New periodograms separating orbital radial velocities and spectral shape variation

Binnenfeld, Avraham; Shahaf, Sahar; Anderson, Richard I.; Zucker, S.

doi:10.1051/0004-6361/202141406

Cited by 9 publications

(3 citation statements)

References 33 publications

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“…When it is known that time series might contain scan-angledependent signals, as in Gaia DR3, the most desirable option is to co-model the disturbing scan-angle signal in addition to the source signal that is searched for, for instance, following the concept of partial distance correlation presented in Binnenfeld et al (2022). For photometry, the nuisance model could be parametrised as in Eq.…”

Section: Co-modelling the Scan-angle-dependent Signalmentioning

confidence: 99%

GaiaData Release 3

Holl¹,

Fabricius²,

Portell³

et al. 2023

A&A

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Context. Gaia Data Release 3 (Gaia DR3) time series data may contain spurious signals related to the time-dependent scan angle. Aims. We aim to explain the origin of scan-angle-dependent signals and how they can lead to spurious periods, provide statistics to identify them in the data, and suggest how to deal with them in Gaia DR3 data and in future releases. Methods. Using real Gaia (DR3) data alongside numerical and analytical models, we visualise and explain the features observed in the data. Results. We demonstrated with Gaia (DR3) data that source structure (multiplicity or extendedness) or pollution from close-by bright objects can cause biases in the image parameter determination from which photometric, astrometric, and (indirectly) radial velocity time series are derived. These biases are a function of the time-dependent scan direction of the instrument and thus can introduce scan-angle-dependent signals, which due to the scanning-law-induced sampling of Gaia can result in specific spurious periodic signals. Numerical simulations in which a period search is performed on Gaia time series with a scan-angle-dependent signal qualitatively reproduce the general structure observed in the spurious period distribution of photometry and astrometry, and the associated spatial distributions on the sky. A variety of statistics allows for the deeper understanding and identification of affected sources. Conclusions. The origin of the scan-angle-dependent signals and subsequent spurious periods is well understood and is mostly caused by fixedorientation optical pairs with a separation < 0.5 (including binaries with P 5y) and (cores of) distant galaxies. Although most of the sources with affected derived parameters have been filtered out from the Gaia archive nss_two_body_orbit and several vari-tables, Gaia DR3 data remain that should be treated with care (no sources were filtered from gaia_source). Finally, the various statistics discussed in the paper can be used to identify and filter affected sources and also reveal new information about them that is not available through other means, especially in terms of binarity on sub-arcsecond scale.

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Section: Co-modelling the Scan-angle-dependent Signalmentioning

confidence: 99%

GaiaData Release 3

Holl¹,

Fabricius²,

Portell³

et al. 2023

A&A

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show abstract

“…Though efforts have been made to mitigate the effect of magnetic activity with various methods (Collier Cameron et al 2021;Binnenfeld et al 2022), the most reliable way to exclude false positive detections to date is to measure the stellar rotation period and demonstrate it to be different from the planetary candidate signal. This can be achieved by analysing photospheric activity indicators (i.e.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the public HARPS/ESO spectroscopic archive

Perdelwitz,

Trifonov,

Teklu

et al. 2024

A&A

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$ due to active regions on their surfaces. Time series of chromospheric activity indicators, such as the Ca ii H K lines, can be utilized to reduce the impact of such activity phenomena on exoplanet search programmes. In addition, the identification and correction of instrumental effects can improve the precision of RV exoplanet surveys. We aim to update the HARPS-RVBank RV database and include an additional $3.5$ years of time series and Ca ii H K lines ($R_ HK chromospheric activity indicators. This additional data will aid in the analysis of the impact of stellar magnetic activity on the RV time series obtained with the HARPS instrument. Our updated database aims to provide a valuable resource for the exoplanet community in understanding and mitigating the effects of such stellar magnetic activity on RV measurements. The new HARPS-RVBank database includes all stellar spectra obtained with the HARPS instrument prior to January 2022. The RVs corrected for small but significant nightly zero-point variations were calculated using an established method. The $R_ HK estimates were determined from both individual spectra and co-added template spectra with the use of model atmospheres. As input for our derivation of HK we derived stellar parameters from co-added, high signal-to-noise ratio (S/N) templates for a total of 3\,230 stars using the stellar parameter code SPECIES The new version of the HARPS RV database has a total of 252\,615 RVs of 5\,239 stars. Of these, 195\,387 have HK values, which corresponds to 77<!PCT!> of all publicly available HARPS spectra. Currently, this is the largest public database of high-precision (down to $ $) RVs, and the largest compilation of $R_ HK measurements. We also derived lower limits for the RV jitter of F-, G-, and K-type stars as a function of HK prime$.

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“…Cretignier et al (2022), based on the knowledge that the impact of stellar activity is line-depth dependant (Cretignier et al 2020a), used PCA to model stellar activity in the flux-flux gradient space (named the "shell" space) and results on HD10700 (τ Ceti) and HD12861 (α Cen B) indicates the method can successfully remove variations from non-Doppler origin. Last by not least, Binnenfeld et al (2020Binnenfeld et al ( , 2022 are developing the unit-sphere representation periodogram (USuRPER), to seperate Doppler from other RV variations. This technique is based on representing spectra as unit vectors in a multidimensional hyperspace.…”

Section: Introductionmentioning

confidence: 99%

SOAP-GPU: Efficient spectral modeling of stellar activity using graphical processing units

Zhao

Dumusque

2023

A&A

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Context. Stellar activity mitigation is one of the major challenges for the detection of earth-like exoplanets in radial velocity measurements. Several promising techniques are now investigating the use of spectral time-series, to differentiate between stellar and planetary perturbations. In this context, developing a software that can efficiently explore the parameter space of stellar activity at the spectral level is of great importance. Aims. The goal of this paper is to present a new version of the Spot Oscillation And Planet (SOAP) 2.0 code that can model stellar activity at the spectral level using graphical processing units (GPUs). Methods. We take advantage of the computational power of GPUs to optimise the computationally expensive algorithms behind the original SOAP 2.0 code. For that purpose, we developed GPU kernels that allow to model stellar activity on any given wavelength range. In addition to the treatment of stellar activity at the spectral level, SOAP-GPU also includes the change of spectral line bisectors from center to limb, and can take as input PHOENIX spectra to model the quiet photosphere, spots and faculae, which allow to simulate stellar activity for a wider space in stellar properties. Results. Benchmark calculations show that for the same accuracy, this new code improves the computational speed by a factor of 60 compared with a modified version of SOAP 2.0 that generates spectra, when modeling stellar activity on the full visible spectral range with a resolution of R=115'000. Although the code now includes the variation of spectral line bisector with center-to-limb angle, the effect on the derived RVs is small. We also show that it is not possible to fully separate the flux from the convective blueshift effect when modeling spots, due to their lower temperature and thus the appearance of molecular absorption in their spectra. Rather negligible for the Sun, this degeneracy between the flux and convective blueshift effect become more important when we move to cooler stars, however, this issue does not impact the estimation of the total effect (flux plus convection), and therefore users can trust this output. Conclusions. The publicly available SOAP-GPU code allows to efficiently model stellar activity at the spectral level, which is essential to test further stellar activity mitigation techniques working at the level of spectral timeseries not affected by other sources of noise. Besides a huge gain in performance, SOAP-GPU also includes more physics and is able to model different stars than the Sun, from F to K dwarfs, thanks to the use of the PHOENIX spectral library. We however note that due to the limited understanding of stellar convection and activity on other stars than the Sun, the more we go away from the solar case, the more the output of the code should be taken with care.

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New periodograms separating orbital radial velocities and spectral shape variation

Cited by 9 publications

References 33 publications

GaiaData Release 3

GaiaData Release 3

Analysis of the public HARPS/ESO spectroscopic archive

SOAP-GPU: Efficient spectral modeling of stellar activity using graphical processing units

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