adsabs/SciX_UAT_keywords huggingface dataset:
Estimation of the Flux at 1450 MHz of OB Stars for FAST and SKA

Radio observation is crucial to understanding the wind mechanism of OB stars but very scarce. This work estimates the flux at 1450 MHz (S 1.4GHz) of about 5000 OB stars identified by the LAMOST spectroscopic survey and confirmed by the Gaia astrometric as well as astrophysical measurements. The calculation is performed under the free-free emission mechanism for wind with the mass-loss rate derived from stellar parameters. The estimated S 1.4GHz distributes from 10-11 to 10-3 Jy with the peak at about 10-8 Jy. This implies that the complete SKA-II can detect more than half of them, and some tens of objects are detectable by FAST without considering source confusion. An array of FAST would increase the detectable sample by 2 orders of magnitude.

Keywords: ob stars; radio continuum emission; stellar winds; radio telescopes
Tracing the Evolution of SMBHs and Stellar Objects in Galaxy Mergers: A Multi-mass Direct N-body Model

By using direct N-body numerical simulations, we model the dynamical coevolution of two supermassive black holes (SMBHs) and the surrounding stars in merging galaxies. In order to investigate how different stellar components evolve during the merger, we generate evolved stellar distributions with an initial mass function. Special schemes have also been developed to deal with some rare but interesting events, such as the tidal disruption of main-sequence stars, plunging low-mass stars, white dwarfs, neutron stars and stellar-mass black holes, and the partial tidal disruption of red giants or asymptotic giant branch stars. Our results indicate that the formation of a bound SMBH binary will enhance the capture rates of stellar objects by SMBHs. Compared to the equal stellar mass model, the multi-mass model tends to result in a higher average mass of disrupted stars. Instead of being tidally disrupted by the SMBH, roughly half of the captured main-sequence stars will directly plunge into the SMBH because of their small stellar radii. Giant stars, on the other hand, can be stripped of their envelopes if they are close enough to the SMBH. Though most remnants of the giant stars can survive after the disruption, a small fraction still could plunge into the SMBH quickly or after many orbital periods. Our results also indicate significant mass segregation of compact stars at the beginning of the merger, and then this effect is destroyed as the two SMBHs form a bound binary.

Keywords: galaxy evolution; galaxy mergers; galaxy nuclei; galaxy dynamics; computational astronomy; gravitational wave sources
The Undiscovered Ultradiffuse Galaxies of the Local Group

Ultradiffuse galaxies (UDGs) are attractive candidates to probe cosmological models and test theories of galaxy formation at low masses; however, they are difficult to detect because of their low surface brightness. In the Local Group a handful of UDGs have been found to date, most of which are satellites of the Milky Way and M31, and only two are isolated galaxies. It is unclear whether so few UDGs are expected. We address this by studying the population of UDGs formed in hydrodynamic constrained simulations of the Local Group from the HESTIA suite. For a Local Group with a total enclosed mass M LG( < 2.5 Mpc) = 8 × 1012 M⊙, we predict that there are 12 ± 3 isolated UDGs (68% confidence) with stellar masses 106 ≤ M */M⊙ < 109, and effective radii R e ≥ 1.5 kpc, within 2.5 Mpc of the Local Group, of which ${2}_{-1}^{+2}$ (68% confidence) are detectable in the footprint of the Sloan Digital Sky Survey (SDSS). Accounting for survey incompleteness, we find that almost the entire population of UDGs in the Local Group field would be observable in a future all-sky survey with a depth similar to the SDSS, the Dark Energy Survey, or the Legacy Survey of Space and Time. Our results suggest that there is a population of UDGs in the Local Group awaiting discovery.

Keywords: dwarf galaxies; galaxy formation; galaxy interactions; local group; low surface brightness galaxies; luminosity function
TANSPEC: TIFR-ARIES Near-infrared Spectrometer

We present the design and performance of the TANSPEC, a medium-resolution 0.55-2.5 μm cryogenic spectrometer and imager, now in operation at the 3.6 m Devasthal Optical Telescope (DOT), Nainital, India. The TANSPEC provides three modes of operation, which include photometry with broad- and narrowband filters, spectroscopy with short slits of 20″ length and different widths (from 0.″5 to 4.″0) in cross-dispersed mode at a resolving power R of ~2750, and spectroscopy with long slits of 60″ length and different widths (from 0.″5 to 4.″0) in prism mode at a resolving power R of ~100-350. TANSPEC's imager mode provides a field of view of 60″ × 60″ with a plate scale of 0.″245 pixel-1 on the 3.6 m DOT. The TANSPEC was successfully commissioned during 2019 April-May, and the subsequent characterization and astronomical observations are presented here. The TANSPEC was made available to the worldwide astronomical community for science observations from 2020 October.

Keywords: spectrometers; direct imaging; near infrared astronomy; optical observation
Resolving the Circumstellar Environment of the Galactic B[e] Supergiant Star MWC 137.II. Nebular Kinematics and Stellar Variability

The Galactic B[e] supergiant MWC 137 is surrounded by a large-scale optical nebula. To shed light on the physical conditions and kinematics of the nebula, we analyze the optical forbidden emission lines [N II] λλ 6548,6583 and [S II] λλ 6716,6731 in long-slit spectra taken with ALFOSC at the Nordic Optical Telescope. The radial velocities display a complex behavior but, in general, the northern nebular features are predominantly approaching while the southern ones are mostly receding. The electron density shows strong variations across the nebula with values spreading from about zero to ~800 cm-3. Higher densities are found closer to MWC 137 and in regions of intense emission, whereas in regions with high radial velocities the density decreases significantly. We also observe the entire nebula in the two [S II] lines with the scanning Fabry-Perot interferometer attached to the 6 m telescope of the Special Astrophysical Observatory. These data reveal a new bow-shaped feature at P.A. = 225°-245° and a distance 80″ from MWC 137. A new Hα image has been taken with the Danish 1.54 m telescope on La Silla. No expansion or changes in the nebular morphology appear within 18.1 yr. We derive a mass of ${37}_{-5}^{+9}\,{M}_{\odot }$ and an age of 4.7 ± 0.8 Myr for MWC 137. Furthermore, we detect a period of 1.93 d in the time series photometry collected with the TESS satellite, which could suggest stellar pulsations. Other, low-frequency variability is seen as well. Whether these signals are caused by internal gravity waves in the early-type star or by variability in the wind and circumstellar matter currently cannot be distinguished. * Based on observations collected with (1) the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias, (2) the Danish 1.54 m telescope at La Silla, Chile, and (3) the 6 m telescope of the Special Astrophysical Observatory (SAO), Russia.

Keywords: circumstellar matter; early-type stars; massive stars; supergiant stars
Periodic Oscillations in LASCO Coronal Mass Ejection Speeds: Space Seismology

Coronal mass ejections (CMEs) are energetic eruptions of organized magnetic structures from the Sun. Therefore, the reconnection of the magnetic field during ejection can excite periodic speed oscillations of CMEs. A previous study showed that speed oscillations are frequently associated with CME propagation. The Solar and Heliospheric Observatory mission's white-light coronagraphs have observed about 30,000 CMEs from 1996 January to the end of 2019 December. This period of time covers two solar cycles (23 and 24). In the present study, the basic attributes of speed oscillations during this period of time were analyzed. We showed that the oscillation parameters (period and amplitude) significantly depend not only on the phase of a given solar cycle but also on the intensity of individual cycles as well. This reveals that the basic attributes of speed oscillation are closely related to the physical conditions prevailing inside the CMEs as well as in the interplanetary medium in which they propagate. Using this approximation, we estimated that, on average, the CME internal magnetic field varies from 18 up to 25 mG between minimum and maximum solar activity. The obtained results show that a detailed analysis of speed oscillations can be a very efficient tool for studying not only the physical properties of the ejections themselves but also the condition of the interplanetary medium in which they expand. This creates completely new perspectives for studying the physical parameters of CMEs shortly after their eruption in the Sun's environment (space seismology).

Keywords: the sun; solar activity; solar physics
Could Switchbacks Originate in the Lower Solar Atmosphere? I. Formation Mechanisms of Switchbacks

The recent rediscovery of magnetic field switchbacks or deflections embedded in the solar wind flow by the Parker Solar Probe mission lead to a huge interest in the modeling of the formation mechanisms and origin of these switchbacks. Several scenarios for their generation were put forth, ranging from lower solar atmospheric origins by reconnection, to being a manifestation of turbulence in the solar wind, and so on. Here we study some potential formation mechanisms of magnetic switchbacks in the lower solar atmosphere, using three-dimensional magnetohydrodynamic (MHD) numerical simulations. The model is that of an intense flux tube in an open magnetic field region, aiming to represent a magnetic bright point opening up to an open coronal magnetic field structure, e.g., a coronal hole. The model is driven with different plasma flows in the photosphere, such as a fast up-shooting jet, as well as shearing flows generated by vortex motions or torsional oscillations. In all scenarios considered, we witness the formation of magnetic switchbacks in regions corresponding to chromospheric heights. Therefore, photospheric plasma flows around the foot-points of intense flux tubes appear to be suitable drivers for the formation of magnetic switchbacks in the lower solar atmosphere. Nevertheless, these switchbacks do not appear to be able to enter the coronal heights of the simulation in the present model. In conclusion, based on the presented simulations, switchbacks measured in the solar wind are unlikely to originate from photospheric or chromospheric dynamics.

Keywords: solar atmosphere; solar physics; magnetohydrodynamics
Similarity between Compact Extremely Red Objects Discovered with JWST in Cosmic Dawn and Blue-excess Dust-obscured Galaxies Known in Cosmic Noon

Spatially compact objects with extremely red color in the rest-frame optical to near-infrared (0.4-1 μm) and blue color in the rest-frame ultraviolet (UV; 0.2-0.4 μm) have been discovered at 5 < z < 9 using the James Webb Space Telescope (JWST). These extremely red objects (JWST-EROs) exhibit spectral energy distributions (SEDs) that are difficult to explain using a single component of either star-forming galaxies or quasars, leading to two-component models in which the blue UV and extremely red optical are explained using less-dusty and dusty spectra of galaxies or quasars, respectively. Here, we report the remarkable similarity in SEDs between JWST-EROs and blue-excess dust-obscured galaxies (BluDOGs) identified at 2 < z < 3. BluDOGs are a population of active galactic nuclei (AGNs) with black hole masses of ~108-9 M ⊙, which are 1 order of magnitude larger than those in some JWST-EROs. The Eddington ratios of BluDOGs are 1 or higher, whereas those of JWST-EROs are in the range of 0.1-1. Therefore, JWST-EROs are less massive, less active, and more common counterparts in higher-z of BluDOGs in cosmic noon. Conversely, JWST-EROs have a significantly higher fraction of those with blue excess than DOGs. We present the average UV spectra of BluDOGs as a comparison to JWST-EROs and discuss a coherent evolutionary scenario for dusty AGN populations.

Keywords: active galactic nuclei; galaxy evolution
The Second Plateau in X-Ray Afterglow Providing Additional Evidence for Rapidly Spinning Magnetars as the GRB Central Engine

Evidence for the central engine of gamma-ray bursts (GRBs) has been collected in the Neil Gehrels Swift data. For instance, some GRBs show an internal X-ray plateau followed by very steep decay, which is difficult interpret within the framework of a black hole (BH) central engine, but is consistent within a rapidly spinning magnetar engine picture. The very steep decay at the end of the plateau suggests a sudden cessation of the central engine, which is explained as the collapse of a supramassive magnetar into a BH when it spins down. Here we propose that some additional evidence, such as a second X-ray plateau feature, would show up if the fallback accretion could activate the newborn BH and sufficient energy could be transferred from the newborn BH to the GRB blast wave. With a systematic data analysis for all long GRBs, we find three candidates in the Swift sample, I.e., GRBs 070802, 090111, and 120213A, whose X-ray afterglow lightcurves contain two plateaus, with the first one being an internal plateau. We find that in a fairly loose and reasonable parameter space, the second X-ray plateau data for all 3 GRBs could be interpreted with our proposed model. Future observations are likely to discover similar events, which could offer more information on the properties of the magnetar, as well as the newborn BH.

Keywords: gamma-ray bursts
DELVE 6: An Ancient, Ultra-faint Star Cluster on the Outskirts of the Magellanic Clouds

We present the discovery of DELVE 6, an ultra-faint stellar system identified in the second data release of the DECam Local Volume Exploration (DELVE) survey. Based on a maximum-likelihood fit to its structure and stellar population, we find that DELVE 6 is an old (τ > 9.8 Gyr at 95% confidence) and metal-poor ([Fe/H] < -1.17 dex at 95% confidence) stellar system with an absolute magnitude of ${M}_{V}=-{1.5}_{-0.6}^{+0.4}$ mag and an azimuthally averaged half-light radius of ${r}_{1/2}={10}_{-3}^{+4}$ pc. These properties are consistent with the population of ultra-faint star clusters uncovered by recent surveys. Interestingly, DELVE 6 is located at an angular separation of ~10° from the center of the Small Magellanic Cloud (SMC), corresponding to a 3D physical separation of ~20 kpc given the system's observed distance (D ⊙ = 80 kpc). This also places the system ~35 kpc from the center of the Large Magellanic Cloud (LMC), lying within recent constraints on the size of the LMC's dark matter halo. We tentatively measure the proper motion of DELVE 6 using data from Gaia, which we find supports a potential association between the system and the LMC/SMC. Although future kinematic measurements will be necessary to determine its origins, we highlight that DELVE 6 may represent only the second or third ancient (τ > 9 Gyr) star cluster associated with the SMC, or one of fewer than two dozen ancient clusters associated with the LMC. Nonetheless, we cannot currently rule out the possibility that the system is a distant Milky Way halo star cluster.

Keywords: star clusters; magellanic clouds; sky surveys
Characterizing Undetected Stellar Companions with Combined Data Sets

Binaries play a critical role in the formation, evolution, and fundamental properties of planets, stars, and stellar associations. Observational studies in these areas often include a mix of observations aimed at detecting or ruling out the presence of stellar companions. Rarely can nondetections rule out all possible binary configurations. Here we present MOLUSC, our framework for constraining the range of properties of unseen companions using astrometric, imaging, and velocity information. We showcase the use of MOLUSC on a number of systems, ruling out stellar false positives in the signals of HIP 67522b and DS Tuc Ab. We also demonstrate how MOLUSC could be used to predict the number of missing companions in a stellar sample using the ZEIT sample of young planet hosts. Although our results are not significant, with a larger sample, MOLUSC could be used to see if close-in planets are less common in young binary systems, as is seen for their older counterparts.

Keywords: binary stars; astronomy software; radial velocity; spectroscopic binary stars; astrometric binary stars
Searches for Neutrinos from Large High Altitude Air Shower Observatory Ultra-high-energy γ-Ray Sources Using the IceCube Neutrino Observatory

Galactic PeV cosmic-ray accelerators (PeVatrons) are Galactic sources theorized to accelerate cosmic rays up to PeV in energy. The accelerated cosmic rays are expected to interact hadronically with nearby ambient gas or the interstellar medium, resulting in γ-rays and neutrinos. Recently, the Large High Altitude Air Shower Observatory (LHAASO) identified 12 γ-ray sources with emissions above 100 TeV, making them candidates for PeVatrons. While at these high energies the Klein-Nishina effect exponentially suppresses leptonic emission from Galactic sources, evidence for neutrino emission would unequivocally confirm hadronic acceleration. Here, we present the results of a search for neutrinos from these γ-ray sources and stacking searches testing for excess neutrino emission from all 12 sources as well as their subcatalogs of supernova remnants and pulsar wind nebulae with 11 yr of track events from the IceCube Neutrino Observatory. No significant emissions were found. Based on the resulting limits, we place constraints on the fraction of γ-ray flux originating from the hadronic processes in the Crab Nebula and LHAASO J2226+6057.

Keywords: neutrino astronomy; high energy astrophysics; galactic cosmic rays
Exploring the Individual Pulse Behavior of Pulsar J1701-3726 with Parkes

We have carried out a detailed study of polarimetric individual pulse emission from the pulsar J1701-3726 (B1658-37), observed at 1369 MHz using the Parkes 64 m radio telescope. The single-pulse sequences reveal the presence of the three major emission phenomena of pulse nulling, mode changing, and subpulse drifting. Trimodal distribution of the pulse energy is present, implying one population of nulls and two others of emission in the phase window. The mean flux density of the normal mode is almost two times that of the abnormal mode. Our data show that, for PSR J1701-3726, 64% of the time was spent in the normal mode and 12% was in the abnormal mode. The single pulses show the presence of two distinct periodic modulations using a fluctuation spectral analysis. About 24% of the nulls are found to create alternating bunches of nulls and bursts in a quasiperiodic manner with a longer periodicity of 48 ± 4 rotational periods. Additionally, the pulsar presents a steady even-odd modulated feature with a stationary longitude within the pulse window. The ramifications for constraining the viewing geometry and understanding the radio emission mechanisms are discussed.

Keywords: radio pulsars
Introducing the Condor Array Telescope. I. Motivation, Configuration, and Performance

The "Condor Array Telescope" or "Condor" is a high-performance "array telescope" comprised of six apochromatic refracting telescopes of objective diameter 180 mm, each equipped with a large-format, very low-read-noise (≈1.2 e-), very rapid-read-time (<1 s) CMOS camera. Condor is located at a very dark astronomical site in the southwest corner of New Mexico, at the Dark Sky New Mexico observatory near Animas, roughly midway between (and more than 150 km from either) Tucson and El Paso. Condor enjoys a wide field of view (2.29 × 1.53 deg2 or 3.50 deg2), is optimized for measuring both point sources and extended, very low-surface-brightness features, and for broad-band images can operate at a cadence of 60 s (or even less) while remaining sky-noise limited with a duty cycle near 100%. In its normal mode of operation, Condor obtains broad-band exposures of exposure time 60 s over dwell times spanning dozens or hundreds of hours. In this way, Condor builds up deep, sensitive images while simultaneously monitoring tens or hundreds of thousands of point sources per field at a cadence of 60 s. Condor is also equipped with diffraction gratings and with a set of He II 468.6 nm, [O III] 500.7 nm, He I 587.5 nm, Hα 656.3 nm, [N II] 658.4 nm, and [S II] 671.6 nm narrow-band filters, allowing it to address a variety of broad- and narrow-band science issues. Given its unique capabilities, Condor can access regions of "astronomical discovery space" that have never before been studied. Here we introduce Condor and describe various aspects of its performance.

Keywords: automated telescopes; telescopes; automatic patrol telescopes; astronomical detectors
Hidden Companions to Intermediate-mass Stars. XVIII. Discovery of a 0.88M ⊙, 26 au Companion to n Centauri

n Centauri is a nearby A-type star. Here we report the discovery of a companion with an H band flux ratio $\tfrac{{f}_{{\rm{B}}}}{{f}_{{\rm{A}}}}=3.9 \% \pm 0.4 \% $ at a projected separation ρ = 570 mas ↔ 26 au based on the acquisition camera image of a VLTI/GRAVITY observation. Isochrone fitting yields masses M A = 2.07M ⊙ and M B = 0.88M ⊙ and an age of 900 Myr. The newly discovered companion explains the Δv = 2.3 ± 0.1 km s‑1 Gaia-Hipparcos proper motion change of n Cen in both direction and magnitude as well as its X-ray emission. The interferometric data excludes the presence of any additional companion to the primary with a K band flux ratio higher than 0.9% (M ≳ 0.52M ⊙ for a main sequence star) within ρ > 5 mas ↔ 0.23 au. *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Keywords: multiple stars; a stars; optical interferometry
Double- and Triple-line Spectroscopic Candidates in the LAMOST Medium-Resolution Spectroscopic Survey

The LAMOST Medium-Resolution Spectroscopic Survey (LAMOST-MRS) provides an unprecedented opportunity for detecting multiline spectroscopic systems. Based on the cross correlation function and successive derivatives, we search for spectroscopic binaries and triples and derive their radial velocities (RVs) from the LAMOST-MRS spectra. A Monte Carlo simulation is adopted to estimate the RV uncertainties. After examining over 1.3 million LAMOST DR7 MRS blue-arm spectra, we obtain 3133 spectroscopic binary (SB) and 132 spectroscopic triple (ST) candidates, which account for 1.2% of the LAMOST-MRS stars. Over 95% of the candidates are newly discovered. It is found that all of the ST candidates are on the main sequence, while around 10% of the SB candidates may have one or two components on the red giant branch.

Keywords: spectroscopic binary stars; catalogs; radial velocity