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LATIS: The Lyα Tomography IMACS Survey

We introduce LATIS, the Lyα Tomography IMACS Survey, a spectroscopic survey at Magellan designed to map the z = 2.2-2.8 intergalactic medium (IGM) in three dimensions by observing the Lyα forest in the spectra of galaxies and QSOs. Within an area of 1.7 deg2, we will observe approximately half of ≳L* galaxies at z = 2.2-3.2 for typically 12 hr, providing a dense network of sightlines piercing the IGM with an average transverse separation of 2.5 h-1 comoving Mpc (1 physical Mpc). At these scales, the opacity of the IGM is expected to be closely related to the dark matter density, and LATIS will therefore map the density field in the z ∼ 2.5 universe at ∼Mpc resolution over the largest volume to date. Ultimately, LATIS will produce approximately 3800 spectra of z = 2.2-3.2 galaxies that probe the IGM within a volume of 4 × 106h-3 Mpc3, large enough to contain a representative sample of structures from protoclusters to large voids. Observations are already complete over one-third of the survey area. In this paper, we describe the survey design and execution. We present the largest IGM tomographic maps at comparable resolution yet made. We show that the recovered matter overdensities are broadly consistent with cosmological expectations based on realistic mock surveys, that they correspond to galaxy overdensities, and that we can recover structures identified using other tracers. LATIS is conducted in Canada-France-Hawaii Telescope Legacy Survey fields, including COSMOS. Coupling the LATIS tomographic maps with the rich data sets collected in these fields will enable novel studies of environment-dependent galaxy evolution and the galaxy-IGM connection at cosmic noon.

Keywords: dark matter distribution; galaxy environments; high-redshift galaxy clusters; intergalactic medium; lyman alpha forest
Photometric Observations of Flares on AD Leo from GWAC-F30 and TESS

We observed active M dwarf star AD Leo for 146 hr in photometry by GWAC-F30 and also analyzed 528 hr of photometric data of the star from the Transiting Exoplanet Survey Satellite (TESS). A total of 9 and 70 flares are detected from GWAC-F30 and TESS, respectively. Flare durations, amplitudes and energies are calculated. The distributions of the three properties and flare frequency distributions (FFDs) are given. Within the same energy range of flares, the FFDs of AD Leo obtained in this research and the previous study are basically consistent, which suggests that the magnetic activity of this star has not significantly changed compared to decades ago. Comparing with the average FFD of M-type stars, AD Leo's FFD is twice higher, indicating that its magnetic activity is more active than that of the average level of the M-type. Based on the TESS light curve, AD Leo's rotation period is calculated as ${2.21}_{-0.01}^{+0.01}$ days, supporting the result given in previous research. During the decay phase of the most energetic flare from TESS, we identified quasi-periodic pulsations and determined a 26.5 minute oscillation period, which is currently the longest period for AD Leo, suggesting that long periodic physical processes existed during the flare of this star.

Keywords: flare stars; late-type stars; m dwarf stars
Muted Features in the JWST NIRISS Transmission Spectrum of Hot Neptune LTT 9779b

The hot Neptune desert is one of the most sparsely populated regions of the exoplanet parameter space, and atmosphere observations of its few residents can provide insights into how such planets have managed to survive in such an inhospitable environment. Here, we present transmission observations of LTT 9779 b, the only known hot Neptune to have retained a significant H/He-dominated atmosphere, taken with JWST NIRISS/SOSS. The 0.6–2.85 μm transmission spectrum shows evidence for muted spectral features, rejecting a perfectly flat line at >5σ. We explore water- and methane-dominated atmosphere scenarios for LTT 9779 b's terminator, and retrieval analyses reveal a continuum of potential combinations of metallicity and cloudiness. Through comparisons to previous population synthesis works and our own interior structure modeling, we are able to constrain LTT 9779 b's atmosphere metallicity to 20–850× solar. Within this range of metallicity, our retrieval analyses prefer solutions with clouds at millibar pressures, regardless of whether the atmosphere is water or methane dominated—though cloud-free atmospheres with metallicities >500× solar cannot be entirely ruled out. By comparing self-consistent atmosphere temperature profiles with cloud condensation curves, we find that silicate clouds can readily condense in the terminator region of LTT 9779 b. Advection of these clouds onto the dayside could explain the high dayside albedo previously inferred for this planet and be part of a feedback loop aiding the survival of LTT 9779 b's atmosphere in the hot Neptune desert.

Keywords: exoplanets; hot neptunes; exoplanet atmospheres; planetary atmospheres
Resolving Red Giant Winds with the Hubble Space Telescope

We describe recent spectroscopic observations of red giant stars made by the Space Telescope Imaging Spectrograph (STIS) instrument on board the Hubble Space Telescope, which has provided spatially resolved observations of the warm chromospheric winds that predominate for early K to mid-M giants. The H I Lyα lines of a set of 11 red giants observed with the STIS/E140M echelle grating are first analyzed to ascertain wind H I column densities and total wind mass-loss rates. The M giants have estimated mass-loss rates of M ⊙ yr‑1, while the K giants with detected wind absorption have weaker winds with M ⊙ yr‑1. We use long-slit spectra of H I Lyα for two particular red giants, α Tau (K5 III) and γ Cru (M3.5 III), to study the spatial extent of the Lyα emission. From these data we estimate limits for the extent of detectable emission, which are r = 193 R * for γ Cru and r = 44 R * for α Tau. The cross-dispersion emission profiles in the STIS echelle spectra of the larger sample of red giants also show evidence for spatial resolution, not only for H I Lyα but for other lines with visible wind absorption, such as Fe II, Mg II, Mg I, O I, and C II. We characterize the nature of these spatial signatures. The spatial extent is far more apparent for the M giants than for the K giants, consistent with the stronger winds found for the M giants from the Lyα analysis. *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-15903 and GO-15904.

Keywords: stellar winds; ultraviolet spectroscopy; red giant stars; interstellar absorption
Is Betelgeuse the Outcome of a Past Merger?

We explore the possibility that the star α Orionis (Betelgeuse) is the outcome of a merger that occurred in a low-mass-ratio ( $q={{ \mathcal M }}_{2}/{{ \mathcal M }}_{1}\,=$ 0.07-0.25) binary system some time in the past hundreds of thousands of years. To that goal, we present a simple analytical model to approximate the perturbed internal structure of a post-merger object following the coalescence of a secondary in the mass range 1-4 M⊙ into the envelope of a 15-17 M⊙ primary. We then compute the long-term evolution of post-merger objects for a grid of initial conditions and make predictions about their surface properties for evolutionary stages that are consistent with the observed location of Betelgeuse in the Hertzsprung-Russell diagram. We find that if a merger occurred after the end of the primary's main-sequence phase, while it was expanding toward becoming a red supergiant star and typically with radius ∼200-300 R⊙, then its envelope is spun up to values that remain in a range consistent with Betelgeuse observations for thousands of years of evolution. We argue that the best scenario that can explain both the fast rotation of Betelgeuse and its observed large space velocity is one where a binary was dynamically ejected by its parent cluster a few million years ago and then subsequently merged. An alternative scenario in which the progenitor of Betelgeuse was spun up by accretion in a binary and released by the supernova explosion of the companion requires a finely tuned set of conditions but cannot be ruled out.

Keywords: stellar mergers; binary stars; close binary stars; stellar evolutionary models; stellar rotation; supergiant stars
High-energy Neutrinos from Magnetized Coronae of Active Galactic Nuclei and Prospects for Identification of Seyfert Galaxies and Quasars in Neutrino Telescopes

Particles may be accelerated in magnetized coronae via magnetic reconnections and/or plasma turbulence, leading to high-energy neutrinos and soft γ-rays. We evaluate the detectability of neutrinos from nearby bright Seyfert galaxies identified by X-ray measurements. In the disk-corona model, we find that NGC 1068 is the most promising Seyfert galaxy in the Northern sky, where IceCube is the most sensitive, and show prospects for the identification of aggregated neutrino signals from Seyfert galaxies bright in X-rays. Moreover, we demonstrate that nearby Seyfert galaxies are promising targets for the next generation of neutrino telescopes such as KM3NeT and IceCube-Gen2. For KM3NeT, Cen A can be the most promising source in the Southern sky if a significant fraction of the observed X-rays come from the corona, and it could be identified in few years of KM3NeT operation. Our results reinforce the idea that hidden cores of supermassive black holes are the dominant sources of the high-energy neutrino emission and underlines the necessity of better sensitivity to medium-energy ranges in future neutrino detectors for identifying the origin of high-energy cosmic neutrinos.

Keywords: particle astrophysics; high energy astrophysics; gamma-rays; agn host galaxies; active galaxies; active galactic nuclei; non-thermal radiation sources; neutrino astronomy; neutrino telescopes
Submillimeter and Far-infrared Spectroscopy of Monodeuterated Amidogen Radical (NHD): Improved Rest Frequencies for Astrophysical Observations

Observations of ammonia in interstellar environments have revealed high levels of deuteration, and all its D-containing variants, including ND3, have been detected in cold prestellar cores and around young protostars. The observation of these deuterated isotopologues is very useful for elucidating the chemical and physical processes taking place during the very early stages of star formation, as the abundance of deuterated molecules is highly enhanced in dense and cold gas. Nitrogen hydride radicals are key species lying at the very beginning of the reaction pathway leading to the formation of NH3 and organic molecules of prebiotic interest, but relatively little is known about their D-bearing isotopologues. To date, only ND has been detected in interstellar gas. To aid the identification of further deuterated nitrogen radicals, we have thoroughly reinvestigated the rotational spectrum of NHD by employing two different instruments: a frequency-modulation submillimeter spectrometer operating in the THz region and a synchrotron-based Fourier-transform infrared spectrometer operating in the 50-240 cm-1 frequency range. NHD was produced in a plasma of NH3 and D2. A wide range of rotational energy levels have been probed thanks to the observation of high-N (up to 15) and high-Ka (up to 9) transitions. A global analysis including our new data and data from the literature has provided a comprehensive set of very accurate spectroscopic parameters. A highly reliable line catalog has been generated to assist archival data searches and future astronomical observations of NHD at submillimeter and THz regimes.

Keywords: laboratory astrophysics; high resolution spectroscopy; line positions; spectral line lists; interstellar medium; interstellar molecules; isotopic abundances
Improved Model of X-Ray Emission from Hot Accretion Flows

We have developed an improved model of X-ray emission from optically thin, two-temperature accretion flows, kerrflow, using an exact Monte Carlo treatment of global Comptonization as well as with a fully general relativistic description of both the radiative and hydrodynamic processes. It also includes pion-decay electrons, whose synchrotron emission dominates the seed photon yield at $\dot{M}/{\dot{M}}_{\mathrm{Edd}}\gtrsim 0.1$ in flows around supermassive black holes. We consider in detail the dependence of the model spectra on the black hole spin, the electron heating efficiency, the plasma magnetization, and the accretion rate, and we discuss the feasibility of constraining these parameters by analyzing X-ray spectra of nearby low-luminosity active galactic nuclei. We note some degeneracies that hinder precise estimations of these parameters when individual X-ray spectra are analyzed. These degeneracies are eliminated when several spectra from a given source are fitted jointly, which then allows us to reliably measure the model parameters. We find significant differences with previous spectral models of hot-flow emission, related with the computational methods for Comptonization. Finally, we briefly consider and discuss the dependence on the viscosity parameter and on the outflow strength.

Keywords: accretion; x-ray active galactic nuclei; kerr black holes
Stellar Density Profiles of Dwarf Spheroidal Galaxies

We apply a flexible parametric model, a combination of generalized Plummer profiles, to infer the shapes of the stellar density profiles of the Milky Way's satellite dwarf spheroidal galaxies (dSphs). We apply this model to 40 dSphs using star counts from the Sloan Digital Sky Survey, PanStarrs-1 Survey, Dark Energy Survey, and Dark Energy Camera Legacy Survey. Using mock data, we examine systematic errors associated with modeling assumptions and identify conditions under which our model can identify "non-standard" stellar density profiles that have central cusps and/or steepened outer slopes. Applying our model to real dwarf spheroidals, we do not find evidence for centrally cusped density profiles among the fifteen Milky Way satellites for which our tests with mock data indicate there would be sufficient detectability. We do detect steepened (with respect to a standard Plummer model) outer profiles in several dSphs—Fornax, Leo I, Leo II, and Reticulum II—which may point to distinct evolutionary pathways for these objects. However, the outer slope of the stellar density profile does not yet obviously correlate with other observed galaxy properties.

Keywords: dwarf spheroidal galaxies
Observations of Multiphase, High-velocity, Shocked Gas in the Vela Supernova Remnant

We present an analysis of high-resolution far-UV archival spectra obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope of the star HD 75309, which probes high-velocity shocked gas in the Vela supernova remnant (SNR). We examine high-velocity features from intrinsically strong absorption lines of O I, Si II, Si II*, C II, C II*, and Si III. We also detect high-velocity components in the N V doublet and compare these features to observations of high-velocity O VI absorption, available from archival Far Ultraviolet Spectroscopic Explorer data. Kinetic temperatures are derived from the observed fractional abundances of the various ions, while gas densities and thermal pressures are obtained from the relative populations in excited fine-structure levels of C II and Si II. Our results indicate that the highly ionized species at high velocity probe gas in a region immediately behind a shock driven into an interstellar cloud, while the lower-ionization species trace material further downstream in the cooling region of the postshock flow. Low-velocity N V and O VI absorption may trace gas in a conductive boundary layer between the unshocked portion of the cloud and the hot X-ray-emitting intercloud medium. Temporal variations in high-velocity Ca II absorption features observed toward HD 75309 further confirm the highly inhomogeneous nature of the interstellar medium interacting with the Vela SNR. *Based on observations made with the NASA/ESA Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer, obtained from the MAST data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based in part on data collected at the European Southern Observatory under ESO programs 194.C-0833(B) and 099.C-0637(A).

Keywords: interstellar medium; interstellar line absorption; interstellar abundances; supernova remnants; diffuse interstellar clouds
Distances to Nearby Molecular Clouds Traced by Young Stars

I present a catalog of distances to 63 molecular clouds located within ~2.5 kpc of the Sun. The cloud distances are derived based on utilizing the Gaia DR3 parallaxes of the young stellar objects (YSOs). By identifying AllWISE YSO candidates (YSOCs) with infrared excesses and combining them with published YSOC catalogs, I compile an all-sky YSOC sample that is devoid of a significant proportion of contaminants. Using Gaia DR3 astrometric measurements, I associate over 3000 YSOCs with 63 local clouds and obtain the average distance to each cloud by fitting the YSOC parallax distribution within the cloud. I find good agreements with typical scatter of ≲10% between my new cloud distances and previous distance estimates. Unlike cloud distances obtained using stellar extinction, my catalog provides distances to the relatively dense areas of local clouds, which makes them more appropriate references for investigating the physical properties of nearby dense regions.

Keywords: molecular clouds; young stellar objects; stellar distance; solar neighborhood
Multicolor Photometry of Tiny Near-Earth Asteroid 2015 RN35 across a Wide Range of Phase Angles: Possible Mission-accessible A-type Asteroid

Studying small near-Earth asteroids is important in order to understand their dynamical histories and origins as well as to mitigate the damage caused by asteroid impacts on Earth. We report the results of multicolor photometry of the tiny near-Earth asteroid 2015 RN35 using the 3.8 m Seimei telescope in Japan and the TRAPPIST-South telescope in Chile over 17 nights in 2022 December and 2023 January. We observed 2015 RN35 across a wide range of phase angles from 2° to 30° in the g, r, i, and z bands in the Pan-STARRS system. These lightcurves show that 2015 RN35 is in a nonprincipal axis spin state with two characteristic periods of 1149.7 ± 0.3 s and 896.01 ± 0.01 s. We found that the slope of the visible spectrum of 2015 RN35 is as red as asteroid (269) Justitia, one of the very red objects in the main belt, which indicates that 2015 RN35 can be classified as an A- or Z-type asteroid. In conjunction with the shallow slope of the phase curve, we suppose that 2015 RN35 is a high-albedo A-type asteroid. We demonstrated that surface properties of tiny asteroids could be well constrained by intensive observations across a wide range of phase angles. 2015 RN35 is a possible mission-accessible A-type near-Earth asteroid with a small Δv of 11.801 km s-1 in the launch window between 2030 and 2035.

Keywords: asteroids; near-earth objects; photometry; multi-color photometry; light curves
A Rosetta Stone for Eccentric Gravitational Waveform Models

Orbital eccentricity is a key signature of dynamical binary black hole formation. The gravitational waves from a coalescing binary contain information about its orbital eccentricity, which may be measured if the binary retains sufficient eccentricity near merger. Dedicated waveforms are required to measure eccentricity. Several models have been put forward, and show good agreement with numerical relativity at the level of a few percent or better. However, there are multiple ways to define eccentricity for inspiralling systems, and different models internally use different definitions of eccentricity, making it difficult to compare eccentricity measurements directly. In this work, we systematically compare two eccentric waveform models, SEOBNRE and TEOBResumS, by developing a framework to translate between different definitions of eccentricity. This mapping is constructed by minimizing the relative mismatch between the two models over eccentricity and reference frequency, before evolving the eccentricity of one model to the same reference frequency as the other model. We show that for a given value of eccentricity passed to SEOBNRE, one must input a 20%-50% smaller value of eccentricity to TEOBResumS in order to obtain a waveform with the same empirical eccentricity. We verify this mapping by repeating our analysis for eccentric numerical relativity simulations, demonstrating that TEOBResumS reports a correspondingly smaller value of eccentricity than SEOBNRE.

Keywords: gravitational waves; compact binary stars; stellar mass black holes; eccentricity
A Rapidly Evolving High-amplitude δ Scuti Star Crossing the Hertzsprung Gap

In this work, we report the discovery of the rapidly evolving high-amplitude δ Scuti star KIC 6382916 (J19480292+4146558), which is crossing the Hertzsprung gap. According to the analysis of the archival data, we find three independent pulsation modes, whose amplitudes and frequencies vary distinctly in 4 yr. The linear period variation rates of the first two modes are about 3-4 times larger than the best seismic model constructed by the standard evolution theory, while that of the third one is about 8 times larger than the first two modes. What is more interesting is that almost all the combinations of the third mode have frequency peaks 0.0815 c day-1 away from them in the frequency domain. A framework is proposed to interpret the markedly large frequency and amplitude variation rates of the third mode, in which we employ a new pulsation mode (resonating integration mode) generated by the resonance between a radial p-mode and a nonradial mixed mode. Moreover, global analysis of the interactions between the three independent pulsation modes and their harmonics/combinations is performed based on the interaction diagrams of their amplitudes and phases, which would be a useful tool for future asteroseismology research.

Keywords: stellar evolution; delta scuti variable stars; asteroseismology; pulsating variable stars
Solar Flare Irradiance: Observations and Physical Modeling

We examine Solar Dynamics Observatory (SDO)/EUV Variability Experiment (EVE) data to better understand solar flare irradiance, and how that irradiance may vary for large events. We measure scaling laws relating Geostationary Orbital Environmental Satellites (GOES) flare classes to irradiance in 21 lines measured with SDO/EVE, formed across a wide range of temperatures, and find that this scaling depends on the line-formation temperature. We extrapolate these irradiance values to large events, exceeding X10. In order to create full spectra, however, we need a physical model of the irradiance. We present the first results of a new physical model of solar flare irradiance, NRLFLARE, that sums together a series of flare loops to calculate the spectral irradiance ranging from the X-rays through the far-UV (≈0 to 1250 Å), constrained only by GOES/X-ray Sensors observations. We test this model against SDO/EVE data. The model spectra and time evolution compares well in high-temperature emission, but cooler lines show large discrepancies. We speculate that the discrepancies are likely due to both a nonuniform cross-section of the flaring loops as well as opacity effects. We then show that allowing the cross-sectional area to vary with height significantly improves agreement with observations, and is therefore a crucial parameter needed to accurately model the intensity of spectral lines, particularly in the transition region from $4.7\lesssim \mathrm{log}T\lesssim 6$ .

Keywords: solar flares; solar flare spectra; solar x-ray flares; solar activity; solar spectral irradiance