# ECHOPLEX

Today — 22 October 2021The Astrophysical Journal - latest papers

# Multi-wavelength Observations of AT2019wey: a New Candidate Black Hole Low-mass X-ray Binary

AT2019wey (SRGA J043520.9+552226, SRGE J043523.3+552234) is a transient first reported by the ATLAS optical survey in 2019 December. It rose to prominence upon detection, three months later, by the Spektrum-Roentgen-Gamma (SRG) mission in its first all-sky survey. X-ray observations reported in Yao et al. suggest that AT2019wey is a Galactic low-mass X-ray binary (LMXB) with a black hole (BH) or neutron star (NS) accretor. Here we present ultraviolet, optical, near-infrared, and radio observations of this object. We show that the companion is a short-period ( P ≲ 16 hr) low-mass (<1 M ⊙ ) star. We consider AT2019wey to be a candidate BH system since its locations on the L radio – L X and L opt – L X diagrams are closer to BH binaries than NS binaries. We demonstrate that from 2020 June to August, despite the more than 10 times brightening at radio and X-ray wavelengths, the optical lumi...
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# A Comprehensive X-Ray Report on AT2019wey

Here, we present MAXI, Swift, NICER, NuSTAR, and Chandra observations of the X-ray transient AT2019wey (SRGA J043520.9+552226, SRGE J043523.3+552234). From spectral and timing analyses we classify it as a Galactic low-mass X-ray binary (LMXB) with a black hole (BH) or neutron star (NS) accretor. AT2019wey stayed in the low/hard state (LHS) from 2019 December to 2020 August 21, and the hard-intermediate state (HIMS) from 2020 August 21 to 2020 November. For the first six months of the LHS, AT2019wey had a flux of ∼1 mCrab, and displayed a power-law X-ray spectrum with photon index Γ = 1.8. From 2020 June to August, it brightened to ∼20 mCrab. Spectral features characteristic of relativistic reflection became prominent. On 2020 August 21, the source left the “hard line” on the rms–intensity diagram, and transitioned from LHS to HIMS. The thermal disk component became comparable to the power-law component. A low-frequency quasi-periodic oscillation (QPO) was observed. The QPO centr...
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# High-frequency Wave Power Observed in the Solar Chromosphere with IBIS and ALMA

We present observational constraints on the chromospheric heating contribution from acoustic waves with frequencies between 5 and 50 mHz. We use observations from the Dunn Solar Telescope in New Mexico, complemented with observations from the Atacama Large Millimeter Array collected on 2017 April 23. The properties of the power spectra of the various quantities are derived from the spectral lines of Ca ii 854.2 nm, H i 656.3 nm, and the millimeter continuum at 1.25 and 3 mm. At the observed frequencies, the diagnostics almost all show a power-law behavior, whose particulars (slope, peak, and white-noise floors) are correlated with the type of solar feature (internetwork, network, and plage). In order to disentangle the vertical versus transverse Alfvénic plasma motions, we examine two different fields of view: one near disk center, and the other close to the limb. To infer the acoustic flux in the middle chromosphere, we compare ...
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Yesterday — 21 October 2021The Astrophysical Journal - latest papers

# A Detailed View of the Broad-line Region in NGC 3783 from Velocity-resolved Reverberation Mapping

We have modeled the full velocity-resolved reverberation response of the H β and He ii optical broad emission lines in NGC 3783 to constrain the geometry and kinematics of the low-ionization and high-ionization broad-line region (BLR). The geometry is found to be a thick disk that is nearly face-on, inclined at ∼18° to our line of sight, and exhibiting clear ionization stratification, with an extended H β -emitting region ( ##IMG## [http://ej.iop.org/images/0004-637X/920/2/112/apjac19afieqn1.gif] {${r}_{\mathrm{median}}={10.07}_{-1.12}^{+1.10}$} lt-day) and a more compact and centrally located He ii -emitting region ( ##IMG## [http://ej.iop.org/images/0004-637X/920/2/112/apjac19afieqn2.gif] {${r}_{\mathrm{median}}={1.33}_{-0.42}^{=+0.34}$} lt-day). In the H β -emitting region, the kinematics are dominated by near-circular Keplerian orbits, but with ∼40% of the orbits inflow...
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# Evolution of a Mode of Oscillation within Turbulent Accretion Disks

20 October 2021 at 16:00
We investigate the effects of subsonic turbulence on a normal mode of oscillation (a possible origin of the high-frequency quasi-periodic oscillations (HFQPOs) within some black hole accretion disks). We consider perturbations of a time-dependent background (steady-state disk plus turbulence), obtaining an oscillator equation with stochastic damping, (mildly) nonlinear restoring, and stochastic driving forces. The (long-term) mean values of our turbulent functions vanish. In particular, turbulence does not damp the oscillation modes, so “turbulent viscosity” is not operative. However, the frequency components of the turbulent driving force near that of the mode can produce significant changes in the amplitude of the mode. Even with an additional (phenomenological constant) source of damping, this leads to an eventual “blowout” (onset of effects of nonlinearity) if the turbulence is sufficiently strong or the damping constant is sufficiently small. The infrequent large increases ...
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# Multi-Wavelength Study of 4C+28.07

20 October 2021 at 16:00
4C+28.07 is a γ -ray flat-spectrum-radio-quasar-type source. It is often monitored at different frequencies, though long-term multi-wavelength data of this source have not been modeled in detail before. We have analyzed ∼12 yr (2008 August–2020 May) of Fermi-LAT data with a binning of 10 day timescale and observed three distinctive flaring states. Each flaring state consists of different phases of activity, namely, pre-flare, flare, and post-flare regions. γ -ray spectral analysis of these different activity phases has been performed and the best-fit model for its spectra is found to be a log-parabola model. We have also studied the correlation of simultaneous γ -ray light curves with the optical & radio counterparts in these flaring states and report the DCF with 95% significance level. A large time delay is found between radio and gamma-ray data for two flares, indicating two zones of emission. We have fitted the multi-wavelength data with a two-zone lept...
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# The JCMT Transient Survey: Four-year Summary of Monitoring the Submillimeter Variability of Protostars

We present the four-year survey results of monthly submillimeter monitoring of eight nearby (<500 pc) star-forming regions by the JCMT Transient Survey. We apply the Lomb–Scargle Periodogram technique to search for and characterize variability on 295 submillimeter peaks brighter than 0.14 Jy beam −1 , including 22 disk sources (Class II), 83 protostars (Class 0/I), and 190 starless sources. We uncover 18 secular variables, all of them protostars. No single-epoch burst or drop events and no inherently stochastic sources are observed. We classify the secular variables by their timescales into three groups: Periodic, Curved, and Linear. For the Curved and Periodic cases, the detectable fractional amplitude, with respect to mean peak brightness, is ∼4% for sources brighter than ∼0.5 Jy beam −1 . Limiting our sample to only these bright sources, the observed variable fraction is 37% (16 out of 43). Considering source evolution, we find a similar fraction of brigh...
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# Which Molecular Cloud Structures Are Bound?

We analyze surveys of molecular cloud structures defined by tracers ranging from CO J = 1 → 0 through 13 CO J = 1 → 0 to dust emission together with NH 3 data. The mean value of the virial parameter and the fraction of mass in bound structures depends on the method used to identify structures. Generally, the virial parameter decreases and the fraction of mass in bound structures increases with the effective density of the tracer, the surface density and mass of the structures, and the distance from the center of a galaxy. For the most complete surveys of structures in the Galaxy defined by CO J = 1 → 0, the fraction of mass that is in bound structures is 0.19. For catalogs of other galaxies based on CO J = 2 → 1, the fraction is 0.35. These results offer substantial alleviation of the fundamental problem of slow star formation. If only clouds found to be bound are counted and they are assumed to collapse in a freefall time at their...
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# The Nuclear Star Cluster and Nuclear Stellar Disk of the Milky Way: Different Stellar Populations and Star Formation Histories

20 October 2021 at 16:00
The Milky Way’s nuclear stellar disk (NSD) and nuclear star cluster (NSC) are the main features of the Galactic center. Nevertheless, their observation is hampered by the extreme source crowding and high extinction. Hence, their relation and formation scenario are not fully clear yet. We aim to detect the stellar populations from the NSC and the NSD along the line of sight toward the NSC and assess whether they have different stellar populations and star formation histories. We analyzed the color–magnitude diagram, K s versus H − K s , of a region of 8.′2 × 2.′8 centered on the NSC, and detected two different stellar groups with different extinctions. We studied their red clumps to find the features associated with each of the stellar populations. We obtained that the two groups of stars correspond to the NSD and the NSC and found that they have significantly different stellar populations and star formation histories. We ...
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# Simulating Observations of Ices in Protoplanetary Disks

20 October 2021 at 16:00
Ices are an important constituent of protoplanetary disks. New observational facilities, notably the James Webb Space Telescope (JWST), will greatly enhance our view of disk ices by measuring their infrared spectral features. We present a suite of models to complement these upcoming observations. Our models use a kinetics-based gas–grain chemical evolution code to simulate the distribution of ices in a disk, followed by a radiative transfer code using a subset of key ice species to simulate the observations. We present models reflecting both molecular inheritance and chemical reset initial conditions. We find that near-to-mid-IR absorption features of H 2 O, CO 2 , and CH 3 OH are readily observable in disk-integrated spectra of highly inclined disks while CO, NH 3 , and CH 4 ice do not show prominent features. CH 3 OH ice has low abundance and is not observable in the reset model, making this species an excellent diagnostic...
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# Collision between Radiative and Adiabatic Supersonic Flows

The self-similar dynamics of the collision between radiative and adiabatic supersonic planar flows are performed assuming homogeneous radiation cooling. New self-similar solutions relevant to both astrophysical objects and laboratory experiments are derived. Numerical simulations investigate the formation of the radiative cooling shock in the interstellar medium and laboratory Xenon plasma to demonstrate the self-similarity of the interaction in the special case of balanced ram pressure. When the radiation cooling is inhomogeneous, the flow can become thermally unstable and deviate from the self-similar solution.
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# AT 2019qyl in NGC 300: Internal Collisions in the Early Outflow from a Very Fast Nova in a Symbiotic Binary

Nova eruptions, thermonuclear explosions on the surfaces of white dwarfs (WDs), are now recognized to be among the most common shock-powered astrophysical transients. We present the early discovery and rapid ultraviolet (UV), optical, and infrared (IR) temporal development of AT 2019qyl, a recent nova in the nearby Sculptor Group galaxy NGC 300. The light curve shows a rapid rise lasting ≲1 day, reaching a peak absolute magnitude of M V = −9.2 mag and a very fast decline, fading by 2 mag over 3.5 days. A steep dropoff in the light curves after 71 days and the rapid decline timescale suggest a low-mass ejection from a massive WD with M WD ≳ 1.2 M ⊙ . We present an unprecedented view of the early spectroscopic evolution of such an event. Three spectra prior to the peak reveal a complex, multicomponent outflow giving rise to internal collisions and shocks in the ejecta of an He/N-class nova. We identify a coincident IR-v...
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# Predicting the Redshift of γ -Ray-loud AGNs Using Supervised Machine Learning

Active galactic nuclei (AGNs) are very powerful galaxies characterized by extremely bright emissions coming from their central massive black holes. Knowing the redshifts of AGNs provides us with an opportunity to determine their distance to investigate important astrophysical problems, such as the evolution of the early stars and their formation, along with the structure of early galaxies. The redshift determination is challenging because it requires detailed follow-up of multiwavelength observations, often involving various astronomical facilities. Here we employ machine-learning algorithms to estimate redshifts from the observed γ -ray properties and photometric data of γ -ray-loud AGNs from the Fourth Fermi-LAT Catalog. The prediction is obtained with the Superlearner algorithm using a LASSO-selected set of predictors. We obtain a tight correlation, with a Pearson correlation coefficient of 71.3% between the inferred and observed redshifts and an average Δ z ...
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# A New “Non-energetic” Route to Complex Organic Molecules in Astrophysical Environments: The C + H 2 O → H 2 CO Solid-state Reaction

20 October 2021 at 16:00
The solid-state reaction C + H 2 O → H 2 CO was studied experimentally following the co-deposition of C atoms and H 2 O molecules at low temperatures. In spite of the reaction barrier and absence of energetic triggering, the reaction proceeds fast on the experimental timescale pointing to its quantum tunneling mechanism. This route to formaldehyde shows a new “non-energetic” pathway to complex organic and prebiotic molecules in astrophysical environments. Energetic processing by UV irradiation of the ice produced by co-deposition of C and H 2 O reactants leads mainly to the destruction of H 2 CO and the formation of CO 2 , challenging the role of energetic processing in the synthesis of complex organic molecules under astrophysically relevant conditions.
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# Breaching the Limit: Formation of GW190521-like and IMBH Mergers in Young Massive Clusters

The LIGO-Virgo-Kagra Collaboration (LVC) discovered recently GW190521, a gravitational wave (GW) source associated with the merger between two black holes (BHs) with mass 66 and >85 M ⊙ . GW190521 represents the first BH binary merger with a primary mass falling in the upper-mass gap and the first leaving behind an ∼150 M ⊙ remnant. So far, the LVC has reported the discovery of four further mergers having a total mass >100 M ⊙ , i.e., in the intermediate-mass black hole (IMBH) mass range. Here, we discuss results from a series of 80 N -body simulations of young massive clusters that implement relativistic corrections to follow compact object mergers. We discover the development of a GW190521-like system as the result of a third-generation merger, and four IMBH-BH mergers with total mass (300–350) M ⊙ . We show that these IMBH-BH mergers are low-frequency GW sources detectable with LISA and Dec...
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# Grain Growth in Escaping Atmospheres: Implications for the Radius Inflation of Super-Puffs

20 October 2021 at 16:00
Super-puffs—low-mass exoplanets with extremely low bulk density—are attractive targets for exploring their atmospheres and formation processes. Recent studies suggested that the large radii of super-puffs may be caused by atmospheric dust entrained in the escaping atmospheres. In this study, we investigate how the dust grows in escaping atmospheres and influences the transit radii using a microphysical model of grain growth. Collision growth is efficient in many cases, hindering the upward transport of dust via enhanced gravitational settling. We find that the dust abundance in the outflow hardly exceeds the Mach number at the dust production region. Thus, dust formed in the upper atmospheres, say at P ≲ 10 −5 bar, is needed to launch a dusty outflow with a high dust abundance. With sufficiently high dust production altitudes and rates, the dusty outflow can enhance the observable radius by a factor of ∼2 or even more. We suggest that photochemical haze is a pro...
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# Comparative Analysis of the 2020 November 29 Solar Energetic Particle Event Observed by Parker Solar Probe

We analyze two specific features of the intense solar energetic particle (SEP) event observed by Parker Solar Probe (PSP) between 2020 November 29 and 2020 December 2. The interplanetary counterpart of the coronal mass ejection (CME) on 2020 November 29 that generated the SEP event (hereafter ICME-2) arrived at PSP (located at 0.8 au from the Sun) on 2020 December 1. ICME-2 was preceded by the passage of an interplanetary shock at 18:35 UT on 2020 November 30 (hereafter S2), that in turn was preceded by another ICME (i.e., ICME-1) observed in situ on 2020 November 30. The two interesting features of this SEP event at PSP are the following: First, the presence of the intervening ICME-1 affected the evolution of the ≲8 MeV proton intensity-time profiles resulting in the observation of inverted energy spectra throughout the passage of ICME-1. Second, the sheath region preceding ICME-2 was characterized by weak magnetic fields compared to those measured immediately after the passage...
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# The Final Fates of Close Hot Subdwarf–White Dwarf Binaries: Mergers Involving He/C/O White Dwarfs and the Formation of Unusual Giant Stars with C/O-Dominated Envelopes

20 October 2021 at 16:00
Recently, a class of Roche-lobe-filling binary systems consisting of hot subdwarf stars and white dwarfs (WDs) with sub-hour periods has been discovered. At present, the hot subdwarf is in a shell He-burning phase and is transferring some of its remaining thin H envelope to its WD companion. As the evolution of the hot subdwarf continues, it is expected to detach, leaving behind a low-mass C/O-core WD secondary with a thick He layer. Then, on a timescale of ∼10 Myr, gravitational wave radiation will again bring the systems into contact. If the mass transfer is unstable and results in a merger and a catastrophic thermonuclear explosion is not triggered, it creates a remnant with a C/O-dominated envelope, but one still rich enough in He to support an R Corona Borealis-like shell-burning phase. We present evolutionary calculations of this phase and discuss its potential impact on the cooling of the remnant WD.
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# Forward Modeling of Solar Coronal Magnetic-field Measurements Based on a Magnetic-field-induced Transition in Fe x

It was recently proposed that the intensity ratios of several extreme ultraviolet spectral lines from Fe x ions can be used to measure the solar coronal magnetic field based on magnetic-field-induced transition (MIT) theory. To verify the suitability of this method, we performed forward modeling with a three-dimensional radiation magnetohydrodynamic model of a solar active region. Intensities of several spectral lines from Fe x were synthesized from the model. Based on MIT theory, the intensity ratios of the MIT line Fe x 257 Å to several other Fe x lines were used to derive magnetic-field strengths, which were then compared with the field strengths in the model. We also developed a new method to simultaneously estimate the coronal density and temperature from the Fe x 174/175 and 184/345 Å line ratios. Using these estimates, we demonstrated that the MIT t...
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# Detection of Lyman Continuum from 3.0 < z < 3.5 Galaxies in the HETDEX Survey

Questions as to what drove the bulk reionization of the universe, how that reionization proceeded, and how the hard ionizing radiation reached the intergalactic medium remain open and debated. Observations probing that epoch are severely hampered by the increasing amounts of neutral gas with increasing redshift, so a small, but growing, number of experiments are targeting star-forming galaxies ( z ∼ 3) as proxies. However, these studies, while providing fantastic detail, are time intensive, contain relatively few targets, and can suffer from selection biases. As a complementary alternative, we investigate whether stacking the already vast (and growing) numbers of low-resolution (Δ λ / λ = 800) Ly α-e mitting (LAE) galaxy spectra from the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) can be used to measure ionizing photons (rest-frame 880–910 Å) escaping their galaxy hosts. As a blind survey, HETDEX avoids the biases from continuum-selected galaxies...
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# ASASSN-15hy: An Underluminous, Red 03fg-like Type Ia Supernova

We present photometric and spectroscopic observations of the 03fg-like Type Ia supernova (SN Ia) ASASSN-15hy from the ultraviolet (UV) to the near-infrared (NIR). ASASSN-15hy shares many of the hallmark characteristics of 03fg-like SNe Ia, previously referred to as “super-Chandrasekhar” SNe Ia. It is bright in the UV and NIR, lacks a clear i -band secondary maximum, shows a strong and persistent C ii feature, and has a low Si ii λ 6355 velocity. However, some of its properties are also extreme among the subgroup. ASASSN-15hy is underluminous ( M B ,peak = ##IMG## [http://ej.iop.org/images/0004-637X/920/2/107/apjac1606ieqn1.gif] {$-{19.14}_{-0.16}^{+0.11}$} mag), red ( ##IMG## [http://ej.iop.org/images/0004-637X/920/2/107/apjac1606ieqn2.gif] {${(B-V)}_{B\max }={0.18}_{-0.03}^{+0.01}$} mag), yet slowly declining (Δ m 15 ( B ) = 0.72 ...
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Before yesterdayThe Astrophysical Journal - latest papers

# The MOSDEF-LRIS Survey: Probing the ISM/CGM Structure of Star-forming Galaxies at z ∼ 2 Using Rest-UV Spectroscopy

The complex structure of gas, metals, and dust in the interstellar and circumgalactic medium (ISM and CGM, respectively) in star-forming galaxies can be probed by Ly α emission and absorption, low-ionization interstellar (LIS) metal absorption, and dust reddening E ( B − V ). We present a statistical analysis of the mutual correlations among Ly α equivalent width (EW Ly α ), LIS equivalent width (EW LIS ), and E ( B − V ) in a sample of 157 star-forming galaxies at z ∼ 2.3. With measurements obtained from individual deep rest-UV spectra and spectral energy distribution modeling, we find that the tightest correlation exists between EW LIS and E ( B − V ), although correlations among all three parameters are statistically significant. These results signal a direct connection between dust and metal-enriched H i gas and that they are likely cospatial. ...
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# Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph. I. An Accurate Look at the L-to-T Transition at ∼300 Myr from Optical Through Mid-infrared Spectrophotometry

We present Spitzer IRS 5–14 μ m spectra and 16 μ m and 22 μ m photometry of the T2.5 companion to the ∼300 Myr old G0V star HN Peg. We incorporate previous 0.8–5 μ m observations to obtain the most comprehensive spectral energy distribution (SED) of an intermediate-gravity L/T-transition dwarf that, together with an accurate Gaia EDR3 parallax of the primary, enables us to derive precise fundamental parameters. We find that young (≈0.1–0.3 Gyr) early-T dwarfs on average have ≈140 K lower effective temperatures, ≈20% larger radii, and similar bolometric luminosities compared to ≳1 Gyr old field dwarfs with similar spectral types. Our accurate infrared spectrophotometry offers new detail at wavelengths where the dominant carbon-bearing molecules have their strongest transitions: at 3.4 μ m for methane and at 4.6 μ m for carbon monoxide. We assess the performance of various widely available photospheric models and find that models with condensate...
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# Weather on Other Worlds. VI. Optical Spectrophotometry of Luhman 16B Reveals Large-amplitude Variations in the Alkali Lines

19 October 2021 at 16:00
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 photomet...
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# The Consistency of Chemical Clocks among Coeval Stars

19 October 2021 at 16:00
The abundance ratios of some chemical species have been found to correlate with stellar age, leading to the possibility of using stellar atmospheric abundances as stellar age indicators. These chemical clocks have already been calibrated with solar twins and open clusters, but it remains to be seen whether they can be effective at identifying coeval stars in a population that spans a broad parameter space (i.e., the promise of chemical tagging). Since the components of wide binaries are known to be stars of common origins, they constitute ideal laboratories for testing the usefulness of chemical clocks for the age dating of field stars. Using a combination of our new measurements and literature data on wide binaries, we show for the first time that chemical clocks are even more consistent among the components of wide binaries than their individual abundances. Moreover, the special case of HIP 34426/HIP 34407 may indicate that chemical clocks are consistent for coeval stars even ...
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# DirtyGrid II: An Analysis of the Dust and Stellar Properties in Nearby Star-forming Galaxies

19 October 2021 at 16:00
We study the dust and stellar properties of the Spitzer Infrared Nearby Galaxies Survey galaxies by fitting the ultraviolet (UV) to far-infrared (FIR) spectral energy distributions using the Dirty Grid stellar and dust radiative transfer models. We find a minimum of two components of different stellar ages are needed, representing a young and an old stellar population, in order to obtain good fits for most of the galaxies. Our total dust masses agree with literature dust masses to within a factor of 2, and the residuals correlate most strongly with the stellar mass surface density of the old component. The LMC-2 dust grain model best describes the dust found in these normal star-forming galaxies. The derived attenuation curves are steeper than those found previously for starburst galaxies, and possess a weak 2175 Å feature. The relative contribution of the young and old stellar components as a function of wavelength reveals that the young component domina...
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# The Star Formation History of a Post-starburst Galaxy Determined from Its Cluster Population

The recent star formation histories (SFHs) of post-starburst galaxies have been determined almost exclusively from detailed modeling of their composite starlight. This has provided important but limited information on the number, strength, and duration of bursts of star formation. In this work, we present a direct and independent measure of the recent SFH of the post-starburst galaxy S12 (plate-mjd-fiber for SDSS 623-52051-207; designated EAS12 in Smercina et al.) from its star cluster population. We detect clusters from high-resolution, UBR optical images taken with the Hubble Space Telescope and compare their luminosities and colors with stellar population models to estimate the ages and masses of the clusters. No clusters younger than ∼70 Myr are found, indicating star formation shut off at this time. Clusters formed ∼120 Myr ago reach masses up to a ∼few × 10 7 M ⊙ , several times higher than similar-age counterparts formed in actively mergi...
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# Survival Times of Supramassive Neutron Stars Resulting from Binary Neutron Star Mergers

19 October 2021 at 16:00
A binary neutron star (BNS) merger can lead to various outcomes, from indefinitely stable neutron stars, through supramassive neutron stars (SMNSs) or hypermassive neutron stars supported only temporarily against gravity, to black holes formed promptly after the merger. Up-to-date constraints on the BNS total mass and the neutron star equation of state suggest that a long-lived SMNS may form in ∼0.45–0.9 of BNS mergers. A maximally rotating SMNS needs to lose ∼(3–6) × 10 52 erg of its rotational energy before it collapses, on a fraction of the spin-down timescale. An SMNS formation imprints on the electromagnetic counterparts to the BNS merger. However, a comparison with observations reveals tensions. First, the distribution of collapse times is too wide and that of released energies too narrow (and the energy itself too large) to explain the observed distributions of internal X-ray plateaus, invoked as evidence for SMNS-powered energy injection. Second, the immense en...
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# The Resolved Sunyaev–Zel’dovich Profiles of Nearby Galaxy Groups

19 October 2021 at 16:00
Many of the baryons in galaxy groups are thought to have been driven out to large distances (≳ R 500 ) by feedback, but there are few constraining observations of this extended gas. This work presents the resolved Sunyaev–Zel’dovich (SZ) profiles for a stacked sample of 10 nearby galaxy groups within the mass range ##IMG## [http://ej.iop.org/images/0004-637X/920/2/104/apjac1796ieqn1.gif] {${\mathrm{log}}_{10}({M}_{500}[{M}_{\odot }])=13.6\mbox{--}13.9$} . We measured the SZ profiles using the publicly available y -map from the Planck Collaboration as well as our own y -maps constructed from more recent versions of Planck data. The y -map extracted from the latest data release yielded a significant SZ detection out to 3 R 500 . In addition, the stacked profile from these data was consistent with simulations that included AGN feedback. Our best-fit model using the latest Planck data suggested a baryon fraction...
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