More Like this

1. An Optical Distortion Solution for the Keck I OSIRIS Imager

   https://doi.org/10.3847/1538-3881/aceaf7  

   Freeman, Matthew S. R. ; Lu, Jessica R. ; Lyke, Jim ; Gautam, Abhimat ; Kupke, Renate ; Ghez, Andrea ; Sakai, Shoko ; Anderson, Jay ; Bellini, Andrea ( August 2023 , The Astronomical Journal)

   The astrometric precision and accuracy of an imaging camera is often limited by geometric optical distortions. These must be calibrated and removed to measure precise proper motions, orbits, and gravitationally lensed positions of interesting astronomical objects. Here, we derive a distortion solution for the OSIRIS Imager fed by the Keck I adaptive optics system at the W. M. Keck Observatory. The distortion solution was derived from images of the dense globular clusters M15 and M92 taken with OSIRIS in 2020 and 2021. The set of 403 starlists, each containing ∼1000 stars, were compared to reference Hubble catalogs to measure the distortion-induced positional differences. OSIRIS was opened and optically realigned in 2020 November and the distortion solutions before and after the opening show slight differences at the ∼20 mas level. We find that the OSIRIS distortion closely matches the designed optical model: large, reaching 20 pixels at the corners, but mostly low order, with the majority of the distortion in the 2nd-order mode. After applying the new distortion correction, we find a median residual of [x, y] = [0.052, 0.056] pixels ([0.51, 0.56] mas) for the 2020 solution, and [x, y] = [0.081, 0.071] pixels ([0.80, 0.71] mas) for the 2021 solution. Comparison between NIRC2 images and OSIRIS images of the Galactic center show that the mean astrometric difference between the two instruments reduces from 10.7 standard deviations to 1.7 standard deviations when the OSIRIS distortion solution is applied. The distortion model is included in the Keck AO Imaging data-reduction pipeline and is available for use on OSIRIS data.

    

   more » « less
2. Astrometric Accelerations as Dynamical Beacons: A Giant Planet Imaged inside the Debris Disk of the Young Star AF Lep

   https://doi.org/10.3847/2041-8213/acd6f6  

   Franson, Kyle ; Bowler, Brendan P. ; Zhou, Yifan ; Pearce, Tim D. ; Bardalez Gagliuffi, Daniella C. ; Biddle, Lauren I. ; Brandt, Timothy D. ; Crepp, Justin R. ; Dupuy, Trent J. ; Faherty, Jacqueline ; et al ( June 2023 , The Astrophysical Journal Letters)

   We present the direct-imaging discovery of a giant planet orbiting the young star AF Lep, a 1.2M_⊙member of the 24 ± 3 MyrβPic moving group. AF Lep was observed as part of our ongoing high-contrast imaging program targeting stars with astrometric accelerations between Hipparcos and Gaia that indicate the presence of substellar companions. Keck/NIRC2 observations in$L\prime$with the vector vortex coronagraph reveal a point source, AF Lep b, at ≈340 mas, which exhibits orbital motion at the 6σlevel over the course of 13 months. A joint orbit fit yields precise constraints on the planet’s dynamical mass of${3.2}_{-0.6}^{+0.7}$M_Jup, semimajor axis of${8.4}_{-1.3}^{+1.1}$au, and eccentricity of${0.24}_{-0.15}^{+0.27}$. AF Lep hosts a debris disk located at ∼50 au, but it is unlikely to be sculpted by AF Lep b, implying there may be additional planets in the system at wider separations. The stellar inclination (i_*=${54}_{-9}^{+11}°$) and orbital inclination (i_o=${50}_{-12}^{+9}°$) are in good agreement, which is consistent with the system having spin–orbit alignment. AF Lep b is the lowest-mass imaged planet with a dynamical mass measurement and highlights the promise of using astrometric accelerations as a tool to find and characterize long-period planets.

    

   more » « less
3. The black widow pulsar J1641+8049 in the optical, radio, and X-rays

   https://doi.org/10.1093/mnras/stad3391  

   Kirichenko, A. Yu ; Zharikov, S. V. ; Karpova, A. V. ; Fonseca, E. ; Zyuzin, D. A. ; Shibanov, Yu A. ; López, E. A. ; Gilfanov, M. R. ; Cabrera-Lavers, A. ; Geier, S. ; et al ( November 2023 , Monthly Notices of the Royal Astronomical Society)

   PSR J1641+8049 is a 2 ms black widow pulsar with the 2.2 h orbital period detected in the radio and γ-rays. We performed new phase-resolved multiband photometry of PSR J1641+8049 using the OSIRIS instrument at the Gran Telescopio Canarias. The obtained data were analysed together with the new radio-timing observations from the Canadian Hydrogen Intensity Mapping Experiment (CHIME), the X-ray data from the Spectrum-RG/eROSITA all-sky survey, and all available optical photometric observations. An updated timing solution based on CHIME data is presented, which accounts for secular and periodic modulations in pulse dispersion. The system parameters obtained through the light-curve analysis, including the distance to the source 4.6–4.8 kpc and the orbital inclination 56–59 deg, are found to be consistent with previous studies. However, the optical flux of the source at the maximum brightness phase faded by a factor of ∼2 as compared to previous observations. Nevertheless, the face of the J1641+8049 companion remains one of the most heated (8000–9500 K) by a pulsar among the known black widow pulsars. We also report a new estimation on the pulsar proper motion of ≈2 mas yr−1, which yields a spin-down luminosity of ≈4.87 × 1034 erg s−1 and a corresponding heating efficiency of the companion by the pulsar of 0.3–0.7. The pulsar was not detected in X-rays implying its X-ray-luminosity was $\lesssim$3 × 1031 erg s−1 at the date of observations.

    

   more » « less
4. Astrometric Calibration of the Beijing–Arizona Sky Survey

   https://doi.org/10.3847/1538-3881/acbc78  

   Peng, Xiyan ; Qi, Zhaoxiang ; Zhang, Tianmeng ; Wu, Zhenyu ; Zhou, Zhimin ; Nie, Jundan ; Zou, Hu ; Fan, Xiaohui ; Jiang, Linhua ; McGreer, Ian ; et al ( March 2023 , The Astronomical Journal)

   We present the astrometric calibration of the Beijing–Arizona Sky Survey (BASS). The BASS astrometry was tied to the International Celestial Reference Frame via the Gaia Data Release 2 reference catalog. For effects that were stable throughout the BASS observations, including differential chromatic refraction and the low charge transfer efficiency of the CCD, we corrected for these effects at the raw image coordinates. Fourth-order polynomial intermediate longitudinal and latitudinal corrections were used to remove optical distortions. The comparison with the Gaia catalog shows that the systematic errors, depending on color or magnitude, are less than 2 milliarcseconds (mas). The position systematic error is estimated to be about −0.01 ± 0.7 mas in the region between 30° and 60° of decl. and up to −0.07 ± 0.9 mas in the region north of decl. 60°.

    

   more » « less
5. Point spread function reconstruction of adaptive-optics imaging: meeting the astrometric requirements for time-delay cosmography

   https://doi.org/10.1093/mnras/stab2587  

   Chen, Geoff C-F ; Treu, Tommaso ; Fassnacht, Christopher D ; Ragland, Sam ; Schmidt, Thomas ; Suyu, Sherry H ( September 2021 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Astrometric precision and knowledge of the point spread function are key ingredients for a wide range of astrophysical studies including time-delay cosmography in which strongly lensed quasar systems are used to determine the Hubble constant and other cosmological parameters. Astrometric uncertainty on the positions of the multiply-imaged point sources contributes to the overall uncertainty in inferred distances and therefore the Hubble constant. Similarly, knowledge of the wings of the point spread function is necessary to disentangle light from the background sources and the foreground deflector. We analyse adaptive optics (AO) images of the strong lens system J 0659+1629 obtained with the W. M. Keck Observatory using the laser guide star AO system. We show that by using a reconstructed point spread function we can (i) obtain astrometric precision of <1 mas, which is more than sufficient for time-delay cosmography; and (ii) subtract all point-like images resulting in residuals consistent with the noise level. The method we have developed is not limited to strong lensing, and is generally applicable to a wide range of scientific cases that have multiple point sources nearby. 

   more » « less