The increasing use of adaptive secondary mirrors (ASMs) require robust on-sky calibration approaches in the presence of optical turbulence. One critical calibration is the interaction matrix that calibrates the wave front sensor response to the movement of the ASM actuators. While parametrically adjusted theoretical interaction matrices is a common practice, a fully empirical, model-free method is robust to errors in the model assumptions and the parameter estimation. Our previous random-pattern method (DO-CRIME) assumed the system response was faster than the noise injection rate—which is not always true in AO systems. To overcome this, we developed the Cosine Amplitude Calibration Organized in Frequency for On-sky Nimble Interaction-matrix (CACOFONI), a novel method that utilizes the system’s frequency response function. CACOFONI applies sinusoidal modulations with unique frequencies to each actuator and demodulates the wave front sensor response from the AO telemetry stream. This technique builds the full interaction matrix in a temporal frequency comb and can be applied in either open or closed loop operation. The minimum step between modulation frequencies is determined by the telemetry sample length; for a system with a wave front sensor sampling rate of 1 kHz, a 30 s long telemetry stream yields a 0.1 Hz separation between actuators or modes. The empirically measured CACOFONI matrix showed excellent agreement with our simple synthetic matrices, and we successfully demonstrated closed-loop AO operation with an adaptive secondary mirror using both the heuristic matrix and a parametrically adjusted simulated matrix. We also show how manipulating the frequency range and spacing allow the method to scale to ASMs with several thousands of actuators.
We present a spectroscopic database and analysis of satellite streaks in Public Data Release 1 (PDR1) from the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX), covering 6778 observations and ∼90 deg ^2 of sky from 2017 January to 2024 July. We detect 527 streaks across 492 observations, a contamination fraction of 7.3% that rises to monthly values above 20% by 2023–2024, although the streaks mask only 0.09% of the survey area. Of the 527 streaks, 475 (90.1%) are identified with a cataloged object using archival two-line elements: 258 (54%) lie in low or medium Earth orbit, and 217 (46%) are geostationary or highly elliptical. Only 35% were launched since 2010; the rest are spent rocket bodies, debris, and older spacecraft. This reflects HETDEX’s sensitivity to faint objects and its 2017–2024 observing baseline. The Hobby–Eberly Telescope’s large 10 m aperture and HETDEX’s ∼6 minute exposures result in similar observed magnitudes for low Earth orbit (LEO) and geostationary Earth orbit (GEO) objects (median g _AB = 16.2 ± 1.1 for LEO, 16.7 ± 1.1 for GEO). However, once transit time is corrected for, instantaneous magnitudes differ widely: g _inst = 7.4 for LEO versus g _inst = 13.0 for GEO objects, a difference of 5.6 mag, while the exposure-averaged magnitudes differ by only 0.5 mag. Normalized to 550 km, the 34 Starlink streaks give g (550 km) = 5.95, consistent with the mean V (550 km) = 5.92 ± 0.04 reported for VisorSat-design spacecraft. The spectra are consistent with reflected sunlight, with modest, signal-to-noise-driven differences in slope. The catalog, spectra, and code are archived on Zenodo (doi: http://dx.doi.org/10.5281/zenodo.22962479 ).
We present precise radial velocity (RV) measurements of the northern circumpolar giant stars HD 58545 and HD 112987 obtained over 8 yr with the Bohyunsan Observatory Echelle Spectrograph and supplemented during the final 3 yr by the Network of Robotic Echelle Spectrographs. RV variations in giant stars may arise from orbiting companions or intrinsic phenomena, including pulsations, chromospheric activity, and rotational modulation. To distinguish these possibilities, we analyzed line-profile variations, line bisectors, chromospheric activity indicators, and photometric data, and modeled the RV time series with Keplerian orbits using Markov Chain Monte Carlo sampling. For HD 58545, the best-fitting Keplerian model yields an orbital period of 450.44 ${}_{-4.63}^{+3.35}$ days and a minimum companion mass of 3.65 ${}_{-0.58}^{+0.61}\,{M}_{{\rm{J}}}$ . For HD 112987, we derive an orbital period of 554.96 ${}_{-4.67}^{+4.14}$ days and a minimum companion mass of 8.48 ${}_{-0.73}^{+0.96}\,{M}_{{\rm{J}}}$ . None of the activity diagnostics for HD 112987 exhibits significant variability at the RV period, consistent with a Keplerian interpretation. In contrast, several activity diagnostics of HD 58545 exhibit periodicities comparable to the RV period, which is also consistent within the uncertainties with the projected rotational timescale, ${P}_{\mathrm{rot}}/\sin i=462\pm 33\,\mathrm{days}$ . Thus, rotationally modulated stellar variability may contribute to the RV signal. Although the signal can be described by a Keplerian model, the current data cannot distinguish unambiguously between a planetary companion and intrinsic stellar variability. We therefore conclude that HD 112987 hosts a planetary companion, whereas further monitoring is required to determine the origin of the RV signal in HD 58545.
We report [O iii ] narrowband imaging of an extremely large-scale nebula, the Silk Nebula, discovered by the Super Wide-Field [O iii] Narrow-band Survey (SWONS), together with multifiber medium-resolution spectroscopic data covering the H α , [N ii ], [S ii ], and [O iii ] emission lines, acquired with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) as part of the Medium-Resolution Spectroscopic Survey of Nebulae (MRS-N). Based on 2684 high-quality spectra, we measured its physical parameters, including relative line intensities, radial velocities, and full widths at half-maximum. The [S ii ]/H α ratio of the nebula significantly exceeds the shock-excitation threshold of 0.4. Its location in BPT diagnostic diagrams and spatial morphology of [O iii ] both support the optical emission is dominated by shock-heated gas. The oxygen abundance is near solar and spatially uniform, consistent with a shock propagating into the ambient interstellar medium. Because [O iii ] is the only emission line that clearly traces the nebular morphology, we base our distance estimate exclusively on the [O iii ] kinematics, obtaining a fiducial distance of ∼160 pc. At this distance, the nebula has a physical extent of ∼28 pc along the north–south direction. We suggest that the Silk Nebula is a large [O iii ] filament possibly associated with a supernova remnant, although a diffuse-ionized-gas (DIG) or ionized-bubble origin cannot be ruled out with the present data, and one of the largest angular-scale [O iii ] emission structures documented to date. Future deep X-ray observations and shock-modeling efforts are required to firmly establish its nature.
In the search for technosignatures, it can be useful to narrow down the cosmic haystack by prioritizing time-coordinate “Schelling points” at which a beacon may be more likely to be transmitted. One such Schelling point is the antisolar point (ASP), the place and moment at which Earth would lie directly between a hypothetical transmitter in the Earth's transit zone (i.e., ecliptic) and the Sun. In this work, we describe a campaign to survey the ASP for radio technosignatures using the Allen Telescope Array, report the results of 3 initial nights of data from a pilot study in summer 2023, and discuss the future of the campaign. In the pilot study, we find no sky-localized narrowband 1–2.4 GHz technosignatures within an R.A. range of approximately 20.266–21.312 hr during the ASP, setting an upper limit flux density threshold of 115–936 Jy.
