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).”

“The lack of a significant correlation between the CCF bisector spans and the RVs indicates that the Doppler shifts observed in Kepler-432 are most likely induced by the orbital motion of a planet and not by a blended eclipsing binary or stellar activity (see, e.g., Queloz et al. 2001).”

“The impact of star spots on high precision RV surveys on rotational timescales is well documented by several observation l detections collected in the past years (see e.g. Queloz et al. 2001 and Paulson et al. 2004).”

“The bisector span values were calculated as described in Queloz et al. (2001).”

“This very low limit to brightness variability in HD 168443 on the 58 day orbital period indicates that rotational modulation of starspots is not the cause of the RV variations (see, e.g., Queloz et al. 2001).”

“The radial velocity measurements show low-amplitude variations, compatible with the existence of orbiting planets, and are not correlated with the bisector spans (available for CORALIE and SOPHIE data) (Queloz et al. 2001), which rules out stellar blend configurations.”

“Another common diagnostic of stellar activity—a linear regression of RV onto an activity indicator (e.g., Queloz et al. 2001; Huélamo et al. 2008; Queloz et al. 2009; Tal-Or et al. 2018)—fails when the RV and activity signals are not in phase, as seen in the RV, S-index, and Hα-index measurements…”

“Therefore, we also explored any possible correlation between the RV and several line-profile indicators such as FWHM, Bisector Inverse Slope (BIS, Queloz et al. 2001), Vspan (Boisse et al. 2011), biGauss (Nardetto et al. 2006) and Vasy, BIS+ and BIS- (Figueira et al. 2013) by using the python code…”

“Photometric variability on the timescale of the orbital period may indicate that the RV fluctuations are the result of rotational modulation of star spots (Queloz et al. 2001).”

“For this we calculate the BIS as defined by Queloz et al. (2001) from the HARPS and HARPS-N CCFs and searched for a correlation with the measured RVs.”

“A negative correlation between the bisector spans and the radial velocities usually indicates that the distortion of stellar lines due to spot activity produces radial-velocity jitter (Queloz et al. 2001; Boisse et al. 2012), and the planet interpretation may be compromised.”

“In the end, unlike other planet-like RV signals that were caused by stellar activity (Queloz et al. 2001; Desidera et al. 2004; Paulson et al. 2004), HD 192263b made a convincing comeback in Santos et al. (2003).”

“However, other effects can cause stellar wobble thus it is important to study these in order to avoid erroneous new planet announcements, as it already happened in the past (Queloz et al. 2001; Santos et al. 2002).”

“To exclude the possibility that the RV signal originates from spectral line distortions caused by a blended eclipsing binary, we analyzed the CORALIE cross-correlation functions using the line-bisector technique described in Queloz et al. (2001).”

“This confirms to very high precision the lack of stellar activity that might otherwise mimic periodic radial velocity variations in HD 114762 (see, e.g., Queloz et al. (2001); Paulson et al. (2004); Bonfils et al. (2007); Forveille et al. (2009)).”

“An anti-correlation between the RV and the BISis a signature of activity-induced RV variations.”

“2) and the lack of any correlation between this variation and the bisector span establish the presence of a planetary mass companion to this star (Queloz et al. 2001).”

“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).”

“…the spectra using the CERES pipeline ( Brahm et al. 2017a ) , which provides both RVs and several activity indicators: the CCF bisector ( BIS; e.g., Queloz et al. 2001a ) , and the H α ( Boisse et al. 2009 ) , log ( ¢ R HK ) ( Duncan et al. 1991; Noyes et al. 1984 ) , Na II , and He I ( Gomes da…”

“Stellar activity is also known to produce variations in the BVS over the timescale of the rotational period of the star (see e.g. Boisse et al. 2011b) and also throughout stellar activity cycles (see e.g. Díaz et al. 2016).”

“̧ The bisector span, a reliable activity indicator, was measured using the cross-correlation profile (see method in Queloz et al. (2001)), and its errors were estimated to be twice the RV errors.”

“This rules out the possibility that the 14.3-day radial velocity variations are simply jitter induced by stellar activity, as has been documented in slightly more active stars, for instance, by Queloz et al. (2001), Paulson et al. (2004), and Boisse et al. (2012).”

“The literature provides many examples and techniques used to pinpoint these signals (e.g. Queloz et al. 2001; Santos et al. 2002; Melo et al. 2007; Huélamo et al. 2008; Figueira et al. 2010) or to average them out (Dumusque et al. 2011b,a).”

“There are numerous examples of this occurring in the lierature, e.g. HD 166435, HD 219542, TW Hya, LkCa19 and BD +20 1790 (Queloz et al. 2001; Desidera et al. 2004; Huélamo et al. 2008; Huerta et al. 2008; Figueira et al. 2010).”

“Additionally, the bisector velocity span of the CCF is computed in the way described by Queloz et al. (2001) for further analysis, as well as the radial velocity computed considering only the blue or red halves of each spectral order, which we call RVblue, and RVred, respectively (see §3.4.1).”

“It was shown by Queloz et al. (2001) that the Bisector Inverse Slope (BIS) ofthe CCF is a good qualitative measure of the distortion of the spectral lines caused by activity, and we have calculated the BISfor all CCFs following the procedure of Dall et al. (2006).”

“4), a clear indication that the radial velocity oscillation is not due to dark spots moving across the star’s surface or other stellar activity (Queloz et al. 2001).”

“To directly search for the presence of distortions of line profiles (ideally on the same spectra on which RVs are derived), as done by e.g. Hatzes et al. (1998) for 51 Peg and Queloz et al. (2001) for HD 166435 2.”

“We reduced the spectra using the HARPS online data reduction software (DRS; Bouchy, Pepe & Queloz 2001).”

“The resulting quantity (the bisector inverse slope, BIS) can be used to measure the line bisector variations (Queloz et al. 2001).”

“For example, the bisector of the cross correlation function (CCF) can show a correlation with RV measure- ments for a spotted star (Queloz et al. 2001); emission in the core of the Ca II H & K lines is an indicator of magnetic activity (Saar et al. 1998); and the full width half maximum of the CCF…”

“Because stellar activity can cause apparent RV shifts which may obscure (Dumusque et al. 2012) or imitate (Queloz et al. 2001) a Keplerian planet signal, it is essential to consider activity indicators when analyzing RV data.”

“Notable examples of this are TW Hydrae (Setiawan et al. 2008, Huélamo et al. 2008), BD+20 1790 (Hernán-Obispo et al. 2010, Figueira et al. 2010) and HD166435 (Queloz et al. 2001).”

“When the starspot pattern is long-lived, variations in line asymmetry are modulated by the rotational period of the star and can mimic a planetary signal (e.g. Queloz et al. 2001; Bonfils et al. 2007).”

“These variations could either be induced by a background blended binary (Queloz et al. 2001) or by stellar photometric activity (Santos et al. 2002).”

“To investigate whether this variation may be due to a low-mass companion, we measured the line bisectors using the procedure of Queloz et al. (2001).”

“A well known example is HD 166435 (Queloz et al. 2001).”

“As expected due to the short time coverage of the HARPS spectra, we did not see any correlation between the bisector inverse slope (as defined in Queloz et al. 2001) and the radial velocities of HIP 67620.”

“Following Toner & Gray (1988) and Queloz et al. (2001), we define the CCF BIS as the difference between the average velocities in two different regions of the bisector, one at the top and one close to the bottom.”

“Spectral line bisectors (see e.g. Gray 1983; Hatzes et al. 1998; Povich et al. 2001; Gray 2005) and that of CCFs (Queloz et al. 2001; Dall et al. 2006; Baştürk et al. 2011) are both well-recognised means to assess if a star’s surface dynamics and irregular features can significantly influence RVs,…”

“In particular, the typical lifetime of a spot is ∼2 weeks for the Sun, but other stars have both shorter and longer lifetimes, up to several months in some cases (Queloz et al. 2001).”

“Line bisector variations showed that surface features were the cause of the RV variations in the mainsequence star HD 166435 (Queloz et al. 2001) and the K giant HD 78647 (Setiawan et al. 2004).”

“Queloz et al. (2001) report that the analysis of the line bisector can distinguish the origin of the observed RV variations, which is very useful for the messy K-giant stars.”

“The amplitude of the radial velocity variation with the same period as the transit light curve (Figure 3) and the lack of any correlation between this variation and the BS establish the presence of a planetary mass companion to this star (Queloz et al. 2001).”

“To ensure that the radial velocity signal does not originate from cool stellar spots or a blended eclipsing binary, we checked for correlations between the line bisector spans (Queloz et al. 2001a) and the radial velocity measurements.”

“Usually the width of the CCF is estimated using the full width half maximum (FWHM) of the fitted Normal density and its asymmetry by calculating the CCF bisector and measuring the bisector inverse slope span (BIS SPAN; Queloz et al. 2001).”

“To exclude stellar activity as the origin of the observed RV variations, we verified that bisector spans and RVs are uncorrelated (Queloz et al. 2001; Pearson coefficients are -0.19, -0.16, -0.24 and 0.06 for WASP-147, 160, 164 and 165, respectively).”

“…dwarfs are on average more active and display more stellar spots (e.g., Shkolnik et al. 2009; Morin et al. 2010; Shkolnik et al. 2012; Malo et al. 2014; Schmidt et al. 2015), which can induce RV signals very similar to those of planetary companions (e.g., Queloz et al. 2001; Paulson & Yelda 2005).”

“In particular, the evolution of star spots, magnetic fields, and pulsations have well-studied effects on stellar radial velocity variations (Saar & Donahue 1997; Queloz et al. 2001; Desort et al. 2007; Hébrard et al. 2014).”

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

“The analysis of a line shape can help to determine the origin of the observed RV variations (Queloz et al. 2001).”

“In one exceptional case, photometric variations of the star HD~166151 revealed that its suspected planet did not exist (Queloz et al. 2001).”

“…of the orbital period of TIC-231005575 using NGTS and LCO, we took ten spectroscopic observations of TIC-231005575 using CORALIE - a fiber-fed échelle spectrograph installed on the 1.2-m Leonard Euler telescope at the ESO La Silla Observatory (Queloz et al. 2001) using an exposure time of 600 s.”

“Our analysis method is based on that adopted in Queloz et al (2001).”

“For K2-237, we measured the Bisector Inverse Span (BIS, Queloz et al. 2001; Toner & Gray 1988), and the CaII H and K S-index (Jenkins et al. 2008, 2011).”

“The enhanced activity of young Sun-like stars, linked to their fast rotation rate (Gallet & Bouvier 2013), is the main barrier to RV measurements (Saar & Donahue 1997; Queloz et al. 2001).”

“If the velocities were the result of a blend with an eclipsing binary (Mandushev et al. 2005) or starspots (Queloz et al. 2001), we would expect the line bisectors to vary in phase with the photometric period with an amplitude similar to that of the velocities.”

“¢Rlog HK , BIS, and FWHM are indicators of stellar activity (Queloz et al. 2001; also see Haywood 2015, and references therein).”

“The induced RV signal tends to mimic planet signatures, making the former extremely troublesome to filter (e.g. Saar & Donahue 1997; Queloz et al. 2001; Desort et al. 2007; Dumusque et al. 2011; Borgniet et al. 2015).”

“It has been well established (e.g., Queloz et al. 2001, Torres et al. 2005) that if the observed RV pattern were a result of a blend with an eclipsing binary, the spectral line bisectors (see Tables 2, 3, and 4) would follow a similar pattern, that is, they would vary in phase with the photometric…”

“But measurements derived from bisection, as valuable as it is, is essentially limited to assessing the profile for asymmetry against which velocities can be compared e.g. convective velocities Gray (1982)or suspected planet signals e.g. Queloz et al. (2001).”

“RV extrasolar planet surveys use the line-bisector analysis (e.g., Queloz et al. 2001) to quantify such time-dependent asymmetries.”

“Such stellar activity-induced radial velocity variations not only produce statistically significant signals in the periodograms (Queloz et al. 2001), but also pose a significant challenge in characterizing sub-m s − 1 signals (Fischer et al. 2016).”

“From this pipeline, we obtained RV and stellar activity indicator such as CCF bisector spans (BIS, e.g., Queloz et al. (2001)), H α (Boisse et al. 2009), log( R ′ HK ) (Noyes et al. 1984; Duncan et al. 1991), Na II, and He I (Gomes da Silva et al. 2011).”

“Additionally, we compute the bisector-span (Queloz et al. 2001) of the CCF and spectral indices tracing chromospheric activity (Boisse et al. 2009; Gomes da Silva et al. 2011).”

“These include the CCF FWHM (e.g. Queloz et al. 2009; Hatzes et al. 2010) and bisector span (Queloz et al. 2001) – although recent work has demonstrated that using a Skewed-Normal distribution provides a more self-consistent result than measuring CCF parameters and bisector span separately (Simola…”

“CORALIE is mounted on the 1.2-m Leonard Euler telescope and has a spectral resolution of R = 60,000 (Queloz et al. 2001b).”

“The first two can be minimized using an optimised observational strategy (O’Toole et al. 2008), while other have much longer time-scales and can produce periodic signals in RV measurements via line profile variations (e.g., Saar & Donahue 1997; Queloz et al. 2001; Huélamo et al. 2008).”

“We apply a Gaussian fit on the CCFs to obtain the radial velocities (Baranne et al. 1996; Pepe et al. 2002), and also to extract the CCF parameters (FWHM and contrast) and the bisector span (BIS), as described by Queloz et al. (2001).”

“The activity-induced signals can be diagnosed using activity proxies like line-profile indicators (Queloz et al. 2001; Dumusque et al. 2011a; Boisse et al. 2011) or the log R′HK values (e.g. Bonfils et al. 2007).”

“It has been shown that intrinsic stellar phenomena such as magnetic activity can produce a periodic radial velocity signal th t can be misinterpretated as a substellar companion (Queloz et al. 2001).”

“Queloz et al. (2001) and Paulson et al. (2004) have demonstrated how starspots can result in periodic radial velocity variations that mimic the presence of planetary companions.”

“The RV variations produced by the rotational modulation of the surface inhomogeneities should produce some changes in the spectral line shape, such as line asymmetry (Queloz et al. 2001).”

“…introduces signals in the RV data that can mimic planetary signatures, sometimes coinciding with the periods of putative planets orbiting within the habitable zone of the star (e.g., Queloz et al. 2001; Huélamo et al. 2008; Figueira et al. 2010; Robertson et al. 2014; Suárez Mascareño et al. 2017).”

“In particular, anticorrelation between BIS and RVs can be considered a signature of short-term photospheric variability (Queloz et al. 2001).”

“Because the RVs are measured from small shifts in spectral absorption lines and stellar activity can change the shape of absorption lines, stellar activity can significantly affect RV observations (e.g., Queloz et al. 2001; Haywood 2015; Rajpaul et al. 2015).”

“The effect is modulated by the stellar rotation, and therefore can be confused for an exoplanet with an orbital period at a harmonic of the stellar rotation period (Queloz et al. 2001), especially in under-sampled radial velocity datasets.”

“A significant correlation between BS and RV may indicate a transit mimic, such as a blended eclipsing binary (Queloz et al. 2001).”

“For instance, Queloz et al. (2001) found that the RV variation of a G0V star, HD 166435, is not due to the presence of an exoplanet, but rather, the surface spot activity.”

“They adopted the definiton of velocity span as the difference of average velocities between 10-40% and 55-90% of the line depth from the top, which is thebisector inverse slope(Queloz et al. 2001), leaving the term “velocity span” for classical single line bisectors.”

“3 indicates that the RV variations are not due to an unresolved eclipsing binary (Queloz et al. 2001).”

“…starspots, and stellar magnetic activity can produce RV amplitudes on the order of 1 to several m s−1 for timescales of a few minutes, to hours and days, to months, and even years for stellar magnetic cycles (Queloz et al. 2001; Butler et al. 2004; Dumusque et al. 2011; Gomes da Silva et al. 2012).”

“…Valley; photometric observations made with the robotic telescope APT2 (within the EXORAP programme) located at Serra La Nave on Mt. Etna. towards dwarf stars of spectral type G or K, usually in a range around the mass of the Sun (e.g. Queloz et al. 2001; Valenti & Fischer 2005; Tamuz et al. 2008).”