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).”

“Along with each RV calculation, the bisector inverse slope was computed on the stellar cross-correlation function following the procedure described in Queloz et al. (2001).”

“…the photospheric contributions to the radial velocity using diagnostic information such as the line bisector span (“BIS SPAN”; as defined in Queloz et al. 2001) or FWHM of the cross correlation func- tion, or emission in spectral lines that form in the lower chromosphere such as Ca II…”

“Recognising and characterising them is key to disentangle the true planet induced signals (Queloz et al. 2001; Dumusque et al. 2012; Santos et al. 2014; Robertson et al. 2014).”

“Similarly, we computed the bisector velocity span (BVS; Toner & Gray 1988; Queloz et al. 2001) and the full width at half maximum (FWHM) variations of the crosscorrelation function (CCF), from FEROS spectra.”

“Those metrics, derived from the crosscorrelation function (CCF) are the bisector inverse slope (BIS), described fully in Queloz et al. (2001), and the CCF FWHM.”

“…are a number of ways to characterise the bisector shape; herein, we utilise the bisector inverse slope3 (BIS), curvature (C and Calt), bisector velocity displacement (Vb), and bisector amplitude (Ab) – see Figure 6 and Queloz et al. (2001); Povich et al. (2001); Dall et al. (2006) for definitions.”

“Several examples of periodic radial velocity variations in solar-type stars caused by photospheric spots and plages have been documented by Queloz et al. (2001) and Paulson et al. (2004).”

“For instance, Lanza et al. (2018) describe a procedure for deriving a set of CCF asymmetry indicators such as the Bisector Inverse Slope (BIS, e.g. Queloz et al. 2001), the Vasy(mod) (re-adapted from the original definition by Figueira et al. 2013), and the ∆V (Nardetto et al. 2006).”

“This is particularly relevant since planet detection is highly dependent on the stellar activity (Queloz et al. 2001; Martı́nez-Arnáiz 2011; Santerne et al. 2016) and that the effects of metallicity on planet formation and detection is gaining attention in the literature (see e.g. Adibekyan 2019;…”

“The idea is to check for periodic modulation of these proxies, in order to assess whether the observed RV signal is caused by activity rather than by a planet (see Queloz et al. 2001).”

“4), the possibility that stellar activity might have induced the signal is rejected (Queloz et al. 2001).”

“Queloz et al. (2001) pioneered the use of bisectors of CCFs.”

“…stars by detecting the anomalous Doppler shift that results from the line profile distortions during transit (the Rossiter–McLaughlin effect, e.g., Queloz et al. 2001), fully resolving the line profile distortions leads to a measurement of this angle that is both significantly more precise and…”

“An apparent radial-velocity orbit can be induced by a genuine planet, spots rotating on the stellar surface (Queloz et al. 2001), or a blended stellar binary (Mandushev et al. 2005).”

“…computed with the above model can be regarded as a cross-correlation function (hereafter CCF) obtained by cross-correlating the whole stellar spectrum with a line mask consisting of Dirac delta functions giving the rest wavelength and depth of each individual line (e.g., Queloz et al. 2001).”

“The analysis of the line profile (in the following bisector) is routinely applied in the search for extrasolar planets when the RV technique is used in order to identify if the observed periodic RV variations are caused by stellar activity or due toa companion (e.g. Queloz et al. 2001).”

“Such variations have been shown to be a robust tracer of line asymmetries that can impact stellar radial-velocity measurements (Queloz et al. 2001; Henry et al. 2002).”

“Even so, we checked the stability of the line bisectors using the method presented in Queloz et al. (2001).”

“The recent results of Queloz et al. (2001) for HD166435, in particular, provide a valuable cautionary tale.”

“We exploit the fact that stellar noise can be correlated with the bisector span (Queloz et al. 2001), the full width at half maximum (FWHM) and the logR′HK .”

“HD 166435 is a prime example; its radial velocity variations were shown to be stellar in nature, explaining the apparent orbital period equalling the stellar rotation period (Queloz et al. 2001).”

“For each case we verified the correlation between the RVs and the bisector span of the CCF (calculated following Queloz et al. 2001) or with the full width at half maximum (FWHM) of the CCF. YBP401.”

“Stellar activity is one of the main limitations to the detection of low-mass and/or long-period planets using the radial-velocity method (e.g. Saar & Donahue 1997; Santos et al. 2000; Queloz et al. 2001; Boisse et al. 2009, 2011; Dumusque et al. 2011b; Lovis et al. 2011; Gomes da Silva et al. 2012).”

“Thus there is no evidence in the TRES spectra that the RV variations are due to phenomena other than orbital motion, such as an unresolved blend with a faint eclipsing binary or spots coupled with stellar rotation (Queloz et al. 2001).”

“Following the method outlined in Queloz et al. (2001), we performed an analysis of the Sandiford and FIES CCF bisector spans to exclude the presence of periodic distortions in thespectral line profile that might be caused either by stellar magnetic activity (i.e., photospheric spots and plages), or…”

“Photometry and line bisector analysis, which are efficient stellar activity indicators, have been routinely used to verify the authenticity of planet detections by means of the RV method (e.g. Queloz et al. 2001).”

“…in the line profiles arising from contamination of the spectrum by the presence of a binary with a period of 3.92days, we would expect the BSs (which measure line asymmetry) to vary with this period, resulting in a correlation between BS and RV (see, e.g., Queloz et al. 2001; Torres et al. 2005).”

“Observations with an accuracy of a few m s−1 are obtained regularly (see e.g. Marcy & Butler (2000), Queloz et al. (2001b)) and detections of amplitudes of 1 m s−1 are nowadays possible with e.g. HARPS (Pepe et al. 2003).”

“Following the formulation of Bouchy, Pepe &Queloz (2001) for line shifts that are small compared to the line width, we measure Doppler shifts using a first-order Taylor-series approximation to the instantaneous CCF profile shape at the time 𝑡 𝑗 of the 𝑗 th observation.”

“In Queloz et al. (2001), the authors used this technique to demonstrate that a 3.8 day period, 83 m s−1 signal on HD 166435 was in fact activity related and not a large planetary companion.”

“The lack of significant correlation between the CCF bisector spans and the RVs indicates that most likely the Doppler shifts observed in KOI-183 are induced by the orbital motion of the companion rather than stellar activity or a blended eclipsing binary (see, e.g., Queloz et al. 2001).”

“RV noise, or “jitter”, is a particularly pernicious problem that has resulted in false detections (Queloz et al. 2001) and complicated the confirmation of transiting planets (Bakos et al. 2010; Hartman et al. 2011).”

“For each case we verified the correlation between the RVs and the bisector span of the CCF (calculated following Queloz et al. 2001) or with the FWHM of the CCF.”

“To ensure that the radial velocity signal originates from a planet orbiting NGTS-4, we analysed the HARPS cross-correlation functions (CCF) using the line bisector technique of Queloz et al. (2001).”

“For each star, the bisector spans (BSs; Queloz et al. 2001) of the cross-correlation functions (CCF) have standard deviations close to their average errors (122 versus 80 ms−1, 116 versus 125 ms−1, and 87 versus 97 ms−1 for WASP-161, WASP-163, and WASP-170 respectively).”

“This apparent Doppler shift can easily mimic a Keplerian orbit (e.g., Queloz et al. 2001; Bonfils et al. 2007).”

“As such, it is mandatory to track and characterize activity signals in order to disentangle the real exoplanet RV signal (e.g., Hatzes 2013a,b; Queloz et al. 2001; Santos et al. 2014; Robertson et al. 2014; Suárez Mascareño et al.”

“Spectral line bisectors have become a common tool to ensure that RV variations attributed to orbital motion are not in fact due to intrinsic stellar variations (Hatzes et al. 1998; Queloz et al. 2001).”

“The SOPHIE pipeline also measures the FWHM of the CCF and its bisector velocity span (Queloz et al. 2001).”

“126–128).”

“These can be large enough to mask or imitate planetary companions (Queloz et al. 2001; Isaacson & Fischer 2010; Dumusque et al. 2012; Hatzes 2013; Robertson et al. 2013) with the largest impact on the detection of low mass planets.”

“…1 and 2 and we highlight the RM effects in Figure 3 For each star, we tested the hypothesis that the RV variations are due to spectral-line distortions caused by a blended eclipsing binary or starspots by performing a line-bisector analysis of the cross-correlation functions (Queloz et al. 2001).”

“The method was used subsequently by Queloz et al. (2001) to look for a correlation between the slope of the bisectors of the spectrum’s cross-correlation function (CCF) and the measured radial velocity of the star.”

“Equivalently, the bisector velocity span method can be applied to the cross-correlation function used for the RV computation (Queloz et al. 2001).”

“These include various CCF bisector asymmetry measurements (e.g., Queloz et al. 2001; Povich et al. 2001) or the FWHM of the CCF (e.g., Queloz et al. 2009).”

“HD 1397 was observed with the high resolution spectrograph CORALIE on the Swiss 1.2 m Euler telescope at La Silla Observatory (Queloz et al. 2001a) between 2018 Sep 8 and 2018 Dec 20.”

“We measure line bisector spans to check for variations from background blends (Mandushev et al. 2005) or star spots (Queloz et al. 2001).”

“Bisector span is also a key CCF diagnostics which is very sensitive to stellar activity and additional blended stellar component (Queloz et al. 2001; Bouchy et al. 2009b, Santerne et al., in prep.).”

“Queloz et al. (2001) ruled out a planet around HD 166435 in part using the rotational modulation of the magnetic activity indicator S.”

“These observations help to determine if the radial velocity variations are caused by intrinsic stellar activity (Queloz et al. 2001) or by stellar reflex motion caused by the presence of an orbiting companion.”

“Queloz et al. (2001) and Paulson et al. (2004) have presented several examples of periodic RV variations in solar-type stars caused by photospheric spots and plages.”

“They provide good diagnostics for stellar activity (e.g. Queloz et al. 2001; Huélamo et al. 2008).”

“Knowledge of the stellar rotation period helps to disentangle spurious RV signals arising from rotation and true RV signals due to orbital motion (e.g., Queloz et al. 2001; Cloutier et al. 2017).”

“9 A correlation can be explained by a bes or a hts but also by stellar activity (e.g. Queloz et al. 2001).”

“The HARPS DRS provides the full width at half maximum (FWHM) and the bisector span of the cross-correlation function (Queloz et al. 2001), which are both useful probes of stellar Table 2.”

“The bisector velocity span was calculated using the method described by Queloz et al. (2001).”

“Queloz et al. (2001) examined the photometrically variable and magnetically active star HD 166435, which had displayed low-amplitude RV variations with a period of just under 4 days, implying a close-in planetary com- panion.”

“…with radial velocity timeseries data, indicating that a given frequency detected in the velocities is not due to a genuine Doppler motion, but originates from the star itself, from processes that induce line asymmetries in the optical spectra of stars (e.g. Queloz et al. 2001; Santos et al. 2010).”

“To test the hypothesis that the RV variations are due to spectral line distortions caused by a blended eclipsing binary or starspots, we performed a line-bisector analysis (Queloz et al. 2001) of the CORALIE cross-correlation functions.”

“We also determined the variations in the bisector span (following Queloz et al. 2001) as function of both radial velocity and orbital phase, which are shown in Fig.”

“Moreover, the analysis of the bisector shape of the cross-correlation function (see Queloz et al. 2001) shows no variations in the CCF profile down to the photon noise level, giving strong support to the planetary interpretation of the RV variations.”

“This can be achieved through different indicators, such as the bisectors of the spectral cross-correlation function (Queloz et al. 2001), Hα (Bonfils et al. 2007; Robertson et al. 2014) and log R′HK (Noyes et al. 1984; Delisle et al. 2018).”

“Stellar activity and light blending We check if any observed RV signal could be caused by stellar activity, by calculating the bisectors (BIS) as defined by Queloz et al. (2001) for the HARPS and FIES observations.”

“In order to test whether the observed Doppler signal could be associated with stellar activity, we plotted the measured Doppler shifts against the bisector span (BIS, defined by Queloz et al. 2001) derived from the cross-correlation functions of the obtained HARPS spectra.”

“Temperature contrast spots and/or magnetic spots are known to show correlation with spurious Doppler signals (e.g. Queloz et al., 2001; Reiners et al., 2013).”

“For example, Queloz et al. (2001) measured velocity variations in HD 165435 with an amplitude of 80 m s−1 that correlated with photometric variability.”

“…corresponding bisection velocities: the velocity span Vsp = v75 − v30, velocity displacement Vdis = (v30 + v60 + v75)/3 − Vccf , where Vccf is the velocity measured by our Gaussian fit and the bisector inverse slope BIS = (v20+v30)/2− (v60 + v75)/2 (see e.g. Povich et al. 2001; Queloz et al. 2001).”

“Further such correlation between radial velocity rms and photometric variability was found by Queloz et al. (2001) who observed a vr amplitude of ∼ 180 m/s for HD 166435 (age 200 Myr), a star without a planet.”

“Conclusion Our BEBOP radial velocity survey for circumbinary planets has started by using the CORALIE spectrograph.”

“…which causes different radial velocity variations at different timescales and of different magnitude (see e.g. Saar et al. 1998; Santos et al. 2000; Queloz et al. 2001; Boisse et al. 2011; Dumusque et al. 2011; Robertson et al. 2014; Rajpaul et al. 2015; Su´arez Mascare˜no et al. 2017c; Dumusque…”

“In order to rule out non-planetary causes for the radial-velocity variation, such as a blended eclipsing binary system, we examined the bisector spans (e.g. Queloz et al. 2001), which exhibit no correlation with radial velocity (Figure.”

“This type of study can be carried out by considering variations of line bisectors, that may be thought of as direct measure of activity jitter (Queloz et al. 2001) through the evidence of variations of the asymmetries which appear in spectral lines.”

“This result, at its most basic level, is unsurprising; rapidly rotating dwarfs of all spectral types are known to exhibit activity-induced RV signals (e.g., Queloz et al. 2001; Haywood et al. 2014; Zechmeister et al. 2018).”

“The bisector velocity span (BVS; Queloz et al. 2001) versus RV diagram shows a vertical spread on the 2018 observations and our last epoch shows sinusoidal variations over one hour (see Fig.”

“The combination of surface inhomogeneities and stellar rotation easily mimic those of planetary origin (Queloz et al. 2001; Bonfils et al. 2007; Boisse et al. 2011; Robertson et al. 2014; Howard et al. 2014; Suárez Mascareño et al. 2015; Newton et al. 2016; Vanderburg et al. 2016; Suárez Mascareño…”

“…instrument, errors in the analysis, and velocities in the stellar photosphere from spots, faculae, granulation, p-mode oscillations, or meridional flows (e.g., Saar & Fischer 2000; Santos et al. 2000; Queloz et al. 2001; Wright 2005; Lagrange et al. 2010; Meunier et al. 2010; Borgniet et al. 2015).”

“Following Torres et al. (2007), we explored the possibility that the measured radial velocities are not real, but are instead caused by distortions in the spectral line profiles due to contamination from a nearby unresolved eclipsing binary (Queloz et al. 2001).”

“While the astrometric effects cannot yet be tested observationally, it is possible to correlate the photometricand radial-velocity variations for some stars (Queloz et al. 2001; Henry et al. 2002).”

“Queloz et al. (2001) and Paulson et al. (2004) have shown that photospheric features such as spots and plages on solar-type stars can result in low-amplitude, periodic RV variations capable of mimicking the presence of a planetary companion.”

“Moreover, the bisector spans (BIS) and full-width-athalf-maximum (FWHM) of each CCF are computed following Queloz et al. (2001).”

“The amplitude would be similar to that of the velocities (Queloz et al. 2001; Mandushev et al. 2005).”

“To discard any false-positive scenarios that could create RV variations that mimic planetary signatures, we checked the CORALIE cross-correlation functions (CCF) bisector spans, according to the technique described by Queloz et al. (2001).”

“Queloz et al. (2001) and Paulson et al. (2004) have demonstrated how rotational modulation of starspots on active stars can result in periodic radial velocity variations that mimic the presence of a planetary companion.”

“To exclude the possibility that this signal was caused by stellar activity, span bisector analysis was performed (Queloz et al. 2001) using the coralie data.”

“To understand if the periodic radial-velocity signal observed could have a non-planetary origin (see e.g. Saar & Donahue 1997; Queloz et al. 2000; Santos et al. 2002, 2009), we also analyzed the bisector inverse slope (BIS) 2 Tables 3, 4, and 5, with the HARPS radial-velocities for HD5388, HD181720, and HD190984, resp…”

“One contributing factor is the expected time lag between RVs and other indicators, noted in the case of RV and photometry (Queloz et al. 2001, Santos et al. 2003, Queloz et al. 2009) and other indicators (Suárez Mascareño et al. 2017).”

“(e.g., Queloz et al. 2001a), and the Hα, log( ¢RHK), Na II, and He I activity indices, which trace chromospheric activity.”

“A stellar spectrograph measures the integrated output from the stellar surface, and stars with rapidly moving features in their photospheres exhibit jitter, creating variation in their apparent Doppler velocities (e.g. Queloz et al. 2001).”