrieve values consistent with the planet being aligned with the rotation plane of the star. We determined a conservative spin-orbit angle λ value of −2.96−10.30+10.44 degrees, indicative that the formation and migration of the planets of the AU Mic system occurred within the disc. Unfortunately, and despite the large signal-to-noise ratio of our measurements, the degree of stellar activity prevented us from detecting any features from the planetary atmosphere. In fact, our results suggest that transmission spectroscopy for recently formed planets around active young stars is going to remain very challenging, if at all possible, for the near future.

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Spin-orbit alignment of exoplanet systems: how can Asteroseismology help us?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316002428 ◽

2015 ◽

Vol 11 (A29A) ◽

pp. 71-76

Author(s):

Tiago L. Campante

Keyword(s):

Signal To Noise Ratio ◽

Spin Orbit ◽

Hot Jupiters ◽

Long Period ◽

Oscillation Modes ◽

And Migration ◽

Stellar Properties ◽

Orbit Geometry ◽

Exoplanet Systems ◽

Host Stars

AbstractMeasuring the obliquities of exoplanet-host stars provides invaluable diagnostic information for theories of planetary formation and migration. Most of these results have so far been obtained by measuring the Rossiter--McLaughlin effect, clearly favoring systems that harbor hot Jupiters. While it would be extremely helpful to extend these measurements to long-period and multiple-planet systems, it is also true that the latter systems tend to involve smaller planets, making it ever so difficult to apply such techniques. Asteroseismology provides a powerful method of determining the inclination of the stellar spin axis from an analysis of the rotationally-induced splittings of the oscillation modes. This provides an estimate of the obliquity independently of other methods. The applicability of the asteroseismic method is determined by the stellar properties and not by the signal-to-noise ratio of the transit data. Here we present a recap of the spin-orbit geometry, explain how the asteroseismic method works, and review previous applications of the method to exoplanet-host stars.

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Spin-orbit alignment of exoplanet systems: analysis of an ensemble of asteroseismic observations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316006232 ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 636-641

Author(s):

Tiago L. Campante

Keyword(s):

Signal To Noise Ratio ◽

Spin Orbit ◽

Planetary Formation ◽

Hot Jupiters ◽

Transiting Planets ◽

Oscillation Modes ◽

Solar Type ◽

And Migration ◽

Exoplanet Systems ◽

Host Stars

AbstractMeasuring the obliquities of exoplanet-host stars provides invaluable diagnostic information for theories of planetary formation and migration. Most of these results have so far been obtained by measuring the Rossiter–McLaughlin effect, clearly favoring systems that harbor hot Jupiters. While it would be extremely helpful to extend these measurements to long-period and multiple-planet systems, it is also true that the latter systems tend to involve smaller planets, making it ever so difficult to apply such techniques. Asteroseismology provides a powerful method of determining the inclination of the stellar spin axis — from an analysis of the rotationally-induced splittings of the oscillation modes — whose applicability is ultimately determined by the stellar parameters and not by the signal-to-noise ratio of the transit data. Here we present the first statistical analysis of an ensemble of asteroseismic obliquity measurements obtained for solar-type stars with transiting planets. The sample consists of 25 Kepler planet-candidate host stars, 14 of which are multi-transiting systems. We seek empirical constraints on the spin-orbit alignment of exoplanet systems and discuss the implications for theories of planetary formation and migration.

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Accuracy of a Model-Free Algorithm for Temporal InSAR Tropospheric Correction

Remote Sensing ◽

10.3390/rs13030409 ◽

2021 ◽

Vol 13 (3) ◽

pp. 409

Author(s):

Howard Zebker

Keyword(s):

Time Series ◽

Signal To Noise Ratio ◽

Artifact Reduction ◽

Interferometric Synthetic Aperture Radar ◽

Spatial Properties ◽

Model Free ◽

Weather Model ◽

Phase Variations ◽

Source Of Error ◽

Signal Correlation

Atmospheric propagational phase variations are the dominant source of error for InSAR (interferometric synthetic aperture radar) time series analysis, generally exceeding uncertainties from poor signal to noise ratio or signal correlation. The spatial properties of these errors have been well studied, but, to date, their temporal dependence and correction have received much less attention. Here, we present an evaluation of the magnitude of tropospheric artifacts in derived time series after compensation using an algorithm that requires only the InSAR data. The level of artifact reduction equals or exceeds that from many weather model-based methods, while avoiding the need to globally access fine-scale atmosphere parameters at all times. Our method consists of identifying all points in an InSAR stack with consistently high correlation and computing, and then removing, a fit of the phase at each of these points with respect to elevation. A comparison with GPS truth yields a reduction of three, from a rms misfit of 5–6 to ~2 cm over time. This algorithm can be readily incorporated into InSAR processing flows without the need for outside information.

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The influence of the lunar nodal cycle on Arctic climate

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2005.07.015 ◽

2006 ◽

Vol 63 (3) ◽

pp. 401-420 ◽

Cited By ~ 23

Author(s):

Harald Yndestad

Keyword(s):

Time Series ◽

Signal To Noise Ratio ◽

Phase Relationship ◽

Harmonic Spectrum ◽

Arctic Climate ◽

The Arctic ◽

Major Influence ◽

Sea Temperature ◽

Arctic Ice

Abstract The Arctic Ocean is a substantial energy sink for the northern hemisphere. Fluctuations in its energy budget will have a major influence on the Arctic climate. The paper presents an analysis of the time-series for the polar position, the extent of Arctic ice, sea level at Hammerfest, Kola section sea temperature, Røst winter air temperature, and the NAO winter index as a way to identify a source of dominant cycles. The investigation uses wavelet transformation to identify the period and the phase in these Arctic time-series. System dynamics are identified by studying the phase relationship between the dominant cycles in all time-series. A harmonic spectrum from the 18.6-year lunar nodal cycle in the Arctic time-series has been identified. The cycles in this harmonic spectrum have a stationary period, but not stationary amplitude and phase. A sub-harmonic cycle of about 74 years may introduce a phase reversal of the 18.6-year cycle. The signal-to-noise ratio between the lunar nodal spectrum and other sources changes from 1.6 to 3.2. A lunar nodal cycle in all time-series indicates that there is a forced Arctic oscillating system controlled by the pull of gravity from the moon, a system that influences long-term fluctuations in the extent of Arctic ice. The phase relation between the identified cycles indicates a possible chain of events from lunar nodal gravity cycles, to long-term tides, polar motions, Arctic ice extent, the NAO winter index, weather, and climate.

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Kinematic interpretation in the prestack depth‐migrated domain

Geophysics ◽

10.1190/1.1444224 ◽

1997 ◽

Vol 62 (4) ◽

pp. 1226-1237 ◽

Cited By ~ 8

Author(s):

Irina Apostoiu‐Marin ◽

Andreas Ehinger

Keyword(s):

Signal To Noise Ratio ◽

Velocity Model ◽

Point Of View ◽

Prestack Depth Migration ◽

Depth Migration ◽

Velocity Models ◽

Time Domain Data ◽

And Migration ◽

Point To Point ◽

Homogeneous Media

Prestack depth migration can be used in the velocity model estimation process if one succeeds in interpreting depth events obtained with erroneous velocity models. The interpretational difficulty arises from the fact that migration with erroneous velocity does not yield the geologically correct reflector geometries and that individual migrated images suffer from poor signal‐to‐noise ratio. Moreover, migrated events may be of considerable complexity and thus hard to identify. In this paper, we examine the influence of wrong velocity models on the output of prestack depth migration in the case of straight reflector and point diffractor data in homogeneous media. To avoid obscuring migration results by artifacts (“smiles”), we use a geometrical technique for modeling and migration yielding a point‐to‐point map from time‐domain data to depth‐domain data. We discover that strong deformation of migrated events may occur even in situations of simple structures and small velocity errors. From a kinematical point of view, we compare the results of common‐shot and common‐offset migration. and we find that common‐offset migration with erroneous velocity models yields less severe image distortion than common‐shot migration. However, for any kind of migration, it is important to use the entire cube of migrated data to consistently interpret in the prestack depth‐migrated domain.

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Local Geometric Projection-Based Noise Reduction for Vibration Signal Analysis in Rolling Bearings

Volume 11: Mechanical Systems and Control ◽

10.1115/imece2008-66937 ◽

2008 ◽

Author(s):

Ruqiang Yan ◽

Robert X. Gao ◽

Kang B. Lee ◽

Steven E. Fick

Keyword(s):

Time Series ◽

Phase Space ◽

Noise Reduction ◽

Signal Analysis ◽

Signal To Noise Ratio ◽

Multifractal Spectrum ◽

Vibration Signal ◽

Rolling Bearings ◽

One Dimensional ◽

Vibration Signal Analysis

This paper presents a noise reduction technique for vibration signal analysis in rolling bearings, based on local geometric projection (LGP). LGP is a non-linear filtering technique that reconstructs one dimensional time series in a high-dimensional phase space using time-delayed coordinates, based on the Takens embedding theorem. From the neighborhood of each point in the phase space, where a neighbor is defined as a local subspace of the whole phase space, the best subspace to which the point will be orthogonally projected is identified. Since the signal subspace is formed by the most significant eigen-directions of the neighborhood, while the less significant ones define the noise subspace, the noise can be reduced by converting the points onto the subspace spanned by those significant eigen-directions back to a new, one-dimensional time series. Improvement on signal-to-noise ratio enabled by LGP is first evaluated using a chaotic system and an analytically formulated synthetic signal. Then analysis of bearing vibration signals is carried out as a case study. The LGP-based technique is shown to be effective in reducing noise and enhancing extraction of weak, defect-related features, as manifested by the multifractal spectrum from the signal.

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Gravity meter observation of free modes excited by the August 19, 1977 Indonesia earthquake

Bulletin of the Seismological Society of America ◽

10.1785/bssa0690051445 ◽

1979 ◽

Vol 69 (5) ◽

pp. 1445-1454

Author(s):

John A. Linton ◽

D. E. Smylie ◽

O. G. Jensen

Keyword(s):

Signal To Noise Ratio ◽

Quartz Fiber ◽

Large Signal ◽

Signal To Noise ◽

Definitive Evidence ◽

Long Period ◽

Noise Ratio

abstract Free modes with signal-to-noise ratio in the range of 40 to 55 dB were observed in the record taken by a vertical broadband quartz fiber gravimeter system opeating in Montreal following the event of August 19, 1977 in Indonesia. The large signal-to-noise ratio has permitted very stable Q estimates to be made for a number of the fundamental spheroidal modes. The very long-period band shows no definitive evidence of signal other than the expected tidal lines.

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Propagating Wave and Irregular Dynamics: Spatiotemporal Patterns of Cholinergic Theta Oscillations in Neocortex In Vitro

Journal of Neurophysiology ◽

10.1152/jn.00715.2002 ◽

2003 ◽

Vol 90 (1) ◽

pp. 333-341 ◽

Cited By ~ 45

Author(s):

Weili Bao ◽

Jian-Young Wu

Keyword(s):

Phase Distribution ◽

Signal To Noise Ratio ◽

Human Subjects ◽

Local Oscillator ◽

Spatiotemporal Patterns ◽

Spatiotemporal Pattern ◽

Large Signal ◽

Local Oscillators ◽

Theta Oscillation

Neocortical “theta” oscillation (5–12 Hz) has been observed in animals and human subjects but little is known about how the oscillation is organized in the cortical intrinsic networks. Here we use voltage-sensitive dye and optical imaging to study a carbachol/bicuculline induced theta (∼8 Hz) oscillation in rat neocortical slices. The imaging has large signal-to-noise ratio, allowing us to map the phase distribution over the neocortical tissue during the oscillation. The oscillation was organized as spontaneous epochs and each epoch was composed of a “first spike,” a “regular” period (with relatively stable frequency and amplitude), and an “irregular” period (with variable frequency and amplitude) of oscillations. During each cycle of the regular oscillation, one wave of activation propagated horizontally (parallel to the cortical lamina) across the cortical section at a velocity of ∼50 mm/s. Vertically the activity was synchronized through all cortical layers. This pattern of one propagating wave associated with one oscillation cycle was seen during all the regular cycles. The oscillation frequency varied noticeably at two neighboring horizontal locations (330 μm apart), suggesting that the oscillation is locally organized and each local oscillator is about ≤300 μm wide horizontally. During irregular oscillations, the spatiotemporal patterns were complex and sometimes the vertical synchronization decomposed, suggesting a de-coupling among local oscillators. Our data suggested that neocortical theta oscillation is sustained by multiple local oscillators. The coupling regime among the oscillators may determine the spatiotemporal pattern and switching between propagating waves and irregular patterns.

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