Precise Radial Velocity Measurements Research Articles

Radar Odometry on $SE(3)$ With Constant Velocity Motion Prior

This letter presents an approach to estimating vehicle odometry on SE(3) using a high resolution automotive radar sensor. We combine a constant velocity SE(3) motion prior with a 3D radar point cloud measurement model in a sliding window optimization scheme. We leverage radar's highly precise radial velocity measurement to compensate for point cloud sparsity and improve data association. Our approach is tested using real-world measurements from a prototype high-resolution radar sensor. We demonstrate the results of this approach for 6D motion estimation. In addition, we show that our approach is comparable to state-of-the-art SE(2) radar odometry estimates while running a full order of magnitude faster.

The HARPS search for southern extra-solar planets

Context.We present precise radial-velocity measurements of five solar-type stars observed with the HARPS Echelle spectrograph mounted on the 3.6-m telescope in La Silla (ESO, Chile). With a time span of more than 10 yr and a fairly dense sampling, the survey is sensitive to low mass planets down to super-Earths on orbital periods up to 100 days.Aims.Our goal was to search for planetary companions around the stars HD 39194, HD 93385, HD 96700, HD 154088, and HD 189567 and use Bayesian model comparison to make an informed choice on the number of planets present in the systems based on the radial velocity observations. These findings will contribute to the pool of known exoplanets and better constrain their orbital parameters.Methods.A first analysis was performed using the Data & Analysis Center for Exoplanets online tools to assess the activity level of the star and the potential planetary content of each system. We then used Bayesian model comparison on all targets to get a robust estimate on the number of planets per star. We did this using the nested sampling algorithm POLYCHORD. For some targets, we also compared different noise models to disentangle planetary signatures from stellar activity. Lastly, we ran an efficient Markov chain Monte Carlo algorithm for each target to get reliable estimates for the planets’ orbital parameters.Results.We identify 12 planets within several multiplanet systems. These planets are all in the super-Earth and sub-Neptune mass regime with minimum masses ranging between 4 and 13M⊕and orbital periods between 5 and 103 days. Three of these planets are new, namely HD 93385 b, HD 96700 c, and HD 189567 c.

Precision wavelength calibration for radial velocity measurements using uranium lines between 3800 and 6900 Å

We present here the precise wavelength calibration of a high-resolution spectrum using Uranium (U) lines in the wavelength range of 3809 - 6833 \AA\ for precision radial velocity measurements for exoplanet detection or related astrophysical sciences. We identify 1540 well-resolved U lines from a high-resolution (R=67,000) spectrum of the uranium-argon hollow cathode lamp (UAr HCL) using PARAS spectrograph in the aforesaid wavelength range. We calculate the neutral and first allowed transitions (Ritz wavelength) of U from its known energy levels and compare them with our observed central wavelengths. We measure an offset of -0.15 m\AA\space in our final U line list. The line list has an average measurement uncertainty of 15 m s$^{-1}$ (0.013 pixels or 0.28 m\AA). We included these lines to the PARAS data analysis framework to perform the wavelength calibration and then calculate the multi-order Radial Velocity (RV) of PARAS spectra. The typical dispersion of residuals around the wavelength solution of a UAr spectrum, using U lines, is found to be 0.8 m\AA\space($\sim$45 m s$^{-1}$). With the use of this line list, we present our results for the precision RV of an on-sky source (A RV standard star), and an off-sky source (A HCL) observed with PARAS along with UAr HCL. We measure the dispersion in absolute drift difference between two fibers (inter-fiber drift) for a span of 6.5 hours to be 88 cm s$^{-1}$, and the RV dispersion (${\sigma_{RV}}$) for a RV standard star, HD55575 over the course of $\sim$450 days to be 3.2 m s$^{-1}$. These results are in good agreement with the previous ones measured using the ThAr HCL. It proves that the ThAr HCL with $\sim$ 99\% pure-Th are replaceable with the UAr HCL for the wavelength calibration of the high-resolution spectrographs such as PARAS (R $\leq$ 67,000) to achieve a RV precision of 1-3 m s$^{-1}$ in the visible region.

TOI-1634 b: An Ultra-short-period Keystone Planet Sitting inside the M-dwarf Radius Valley

Abstract Studies of close-in planets orbiting M dwarfs have suggested that the M-dwarf radius valley may be well explained by distinct formation timescales between enveloped terrestrials and rocky planets that form at late times in a gas-depleted environment. This scenario is at odds with the picture that close-in rocky planets form with a primordial gaseous envelope that is subsequently stripped away by some thermally driven mass-loss process. These two physical scenarios make unique predictions of the rocky/enveloped transition’s dependence on orbital separation such that studying the compositions of planets within the M-dwarf radius valley may be able to establish the dominant physics. Here, we present the discovery of one such keystone planet: the ultra-short-period planet TOI-1634 b (P = 0.989 days, F = 121 F ⊕ , r p = 1.790 − 0.081 + 0.080 R ⊕) orbiting a nearby M2 dwarf (K s = 8.7, R s = 0.450 R ⊙, M s = 0.502 M ⊙) and whose size and orbital period sit within the M-dwarf radius valley. We confirm the TESS-discovered planet candidate using extensive ground-based follow-up campaigns, including a set of 32 precise radial velocity measurements from HARPS-N. We measure a planetary mass of 4.91 − 0.70 + 0.68 M ⊕, which makes TOI-1634 b inconsistent with an Earth-like composition at 5.9 σ and thus requires either an extended gaseous envelope, a large volatile-rich layer, or a rocky composition that is not dominated by iron and silicates to explain its mass and radius. The discovery that the bulk composition of TOI-1634 b is inconsistent with that of Earth supports the gas-depleted formation mechanism to explain the emergence of the radius valley around M dwarfs with M s ≲ 0.5 M ⊙.

Looking for Astrometric Signals below 20 m s−1: A Jupiter-mass Planet Signature in ε Eri

Abstract The USNO ground-based astrometric program URAT-Bright in combination with the Hipparcos mission epoch astrometry provides precise proper motions of a thousand bright stars in the southern hemisphere on a time basis of about 25 yr. Small but statistically significant differences between these proper motions and Gaia EDR3 data can reveal long-period exoplanets similar to Jupiter in the nearest star systems. The presence of such a planet orbiting the magnetically active dwarf ε Eri is confirmed from both URAT-Hipparcos-EDR3 data and Hipparcos-EDR3 data with a corresponding projected velocity of (+5, +8) and (+6, +13) m s−1, respectively. These signals are formally significant at a 0.989 and 1.0 confidence. We conclude that the newest astrometric results confirm the existence of a long-period exoplanet orbiting ε Eri, which was marginally detected from precision radial velocity measurements some 20 yr ago.

An ultra-short-period transiting super-Earth orbiting the M3 dwarf TOI-1685

Dynamical histories of planetary systems, as well as the atmospheric evolution of highly irradiated planets, can be studied by characterizing the ultra-short-period planet population, which the TESS mission is particularly well suited to discover. Here, we report on the follow-up of a transit signal detected in the TESS sector 19 photometric time series of the M3.0 V star TOI-1685 (2MASS J04342248+4302148). We confirm the planetary nature of the transit signal, which has a period ofPb= 0.6691403−0.0000021+0.0000023d, using precise radial velocity measurements taken with the CARMENES spectrograph. From the joint photometry and radial velocity analysis, we estimate the following parameters for TOI-1685 b: a mass ofMb= 3.78−0.63+0.63M⊕, a radius ofRb= 1.70−0.07+0.07R⊕, which together result in a bulk density ofρb= 4.21−0.82+0.95g cm−3, and an equilibrium temperature ofTeq= 1069−16+16K. TOI-1685 b is the least dense ultra-short-period planet around an M dwarf known to date. TOI-1685 b is also one of the hottest transiting super-Earth planets with accurate dynamical mass measurements, which makes it a particularly attractive target for thermal emission spectroscopy. Additionally, we report with moderate evidence an additional non-transiting planet candidate in the system, TOI-1685 [c], which has an orbital period ofPc= 9.02−0.12+0.10d.

TOI-220 b: a warm sub-Neptune discovered byTESS

ABSTRACTIn this paper, we report the discovery of TOI-220 b, a new sub-Neptune detected by the Transiting Exoplanet Survey Satellite (TESS) and confirmed by radial velocity follow-up observations with the HARPS spectrograph. Based on the combined analysis of TESS transit photometry and high precision radial velocity measurements, we estimate a planetary mass of 13.8 ± 1.0 M⊕ and radius of 3.03 ± 0.15 R⊕, implying a bulk density of 2.73 ± 0.47 $\rm {g\,cm}^{-3}$. TOI-220 b orbits a relative bright (V= 10.4) and old (10.1 ± 1.4 Gyr) K dwarf star with a period of ∼10.69 d. Thus, TOI-220 b is a new warm sub-Neptune with very precise mass and radius determinations. A Bayesian analysis of the TOI-220 b internal structure indicates that due to the strong irradiation it receives, the low density of this planet could be explained with a steam atmosphere in radiative–convective equilibrium and a supercritical water layer on top of a differentiated interior made of a silicate mantle and a small iron core.

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N

Context. We present the current status of and new results from our search for exoplanets in a sample of solar-mass evolved stars observed with the HARPS-N and the 3.6 m Telescopio Nazionale Galileo (TNG), and the High-Resolution Spectrograph (HRS) and the 9.2 m Hobby-Eberly Telescope (HET). Aims. The aim of this project is to detect and characterize planetary-mass companions to solar-mass stars in a sample of 122 targets at various stages of evolution from the main sequence to the red giant branch, mostly subgiants and giants, selected from the Pennsylvania-Toruń Planet Search sample, and to use this sample to study relations between stellar properties, such as metallicity, luminosity, and the planet occurrence rate. Methods. This work is based on precise radial velocity (RV) measurements. We have observed the program stars for up to 14 yr with the HET/HRS and the TNG/HARPS-N. Results. We present the analysis of RV measurements with the HET/HRS and the TNG/HARPS-N of four solar-mass stars, HD 4760, HD 96992, BD+02 3313, and TYC 0434-04538-1. We found that HD 4760 hosts a companion with a minimum mass of 13.9 MJ (a = 1.14 au, e = 0.23); HD 96992 is a host to a m sin i = 1.14 MJ companion on an a = 1.24 au and e = 0.41 orbit, and TYC 0434-04538-1 hosts an m sin i = 6.1 MJ companion on an a = 0.66 au and e = 0.08 orbit. In the case of BD+02 3313 we found a correlation between the measured RVs and one of the stellar activity indicators, suggesting that the observed RV variations may either originate in stellar activity or be caused by the presence of an unresolved companion. We also discuss the current status of the project and a statistical analysis of the RV variations in our sample of target stars. Conclusions. In our sample of 122 solar-mass stars, 49 ± 5% of them appear to be single and 16 ± 3% spectroscopic binaries. The three giants hosting low-mass companions presented in this paper join the six previously identified giants in the sample.

Observable Predictions from Perturber-coupled High-eccentricity Tidal Migration of Warm Jupiters

Abstract The origin of warm Jupiters (gas giant planets with periods between 10 and 200 days) is an open question in exoplanet formation and evolution. We investigate a particular migration theory in which a warm Jupiter is coupled to a perturbing companion planet that excites secular eccentricity oscillations in the warm Jupiter, leading to periodic close stellar passages that can tidally shrink and circularize its orbit. If such companions exist in warm Jupiter systems, they are likely to be massive and close-in, making them potentially detectable. We generate a set of warm Jupiter-perturber populations capable of engaging in high-eccentricity tidal migration and calculate the detectability of the perturbers through a variety of observational metrics. We show that a small percentage of these perturbers should be detectable in the Kepler light curves, but most should be detectable with precise radial velocity measurements over a 3 month baseline and Gaia astrometry. We find these results to be robust to the assumptions made for the perturber parameter distributions. If a high-precision radial velocity search for companions to warm Jupiters does not find evidence of a significant number of massive companions over a 3 month baseline, it will suggest that perturber-coupled high-eccentricity migration is not the predominant delivery method for warm Jupiters.

The GAPS Programme at TNG

Context. Young stars and multi-planet systems are two types of primary objects that allow us to study, understand, and constrain planetary formation and evolution theories. Aims. We validate the physical nature of two Neptune-sized planets transiting TOI-942 (TYC 5909-319-1), a previously unacknowledged young star (50−20+30 Myr) observed by the TESS space mission in Sector 5. Methods. Thanks to a comprehensive stellar characterization, TESS light curve modeling and precise radial-velocity measurements, we validated the planetary nature of the TESS candidate and detected an additional transiting planet in the system on a larger orbit. Results. From photometric and spectroscopic observations we performed an exhaustive stellar characterization and derived the main stellar parameters. TOI-942 is a relatively active K2.5V star (log R′HK = −4.17 ± 0.01) with rotation period Prot = 3.39 ± 0.01 days, a projected rotation velocity v sin i⋆ = 13.8 ± 0.5 km s−1, and a radius of ~0.9 R⊙. We found that the inner planet, TOI-942 b, has an orbital period Pb = 4.3263 ± 0.0011 days, a radius Rb = 4.242−0.313+0.376 R⊕, and a mass upper limit of 16 M⊕ at 1σ confidence level. The outer planet, TOI-942 c, has an orbital period Pc = 10.1605−0.0053+0.0056 days, a radius Rc = 4.793−0.351+0.410 R⊕, and a mass upper limit of 37 M⊕ at 1σ confidence level.

A Collage of Small Planets from the Lick–Carnegie Exoplanet Survey: Exploring the Super-Earth and Sub-Neptune Mass Regime*

Abstract Analysis of new precision radial velocity (RV) measurements from the Lick Automated Planet Finder and Keck HIRES has yielded the discovery of three new exoplanet candidates orbiting the nearby stars HD 190007 and HD 216520. We also report new velocities from the APF and the Planet Finder Spectrograph and updated orbital fits for the known exoplanet host stars GJ 686 and HD 180617. Of the newly discovered planets, HD 190007 b has a period of P = 11.72 days, an RV semiamplitude of K = 5.64 ± 0.55 m s−1, a minimum mass of M pl = 16.46 ± 1.66 M ⊕, and orbits the slightly metal-rich, active K4V star HD 190007. For HD 216520 b, we find P = 35.45 days, K = 2.28 ± 0.20 m s−1, and M pl = 10.26 ± 0.99 M ⊕, while for HD 216520 c, P = 154.43 days, K = 1.29 ± 0.22 m s−1, and M pl = 9.44 ± 1.63 M ⊕. Both planets orbit the slightly metal-poor, inactive K0V star HD 216520. Our updated best-fit models for HD 180617 b and GJ 686 b are in good agreement with the published results. For HD 180617 b, we obtain P = 105.91 days and M pl = 12.214 ± 1.05 M ⊕. For GJ 686 b, we find P = 15.53 days and M pl = 6.624 ± 0.432 M ⊕. 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 2, in marked contrast to ∼85% of planets in this mass and period range discovered by Kepler.

The HD 217107 planetary system: Twenty years of radial velocity measurements

AbstractThe hot Jupiter HD 217107 b was one of the first exoplanets detected using the radial velocity (RV) method, originally reported in the literature in 1999. Today, precise RV measurements of this system span more than 20 years, and there is clear evidence of a longer‐period companion, HD 217107 c. Interestingly, both the short‐period planet (Pb ∼ 7.13 d) and long‐period planet (Pc ∼ 5059 d) have significantly eccentric orbits (eb ∼ 0.13 and ec ∼ 0.40). We present 42 additional RV measurements of this system obtained with the MINERVA telescope array and carry out a joint analysis with previously published RV measurements from four different facilities. We confirm and refine the previously reported orbit of the long‐period companion. HD 217107 b is one of a relatively small number of hot Jupiters with an eccentric orbit, opening up the possibility of detecting the precession of the planetary orbit due to general relativistic effects and perturbations from other planets in the system. In this case, the argument of periastron, ω, is predicted to change at the level of ∼0.8∘ century−1. Despite the long time baseline of our observations and the high quality of the RV measurements, we are only able to constrain the precession to be century−1. We discuss the limitations of detecting the subtle effects of precession in exoplanet orbits using RV data.

Dynamical traceback age of theβPictoris moving group

Context.TheβPictoris moving group is one of the most well-known young associations in the solar neighbourhood and several members are known to host circumstellar discs, planets, and comets. Measuring its age precisely is essential to the study of several astrophysical processes, such as planet formation and disc evolution, which are strongly age-dependent.Aims.We aim to determine a precise and accurate dynamical traceback age for theβPictoris moving group.Methods.Our sample combines the extremely preciseGaiaDR2 astrometry with ground-based radial velocities measured in an homogeneous manner. We use an updated version of our algorithm to determine dynamical ages. The new approach takes into account a robust estimate of the spatial and kinematic covariance matrices of the association to improve the sample selection process and to perform the traceback analysis.Results.We estimate a dynamical age of 18.5−2.4+2.0Myr for theβPictoris moving group. We investigated the spatial substructure of the association at the time of birth and we propose the existence of a core of stars that is more concentrated. We also provide precise radial velocity measurements for 81 members ofβPic, including ten stars with the first determinations of their radial velocities.Conclusions.Our dynamical traceback age is three times more precise than previous traceback age estimates and, more importantly, for the first time it reconciles the traceback age with the most recent estimates of other dynamical, lithium depletion boundaries and isochronal ages. This has been possible thanks to the excellent astrometric and spectroscopic precisions, the homogeneity of our sample, and the detailed analysis of binaries and membership.

Precision radial velocity measurements by the forward-modeling technique in the near-infrared

Abstract Precision radial velocity (RV) measurements in the near-infrared are a powerful tool to detect and characterize exoplanets around low-mass stars or young stars with higher magnetic activity. However, the presence of strong telluric absorption lines and emission lines in the near-infrared that significantly vary in time can prevent extraction of RV information from these spectra by classical techniques, which ignore or mask the telluric lines. We present a methodology and pipeline to derive precision RVs from near-infrared spectra using a forward-modeling technique. We applied this to spectra with a wide wavelength coverage (Y, J, and H bands, simultaneously), taken by the InfraRed Doppler (IRD) spectrograph on the Subaru 8.2 m telescope. Our pipeline extracts the instantaneous instrumental profile of the spectrograph for each spectral segment, based on a reference spectrum of the laser-frequency comb that is injected into the spectrograph simultaneously with the stellar light. These profiles are used to derive the intrinsic stellar template spectrum, which is free from instrumental broadening and telluric features, as well as model and fit individual observed spectra in the RV analysis. Implementing a series of numerical simulations using theoretical spectra that mimic IRD data, we test the pipeline and show that IRD can achieve <2 m s−1 precision for slowly rotating mid-to-late M dwarfs with a signal-to-noise ratio ≳100 per pixel at 1000 nm. Dependences of RV precision on various stellar parameters (e.g., Teff, vsin i, [Fe/H]) and the impact of telluric-line blendings on the RV accuracy are discussed through the mock spectra analyses. We also apply the RV-analysis pipeline to the observed spectra of GJ 699 and TRAPPIST-1, demonstrating that the spectrograph and the pipeline are capable of an RV accuracy of <3 m s−1 at least on a time-scale of a few months.

The EXPRES Stellar-signals Project. I. Description of Data

Abstract The EXPRES Stellar-Signals Project is providing sets of high-fidelity, spectroscopic and photometric observations to enable direct comparisons of various approaches for disentangling stellar signals and true radial velocities (RVs). We will provide all EXPRES RVs, meta data, and activity indicators as well as high-precision photometric data from the Fairborn Automatic Photoelectric Telescopes (APTs) for HD 101501, HD 34411, HD 217014, and HD 10700. Intrinsic stellar variability and the resulting apparent RVs are widely believed to dominate the error budget for extremely precise radial-velocity (EPRV) measurements. Several new methods to disentangle photospheric velocities from Keplerian velocities are being developed throughout the EPRV community. In addition to releasing data sets for testing these methods, the EXPRES Stellar-Signals Project will publish a summary of the current state of the field circa 2020 to guide next steps toward mitigating photospheric velocities in EPRV data. More information can be found on http://exoplanets.astro.yale.edu/science/activity.php.

Barycentric Corrections for Precise Radial Velocity Measurements of Sunlight

Abstract We provide formulae for the calculation of precise Doppler velocities of sunlight, in both the case of direct observations of the Sun and in reflection from the surfaces of solar system objects such as the Moon or asteroids. We discuss the meaning of a “barycentric correction” of measurements of these Doppler velocities, which is a different procedure from the analogous correction for starlight, and provide a formula for reducing such measurements to the component of the Sun’s motion in the direction of Earth or other solar system object. We have implemented this procedure in the public barycorrpy Python package and use it to explore the properties of the barycentric-corrected Doppler velocity of sunlight over 30 yr. When measured directly, we show that it is dominated by nonperiodic motion due to Jupiter and that the signals of the other planets, including Venus, are not discernible in Fourier space. We show that “detecting” Venus in Doppler velocities of sunlight will require either observing sunlight in reflection from an asteroid or modeling their individual contributions to the motion of the Sun in counterfactual kinematic or dynamical simulations of the solar system with and without them.

NGTS-11 b (TOI-1847 b): A Transiting Warm Saturn Recovered from a TESS Single-transit Event

Abstract We report the discovery of NGTS-11 b (=TOI-1847b), a transiting Saturn in a 35.46 day orbit around a mid K-type star ( = 5050 ± 80 K). We initially identified the system from a single-transit event in a TESS full-frame image light curve. Following 79 nights of photometric monitoring with an NGTS telescope, we observed a second full transit of NGTS-11 b approximately one year after the TESS single-transit event. The NGTS transit confirmed the parameters of the transit signal and restricted the orbital period to a set of 13 discrete periods. We combined our transit detections with precise radial-velocity measurements to determine the true orbital period and measure the mass of the planet. We find NGTS-11 b has a radius of , a mass of , and an equilibrium temperature of just K, making it one of the coolest known transiting gas giants. NGTS-11 b is the first exoplanet to be discovered after being initially identified as a TESS single-transit event, and its discovery highlights the power of intense photometric monitoring in recovering longer-period transiting exoplanets from single-transit events.

A Pair of TESS Planets Spanning the Radius Valley around the Nearby Mid-M Dwarf LTT 3780

Abstract We present the confirmation of two new planets transiting the nearby mid-M dwarf LTT 3780 (TIC 36724087, TOI-732, V = 13.07, K s = 8.204, R s = 0.374 R ⊙, M s = 0.401 M ⊙, d = 22 pc). The two planet candidates are identified in a single Transiting Exoplanet Survey Satellite sector and validated with reconnaissance spectroscopy, ground-based photometric follow-up, and high-resolution imaging. With measured orbital periods of P b = 0.77, P c = 12.25 days and sizes r p,b = 1.33 ± 0.07, r p,c = 2.30 ± 0.16 R ⊕, the two planets span the radius valley in period–radius space around low-mass stars, thus making the system a laboratory to test competing theories of the emergence of the radius valley in that stellar mass regime. By combining 63 precise radial velocity measurements from the High Accuracy Radial velocity Planet Searcher (HARPS) and HARPS-N, we measure planet masses of and M ⊕, which indicates that LTT 3780b has a bulk composition consistent with being Earth-like, while LTT 3780c likely hosts an extended H/He envelope. We show that the recovered planetary masses are consistent with predictions from both photoevaporation and core-powered mass-loss models. The brightness and small size of LTT 3780, along with the measured planetary parameters, render LTT 3780b and c as accessible targets for atmospheric characterization of planets within the same planetary system and spanning the radius valley.

Modeling Stellar Jitter for the Detection of Earth-Mass Exoplanets via Precision Radial Velocity Measurements

AbstractThe detection of Earth-size exoplanets is a technological and data analysis challenge. Future progress in Earth-mass exoplanet detection is expected from the development of extreme precision radial velocity measurements. Increasing radial velocity precision requires developing a new physics-based data analysis methodology to discriminate planetary signals from host-star-related effects, taking stellar variability and instrumental uncertainties into account. In this work, we investigate and quantify stellar disturbances of the planet-hosting solar-type star HD121504 (G2V spectral type) from 3D radiative modeling obtained with the StellarBox code. The model has been used for determining statistical properties of the turbulent plasma and obtaining synthetic spectroscopic observations for several Fe I lines at different locations on the stellar disk to mimic high-resolution spectroscopic observations.

The CARMENES search for exoplanets around M dwarfs

Context. GJ 1148 is an M-dwarf star hosting a planetary system composed of two Saturn-mass planets in eccentric orbits with periods of 41.38 and 532.02 days. Aims. We reanalyze the orbital configuration and dynamics of the GJ 1148 multi-planetary system based on new precise radial velocity measurements taken with CARMENES. Methods. We combined new and archival precise Doppler measurements from CARMENES with those available from HIRES for GJ 1148 and modeled these data with a self-consistent dynamical model. We studied the orbital dynamics of the system using the secular theory and direct N-body integrations. The prospects of potentially habitable moons around GJ 1148 b were examined. Results. The refined dynamical analyses show that the GJ 1148 system is long-term stable in a large phase-space of orbital parameters with an orbital configuration suggesting apsidal alignment, but not in any particular high-order mean-motion resonant commensurability. GJ 1148 b orbits inside the optimistic habitable zone (HZ). We find only a narrow stability region around the planet where exomoons can exist. However, in this stable region exomoons exhibit quick orbital decay due to tidal interaction with the planet. Conclusions. The GJ 1148 planetary system is a very rare M-dwarf planetary system consisting of a pair of gas giants, the inner of which resides in the HZ. We conclude that habitable exomoons around GJ 1148 b are very unlikely to exist.