415 research outputs found
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
Prospects for hybrid integration of Si and SiN waveguides with graphene and other 2D-materials
RVSPY -- Radial Velocity Survey for Planets around Young Stars. Target characterization and high-cadence survey
We introduce our Radial Velocity Survey for Planets around Young stars
(RVSPY), characterise our target stars, and search for substellar companions at
orbital separations smaller than a few au from the host star. We use the FEROS
spectrograph to obtain high signal-to-noise spectra and time series of precise
radial velocities (RVs) of 111 stars most of which are surrounded by debris
discs. Our target stars have spectral types between early F and late K, a
median age of 400 Myr, and a median distance of 45 pc. We determine for all
target stars their basic stellar parameters and present the results of the
high-cadence RV survey and activity characterization. We achieve a median
single-measurement RV precision of 6 m/s and derive the short-term intrinsic RV
scatter of our targets (median 22 m/s), which is mostly caused by stellar
activity and decays with age from >100 m/s at 500 Myr.
We discover six previously unknown close companions with orbital periods
between 10 and 100 days, three of which are low-mass stars, and three are in
the brown dwarf mass regime. We detect no hot companion with an orbital period
<10 days down to a median mass limit of ~1 M_Jup for stars younger than 500
Myr, which is still compatible with the established occurrence rate of such
companions around main-sequence stars. We find significant RV periodicities
between 1.3 and 4.5 days for 14 stars, which are, however, all caused by
rotational modulation due to starspots. We also analyse the TESS photometric
time series data and find significant periodicities for most of the stars. For
11 stars, the photometric periods are also clearly detected in the RV data. We
also derive stellar rotation periods ranging from 1 to 10 days for 91 stars,
mostly from TESS data. From the intrinsic activity-related short-term RV
jitter, we derive the expected mass-detection thresholds for longer-period
companions.Comment: 24 pages, 14 figures, 4 tables; Accepted for publication in A&
The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
HD3167 is a bright (V=8.9 mag) K0V star observed by the NASA's K2 space
mission during its Campaign 8. It has been recently found to host two small
transiting planets, namely, HD3167b, an ultra short period (0.96 d)
super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit
(29.85 d). Here we present an intensive radial velocity follow-up of HD3167
performed with the FIES@NOT, [email protected], and HARPS-N@TNG spectrographs. We
revise the system parameters and determine radii, masses, and densities of the
two transiting planets by combining the K2 photometry with our spectroscopic
data. With a mass of 5.69+/-0.44 MEarth, radius of 1.574+/-0.054 REarth, and
mean density of 8.00(+1.0)(-0.98) g/cm^3, HD3167b joins the small group of
ultra-short period planets known to have a rocky terrestrial composition.
HD3167c has a mass of 8.33 (+1.79)(-1.85) MEarth and a radius of
2.740(+0.106)(-0.100) REarth, yielding a mean density of 2.21(+0.56)(-0.53)
g/cm^3, indicative of a planet with a composition comprising a solid core
surrounded by a thick atmospheric envelope. The rather large pressure scale
height (about 350 km) and the brightness of the host star make HD3167c an ideal
target for atmospheric characterization via transmission spectroscopy across a
broad range of wavelengths. We found evidence of additional signals in the
radial velocity measurements but the currently available data set does not
allow us to draw any firm conclusion on the origin of the observed variation.Comment: 18 pages, 11 figures, 5 table
- …