adsabs/SciX_UAT_keywords huggingface dataset:
A Glimpse of the Stellar Populations and Elemental Abundances of Gravitationally Lensed, Quiescent Galaxies at z ≳ 1 with Keck Deep Spectroscopy

Gravitational lenses can magnify distant galaxies, allowing us to discover and characterize the stellar populations of intrinsically faint, quiescent galaxies that are otherwise extremely difficult to directly observe at high redshift from ground-based telescopes. Here, we present the spectral analysis of two lensed, quiescent galaxies at z ≳ 1 discovered by the ASTRO 3D Galaxy Evolution with Lenses survey: AGEL1323 (M * ~ 1011.1 M ⊙, z = 1.016, μ ~ 14.6) and AGEL0014 (M * ~ 1011.5 M ⊙, z = 1.374, μ ~ 4.3). We measured the age, [Fe/H], and [Mg/Fe] of the two lensed galaxies using deep, rest-frame-optical spectra (S/N ≳40 Å-1) obtained on the Keck I telescope. The ages of AGEL1323 and AGEL0014 are ${5.6}_{-0.8}^{+0.8}$ Gyr and ${3.1}_{-0.3}^{+0.8}$ Gyr, respectively, indicating that most of the stars in the galaxies were formed less than 2 Gyr after the Big Bang. Compared to nearby quiescent galaxies of similar masses, the lensed galaxies have lower [Fe/H] and [Mg/H]. Surprisingly, the two galaxies have comparable [Mg/Fe] to similar-mass galaxies at lower redshifts, despite their old ages. Using a simple analytic chemical evolution model connecting the instantaneously recycled element Mg with the mass-loading factors of outflows averaged over the entire star formation history, we found that the lensed galaxies may have experienced enhanced outflows during their star formation compared to lower-redshift galaxies, which may explain why they quenched early.

Keywords: gravitational lensing; scaling relations; high-redshift galaxies; chemical abundances; abundance ratios; metallicity; stellar abundances; galaxy properties; galaxy physics; galaxy ages; stellar populations; ground-based astronomy
A Large (≈ 1 pc) Contracting Envelope Around the Prestellar Core L1544

Prestellar cores, the birthplace of Sun-like stars, form from the fragmentation of the filamentary structure that composes molecular clouds, from which they must inherit at least partially the kinematics. Furthermore, when they are on the verge of gravitational collapse, they show signs of subsonic infall motions. How extended these motions are, which depends on how the collapse occurs, remains largely unknown. We want to investigate the kinematics of the envelope that surrounds the prototypical prestellar core L1544, studying the cloud-core connection. To our aims, we observed the HCO+ (1-0) transition in a large map. HCO+ is expected to be abundant in the envelope, making it an ideal probe of the large-scale kinematics in the source. We modeled the spectrum at the dust peak by means of a nonlocal thermodynamical equilibrium radiative transfer. In order to reproduce the spectrum at the dust peak, a large (~1 pc) envelope is needed, with low density (tens of cm-3 at most) and contraction motions, with an inward velocity of ≈ 0.05 km s-1. We fitted the data cube using the Hill5 model, which implements a simple model for the optical depth and excitation temperature profiles along the line of sight, in order to obtain a map of the infall velocity. This shows that the infall motions are extended, with typical values in the range 0.1-0.2 km s-1. Our results suggest that the contraction motions extend in the diffuse envelope surrounding the core, which is consistent with recent magnetic field measurements in the source, which showed that the envelope is magnetically supercritical. *This work is based on observations carried out with the IRAM 30m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Keywords: astrochemistry; star formation; low mass stars; interstellar medium; gravitational collapse
Emission-line Data Cubes of the HH 32 Stellar Jet

We analyze data cubes of over 60 emission lines in the HH 32 stellar jet acquired with the Keck Cosmic Web Imager (KCWI). The data cover the less explored blue portion of the spectrum between 3586 and 6351 Å and have both high spectral (R ∼ 10,000) and spatial (≲1″) resolution. The study includes all three major ionization states of oxygen, three Balmer lines, multiple lines of Fe II and Fe III, and the first data cubes ever acquired for important unblended diagnostic lines such as He II λ4686, Ca I λ3933, and Mg I] λ4571. The data cubes generally sort according to excitation and have a relatively continuous progression from the highest-excitation ions (He II, O III) through the intermediate-excitation ions (O I and H I) to the lowest-excitation ions (Ca II and Mg I). Merging the KCWI cubes with Hubble Space Telescope images leads to several new insights about the flow, including evidence for bow shocks, partial bow shocks, spur shocks, Mach disks, jet deflection shocks, a wiggling jet, and potential shock precursors. The most surprising result is that one of the velocity components of Fe II in the Mach disk suddenly increases in flux relative to other lines by a factor of two, implying that the Mach disk vaporizes dust in the jet. Hence, jets must accelerate or entrain dust to speeds of over 300 km s-1 without destroying the grains.

Keywords: herbig-haro objects; stellar jets; shocks
First Analysis of In Situ Observation of Surface Alfvén Waves in an ICME Flux Rope

Alfvén waves (AWs) are ubiquitous in space and astrophysical plasma. Their crucial role in various physical processes has triggered intense research in solar-terrestrial physics. Simulation studies have proposed the generation of AWs along the surface of a cylindrical flux rope, referred to as surface AWs (SAWs); however, the observational verification of this distinct wave has been elusive to date. We report the first in situ observation of SAWs in a flux rope of an interplanetary coronal mass ejection. We apply the Walén test to identify them. We have used Elsässer variables to estimate the characteristics of SAWs. They may be excited by the movement of the flux rope's footpoints or by instabilities along the boundaries of the plasma magnetic cloud. Here, the change in plasma density or field strength in the surface-aligned magnetic field may trigger SAWs.

Keywords: alfven waves; space plasmas; solar coronal mass ejections
Numerical Models of Externally Irradiated Herbig-Haro Objects

We use 3D radiation-hydrodynamic simulations to study the effects of an external photoionization source on the structure of a Herbig-Haro (HH) jet launched from a young stellar object. Different ionizing photon rates are considered as well as a time-dependent ejection velocity and density. From our numerical results, synthetic Hα emission maps are computed in order to study how the external ionizing source affects the observed morphology of the jet and counterjet. We find that, as expected, the outflow has jet/counterjet and side-to-side asymmetries (with brighter Hα emission toward the external photoionizing source). We find that, for a variable ejection velocity, jet morphologies similar to different observed externally irradiated jets can be straightforwardly obtained. Models of jets with a variable ejection density (and constant outflow velocity) produce morphologies that are not seen in observed HH jets and are, therefore, not justified by the presently available observations.

Keywords: interstellar medium; computational methods; herbig-haro objects; stellar jets
Dust Attenuation Curve for Local Subgalactic Star-forming Regions

We compile a sample of about 157,000 spaxels from the Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey to derive the average dust attenuation curve for subgalactic star-forming regions of local star-forming galaxies (SFGs) in the optical wavelength, following the method of Calzetti et al. We obtain a ${D}_{n}(4000)$ -independent average attenuation curve for spaxels with 1.1 ≤ Dn(4000) < 1.3, which is similar to the one derived from either local starbursts or normal SFGs. We examine whether and how the shape of the average attenuation curve changes with several local and global physical properties. For spaxels with 1.2 ≤ Dn(4000) < 1.3, we find no dependence on either local or global physical properties for the shape of the average attenuation curve. However, for spaxels with younger stellar population (1.1 ≤ Dn(4000) < 1.2), shallower average attenuation curves are found for star-forming regions with smaller stellar mass surface density, smaller star formation rate surface density, or those residing in the outer region of galaxies. These results emphasize the risk of using one single attenuation curve to correct the dust reddening for all type of star-forming regions, especially for those with fairly young stellar population.

Keywords: interstellar dust extinction; galaxy evolution; interstellar medium; galaxies; h ii regions
Peculiar Spectral Property of Coherent Radio Emission from a Hot Magnetic Star: The Case of an Extreme Oblique Rotator

We report ultra-wideband (0.4-4.0 GHz) observation of coherent radio emission via electron cyclotron maser emission (ECME) produced by the hot magnetic star HD 142990. With nearly perpendicular rotation and magnetic dipole axes, it represents an extreme case of oblique rotators. The large obliquity is predicted to cause a complex distribution of stellar wind plasma in the magnetosphere. It has been proposed that such a distribution will give rise to a nontrivial frequency dependence of ECME. Indeed we discovered strong frequency dependence of different pulse properties, such as the appearance of secondary pulses, different cutoff frequencies for pulses observed at different rotational phases, etc. But the unique feature that we observed is that while at sub-gigahertz frequencies, the star appears to produce ECME in the extraordinary mode, at gigahertz frequencies, the mode indicated by the pulse property is the ordinary mode. By considering the physical condition needed by such a scenario, we conclude that the required transition of the magnetoionic mode with frequency is unlikely to occur, and the most promising scenario is refraction caused by the complex plasma distribution surrounding the star. This suggests that the conventional way to deduce the magnetoionic mode based on ECME observed at a given frequency is not a reliable method for stars with large misalignment between their rotation and magnetic axes. We also find that ECME exhibits an upper cutoff at ≲3.3 GHz, which is much smaller than the frequency corresponding to the maximum stellar magnetic field strength.

Keywords: astrophysical masers; non-thermal radiation sources; early-type stars; magnetic stars; radio continuum emission; main sequence stars; magnetic variable stars; ob stars; observational astronomy; periodic variable stars
Revealing the CO X-factor in Dark Molecular Gas through Sensitive ALMA Absorption Observations

Carbon-bearing molecules, particularly CO, have been widely used as tracers of molecular gas in the interstellar medium (ISM). In this work, we aim to study the properties of molecules in diffuse, cold environments, where CO tends to be underabundant and/or subthermally excited. We performed one of the most sensitive (down to ${\tau }_{\mathrm{rms}}^{\mathrm{CO}}\sim 0.002$ and ${\tau }_{\mathrm{rms}}^{{\mathrm{HCO}}^{+}}\sim 0.0008$ ) submillimeter molecular absorption line observations toward 13 continuum sources with the ALMA. CO absorption was detected in diffuse ISM down to ${A}_{{\rm{V}}}\lt 0.32\,\mathrm{mag}$ and HCO+ was detected down to ${A}_{{\rm{V}}}\lt 0.2\,\mathrm{mag}$ , where atomic gas and dark molecular gas start to dominate. Multiple transitions measured in absorption toward 3C454.3 allow for a direct determination of excitation temperatures Tex of 4.1 and 2.7 K, for CO and for HCO+, respectively, which are close to the cosmic microwave background and explain their being undercounted in emission surveys. A stronger linear correlation was found between ${N}_{{\mathrm{HCO}}^{+}}$ and ${N}_{{{\rm{H}}}_{2}}$ (Pearson correlation coefficient P ∼ 0.93) than that of NCO and ${N}_{{{\rm{H}}}_{2}}$ (P ∼ 0.33), suggesting HCO+ is a better tracer of H2 than CO in diffuse gas. The derived CO-to-H2 conversion factor (the CO X-factor) of (14 ± 3) × 1020 cm-2 (K $\mathrm{km}\,{{\rm{s}}}^{-1}$ )-1 is approximately six times larger than the average value found in the Milky Way.

Keywords: interstellar medium; interstellar absorption; interstellar molecules
Machine Learning as a Flaring Storm Warning Machine: Was a Warning Machine for the 2017 September Solar Flaring Storm Possible?

Machine learning is now one of the methodologies of choice for flare forecasting, and supervised techniques, in both their traditional and deep versions, are becoming more frequently used for prediction in this area of space weather. Most studies assess the prediction effectiveness of machine-learning methods by computing confusion matrices, which are typically highly non-diagonal, particularly in applications concerning the forecasting of X-class flares. The present study suggests that the reliability of the outcomes of a supervised machine-learning method could be better assessed by using it as a warning machine, sounding binary alerts unrolled over time, and by comparing the number of alerts sounded by the machine in specific time windows with the number of events actually observed in those time windows. Indeed, when applied to the prediction of the events associated with the 2017 September solar storm, a hybrid LASSO algorithm was able to sound alerts every day a flare actually occurred; it also identified the corresponding flare class. In addition, the machine was able to predict with some accuracy a reliable proxy of the energy budget daily released by magnetic reconnection during the entire course of the storm. Finally, the analysis shows that the combination of sparsity-enhancing machine learning and feature ranking could allow the identification of the prominent role that the Ising energy played as an active region property in the forecasting process.

Keywords: solar flares; solar active regions; astronomy data modeling
The Discovery of the 528.6 Hz Accreting Millisecond X-Ray Pulsar MAXI J1816-195

We present the discovery of 528.6 Hz pulsations in the new X-ray transient MAXI J1816-195. Using NICER, we observed the first recorded transient outburst from the neutron star low-mass X-ray binary MAXI J1816-195 over a period of 28 days. From a timing analysis of the 528.6 Hz pulsations, we find that the binary system is well described as a circular orbit with an orbital period of 4.8 hr and a projected semimajor axis of 0.26 lt-s for the pulsar, which constrains the mass of the donor star to 0.10-0.55 M ⊙. Additionally, we observed 15 thermonuclear X-ray bursts showing a gradual evolution in morphology over time, and a recurrence time as short as 1.4 hr. We did not detect evidence for photospheric radius expansion, placing an upper limit on the source distance of 8.6 kpc.

Keywords: low-mass x-ray binary stars; millisecond pulsars; x-ray bursts
An Observational Test of Solar Plasma Heating by Magnetic Flux Cancellation

Recent observations suggest that magnetic flux cancellation may play a crucial role in heating the Sun's upper atmosphere (chromosphere, transition region, corona). Here, we intended to validate an analytic model for magnetic reconnection and consequent coronal heating, driven by a pair of converging and canceling magnetic flux sources of opposite polarities. For this test, we analyzed photospheric magnetic field and multiwavelength ultraviolet/extreme ultraviolet (EUV) observations of a small-scale flux cancellation event in a quiet-Sun internetwork region over a target interval of 5.2 hr. The observed cancellation event exhibits a converging motion of two opposite-polarity magnetic patches on the photosphere and redshifted Doppler velocities (downflows) therein consistently over the target interval, with a decrease in magnetic flux of both polarities at a rate of 1015 Mx s-1. Several impulsive EUV brightenings, with differential emission measure values peaked at 1.6-2.0 MK, are also observed in the shape of arcades with their two footpoints anchored in the two patches. The rate of magnetic energy released as heat at the flux cancellation region is estimated to be in the range of (0.2-1) × 1024 erg s-1 over the target interval, which can satisfy the requirement of previously reported heating rates for the quiet-Sun corona. Finally, both short-term (a few to several tens of minutes) variations and long-term (a few hours) trends in the magnetic energy release rate are clearly shown in the estimated rate of radiative energy loss of electrons at temperatures above 2.0 MK. All these observational findings support the validity of the investigated reconnection model for plasma heating in the upper solar atmosphere by flux cancellation.

Keywords: astronomy data analysis; solar photosphere; quiet solar corona; solar magnetic fields; quiet sun; solar coronal heating; solar magnetic reconnection; solar ultraviolet emission; solar extreme ultraviolet emission
Absorption-line Observations of {{H}}_{3}(+) and CO in Sight Lines Toward the Vela and W28 Supernova Remnants

Supernova remnants act as particle accelerators, providing the cosmic-ray protons that permeate the interstellar medium and initiate the ion-molecule reactions that drive interstellar chemistry. Enhanced fluxes of cosmic-ray protons in close proximity to supernova remnants have been inferred from observations tracing particle interactions with nearby molecular gas. Here I present observations of ${{\rm{H}}}_{3}^{+}$ and CO absorption, molecules that serve as tracers of the cosmic-ray ionization rate and gas density, respectively, in sight lines toward the W28 and Vela supernova remnants. Cosmic-ray ionization rates inferred from these observations range from about 2 to 10 times the average value in Galactic diffuse clouds (~3 × 10-16 s-1), suggesting that the gas being probed is experiencing an elevated particle flux. While it is difficult to constrain the line-of-sight locations of the absorbing gas with respect to the supernova remnants, these results are consistent with a scenario where cosmic rays are diffusing away from the acceleration site and producing enhanced ionization rates in the surrounding medium.

Keywords: cosmic rays; supernova remnants; diffuse molecular clouds; infrared spectroscopy
No Large Dependence of Planet Frequency on Galactocentric Distance

Gravitational microlensing is currently the only technique that helps study the Galactic distribution of planets as a function of distance from the Galactic center. The Galactic location of a lens system can be uniquely determined only when at least two of the three quantities that determine the mass-distance relations are measured. However, even if only one mass-distance relation can be obtained, a large sample of microlensing events can be used to statistically discuss the Galactic distribution of the lenses. In this study, we extract the Galactic distribution of planetary systems from the distribution of the lens-source proper motion, μrel, for a given Einstein radius crossing time, tE, measured for the 28 planetary events in the statistical sample by Suzuki et al. Because microlensing is randomly caused by stars in our Galaxy, the observational distribution can be predicted using a Galactic model. We incorporate the planet-hosting probability, ${P}_{\mathrm{host}}\propto {M}_{{\rm{L}}}^{m}{R}_{{\rm{L}}}^{r}$ , into a Galactic model for random-selected stars, where ML is the lens mass (~host mass), and RL is the Galactocentric distance. By comparing the observed distribution with the model-predicted μrel distribution for a given tE at various combinations of (m, r), we obtain an estimate r = 0.2 ± 0.4 under a plausible uniform prior for m of 0 < m < 2. This indicates that the dependence of the planet frequency on the Galactocentric distance is not large, and suggests that the Galactic bulge does have planets.

Keywords: exoplanets; gravitational microlensing; galactic bulge
LTD064402+245919, Compact Binary or Subgiant with Red Star Eclipsing Binary?

Recently, a single-line spectroscopic binary, LTD064402+245919, has been discovered by Yang et al. Using data from LAMOST and ZTF, the unseen companion is estimated to have a mass of 1-3 M ⊙, orbiting a subgiant with orbital period of 14.50 days, making it a good compact binary candidate without X-ray emission. However, new light curves from ZTF and ASAS-SN, has shown the depth of one dip increases toward a bluer wavelength, indicating LTD064402+245919 is more likely to be a subgaint with a red star. Using both Wilson-Devinney code and Phoebe, the derived T eff of secondary is about 3400 K, corresponding to a red M2/3 star. Additionally, the 20% error of parallax from Gaia is large. The mass of subgiant will be 1.28 M ⊙ instead of 2.77 M ⊙, if the refined distance of 5.0 kpc is used. Nevertheless, new multi-color photometry are warranted for the final confirmation of binaries properties.

Keywords: spectroscopic binary stars; semi-detached binary stars; neutron stars; stellar mass black holes
HST Far-ultraviolet Transit Observations of Two Neptune Progenitors Younger than 30 Myr

Photoevaporation is believed to dominate the removal of planetary atmospheres when they are young (<100 Myr). Signatures of atmospheric mass-loss can be observed in the ultraviolet (UV) through the near-infrared. We present Far-UV transit observations of AU Mic b (∼22 Myr) and V1298 Tau c (∼28 Myr) with the Hubble Space Telescope. We search for evidence of escaping metals in the C II, Si II, and Si III emission lines and compare their behavior to tracers of stellar activity. We detect no evidence of atmospheric mass loss, and place upper limits on the radii of AU Mic b and V1298 Tau c.

Keywords: transits; time series analysis; ultraviolet spectroscopy; atmospheric evolution
HALO7D. III. Chemical Abundances of Milky Way Halo Stars from Medium-resolution Spectra

The Halo Assembly in Lambda Cold Dark Matter: Observations in 7 Dimensions (HALO7D) survey measures the kinematics and chemical properties of stars in the Milky Way (MW) stellar halo to learn about the formation of our Galaxy. HALO7D consists of Keck II/DEIMOS spectroscopy and Hubble Space Telescope-measured proper motions of MW halo main-sequence turnoff stars in the four Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields. HALO7D consists of deep pencil beams, making it complementary to other contemporary wide-field surveys. We present the [Fe/H] and [α/Fe] abundances for 113 HALO7D stars in the Galactocentric radial range of ~10-40 kpc along four separate pointings. Using the full 7D chemodynamical data (3D positions, 3D velocities, and abundances) of HALO7D, we measure the velocity anisotropy, β, of the halo velocity ellipsoid for each field and for different metallicity-binned subsamples. We find that two of the four fields have stars on very radial orbits, while the remaining two have stars on more isotropic orbits. Separating the stars into high-, mid-, and low-[Fe/H] bins at -2.2 and -1.1 dex for each field separately, we find differences in the anisotropies between the fields and between the bins; some fields appear dominated by radial orbits in all bins, while other fields show variation between the [Fe/H] bins. These chemodynamical differences are evidence that the HALO7D fields have different fractional contributions from the progenitors that built up the MW stellar halo. Our results highlight the additional information available on smaller spatial scales compared to results from a spherical average of the stellar halo.

Keywords: milky way galaxy; milky way stellar halo; stellar abundances; astrostatistics