5,129 research outputs found
Ultraviolet Spectroscopy of Rapidly-Rotating Solar-Mass Stars: Emission Line Redshifts as a Test of the Solar-Stellar Connection
We compare high-resolution ultraviolet spectra of the Sun and thirteen
solarmass main sequence stars with different rotational periods that serve as
proxies for their different ages and magnetic field structures. In this the
second paper in the series, we study the dependence of ultraviolet
emission-line centroid velocities on stellar rotation period, as rotation rates
decrease from that of the Pleiades star HII314 (Prot = 1.47 days) to Alpha Cen
A (Prot = 28 days). Our stellar sample of F9 V to G5 V stars consists of six
stars observed with the Cosmic Origins 1Guest Observer, NASA/ESA Hubble Space
Telescope and User of the Data Archive at the Space Telescope Science
Institute. Spectrograph on HST and eight stars observed with the Space
Telescope Imaging Spectrograph on HST. We find a systematic trend of increasing
redshift with more rapid rotation (decreasing rotation period) that is similar
to the increase in line red shift between quiet and plage regions on the Sun.
The fastest-rotating solar-mass star in our study, HII314, shows significantly
enhanced redshifts at all temperatures above log T = 4.6, including the corona,
which is very different from the redshift pattern observed in the more
slowly-rotating stars. This difference in the redshift pattern suggests that a
qualitative change in the magnetic-heating process occurs near Prot = 2 days.
We propose that HII314 is an example of a solar-mass star with a magnetic
heating rate too large for the physical processes responsible for the redshift
pattern to operate in the same way as for the more slowly rotating stars.
HII314 may therefore lie above the high activity end of the set of solar-like
phenomena that is often called the "solar-stellar connection".Comment: 36 pages, 7 figures, 6 tables, to appear in the Astrophysical Journal
July 201
Volcanological constraints of Archaean tectonics
Volcanological and trace element geochemical data can be integrated to place some constraints upon the size, character and evolutionary history of Archean volcanic plumbing, and hence indirectly, Archean tectonics. The earliest volcanism in any greenhouse belt is almost universally tholeitic basalt. Archean mafic magma chambers were usually the site of low pressure fractionation of olivine, plagioclase and later Cpx + or - an oxide phase during evolution of tholeitic liquids. Several models suggest basalt becoming more contaminated by sial with time. Data in the Uchi Subprovince shows early felsic volcanics to have fractionated REE patterns followed by flat REE pattern rhyolites. This is interpreted as initial felsic liquids produced by melting of a garnetiferous mafic source followed by large scale melting of LIL-rich sial. Rare andesites in the Uchi Subprovince are produced by basalt fractionation, direct mantle melts and mixing of basaltic and tonalitic liquids. Composite dikes in the Abitibi Subprovince have a basaltic edge with a chill margin, a rhyolitic interior with no basalt-rhyolite chill margin and partially melted sialic inclusions. Ignimbrites in the Uchi and Abitibi Subprovinces have mafic pumice toward the top. Integration of these data suggest initial mantle-derived basaltic liquids pond in a sialic crust, fractionate and melt sial. The inirial melts low in heavy REE are melts of mafic material, subsequently melting of adjacent sial produces a chamber with a felsic upper part underlain by mafic magma
Defining Insanity: How an Individual\u27s View Can Impact a Trial
The insanity plea has always been a controversial topic among anyone. No one sees eye to eye on the matter. This can present a problem within professional fields. When insanity cases are brought into courtrooms, legal and psychology professionals need to be able to agree to some extent. However, these professionals have no true control on how jurors define insanity. Jurors tend to determine guilty or not guilty in insanity cases, based on their own personal views. The current study is a replication of Doctor John Geiger’s 2003 and 2008 study of how legal professionals and undergraduate psychology students view the seven different definitions of insanity. In this article it will show how undergraduate criminal justice and psychology students define and view insanity
Lunar robotic maintenance module
A design for a robotic maintenance module that will assist a mobile 100-meter lunar drill is introduced. The design considers the following areas of interest: the atmospheric conditions, actuator systems, power supply, material selection, weight, cooling system and operation
The Undergraduate Research Scholarship Scheme: a co-created approach to transforming student learning
The value of student as researcher/‘co-producer’ has been well documented in the research literature. This case study outlines an institutional 'student as researcher' initiative that was introduced to enable the co-creation of research by undergraduate students working in partnership with members of academic staff. The paper outlines the establishment and implementation of the scheme and offers a reflection upon and exploration of its perceived value, through the lens of staff and students who participated in it
Solar Carbon Monoxide, Thermal Profiling, and the Abundances of C, O, and their Isotopes
A solar photospheric "thermal profiling" analysis is presented, exploiting
the infrared rovibrational bands of carbon monoxide (CO) as observed with the
McMath-Pierce Fourier transform spectrometer (FTS) at Kitt Peak, and from above
the Earth's atmosphere by the Shuttle-borne ATMOS experiment. Visible continuum
intensities and center-limb behavior constrained the temperature profile of the
deep photosphere, while CO center-limb behavior defined the thermal structure
at higher altitudes. The oxygen abundance was self consistently determined from
weak CO absorptions. Our analysis was meant to complement recent studies based
on 3-D convection models which, among other things, have revised the historical
solar oxygen (and carbon) abundance downward by a factor of nearly two;
although in fact our conclusions do not support such a revision. Based on
various considerations, an oxygen abundance of 700+/-100 ppm (parts per million
relative to hydrogen) is recommended; the large uncertainty reflects the model
sensitivity of CO. New solar isotopic ratios also are reported for 13C, 17O,
and 18O.Comment: 90 pages, 19 figures (some with parts "a", "b", etc.); to be
published in the Astrophysical Journal Supplement
Structure of the outer layers of cool standard stars
Context: Among late-type red giants, an interesting change occurs in the
structure of the outer atmospheric layers as one moves to later spectral types
in the Hertzsprung-Russell diagram: a chromosphere is always present, but the
coronal emission diminishes and a cool massive wind steps in.
Aims: Where most studies have focussed on short-wavelength observations, this
article explores the influence of the chromosphere and the wind on
long-wavelength photometric measurements.
Methods: The observational spectral energy distributions are compared with
the theoretical predictions of the MARCS atmosphere models for a sample of 9 K-
and M-giants. The discrepancies found are explained using basic models for flux
emission originating from a chromosphere or an ionized wind.
Results: For 7 out of 9 sample stars, a clear flux excess is detected at
(sub)millimeter and/or centimeter wavelengths. The precise start of the excess
depends upon the star under consideration. The flux at wavelengths shorter than
about 1 mm is most likely dominated by an optically thick chromosphere, where
an optically thick ionized wind is the main flux contributor at longer
wavelengths.
Conclusions: Although the optical to mid-infrared spectrum of the studied K-
and M-giants is well represented by a radiative equilibrium atmospheric model,
the presence of a chromosphere and/or ionized stellar wind at higher altitudes
dominates the spectrum in the (sub)millimeter and centimeter wavelength ranges.
The presence of a flux excess also has implications on the role of these stars
as fiducial spectrophotometric calibrators in the (sub)millimeter and
centimeter wavelength range.Comment: 13 pages, 6 figures, 7 pages of online material, submitted to A&
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