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1. Discovery of H α Emission from a Protoplanet Candidate around the Young Star 2MASS J16120668–3010270 with MagAO-X

   https://doi.org/10.3847/2041-8213/adfcbd  

   Li_李, Jialin 嘉霖; Close, Laird M; Long_龙, Feng 凤; Males, Jared R; Haffert, Sebastiaan Y; Weinberger, Alycia; Follette, Katherine; Andrews, Sean; Carpenter, John; Foster, Warren B; et al (September 2025, The Astrophysical Journal Letters)

   Abstract 2MASS J16120668–3010270 (hereafter 2MJ1612) is a young M0 star that hosts a protoplanetary disk in the Upper Scorpius star-forming region. Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations of 2MJ1612 show a mildly inclined disk (i = 37°) with a large dust-depleted gap (R_cav ≈ 0 $\stackrel{\text{″}}{.}$4 or 53 au). We present high-contrast Hαobservations from MagAO-X on the 6.5 m Magellan telescope and new high-resolution submillimeter dust continuum observations with ALMA of 2MJ1612. On both 2025 April 13 and 16, we recovered a point source with Hαexcess with a signal-to-noise ratio ≳5 within the disk gap in our MagAO-X angular and spectral differential images at a separation of 141.96 ± 2.10 mas (23.45 ± 0.29 au deprojected) from the star and a position angle ​​​​​of 159 $\stackrel{\text{°}}{.}$00 ± 0 $\stackrel{\text{°}}{.}$55. Furthermore, this Hαsource is within close proximity to aK-band point source in the SPHERE/IRDIS observation taken on 2023 July 21. The astrometric offset between theKband and Hαsource can be explained by orbital motion of a bound companion. Thus, our observations can be best explained by the discovery of an accreting protoplanet, 2MJ1612 b, with an estimated mass of 4M_Jupand a Hαline flux ranging from (29.7 ± 7.5) × 10⁻¹⁶erg s cm²to (8.2 ± 3.4) × 10⁻¹⁶erg s cm². 2MJ1612 b is likely the third example of an accreting Hαprotoplanet responsible for carving the gap in its host disk, joining PDS 70 b and c. Further study is necessary to confirm and characterize this protoplanet candidate and to identify any additional protoplanets that may also play a role in shaping the gap. 

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2. MAMMOTH: confirmation of two massive galaxy overdensities at z = 2.24 with Hα emitters

   https://doi.org/10.1093/mnras/staa2882  

   Zheng, Xian Zhong; Cai, Zheng; An, Fang Xia; Fan, Xiaohui; Shi, Dong Dong (December 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Massive galaxy overdensities at the peak epoch of cosmic star formation provide ideal testbeds for the formation theories of galaxies and large-scale structure. We report the confirmation of two massive galaxy overdensities at z = 2.24, BOSS1244 and BOSS1542, selected from the Mapping the Most Massive Overdensities Through Hydrogen (MAMMOTH) project using Lyα absorption from the intergalactic medium over the scales of 15−30 h−1 Mpc imprinted on the quasar spectra. We use Hα emitters (HAEs) as the density tracer and identify them using deep narrow-band H2S(1) and broad-band Ks imaging data obtained with the wide-field infrared camera (WIRCam) at the Canada–France–Hawaii Telescope. In total, 244 and 223 line emitters are detected in these two fields, and 196 ± 2 and 175 ± 2 are expected to be HAEs with an Hα flux of >2.5 × 10−17 erg s−1 cm−2 (corresponding to a star formation rate of >5 M⊙ yr−1). The detection rate of HAE candidates suggests an overdensity factor of δgal = 5.6 ± 0.3 and 4.9 ± 0.3 over the volume of 54 × 32 × 32 co-moving Mpc3. The overdensity factor increases two to three times when focusing on the high-density regions of scales 10–15  co-moving Mpc. Interestingly, the HAE density maps reveal that BOSS1244 contains a dominant structure, while BOSS1542 manifests as a giant filamentary structure. We measure the Hα luminosity functions (HLFs), finding that BOSS1244’s HLF is nearly identical to that of the general field at the same epoch, while BOSS1542 shows an excess of HAEs with high Hα luminosity, indicating the presence of enhanced star formation or active galactic nuclei activity. We conclude that the two massive MAMMOTH overdensities are undergoing a rapid galaxy mass assembly. 

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3. Improved Orbital Constraints and Hα Photometric Monitoring of the Directly Imaged Protoplanet Analog HD 142527 B

   https://doi.org/10.3847/1538-3881/ac73f4  

   Balmer, William O.; Follette, Katherine B.; Close, Laird M.; Males, Jared R.; De Rosa, Robert J.; Adams Redai, Jéa I.; Watson, Alex; Weinberger, Alycia J.; Morzinski, Katie M.; Morales, Julio; et al (July 2022, The Astronomical Journal)

   Abstract Companions embedded in the cavities of transitional circumstellar disks have been observed to exhibit excess luminosity at H α , an indication that they are actively accreting. We report 5 yr (2013–2018) of monitoring of the position and H α excess luminosity of the embedded, accreting low-mass stellar companion HD 142527 B from the MagAO/VisAO instrument. We use pyklip , a Python implementation of the Karhunen–Loeve Image Processing algorithm, to detect the companion. Using pyklip forward modeling, we constrain the relative astrometry to 1–2 mas precision and achieve sufficient photometric precision (±0.2 mag, 3% error) to detect changes in the H α contrast of the companion over time. In order to accurately determine the relative astrometry of the companion, we conduct an astrometric calibration of the MagAO/VisAO camera against 20 yr of Keck/NIRC2 images of the Trapezium cluster. We demonstrate agreement of our VisAO astrometry with other published positions for HD 142527 B, and use orbitize! to generate a posterior distribution of orbits fit to the relative astrometry of HD 142527 B. Our data suggest that the companion is close to periastron passage, on an orbit significantly misaligned with respect to both the wide circumbinary disk and the recently observed inner disk encircling HD 142527 A. We translate observed H α contrasts for HD 142527 B into mass accretion rate estimates on the order of 4–9 × 10 −10 M ⊙ yr −1 . Photometric variation in the H α excess of the companion suggests that the accretion rate onto the companion is variable. This work represents a significant step toward observing accretion-driven variability onto protoplanets, such as PDS 70 b&c. 

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4. OGLE-2016-BLG-1195 AO: Lens, Companion to Lens or Source, or None of the Above?

   https://doi.org/10.3847/1538-3881/aced3c  

   Gould, Andrew; Shvartzvald, Yossi; Zhang, Jiyuan; Yee, Jennifer C; Calchi_Novati, Sebastiano; Zang, Weicheng; Ofek, Eran O (September 2023, The Astronomical Journal)

   Abstract We systematically investigate Vandorou et al.’s claim to have detected the host star of the low-mass-ratio (q< 10⁻⁴) microlensing planet OGLE-2016-BLG-1195Lb, via Keck adaptive optics (AO) measurements Δt= 4.12 yr after the event’s peak (t₀). If correct, this measurement would contradict the microlens-parallax measurement derived from Spitzer observations taken neart₀. We show that this host identification would be in 4σconflict with the original ground-based relative lens–source proper-motion measurements. By contrast, Gould estimated a probabilityp= 10% that the “other star” resolved by single-epoch late-time AO would be a companion to the host or the microlensed source, which is much more probable than a 4σstatistical fluctuation. Independent of this proper-motion discrepancy, the kinematics of this host identification are substantially less probable than those of the Spitzer solution. Hence, this identification should not be accepted, pending additional observations that would either confirm or contradict it, which could be taken in 2023. Motivated by this tension, we present two additional investigations. We explore the possibility that Vandorou et al. identified the wrong “star” for their analysis. Astrometry of KMT and Keck images favors a star (or asterism) lying about 175 mas northwest of Vandorou et al.’s star. We also present event parameters from a combined fit to all survey data, which yields a more precise mass ratio,q= (4.6 ± 0.4) × 10⁻⁵. Finally, we discuss the broader implications of minimizing such false positives for the first measurement of the planet mass function, which will become possible when AO on next-generation telescopes are applied to microlensing planets. 

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5. The Giant Accreting Protoplanet Survey (GAPlanetS)—Results from a 6 yr Campaign to Image Accreting Protoplanets

   https://doi.org/10.3847/1538-3881/acc183  

   Follette, Katherine B.; Close, Laird M.; Males, Jared R.; Ward-Duong, Kimberly; Balmer, William O.; Redai, Jéa Adams; Morales, Julio; Sarosi, Catherine; Dacus, Beck; De Rosa, Robert J.; et al (May 2023, The Astronomical Journal)

   Abstract 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 H α 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 H α ; 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 H α contrasts do not preclude most protoplanets, and we report limiting H α 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 H α differential imaging for protoplanet identification. 

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