Radial Velocity Information in Sour-Type Spectra

1984 ◽  
Vol 88 ◽  
pp. 87-98 ◽  
Author(s):  
W.J. Merline
Keyword(s):  
Radial Velocity ◽  
Signal To Noise Ratio ◽  
A Priori ◽  
Planetary Systems ◽  
High Signal ◽  
Stellar Oscillations ◽  
Rotation Axes ◽  
Visual Magnitude ◽  
Velocity Information ◽  
Large Telescopes

Recent advances in instrumentation and technique have provided hope that changes in stellar radial velocities can be measured with an accuracy of 10 m/s. This tremendous increase in the precision of radial velocity measurements should yield a wealth of new information from studies of stellar oscillations and surface phenomena, as well as offer clues to help answer perhaps the most exciting question, that of the existence of extra-solar planetary systems. The stringent requirements of light scrambling, high signal-to-noise ratio, and the need for frequent or simultaneous calibration (Griffin and Griffin 1973; Serkowski 1978) mean that these new techniques are inherently inefficient. This has limited studies to bright stars and to the use of large telescopes. Without a priori knowledge of the inclination of the rotation axes of the stars under study, searches for planetary systems will require a relatively large number of stars to statistically determine the probability that any of these stars harbor planets. Therefore, it is necessary to extend the limits for precise radial velocity studies to 5th or 6th blue/visual magnitude. Efficient extraction of radial velocity information from the spectrum is essential. Furthermore, attempts to increase limiting precision or decrease limiting magnitudes using conventional techniques will also benefit from increased efficiency.

scholarly journals Detection and localization of multiple small damages in beam

2021 ◽  
Vol 13 (1) ◽  
pp. 168781402098732
Author(s):  
Ayisha Nayyar ◽  
Ummul Baneen ◽  
Syed Abbas Zilqurnain Naqvi ◽  
Muhammad Ahsan
Keyword(s):  
Frequency Response ◽  
Natural Frequencies ◽  
Signal To Noise Ratio ◽  
Moving Average ◽  
A Priori ◽  
Damage Index ◽  
High Signal ◽  
Frequency Range ◽  
Spatial Locality ◽  
System Frequency

Localizing small damages often requires sensors be mounted in the proximity of damage to obtain high Signal-to-Noise Ratio in system frequency response to input excitation. The proximity requirement limits the applicability of existing schemes for low-severity damage detection as an estimate of damage location may not be known  a priori. In this work it is shown that spatial locality is not a fundamental impediment; multiple small damages can still be detected with high accuracy provided that the frequency range beyond the first five natural frequencies is utilized in the Frequency response functions (FRF) curvature method. The proposed method presented in this paper applies sensitivity analysis to systematically unearth frequency ranges capable of elevating damage index peak at correct damage locations. It is a baseline-free method that employs a smoothing polynomial to emulate reference curvatures for the undamaged structure. Numerical simulation of steel-beam shows that small multiple damages of severity as low as 5% can be reliably detected by including frequency range covering 5–10th natural frequencies. The efficacy of the scheme is also experimentally validated for the same beam. It is also found that a simple noise filtration scheme such as a Gaussian moving average filter can adequately remove false peaks from the damage index profile.

scholarly journals Tidally induced stellar oscillations: converting modelled oscillations excited by hot Jupiters into observables

2020 ◽  
Vol 500 (2) ◽  
pp. 2711-2731
Author(s):  
Andrew Bunting ◽  
Caroline Terquem
Keyword(s):  
Radial Velocity ◽  
Orbital Period ◽  
Planetary Systems ◽  
Velocity Signal ◽  
Convective Flux ◽  
Hot Jupiters ◽  
Stellar Oscillations ◽  
Orbital Periods ◽  
Hot Jupiter

ABSTRACT We calculate the conversion from non-adiabatic, non-radial oscillations tidally induced by a hot Jupiter on a star to observable spectroscopic and photometric signals. Models with both frozen convection and an approximation for a perturbation to the convective flux are discussed. Observables are calculated for some real planetary systems to give specific predictions. The photometric signal is predicted to be proportional to the inverse square of the orbital period, P−2, as in the equilibrium tide approximation. However, the radial velocity signal is predicted to be proportional to P−1, and is therefore much larger at long orbital periods than the signal corresponding to the equilibrium tide approximation, which is proportional to P−3. The prospects for detecting these oscillations and the implications for the detection and characterization of planets are discussed.

scholarly journals Public HARPS radial velocity database corrected for systematic errors

2020 ◽  
Vol 636 ◽  
pp. A74 ◽  
Author(s):  
Trifon Trifonov ◽  
Lev Tal-Or ◽  
Mathias Zechmeister ◽  
Adrian Kaminski ◽  
Shay Zucker ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Signal To Noise Ratio ◽  
Auxiliary Information ◽  
Easy Access ◽  
High Signal ◽  
M Dwarfs ◽  
Data Set ◽  
New Public ◽  
Systematic Effects ◽  
User Friendly

Context. The High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph has been mounted since 2003 at the ESO 3.6 m telescope in La Silla and provides state-of-the-art stellar radial velocity (RV) measurements with a precision down to ∼1 m s−1. The spectra are extracted with a dedicated data-reduction software (DRS), and the RVs are computed by cross-correlating with a numerical mask. Aims. This study has three main aims: (i) Create easy access to the public HARPS RV data set. (ii) Apply the new public SpEctrum Radial Velocity AnaLyser (SERVAL) pipeline to the spectra, and produce a more precise RV data set. (iii) Determine whether the precision of the RVs can be further improved by correcting for small nightly systematic effects. Methods. For each star observed with HARPS, we downloaded the publicly available spectra from the ESO archive and recomputed the RVs with SERVAL. This was based on fitting each observed spectrum with a high signal-to-noise ratio template created by coadding all the available spectra of that star. We then computed nightly zero-points (NZPs) by averaging the RVs of quiet stars. Results. By analyzing the RVs of the most RV-quiet stars, whose RV scatter is < 5 m s−1, we find that SERVAL RVs are on average more precise than DRS RVs by a few percent. By investigating the NZP time series, we find three significant systematic effects whose magnitude is independent of the software that is used to derive the RV: (i) stochastic variations with a magnitude of ∼1 m s−1; (ii) long-term variations, with a magnitude of ∼1 m s−1 and a typical timescale of a few weeks; and (iii) 20–30 NZPs that significantly deviate by a few m s−1. In addition, we find small (≲1 m s−1) but significant intra-night drifts in DRS RVs before the 2015 intervention, and in SERVAL RVs after it. We confirm that the fibre exchange in 2015 caused a discontinuous RV jump that strongly depends on the spectral type of the observed star: from ∼14 m s−1 for late F-type stars to ∼ − 3 m s−1 for M dwarfs. The combined effect of extracting the RVs with SERVAL and correcting them for the systematics we find is an improved average RV precision: an improvement of ∼5% for spectra taken before the 2015 intervention, and an improvement of ∼15% for spectra taken after it. To demonstrate the quality of the new RV data set, we present an updated orbital solution of the GJ 253 two-planet system. Conclusions. Our NZP-corrected SERVAL RVs can be retrieved from a user-friendly public database. It provides more than 212 000 RVs for about 3000 stars along with much auxiliary information, such as the NZP corrections, various activity indices, and DRS-CCF products.

scholarly journals A study of synthetic <sup>13</sup>CH<sub>4</sub> retrievals from TROPOMI and Sentinel-5/UVNS

2019 ◽  
Vol 12 (12) ◽  
pp. 6273-6301
Author(s):  
Edward Malina ◽  
Haili Hu ◽  
Jochen Landgraf ◽  
Ben Veihelmann
Keyword(s):  
Near Infrared ◽  
Signal To Noise Ratio ◽  
A Priori ◽  
Ultra Violet ◽  
High Signal ◽  
Atmospheric Methane ◽  
Δ13c Values ◽  
Temporal Averaging ◽  
A Minor ◽  
Shortwave Infrared

Abstract. Retrievals of methane isotopologues have the potential to differentiate between natural and anthropogenic methane sources types, which can provide much needed information about the current global methane budget. We investigate the feasibility of retrieving the second most abundant isotopologue of atmospheric methane (13CH4, roughly 1.1 % of total atmospheric methane) from the shortwave infrared (SWIR) channels of the future Sentinel-5/ultra-violet, visible, near-infrared, shortwave infrared (UVNS) and current Copernicus Sentinel-5 Precursor TROPOspheric Monitoring Instrument (TROPOMI) instruments. With the intended goal of calculating the δ13C value, we assume that a δ13C uncertainty of better than 1 ‰ is sufficient to differentiate between source types, which corresponds to a 13CH4 uncertainty of <0.02 ppb. Using the well-established information content analysis techniques and assuming clear-sky, non-scattering conditions, we find that the SWIR3 (2305–2385 nm) channel on the TROPOMI instrument can achieve a mean uncertainty of <1 ppb, while the SWIR1 channel (1590–1675 nm) on the Sentinel-5 UVNS instrument can achieve <0.68 ppb or <0.2 ppb in high signal-to-noise ratio (SNR) cases. These uncertainties combined with significant spatial and/or temporal averaging techniques can reduce δ13C uncertainty to the target magnitude or better. However, we find that 13CH4 retrievals are highly sensitive to errors in a priori knowledge of temperature and pressure, and accurate knowledge of these profiles is required before 13CH4 retrievals can be performed on TROPOMI and future Sentinel-5/UVNS data. In addition, we assess the assumption that scattering-induced light path errors are cancelled out by comparing the δ13C values calculated for non-scattering and scattering scenarios. We find that there is a minor bias in δ13C values from scattering and non-scattering retrievals, but this is unrelated to scattering-induced errors.

scholarly journals Study of Spectroscopic Binaries with the Objective Prism Method

1983 ◽  
Vol 62 ◽  
pp. 104-107
Author(s):  
Frank Gieseking
Keyword(s):  
Radial Velocity ◽  
Frequency Distribution ◽  
Radial Velocities ◽  
Spectroscopic Binaries ◽  
Steep Decrease ◽  
Visual Magnitude ◽  
Objective Prism ◽  
The Individual ◽  
Large Telescopes

The frequency distribution of SB’s over apparent visual magnitude emerging from the catalogue of Batten et. al. (1978) shows a very steep decrease of the number of spectroscopically detected SB’s already for such bright stars of magnitude 7. Considering the number of all stars in the individual magnitude intervals, we find a kind of completeness parameter of the spectroscopic surveys: If we scale it somewhat optimistically at 100% between 0 and 3 mag, we see a 50% decrease of the completeness of our knowledge of stellar radial velocities already for stars fainter than 4.5 mag.This situation is mainly due to the fact that the measurement of radial velocities with conventional slit spectrographs is extremely laborious, requiring long exposure times at large telescopes for the exposure of only one spectrum at a time. – Therefore more efficient methods for radial velocity determinations of fainter stars are urgently needed.

scholarly journals Nonradial pulsations in the open cluster NGC 3766

2009 ◽  
Vol 5 (S266) ◽  
pp. 518-521
Author(s):  
Rachael M. Roettenbacher ◽  
Ernest C. Amouzou ◽  
M. Virginia McSwain
Keyword(s):  
Signal To Noise Ratio ◽  
Large Fraction ◽  
Open Cluster ◽  
Spectroscopic Studies ◽  
High Resolution Spectroscopy ◽  
High Signal ◽  
Be Stars ◽  
B Stars ◽  
Be Star ◽  
Large Telescopes

AbstractNonradial pulsations (NRPs) are a proposed mechanism for the formation of decretion disks around Be stars. They are important tools to study the internal structure of stars. NGC 3766 has an unusually large fraction of transient Be stars, so it is an excellent location to study the formation mechanism of Be-star disks. High-resolution spectroscopy can reveal line-profile variations from NRPs, allowing measurements of both the degree, l, and azimuthal order, m. However, spectroscopic studies require large amounts of time with large telescopes to achieve the necessary high signal-to-noise ratio and time-domain coverage. On the other hand, multicolor photometry can be performed more easily with small telescopes to measure l only. Here, we present representative light curves of Be stars and nonemitting B stars in NGC 3766 from the CTIO 0.9m telescope in an effort to study NRPs in this cluster.

FIESTA – disentangling stellar variability from exoplanets in the Fourier domain

2019 ◽  
Vol 491 (3) ◽  
pp. 4131-4146 ◽  
Author(s):  
J Zhao ◽  
C G Tinney
Keyword(s):  
Radial Velocity ◽  
Line Profile ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Stellar Activity ◽  
Orbital Parameters ◽  
Velocity Shift ◽  
Analysis Methodology ◽  
Spectral Line Profile ◽  
Periodogram Analysis

ABSTRACT We propose a new analysis methodology – FourIEr phase SpecTrum Analysis (FIESTA, or $\mathit {\Phi }$ESTA) – for the study of spectral line profile variability in Fourier space. The philosophy of $\mathit {\Phi }$ESTA is highlighted in its interpretation of a line deformation as various shifts of the composing Fourier modes. With this ability, $\mathit {\Phi }$ESTA excels in distinguishing the effects of a bulk shift in a line profile, from changes in a line profile shape. In other words, it can distinguish a radial velocity shift due to orbiting companions like planets, from an apparent radial velocity shift due to stellar variability (often referred to as ‘jitter’). Most importantly, it can quantify the radial velocity impact of stellar jitter on each epoch. Our simulations show that (compared to a model that does not account for stellar activity), $\mathit {\Phi }$ESTA can almost triple the fraction of planets recovered with orbital parameters measured to within 10 per cent of their input parameters, when extracting a 2 m s−1 amplitude planetary signal in the midst of ∼2 m s−1 amplitude starspot jitter for high signal-to-noise ratio (&gt;200 pixel−1) data. $\mathit {\Phi }$ESTA can also be used to identify stellar activity related periods in a periodogram analysis and classify relative amplitudes of stellar jitter and planetary signals, with examples for the analysis of HARPS data of the active star HD 224789 and the active planet-host star HD 103720. In the end, we demonstrate that $\mathit {\Phi }$ESTA’s framework is working as well as other activity indicators in correlating with stellar jitter.

scholarly journals Multiple stellar systems

1986 ◽  
Vol 118 ◽  
pp. 441-442
Author(s):  
A. Duquennoy ◽  
M. Mayor
Keyword(s):  
Radial Velocity ◽  
Small Amplitude ◽  
Cross Correlation ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Correlation Technique ◽  
Multiple Systems ◽  
Triple Systems ◽  
The Cross

A spectroscopic survey of visual binaries with known orbital elements has been carried out with the radial velocity scanner CORAVEL at the Haute-Provence Observatory, since 1977, (Baranne, Mayor, Poncet, 1979). This survey of more than 100 visual systems, selected from Dommanget's catalogue (1967) (see also a new edition 1982) was first devoted to the determination of stellar masses. Several multiple systems were detected and have permitted also a study of the structure of triple systems. We have detected and measured in particular a class of triple systems with radial velocity variations of small amplitude. Taking advantage of the high resolution and high signal-to-noise ratio accessible with the cross-correlation technique, such small amplitude radial velocity curves are sometimes derived only through the change of width and shape of the cross-correlation function. Let us recall that the cc-function of a SB2 (or SB3) system is only the weighted sum of the individual cc-functions (Mayor, 1985). This property of the cross-correlation combined with the linearity of the detector allow a very simple analysis of blended dips. The full width at half depth of the cross-correlation dip is about FWHD = 16 km/s (in absence of noticeable rotation). Analysis of blended systems allows a good determination of the two individual velocities if the difference |vr1 -Vr2| is equal or larger than about 0.15 *FWHD (about 2 km/s).

scholarly journals The rt-TEP tool: real-time visualization of TMS-evoked potentials to maximize cortical activation and minimize artifacts

2021 ◽  
Author(s):  
Silvia Casarotto ◽  
Matteo Fecchio ◽  
Mario Rosanova ◽  
Giuseppe Varone ◽  
Sasha D'Ambrosio ◽  
...  
Keyword(s):  
Evoked Potentials ◽  
Real Time ◽  
Cortical Neurons ◽  
Signal To Noise Ratio ◽  
A Priori ◽  
Software Tool ◽  
Cortical Activation ◽  
High Signal ◽  
Real Time Visualization ◽  
The Impact

Background The impact of transcranial magnetic stimulation (TMS) on cortical neurons is currently hard to predict based on a priori biophysical and anatomical knowledge alone. This problem can hamper the reliability and reproducibility of protocols aimed at measuring electroencephalographic (EEG) responses to TMS. New Method We introduce and release a novel software tool to facilitate and standardize the acquisition of TMS-evoked potentials (TEPs). The tool, rt-TEP (real-time TEP), interfaces with different EEG amplifiers and offers a series of informative visualization modes to assess in real time the immediate impact of TMS on the underlying neuronal circuits. Results We show that rt-TEP can be used to abolish or minimize magnetic and muscle artifacts contaminating the post-stimulus period thus affording a clear visualization and quantification of the amplitude of the early (<50 ms) EEG response after averaging a limited number of trials. This real-time readout can then be used to adjust TMS parameters (e.g. site, orientation, intensity) and experimental settings (e.g. loudness and/or spectral features of the noise masking) to ultimately maximize direct cortical effects over the undesired sensory effects of the coil's discharge. Comparison with Existing Methods The ensemble of real-time visualization modes of rt-TEP are not implemented in any current commercial software and provide a key readout to titrate TMS parameters beyond the a priori information provided by anatomical models. Conclusions Real-time optimization of stimulation parameters with rt-TEP can facilitate the acquisition of reliable TEPs with a high signal-to-noise ratio and improve the standardization and reproducibility of data collection across laboratories.

scholarly journals Sentinel-5P TROPOMI NO<sub>2</sub> retrieval: impact of version v2.2 improvements and comparisons with OMI and ground-based data

2021 ◽  
Author(s):  
Jos van Geffen ◽  
Henk Eskes ◽  
Steven Compernolle ◽  
Gaia Pinardi ◽  
Tijl Verhoelst ◽  
...  
Keyword(s):  
Power Plants ◽  
Surface Albedo ◽  
Signal To Noise Ratio ◽  
A Priori ◽  
Weather Data ◽  
High Signal ◽  
High Latitudes ◽  
Individual Measurement ◽  
Tropospheric No2 ◽  
Global Coverage

Abstract. Nitrogen dioxide (NO2) is one of the main data products measured by the Tropospheric Monitoring Instrument (TROPOMI) on the Sentinel-5 Precursor (S5P) satellite, which combines a high signal-to-noise ratio with daily global coverage and high spatial resolution. TROPOMI provides a valuable source of information to monitor emissions from local sources such as power plants, industry, cities, traffic and ships, and variability of these sources in time. Validation exercises of NO2 version v1.2-v1.3 data, however, have revealed that TROPOMI's tropospheric vertical columns (VCDs) are too low by up to 50 % over highly polluted areas. These findings are mainly attributed to biases in the cloud pressure retrieval, the surface albedo climatology and the low resolution of the a-priori profiles derived from global simulations of the TM5-MP chemistry model. This study describes improvements in the TROPOMI NO2 retrieval leading to version v2.2, operational since 1 July 2021. Compared to v1.x, the main changes are: (1) The NO2-v2.2 data is based on version 2 level-1B (ir)radiance spectra with improved calibration, which results in a small and fairly homogeneous increase of the NO2 slant columns of 3 to 4 %, most of which ends up as a small increase of the stratospheric columns; (2) The cloud pressures are derived with a new version of the FRESCO cloud retrieval already introduced in NO2-v1.4, which lead to a lowering of the cloud pressure, resulting in larger tropospheric NO2 columns over polluted scenes with a small but non-zero cloud coverage; (3) For cloud-free scenes a surface albedo correction is introduced based on the observed reflectance, which also leads to a general increase of the tropospheric NO2 columns over polluted scenes of order 15 %; (4) An outlier removal was implemented in the spectral fit, which increases the number of good quality retrievals over the South-Atlantic Anomaly region and over bright clouds where saturation may occur; (5) Snow-Ice information is now obtained from ECMWF weather data, increasing the number of valid retrievals at high latitudes. On average the NO2-v2.2 data have tropospheric VCDs that are between 10 and 40 % larger than the v1.x data, depending on the level of pollution and season; the largest impact is found at mid- and high-latitudes in wintertime. This has brought these tropospheric NO2 closer to OMI observations. Ground-based validation shows on average an improvement of the negative bias of the stratospheric (from −6 % to −3 %), tropospheric (from −32 % to −23 %) and total (from −12 % to −5 %) columns. For individual measurement stations, however, the picture is more complicated, in particular for the tropospheric and total columns.

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