20 research outputs found
Design principles of a rotating medium speed mechanism
Design principles of a medium speed mechanism (MSM) are presented, including discussion on the relative merits of beryllium and aluminium as structural materials. Rotating at a speed of 60 rpm, the application envisaged for the MSM was as a despin bearing for the despun platform or despun antenna of a spin stabilized satellite. The MSM was built and tested to qualification level and is currently undergoing real time life testing
High resolution spectroscopy of the 11.3 micron emission band
High resolution spectra of the 11.3 micron emission band in M82 and NGC 7027 were obtained using the University of Texas IR echelle spectrometer on the IRTF in April 1988. The spectral resolution was 0.004 micron, with coverage from 11.0 to 11.6 microns. Spectra were measured at ten positions along a 10 min. long slit. Analysis of the data is still in progress, but initial results show no clear evidence of narrow structure within the feature. The analysis will involve comparison of the observed spectra to laboratory and predicted spectra of Polycylic Aromatic Hydrocarbons (PAHs) and Quenched Carbonaceous Composite (QCCs) to determine which may be responsible for the emission. The spectra will be examined with a goal of determining whether the emission is caused by molecular or solid state material. The data are also examined for evidence of variations in the shape and strength of the 11.3 micron feature with position on the sky. In NGC 7027 the 10 min. long slit went across the edge of the ionized nebulae, allowing comparison of emission from both ionized and neutral regions
The Nuclear Starburst in NGC 253
We have obtained long-slit spectra of NGC 253 in the J, H, K, and N bands,
broadband images in the J, H, and Ks bands, narrowband images centered at the
wavelengths of BrGamma and H2(1,0)S(1), and imaging spectroscopy centered on
[NeII](12.8um). We use these data and data from the literature in a
comprehensive re-assessment of the starburst in this galaxy. We derive the
supernova rate from the strength of the infrared [FeII] lines. We find that
most of the H2 infrared luminosity is excited by fluorescence in low density
gas. We derive a strong upper limit of ~37,000K for the stars exciting the
emission lines. We use velocity-resolved infrared spectra to determine the mass
in the starburst region. Most of this mass appears to be locked up in the old,
pre-existing stellar population. Using these constraints and others to build an
evolutionary synthesis model, we find that the IMF originally derived to fit
the starburst in M 82 (similar to a Salpeter IMF) also accounts for the
properties of NGC 253. The models indicate that rapid massive star formation
has been ongoing for 20-30 million years in NGC 253---that is, it is in a late
phase of its starburst. We model the optical emission line spectrum expected
from a late phase starburst and demonstrate that it reproduces the observed
HII/weak-[OI] LINER characteristics.Comment: 48 pages, 14 figures, uses AASTeX macros, to appear in Ap
A mid-infrared spectroscopic survey of starburst galaxies: excitation and abundances
We present spectroscopy of MIR emission lines in twelve starburst regions,
located in eleven starburst galaxies, for which a significant number of lines
between 2.38 and 45micron were observed with the ISO Short Wavelength
Spectrometer, with the intention of providing a reference resource for MIR
spectra of starburst galaxies. The observation apertures were centred on
actively star forming regions, including those which are inaccessible at
optical wavelengths due to high levels of obscuration. We use this data set,
which includes fine structure and hydrogen recombination lines, to investigate
excitation and to derive gas phase abundances of neon, argon, and sulphur of
the starburst galaxies. The derived Ne abundances span approximately an order
of magnitude, up to values of ~3 times solar. The excitation ratios measured
from the Ne and Ar lines correlate well with each other (positively) and with
abundances (negatively). Both in excitation and abundance, a separation of
objects with visible Wolf-Rayet features (high excitation, low abundance) is
noted from those without (low excitation, high abundance). For a given
abundance, the starbursts are of relatively lower excitation than a comparative
sample of HII regions, possibly due to ageing stellar populations. By
considering the abundance ratios of S with Ne and Ar we find that, in our
higher metallicity systems, S is relatively underabundant by a factor of ~3. We
discuss the origin of this deficit and favour depletion of S onto dust grains
as a likely explanation. This weakness of the MIR fine structure lines of S has
ramifications for future infrared missions such as SIRTF and Herschel since it
indicates that the S lines are less favourable tracers of star formation than
is suggested by nebular models which do not consider this effect.Comment: 20 pages, 23 figures, Accepted for publication in A&
ROBISAT, Konzept- und Durchfuehrbarkeitsstudie Phase A Abschlussbericht. Abschlussdatum: September 1980
SIGLETechnische Informationsbibliothek Hannover: RA 674 (80-033) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman