A super-Earth on a close-in orbit around the M1V star GJ 740. A HADES and CARMENES collaboration
B. Toledo-Padrón, A. Suárez Mascareño, J. I. González Hernández, R. Rebolo, M. Pinamonti, M. Perger, G. Scandariato, M. Damasso, A. Sozzetti, J. Maldonado, S. Desidera, I. Ribas, G. Micela, L. Affer, E. González-Alvarez, G. Leto, I. Pagano, R. Zanmar Sánchez, P. Giacobbe, E. Herrero, J. C. Morales, P. J. Amado, J. A. Caballero, A. Quirrenbach, A. Reiners, M. Zechmeister
AAstronomy & Astrophysics manuscript no. A_super-Earth_on_a_close-in_orbit_around_the_M1V_star_GJ740 © ESO 2021February 19, 2021
A super-Earth on a close-in orbit around the M1V star GJ 740 (cid:63) (cid:63)(cid:63)
A HADES and CARMENES collaboration
B. Toledo-Padrón , A. Suárez Mascareño , , J. I. González Hernández , , R. Rebolo , , , M. Pinamonti ,M. Perger , , G. Scandariato , M. Damasso , A. Sozzetti , J. Maldonado , S. Desidera , I. Ribas , , G. Micela ,L. A ff er , E. González-Alvarez , G. Leto , I. Pagano , R. Zanmar Sánchez , P. Giacobbe , E. Herrero , ,J. C. Morales , , P. J. Amado , J. A. Caballero , A. Quirrenbach , A. Reiners , and M. Zechmeister Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spaine-mail: [email protected] Universidad de La Laguna, Departamento de Astrofísica, E-38206 La Laguna, Tenerife, Spain Consejo Superior de Investigaciones Científicas, E-28006 Madrid, Spain INAF-Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italia Institut de Ciències de l’Espai, Campus UAB, C / Can Magrans s / n, 08193 Bellaterra, Spain Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain INAF-Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italia INAF-Osservatorio Astronomico di Palermo, Piazza Parlamento 1, 90134 Palermo, Italy INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italia Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s / n, 18008 Granada, Spain Centro de Astrobiología (CSIC–INTA), ESAC, Camino Bajo del Castillo s / n, 28691 Villanueva de la Cañada, Madrid, Spain Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, GermanyReceived December 10, 2020 / Accepted February 10, 2021
ABSTRACT
Context.
M-dwarfs have proven to be ideal targets for planetary radial velocity (RV) searches due to their higher planet-star masscontrast, which favors the detection of low-mass planets. The abundance of super-Earth and Earth-like planets detected around thistype of stars motivates further such research on hosts without reported planetary companions.
Aims.
The HADES and CARMENES programs aim to carry out extensive searches of exoplanetary systems around M-type stars in thenorthern hemisphere, allowing us to address statistically the properties of the planets orbiting these objects. In this work, we performa spectroscopic and photometric study of one of the program stars (GJ 740), which exhibits a short-period RV signal compatible witha planetary companion.
Methods.
We carried out a spectroscopic analysis based on 129 HARPS-N spectra taken over a time-span of 6 yr combined with 57HARPS spectra taken over 4 yr, as well as 32 CARMENES spectra taken during more than 1 yr, resulting in a dataset with a timecoverage of 10 yr. We also relied on 459 measurements from the public ASAS survey with a time-coverage of 8 yr along with 5 yr ofphotometric magnitudes from the EXORAP project taken in the V , B , R , and I filters to carry out a photometric study. Both analyseswere made using Markov Chain Monte Carlo (MCMC) simulations and Gaussian Process regression to model the activity of the star. Results.
We present the discovery of a short-period super-Earth with an orbital period of 2.37756 + . − . d and a minimum mass of2.96 + . − . M ⊕ . We o ff er an update to the previously reported characterization of the magnetic cycle and rotation period of the star,obtaining values of P rot = ± P cycle = ±
150 d. Furthermore, the RV time-series exhibits a possibly periodic long-term signal which might be related to a Saturn-mass planet of ∼
100 M ⊕ . Key words.
Techniques: radial velocities – Techniques: photometric – Instrumentation: spectrographs – Stars: individual: GJ 740 –Stars: activity – Planets and satellites: detection (cid:63)
Based on observations made with the Italian Telescopio NazionaleGalileo (TNG), operated on the island of La Palma by the INAF - Fun-dación Galileo Galilei at the Roche de Los Muchachos Observatory ofthe Instituto de Astrofísica de Canarias (IAC); and the CARMENES in-strument installed at the 3.5m telescope of the Calar Alto Observatory,Spain. (cid:63)(cid:63)
The RVs used in this paper are available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/
1. Introduction
The development of second and third-generation echelle spec-trographs has produced a significant boost in the radial veloc-ity (RV) searches for Earth-like planets around M-dwarfs. Sincethe first discovery of an exoplanet orbiting an M-type star us-ing the RV method (Delfosse et al. 1998; Marcy et al. 1998), atotal of 116 planets have been discovered around M-dwarfs us-ing this technique . The vast majority of them (75%) have been https:/exoplanets.nasa.gov/ Article number, page 1 of 18 a r X i v : . [ a s t r o - ph . E P ] F e b & A proofs: manuscript no. A_super-Earth_on_a_close-in_orbit_around_the_M1V_star_GJ740 detected in the last decade via instruments such as HARPS-N(e.g., A ff er et al. 2019; Pinamonti et al. 2019), HARPS (e.g.,Dreizler et al. 2020; Grandjean et al. 2020), CARMENES (e.g.,Lalitha et al. 2019; Zechmeister et al. 2019), SOPHIE (e.g., Hob-son et al. 2019), or PFS (e.g., Feng et al. 2019).Despite the fact that M-dwarfs are the most common stars inthe Milky Way (Chabrier & Bara ff e 2000; Winters et al. 2015),only 10% of all known planetary companions have been detectedaround this type of stars. From the complete four-year Kepler dataset, Dressing & Charbonneau (2015) found 156 planet can-didates orbiting M-type stars, estimating an average of ∼ P orb <
200 d and R = ⊕ regime. Thisoccurrence rate, combined with their closer habitable zones dueto their lower luminosities, makes such low-mass stars ideal tar-gets for the search of temperate Earth-like planets. However, thecomplexity of the characteristic stellar activity pattern of thesestars requires a careful analysis of the chromospheric activityindicators in order to identify false planetary signals induced bythe rotation of the star (Bonfils et al. 2007; Robertson et al. 2014;Suárez Mascareño et al. 2018; Toledo-Padrón et al. 2019).The planetary formation scenario provided by the core ac-cretion theory (Pollack et al. 1996) indicates that the most com-mon planets around M-dwarfs are super-Earth and Neptune-mass planets (Reiners et al. 2018; Luque et al. 2018; Perger et al.2019; González-Álvarez et al. 2020), most of them located in the P orb <
100 d region. Nonetheless, there have also been some de-tections of gas giants orbiting late-type stars (Butler et al. 2006;Gaudi et al. 2008; Howard et al. 2010; Morales et al. 2019), al-though their location tends to be beyond the snow line of the sys-tem (where volatile compounds such as water or carbon dioxidecould condense into solid ice grains). Endl et al. (2006) esti-mated a frequency < ff er et al. 2016; Perger et al. 2017b; Suárez Mascareño et al.2017; Pinamonti et al. 2018; A ff er et al. 2019; Perger et al. 2019;Pinamonti et al. 2019). In this work, we also explore the possi-bility of an outer high-mass planetary companion characterizedby a long orbital period and its impact on the planetary configu-ration.The paper is structured as follows. Section 2 presents thedataset used in this work, including both spectroscopy and pho-tometry. Section 3 details the stellar properties of GJ 740. Sec-tion 4 shows the techniques used for the RV and stellar activ-ity indicators measurements. Section 5 describes the analysis ofthese and the photometric measurements. Section 6 features thediscussion of these results and Section 7 provides the conclu-sions of this study.
2. Data
The HADES RV program monitored GJ 740 from 26 May2013 (BJD = = ∼
115 000 provided by this fiber-fed echelle spec-trograph along with its spectral range from 3830 to 6900 Å areideal for high-precision RV searches. We obtained a total of 129HARPS-N spectra over a time-span of 6 yr. Every spectrum wastaken using an exposure time of 900 s to average out the short-time periodic oscillations of the star (Dumusque et al. 2011), al-though this phenomenon has not yet been detected in M-dwarfs(Berdiñas et al. 2017). The average signal-to-noise ratio (S / N)achieved at 5500 Å per pixel was 110, enough to ensure a goodexposure level of the blue part of the spectra, which contains theCa II H&K lines that are especially weak for M-type stars (Gi-ampapa et al. 1989; Lovis et al. 2011). Some of the spectra wereobtained using a Fabry-Pérot (FP) interferometer (Wildi et al.2010) for the wavelength calibration due to the lack of availabil-ity of the Th-Ar lamp for the simultaneous calibration. In thosecases, the Th-Ar lamp was used to obtain the absolute calibra-tion prior to the observations, and then all the FP spectra werereferred to the Th-Ar calibration spectrum with a drift value. Theinterferometer provides a high level of short-term RV precisionand has the advantage of avoiding possible contamination of theCa II H&K lines, but lacks the precise drift correction providedby the Th-Ar lamp. However, the mean inter-night instrumentaldrift calculated by Perger et al. (2017a) for the whole HADESsample was about 1 m s − .We also acquired 32 spectra with the CARMENES spectro-graph at the Calar Alto Observatory (Quirrenbach et al. 2018)overlapping the epoch during which the HARPS-N observa-tions were carried out. CARMENES allows for simultaneousobservations in two di ff erent channels that cover the visible (be-tween 5200 and 9600 Å) and near-infrared (between 9600 and17 100 Å) regions of the spectra, with resolutions of R ∼
94 600and R ∼
80 400, respectively. The RV precision provided by bothchannels is ∼ − , similar to the one obtained in HARPS-N.The CARMENES spectra were acquired from 11th April 2016(BJD = = / N per pixel of 122. Hol-low cathode lamps combined with an FP etalon were used toobtain the wavelength calibration of these spectra (Bauer et al.2015).Additionally, this star has been monitored from the southernhemisphere using the HARPS spectrograph (Mayor et al. 2003)installed at the 3.6m telescope of La Silla Observatory, Chile.This fiber-fed echelle spectrograph has similar characteristics toits northern counterpart. It is contained in a vacuum vessel tominimize the RV drifts produced by temperature and pressurevariations. We used 57 HARPS spectra from the ESO publicdatabase taken over a time-span of more than 4 yr: from 30 June2008 (BJD = = / N per pixel at 5500 Å of 81.5. In thiscase, the majority of the spectra were calibrated with an FP in-terferometer.
Article number, page 2 of 18. Toledo-Padrón et al.: A super-Earth on a close-in orbit around the M1V star GJ 740
To complement the spectroscopic analysis, we used 474 pho-tometric measurements from ASAS (All Sky Automated Sur-vey) (Pojmanski 1997). The measurements come from one ofthe three observing stations of the project (ASAS-S / ASAS-3),located at the Las Campanas Observatory, Chile. This surveycarries out observations in the V and I bands simultaneously witha plate scale of 14" / pixel and an average accuracy of ∼ V ∼ = = ff erence between the two systems of upto 8 s due to the motion of the Sun (the reference frame in thiscase) caused mainly by Jupiter and Saturn (Eastman et al. 2010).We also relied on the publicly available light curve from theSuperWASP database (Pollacco et al. 2006). The data were takenwith the survey facilities located at the South African Astronom-ical Observatory and the Roque de los Muchachos Observatory.The cameras used feature a plate scale of 13.7" / pixel and an aver-age accuracy better than 1% for objects with V ∼ = = ∼ B , V , R , and I -band photometry at the INAF-Catania Astrophysical Observatory with an 80 cm f / procedures and we vi-sually inspected the data to check the quality (see A ff er et al.2016 for details). Errors in the individual photometric points in-clude the intrinsic noise (photon noise and sky noise) and theroot-mean-square (RMS) of the ensemble stars used for comput-ing the di ff erential photometry. The final dataset contains ∼ B , V , and R bands distributedover five consecutive seasons, between BJD = = I -band photome-try contains only 100 points covering the first four seasons.
3. GJ 740
GJ 740 (HD 176029, BD +
05 3993) is a bright ( m V = IRAF is distributed by the National Optical Astronomy Observato-ries, which are operated by the Association of Universities for Researchin Astronomy, Inc., under a cooperative agreement with the NationalScience Foundation.
Table 1.
Stellar properties of GJ 740.
Parameter GJ 740 Ref.RA (J2000) 18:58:00.14 [1]Dec (J2000) + µ α cos δ [mas yr − ] − ± µ δ [mas yr − ] − ± ± m B m V T e ff [K] 3913 ±
51 [5]log g [cgs] 4.68 ± / H] [dex] 0.08 ± M (cid:63) [M (cid:12) ] 0.58 ± R (cid:63) [R (cid:12) ] 0.56 ± L (cid:63) / L (cid:12) ) − ± L x / L bol ) − ± v sin i [km s − ] 0.92 ± i [deg] >
25 [7] a sec [m s − yr − ] 0.3903 ± ( R (cid:48) HK ) − ± P rot [d] 35.563 ± References: [1] Gaia Collaboration et al. (2018); [2] Bailer-Jones et al.(2018) [3] Cifuentes et al. (2020); [4] Maldonado et al. (2017); [5]Passegger et al. (2018); [6] González-Álvarez et al. (2019); [7] SuárezMascareño et al. (2018) ; [8] Calculated following Zechmeister et al.(2009); [9] This work. by Giacobbe et al. (2020) as part of the APACHE (A PAthwaytowards the CHaracterization of Habitable Earths) photometrictransit search project (Sozzetti et al. 2013), recovering a periodof 35.6422 ± ± P rot = ± R (cid:48) HK ) = − ± ff ects on the RVmeasurements.
4. Determination of RVs and stellar activityindicators
For the RV calculation in the HARPS-N and HARPS datasets,we followed two di ff erent approaches. The first one is based onthe HARPS-N DRS (Data Reduction Software) pipeline (Lovis& Pepe 2007), which builds a cross-correlation function (CCF)for a certain template mask driven by the spectral type. ForGJ 740, we used the M2 mask, which contains 9196 wavelengthintervals of 0.02 Å width with di ff erent depths located at the po-sitions of isolated stellar lines. This mask is shifted 161 times in Article number, page 3 of 18 & A proofs: manuscript no. A_super-Earth_on_a_close-in_orbit_around_the_M1V_star_GJ740 an RV range of ∼
40 km s − , providing a CCF for each echelleorder. The resulting CCFs are fitted by a Gaussian along with ano ff set constant to obtain an RV measurement per echelle order.These measurements are weighted in terms of the flux of eachorder to obtain the final RV value. We modify this last step ofthe process by weighting each CCF order according to its meanflux, performing a secular acceleration correction based on theproper motion of the star, and fitting the combined CCF with aGaussian along with a second-order polynomial, which providesslightly better results. The RVs computed through this method-ology exhibit an RMS = − with a mean RV uncertaintyof 1.4 m s − in the case of HARPS and an RMS = − with amean RV uncertainty error of 1.2 m s − in the case of HARPS-N.The di ff erence between both datasets is caused by the RV trendpresent in the HARPS-N measurements.The second approach that we implemented for computingthe RVs of the HARPS-N and HARPS spectra is based on theTERRA (Template-Enhanced Radial velocity Re-analysis Ap-plication) reduction software (Anglada-Escudé & Butler 2012).TERRA corrects the spectra for the blaze function, secular accel-eration (Kürster et al. 2003), and then puts the spectra in the solarsystem barycentric frame by correcting for the barycentric andstellar RV. Then it performs a template matching with the high-est S / N spectra, carrying out a least-squares fit on the residualsfor every shift and providing an RV value from the minimum χ value. The RVs computed by TERRA yield an RMS = − and a mean uncertainty error of 0.9 m s − in the case of HARPSand RMS = − and mean uncertainty error of 0.8 m s − inthe case of HARPS-N. These results support the superior per-formance of the TERRA pipeline for M-dwarfs (Perger et al.2017a). For this reason, we opted for this reduction procedure inour analysis.In the case of the CARMENES dataset, the spectra were re-duced using the CARACAL pipeline (Caballero et al. 2016), andthe RVs were computed using the SERVAL tool (Zechmeisteret al. 2018), which is a public code similar to TERRA. Thistool performs a template-matching using a high S / N templatebuilt from the available spectra of the star as a reference. TheCARMENES RV time-series computed by SERVAL presents anRMS = − with a mean uncertainty of 1.8 m s − .In order to model the stellar activity e ff ects on the RV mea-surements, we studied the flux variations of certain spectral linesconnected with several chromospheric activity indicators. Themeasurements were made on the spectra corrected from the blazefunction (using a blaze spectrum given by the DRS pipeline), thebarycentric velocity of the Earth, and the radial velocity of thestar. We also carried out a re-binning of the spectra in order to ob-tain the same wavelength width per pixel (0.01 Å). To avoid anywavelength shifts that can a ff ect the flux measurements, we cor-related the spectra using the first spectrum taken by each spec-trograph as a reference. All these spectra were co-added into anaverage spectrum that was normalized and used for calculatingthe weight of each echelle order for the individual spectra. Onceall these corrections had been applied to the individual spectra,we derived three activity indicators: H α (Kürster et al. 2003;Gomes da Silva et al. 2011), the S mw index associated with theCa II H&K lines (Noyes et al. 1984; Lovis et al. 2011), and theNaD index associated with the doublet of NaI D and D lines(Díaz et al. 2007; Houdebine et al. 2009). The continuum pass-bands of this last index were modified following Toledo-Padrónet al. (2019) in order to have them in the same echelle orderof the core lines, avoiding the overlap zones between spectral https://github.com/mzechmeister/serval Table 2.
Properties of all the datasets used in this work.
Index Mean Value RMS Mean ErrorRV [m s − ] 10619 6.166 1.209FWHM [m s − ] 4505 10.35 1.978H α mw V (ASAS) 9.224 0.019 0.012m B (EXORAP) 4.723 0.015 0.0011m V (EXORAP) 3.448 0.010 0.0016m R (EXORAP) 2.279 0.0094 0.0013m I (EXORAP) 1.550 0.011 0.0011orders. Moreover, we calibrated the Mount-Wilson S-index fol-lowing Lovis et al. (2011) and Suárez Mascareño et al. (2015).The CARMENES spectra do not cover this index in their wave-length range. The error on all the measurements was calculatedusing the RMS on the spectral bands related to each index (corelines and continuum passbands) along with error propagation.The stellar activity can also be tracked using propertiesrelated to the CCF such as the full width at half maximum(FWHM) or the bisector span (BIS). We measured the FWHMusing the CCFs from the DRS pipeline weighted, corrected fromsecular acceleration, and fitted by a Gaussian with a second-order polynomial. For the BIS measurements, we used the bisec-tor fits provided by the same pipeline, although this time-seriesdid not provide any relevant information for the stellar activitystudy since the BIS is not well defined for M-dwarfs due to thebumps present on the wings of the CCF (Rainer et al. 2020).To remove outliers in all time-series we applied a 3 σ -clipping in values and another 3 σ -clipping in errors to each oneof them, using the median value and error as a reference. Thisserves to discard points that can be related to stellar flares, aphenomenon especially important in active M-type stars (Rein-ers 2009; Hawley et al. 2014). For consistency, a measurementcataloged as an outlier in one of the time-series is discarded inthe rest of the time-series. The final measurements resulting fromthis process are shown in Fig. 1 along with the photometric time-series, and the properties of each dataset are listed in Table 2.
5. Time-series analysis
We analyzed the periodic signals present in the time-series ofRVs, photometric observations, and chromospheric activity in-dicators related to stellar rotation and magnetic activity. First,we built the Generalized Lomb Scargle (GLS) periodograms(Lomb 1976; Zechmeister & Kürster 2009), and establishedthree threshold levels related to the False Alarm Probability(FAP) of these signals (Horne & Baliunas 1986). The thresh-old levels were obtained by randomizing each time-series sepa-rately in a bootstrapping process of 10000 iterations (Endl et al.2001). We then studied the most significant peaks in the peri-odograms based on these threshold levels. For this study, weadopted the significance standards established in Toledo-Padrónet al. (2019), with the 0.1% and 10% levels FAP separating thestatistically significant signals, those whose significance is un-clear, and the non-significant ones. The first periodograms fromthe stellar activity indicators, along with the photometric dataand the RVs are shown in Fig. 2.
Article number, page 4 of 18. Toledo-Padrón et al.: A super-Earth on a close-in orbit around the M1V star GJ 740 − − − ∆ R V [ m / s ] − − − ∆ F W H M [ m / s ] − . − . . . . . ∆ H α − . − . . . . ∆ S m w BJD - 2450000 − . − . . . . ∆ N a D BJD - 2450000 − . − . . . . ∆ m V [ m ag ] BJD - 2450000 − . − . . . . ∆ m B [ m ag ] BJD - 2450000 − . − . . . . ∆ m V [ m ag ] BJD - 2450000 − . − . . . . ∆ m R [ m ag ] BJD - 2450000 − . − . . . . ∆ m I[ m ag ] Fig. 1. Top:
Time-series of the RV and the chromospheric activity indi-cators with combined measurements from HARPS (represented in vio-let), HARPS-N (represented in cyan), and CARMENES (represented inyellow).
Bottom:
Time-series of the photometric magnitudes taken withASAS (represented in dark red) and EXORAP (represented in orange)in the V , B , R , and I filters. Using the S-index values we computed a mean chromo-spheric activity level of log (R (cid:48) HK ) = − ± P rot = ± PS D P=3571.43dP=3571.43d RV PS D P=2702.70dP=2702.70d
FWHM PS D P=2777.78dP=2777.78d H α PS D P=2777.78dP=2777.78d
Smw PS D P=2857.14dP=2857.14d
NaD PS D P=35.13dP=35.13d
Phot ASAS PS D P=35.54dP=35.54d
Phot EXORAPb PS D P=35.49dP=35.49d
Phot EXORAPv
10 100 1000 10000
Period [d] PS D P=35.66dP=35.66d
Phot EXORAPr
Fig. 2.
Periodograms of the RV, FWHM, H α , S mw , NaD, ASAS V , EX-ORAP B , EXORAP V , and EXORAP R -band magnitude time-series.The periods related to stellar rotation, planetary companion, and possi-ble magnetic cycle have been represented as yellow, cyan, and brownvertical lines, respectively. The green, brown, and red horizontal linesindicate the 0.1%, 1%, and 10% FAP levels, respectively. the rotation signal is exceeded by a long-period signal that couldbe associated with the magnetic cycle of the star. The most significant peak in all the spectroscopic GLS pe-riodograms of Fig. 2 is related to a long-term signal whoseperiodicity around 8 yr makes it compatible with a magneticcycle similar to the one observed in the Sun. The lengthof the photometric campaigns is not enough to detect a sig-nal with this periodicity. This signal has a significance muchgreater than the 0.1% FAP level in all cases. We fitted this
Article number, page 5 of 18 & A proofs: manuscript no. A_super-Earth_on_a_close-in_orbit_around_the_M1V_star_GJ740
Fig. 3. Left:
RV, FWHM, H α , S mw , and NaD time-series with their re-spective model of the long-term signal. Center:
Posterior distributionfor the periodicity of the long-term signal.
Right:
Periodograms of theresiduals after subtracting the model. The blue, green, and red horizon-tal lines indicate the 0.1%, 1%, and 10% FAP levels, respectively. Thehighest peak of the periodogram is marked with a blue shaded area. signal with a sinusoidal model that includes o ff set and jitterterms for each spectrograph. We first used an implementationof the Broyden–Fletcher–Goldfarb–Shanno (BFGS) algorithm(Schraudolph et al. 2007) available in the minimize packagefrom the scipy library to optimize the parameters of the model.Then we carried out an MCMC analysis based on the resultsof the BFGS algorithm using the emcee package (Foreman-Mackey et al. 2013), performing simulations within a Bayesianframework to infer the probability distribution over all the pa-rameters considered. We used 10 000 steps for the burn-in stage,50 000 steps for the construction stage, and 512 walkers to sam-ple the parameter space. We established a convergence criterionbased on the auto-correlation function to ensure that the previ-ous setup produces a correct parameter distribution. This anal-ysis provided the results shown in Fig. 3 when the long-termcomponent is modeled along with the rotation component.In the middle panels of Fig. 3, we show how the long-termsignal in the RV time-series presents a shift in periodicity withrespect to the signals detected in the activity indicators, display-ing compatibility with them at 2 σ . The periodicity of the sig-nal in the activity indices is around 2820 d (2701 + − in FWHM,2832 + − in H α , 2848 + − in S mw , and 2913 + − in NaD), whilein the RV time-series is located at 3363 + − d. Our time-spanof ∼ ff set applied to all the measurements. In theseplots, the bumps at 330 d and 440 d from Fig. 2 have completelydisappeared from the periodograms, which indicates that thesesignals were aliases of the long-term signal. We found signalsrelated to the rotation of the star around 40 d in the RV, H α , S mw ,and NaD time-series as the main peaks. In the FWHM case, thesignal related to the first harmonic of the stellar rotation shows agreater amplitude than the forest of peaks around 40 d. Fig. 4. Left:
RV, FWHM, H α , S mw , and NaD time-series with theirrespective model of the long-term signal and the rotation signal. Theshaded regions indicate the 1 σ confidence band of the GP model. Cen-ter:
Posterior distribution for the periodicity of the rotation signal.
Right:
Periodograms of the residuals after subtracting the model. Theblue, green, and red horizontal lines indicate the 0.1%, 1%, and 10%FAP levels, respectively. The highest peak of the periodogram is markedwith a blue shaded area.
For the next step of the analysis, we used the original time-series to characterize the rotation through a Gaussian Process(GP) regression (Haywood et al. 2014; Rajpaul et al. 2015; Am-bikasaran et al. 2015), and simultaneously recompute the activ-ity cycle model previously used. To model the stellar rotation,we used the following quasi-periodic kernel: κ ( τ ) = K + C e − τ/ t s (cid:34) cos (cid:32) πτ P rot (cid:33) + (1 + C ) (cid:35) + (cid:16) σ ( t ) + σ (cid:17) δ τ (1)which contains the squared amplitude of the signal K , the pe-riodicity of the signal P rot , and the timescale of the surface phe-nomena in the star t s . The kernel also contains a term named C whose role is to measure the relative importance between the twocomponents of the kernel: the periodic (i.e., the cosine) and non-periodic (i.e., the exponential). This kernel has proven to providegood results in the activity analysis of Proxima Centauri per-formed by Suárez Mascareño et al. (2020). We fitted the param-eters of the kernel using the celerite code (Foreman-Mackeyet al. 2017) with the same setup of steps, walkers, and conver-gence criterion as the one described in the previous subsection.The parameters obtained for all of the time-series (including thenew values of the parameters related to the long-term signal) arelisted in Table 3 and the results are shown in Fig. 4.The middle panels of Fig. 4 show that the rotation period inthe RV time-series is not well constrained, with a wide distri-bution reaching its maximum peak close to the first harmonicof the rotation period. The coherence time recovered from theRV kernel is much shorter than the one obtained in the rest ofthe time-series. In the chromospheric activity indicators time-series we detected the rotation signal with a periodicity of ∼
37 d(36.9 + . − . in FWHM, 36.1 + . − . in H α , 37.1 + . − . in S mw , and 36.5 + . − . in NaD). The fact that the parameter t s is a few stellar rotations inthe activity indices is consistent with the evolutionary timescale Article number, page 6 of 18. Toledo-Padrón et al.: A super-Earth on a close-in orbit around the M1V star GJ 740
Table 3.
Priors and parameters related to the long-term and rotation signals obtained from the final stellar activity MCMC analysis of all thetime-series.
Parameter RV FWHM H α S mw NaDCycle Priors K cycle U (0.01, 20.0) U (0.01, 20.0) U (10 − , 0.02) U (10 − , 0.4) U (10 − , 0.4) P cycle [d] U (2300.0, 3900.0) U (2300.0, 3900.0) U (2300.0, 3900.0) U (2300.0, 3900.0) U (2300.0, 3900.0) T [d] U (2500.0, 3600.0) U (2500.0, 3600.0) U (2500.0, 3600.0) U (2500.0, 3600.0) U (2500.0, 3600.0)Cycle Values K cycle + . − . m s − + . − . m s − + . − . + . − . + . − . P cycle [d] 3363 + − + − + − + − + − T [d] 2976 + − + − + − + − + − Rotation Priors K LU (8.0, 40.0) LU (20.0, 100.0) LU (10 − , 0.1) LU (4 × − , 0.03) LU (10 − , 0.1) P rot [d] LU (15.0, 45.0) LU (15.0, 45.0) LU (15.0, 45.0) LU (15.0, 45.0) LU (15.0, 45.0) t s [d] LU (1.0, 300.0) LU (1.0, 300.0) LU (1.0, 300.0) LU (1.0, 300.0) LU (1.0, 300.0) C LU (0.0, 1.0) LU (0.0, 1.0) LU (0.0, 1.0) LU (0.0, 1.0) LU (0.0, 1.0)Rotation Values K rot ( ∗ ) + . − . m s − + . − . m s − + . − . + . − . + . − . P rot [d] 18.6 + . − . + . − . + . − . + . − . + . − . t s [d] 12.0 + . − . + − + − + − + − log C − + − − + − − + − − + − − + − Remaining Priorsjitter
HARPS LU (0.01, 4.0) LU (3.0, 9.0) LU (0.001, 0.02) LU (0.01, 0.10) LU (10 − , 0.005)jitter HARPS − N LU (0.01, 4.0) LU (3.0, 9.0) LU (0.001, 0.02) LU (0.01, 0.10) LU (10 − , 0.005)jitter CARMENES LU (0.01, 4.0) · · · LU (0.001, 0.02) · · · LU (10 − , 0.005)o ff set HARPS U ( − U ( − U ( − U ( − U ( − ff set HARPS − N U ( − U ( − U ( − U ( − U ( − ff set CARMENES U ( − · · · U ( − · · · U ( − HARPS + . − . m s − + . − . m s − + . − . + . − . + . − . jitter HARPS − N + . − . m s − + . − . m s − + . − . + . − . + . − . jitter CARMENES + . − . m s − · · · + . − . · · · + . − . o ff set HARPS − + . − . m s − + . − . m s − − + . − . − + . − . − + . − . o ff set HARPS − N + . − . m s − − + . − . m s − + . − . + . − . − + . − . o ff set CARMENES − + . − . m s − · · · − + . − . · · · − + . − . ( ∗ ) The K rot values were calculated as the root square of the K posterior distribution results. of the active regions (Scandariato et al. 2017). Of these activityindices, H α exhibits the most significant stellar rotation signal(see Fig. 3) and provides the most stable stellar activity charac-terization, with lower relatives errors in the rotation parametersfitted (see Table 3). A zoom-in of the H α model is shown inFig. 5.We then computed the Bayesian evidence log Z (Perrakiset al. 2014) for all the time-series. When comparing the log Z values of two di ff erent models, a di ff erence between their log Z values greater than 10 indicates a significant preference forthe model with the higher log Z . The results indicate that therotation + long-term signal model is preferred over the long-termsignal model. The first model is characterized by greater log Z values in all the time-series, presenting a di ff erence greater than30 with respect to the values computed for the second model.This Bayesian parameter is shown in Table 4 for all the modelsconsidered in this work. Article number, page 7 of 18 & A proofs: manuscript no. A_super-Earth_on_a_close-in_orbit_around_the_M1V_star_GJ740
Table 4. log Z values computed for the di ff erent models implemented in this paper within their corresponding time-series. Model RV FWHM H α S mw NaDCycle − −
632 625 141 672Cycle + Rotation − −
601 683 208 721Cycle + Rotation + Keplerian Planet − · · · · · · · · · · · · Cycle + Rotation + Circular Planet − · · · · · · · · · · · · BJD - 2450000 − . − . . . . . ∆ H α HARPSHARPS-NCARMENES
BJD - 2450000 − . . . . ∆ H α BJD - 2450000
BJD - 2450000
Fig. 5. Top:
Model obtained for the H α time-series using Gaussian Pro-cesses to treat the rotation signal and a sinusoidal function to treat thelong-term signal. The shaded regions indicate the 1 σ confidence bandof the GP model. Bottom:
Zoom on di ff erent time-windows. In Fig. 2 we previously observed how the ASAS photometricdataset exhibit the same rotation signal as the one found in thechromospheric time-series. The GP regression with the rotationkernel reveals a periodicity of P rot = + . − . d for this signal. Noadditional significant signals were detected after this model wassubtracted.The analysis of the SuperWASP photometric time-series didnot reveal any clear information about the rotation of GJ 740since all the short-term signals have low significance. This time-series presents the problem that the majority of its photometricmagnitudes were measured in a time-span of 130 d, with only 9 dof observations outside this range. The time-span of the datasetand the density of points is not enough to have a good characteri-zation of the long-term behavior of the star, a fact that is reflectedin the lack of long-term significant peaks after the trend cor-rection. We found a similar time-span problem in the APACHEdataset analyzed in Giacobbe et al. (2020) in regards to the long-term signal.We also carried out a pre-whitening analysis of the four EX-ORAP light curves. The main feature of the periodograms of thepre-whitened B and V light curves is a forest of strong peaks be-tween 20 and 60 days, which are aliases of the strongest peakat ∼
36 days with FAP < R - band light curve, where the 36 d period has a slightly higherFAP ∼ I -band all the signals are non-statistical sig-nificant (i.e., FAP > emcee package (Foreman-Mackeyet al. 2013). We included a GP to characterize the red noise in thedata introduced by stellar activity, allowing independent o ff setsfor the two di ff erent instrumental setups used during the survey.The posterior distribution of the B , V , and R light curves showsthat the correlated noise is consistent with the periodicity of 36days returned by the periodograms. The combination of thesedistributions provides an orbital period of 35.563 ± I -band light curve does not lead to any conclusive re-sult. This is due to the fact that this light curve is shorter in timecoverage, contains fewer data, and the activity signal in this redband is expected to be lower than in the previous cases.The periodograms of the stellar indices residuals in the rightpanels of Fig. 4 show that following the rotation subtraction nomore signals were detected with a statistical significance higherthan the 10% FAP level (except in the RV case). This indicatesthat the signals previously detected at ∼
19 d were related to thefirst harmonic of the rotation period. In the case of the RV time-series, we found a short-period signal of 2.4 d with a significancegreater than the 0.1% level of FAP, which could have a planetaryorigin since it is not present in the activity proxy time-series.
We explored the possible presence of a planetary signal at 2.38 din the RV time-series by adding a Keplerian component to ourprevious MCMC model that included the stellar rotation andlong-term signal terms. We performed an MCMC analysis usingthe H α model shown in Fig. 5 to establish the boundaries for theRV rotation parameters. The Keplerian parameters of the candi-date planet converged to the distributions shown in Fig. 6. Therest of the parameters are displayed in Table A.1 and Fig. A.1.The posterior distributions from this MCMC analysis ex-hibit a good convergence based on the auto-correlation of thechains to an orbital period of 2.37756 + . − . d for GJ 740 b. Thesignal is characterized by an amplitude of 2.13 + . − . m s − andan eccentricity of 0.24 + . − . . The log Z value computed for thismodel indicates a significantly better Bayesian result than theone obtained for the previous models implemented for the RVtime-series, with a ∆ log Z greater than 20 in favor of the plan-etary model. The planetary nature of this signal is further sup-ported by the steady increase of its statistical significance andthe consistency of the RV semi-amplitude with the number ofmeasurements shown in Fig. A.2. Fig. 7 depicts the RV time-series phased to the period of this planetary signal. Article number, page 8 of 18. Toledo-Padrón et al.: A super-Earth on a close-in orbit around the M1V star GJ 740
Fig. 6.
Posterior distributions of the GJ 740 b fitted parameters. The 16th-84th percentiles are represented through vertical dashed lines. − . − . . . . ∆ R V [ m / s ] RMS = 1.76 m/s
HARPSHARPS-NCARMENES . . . . . . Phase − . − . . . . O - C [ m / s ] RMS = 1.00 m/s
Fig. 7. Top:
Phase-folded curve of the RV time-series using theGJ 740 b orbital period after subtracting the long-term signal and therotation period. The jitter terms of each spectrograph have been addedto the original RV errors. The red solid line represents the planetarymodel.
Bottom:
Residuals after subtracting the model.
The nominal eccentricity obtained is larger than the one ex-pected for a short orbital period planet such as GJ 740 b, but itis consistent with zero at the 2 σ level. For this reason, we triedan additional model using a sinusoidal function to represent theplanetary signal. This model is characterized by a Bayesian evi-dence of log Z = − ff erence between the twomodels is below the limit to consider one of them more signifi-cant than the other.Using the orbital period obtained we computed the semi-axisof the planet using the mass of the host star from Table 1. Thisparameter allowed us to calculate the flux received by the planet,its equilibrium temperature, and the probability that the planetcould transit its host star. We listed in Table 5 all the MCMCparameters along with these derived properties.Figure 7 shows how the RV values are fitted nicely by theplanetary model, leaving minor residuals. As shown in the bot-tom panel of Fig. 7, the RMS of the residuals after subtractingthe final model is only 1 m s − . The periodogram of these resid-uals produces only non-significant signals (i.e., lower than thePSD value related to the 10% level of FAP), with a similar dis-tribution to the one found in the other activity indices after sub- Article number, page 9 of 18 & A proofs: manuscript no. A_super-Earth_on_a_close-in_orbit_around_the_M1V_star_GJ740
Table 5.
MCMC and derived planetary parameters of GJ 740 b obtainedfrom the final RV time-series analysis.
Parameter Priors ValueMCMC K b [m s − ] U (0.0, 5.0) 2.13 + . − . P b [d] U (1.5, 3.5) 2.37756 + . − . T b -2454647.7 [d] U (0.0, 1.6) 0.87 + . − . ω b [rad] U (- π , π ) − + . − . e b U (0.0, 1.0) 0.24 + . − . Derived M p sin i [M ⊕ ] · · · + . − . a [AU] · · · + . − . T eq [K] ( ∗ ) · · · + − Insolation [S ⊕ ] · · · + − Transit Probability · · ·
Note: ( ∗ ) Computed assuming null bond albedo. tracting the rotation and the long-term signal. We added both aKeplerian and a sinusoidal model to try to track the presence ofan additional planetary signal in the RV residuals, but the simu-lations did not match the convergence criteria.
Taking into account the high transit probability shown in Ta-ble 5, we computed the BoxLeastSquares (BLS) periodogram(Kovács et al. 2002) for the ASAS time-series and carried outan MCMC analysis similar to the one performed in the RV time-series (without modeling any long-term signal since it was notdetected in photometry) to search for the planetary signal. Theposterior distribution of the planetary parameters did not meetthe convergence criteria and therefore there is no evidence ofdetection. The SuperWASP and EXORAP datasets do not showany hint of a short-period signal in the P <
10 d region withenough statistical significance to be reliable.
To ensure that the GP regression is not overfitting and absorb-ing signals not related to stellar activity, we replaced the GP ro-tation model with a simpler one based on a double sinusoidalfunction. The periodogram of the RV residuals after subtractingthis new model reveals the presence of a previously non-detected15 d signal. The inclusion of an additional sinusoidal function inour MCMC model to fit this signal (along with the long-term si-nusoidal, the GP rotation term, and the GJ 740 b Keplerian) pro-vides a greater log Z value than the one related to the previousmodel (without the short-term sinusoidal). However, the ampli-tude of this signal is below the 3 σ significance level and its pe-riodicity requires a narrow prior to be constrained. Additionally,this 15 d signal is also present in the H α and S mw indicators. Weperformed the same MCMC analysis on these time-series, andwe obtained a good convergence based on the auto-correlation ofthe chains, which indicates that this signal is most likely causedby stellar activity.
6. Discussion
We compared our results with those reported in Suárez Mas-careño et al. (2018), where the long-term signal of GJ 740 wasdetected with a periodicity of 2040 d in the FWHM, H α , andS mw time-series with lower semi-amplitudes (2.58 m s − , 0.165,and 0.00658, respectively). The di ff erences with the results pre-sented in this paper could be explained by the larger dataset usedin our analysis. Although the baseline of our data is su ffi cient tohave a good estimation of the period of the presumed magneticcycle, the most significant long-term peak di ff ers between thedi ff erent time-series. Merging the probability distribution of theFWHM, H α , S mw , and NaD datasets, we obtain a mean value of2800 ±
150 d.In the analysis presented in Suárez Mascareño et al. (2018),we also detected the rotation period at 38 d in the H α andS mw time-series, with an additional peak in the first harmonicat ∼
19 d. In the case of the FWHM time-series, the peaks wereshifted to 35 and 18 d, respectively. The presence of the first har-monic of rotation in these time-series could be caused by the ge-ometric distribution of active regions. The photometry analysiscarried out in the article supported the detection of the rotationsignal at 35 d. The average results from our analysis includingthe NaD time-series characterized the rotation of the star with aperiodicity of 36.5 ± ff ected by the ef-fects of an irregularly spotted stellar surface coupled with stellarrotation. This scenario is consistent with the fact that the activ-ity signal is stronger at bluer wavelengths, where the contrastbetween the photosphere and cool spots is larger. Furthermore,we notice that B and V photometry get dimmer with time, sug-gesting that the spot coverage increases during the observationcampaign. This is consistent with an increasing level of stellaractivity as also suggested by the chromospheric indices shownin Fig. 1.The coherence time obtained in the posterior distribution ofthe rotation parameters in the EXORAP analysis is comparablewith the stellar rotation, which contrasts with the results obtainedin Scandariato et al. (2017), where the evolutionary timescale ofactive regions found shows typically longer values, on the orderof a few stellar rotations. This indicates that the photosphere ofGJ 740 is more dynamic than what is typically found for fieldM-dwarfs. The amplitude of the correlated noise decreases withincreasing wavelength. Consistently with the periodogram anal-ysis, this suggests that the correlated signal is due to the pres-ence of cool spots corotating with the stellar surface. The stellardimming during the survey is confirmed, supporting the scenariowhere the spot coverage (and the activity level) increases withtime. With regard to the planetary signal, the semi-major axis valueshown in Table 5 positions GJ 740 b in a close-in orbit to itsparent star. We computed the habitable zone of GJ 740 basedon the methodologies published by Selsis et al. (2007) and Kop-parapu (2013). The first one provides a range between 0.14 and0.66 AU, while the second one results in a conservative range be-tween 0.25 and 0.48 AU, and an optimistic range between 0.20and 0.51 AU. Therefore, we found that GJ 740 b is located out ofthe habitable zone of its parent star. The lack of a radius measure-
Article number, page 10 of 18. Toledo-Padrón et al.: A super-Earth on a close-in orbit around the M1V star GJ 740 P orb [d] M a ss [ M ⊕ ] M Jup M Sat M Nep M Earth
GJ740bHADESM0M1M2M3M4M5M8GJ740bHADESM0M1M2M3M4M5M8
Fig. 8.
Mass-period diagram including the detected exoplanets fromNASA exoplanets archive with published masses and orbital periods or-biting around M-type stars. The sub-spectral type of the parent star is in-dicated with a unique symbol and color. GJ 740 b has been representedwith an unfilled black square, and the HADES detections (GJ 3998b andGJ 3998c, A ff er et al. 2016 ; GJ 625b, Suárez Mascareño et al. 2017 :GJ 3942 b, Perger et al. 2017b ; Gl 15 A b and Gl 15 A c, Pinamontiet al. 2018 ; Gl 686 b, A ff er et al. 2019 ; Gl 49 b, Perger et al. 2019 ;and GJ 685 b, Pinamonti et al. 2019) have been marked with pink un-filled dots. The four horizontal dashed lines indicate the mass of Jupiter,Saturn, Neptune, and the Earth as a reference. The top and right panelscontain the mass and orbital period distribution of the sample. ment does not allow for a precise description of the compositionof GJ 740 b with theoretical models, but its mass and short or-bital period suggest a rocky composition (Weiss & Marcy 2014).The posterior distribution of the eccentricity of the planet pre-sented in Fig. 6 shows compatibility with a null value at 2 σ .This has been proven to be usual for short-period Keplerian or-bits (Kipping 2013) and cases similar to the one of GJ 740 b canbe found in the literature (Astudillo-Defru et al. 2017c; Melén-dez et al. 2017; Feng et al. 2019). To compare GJ 740 b withother detected planets around M-dwarfs with measured masseswe created the mass-period diagram represented in Fig. 8.Figure 8 shows that GJ 740 b falls within the peak of theorbital period distribution and is very close to the mass peak. Itis positioned as the planet with the second shortest orbital periodaround an M1 star after L 168-9 b (Astudillo-Defru et al. 2020).The super-Earth region of the diagram (between 2 and 10 M ⊕ )is the most crowded zone, lacking any detected sub-Neptunes,Neptune-like, and Jovian planets at short periods. The diagramalso shows a gap of low-mass planets with long periods due toinstrumental limitations.The search for a photometric counterpart of the planetarysignal caused by the transits of the planet did not reveal anymatch within our photometric datasets. Using the mass-radiusrelation for exoplanets found by Otegi et al. (2020) we esti-mate a radius of 1.43 + . − . R ⊕ for GJ 740 b assuming a density P orb [d] M a ss [ M ] RMS [m/s]
Fig. 9.
Distribution of the RMS of the residuals in the RV time-seriesafter subtracting the long-term signal with a sinusoidal function whoseamplitude is calculated from the considered values of mass and period. of ρ P > − . Such a radius value leads to a transit depthof 0.5 mmag, which is out of the precision range provided by thephotometric instruments used in this work. The lack of a TESS light curve for this target precludes a deeper analysis of this pos-sible photometric signal. Future
TESS observations on this targetare planned between 9 July and 5 August of 2022 within Sec-tor 54. The
CHEOPS (CHaracterising ExOPlanet Satellite) tele-scope would be an ideal instrument to check for the occurrenceof transits.
We studied the possibility of having a second planet causingthe ∼ ff erences with respect to the resultsobtained from the activity indicators. We calculated the range ofmasses associated with the plausible orbital period of this planetin Fig. 9 using a sinusoidal model.Figure 9 indicates that this second planet would be char-acterized by a mass of ∼
100 M ⊕ . The existence of this high-mass companion is favored by the greater statistical possibilityof finding super-Earths like GJ 740 b in multi-planetary systems(Batalha et al. 2013; Ribas et al. 2018). Nevertheless, super-Earths with short orbital periods have been proven to be morelikely to be on single-planetary systems than their analogs withlonger orbital periods (Weiss et al. 2018); although only a few gi-ant planets have been detected around M-dwarfs (Correia et al.2010; Forveille et al. 2011; Anglada-Escudé et al. 2012; Leeet al. 2013; Morales et al. 2019). In Fig. 8, only two planetswith a period greater than 1000 d orbiting a M1 star are shown:GJ 328 b (Robertson et al. 2013b) and GJ 832 b (Bailey et al.2009). Both of them are Jupiter like planets with a mass of2.30 ± Jup and 0.64 ± Jup , and orbital separation of4.5 ± ± Article number, page 11 of 18 & A proofs: manuscript no. A_super-Earth_on_a_close-in_orbit_around_the_M1V_star_GJ740
Orbital Separation [AU] C o m pan i on M a ss [ M J up ] Fig. 10.
Diagram of the minimum mass of a planetary companion forGJ 740 at di ff erent orbital radius based on the proper motion di ff erencemethod. To explore the possible origins of this signal, we performed acorrelation study between the RV and the stellar activity indica-tors based on the Pearson coe ffi cient (Pearson 1895). We calcu-lated this coe ffi cient along with the p-value crossing all the time-series for each individual spectrograph first, obtaining a low non-significant correlation in HARPS and an intermediate significantcorrelation in HARPS-N. This indicates a di ff erent behavior inthe stellar activity in the epoch when the HARPS-N measure-ments were taken. We then subtract the S mw contribution to theRV time-series, which causes a decrease in the PSD associatedwith the long-term signal in the periodogram but keeping a FAPbelow the 0.1% level. Thus, we cannot conclude that this signalis entirely related to the stellar activity of GJ 740.Considering that GJ 740 is su ffi ciently bright to be observedby both Gaia and Hipparcos, we quantified the detection lim-its in the mass-separation diagram based on the proper motiondi ff erence technique. Using the formalism presented in Kervellaet al. (2019) (Equations 13, 14, and 15) we produced the diagramshown in Fig. 10.Although there is no evidence for a statistically significantproper motion anomaly in GJ 740, Fig. 10 indicates that an ob-ject at 3-4 AU (encompassing the orbital period of 9.3 yr of thecandidate planet) with a mass of around 0.6 M Jup can be ruled outat the 1-sigma level. This means that we can place an approxi-mate limit on the inclination of the possible companion around30 deg. To acquire sensitivity to a Saturn-mass object, such asthe one we might be seeing in the RV time-series, we will haveto wait for future Gaia data release, starting with DR3 (in lessthan two years’ time). An improvement of a factor of 2 in masssensitivity at that period is likely to be achieved by combiningimproved calibration schemes for bright stars such as GJ 740and more data undergoing processing.The possibility that the signal is related to the magnetic cy-cle of the star is not clear due to the uncertainties in the peri-odicity of the signal from all the time-series and the time cov-erage of our dataset, which is not enough to trace two periodsof the cycle. This explanation for the signal is di ffi cult to proveif we look at the low number of M-dwarfs with published andwell-measured long-period cycles in the literature (Gomes daSilva et al. 2012; Savanov 2012; Robertson et al. 2013a; Toledo-Padrón et al. 2019), along with the probability that an M-dwarfthat presents long-term activity variability may not present RV changes related to the magnetic cycle (Gomes da Silva et al.2012). The peak of the cycle length for early M-type stars hasbeen located around 6 yr (Gomes da Silva et al. 2012; SuárezMascareño et al. 2016). The case of BD-114672, studied by Bar-bato et al. (2020), is a similar case to GJ 740, showing how alate K-type star with a mass similar to GJ 740 can exhibit botha long-period planet and cycle. Consequently, we conclude thatthe origin of the long-term RV signal is unclear until further ob-servations are carried out on GJ 740.Considering the mass of the candidate, the moderately oldage of the system, and a favorable projected separation of ∼
7. Conclusions
Our analysis of the 129 HARPS-N, 57 HARPS, and 32CARMENES spectra of GJ 740 taken over 11 yr shows the pres-ence of a super-Earth orbiting the star with an orbital period of2.37756 + . − . d and an RV semi-amplitude of 2.13 + . − . m s − .This planet presents a minimum mass of M p sin i = + . − . M ⊕ and a transit probability of 9%. We analyzed 474 photometricmeasurements from ASAS, 2350 SuperWASP measurements,and 5 years’ worth of EXORAP measurements to search for apossible periodic signal caused by the transit of the planet inthese time-series; however, none of the peaks in the periodogramaround the orbital period of the planet present enough statisticalsignificance.Our study of five di ff erent spectroscopic time-series revealsthat GJ 740 presents variations consistent with a long-term cycleof 7.67 ± ± + . − . d and 35.563 ± σ . The MCMC analysis carriedout on this signal did not converge to a clear eccentricity valueand its origin cannot be determined given the time-span of ourcurrent dataset. Acknowledgements.
B.T.P. acknowledges Fundación La Caixa for the financialsupport received in the form of a Ph.D. contract. A.S.M. acknowledges finan-cial support from the Spanish Ministry of Science and Innovation (MICINN)under the 2019 Juan de la Cierva Programme. J.I.G.H. acknowledges finan-cial support from Spanish MICINN under the 2013 Ramón y Cajal programRYC-2013-14875. B.T.P., A.S.M., J.I.G.H., R.R. acknowledge financial sup-port from the Spanish MICINN AYA2017-86389-P. I.R. and M.Pe. acknowledgesupport from the Spanish MICINN and the Fondo Europeo de Desarrollo Re-gional (FEDER) through grant PGC2018-098153-B-C33, as well as the supportof the Generalitat de Catalunya / CERCA program. GAPS acknowledges supportfrom INAF through the Progetti Premiali funding scheme of the Italian Min-istry of Education, University, and Research. GAPS acknowledges financial sup-port from Progetto Premiale 2015 FRONTIERA (OB.FU. 1.05.06.11) fundingscheme of the Italian Ministry of Education, University, and Research. G.S. ac-knowledges the funding support from Italian Space Agency (ASI) regulated by“Accordo ASI-INAF n. 2013-016-R.0 del 9 luglio 2013 e integrazione del 9luglio 2015”. This research has received financial support from the agreementASI-INAF n.2018-16-HH.0. The results of this paper were based on observa-tions made with the Italian Telescopio Nazionale Galileo (TNG), operated onthe island of La Palma by the INAF-Fundación Galileo Galilei at the Roque deLos Muchachos Observatory of the Instituto de Astrofísica de Canarias (IAC);observations made with the HARPS instrument on the ESO 3.6-m telescope atLa Silla Observatory (Chile); and observations made with the CARMENES in-strument. CARMENES is an instrument for the Centro Astronómico Hispano-Alemán de Calar Alto (CAHA, Almería, Spain). CARMENES is funded by
Article number, page 12 of 18. Toledo-Padrón et al.: A super-Earth on a close-in orbit around the M1V star GJ 740 the German Max-Planck-Gesellschaft (MPG), the Spanish Consejo Superior deInvestigaciones Científicas (CSIC), the European Union through FEDER / ERFFICTS-2011-02 funds, and the members of the CARMENES Consortium (Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Andalucía, Lan-dessternwarte Königstuhl, Institut de Ciències de l’Espai, Insitut für Astro-physik Göttingen, Universidad Complutense de Madrid, Thüringer Landesstern-warte Tautenburg, Instituto de Astrofísica de Canarias, Hamburger Sternwarte,Centro de Astrobiología and Centro Astronómico Hispano-Alemán), with addi-tional contributions by the Spanish MICINN through projects RYC2013-14875,AYA2015-69350-C3-2-P, AYA2016-79425-C3-1 / / / / http://research.cs.wisc.edu/htcondor/ ), partlyfinanced by the MICINN with FEDER funds, code IACA13-3E-2493. This re-search has made use of the NASA Exoplanet Archive, which is operated bythe California Institute of Technology, under contract with the National Aero-nautics and Space Administration under the Exoplanet Exploration Program.This paper makes use of data from the first public release of the WASP data(Butters et al. 2010) as provided by the WASP consortium and services at theNASA Exoplanet Archive, which is operated by the California Institute of Tech-nology, under contract with the National Aeronautics and Space Administra-tion under the Exoplanet Exploration Program. This work has made use ofdata from the European Space Agency (ESA) mission Gaia ( ), processed by the Gaia
Data Processing and Anal-ysis Consortium (DPAC, ). Funding for the DPAC has been provided by national institutions,in particular, the institutions participating in the
Gaia
Multilateral Agreement.
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Appendix A: Additional figures
Article number, page 15 of 18 & A proofs: manuscript no. A_super-Earth_on_a_close-in_orbit_around_the_M1V_star_GJ740
Table A.1.
Priors and parameters related to the long-term and rotation signals obtained from the final RV MCMC analysis.
Parameter Priors ValueCycle K cycle [m s − ] U (0.01, 20.0) 4.22 + . − . P cycle [d] U (2300.0, 3900.0) 3363 + − T [d] U (2500.0, 3600.0) 261 + − Rotation K LU (8.0, 40.0) 4.3 + . − . m s − ∗ ) P rot [d] Fixed 36.1 + . − . t s [d] LU (1.0, 300.0) 5.2 + . − . log(C) LU (0.0, 1.0) − + − Remaining Parametersjitter
HARPS [m s − ] LU (0.01, 4.0) 0.20 + . − . jitter HARPS − N [m s − ] LU (0.01, 4.0) 1.21 + . − . jitter CARMENES [m s − ] LU (0.01, 4.0) 0.87 + . − . o ff set HARPS [m s − ] U ( − − + . − . o ff set HARPS − N [m s − ] U ( − + . − . o ff set CARMENES [m s − ] U ( − − + . − . ( ∗ ) This value was calculated as the root square of the K posterior distribution results.Article number, page 16 of 18. Toledo-Padrón et al.: A super-Earth on a close-in orbit around the M1V star GJ 740 Fig. A.1.
Posterior distributions of the cycle and rotation fitted parameters from the cycle + rotation + Keplerian model applied to the RV time-series.The 16th-84th percentiles are represented through vertical dashed lines. Article number, page 17 of 18 & A proofs: manuscript no. A_super-Earth_on_a_close-in_orbit_around_the_M1V_star_GJ740