adsabs/SciX_UAT_keywords huggingface dataset:
TESS Photometry of AM Her and AR UMa: Binary Parameters, Cyclotron Emission Modeling, and Mass Transfer Duty Cycles

Transiting Exoplanet Survey Satellite (TESS) photometry of the polars AM Herculis (AM Her) and AR Ursae Majoris (AR UMa) is presented, along with high-speed photometry. AM Her shows a variety of high states with frequent transitions between them. TESS photometry of AR UMa in the low state reveals no evidence of accretion, while the McDonald 2.1 m telescope caught AR UMa in its high accretion state. Roche-lobe overflow is shut off during low states of AR UMa, while accretion often still takes place during low states of AM Her. We derive inclinations of 50° and 70° for AM Her and AR UMa respectively. To model the high-state light curves of AM Her, we employ a self-organized map light-curve classification scheme to establish common accretion configurations. The cyclotron radiation properties then allow the production of emission region maps on the surface of the white dwarf. The accretion geometry of AM Her is most consistent with a multipolar field structure. The high-state photometry of AR UMa has stochastic accretion flaring, which we attribute to magnetically buffeted mass transfer through the inner Lagrangian point L1. To consider this possibility, we examine the magnetism of both stars and argue that the local magnetic field near L1 can initiate short-lived accretion events and affect transitions between high and low accretion states in both AM Her and AR UMa. In particular, AR UMa has the low state as its default, while AM Her and most other active polars are in the high state by default.

Keywords: magnetic stars; white dwarf stars; cataclysmic variable stars; stellar accretion; accretion
Expanding the Y Dwarf Census with Spitzer Follow-up of the Coldest CatWISE Solar Neighborhood Discoveries

We present Spitzer 3.6 and 4.5 μm follow-up of 170 candidate extremely cool brown dwarfs newly discovered via the combination of Wide-field Infrared Survey Explorer (WISE) and NEOWISE imaging at 3-5 μm. CatWISE, a joint analysis of archival WISE and NEOWISE data, has improved upon the motion measurements of AllWISE by leveraging a >10× time baseline enhancement, from 0.5 yr (AllWISE) to 6.5 yr (CatWISE). As a result, CatWISE motion selection has yielded a large sample of previously unrecognized brown dwarf candidates, many of which have archival detections exclusively in the WISE 4.6 μm (W2) channel, suggesting that they could be both exceptionally cold and nearby. Where these objects go undetected in WISE W1 (3.4 μm), Spitzer can provide critically informative detections at 3.6 μm. Of our motion-confirmed discoveries, 17 have a best-fit Spitzer [3.6]-[4.5] color most consistent with spectral type Y. It is likely that CWISEP J144606.62-231717.8 (μ ≈ 1"3 yr-1) is the reddest, and therefore potentially coldest, member of our sample with a very uncertain [3.6]-[4.5] color of 3.71 ± 0.44 mag. We also highlight our highest proper-motion discovery, WISEA J153429.75-104303.3, with μ ≈ 2"7 yr-1. Given that the prior list of confirmed and presumed Y dwarfs consists of just 27 objects, the Spitzer follow-up presented in this work has substantially expanded the sample of identified Y dwarfs. Our new discoveries thus represent significant progress toward understanding the bottom of the substellar mass function, investigating the diversity of the Y dwarf population, and selecting optimal brown dwarf targets for James Webb Space Telescope spectroscopy.

Keywords: brown dwarfs; y dwarfs; solar neighborhood; t dwarfs; proper motions
The Ultimately Large Telescope: What Kind of Facility Do We Need to Detect Population III Stars?

The launch of the James Webb Space Telescope (JWST) will open up a new window for observations at the highest redshifts, reaching out to $z\approx 15$ . However, even with this new facility, the first stars will remain out of reach, as they are born in small minihalos with luminosities too faint to be detected even by the longest exposure times. In this paper, we investigate the basic properties of the Ultimately Large Telescope, a facility that can detect Population III star formation regions at high redshift. Observations will take place in the near-infrared and therefore a Moon-based facility is proposed. An instrument needs to reach magnitudes as faint as 39 magAB, corresponding to a primary mirror size of about 100 m in diameter. Assuming JWST NIRCam filters, we estimate that Population III sources will have unique signatures in a color-color space and can be identified unambiguously.

Keywords: population iii stars; early universe; infrared telescopes
Terahertz Water Masers. II. Further SOFIA/GREAT Detections Toward Circumstellar Outflows, and a Multitransition Analysis

Following up on our discovery of terahertz water masers, reported in 2017, we report two further detections of water maser emission at frequencies above 1 THz. Using the GREAT instrument on SOFIA, we have detected emission in the 1.296411 THz 827 - 734 transition of water toward two additional oxygen-rich evolved stars, omicron Ceti (Mira) and R Crateris, and obtained an upper limit on the 1.296 THz line emission from U Orionis. Toward these three sources, and toward the red supergiant star VY Canis Majorae from which 1.296 THz line emission was reported previously, we have also observed several lower-frequency (sub)millimeter water maser transitions using the APEX 12 m telescope along with the 22 GHz transition using the Effelsberg 100 m telescope. We have used a simple model to analyze the multitransition data thereby obtained. Adopting, as a prior, independent literature estimates of the mass-loss rates in these four sources and in W Hydrae, we infer water abundances in a remarkably narrow range: n(H2O)/n(H2) = 1.4-2.5 × 10-4. For o Cet, VY CMa, and W Hya, the model is successful in predicting the maser line fluxes to within a typical factor ∼1.6-3. For R Crt and U Ori, the model is less successful, with typical line flux predictions lying an order of magnitude above or below the observations; such discrepancies are perhaps unsurprising given the exponential nature of maser amplification. * GREAT, the German REceiver for Astronomy at Terahertz frequencies, is a development by the MPI für Radioastronomie and the KOSMA/Universität zu Köln, in cooperation with the DLR Institut für Optische Sensorsysteme.

Keywords: astrophysical masers; circumstellar envelopes; submillimeter astronomy
Nondetection of Water-ice Grains in the Coma of Comet 46P/Wirtanen and Implications for Hyperactivity

Hyperactive comets have high water production rates, with inferred sublimation areas of order the surface area of the nucleus. Comets 46P/Wirtanen and 103P/Hartley 2 are two examples of this cometary class. Based on observations of comet Hartley 2 by the Deep Impact spacecraft, hyperactivity appears to be caused by the ejection of water-ice grains and/or water-ice-rich chunks of nucleus into the coma. These materials increase the sublimating surface area and yield high water production rates. The historic close approach of comet Wirtanen to Earth in 2018 afforded an opportunity to test Hartley 2-style hyperactivity in a second Jupiter-family comet. We present high spatial resolution, near-infrared spectroscopy of the inner coma of Wirtanen. No evidence for the 1.5 or 2.0 μm water-ice absorption bands is found in six 0.8-2.5 μm spectra taken around perihelion and closest approach to Earth. In addition, the strong 3.0 μm water-ice absorption band is absent in a 2.0-5.3 μm spectrum taken near perihelion. Using spectroscopic and sublimation lifetime models, we set constraints on the physical properties of the ice grains in the coma, assuming they are responsible for the comet's hyperactivity. We rule out pure water-ice grains of any size, given their long lifetime. Instead, the hyperactivity of the nucleus and lack of water-ice absorption features in our spectra can be explained either by icy grains on the order of 1 μm in size with a small amount of low-albedo dust (greater than 0.5% by volume) or by large chunks containing significant amounts of water ice.

Keywords: coma dust; comae; short period comets; near infrared astronomy; spectroscopy
Identification of Possible Stellar Companions via Speckle Interferometry in a Sample of Be Stars

We present speckle interferometric measurements of Be stars made with the 1.60 m Perkin-Elmer telescope at the Pico dos Dias Observatory of the Laboratório Nacional de Astrofísica in Brazil. Using three different filters (V, R, and I), we obtained astrometric measurements for 23 stars, during three observing runs allocated in 2017 March, 2018 April, and 2019 July. We identified pairs with angular separation ranging from 0"10 to 6"69, including six systems with separations smaller than 1"0. We estimated a mean error in separation of 15 mas, 1°2 in position angle, and 0.29 mag for the magnitude difference. We discovered three new possible double systems that are not identified in the literature: HD 174886, HD 159032, and HD 168135 with an average angular separation of 0"20, 3"23, and 5"41, respectively. In addition, we identified four new pairs in multiple systems previously known in the Washington Double Star Catalog. However, for 16 stars of our sample, we did not find evidence of binarity, based on the diffraction-limited resolution, the field of view, and/or the sensitivity of our observations. From the cross-match with data from Gaia Data Release 2, we verified the possibility of some of these systems be gravitationally bound or not.

Keywords: be stars; speckle interferometry; visual binary stars
X-Ray Cavity Dynamics and Their Role in the Gas Precipitation in Planck Sunyaev-Zeldovich (SZ) Selected Clusters

We study active galactic nucleus (AGN) feedback in nearby (z < 0.35) galaxy clusters from the Planck Sunyaev-Zeldovich sample using Chandra observations. This nearly unbiased mass-selected sample includes both relaxed and disturbed clusters and may reflect the entire AGN feedback cycle. We find that relaxed clusters better follow the one-to-one relation of cavity power versus cooling luminosity, while disturbed clusters display higher cavity power for a given cooling luminosity, likely reflecting a difference in cooling and feedback efficiency. Disturbed clusters are also found to contain asymmetric cavities when compared to relaxed clusters, hinting toward the influence of the intracluster medium (ICM) "weather" on the distribution and morphology of the cavities. Disturbed clusters do not have fewer cavities than relaxed clusters, suggesting that cavities are difficult to disrupt. Thus, multiple cavities are a natural outcome of recurrent AGN outbursts. As in previous studies, we confirm that clusters with short central cooling times, t cool, and low central entropy values, K 0, contain warm ionized (10,000 K) or cold molecular (<100 K) gas, consistent with ICM cooling and a precipitation/chaotic cold accretion scenario. We analyzed archival Multi-Unit Spectroscopic Explorer observations that are available for 18 clusters. In 11/18 of the cases, the projected optical line emission filaments appear to be located beneath or around the cavity rims, indicating that AGN feedback plays an important role in forming the warm filaments by likely enhancing turbulence or uplift. In the remaining cases (7/18), the clusters either lack cavities or their association of filaments with cavities is vague, suggesting alternative turbulence-driven mechanisms (sloshing/mergers) or physical time delays are involved.

Keywords: galaxy clusters; galactic and extragalactic astronomy; cooling flows; high energy astrophysics; warm ionized medium; brightest cluster galaxies
Spectral Signatures of PeVatrons

We analyze the energy distributions of final (stable) products—gamma rays, neutrinos, and electrons—produced in inelastic proton-proton collisions in the PeV energy regime. We also calculate the energy spectrum of synchrotron radiation from secondary electrons, assuming that these are promptly cooled in the surrounding magnetic field. We show that the synchrotron radiation has an energy distribution much shallower than that of primary protons, hence we suggest taking advantage of such a feature in the spectral analysis of the highest-energy (cutoff) emission region from particle accelerators. For a broad range of energy distributions in the parent protons, we propose simple analytical presentations for the spectra of secondaries in the cutoff region. These results can be used in the interpretation of high-energy radiation from PeVatrons—cosmic-ray factories accelerating protons to energies up to 1 PeV.

Keywords: spectral energy distribution; gamma-rays; particle astrophysics; high-energy cosmic radiation
Impacts of Dust Grains Accelerated by Supernovae on the Moon

There is evidence that ejecta from nearby supernovae have rained down on Earth in the past. Supernovae can accelerate preexisting dust grains in the interstellar medium to speeds of ∼0.01c. We investigate the survival and impact of dust grains from supernovae on the Moon, finding that supernova dust grains can form detectable tracks with widths of ∼0.01-0.07 μm and depths of ∼0.1-0.7 mm in lunar rocks. These tracks could potentially shed light on the timings, luminosities, and directions of nearby supernovae.

Keywords: supernovae; the moon; meteoroids
Outshining by Recent Star Formation Prevents the Accurate Measurement of High-z Galaxy Stellar Masses

We demonstrate that the inference of galaxy stellar masses via spectral energy distribution (SED) fitting techniques for galaxies formed in the first billion years after the Big Bang carries fundamental uncertainties owing to the loss of star formation history (SFH) information from the very first episodes of star formation in the integrated spectra of galaxies. While this early star formation can contribute substantially to the total stellar mass of high-redshift systems, ongoing star formation at the time of detection outshines the residual light from earlier bursts, hampering the determination of accurate stellar masses. As a result, order-of-magnitude uncertainties in stellar masses can be expected. We demonstrate this potential problem via direct numerical simulation of galaxy formation in a cosmological context. In detail, we carry out two cosmological simulations with significantly different stellar feedback models, which span a significant range in SFH burstiness. We compute the mock SEDs for these model galaxies at z = 7 via calculations of 3D dust radiative transfer, and then backward fit these SEDs with PROSPECTOR SED fitting software. The uncertainties in derived stellar masses that we find for z > 7 galaxies motivate the development of new techniques and/or priors for SFH to model star formation in the early Universe.

Keywords: galaxies; galaxy ages; high-redshift galaxies; starburst galaxies
Weather on Other Worlds. VI. Optical Spectrophotometry of Luhman 16B Reveals Large-amplitude Variations in the Alkali Lines

Using a novel wide-slit, multiobject approach with the GMOS spectrograph on the 8 m Gemini South telescope, we have obtained precise time-series spectrophotometry of the binary brown dwarf Luhman 16 at optical wavelengths over two full nights. The B component of this binary system is known to be variable in the red optical and near-infrared with a period of 5 hr and an amplitude of 5%-20%. Our observations probe its spectrally resolved variability in the 6000-10000 Å range. At wavelengths affected by the extremely strong, broadened spectral lines of the neutral alkali metals (the potassium doublet centered near 7682 Å and the sodium doublet at 5893 Å), we see photometric variations that differ strikingly from those of the 8000-10000 Å "red continuum" that dominates our detected flux. On UT 2014 February 24, these variations are anticorrelated with the red continuum, while on February 25 they have a large relative phase shift. The extent to which the wavelength-dependent photometric behavior diverges from that of the red continuum appears to correlate with the strength of the alkali absorption. We consider but ultimately reject models in which our observations are explained by lightning or auroral activity. A more likely cause is cloud-correlated, altitude-dependent variations in the gas-phase abundances of sodium and potassium, which are in chemical equilibrium with their chlorides in brown dwarf atmospheres. Clouds could influence these chemical equilibria by changing the atmospheric temperature profile and/or through cloud particles acting as chemical catalysts.

Keywords: brown dwarfs; atmospheric clouds; exoplanet atmospheric variability; variable stars; spectrophotometry; time series analysis
Testing the Interaction between a Substellar Companion and a Debris Disk in the HR 2562 System

The HR 2562 system is a rare case where a brown dwarf companion resides in a cleared inner hole of a debris disk, offering invaluable opportunities to study the dynamical interaction between a substellar companion and a dusty disk. We present the first ALMA observation of the system as well as the continued Gemini Planet Imager monitoring of the companion's orbit with six new epochs from 2016 to 2018. We update the orbital fit, and in combination with absolute astrometry from GAIA, place a 3σ upper limit of 18.5 M J on the companion's mass. To interpret the ALMA observations, we used radiative transfer modeling to determine the disk properties. We find that the disk is well resolved and nearly edge-on. While the misalignment angle between the disk and the orbit is weakly constrained, due to the short orbital arc available, the data strongly support a (near) coplanar geometry for the system. Furthermore, we find that the models that describe the ALMA data best have inner radii that are close to the companion's semimajor axis. Including a posteriori knowledge of the system's SED further narrows the constraints on the disk's inner radius and places it at a location that is in reasonable agreement with (possibly interior to) predictions from existing dynamical models of disk truncation by an interior substellar companion. HR 2562 has the potential over the next few years to become a new test bed for dynamical interaction between a debris disk and a substellar companion.

Keywords: debris disks; substellar companion stars; brown dwarfs; orbit determination; gravitational interaction
Did Earth Eat Its Leftovers? Impact Ejecta as a Component of the Late Veneer

The presence of highly siderophile elements in Earth's mantle indicates that a small percentage of Earth's mass was delivered after the last giant impact in a stage of "late accretion." There is ongoing debate about the nature of late-accreted material and the sizes of late-accreted bodies. Earth appears isotopically most similar to enstatite chondrites and achondrites. It has been suggested that late accretion must have been dominated by enstatite-like bodies that originated in the inner disk, rather than ordinary or carbonaceous chondrites. Here we examine the provenances of "leftover" planetesimals present in the inner disk in the late stages of accretion simulations. Dynamically excited planet formation produces planets and embryos with similar provenances, suggesting that the Moon-forming impactor may have had a stable isotope composition very similar to the proto-Earth. Commonly, some planetesimal-sized bodies with similar provenances to the Earth-like planets are left at the end of the main stage of growth. The most chemically similar planetesimals are typically fragments of protoplanets ejected millions of years earlier. If these similar-provenance bodies are later accreted by the planet, they will represent late-accreted mass that naturally matches Earth's composition. The planetesimal-sized bodies that exist during the giant impact phase can have large core mass fractions, with core provenances similar to the proto-Earth. These bodies are an important potential source for highly siderophile elements. The range of core fractions in leftover planetesimals complicates simple inferences as to the mass and origin of late accretion based on the highly siderophile elements in the mantle.

Keywords: earth (planet); impact phenomena; planetesimals; planet formation; cosmochemistry; planetary science; meteorites; solar system formation
Hubble Space Telescope Observations of Mira Variables in the SN Ia Host NGC 1559: An Alternative Candle to Measure the Hubble Constant

We present year-long, near-infrared Hubble Space Telescope (HST) WFC3 observations used to search for Mira variables in NGC 1559, the host galaxy of the Type Ia supernova (SN Ia) SN 2005df. This is the first dedicated search for Miras, highly evolved low-mass stars, in an SN Ia host, and subsequently the first calibration of the SN Ia luminosity using Miras in a role historically played by Cepheids. We identify a sample of 115 O-rich Miras with P < 400 days based on their light-curve properties. We find that the scatter in the Mira period-luminosity relation (PLR) is comparable to Cepheid PLRs seen in SN Ia host galaxies. Using a sample of O-rich Miras discovered in NGC 4258 with HSTF160W and its maser distance, we measure a distance modulus for NGC 1559 of ${\mu }_{1559}=31.41\pm 0.050$ (statistical) $\pm 0.060$ (systematic) mag. Based on the light curve of the normal, well-observed, low-reddening SN 2005df, we obtain a measurement of the fiducial SN Ia absolute magnitude of ${M}_{B}^{0}=-19.27\pm 0.13$ mag. With the Hubble diagram of SNe Ia we find ${H}_{0}=72.7\pm 4.6$ km s-1 Mpc-1. Combining the calibration from the NGC 4258 megamaser and the Large Magellanic Cloud detached eclipsing binaries gives a best value of ${H}_{0}=73.3\pm 4.0$ km s-1 Mpc-1. This result is within 1σ of the Hubble constant derived using Cepheids and multiple calibrating SNe Ia. This is the first of four expected calibrations of the SN Ia luminosity from Miras that should reduce the error in H0 via Miras to ∼3%. In light of the present Hubble tension and JWST, Miras have utility in the extragalactic distance scale to check Cepheid distances or calibrate nearby SNe in early-type host galaxies that would be unlikely targets for Cepheid searches.

Keywords: cosmology; distance indicators; mira variable stars; cosmological parameters; hubble constant; galaxy distances
The 2013 November 12 Solar Energetic Electron Event Associated with Solar Jets

We investigate the hard X-ray (HXR) flare-associated "prompt" solar energetic electron (SEE) 2013 November 12 event with joint EUV jet observations from Solar Dynamics Observatory/Atmospheric Imaging Assembly and STEREO-A/EUVI. The SEE energy spectrum observed by Wind/3D Plasma and Energetic Particle shows a triple-power-law shape with a low-energy break of 10.0 ± 1.7 keV and a high-energy break of 56.6 ± 8.9 keV, which has never been reported before for jet-related SEE events. Associated HXR emissions observed by RHESSI and FGST/Gamma-ray Burst Monitor show three distinctive peaks with different spectral indices β HPE of HXR-producing electrons (HPEs) derived by means of thick-target bremsstrahlung model. The high-energy spectral index β 3 = 4.63 ± 0.65 of SEE is consistent with the HPE spectral index β HPE derived in HXR peak 1 but different from β HPE of HXR peak 2 and peak 3. The main stream of EUV jets reaches a speed of 370 ± 25 km s-1 after an acceleration of up to 2.9 ± 0.4 km s-2 in a timescale of ~2 minutes, and the acceleration time coincides with the decay phase of HXR peak 1. EUV observations from two different viewing directions help to reconstruct the jet magnetic configurations. After the investigation on HXR emissions and jet configurations, the interchange-reconnection model triggered by the emerging flux could be a satisfactory explanation for this jet event.

Keywords: plasma jets; solar flares; solar energetic particles