arXiv subjects

Steven S. Vogt

Publications and source records attributed to Steven S. Vogt.

At least 19 recordsLinked to original sources

arXiv2026

Radial Velocity Evidence for a Post-Mass-Transfer Massive Binary System NaSt1

We present multi-epoch high-resolution optical spectroscopy ($R \simeq 80{,}000$) of the emission-line object NaSt1 to test its proposed binary nature, along with long-term multiband photometry, mid-infrared spectroscopy, and spatially resolved integral field unit (IFU) spectroscopy to probe the circumstellar kinematics of the system. We detect two groups of 36 emission lines showing radial velocity (RV) variation with a mean period of 311 $\pm$ 5 d, but varying in opposite phase. We associate these two groups with the optically thick wind of the stripped primary star and the wind-wind collision region with the companion star, providing strong evidence for binarity. The RV and light curve (LC) periods are consistent within the uncertainties, ruling out ellipsoidal modulation, which would require an orbital period of about 620 d. The RV-LC phase relationship and high-ionization lines favor binary interaction over pulsations. We model the 1--5~$μ$m spectrum of NaSt1 and find two optically thin dust components: hot $T_{\rm h} \simeq 1230$ K, $M_{\rm h} \simeq 2 \times 10^{-10} M_{\odot}$ and warm $T_{\rm c} \simeq 660$ K, $M_{\rm c} \simeq 3 \times 10^{-8} M_{\odot}$. IFU spectroscopy spatially resolves the circumstellar medium in the [\ion{N}{2}] $\lambda6548$ and $\lambda6584$ emission lines, showing a deprojected expansion velocity of $\sim31$ km~s$^{-1}$, implying a dynamical age of $\sim40$ yr. This short timescale suggests that the nebula was produced by recent mass loss. The system may represent a Galactic analog of a massive binary undergoing a mass-loss process to become a stripped-envelope supernova progenitor.

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arXiv2026

The Discovery of K2-232c: Divergent Formation Histories for Hot and Warm Jupiters Based on Outer Companion Eccentricity

Ever since their discovery, hot Jupiters have been one of the most studied types of exoplanets to exist thanks to their significant size, their proximity to their host star, and their significant departure from anything present in our solar system. Yet, the details of their formation and evolution remain unclear, including their connection, if any, to the wider-orbiting warm Jupiter population. In this work, we present the discovery of K2-232c, an eccentric cold Jupiter ($P = 1950 ^{+140}_{-120}$ days, $e=0.352^{+0.095}_{-0.076}$, $M\sin{i} = 5.31^{+0.48}_{-0.45} {M_{\rm Jup}}$) companion in a known warm Jupiter ($P = 11.1684377 \pm 0.0000010$ days, $e=0.245^{+0.023}_{-0.024}$, $M = 0.427^{+0.039}_{-0.036} {M_{\rm Jup}}$) system. Placing this system in context with the literature, we find that cold Jupiter eccentricities are generally higher in hot Jupiter systems as compared to warm Jupiter systems, suggesting the formation of hot Jupiters is more dynamically violent than warm Jupiters. This adds further evidence to the claim that these two populations are independent from one another with cold Jupiters appearing to play a crucial role in shaping the formation of both.

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arXiv2025

An updated catalog of HIRES/Keck radial velocity measurements. Including Ca II H&K measurements

The first HIRES/Keck precision radial velocity (RV) catalog was released in 2017; it was followed by a second release in 2019, which incorporated corrections for small but significant systematic errors. The manifestation of stellar activity accompanied by systematic errors could affect the detection of exoplanets via the RV method. We expanded the HIRES catalog to March 2023 using publicly available spectra. Furthermore, we included the chromospheric emission line Ca II H&K indicator ($R_{\mathrm{HK}}^\prime$), which is among the most prominent tracers of stellar activity. The precision RVs were obtained using an iodine gas absorption cell and corrected for minor systematic errors. $R_{\mathrm{HK}}^\prime$ measurements were derived by rectifying the observed spectra with PHOENIX synthetic spectra models in six narrow bands surrounding the H and K lines, then subtracting the photospheric contribution. We present an updated HIRES/Keck precision RV catalog featuring 78,920 RV measurements for 1,702 stars. High-quality $R_{\mathrm{HK}}^\prime$ measurements are provided for ~ 40% of the HIRES catalog. The updated catalog can help distinguish stellar activity effects from planetary signals in RV time series, thereby corroborating previously detected planetary candidates and aiding in the detection of new ones.

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arXiv2023

Revised orbits of the two nearest Jupiters

With its near-to-mid-infrared high contrast imaging capabilities, JWST is ushering us into a golden age of directly imaging Jupiter-like planets. As the two closest cold Jupiters, $\varepsilon$ Ind A b and $\varepsilon$ Eridani b have sufficiently wide orbits and adequate infrared emissions to be detected by JWST. To detect more Jupiter-like planets for direct imaging, we develop a GOST-based method to analyze radial velocity data and multiple Gaia data releases simultaneously. Without approximating instantaneous astrometry by catalog astrometry, this approach enables the use of multiple Gaia data releases for detection of both short-period and long-period planets. We determine a mass of $2.96_{-0.38}^{+0.41}$ $M_{\rm Jup}$ and a period of $42.92_{-4.09}^{+6.38}$ yr for $\varepsilon$ Ind A b. We also find a mass of $0.76_{-0.11}^{+0.14}$ $M_{\rm Jup}$, a period of $7.36_{-0.05}^{+0.04}$ yr, and an eccentricity of 0.26$_{-0.04}^{+0.04}$ for $\varepsilon$ Eridani b. The eccentricity differs from that given by some previous solutions probably due to the sensitivity of orbital eccentricity to noise modeling. Our work refines the constraints on orbits and masses of the two nearest Jupiters and demonstrate the feasibility of using multiple Gaia data releases to constrain Jupiter-like planets.

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arXiv2023

Doppler Constraints on Planetary Companions to Nearby Sun-like Stars: An Archival Radial Velocity Survey of Southern Targets for Proposed NASA Direct Imaging Missions

Directly imaging temperate rocky planets orbiting nearby, Sun-like stars with a 6-m-class IR/O/UV space telescope, recently dubbed the Habitable Worlds Observatory, is a high priority goal of the Astro2020 Decadal Survey. To prepare for future direct imaging surveys, the list of potential targets should be thoroughly vetted to maximize efficiency and scientific yield. We present an analysis of archival radial velocity data for southern stars from the NASA/NSF Extreme Precision Radial Velocity Working Group's list of high priority target stars for future direct imaging missions (drawn from the HabEx, LUVOIR, and Starshade studies). For each star, we constrain the region of companion mass and period parameter space we are already sensitive to based on the observational baseline, sampling, and precision of the archival RV data. Additionally, for some of the targets we report new estimates of magnetic activity cycle periods, rotation periods, improved orbital parameters for previously known exoplanets, and new candidate planet signals that require further vetting or observations to confirm. Our results show that for many of these stars we are not yet sensitive to even Saturn-mass planets in the habitable zone, let alone smaller planets, highlighting the need for future EPRV vetting efforts before the launch of a direct imaging mission. We present evidence that the candidate temperate super-Earth exoplanet HD 85512 b is most likely due to the star's rotation, and report an RV acceleration for delta Pav which supports the existence of a distant giant planet previously inferred from astrometry.

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arXiv2022

3-D selection of 167 sub-stellar companions to nearby stars

We analyze 5108 AFGKM stars with at least five high precision radial velocity points as well as Gaia and Hipparcos astrometric data utilizing a novel pipeline developed in previous work. We find 914 radial velocity signals with periods longer than 1000\,d. Around these signals, 167 cold giants and 68 other types of companions are identified by combined analyses of radial velocity, astrometry, and imaging data. Without correcting for detection bias, we estimate the minimum occurrence rate of the wide-orbit brown dwarfs to be 1.3\%, and find a significant brown dwarf valley around 40 $M_{\rm Jup}$. We also find a power-law distribution in the host binary fraction beyond 3 au similar to that found for single stars, indicating no preference of multiplicity for brown dwarfs. Our work also reveals nine sub-stellar systems (GJ 234 B, GJ 494 B, HD 13724 b, HD 182488 b, HD 39060 b and c, HD 4113 C, HD 42581 d, HD 7449 B, and HD 984 b) that have previously been directly imaged, and many others that are observable at existing facilities. Depending on their ages we estimate that an additional 10-57 sub-stellar objects within our sample can be detected with current imaging facilities, extending the imaged cold (or old) giants by an order of magnitude.

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arXiv2022

A new third planet and the dynamical architecture of the HD33142 planetary system

Based on recently-taken and archival HARPS, FEROS and HIRES radial velocities (RVs), we present evidence for a new planet orbiting the first ascent red giant star HD33142 (with an improved mass estimate of 1.52$\pm$0.03 M$_\odot$), already known to host two planets. We confirm the Jovian mass planets HD33142 b and c with periods of $P_{\rm b}$ = 330.0$_{-0.4}^{+0.4}$ d and $P_{\rm c}$ = 810.2$_{-4.2}^{+3.8}$ d and minimum dynamical masses of $m_{\rm b}\sin{i}$ = 1.26$_{-0.05}^{+0.05}$ M$_{\rm Jup}$ and $m_{\rm c}\sin{i}$ = 0.89$_{-0.05}^{+0.06}$ M$_{\rm Jup}$. Furthermore, our periodogram analysis of the precise RVs shows strong evidence for a short-period Doppler signal in the residuals of a two-planet Keplerian fit, which we interpret as a third, Saturn-mass planet with $m_\mathrm{d}\sin{i}$ = 0.20$_{-0.03}^{+0.02}$ M$_{\rm Jup}$ on a close-in orbit with an orbital period of $P_{\rm d}$ =89.9$_{-0.1}^{+0.1}$ d. We study the dynamical behavior of the three-planet system configurations with an N-body integration scheme, finding it long-term stable with the planets alternating between low and moderate eccentricities episodes. We also performed N-body simulations, including stellar evolution and second-order dynamical effects such as planet-stellar tides and stellar mass-loss on the way to the white dwarf phase. We find that planets HD33142 b, c and d are likely to be engulfed near the tip of the red giant branch phase due to tidal migration. These results make the HD33142 system an essential benchmark for the planet population statistics of the multiple-planet systems found around evolved stars.

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arXiv2022

Revisiting the Full Sets of Orbital Parameters for the XO-3 System: No evidence for Temporal Variation of the Spin-Orbit Angle

We present 12 new transit light curves and 16 new out-of-transit radial velocity measurements for the XO-3 system. By modelling our newly collected measurements together with archival photometric and Doppler velocimetric data, we confirmed the unusual configuration of the XO-3 system, which contains a massive planet ($M_P=11.92^{+0.59}_{-0.63} M_J$) on a relatively eccentric ($e=0.2853^{+0.0027}_{-0.0026}$) and short-period ($3.19152 \pm 0.00145\,$day) orbit around a massive star ($M_*=1.219^{+0.090}_{-0.095} M_{\odot}$). Furthermore, we find no strong evidence for a temporal change of either $V\sin i_{*}$ (and by extension, the stellar spin vector of XO-3), or the transit profile (and thus orbital angular momentum vector of XO-3b). We conclude that the discrepancy in previous Rossiter-McLaughlin measurements ($70.0^{\circ} \pm 15.0^{\circ}$ (Hebrard et al. 2008); $37.3^{\circ} \pm 3.7^{\circ}$ (Winn et al. 2009); $37.3^{\circ} \pm 3.0^{\circ}$ (Hirano et al. 2011)) may have stemmed from systematic noise sources.

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arXiv2021

Optimized modeling of Gaia-Hipparcos astrometry for the detection of the smallest cold Jupiter and confirmation of seven low mass companions

To fully constrain the orbits of low mass circumstellar companions, we conduct combined analyses of the radial velocity data as well as the Gaia and Hipparcos astrometric data for eight nearby systems. Our study shows that companion-induced position and proper motion differences between Gaia and Hipparcos are significant enough to constrain orbits of low mass companions to a precision comparable with previous combined analyses of direct imaging and radial velocity data. We find that our method is robust to whether we use Gaia DR2 or Gaia EDR3, as well as whether we use all of the data, or just proper motion differences. In particular, we fully characterize the orbits of HD 190360 b and HD 16160 C for the first time. With a mass of 1.8$\pm$0.2$m_{\rm Jup}$ and an effective temperature of 123-176 K and orbiting around a Sun-like star, HD 190360 b is the smallest Jupiter-like planet with well-constrained mass and orbit, belonging to a small sample of fully characterized Jupiter analogs. It is separated from its primary star by 0.25$''$ and thus may be suitable for direct imaging by the CGI instrument of the Roman Space Telescope.

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arXiv2021

The Aligned Orbit of the Eccentric Warm Jupiter K2-232b

Measuring the obliquity distribution of stars hosting warm Jupiters may help us to understand the formation of close-orbiting gas giants. Few such measurements have been performed due to practical difficulties in scheduling observations of the relatively infrequent and long-duration transits of warm Jupiters. Here, we report a measurement of the Rossiter-McLaughlin effect for K2-232b, a warm Jupiter (M_P=0.39 M_Jup) on an 11.17-day orbit with an eccentricity of 0.26. The data were obtained with the Automated Planet Finder during two separate transits. The planet's orbit appears to be well-aligned with the spin axis of the host star, with a projected spin-orbit angle of lambda = -11.1+/-6.6 deg. Combined with the other available data, we find that high obliquities are almost exclusively associated with planets that either have an orbital separation greater than 10 stellar radii or orbit stars with effective temperatures hotter than 6,000K. This pattern suggests that the obliquities of the closest-orbiting giant planets around cooler stars have been damped by tidal effects.

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arXiv2020

A collage of small planets from the Lick Carnegie Exoplanet Survey : Exploring the super-Earth and sub-Neptune mass regime

Analysis of new precision radial velocity (RV) measurements from the Lick Automated Planet Finder (APF) and Keck HIRES have yielded the discovery of three new exoplanet candidates orbiting two nearby K dwarfs not previously reported to have companions (HD 190007 & HD 216520). We also report new velocities from both the APF and the Planet Finder Spectrograph (PFS) for the previously reported planet host stars GJ 686 and HD 180617 and update the corresponding exoplanet orbital models. Of the newly discovered planets, HD 190007 b has a period of 11.72 days, an RV semi-amplitude of K = 5.64$\pm$0.55 m s$^{-1}$, a minimum mass of 16.46$\pm$1.66 $\rm M_{\oplus}$, and orbits the slightly metal-rich, active K4 dwarf star HD 190007 (d = 12.7 pc). HD 216520 b has an orbital period of 35.45 days, an RV semi-amplitude of K = 2.28$\pm$0.20 m s$^{-1}$, and a minimum mass of 10.26$\pm$0.99 $\rm M_{\oplus}$, while HD 216520 c has an orbital period of P = 154.43 days, an RV semi-amplitude of K = 1.29$\pm0.22$ m s$^{-1}$, and a minimum mass of 9.44$\pm$1.63 $\rm M_{\oplus}$. Both of these planets orbit the slightly metal-poor, inactive K0 dwarf star HD 216520 (d = 19.6 pc). We find that our updated best fit models for HD 180617 b and GJ 686 b are in good agreement with the previously published results. For HD 180617 b we obtain an orbital period of 105.91 days, an RV semi-amplitude of K = 2.696$\pm$0.22 m s$^{-1}$, and a minimum mass of 2.214$\pm$1.05 $\rm M_{\oplus}$. For GJ 686 b we find the orbital period to be 15.53 days, the RV semi-amplitude to be K = 3.00$\pm$0.18 m s$^{-1}$, and the minimum mass to be 6.624$\pm$0.432 $\rm M_{\oplus}$. Using an injection-recovery exercise, we find that HD 190007 b and HD 216520 b are unlikely to have additional planets with masses and orbital periods within a factor of two, in marked contrast to $\sim$85\% of planets in this mass and period range found with Kepler.

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arXiv2020

Exploring the robustness of Keplerian signals to the removal of active and telluric features

We examine the influence of activity- and telluric-induced radial velocity signals on high resolution spectra taken with an iodine absorption cell. We exclude 2 Angstrom spectral chunks containing active and telluric lines based on the well characterised K1V star Alpha Centauri B and illustrate the method on Epsilon Eridani - an active K2V star with a long period low amplitude planetary signal. After removal of the activity- and telluric-sensitive parts of the spectrum from the radial velocity calculation, the significance of the planetary signal is increased and the stellar rotation signal disappears. In order to assess the robustness of the procedure, we perform Monte Carlo simulations based on removing random chunks of the spectrum. Simulations confirm that the removal of lines impacted by activity and tellurics provides a method for checking the robustness of a given Keplerian signal. We also test the approach on HD 40979 which is an active F8V star with a large amplitude planetary signal. Our Monte Carlo simulations reveal that the significance of the Keplerian signal in the F star is much more sensitive to wavelength. Unlike the K star the removal of active lines from the F star greatly reduces the radial velocity precision. In this case, our removal of a K star active lines from an F star does not a provide a simple useful diagnostic because it has far less radial velocity information and heavily relies on the strong active lines.

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arXiv2020

Search for Nearby Earth Analogs. III. Detection of ten new planets, three planet candidates, and confirmation of three planets around eleven nearby M dwarfs

Earth-sized planets in the habitable zones of M dwarfs are good candidates for the study of habitability and detection of biosignatures. To search for these planets, we analyze all available radial velocity data and apply four signal detection criteria to select the optimal candidates. We find ten strong candidates satisfying these criteria and three weak candidates showing inconsistency over time due to data samplings. We also confirm three previous planet candidates and improve their orbital solutions through combined analyses of updated data sets. Among the strong planet candidates, HIP 38594 b is a temperate super-Earth with a mass of $8.2 \pm 1.7$ $M_\oplus$ and an orbital period of $60.7\pm0.1$ days, orbiting around an early-type M dwarf. Early-type M dwarfs are less active and thus are better hosts for habitable planets than mid-type and late-type M dwarfs. Moreover, we report the detection of five two-planet systems, including two systems made up of a warm or cold Neptune and a cold Jupiter, consistent with a positive correlation between these two types of planets. We also detect three temperate Neptunes, four cold Neptunes, and four cold Jupiters, contributing to a rarely explored planet population. Due to their proximity to the Sun, these planets on wide orbits are appropriate targets for direct imaging by future facilities such as HabEx and ELT.

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arXiv2019

Two Jovian planets around the giant star HD202696. A growing population of packed massive planetary pairs around massive stars?

We present evidence for a new two-planet system around the giant star HD202696 (= HIP105056, BD+26 4118). The discovery is based on public HIRES radial velocity measurements taken at Keck Observatory between July 2007 and September 2014. We estimate a stellar mass of 1.91$^{+0.09}_{-0.14}M_\odot$ for HD202696, which is located close to the base of the red giant branch. A two-planet self-consistent dynamical modeling MCMC scheme of the radial velocity data followed by a long-term stability test suggests planetary orbital periods of $P_{\rm b}$ = 517.8$_{-3.9}^{+8.9}$ days and $P_{\rm c}$ = 946.6$_{-20.9}^{+20.7}$ days, eccentricities of $e_{\rm b}$ = 0.011$_{-0.011}^{+0.078}$ and $e_{\rm c}$ = 0.028$_{-0.012}^{+0.065}$ , and minimum dynamical masses of $m_{\rm b}$ = 2.00$_{-0.10}^{+0.22}$\,$M_{\mathrm{Jup}}$ and $m_{\rm c}$ = 1.86$_{-0.23}^{+0.18}$,$M_{\mathrm{Jup}}$, respectively. Our stable MCMC samples are consistent with orbital configurations predominantly in a mean period ratio of 11:6 and its close-by high order mean-motion commensurabilities with low eccentricities. For the majority of the stable configurations we find an aligned or anti-aligned apsidal libration (i.e.\ $Δω$ librating around 0$^\circ$ or 180$^\circ$), suggesting that the HD202696 system is likely dominated by secular perturbations near the high-order 11:6 mean-motion resonance. The HD202696 system is yet another Jovian mass pair around an intermediate mass star with a period ratio below the 2:1 mean motion resonance. Therefore, the HD202696 system is an important discovery, which may shed light on the primordial disk-planet properties needed for giant planets to break the strong 2:1 mean motion resonance and settle in more compact orbits.

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arXiv2018

AD Leonis: Radial velocity signal of stellar rotation or spin-orbit resonance?

AD Leonis is a nearby magnetically active M dwarf. We find Doppler variability with a period of 2.23 days as well as photometric signals: (1) a short period signal which is similar to the radial velocity signal albeit with considerable variability; and (2) a long term activity cycle of 4070$\pm$120 days. We examine the short-term photometric signal in the available ASAS and MOST photometry and find that the signal is not consistently present and varies considerably as a function of time. This signal undergoes a phase change of roughly 0.8 rad when considering the first and second halves of the MOST data set which are separated in median time by 3.38 days. In contrast, the Doppler signal is stable in the combined HARPS and HIRES radial velocities for over 4700 days and does not appear to vary in time in amplitude, phase, period or as a function of extracted wavelength. We consider a variety of star-spot scenarios and find it challenging to simultaneously explain the rapidly varying photometric signal and the stable radial velocity signal as being caused by starspots co-rotating on the stellar surface. This suggests that the origin of the Doppler periodicity might be the gravitational tug of a planet orbiting the star in spin-orbit resonance. For such a scenario and no spin-orbit misalignment, the measured $v \sin i$ indicates an inclination angle of 15.5$\pm$2.5 deg and a planetary companion mass of 0.237$\pm$0.047 M$_{\rm Jup}$.

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arXiv2018

The test case of HD26965: difficulties disentangling weak Doppler signals from stellar activity

We report the discovery of a radial velocity signal that can be interpreted as a planetary-mass candidate orbiting the K dwarf HD26965, with an orbital period of 42.364$\pm$0.015 days, or alternatively, as the presence of residual, uncorrected rotational activity in the data. Observations include data from HIRES, PFS, CHIRON, and HARPS, where 1,111 measurements were made over 16 years. Our best solution for HD26965 $b$ is consistent with a super-Earth that has a minimum mass of 6.92$\pm$0.79 M$_{\oplus}$ orbiting at a distance of 0.215$\pm$0.008 AU from its host star. We have analyzed the correlation between spectral activity indicators and the radial velocities from each instrument, showing moderate correlations that we include in our model. From this analysis, we recover a $\sim$38 day signal, which matches some literature values of the stellar rotation period. However, from independent Mt. Wilson HK data for this star, we find evidence for a significant 42 day signal after subtraction of longer period magnetic cycles, casting doubt on the planetary hypothesis for this period. Although our statistical model strongly suggests that the 42-day signal is Doppler in origin, we conclude that the residual effects of stellar rotation are difficult to fully model and remove from this dataset, highlighting the difficulties to disentangle small planetary signals and photospheric noise, particularly when the orbital periods are close to the rotation period of the star. This study serves as an excellent test case for future works that aim to detect small planets orbiting `Sun-like' stars using radial velocity measurements.

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arXiv2017

A Six-Planet System Around the Star HD 34445

We present a new precision radial velocity dataset that reveals a multi-planet system orbiting the G0V star HD 34445. Our 18-year span consists of 333 precision radial velocity observations, 56 of which were previously published, and 277 which are new data from Keck Observatory, Magellan at Las Campanas Observatory, and the Automated Planet Finder at Lick Observatory. These data indicate the presence of six planet candidates in Keplerian motion about the host star with periods of 1057, 215, 118, 49, 677, and 5700 days, and minimum masses of 0.63, 0.17, 0.1, 0.05, 0.12 and 0.38 Jupiter masses respectively. The HD 34445 planetary system, with its high degree of multiplicity, its long orbital periods, and its induced stellar radial velocity half-amplitudes in the range $2 \,{\rm m\, s^{-1}} \lesssim K \lesssim 5\,{\rm m\, s^{-1}}$ is fundamentally unlike either our own solar system (in which only Jupiter and Saturn induce significant reflex velocities for the Sun), or the Kepler multiple-transiting systems (which tend to have much more compact orbital configurations)

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arXiv2017

Color difference makes a difference: four planet candidates around tau Ceti

The removal of noise typically correlated in time and wavelength is one of the main challenges for using the radial velocity method to detect Earth analogues. We analyze radial velocity data of tau Ceti and find robust evidence for wavelength dependent noise. We find this noise can be modeled by a combination of moving average models and "differential radial velocities". We apply this noise model to various radial velocity data sets for tau Ceti, and find four periodic signals at 20.0, 49.3, 160 and 642 d which we interpret as planets. We identify two new signals with orbital periods of 20.0 and 49.3 d while the other two previously suspected signals around 160 and 600 d are quantified to a higher precision. The 20.0 d candidate is independently detected in KECK data. All planets detected in this work have minimum masses less than 4$M_\oplus$ with the two long period ones located around the inner and outer edges of the habitable zone, respectively. We find that the instrumental noise gives rise to a precision limit of the HARPS around 0.2 m/s. We also find correlation between the HARPS data and the central moments of the spectral line profile at around 0.5 m/s level, although these central moments may contain both noise and signals. The signals detected in this work have semi-amplitudes as low as 0.3 m/s, demonstrating the ability of the radial velocity technique to detect relatively weak signals.

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