107 research outputs found
Observability of Forming Planets and their Circumplanetary Disks I. -- Parameter Study for ALMA
We present mock observations of forming planets with ALMA. The possible
detections of circumplanetary disks (CPDs) were investigated around planets of
Saturn, 1, 3, 5, and 10 Jupiter-masses that are placed at 5.2 AU from their
star. The radiative, three dimensional hydrodynamic simulations were then
post-processed with RADMC3D and the ALMA Observation Simulator. We found that
even though the CPDs are too small to be resolved, they are hot due to the
accreting planet in the optically thick limit, therefore the best chance to
detect them with continuum observations in this case is at the shortest ALMA
wavelengths, such as Band 9 (440 microns). Similar fluxes were found in the
case of Saturn and Jupiter-mass planets, as for the 10
gas-giant, due to temperature weighted optical depth effects: when no deep gap
is carved, the planet region is blanketed by the optically thick circumstellar
disk leading to a less efficient cooling there. A test was made for a 52 AU
orbital separation, showed that optically thin CPDs are also detectable in band
7 but they need longer integration times (5hrs). Comparing the gap profiles
of the same simulation at various ALMA bands and the hydro simulation confirmed
that they change significantly, first because the gap is wider at longer
wavelengths due to decreasing optical depth; second, the beam convolution makes
the gap shallower and at least 25% narrower. Therefore, caution has to be made
when estimating planet masses based on ALMA continuum observations of gaps.Comment: Accepted for publication at MNRAS. Typos are corrected since previous
version. 11 pages, 5 tables, 4 figure
Stellar and circumstellar properties of visual binaries in the Orion Nebula Cluster
Our general understanding of multiple star and planet formation is primarily
based on observations of young multiple systems in low density regions like
Tau-Aur and Oph. Since many, if not most, of the stars are born in clusters,
observational constraints from young binaries in those environments are
fundamental for understanding both the formation of multiple systems and
planets in multiple systems throughout the Galaxy. We build upon the largest
survey for young binaries in the Orion Nebula Cluster (ONC) which is based on
Hubble Space Telescope observations to derive both stellar and circumstellar
properties of newborn binary systems in this cluster environment. We present
Adaptive Optics spatially-resolved JHKL'-band photometry and K-band
R\,5000 spectra for a sample of 8 ONC binary systems from this database.
We characterize the stellar properties of binary components and obtain a census
of protoplanetary disks through K-L' color excess. For a combined sample of ONC
binaries including 7 additional systems with NIR spectroscopy from the
literature, we derive mass ratio and relative age distributions. We compare the
stellar and circumstellar properties of binaries in ONC with those in Tau-Aur
and Oph from samples of binaries with stellar properties derived for each
component from spectra and/or visual photometry and with a disk census obtained
through K-L color excess. The mass ratio distribution of ONC binaries is found
to be indistinguishable from that of Tau-Aur and, to some extent, to that of
Oph in the separation range 85-560\,AU and for primary mass in the range 0.15
to 0.8\,M_{\sun}.A trend toward a lower mass ratio with larger separation is
suggested in ONC binaries which is not seen in Tau-Aur binaries.The components
of ONC binaries are found to be significantly more coeval than the overall ONC
population and as coeval as components of binaries in Tau-Aur and Oph[...]Comment: Accepted for publication in Astronomy & Astrophysic
Discovery of a stellar companion to the nearby solar-analogue HD 104304
Sun-like stars are promising candidates to host exoplanets and are often
included in exoplanet surveys by radial velocity (RV) and direct imaging. In
this paper we report on the detection of a stellar companion to the nearby
solar-analogue star HD 104304, which previously was considered to host a
planetary mass or brown dwarf companion. We searched for close stellar and
substellar companions around extrasolar planet host stars with high angular
resolution imaging to characterize planet formation environments. The detection
of the stellar companion was achieved by high angular resolution measurements,
using the "Lucky Imaging" technique at the ESO NTT 3.5m with the AstraLux Sur
instrument. We combined the results with VLT/NACO archive data, where the
companion could also be detected. The results were compared to precise RV
measurements of HD 104304, obtained at the Lick and Keck observatories from
2001-2010.
We confirmed common proper motion of the binary system. A spectral type of
M4V of the companion and a mass of 0.21 M_Sun was derived. Due to comparison of
the data with RV measurements of the unconfirmed planet candidate listed in the
Extrasolar Planets Encyclopaedia, we suggest that the discovered companion is
the origin of the RV trend and that the inclination of the orbit of
approximately 35 degrees explains the relatively small RV signal.Comment: 4 pages, 4 PNG figures, use aa.cls, accepted for publication in
Astronomy & Astrophysic
Lucky Imaging survey for southern M dwarf binaries
While M dwarfs are the most abundant stars in the Milky Way, there is still
large uncertainty about their basic physical properties (mass, luminosity,
radius, etc.) as well as their formation environment. Precise knowledge of
multiplicity characteristics and how they change in this transitional mass
region, between Sun-like stars on the one side and very low mass stars and
brown dwarfs on the other, provide constraints on low mass star and brown dwarf
formation. In the largest M dwarf binary survey to date, we search for
companions to active, and thus preferentially young, M dwarfs in the solar
neighbourhood. We study their binary/multiple properties, such as the
multiplicity frequency and distributions of mass ratio and separation, and
identify short period visual binaries, for which orbital parameters and hence
dynamical mass estimates can be derived in the near future. The observations
are carried out in the SDSS i' and z' band using the Lucky Imaging camera
AstraLux Sur at the ESO 3.5 m New Technology Telescope. In the first part of
the survey, we observed 124 M dwarfs of integrated spectral types M0-M6 and
identified 34 new and 17 previously known companions to 44 stars. We derived
relative astrometry and component photometry for these systems. More than half
of the binaries have separations smaller than 1 arcsec and would have been
missed in a simply seeing-limited survey. Correcting our sample for selection
effects yields a multiplicity fraction of 32+/-6% for 108 M dwarfs within 52 pc
and with angular separations of 0.1-6.0 arcsec, corresponding to projected
separation 3-180 AU at median distance 30 pc. Compared to early-type M dwarfs
(M>0.3M_Sun), later type (and hence lower mass) M dwarf binaries appear to have
closer separations, and more similar masses.Comment: 18 pages, 9 figures. Minor corrections and changes. Revised to match
accepted A&A versio
Protoplanetary disk evolution and stellar parameters of T Tauri binaries in Chamaeleon I
This study aims to determine the impact of stellar binary companions on the
lifetime and evolution of circumstellar disks in the Chamaeleon I (Cha I)
star-forming region by measuring the frequency and strength of accretion and
circumstellar dust signatures around the individual components of T Tauri
binary stars. We used high-angular resolution adaptive optics JHKL'-band
photometry and 1.5-2.5mu spectroscopy of 19 visual binary and 7 triple stars in
Cha I - including one newly discovered tertiary component - with separations
between ~25 and ~1000au. The data allowed us to infer stellar component masses
and ages and, from the detection of near-infrared excess emission and the
strength of Brackett-gamma emission, the presence of ongoing accretion and hot
circumstellar dust of the individual stellar component of each binary. Of all
the stellar components in close binaries with separations of 25-100au,
10(+15-5)% show signs of accretion. This is less than half of the accretor
fraction found in wider binaries, which itself appears significantly reduced
(~44%) compared with previous measurements of single stars in Cha I. Hot dust
was found around 50(+30-15)% of the target components, a value that is
indistinguishable from that of Cha I single stars. Only the closest binaries
(<25au) were inferred to have a significantly reduced fraction (<~25%) of
components that harbor hot dust. Accretors were exclusively found in binary
systems with unequal component masses M_secondary/M_primary < 0.8, implying
that the detected accelerated disk dispersal is a function of mass-ratio. This
agrees with the finding that only one accreting secondary star was found, which
is also the weakest accretor in the sample. The results imply that disk
dispersal is more accelerated the stronger the dynamical disk truncation, i.e.,
the smaller the inferred radius of the disk. (abridged)Comment: Accepted for publication in A&A. 25 pages, 20 figure
VIBES: VIsual Binary Exoplanet survey with SPHERE Upper limits on wide S-planet and S-BD frequencies, triple system discovery, and astrometric confirmation of 20 stellar binaries and three triple systems
Recent surveys indicate that planets in binary systems are more abundant than
previously thought, which is in agreement with theoretical work on disc
dynamics and planet formation in binaries. In order to measure the abundance
and physical characteristics of wide-orbit giant exoplanets in binary systems,
we have designed the 'VIsual Binary Exoplanet survey with Sphere' (VIBES) to
search for planets in visual binaries. It uses the SPHERE instrument at VLT to
search for planets in 23 visual binary and four visual triple systems with ages
of <145 Myr and distances of <150 pc. We used the IRDIS dual-band imager on
SPHERE to acquire high-contrast images of the sample targets. For each binary,
the two components were observed at the same time with a coronagraph masking
only the primary star. For the triple star, the tight components were treated
as a single star for data reduction. This enabled us to effectively search for
companions around 50 individual stars in binaries and four binaries in triples.
We derived upper limits of 13.7\% for the frequency of sub-stellar
companions around primaries in visual binaries, 26.5\% for the fraction of
sub-stellar companions around secondaries in visual binaries, and an occurrence
rate of 9.0\% for giant planets and brown dwarfs around either component of
visual binaries. We have combined our observations with literature measurements
to astrometrically confirm, for the first time, that 20 binaries and two triple
systems, which were previously known, are indeed physically bound. Finally, we
discovered a third component of the binary HD~121336. The upper limits we
derived are compatible with planet formation through the core accretion and the
gravitational instability processes in binaries. These limits are also in line
with limits found for single star and circumbinary planet search surveys.Comment: Accepted for publication in Astronomy & Astrophysics on 18.09.2020 21
pages, 11 figure
Binarity of Transit Host Stars - Implications on Planetary Parameters
Straight-forward derivation of planetary parameters can only be achieved in
transiting planetary systems. However, planetary attributes such as radius and
mass strongly depend on stellar host parameters. Discovering a transit host
star to be multiple leads to a necessary revision of the derived stellar and
planetary parameters. Based on our observations of 14 transiting exoplanet
hosts, we derive parameters of the individual components of three transit host
stars (WASP-2, TrES-2, and TrES-4) which we detected to be binaries. Two of
these have not been known to be multiple before. Parameters of the
corresponding exoplanets are revised. High-resolution "Lucky Imaging" with
AstraLux at the 2.2m Calar Alto telescope provided near diffraction limited
images in i' and z' passbands. These results have been combined with existing
planetary data in order to recalibrate planetary attributes. Despite the
faintness (delta mag ~ 4) of the discovered stellar companions to TrES-2,
TrES-4, and WASP-2, light-curve deduced parameters change by up to more than
1sigma. We discuss a possible relation between binary separation and planetary
properties, which - if confirmed - could hint at the influence of binarity on
the planet formation process.Comment: 9 pages, 3 Figures. Accepted by A&
The magnetically-active, low-mass, triple system WDS 19312+3607
Aims: We investigated in detail the system WDS 19312+3607, whose primary is
an active M4.5Ve star previously thought to be young (tau ~ 300-500 Ma) based
on high X-ray luminosity. Methods: We collected intermediate- and
low-resolution optical spectra taken with 2 m-class telescopes, photometric
data from the to 8 mum bands, and eleven astrometric epochs with a time
baseline of over 56 years for the two components in the system, G 125-15 and G
125-14. Results: We derived M4.5V spectral types for both stars, confirmed
their common proper motion, estimated the heliocentric distance and projected
physical separation, determined the galactocentric space velocities, and
deduced a most-probable age older than 600 Ma. We discovered that the primary,
G 125-15, is in turn an inflated, double-lined, spectroscopic binary with a
short period of photometric variability of P ~ 1.6 d, which we associated to
orbital synchronisation. The observed X-ray and Halpha emissions, photometric
variability, and abnormal radius and effective temperature of G 125-15 AB
indicate strong magnetic activity, possibly due to fast rotation. Besides, the
estimated projected physical separation between G 125-15 AB and G 125-14 of
about 1200 AU makes WDS 19312+3607 to be one of the widest systems with
intermediate M-type primaries. Conclusions: G 125-15 AB is a nearby (d ~ 26
pc), bright (J ~ 9.6 mag), active spectroscopic binary with a single
proper-motion companion of the same spectral type at a wide separation. They
are thus ideal targets for specific follow-ups to investigate wide and close
multiplicity or stellar expansion and surface cooling due to reduced convective
efficiency.Comment: A&A, in pres
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