adsabs/SciX_UAT_keywords huggingface dataset:
Thunder and Lightning: Using Neutron-star Mergers as Simultaneous Standard Candles and Sirens to Measure Cosmological Parameters

With the detection of gravitational wave (GW) GW170817 and its associated electromagnetic (EM) counterparts from a binary neutron star (NS) merger, the "standard siren" method for Hubble-constant measurements is expected to play a role in the Hubble-constant tension in the next few years. One intriguing proposal put forward in multiple studies is to use an NS merger's optical counterpart, known as a kilonova, as a standard candle, because its absolute magnitude can in principle be calculated from simulations. In this work, I detail the statistical framework for performing joint standard-candle and standard-siren measurements using GWs, EM follow-up data, and simulations of EM counterparts. I then perform an example analysis using GW170817 and its optical counterpart AT2017gfo to illustrate the method and the method's limitations. Crucially, the inferences using this method are only as robust as the EM counterpart models, so significant theoretical advances are needed before this method can be employed for precision cosmology.

Keywords: neutron stars; hubble constant; cosmological parameters; gravitational waves
Past, Present, and Future of Mars Polar Science: Outcomes and Outlook from the 7th International Conference on Mars Polar Science and Exploration

Mars Polar Science is a subfield of Mars science that encompasses all studies of the cryosphere of Mars and its interaction with the Martian environment. Every 4 yr, the community of scientists dedicated to this subfield meets to discuss new findings and debate open issues in the International Conference on Mars Polar Science and Exploration (ICMPSE). This paper summarizes the proceedings of the seventh ICMPSE and the progress made since the sixth edition. We highlight the most important advances and present the most salient open questions in the field today, as discussed and agreed upon by the participants of the conference. We also feature agreed-upon suggestions for future methods, measurements, instruments, and missions that would be essential to answering the main open questions presented. This work is thus an overview of the current status of Mars Polar Science and is intended to serve as a road map for the direction of the field during the next 4 yr and beyond, helping to shape its contribution within the larger context of planetary science and exploration.

Keywords: mars; planetary climates; polar caps; planetary polar regions; planetary science
Sample Variance in Cosmological Observations with a Narrow Field of View

Surveys with a narrow field of view can play an important role in probing cosmology, but inferences from these surveys suffer from large sample variance, arising from random fluctuations around the cosmic mean. The standard method for computing the sample variance is based on two key approximations: treating perturbations linearly and the survey geometry as a box. We demonstrate that it can lead to a significant underestimate of the sample variance in narrow surveys. We present a new method for accurately computing the sample variance and apply our method to the recent observations of the warm-hot intergalactic medium (WHIM) based on spectroscopic measurements of blazars. We find that the sample variances in these surveys are significantly larger than the quoted measurement errors; for example, the cosmic mean baryon density contained in the WHIM could be lower by 54% at 1σ fluctuation than estimated in one observation. Accurately quantifying the sample variance is essential in deriving correct interpretations of the measurements in surveys with a small field of view.

Keywords: observational cosmology; cosmology
Third Epoch HST Imaging of a Nonradiative Shock in the Cygnus Loop Supernova Remnant

We present new HST/WFC3 optical images of a region in the northeastern part of the Cygnus Loop supernova remnant, which includes a well-studied Balmer-line filament. These data represent the third epoch of HST Hα imaging and a second epoch of [O III] λ5007 imaging of that particular filament. The Hα images were used to measure the proper motions at various locations along the shock front, and the values ranged from 55 to 85 mas yr-1 with a median value of 70 mas yr-1, which corresponds to a shock velocity of 240 km s-1. The proper motions between epochs 1 and 2 were the same as between epochs 2 and 3, implying that there has been no measurable deceleration of the shock in the 22 yr period between the first and third epochs. The range of proper motions (and therefore shock velocities) along the filament indicate variations of over a factor of two in the preshock density. The [O III] emission is prominent toward one end of the filament where the shock has transitioned from nonradiative to radiative. The proper motion is smaller than for the Hα filaments, and it corresponds to a shock velocity of about 155 km s-1. The images obtained about 18 yr apart show that the [O III] morphology has not changed, which places limits on any short-timescale variations due to catastrophic cooling or thermal instabilities. We find that the effective shock age is less than the eddy turnover timescale, which implies that turbulence has not yet influenced the dynamics of the shock.

Keywords: shocks; filamentary nebulae; supernova remnants
Impact of Dust on Spectral Distortion Measurements of the Cosmic Microwave Background

Spectral distortions of the cosmic microwave background (CMB) are sensitive to energy injection by exotic physics in the early universe. The proposed Primordial Inflation Explorer (PIXIE) mission has the raw sensitivity to provide meaningful limits on new physics, but only if foreground emission can be adequately modeled. We quantify the impact of interstellar dust on Compton y and μ measurements by considering a range of grain size distributions and compositions constrained by theoretical and observational priors. We find that PIXIE can marginalize over a modest number of dust parameters and still recover y and μ estimates, though with increased uncertainty. As more foreground components are included (synchrotron, free-free), estimates of y degrade, and measurement of μ in the range sometimes considered for the standard ΛCDM of 2 × 10-8 becomes infeasible without ancillary low-frequency foreground information. An additional concern is dust absorption of the CMB monopole, a subtle effect that must be included. We quantify one form of model discrepancy error, finding that the error introduced by fitting our interstellar medium dust model with a modified blackbody is too large for CMB spectral distortions to be detectable. The greatest challenge may be the cosmic infrared background (CIB). We find that μ and y are extremely sensitive to modeling choices for the CIB, and quantify biases expected for a range of assumptions.

Keywords: interstellar dust; cosmic microwave background radiation; interstellar dust extinction; interstellar medium; astrosphere interstellar medium interactions; cmbr detectors; cosmology; observational cosmology; infrared astronomy
Estimating Statistical Uncertainties of Internal Kinematics of Galaxies and Star Clusters Derived Using Full Spectrum Fitting

Pixel-space full spectrum fitting exploiting nonlinear χ2 minimization became a de facto standard way of deriving internal kinematics from absorption line spectra of galaxies and star clusters. However, reliable estimation of uncertainties for kinematic parameters remains a challenge and is usually addressed by running computationally expensive Monte-Carlo simulations. Here we derive simple formulae for the radial velocity and velocity dispersion uncertainties based solely on the shape of a template spectrum used in the fitting procedure and signal-to-noise information. Comparison with Monte-Carlo simulations provides agreement within a few per cent for different templates, signal-to-noise ratios and input velocity dispersions between 0.5 and 10 times the instrumental spectral resolution. For moderate template mismatch our technique returns uncertainties consistent within 20%-30% with those reported by Monte-Carlo simulations. We provide IDL and PYTHON implementations of our approach. The main applications are: (i) exposure time calculators; (ii) design of observational programs and estimates on expected uncertainties for spectral surveys of galaxies and star clusters; (iii) a cheap and accurate substitute for Monte-Carlo simulations when running them for large samples of thousands of spectra is unfeasible.

Keywords: analytical mathematics; astronomy data analysis; galaxy kinematics; galaxy dynamics
Measuring Frequency and Period Separations in Red-giant Stars Using Machine Learning

Asteroseismology is used to infer the interior physics of stars. The Kepler and TESS space missions have provided a vast data set of red-giant lightcurves, which may be used for asteroseismic analysis. These data sets are expected to significantly grow with future missions such as PLATO, and efficient methods are therefore required to analyze these data rapidly. Here, we describe a machine-learning algorithm that identifies red giants from the raw oscillation spectra and captures p- and mixed-mode parameters from the red-giant power spectra. We report algorithmic inferences for large frequency separation (Δν), frequency at maximum amplitude ( ${\nu }_{\max }$ ), and period separation (ΔΠ) for an ensemble of stars. In addition, we have discovered ~25 new probable red giants among 151,000 Kepler long-cadence stellar-oscillation spectra analyzed by this method, among which four are binary candidates that appear to possess red-giant counterparts. To validate the results of this method, we selected ~3000 Kepler stars, at various evolutionary stages ranging from subgiants to red clumps, and compare inferences of Δν, ΔΠ, and ${\nu }_{\max }$ with estimates obtained using other techniques. The power of the machine-learning algorithm lies in its speed: It is able to accurately extract seismic parameters from 1000 spectra in ~5 s on a modern computer (a single core of the Intel® Xeon® Platinum 8280 CPU).

Keywords: asteroseismology; neural networks; red giant branch; pulsation modes; stellar oscillations
Absolute Calibration. IV. Use of G-type Stars as Primary Calibrators

We demonstrate an approach to determine spectral energy distribution (SED) templates that are accurate to the 1% level from the visible through the infrared for nearby (unextincted) solar-type stars. Our approach is based only on measurements of T eff, log(g), and M/H and the use of standard theoretical SED models. The success of this approach confirms that the existing absolute calibration is likely to be accurate to this level throughout this spectral range. We then demonstrate how to measure and correct for extinction, allowing extension of this calibration approach to faint levels (and more distant stars). We provide template SEDs in digital form for 11 G-dwarf stellar calibrators.

Keywords: fundamental parameters of stars; infrared photometry; astronomical techniques
On the Existence of the Plateau Emission in High-energy Gamma-Ray Burst Light Curves Observed by Fermi-LAT

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) shows long-lasting high-energy emission in many gamma-ray bursts (GRBs), similar to X-ray afterglows observed by the Neil Gehrels Swift Observatory (Swift). Some LAT light curves (LCs) show a late-time flattening reminiscent of X-ray plateaus. We explore the presence of plateaus in LAT temporally extended emission analyzing GRBs from the second Fermi-LAT GRB Catalog from 2008 to 2016 May with known redshifts, and check whether they follow closure relations corresponding to four distinct astrophysical environments predicted by the external forward shock model. We find that three LCs can be fit by the same phenomenological model used to fit X-ray plateaus and show tentative evidence for the existence of plateaus in their high-energy extended emission. The most favorable scenario is a slow-cooling regime, whereas the preferred density profile for each GRBs varies from a constant-density interstellar medium to an r-2 wind environment. We also compare the end time of the plateaus in γ-rays and X-rays using a statistical comparison with 222 Swift GRBs with plateaus and known redshifts from 2005 January to 2019 August. Within this comparison, the case of GRB 090510 shows an indication of chromaticity at the end time of the plateau. Finally, we update the 3D fundamental plane relation among the rest-frame end time of the plateau, its correspondent luminosity, and the peak prompt luminosity for 222 GRBs observed by Swift. We find that these three LAT GRBs follow this relation.

Keywords: gamma-ray bursts
How Efficient Is the Streaming Instability in Viscous Protoplanetary Disks?

The streaming instability is a popular candidate for planetesimal formation by concentrating dust particles to trigger gravitational collapse. However, its robustness against the physical conditions expected in protoplanetary disks is unclear. In particular, particle stirring by turbulence may impede the instability. To quantify this effect, we develop the linear theory of the streaming instability with external turbulence modeled by gas viscosity and particle diffusion. We find the streaming instability is sensitive to turbulence, with growth rates becoming negligible for alpha viscosity parameters α ≳ St1.5, where St is the particle Stokes number. We explore the effect of nonlinear drag laws, which may be applicable to porous dust particles, and find growth rates are modestly reduced. We also find that gas compressibility increases growth rates by reducing the effect of diffusion. We then apply the linear theory to global models of viscous protoplanetary disks. For minimum-mass solar nebula disk models, we find the streaming instability only grows within disk lifetimes beyond tens of astronomical units, even for centimeter-sized particles and weak turbulence (α ∼ 10-4). Our results suggest it is rather difficult to trigger the streaming instability in nonlaminar protoplanetary disks, especially for small particles.

Keywords: planetary theory; exoplanet formation; hydrodynamics; planet formation
TOI-1695 b: A Water World Orbiting an Early-M Dwarf in the Planet Radius Valley

Characterizing the bulk compositions of transiting exoplanets within the M dwarf radius valley offers a unique means to establish whether the radius valley emerges from an atmospheric mass-loss process or is imprinted by planet formation itself. We present the confirmation of such a planet orbiting an early-M dwarf (T mag = 11.0294 ± 0.0074, M s = 0.513 ± 0.012 M ⊙, R s = 0.515 ± 0.015 R ⊙, and T eff = 3690 ± 50 K): TOI-1695 b (P = 3.13 days and ${R}_{p}={1.90}_{-0.14}^{+0.16}\ {R}_{\oplus }$ ). TOI-1695 b's radius and orbital period situate the planet between model predictions from thermally driven mass loss versus gas depleted formation, offering an important test case for radius valley emergence models around early-M dwarfs. We confirm the planetary nature of TOI-1695 b based on five sectors of TESS data and a suite of follow-up observations including 49 precise radial velocity measurements taken with the HARPS-N spectrograph. We measure a planetary mass of 6.36 ± 1.00 M ⊕, which reveals that TOI-1695 b is inconsistent with a purely terrestrial composition of iron and magnesium silicate, and instead is likely a water-rich planet. Our finding that TOI-1695 b is not terrestrial is inconsistent with the planetary system being sculpted by thermally driven mass loss. We present a statistical analysis of seven well-characterized planets within the M dwarf radius valley demonstrating that a thermally driven mass-loss scenario is unlikely to explain this population.

Keywords: exoplanets; exoplanet formation; planet formation; exoplanet evolution; m dwarf stars; exoplanet atmospheric evolution; transit photometry; radial velocity; stellar properties
Two Repeated Transient Quasiperiodic Oscillations in the γ-Ray Emission from the Blazar 3C 279

In this work, we report for the first time two repeated transient quasiperiodic oscillations (QPOs) in the γ-ray light curve of the TeV blazar 3C 279. We search for the periodicity in the light curve and estimate its confidence level using the weighted wavelet Z-transform, the Lomb–Scargle periodogram, and the REDFIT techniques. The main results are as follows: (1) a QPO of ∼33 days (>2.5σ) is found during the flare of 117 days (MJD 55008–55125) from 2009 June to November. Interestingly, the same QPO (∼39 days) reappeared in the flaring duration from MJD 59430 to 59585, with the confidence level of >4σ. (2) Another transient QPO of ∼91 days with a significance of >3.8σ is found during a period with 455 days (MJD 58430–58985) from 2019 February to 2020 May. Under the premise of considering the QPOs reported in the literature, the QPO of ∼40 days is repeated three times and the QPO of ∼91 days is repeated twice. We discuss several physical models explaining the QPOs of this blazar. Our study may suggest that the two QPOs originate from the twin jets of the binary black holes at the center of 3C 279. The repeated occurrence of QPOs of a similar scale strongly supports the geometric scenario of a blob spiraling within the jet. Furthermore, the hypothesis of a sheath in the jet may also be a potential explanation for the repetitive γ-ray flare patterns observed in the light curve.

Keywords: blazars
Iron-peak Element Abundances in Warm Very Metal-poor Stars

We have derived new detailed abundances of Mg, Ca, and the Fe-group elements Sc through Zn (Z = 21-30) for 37 main-sequence turnoff very metal-poor stars ([Fe/H] ≲-2.1). We analyzed Keck HIRES optical and near-UV high signal-to-noise spectra originally gathered for a Be abundance survey. Using typically ~400 Fe-group lines with accurate laboratory transition probabilities for each star, we have determined accurate LTE metallicities and abundance ratios for neutral and ionized species of the 10 Fe-group elements as well as α elements Mg and Ca. We find good neutral/ion abundance agreement for the six elements that have detectable transitions of both species in our stars in the 3100-5800 Å range. Earlier reports of correlated Sc-Ti-V relative overabundances are confirmed, and appear to slowly increase with decreasing metallicity. To this element trio we add Zn; it also appears to be increasingly overabundant in the lowest-metallicity regimes. Co appears to mimic the behavior of Zn, but issues surrounding its abundance reliability cloud its interpretation.

Keywords: nucleosynthesis; chemical abundances; population ii stars; stellar spectral lines
TIC 454140642: A Compact, Coplanar, Quadruple-lined Quadruple Star System Consisting of Two Eclipsing Binaries

We report the discovery of a compact, coplanar, quadruple-lined, eclipsing quadruple star system from Transiting Exoplanet Survey Satellite data, TIC 454140642, also known as TYC 0074-01254-1. The target was first detected in Sector 5 with a 30-minute cadence in full-frame images and then observed in Sector 32 with a 2-minute cadence. The light curve exhibits two sets of primary and secondary eclipses with periods of PA = 13.624 days (binary A) and PB = 10.393 days (binary B). Analysis of archival and follow-up data shows clear eclipse-timing variations and divergent radial velocities, indicating dynamical interactions between the two binaries and confirming that they form a gravitationally bound quadruple system with a 2 + 2 hierarchy. The Aa+Ab binary, Ba+Bb binary, and A-B system are aligned with respect to each other within a fraction of a degree: the respective mutual orbital inclinations are 0°25 (A versus B), 0°37 (A versus A-B), and 0°47 (B versus A-B). The A-B system has an orbital period of 432 days-the second shortest of the confirmed quadruple systems-and an orbital eccentricity of 0.3.

Keywords: eclipsing binary stars; transit photometry; multiple stars; astronomy data analysis; astronomy data modeling
The CO Outflow Components Ejected by a Recent Accretion Event in B335

Protostellar outflows often present a knotty appearance, providing evidence of sporadic accretion in stellar mass growth. To understand the direct relation between mass accretion and ejection, we analyze the contemporaneous accretion activity and associated ejection components in B335. B335 has brightened in the mid-IR by 2.5 mag since 2010, indicating increased luminosity, presumably due to an increased mass accretion rate onto the protostar. Atacama Large Millimeter/submillimeter Array (ALMA) observations of 12CO emission in the outflow reveal high-velocity emission, estimated to have been ejected 4.6-2 yr before the ALMA observations and consistent with the jump in mid-IR brightness. The consistency in timing suggests that the detected high-velocity ejection components are directly linked to the most recent accretion activity. We calculated the kinetic energy, momentum, and force for the ejection component associated with the most recent accretion activity and found that, at least, about 1.0% of the accreted mass has been ejected. More accurate information on the jet inclination and the temperature of the ejected gas components will better constrain the ejected mass induced by the recently enhanced accretion event.

Keywords: young stellar objects; protostars; stellar jets; stellar accretion
The ELM Survey. IX. A Complete Sample of Low-mass White Dwarf Binaries in the SDSS Footprint

We present the discovery of 17 double white dwarf (WD) binaries from our ongoing search for extremely low mass (ELM) < 0.3 M ⊙ WDs, objects that form from binary evolution. Gaia parallax provides a new means of target selection that we use to evaluate our original ELM Survey selection criteria. Cross-matching the Gaia and Sloan Digital Sky Survey (SDSS) catalogs, we identify an additional 36 ELM WD candidates with 17 < g < 19 mag and within the 3σ uncertainties of our original color selection. The resulting discoveries imply the ELM Survey sample was 90% complete in the color range -0.4 < (g - r)0 < -0.1 mag (approximately 9000 K < T eff < 22,000 K). Our observations complete the sample in the SDSS footprint. Two newly discovered binaries, J123950.370-204142.28 and J232208.733+210352.81, have orbital periods of 22.5 and 32 minutes, respectively, and are future Laser Interferometer Space Antenna gravitational-wave sources.

Keywords: compact binary stars; white dwarf stars; da stars