Katie M. Morzinski

Most known white dwarfs in multiple systems with main-sequence stars have been discovered with M-type companions, because the white dwarf causes detectable UV excess and bluer colors than expected from a single M star. Surveys have shown that the number of white dwarfs in Sirius-like systems within 100 pc of the Sun is lower than expected, suggesting that white dwarfs are being missed in the glare of their main-sequence companions. In this work we have leveraged the angular resolution and high-contrast capabilities, as well as optimization for visible wavelengths, of the extreme adaptive optics (ExAO) instrument MagAO-X to detect new white dwarf companions to AFGK stars. We present the first results of our survey with the ExAO instrument MagAO-X, called The ExAO Pup Search, of 18 targets with seven new candidate companions, five of which are confirmed to be white dwarfs. We discuss the new detections in the context of previous surveys and other detection metric sensitivities and show that we are sensitive to a region not probed by other surveys. Finally we discuss the future of the Pup Search in light of developing technologies.

We present resolved images of the inner disk component around HD 141569A using the Magellan adaptive optics system with the Clio2 1–5 μm camera, offering a glimpse of a complex system thought to be in a short evolutionary phase between protoplanetary and debris disk stages. We use a reference star along with the Karhunen–Loéve image projection (KLIP) algorithm for point-spread function subtraction to detect the disk inward to about 0.″24 (∼25 au assuming a distance of 111 pc) at high signal-to-noise ratios at L ′ (3.8 μm), Ls (3.3 μm), and narrowband Ice (3.1 μm). We identify an arc or spiral arm structure at the southeast extremity, consistent with previous studies. We implement forward modeling with a simple disk model within the framework of a Markov Chain Monte Carlo sampler to better constrain the geometrical attributes and photometry using our KLIP-reduced disk images. We then leverage these modeling results to facilitate a comparison of the measured brightness in each passband to find a reduction in scattered light from the disk in the Ice filter, implying significant absorption due to water ice in the dust. Additionally, our best-fit disk models exhibit peak brightness in the southwestern, back-scattering region of the disk, which we suggest to be possible evidence of 3.3 μm polycyclic aromatic hydrocarbon emission. However, we point out the need for additional observations with bluer filters and more complex modeling to confirm these hypotheses.

Accreting protoplanets are windows into planet formation processes, and high-contrast differential imaging is an effective way to identify them. We report results from the Giant Accreting Protoplanet Survey (GAPlanetS), which collected Hα differential imagery of 14 transitional disk host stars with the Magellan Adaptive Optics System. To address the twin challenges of morphological complexity and point-spread function instability, GAPlanetS required novel approaches for frame selection and optimization of the Karhounen–Loéve Image Processing algorithm pyKLIP. We detect one new candidate, CS Cha “c,” at a separation of 68 mas and a modest Δmag of 2.3. We recover the HD 142527 B and HD 100453 B accreting stellar companions in several epochs, and the protoplanet PDS 70 c in 2017 imagery, extending its astrometric record by nine months. Though we cannot rule out scattered light structure, we also recover LkCa 15 “b,” at Hα; its presence inside the disk cavity, absence in Continuum imagery, and consistency with a forward-modeled point source suggest that it remains a viable protoplanet candidate. Through targeted optimization, we tentatively recover PDS 70 c at two additional epochs and PDS 70 b in one epoch. Despite numerous previously reported companion candidates around GAplanetS targets, we recover no additional point sources. Our moderate Hα contrasts do not preclude most protoplanets, and we report limiting Hα contrasts at unrecovered candidate locations. We find an overall detection rate of ∼36 − 22 + 26 % , considerably higher than most direct imaging surveys, speaking to both GAPlanetS’s highly targeted nature and the promise of Hα differential imaging for protoplanet identification.

We use observations with the infrared-optimized Magellan Adaptive Optics (MagAO) system and Clio camera in 3.9 μm light to place stringent mass constraints on possible undetected companions to Sirius A. We suppress the light from Sirius A by imaging it through a grating vector-apodizing phase plate coronagraph with a 180° dark region (gvAPP-180). To remove residual starlight in postprocessing, we apply a time-domain principal-components-analysis-based algorithm we call PCA-Temporal, which uses eigen time series rather than eigenimages to subtract starlight. By casting the problem in terms of eigen time series, we reduce the computational cost of postprocessing the data, enabling the use of the fully sampled data set for improved contrast at small separations. We also discuss the impact of retaining fine temporal sampling of the data on final contrast limits. We achieve postprocessed contrast limits of 1.5 × 10⁻⁶–9.8 × 10⁻⁶ outside of 0.″75, which correspond to planet masses of 2.6–8.0 M _J. These are combined with values from the recent literature of high-contrast imaging observations of Sirius to synthesize an overall completeness fraction as a function of mass and separation. After synthesizing these recent studies and our results, the final completeness analysis rules out 99% of ≥9 M _J planets from 2.5 to 7 au.

Accreting protoplanets represent a window into planet formation processes. We report H{\alpha} differential imaging results from the deepest and most comprehensive accreting protoplanet survey to date, acquired with the Magellan Adaptive Optics (MagAO) system's VisAO camera. The fourteen transitional disks targeted are ideal candidates for protoplanet discovery due to their wide, heavily depleted central cavities, wealth of non-axisymmetric circumstellar disk features evocative of ongoing planet formation, and ongoing stellar accretion. To address the twin challenges of morphological complexity in the target systems and PSF instability, we develop novel approaches for frame selection and optimization of the Karhounen-Loeve Image Processing algorithm pyKLIP. We detect one new candidate protoplanet, CS Cha "c", at a separation of 75mas and a Delta mag of 5.1 and robustly recover the HD142527 B and HD100453 B low mass stellar companions across multiple epochs. Though we cannot rule out a substantial scattered light contribution to its emission, we also recover LkCa 15 b. Its presence inside of the cleared disk cavity and consistency with a forward-modeled point source suggest that it remains a viable protoplanet candidate. The protoplanet PDS 70 c was marginally recovered under our conservative general methodology. However, through targeted optimization in H-alpha} imagery, we tentatively recover PDS 70 c in three epochs and PDS 70 b in one epoch. Of the many other previously-reported companions and companion candidates around objects in the sample, we do not recover any additional robust candidates. However, lack of recovery at moderate H-alpha contrast does not rule out the presence of protoplanets at these locations, and we report limiting H-alpha contrasts in such cases.

We report the confirmation of HIP 67506 C, a new stellar companion to HIP 67506 A. We previously reported a candidate signal at 2λ/D (240 mas) in L′ in MagAO/Clio imaging using the binary differential imaging technique. Several additional indirect signals showed that the candidate signal merited follow-up: significant astrometric acceleration in Gaia DR3, Hipparcos–Gaia proper motion anomaly, and overluminosity compared to single main-sequence stars. We confirmed the companion, HIP 67506 C, at 0.1 arcsec with MagAO-X in 2022 April. We characterized HIP 67506 C MagAO-X photometry and astrometry, and estimated spectral-type K7-M2; we also re-evaluated HIP 67506 A in light of the close companion. Additionally, we show that a previously identified 9 arcsec companion, HIP 67506 B, is a much further distant unassociated background star. We also discuss the utility of indirect signposts in identifying small inner working angle candidate companions.

High-contrast imaging has afforded astronomers the opportunity to study light directly emitted by adolescent (tens of megayears) and “proto” (α (656 nm) synthetic planets injected into contemporaneous continuum (643 nm) images. These metrics include peak (single-pixel) signal-to-noise ratio (S/N), average (multipixel average) S/N, 5σ contrast, and false-positive fraction. We apply continuum-optimized KLIP reduction parameters to six Hα direct detections of the low-mass stellar companion HD 142527 B and recover the companion at a range of separations. Relative to a single-informed, nonoptimized set of KLIP parameters applied to all data sets uniformly, our multimetric grid search optimization led to improvements in companion S/N of up to 1.2σ, with an average improvement of 0.6σ. Since many direct imaging detections lie close to the canonical 5σ threshold, even such modest improvements may result in higher yields in future imaging surveys.