14,320 research outputs found
Applicability of ERTS-1 to lineament and photogeologic mapping in Montana: Preliminary report
A lineament map prepared from a mosaic of western Montana shows about 85 lines not represented on the state geologic map, including elements of a northeast-trending set through central western Montana which merit ground truth checking and consideration in regional structural analysis. Experimental fold annotation resulted in a significant local correction to the state geologic map. Photogeologic mapping studies produced only limited success in identification of rock types, but they did result in the precise delineation of a late Cretaceous or early Tertiary volcanic field (Adel Mountain field) and the mapping of a connection between two granitic bodies shown on the state map. Imagery was used successfully to map clay pans associated with bentonite beds in gently dipping Bearpaw Shale. It is already apparent that ERTS imagery should be used to facilitate preparation of a much needed statewide tectonic map and that satellite imagery mapping, aided by ground calibration, provides and economical means to discover and correct errors in the state geologic map
Turbulent Characteristics of Two-Phase, Gas-Liquid Stratified Channel Flow
The turbulence characteristics of the bulk phases were studied in a stratified, two-dimensional, gas- liquid channel flow. Initial results are presented comparing mean velocity and turbulent intensity profiles with those obtained in a prior study at the same bulk phase Reynolds numbers. The results indicate that comparison of two realizations of stratified gas- liquid flow cannot be adequately done on the basis of bulk-phase Reynolds numbers. Comparisons must be based on some more fundamental relationships involving the gas-liquid interactions
El Niño and the delayed action oscillator
We study the dynamics of the El Niño phenomenon using the mathematical model of delayedaction oscillator (DAO). Topics such as the influence of the annual cycle, global warming, stochastic influences due to weather conditions and even off-equatorial heat-sinks can all be discussed using only modest analytical and numerical resources. Thus the DAO allows for a pedagogical introduction to the science of El Niño and La Niña while at the same time avoiding the need for large-scale computing resources normally associated with much more sophisticated coupled atmosphere-ocean general circulation models. It is an approach which is ideally suited for student projects both at high school and undergraduate level
Novel π-Extended Quinazoline-Ferrocene Conjugates: Synthesis, Structure, and Redox Behavior
Novel ferrocene conjugates of tricyclic quinazoline derivatives are prepared by condensation of active C-6 methylene groups of mackinazolinones with ferrocenecarbaldehyde. Following this route the conjugated parent alkaloid as well as derivatives with nitro, amino, and alkanoylamino groups at C-2 were attached at the ferrocene moiety, thereby significantly extending the delocalized π system. In addition, the parent compound was subjected to the reaction with ferrocene-1,1'-dicarbaldehyde, giving rise to the symmetrical and unsymmetrical double condensation products – 1,1'-disubstituted ferrocene derivatives, which bear two alkaloid substituents. Some of the compounds obtained were subjected to X-ray crystallographic analyses. The influence of the substituents at C-2 through the extended conjugated π system on the iron atom is reflected by results of cyclovoltammetric measurements
The Angular Momentum Content and Evolution of Class I and Flat-Spectrum Protostars
We report on the angular momentum content of heavily embedded protostars
based on our analysis of the projected rotation velocities (v sin i s) of 38
Class I/flat spectrum young stellar objects presented by Doppmann et al (2005).
After correcting for projection effects, we find that infrared-selected Class
I/flat spectrum objects rotate significantly more quickly (median equatorial
rotation velocity ~ 38 km/sec) than Classical T Tauri stars (CTTSs; median
equatorial rotation velocity ~ 18 km/sec) in the Rho Ophiuchi and
Taurus-Aurigae regions. The detected difference in rotation speeds between
Class I/flat spectrum sources and CTTSs proves difficult to explain without
some mechanism which transfers angular momentum out of the protostar between
the two phases. Assuming Class I/flat spectrum sources possess physical
characteristics (M_*,R_*,B_*) typical of pre-main sequence stars, fully disk
locked Class I objects should have co-rotation radii within their protostellar
disks that match well (within 30%) with the predicted magnetic coupling radii
of Shu et al (1994). The factor of two difference in rotation rates between
Class I/flat spectrum and CTTS sources, when interpreted in the context of disk
locking models, also imply a factor of 5 or greater difference in mass
accretion rates between the two phases.Comment: 13 pages, 6 figures. Accepted for publication in the Astronomical
Journal (tentatively for June 2005 edition
Effective Temperatures of Low-Mass Stars from High-Resolution H-band Spectroscopy
High-resolution, near-infrared spectra will be the primary tool for finding
and characterizing Earth-like planets around low-mass stars. Yet, the
properties of exoplanets can not be precisely determined without accurate and
precise measurements of the host star. Spectra obtained with the Immersion
GRating INfrared Spectrometer (IGRINS) simultaneously provide diagnostics for
most stellar parameters, but the first step in any analysis is the
determination of the effective temperature. Here we report the calibration of
high-resolution H-band spectra to accurately determine effective temperature
for stars between 4000-3000 K (K8--M5) using absorption line depths of Fe
I, OH, and Al I. The field star sample used here contains 254 K and M stars
with temperatures derived using BT-Settl synthetic spectra. We use 106 stars
with precise temperatures in the literature to calibrate our method with
typical errors of about 140 K, and systematic uncertainties less than 120
K. For the broadest applicability, we present T--line-depth-ratio
relationships, which we test on 12 members of the TW Hydrae Association and at
spectral resolving powers between 10,000--120,000. These ratios offer a
simple but accurate measure of effective temperature in cool stars that is
distance and reddening independent.Comment: 19 pages, 11 figures and 3 tables. Accepted in Ap
Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5 Dwarf TVLM513-46546
[Abridged] We present the first simultaneous radio, X-ray, ultraviolet, and
optical spectroscopic observations of the M8.5 dwarf TVLM513-46546, with a
duration of 9 hours. These observations are part of a program to study the
origin of magnetic activity in ultracool dwarfs, and its impact on
chromospheric and coronal emission. Here we detect steady quiescent radio
emission superposed with multiple short-duration, highly polarized flares;
there is no evidence for periodic bursts previously reported for this object,
indicating their transient nature. We also detect soft X-ray emission, with
L_X/L_bol~10^-4.9, the faintest to date for any object later than M5, and a
possible weak X-ray flare. TVLM513-46546 continues the trend of severe
violation of the radio/X-ray correlation in ultracool dwarfs, by nearly 4
orders of magnitude. From the optical spectroscopy we find that the Balmer line
luminosity exceeds the X-ray luminosity by a factor of a few, suggesting that,
unlike in early M dwarfs, chromospheric heating may not be due to coronal X-ray
emission. More importantly, we detect a sinusoidal H-alpha light curve with a
period of 2 hr, matching the rotation period of TVLM513-46546. This is the
first known example of such Balmer line behavior, which points to a co-rotating
chromospheric hot spot or an extended magnetic structure, with a covering
fraction of about 50%. This feature may be transitory based on the apparent
decline in light curve peak during the four observed maxima. From the radio
data we infer a large scale steady magnetic field of ~100 G, in good agreement
with the value required for confinement of the X-ray emitting plasma. The radio
flares, on the other hand, are produced in a component of the field with a
strength of ~3 kG and a likely multi-polar configuration.Comment: 13 pages, 4 figure
The 1995-1996 Decline of R Coronae Borealis - High Resolution Optical Spectroscopy
A set of high-resolution optical spectra of RCrB acquired before, during, and
after its 1995-1996 decline is discussed. All of the components reported from
earlier declines are seen. This novel dataset provides new information on these
components including several aspects not previously seen in declines of RCrB
and other RCBs. In the latter category is the discovery that the decline's
onset is marked by distortions of absorption lines of high-excitation lines,
and quickly followed by emission in these and in low excitation lines. This
'photospheric trigger' implies that dust causing the decline is formed close to
the star. These emission lines fade quickly. After 1995 November 2, low
excitation narrow (FWHM ~12 km s-1) emission lines remain. These appear to be a
permanent feature, slightly blue-shifted from the systemic velocity, and
unaffected by the decline except for a late and slight decrease of flux at
minimum light. The location of the warm, dense gas providing these lines is
uncertain. Absorption lines unaffected by overlying sharp emission are greatly
broadened, weakened, and red-shifted at the faintest magnitudes when scattered
light from the star is a greater contributor than direct light transmitted
through the fresh soot cloud. A few broad lines are seen at and near minimum
light with approxiamately constant flux: prominent among these are the He I
triplet series, Na I D, and [N II] lines. These lines are blue-shifted by about
30 km s(-1) relative to the systemic velocity with no change in velocity over
the several months for whicht he lines were seen. It is suggested that these
lines, especially the He I lines, arise from an accretion disk around an unseen
compact companion, which may be a low-mass white dwarf. If so, R CrB is similar
to the unusual post-AGB star 89 Her.Comment: 31 pages, 26 figure
Observation of enhanced X-ray emission from the CTTS AA Tau during a transit of an accretion funnel
AA Tau was observed for about 5h per XMM orbit (2 days) over 8 successive
orbits, which covers two optical eclipse periods (8.2 days). The XMM optical/UV
monitor simultaneously provided UV photometry with a ~15 min sampling rate.
Some V-band photometry was also obtained from the ground during this period in
order to determine the dates of the eclipses. Two X-ray and UV measurements
were secured close to the center of the eclipse. The UV flux is the highest
just before the eclipse starts and the lowest towards the end of it. We model
the UV flux variations with a weekly modulation (inner disk eclipse), plus a
daily modulation, which suggests a non-steady accretion. No eclipses are
detected in X-rays. For one measurement, the X-ray count rate was nearly 50
times stronger than the minimum observed level, and the plasma temperature
reached 60 MK, i.e., a factor of 2-3 higher than in the other observations.
This X-ray event, observed close to the center of the optical eclipse, is
interpreted as an X-ray flare. We identify the variable column density with the
low-density accretion funnel flows blanketing the magnetosphere. The lack of
X-ray eclipses indicates that X-ray emitting regions are located at high
latitudes. Furthermore, the occurrence of a strong X-ray flare near the center
of the optical eclipse suggests that the magnetically active areas are closely
associated with the base of the high-density accretion funnel flow. We
speculate that the impact of this free falling accretion flow onto the strong
magnetic field of the stellar corona may boost the X-ray emission (abridged).Comment: 17 pages and 9 Figures. Accepted by A&
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