Engineering topics

Levine, Stephen E.

Publications and source records attributed to Levine, Stephen E..

4 records

DOE OSTI2021

Occultation of a Large Star by the Large Plutino (28978) Ixion on 2020 October 13 UTC

We observed the occultation of the star Gaia DR2 4056440205544338944 by (28978) Ixion. The event was observed from two Lowell Observatory sites, using the 4.3 m Lowell Discovery Telescope (LDT), near Happy Jack, AZ, USA, and a 0.32 m telescope co-mounted with the Titan Monitoring telescope on Lowell’s Mars Hill campus in Flagstaff, AZ. The LDT chord, at 44.86 s, was roughly 30% longer than the longest predicted possible chord. Under the assumption of a spherical body, Ixion’s fitted diameter D = 709.6 ± 0.2 km. The LDT light-curve profile was used to place an upper limit on the surface pressure P < 2 μbar on any possible atmosphere of Ixion. At the distance of Ixion, the occulted star had a fitted projected diameter of 19.25 ± 0.3 km assuming uniform disk illumination, giving a stellar angular diameter of 0.675 ± 0.010 mas. Using the Gaia EDR3 parallax of 0.565 mas, the stellar radius is 130{sub −17}{sup +20} R{sub ⊙}. The measured size is consistent with prior spectral classification of this star as a reddened mid-M giant. This is one of only a modest number of M5 III stars to have a directly measured diameter, and is more distant than most.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

The shape of LITTLE THINGS dwarf galaxies DDO 46 and DDO 168: Understanding the stellar and gas kinematics

Determining the shape of dwarf irregular (dIrr) galaxies is controversial because if one assumes that these objects are disks and if these disks are randomly distributed over the sky, then their projected minor-to-major axis ratios should follow a particular statistical distribution, which is not observed. Thus, different studies have led to different conclusions. Some believe that the observed distributions can be explained by assuming the dIrrs are thick disks while others have concluded that dIrrs are triaxial. Fortunately, the central stellar velocity dispersion, σ{sub z,0}, combined with maximum rotation speed, V{sub max}, provides a kinematic measure, V{sub max}/σ{sub z,0}, which gives the three-dimensional shape of a system. In this work, we present the stellar and gas kinematics of DDO 46 and DDO 168 from the Local Irregulars That Trace Luminosity Extremes; The H i Nearby Galaxy Survey (LITTLE THINGS) and determine their respective V{sub max}/σ{sub z,0} values. We used the Kitt Peak National Observatory's Mayall 4 m telescope with the Echelle spectrograph as a long-slit spectrograph, which provided a two-dimensional, 3′-long slit. We acquired spectra of DDO 168 along four position angles (PAs) by placing the slit over the morphological major and minor axes and two intermediate PAs. However, due to poor weather conditions during our observing run for DDO 46, we were able to extract only one useful data point from the morphological major axis. We determined a central stellar velocity dispersion perpendicular to the disk, σ{sub z,0}, of 13.5 ± 8 km s{sup −1} for DDO 46 and 〈σ{sub z,0}〉 of 10.7 ± 2.9 km s{sup −1} for DDO 168. We then derived the maximum rotation speed in both galaxies using the LITTLE THINGS H i data. We separated bulk motions from non-circular motions using a double Gaussian decomposition technique and applied a tilted-ring model to the bulk velocity field. We corrected the observed H i rotation speeds for asymmetric drift and found a maximum velocity, V{sub max}, of 77.4 ± 3.7 and 67.4 ± 4.0 for DDO 46 and DDO 168, respectively. Thus, we derived a kinematic measure, V{sub max}/σ{sub z,0}, of 5.7 ± 0.6 for DDO 46 and 6.3 ± 0.3 for DDO 168. Comparing these values to ones determined for spiral galaxies, we find that DDO 46 and DDO 168 have V{sub max}/σ{sub z,0} values indicative of thin disks, which is in contrast to minor-to-major axis ratio studies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

The binary white dwarf LHS 3236

The white dwarf LHS 3236 (WD1639+153) is shown to be a double-degenerate binary, with each component having a high mass. Astrometry at the U.S. Naval Observatory gives a parallax and distance of 30.86 ± 0.25 pc and a tangential velocity of 98 km s{sup –1}, and reveals binary orbital motion. The orbital parameters are determined from astrometry of the photocenter over more than three orbits of the 4.0 yr period. High-resolution imaging at the Keck Observatory resolves the pair with a separation of 31 and 124 mas at two epochs. Optical and near-IR photometry give a set of possible binary components. Consistency of all data indicates that the binary is a pair of DA stars with temperatures near 8000 and 7400 K and with masses of 0.93 and 0.91 M {sub ☉}; also possible is a DA primary and a helium DC secondary with temperatures near 8800 and 6000 K and with masses of 0.98 and 0.69 M {sub ☉}. In either case, the cooling ages of the stars are ∼3 Gyr and the total ages are <4 Gyr. The combined mass of the binary (1.66-1.84 M {sub ☉}) is well above the Chandrasekhar limit; however, the timescale for coalescence is long.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1994

The stability of perfect elliptic disks. 1: The maximum streaming case

Self-consistent distribution functions are constructed for two-dimensional perfect elliptic disks (for which the potential is exactly integrable) in the limit of maximum streaming; these are tested for stability by N-body integration. To obtain a discrete representation for each model, simulated annealing is used to choose a set of orbits which sample the distribution function and reproduce the required density profile while carrying the greatest possible amount of angular momentum. A quiet start technique is developed to place particles on these orbits uniformly in action-angle space, making the initial conditions as smooth as possible. The roundest models exhibit spiral instabilities similar to those of cold axisymmetric disks; the most elongated models show bending instabilities like those seen in prolate systems. Between these extremes, there is a range of axial ratios 0.25 approximately less than b/a approximately less than 0.6 within which these models appear to be stable. All the methods developed in this investigation can easily be extended to integrable potentials in three dimensions.

Levine, Stephen E.↗