36 research outputs found
Disentangling 2:1 resonant radial velocity orbits from eccentric ones and a case study for HD 27894
In radial velocity observations, a pair of extrasolar planets near a 2:1
orbital resonance can be misinterpreted as a single eccentric planet, if data
are sparse and measurement precision insufficient to distinguish between these
models. We determine the fraction of alleged single-planet RV detected systems
for which a 2:1 resonant pair of planets is also a viable model and address the
question of how the models can be disentangled. By simulation we quantified the
mismatch arising from applying the wrong model. Model alternatives are
illustrated using the supposed single-planet system HD 27894 for which we also
study the dynamical stability of near-2:1 resonant solutions. From the data
scatter around the fitted single-planet Keplerians, we find that for of
the putative single-planet systems, a 2:1 resonant pair cannot be
excluded as a viable model, since the error due to the wrong model is smaller
than the scatter. For stars -probabilities can be used to reject
the Keplerian models with a confidence of for of the stars and
with for of the stars. For HD 27894 a considerable fit
improvement is obtained when adding a low-mass planet near half the orbital
period of the known Jovian planet. Dynamical analysis demonstrates that this
system is stable when both planets are initially placed on circular orbits. For
fully Keplerian orbits a stable system is only obtained if the eccentricity of
the inner planet is constrained to . A large part of the allegedly RV
detected single-planet systems should be scrutinized in order to determine the
fraction of systems containing near-2:1 resonant pairs of planets. Knowing the
abundance of such systems will allow us to revise the eccentricity distribution
for extrasolar planets and provide direct constraints for planetary system
formation.Comment: 12 pages, 8 figures, one of them composed by two files, accepted by
A&A, citations may appear in a non-standard way (double brackets) due to
reformatting needs. Abstract slightly adjuste
TESS exoplanet candidates validated with HARPS archival data. A massive Neptune around GJ143 and two Neptunes around HD23472
We aim at the discovery of new planetary systems by exploiting the transit
light curve results from TESS orbital observatory's Sector 1 and 2 observations
and validating them with precise Doppler measurements obtained from archival
HARPS data. Taking advantage of the reported TESS transit events around GJ143
(TOI 186) and HD23472 (TOI 174) we model their HARPS precise Doppler
measurements and derive orbital parameters for these two systems. For the GJ143
system TESS has reported only a single transit, and thus its period is
unconstrained from photometry. Our RV analysis of GJ143 reveal the full
Keplerian solution of the system, which is consistent with an eccentric planet
with a mass almost twice that of Neptune and a period of =
days. Our estimates of the GJ143 b planet are fully
consistent with the transit timing from TESS. We confirm the two-planet system
around HD23472, which according to our analysis is composed of two Neptune mass
planets in a possible 5:3 MMR.Comment: Submitted to A&A on 10th December 2018, Accepted on 14 January 2019,
Published online on 30 January 201
Radial-velocity jitter of stars as a function of observational timescale and stellar age
Stars show various amounts of radial velocity (RV) jitter due to varying
stellar activity levels. The typical amount of RV jitter as a function of
stellar age and observational timescale has not yet been systematically
quantified, although it is often larger than the instrumental precision of
modern high-resolution spectrographs used for Doppler planet detection and
characterization. We aim to empirically determine the intrinsic stellar RV
variation for mostly G and K dwarf stars on different timescales and for
different stellar ages independently of stellar models. We also focus on young
stars ( 30 Myr), where the RV variation is known to be large. We use
archival FEROS and HARPS RV data of stars which were observed at least 30 times
spread over at least two years. We then apply the pooled variance (PV)
technique to these data sets to identify the periods and amplitudes of
underlying, quasiperiodic signals. We show that the PV is a powerful tool to
identify quasiperiodic signals in highly irregularly sampled data sets. We
derive activity-lag functions for 20 putative single stars, where lag is the
timescale on which the stellar jitter is measured. Since the ages of all stars
are known, we also use this to formulate an activity--age--lag relation which
can be used to predict the expected RV jitter of a star given its age and the
timescale to be probed. The maximum RV jitter on timescales of decades
decreases from over 500 m/s for 5 Myr-old stars to 2.3 m/s for stars with ages
of around 5 Gyr. The decrease in RV jitter when considering a timescale of only
1 d instead of 1 yr is smaller by roughly a factor of 4 for 5 Myr old stars,
and a factor of 1.5 for stars with an age of 5 Gyr. The rate at which the RV
jitter increases with lag strongly depends on stellar age and ranges from a few
days for a few 10 Myr old stars to presumably decades for stars with an age of
a few gigayears.Comment: 15 pages, 7 Figures; Changelog v2: Updated link to CDS for table E.1;
rearranged Fig. 2 to match journal layou
Pathfinder first light: alignment, calibration, and commissioning of the LINC-NIRVANA ground-layer adaptive optics subsystem
We present descriptions of the alignment and calibration tests of the
Pathfinder, which achieved first light during our 2013 commissioning campaign
at the LBT. The full LINC-NIRVANA instrument is a Fizeau interferometric imager
with fringe tracking and 2-layer natural guide star multi-conjugate adaptive
optics (MCAO) systems on each eye of the LBT. The MCAO correction for each side
is achieved using a ground layer wavefront sensor that drives the LBT adaptive
secondary mirror and a mid-high layer wavefront sensor that drives a Xinetics
349 actuator DM conjugated to an altitude of 7.1 km. When the LINC-NIRVANA MCAO
system is commissioned, it will be one of only two such systems on an 8-meter
telescope and the only such system in the northern hemisphere. In order to
mitigate risk, we take a modular approach to commissioning by decoupling and
testing the LINC-NIRVANA subsystems individually. The Pathfinder is the
ground-layer wavefront sensor for the DX eye of the LBT. It uses 12 pyramid
wavefront sensors to optically co-add light from natural guide stars in order
to make four pupil images that sense ground layer turbulence. Pathfinder is now
the first LINC-NIRVANA subsystem to be fully integrated with the telescope and
commissioned on sky. Our 2013 commissioning campaign consisted of 7 runs at the
LBT with the tasks of assembly, integration and communication with the LBT
telescope control system, alignment to the telescope optical axis, off-sky
closed loop AO calibration, and finally closed loop on-sky AO. We present the
programmatics of this campaign, along with the novel designs of our alignment
scheme and our off-sky calibration test, which lead to the Pathfinder's first
on-sky closed loop images
New HARPS and FEROS observations of GJ1046
In this paper we present new precise Doppler data of GJ1046 taken between
November 2005 and July 2018 with the HARPS and the FEROS high-resolution
spectographs. In addition, we provide a new stellar mass estimate of GJ1046 and
we update the orbital parameters of the GJ1046 system. These new data and
analysis could be used together with the GAIA epoch astrometry, when available,
for braking the degeneracy and revealing the true mass of the GJ1046
system.Comment: 2 pages, 1 figure, 1 table with RV data (available only in the
Astro-PH version of the paper), Accepted by RNAA
The Extrasolar Planet epsilon Eridani b - Orbit and Mass
Hubble Space Telescope observations of the nearby (3.22 pc), K2 V star
epsilon Eridani have been combined with ground-based astrometric and radial
velocity data to determine the mass of its known companion. We model the
astrometric and radial velocity measurements simultaneously to obtain the
parallax, proper motion, perturbation period, perturbation inclination, and
perturbation size. Because of the long period of the companion, \eps b, we
extend our astrometric coverage to a total of 14.94 years (including the three
year span of the \HST data) by including lower-precision ground-based
astrometry from the Allegheny Multichannel Astrometric Photometer. Radial
velocities now span 1980.8 -- 2006.3. We obtain a perturbation period, P = 6.85
+/- 0.03 yr, semi-major axis, alpha =1.88 +/- 0.20 mas, and inclination i =
30.1 +/- 3.8 degrees. This inclination is consistent with a previously measured
dust disk inclination, suggesting coplanarity. Assuming a primary mass M_* =
0.83 M_{\sun}, we obtain a companion mass M = 1.55 +/- 0.24 M_{Jup}. Given the
relatively young age of epsilon Eri (~800 Myr), this accurate exoplanet mass
and orbit can usefully inform future direct imaging attempts. We predict the
next periastron at 2007.3 with a total separation, rho = 0.3 arcsec at position
angle, p.a. = -27 degrees. Orbit orientation and geometry dictate that epsilon
Eri b will appear brightest in reflected light very nearly at periastron.
Radial velocities spanning over 25 years indicate an acceleration consistent
with a Jupiter-mass object with a period in excess of 50 years, possibly
responsible for one feature of the dust morphology, the inner cavity
Evidence for a Long-period Planet Orbiting Epsilon Eridani
High precision radial velocity (RV) measurements spanning the years
1980.8--2000.0 are presented for the nearby (3.22 pc) K2 V star Eri.
These data, which represent a combination of six independent data sets taken
with four different telescopes, show convincing variations with a period of
7 yrs. A least squares orbital solution using robust estimation
yields orbital parameters of period, = 6.9 yrs, velocity -amplitude
19 {\ms}, eccentricity 0.6, projected companion mass sin = 0.86
, and semi-major axis 3.3 AU. Ca II H&K S-index
measurements spanning the same time interval show significant variations with
periods of 3 and 20 yrs, yet none at the RV period. If magnetic activity were
responsible for the RV variations then it produces a significantly different
period than is seen in the Ca II data. Given the lack of Ca II variation with
the same period as that found in the RV measurements, the long-lived and
coherent nature of these variations, and the high eccentricity of the implied
orbit, Keplerian motion due to a planetary companion seems to be the most
likely explanation for the observed RV variations. The wide angular separation
of the planet from the star (approximately 1 arc-second) and the long orbital
period make this planet a prime candidate for both direct imaging and
space-based astrometric measurements.Comment: To appear in Astrophysical Journal Letters. 9 pages, 2 figure
Deep imaging survey of the environment of Alpha Centauri - I. Adaptive optics imaging of Alpha Cen B with VLT-NACO
Context: Alpha Centauri is our closest stellar neighbor, at a distance of
only 1.3 pc, and its two main components have spectral types comparable to the
Sun. This is therefore a favorable target for an imaging search for extrasolar
planets. Moreover, indications exist that the gravitational mass of Alpha Cen B
is higher than its modeled mass, the difference being consistent with a
substellar companion of a few tens of Jupiter masses. Aims: We searched for
faint comoving companions to Alpha Cen B. As a secondary objective, we built a
catalogue of the detected background sources. Methods: We used the NACO
adaptive optics system of the VLT in the J, H, and Ks bands to search for
companions to Alpha Cen B. This instrument allowed us to achieve a very high
sensitivity to point-like sources, with a limiting magnitude of m\_Ks ~ 18 at
7" from the star. We complemented this data set with archival coronagraphic
images from the HST-ACS instrument to obtain an accurate astrometric
calibration. Results: Over the observed area, we did not detect any comoving
companion to Alpha Cen B down to an absolute magnitude of 19-20 in the H and Ks
bands. However, we present a catalogue of 252 background objects within about
15" of the star. This catalogue fills part of the large void area that
surrounds Alpha Cen in sky surveys due to the strong diffused light. We also
present a model of the diffused light as a function of angular distance for the
NACO instrument, that can be used to predict the background level for bright
star observations. Conclusions: According to recent numerical models, the
limiting magnitude of our search sets the maximum mass of possible companions
to 20-30 times Jupiter, between 7 and 20 AU from Alpha Cen B.Comment: 15 pages, accepted for publication in A&