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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

An Improved Method to Measure the Cosmic Curvature

In this paper, we propose an improved model-independent method to constrain the cosmic curvature by combining the most recent Hubble parameter H ( z ) and supernovae Ia (SNe Ia) data. Based on the H ( z ) data, we first use the model-independent smoothing technique, Gaussian processes, to construct a distance modulus μ {sub H} ( z ), which is susceptible to the cosmic curvature parameter Ω{sub k}. In contrary to previous studies, the light-curve-fitting parameters, which account for the distance estimation of SN (μ {sub SN}( z )), are set free to investigate whether Ω {sub k} has a dependence on them. By comparing μ {sub H} ( z ) to μ {sub SN}(z), we put limits on Ω {sub k}. Our results confirm that Ω {sub k} is independent of the SN light-curve parameters. Moreover, we show that the measured Ω {sub k} is in good agreement with zero cosmic curvature, implying that there is no significant deviation from a flat universe at the current observational data level. We also test the influence of different H(z) samples and different Hubble constant H {sub 0} values, finding that different H(z) samples do not have a significant impact on the constraints. However, different H {sub 0} priors can affect the constraints of Ω {sub k} to some degree. The prior of H {sub 0} = 73.24 ± 1.74 km s{sup −1} Mpc{sup −1} gives a value of Ω {sub k}, a little bit above the 1 σ confidence level away from 0, but H{sub 0} = 69.6 ± 0.7 km s{sup −1} Mpc{sup −1} gives it below 1 σ .

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Far-ultraviolet to Near-infrared Spectroscopy of a Nearby Hydrogen-poor Superluminous Supernova Gaia16apd

We report the first maximum-light far-ultraviolet (FUV) to near-infrared (NIR) spectra (1000 Å − 1.62 μm, rest) of a hydrogen-poor superluminous supernova, Gaia16apd. At z = 0.1018, it is the second closest and the UV brightest SLSN-I, with 17.4 mag in Swift UVW2 band at −11 days pre-maximum. The coordinated observations with HST, Palomar, and Keck were taken at −2 to +25 days. Assuming an exponential (or t {sup 2}) form, we derived the rise time of 33 days and the peak bolometric luminosity of 3 × 10{sup 44} erg s{sup −1}. At the maximum, the photospheric temperature and velocity are 17,000 K and 14,000 km s{sup −1}, respectively. The inferred radiative and kinetic energy are roughly 1 × 10{sup 51} and 2 × 10{sup 52} erg. Gaia16apd is extremely UV luminous, and emits 50% of its total luminosity at 1000–2500 Å. Compared to the UV spectra (normalized at 3100 Å) of well studied SN1992A (Ia), SN2011fe (Ia), SN1999em (IIP), and SN1993J (IIb), it has orders of magnitude more FUV emission. This excess is interpreted primarily as a result of weaker metal-line blanketing due to a much lower abundance of iron group elements in the outer ejecta. Because these elements originate either from the natal metallicity of the star, or have been newly produced, our observation provides direct evidence that little of these freshly synthesized material, including {sup 56}Ni, were mixed into the outer ejecta, and the progenitor metallicity is likely sub-solar. This disfavors Pair-instability Supernova models with helium core masses ⩾90 M{sub ⊙}, where substantial {sup 56}Ni material is produced. A higher photospheric temperature definitely contributes to the FUV excess from Gaia16apd. Compared with Gaia16apd, we find PS1-11bam is also UV luminous.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Three-dimensional Expansion of the Ejecta from Tycho's Supernova Remnant

We present the first 3D measurements of the velocity of various ejecta knots in Tycho’s supernova remnant, known to result from a Type Ia explosion. Chandra X-ray observations over a 12 yr baseline from 2003 to 2015 allow us to measure the proper motion of nearly 60 “tufts” of Si-rich ejecta, giving us the velocity in the plane of the sky. For the line-of-sight velocity, we use two different methods: a nonequilibrium ionization model fit to the strong Si and S lines in the 1.2–2.8 keV regime, and a fit consisting of a series of Gaussian lines. These methods give consistent results, allowing us to determine the redshift or blueshift of each of the knots. Assuming a distance of 3.5 kpc, we find total velocities that range from 2400 to 6600 km s{sup −1}, with a mean of 4430 km s{sup −1}. We find several regions where the ejecta knots have overtaken the forward shock. These regions have proper motions in excess of 6000 km s{sup −1}. Some SN Ia explosion models predict a velocity asymmetry in the ejecta. We find no such velocity asymmetries in Tycho, and we discuss our findings in light of various explosion models, favoring those delayed-detonation models with relatively vigorous and symmetrical deflagrations. Finally, we compare measurements with models of the remnant’s evolution that include both smooth and clumpy ejecta profiles, finding that both ejecta profiles can be accommodated by the observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Optical and UV Spectra of the Remnant of SN 1885 (S And) in M31

We present multi-slit, 1D and 2D optical and UV spectra of the remnant of supernova 1885 (SN 1885; S And) taken using the Hubble Space Telescope’s Imaging Spectrograph (HST/STIS). These spectra of this probable subluminous Type Ia remnant, seen in silhouette against the central bulge of the Andromeda galaxy (M31), show strong and broad absorptions from neutral and singly ionized species of calcium, magnesium, and iron but with strikingly different distributions. Calcium H and K absorption indicates spherically distributed Ca-rich ejecta, densest in a lumpy shell expanding at 2000–6000 km s{sup −1}. Equally broad but weaker Ca i 4227 Å absorption is seen to extend out to velocities of ∼13,000 km s{sup −1}. Magnesium-rich ejecta in the remnant are detected for the first time through Mg i 2852 Å and Mg ii 2796, 2803 Å absorptions concentrated in a shell with expansion velocities from ≃7000 km s{sup −1} to at least 10,000 km s{sup −1}. Fe i 3720 Å absorption is detected as two discrete blueshifted and redshifted absorptions suggestive of an Fe i shell with expansion velocities of ±2000–8000 km s{sup −1}. Weak Fe ii resonance absorptions in the wavelength region 2300–2700 Å are consistent with prior HST UV images showing Fe ii–rich ejecta confined to a small number of optically thick plumes. The presence of such iron plumes extending out from the remnant’s core plus layered shells of calcium and magnesium point to a delayed-detonation explosion. The spectra also suggest a roughly spherical explosion, contrary to that expected by a merger or collision of two white dwarfs. We conclude that SN 1885 likely was an off-center, delayed-detonation explosion leading to a subluminous SN Ia similar to SN 1986G.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Measuring Dark Energy Properties with Photometrically Classified Pan-STARRS Supernovae. II. Cosmological Parameters

We use 1169 Pan-STARRS supernovae (SNe) and 195 low-z (z <0.1) SNe Ia to measure cosmological parameters. Though most Pan-STARRS SNe lack spectroscopic classifications, in a previous paper(I) we demonstrated that photometrically classified SNe can be used to infer unbiased cosmological parameters by using a Bayesian methodology that marginalizes over core-collapse (CC) SN contamination. Our sample contains nearly twice as many SNe as the largest previous SN Ia compilation.Combining SNe with Cosmic Microwave Background (CMB) constraints from Planck, we measure the dark energy equation of state parameter w to be -0.989±0.057 (stat+sys). If w evolves with redshift as w(a) =w 0 +w a (1-α), we find w 0 =-0.912 ± 0.149 and w a = -0.513 ± 0.826. These results are consistent with cosmological parameters from the Joint Light-curve Analysis and the Pantheon sample.We try four different photometric classification priors for Pan-STARRS SNe and two alternate ways of modeling CC SN contamination, finding that no variant gives a w differing by more than 2% from the baseline measurement. The systematic uncertainty on w due to marginalizing over CC SN contamination, σ$^{CC}_{w}$=0.012, is the third-smallest source of systematic uncertainty in this work. We find limited(1.6σ) evidence for evolution of the SN color-luminosity relation with redshift, a possible systematic that could constitute a significant uncertainty in future high-z analyses. Our data provide one of the best current constraints on w, demonstrating that samples with~5% CC SN contamination can give competitive cosmological constraints when the contaminating distribution is marginalized over in a Bayesian framework

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Simulations of the WFIRST Supernova Survey and Forecasts of Cosmological Constraints

The Wide Field InfraRed Survey Telescope (WFIRST) was the highest-ranked large space-based mission of the 2010 New Worlds, New Horizons decadal survey. It is now a NASA mission in formulation with a planned launch in the mid 2020s. A primary mission objective is to precisely constrain the nature of dark energy through multiple probes, including Type Ia supernovae (SN Ia). Here, we present the first realistic simulations of the WFIRST SN survey based on current hardware specifications and using open-source tools. We simulate SN light curves and spectra as viewed by the WFIRST wide-field channel (WFC) imager and integral field channel (IFC) spectrometer, respectively. We examine 11 survey strategies with different time allocations between the WFC and IFC, two of which are based upon the strategy described by the WFIRST Science Definition Team, which measures SN distances exclusively from IFC data. We propagate statistical and, crucially, systematic uncertainties to predict the Dark Energy Task Force figure of merit (FoM) for each strategy. Of the strategies investigated, we find the most successful to be WFC focused. However, further work in constraining systematics is required to fully optimize the use of the IFC. Even without improvements to other cosmological probes, the WFIRST SN survey has the potential to increase the FoM by more than an order of magnitude from the current values. Although the survey strategies presented here have not been fully optimized, these initial investigations are an important step in the development of the final hardware design and implementation of the WFIRST mission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

The Aemulus Project. II. Emulating the Halo Mass Function

Existing models for the dependence of the halo mass function on cosmological parameters will become a limiting source of systematic uncertainty for cluster cosmology in the near future. We present a halo mass function emulator and demonstrate improved accuracy relative to state-of-the-art analytic models. In this work, mass is defined using an overdensity criteria of 200 relative to the mean background density. Our emulator is constructed from the AEMULUS simulations, a suite of 40 N-body simulations with snapshots from z = 3 to z = 0. These simulations cover the flat wCDM parameter space allowed by recent cosmic microwave background, baryon acoustic oscillation and SNe Ia results, varying the parameters w, Omega(m), Omega(b), sigma(8), N-eff, n(s), and H-0. We validate our emulator using five realizations of seven different cosmologies, for a total of 35 test simulations. These test simulations were not used in constructing the emulator, and were run with fully independent initial conditions. We use our test simulations to characterize the modeling uncertainty of the emulator, and introduce a novel way of marginalizing over the associated systematic uncertainty. We confirm nonuniversality in our halo mass function emulator as a function of both cosmological parameters and redshift. Our emulator achieves better than 1% precision over much of the relevant parameter space, and we demonstrate that the systematic uncertainty in our emulator will remain a negligible source of error for cluster abundance studies through at least the LSST Year 1 data set.

large-scale structure of universe↗
DOE OSTI2019

The Aemulus Project. I. Numerical Simulations for Precision Cosmology

The rapidly growing statistical precision of galaxy surveys has led to a need for ever more precise predictions of the observables used to constrain cosmological and galaxy formation models. The primary avenue through which such predictions will be obtained is suites of numerical simulations. These simulations must span the relevant model parameter spaces, be large enough to obtain the precision demanded by upcoming data, and be thoroughly validated in order to ensure accuracy. In this paper, we present one such suite of simulations, forming the basis for the AEMULUS Project, a collaboration devoted to precision emulation of galaxy survey observables. We have run a set of 75 (1.05 h(-1) Gpc)(3) simulations with mass resolution and force softening of 3.51 x 10(10) (Omega(m)/0.3) h(-1) M-circle dot and 20 h(-1) kpc, respectively, in 47 different wCDM cosmologies spanning the range of parameter space allowed by the combination of recent cosmic microwave background, baryon acoustic oscillation, and Type Ia supernova results. We present convergence tests of several observables including spherical overdensity halo mass functions, galaxy projected correlation functions, galaxy clustering in redshift space, and matter and halo correlation functions and power spectra. We show that these statistics are converged to 1% (2%) or to the sample variance of the statistic, whichever is larger, for halos with more than 500 (200) particles, respectively, and scales of r > 200 h(-1) kpc. in real space or k similar to 3 h Mpc(-1). in harmonic space for z <= 1. We find that the dominant source of uncertainty comes from varying the particle loading of the simulations. This leads to large systematic errors for statistics using halos with fewer than 200 particles and scales smaller than k similar to 4 h Mpc(-1). We provide the halo catalogs and snapshots detailed in this work to the community at. https://AemulusProject.github.io.

large-scale structure of universe↗
DOE OSTI2019

Nuclear Ignition of White Dwarf Stars by Relativistic Encounters with Rotating Intermediate Mass Black Holes

We present results from general relativistic calculations of nuclear ignition in white dwarf stars triggered by near encounters with rotating intermediate mass black holes with different spin and alignment parameters. These encounters create thermonuclear environments characteristic of Type Ia supernovae capable of producing both calcium and iron-group elements in arbitrary ratios, depending primarily on the proximity of the interaction which acts as a strong moderator of nucleosynthesis. Here, we explore the effects of black hole spin and spin-orbital alignment on burn-product synthesis to determine whether they might also be capable of moderating reactive flows. When normalized to equivalent impact penetration, accounting for frame-dragging corrections, the influence of spin is weak, no more than 25% as measured by nuclear energy release and mass of burn products, even for near maximally rotating black holes. Stars on prograde trajectories approach closer to the black hole and produce significantly more unbound debris and iron-group elements than is possible by encounters with nonrotating black holes or by retrograde orbits, at more than 50% mass conversion efficiency. The debris contains several radioisotopes, most notably 56 Ni, made in amounts that produce subluminous (but still observable) light curves compared to branch-normal SNe Ia.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Mass Dependence of Galaxy–Halo Alignment in LOWZ and CMASS

We measure the galaxy-ellipticity (GI) correlations for the Sloan Digital Sky Survey Data Release 12 LOWZ and CMASS samples with the shape measurements from the DESI Legacy Imaging Surveys. We model the GI correlations in an N-body simulation with our recent accurate stellar–halo mass relation from the Photometric object Around Cosmic webs (PAC) method. The large data set and our accurate modeling turns out an accurate measurement of the alignment angle between central galaxies and their host halos. We find that the alignment of central elliptical galaxies with their host halos increases monotonically with galaxy stellar mass or host halo mass, which can be well described by a power law for the massive galaxies. We also find that central elliptical galaxies are more aligned with their host halos in LOWZ than in CMASS, which might indicate an evolution of galaxy–halo alignment, though future studies are needed to verify this is not induced by the sample selections. In contrast, central disk galaxies are aligned with their host halos about 10 times more weakly in the GI correlation. These results have important implications for intrinsic alignment (IA) correction in weak lensing studies, IA cosmology, and theory of massive galaxy formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Evaluating the Consistency of Cosmological Distances Using Supernova Siblings in the Near-infrared

Abstract The study of supernova (SN) siblings, supernovae with the same host galaxy, is an important avenue for understanding and measuring the properties of Type Ia SN Ia light curves (LCs). Thus far, sibling analyses have mainly focused on optical LC data. Considering that LCs in the near-infrared (NIR) are expected to be better standard candles than those in the optical, we carry out the first analysis compiling SN siblings with only NIR data. We perform an extensive literature search of all SN siblings and find six sets of siblings with published NIR photometry. We calibrate each set of siblings ensuring they are on homogeneous photometric systems, fit the LCs with the SALT3-NIR and SNooPy models, and find median absolute differences inμvalues between siblings of 0.248 and 0.186 mag, respectively. To evaluate the significance of these differences beyond measurement noise, we run simulations that mimic these LCs and provide an estimate for uncertainty on these median absolute differences of ∼0.052 mag, and we find that, statistically, our analysis rules out the nonexistence of intrinsic scatter in the NIR at the 99% level. When comparing the same sets of SN siblings, we observe a median absolute difference inμvalues between siblings of 0.177 mag when using optical data alone as compared to 0.186 mag when using NIR data alone. It is unclear if these results may be due to limited statistics or poor quality NIR data, all of which will be improved with the Nancy Grace Roman Space Telescope.

Astronomy & Astrophysics↗
DOE OSTI2017

Statistical Analysis of Supernova Remnants in the Large Magellanic Cloud

We construct the most complete sample of supernova remnants (SNRs) in any galaxy—the Large Magellanic Cloud (LMC) SNR sample. We study their various properties such as spectral index (α), size, and surface brightness. We suggest an association between the spatial distribution and environment density of LMC SNRs, and their tendency to be located around supergiant shells. We find evidence that the 16 known type Ia LMC SNRs are expanding in a lower density environment compared to the Core-Collapse (CC) type. The mean diameter of our entire population (74) is 41 pc, which is comparable to nearby galaxies. We did not find any correlation between the type of SN explosion, ovality, or age. The N(<D) relationship with slope a = 0.96 implies that the randomized diameters are readily mimicking such an exponent. The rate of SNe occurring in the LMC is estimated to be ∼1 per 200 yr. The mean α of the entire LMC SNR population is −0.52, which is typical of most SNRs. However, our estimates show a clear flattening of the synchrotron α as the remnants age. As predicted, the CC SNRs in our sample are significantly brighter radio emitters than type Ia remnants. We also estimate the Σ--D relation for the LMC to have a slope ∼3.8, which is comparable with other nearby galaxies. We also find the residency time of electrons in the galaxy (4.0–14.3 Myr), implying that SNRs should be the dominant mechanism for the production and acceleration of CRs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Real-time Recovery Efficiencies and Performance of the Palomar Transient Factory's Transient Discovery Pipeline

In this paper, we present the transient source detection efficiencies of the Palomar Transient Factory (PTF), parameterizing the number of transients that PTF found versus the number of similar transients that occurred over the same period in the survey search area but were missed. PTF was an optical sky survey carried out with the Palomar 48 inch telescope over 2009–2012, observing more than 8000 square degrees of sky with cadences of between one and five days, locating around 50,000 non-moving transient sources, and spectroscopically confirming around 1900 supernovae. We assess the effectiveness with which PTF detected transient sources, by inserting $\simeq 7$ million artificial point sources into real PTF data. We then study the efficiency with which the PTF real-time pipeline recovered these sources as a function of the source magnitude, host galaxy surface brightness, and various observing conditions (using proxies for seeing, sky brightness, and transparency). The product of this study is a multi-dimensional recovery efficiency grid appropriate for the range of observing conditions that PTF experienced and that can then be used for studies of the rates, environments, and luminosity functions of different transient types using detailed Monte Carlo simulations. Finally, we illustrate the technique using the observationally well-understood class of type Ia supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

ZTF 18aaqeasu (SN2018byg): A Massive Helium-shell Double Detonation on a Sub-Chandrasekhar-mass White Dwarf

The detonation of a helium shell on a white dwarf (WD) has been proposed as a possible explosion triggering mechanism for SNe Ia. Here, we report ZTF 18aaqeasu (SN 2018byg/ATLAS 18pqq), a peculiar Type I supernova, consistent with being a helium-shell double-detonation. With a rise time of ≈18 days from explosion, the transient reached a peak absolute magnitude of M R ≈ -18.2 mag, exhibiting a light curve akin to sub-luminous SN 1991bg-like SNe Ia, albeit with an unusually steep increase in brightness within a week from explosion. Spectra taken near peak light exhibit prominent Si absorption features together with an unusually red color ( g - r ≈ 2 mag) arising from nearly complete line blanketing of flux blueward of 5000 Å. This behavior is unlike any previously observed thermonuclear transient. Nebular phase spectra taken at and after ≈30 days from peak light reveal evidence of a thermonuclear detonation event dominated by Fe-group nucleosynthesis. We show that the peculiar properties of ZTF 18aaqeasu are consistent with the detonation of a massive (≈0.15 M ⊙ ) helium shell on a sub-Chandrasekhar mass (≈0.75 ) WD after including mixing of ≈0.2 M ⊙ of material in the outer ejecta. Furthermore, these observations provide evidence of a likely rare class of thermonuclear supernovae arising from detonations of massive helium shells.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1981

Absolute energy curves from late B-type supergiants

Energy curves were determined for six late B and early A type supergiants using IUE data and other ultraviolet and ground based photometry. Effective temperatures and angular diameters are presented as well as estimates of the outflow velocity of the wind. All six stars show a strong Balmer continuum in emission; the Ia supergiants also show an infrared excess which reaches into the visible range. Evidence is found for the presence of a warm mantle as well as for wind from the Ia stars.

Underhill, A. B.↗
NASA NTRS1981

UV chromospheric and circumstellar diagnostic features among F supergiant stars

A survey of F supergiant stars to evaluate the extension of chromospheric and circumstellar characteristics commonly observed in the slightly cooler G, K, and M supergiant is discussed. An ultraviolet survey was elected since UV features of Mg II and Fe II might persist in revealing outer atmosphere phenomena even among F supergiants. The encompassed spectral types F0 to G0, and luminosity classes Ib, Ia, and Ia-0. In addition, the usefulness of the emission line width-to-luminosity correlation for the G-M stars in both the Ca II and Mg II lines is examined.

Stencel, R. E.↗
NASA NTRS1981

Concerning the Wolf-Rayet and other luminous early-type stars

Effective temperatures, radii, and luminosities were determined from S2/68, ANS, UBV, and uvby photometry for four B0/B1 supergiants, four O4 stars, and four WN7/WN8 stars as well as for four test stars having spectral types between B1.5 V and 09 V and five stars with known angular diameters and effective temperatures. The effective temperatures of B1 Ia+ stars are found to be near 17,000 K, those of O4 stars near 45,000, and those of WN7/WN8 stars near 26,000 K. The question of modeling the atmospheres of hot luminous stars is examined, and it is noted that the photosphere can be modeled adequately using a classical plane-parallel layer model atmosphere. In addition, it is found that the Wolf-Rayet stars of types WN7/WN8 fall in the H-R diagram near the B0 Ia stars, while the others fall near B0.5 III stars. The evolutionary relationship between the Wolf-Rayet and O stars is considered; it is suggested that a Wolf-Rayet spectrum is a short-lived phase in the life of a massive star.

Underhill, A. B.↗
NASA NTRS1982

Documentation for the machine-readable version of the catalogue of stars within 25 parsecs of the Sun

The machine-readable version of the Catalogue of Stars within twenty-five parsecs of the Sun contains essentially all information given in Table Ia of the published catalog, plus positional data and all cross references to other catalog numbers given in Table IIa. Not included from Table Ia are the flags (asterisks appended to catalog numbers) indicating notes in the published catalog, nor are the notes in machine-readable form. Omitted from Table IIa are the finding chart identifiers (Lowell G numbers or notes reference) and miscellaneous cross identifications to other names and catalog identifiers. The machine-readable version of the subject catalog is currently available on magnetic tape from the Astronomical Data Center.

Warren, W. H., Jr.↗