136 research outputs found
Exploring the realm of scaled Solar System analogs with HARPS
The assessment of the frequency of planetary systems reproducing the Solar
System's architecture is still an open problem. Detailed study of multiplicity
and architecture is generally hampered by limitations in quality, temporal
extension and observing strategy, causing difficulties in detecting low-mass
inner planets in the presence of outer giant planetary bodies.
We present the results of high-cadence and high-precision HARPS observations
on 20 solar-type stars known to host a single long-period giant planet in order
to search for additional inner companions and estimate the occurence rate
of scaled Solar System analogs, i.e. systems featuring lower-mass inner planets
in the presence of long-period giant planets.
We carry out combined fits of our HARPS data with literature radial
velocities using differential evolution MCMC to refine the literature orbital
solutions and search for additional inner planets. We then derive the survey
detection limits to provide preliminary estimates of .
We generally find better constrained orbital parameters for the known planets
than those found in the literature. While no additional inner planet is
detected, we find evidence for previously unreported long-period massive
companions in systems HD 50499 and HD 73267. We finally estimate the frequency
of inner low mass (10-30 M) planets in the presence of outer giant
planets as for P<150 days.
Our preliminary estimate of is significantly lower than the values
found in the literature; the lack of inner candidate planets found in our
sample can also be seen as evidence corroborating the inward migration
formation model for super-Earths and mini-Neptunes. Our results also underline
the need for high-cadence and high-precision follow-up observations as the key
to precisely determine the occurence of Solar System analogs.Comment: 32 pages, 27 figures, accepted for publication in A&
A High-Contrast Search for Variability in HR 8799bc with VLT-SPHERE
The planets HR8799bc display nearly identical colours and spectra as variable
young exoplanet analogues such as VHS 1256-1257ABb and PSO J318.5-22, and are
likely to be similarly variable. Here we present results from a 5-epoch SPHERE
IRDIS broadband- search for variability in these two planets. HR 8799b
aperture photometry and HR 8799bc negative simulated planet photometry share
similar trends within uncertainties. Satellite spot lightcurves share the same
trends as the planet lightcurves in the August 2018 epochs, but diverge in the
October 2017 epochs. We consider to trace
non-shared variations between the two planets, and rule out non-shared
variability in to the 10-20 level over
4-5 hours. To quantify our sensitivity to variability, we simulate variable
lightcurves by inserting and retrieving a suite of simulated planets at similar
radii from the star as HR 8799bc, but offset in position angle. For HR 8799b,
for periods .
For HR 8799c, our sensitivity is limited to variability for similar
periods.Comment: 41 pages, 24 figures, accepted to MNRA
Investigating point sources in MWC 758 with SPHERE
Context. Spiral arms in protoplanetary disks could be shown to be the
manifestation of density waves launched by protoplanets and propagating in the
gaseous component of the disk. At least two point sources have been identified
in the L band in the MWC 758 system as planetary mass object candidates. Aims.
We used VLT/SPHERE to search for counterparts of these candidates in the H and
K bands, and to characterize the morphology of the spiral arms . Methods. The
data were processed with now-standard techniques in high-contrast imaging to
determine the limits of detection, and to compare them to the luminosity
derived from L band observations. Results. In considering the evolutionary,
atmospheric, and opacity models we were not able to confirm the two former
detections of point sources performed in the L band. In addition, the analysis
of the spiral arms from a dynamical point of view does not support the
hypothesis that these candidates comprise the origin of the spirals.
Conclusions. Deeper observations and longer timescales will be required to
identify the actual source of the spiral arms in MWC 758.Comment: Accepted for publication in Astronomy and Astrophysic
Direct Discovery of the Inner Exoplanet in the Hd 206893 System: Evidence for Deuterium Burning in a Planetary-Mass Companion
Aims. HD 206893 is a nearby debris disk star that hosts a previously identified brown dwarf companion with an orbital separation of ~ 10 au. Long-Term precise radial velocity (RV) monitoring, as well as anomalies in the system proper motion, has suggested the presence of an additional, inner companion in the system. Methods. Using information from ongoing precision RV measurements with the HARPS spectrograph, as well as Gaia host star astrometry, we have undertaken a multi-epoch search for the purported additional planet using the VLTI/GRAVITY instrument. Results. We report a high-significance detection over three epochs of the companion HD 206893c, which shows clear evidence for Keplerian orbital motion. Our astrometry with ~ 50-100 µarcsec precision afforded by GRAVITY allows us to derive a dynamical mass of 12.7MJup and an orbital separation of 3.53 au for HD 206893c. Our fits to the orbits of both companions in the system use both Gaia astrometry and RVs to also provide a precise dynamical estimate of the previously uncertain mass of the B component, and therefore allow us to derive an age of 155 ± 15 Myr for the system. We find that theoretical atmospheric and evolutionary models that incorporate deuterium burning for HD 206893c, parameterized by cloudy atmosphere models as well as a hybrid sequence (encompassing a transition from cloudy to cloud-free), provide a good simultaneous fit to the luminosity of both HD 206893B and c. Thus, accounting for both deuterium burning and clouds is crucial to understanding the luminosity evolution of HD 206893c. Conclusions. In addition to using long-Term RV information, this effort is an early example of a direct imaging discovery of a bona fide exoplanet that was guided in part by Gaia astrometry. Utilizing Gaia astrometry is expected to be one of the primary techniques going forward for identifying and characterizing additional directly imaged planets. In addition, HD 206893c is an example of an object narrowly straddling the deuterium-burning limit but unambiguously undergoing deuterium burning. Additional discoveries like this may therefore help clarify the discrimination between a brown dwarf and an extrasolar planet. Lastly, this discovery is another example of the power of optical interferometry to directly detect and characterize extrasolar planets where they form, at ice-line orbital separations of 2-4 au
In-depth study of moderately young but extremely red, very dusty substellar companion HD206893B
Accepted for publication in Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.The substellar companion HD206893b has recently been discovered by direct imaging of its disc-bearing host star with the SPHERE instrument. We investigate the atypical properties of the companion, which has the reddest near-infrared colours among all known substellar objects, either orbiting a star or isolated, and we provide a comprehensive characterisation of the host star-disc-companion system. We conducted a follow-up of the companion with adaptive optics imaging and spectro-imaging with SPHERE, and a multiinstrument follow-up of its host star. We obtain a R=30 spectrum from 0.95 to 1.64 micron of the companion and additional photometry at 2.11 and 2.25 micron. We carried out extensive atmosphere model fitting for the companions and the host star in order to derive their age, mass, and metallicity. We found no additional companion in the system in spite of exquisite observing conditions resulting in sensitivity to 6MJup (2MJup) at 0.5" for an age of 300 Myr (50 Myr). We detect orbital motion over more than one year and characterise the possible Keplerian orbits. We constrain the age of the system to a minimum of 50 Myr and a maximum of 700 Myr, and determine that the host-star metallicity is nearly solar. The comparison of the companion spectrum and photometry to model atmospheres indicates that the companion is an extremely dusty late L dwarf, with an intermediate gravity (log g 4.5-5.0) which is compatible with the independent age estimate of the system. Though our best fit corresponds to a brown dwarf of 15-30 MJup aged 100-300 Myr, our analysis is also compatible with a range of masses and ages going from a 50 Myr 12MJup planetary-mass object to a 50 MJup Hyades-age brown dwarf...Peer reviewedFinal Accepted Versio
TOI-179: a young system with a transiting compact Neptune-mass planet and a low-mass companion in outer orbit
Transiting planets around young stars are key benchmarks for our
understanding of planetary systems. One of such candidates was identified
around the K dwarf HD 18599 by TESS, labeled as TOI-179. We present the
confirmation of the transiting planet and the characterization of the host star
and of the TOI-179 system over a broad range of angular separations. To this
aim, we exploited the TESS photometric time series, intensive radial velocity
monitoring performed with HARPS, and deep high-contrast imaging observations
obtained with SPHERE and NACO at VLT. The inclusion of Gaussian processes
regression analysis is effective to properly model the magnetic activity of the
star and identify the Keplerian signature of the transiting planet. The star,
with an age of 400+-100 Myr, is orbited by a transiting planet with period
4.137436 days, mass 24+-7 Mearth, radius 2.62 (+0.15-0.12) Rearth, and
significant eccentricity (0.34 (+0.07-0.09)). Adaptive optics observations
identified a low-mass companion at the boundary between brown dwarfs and very
low mass stars (mass derived from luminosity 83 (+4-6) Mjup) at a very small
projected separation (84.5 mas, 3.3 au at the distance of the star). Coupling
the imaging detection with the long-term radial velocity trend and the
astrometric signature, we constrained the orbit of the low mass companion,
identifying two families of possible orbital solutions. The TOI-179 system
represents a high-merit laboratory for our understanding of the physical
evolution of planets and other low-mass objects and of how the planet
properties are influenced by dynamical effects and interactions with the parent
star.Comment: 25 pages, 24 figures, A&A, in pres
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