adsabs/SciX_UAT_keywords huggingface dataset:
Direct Imaging Discovery of a Young Brown Dwarf Companion to an A2V Star

We present the discovery and spectroscopy of HIP 75056Ab, a companion directly imaged at a very small separation of 0"125 to an A2V star in the Scorpius-Centaurus OB2 association. Our observations utilized Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet Research Experiment between 2015 and 2019, enabling low-resolution spectroscopy (0.95-1.65 μm), dual-band imaging (2.1-2.25 μm), and relative astrometry over a four-year baseline. HIP 75056Ab is consistent with spectral types in the range of M6-L2 and Teff ∼ 2000-2600 K. A comparison of the companion's brightness to evolutionary tracks suggests a mass of ∼20-30 MJup. The astrometric measurements are consistent with an orbital semimajor axis of ∼15-45 au and an inclination close to face-on (i ≲ 35°). In this range of mass and orbital separation, HIP 75056Ab is likely at the low-mass end of the distribution of companions formed via disk instability, although a formation of the companion via core accretion cannot be excluded. The orbital constraints are consistent with the modest eccentricity values predicted by disk instability, a scenario that can be confirmed by further astrometric monitoring. HIP 75056Ab may be utilized as a low-mass atmospheric comparison to older, higher-mass brown dwarfs, and also to young giant planets. Finally, the detection of HIP 75056Ab at 0"125 represents a milestone in detecting low-mass companions at separations corresponding to the habitable zones of nearby Sun-like stars.

Keywords: brown dwarfs; direct imaging; exoplanets
The TESS-Keck Survey. III. A Stellar Obliquity Measurement of TOI-1726 c

We report the measurement of a spectroscopic transit of TOI-1726c, one of two planets transiting a G-type star with V = 6.9 in the Ursa Major Moving Group (∼400 Myr). With a precise age constraint from cluster membership, TOI-1726 provides a great opportunity to test various obliquity excitation scenarios that operate on different timescales. By modeling the Rossiter-McLaughlin (RM) effect, we derived a sky-projected obliquity of $-{1}_{-32}^{{+35}^\circ} $ . This result rules out a polar/retrograde orbit and is consistent with an aligned orbit for planet c. Considering the previously reported, similarly prograde RM measurement of planet b and the transiting nature of both planets, TOI-1726 tentatively conforms to the overall picture that compact multitransiting planetary systems tend to have coplanar, likely aligned orbits. TOI-1726 is also a great atmospheric target for understanding differential atmospheric loss of sub-Neptune planets (planet b 2.2 R⊕ and c 2.7 R⊕ both likely underwent photoevaporation). The coplanar geometry points to a dynamically cold history of the system that simplifies any future modeling of atmospheric escape.

Keywords: exoplanet dynamics; exoplanet formation
Multiple Stellar Populations in Metal-poor Globular Clusters with JWST: A NIRCam View of M92

Recent work on metal-intermediate globular clusters (GCs) with [Fe/H] = -1.5 and -0.75 has illustrated the theoretical behavior of multiple populations in photometric diagrams obtained with the JWST. These results are confirmed by observations of multiple populations among the M dwarfs of 47 Tucanae. Here we explore multiple populations in metal-poor GCs with [Fe/H] = -2.3. We take advantage of synthetic spectra and isochrones that account for the chemical composition of multiple populations to identify photometric diagrams that separate the distinct stellar populations of GCs. We derive high-precision photometry and proper motion for main-sequence (MS) stars in the metal-poor GC M92 from JWST and Hubble Space Telescope images. We identify a first-generation (1G) and two main groups of second-generation (2GA and 2GB) stars and investigate their kinematics and chemical composition. We find isotropic motions with no differences among the distinct populations. The comparison between the observed colors of the M92 stars and the colors derived by synthetic spectra reveals that the helium abundances of 2GA and 2GB stars are higher than those of the 1G by ΔY ~ 0.01 and 0.04, respectively. The m F090W versus m F090W - m F277W color-magnitude diagram shows that below the knee MS stars exhibit a wide color broadening due to multiple populations. We constrain the amount of oxygen variation needed to reproduce the observed MS width, which is consistent with results on red giant branch stars. We conclude that multiple populations with masses of ~0.1-0.8 M ⊙ share similar chemical compositions.

Keywords: globular star clusters; population ii stars; stellar abundances; photometry
Magnetic Energy Transfer and Distribution between Protons and Electrons for Alfvénic Waves at Kinetic Scales in Wavenumber Space

Turbulent dissipation is considered a main source of heating and acceleration in cosmic plasmas. The alternating current Joule-like term, $\langle \delta {\boldsymbol{j}}\cdot \delta {\boldsymbol{E}}\rangle $ , is used to measure the energy transfer between electromagnetic fields and particles. Because the electric field depends on the reference frame, in which frame to calculate $\langle \delta {\boldsymbol{j}}\cdot \delta {\boldsymbol{E}}\rangle $ is an important issue. We compute the scale-dependent energy transfer rate spectrum in wavevector space, and investigate the electric-field fluctuations in two reference frames: $\delta {\boldsymbol{E}}$ in the mean bulk flow frame and $\delta {\boldsymbol{E}}^{\prime} $ in the local bulk flow frame (non-inertial reference frame). Considering Alfvénic waves, we find that $\langle \delta {\boldsymbol{j}}\cdot \delta {{\boldsymbol{E}}}^{{\prime} }\rangle $ , which neglects the contribution of work done by the ion inertial force, is not consistent with the magnetic field energy damping rate (2γδB2) according to linear Maxwell-Vlasov theory, while $\langle \delta {\boldsymbol{j}}\cdot \delta {\boldsymbol{E}}\rangle $ is exactly the same as 2γδB2 in wavenumber space (k∥, k⊥), where γ is the linear damping rate. Under typical conditions of solar wind at 1 au, we find in our theoretical calculation that the field energy is mainly converted into proton kinetic energy leaving the residual minor portion for electrons. Although the electrons gain energy in the direction perpendicular to the mean magnetic field, they return a significant fraction of their kinetic energy in the parallel direction. Magnetic-field fluctuations can transfer particle energy between the parallel and perpendicular degrees of freedom. Therefore, $\langle \delta {{\boldsymbol{j}}}_{\parallel }\cdot \delta {{\boldsymbol{E}}}_{\parallel }\rangle $ and $\langle \delta {{\boldsymbol{j}}}_{\perp }\cdot \delta {{\boldsymbol{E}}}_{\perp }\rangle $ do not solely describe the energy transfer in the parallel direction and perpendicular direction, respectively.

Keywords: solar wind; interplanetary turbulence; alfven waves
X-Ray Jet, Counter-jet, and Trail of the Fast-moving Pulsar PSR B2224+65

I report the detection of linear X-ray features associated with PSR B2224+65, based on a new Chandra observation, plus two obtained ∼6 and 12 yr earlier. This mid-aged pulsar is known for its extreme proper motion and its associated guitar-shaped optical nebula in the opposite direction. The main jet-like feature with the same proper motion is $\sim 2\buildrel{\,\prime}\over{.} 4$ long and directed 62° away from the nebula, which is associated with a faint X-ray tail detected for the first time. Also now clearly revealed are the sharp forward edge and epoch-dependent substructures of the feature and its curvature near the pulsar, as well as a much fainter/shorter counter-jet. Magnetic field appears to play a central role in the formation of the features, which represent the synchrotron radiation of energetic particles leaked out from the bow shock nebula through small holes, produced probably by localized magnetic reconnection, and streaming along interstellar magnetic field lines.

Keywords: pulsars; magnetic fields; plasma jets; x-ray astronomy
A Quasi-periodic Oscillation in the γ-Ray Emission from the Non-blazar Active Galactic Nucleus PKS 0521-36

Long-term γ-ray variability of a non-blazar Active Galactic Nucleus PKS 0521-36 is investigated by using Fermi Large Area Telescope (Fermi-LAT) pass 8 data covering from 2008 August to 2021 March. The results show that the histogram of the γ-ray fluxes follows a log-normal distribution. Interestingly, in the analysis of ~5.8 yr (from MJD 56317-58447) LAT data between two outbursts (occurring during 2012 October and 2019 May respectively), a quasi-periodic oscillation (QPO) with a period of ~1.1 yr (~5σ of significance) is found in the Lomb-Scargle Periodogram (LSP), the Weighted Wavelet Z-transform, and the REDFIT results. This quasiperiodic signal also appears in the results of Gaussian process modeling the light curve. Therefore, the robustness of the QPO is examined by four different methods. This is the first γ-ray QPO found in a mildly beamed jet. Our results imply that the γ-ray outbursts play an important role in the formation of the γ-ray QPO.

Keywords: active galactic nuclei; gamma-rays; time series analysis; period search; jets
The Stability of Some Galaxy Disks is Still Perplexing

The problem of how some disk galaxies avoid forming bars remains unsolved. Many galaxy models having reasonable properties continue to manifest vigorous instabilities that rapidly form strong bars and no widely accepted idea has yet been advanced to account for how some disk galaxies manage to avoid this instability. It is encouraging that not all galaxies formed in recent cosmological simulations possess bars, but the dynamical explanation for this result is unclear. The unstable mode that creates a bar is understood as a standing wave in a cavity that reflects off the disk center and the corotation radius, with amplification at corotation. Here we use simulations to address one further idea that may inhibit the feedback loop and therefore contribute to stability, which is to make the disk center dynamically hot and/or to taper away mass from the inner disk, which could be masked by a bulge. Unfortunately, we find that neither strategy makes much difference to the global stability of the disk in the models we have tried. While deep density cutouts do indeed prevent feedback through the center, they still reflect incoming waves and thereby provoke a slightly different instability that again leads to a strong bar.

Keywords: spiral galaxies; galaxy structure; galaxy dynamics; galaxy evolution
Anomalous Response of Mercury's Magnetosphere to Solar Wind Compression: Comparison to Earth

Magnetic field intensity increases when solar wind compresses a planet's magnetosphere. The compression can be measured using the ratio of compressed magnetic fields to purely dipolar magnetic fields just inside the magnetopause. For Earth, the ratio is proportional to the subsolar standoff distance of the magnetopause. Data from in-orbit observations by the MESSENGER spacecraft indicate an opposite ratio for Mercury; the compression ratio is inversely proportional to the subsolar standoff distance. The additional magnetic fields induced by currents at the top of Mercury's core enhance the total magnetic field strength. We also evaluated differences in the subsolar standoff of Mercury's magnetopause according to the north-south polarity of the interplanetary magnetic field (IMF). Previous studies have not identified meaningful differences in subsolar standoff distance between those in northward versus southward IMF polarities for Mercury; however, we found that the difference is statistically significant at a large IMF B Z (15-20 nT). The magnetic reconnection that occurs behind the cusp for a large northward IMF transfers the magnetic flux to the dayside and increases the subsolar standoff distance. The eroded magnetic flux for a large southward IMF is compensated by the induced magnetic fields.

Keywords: mercury (planet); planetary magnetospheres; planetary science; interplanetary magnetic fields; solar-planetary interactions; space plasmas; solar wind
The Coma Dust of Comet C/2013 US10 (Catalina): A Window into Carbon in the Solar System

Comet C/2013 US10 (Catalina) was a dynamically new Oort cloud comet whose apparition presented a favorable geometry for observations near close-Earth approach (≃0.93 au) at heliocentric distances ≲2 au when insolation and sublimation of volatiles drive maximum activity. Here we present mid-infrared 6.0 ≲ λ(μm) ≲ 40 spectrophotometric observations at two temporal epochs from NASA's Stratospheric Observatory for Infrared Astronomy and the NASA Infrared Telescope Facility that yield an inventory of the refractory materials and their physical characteristics through thermal modeling analysis. The grain composition is dominated by dark dust grains (modeled as amorphous carbon) with a silicate-to-carbon ratio ≲0.9, little crystalline stoichiometry (no distinct 11.2 μm feature attributed to Mg-rich crystalline olivine), and the submicron grain-size distribution peaking at ≃0.6 μm. The 10 μm silicate feature was weak, ≈12.8% ± 0.1% above the local continuum, and the bolometric grain albedo was low (≲14%). Comet C/2013 US10 (Catalina) is a carbon-rich object. This material, which is well represented by the optical constants of amorphous carbon, is similar to the material that darkens and reddens the surface of comet 67P/Churyumov-Gerasimenko. We argue this material is endemic to the nuclei of comets, synthesizing results from the study of Stardust samples, interplanetary dust particle investigations, and micrometeoritic analyses. The atomic carbon-to-silicate ratio of comet C/2013 US10 (Catalina) and other comets joins a growing body of evidence suggesting the existence of a C/Si gradient in the primitive solar system, providing new insight into planetesimal formation and the distribution of isotopic and compositional gradients extant today.

Keywords: long period comets; coma dust; interplanetary dust; astrophysical dust processes; near infrared astronomy
Observational Evidence Points at AGB Stars as Possible Progenitors of CEMP-s and CEMP-r/s Stars

The origin of enhanced abundance of heavy elements observed in the surface chemical composition of carbon-enhanced metal-poor (CEMP) stars still remains poorly understood. Here, we present detailed abundance analysis of seven CEMP stars based on high-resolution (R ~ 50,000) spectra that reveal enough evidence of asymptotic giant branch (AGB) stars being possible progenitors for these objects. For the objects HE 0110-0406, HE 1425-2052, and HE 1428-1950, we present for the first time a detailed abundance analysis. Our sample is found to consist of one metal-poor ([Fe/H] < -1.0) and six very metal-poor ([Fe/H] < -2.0) stars with enhanced carbon and neutron-capture elements. We have critically analyzed the observed abundance ratios of [O/Fe], [Sr/Ba], and [hs/ls] and examined the possibility of AGB stars being possible progenitors. The abundance of oxygen estimated in the program stars is characteristic of AGB progenitors except for HE 1429-0551 and HE 1447+0102. The estimated values of [Sr/Ba] and [hs/ls] ratios also support AGB stars as possible progenitors. The locations of the program stars in the absolute carbon abundance A(C) versus [Fe/H] diagram, along with the Group I objects, hint at the binary nature of the object. We have studied the chemical enrichment histories of the program stars based on abundance ratios [Mg/C], [Sc/Mn], and [C/Cr]. Using [C/N] and 12C/13C ratios, we have examined whether any internal mixing had modified their surface chemical compositions. Kinematic analysis shows that the objects HE 0110-0406 and HE 1447+0102 are thick-disk objects and the remaining five objects belong to the halo population of the Galaxy. * Based on data collected at Himalayan Chandra Telescope, IAO, Hanle, India, and at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. The Subaru data are retrieved from the JVO portal (http://jvo.nao.ac.jp/portal/v2/) operated by the NAOJ.

Keywords: population ii stars
Scatter Analysis along the Multidimensional Radius-Luminosity Relations for Reverberation-mapped Mg II Sources

The usage of the radius-luminosity (R-L) relation for the determination of black hole masses across the cosmic history, as well as its application for cosmological studies, motivates us to analyze its scatter, which has recently increased significantly for both the optical (Hβ) and UV (Mg II) lines. To this purpose, we determined the scatter along the R-L relation for an up-to-date reverberation-mapped Mg II sample. Studying linear combinations of the luminosity at 3000 Å with independent parameters such as the FWHM, the UV Fe II strength (RFe II), and the fractional variability (Fvar) for the whole sample, we get only a small decrease in the scatter ( ${\sigma }_{\mathrm{rms}}=0.29\,-0.30$ dex). Linear combinations with the dimensionless accretion rate ( $\dot{\,{ \mathcal M }}$ ) and the Eddington ratio lead to significant reductions of the scatter ( ${\sigma }_{\mathrm{rms}}\sim 0.1$ dex), albeit both suffering from the interdependency on the observed time delay. After the division into two subsamples considering the median value of the $\dot{\,{ \mathcal M }}$ in the full sample, we find that the scatter decreases significantly for the highly accreting subsample. In particular, the smallest scatter of ${\sigma }_{\mathrm{rms}}=0.17$ dex is associated with the independent parameter RFe II, followed by the combination with Fvar with ${\sigma }_{\mathrm{rms}}=0.19$ dex. Both of these independent observationally inferred parameters are in turn correlated with $\dot{{ \mathcal M }}$ and ${L}_{\mathrm{bol}}/{L}_{\mathrm{Edd}}$ . These results suggest that the large scatter along the R-L relation is driven mainly by the accretion rate intensity.

Keywords: active galaxies; supermassive black holes
Extreme Red-wing Enhancements of UV Lines during the 2022 March 30 X1.3 Solar Flare

Here, we present the study of a compact emission source during an X1.3 flare on 2022 March 30. Within a ~41 s period (17:34:48 UT to 17:35:29 UT), Interface Region Imaging Spectrograph observations show spectral lines of Mg II, C II, and Si IV with extremely broadened, asymmetric red wings. This source of interest (SOI) is compact, ~1.″6, and is located in the wake of a passing ribbon. Two methods were applied to measure the Doppler velocities associated with these red wings: spectral moments and multi-Gaussian fits. The spectral-moments method considers the averaged shift of the lines, which are 85, 125, and 115 km s-1 for the Mg II, C II, and Si IV lines respectively. The red-most Gaussian fit suggests a Doppler velocity up to ~160 km s-1 in all of the three lines. Downward mass motions with such high speeds are very atypical, with most chromospheric downflows in flares on the order 10-100 km s-1. Furthermore, extreme-UV (EUV) emission is strong within flaring loops connecting two flare ribbons located mainly to the east of the central flare region. The EUV loops that connect the SOI and its counterpart source in the opposite field are much less brightened, indicating that the density and/or temperature is comparatively low. These observations suggest a very fast downflowing plasma in the transition region and upper chromosphere, which decelerates rapidly since there is no equivalently strong shift of the O I chromospheric lines. This unusual observation presents a challenge that models of the solar atmosphere's response to flares must be able to explain.

Keywords: solar flare spectra; solar flares; active solar chromosphere; solar chromosphere; solar transition region
The Mass Distribution of Neutron Stars in Gravitational-wave Binaries

The discovery of two neutron star-black hole coalescences by LIGO and Virgo brings the total number of likely neutron stars observed in gravitational waves to six. We perform the first inference of the mass distribution of this extragalactic population of neutron stars. In contrast to the bimodal Galactic population detected primarily as radio pulsars, the masses of neutron stars in gravitational-wave binaries are thus far consistent with a uniform distribution, with a greater prevalence of high-mass neutron stars. The maximum mass in the gravitational-wave population agrees with that inferred from the neutron stars in our Galaxy and with expectations from dense matter.

Keywords: neutron stars; gravitational waves; compact objects; bayesian statistics
Abundance Ratios of OH/CO and HCO+/CO as Probes of the Cosmic-Ray Ionization Rate in Diffuse Clouds

The cosmic-ray ionization rate (CRIR, ζ 2) is one of the key parameters controlling the formation and destruction of various molecules in molecular clouds. However, the current most commonly used CRIR tracers, such as ${{\rm{H}}}_{3}^{+}$ , OH+, and H2O+, are hard to detect and require the presence of background massive stars for absorption measurements. In this work, we propose an alternative method to infer the CRIR in diffuse clouds using the abundance ratios of OH/CO and HCO+/CO. We have analyzed the response of chemical abundances of CO, OH, and HCO+ on various environmental parameters of the interstellar medium in diffuse clouds and found that their abundances are proportional to ζ 2. Our analytic expressions give an excellent calculation of the abundance of OH for ζ 2 ≤ 10-15 s-1, which are potentially useful for modeling chemistry in hydrodynamical simulations. The abundances of OH and HCO+ were found to monotonically decrease with increasing density, while the CO abundance shows the opposite trend. With high-sensitivity absorption transitions of both CO (1-0) and (2-1) lines from Atacama Large Millimeter/submillimeter Array, we have derived the H2 number densities ( ${n}_{{{\rm{H}}}_{2}}$ ) toward 4 lines of sight; assuming a kinetic temperature of T k = 50 K, we find a range of (0.14 ± 0.03-1.2 ± 0.1) × 102 cm-3. By comparing the observed and modeled HCO+/CO ratios, we find that ζ 2 in our diffuse gas sample is in the range of ${1.0}_{-1.0}^{+14.8}$ × 10 ${}^{-16}\mbox{--}{2.5}_{-2.4}^{+1.4}$ × 10-15 s-1. This is ~2 times higher than the average value measured at higher extinction, supporting an attenuation of CRs as suggested by theoretical models.

Keywords: interstellar absorption; interstellar medium; interstellar molecules; interstellar abundances; molecular clouds; chemical abundances