46 research outputs found
Laboratory demonstration of the triple-grating vector vortex coronagraph
The future Habitable Worlds Observatory aims to characterize the atmospheres
of rocky exoplanets around solar-type stars. The vector vortex coronagraph
(VVC) is a main candidate to reach the required contrast of .
However, the VVC requires polarization filtering and every observing band
requires a different VVC. The triple-grating vector vortex coronagraph (tgVVC)
aims to mitigate these limitations by combining multiple gratings that minimize
the polarization leakage over a large spectral bandwidth. In this paper, we
present laboratory results of a tgVVC prototype using the In-Air Coronagraphic
Testbed (IACT) facility at NASA's Jet Propulsion Laboratory and the Space
Coronagraph Optical Bench (SCoOB) at the University of Arizona Space
Astrophysics Lab (UASAL). We study the coronagraphic performance with
polarization filtering at 633 nm and reach a similar average contrast of between 3-18 at the IACT, and
between 3-14 at SCoOB. We explore the limitations of the tgVVC by
comparing the testbed results. We report on other manufacturing errors and ways
to mitigate their impact.Comment: 9 pages, 5 figures, SPIE Optics + Photonics - Techniques and
Instrumentation for Detection of Exoplanets X
Searching for proto-planets with MUSE
Protoplanetary disks contain structures such as gaps, rings, and spirals,
which are thought to be produced by the interaction between the disk and
embedded protoplanets. However, only a few planet candidates are found orbiting
within protoplanetary disks, and most of them are being challenged as having
been confused with disk features. We aim to discover more proto-planetary
candidates with MUSE, with a secondary aim of improving the high-resolution
spectral differential imaging (HRSDI) technique by analyzing the instrumental
residuals of MUSE. We analyzed MUSE observations of five young stars and
applied the HRSDI technique to perform high-contrast imaging. With a 30 min
integration time, MUSE can reach 5 detection limits in apparent
H line flux down to 10 and 10 erg s cm at
0.075" and 0.25", respectively. In addition to PDS 70 b and c, we did not
detect any clear accretion signatures in PDS 70, J1850-3147, and V1094 Sco down
to 0.1". MUSE avoids the small sample statistics problem by measuring the noise
characteristics in the spatial direction at multiple wavelengths. We detected
two asymmetric atomic jets in HD 163296. The HRSDI technique when applied to
MUSE data allows us to reach the photon noise limit at small separations (i.e.,
< 0.5"). With a higher spectral resolution, MUSE can achieve fainter detection
limits in apparent line flux than SPHERE/ZIMPOL by a factor of 5. MUSE
has some instrumental issues that limit the contrast that appear in cases with
strong point sources, which can be either a spatial point source due to high
Strehl observations or a spectral point source due to a high line-to-continuum
ratio. We modified the HRSDI technique to better handle the instrumental
artifacts and improve the detection limits.Comment: 14 pages, 15 figures, 4 tables. Accepted for publication in A&
Two accreting protoplanets around the young star PDS 70
Newly forming proto-planets are expected to create cavities and substructures
in young, gas-rich proto-planetary disks, but they are difficult to detect as
they could be confused with disk features affected by advanced image-analysis
techniques. Recently, a planet was discovered inside the gap of the
transitional disk of the T-Tauri star PDS 70. Here we report on the detection
of strong H-alpha emission from two distinct locations in the PDS 70 system,
one corresponding to the previously discovered planet PDS 70 b, which confirms
the earlier H detection, and another located close to the outer-edge of
the gap, coinciding with a previously identified bright dust spot in the disk
and with a small opening in a ring of molecular emission. We identify this
second H peak as a second proto-planet in the PDS 70 system. The
H emission spectra of both proto-planets indicate ongoing accretion
onto the proto-planets, which appear to be near a 2:1 mean motion resonance.
Our observations show that adaptive-optics-assisted, medium-resolution,
integral-field spectroscopy with MUSE targeting accretion signatures will be a
powerful way to trace ongoing planet formation in transitional disks at
different stages of their evolution. Finding more young planetary systems in
mean motion resonance would give credibility to the Grand Tack hypothesis in
which Jupiter and Saturn migrated in a resonance orbit during the early
formation period of our Solar System.Comment: Nature Astronomy, June 3, 2019; 15 pages, 3 Figs, 1 Tabl
Estimation of polarization aberrations and their effect on the coronagraphic performance for future space telescopes
A major goal of proposed future space observatories, such as the Habitable
World Observatory, is to directly image and characterize Earth-like planets
around Sun-like stars to search for habitability signatures requiring the
starlight suppression (contrast) of 1e-10. One of the significant aspects
affecting this contrast is the polarization aberrations generated from the
reflection from mirror surfaces. The polarization aberrations are the
phase-dependent amplitude and phase patterns originating from the Fresnel
reflections of the mirror surfaces. These aberrations depend on the angle of
incidence and coating parameters of the surface. This paper simulates the
polarization aberrations for an on-axis and off-axis TMA telescope of a 6.5 m
monolithic primary mirror. We analyze the polarization aberrations and their
effect on the coronagraphic performance for eight different recipes of mirror
coatings for Astronomical filter bands g-I: three single-layer metal coatings
and five recipes of protective coatings. First, the Jones pupils are estimated
for each coating and filter band using the polarization ray tracing in Zemax.
Then, we propagate these Jones pupils through a Vector Vortex Coronagraph and
Perfect Coronagraphs using hcipy, a physical optics-based simulation framework.
The analysis shows that the two main polarization aberrations generated from
the four mirrors are the retardance-defocus and retardance-tilt. The
simulations also show that the coating plays a significant role in determining
the strength of the aberrations. The bare/oxi-aluminum and Al+18nm LiF coating
outperforms all the other coatings by one order of magnitude.Comment: 13 pages, 11 figures, SPIE Optics+Photonics 2023 proceeding, Paper
no: 12680-2
CS Cha B: A disc-obscured M-type star mimicking a polarised planetary companion
Context. Direct imaging provides a steady flow of newly discovered giant
planets and brown dwarf companions. These multi-object systems can provide
information about the formation of low-mass companions in wide orbits and/or
help us to speculate about possible migration scenarios. Accurate
classification of companions is crucial for testing formation pathways. Aims.
In this work we further characterise the recently discovered candidate for a
planetary-mass companion CS Cha b and determine if it is still accreting.
Methods. MUSE is a four-laser-adaptive-optics-assisted medium-resolution
integral-field spectrograph in the optical part of the spectrum. We observed
the CS Cha system to obtain the first spectrum of CS Cha b. The companion is
characterised by modelling both the spectrum from 6300 \unicode{x212B} to
9300 \unicode{x212B} and the photometry using archival data from the visible
to the near-infrared (NIR). Results. We find evidence of accretion and outflow
signatures in H and OI emission. The atmospheric models with
the highest likelihood indicate an effective temperature of K with
a of dex. Based on evolutionary models, we find that the
majority of the object is obscured. We determine the mass of the faint
companion with several methods to be between 0.07 and 0.71
with an accretion rate of
Myr. Conclusions. Our results show that CS Cha B is most likely a
mid-M-type star that is obscured by a highly inclined disc, which has led to
its previous classification using broadband NIR photometry as a planetary-mass
companion. This shows that it is important and necessary to observe over a
broad spectral range to constrain the nature of faint companionsComment: 9 pages, 6 figures, accepted for publication by A&
Accreting protoplanets: Spectral signatures and magnitude of gas and dust extinction at H α
Context. Accreting planetary-mass objects have been detected at H α, but targeted searches have mainly resulted in non-detections. Accretion tracers in the planetary-mass regime could originate from the shock itself, making them particularly susceptible to extinction by the accreting material. High-resolution (R > 50 000) spectrographs operating at H α should soon enable one to study how the incoming material shapes the line profile.
Aims. We calculate how much the gas and dust accreting onto a planet reduce the H α flux from the shock at the planetary surface and how they affect the line shape. We also study the absorption-modified relationship between the H α luminosity and accretion rate.
Methods. We computed the high-resolution radiative transfer of the H α line using a one-dimensional velocity–density–temperature structure for the inflowing matter in three representative accretion geometries: spherical symmetry, polar inflow, and magnetospheric accretion. For each, we explored the wide relevant ranges of the accretion rate and planet mass. We used detailed gas opacities and carefully estimated possible dust opacities.
Results. At accretion rates of Ṁ ≲ 3 × 10−6 MJ yr−1, gas extinction is negligible for spherical or polar inflow and at most AH α ≲ 0.5 mag for magnetospheric accretion. Up to Ṁ ≈ 3 × 10−4 MJ yr−1, the gas contributes AH α ≲ 4 mag. This contribution decreases with mass. We estimate realistic dust opacities at H α to be κ ~ 0.01–10 cm2 g−1, which is 10–104 times lower than in the interstellar medium. Extinction flattens the LH α –Ṁ relationship, which becomes non-monotonic with a maximum luminosity LH α ~ 10−4 L⊙ towards Ṁ ≈ 10−4 MJ yr−1 for a planet mass ~10 MJ. In magnetospheric accretion, the gas can introduce features in the line profile, while the velocity gradient smears them out in other geometries.
Conclusions. For a wide part of parameter space, extinction by the accreting matter should be negligible, simplifying the interpretation of observations, especially for planets in gaps. At high Ṁ, strong absorption reduces the H α flux, and some measurements can be interpreted as two Ṁ values. Highly resolved line profiles (R ~ 105) can provide (complex) constraints on the thermal and dynamical structure of the accretion flow
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