SEARCH · Engineering Papers

Results for “INCLINATION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,279 records · Page 71

All sources NASA NTRS DOE OSTI

DOE OSTI2015

STABLE CONIC-HELICAL ORBITS OF PLANETS AROUND BINARY STARS: ANALYTICAL RESULTS

Studies of planets in binary star systems are especially important because it was estimated that about half of binary stars are capable of supporting habitable terrestrial planets within stable orbital ranges. One-planet binary star systems (OBSS) have a limited analogy to objects studied in atomic/molecular physics: one-electron Rydberg quasimolecules (ORQ). Specifically, ORQ, consisting of two fully stripped ions of the nuclear charges Z and Z′ plus one highly excited electron, are encountered in various plasmas containing more than one kind of ion. Classical analytical studies of ORQ resulted in the discovery of classical stable electronic orbits with the shape of a helix on the surface of a cone. In the present paper we show that despite several important distinctions between OBSS and ORQ, it is possible for OBSS to have stable planetary orbits in the shape of a helix on a conical surface, whose axis of symmetry coincides with the interstellar axis; the stability is not affected by the rotation of the stars. Further, we demonstrate that the eccentricity of the stars’ orbits does not affect the stability of the helical planetary motion if the center of symmetry of the helix is relatively close to the star of the larger mass. We also show that if the center of symmetry of the conic-helical planetary orbit is relatively close to the star of the smaller mass, a sufficiently large eccentricity of stars’ orbits can switch the planetary motion to the unstable mode and the planet would escape the system. We demonstrate that such planets are transitable for the overwhelming majority of inclinations of plane of the stars’ orbits (i.e., the projections of the planet and the adjacent start on the plane of the sky coincide once in a while). This means that conic-helical planetary orbits at binary stars can be detected photometrically. We consider, as an example, Kepler-16 binary stars to provide illustrative numerical data on the possible parameters and the stability of the conic-helical planetary orbits, as well as on the transitability. Then for the general case, we also show that the power of the gravitational radiation due to this planet can be comparable or even exceed the power of the gravitational radiation due to the stars in the binary. This means that in the future, with a progress of gravitational wave detectors, the presence of a planet in a conic-helical orbit could be revealed by the noticeably enhanced gravitational radiation from the binary star system.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Gas inside the 97 AU cavity around the transition disk Sz 91

We present ALMA (Cycle 0) band 6 and band 3 observations of the transition disk Sz 91. The disk inclination and position angle are determined to be i = 49.°5 ± 3.°5°and PA = 18.°2 ± 3.°5 and the dusty and gaseous disk are detected up to ∼220 and ∼400 AU from the star, respectively. Most importantly, our continuum observations indicate that the cavity size in the millimeter-sized dust distribution must be ∼97 AU in radius, the largest cavity observed around a T Tauri star. Our data clearly confirm the presence of {sup 12}CO (2–1) well inside the dust cavity. Based on these observational constraints we developed a disk model that simultaneously accounts for the {sup 12}CO and continuum observations (i.e., gaseous and dusty disk). According to our model, most of the millimeter emission comes from a ring located between 97 and 140 AU. We also find that the dust cavity is divided into an innermost region largely depleted of dust particles ranging from the dust sublimation radius up to 85 AU, and a second, moderately dust-depleted region, extending from 85 to 97 AU. The extremely large size of the dust cavity, the presence of gas and small dust particles within the cavity, and the accretion rate of Sz 91 are consistent with the formation of multiple (giant) planets.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

TRUE MASSES OF RADIAL-VELOCITY EXOPLANETS

We study the task of estimating the true masses of known radial-velocity (RV) exoplanets by means of direct astrometry on coronagraphic images to measure the apparent separation between exoplanet and host star. Initially, we assume perfect knowledge of the RV orbital parameters and that all errors are due to photon statistics. We construct design reference missions for four missions currently under study at NASA: EXO-S and WFIRST-S, with external star shades for starlight suppression, EXO-C and WFIRST-C, with internal coronagraphs. These DRMs reveal extreme scheduling constraints due to the combination of solar and anti-solar pointing restrictions, photometric and obscurational completeness, image blurring due to orbital motion, and the “nodal effect,” which is the independence of apparent separation and inclination when the planet crosses the plane of the sky through the host star. Next, we address the issue of nonzero uncertainties in RV orbital parameters by investigating their impact on the observations of 21 single-planet systems. Except for two—GJ 676 A b and 16 Cyg B b, which are observable only by the star-shade missions—we find that current uncertainties in orbital parameters generally prevent accurate, unbiased estimation of true planetary mass. For the coronagraphs, WFIRST-C and EXO-C, the most likely number of good estimators of true mass is currently zero. For the star shades, EXO-S and WFIRST-S, the most likely numbers of good estimators are three and four, respectively, including GJ 676 A b and 16 Cyg B b. We expect that uncertain orbital elements currently undermine all potential programs of direct imaging and spectroscopy of RV exoplanets.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

A measurement of the black hole mass in NGC 1097 using ALMA

We present an estimate of the mass of the supermassive black hole (SMBH) in the nearby type-1 Seyfert galaxy NGC 1097 using Atacamma Large Millimeter/submillimeter Array (ALMA) observations of dense gas kinematics. Dense molecular gas dynamics are traced with HCN(J=1−0) and HCO{sup +}(J=1−0) emission lines. Assuming a host galaxy inclination of 46{sup ∘}, we derive an SMBH mass, M{sub BH}=1.40{sub −0.32}{sup +0.27}×10{sup 8 }M{sub ⊙}, and an I-band mass to light ratio to be 5.14{sub −0.04}{sup +0.03}, using HCN(J=1−0). The estimated parameters are consistent between the two emission lines. The measured SMBH mass is in good agreement with the SMBH mass and bulge velocity dispersion relationship. Our result showcases ALMA’s potential for deriving accurate SMBH masses, especially for nearby late-type galaxies. Larger samples and accurate SMBH masses will further elucidate the relationship between the black hole (BH) and host galaxy properties and constrain the coevolutionary growth of galaxies and BHs.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

THE DISTRIBUTION AND ANNIHILATION OF DARK MATTER AROUND BLACK HOLES

We use a Monte Carlo code to calculate the geodesic orbits of test particles around Kerr black holes, generating a distribution function of both bound and unbound populations of dark matter (DM) particles. From this distribution function, we calculate annihilation rates and observable gamma-ray spectra for a few simple DM models. The features of these spectra are sensitive to the black hole spin, observer inclination, and detailed properties of the DM annihilation cross-section and density profile. Confirming earlier analytic work, we find that for rapidly spinning black holes, the collisional Penrose process can reach efficiencies exceeding 600%, leading to a high-energy tail in the annihilation spectrum. The high particle density and large proper volume of the region immediately surrounding the horizon ensures that the observed flux from these extreme events is non-negligible.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Global structure of isothermal diffuse X-ray emission along the Fermi bubbles

In our previous works, we found absorbed thermal X-ray plasma with kT ≃ 0.3 keV observed ubiquitously near the edges of the Fermi bubbles and interpreted this emission as weakly shock-heated Galactic halo gas. Here we present a systematic and uniform analysis of archival Suzaku (29 pointings; 6 newly presented) and Swift (68 pointings; 49 newly presented) data within Galactic longitudes |l| < 20° and latitude 5°≲ |b| < 60°, covering the whole extent of the Fermi bubbles. We show that the plasma temperature is constant at kT ≃ 0.30 ± 0.07 keV, while the emission measure (EM) varies by an order of magnitude, increasing toward the Galactic center (i.e., low |b|) with enhancements at the North Polar Spur (NPS), SE-claw, and NW-clump features. Moreover, the EM distribution of kT ≃ 0.30 keV plasma is highly asymmetric in the northern and southern bubbles. Although the association of the X-ray emission with the bubbles is not conclusive, we compare the observed EM properties with simple models assuming (i) a filled halo without bubbles, whose gas density follows a hydrostatic isothermal model (King profile), and (ii) a bubble-in-halo in which two identical bubbles expand into the halo, forming thick shells of swept halo gas. We argue that the EM profile in the north (b > 0°) favors (ii), whereas that of the south (b < 0°) is rather close to (i), but a weak excess signature is clearly detected also in the south like NPS (South Polar Spur). Such an asymmetry, if due to the bubbles, cannot be fully understood only by the inclination of bubbles’ axis against the Galactic disk normal, thus suggesting asymmetric outflow due to different environmental/initial conditions.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

A FWHM–K{sub 2} correlation in black hole transients

We compare H{sub α} emission profiles of 12 dynamically confirmed black holes (BHs) and 2 neutron star X-ray transients (SXTs) in quiescence with those of a sample of 43 Cataclysmic Variables (CVs), also quiescent. The FWHM of the H{sub α} line in SXTs is tightly correlated with the velocity semi-amplitude of the donor star K{sub 2}=0.233(13)FWHM. This new correlation, when combined with orbital periods (i.e., through photometric light curves), allows for the possibility of estimating compact object mass functions from single integration, low-resolution spectroscopy. On the other hand, CVs above the period gap are found to follow a flatter correlation, a likely consequence of their larger mass ratios. We also find that the FWHM traces the disk velocity at ≈42% R{sub L1}, independently of binary mass ratio. In addition, for a given FWHM, BHs tend to have lower EWs than CVs. This might be explained by the fact that CVs must be seen at higher inclinations to mimic the same projected disk velocities as BH SXTs. For the same reason, CVs with FWHM≳1500 km s{sup −1} are mostly eclipsing while none of our sample BHs are. Furthermore, we show that there is a vacant/unoccupied region for CVs in the FWHM–EW plane defined by FWHM>2568√((1−(9/EW){sup 2})) (km s{sup −1}). Both the FWHM–K{sub 2} correlation and the FWHM–EW plane can be exploited, together with photometric light curves, to efficiently discover quiescent BHs in deep H{sub α} surveys of the Galactic plane.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

HEARTBEAT STARS: SPECTROSCOPIC ORBITAL SOLUTIONS FOR SIX ECCENTRIC BINARY SYSTEMS

We present multi-epoch spectroscopy of “heartbeat stars,” eccentric binaries with dynamic tidal distortions and tidally induced pulsations originally discovered with the Kepler satellite. Optical spectra of six known heartbeat stars using the Wyoming Infrared Observatory 2.3 m telescope allow measurement of stellar effective temperatures and radial velocities from which we determine orbital parameters including the periods, eccentricities, approximate mass ratios, and component masses. These spectroscopic solutions confirm that the stars are members of eccentric binary systems with eccentricities e > 0.34 and periods P = 7–20 days, strengthening conclusions from prior works that utilized purely photometric methods. Heartbeat stars in this sample have A- or F-type primary components. Constraints on orbital inclinations indicate that four of the six systems have minimum mass ratios q = 0.3–0.5, implying that most secondaries are probable M dwarfs or earlier. One system is an eclipsing, double-lined spectroscopic binary with roughly equal-mass mid-A components (q = 0.95), while another shows double-lined behavior only near periastron, indicating that the F0V primary has a G1V secondary (q = 0.65). This work constitutes the first measurements of the masses of secondaries in a statistical sample of heartbeat stars. The good agreement between our spectroscopic orbital elements and those derived using a photometric model support the idea that photometric data are sufficient to derive reliable orbital parameters for heartbeat stars.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

KEPLER 453 b—THE 10th KEPLER TRANSITING CIRCUMBINARY PLANET

We present the discovery of Kepler-453 b, a 6.2 R{sub ⊕} planet in a low-eccentricity, 240.5 day orbit about an eclipsing binary. The binary itself consists of a 0.94 and 0.195 M{sub ⊙} pair of stars with an orbital period of 27.32 days. The plane of the planet's orbit is rapidly precessing, and its inclination only becomes sufficiently aligned with the primary star in the latter portion of the Kepler data. Thus three transits are present in the second half of the light curve, but none of the three conjunctions that occurred during the first half of the light curve produced observable transits. The precession period is ∼103 years, and during that cycle, transits are visible only ∼8.9% of the time. This has the important implication that for every system like Kepler-453 that we detect, there are ∼11.5 circumbinary systems that exist but are not currently exhibiting transits. The planet's mass is too small to noticeably perturb the binary, and consequently its mass is not measurable with these data; however, our photodynamical model places a 1σ upper limit of 16 M{sub ⊕}. With a period 8.8 times that of the binary, the planet is well outside the dynamical instability zone. It does, however, lie within the habitable zone of the binary, making it the third of 10 Kepler circumbinary planets to do so.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Observational signatures of planets in protoplanetary disks. I. Gaps opened by single and multiple young planets in disks

It has been suggested that the gaps and cavities recently discovered in transitional disks are opened by planets. To explore this scenario, we combine two-dimensional two fluid (gas + particle) hydrodynamical calculations with three-dimensional Monte Carlo Radiative Transfer simulations and study the observational signatures of gaps opened by one or several planets, making qualitative comparisons with observations. We find that a single planet as small as 0.2 M{sub J} can produce a deep gap at millimeter wavelengths and almost no features at near-infrared (NIR) wavelengths, while multiple planets can open up a few ×10 AU wide common gap at both wavelengths. Both the contrast ratio of the gaps and the wavelength dependence of the gap sizes are broadly consistent with data. We also confirm previous results that NIR gap sizes may be smaller than millimeter gap sizes due to dust–gas coupling and radiative transfer effects. When viewed at a moderate inclination angle, a physically circular on-centered gap could appear to be off-centered from the star due to shadowing. Planet-induced spiral arms are more apparent at NIR than at millimeter wavelengths. Overall, our results suggest that the planet-opening-gap scenario is a promising way to explain the origin of the transitional disks. Finally, inspired by the recent Atacama Large Millimeter Array release of the image of the HL Tau disk, we show that multiple narrow gaps, well separated by bright rings, can be opened by 0.2M{sub J} planets soon after their formation in a relatively massive disk.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

An empirical sequence of disk gap opening revealed by rovibrational CO

The fundamental rovibrational band of CO near 4.7 μm is a sensitive tracer of the presence and location of molecular gas in the planet-forming region of protoplanetary disks at 0.01–10 AU. We present a new analysis of a high-resolution spectral survey (R ∼ 96,000, or ∼3.2 km s{sup −1}) of CO rovibrational lines from protoplanetary disks spanning a wide range of stellar masses and of evolutionary properties. We find that the CO emission originates in two distinct velocity components. Line widths of both components correlate strongly with disk inclination, as expected for gas in Keplerian rotation. By measuring the line flux ratios between vibrational transitions F{sub v=2−1}/F{sub v=1−0}, we find that the two velocity components are clearly distinct in excitation. The broad component (FWHM=50−200 km s{sup −1}) probes the disk region near the magnetospheric accretion radius at ≈0.05 AU, where the gas is hot (800−1500 K). The narrow component (FWHM=10−50 km s{sup −1}) probes the disk at larger radii of 0.1–10 AU, where the gas is typically colder (200–700 K). CO excitation temperatures and orbital radii define an empirical temperature–radius relation as a power law with index −0.3 ± 0.1 between 0.05 and 3 AU. The broad CO component, co-spatial with the observed orbital distribution of hot Jupiters, is rarely detected in transitional and Herbig Ae disks, providing evidence for an early dissipation of the innermost disk. An inversion in the temperature profile beyond 3 AU is interpreted as a tracer of a regime dominated by UV pumping in largely devoid inner disks, and may be a signature of the last stage before the disk enters the gas-poor debris phase.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

ON THE POLAR CAP CASCADE PAIR MULTIPLICITY OF YOUNG PULSARS

We study the efficiency of pair production in polar caps of young pulsars under a variety of conditions to estimate the maximum possible multiplicity of pair plasma in pulsar magnetospheres. We develop a semi-analytic model for calculation of cascade multiplicity which allows efficient exploration of the parameter space and corroborate it with direct numerical simulations. Pair creation processes are considered separately from particle acceleration in order to assess different factors affecting cascade efficiency, with acceleration of primary particles described by recent self-consistent non-stationary model of pair cascades. We argue that the most efficient cascades operate in the curvature radiation/synchrotron regime, the maximum multiplicity of pair plasma in pulsar magnetospheres is ∼few × 10{sup 5}. The multiplicity of pair plasma in magnetospheres of young energetic pulsars weakly depends on the strength of the magnetic field and the radius of curvature of magnetic field lines and has a stronger dependence on pulsar inclination angle. This result questions assumptions about very high pair plasma multiplicity in theories of pulsar wind nebulae.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

SIGNATURES OF RECENT ASTEROID DISRUPTIONS IN THE FORMATION AND EVOLUTION OF SOLAR SYSTEM DUST BANDS

We have performed detailed dynamical modeling of the structure of a faint dust band observed in coadded InfraRed Astronomical Satellite data at an ecliptic latitude of 17° that convincingly demonstrates that it is the result of a relatively recent (significantly less than 1 Ma) disruption of an asteroid and is still in the process of forming. We show here that young dust bands retain information on the size distribution and cross-sectional area of dust released in the original asteroid disruption, before it is lost to orbital and collisional decay. We find that the Emilkowalski cluster is the source of this partial band and that the dust released in the disruption would correspond to a regolith layer ∼3 m deep on the ∼10 km diameter source body's surface. The dust in this band is described by a cumulative size-distribution inverse power-law index with a lower bound of 2.1 (implying domination of cross-sectional area by small particles) for dust particles with diameters ranging from a few μm up to a few cm. The coadded observations show that the thermal emission of the dust band structure is dominated by large (mm–cm size) particles. We find that dust particle ejection velocities need to be a few times the escape velocity of the Emilkowalski cluster source body to provide a good fit to the inclination dispersion of the observations. We discuss the implications that such a significant release of material during a disruption has for the temporal evolution of the structure, composition, and magnitude of the zodiacal cloud.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

An extreme metallicity, large-scale outflow from a star-forming galaxy at z ∼ 0.4

We present a detailed analysis of a large-scale galactic outflow in the circumgalactic medium of a massive (M{sub h}∼10{sup 12.5} M{sub ⊙}), star-forming (∼6.9 M{sub ⊙} yr{sup −1}), sub-L{sub *} (∼0.5L{sub B}{sup ∗}) galaxy at z = 0.39853 that exhibits a wealth of metal-line absorption in the spectra of the background quasar Q 0122−003 at an impact parameter of 163 kpc. The galaxy inclination angle (i=63{sup ∘}) and the azimuthal angle (Φ=73{sup ∘}) imply that the QSO sightline is passing through the projected minor-axis of the galaxy. The absorption system shows a multiphase, multicomponent structure with ultra-strong, wide velocity spread O VI (logN=15.16±0.04, Δv{sub 90} = 419 km s{sup −1}) and N V (logN=14.69±0.07, Δv{sub 90} = 285 km s{sup −1}) lines that are extremely rare in the literature. The highly ionized absorption components are well explained as arising in a low density (∼10{sup −4.2} cm{sup −3}), diffuse (∼10 kpc), cool (∼10{sup 4} K) photoionized gas with a super-solar metallicity ([X/H]≳0.3). From the observed narrowness of the Lyβ profile, the non-detection of S IV absorption, and the presence of strong C IV absorption in the low-resolution FOS spectrum, we rule out equilibrium/non-equilibrium collisional ionization models. The low-ionization photoionized gas with a density of ∼10{sup −2.5} cm{sup −3} and a metallicity of [X/H]≳−1.4 is possibly tracing recycled halo gas. We estimate an outflow mass of ∼2×10{sup 10} M{sub ⊙}, a mass-flow rate of ∼54 M{sub ⊙} yr{sup −1}, a kinetic luminosity of ∼9×10{sup 41} erg s{sup −1}, and a mass loading factor of ∼8 for the outflowing high-ionization gas. These are consistent with the properties of “down-the-barrel” outflows from infrared-luminous starbursts as studied by Rupke et al. Such powerful, large-scale, metal-rich outflows are the primary means of sufficient mechanical and chemical feedback as invoked in theoretical models of galaxy formation and evolution.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

EFFECTS OF SPOT SIZE ON NEUTRON-STAR RADIUS MEASUREMENTS FROM PULSE PROFILES

We calculate the effects of spot size on pulse profiles of moderately rotating neutron stars. Specifically, we quantify the bias introduced in radius measurements from the common assumption that spots are infinitesimally small. We find that this assumption is reasonable for spots smaller than 10°–18° and leads to errors that are ≤10% in the radius measurement, depending on the location of the spot and the inclination of the observer. We consider the implications of our results for neutron star radius measurements with the upcoming and planned X-ray missions NICER and LOFT. We calculate the expected spot size for different classes of sources and investigate the circumstances under which the assumption of a small spot is justified.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

ACCRETION KINEMATICS THROUGH THE WARPED TRANSITION DISK IN HD 142527 FROM RESOLVED CO(6–5) OBSERVATIONS

The finding of residual gas in the large central cavity of the HD 142527 disk motivates questions regarding the origin of its non-Keplerian kinematics and possible connections with planet formation. We aim to understand the physical structure that underlies the intra-cavity gaseous flows, guided by new molecular-line data in CO(6–5) with unprecedented angular resolutions. Given the warped structure inferred from the identification of scattered-light shadows cast on the outer disk, the kinematics are consistent, to first order, with axisymmetric accretion onto the inner disk occurring at all azimuths. A steady-state accretion profile, fixed at the stellar accretion rate, explains the depth of the cavity as traced in CO isotopologues. The abrupt warp and evidence for near free-fall radial flows in HD 142527 resemble theoretical models for disk tearing, which could be driven by the reported low-mass companion, whose orbit may be contained in the plane of the inner disk. The companion’s high inclination with respect to the massive outer disk could drive Kozai oscillations over long timescales; high-eccentricity periods may perhaps account for the large cavity. While shadowing by the tilted disk could imprint an azimuthal modulation in the molecular-line maps, further observations are required to ascertain the significance of azimuthal structure in the density field inside the cavity of HD 142527.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Gas-phase oxygen abundances and radial metallicity gradients in the two nearby spiral galaxies NGC 7793 and NGC 4945

Gas-phase abundances in H ii regions of two spiral galaxies, NGC 7793 and NGC 4945, have been studied to determine their radial metallicity gradients. We used the strong-line method to derive oxygen abundances from spectra acquired with GMOS-S, the multi-object spectrograph on the 8 m Gemini South telescope. We found that NGC 7793 has a well-defined gas-phase radial oxygen gradient of −0.321 ± 0.112 dex R{sub 25}{sup −1} (or −0.054 ± 0.019 dex kpc{sup −1}) in the galactocentric range 0.17 < R{sub G}/R{sub 25} < 0.82, not dissimilar from gradients calculated with direct abundance methods in galaxies of similar mass and morphology. We also determined a shallow radial oxygen gradient in NGC 4945, −0.253 ± 0.149 dex R{sub 25}{sup −1} (or −0.019 ± 0.011 dex kpc{sup −1}) for 0.04 < R{sub G}/R{sub 25} < 0.51, where the larger relative uncertainty derives mostly from the larger inclination of this galaxy. NGC 7793 and NGC 4945 have been selected for this study because they are similar, in mass and morphology, to M33 and the Milky Way, respectively. Since at zeroth order we expect the radial metallicity gradients to depend on mass and galaxy type, we compared our galaxies in the framework of radial metallicity models best suited for M33 and the Galaxy. We found a good agreement between M33 and NGC 7793, pointing toward similar evolution for the two galaxies. We notice instead differences between NGC 4945 and the radial metallicity gradient model that best fits the Milky Way. We found that these differences are likely related to the presence of an active galactic nucleus combined with a bar in the central regions of NGC 4945, and to its interacting environment.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

GEOMETRIC AND KINEMATIC STRUCTURE OF THE OUTFLOW/ENVELOPE SYSTEM OF L1527 REVEALED BY SUBARCSECOND-RESOLUTION OBSERVATION OF CS

Subarcsecond-resolution images of the rotational line emissions of CS and c-C{sub 3}H{sub 2} obtained toward the low-mass protostar IRAS 04368+2557 in L1527 with the Atacama Large Millimeter/submillimeter Array are investigated to constrain the orientation of the outflow/envelope system. The distribution of CS consists of an envelope component extending from north to south and a faint butterfly shaped outflow component. The kinematic structure of the envelope is well reproduced by a simple ballistic model of an infalling rotating envelope. Although the envelope has a nearly edge-on configuration, we find that the western side of the envelope faces the observer. This configuration is opposite to the direction of the large-scale (∼10{sup 4} AU) outflow suggested previously from the {sup 12}CO (J = 3–2) observation, and to the morphology of infrared reflection near the protostar (∼200 AU). The latter discrepancy could originate from high extinction by the outflow cavity of the western side, or may indicate that the outflow axis is not parallel to the rotation axis of the envelope. Position–velocity diagrams show the accelerated outflow cavity wall, and its kinematic structure in the 2000 AU scale is explained by a standard parabolic model with the inclination angle derived from the analysis of the envelope. The different orientation of the outflow between the small and large scale implies a possibility of precession of the outflow axis. The shape and the velocity of the outflow in the vicinity of the protostar are compared with those of other protostars.

79 ASTRONOMY AND ASTROPHYSICS↗