30 research outputs found
How many suns are in the sky? A SPHERE multiplicity survey of exoplanet host stars I -- Four new close stellar companions including a white dwarf
We are studying the influence of stellar multiplicity on exoplanet systems,
in particular systems that have been detected via radial-velocity searches. We
are in particular interested in the closest companions as they would have a
strong influence on the evolution of the original planet forming disks. In this
study we present new companions detected during our ongoing survey of exoplanet
hosts with VLT/SPHERE. We are using the extreme adaptive optics imager SPHERE
at the ESO/VLT to search for faint (sub)stellar companions. We utilized the
classical coronagraphic imaging mode to perform a snapshot survey (3-6 min
integration time) of exoplanet host stars in the Ks-band. We detected new
stellar companions to the exoplanet host stars HD1666, HIP68468, HIP107773, and
HD109271. With an angular separation of only 0.38" (40 au of projected
separation) HIP107773 is among the closest companions found to exoplanet host
stars. The presence of the stellar companion explains the linear
radial-velocity trend seen in the system. At such a small separation the
companion likely had significant influence on the evolution of the planet
forming disk around the primary star. We find that the companion in the HD1666
system may well be responsible for the high orbit eccentricity (0.63) of the
detected Jupiter class planet, making this system one of only a few where such
a connection can be established. A cross-match with the Gaia DR2 catalog showed
furthermore that the near infrared faint companion around HD109271 had been
detected in the optical and is significantly brighter than in the near infrared
making it a white dwarf companion.Comment: 8 pages, 4 figures, accepted for publication by A&
Apocenter pile-up and arcs: a narrow dust ring around HD 129590
Observations of debris disks have significantly improved over the past
decades, both in terms of sensitivity and spatial resolution. At near-infrared
wavelengths, new observing strategies and post-processing algorithms allow us
to drastically improve the final images, revealing faint structures in the
disks. These structures inform us about the properties and spatial distribution
of the small dust particles. We present new -band observations of the disk
around HD 129590, which display an intriguing arc-like structure in total
intensity but not in polarimetry, and propose an explanation for the origin of
this arc. Assuming geometric parameters for the birth ring of planetesimals,
our model provides the positions of millions of particles of different sizes to
compute scattered light images. We demonstrate that if the grain size
distribution is truncated or strongly peaks at a size larger than the radiation
pressure blow-out size we are able to produce an arc quite similar to the
observed one. If the birth ring is radially narrow, given that particles of a
given size have similar eccentricities, they will have their apocenters at the
same distance from the star. Since this is where the particles will spend most
of their time, this results in a "apocenter pile-up" that can look like a ring.
Due to more efficient forward scattering this arc only appears in total
intensity observations and remains undetected in polarimetric data. This
scenario requires sharp variations either in the grain size distribution or for
the scattering efficiencies . Alternative possibilities such as
a wavy size distribution and a size-dependent phase function are interesting
candidates to strengthen the apocenter pile-up. We also discuss why such arcs
are not commonly detected in other systems, which can mainly be explained by
the fact that most parent belts are usually broad.Comment: Accepted for publication in A&A, abstract shortene
Morphology of the gas-rich debris disk around HD 121617 with SPHERE observations in polarized light
Debris disks are the signposts of collisionally eroding planetesimal
circumstellar belts, whose study can put important constraints on the structure
of extrasolar planetary systems. The best constraints on the morphology of
disks are often obtained from spatially resolved observations in scattered
light. Here, we investigate the young (~16 Myr) bright gas-rich debris disk
around HD121617. We use new scattered-light observations with VLT/SPHERE to
characterize the morphology and the dust properties of this disk. From these
properties we can then derive constraints on the physical and dynamical
environment of this system, for which significant amounts of gas have been
detected. The disk morphology is constrained by linear-polarimetric
observations in the J band. Based on our modeling results and archival
photometry, we also model the SED to put constraints on the total dust mass and
the dust size distribution. We explore different scenarios that could explain
these new constraints. We present the first resolved image in scattered light
of the debris disk HD121617. We fit the morphology of the disk, finding a
semi-major axis of 78.30.2 au, an inclination of 43.10.2{\deg} and a
position angle of the major axis with respect to north, of 239.80.3{\deg},
compatible with the previous continuum and CO detection with ALMA. Our analysis
shows that the disk has a very sharp inner edge, possibly sculpted by a
yet-undetected planet or gas drag. While less sharp, its outer edge is steeper
than expected for unperturbed disks, which could also be due to a planet or gas
drag, but future observations probing the system farther from the main belt
would help explore this further. The SED analysis leads to a dust mass of
0.210.02 M and a minimum grain size of 0.870.12 m,
smaller than the blowout size by radiation pressure, which is not unexpected
for very bright col...Comment: 12 pages, 7 figures. Accepted in A&A (06/02/2023
FALCO simulations of high-contrast polarimetry with the Nancy Grace Roman Space Telescope Coronagraph Instrument
The Coronagraph Instrument of the Nancy Grace Roman Space Telescope (Roman
Coronagraph) will be capable of both total intensity and polarization
measurements of circumstellar disks. The polarimetric performance is impacted
by polarization effects introduced by all mirrors before the Wollaston prisms.
In this paper, we aim to characterize these effects for the Roman Coronagraph
in bands 1 and 4 using the FALCO and PROPER packages. We simulate the effect of
polarization aberrations that impact the polarimetric contrast and the
instrumental polarization effects to study the polarimetric accuracy. We
include spacecraft rolls, but leave out systematic camera noise. We find that
polarimetric differential imaging (PDI) improves the contrast by a factor of
six. The PDI contrast of is limited by polarized
speckles from instrumental polarization effects and polarization aberrations.
By injecting polarized companions with at various contrast levels and
demodulating their polarimetric signal, we recover their source Stokes vector
within 2%.Comment: 16 pages, 16 figures, SPIE Optics + Photonics - Techniques and
Instrumentation for Detection of Exoplanets X
Original use of MUSE's laser tomography adaptive optics to directly image young accreting exoplanets
We present recent results obtained with the VLT/MUSE Integral Field
Spectrograph fed by the 4LGSF and its laser tomography adaptive optics module
GALACSI. While this so-called narrow-field mode of MUSE was not designed to
perform directly imaging of exoplanets and outflows, we show that it can be a
game changer to detect and characterize young exoplanets with a prominent
emission lines (i.e H{\alpha}, tracer of accretion), at moderate contrasts.
These performances are achieved thanks to the combo of a near-diffraction
limited PSF and a medium resolution spectrograph and a cross-correlation
approach in post-processing . We discuss this in the context of ground and
space, infrared and visible wavelengths, preparing for missions like JWST and
WFIRST in great synergy and as pathfinder for future ELT/GSMT (Extremely Large
and/or Giant Segmented Mirror Telescopes) instruments.Comment: AO4ELT6 Conference Proceedings (2019), 12 pages, 6 figures
(http://ao4elt6.copl.ulaval.ca/proceedings.html
Polarization aberrations in next-generation giant segmented mirror telescopes (GSMTs) I. Effect on the coronagraphic performance
Next-generation large segmented mirror telescopes are expected to perform
direct imaging and characterization of Earth-like rocky planets, which requires
contrast limits of to at wavelengths from I to J band. One
critical aspect affecting the raw on-sky contrast are polarization aberrations
arising from the reflection from the telescope's mirror surfaces and instrument
optics. We simulate the polarization aberrations and estimate their effect on
the achievable contrast for three next-generation ground-based large segmented
mirror telescopes. We performed ray-tracing in Zemax and computed the
polarization aberrations and Jones pupil maps using the polarization
ray-tracing algorithm. The impact of these aberrations on the contrast is
estimated by propagating the Jones pupil maps through a set of idealized
coronagraphs using hcipy, a physical optics-based simulation framework. The
optical modeling of the giant segmented mirror telescopes (GSMTs) shows that
polarization aberrations create significant leakage through a coronagraphic
system. The dominant aberration is retardance defocus, which originates from
the steep angles on the primary and secondary mirrors. The retardance defocus
limits the contrast to to at 1 at visible
wavelengths, and to at infrared wavelengths. The
simulations also show that the coating plays a major role in determining the
strength of the aberrations. Polarization aberrations will need to be
considered during the design of high-contrast imaging instruments for the next
generation of extremely large telescopes. This can be achieved either through
compensation optics, robust coronagraphs, specialized coatings, calibration,
and data analysis approaches or by incorporating polarimetry with high-contrast
imaging to measure these effects.Comment: 18 pages, 12 figures, Accepted in Astronomy & Astrophysics manuscript
no. aa45651-2
A low-mass stellar companion to the young variable star RZ Psc
RZ Psc is a young Sun-like star with a bright and warm infrared excess that is occasionally dimmed significantly by circumstellar dust structures. Optical depth arguments suggest that the dimming events do not probe a typical sightline through the circumstellar dust, and are instead caused by structures that appear above an optically thick mid-plane. This system may therefore be similar to systems where an outer disc is shadowed by material closer to the star. Here, we report the discovery that RZ Psc hosts a 0.12Mâ companion at a projected separation of 23 au. We conclude that the disc must orbit the primary star. While we do not detect orbital motion, comparison of the angle of linear polarization of the primary with the companion's on-sky position angle provides circumstantial evidence that the companion and disc may not share the same orbital plane. Whether the companion severely disrupts the disc, truncates it, or has little effect at all will require further observations of both the companion and disc
Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): Diverse outcomes of binary-disk interactions
Circumstellar disks do not evolve in isolation, as about half of solar-type
stars were born in binary or multiple systems. Resolving disks in binary
systems provides the opportunity to examine the influence of stellar companions
on the outcomes of planet formation. We aim to investigate and compare disks in
stellar multiple systems with near-infrared scattered-light imaging as part of
the Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS)
program. We used polarimetric differential imaging with SPHERE/IRDIS at the VLT
to search for scattered light from the circumstellar disks in three multiple
systems, CHX 22, S CrA, and HP Cha. We performed astrometric and orbit analyses
for the stellar companions using archival HST, VLT/NACO, and SPHERE data.
Combined with the age and orbital constraints, the observed disk structures
provide insights into the evolutionary history and the impact of the stellar
companions. The small grains in CHX 22 form a tail-like structure surrounding
the close binary, which likely results from a close encounter and capture of a
cloudlet. S CrA shows intricate structures (tentative ringed and spiral
features) in the circumprimary disk as a possible consequence of perturbations
by companions. The circumsecondary disk is truncated and connected to the
primary disk via a streamer, suggesting tidal interactions. In HP Cha, the
primary disk is less disturbed and features a tenuous streamer, through which
the material flows towards the companions. The comparison of the three systems
spans a wide range of binary separation (50 - 500 au) and illustrates the
decreasing influence on disk structures with the distance of companions. This
agrees with the statistical analysis of exoplanet population in binaries, that
planet formation is likely obstructed around close binary systems, while it is
not suppressed in wide binaries.Comment: 19 pages, 6 figures, accpeted for publication in A&
Calibration of the instrumental polarization effects of SCExAO-CHARISâ spectropolarimetric mode
SCExAO at the Subaru telescope is a visible and near-infrared high-contrast imaging instrument employing extreme adaptive optics and coronagraphy. The instrument feeds the near-infrared light (JHK) to the integral field spectrograph CHARIS. Recently, a Wollaston prism was added to CHARISâ optical path, giving CHARIS a spectropolarimetric capability that is unique among high-contrast imaging instruments. We present a comprehensive and detailed Mueller matrix model describing the instrumental polarization effects of the complete optical path, thus the telescope and instrument, using measurements with the internal source and observations of standard stars. The 22 wavelength bins of CHARIS provide a unique opportunity to investigate in detail the wavelength dependence of the instrumental polarization effects. We find that the image derotator (K-mirror) produces strongly wavelength-dependent crosstalk, in the worst case converting ~95% of the incident linear polarization to circularly polarized light that cannot be measured. We fit the crosstalk of the half-wave plate (HWP) for all wavelengths with a simple two-parameter model of an achromatic HWP consisting of a layer of quartz and a layer of MgF2. While the magnitude of the telescope-induced polarization varies with wavelength, its angle varies solely with the altitude angle of the telescope. We show initial steps toward correcting on-sky data for the instrumental polarization effects, with which we aim to achieve a polarimetric accuracy <0.1% in the degree of linear polarization. Our calibrations of CHARISâ spectropolarimetric mode enable unique quantitative polarimetric studies of circumstellar disks and planetary and brown dwarf companions