adsabs/SciX_UAT_keywords huggingface dataset:
Unveiling the Intrinsic Alignment of Galaxies with Self-calibration and DECaLS DR3 Data

Galaxy intrinsic alignment (IA) is a source of both systematic contamination of cosmic shear measurement and its cosmological applications and valuable information on the large-scale structure of the universe and galaxy formation. The self-calibration (SC) method was designed to separate IA from cosmic shear, free of IA modeling. It was first successfully applied to the KiDS450 and KV450 data. We improve the SC method in several aspects and apply it to the DECaLS DR3 shear + photo-z catalog and significantly improve the IA detection to ∼14σ. We find a strong dependence of IA on galaxy color, with strong IA signal (∼17.6σ) for red galaxies, while the IA signal for blue galaxies is consistent with zero. The detected IAs for red galaxies are in reasonable agreement with the nonlinear tidal alignment model, and the inferred IA amplitude increases with redshift. Our measurements rule out the constant IA amplitude assumption at ∼3.9σ for the red sample. We address the systematics in the SC method carefully and perform several sanity checks. We discuss various caveats, such as redshift/shear calibrations and possible improvements in the measurement, theory, and parameter fitting that will be addressed in future works.

Keywords: weak gravitational lensing; galaxy formation; galaxy physics; large-scale structure of the universe; astrostatistics techniques; two-point correlation function
Fundamental Parameters of the Eclipsing Binary DD CMa and Evidence for Mass Exchange

We present a detailed photometric and spectroscopic analysis of DD CMa, based on published survey photometry and new spectroscopic data. We find an improved orbital period of Po = 2.0084530(6) days. Our spectra reveal Hβ and Hα absorptions with weak emission shoulders, and we also find a color excess in the Wide-field Infrared Survey Explorer multiband photometry, interpreted as signatures of circumstellar matter. We model the V-band orbital light curve derived from the ASAS and ASAS-SN surveys, assuming a semidetached configuration and using the mass ratio and temperature of the hotter star derived from our spectroscopic analysis. Our model indicates that the system consists of a B2.5 dwarf and a B9 giant of radii 3.2 and 3.7 R⊙, respectively, orbiting in a circular orbit of radius 6.75 R⊙. We also found Mc = 1.7 ± 0.1 M⊙, Tc = 11,350 ± 100 K, and Mh = 6.4 ± 0.1 M⊙, Th = 20,000 ± 500 K, for the cooler and hotter star, respectively. We find broad single emission peaks in Hα and Hβ after subtracting the synthetic stellar spectra. Our results are consistent with mass exchange between the stars and suggest the existence of a stream of gas being accreted onto the early B-type star.

Keywords: close binary stars; eclipsing binary stars; stellar activity; circumstellar matter; fundamental parameters of stars
The Rise and Fall of ASASSN-18pg: Following a TDE from Early to Late Times

We present nearly 500 days of observations of the tidal disruption event (TDE) ASASSN-18pg, spanning from 54 days before peak light to 441 days after peak light. Our data set includes X-ray, UV, and optical photometry, optical spectroscopy, radio observations, and the first published spectropolarimetric observations of a TDE. ASASSN-18pg was discovered on 2018 July 11 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d = 78.6 Mpc; with a peak UV magnitude of m ≃ 14, it is both one of the nearest and brightest TDEs discovered to-date. The photometric data allow us to track both the rise to peak and the long-term evolution of the TDE. ASASSN-18pg peaked at a luminosity of L ≃ 2.4 × 1044 erg s-1, and its late-time evolution is shallower than a flux ∝t-5/3 power-law model, similar to what has been seen in other TDEs. ASASSN-18pg exhibited Balmer lines and spectroscopic features consistent with Bowen fluorescence prior to peak, which remained detectable for roughly 225 days after peak. Analysis of the two-component Hα profile indicates that, if they are the result of reprocessing of emission from the accretion disk, the different spectroscopic lines may be coming from regions between ∼10 and ∼60 lt-days from the black hole. No X-ray emission is detected from the TDE, and there is no evidence of a jet or strong outflow detected in the radio. Our spectropolarimetric observations indicate that the projected emission region is likely not significantly aspherical, with the projected emission region having an axis ratio of ≳0.65.

Keywords: black holes; accretion; galaxy accretion disks; black hole physics; supermassive black holes; tidal disruption
Performing Point-spread Function Fitting with Photutils on Hubble Space Telescope Images

The low mass end of the Initial Mass Function (IMF) is a component of star formation that is not well understood. By analyzing Hubble Space Telescope (HST) images of star-forming regions, we aimed to provide data to constrain the shape of the low-mass IMF. We performed point-spread function (PSF) fitting using the Astropy Photutils package v0.6 on shallow HST Wide Field Camera 3 images taken in filters F110W, F139M, and F160W with the goal of identifying low mass stars and brown dwarfs. Residual images from our PSF fitting routine showed that fainter sources were effectively fit while fits to the brighter sources left residuals. Despite this, analysis confirmed that our PSF magnitudes are consistent with aperture magnitudes and mostly have smaller errors; 85%-100% of the flux was captured by the PSF fitting in most cases. PSF fitting of WFC3-IR images using Photutils shows promise for precise photometry.

Keywords: photometry; initial mass function
Macro Magnetic Holes Caused by Ripples in Heliospheric Current Sheet from Coordinated Imaging and Parker Solar Probe Observations

Macro magnetic holes (MMHs), which are significant magnetic field decreases in the solar wind lasting tens of minutes, were found during the first four orbits of the Parker Solar Probe (PSP). We performed a detailed analysis of the 2020 January 30 event and found the possible cause of the MMH using coordinated remote sensing observations from STEREO A and PSP in situ measurements. The results indicate that an MMH represents a brief encounter with the rippled heliospheric current sheet (HCS). Out of the data from the first four orbits of PSP, we identified 17 MMHs and carried out a statistical analysis. Basic characteristics of MMHs include (1) MMHs usually last tens of minutes; (2) the magnetic field strength inside the events is much lower than that in the ambient solar wind; (3) enhanced plasma density, radial velocity, and plasma β are usually found inside the MMHs; and (4) the radial magnetic field has the same polarity before and after an MMH. Based on potential field-source surface and magnetohydrodynamics models, for each of the events we roughly estimate the radial size and the lower limit of the vertical size (i.e., the separation distance between PSP and the HCS), which are 2 R⊙ and 10 R⊙ on average, respectively. These results suggest that MMHs are a frequent phenomenon that may shed light on the dynamics of the HCS and the origins and evolutions of the solar wind structures in the heliosphere.

Keywords: solar wind; heliosphere; solar magnetic fields
The Silicon Lines in the Far Ultraviolet Spectrum of HD 172883

The comparison of the mean high resolution spectrum of the chemically peculiar star HD 172883 recorded by the SWP camera on board the International Ultraviolet Explorer with the mean spectrum of HD 38899, a normal late B-type star having similar fundamental parameters, reveals the large flux deficiency of HD 172883 shortwards of 1700 Å. This flux deficiency is due to the strong lines, photoionization edges and autoionization transitions of Si II. The three strongest autoionization lines of Si II are present The strong resonance line of Al II conspicuous in HD 38899 is very ewak in HD 172883 highlighting a strong aluminum deficiency in HD 172883. Conversely, the Hg II resonance line at 1649.94 Å is much stronger in HD 172883, confirming the large overabundance of mercury in this star.

Keywords: chemically peculiar stars; mercury-manganese stars
Orbital Stability of Exomoons and Submoons with Applications to Kepler 1625b-I

An intriguing question in the context of dynamics arises: could a moon possess a moon itself? Such a configuration does not exist in the solar system, although this may be possible in theory. Kollmeier & Raymond determined the critical size of a satellite necessary to host a long-lived subsatellite, or submoon. However, the orbital constraints for these submoons to exist are still undetermined. Domingos et al. indicated that moons are stable out to a fraction of the host planet's Hill radius RH,p, which in turn depend on the eccentricity of its host's orbit. Motivated by this, we simulate systems of exomoons and submoons for 105 planetary orbits, while considering many initial orbital phases to obtain the critical semimajor axis in terms of RH,p or the host satellite's Hill radius RH,sat, respectively. We find that, assuming circular coplanar orbits, the stability limit for an exomoon is 0.40 RH,p and for a submoon is 0.33 RH,sat. Additionally, we discuss the observational feasibility of detecting these subsatellites through photometric, radial velocity, or direct imaging observations using the Neptune-sized exomoon candidate Kepler 1625b-I and identify how stability can shape the identification of future candidates.

Keywords: orbits; exoplanet dynamics; exoplanets; natural satellites (extrasolar)
Vertical Phase Mixing across the Galactic Disk

By combining the Large Sky Area Multi-object Fiber Spectroscopic Telescope and Gaia data, we investigate the vertical phase mixing across the Galactic disk. Our results confirm the existence of phase space snail shells (or phase spirals) from 6-12 kpc. We find that grouping stars by the guiding radius (Rg), instead of the present radius (R), further enhances the snail shell signal in the following aspects: (1) clarity of the snail shell shape is increased; (2) more wraps of the snail shell can be seen; (3) the phase spaces are less affected by the lack of stars closer to the disk midplane due to extinction; and (4) the phase space snail shell is amplified in greater radial ranges. Compared to the R-based snail shell, the quantitatively measured shapes are similar, except that the Rg-based snail shells show more wraps with a better contrast. These lines of evidence lead to the conclusion that the guiding radius (angular momentum) is a fundamental parameter tracing the phase space snail shell across the Galactic disk. Results of our test particle simulations with impulse approximation verify that particles grouped according to Rg reveal well-defined and sharper snail shell features. By comparing the radial profiles of the snail shell pitch angle between the observation and simulation, the external perturbation can be constrained to ∼500-700 Myr ago. For future vertical phase mixing study, it is recommended to use the guiding radius with additional constraints on orbital hotness (ellipticity) to improve the clarity of the phase snail.

Keywords: milky way dynamics; milky way disk; milky way evolution
Intrinsic Color Indices of Early-type Dwarf Stars

Early-type stars are short lived and scarce in comparison with other types. Based on the recently released catalogs of early-type stars from the largest Large Sky Area Multi-Object Fiber Spectroscopic Telescope spectroscopic survey, the intrinsic colors of the stars with effective temperature up to 32,000 K are determined for the bands from ultraviolet to infrared using the blue-edge method. Analytic relations are derived for the intrinsic color index with the effective temperature for the Wide-field Infrared Survey Explorer, Two Micron All Sky Survey, Gaia, AAVSO Photometric All-Sky Survey, Sloan Digital Sky Survey, the Panoramic Survey Telescope and Rapid Response System 1, and Galaxy Evolution Explorer bands. The results are generally consistent with previous works. In addition, the intrinsic colors of O-type dwarfs and OB supergiants are roughly estimated.

Keywords: fundamental parameters of stars; stellar colors; early-type stars
Empirical Limb-darkening Coefficients and Transit Parameters of Known Exoplanets from TESS

Although the main goal of the Transiting Exoplanet Survey Satellite (TESS) is to search for new transiting exoplanets, its data can also be used to study already-known systems in further detail. The TESS bandpass is particularly interesting to study the limb-darkening effect of the stellar host that is imprinted in transit light curves, as the widely used PHOENIX and ATLAS stellar models predict different limb-darkening profiles. Here we study this effect by fitting the transit light curves of 176 known exoplanetary systems observed by TESS, which allows us to extract empirical limb-darkening coefficients (LDCs) for the widely used quadratic law but also updated transit parameters (including ephemeride refinements) as a by-product. Comparing our empirically obtained LDCs with theoretical predictions, we find significant offsets when using tabulated TESS LDCs. Specifically, the u 2 coefficients obtained using PHOENIX models show the largest discrepancies depending on the method used to derive them, with offsets that can reach up to Δu 2 ≈ 0.2, on average. Most of those average offsets disappear, however, if one uses the SPAM algorithm introduced by Howarth to calculate the LDCs instead. Our results suggest, however, that for stars cooler than about 5000 K, no methodology is good enough to explain the limb-darkening effect; we observe a sharp deviation between measured and predicted LDCs on both quadratic LDCs of order Δu 1, Δu 2 ≈ 0.2 for those cool stars. We recommend caution when assuming LDCs as perfectly known, in particular for these cooler stars when analyzing TESS transit light curves.

Keywords: transit photometry; limb darkening; exoplanets
First Observations of Anomalous Cosmic Rays in to 36 Solar Radii

NASA's Parker Solar Probe mission continues to travel closer to the Sun than any prior human-made object, with an expected closest approach of <10 solar radii (<0.046 au) by 2024. On board, the Integrated Science Investigation of the Sun instrument suite makes unprecedented in situ measurements of energetic particles in the near-Sun environment. The current low level of solar activity offers a prime opportunity to measure cosmic rays closer to the Sun than ever before. We present the first observations of anomalous cosmic rays in to 36 solar radii (0.166 au), focusing specifically on helium. Our results indicate a strong radial intensity gradient of ∼25 ± 5%/au over energies of ∼4 to ∼45 MeV/nuc. These values are larger than prior observations, further out in the heliosphere, and come at a unique time in our understanding and modeling of particle transport and acceleration, particularly as both Voyagers have crossed the heliopause and IBEX has accumulated a full solar cycle of observations. Thus, continued measurements of cosmic rays by Parker Solar Probe will play a critical role in linking past observations with our present knowledge and significantly advancing our understanding of cosmic ray transport in the heliosphere.

Keywords: cosmic rays; solar wind; heliosphere; solar energetic particles; solar physics; solar cycle; quiet sun; particle astrophysics; interplanetary magnetic fields; plasma astrophysics; interplanetary particle acceleration; pickup ions
Predicting the Geoeffectiveness of CMEs Using Machine Learning

Coronal mass ejections (CMEs) are the most geoeffective space weather phenomena, being associated with large geomagnetic storms, and having the potential to cause disturbances to telecommunications, satellite network disruptions, and power grid damage and failures. Thus, considering these storms' potential effects on human activities, accurate forecasts of the geoeffectiveness of CMEs are paramount. This work focuses on experimenting with different machine-learning methods trained on white-light coronagraph data sets of close-to-Sun CMEs, to estimate whether such a newly erupting ejection has the potential to induce geomagnetic activity. We developed binary classification models using logistic regression, k-nearest neighbors, support vector machines, feed-forward artificial neural networks, and ensemble models. At this time, we limited our forecast to exclusively use solar onset parameters, to ensure extended warning times. We discuss the main challenges of this task, namely, the extreme imbalance between the number of geoeffective and ineffective events in our data set, along with their numerous similarities and the limited number of available variables. We show that even in such conditions adequate hit rates can be achieved with these models.

Keywords: solar coronal mass ejections; solar wind; space weather; neural networks; support vector machine; regression
Detection Possibility of Continuous Gravitational Waves from Rotating Magnetized Neutron Stars

In recent decades, several neutron stars (NSs), particularly pulsars, with masses of M > 2 M ⊙ have been observed. On the other hand, the existence of massive white dwarfs, even violating the Chandrasekhar mass limit, was inferred from the peak luminosities of Type Ia supernovae. Hence, there is a generic question of the origin of massive compact objects. Here we explore the existence of massive, magnetized, rotating NSs with the soft and steep equations of state by solving axisymmetric stationary stellar equilibria in general relativity. For our purposes, we consider the Einstein equation solver for stellar structure XNS code. Such rotating NSs with magnetic fields and rotation axes misaligned, and hence a nonzero obliquity angle, can emit continuous gravitational waves (GWs), which can be detected by upcoming detectors, e.g., the Einstein Telescope, etc. We discuss the decay of the magnetic field, angular velocity, and obliquity angle with time due to angular momentum extraction by GWs and dipole radiation, which determine the timescales related to the GW emission. Further, in the Alfvén timescale, a differentially rotating, massive proto-NS rapidly settles into a uniformly rotating, less massive NS due to magnetic braking and viscosity. These explorations suggest that detecting massive NSs is challenging and sets a timescale for detection. We calculate the signal-to-noise ratio of GW emission, which confirms that any detector cannot detect them immediately, but that they are detectable by the Einstein Telescope and Cosmic Explorer over months of integration time, leading to direct detection of NSs.

Keywords: gravitational waves; neutron stars; magnetic stars; gravitation; astronomical radiation sources; gravitational wave sources; pulsars; stellar magnetic fields
The Hipparcos-Gaia Catalog of Accelerations: Gaia EDR3 Edition

We present a cross-calibration of Hipparcos and Gaia EDR3 intended to identify astrometrically accelerating stars and to fit orbits to stars with faint, massive companions. The resulting catalog, the EDR3 edition of the Hipparcos-Gaia Catalog of Accelerations (HGCA), provides three proper motions with calibrated uncertainties on the EDR3 reference frame: the Hipparcos proper motion, the Gaia EDR3 proper motion, and the long-term proper motion given by the difference in position between Hipparcos and Gaia EDR3. Our approach is similar to that for the Gaia DR2 edition of the HGCA but offers a factor of ∼3 improvement in precision thanks to the longer time baseline and improved data processing of Gaia EDR3. We again find that a 60/40 mixture of the two Hipparcos reductions outperforms either reduction individually, and we find strong evidence for locally variable frame rotations between all pairs of proper motion measurements. The substantial global frame rotation seen in DR2 proper motions has been removed in EDR3. We also correct for color- and magnitude-dependent frame rotations at a level of up to ∼50 μas yr-1 in Gaia EDR3. We calibrate the Gaia EDR3 uncertainties using a sample of radial velocity standard stars without binary companions; we find an error inflation factor (a ratio of total to formal uncertainty) of 1.37. This is substantially lower than the position-dependent factor of ∼1.7 found for Gaia DR2 and reflects the improved data processing in EDR3. While the catalog should be used with caution, its proper motion residuals provide a powerful tool to measure the masses and orbits of faint, massive companions to nearby stars.

Keywords: astrometry; astrometric exoplanet detection; astrometric binary stars
Simulating Solar Flare Irradiance with Multithreaded Models of Flare Arcades

Understanding how energy is released in flares is one of the central problems of solar and stellar astrophysics. Observations of high-temperature flare plasma hold many potential clues as to the nature of this energy release. It is clear, however, that flares are not composed of a few impulsively heated loops, but are the result of heating on many small-scale threads that are energized over time, making it difficult to compare observations and numerical simulations in detail. Several previous studies have shown that it is possible to reproduce some aspects of the observed emission by considering the flare as a sequence of independently heated loops, but these studies generally focus on small-scale features while ignoring the global features of the flare. In this paper, we develop a multithreaded model that encompasses the time-varying geometry and heating rate for a series of successively heated loops composing an arcade. To validate, we compare with spectral observations of five flares made with the MinXSS CubeSat, as well as light curves measured with GOES/XRS and SDO/AIA. We show that this model can successfully reproduce the light curves and quasi-periodic pulsations in GOES/XRS, the soft X-ray spectra seen with MinXSS, and the light curves in various AIA passbands. The AIA light curves are most consistent with long-duration heating, but elemental abundances cannot be constrained with the model. Finally, we show how this model can be used to extrapolate to spectra of extreme events that can predict irradiance across a wide wavelength range, including unobserved wavelengths.

Keywords: solar x-ray flares; solar flares; hydrodynamical simulations
Internal Shock with a Background Magnetic Field for the Prompt Emission of Gamma-Ray Bursts-A Case Study of GRB 211211A

It is proposed that the synchrotron emission from an internal shock with a decaying shock-generated magnetic field can account for the prompt emission of gamma-ray bursts (GRBs). Generally, a jet from the central engine of a GRB is launched with a significant magnetization, and thus there would be a background magnetic field, rather than only the shock-generated magnetic field, in the emission region. In this paper, we study the synchrotron emission of internal shocks with both a decaying shock-generated magnetic field and a nondecaying background magnetic field. It is found that a shoulder with spectral index -1/2 appears in the low-energy regime of the radiation spectrum. The shoulder becomes dominant by increasing the ratio of the background magnetic field energy to the initial value of the shock-generated magnetic field energy f B. Correspondingly, a radiation spectrum with two bumps or a plateau around the peak of the ν F ν -ν spectrum may appear. Owing to the decay of the shock-generated magnetic field, the radiation spectral morphology in the high-energy regime is not a power-law function even though a power-law distribution of electrons is injected. We apply our model to GRB 211211A, of which the hard main emission is suggested to originate from the synchrotron emission. Compared with the spectral fitting results with a Band function and the synchrotron emission from the standard straightforward internal shocks, our model presents a perfect fitting to the observations. The fitting results show that f B is around 0.41-0.99 for the hard main emission of this burst.

Keywords: gamma-ray bursts