adsabs/SciX_UAT_keywords huggingface dataset:
Enhanced Star Formation Efficiency in the Central Regions of Nearby Quasar Hosts

We combine Atacama Large Millimeter/submillimeter Array and Multi Unit Spectroscopic Explorer observations tracing the molecular gas, millimeter continuum, and ionized gas emission in six low-redshift (z ≲ 0.06) Palomar-Green (PG) quasar host galaxies to investigate their ongoing star formation at roughly kiloparsec-scale resolution. The AGN contribution to the cold dust emission and the optical emission-line flux is carefully removed to derive spatial distributions of the star formation rate (SFR), which, complemented with the molecular gas data, enables the mapping of the depletion time (t dep). We report ubiquitous star formation activity within the quasar host galaxies, with the majority of the ongoing star formation occurring in the galactic center. The rise of the SFR surface density (ΣSFR) toward the nucleus is steeper than that observed for the cold molecular gas surface density, reaching values up to ΣSFR ≈ 0.15-0.80 M ⊙ yr-1 kpc-2. The gas in the nuclear regions is converted into stars at a shortened depletion time (t dep ≈ 0.2-2.0 Gyr), suggesting that those zones can be deemed as starbursts. At large galactocentric radius, we find that the ongoing star formation takes place within spiral arms or H II region complexes, with an efficiency comparable to that reported for nearby inactive spirals (t dep ≈ 1.8 Gyr). We find no evidence of star formation activity shutoff in the PG quasar host galaxies. On the contrary, these observations shed light on how the central environments of galaxies hosting actively accreting supermassive black holes build up stellar mass.

Keywords: active galaxies; quasars; star formation
Post-new-horizons Orbits and Masses for the Satellites of Pluto

We report on ephemerides for the satellites of Pluto based on the large set of astrometric measurements. Our orbit fit yielded the following masses with 1σ uncertainties: GM Pluto = 869.3 ± 0.4 km3 s‑2, GM Charon = 106.1 ± 0.3 km3 s‑2, GM Nix = 1.50 ± 0.52 × 10‑3 km3 s‑2, GM Hydra = 2.01 ± 0.27 × 10‑3 km3 s‑2, corresponding to the densities of ρ Pluto = 1.853 ± 0.004 g cm‑3, ρ Charon = 1.705 ± 0.006 g cm‑3, ρ Nix = 0.88 ± 0.31 g cm‑3, and ρ Hydra = 1.21 ± 0.19 g cm‑3. Masses of Kerberos and Styx remain unconstrained, and it is unlikely that we will be able to measure them even if we obtain abundant 1 mas precision astrometry during the next 20 yr. We summarize the results of orbit integration in terms of osculating and precessing ellipse model mean elements. All satellites reside in near-circular orbits, and Kerberos and Styx have 0.4 deg and 0.3 deg inclinations with respect to Charon's orbit plane. The nodal regression periods for Kerberos and Hydra are ∼9 and ∼14 yr respectively. We found that Charon's orbit pole can be approximated as: R.A. = 133.0073 + 0.0036T deg, and decl. = –6.2449 + 2.5 × 10‑5 T deg, where T is Julian centuries from the epoch J2000, based on 5000 yr of orbit integration.

Keywords: plutonian satellites; orbit determination; orbital elements; natural satellites (solar system)
Fringing Analysis and Simulation for the Vera C. Rubin Observatory's Legacy Survey of Space and Time

The presence of fringing in astronomical Charge-Coupled Device (CCD) images will have an impact on photometric quality and measurements. Yet its impact on the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) has not been fully studied. We present a detailed study on fringing for CCDs already implemented on the Rubin Observatory LSST Camera's focal plane. After making physical measurements and knowing the compositions, we developed a model for the e2v CCDs. We present a method to fit for the internal height variation of the epoxy layer within the sensors based on fringing measurements in a laboratory setting. This method is generic enough that it can be easily modified to work for other CCDs. Using the derived fringing model, we successfully reproduce comparable fringing amplitudes that match the observed levels in images taken by existing telescopes with different optical designs. This model is then used to forecast the expected level of fringing in a single LSST y-band sky background exposure with Rubin telescope optics in the presence of a realistic time-varying sky spectrum. The predicted fringing amplitude in LSST images ranges from 0.04% to 0.2% depending on the location of a CCD on the focal plane. We find that the predicted variation in surface brightness caused by fringing in LSST y-band sky background images is about 0.6 $\mu \mathrm{Jy}\ {\mathrm{arcsec}}^{-2}$ , which is 40 times larger than the current measurement error. We conclude that it is necessary to include fringing correction in the Rubin's LSST image processing pipeline.

Keywords: astronomical instrumentation; ccd observation; observational cosmology; astronomy data modeling
Modeling the GRB 170202A Fireball from Continuous Observations with the Zadko and the Virgin Island Robotic Telescopes

We present coordinated observations of GRB 170202A carried out by the Zadko and the Virgin Island Robotic Telescopes. The observations started 59 s after the event trigger, and provided nearly continuous coverage for two days, due to the unique locations of these telescopes. We clearly detected an early rise in optical emission, followed by late optical flares. By complementing these data with archival observations, we show that GRB 170202A is well described by the standard fireball model if multiple reverse shocks are taken into account. Its fireball is evidenced as expanding within a constant-density interstellar medium, with most burst parameters being consistent with the usual ranges found in the literature. The electron and magnetic energy parameters (ϵ e , ϵ B ) are orders of magnitude smaller than the commonly assumed values. We argue that the global fit of the fireball model achieved by our study should be possible for any burst, pending the availability of a sufficiently comprehensive data set. This conclusion emphasizes the crucial importance of coordinated observation campaigns of gamma-ray bursts, such as the one central to this work, to answer outstanding questions about the underlying physics driving these phenomena.

Keywords: gamma-ray bursts
Searching for Quasiperiodic Modulations in γ-Ray Active Galactic Nuclei

We perform a systematic search of quasiperiodic variabilities in γ-ray active galactic nuclei in the third Fermi Large Area Telescope source catalog (3FGL). We employ two techniques, Lomb-Scargle Periodogram and Weighted Wavelet Z-transform, to obtain power spectra of γ-ray light curves covering from 2008 August to 2016 December. The results show that besides several objects that have been reported in previous works, an additional source, the flat spectrum radio quasars PKS 0601-70 has a possible quasiperiodic variability of 450 days in its γ-ray light curves with the significance of >3σ. The physical implications of our findings are discussed.

Keywords: jets; active galactic nuclei; blazars; gamma-rays
Zwicky Transient Facility Constraints on the Optical Emission from the Nearby Repeating FRB 180916.J0158+65

The discovery rate of fast radio bursts (FRBs) is increasing dramatically thanks to new radio facilities. Meanwhile, wide-field instruments such as the 47 deg2 Zwicky Transient Facility (ZTF) survey the optical sky to study transient and variable sources. We present serendipitous ZTF observations of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) repeating source FRB 180916.J0158+65 that was localized to a spiral galaxy 149 Mpc away and is the first FRB suggesting periodic modulation in its activity. While 147 ZTF exposures corresponded to expected high-activity periods of this FRB, no single ZTF exposure was at the same time as a CHIME detection. No >3σ optical source was found at the FRB location in 683 ZTF exposures, totaling 5.69 hr of integration time. We combined ZTF upper limits and expected repetitions from FRB 180916.J0158+65 in a statistical framework using a Weibull distribution, agnostic of periodic modulation priors. The analysis yielded a constraint on the ratio between the optical and radio fluences of η ≲ 200, corresponding to an optical energy Eopt ≲ 3 × 1046 erg for a fiducial 10 Jy ms FRB (90% confidence). A deeper (but less statistically robust) constraint of η ≲ 3 can be placed assuming a rate of $r(\gt 5\,\mathrm{Jy}\,\mathrm{ms})=1\,{\mathrm{hr}}^{-1}$ and 1.2 ± 1.1 FRB occurring during exposures taken in high-activity windows. The constraint can be improved with shorter per-image exposures and longer integration time, or observing FRBs at higher Galactic latitudes. This work demonstrated how current surveys can statistically constrain multiwavelength counterparts to FRBs even without deliberately scheduled simultaneous radio observation.

Keywords: neutron stars; transient sources; optical bursts; radio bursts; compact objects
Searching for Small Circumbinary Planets. I. The STANLEY Automated Algorithm and No New Planets in Existing Systems

No circumbinary planets have been discovered smaller than 3 R⊕, yet planets of this small size comprise over 75% of the discoveries around single stars. The observations do not prove the nonexistence of small circumbinary planets; rather, they are much harder to find than around single stars because their transit timing variations are much larger than the transit durations. We present STANLEY, an automated algorithm to find small circumbinary planets. It employs custom methods to detrend eclipsing binary light curves and stack shallow transits of variable duration and interval using N-body integrations. Applied to the Kepler circumbinaries, we recover all known planets, including the three planets of Kepler-47, and constrain the absence of additional planets of similar or smaller size. We also show that we could have detected <3 R⊕ planets in half of the known systems. Our work will ultimately be applied to a broad sample of eclipsing binaries to (hopefully) produce new discoveries and derive a circumbinary size distribution that can be compared to that for single stars.

Keywords: eclipsing binary stars; exoplanet detection methods; transit timing variation method; transit duration variation method; extrasolar rocky planets; n-body simulations
Simulation of Space Weathering on Asteroid Spectra through Hydrogen Ion Irradiation of Meteorites

Space weathering can be defined as the combination of physical and chemical changes that occur in material exposed to an interplanetary environment on the surface of airless bodies. This process results in alterations in material spectroscopic features. Eventually, it can lead to misinterpretation of remotely sensed data in the visible-near-infrared wavelength range. This study simulates the solar wind effect on asteroid spectra through low-energy 1 keV H+ irradiation of meteorite pressed-powder samples under three fluences, 2 × 1017, 5 × 1017, and 1 × 1018 H+ cm-2, and evaluates changes associated with reflectance spectra. The meteorites subjected to the study are Bjurböle (L/LL4), Avanhandava (H4), and Luotolax (howardite). The most prominent changes in all three meteorites are (1) a decrease of 550 nm reflectance, (2) reddening in the 1 μm region, and (3) a monotonous decrease in absorption band strengths in Bjurböle. No significant changes were observed in the 2 μm region. The results imply that at short timescales (102-103 yr), radiation damage as amorphization and vesicle formation caused by low-energy solar wind is the dominant space weathering factor in all three meteorite compositions, causing spectral changes predominantly in the 1 μm region.

Keywords: meteorites; chondrites; achondrites; solar wind
A New Method of Fluxgate Magnetometer Offset Vector Determination in the Solar Wind Using Any Magnetic Field Variations

In-depth study of dynamic processes in the astrophysical plasma environment relies on high-precision measurement of the magnetic field. Fluxgate magnetometers (FGMs) are commonly used on spacecraft to measure the magnetic field. However, their zero offsets vary slowly with time, and therefore need regularly in-flight calibration. Traditional methods of calculating the zero offset are based on properties of Alfvén waves, mirror mode structures, or current sheets. Here, we develop a new method of calculating the zero offset using any interplanetary magnetic field (IMF) variations. We create an offset cube according to the possible range of the IMF strength. The average values of B L for the IMF variation events approximately obey the normal distribution if there are enough events, where B L is the magnetic field in the maximum variance direction. Any constant vector added to the natural magnetic field data of the events will make the standard deviation of the normal distribution larger. Thereby, the point is determined to be the zero offset so that the corresponding standard deviation at this point is the minimum in the offset cube. Our test results show that this method has a 95.5% probability of obtaining the zero offset with an error of less than 0.3 nT when 10-21 hr of data are used. Our method provides an option for the in-flight calibration of the spaceborne FGM in the solar wind when there are not enough Alfvén waves, mirror modes, or current sheets.

Keywords: solar wind; planetary magnetospheres; interplanetary magnetic fields
Detecting Exoplanets Using Eclipsing Binaries as Natural Starshades

We investigate directly imaging exoplanets around eclipsing binaries using the eclipse as a natural tool for dimming the binary and thus increasing the planet to star brightness contrast. At eclipse, the binary becomes pointlike, making coronagraphy possible. We select binaries where the planet-star contrast would be boosted by >10× during eclipse, making it possible to detect a planet that is ≳10× fainter or in a star system that is ∼2-3× more massive than otherwise. Our approach will yield insights into planet occurrence rates around binaries versus individual stars. We consider both self-luminous (SL) and reflected light (RL) planets. In the SL case, we select binaries whose age is young enough so that an orbiting SL planet would remain luminous; in U Cep and AC Sct, respectively, our method is sensitive to SL planets of ∼4.5 and ∼9 MJ with current ground- or near-future space-based instruments and ∼1.5 and ∼6 MJ with future ground-based observatories. In the RL case, there are three nearby (≲50 pc) systems—V1412 Aql, RR Cae, and RT Pic—around which a Jupiter-like planet at a planet-star separation of ≳20 mas might be imaged with future ground- and space-based coronagraphs. A Venus-like planet at the same distance might be detectable around RR Cae and RT Pic. A habitable Earth-like planet represents a challenge; while the planet-star contrast at eclipse and planet flux are accessible with a 6-8 m space telescope, the planet-star separation is 1/3-1/4 of the angular separation limit of modern coronagraphy.

Keywords: eclipsing binary stars; exoplanets; direct imaging; coronagraphic imaging
An Interstellar Synthesis of Glycerol Phosphates

Glycerol phosphates define key molecules pertaining to the Origin of Life question and represent the essential stereo-dictating unit of phospholipids that may self-assemble in aqueous media into prebiotic cell membranes. However, the prebiotic formation pathways to glycerol phosphate have remained elusive to date. In this Letter, we expose a facile pathway toward the abiotic synthesis of glycerol phosphate isomers in phosphine (PH3) doped interstellar analog ices of methanol (CH3OH), carbon dioxide (CO2), or water (H2O) upon exposure to energetic electrons as a proxy of secondary electrons generated by the penetration of Galactic cosmic rays into interstellar ices at 10 K. The synthetic routes proposed here overcome obstacles of terrestrial-based scenarios that are inhibited by the low solubility of phosphates in water and the unfavorable nature of phosphorylation reactions in aqueous solution, thus revealing a potential pathway to prebiotic glycerol phosphates.

Keywords: pre-biotic astrochemistry; astrochemistry; laboratory astrophysics; interstellar medium; astrobiology
Low-mass Group Environments Have No Substantial Impact on the Circumgalactic Medium Metallicity

We explore how environment affects the metallicity of the circumgalactic medium (CGM) using 13 low-mass galaxy groups (two to five galaxies) at $\langle {z}_{\mathrm{abs}}\rangle =0.25 identified near background quasars. Using quasar spectra from the Hubble Space Telescope/COS and from Keck/HIRES or the Very Large Telescope/UVES, we measure column densities of or determine limits on CGM absorption lines. We use a Markov Chain Monte Carlo approach with Cloudy to estimate metallicities of cool (T ∼ 104 K) CGM gas within groups and compare them to CGM metallicities of 47 isolated galaxies. Both group and isolated CGM metallicities span a wide range (-2 < [Si/H] < 0), where the mean group (-0.54 ± 0.22) and isolated (-0.77 ± 0.14) CGM metallicities are similar. Group and isolated environments have similar distributions of ${\rm{H}}\,{\rm{I}} column densities as a function of impact parameter. However, contrary to isolated galaxies, we do not find an anticorrelation between ${\rm{H}}\,{\rm{I}} column density and the nearest group galaxy impact parameter. We additionally divided the groups by member luminosity ratios (i.e., galaxy-galaxy and galaxy-dwarf groups). While there was no significant difference in their mean metallicities, a modest increase in sample size should allow one to statistically identify a higher CGM metallicity in galaxy-dwarf groups compared to galaxy-galaxy groups. We conclude that either environmental effects have not played an important role in the metallicity of the CGM at this stage and expect that this may only occur when galaxies are strongly interacting or merging or that some isolated galaxies have higher CGM metallicities due to past interactions. Thus, environment does not seem to be the cause of the CGM metallicity bimodality.

Keywords: circumgalactic medium; quasar absorption line spectroscopy; metallicity; galaxy environments
An Algorithm for the Determination of Coronal Mass Ejection Kinematic Parameters Based on Machine Learning

Coronal mass ejections (CMEs) constitute the major source of severe space weather events, with the potential to cause enormous damage to humans and spacecraft in space. It is becoming increasingly important to detect and track CMEs, since there are more and more space activities and facilities. We have developed a new algorithm to automatically derive a CME's kinematic parameters based on machine learning. Our method consists of three steps: recognition, tracking, and the determination of parameters. First, we train a convolutional neural network to classify images from Solar and Heliospheric Observatory Large Angle Spectrometric Coronagraph observations into two categories, containing CME(s) or not. Next, we apply the principal component analysis algorithm and Otsu's method to acquire binary-labeled CME regions. Then, we employ the track-match algorithm to track a CME's motion in time-series images and finally determine the CME's kinematic parameters, e.g., velocity, angular width, and central position angle. The results of four typical CME events with different morphological characteristics are presented and compared with a manual CME catalog and several automatic CME catalogs. Our algorithm shows some advantages in the recognition of CME structure and the accuracy of the kinematic parameters. This algorithm can be helpful for real-time CME warnings and predictions. In the future, this algorithm is capable of being applied to CME initialization in magnetohydrodynamic simulations to study the propagation characteristics of real CME events and to provide more efficient predictions of CMEs' geoeffectiveness.

Keywords: solar coronal mass ejections; space weather; convolutional neural networks
The Depth and the Vertical Extent of the Energy Deposition Layer in a Medium-class Solar Flare

We analyze here variations of the position and the vertical extent of the energy deposition layer (EDL) in the C1.6 GOES-class solar flare observed at 10:20 UT on 2012 September 10. The variations of the EDL are contrasted with the variations of the spectra and emission intensities recorded in the Hα line with very high time resolution using the MSDP spectrograph at Białków Observatory. The flare radiated hard X-rays (HXR) detectable up to a energy of 70 keV. A numerical model of the flare used in the analysis assumes that the nonthermal electrons (NTEs) carried the external energy to the flare. The energy flux of the NTEs was derived from a nonthermal component seen in RHESSI spectra. The main geometrical parameters of the flare were derived using restored RHESSI imaging data. We found that the variations of the X-ray fluxes recorded in various energy bands and the variations of the Hα intensities were well-correlated in time during the pre-impulsive and impulsive phases of the flare, and they agreed with the variations of the calculated position and vertical extent of the EDL. The variations of the emission noticed in various parts of the Hα line profile were caused by individual episodes of energy deposition by the beams of NTEs of various energy spectra on various depths in the chromospheric plasma. These results supplement our previous findings for the solar flare on 2013 June 21, having nearly the same GOES class of C1.1 but HXR emission below 34 keV only.

Keywords: the sun
A Heating Mechanism via Magnetic Pumping in the Intracluster Medium

Turbulence driven by active galactic nuclei activity, cluster mergers, and galaxy motion constitutes an attractive energy source for heating the intracluster medium (ICM). How this energy dissipates into the ICM plasma remains unclear, given its low collisionality and high magnetization (precluding viscous heating by Coulomb processes). Kunz et al. proposed a viable heating mechanism based on the anisotropy of the plasma pressure under ICM conditions. The present paper builds upon that work and shows that particles can be heated by large-scale turbulent fluctuations via magnetic pumping. We study how the anisotropy evolves under a range of forcing frequencies, what waves and instabilities are generated, and demonstrate that the particle distribution function acquires a high-energy tail. For this, we perform particle-in-cell simulations where we periodically vary the mean magnetic field B (t). When B (t) grows (dwindles), a pressure anisotropy P ⊥ > P ∥(P ⊥ < P ∥) builds up (P ⊥ and P ∥ are, respectively, the pressures perpendicular and parallel to B (t)). These pressure anisotropies excite mirror (P ⊥ > P ∥) and oblique firehose (P ∥ > P ⊥) instabilities, which trap and scatter the particles, limiting the anisotropy, and providing a channel to heat the plasma. The efficiency of this mechanism depends on the frequency of the large-scale turbulent fluctuations and the efficiency of the scattering the instabilities provide in their nonlinear stage. We provide a simplified analytical heating model that captures the phenomenology involved. Our results show that this process can be relevant in dissipating and distributing turbulent energy at kinetic scales in the ICM.

Keywords: intracluster medium; plasma astrophysics; galaxy clusters; galaxies; magnetic fields; high energy astrophysics