New Methods for Finding Activity-sensitive Spectral Lines: Combined Visual Identification and an Automated Pipeline Find a Set of 40 Activity Indicators

Wise, Alexander; Dodson-Robinson, Sarah; Bevenour, Kelsey; Provini, Anthony

doi:10.3847/1538-3881/aadd94

Cited by 53 publications

(76 citation statements)

References 53 publications

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“…In Davis et al (2017), the authors show, using PCA on data simulated with SOAP 2.0 (Dumusque et al 2014), that spectral lines seems to be affected differently by activity. A similar result is also shown in Thompson et al (2017) and Wise et al (2018), were the authors demonstrate that stellar activity modifies the equivalent width of spectral lines. However, although variation in spectral line is seen in those analyses, it is not clear if those variations induce a change in RV.…”

Section: Mitigating Stellar Activity In Radial-velocity Measurementssupporting

confidence: 79%

“…The idea behind this study is to use the wealth of information contained in high-resolution stellar spectra rather than averaging all the information into the few parameters derived from the cross-correlation functions (Baranne et al 1996). Some preliminary works from Davis et al (2017), Thompson et al (2017) and Wise et al (2018) show that stellar activity affects spectral lines in a different way. This is not surprising as each spectral line have its how sensitivity to temperature, to magnetic field strength and to convection velocity, three physical parameters that are strongly modified in the presence of stellar activity.…”

Section: Introductionmentioning

confidence: 99%

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Measuring precise radial velocities on individual spectral lines

Dumusque

2018

A&A

153

177

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Context. Stellar activity is the main limitation to the detection of an Earth-twin using the radial-velocity (RV) technique. Despite many efforts in trying to mitigate the effect of stellar activity using empirical and statistical techniques, it seems that we are facing an obstacle that will be extremely difficult to overcome using current techniques. Aims. In this paper, we investigate a novel approach to derive precise RVs considering the wealth of information present in high-resolution spectra. Methods. This new method consists of building a master spectrum from all available observations and measure the RVs of each individual spectral line in a spectrum relative to this master. When analysing several spectra, the final product of this approach is the RVs of each individual line as a function of time. Results. We demonstrate on three stars intensively observed with HARPS that our new method gives RVs that are extremely similar to the one derived from the HARPS data reduction software. Our new approach to derive RVs demonstrates that the non-stability of daily HARPS wavelength solution induces night-to-night RV offsets with an standard deviation of 0.4 m s−1, and we propose a solution to correct for this systematic. Finally, and this is probably the most astrophysically relevant result of this paper, we demonstrate that some spectral lines are strongly affected by stellar activity while others are not. By measuring the RVs on two carefully selected subsample of spectral lines, we demonstrate that we can boost by a factor of two or mitigate by a factor of 1.6 the red noise induced by stellar activity in the 2010 RV measurements of α Cen B. Conclusions. By measuring the RVs of each spectral line, we are able to reach the same RV precision as other approved techniques. In addition, this new approach allows us to demonstrate that each spectral line is differently affected by stellar activity. Preliminary results show that studying in details the behaviour of each spectral line is probably the key to overcome the obstacle of stellar activity.

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Section: Mitigating Stellar Activity In Radial-velocity Measurementssupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Measuring precise radial velocities on individual spectral lines

Dumusque

2018

A&A

153

177

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“…Some are definitely sensitive to activity, but don't correlate with Ca H & K lines, which could mean the variations are produced via different processes. In addition, several spectral lines identified in Wise et al (2018) (e.g. Fe i 4602.95Å) do not show correlation between the equivalent width and Sindex.…”

Section: Resultsmentioning

confidence: 82%

Activity and telluric contamination in HARPS observations of Alpha Centauri B

Lisogorskyi

Jones

Feng

2019

Monthly Notices of the Royal Astronomical Society

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The Alpha Centauri system is the primary target for planet search as it is the closest star system composed of a solar twin α Cen A, a K-dwarf α Cen B and an M-dwarf Proxima Centauri, which has a confirmed planet in the temperate zone. α Cen A & B were monitored intensively with the HARPS spectrograph for over 10 years, providing high-precision radial velocity measurements. In this work we study the available data to better understand the stellar activity and other contaminating signals. We highlight the importance of telluric contamination and its impact on the radial velocity measurements. Our suggested procedures lead to discarding about 5% of HARPS data, providing a dataset with an RMS improved by a factor of 2. We compile and quantify the behaviour of 345 spectral lines with a wide range of line shapes and sensitivity to activity.

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“…The core of the line at 5420 Å is slightly too weak, compared with the observations. This could be due to its sensitivity to activity (Wise et al 2018). Note that also the 5394, 5432, and 6013 lines could be affected (Wise et al 2018), and in particular, the 5394 Å line has a long history of research owing to its variation with the global solar activity cycle (Danilovic & Vince 2005;Livingston et al 2007).…”

Section: Solar Mn Abundancementioning

confidence: 99%

“…This could be due to its sensitivity to activity (Wise et al 2018). Note that also the 5394, 5432, and 6013 lines could be affected (Wise et al 2018), and in particular, the 5394 Å line has a long history of research owing to its variation with the global solar activity cycle (Danilovic & Vince 2005;Livingston et al 2007). Some studies suggest that the line is not as sensitive to granular motions as other features, because of its wide HFS, and is more sensitive to the intergranular magnetic concentrations, similar to the CH G-band (Vitas et al 2009).…”

Section: Solar Mn Abundancementioning

confidence: 99%

Observational constraints on the origin of the elements

Bergemann

Gallagher

Eitner

et al. 2019

A&A

125

104

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Manganese (Mn) is a key Fe-group element, commonly employed in stellar population and nucleosynthesis studies to explore the role of SN Ia. We have developed a new non-local thermodynamic equilibrium (NLTE) model of Mn, including new photo-ionisation cross-sections and new transition rates caused by collisions with H and H− atoms. We applied the model in combination with one-dimensional (1D) LTE model atmospheres and 3D hydrodynamical simulations of stellar convection to quantify the impact of NLTE and convection on the line formation. We show that the effects of NLTE are present in Mn I and, to a lesser degree, in Mn II lines, and these increase with metallicity and with the effective temperature of a model. Employing 3D NLTE radiative transfer, we derive a new abundance of Mn in the Sun, A(Mn) = 5.52 ± 0.03 dex, consistent with the element abundance in C I meteorites. We also applied our methods to the analysis of three metal-poor benchmark stars. We find that 3D NLTE abundances are significantly higher than 1D LTE. For dwarfs, the differences between 1D NLTE and 3D NLTE abundances are typically within 0.15 dex, however, the effects are much larger in the atmospheres of giants owing to their more vigorous convection. We show that 3D NLTE successfully solves the ionisation and excitation balance for the RGB star HD 122563 that cannot be achieved by 1D LTE or 1D NLTE modelling. For HD 84937 and HD 140283, the ionisation balance is satisfied, however, the resonance Mn I triplet lines still show somewhat lower abundances compared to the high-excitation lines. Our results for the benchmark stars confirm that 1D LTE modelling leads to significant systematic biases in Mn abundances across the full wavelength range from the blue to the IR. We also produce a list of Mn lines that are not significantly biased by 3D and can be reliably, within the 0.1 dex uncertainty, modelled in 1D NLTE.

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New Methods for Finding Activity-sensitive Spectral Lines: Combined Visual Identification and an Automated Pipeline Find a Set of 40 Activity Indicators

Cited by 53 publications

References 53 publications

Measuring precise radial velocities on individual spectral lines

Measuring precise radial velocities on individual spectral lines

Activity and telluric contamination in HARPS observations of Alpha Centauri B

Observational constraints on the origin of the elements

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