adsabs/SciX_UAT_keywords huggingface dataset:
Likelihood-based Jump Detection and Cosmic Ray Rejection for Detectors Read Out Up-the-ramp

This paper implements likelihood-based jump detection for detectors read out up-the-ramp, using the entire set of reads to compute likelihoods. The approach compares the χ 2 value of a fit with and without a jump for every possible jump location. I show that this approach can be substantially more sensitive than one that only uses the difference between sequential groups of reads, especially for long ramps and for jumps that occur in the middle of a group of reads. It can also be implemented for a computational cost that is linear in the number of resultants. I provide and describe a pure Python implementation that can process a 10-resultant ramp on a 4096 × 4096 detector in ≈20 s, including iterative cosmic ray detection and removal, on a single core of a 2020 Macbook Air. This Python implementation, together with tests and a tutorial notebook, are available at https://github.com/t-brandt/fitramp. I also provide tests and demonstrations of the full ramp fitting and cosmic ray rejection approach on data from the JWST.

Keywords: astronomical detectors; astronomical instrumentation
Detection of Periodicity in SiO Maser Intensity and Velocity Shift of the Symbiotic Star CH Cyg

We performed simultaneous monitoring observations of H2O 616-523 and SiO V = 1, 2, $J=1\to $ 0, SiO V = 1, $J=2\to $ 1, $3\to 2$ maser lines toward the symbiotic star CH Cyg from 2012 December to 2019 November using the Korean very long baseline interferometry Network single-dish telescope. SiO V = 1, 2, $J=1\to 0$ and V = 1, $J=2\to 1$ maser lines were detected for the first time. A periodicity of about 2.5 yr in the SiO maser intensity was found, showing its association with the pulsation of the M giant in CH Cyg. Only the SiO V = 2, $J=1\to 0$ maser, without detections of the V = 1, $J=1\to 0$ maser, was detected in 6 epochs out of 15 V = 2, J = 1-0 maser detected epochs. In addition, the SiO V = 1, $J=2\to 1$ maser intensity was always stronger than that of the V = 1, $J=1\to 0$ maser except for one epoch, providing a critical constraint on the different masing conditions by different transitions, according to changes of the CH Cyg symbiotic system. We also found the gradual redshifted peak velocities of the SiO masers had about a 2.5 yr periodicity corresponding to the period of peak intensities (redshifted up to about $+40\,\mathrm{km}\,{{\rm{s}}}^{-1}$ with respect to the stellar velocity of the M giant). Two possible explanations can be suggested for the 2.5 yr period of the SiO maser intensity and velocity behaviors, although their actual causes remain uncertain.

Keywords: roche lobe overflow; circumstellar masers; silicon monoxide masers; symbiotic binary stars
Ice, Ice, Maybe? Investigating 46P/Wirtanen's Inner Coma for Icy Grains

The release of volatiles from comets is usually from direct sublimation of ices on the nucleus, but for very or hyperactive comets other sources have to be considered to account for the total production rates. In this work, we present new near-IR (NIR) imaging and spectroscopic observations of 46P/Wirtanen taken during its close approach to Earth on 2018 December 19 with the MMIRS instrument at the MMT Observatory to search for signatures of icy or ice-rich grains in its inner coma that might explain its previously reported excess water production. The morphology of the images does not suggest any change in grain properties within the field of view, and the NIR spectra do not show the characteristic absorption features of water ice. Using a new Markov Chain Monte Carlo-based implementation of the spectral modeling approach of Protopapa et al., we estimate the areal water ice fraction of the coma to be <0.6%. When combined with slit-corrected Af ρ values for the J, H, and K bands and previously measured dust velocities for this comet, we estimate an icy grain production rate of less than 4.6 kg s-1. This places a strict constraint on the water production rate from pure icy grains in the coma, and in turn we find that for the 2018-2019 apparition approximately 64% of 46P's surface was actively sublimating water near perihelion. We then discuss 46P's modern properties within the context of other (formerly) hyperactive comets to understand how these complex objects evolve.

Keywords: comae; comet nuclei; comet volatiles; short period comets; ice composition
X-Ray Properties of Optically Variable Low-mass AGN Candidates

We present an X-ray analysis of 14 nearby (z < 0.044) active galactic nuclei (AGNs) in low-mass galaxies (M * ≲ 5 × 109 M ⊙) selected based on their optical variability. Comparing and contrasting different AGN selection techniques in low-mass galaxies is essential for obtaining an accurate estimate of the active fraction in this regime. We use both new and archival observations from the Chandra X-ray Observatory to search for X-ray point sources consistent with AGNs. Four objects have detected nuclear X-ray emission with luminosities ranging from L 0.5-7 ≈ 3 × 1040 to 9 × 1042 erg s-1 with two more marginal detections. All of the detected galaxies have luminosities exceeding those anticipated from X-ray binaries, and all sources are nuclear, suggesting the X-ray emission in most sources is due to an AGN. These observations demonstrate the success of variability at identifying AGNs in low-mass galaxies. We also explore emission-line diagnostics and discuss the differences in the results of these methods for AGN selection, in particular regarding low-mass and low-metallicity systems.

Keywords: active galactic nuclei; dwarf galaxies; time domain astronomy; x-ray active galactic nuclei
Correlated Depletion and Dilution of Lithium and Beryllium Revealed by Subgiants in M67

The surface content of lithium (Li) and beryllium (Be) provides insight into the mixing and circulation mechanisms in stellar interiors. The old open cluster, M67, has been well-studied for Li abundances in both main-sequence and evolved stars. The Be abundances give us a probe to a deeper level in stars. We have taken high-resolution spectra with Keck I with HIRES to determine Be abundances along the subgiant branch of M67, where there are dramatic depletions of Li. These subgiants range in mass from 1.26 to 1.32 M ⊙ and have evolved from main-sequence stars that would have occupied the region of the Li-Be dip found in younger clusters. Lithium abundances have been adjusted to the same scale for 103 stars in M67 by Pace et al. The more massive stars—now the coolest and furthest-evolved from the main sequence—show a drop in Li by a factor of 400 across the subgiant branch. Our new Be abundances also show a decline, but by a factor of ∼50. The two elements decline together with Li showing a steeper decline in these subgiants than it does in the Li-Be dip stars. The relative decline in Be abundance compared to Li is remarkably well fit by the models of Sills & Deliyannis, made specifically for the subgiants in M67. Those models include the effects of mixing induced by stellar rotation. These M67 subgiants show the effects of both main-sequence depletion and post-main-sequence dilution of both Li and Be.

Keywords: open star clusters; stellar abundances; a subgiant stars; stellar evolution
Polarization of Circumstellar Debris Disk Light Echoes

Light echoes of debris disks around active stars can reveal disk structure and composition even when disks are not spatially resolved. Unfortunately, distinguishing reflected light from quiescent starlight and unexpected post-peak flare structure is challenging, especially for edge-on geometries where the time delay between observed flare photons and light scattered from the near side of the disk is short. Here, we take advantage of the fact that scattered light from a dusty disk is polarized, depending on the location of the scattering site and the orientation of the disk relative to a distant observer. Filtering reflected light into its polarized components allows echoes to stand out in predictable ways. We test this idea with a simple model for a disk around an active M dwarf. Our results demonstrate that the use of polarimetric data of flaring stars can significantly enhance echo signals relative to starlight and yield more robust and accurate fits to disk parameters compared to analyses based on the total intensity alone.

Keywords: debris disks; starlight polarization; flare stars
Detection of Extended Millimeter Emission in the Host Galaxy of 3C 273 and Its Implications for QSO Feedback via High Dynamic Range ALMA Imaging

We estimate the amount of negative feedback energy injected into the interstellar medium (ISM) of the host galaxy of 3C 273, a prototypical radio-loud quasar. We obtained 93, 233, and 343 GHz continuum images with the Atacama Large Millimeter/submillimeter Array (ALMA). After self-calibration and point-source subtraction, we reach an image dynamic range of ~85,000 at 93 GHz, ~39,000 at 233 GHz, and ~2500 at 343 GHz. These are currently the highest image dynamic range obtained using ALMA. We detect spatially extended millimeter emission associated with the host galaxy, cospatial with the extended emission line region (EELR) observed in the optical. The millimeter spectral energy distribution and comparison with centimeter data show that the extended emission cannot be explained by dust thermal emission or synchrotron or thermal bremsstrahlung arising from massive star formation. We interpret the extended millimeter emission as thermal bremsstrahlung from gas directly ionized by the central source. The extended flux indicates that at least ~7% of the bolometric flux of the nuclear source was used to ionize atomic hydrogen in the host galaxy. The ionized gas is estimated to be as massive as 1010-1011 M ⊙, but the molecular gas fraction with respect to the stellar mass is consistent with other ellipticals, suggesting that direct ionization ISM by the QSO may not be sufficient to suppress star formation, or we are witnessing a short timescale before negative feedback becomes observable. The discovery of a radio counterpart to EELRs provides a new pathway to studying the QSO-host ISM interaction.

Keywords: galaxy environments; agn host galaxies; quasars; interstellar thermal emission; interstellar synchrotron emission
An Updated Dust-to-Star Geometry: Dust Attenuation Does Not Depend on Inclination in 1.3 ≤z ≤2.6 Star-forming Galaxies from MOSDEF

We investigate dust attenuation and its dependence on viewing angle for 308 star-forming galaxies at 1.3 ≤ z ≤ 2.6 from the MOSFIRE Deep Evolution Field survey. We divide galaxies with a detected Hα emission line and coverage of Hβ into eight groups by stellar mass, star formation rate (SFR), and inclination (i.e., axis ratio), and we then stack their spectra. From each stack, we measure the Balmer decrement and gas-phase metallicity, and then we compute the median A V and UV continuum spectral slope (β). First, we find that none of the dust properties (Balmer decrement, A V, or β) varies with the axis ratio. Second, both stellar and nebular attenuation increase with increasing galaxy mass, showing little residual dependence on SFR or metallicity. Third, nebular emission is more attenuated than stellar emission, and this difference grows even larger at higher galaxy masses and SFRs. Based on these results, we propose a three-component dust model in which attenuation predominantly occurs in star-forming regions and large, dusty star-forming clumps, with minimal attenuation in the diffuse ISM. In this model, nebular attenuation primarily originates in clumps, while stellar attenuation is dominated by star-forming regions. Clumps become larger and more common with increasing galaxy mass, creating the above mass trends. Finally, we argue that a fixed metal yield naturally leads to mass regulating dust attenuation. Infall of low-metallicity gas increases the SFR and lowers the metallicity, but leaves the dust column density mostly unchanged. We quantify this idea using the Kennicutt-Schmidt and fundamental metallicity relations, showing that galaxy mass is indeed the primary driver of dust attenuation.

Keywords: galaxy properties; galaxy evolution; high-redshift galaxies; star formation
The Polytropic Behavior of Solar Wind Protons as Observed by the Ulysses Spacecraft during Solar Minimum

We analyze proton bulk parameters derived from Ulysses observations and investigate the polytropic behavior of solar wind protons over a wide range of heliocentric distances and latitudes. The large-scale variations of the proton density and temperature over heliocentric distance indicate that plasma protons are governed by subadiabatic processes (polytropic index γ < 5/3), if we assume protons with three effective kinetic degrees of freedom. From the correlation between the small-scale variations of the plasma density and temperature in selected subintervals, we derive a polytropic index γ ~ 1.4 on average. Further examination shows that the polytropic index does not have an apparent dependence on the solar wind speed. This agrees with the results of previous analyses of solar wind protons at ~1 au. We find that the polytropic index varies slightly over the range of the heliocentric distances and heliographic latitudes explored by Ulysses. We also show that the homogeneity of the plasma and the accuracy of the polytropic model applied to the data points vary over Ulysses' orbit. We compare our results with the results of previous studies that derive the polytropic index of solar wind ions within the heliosphere using observations from various spacecraft. We finally discuss the implications of our findings in terms of heating mechanisms and the effective degrees of freedom of the plasma protons.

Keywords: heliosphere; plasma physics; polytropes; space plasmas
The Calibration of the 35-40 GHz Solar Radio Spectrometer with the New Moon and a Noise Source

Calibrating solar radio flux has always been a concern in the solar community. Previously, fluxes were calibrated by matching load or the new Moon for relative calibration, and at times with the assistance of other stations' data. Moreover, the frequency coverage seldom exceeded 26 GHz. This paper reports the upgraded and calibrated Chashan Broadband Solar millimeter spectrometer (CBS) working from 35 to 40 GHz at the Chashan Solar Observatory (CSO). Initially, the calibration of the solar radiation brightness temperature is accomplished using the new Moon as the definitive source. Subsequently, the 35-40 GHz standard flux is achieved by establishing the correlation between the solar radio flux, brightness temperature, and frequency. Finally, the calibration of the solar radio flux is implemented by utilizing a constant temperature-controlled noise source as a reference. The calibration in 2023 February and March reveals that the solar brightness temperature is 11,636 K at 37.25 GHz with a standard deviation (STD) of 652 K. The solar radio flux's intensity is ~3000-4000 solar flux units (SFU) in the range of 35-40 GHz with a consistency bias of ±5.3%. The system sensitivity is about ~5-8 SFU by a rough evaluation, a noise factor of about 200 K, and the coefficient of variation of the system transmission slope of 6.5% @ 12 hr at 37.25 GHz. It is expected that the upgraded CBS will capture more activity during the upcoming solar cycle.

Keywords: calibration; astronomical techniques
A 700 pc Extended Coronal Gas Emission in the Circinus Galaxy

We report the first characterization of an extended outflow of high ionized gas in the Circinus Galaxy by means of the coronal line (CL) [Fe VII] λ6087. This emission is located within the ionization cone already detected in the [O III] λ5007 line and is found to extend up to a distance of ∼700 pc from the active galactic nucleus. The gas distribution appears clumpy, with several knots of emission. Its kinematics is complex, with split profiles and line centroids shifted from the systemic velocity. The physical conditions of the gas show that the extended coronal emission is likely the remnant of shells inflated by the passage of a radio jet. This scenario is supported by extended X-ray emission, which is spatially coincident with the morphology and extension of the [Fe VII] λ6087 gas in the NW side of the galaxy. The extension of the coronal gas in the Circinus galaxy is unique among active galaxies and demonstrates the usefulness of CLs for tracing the shock ionization component in these objects.

Keywords: shocks; active galactic nuclei; radio jets; line intensities
Spectral and Timing Analysis of NuSTAR and Swift/XRT Observations of the X-Ray Transient MAXI J0637-430

We present results for the first observed outburst from the transient X-ray binary source MAXI J0637-430. This study is based on eight observations from the Nuclear Spectroscopic Telescope Array (NuSTAR) and six observations from the Neil Gehrels Swift Observatory X-Ray Telescope (Swift/XRT) collected from 2019 November 19 to 2020 April 26 as the 3-79 keV source flux declined from 8.2 × 10-10 to 1.4 × 10-12 erg cm-2 s-1. We see the source transition from a soft state with a strong disk-blackbody component to a hard state dominated by a power-law or thermal Comptonization component. NuSTAR provides the first reported coverage of MAXI J0637-430 above 10 keV, and these broadband spectra show that a two-component model does not provide an adequate description of the soft-state spectrum. As such, we test whether blackbody emission from the plunging region could explain the excess emission. As an alternative, we test a reflection model that includes a physical Comptonization continuum. Finally, we also test a spectral component based on reflection of a blackbody illumination spectrum, which can be interpreted as a simple approximation to the reflection produced by returning disk radiation due to the bending of light by the strong gravity of the black hole. We discuss the physical implications of each scenario and demonstrate the value of constraining the source distance.

Keywords: accretion; low-mass x-ray binary stars; black hole physics
Prior Probability Distributions of Neutron Star Crust Models

To make best use of multifaceted astronomical and nuclear data sets, probability distributions of neutron star models that can be used to propagate errors consistently from one domain to another are required. We take steps toward a consistent model for this purpose, highlight where model inconsistencies occur, and assess the resulting model uncertainty. Using two distributions of nuclear symmetry energy parameters-one uniform, the other based on pure neutron matter theory-we prepare two ensembles of neutron star inner crust models. We use an extended Skyrme energy density functional within a compressible liquid drop model (CLDM). We fit the surface parameters of the CLDM to quantum 3D Hartree-Fock calculations of crustal nuclei. All models predict that more than 50% of the crust by mass and 15% of the crust by thickness comprises pasta with medians of around 62% and 30%, respectively. We also present 68% and 95% ranges for the crust composition as a function of density. We examine the relationships between crust-core boundary and pasta transition properties, the thickness of the pasta layers, the symmetry energy at saturation and subsaturation densities, and the neutron skins of 208Pb and 48Ca. We quantify the correlations using the maximal information coefficient, which can effectively characterize nonlinear relationships. Future measurements of neutron skins, information from nuclear masses and giant resonances, and theoretical constraints on PNM will be able to place constraints on the location of the pasta and crust-core boundaries and the amount of pasta in the crust.

Keywords: neutron stars; nuclear astrophysics; pulsars
New Positions of Triton Based on Gaia DR2 and New Image-processing Methods

The large time span and precise observational data of natural satellites is of great significance for updating their ephemerides and studying their dynamic characteristics. With the help of the new image-processing methods and the Gaia DR2 catalog, all CCD images of Triton taken with the 1.56 m telescope of Shanghai Astronomical Observatory during 2005-2009 were reanalyzed. The median filtering algorithm is used for image preprocessing to remove the influence of the halo of Neptune, and an upgraded modified moment, called the intensity-square-weighted centroiding method, is applied to determine the centroids of the stars and Triton. A total of 2299 positions of Triton were obtained, including 263 new observed positions and 2036 updated observed positions. Such five-year time span data with high precision will be very helpful to improve the orbit parameters of Triton.

Keywords: natural satellites (solar system); neptunian satellites
Lithium Abundances from the LAMOST Medium-resolution Survey Data Release 9

Lithium is a fragile but crucial chemical element in the Universe, and exhibits interesting and complex behaviors. Thanks to the mass of spectroscopic data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) medium-resolution survey (MRS), we can investigate the lithium abundances in a large and diverse sample of stars, which could bring vital help in studying the origin and evolution of lithium. In this work, we use the Li I 6707.8 Å line to derive the lithium abundance through a template-matching method. A catalog of precise lithium abundance is presented for 795,384 spectra corresponding to 455,752 stars from the LAMOST MRS Data Release 9. Comparing our results with those of external high-resolution references, we find good consistency with a typical deviation of σ A(Li) ∼ 0.2 dex. We also analyze the internal errors using stars that have multiple LAMOST MRS observations, which will reach as low as 0.1 dex when the signal-to-noise ratio of the spectra is >20. Besides, our result indicates that a small fraction of giant stars still exhibit a surprisingly high lithium content, and 967 stars are identified as Li-rich giants with A(Li) > 1.5 dex, accounting for ∼2.6% of our samples. If one takes into account the fact that nearly all stars deplete lithium during the main sequence, then the fraction of Li-rich stars may far exceed 2.6%. This new catalog covers a wide range of stellar evolutionary stages from pre-main sequence to giants, and will provide help to the further study of the chemical evolution of lithium.

Keywords: chemical abundances; stellar evolution; lithium stars; sky surveys; catalogs; chemically peculiar stars; late-type stars; nucleosynthesis; fundamental parameters of stars; low mass stars
A Possible Selection Rule for Flares Causing Sunquakes

Sunquakes are helioseismic power enhancements initiated by solar flares, but not all flares generate sunquakes. It is curious why some flares cause sunquakes while others do not. Here we propose a hypothesis to explain the disproportionate occurrence of sunquakes: during a flare's impulsive phase when the flare's impulse acts upon the photosphere, delivered by shock waves, energetic particles from higher atmosphere, or by downward Lorentz Force, a sunquake tends to occur if the background oscillation at the flare footpoint happens to oscillate downward in the same direction with the impulse from above. To verify this hypothesis, we select 60 strong flares in Solar Cycle 24, and examine the background oscillatory velocity at the sunquake sources during the flares' impulsive phases. Since the Doppler velocity observations at sunquake sources are usually corrupted during the flares, we reconstruct the oscillatory velocity in the flare sites using helioseismic holography method with an observation-based Green's function. A total of 24 flares are found to be sunquake active, giving a total of 41 sunquakes. It is also found that in 3-5 mHz frequency band, 25 out of 31 sunquakes show net downward oscillatory velocities during the flares' impulsive phases, and in the 5-7 mHz frequency band, 33 out of 38 sunquakes show net downward velocities. These results support the hypothesis that a sunquake more likely occurs when a flare impacts a photospheric area with a downward background oscillation.

Keywords: helioseismology; solar oscillations; solar flares