No planet for HD 166435

“…we began a campaign of highprecision photometric observations with an automatic photoelectric telescope (APT) at Fairborn Observatory in Arizona to search for planetary transits and made tentative plans to announce the new planet at the Protostars and Planets IV conference (Mannings et al. 2000).”

“This phenomena is observed on the Sun to a lesser degree where leader spots tend to be larger and to live longer than follower spots, resulting in a displacement up to 5 0 between the photocenters of the spot and the associated plages (Dobson-Hockey & Radick 1986).”

“From 1998 June to 1998 August, 141 Ca II H and K measurements were made on 20 nights with the 100-inch telescope at Mount Wilson Observatory as part of the HK Project (Baliunas et al. 1998).”

“In addition to the stellar radial velocity, the cross-correlation function (CCF) provides additional information about features in the averaged spectral lines (see Queloz 1994 for a review).”

“In order to check for line asymmetries, we determined the values of the bisector span (following Queloz et al. 2001) as a function of orbital phase which are shown in Fig.”

“Precision photometry complements Doppler observations by establishing whether the observed radial velocity variations are caused by the reflex motion induced by a planetary companion or by stellar magnetic activity (e.g., Henry et al. 2000a; Queloz et al. 2001; and Paulson et al. 2004).”

“In active stars, a clear anti-correlation is often seen between bisector velocity span and radial velocity, which, in certain cases, would make it possible to approximately correct the velocities for the influence of the spot (Queloz et al. 2001).”

“The DRS pipeline also provides the CCF’s FWHM and the Bisector Inverse Slope span (BIS-span) measurements, which are valuable stellar activity indicators (Queloz et al. 2001).”

“As line depth does not affect CCF-based RV measurements, except in cases of blended lines or template errors, this line core flux correlation is distinct from traditional measurements of line shape changes such as bisector span and chromatic index (e.g. Queloz et al. 2001; Zechmeister et al. 2018).”

“…correlations with traditional activity indicators such as the equivalent width of Hα (Herbst & Miller 1989), the line profile FWHM (Queloz et al. 2009), the line profile’s bisector (Queloz et al. 2001), and data-driven and machine-learning methods (e.g., Pearson et al. 2018; de Beurs et al. 2020).”

“Clearly, the FWHM and SAFE statistics have more power for detecting stellar activity than the BIS, BiSlope, BiGauss, and V-span in this simulation setting.”

“CoRoT-7b CoRoT-7c Reference 4.8±0.8M⊕ 8.4±0.9M⊕ Queloz et al. (2009) 6.9±1.4M⊕ 12.4±0.42M⊕ Hatzes et al. (2010) 7.42±1.21M⊕ . . . Hatzes et al. (2011) 2.3±1.8M⊕ . . . Pont et al. (2011) 5.7±2.5M⊕ 13.2±4.1M⊕ Boisse et al. (2011) 8.0±1.2M⊕ 13.6±1.4M⊕ Ferraz-Mello et al. (2011) 4.8±2.4M⊕ 11.8±3.4M⊕ Tuomi et al. (2014) 4.…”

“When possible, we computed for each target the crosscorrelation function (hereafter CCF) of the spectrum and the corresponding bisector and bisector velocity span (hereafterBIS; see e.g. Queloz et al., 2001, Galland et al., 2005a, 2006).”

“The HARPS-N CCF line bisectors were calculated as a mean velocity difference between 0.1–0.4 and 0.55–0.9 of the line depth (Queloz et al. 2001).”

“The contamination by stellar activity could swallow the signal from a potential planetary companion and also provide false planetary detections (Queloz et al. 2001, Huélamo et al. 2008).”

“In addition, starspots can resemble an orbiting planet by generating periodic RV fluctuations (Queloz et al. 2001).”

“The CCF was computed for regions which include the photospheric lines commonly used in the Doppler Imaging technique, while excluding chromospheric and telluric lines (Queloz et al. 2001).”

“This, in turn, affects the observed stellar spectra and can induce RV signals that mimic those from planets (e.g., Queloz et al. 2001; Figueira et al. 2010; Boisse et al. 2011; D´ıaz et al. 2016).”

“Additionally, the line bisector was analyzed to ensure that the observed signal was indeed from an orbiting body and not a blended binary (Queloz et al. 2001).”

“The BIS was early on identified as a useful line profile indicator for tracking photospheric stellar activity (Queloz et al. 2001), and has seen extensive use.”

“Magnetic activity and rotation can disguise or even mimic planetary signals, hampering the detection and characterization of planets (e.g. Queloz et al., 2001; Oshagh et al., 2013; Meunier et al., 2020).”

“From HARPS-DRS the parameters of a cross-correlation with a line-list template are obtained, namely, the FWHM, bisector inverse slope (BIS), and Contrast of the cross-correlation function (for more on this method see Queloz et al. 2001; Pepe et al. 2002).”

“This confirms that radial velocity variations in WASP-74 are indeed due to planetary reflex motion and not line-profile variations due to spots (e.g., Queloz et al. 2001; Paulson et al. 2004).”

“We observed NGTS-14A with the CORALIE spectrograph on the Swiss 1.2 m Euler telescope at La Silla Observatories, Chile (Queloz et al. 2001b), between 3 November and 4 December 2018.”

“First we compute the CCF profile indicators, that is the contrast (relative depth of the CCF at its central wavelength), FWHM, BIS (cf. Queloz et al. 2001), ∆V of Nardetto et al. (2006), and Vasy(mod) (see Sect.”

“By now it is well understood (e.g., Queloz et al. 2001; Torres et al. 2005) that if measured RVs were a result of a blend with an EB, the line bisectors would vary in phase with the photometric period and with an amplitude similar to that of the RV curve.”

“A clear correlation between these two quantities is expected when CCF profiles are subject to asymmetries caused by stellar spots (Queloz et al. 2001).”

“The HARPS pipeline also derives values for other parameters such as the Bisector Inverse Slope (BIS – Queloz et al. 2001), the Cross-Correlation Function (CCF) parameters FWHM and Contrast, as well as the activity level of the star using the Ca iiK and K lines (log R′HK).”

“By combining RV measurements with bisector measurements it is possible to evaluate the contribution of stellar activity to the RV variations (e.g, Queloz et al. 2001; Povich et al. 2001; Dall et al. 2006; Pont et al. 2010; Figueira et al.2010).”

“At this stage we eliminate hierarchical triples by testing for correlation of the span bisector with the radial velocity (Queloz et al. 2001).”

“Cool spots linked with magnetic activity are unlikely because in this case, the slope is negative (Queloz et al. 2001).”

“In radial velocity measurements, starspots, faculae, and plages distort spectral line profiles as the star rotates, inducing RV shifts unrelated to planetary motion (S. H. Saar & R. A. Donahue 1997; D. Queloz et al. 2001; I. Boisse et al. 2011).”

“These indicators include the bisector inverse slope (BIS; Queloz et al. (2001)) measuring the skewness/asymmetry of the CCF (see also V span ; Boisse et al. (2011)) or the full-width at half maximum (FWHM; Queloz et al. (2009)) tracing the CCF width change.”

“Such possibility could sometimes be ver- ified by checking the CCF bisector span, or bisector inverse slope (BIS) that describes the overall change in line skewness caused by stellar magnetic activity (Queloz et al. 2001).”

“A rotating star with surface features such as spots or plage caused by magnetic activity will exhibit periodic RV variations, which can be misinterpreted as a planetary signal (Queloz et al. 2001).”

“We also derived the FWHM, contrast, and bisector span of the cross-correlation function (CCF) as described by Queloz et al. (2001).”

“To check that RV variations were not due to a blended spectrum, we computed the bisector slope of the cross-correlation function for each observation as described by Queloz et al. (2001), see Table 1.”

“In order to investigate other causes that may produce apparent RV variations, such as stellar rotational modulations or pulsations rather than the orbital motion, a spectral line shape analysis was performed using high-resolution stellar lines (Hatzes et al. 1998; Queloz et al. 2001).”

“Studying the variation in the radial velocity (RV) induced by the chromospheric activity is important to distinguish it fromthe Keplerian motion of the star that may be caused by a planet (see e.g. Queloz et al. 2001; Dumusque et al. 2011; Robertson et al. 2014).”

“In exoplanet search it is well known that the presence of stellar spots can induce features either in the observed lightcurves and in the radial velocity profiles, and may mimic the signal due to one or more planets orbiting around the star (Queloz et al. 2001).”

“Thus, the analysis of the shapes of the spectral lines, in particular the analysis of the line bisectors, may identify the origin of observed RV variations and prove or disprove the existence of planetary companions (e.g., Queloz et al. 2001).”

“The analysis of spectral line asymmetries throughline bisectors provides a strong tool to understand the shape and origin of line profiles, and is widely used in stellar astrophysics (see e. g. Queloz et al. 2001; Dall et al. 2006; Martı́nez-Fiorenzano 2008).”

“TOI-6695 was observed with the CORALIE spectrograph ( D. Queloz et al. 2001b ) at the Swiss 1.2 m Euler telescope at La Silla by both the WINE and Swiss teams.”

“Additionally, the use of spectroscopic indicators like the line bisector (Queloz et al., 2001) and the Ca II H&K chromosphere index help in identifying and correcting for activity-related distortions in RV data.”

“The BIS ( Queloz et al. 2001 ) is given by the following: where v t is the average velocity of the bisector between 10% and 40% of the line depth, and v b is the average velocity between 55% and 90%.”

“This test is conducted as spectral indicators that trace distortions in the spectral line profile induced by starspots may correlate with RV measurements (e.g., Queloz et al. 2001; Boisse et al. 2011; Meunier & Lagrange 2013).”

“For these searches, magnetic activity is a noise source that needs to be understood to avoid false-positives (Queloz et al. 2001; Dumusque et al. 2014).”

“These activity-induced signals may lead to masking or mimicking of exoplanet signals (e.g., Queloz et al., 2001; Dumusque et al., 2012; Oshagh et al., 2013; Santos et al., 2014).”

“…velocity period gives a formal semi-amplitude of just 0.000352 ± 0.000076 mag, thus confirming that the periodic radial velocity variations are due to planetary reflex motion and not to intrinsic stellar brightness variations (see, e.g., Queloz et al. 2001; Paulson et al. 2004; Boisse et al. 2012).”

“…six physics-based components derived from established RV theory and split into three difficulty levels (Cumming, 2004; Anglada-Escud´e et al., 2009; Queloz et al., 2001; Haywood et al., 2014): planet multiplicity, SNR, resonant configurations, period coverage, observation count, and correlated…”

“3,4).”

“The spectra were reduced using the standard CORALIE Data Reduction Software (DRS) before being cross-correlated with an A0 stellar mask close to the spectral type of the host star to obtain a cross-correlation function (CCF; e.g. Baranne et al. 1996; Pepe et al. 2002).”

“In order to quantify the extent of the asymmetry, it is useful to evaluate the difference between average values of velocities in regions at the top and at the bottom parts of the line profile (see Figure 5 in [27]), which is defined as the bisector velocity span (BVS [28]).”

“We know that RV signals can be induced by surface inhomogeneities, for example stellar spots [14], so a planet discovery can be confused with a variation due to such”

“…et al. 2023 ) , ( iii ) spots and faculae ( D. Dravins 1982; W. C. Livingston 1982; F. Cavallini et al. 1985; S. H. Saar & R. A. Donahue 1997; D. Queloz et al. 2001; N. Huélamo et al. 2008; A. M. Lagrange et al. 2010; N. Meunier et al. 2010 ) , which can produce RV scatter on the order of ∼…”

“Indicators such as the FWHM of the CCF, the CCF contrast (i.e. depth), and the CCF Bisector Inverse Slope (BIS, Queloz et al. 2001) also provide measures of the amplitude of stellar signals present in a RV measurement.”

“These fluctuations are often quasiperiodic and can both mask and mimic dynamical signals induced by planets (e.g., Queloz et al. 2001a; Boisse et al. 2011; Aigrain et al. 2012; Rajpaul et al. 2015; Haywood et al. 2016; Dumusque 2018).”

“It is clearly possible to distinguish the e ff ects of magnetic activity on spectral lines from center-of-mass motions (Queloz et al. 2001).”

“…have higher levels of stellar activity than older stars ( Lagrange et al. 2013; Gallet & Bouvier 2015 ) , which results in signi fi cant RV variability ( Queloz et al. 2001; Huerta et al. 2008; Luhn et al. 2020 ) and photometric variability ( McQuillan et al. 2012; Biddle et al. 2021 ) , often…”

“We also calculated the deformation spectral line profiles and the flux of the chromospheric Ca II H line cores be- cause line profile deformation and stellar chromospheric activity can both result in RV variations and mimic plan- etary signals (Queloz et al. 2001).”

“Spots of sufficient size to cause a very large such shift will also be apparent photometrically as stellar brightness and color variations with a π/2 phase shift with respect to the radial velocities, as in the case of HD 166435 (Queloz et al. 2001).”

“The phenomena caused by stellar activity can also have similar effects on stellar brightness and radial velocity as orbiting planets, making it at times difficult to distinguish between planets and activity signatures (see, e.g., Queloz et al. 2001).”

“…al. 2013; Rajpaul et al. 2015; Delisle et al. 2018), as well as use alternative forms of the cross-correlation method to correct for activity (e.g., Queloz et al. 2001; Simola et al. 2019), these have had limited success in disentangling it from a true Doppler shift at RV’s below 1 m s−1 (Dumusque…”

“Many quantities have been defined in relation to the bisector, such as the bisector velocity span (Toner and Gray 1988), the curvature of the line bisector (Hatzes 1996), and the bisector inverse slope (Queloz et al. 2001); see Figueira et al. (2013) and references therein for more detail.”

“Because activity-induced surface features such as starspots and faculae produce apparent RV variations, activity can often mask or mimic exoplanet-induced signals (Queloz et al. 2001; Borgniet et al. 2015).”

“In addition, the bisector spans measured on the CCF show no signi fi cant variations nor correlations with the observed radial velocity variations, as it might also be expected in cases of blended eclipsing binaries perturbing the pro fi les of the spectral lines ( D. Queloz et al. 2001 ) .”

“These nuisance effects can obscure or mimic planetary signals (Desidera, S. et al. 2004; Queloz et al. 2001; Desort, M. et al. 2007; Robertson et al. 2014).”