126 research outputs found
Unbiasing the density of TTV-characterised sub-Neptunes: Update of the mass-radius relationship of 34 Kepler planets
Transit Timing Variations (TTVs) can provide useful information on compact
multi-planetary systems observed by transits, by putting constraints on the
masses and eccentricities of the observed planets. This is especially helpful
when the host star is not bright enough for radial velocity follow-up. However,
in the past decades, numerous works have shown that TTV-characterised planets
tend to have a lower densities than RV-characterised planets. Re-analysing 34
Kepler planets in the super-Earth to sub-Neptunes range using the RIVERS
approach, we show that at least part of these discrepancies was due to the way
transit timings were extracted from the light curve, which had a tendency to
under-estimate the TTV amplitudes. We recover robust mass estimates (i.e. low
prior dependency) for 23 of the planets. We compare these planets the
RV-characterised population. A large fraction of these previously had a
surprisingly low density now occupy a place of the mass-radius diagram much
closer to the bulk of the known planets, although a slight shift toward lower
densities remains, which could indicate that the compact multi-planetary
systems characterised by TTVs are indeed composed of planets which are
different from the bulk of the RV-characterised population. These results are
especially important for obtaining an unbiased view of the compact
multi-planetary systems detected by Kepler, TESS, and the upcoming PLATO
mission
The CORALIE survey for southern extrasolar planets XIX. Brown dwarfs and stellar companions unveiled by radial velocity and astrometry
A historical planet-search on a sample of 1647 nearby southern main sequence
stars has been ongoing since 1998 with the CORALIE spectrograph at La Silla
Observatory, with a backup subprogram dedicated to the monitoring of binary
stars. We review 25 years of CORALIE measurements and search for Doppler
signals consistent with stellar or brown dwarf companions to produce an updated
catalog of both known and previously unpublished binary stars in the
planet-search sample, assessing the binarity fraction of the stellar population
and providing perspective for more precise planet-search in the binary sample.
We perform new analysis on the CORALIE planet-search sample radial velocity
measurements, searching for stellar companions and obtaining orbital solutions
for both known and new binary systems. We perform simultaneous radial velocity
and proper motion anomaly fits on the subset of these systems for which
Hipparcos and Gaia astrometry measurements are available, obtaining accurate
estimates of true mass for the companions. We find 218 stars in the CORALIE
sample to have at least one stellar companion, 130 of which are not yet
published in the literature and for which we present orbital solutions. The use
of proper motion anomaly allow us to derive true masses for the stellar
companions in 132 systems, which we additionally use to estimate stability
regions for possible planetary companions on circumprimary or circumbinary
orbits. Finally, we produce detection limit maps for each star in the sample
and obtain occurrence rates of and
for brown dwarf and stellar companions respectively
in the CORALIE sample.Comment: 34 pages, 15 figures, accepted for publication in A&
Mass Determinations of the Three Mini-Neptunes Transiting TOI-125
The Transiting Exoplanet Survey Satellite, TESS, is currently carrying out an all-sky search for small planets transiting bright stars. In the first year of the TESS survey, a steady progress was made in achieving the mission’s primary science goal of establishing bulk densities for 50 planets smaller than Neptune. During that year, the TESS’s observations were focused on the southern ecliptic hemisphere, resulting in the discovery of three mini-Neptunes orbiting the star TOI-125, a V = 11.0 K0 dwarf. We present intensive HARPS radial velocity observations, yielding precise mass measurements for TOI-125b, TOI-125c, and TOI-125d. TOI-125b has an orbital period of 4.65 d, a radius of 2.726 ± 0.075 RE, a mass of 9.50 ± 0.88 ME, and is near the 2:1 mean motion resonance with TOI-125c at 9.15 d. TOI-125c has a similar radius of 2.759 ± 0.10 RE and a mass of 6.63 ± 0.99 ME, being the puffiest of the three planets. TOI-125d has an orbital period of 19.98 d and a radius of 2.93 ± 0.17 RE and mass 13.6 ± 1.2 ME. For TOI-125b and d, we find unusual high eccentricities of 0.19 ± 0.04 and 0.17+0.08−0.06, respectively. Our analysis also provides upper mass limits for the two low-SNR planet candidates in the system; for TOI-125.04 (RP = 1.36 RE, P = 0.53 d), we find a 2σ upper mass limit of 1.6 ME, whereas TOI-125.05 (RP=4.2+2.4−1.4 RE, P = 13.28 d) is unlikely a viable planet candidate with an upper mass limit of 2.7 ME. We discuss the internal structure of the three confirmed planets, as well as dynamical stability and system architecture for this intriguing exoplanet system
Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946
We report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 ( = 1.17 M, = 1.31 R) star, which hosts a transiting planet recently discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS, we measure the radius and mass from the transit and RV observations, and find that the planet, HD 77946 b, orbits with period = d, has a mass of M, and a radius of R. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a 1\% H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with K, water may be in a supercritical state. The characterisation of HD 77946 b, adding to the small sample of well-characterised sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets
Near-IR and optical radial velocities of the active M-dwarf star Gl 388 (AD Leo) with SPIRou at CFHT and SOPHIE at OHP
Context: The search for extrasolar planets around the nearest M-dwarfs is a
crucial step towards identifying the nearest Earth-like planets. One of the
main challenges in this search is that M-dwarfs can be magnetically active and
stellar activity can produce radial velocity (RV) signals that could mimic
those of a planet.
Aims: We aim to investigate whether the 2.2 day period observed in optical
RVs of the nearby active M-dwarf star Gl 388 (AD Leo) is due to stellar
activity or to a planet which co-rotates with the star as suggested in the
past.
Methods: We obtained quasi-simultaneous optical RVs of Gl 388 from 2019 to
2021 with SOPHIE (R75k) at the OHP in France, and near-IR RV and Stokes V
measurements with SPIRou at the CFHT (R70k).
Results: The SOPHIE RV time-series displays a periodic signal with
2.230.01 days period and 23.60.5 m/s amplitude, which is consistent
with previous HARPS observations obtained in 2005-2006. The SPIRou RV
time-series is flat at 5 m/s rms and displays no periodic signals. RV signals
of amplitude higher than 5.3 m/s at a period of 2.23 days can be excluded with
a confidence level higher than 99%. Using the modulation of the longitudinal
magnetic field (Bl) measured with SPIRou, we derive a stellar rotation period
of 2.23050.0016 days.
Conclusions: SPIRou RV measurements provide solid evidence that the periodic
variability of the optical RVs of Gl 388 is due to stellar activity rather than
to a co-rotating planet. The magnetic activity nature of the optical RV signal
is further confirmed by the modulation of Bl with the same period. The SPIRou
campaign on Gl 388 demonstrates the power of near-IR RV to confirm or infirm
planet candidates discovered in the optical around active stars. SPIRou
observations reiterate how effective spectropolarimetry is at determining the
stellar rotation period.Comment: 25 pages, 23 figures, Accepted by Astronomy and Astrophysic
An unusually low density ultra-short period super-Earth and three mini-Neptunes around the old star TOI-561
Based on HARPS-N radial velocities (RVs) and TESS photometry, we present a
full characterisation of the planetary system orbiting the late G dwarf
TOI-561. After the identification of three transiting candidates by TESS, we
discovered two additional external planets from RV analysis. RVs cannot confirm
the outer TESS transiting candidate, which would also make the system
dynamically unstable. We demonstrate that the two transits initially associated
with this candidate are instead due to single transits of the two planets
discovered using RVs. The four planets orbiting TOI-561 include an ultra-short
period (USP) super-Earth (TOI-561 b) with period d, mass
M and radius
R, and three mini-Neptunes: TOI-561 c, with d,
M, R;
TOI-561 d, with d, M,
R; and TOI-561 e, with
d, M,
R. Having a density of g cm, TOI-561 b is the
lowest density USP planet known to date. Our N-body simulations confirm the
stability of the system and predict a strong, anti-correlated, long-term
transit time variation signal between planets d and e. The unusual density of
the inner super-Earth and the dynamical interactions between the outer planets
make TOI-561 an interesting follow-up target
Three Short Period Jupiters from TESS. HIP 65Ab, TOI-157b and TOI-169b
We report the confirmation and mass determination of three hot Jupiters discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HIP 65Ab (TOI-129, TIC-201248411) is an ultra-short-period Jupiter orbiting a bright (V = 11.1 mag) K4-dwarf every 0.98 days. It is a massive 3.213 ± 0.078 M_J planet in a grazing transit configuration with an impact parameter of b = 1.17_(−0.08)^(+0.10). As a result the radius is poorly constrained, 2.03_(−0.49)^(+0.61)R_J. The planet’s distance to its host star is less than twice the separation at which it would be destroyed by Roche lobe overflow. It is expected to spiral into HIP 65A on a timescale ranging from 80 Myr to a few gigayears, assuming a reduced tidal dissipation quality factor of Qs′ = 10⁷ − 10⁹. We performed a full phase-curve analysis of the TESS data and detected both illumination- and ellipsoidal variations as well as Doppler boosting. HIP 65A is part of a binary stellar system, with HIP 65B separated by 269 AU (3.95 arcsec on sky). TOI-157b (TIC 140691463) is a typical hot Jupiter with a mass of 1.18 ± 0.13 M_J and a radius of 1.29 ± 0.02 R_J. It has a period of 2.08 days, which corresponds to a separation of just 0.03 AU. This makes TOI-157 an interesting system, as the host star is an evolved G9 sub-giant star (V = 12.7). TOI-169b (TIC 183120439) is a bloated Jupiter orbiting a V = 12.4 G-type star. It has a mass of 0.79 ±0.06 M_J and a radius of 1.09_(−0.05)^(+0.08)R_J. Despite having the longest orbital period (P = 2.26 days) of the three planets, TOI-169b receives the most irradiation and is situated on the edge of the Neptune desert. All three host stars are metal rich with [Fe / H] ranging from 0.18 to 0.24
Three Short Period Jupiters from TESS
We report the confirmation and mass determination of three hot Jupiters
discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HIP
65Ab (TOI-129, TIC-201248411) is an ultra-short-period Jupiter orbiting a
bright (V=11.1 mag) K4-dwarf every 0.98 days. It is a massive 3.213 +/- 0.078
Mjup planet in a grazing transit configuration with an impact parameter of b =
1.17 +0.10/-0.08. As a result the radius is poorly constrained, 2.03
+0.61/-0.49 Rjup. The planet's distance to its host star is less than twice the
separation at which it would be destroyed by Roche lobe overflow. It is
expected to spiral into HIP 65A on a timescale ranging from 80 Myr to a few
gigayears, assuming a reduced tidal dissipation quality factor of Qs' = 10^7 -
10^9. We performed a full phase-curve analysis of the TESS data and detected
both illumination- and ellipsoidal variations as well as Doppler boosting. HIP
65A is part of a binary stellar system, with HIP 65B separated by 269 AU (3.95
arcsec on sky). TOI-157b (TIC 140691463) is a typical hot Jupiter with a mass
of 1.18 +/- 0.13 Mjup and a radius of 1.29 +/- 0.02 Rjup. It has a period of
2.08 days, which corresponds to a separation of just 0.03 AU. This makes
TOI-157 an interesting system, as the host star is an evolved G9 sub-giant star
(V=12.7). TOI-169b (TIC 183120439) is a bloated Jupiter orbiting a V=12.4
G-type star. It has a mass of 0.79 +/- 0.06 Mjup and a radius of 1.09
+0.08/-0.05 Rjup. Despite having the longest orbital period (P = 2.26 days) of
the three planets, TOI-169b receives the most irradiation and is situated on
the edge of the Neptune desert. All three host stars are metal rich with [Fe/H]
ranging from 0.18 - 0.24.Comment: Published in A&
Optical and near-infrared stellar activity characterization of the early M dwarf Gl~205 with SOPHIE and SPIRou
The stellar activity of M dwarfs is the main limitation for discovering and
characterizing exoplanets orbiting them since it induces quasi-periodic RV
variations. We aim to characterize the magnetic field and stellar activity of
the early, moderately active, M dwarf Gl205 in the optical and nIR domains. We
obtained high-precision quasi-simultaneous spectra in the optical and nIR with
the SOPHIE spectrograph and SPIRou spectropolarimeter between 2019 and 2022. We
computed the RVs from both instruments and the SPIRou Stokes V profiles. We
used ZDI to map the large-scale magnetic field over the time span of the
observations. We studied the temporal behavior of optical and nIR RVs and
activity indicators with the Lomb-Scargle periodogram and a quasi-periodic GP
regression. In the nIR, we studied the equivalent width of Al I, Ti I, K I, Fe
I, and He I. We modeled the activity-induced RV jitter using a
multi-dimensional GP regression with activity indicators as ancillary time
series. The optical and nIR RVs have similar scatter but nIR shows a more
complex temporal evolution. We observe an evolution of the magnetic field
topology from a poloidal dipolar field in 2019 to a dominantly toroidal field
in 2022. We measured a stellar rotation period of Prot=34.40.5 d in the
longitudinal magnetic field. Using ZDI we measure the amount of latitudinal
differential rotation (DR) shearing the stellar surface yielding rotation
periods of Peq=32.01.8 d at the stellar equator and Ppol=45.50.3 d at
the poles. We observed inconsistencies in the activity indicators'
periodicities that could be explained by these DR values. The multi-dimensional
GP modeling yields an RMS of the RV residuals down to the noise level of 3 m/s
for both instruments, using as ancillary time series H and the BIS in
the optical, and the FWHM in the nIR.Comment: 41 pages, 24 figures. Accepted for publication in A&A. Improved
quality of figures and reduced size of Appendi
Constraining the reflective properties of WASP-178b using Cheops photometry
Multiwavelength photometry of the secondary eclipses of extrasolar planets is
able to disentangle the reflected and thermally emitted light radiated from the
planetary dayside. This leads to the measurement of the planetary geometric
albedo , which is an indicator of the presence of clouds in the
atmosphere, and the recirculation efficiency , which quantifies the
energy transport within the atmosphere. In this work we aim to measure
and for the planet WASP-178 b, a highly irradiated giant planet with
an estimated equilibrium temperature of 2450 K.} We analyzed archival spectra
and the light curves collected by Cheops and Tess to characterize the host
WASP-178, refine the ephemeris of the system and measure the eclipse depth in
the passbands of the two respective telescopes. We measured a marginally
significant eclipse depth of 7040 ppm in the Tess passband and
statistically significant depth of 7020 ppm in the Cheops passband.
Combining the eclipse depth measurement in the Cheops (lambda_eff=6300 AA) and
Tess (lambda_eff=8000 AA) passbands we constrained the dayside brightness
temperature of WASP-178 b in the 2250-2800 K interval. The geometric albedo
0.1<<0.35 is in general agreement with the picture of poorly
reflective giant planets, while the recirculation efficiency 0.7
makes WASP-178 b an interesting laboratory to test the current heat
recirculation models.Comment: Accepted by Astronomy and Astrophysics on 31/08/202
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