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DOE OSTI2018

Mass measurement of 51 Fe for the determination of the 51 Fe($p, γ$) 52 Co reaction rate

Background: The 51 Fe(p, γ) 52 Co reaction lies along the main rp-process path leading up to the 56 Ni waiting point. The uncertainty in the reaction Q value, which determines the equilibrium between the forward protoncapture and reverse photodisintegration 52 Co(γ,p) 51 Fe reaction, contributes to considerable uncertainty in the reaction rate in the temperature range of interest for Type I x-ray bursts and thus to an ≈10% uncertainty in burst ashes lighter than A = 56. Purpose: With a recent Penning trap mass measurement of 52 Co reducing the uncertainty on its mass to 6.6 keV [Nesterenko et al., J. Phys. G 44, 065103 (2017)], the dominant source of uncertainty in the reaction Q value is now the mass of 51 Fe, reported in the 2016 atomic mass evaluation to a precision of 9 keV [Wang et al., Chin.Phys. C 41, 030003 (2017)]. A new, high-precision Penning trap mass measurement of 51 Fe was performed to allow the determination of an improved precision Q value and thus new reaction rates. Method: 51 Fe was produced using projectile fragmentation at the Coupled Cyclotron Facility at the National Superconducting Cyclotron Laboratory, and separated using the A1900 fragment separator. The resulting secondary beam was then thermalized in the beam stopping area before a mass measurement was performed using the LEBIT 9.4T Penning trap mass spectrometer. Results: The new mass excess, ME = -40189.2(1.6) keV, is sixfold more precise than the current AME value, and 1.6σ less negative. This value was used to calculate a new proton separation energy for 52 Co of 1431(7) keV. New excitation levels were then calculated for 52 Co using the NUSHELLX code with the GXPF1A interaction, and a new reaction rate and burst ash composition was calculated. Conclusions:With a new measured Q value, the uncertainty on the 51 Fe(p, γ ) reaction rate is dominated by the poorly measured 52 Co level structure. Finally, reducing this uncertainty would allow a more precise rate calculation and a better determination of the mass abundances in the burst ashes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

THE SOLAR NEIGHBORHOOD. XXXVII. THE MASS–LUMINOSITY RELATION FOR MAIN-SEQUENCE M DWARFS

We present a mass–luminosity relation (MLR) for red dwarfs spanning a range of masses from 0.62 M{sub ⊙} to the end of the stellar main sequence at 0.08 M{sub ⊙}. The relation is based on 47 stars for which dynamical masses have been determined, primarily using astrometric data from Fine Guidance Sensors (FGS) 3 and 1r, white-light interferometers on the Hubble Space Telescope (HST), and radial velocity data from McDonald Observatory. For our HST/FGS sample of 15 binaries, component mass errors range from 0.4% to 4.0% with a median error of 1.8%. With these and masses from other sources, we construct a V-band MLR for the lower main sequence with 47 stars and a K-band MLR with 45 stars with fit residuals half of those of the V band. We use GJ 831 AB as an example, obtaining an absolute trigonometric parallax, π {sub abs} = 125.3 ± 0.3 mas, with orbital elements yielding M{sub A}=0.270±0.004 M{sub ⊙} and M{sub B}=0.145±0.002 M{sub ⊙}. The mass precision rivals that derived for eclipsing binaries. A remaining major task is the interpretation of the intrinsic cosmic scatter in the observed MLR for low-mass stars in terms of physical effects. In the meantime, useful mass values can be estimated from the MLR for the ubiquitous red dwarfs that account for 75% of all stars, with applications ranging from the characterization of exoplanet host stars to the contribution of red dwarfs to the mass of the universe.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

A SEARCH FOR MASS LOSS ON THE CEPHEID INSTABILITY STRIP USING H i 21 cm LINE OBSERVATIONS

We present the results of a search for H i 21 cm line emission from the circumstellar environments of four Galactic Cepheids (RS Pup, X Cyg, ζ Gem, and T Mon) based on observations with the Karl G. Jansky Very Large Array. The observations were aimed at detecting gas associated with previous or ongoing mass loss. Near the long-period Cepheid T Mon, we report the detection of a partial shell-like structure whose properties appear consistent with originating from an earlier epoch of Cepheid mass loss. At the distance of T Mon, the nebula would have a mass (H i+He) of ∼0.5M{sub ⊙}, or ∼6% of the stellar mass. Assuming that one-third of the nebular mass comprises swept-up interstellar gas, we estimate an implied mass-loss rate of M-dot ∼(0.6--2)×10{sup −5} M{sub ⊙} yr{sup −1}. No clear signatures of circumstellar emission were found toward ζ Gem, RS Pup, or X Cyg, although in each case, line-of-sight confusion compromised portions of the spectral band. For the undetected stars, we derive model-dependent 3σ upper limits on the mass-loss rates, averaged over their lifetimes on the instability strip, of ≲(0.3--6)×10{sup −6} M{sub ⊙} yr{sup −1} and estimate the total amount of mass lost to be less than a few percent of the stellar mass.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Constraining the warm dark matter particle mass through ultra-deep UV luminosity functions at z = 2

We compute the mass function of galactic dark matter halos for different values of the warm dark matter (WDM) particle mass m{sub X} and compare it with the number density of ultra-faint galaxies derived from the deepest UV luminosity function available so far at redshift z ≈ 2. The magnitude limit M{sub UV} = −13 reached by such observations allows us to probe the WDM mass functions down to scales close to or smaller than the half-mass mode mass scale ∼10{sup 9} M{sub ⊙}. This allowed for an efficient discrimination among predictions for different m{sub X} which turn out to be in practice independent of the star formation efficiency η adopted to associate the observed UV luminosities of galaxies to the corresponding dark matter halo masses. Adopting a conservative approach to take into account the existing theoretical uncertainties in the galaxy halo mass function, we obtain a robust limit m{sub X} ≥ 1.8 keV for the mass of thermal relic WDM particles when comparing with the measured abundance of the faintest galaxies, while m{sub X} ≥ 1.5 keV is obtained when we compare with the Schechter fit to the observed luminosity function. The corresponding lower limit for sterile neutrinos depends on the modeling of the production mechanism; for instance m{sub sterile} ≳ 4 keV holds for the Shi–Fuller mechanism. We discuss the impact of observational uncertainties on the above bound on m{sub X}. In the cold dark matter (CDM) limit m{sub X}≫1 keV we recover the generic CDM result that very inefficient star formation efficiency is required to match the observed galaxy abundances. As a baseline for comparison with forthcoming observational results from the Hubble Space Telescope Frontier Field project, we provide predictions for the number density of faint galaxies with M{sub UV} = −13 for different values of the WDM particle mass and of the star formation efficiency η, which are valid up to z ≈ 4.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Clustering properties and halo masses for central galaxies in the local universe

We investigate the clustering and dark matter halo mass for a sample of ∼16,000 central galaxies selected from the SDSS/DR7 group catalog. We select subsamples of central galaxies on three two-dimensional planes, each formed by stellar mass (M{sub ∗}) and one other property out of optical color (g − r), surface stellar mass density (μ{sub ∗}), and central stellar velocity dispersion (σ{sub ∗}). For each subsample we measure both the projected cross-correlation function (w{sub p}(r{sub p})) relative to a reference galaxy sample, and an average mass of the host dark matter halos (M{sub h}). Both w{sub p}(r{sub p}) and M{sub h} show the strongest dependence on M{sub ∗}, and there is no clear dependence on the other properties when M{sub ∗} is fixed. This result provides strong support to the previously adopted assumption that, for central galaxies, stellar mass is the best indicator of the host dark halo mass. For comparison we have estimated w{sub p}(r{sub p}) for the full galaxy population and the population of satellite galaxies. Both populations show similar clustering properties in all cases, but they are similar to the centrals only at high masses (M{sub ∗} ≳10{sup 11} M{sub ⊙}). At lower masses, their w{sub p}(r{sub p}) depends more strongly on σ{sub ∗} and g − r than on M{sub ∗}. It is thus necessary to consider central and satellite galaxies separately when studying the link between galaxies and dark matter halos. We discuss the implications of our results for the relative roles of halo mass and galaxy structure in quenching the star formation in central galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

ISM masses and the star formation law at Z = 1 to 6: ALMA observations of dust continuum in 145 galaxies in the cosmos survey field

ALMA Cycle 2 observations of long-wavelength dust emission in 145 star-forming galaxies are used to probe the evolution of the star-forming interstellar medium (ISM). We also develop a physical basis and empirical calibration (with 72 low-z and z ∼ 2 galaxies) for using the dust continuum as a quantitative probe of ISM masses. The galaxies with the highest star formation rates (SFRs) at 〈z〉 = 2.2 and 4.4 have gas masses up to 100 times that of the Milky Way and gas mass fractions reaching 50%–80%, i.e., gas masses 1-4× their stellar masses. We find a single high-z star formation law: SFR=35 M{sub mol}{sup 0.89}×(1+z){sub z=2}{sup 0.95}×(sSFR){sub MS}{sup 0.23} M{sub ⊙} yr{sup −1}—an approximately linear dependence on the ISM mass and an increased star formation efficiency per unit gas mass at higher redshift. Galaxies above the main sequence (MS) have larger gas masses but are converting their ISM into stars on a timescale only slightly shorter than those on the MS; thus, these “starbursts” are largely the result of having greatly increased gas masses rather than an increased efficiency of converting gas to stars. At z > 1, the entire population of star-forming galaxies has ∼2–5 times shorter gas depletion times than low-z galaxies. These shorter depletion times indicate a different mode of star formation in the early universe—most likely dynamically driven by compressive, high-dispersion gas motions—a natural consequence of the high gas accretion rates.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

ORBITAL STABILITY OF MULTI-PLANET SYSTEMS: BEHAVIOR AT HIGH MASSES

In the coming years, high-contrast imaging surveys are expected to reveal the characteristics of the population of wide-orbit, massive, exoplanets. To date, a handful of wide planetary mass companions are known, but only one such multi-planet system has been discovered: HR 8799. For low mass planetary systems, multi-planet interactions play an important role in setting system architecture. In this paper, we explore the stability of these high mass, multi-planet systems. While empirical relationships exist that predict how system stability scales with planet spacing at low masses, we show that extrapolating to super-Jupiter masses can lead to up to an order of magnitude overestimate of stability for massive, tightly packed systems. We show that at both low and high planet masses, overlapping mean-motion resonances trigger chaotic orbital evolution, which leads to system instability. We attribute some of the difference in behavior as a function of mass to the increasing importance of second order resonances at high planet–star mass ratios. We use our tailored high mass planet results to estimate the maximum number of planets that might reside in double component debris disk systems, whose gaps may indicate the presence of massive bodies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Constraining warm dark matter mass with cosmic reionization and gravitational waves

We constrain the warm dark matter (WDM) particle mass with observations of cosmic reionization and CMB optical depth. We suggest that the gravitational waves (GWs) from stellar-mass black holes (BHs) could give a further constraint on WDM particle mass for future observations. The star formation rates (SFRs) of Population I/II (Pop I/II) and Population III (Pop III) stars are also derived. If the metallicity of the universe is enriched beyond the critical value of Z{sub crit}=10{sup −3.5} Z{sub ⊙}, the star formation shifts from Pop III to Pop I/II stars. Our results show that the SFRs are quite dependent on the WDM particle mass, especially at high redshifts. Combined with the reionization history and CMB optical depth derived from the recent Planck mission, we find that the current data require the WDM particle mass to be in a narrow range of 1 keV≲m{sub x}≲3 keV. Furthermore, we suggest that the stochastic gravitational wave background (SGWB) produced by stellar BHs could give a further constraint on the WDM particle mass for future observations. For m{sub x}=3 keV, with Salpeter (Chabrier) initial mass function (IMF), the SGWB from Pop I/II BHs has a peak amplitude of Ω{sub GW}≈2.8×10{sup −9} (5.0×10{sup −9}) at f=316Hz, while the GW radiation at f<10 Hz is seriously suppressed. For m{sub x}=1 keV, the SGWB peak amplitude is the same as that for m{sub x}=1 keV, but a little lower at low frequencies. Therefore, it is hard to constrain the WDM particle mass by the SGWB from Pop I/II BHs. To assess the detectability of the GW signal, we also calculate the signal-to-noise ratios (S/N), which are S/N=37.7 (66.5) and 27 (47.7) for m{sub x}=3 keV and m{sub x}=1 keV for the Einstein Telescope with Salpeter (Chabrier) IMF, respectively. The SGWB from Pop III BHs is very dependent on the WDM particle mass, the GW strength could be an order of magnitude different, and the frequency band could be two times different for m{sub x}=1 keV and m{sub x}=3 keV. Moreover, the SGWB from Pop III BHs with m{sub x}=1 keV could be detected by the Laser Interferometer Space Antenna for one year of observation, but it cannot be detected for those with m{sub x}=3 keV.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

An Upper Limit on the Mass of the Circumplanetary Disk for DH Tau b

DH Tau is a young (∼1 Myr) classical T Tauri star. It is one of the few young PMS stars known to be associated with a planetary mass companion, DH Tau b, orbiting at large separation and detected by direct imaging. DH Tau b is thought to be accreting based on copious Hα emission and exhibits variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place constraints on the disk dust mass for both DH Tau b and the primary in a regime where the disks will appear optically thin. We estimate a disk dust mass for the primary, DH Tau A of 17.2±1.7 M{sub ⊕}, which gives a disk to star mass ratio of 0.014 (assuming the usual gas to dust mass ratio of 100 in the disk). We find a conservative disk dust mass upper limit of 0.42 M {sub ⊕} for DH Tau b, assuming that the disk temperature is dominated by irradiation from DH Tau b itself. Given the environment of the circumplanetary disk, variable illumination from the primary or the equilibrium temperature of the surrounding cloud would lead to even lower disk mass estimates. A MCFOST radiative transfer model, including heating of the circumplanetary disk by DH Tau b and DH Tau A, suggests that a mass-averaged disk temperature of 22 K is more realistic, resulting in a dust disk mass upper limit of 0.09 M {sub ⊕} for DH Tau b. We place DH Tau b in context with similar objects and discuss the consequences for planet formation models.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

The quenched mass portion of star-forming galaxies and the origin of the star formation sequence slope

Observationally, a massive disk galaxy can harbor a bulge component that is comparably inactive as a quiescent galaxy. It has been speculated that the quenched component contained in star-forming galaxies (SFGs) is the reason why the star formation main sequence (MS) has a shallow slope at high masses. In this paper, we present a toy model to quantify the quenched mass portion of SFGs (f{sub Q}) at fixed stellar mass (M{sub *}) and to reconcile the MS slopes in both the low- and the high-mass regimes. In this model, each SFG is composed of a star-forming plus a quenched component. The mass of the star-forming component (M{sub SF}) correlates with the star formation rate (SFR) following a relation SFR ∝ M{sub SF}{sup α{sub S}{sub F}}, where α{sub SF} ∼ 1.0. The quenched component contributes to the stellar mass but not to the SFR. It is thus possible to quantify f{sub Q} based on the departure of the observed MS slope α from α{sub SF}. Adopting the redshift-dependent MS slope reported by Whitaker et al., we explore the evolution of the f{sub Q}--M{sub ∗} relations over z = [0.5, 2.5]. We find that Milky Way-like SFGs (with M{sub ∗}≈10{sup 10.7} M{sub ⊙}) typically have an f{sub Q} = 30%–40% at z ∼ 2.25, whereas this value rapidly rises up to 70%–80% at z ∼ 0.75. The origin of an α ∼ 1.0 MS slope seen in the low-mass regime is also discussed. We argue for a scenario in which the majority of low-mass SFGs stay in a “steady-stage” star formation phase. In this phase, the SFR is mainly regulated by stellar feedback and not significantly influenced by the quenching mechanisms, thus remaining roughly constant over cosmic time. This scenario successfully produces an α ∼ 1.0 MS slope, as well as the observed MS evolution from z = 2.5 to z = 0 at low masses.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

A black hole mass determination for the compact galaxy MRK 1216

Mrk 1216 is a nearby, early-type galaxy with a small effective radius of 2.8 kpc and a large stellar velocity dispersion of 308 km s{sup −1} for its K-band luminosity of 1.4×10{sup 11} L{sub ⊙}. Using integral field spectroscopy assisted by adaptive optics from Gemini North, we measure spatially resolved stellar kinematics within ∼450 pc of the galaxy nucleus. The galaxy exhibits regular rotation with velocities of ±180 km s{sup −1} and a sharply peaked velocity dispersion profile that reaches 425 km s{sup −1} at the center. We fit axisymmetric, orbit-based dynamical models to the combination of these high angular resolution kinematics, large-scale kinematics extending to roughly three effective radii, and Hubble Space Telescope imaging, resulting in a constraint of the mass of the central black hole in Mrk 1216. After exploring several possible sources of systematics that commonly affect stellar-dynamical black hole mass measurements, we find a black hole mass of M{sub BH}=(4.9±1.7)×10{sup 9} M{sub ⊙} and an H-band stellar mass-to-light ratio of Υ{sub H}=1.3±0.4 Υ{sub ⊙} (1σ uncertainties). Mrk 1216 is consistent with the local black hole mass–stellar velocity dispersion relation, but is a factor of ∼5–10 larger than expectations from the black hole mass–bulge luminosity and black hole mass–bulge mass correlations when conservatively using the galaxy’s total luminosity or stellar mass. This behavior is quite similar to the extensively studied compact galaxy NGC 1277. Resembling the z∼2 quiescent galaxies, Mrk 1216 may be a passively evolved descendant, and perhaps reflects a previous era when galaxies contained over-massive black holes relative to their bulge luminosities/masses, and the growth of host galaxies had yet to catch up.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Evolutionary Description of Giant Molecular Cloud Mass Functions on Galactic Disks

Recent radio observations show that giant molecular cloud (GMC) mass functions noticeably vary across galactic disks. High-resolution magnetohydrodynamics simulations show that multiple episodes of compression are required for creating a molecular cloud in the magnetized interstellar medium. In this article, we formulate the evolution equation for the GMC mass function to reproduce the observed profiles, for which multiple compressions are driven by a network of expanding shells due to H ii regions and supernova remnants. We introduce the cloud–cloud collision (CCC) terms in the evolution equation in contrast to previous work (Inutsuka et al.). The computed time evolution suggests that the GMC mass function slope is governed by the ratio of GMC formation timescale to its dispersal timescale, and that the CCC effect is limited only in the massive end of the mass function. In addition, we identify a gas resurrection channel that allows the gas dispersed by massive stars to regenerate GMC populations or to accrete onto pre-existing GMCs. Our results show that almost all of the dispersed gas contributes to the mass growth of pre-existing GMCs in arm regions whereas less than 60% contributes in inter-arm regions. Our results also predict that GMC mass functions have a single power-law exponent in the mass range <10{sup 5.5} M{sub ⊙} (where M{sub ⊙} represents the solar mass), which is well characterized by GMC self-growth and dispersal timescales. Measurement of the GMC mass function slope provides a powerful method to constrain those GMC timescales and the gas resurrecting factor in various environments across galactic disks.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Formation and Assembly History of Stellar Components in Galaxies as a Function of Stellar and Halo Mass

Galaxy mass assembly is an end product of structure formation in the ΛCDM cosmology. As an extension of Lee and Yi, we investigate the assembly history of stellar components in galaxies as a function of halo environments and stellar mass using semi-analytic approaches. In our fiducial model, halo mass intrinsically determines the formation and assembly of the stellar mass. Overall, the ex situ fraction slowly increases in central galaxies with increasing halo mass but sharply increases for logM{sub ∗}/M{sub ⊙}≳11. A similar trend is also found in satellite galaxies, which implies that mergers are essential to build stellar masses above logM{sub ∗}/M{sub ⊙}∼11. We also examine the time evolution of the contribution of mass growth channels. Mergers become the primary channel in the mass growth of central galaxies when their host halo mass begins to exceed logM{sub 200}/M{sub ⊙}∼13. However, satellite galaxies seldom reach the merger-dominant phase despite their reduced star-formation activities due to environmental effects.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Constraining the H i–Halo Mass Relation from Galaxy Clustering

We study the dependence of galaxy clustering on H i mass using ∼16,000 galaxies with redshift in the range of 0.0025 10{sup 8} M{sub ⊙}, drawn from the 70% complete sample of the Arecibo Legacy Fast ALFA survey. We construct subsamples of galaxies with M{sub HI} above different thresholds and make volume-limited clustering measurements in terms of three statistics: the projected two-point correlation function, the projected cross-correlation function with respect to a reference sample, and the redshift-space monopole moment. In contrast to previous studies, which found no/weak H i mass dependence, we find both the clustering amplitudes on scales above a few megaparsecs and the bias factors to increase significantly with increasing H i mass for M{sub HI}>10{sup 9} M{sub ⊙}. For H i mass thresholds below ∼10{sup 9} M{sub ⊙}, the inferred galaxy bias factors are systematically lower than the minimum halo bias from mass-selected halo samples. We extend the simple halo model, in which the galaxy content is only determined by halo mass, by including the halo formation time as an additional parameter. A model that puts H i-rich galaxies into halos that formed late can reproduce the clustering measurements reasonably well. We present the implications of our best-fitting model on the correlation of H i mass with halo mass and formation time, as well as the halo occupation distributions and H i mass functions for central and satellite galaxies. These results are compared with the predictions from semianalytic galaxy formation models and hydrodynamic galaxy formation simulations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Next Generation Virgo Cluster Survey. XXI. The Weak Lensing Masses of the CFHTLS and NGVS RedGOLD Galaxy Clusters and Calibration of the Optical Richness

We measured stacked weak lensing cluster masses for a sample of 1323 galaxy clusters detected by the RedGOLD algorithm in the Canada–France–Hawaii Telescope Legacy Survey W1 and the Next Generation Virgo Cluster Survey at 0.2<z<0.5, in the optical richness range 10<λ<70. This is the most comprehensive lensing study of a ∼100% complete and ∼80% pure optical cluster catalog in this redshift range. We test different mass models, and our final model includes a basic halo model with a Navarro Frenk and White profile, as well as correction terms that take into account cluster miscentering, non-weak shear, the two-halo term, the contribution of the Brightest Cluster Galaxy, and an a posteriori correction for the intrinsic scatter in the mass–richness relation. With this model, we obtain a mass–richness relation of logM{sub 200}/M{sub ⊙} =(14.46±0.02)+(1.04±0.09)log(λ/40) (statistical uncertainties). This result is consistent with other published lensing mass–richness relations. We give the coefficients of the scaling relations between the lensing mass and X-ray mass proxies, L {sub X} and T {sub X}, and compare them with previous results. When compared to X-ray masses and mass proxies, our results are in agreement with most previous results and simulations, and consistent with the expected deviations from self-similarity.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

Tidal Stripping of a White Dwarf by an Intermediate-mass Black Hole

During the inspiralling of a white dwarf (WD) into an intermediate-mass black hole (~10 2-5 M ⊙ ), both gravitational waves (GWs) and electromagnetic (EM) radiation are emitted. Once the eccentric orbit's pericenter radius approaches the tidal radius, the WD would be tidally stripped upon each pericenter passage. The accretion of this stripped mass would produce EM radiation. It is suspected that the recently discovered new types of transients, namely the quasiperiodic eruptions and the fast ultraluminous x-ray bursts, might originate from such systems. Modeling these flares requires a prediction of the amount of stripped mass from the WD and the details of the mass supply to the accretion disk. We run hydrodynamical simulations to study the orbital parameter dependence of the stripped mass. We find that our results match the analytical estimate that the stripped mass is proportional to z 5/2 , where z is the excess depth by which the WD overfills its instantaneous Roche lobe at the pericenter. The corresponding fallback rate of the stripped mass is calculated, which may be useful in interpreting the individual flaring light curve in candidate EM sources. We further calculate the long-term mass-loss evolution of a WD during its inspiral and the detectability of the GW and EM signals. The EM signal from the mass-loss stage can be easily detected: the limiting distance is ~320(M h /10 4 M ⊙ ) Mpc for the Einstein Probe. The GW signal, for space-borne detectors such as Laser Interferometer Space Antenna or TianQin, can be detected only within the Local Supercluster (~33 Mpc).

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

The Mass Growth and Stellar Ages of Galaxies: Observations versus Simulations

Using observed stellar mass functions out to z = 5, we measure the main progenitor stellar mass growth of descendant galaxies with masses of logM{sub ∗}/M{sub ⊙}=11.5,11.0,10.5,10.0 at z∼0.1 using an evolving cumulative number density selection. From these mass growth histories, we are able to measure the time at which half the total stellar mass of the descendant galaxy was assembled, t {sub a}, which in order of decreasing mass corresponds to redshifts of z{sub a}=1.28,0.92,0.60, and 0.51. We compare this to the median light-weighted stellar age t {sub *} (z{sub ∗}=2.08,1.49,0.82 and 0.37) of a sample of low-redshift SDSS galaxies (from the literature) and find the timescales are consistent with more massive galaxies forming a higher fraction of their stars ex situ compared to lower-mass descendants. We find that both t {sub *} and t {sub a} strongly correlate with mass, which is in contrast to what is found in the EAGLE hydrodynamical simulation that shows a flat relationship between t {sub a} and M {sub *}. However, the semi-analytic model (SAM) of Henriques et al. is consistent with the observations in both t {sub a} and t {sub *} with M {sub *}, showing that the most recent SAMs are better able to decouple the evolution of the baryons from the dark matter in lower-mass galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2018

Estimation of Heatshield Mass Loss for Mars 2020 Entry Vehicle

The Mars2020 entry vehicle is currently being developed by NASA to safely land its next rover on the Martian surface in 2021. During entry, the vehicle will be protected from aerothermal environments using a PICA (Phenolic Impregnated Carbon Ablator)-tiled heatshield. PICA loses mass through surface recession and in-depth pyrolysis as it is heated. Pre-flight knowledge of heatshield mass loss is required for vehicle balancing during critical mission events. This study attempts to predict the total mass loss experienced by the Mars2020's heatshield during its entry. A grid was created over the half of the heatshield which generated 108 points across a total of 9 spokes. Aero-thermal environments were provided from CFD (Computational Fluid Dynamics) calculations that considered a baselined trajectory. The TPS (Thermal Protection System) stack was a build-up of composite, aluminum, composite, an HT-424 bond, followed by PICA. The FIAT (Fully Implicit Ablation, Thermal-response) 1-D analysis utilized this TPS stack and the CFD environments and was run at each grid point giving mass flux information from the point of atmospheric entry until parachute deployment. The mass flux due to recession and pyrolysis gas was summed and integrated first through time and then across the half heatshield using a polar integration tool. The mass loss results were mirrored to the other half of the heatshield to calculate total mass loss throughout the entry phase of flight. This total mass loss value and its distribution was used by entry vehicle designers to account for CG (Center of Gravity) offset during parachute descent when the heatshield is no longer losing significant mass.

PICA↗