605 research outputs found
HST PSF simulation using Tiny Tim
Tiny Tim is a program which simulates Hubble Space Telescope imaging camera PSF's. It is portable (written and distributed in C) and is reasonably fast. It can model the WFPC, WFPC 2, FOC, and COSTAR corrected FOC cameras. In addition to aberrations such as defocus and spherical, it also includes WFPC obscuration shifting, mirror zonal error maps, and jitter. The program has been used at a number of sites for deconvolving HST images. Tiny Tim is available via anonymous ftp on stsci.edu in the directory software/tinytim
A Multi-Epoch HST Study of the Herbig-Haro Flow from XZ Tauri
We present nine epochs of Hubble Space Telescope optical imaging of the
bipolar outflow from the pre-main sequence binary XZ Tauri. Our data monitors
the system from 1995-2005 and includes emission line images of the flow. The
northern lobe appears to be a succession of bubbles, the outermost of which
expanded ballistically from 1995-1999 but in 2000 began to deform and
decelerate along its forward edge. It reached an extent of 6" from the binary
in 2005. A larger and fainter southern counterbubble was detected for the first
time in deep ACS images from 2004. Traces of shocked emission are seen as far
as 20" south of the binary. The bubble emission nebulosity has a low excitation
overall, as traced by the [S II]/H-alpha line ratio, requiring a nearly
comoving surrounding medium that has been accelerated by previous ejections or
stellar winds.
Within the broad bubbles there are compact emission knots whose alignments
and proper motions indicate that collimated jets are ejected from each binary
component. The jet from the southern component, XZ Tau A, is aligned with the
outflow axis of the bubbles and has tangential knot velocities of 70-200 km/s.
Knots in the northern flow are seen to slow and brighten as they approach the
forward edge of the outermost bubble. The knots in the jet from the other star,
XZ Tau B, have lower velocities of ~100 km/s
Deconvolution of Hubble Space Telescope images using simulated point spread functions
Presented is a study of the use of simulated point spread functions (PSF's) to deconvolve Hubble Space Telescope images. We concentrate on images from the Wide Field and Planetary Camera (WFPC) and examine the affect of position dependence of the PSF and the telescope focus position on deconvolutions. Comparisons will be made to what will be expected from WFPC 2, which will include corrective optics. Since PSF's can be simulated for any specific observation, with the added advantage of being noise free and the ability to subsample them, they may be more suitable for deconvolution than observed ones in some cases. And since finding a suitable observed PSF may be difficult, simulated ones may be easier to use
HST/ACS Images of the GG Tauri Circumbinary Disk
Hubble Space Telescope Advanced Camera for Surveys images of the young binary
GG Tauri and its circumbinary disk in V and I bandpasses were obtained in 2002
and are the most detailed of this system to date. The confirm features
previously seen in the disk including: a "gap" apparently caused by shadowing
from circumstellar material; an asymmetrical distribution of light about the
line of sight on the near edge of the disk; enhanced brightness along the near
edge of the disk due to forward scattering; and a compact reflection nebula
near the secondary star. New features are seen in the ACS images: two short
filaments along the disk; localized but strong variations in disk intensity
("gaplets"); and a "spur" or filament extending from the reflection nebulosity
near the secondary. The back side of the disk is detected in the V band for the
first time. The disk appears redder than the combined light from the stars,
which may be explained by a varied distribution of grain sizes. The brightness
asymmetries along the disk suggest that it is asymmetrically illuminated by the
stars due to extinction by nonuniform circumstellar material or the illuminated
surface of the disk is warped by tidal effects (or perhaps both). Localized,
time-dependent brightness variations in the disk are also seen.Comment: 28 pages, 7 figures, accepted for publication in the Astronomical
Journa
Discovery of an extended debris disk around the F2V star HD 15745
Using the Advanced Camera for Surveys aboard the Hubble Space Telescope, we
have discovered dust-scattered light from the debris disk surrounding the F2V
star HD 15745. The circumstellar disk is detected between 2.0" and 7.5" radius,
corresponding to 128 - 480 AU radius. The circumstellar disk morphology is
asymmetric about the star, resembling a fan, and consistent with forward
scattering grains in an optically thin disk with an inclination of ~67 degrees
to our line of sight. The spectral energy distribution and scattered light
morphology can be approximated with a model disk composed of silicate grains
between 60 and 450 AU radius, with a total dust mass of 10E-7 M_sun (0.03
M_earth) representing a narrow grain size distribution (1 - 10 micron).
Galactic space motions are similar to the Castor Moving Group with an age of
~10E+8 yr, although future work is required to determine the age of HD 15745
using other indicators.Comment: 7 pages, 4 figures, ApJ Letters, in pres
HST Studies of the WLM Galaxy. I. The Age and Metallicity of the Globular Cluster
We have obtained V and I images of the lone globular cluster that belongs to
the dwarf Local Group irregular galaxy known as WLM. The color-magnitude
diagram of the cluster shows that it is a normal old globular cluster with a
well-defined giant branch reaching to M_V=-2.5, a horizontal branch at
M_V=+0.5, and a sub-giant branch extending to our photometry limit of M_V=+2.0.
A best fit to theoretical isochrones indicates that this cluster has a
metallicity of [Fe/H]=-1.52\pm0.08 and an age of 14.8\pm0.6 Gyr, thus
indicating that it is similar to normal old halo globulars in our Galaxy. From
the fit we also find that the distance modulus of the cluster is 24.73\pm0.07
and the extinction is A_V=0.07\pm0.06, both values that agree within the errors
with data obtained for the galaxy itself by others. We conclude that this
normal massive cluster was able to form during the formation of WLM, despite
the parent galaxy's very small intrinsic mass and size.Comment: 14 pages, 5 figures, 1 tabl
High Resolution Infrared Imaging of the Compact Nuclear Source in NGC4258
We present high resolution imaging of the nucleus of NGC4258 from 1 micron to
18 microns. Our observations reveal that the previously discovered compact
source of emission is unresolved even at the near-infrared resolution of about
0.2 arcsec FWHM which corresponds to about 7 pc at the distance of the galaxy.
This is consistent with the source of emission being the region in the
neighborhood of the purported 3.5*10^7 M_sun black hole. After correcting for
about 18 mags of visual extinction, the infrared data are consistent with a
F_nu \propto nu^(-1.4+/-0.1) spectrum from 1.1 micron to 18 micron, implying a
non-thermal origin. Based on this spectrum, the total extinction corrected
infrared luminosity (1-20 micron) of the central source is 2*10^8 L_sun. We
argue that the infrared spectrum and luminosity of the central source obviates
the need for a substantial contribution from a standard, thin accretion disk at
these wavelengths and calculate the accretion rate through an advection
dominated accretion flow to be Mdot \sim 10^(-3) M_sun/yr. The agreement
between these observations and the theoretical spectral energy distribution for
advection dominated flows provides evidence for the existence of an advection
dominated flow in this low luminosity AGN.Comment: 21 pages, 5 figures, Appearing in Mar 2000 ApJ vol. 53
Recent Enhancements to the Development of CFD-Based Aeroelastic Reduced-Order Models
Recent enhancements to the development of CFD-based unsteady aerodynamic and aeroelastic reduced-order models (ROMs) are presented. These enhancements include the simultaneous application of structural modes as CFD input, static aeroelastic analysis using a ROM, and matched-point solutions using a ROM. The simultaneous application of structural modes as CFD input enables the computation of the unsteady aerodynamic state-space matrices with a single CFD execution, independent of the number of structural modes. The responses obtained from a simultaneous excitation of the CFD-based unsteady aerodynamic system are processed using system identification techniques in order to generate an unsteady aerodynamic state-space ROM. Once the unsteady aerodynamic state-space ROM is generated, a method for computing the static aeroelastic response using this unsteady aerodynamic ROM and a state-space model of the structure, is presented. Finally, a method is presented that enables the computation of matchedpoint solutions using a single ROM that is applicable over a range of dynamic pressures and velocities for a given Mach number. These enhancements represent a significant advancement of unsteady aerodynamic and aeroelastic ROM technology
- …