adsabs/SciX_UAT_keywords huggingface dataset:
Disk Assembly of the Milky Way Suggested from the Time-resolved Chemical Abundance

Both simulations and observations suggest that the disk assembly of galaxies is governed by the interplay between coplanar gas inflow, ex-planar gas outflow, and in situ star formation on the disk, known as the leaky accretion disk. This scenario predicts a strong connection between radial distributions of star formation and chemical abundances. The Milky Way, being the sole Galaxy where we can reliably measure star formation histories and the corresponding temporally resolved chemical abundances with individual stars, provides a unique opportunity to scrutinize this scenario. Based on the recent large spectroscopic and photometric surveys of Milky Way stars, we obtain the radial profiles of magnesium abundance ([Mg/H]) and star formation rate surface density at different lookback times. We find the radial profiles of [Mg/H] can be well-reproduced using the leaky accretion disk model with only two free parameters for stars formed within 4 Gyr, as well as the flattening at large radii of metallicity profiles traced by H II regions and Cepheids. Furthermore, the constraint effective yield of the Milky Way and nearby galaxies shows broad consistency with the theoretical predictions from the stellar chemical evolution model with a mass-loading factor of 0–2. These results support that the recent assembly of the Milky Way adheres to the leaky accretion disk scenario, bridging the disk formation of our home Galaxy to the big picture of disk formation in the Universe.

Keywords: galaxy accretion disks; milky way formation; metallicity
Specific Effect of Peculiar Velocities on Dark-energy Constraints from Type Ia Supernovae

Peculiar velocities of Type Ia supernova (SN Ia) host galaxies affect the dark-energy parameter constraints in a small but very specific way: the parameters are biased in a single direction in parameter space that is a priori knowable for a given SN Ia data set. We demonstrate the latter fact with a combination of inference from a cosmological N-body simulation with overwhelming statistics applied to the Pantheon SN Ia data set, then confirm it by simple quantitative arguments. We quantify small modifications to the current analyses that would ensure that the effect of cosmological parameters is essentially guaranteed to be negligible.

Keywords: type ia supernovae; galaxy radial velocities; dark energy
A Statistical Detection of Wide Binary Systems in the Ultrafaint Dwarf Galaxy Reticulum II

Binary stars can inflate the observed velocity dispersion of stars in dark matter-dominated systems such as ultrafaint dwarf galaxies (UFDs). However, the population of binaries in UFDs is poorly constrained by observations, with preferred binary fractions for individual galaxies ranging from a few percent to near unity. Searching for wide binaries through nearest neighbor (NN) statistics (or the two-point correlation function) has been suggested in the literature, and we apply this method for the first time to detect wide binaries in a UFD. By analyzing the positions of stars in Reticulum II (Ret II) from Hubble Space Telescope images, we search for angularly resolved wide binaries in Ret II. We find that the distribution of their NN distances shows an enhancement at projected separations of ≲1″ relative to a model containing no binaries. We show that such an enhancement can be explained by a wide binary fraction of ${f}_{b}\approx {0.007}_{-0.003}^{+0.008}$ at separations of more than 3000 au. Under the assumption that the binary separation distribution is similar to that in the Milky Way, the total binary fraction in Ret II may be on the order of 50%. We also use the observed magnitude distribution of stars in Ret II to constrain the initial mass function over the mass range 0.34-0.78 M ⊙, finding that a shallow power-law slope of 1.01 ≤ α ≤ 1.15 matches the data.

Keywords: dwarf galaxies; binary stars; cold dark matter
The Faint Satellite System of NGC 253: Insights into Low-density Environments and No Satellite Plane

We have conducted a systematic search around the Milky Way (MW) analog NGC 253 (D = 3.5 Mpc), as a part of the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS)—a Magellan+Megacam survey to identify dwarfs and other substructures in resolved stellar light around MW-mass galaxies outside of the Local Group. In total, NGC 253 has five satellites identified by PISCeS within 100 kpc with an absolute V-band magnitude of M V < ‑7. We have additionally obtained deep Hubble Space Telescope imaging of four reported candidates beyond the survey footprint: Do III, Do IV, and dw0036m2828 are confirmed to be satellites of NGC 253, while SculptorSR is found to be a background galaxy. We find no convincing evidence for the presence of a plane of satellites surrounding NGC 253. We construct its satellite luminosity function, which is complete down to M V ≲ ‑8 out to 100 kpc and M V ≲ ‑9 out to 300 kpc, and compare it to those calculated for other Local Volume galaxies. Exploring trends in satellite counts and star-forming fractions among satellite systems, we find relationships with host stellar mass, environment, and morphology, pointing to a complex picture of satellite formation, and a successful model has to reproduce all of these trends. *This paper includes data gathered with the 6.5 m Magellan Telescope at Las Campanas Observatory, Chile.

Keywords: dwarf galaxies; hst photometry; galaxy evolution; galaxies; surveys; stellar populations
A Speed Bump: SN 2021aefx Shows that Doppler Shift Alone Can Explain Early Excess Blue Flux in Some Type Ia Supernovae

We present early-time photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2021aefx. The early-time u-band light curve shows an excess flux when compared to normal SNe Ia. We suggest that the early excess blue flux may be due to a rapid change in spectral velocity in the first few days post explosion, produced by the emission of the Ca II H&K feature passing from the u to the B bands on the timescale of a few days. This effect could be dominant for all SNe Ia that have broad absorption features and early-time velocities over 25,000 km s-1. It is likely to be one of the main causes of early excess u-band flux in SNe Ia that have early-time high velocities. This effect may also be dominant in the UV filters, as well as in places where the SN spectral energy distribution is quickly rising to longer wavelengths. The rapid change in velocity can only produce a monotonic change (in flux-space) in the u band. For objects that explode at lower velocities, and have a more structured shape in the early excess emission, there must also be an additional parameter producing the early-time diversity. More early-time observations, in particular early spectra, are required to determine how prominent this effect is within SNe Ia.

Keywords: type ia supernovae; supernovae; time domain astronomy
Dynamics and Origins of the Near-resonant Kepler Planets

Short-period super-Earths and mini-Neptunes encircle more than ~50% of Sun-like stars and are relatively amenable to direct observational characterization. Despite this, environments in which these planets accrete are difficult to probe directly. Nevertheless, pairs of planets that are close to orbital resonances provide a unique window into the inner regions of protoplanetary disks, as they preserve the conditions of their formation, as well as the early evolution of their orbital architectures. In this work, we present a novel approach toward quantifying transit timing variations within multiplanetary systems and examine the near-resonant dynamics of over 100 planet pairs detected by Kepler. Using an integrable model for first-order resonances, we find a clear transition from libration to circulation of the resonant angle at a period ratio of ≈0.6% wide of exact resonance. The orbital properties of these systems indicate that they systematically lie far away from the resonant forced equilibrium. Cumulatively, our modeling indicates that while orbital architectures shaped by strong disk damping or tidal dissipation are inconsistent with observations, a scenario where stochastic stirring by turbulent eddies augments the dissipative effects of protoplanetary disks reproduces several features of the data.

Keywords: orbital resonances; transit timing variation method; exoplanet dynamics; exoplanet formation
A Theory for Neutron Star and Black Hole Kicks and Induced Spins

Using 20 long-term 3D core-collapse supernova simulations, we find that lower compactness progenitors that explode quasi-spherically due to the short delay to explosion experience smaller neutron star recoil kicks in the ∼100‑200 km s‑1 range, while higher compactness progenitors that explode later and more aspherically leave neutron stars with kicks in the ∼300‑1000 km s‑1 range. In addition, we find that these two classes are correlated with the gravitational mass of the neutron star. This correlation suggests that the survival of binary neutron star systems may in part be due to their lower kick speeds. We also find a correlation between the kick and both the mass dipole of the ejecta and the explosion energy. Furthermore, one channel of black hole birth leaves masses of ∼10 M ⊙, is not accompanied by a neutrino-driven explosion, and experiences small kicks. A second channel is through a vigorous explosion that leaves behind a black hole with a mass of ∼3.0 M ⊙ kicked to high speeds. We find that the induced spins of nascent neutron stars range from seconds to ∼10 ms, but do not yet see a significant spin/kick correlation for pulsars. We suggest that if an initial spin biases the explosion direction, a spin/kick correlation would be a common byproduct of the neutrino mechanism of core-collapse supernovae. Finally, the induced spin in explosive black hole formation is likely large and in the collapsar range. This new 3D model suite provides a greatly expanded perspective and appears to explain some observed pulsar properties by default.

Keywords: supernova neutrinos; supernova dynamics; pulsars; stellar mass black holes
Discovery of a 2.8 s Pulsar in a 2 Day Orbit High-mass X-Ray Binary Powering the Ultraluminous X-Ray Source ULX-7 in M51

We discovered 2.8 s pulsations in the X-ray emission of the ultraluminous X-ray source (ULX) M51 ULX-7 within the UNSEeN project, which was designed to hunt for new pulsating ULXs (PULXs) with XMM-Newton. The pulse shape is sinusoidal, and large variations of its amplitude were observed even within single exposures (pulsed fraction from less than 5% to 20%). Source M51 ULX-7 is variable, generally observed at an X-ray luminosity between 1039 and 1040 erg s-1, located in the outskirts of the spiral galaxy M51a at a distance of 8.6 Mpc. According to our analysis, the X-ray pulsar orbits in a 2 day binary with a projected semimajor axis ${a}_{{\rm{X}}}\sin I\,\simeq $ 28 lt-s. For a neutron star (NS) of 1.4 M⊙, this implies a lower limit on the companion mass of 8 M⊙, placing the system hosting M51 ULX-7 in the high-mass X-ray binary class. The barycentric pulse period decreased by ≃0.4 ms in the 31 days spanned by our 2018 May-June observations, corresponding to a spin-up rate $\dot{P}\simeq -1.5\times {10}^{-10}\,{\rm{s}}\ {{\rm{s}}}^{-1}$ . In an archival 2005 XMM-Newton exposure, we measured a spin period of ∼3.3 s, indicating a secular spin-up of ${\dot{P}}_{\sec }\simeq -{10}^{-9}\,{\rm{s}}\ {{\rm{s}}}^{-1}$ , a value in the range of other known PULXs. Our findings suggest that the system consists of a massive donor, possibly an OB giant or supergiant, and a moderately magnetic (dipole field component in the range 1012 G $\lesssim {B}_{\mathrm{dip}}\lesssim {10}^{13}$ G) accreting NS with weakly beamed emission ( $1/12\lesssim b\lesssim 1/4$ ).

Keywords: neutron stars; stellar accretion; x-ray sources; stellar magnetic fields; x-ray binary stars; pulsars
On the Short-period Eclipsing High-mass X-Ray Binary in NGC 4214

We present the results of our study of the luminous (L X ≈ 1039 erg s-1) X-ray binary CXOU J121538.2+361921 in NGC 4214, the high-mass X-ray binary with the shortest known orbital period. Using Chandra data, we confirm the ≈13,000 s (3.6 hr) eclipse period, and an eclipse duration of ≈2000 s. From this, we estimate a mass ratio M 2/M 1 ≳ 3 and a stellar density ρ ≈ 6 g cm-3, which implies that the donor must be a Wolf-Rayet or a stripped helium star. The eclipse egress is consistently much slower than the ingress. This can be explained by denser gas located either in front of the compact object (as expected for a bow shock) or trailing the donor star (as expected for a shadow wind, launched from the shaded side of the donor). There is no change in X-ray spectral shape with changing flux during the egress, which suggests either variable partial covering of the X-ray source by opaque clumps or, more likely, a gray opacity dominated by electron scattering in a highly ionized medium. We identify the optical counterpart from Hubble images. Photometry blueward of ~5500 Å indicates a bright (M B ≈ -3.6 ± 0.3 mag, for a range of plausible extinctions), hot (T ≈ 90,000 ± 30,000 K) emitter, consistent with the Wolf-Rayet scenario. There is also a bright (M I ≈ -5.2 mag), cool (T ≈ 2700 ± 300 K) component consistent with an irradiated circumbinary disk or with a chance projection of an unrelated asymptotic giant branch star along the same line of sight.

Keywords: high mass x-ray binary stars; wolf-rayet stars; black holes
Deciphering the Pre-solar-storm Features of the 2017 September Storm From Global and Local Dynamics

We investigate whether global toroid patterns and the local magnetic field topology of solar active region (AR) 12673 together can hindcast the occurrence of the biggest X-flares of solar cycle (SC)-24. Magnetic toroid patterns (narrow latitude belts warped in longitude, in which ARs are tightly bound) derived from the surface distributions of ARs, prior and during AR 12673 emergence, reveal that the portions of the south toroid containing AR 12673 was not tipped away from its north-toroid counterpart at that longitude, unlike the 2003 Halloween storms scenario. During the minimum phase there were too few emergences to determine multimode longitudinal toroid patterns. A new emergence within AR 12673 produced a complex nonpotential structure, which led to the rapid buildup of helicity and winding that triggered the biggest X-flare of SC-24, suggesting that this minimum-phase storm can be anticipated several hours before its occurrence. However, global patterns and local dynamics for a peak-phase storm, such as that from AR 11263, behaved like the 2003 Halloween storms, producing the third biggest X-flare of SC-24. AR 11263 was present at the longitude where the north and south toroids tipped away from each other. While global toroid patterns indicate that prestorm features can be forecast with a lead time of a few months, their application to observational data can be complicated by complex interactions with turbulent flows. Complex nonpotential field structure development hours before the storm are necessary for short-term prediction. We infer that minimum-phase storms cannot be forecast accurately more than a few hours ahead, while flare-prone ARs in the peak phase may be anticipated much earlier, possibly months ahead from global toroid patterns.

Keywords: solar activity; solar flares; solar storm; solar active regions
Hubble Space Telescope Imaging of Luminous Extragalactic Infrared Transients and Variables from the Spitzer Infrared Intensive Transients Survey

The SPitzer InfraRed Intensive Transients Survey (SPIRITS) searched for luminous infrared (IR) transients and variables in nearly 200 nearby galaxies from 2014 to 2019, using the warm Spitzer telescope at 3.6 and 4.5 μm. Among the SPIRITS variables are IR-bright objects that are undetected in ground-based optical surveys. We classify them as (1) transients, (2) periodic variables, and (3) irregular variables. The transients include eSPecially Red Intermediate-luminosity Transient Events (SPRITEs), having maximum luminosities fainter than supernovae, red IR colors, and a wide range of outburst durations (days to years). Here we report deep optical and near-IR imaging with the Hubble Space Telescope (HST) of 21 SPIRITS variables. They were initially considered SPRITE transients, but many eventually proved instead to be periodic or irregular variables as more data were collected. HST images show most of these cool and dusty variables are associated with star-forming regions in late-type galaxies, implying an origin in massive stars. Two SPRITEs lacked optical progenitors in deep preoutburst HST images; however, one was detected during eruption at J and H, indicating a dusty object with an effective temperature of ~1050 K. One faint SPRITE turned out to be a dusty classical nova. About half the HST targets proved to be periodic variables, with pulsation periods of 670-2160 days; they are likely dusty asymptotic-giant-branch (AGB) stars with masses of ~5-10 M ⊙. A few of them were warm enough to be detected in deep HST frames, but most are too cool. Out of six irregular variables, two were red supergiants with optical counterparts in HST images; four were too enshrouded for HST detection. * Based in part on observations and archival data from the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555; also in part on observations and archival data made with the Spitzer Space Telescope, operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.

Keywords: supernovae; transient sources; classical novae; variable stars; infrared sources; oh/ir stars; red supergiant stars; luminous blue variable stars
The Sixth Data Release of the Radial Velocity Experiment (RAVE). I. Survey Description, Spectra, and Radial Velocities

The Radial Velocity Experiment (RAVE) is a magnitude-limited (9 < I < 12) spectroscopic survey of Galactic stars randomly selected in Earth's southern hemisphere. The RAVE medium-resolution spectra (R ∼ 7500) cover the Ca-triplet region (8410-8795 Å). The sixth and final data release (DR6) is based on 518,387 observations of 451,783 unique stars. RAVE observations were taken between 2003 April 12 and 2013 April 4. Here we present the genesis, setup, and data reduction of RAVE as well as wavelength-calibrated and flux-normalized spectra and error spectra for all observations in RAVE DR6. Furthermore, we present derived spectral classification and radial velocities for the RAVE targets, complemented by cross-matches with Gaia DR2 and other relevant catalogs. A comparison between internal error estimates, variances derived from stars with more than one observing epoch, and a comparison with radial velocities of Gaia DR2 reveals consistently that 68% of the objects have a velocity accuracy better than 1.4 km s-1, while 95% of the objects have radial velocities better than 4.0 km s-1. Stellar atmospheric parameters, abundances and distances are presented in a subsequent publication. The data can be accessed via the RAVE website (http://rave-survey.org) or the Vizier database.

Keywords: stellar populations; galaxy stellar content; milky way galaxy; milky way dynamics; surveys; sky surveys; catalogs
On the Unusual Variability of 2MASS J06195260-2903592: A Long-lived Disk around a Young Ultracool Dwarf

We present the characterization of the low-gravity M6 dwarf 2MASS J06195260-2903592, previously identified as an unusual field object based on its strong IR excess and variable near-IR spectrum. Multiple epochs of low-resolution (R ≈ 150) near-IR spectra show large-amplitude (≈0.1-0.5 mag) continuum variations on timescales of days to 12 yr, unlike the small-amplitude variability typical for field ultracool dwarfs. The variations between epochs are well-modeled as changes in the relative extinction (ΔA V ≈ 2 mag). Similarly, Panoramic Survey Telescope and Rapid Response System 1 optical photometry varies on timescales as long as 11 yr (and possibly as short as an hour) and implies comparable A V changes. Near Earth Object Wide-field Infrared Survey Explorer mid-IR light curves also suggest changes on 6 month timescales, with amplitudes consistent with the optical/near-IR extinction variations. However, near-IR spectra, near-IR photometry, and optical photometry obtained in the past year indicate that the source can also be stable on hourly and monthly timescales. From comparison to objects of similar spectral type, the total extinction of 2MASS J0619-2903 seems to be A V ≈ 4-6 mag, with perhaps epochs of lower extinction. Gaia Early Data Release 3 (EDR3) finds that 2MASS J0619-2903 has a wide-separation (1.'2 = 10,450 au) stellar companion, with an isochronal age of ${31}_{-10}^{+22}$ Myr and a mass of ${0.30}_{-0.03}^{+0.04}$ M ☉. Adopting this companion's age and EDR3 distance (145.2 ± 0.6 pc), we estimate a mass of 0.11-0.17 M ☉ for 2MASS J0619-2903. Altogether, 2MASS J0619-2903 appears to possess an unusually long-lived primordial circumstellar disk, perhaps making it a more obscured analog to the "Peter Pan" disks found around a few M dwarfs in nearby young moving groups.

Keywords: circumstellar disks; m dwarf stars
Key Parameters Controlling the Photodesorption Yield in Interstellar CO Ice Analogs: The Influence of Ice Deposition Temperature and Thickness

The overabundance of gas molecules in the coldest regions of space points to a nonthermal desorption process. Laboratory simulations show the efficient desorption of CO ice that is exposed to ultraviolet radiation, known as photodesorption, which decreases with increasing ice deposition temperature. However, our understanding of this abnormal phenomenon still remains elusive. In this work, we show that the same phenomenon-and, in particular, a dramatic drop in the photodesorption yield-is observed when the deposition temperature is 19 K and higher. Also, the minimum ice thickness that accounts for a constant photodesorption yield of CO ice is dependent on the deposition temperature, an observation that is reported here for the first time. We propose that the key parameters dominating the absorbed photon energy transfer in CO ice, and contributing to the measured photodesorption yields, are the energy transfer length, the desorption yield contributed by a single ice layer, and the relative effective surface area. These parameters should be incorporated into astrophysical models that simulate the photodesorption of the top CO-rich ice layer in icy dust populations, with a size distribution that is related to the ice thickness.

Keywords: molecular spectroscopy; laboratory astrophysics; interstellar medium
Relativistic Alfvén Waves Entering Charge-starvation in the Magnetospheres of Neutron Stars

Instabilities in a neutron star can generate Alfvén waves in its magnetosphere. Propagation along the curved magnetic field lines strongly shears the wave, boosting its electric current j A. We derive an analytic expression for the evolution of the wavevector k and the growth of j A. In the strongly sheared regime, j A may exceed the maximum current j 0 that can be supported by the background e ± plasma. We investigate these charge-starved waves, first using a simplified two-fluid analytic model, then with first-principles kinetic simulations. We find that the Alfvén wave is able to propagate successfully even when κ ≡ j A/j 0 ≫ 1. It sustains j A by compressing and advecting the plasma along the magnetic field lines with an increasing Lorentz factor, γ ≳ κ 1/2. The simulations show how plasma instabilities lead to gradual dissipation of the wave energy. Our results suggest that an extremely high charge-starvation parameter κ ≳ 104 may be required in order for this mechanism to power the observed fast radio bursts (FRBs) from SGR 1935+2154. However, cosmological FRBs with much higher luminosities are unlikely to be a result of charge-starvation.

Keywords: plasma physics; neutron stars; radio bursts