Adaptive Optics: Performance and Limitations

<p>Neptune&#8217;s atmosphere is covered by tropospheric clouds and elevated hazes that are highly contrasted in hydrogen and methane absorption bands that dominate the red and near-infrared spectrum of the planet. The major cloud systems observed in these wavelengths evolve in time-scales of days, months and years. However, the differential rotation of the atmosphere, and the vertical wind shear implied by the motion of some of these systems, result in challenges in identifying common cloud systems observed in images obtained with a time difference of only a few weeks. Given the small apparent size of Neptune&#8217;s disk (2.3 arc sec at best) there are outstanding difficulties in obtaining sufficient high-resolution data to trace Neptune&#8217;s atmospheric dynamics and study the variability in the atmosphere.</p><p>In 2019 Neptune has been observed by a battery of different large telescopes and techniques including: Adaptive Optics observations from the Keck, Lick and other telescopes, observations from Hubble Space Telescope in two different dates, and lucky-imaging observations with the GranTeCan 10.4m, Calar Alto 2.2m and the 1.05m Pic du Midi telescope. In addition, some ground-based observers using small telescopes of 30-40 cm have been successful to image Neptune&#8217;s major clouds completing a dense time-line of observations. We will present comparative results of Neptune&#8217;s major cloud systems observed with these facilities at a variety of spatial resolutions and long-term drift rates of some of these cloud systems. These will be compared with similar multi-telescope results obtained in the past with several of these telescopes since 2015. Future punctual observations achievable with new observational facilities such as the JWST will benefit from ground-based coordinated campaigns and will require a combination of several telescopes to understand drift rates and evolutionary time-lines of major cloud systems in Neptune.</p>

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High-resolution survey for planetary companions to young stars in the Taurus molecular cloud

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2434 ◽

2020 ◽

Vol 498 (1) ◽

pp. 1382-1396

Author(s):

A L Wallace ◽

J Kammerer ◽

M J Ireland ◽

C Federrath ◽

A L Kraus ◽

...

Keyword(s):

Adaptive Optics ◽

Near Infrared ◽

Semimajor Axis ◽

Infrared Camera ◽

Single Class ◽

Hot Start ◽

Guide Star ◽

Laser Guide ◽

Large Telescopes ◽

Differential Imaging

ABSTRACT Direct imaging in the infrared at the diffraction limit of large telescopes is a unique probe of the properties of young planetary systems. We survey 55 single class I and class II stars in Taurus in the L’ filter using natural and laser guide star adaptive optics and the near-infrared camera (NIRC2) of the Keck II telescope, in order to search for planetary-mass companions. We use both reference star differential imaging and kernel phase techniques, achieving typical 5σ contrasts of ∼6 mag at separations of 0.2 arcsec and ∼8 mag beyond 0.5 arcsec. Although, we do not detect any new faint companions, we constrain the frequency of wide separation massive planets, such as HR 8799 analogues. We find that, assuming hot-start models and a planet distribution with power-law mass and semimajor axis indices of −0.5 and −1, respectively, less than 20 per cent of our target stars host planets with masses >2 MJ at separations >10 au.

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The effect of stellar multiplicity on protoplanetary discs: a near-infrared survey of the Lupus star-forming region

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3674 ◽

2020 ◽

Vol 501 (2) ◽

pp. 2305-2315

Author(s):

Alice Zurlo ◽

Lucas A Cieza ◽

Megan Ansdell ◽

Valentin Christiaens ◽

Sebastián Pérez ◽

...

Keyword(s):

Adaptive Optics ◽

Molecular Cloud ◽

Near Infrared ◽

Main Sequence Stars ◽

Multiple Systems ◽

Star Forming ◽

Very Large Telescope ◽

Pms Stars ◽

First Time ◽

Infrared Survey

ABSTRACT We present results from a near-infrared (NIR) adaptive optics (AO) survey of pre-main-sequence stars in the Lupus molecular cloud with NACO at the Very Large Telescope (VLT) to identify (sub)stellar companions down to ∼20-au separation and investigate the effects of multiplicity on circumstellar disc properties. We observe for the first time in the NIR with AO a total of 47 targets and complement our observations with archival data for another 58 objects previously observed with the same instrument. All 105 targets have millimetre Atacama Large Millimetre/sub-millimetre Array (ALMA) data available, which provide constraints on disc masses and sizes. We identify a total of 13 multiple systems, including 11 doubles and 2 triples. In agreement with previous studies, we find that the most massive (Mdust > 50 M⊕) and largest (Rdust > 70 au) discs are only seen around stars lacking visual companions (with separations of 20–4800 au) and that primaries tend to host more massive discs than secondaries. However, as recently shown in a very similar study of >200 PMS stars in the Ophiuchus molecular cloud, the distributions of disc masses and sizes are similar for single and multiple systems for Mdust < 50 M⊕ and radii Rdust < 70 au. Such discs correspond to ∼80–90 per cent of the sample. This result can be seen in the combined sample of Lupus and Ophiuchus objects, which now includes more than 300 targets with ALMA imaging and NIR AO data, and implies that stellar companions with separations >20 au mostly affect discs in the upper 10${{\ \rm per\ cent}}$ of the disc mass and size distributions.

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High-contrast and resolution near-infrared photometry of the core of R136

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab388 ◽

2021 ◽

Vol 503 (1) ◽

pp. 292-311

Author(s):

Zeinab Khorrami ◽

Maud Langlois ◽

Paul C Clark ◽

Farrokh Vakili ◽

Anne S M Buckner ◽

...

Keyword(s):

Adaptive Optics ◽

Near Infrared ◽

Outer Region ◽

Mass Range ◽

Mass Function ◽

Large Magellanic Cloud ◽

Star Forming ◽

The Core ◽

Very Large Telescope ◽

30 Doradus

ABSTRACT We present the sharpest and deepest near-infrared photometric analysis of the core of R136, a newly formed massive star cluster at the centre of the 30 Doradus star-forming region in the Large Magellanic Cloud. We used the extreme adaptive optics of the SPHERE focal instrument implemented on the ESO Very Large Telescope and operated in its IRDIS imaging mode for the second time with longer exposure time in the H and K filters. Our aim was to (i) increase the number of resolved sources in the core of R136, and (ii) to compare with the first epoch to classify the properties of the detected common sources between the two epochs. Within the field of view (FOV) of 10.8″ × 12.1″ ($2.7\,\text {pc}\times 3.0\, \text {pc}$), we detected 1499 sources in both H and K filters, for which 76 per cent of these sources have visual companions closer than 0.2″. The larger number of detected sources enabled us to better sample the mass function (MF). The MF slopes are estimated at ages of 1, 1.5, and 2 Myr, at different radii, and for different mass ranges. The MF slopes for the mass range of 10–300 M⊙ are about 0.3 dex steeper than the mass range of 3–300 M⊙, for the whole FOV and different radii. Comparing the JHK colours of 790 sources common in between the two epochs, 67 per cent of detected sources in the outer region (r > 3″) are not consistent with evolutionary models at 1–2 Myr and with extinctions similar to the average cluster value, suggesting an origin from ongoing star formation within 30 Doradus, unrelated to R136.

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Final design and on-sky testing of the iLocater SX acquisition camera: broad-band single-mode fibre coupling

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3355 ◽

2020 ◽

Vol 501 (2) ◽

pp. 2250-2267

Author(s):

J Crass ◽

A Bechter ◽

B Sands ◽

D King ◽

R Ketterer ◽

...

Keyword(s):

Adaptive Optics ◽

Near Infrared ◽

Broad Band ◽

Single Mode ◽

Injection System ◽

Single Mode Fibre ◽

Astronomical Instruments ◽

Final Design ◽

Camera Design ◽

And Performance

ABSTRACT Enabling efficient injection of light into single-mode fibres (SMFs) is a key requirement in realizing diffraction-limited astronomical spectroscopy on ground-based telescopes. SMF-fed spectrographs, facilitated by the use of adaptive optics (AO), offer distinct advantages over comparable seeing-limited designs, including higher spectral resolution within a compact and stable instrument volume, and a telescope independent spectrograph design. iLocater is an extremely precise radial velocity (EPRV) spectrograph being built for the Large Binocular Telescope (LBT). We have designed and built the front-end fibre injection system, or acquisition camera, for the SX (left) primary mirror of the LBT. The instrument was installed in 2019 and underwent on-sky commissioning and performance assessment. In this paper, we present the instrument requirements, acquisition camera design, as well as results from first-light measurements. Broad-band SMF coupling in excess of 35 per cent (absolute) in the near-infrared (0.97–1.31 ${\mu {\rm m}}$) was achieved across a range of target magnitudes, spectral types, and observing conditions. Successful demonstration of on-sky performance represents both a major milestone in the development of iLocater and in making efficient ground-based SMF-fed astronomical instruments a reality.

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Multiconjugate Adaptive Optics for Astronomy

Annual Review of Astronomy and Astrophysics ◽

10.1146/annurev-astro-091916-055320 ◽

2018 ◽

Vol 56 (1) ◽

pp. 277-314 ◽

Cited By ~ 10

Author(s):

François Rigaut ◽

Benoit Neichel

Keyword(s):

Adaptive Optics ◽

Near Infrared ◽

Phase Reconstruction ◽

Large Telescope ◽

Wavefront Sensors ◽

Error Sources ◽

New Concepts ◽

Year 2000 ◽

Current Systems ◽

Solar Astronomy

Since the year 2000, adaptive optics (AO) has seen the emergence of a variety of new concepts addressing particular science needs; multiconjugate adaptive optics (MCAO) is one of them. By correcting the atmospheric turbulence in 3D using several wavefront sensors and a tomographic phase reconstruction approach, MCAO aims to provide uniform diffraction limited images in the near-infrared over fields of view larger than 1 arcmin2, i.e., 10 to 20 times larger in area than classical single conjugated AO. In this review, we give a brief reminder of the AO principles and limitations, and then focus on aspects particular to MCAO, such as tomography and specific MCAO error sources. We present examples and results from past or current systems: MAD (Multiconjugate Adaptive Optics Demonstrator) and GeMS (Gemini MCAO System) for nighttime astronomy and the AO system, at Big Bear for solar astronomy. We examine MCAO performance (Strehl ratio up to 40% in H band and full width at half maximum down to 52 mas in the case of MCAO), with a particular focus on photometric and astrometric accuracy, and conclude with considerations on the future of MCAO in the Extremely Large Telescope and post–HST era.

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Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833584 ◽

2018 ◽

Vol 617 ◽

pp. L2 ◽

Cited By ~ 66

Author(s):

A. Müller ◽

M. Keppler ◽

Th. Henning ◽

M. Samland ◽

G. Chauvin ◽

...

Keyword(s):

Adaptive Optics ◽

Near Infrared ◽

Direct Detection ◽

Spectral Energy Distribution ◽

Spectral Energy ◽

Infrared Range ◽

Data Set ◽

Cloud Properties ◽

Spectrophotometric Data ◽

First Time

Context. The observation of planets in their formation stage is a crucial but very challenging step in understanding when, how, and where planets form. PDS 70 is a young pre-main sequence star surrounded by a transition disk, in the gap of which a planetary-mass companion has recently been discovered. This discovery represents the first robust direct detection of such a young planet, possibly still at the stage of formation. Aims. We aim to characterize the orbital and atmospheric properties of PDS 70 b, which was first identified on May 2015 in the course of the SHINE survey with SPHERE, the extreme adaptive-optics instrument at the VLT. Methods. We obtained new deep SPHERE/IRDIS imaging and SPHERE/IFS spectroscopic observations of PDS 70 b. The astrometric baseline now covers 6 yr, which allowed us to perform an orbital analysis. For the first time, we present spectrophotometry of the young planet which covers almost the entire near-infrared range (0.96–3.8 μm). We use different atmospheric models covering a large parameter space in temperature, log g, chemical composition, and cloud properties to characterize the properties of the atmosphere of PDS 70 b. Results. PDS 70 b is most likely orbiting the star on a circular and disk coplanar orbit at ~22 au inside the gap of the disk. We find a range of models that can describe the spectrophotometric data reasonably well in the temperature range 1000–1600 K and log g no larger than 3.5 dex. The planet radius covers a relatively large range between 1.4 and 3.7 RJ with the larger radii being higher than expected from planet evolution models for the age of the planet of 5.4 Myr. Conclusions. This study provides a comprehensive data set on the orbital motion of PDS 70 b, indicating a circular orbit and a motion coplanar with the disk. The first detailed spectral energy distribution of PDS 70 b indicates a temperature typical of young giant planets. The detailed atmospheric analysis indicates that a circumplanetary disk may contribute to the total planetflux.

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