adsabs/SciX_UAT_keywords huggingface dataset:
Reliable Identification of Binary Supermassive Black Holes from Rubin Observatory Time-domain Monitoring

Periodic signatures in time-domain observations of quasars have been used to search for binary supermassive black holes (SMBHs). These searches, across existing time-domain surveys, have produced several hundred candidates. The general stochastic variability of quasars, however, can masquerade as a false-positive periodic signal, especially when monitoring cadence and duration are limited. In this work, we predict the detectability of binary SMBHs in the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST). We apply computationally inexpensive sinusoidal curve fits to millions of simulated LSST Deep Drilling Field light curves of both single, isolated quasars and binary quasars. The period and phase of simulated binary signals can generally be disentangled from quasar variability. Binary amplitude is overestimated and poorly recovered for two-thirds of potential binaries due to quasar accretion variability. Quasars with strong intrinsic variability can obscure a binary signal too much for recovery. We also find that the most luminous quasars mimic current binary candidate light curves and their properties: The false-positive rates are 60% for these quasars. The reliable recovery of binary period and phase for a wide range of input binary LSST light curves is promising for multi-messenger characterization of binary SMBHs. However, pure electromagnetic detections of binaries using photometric periodicity with amplitude greater than 0.1 mag will result in samples that are overwhelmed by false positives. This paper represents an important and computationally inexpensive way forward for understanding the true and false-positive rates for binary candidates identified by Rubin.

Keywords: quasars; gravitational wave sources; surveys; astronomy data analysis; supermassive black holes
Contrast and Temperature Dependence of Multi-epoch High-resolution Cross-correlation Exoplanet Spectroscopy

While high-resolution cross-correlation spectroscopy (HRCCS) techniques have proven effective at characterizing the atmospheres of transiting and nontransiting hot Jupiters, the limitations of these techniques are not well understood. We present a series of simulations of one HRCCS technique, which combines the cross-correlation functions from multiple epochs, to place temperature and contrast limits on the accessible exoplanet population for the first time. We find that planets approximately Saturn-sized and larger within ∼0.2 au of a Sun-like star are likely to be detectable with current instrumentation in the L band, a significant expansion compared with the previously studied population. Cooler (Teq ≤ 1000 K) exoplanets are more detectable than suggested by their photometric contrast alone as a result of chemical changes that increase spectroscopic contrast. The L-band CH4 spectrum of cooler exoplanets enables robust constraints on the atmospheric C/O ratio at Teq ∼ 900 K, which have proven difficult to obtain for hot Jupiters. These results suggest that the multi-epoch approach to HRCCS can detect and characterize exoplanet atmospheres throughout the inner regions of Sun-like systems with existing high-resolution spectrographs. We find that many epochs of modest signal-to-noise ratio (S/Nepoch ∼ 1500) yield the clearest detections and constraints on C/O, emphasizing the need for high-precision near-infrared telluric correction with short integration times.

Keywords: exoplanet atmospheres; exoplanet detection methods; hot jupiters
Study of the Blazhko Type RRc stars in the Stripe 82 Region Using SDSS and ZTF

RR Lyrae stars (RRLs) are pulsating stars, many of which also show a long-term variation called the Blazhko effect which is a modulation of amplitude and phase of the lightcurve. In this work, we searched for the incidence rate of the Blazhko effect in the first-overtone pulsating RR Lyrae (RRc) stars of the Galactic halo. The focus was on the Stripe 82 region in the Galactic halo which was studied by Sesar et al. using the Sloan Digital Sky Survey (SDSS) data. In their work, 104 RRLs were classified as RRc type. We combined their SDSS light curves with Zwicky Transient Facility (ZTF) data, and used them to document the Blazhko properties of these RRc stars. Our analysis showed that among the 104 RRc stars, eight were rather RRd stars, and were excluded from the study. Out of the remaining 96, 34 were Blazhko type, 62 were non-Blazhko type, giving the incidence rate of 35.42% for Blazhko RRc stars. The shortest Blazhko period found was 12.808 ± 0.001 days for SDSS 747380, while the longest was 3088 ± 126 days for SDSS 3585856. Combining SDSS and ZTF data sets increased the probability of detecting the small variations due to the Blazhko effect, and thus provided a unique opportunity to find longer Blazhko periods. We found that 85% of RRc stars had the Blazhko period longer than 200 days.

Keywords: rr lyrae variable stars; rrc variable stars; wide-field telescopes
Surviving Tidal Tails Around the Milky Way Bulge Globular Cluster NGC 6355

We present results of the analysis of a set of images obtained in the field of the Milky Way bulge globular cluster NGC 6355 using the Dark Energy Camera, which is attached to the 4 m Blanco telescope of the Cerro-Tololo Interamerican Observatory. We dealt with a heavy differential absorption across the observed field, a crowded field star population, and the superposition of field stars on to the cluster color–magnitude diagram main features to produce an intrinsic cluster stars density map. The resulting stellar density map reveals the presence of an extended envelope, a tidal tail, and scattered debris; the tidal tails pointing toward the Milky Way center. Such extra-tidal overdensities, detected above the mean star field density, resulted to be between four and six times larger that the local star field density fluctuation. They have also been recently generated by two independent studies which performed numerical simulations of synthetic tidal tails of Milky Way globular clusters. These results contrast with previous theoretical speculations about the possibility to detect tidal tails of globular clusters with chaotic orbits because they would be washed out after they were generated.

Keywords: globular star clusters; astronomical techniques; galactic bulge
3He-rich Solar Energetic Particle Observations at the Parker Solar Probe and near Earth

The Integrated Science Investigation of the Sun (IS⊙IS) instrument suite on the Parker Solar Probe (PSP) spacecraft is making in situ observations of energetic ions and electrons closer to the Sun than any previous mission. Using data collected during its first two orbits, which reached perihelion distances of 0.17 au, we have searched for ${}^{3}\mathrm{He}$ -rich solar energetic particle (SEP) events under very quiet solar minimum conditions. On 2019-110-111 (April 20-21), ${}^{3}\mathrm{He}$ -rich SEPs were observed at energies near 1 MeV nucleon-1 in association with energetic protons, heavy ions, and electrons. This activity was also detected by the Ultra-Low-Energy Isotope Spectrometer and the Electron, Proton, and Alpha Monitor instruments on the Advanced Composition Explorer (ACE) spacecraft located near Earth, 0.99 au from the Sun. At that time, PSP and ACE were both magnetically connected to locations near the west limb of the Sun. Remote sensing measurements showed the presence of type III radio bursts and also helical jets from this region of the Sun. This combination of observations is commonly associated with ${}^{3}\mathrm{He}$ -rich SEP acceleration on the Sun. AR 12738, which was located at Carrington coordinates from which numerous X-ray flares were observed over a period of more than 6 months, was identified as the source of the ${}^{3}\mathrm{He}$ -rich events. This region was also the source of several other SEP events detected at PSP or ACE. Aside from the period in 2019 April, IS⊙IS did not observe any other ${}^{3}\mathrm{He}$ -rich SEPs during orbits 1 and 2.

Keywords: solar energetic particles; solar activity; solar x-ray flares
Ion Kinetics of Plasma Interchange Reconnection in the Lower Solar Corona

The exploration of the inner heliosphere by the Parker Solar Probe has revealed a highly structured solar wind with ubiquitous deflections from the Parker spiral, known as switchbacks. Interchange reconnection (IR) may play an important role in generating these switchbacks, by forming unstable particle distributions that generate wave activity that in turn may evolve to such structures. IR occurs in very low-beta plasmas and in the presence of strong guiding fields. Although IR is unlikely to release enough energy to provide an important contribution to the heating and acceleration of the solar wind, it affects the way the solar wind is connected to its sources, connecting open field lines to regions of closed fields. This "switching on" provides a mechanism by which the plasma near coronal hole boundaries can mix with that trapped inside the closed loops. This mixing can lead to a new energy balance. It may significantly change the characteristics of the solar wind because this plasma is already preheated and can potentially have quite different density and particle distributions. It not only replenishes the solar wind, but also affects the electric field, which in turn affects the energy balance. This interpenetration is manifested by the formation of a bimodal ion distribution, with a core and a beam-like population. Such distributions are indeed frequently observed by the Parker Solar Probe. Here we provide a first step toward assessing the role of such processes in accelerating and heating the solar wind.

Keywords: solar wind; solar coronal heating; solar magnetic reconnection; solar corona
Influence of Irradiation-driven Winds on the Evolution of Intermediate-mass Black Hole X-ray Binaries

In young dense clusters, an intermediate-mass black hole (IMBH) may get a companion star via exchange encounters or tidal capture and then evolve toward the IMBH X-ray binary by the Roche lobe overflow. It is generally thought that IMBH X-ray binaries are potential ultraluminous X-ray sources (ULXs); hence, their evolution is very significant. However, the irradiation-driven winds by the strong X-ray flux from the accretion disks around the IMBHs play an important role in determining the evolution of IMBH X-ray binaries and should be considered in the detailed binary evolution simulation. Employing the models with the MESA code, we focus on the influence of irradiation-driven winds on the evolution of IMBH X-ray binaries. Our simulations indicate that a high wind-driving efficiency (f = 0.01 for Z = 0.02, and f = 0.002 for Z = 0.001) substantially shortens the duration in the ULX stage of IMBH X-ray binaries with an intermediate-mass (5 M⊙) donor star. However, this effect can be ignored for high-mass (10 M⊙) donor stars. The irradiation effect (f = 0.01 or 0.002) markedly shrinks the initial parameter space of IMBH binaries evolving toward ULXs with high luminosity (LX > 1040 erg s-1) and hyperluminous X-ray sources in the donor-star mass versus orbital period diagram. Furthermore, the irradiation effect results in an efficient angular momentum loss, yielding to IMBH X-ray binaries with relatively close orbits. In our simulated parameter space, about 1% of IMBH binaries would evolve toward compact X-ray sources owing to short initial orbital periods, some of which might be detected as low-frequency gravitational-wave sources.

Keywords: black holes; gravitational waves; x-ray binary stars; stellar evolution; galaxy clusters
Estimating the Ultraviolet Emission of M Dwarfs with Exoplanets from Ca II and Hα

M dwarf stars are excellent candidates around which to search for exoplanets, including temperate, Earth-sized planets. To evaluate the photochemistry of the planetary atmosphere, it is essential to characterize the UV spectral energy distribution of the planet's host star. This wavelength regime is important because molecules in the planetary atmosphere such as oxygen and ozone have highly wavelength-dependent absorption cross sections that peak in the UV (900-3200 Å). We seek to provide a broadly applicable method of estimating the UV emission of an M dwarf, without direct UV data, by identifying a relationship between noncontemporaneous optical and UV observations. Our work uses the largest sample of M dwarf star far- and near-UV observations yet assembled. We evaluate three commonly observed optical chromospheric activity indices—Hα equivalent widths and log10 LHα/Lbol, and the Mount Wilson Ca II H&K S and ${R}_{\mathrm{HK}}^{{\prime} }$ indices—using optical spectra from the HARPS, UVES, and HIRES archives and new HIRES spectra. Archival and new Hubble Space Telescope COS and STIS spectra are used to measure line fluxes for the brightest chromospheric and transition region emission lines between 1200 and 2800 Å. Our results show a correlation between UV emission-line luminosity normalized to the stellar bolometric luminosity and Ca II ${R}_{\mathrm{HK}}^{{\prime} }$ with standard deviations of 0.31-0.61 dex (factors of ∼2-4) about the best-fit lines. We also find correlations between normalized UV line luminosity and Hα log10 LHα/Lbol and the S index. These relationships allow one to estimate the average UV emission from M0 to M9 dwarfs when UV data are not available.

Keywords: exoplanet atmospheres; m dwarf stars; stellar chromospheres; hubble space telescope; ultraviolet observatories; optical observatories; stellar activity
Early Results from the HUMDRUM Survey: A Small, Earth-mass Planet Orbits TOI-1450A

M-dwarf stars provide us with an ideal opportunity to study nearby small planets. The HUnting for M Dwarf Rocky planets Using MAROON-X (HUMDRUM) survey uses the MAROON-X spectrograph, which is ideally suited to studying these stars, to measure precise masses of a volume-limited (<30 pc) sample of transiting M-dwarf planets. TOI-1450 is a nearby (22.5 pc) binary system containing a M3 dwarf with a roughly 3000 K companion. Its primary star, TOI-1450A, was identified by the Transiting Exoplanet Survey Satellite (TESS) to have a 2.04 days transit signal, and is included in the HUMDRUM sample. In this paper, we present MAROON-X radial velocities (RVs) which confirm the planetary nature of this signal and measure its mass at nearly 10% precision. The 2.04 days planet, TOI-1450A b, has R b = 1.13 ± 0.04 R ⊕ and M b = 1.26 ± 0.13 M ⊕. It is the second-lowest-mass transiting planet with a high-precision RV mass measurement. With this mass and radius, the planet's mean density is compatible with an Earth-like composition. Given its short orbital period and slightly sub-Earth density, it may be amenable to JWST follow-up to test whether the planet has retained an atmosphere despite extreme heating from the nearby star. We also discover a nontransiting planet in the system with a period of 5.07 days and a . We also find a 2.01 days signal present in the systems's TESS photometry that likely corresponds to the rotation period of TOI-1450A's binary companion, TOI-1450B. TOI-1450A, meanwhile, appears to have a rotation period of approximately 40 days, which is in line with our expectations for a mid-M dwarf.

Keywords: m dwarf stars; extrasolar rocky planets
Spectral Typing with Artificial Intelligence: Classifying Low-resolution Near-infrared Spectra of Standard M/L/T Dwarfs

We investigate the application of supervised machine learning models to directly infer the spectral types of ultracool dwarfs (dwarf spectral types ≥M6) using binned fluxes as feature labels. We compare the ability of two machine learning frameworks, k-Nearest Neighbor (kNN) and Random Forest (RF), to classify low-resolution near-infrared spectra of M6 to T9 dwarfs (3100 K ≳ T eff ≳ 500 K). We used a synthetic training data set of 2400 spectra generated from 24 spectral type standards and validated our models on 315 spectra with previous literature classifications. Classification accuracies within ± 1 subtype were 98.4% ± 0.7% for the kNN model and 95.6% ± 1.2% for the RF model, indicating the kNN performs marginally better for spectral-type estimation. Future studies will explore a broader range of stellar properties such as metallicity, gravity, and cloud characteristics and additional machine learning models.

Keywords: stellar classification; random forests; t dwarfs; l dwarfs; m dwarf stars; brown dwarfs
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. VI. Insights from Radiative Transfer Modeling

We present Markov Chain Monte Carlo radiative transfer modeling of a joint ALMA 345 GHz and spectral energy distribution data set for a sample of 97 protostellar disks from the VLA and ALMA Nascent Disk and Multiplicity Survey of Orion Protostars. From this modeling, we derive disk and envelope properties for each protostar, allowing us to examine the bulk properties of a population of young protostars. We find that disks are small, with a median dust radius of ${29.4}_{-2.7}^{+4.1}$ au and a median dust mass of ${5.8}_{-2.7}^{+4.6}$ M ⊕. We find no statistically significant difference between most properties of Class 0, Class I, and flat-spectrum sources with the exception of envelope dust mass and inclination. The distinction between inclination is an indication that the Class 0/I/flat-spectrum system may be difficult to tie uniquely to the evolutionary state of protostars. When comparing with Class II disk dust masses in Taurus from similar radiative transfer modeling, we further find that the trend of disk dust mass decreasing from Class 0 to Class II disks is no longer present, though it remains unclear whether such a comparison is fair owing to differences in star-forming region and modeling techniques. Moreover, the disks we model are broadly gravitationally stable. Finally, we compare disk masses and radii with simulations of disk formation and find that magnetohydrodynamical effects may be important for reproducing the observed properties of disks.

Keywords: protostars; protoplanetary disks; star formation; planet formation
Constraining Hadron-quark Phase Transition Parameters within the Quark-mean-field Model Using Multimessenger Observations of Neutron Stars

We extend the quark mean-field (QMF) model for nuclear matter and study the possible presence of quark matter inside the cores of neutron stars. A sharp first-order hadron-quark phase transition is implemented combining the QMF for the hadronic phase with "constant-speed-of-sound" parameterization for the high-density quark phase. The interplay of the nuclear symmetry energy slope parameter, L, and the dimensionless phase transition parameters (the transition density ntrans/n0, the transition strength Δɛ/ɛtrans, and the sound speed squared in quark matter ${c}_{\mathrm{QM}}^{2}$ ) are then systematically explored for the hybrid star properties, especially the maximum mass Mmax and the radius and the tidal deformability of a typical 1.4 M⊙ star. We show the strong correlation between the symmetry energy slope L and the typical stellar radius R1.4, similar to that previously found for neutron stars without a phase transition. With the inclusion of phase transition, we obtain robust limits on the maximum mass (Mmax < 3.6 M⊙) and the radius of 1.4 M⊙ stars (R1.4 ≳ 9.6 km), and we find that a phase transition that is too weak (Δɛ/ɛtrans ≲ 0.2) taking place at low densities ≲1.3-1.5 n0 is strongly disfavored. We also demonstrate that future measurements of the radius and tidal deformability of ∼1.4 M⊙ stars, as well as the mass measurement of very massive pulsars, can help reveal the presence and amount of quark matter in compact objects.

Keywords: neutron star cores; neutron stars
Accretion-Induced Collapse of Neutron Stars in the Disks of Active Galactic Nuclei

The disks of active galactic nuclei (AGNs) have emerged as a rich environment for the evolution of stars and their compact remnants. The very dense medium favors rapid accretion, while torques and migration traps enhance binary formation and mergers. Both long and short gamma-ray bursts are hence expected. We show that AGN disks constitute an ideal environment for another interesting phenomenon: the accretion-induced collapse (AIC) of neutron stars (NSs) to black holes (BHs). Rapid accretion in the dense disks can cause NSs to grow to the point of exceeding the maximum mass allowed by their equation of state. General relativistic magnetohydrodynamical simulations have shown that electromagnetic signatures are expected if the NS is surrounded by a minidisk prior to collapse, which then rapidly accretes onto the BH, and/or if the NS is highly magnetized, from reconnection of the magnetosphere during collapse. Here we compute the rates of AICs and their locations within the disks for both isolated NSs and for (initially stable) NSs formed from NS-NS mergers. We find that the global AIC rates are ~0.07-20 Gpc-3 yr-1, and we discuss their observable prospects and signatures as they emerge from the dense disk environments.

Keywords: active galactic nuclei; neutron stars; gamma-ray bursts
Unveiling Shrouded Oceans on Temperate sub-Neptunes via Transit Signatures of Solubility Equilibria versus Gas Thermochemistry

The recent discovery and initial characterization of sub-Neptune-sized exoplanets that receive stellar irradiance of approximately Earth's raised the prospect of finding habitable planets in the coming decade, because some of these temperate planets may support liquid-water oceans if they do not have massive H2/He envelopes and are thus not too hot at the bottom of the envelopes. For planets larger than Earth, and especially planets in the 1.7-3.5 R⊕ population, the mass of the H2/He envelope is typically not sufficiently constrained to assess the potential habitability. Here we show that the solubility equilibria versus thermochemistry of carbon and nitrogen gases typically results in observable discriminators between small H2 atmospheres versus massive ones, because the condition to form a liquid-water ocean and that to achieve the thermochemical equilibrium are mutually exclusive. The dominant carbon and nitrogen gases are typically CH4 and NH3 due to thermochemical recycling in a massive atmosphere of a temperate planet, and those in a small atmosphere overlying a liquid-water ocean are most likely CO2 and N2, followed by CO and CH4 produced photochemically. NH3 is depleted in the small atmosphere by dissolution into the liquid-water ocean. These gases lead to distinctive features in the planet's transmission spectrum, and a moderate number of transit observations with the James Webb Space Telescope should tell apart a small atmosphere versus a massive one on planets like K2-18 b. This framework thus points to a way to use near-term facilities to constrain the atmospheric mass and habitability of temperate sub-Neptune exoplanets.

Keywords: exoplanet atmospheres; extrasolar rocky planets; extrasolar ice giants; habitable planets; ocean planets; transmission spectroscopy
Discovery of an Emission Nebula in Direction of γ Aql

An emission nebula has been discovered in close apparent proximity to γ Aql (aka Tarazed). The diameter of the nebula is about $27\buildrel{\,\prime}\over{.} 4$ and its center is about $7^{\prime} $ away from γ Aql, which is known to be an X-ray source. However, γ Aql is most likely not the ionization source of the nebula. To my knowledge, this emission nebula has not been previously reported in the literature or on the Internet.

Keywords: h ii regions; emission nebulae; nebulae; interstellar medium