520 research outputs found
Three planets around HD 27894. A close-in pair with a 2:1 period ratio and an eccentric Jovian planet at 5.4 AU
Aims. Our new program with HARPS aims to detect mean motion resonant
planetary systems around stars which were previously reported to have a single
bona fide planet, often based only on sparse radial velocity data. Methods.
Archival and new HARPS radial velocities for the K2V star HD 27894 were
combined and fitted with a three-planet self-consistent dynamical model. The
best-fit orbit was tested for long-term stability. Results. We find clear
evidence that HD 27894 is hosting at least three massive planets. In addition
to the already known Jovian planet with a period 18 days
we discover a Saturn-mass planet with 36 days, likely in
a 2:1 mean motion resonance with the first planet, and a cold massive planet
( 5.3 ) with a period 5170
days on a moderately eccentric orbit ( = 0.39). Conclusions. HD
27894 is hosting a massive, eccentric giant planet orbiting around a tightly
packed inner pair of massive planets likely involved in an asymmetric 2:1 mean
motion resonance. HD 27894 may be an important milestone for probing planetary
formation and evolution scenarios.Comment: 4 pages, 2 tables, 3 figures. Accepted for publication in A&A Letters
to the Edito
Spin communication over 30 m long channels of chemical vapor deposited graphene on SiO
We demonstrate a high-yield fabrication of non-local spin valve devices with
room-temperature spin lifetimes of up to 3 ns and spin relaxation lengths as
long as 9 m in platinum-based chemical vapor deposition (Pt-CVD)
synthesized single-layer graphene on SiO/Si substrates. The spin-lifetime
systematically presents a marked minimum at the charge neutrality point, as
typically observed in pristine exfoliated graphene. However, by studying the
carrier density dependence beyond n ~ 5 x 10 cm, via
electrostatic gating, it is found that the spin lifetime reaches a maximum and
then starts decreasing, a behavior that is reminiscent of that predicted when
the spin-relaxation is driven by spin-orbit interaction. The spin lifetimes and
relaxation lengths compare well with state-of-the-art results using exfoliated
graphene on SiO/Si, being a factor two-to-three larger than the best values
reported at room temperature using the same substrate. As a result, the spin
signal can be readily measured across 30 m long graphene channels. These
observations indicate that Pt-CVD graphene is a promising material for
large-scale spin-based logic-in-memory applications
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
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
ISPY – NaCo imaging survey for planets around young stars : a young companion candidate embedded in the R CrA cloud
Context
Within the NaCo-ISPY exoplanet imaging program, we aim at detecting and characterizing the population of low-mass companions at wide separations (≳10 AU), focusing in particular on young stars either hosting a known protoplanetary disk or a debris disk.
Aims
R CrA is one of the youngest (1-3 Myr) and most promising objects in our sample because of two previous studies that suggested the presence of a close companion. Our aim is to directly image and characterize the companion for the first time.
Methods
We observed R CrA twice with the NaCo instrument at the Very Large Telescope (VLT) in the L' filter with a one year time baseline in between. The high-contrast imaging data were reduced and analyzed and the companion candidate was detected in both datasets. We used artificial negative signals to determine the position and brightness of the companion and the related uncertainties.
Results
The companion is detected at a separation of 196.8 ± 4.5/196.6 ± 5.9 mas (18.7 ± 1.3/18.7 ± 1.4 AU) and position angle of 134.7 ± 0.5 ° /133.7 ± 0.7° in the first/second epoch observation. We measure a contrast of 7.29 ± 0.18/6.70 ± 0.15 mag with respect to the primary. A study of the stellar proper motion rejects the hypothesis that the signal is a background object. The companion candidate orbits in the clockwise direction and, if on a face-on circular orbit, its period is ˜43 - 47 yr. This value disagrees with the estimated orbital motion and therefore a face-on circular orbit may be excluded. Depending on the assumed age, extinction, and brightness of the primary, the stellar companion has a mass between 0.10 ± 0.02 M⊙ and 1.03-0.18+0.20 M⊙ range, if no contribution from circumsecondary material is taken into account.
Conclusions
As already hypothesized by previous studies, we directly detected a low-mass stellar companion orbiting the young Herbig Ae/Be star R CrA. Depending on the age assumptions, the companion is among the youngest forming companions imaged to date, and its presence needs to be taken into account when analyzing the complex circumstellar environment of R CrA
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