Star Image Centering with Deep Learning. II. HST/WFPC2 Full Field of ViewCasetti-Dinescu, Dana I.; Baena-Gallé, Roberto; Girard, Terrence M.; Cervantes-Rovira, Alejandro; Todeasa, Sebastian
doi: 10.1088/1538-3873/ad430cpmid: N/A
We present an expanded and improved deep-learning (DL) methodology for determining centers of star images on Hubble Space Telescope/Wide-Field Planetary Camera 2 (WFPC2) exposures. Previously, we demonstrated that our DL model can eliminate the pixel-phase bias otherwise present in these undersampled images; however that analysis was limited to the central portion of each detector. In the current work we introduce the inclusion of global positions to account for the point-spread function (PSF) variation across the entire chip and instrumental magnitudes to account for nonlinear effects such as charge transfer efficiency. The DL model is trained using a unique series of WFPC2 observations of globular cluster 47 Tuc, data sets comprising over 600 dithered exposures taken in each of two filters—F555W and F814W. It is found that the PSF variations across each chip correspond to corrections of the order of ∼100 mpix, while magnitude effects are at a level of ∼10 mpix. Importantly, pixel-phase bias is eliminated with the DL model; whereas, with a classic centering algorithm, the amplitude of this bias can be up to ∼40 mpix. Our improved DL model yields star-image centers with uncertainties of 8–10 mpix across the full field of view of WFPC2.
Atmospheric Parameters and Abundances of Cool Red Giant StarsDencs, Z.; Derekas, A.; Mitnyan, T.; Andersen, M. F.; Cseh, B.; Grundahl, F.; Hegedűs, V.; Kovács, J.; Kriskovics, L.; Palle, P. L.; Pál, A.; Szigeti, L.; Mészáros, Sz.
doi: 10.1088/1538-3873/ad4177pmid: N/A
Understanding the atmospheric parameters of stars on the top of the RGB is essential to reveal the chemical composition of the Milky Way, as they can be used to probe the farthest parts of our Galaxy. Our goal is to determine the chemical composition of 21 RGB stars with Teff < 4200 K selected from the APOGEE-2 DR17 database using new observations carried out with the spectrograph mounted on the 1 m telescope of the Hungarian Piszkéstető Observatory and the SONG spectrograph (R = 77,000) on the Hertzsprung SONG telescope in the 4500–5800 Å wavelength range. This is the first time the spectrograph (R = 18,000) on the 1 m telescope at Piszkéstető Observatory was used to measure the abundances of stars. We created a new LTE spectral library using MARCS model atmospheres and SYNSPEC by including the line list of 23 molecules to determine atmospheric parameters (Teff, logg, [Fe/H], [α/Fe]) and abundances of Si, Ca, Ti, V, Cr, Mn, and Ni with FERRE. The resulting parameters were compared to that of APOGEE. We found a good agreement in general, the average difference is −11.2 K in Teff, 0.11 dex in logg, 0.10 dex in [Fe/H], and −0.01 dex in [α/Fe]. Our analysis successfully demonstrates the ability of the spectrograph at Piszkéstető Observatory to reliably measure the abundance of bright stars.
The Robotic MAAO 0.7 m Telescope System: Performance and Standard Photometric SystemLim, Gu; Kim, Dohyeong; Lim, Seonghun; Im, Myungshin; Choi, Hyeonho; Park, Jaemin; Park, Keun-Hong; Park, Junyeong; Muskaan, Chaudhary; Kim, Donghyun; Jeong, Hayeong
doi: 10.1088/1538-3873/ad3f4fpmid: N/A
We introduce a 0.7 m telescope system at the Miryang Arirang Astronomical Observatory (MAAO), a public observatory in Miryang, Korea. System integration and a scheduling program enable the 0.7 m telescope system to operate completely robotically during nighttime, eliminating the need for human intervention. Using the 0.7 m telescope system, we obtain atmospheric extinction coefficients and the zero-point magnitudes by observing standard stars. As a result, we find that atmospheric extinctions are moderate but they can sometimes increase depending on the weather conditions. The measured 5σ limiting magnitudes reach down to BVRI = 19.4–19.6 AB mag for a point source with a total integrated time of 10 minutes under clear weather conditions, demonstrating comparable performance with other observational facilities operating under similar specifications and sky conditions. We expect that the newly established MAAO 0.7 m telescope system will contribute significantly to the observational studies of astronomy. Particularly, with its capability for robotic observations, this system, although its primary duty is for public viewing, can be extensively used for the time-series observation of transients.
Detecting Moving Objects in Photometric Images Using 3D Hough TransformZhang, Bo; Hu, ShaoMing; Du, Junju; Yang, Xu; Chen, Xu; Jiang, Hai; Cao, Hai; Feng, Shuai
doi: 10.1088/1538-3873/ad481fpmid: N/A
In response to the exponential growth of space debris, an increasing number of observation devices are being used for the observation of moving objects, such as space debris and asteroids, which require further improvements in data-processing capabilities for the detection of moving objects. In this study, we propose a rapid detection algorithm designed for detecting moving objects, leveraging the power of the 3D Hough transform. By the simulated image experiments, our results show that the detection rate increases with the number of continuous images when fully extracting objects. Based on this foundation, the object detection rate is at least 87% regardless of the object number in the image sequence when detecting objects from at least six continuous images. In the observed image experiments, we used source-extractor to extract sources. The results show the method can successfully detect objects with signal-to-noise ratio higher than three from sidereal tracking images and can identify asteroids from asteroid tracking images while maintaining a detection speed that meets the requirements for real-time processing.
From Active Stars to Black Holes: A Discovery Tool for Galactic X-Ray SourcesRodriguez, Antonio C.
doi: 10.1088/1538-3873/ad357cpmid: N/A
Galactic X-ray sources are diverse, ranging from active M dwarfs to compact object binaries, and everything in between. The X-ray landscape of today is rich, with point source catalogs such as those from XMM-Newton, Chandra, and Swift, each with ≳105 sources and growing. Furthermore, X-ray astronomy is on the verge of being transformed through data releases from the all-sky SRG/eROSITA survey. Many X-ray sources can be associated with an optical counterpart, which in the era of Gaia, can be determined to be Galactic or extragalactic through parallax and proper motion information. Here, I present a simple diagram—the “X-ray Main Sequence,” which distinguishes between compact objects and active stars based on their optical color and X-ray-to-optical flux ratio (FX/Fopt). As a proof of concept, I present optical spectroscopy of six exotic accreting WDs discovered using the X-ray Main Sequence as applied to the XMM-Newton catalog. Looking ahead to surveys of the near future, I additionally present SDSS-V optical spectroscopy of new systems discovered using the X-ray Main Sequence as applied to the SRG/eROSITA eFEDS catalog.
Cosmic Ray Jump Detection for the Roman Wide Field InstrumentSharma, Sanjib; Casertano, Stefano
doi: 10.1088/1538-3873/ad4b9epmid: N/A
We investigate algorithms for detecting and correcting for jumps due to cosmic rays in infrared detectors, with emphasis on Roman telescope’s Wide Field Instrument. We use a statistic S based on the excess difference between adjacent resultants (average over a group of reads) normalized to the square root of the expected variance that accommodates the uneven resultants of Roman. We show that it is important to account for the covariance of excess difference with that of the estimated count rate. Due to averaging of reads, the ability to detect jumps is reduced, specially if the jump is in the first or the last resultant. Having the first and last resultants as a single-read resultants improves the ability to detect cosmic rays. The signal due to a jump is split across two resultant differences and this motivates small adjustments to the basic algorithm which improves the jump detection. Bias and false negative rate are investigated using Monte Carlo simulations for a few readout patterns. In order to investigate other scenarios approximate formulas for predicting the bias and the misclassification rate are presented. Using cosmic ray properties based on JWST darks, we show that for high count rates (1000 e−1 s−1) most of the cosmic rays remain undetected, with 65% missed identifications. When averaging over multiple exposures, due to low event rates of cosmic rays, the overall bias in estimated count rate due to undetected cosmic rays is negligible. However, for a single exposure with an undetected cosmic ray, one can have a bias of a few percent. This will manifest as abrupt changes in brightness of targets. Fortunately, the bias ranges between 1 and 5 the measurement uncertainty, and this fact can be used to screen out cosmic rays for scientific applications that seek to detect short duration time domain events.
Mid-infrared Fine Structure Lines from the Galactic Warm Ionized MediumKulkarni, S. R.; Beichman, Charles; Ressler, Michael E.
doi: 10.1088/1538-3873/ace6d9pmid: N/A
The Warm Ionized Medium (WIM) hosts most of the ionized gas in the Galaxy and occupies perhaps a quarter of the volume of the Galactic disk. Decoding the spectrum of the Galactic diffuse ionizing field is of fundamental interest. This can be done via direct measurements of ionization fractions of various elements. Based on current physical models for the WIM we predicted that mid-IR fine structure lines of Ne, Ar and S would be within the grasp of the Mid-Infrared Imager-Medium Resolution Spectrometer (MIRI-MRS), an Integral Field Unit (IFU) spectrograph, aboard the James Webb Space Telescope (JWST). Motivated thus we analyzed a pair of commissioning data sets and detected [Ne ii] 12.81 μm, [S iii] 18.71 μm and possibly [S iv] 10.51 μm. The inferred emission measure for these detections is about 10 cm−6 pc, typical of the WIM. These detections are broadly consistent with expectations of physical models for the WIM. The current detections are limited by uncorrected fringing (and to a lesser extent by baseline variations). In due course, we expect, as with other IFUs, the calibration pipeline to deliver photon-noise-limited spectra. The detections reported here bode well for the study of the WIM. Along most lines-of-sight hour-long MIRI-MRS observations should detect line emission from the WIM. When combined with optical observations by modern IFUs with high spectral resolution on large ground-based telescopes, the ionization fraction and temperature of neon and sulfur can be robustly inferred. Separately, the ionization of helium in the WIM can be probed by NIRspec. Finally, joint JWST and optical IFU studies will open up a new cottage industry of studying the WIM on arcsecond scales.
Robust 1-norm Periodograms for Analysis of Noisy Non-Gaussian Time Series with Irregular Cadences: Application to VLBI Astrometry of QuasarsMakarov, Valeri V.; Lambert, Sébastien; Cigan, Phil; DiLullo, Christopher; Gordon, David
doi: 10.1088/1538-3873/ad4b9fpmid: N/A
Astronomical time series often have non-uniform sampling in time, or irregular cadences, with long gaps separating clusters of observations. Some of these data sets are also explicitly non-Gaussian with respect to the expected model fit, or the simple mean. The standard Lomb–Scargle periodogram is based on the least squares solution for a set of test periods and, therefore, is easily corrupted by a subset of statistical outliers or an intrinsically non-Gaussian population. It can produce completely misleading results for heavy-tailed distribution of residuals. We propose a robust 1-norm periodogram technique, which is based on the principles of robust statistical estimation. This technique can be implemented in weighted or unweighted options. The method is described in detail and compared with the classical least squares periodogram on a set of astrometric VLBI measurements of the ICRF quasar IERS B0642+449. It is uniformly applied to a collection of 259 ICRF3 quasars each with more than 200 epoch VLBI measurements, resulting in a list of 49 objects with quasi-periodic position changes above the 3σ level, which warrant further investigation.