Activity and telluric contamination in HARPS observations of Alpha Centauri B

Lisogorskyi, Maksym; Jones, H. R. A.; Feng, Fabo

doi:10.1093/mnras/stz694

Cited by 19 publications

(20 citation statements)

References 36 publications

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“…These features varied in strength and velocity on time-scales of the stellar rotation period, and also correlated well with the passage of a region of activity as seen in log R H K . This work has since been verified by Wise et al (2018) and Lisogorskyi, Jones & Feng (2019). In addition, in Paper I, we found morphological differences in the pseudo-emission features that pointed to the underlying physics driving the lineprofile changes.…”

supporting

confidence: 72%

The spectral impact of magnetic activity on disc-integrated HARPS-N solar observations: exploring new activity indicators

Thompson

Watson

Haywood

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Stellar activity is the major roadblock on the path to finding true Earth-analogue planets with the Doppler technique. Thus, identifying new indicators that better trace magnetic activity (i.e. faculae and spots) is crucial to aid in disentangling these signals from that of a planet’s Doppler wobble. In this work, we investigate activity related features as seen in disc-integrated spectra from the HARPS-N solar telescope. We divide high-activity spectral echelle orders by low-activity master templates (as defined using both $\log {R^{\prime }_{HK}}$ and images from the Solar Dynamics Observatory, SDO), creating ‘relative spectra’. With resolved images of the surface of the Sun (via SDO), the faculae and spot filling factors can be calculated, giving a measure of activity independent of, and in addition to, $\log {R^{\prime }_{HK}}$. We find pseudo-emission (and pseudo-absorption) features in the relative spectra that are similar to those reported in our previous work on α Cen B. In α Cen B, the features are shown to correlate better to changes in faculae filling factor than spot filling factor. In this work, we more confidently identify changes in faculae coverage of the visible hemisphere of the Sun as the source of features produced in the relative spectra. Finally, we produce trailed spectra to observe the radial velocity component of the features, which show that the features move in a redward direction as one would expect when tracking active regions rotating on the surface of a star.

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supporting

confidence: 72%

The spectral impact of magnetic activity on disc-integrated HARPS-N solar observations: exploring new activity indicators

Thompson

Watson

Haywood

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Moreover, it is possible to fine-tune these values to a specific target and select optimum lines to study the velocity or the activity signals present in the spectrum. It has been shown that it is possible to classify spectral lines according to their sensitivity to stellar activity and, hence, according to their contribution to the activity signal in the final RVs (Wise et al 2018;Dumusque 2018;Lisogorskyi et al 2019;Cretignier et al 2020). Using masks with lines selected to be more or less affected by activity should result in CCF profile parameters that are more or less sensitive to stellar activity variations.…”

Section: Fwhm Range Minimum Contrast Depth Quantilementioning

confidence: 99%

The CARMENES search for exoplanets around M dwarfs

Lafarga

Ribas

Lovis

et al. 2020

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Context. For years, the standard procedure to measure radial velocities (RVs) of spectral observations consisted in cross-correlating the spectra with a binary mask, that is, a simple stellar template that contains information on the position and strength of stellar absorption lines. The cross-correlation function (CCF) profiles also provide several indicators of stellar activity. Aims. We present a methodology to first build weighted binary masks and, second, to compute the CCF of spectral observations with these masks from which we derive radial velocities and activity indicators. These methods are implemented in a python code that is publicly available. Methods. To build the masks, we selected a large number of sharp absorption lines based on the profile of the minima present in high signal-to-noise ratio (S/N) spectrum templates built from observations of reference stars. We computed the CCFs of observed spectra and derived RVs and the following three standard activity indicators: full-width-at-half-maximum as well as contrast and bisector inverse slope. Results. We applied our methodology to CARMENES high-resolution spectra and obtain RV and activity indicator time series of more than 300 M dwarf stars observed for the main CARMENES survey. Compared with the standard CARMENES template matching pipeline, in general we obtain more precise RVs in the cases where the template used in the standard pipeline did not have enough S/N. We also show the behaviour of the three activity indicators for the active star YZ CMi and estimate the absolute RV of the M dwarfs analysed using the CCF RVs.

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“…All the features we have selected correlate with S-index and radial velocity in the data set considered, either in flux or asymmetry. Even the features that seem to produce a symmetric shape variation impact the radial velocity via changing the width of the CCF and the feature producing it moving across a stellar disk (as shown in Thompson et al 2017;Lisogorskyi et al 2019).…”

Section: Active Line Selectionmentioning

confidence: 99%

“…There have been many studies looking for new spectral indices beyond the S-index and RHK to trace the activity across the spectrum (e.g. Thompson et al 2017;Wise et al 2018;Lisogorskyi et al 2019) or to correct for line variation (Dumusque 2018;Cretignier et al 2020). Another approach to the problem is to test signal's wavelength dependence.…”

Section: Introductionmentioning

confidence: 99%

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Exploring the robustness of Keplerian signals to the removal of active and telluric features

Lisogorskyi

Jones

Feng

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We examine the influence of activity- and telluric-induced radial velocity signals on high resolution spectra taken with an iodine absorption cell. We exclude 2 Angstrom spectral chunks containing active and telluric lines based on the well characterised K1V star Alpha Centauri B and illustrate the method on Epsilon Eridani–an active K2V star with a long period low amplitude planetary signal. After removal of the activity- and telluric-sensitive parts of the spectrum from the radial velocity calculation, the significance of the planetary signal is increased and the stellar rotation signal disappears. In order to assess the robustness of the procedure, we perform Monte Carlo simulations based on removing random chunks of the spectrum. Simulations confirm that the removal of lines impacted by activity and tellurics provides a method for checking the robustness of a given Keplerian signal. We also test the approach on HD 40979 which is an active F8V star with a large amplitude planetary signal. Our Monte Carlo simulations reveal that the significance of the Keplerian signal in the F star is much more sensitive to wavelength. Unlike the K star the removal of active lines from the F star greatly reduces the radial velocity precision. In this case, our removal of a K star active lines from an F star does not a provide a simple useful diagnostic because it has far less radial velocity information and heavily relies on the strong active lines.

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Activity and telluric contamination in HARPS observations of Alpha Centauri B

Cited by 19 publications

References 36 publications

The spectral impact of magnetic activity on disc-integrated HARPS-N solar observations: exploring new activity indicators

The spectral impact of magnetic activity on disc-integrated HARPS-N solar observations: exploring new activity indicators

The CARMENES search for exoplanets around M dwarfs

Exploring the robustness of Keplerian signals to the removal of active and telluric features

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