arXiv subjects

Amali Vaz

Publications and source records attributed to Amali Vaz.

At least 19 recordsLinked to original sources

arXiv2024

Resolving the Young 2 Cygni Run-away Star into a Binary using iLocater

Precision radial velocity (RV) spectrographs that use adaptive optics (AO) show promise to advance telescope observing capabilities beyond those of seeing-limited designs. We are building a spectrograph for the Large Binocular Telescope (LBT) named iLocater that uses AO to inject starlight directly into single mode fibers (SMF). iLocater's first acquisition camera system (the `SX' camera), which receives light from one of the 8.4m diameter primary mirrors of the LBT, was initially installed in summer 2019 and has since been used for several commissioning runs. We present results from first-light observations that include on-sky measurements as part of commissioning activities. Imaging measurements of the bright B3IV star 2 Cygni ($V=4.98$) resulted in the direct detection of a candidate companion star at an angular separation of only $\theta = 70$ mas. Follow-up AO measurements using Keck/NIRC2 recover the candidate companion in multiple filters. An $R\approx1500$ miniature spectrograph recently installed at the LBT named ``Lili'' provides spatially resolved spectra of each binary component, indicating similar spectral types and strengthening the case for companionship. Studying the multiplicity of young runaway star systems like 2 Cygni ($36.6 \pm 0.5$ Myr) can help to understand formation mechanisms for stars that exhibit anomalous velocities through the galaxy. This on-sky demonstration illustrates the spatial resolution of the iLocater SX acquisition camera working in tandem with the LBT AO system; it further derisks a number of technical hurdles involved in combining AO with Doppler spectroscopy.

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arXiv2024

Tuning the MAPS Adaptive Secondary Mirror: Actuator Control, PID Tuning, Power Spectra and Failure Diagnosis

The MMT Adaptive optics exoPlanet characterization System (MAPS) is currently in its engineering phase, operating on-sky at the MMT Telescope on Mt. Hopkins in southern Arizona. The MAPS Adaptive Secondary Mirror's actuators are controlled by a closed loop modified PID control law and an open loop feed-forward law, which in combination allows for faster actuator response time. An essential element of achieving the secondary's performance goals involves the process of PID gain tuning. To start, we briefly discuss the design of the MAPS ASM and its actuators. We then describe the actuator positional control system and control law. Next, we discuss a few of the issues that make ASM tuning difficult. We then outline our initial attempts at tuning the actuator controllers and discuss the use of actuator positional power spectra for both tuning and determining the health and failure states of individual actuators. We conclude by presenting the results of our latest round of tuning configuration trials, which have been successful at decreasing mirror latency, increasing operational mirror modes and improving image PSF.

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arXiv2024

ESCAPE: Efficient Synthesis of Calibrations for Adaptive optics through Pseudo-synthetic and Empirical methods

With the commissioning of the refurbished adaptive secondary mirror (ASM) for the 6.5-meter MMT Observatory under way, special consideration had to be made to properly calibrate the mirror response functions to generate an interaction matrix (IM). The commissioning of the ASM is part of the MMT Adaptive optics exoPlanet characterization System (MAPS) upgrade the observatory's legacy adaptive optics (AO) system. Unlike most AO systems, MAPS employs a convex ASM which prevents the introduction of a calibration source capable of simultaneously illuminating its ASM and wavefront sensor (WFS). This makes calibration of the AO system a significant hurdle in commissioning. To address this, we have employed a hybrid calibration strategy we call the Efficient Synthesis of Calibrations for Adaptive Optics through Pseudo-synthetic and Empirical methods (ESCAPE). ESCAPE combines the DO-CRIME on-sky calibration method with the SPRINT method for computing pseudo-synthetic calibration matrices. To monitor quasi-static system change, the ESCAPE methodology rapidly and continuously generates pseudo-synthetic calibration matrices using continual empirical feedback in either open or closed-loop. In addition, by measuring the current IM in the background while in close-loop, we are also able to measure the optical gains for pyramid wavefront sensor (PyWFS) systems. In this paper, we will provide the mathematical foundation of the ESCAPE calibration strategy and on-sky results from its application in calibrating the MMT Observatory's ASM. Additionally, we will showcase the validation of our approach from our AO testbed and share preliminary on-sky results from MMT.

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arXiv2023

SOUL at LBT: commissioning results, science and future

The SOUL systems at the Large Bincoular Telescope can be seen such as precursor for the ELT SCAO systems, combining together key technologies such as EMCCD, Pyramid WFS and adaptive telescopes. After the first light of the first upgraded system on September 2018, going through COVID and technical stops, we now have all the 4 systems working on-sky. Here, we report about some key control improvements and the system performance characterized during the commissioning. The upgrade allows us to correct more modes (500) in the bright end and increases the sky coverage providing SR(K)>20% with reference stars G$_{RP}$<17, opening to extragalcatic targets with NGS systems. Finally, we review the first astrophysical results, looking forward to the next generation instruments (SHARK-NIR, SHARK-Vis and iLocater), to be fed by the SOUL AO correction.

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arXiv2023

The MAPS Adaptive Secondary Mirror: First Light, Laboratory Work, and Achievements

The MMT Adaptive Optics exoPlanet Characterization System (MAPS) is a comprehensive update to the first generation MMT adaptive optics system (MMTAO), designed to produce a facility class suite of instruments whose purpose is to image nearby exoplanets. The system's adaptive secondary mirror (ASM), although comprised in part of legacy components from the MMTAO ASM, represents a major leap forward in engineering, structure and function. The subject of this paper is the design, operation, achievements and technical issues of the MAPS adaptive secondary mirror. We discuss laboratory preparation for on-sky engineering runs, the results of those runs and the issues we discovered, what we learned about those issues in a follow-up period of laboratory work, and the steps we are taking to mitigate them.

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arXiv2021

Resolving Io's Volcanoes from a Mutual Event Observation at the Large Binocular Telescope

Unraveling the geological processes ongoing at Io's numerous sites of active volcanism requires high spatial resolution to, for example, measure the areal coverage of lava flows or identify the presence of multiple emitting regions within a single volcanic center. In de Kleer et al. (2017) we described observations with the Large Binocular Telescope (LBT) during an occultation of Io by Europa at ~6:17 UT on 2015 March 08, and presented a map of the temperature distribution within Loki Patera derived from these data. Here we present emission maps of three other volcanic centers derived from the same observation: Pillan Patera, Kurdalagon Patera, and the vicinity of Ulgen Patera/PV59/N Lerna Regio. The emission is localized by the light curves and resolved into multiple distinct emitting regions in two of the cases. Both Pillan and Kurdalagon Paterae had undergone eruptions in the months prior to our observations, and the location and intensity of the emission is interpreted in the context of the temporal evolution of these eruptions observed from other facilities. The emission from Kurdalagon Patera is resolved into two distinct emitting regions separated by only a few degrees in latitude that were unresolved by Keck observations from the same month.

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arXiv2021

Bringing SOUL on sky

The SOUL project is upgrading the 4 SCAO systems of LBT, pushing the current guide star limits of about 2 magnitudes fainter thanks to Electron Multiplied CCD detector. This improvement will open the NGS SCAO correction to a wider number of scientific cases from high contrast imaging in the visible to extra-galactic source in the NIR. The SOUL systems are today the unique case where pyramid WFS, adaptive secondary and EMCCD are used together. This makes SOUL a pathfinder for most of the ELT SCAO systems like the one of GMT, MICADO and HARMONI of E-ELT, where the same key technologies will be employed. Today we have 3 SOUL systems installed on the telescope in commissioning phase. The 4th system will be installed in a few months. We will present here the results achieved during daytime testing and commissioning nights up to the present date.

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arXiv2020

Design and development of a high-speed Visible Pyramid Wavefront Sensor for the MMT AO system

MAPS, MMT Adaptive optics exoPlanet characterization System, is the upgrade of legacy 6.5m MMT adaptive optics system. It is an NSF MSIP-funded project that includes (i) refurbishing of the MMT Adaptive Secondary Mirror (ASM), (ii) new high sensitive and high spatial order visible and near-infrared pyramid wavefront sensors, and (iii) the upgrade of Arizona Infrared Imager and Echelle Spectrograph (ARIES) and MMT high Precision Imaging Polarimeter (MMTPol) science cameras. This paper will present the design and development of the visible pyramid wavefront sensor. This system consists of an acquisition camera, a fast-steering tip-tilt modulation mirror, a double pyramid, a pupil imaging triplet lens, and a low noise and high-speed frame rate based CCID75 camera. We will report on hardware and software and present the laboratory characterization results of the individual subsystems, and outline the on-sky commissioning plan.

astro-ph.IM↗

arXiv2020

Final Design and On-Sky Testing of the iLocater SX Acquisition Camera: Broadband Single-Mode Fiber Coupling

Enabling efficient injection of light into single-mode fibers (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 fiber 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. Broadband single-mode fiber coupling in excess of 35% (absolute) in the near-infrared (0.97-1.31μm) 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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arXiv2020

Thermal Emission in the Southwest Clump of VY CMa

We present high spatial resolution LBTI/NOMIC $9-12$ $μm$ images of VY CMa and its massive outflow feature, the Southwest (SW) Clump. Combined with high-resolution imaging from HST ($0.4-1$ $μm$) and LBT/LMIRCam ($1-5$ $μm$), we isolate the spectral energy distribution (SED) of the clump from the star itself. Using radiative-transfer code DUSTY, we model both the scattered light from VY CMa and the thermal emission from the dust in the clump to estimate the optical depth, mass, and temperature of the SW Clump. The SW Clump is optically thick at 8.9 $μm$ with a brightness temperature of $\sim$200 K. With a dust chemistry of equal parts silicates and metallic iron, as well as assumptions on grain size distribution, we estimate a dust mass of $5.4\times10^{-5}\,M_\odot$. For a gas--to--dust ratio of 100, this implies a total mass of $5.4\times10^{-3}\,M_\odot$. Compared to the typical mass-loss rate of VY CMa, the SW Clump represents an extreme, localized mass-loss event from $\lesssim300$ years ago.

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arXiv2020

The HOSTS survey for exozodiacal dust: Observational results from the complete survey

The Large Binocular Telescope Interferometer (LBTI) enables nulling interferometric observations across the N band (8 to 13 um) to suppress a star's bright light and probe for faint circumstellar emission. We present and statistically analyze the results from the LBTI/HOSTS (Hunt for Observable Signatures of Terrestrial Systems) survey for exozodiacal dust. By comparing our measurements to model predictions based on the Solar zodiacal dust in the N band, we estimate a 1 sigma median sensitivity of 23 zodis for early type stars and 48 zodis for Sun-like stars, where 1 zodi is the surface density of habitable zone (HZ) dust in the Solar system. Of the 38 stars observed, 10 show significant excess. A clear correlation of our detections with the presence of cold dust in the systems was found, but none with the stellar spectral type or age. The majority of Sun-like stars have relatively low HZ dust levels (best-fit median: 3 zodis, 1 sigma upper limit: 9 zodis, 95% confidence: 27 zodis based on our N band measurements), while ~20% are significantly more dusty. The Solar system's HZ dust content is consistent with being typical. Our median HZ dust level would not be a major limitation to the direct imaging search for Earth-like exoplanets, but more precise constraints are still required, in particular to evaluate the impact of exozodiacal dust for the spectroscopic characterization of imaged exo-Earth candidates.

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arXiv2019

Image Flux Ratios of Gravitationally Lensed HS 0810+2554 with High Resolution Infrared Imaging

We report near simultaneous imaging using LMIRCam on the LBTI of the quadruply imaged lensed quasar HS 0810+2554 at wavelengths of 2.16, 3.7 and $4.78~μ$m with a Full Width Half Max (FWHM) spatial resolution of $0^{\prime\prime}\!\!.13$, $0^{\prime\prime}\!\!.12$ and $0^{\prime\prime}\!\!.15$ respectively, comparable to HST optical imaging. In the $\rm{z} = 1.5$ rest frame of the quasar, the observed wavelengths correspond to 0.86, 1.48, and $1.91~μ$m respectively. The two brightest images in the quad, A and B, are clearly resolved from each other with a separation of $0.187^{\prime\prime}$. The flux ratio of these two images (A/B) trends from 1.79 to 1.23 from 2.16 to $4.78~μ$m. The trend in flux ratio is consistent with the $2.16~μ$m flux originating from a small sized accretion disk in the quasar that experiences only microlensing. The excess flux above the contribution from the accretion disk at the two longer wavelengths originates from a larger sized region that experiences no microlensing. A simple model employing multiplicative factors for image B due to stellar microlensing $(m)$ and sub-structure millilensing $(M)$ is presented. The result is tightly constrained to the product $m\times M=1.79$. Given the observational errors, the 60\% probability contour for this product stretches from $m= 2.6$, $M = 0.69$ to $m= 1.79$, $M = 1.0$, where the later is consistent with microlensing only.

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arXiv2019

Status of commissioning stabilized infrared Fizeau interferometry with LBTI

The Large Binocular Telescope Interferometer (LBTI) has the longest baseline in the world, 22.7 m, for performing astronomical interferometry in Fizeau mode, which involves beam combination in a focal plane and preserves a wide field-of-view. LBTI can operate in this mode at wavelengths of 1.2 to 5 and 8 to 12 μm, making it a unique platform for carrying out high-resolution imaging of circumstellar disks, evolved stars, solar system objects, and possibly searches for planets, in the thermal infrared. Over the past five years, LBTI has carried out a considerable number of interferometric observations by combining the beams near a pupil plane to carry out nulling interferometry. This mode is useful for measuring small luminosity level offsets, such as those of exozodiacal dust disks. The Fizeau mode, by contrast, is more useful for generating an image of the target because it has more (u, v) (Fourier) plane coverage. However, the Fizeau mode is still in an ongoing process of commissioning. Sensitive Fizeau observations require active phase control, increased automation, and the removal of non-common-path aberrations (NCPA) between the science and phase beams. This increased level of control will increase the fringe contrast, enable longer integrations, and reduce time overheads. We are in the process of writing a correction loop to remove NCPA, and have carried out tests on old and synthetic data. We have also carried out on-sky Fizeau engineering tests in fall 2018 and spring 2019. In this article, we share lessons learned and strategies developed as a result of these tests.

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arXiv2018

Speckle statistics in adaptive optics images at visible wavelengths

Residual speckles in adaptive optics (AO) images represent a well-known limitation on the achievement of the contrast needed for faint source detection. Speckles in AO imagery can be the result of either residual atmospheric aberrations, not corrected by the AO, or slowly evolving aberrations induced by the optical system. We take advantage of the high temporal cadence (1 ms) of the data acquired by the System for Coronagraphy with High-order Adaptive Optics from R to K bands-VIS forerunner experiment at the Large Binocular Telescope to characterize the AO residual speckles at visible wavelengths. An accurate knowledge of the speckle pattern and its dynamics is of paramount importance for the application of methods aimed at their mitigation. By means of both an automatic identification software and information theory, we study the main statistical properties of AO residuals and their dynamics. We therefore provide a speckle characterization that can be incorporated into numerical simulations to increase their realism and to optimize the performances of both real-time and postprocessing techniques aimed at the reduction of the speckle noise.

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arXiv2018

The TRENDS High-Contrast Imaging Survey. VII. Discovery of a Nearby Sirius-like White Dwarf System (HD 169889)

Monitoring the long-term radial velocity (RV) and acceleration of nearby stars has proven an effective method for directly detecting binary and substellar companions. Some fraction of nearby RV trend systems are expected to be comprised of compact objects that likewise induce a systemic Doppler signal. In this paper, we report the discovery of a white dwarf companion found to orbit the nearby ($π= 28.297 \pm 0.066$ mas) G9 V star HD 169889. High-contrast imaging observations using NIRC2 at Keck and LMIRCam at the LBT uncover the ($ΔH = 9.76 \pm 0.16$, $ΔL' = 9.60 \pm 0.03$) companion at an angular separation of 0.8'' (28 au). Thirteen years of precise Doppler observations reveal a steep linear acceleration in RV time series and place a dynamical constraint on the companion mass of $M \geq 0.369 \pm 0.010 M_{\odot}$. This "Sirius-like" system adds to the census of white dwarf companions suspected to be missing in the solar neighborhood.

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arXiv2017

Precision Time-series Photometry in the Thermal Infrared with a 'Wall-Eyed' Pointing Mode at the Large Binocular Telescope

Time-series photometry taken from ground-based facilities is improved with the use of comparison stars due to the short timescales of atmospheric-induced variability. However, the sky is bright in the thermal infrared (3-5 um), and the correspondingly small fields-of-view of available detectors make it highly unusual to have a calibration star in the same field as a science target. Here we present a new method of obtaining differential photometry by simultaneously imaging a science target and a calibrator star, separated by <2 amin, onto a 10x10 asec field-of-view detector. We do this by taking advantage of the LBT's unique binocular design to point the two co-mounted telescopes apart and simultaneously obtain both targets in three sets of observations. Results indicate that the achievable scatter in Ls-band (3.3 um) is at the percent level for bright targets, and possibly better with heavier sampling and characterization of the systematics.

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arXiv2017

The Multiplicity of M-Dwarfs in Young Moving Groups

We image 104 newly identified low-mass (mostly M-dwarf) pre-main sequence members of nearby young moving groups with Magellan Adaptive Optics (MagAO) and identify 27 binaries with instantaneous projected separation as small as 40 mas. 15 were previously unknown. The total number of multiple systems in this sample including spectroscopic and visual binaries from the literature is 36, giving a raw multiplicity rate of at least $35^{+5}_{-4}\%$ for this population. In the separation range of roughly 1 - 300 AU in which infrared AO imaging is most sensitive, the raw multiplicity rate is at least $24^{+5}_{-4}\%$ for binaries resolved by the MagAO infrared camera (Clio). The M-star sub-sample of 87 stars yields a raw multiplicity of at least $30^{+5}_{-4}\%$ over all separations, $21^{+5}_{-4}\%$ for secondary companions resolved by Clio from 1 to 300 AU ($23^{+5}_{-4}\%$ for all known binaries in this separation range). A combined analysis with binaries discovered by the Search for Associations Containing Young stars shows that multiplicity fraction as a function of mass and age over the range of 0.2 to 1.2 $M_\odot$ and 10 - 200 Myr appears to be linearly flat in both parameters and across YMGs. This suggests that multiplicity rates are largely set by 100 Myr without appreciable evolution thereafter. After bias corrections are applied, the multiplicity fraction of low-mass YMG members ($< 0.6 M_\odot$) is in excess of the field.

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arXiv2016

Imaging protoplanets: observing transition disks with non-redundant masking

Transition disks, protoplanetary disks with inner clearings, are promising objects in which to directly image forming planets. The high contrast imaging technique of non-redundant masking is well posed to detect planetary mass companions at several to tens of AU in nearby transition disks. We present non-redundant masking observations of the T Cha and LkCa 15 transition disks, both of which host posited sub-stellar mass companions. However, due to a loss of information intrinsic to the technique, observations of extended sources (e.g. scattered light from disks) can be misinterpreted as moving companions. We discuss tests to distinguish between these two scenarios, with applications to the T Cha and LkCa 15 observations. We argue that a static, forward-scattering disk can explain the T Cha data, while LkCa 15 is best explained by multiple orbiting companions.

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