37 research outputs found
Companions to Kepler giant stars: A long-period eccentric substellar companion to KIC 3526061 and a stellar companion to HD 187878
Context. Our knowledge of populations and occurrence of planets orbiting
evolved intermediate-mass stars is still incomplete. In 2010 we started a
planet-search program among 95 giant stars observed by the Kepler mission to
increase the sample of giant stars with planets and with reliable estimates of
stellar masses and radii. Aims. We present the two systems KIC 3526061 and HD
187878 from our planet-search program for which we could characterise their
companions. Methods. We used precise stellar radial velocity measurements taken
with four different echelle spectrographs to derive an orbital solution. We
used Gaia astrometric measurements to obtain the inclination of the HD 187878
system and Kepler photometric observations to estimate the stellar mass and
radius. Results. We report the discovery of a sub-stellar and a stellar
companion around two intermediate-mass red giant branch stars. KIC 3526061 b is
most likely a brown dwarf with a minimum mass of 18.15 Jupiter masses in a
long-period eccentric orbit, with the orbital period 3552 d and orbital
eccentricity 0.85. It is the most evolved system found having a sub-stellar
companion with such a large eccentricity and wide separation. HD 187878 B has a
minimum mass of 78.4 Jupiter masses. Combining the spectroscopic orbital
parameters with the astrometric proper motion anomaly we derived an orbital
inclination 9.8 deg, which corresponds to the companion's mass in the stellar
regime of 0.51 Sun mass. Conclusions. A sub-stellar companion of KIC 3526061
extends the sample of known red giant branch stars with sub-stellar companions
on very eccentric wide orbits and might provide a probe of the dynamical
evolution of such systems over time.Comment: 14 pages, 11 figures. Accepted to A&
HD 191939 revisited: New and refined planet mass determinations, and a new planet in the habitable zone
HD 191939 (TOI-1339) is a nearby (d=54pc), bright (V=9mag), and inactive
Sun-like star (G9 V) known to host a multi-planet transiting system.
Ground-based spectroscopic observations confirmed the planetary nature of the
three transiting sub-Neptunes (HD 191939 b, c, and d) originally detected by
TESS and were used to measure the masses for planets b and c with 3
precision. These previous observations also reported the discovery of an
additional Saturn-mass planet (HD 191939 e) and evidence for a further, very
long-period companion (HD 191939 f). Here, we report the discovery of a new
non-transiting planet in the system and a refined mass determination of HD
191939 d. The new planet, HD 191939 g, has a minimum mass of 13.52.0
M and a period of about 280 d. This period places the planet within
the conservative habitable zone of the host star, and near a 1:3 resonance with
HD 191939 e. The compilation of 362 radial velocity measurements with a
baseline of 677 days from four different high-resolution spectrographs also
allowed us to refine the properties of the previously known planets, including
a 4.6 mass determination for planet d, for which only a 2 upper
limit had been set until now. We confirm the previously suspected low density
of HD 191939 d, which makes it an attractive target for attempting atmospheric
characterisation. Overall, the planetary system consists of three sub-Neptunes
interior to a Saturn-mass and a Uranus-mass planet plus a high-mass long-period
companion. This particular configuration has no counterpart in the literature
and makes HD 191939 an exceptional multi-planet transiting system with an
unusual planet demographic worthy of future observation.Comment: Accepted for publication in A&A. 20 pages, 8 figure
TOI-1130: A photodynamical analysis of a hot Jupiter in resonance with an inner low-mass planet
The TOI-1130 is a known planetary system around a K-dwarf consisting of a gas
giant planet, TOI-1130 c, on an 8.4-day orbit, accompanied by an inner
Neptune-sized planet, TOI-1130 b, with an orbital period of 4.1 days. We
collected precise radial velocity (RV) measurements of TOI-1130 with the HARPS
and PFS spectrographs as part of our ongoing RV follow-up program. We perform a
photodynamical modeling of the HARPS and PFS RVs, and transit photometry from
the Transiting Exoplanet Survey Satellite (TESS) and the TESS Follow-up
Observing Program. We determine the planet masses and radii of TOI-1130 b and
TOI-1130 c to be Mb = 19.28 0.97 M and Rb = 3.56 0.13
R, and Mc = 325.59 5.59 M and Rc = 13.32+1.55-1.41
R, respectively. We spectroscopically confirm TOI-1130 b that was
previously only validated. We find that the two planets orbit with small
eccentricities in a 2:1 resonant configuration. This is the first known system
with a hot Jupiter and an inner lower mass planet locked in a mean-motion
resonance. TOI-1130 belongs to the small yet increasing population of hot
Jupiters with an inner low-mass planet that challenges the pathway for hot
Jupiter formation. We also detect a linear RV trend possibly due to the
presence of an outer massive companion.Comment: 19 pages, Accepted to A&
Radial velocity confirmation of a hot super-Neptune discovered by TESS with a warm Saturn-mass companion
We report the discovery and confirmation of the planetary system TOI-1288.
This late G dwarf harbours two planets: TOI-1288 b and TOI-1288 c. We combine
TESS space-borne and ground-based transit photometry with HARPS-N and HIRES
high-precision Doppler measurements, which we use to constrain the masses of
both planets in the system and the radius of planet b. TOI-1288~b has a period
of d, a radius of
R, and a mass of M, making this planet a hot
transiting super-Neptune situated right in the Neptunian desert. This desert
refers to a paucity of Neptune-sized planets on short period orbits. Our
2.4-year-long Doppler monitoring of TOI-1288 revealed the presence of a
Saturn-mass planet on a moderately eccentric orbit ()
with a minimum mass of M and a period of
d. The 5 sectors worth of TESS data do not cover our expected mid-transit time
for TOI-1288 c, and we do not detect a transit for this planet in these
sectors.Comment: 16 pages, 17 figures, under review MNRA
TOI-1130: A photodynamical analysis of a hot Jupiter in resonance with an inner low-mass planet
The TOI-1130 is a known planetary system around a K-dwarf consisting of a gas giant planet, TOI-1130 c on an 8.4-day orbit that is accompanied by an inner Neptune-sized planet, TOI-1130 b, with an orbital period of 4.1 days. We collected precise radial velocity (RV) measurements of TOI-1130 with the HARPS and PFS spectrographs as part of our ongoing RV follow-up program. We performed a photodynamical modeling of the HARPS and PFS RVs, along with transit photometry from the Transiting Exoplanet Survey Satellite (TESS) and the TESS Follow-up Observing Program (TFOP). We determined the planet masses and radii of TOI-1130 b and TOI-1130 c to be Mb = 19.28 ± 0.97M⊕ and Rb = 3.56 ± 0.13 R⊕, and Mc = 325.59 ± 5.59M⊕ and Rc = 13.32-1.41+1.55 R⊕, respectively. We have spectroscopically confirmed the existence of TOI-1130 b, which had previously only been validated. We find that the two planets have orbits with small eccentricities in a 2:1 resonant configuration. This is the first known system with a hot Jupiter and an inner lower mass planet locked in a mean-motion resonance. TOI-1130 belongs to the small, yet growing population of hot Jupiters with an inner low-mass planet that poses a challenge to the pathway scenario for hot Jupiter formation. We also detected a linear RV trend that is possibly due to the presence of an outer massive companion
The GAPS programme at TNG XLIX. TOI-5398, the youngest compact multi-planet system composed of an inner sub-Neptune and an outer warm Saturn
Short-period giant planets are frequently found to be solitary compared to
other classes of exoplanets. Small inner companions to giant planets with 15 days are known only in five compact systems: WASP-47, Kepler-730,
WASP-132, TOI-1130, and TOI-2000. Here, we report the confirmation of TOI-5398,
the youngest compact multi-planet system composed of a hot sub-Neptune
(TOI-5398 c, = 4.77271 days) orbiting interior to a short-period
Saturn (TOI-5398 b, = 10.590547 days) planet, both transiting
around a 650 150 Myr G-type star. As part of the GAPS Young Object
project, we confirmed and characterised this compact system, measuring the
radius and mass of both planets, thus constraining their bulk composition.
Using multidimensional Gaussian processes, we simultaneously modelled stellar
activity and planetary signals from TESS Sector 48 light curve and our HARPS-N
radial velocity time series. We have confirmed the planetary nature of both
planets, TOI-5398 b and TOI-5398 c, alongside a precise estimation of stellar
parameters. Through the use of astrometric, photometric, and spectroscopic
observations, our findings indicate that TOI-5398 is a young, active G dwarf
star (650 150 Myr), with a rotational period of = 7.34
days. The transit photometry and radial velocity measurements enabled us to
measure both the radius and mass of planets b, ,
, and c, , . TESS observed TOI-5398 during sector 48 and no further
observations are planned in the current Extended Mission, making our
ground-based light curves crucial for ephemeris improvement. With a
Transmission Spectroscopy Metric value of around 300, TOI-5398 b is the most
amenable warm giant (10 < < 100 days) for JWST atmospheric
characterisation.Comment: 29 pages, Paper accepted for publication in Astronomy & Astrophysic
Hot planets around cool stars -- two short-period mini-Neptunes transiting the late K-dwarf TOI-1260
We present the discovery and characterization of two sub-Neptunes in close
orbits, as well as a tentative outer planet of a similar size, orbiting
TOI-1260 - a low metallicity K6V dwarf star. Photometry from TESS yields radii
of and
, and periods of 3.13 and 7.49 days for TOI-1260b and TOI-1260c,
respectively. We combined the TESS data with a series of ground-based follow-up
observations to characterize the planetary system. From HARPS-N high-precision
radial velocities we obtain
and . The
star is moderately active with a complex activity pattern, which necessitated
the use of Gaussian process regression for both the light curve detrending and
the radial velocity modelling, in the latter case guided by suitable activity
indicators. We successfully disentangle the stellar-induced signal from the
planetary signals, underlining the importance and usefulness of the Gaussian
Process approach. We test the system's stability against atmospheric
photoevaporation and find that the TOI-1260 planets are classic examples of the
structure and composition ambiguity typical for the range