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).”

“For example, Queloz et al. (2001) used an anti-correlation between the BIS and the observed radial velocity to show that spots can cause a periodic signal in the apparent radial velocity.”

“Échelle spectrograph installed on the 1.2 m Leonard Euler telescope at the ESO La Silla Observatory (Queloz et al. 2001).”

“The three systems were also monitored with the FEROS spectrograph (Kaufer & Pasquini 1998) mounted on the MPG 2.2m telescope installed at La Silla Observatory.”

“Also given in Table 3 are the bisector span (BS) measurements that characterise the asymmetry in the stellar line profiles for each spectrum (Queloz et al. 2001).”

“A variety of phenomena including stellar activity and stellar pulsation can induce signals in the RVs (e.g. Queloz et al. 2001; Robertson et al. 2014).”

“Despite the fact that the precision of this technique is seriously affected by stellar activity (Queloz et al. 2001) which is particularly true in the case of giant stars (Carney et al. 2003; Setiawan et al. 2004), it remains most efficient in searches for planets around A-F stars with masses as…”

“(see e.g. Queloz et al. 2001; Lovis et al. 2011).”

“We used a line-bisector analysis to look for asymmetries in the spectral line profiles, as could be caused by contamination from an unresolved eclipsing binary (Queloz et al. 2001; Mandushev et al. 2005).”

“We considered the CCF width (FWHM), the bisector span (Queloz et al. 2001, BIS), and its contrast.”

“Another analysis can be done by examining the asymmetry of the line profile, via investigating whether there is a correlation between the CCF bisector inverse slopes (BISs) and the RVs (e.g. Queloz et al. 2001).”

“…starspots on the measure of planetary masses through radial velocity is another active area of investigation (e.g. Saar & Donahue 1997; Hatzes 1999; Queloz et al. 2001; Melo et al. 2007; Desort et al. 2007; Boisse et al. 2011, 2012; Robertson & Mahadevan 2014; Dumusque et al. 2017; Feng et al.…”

“It has been repeatedly shown that stellar activity can be a nuisance both by introducing signals that can be mistaken for that of a planet and by contributing to the noise as a stochastic process (e.g., Queloz et al. 2001; Huélamo et al. 2008; Figueira et al. 2010a).”

“Stellar rotational modulations of surface features can create variablesymmetries in the spectral line profiles (Queloz et al. 2001), and in particular, the variations in the shapes of the spectral line may cause the RV variations.”

“An analysis of the line-bisector spans shows no significant correlation with radial velocity (Figure 3), as would be expcted if the observed radial velocity variations were due to a diluted eclipsing binary or chromospheric activity (Queloz et al. 2001).”

“The signals induced by the stellar rotation can easily mimic those of planetary origin (Queloz et al. 2001; Bonfils et al. 2007; Boisse et al. 2011; Robertson et al. 2014; Suárez Mascareño et al. 2015, 2017a,b; Newton et al. 2016; Vanderburg et al. 2016).”

“The activity-induced RV shift is maximized when the active region is closer to the limb, ∼1/8 phase from center (e.g. Queloz et al. 2001; Aigrain et al. 2012).”

“Rotational modulation of spots or activity cycle of stars cause apparent variations in stellar radial velocities, which can masquerade as a planetary signal (e.g., Queloz et al. 2001).”

“No significant correlation is found between the observed radial-velocity and the shape of the CCF denoted by a measurement of the Bisector Inverse Slope, BIS (defined as in Queloz et al. 2001).”

“The method and its application are described in Queloz et al. (2001).”

“Specifically, the bisector span (BIS) can serve as a diagnostic to search for possible false positive scenarios (e.g., Queloz et al. 2001).”

“(e.g., Saar et al. 1998; Dumusque et al. 2011a,b; Queloz et al. 2001; Santos et al. 2002, 2010, 2014; Boisse et al. 2011a; Díaz et al. 2016).”

“Line bisector analysis is another diagnostic tool to investigate the possible impact of stellar activity on RV measurements (Toner & Gray 1988; Queloz et al. 2001; Wright et al. 2013).”

“Line Bisector Variations Another means of testing for the planetary nature is to search for variations in the shapes of the spectral lines with the spectral line bisector (Hatzes, Cochran, & Johns-Krull 1997; Hatzes, Cochran, & Bakker 1998; Queloz et al. 2001).”

“This is in addition to the fact that stellar signals can masquerade as planetary signals (e.g. Queloz et al. 2001; Desidera et al. 2004; Huélamo et al. 2008; Figueira et al. 2010; Santos et al. 2014; Robertson et al. 2015).”

“In order to rule out the possibility that either system is a blended eclipsing binary, or that the RV variation is a result of stellar activity, we examined the bisector spans (e.g. Queloz et al. 2001).”

“In order to rule out the system as a blended eclipsing binary, we examined the bisector spans (BS) (e.g. Queloz et al. 2001), which exhibit no significant correlation with radial velocity (Figure 2, lower panel), as expected for a true planetary system.”

“This supports each signal’s originas being planetary, rather than due to a blended eclipsing binary system, or to stellar activity (see Queloz et al. 2001).”

“This hypothesis may be interrogated by examining the spectral line profiles for contamination from a nearby unresolved eclipsing binary (Queloz et al. 2001; Torres et al. 2007).”

“Following Torres et al. (2007) and Queloz et al. (2001), we conducted a bisector span analysis as described in §5 of Bakos et al. (2007) of the Keck and FIES spectra to rule out the possibility that the objects are eclipsing binary star systems blended with light from a third star rather than a…”

“…function (CCF) and RV is a powerful method to determine whether the RV variation may be due to stellar activity or a planetary companion (Queloz et al. 2001, Martı́nez- 1 10 100 1000 Period(days) 0 10 20 30 40 50 P ow er 7.78 days 0.35% FAP 1% FAP 5% FAP 0 10 20 30 40 50…”

“Contamination from an unresolved eclipsing binary will cause asymmetries in the spectral line profiles and line bisector span variations (Queloz et al. 2001; Torres et al. 2005).”

“Due to the time-evolving and sometimes periodic nature of these features, they have been mistaken for planets on several occasions (e.g. Setiawan et al. 2008; Huélamo et al. 2008; Queloz et al. 2001) and can severely complicate the interpretation of RV measurements.”

“In the context of exoplanet detection with radial velocity time series, stellar variability could induce signals that mimic planetary signatures (e.g., Queloz et al. 2001).”

“[90] found measurements of the bisector shape [96–98] varied linearly with the induced RV, see Figure 10, and that removing this correlation could reduce the RV rms by ∼50% or more; note, if dividing the bisector into two or three segments (as done in the bisector span and bisector curvature) these ranges had to be fi…”

“In numerous cases, both large and small planet candidates have been challenged as being due to the effects of stellar activity (e.g., HD 166435 Queloz et al. 2001; HIP 13044, Jones & Jenkins 2014; HD 41248, Santos et al. 2014; GJ 581 d, Robertson et al. 2014; Kapteyn b Robertson et al. 2015; α Cen…”

“For instance, Queloz et al. (2001) and Santos et al. (2003) were the first ones to pinpoint the presence of a phase shift between photometry and RV signal.”

“Coralie’s dedicated data reduction pipeline performs bias correction, flatfielding, and cosmic ray removal.”

“Stellar rotational modulations by inhomogeneous surface features can create variable asymmetries in the spectral line profiles (Queloz et al. 2001).”

“It is well known that RV datasets can contain periodic signals resulting from stellar activity rather than planets, which can affect the conclusions we draw about exoplanet systems (e.g. Queloz et al. 2001; Bonfils et al. 2007; Robertson et al. 2014).”

“…barycentric Julian date (BJDUTC−2 450 000.0), the stellar radial velocity (RV) measurements (km s−1), the RV uncertainties (km s−1), and the line bisector span measurements (Vspan; km s−1) as defined by Toner & Gray (1988) and applied to the crosscorrelation function as per Queloz et al. (2001).”

“RV signals containing amplitudes compatible with substellar companions are not necessarily planets or BDs; the RV signal might be mimicked by stellar activity (e.g. Queloz et al. 2001).”

“The BIS values and the FWHMs are taken directly from the HARPS-DRS output and details of their origin and usefulness can be found in Queloz et al. (2001) and Santos et al. (2010).”

“Stellar surface inhomogeneities can hamper the detection, and sometimes even mimic the signal, of exoplanets(e.g., Queloz et al. 2001), and seriously complicate the characterization of their properties.”

“It is already known that of poor understanding of the noise-generating physics may produce misleading results (Queloz et al., 2001), although this is also true for the means the data analysis.”

“Thus the observed variations in radial velocity are not induced by stellar activity and rotation (as is the case of HD 166435 in Queloz et al. 2001).”

“…velocity v sin i should be avoided, as they constitute sources of intrinsic radial velocity “jitter” that can mask, and sometimes even mimic, the presence of orbital reflex motion due to planetary mass companions (Saar et al. 1998; Santos et al. 2000; Queloz et al. 2001; Paulson et al. 2004).”

“To quantify the asymmetry in the CCF, we used the standard bisector inverse slope as defined in Queloz et al. (2001).”

“In order to check RV variation induced by a blended spectrum, we computed the bisector inverse slope (BIS) of the cross-correlation function for each observation in the manner of Queloz et al. (2001).”

“N DRS (the method is provided in Lovis et al. 2011) also available on YABI, and the BIS (see e.g. Queloz et al. 2001) estimated as in Lanza et al. (submitted), starting from the computed CCF of the DRS.”

“The cross-correlation function (CCF) FWHM and bisector span (BS, Queloz et al. 2001) values are also given in Table 2.”

“A correlation between the bisector spans and RV is indicative of a blended eclipsing binary system, or of RV variation as a result of stellar activity (Queloz et al. 2001).”

“Figure 8 shows the clear anti-correlation between the bisector spans and the radial velocity residuals after the Keplerian fit, which is the typ- ical signature of variations induced by stellar activity (Queloz et al. 2001; Boisse et al. 2009).”

“Similar RV-correlated behavior is seen for other activity indicators including the bisector inverse slope (BIS), FWHM, Vspan, and the biGaussian fit differential (as defined by Queloz et al. 2001; Boisse et al. 2011; Figueira et al. 2013).”

“In particular, the bisector analysis (BIS, Queloz et al. 2001) provides a Pearson’s correlation coefficient of 0.007, thus showing no correlation of the RV with the line profile indicator.”

“…the discovery of the lowest-mass planets is that below RV amplitudes of ∼ 5 m s−1, stellar activity will cause velocity shifts that may imitate or distort the signal of an exoplanet (Queloz et al. 2001; Huélamo et al. 2008; Dumusque et al. 2012; Robertson et al. 2013b; Santos et al. 2014).”

“…can lead to stellar activity signals masking or mimicking planets; a problem arising for not only low-mass, low-amplitude planets, but also even higher mass planets such as hot Jupiters (e.g Queloz et al. 2001; Desidera et al. 2004; Huélamo et al. 2008; Huerta et al. 2008; Figueira et al. 2010).”

“Fast rotation broadens the spectral lines, preventing us from computing precision RV variations, whereas stellar activity and spots produce spectral line assymmetries, which might mimic the doppler shift induced by a substellar companion (e.g. Queloz et al. 2001; Huelamo et al. 2008).”

“9, the RVs related to observations performed in late 2010 and in the second half of 2011 are consistent, showing no significant long-term trends in our measurements.”

“As was mentioned earlier, Sartoretti and Schneider (1999) devised the TTV method for detecting moons, although it was not called TTV at the time.”

“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).”

“While this is a useful approximation in the case of the Rossiter–McLaughlin effect, in general, the confusion of these two spectral changes is a major cause of correlated noise in RVtime series (e.g., Queloz et al. 2001).”

“The CCF bisector, in particular the BIS, has been proven to be a powerful tool to detect star spots (Queloz et al. 2001) and background binaries (Santos et al. 2002) that can mimic planetlike signals in RV data.”

“The most widely used activity indicators in these works were variations in the average absorption-line shape, measured via the different moments of the cross-correlation function (CCF, e.g., Queloz et al. 2001), and variations of chromospheric emission lines, such as Ca iiH&K and Hα.”

“A common technique for detecting line profile variations involves measurements of line bisector spans (e.g., see Queloz et al. 2001; Torres et al. 2007).”

“An anticorrelation between the bisector and the radial velocity is usually the signature of radial velocity variations induced by stellar activity (see, e.g., Queloz et al. 2001, Boisse et al. 2009a).”

“…for which intrinsic velocity jitter caused by surface inhomogeneities (e.g., spots, convection) not only degrades the achievable measurement precision, but, when correlated with the stellar rotation period, can even mimic the signal produce by an orbiting companion (e.g., Queloz et al. 2001).”

“These astrophysical phenomena manifest themselves in both photometric and RV variability studies, making exoplanet detection around young stars extremely challenging (Queloz et al. 2001; Bouvier et al. 2007; Robertson et al. 2014).”

“Not only does it introduce noise, but also coherent signals that can mimic those of planetary origin (Queloz et al. 2001; Bonfils et al. 2007; Robertson et al. 2014).”

“Examples abound for systems in which activity-induced RV contributions have obscured (Howard et al. 2013; Pepe et al. 2013; Haywood et al. 2014) or mimicked (Queloz et al. 2001; Santos et al. 2014; Robertson et al. 2014; Johnson et al. 2016) the signals of exoplanets.”

“One promising explanation could be rotational modulation (see e.g. Queloz et al. 2001; Prato et al. 2008; Müller et al. 2011).”

“1Email: jjenkins@das.uchile.cl A radial velocity analysis of the star HD166435 by Queloz et al. (2001) found a repeating short period signal of less than 4 days, suggesting the presence of a planetary companion to the star.”

“Several measures have been used to quantify the shape of bisectors; we employ the bisector inverse slope (BIS), defined as the difference of average velocities between 10%–40% and 55%–85% of the total CCF depth (Queloz et al. 2001).”

“Also, the apparent correlation between logR′HK and the radial velocity jitter is different from the picture seen in the cases of the active stars HD 166435 (Queloz et al. 2001), GJ 674 (Bonfils et al. 2007) or HD 189733 (Boisse et al. 2009).”

“The basic tools to study the origin of radial velocity variations derived from stellar spectra are the analysis of shapes of the spectral lines using the bisector velocity span (Queloz et al. 2001; Hatzes 1996) and of the CaII H&K emission lines.”

“A stellar eclipsing binary that is unresolved from a bright source would manifest itself as a blended system with shallow photometric transits, and with RV variations that are of the same order of magnitude as one can expect from a planetary system (e.g., Queloz et al. 2001).”

“We also plot the bisector spans against phase, where the absence of a correlation is a check against transit mimics (e.g. Queloz et al. 2001).”

“The bisector span was calculated using a modified version of the standard approach from Queloz et al. (2001), where we disregarded the bottom 20 % of the peak of the cross-correlation function (CCF), while averaging over a greater span.”

“The spectral line-profile variations caused by starspots have been confused with a radial velocity signal originating from exoplanets (e.g., Queloz et al. 2001; Huerta et al. 2008) and the sudden brightenings caused by stellar flares can ⋆ E-mail: heidi.h.korhonen@utu.fi mimic microlensing events…”

“Queloz et al. (2001) and Paulson et al. (2004) have documented several examples of solar-type stars whose periodic RV variations were caused by stellar activity.”

“This rules out the possibility that the 38.14-day radial velocity variations in GJ 687 are induced by stellar activity, as has been documented in somewhat more active stars, for instance, by Queloz et al. (2001), Paulson et al. (2004), and Boisse et al. (2012).”

“We checked whether the BVSs correlate with the RV, which is expected if the RV variations are caused by rotational modulation due to starspots (e.g., Queloz et al. 2001).”

“3 indicates that it is highly improbable that the RV variations are due to an unresolved eclipsing binary or chromospheric activity (Queloz et al. 2001).”

“We also calculate the bisector inverse slope (BIS, Queloz et al. 2001), which measures the asymmetry of the CCF.”

“In order to check radial velocity variation induced by a blended spectrum, we computed the bisector slope of the cross-correlation function for each observation in the manner described in (Queloz et al. 2001).”

“The bisector spans as defined by Toner & Gray (1988) were measured, and applied to the crosscorrelation function as in Queloz et al. (2001).”