7,509 research outputs found
Nonsolar astronomy with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a NASA Small Explorer satellite designed to study hard x-ray and gamma-ray emission from solar flares. In addition, its high-resolution array of germanium detectors can see photons from high-energy sources throughout the Universe. Here we discuss the various algorithms necessary to extract spectra, lightcurves, and other information about cosmic gamma-ray bursts, pulsars, and other astrophysical phenomena using an unpointed, spinning array of detectors. We show some preliminary results and discuss our plans for future analyses. All RHESSI data are public, and scientists interested in participating should contact the principal author
Multifluid, Magnetohydrodynamic Shock Waves with Grain Dynamics II. Dust and the Critical Speed for C Shocks
This is the second in a series of papers on the effects of dust on
multifluid, MHD shock waves in weakly ionized molecular gas. We investigate the
influence of dust on the critical shock speed, v_crit, above which C shocks
cease to exist. Chernoff showed that v_crit cannot exceed the grain
magnetosound speed, v_gms, if dust grains are dynamically well coupled to the
magnetic field. We present numerical simulations of steady shocks where the
grains may be well- or poorly coupled to the field. We use a time-dependent,
multifluid MHD code that models the plasma as a system of interacting fluids:
neutral particles, ions, electrons, and various ``dust fluids'' comprised of
grains with different sizes and charges. Our simulations include grain inertia
and grain charge fluctuations but to highlight the essential physics we assume
adiabatic flow, single-size grains, and neglect the effects of chemistry. We
show that the existence of a phase speed v_phi does not necessarily mean that C
shocks will form for all shock speeds v_s less than v_phi. When the grains are
weakly coupled to the field, steady, adiabatic shocks resemble shocks with no
dust: the transition to J type flow occurs at v_crit = 2.76 v_nA, where v_nA is
the neutral Alfven speed, and steady shocks with v_s > 2.76 v_nA are J shocks
with magnetic precursors in the ion-electron fluid. When the grains are
strongly coupled to the field, v_crit = min(2.76 v_nA, v_gms). Shocks with
v_crit < v_s < v_gms have magnetic precursors in the ion-electron-dust fluid.
Shocks with v_s > v_gms have no magnetic precursor in any fluid. We present
time-dependent calculations to study the formation of steady multifluid shocks.
The dynamics differ qualitatively depending on whether or not the grains and
field are well coupled.Comment: 43 pages with 17 figures, aastex, accepted by The Astrophysical
Journa
Bazinganomics: Economics of The Big Bang Theory
url:http://www.bazinganomics.com
The website is designed to provide instructors with clips, explanations, and lesson plans related to economics concepts from TVâs 2nd most watched broadcast show of the 2014-2015 season, CBSâs The Big Bang Theory. The site contains approximately 100 clips. As the show continues to air (currently signed through the 2016-2017 season) the authors plan to increase the number of clips and lesson plans
A Study of Abcission Zone Development In Leaves of Ginkgo Biloba L.
The development of the leaf abscission zone in Ginkgo biloba trees and seedlings was studied. Leaves from Ginkgo seedlings were debladed to enhance anatomical changes in the abscission region. The development of an abscission layer was observed six days after deblading. The formation of the zone was not complete, but an abaxial to adaxial pattern of development was apparent. No evidence of separation was noted. Debladed Ginkgo petioles remained green and did not abscise during the six weeks period of study. The development of an abscission layer was observed in leaves from a Ginkgo tree one week prior to separation. The zone occupied an area approximately eleven cells wide at the junction of the petiole and stem. Separation of the petiole occurred through an apparent dissolution of the middle lamella. The separation was observed in the distal region of the zone between the ninth and tenth cell layers. The pattern of leaf abscission zone development is similar in Ginkgo trees and seedlings
Lesson Plans for Teaching Economics with The Big Bang Theory
Using examples in the classroom from current and past television shows and movies is becoming increasingly common. Being able to relate ideas back to a popular clip or episode allows the instructor to reach students in ways the traditional lecture cannot. Building on the work of Tierney, Mateer, Smith, Wooten, and Geerling (2016), this paper introduces five lesson plans tied to clips from The Big Bang Theory that can be used in high school (9-12) economics courses
Ultraviolet Imaging of the Globular Cluster 47 Tucanae
We have used the Ultraviolet Imaging Telescope to obtain deep far-UV (1620
Angstrom), 40' diameter images of the prototypical metal-rich globular cluster
47 Tucanae. We find a population of about 20 hot (Teff > 9000 K) objects near
or above the predicted UV luminosity of the hot horizontal branch (HB) and
lying within two half-light radii of the cluster center. We believe these are
normal hot HB or post-HB objects rather than interacting binaries or blue
stragglers. IUE spectra of two are consistent with post-HB phases. These
observations, and recent HST photometry of two other metal-rich clusters,
demonstrate that populations with rich, cool HB's can nonetheless produce hot
HB and post-HB stars. The cluster center also contains an unusual diffuse
far-UV source which is more extended than its V-band light. It is possible that
this is associated with an intracluster medium, for which there was earlier
infrared and X-ray evidence, and is produced by C IV emission or scattered
light from grains.Comment: 13 pages AASLaTeX including one postscript figure and one bitmapped
image, JPEG format. Submitted to the Astronomical Jorunal. Full Postscript
version available at http://www.astro.virginia.edu/~bd4r
A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
We present UBVRI photometry obtained from Mosaic images of M31 and M33 using
the KPNO 4-m telescope. The survey covers 2.2 sq degrees of M31, and 0.8 sq
degrees of M33, chosen so as to include all of the regions currently active in
forming massive stars. The catalog contains 371,781 and 146,622 stars in M31
and M33, respectively, where every star has a counterpart (at least) in B, V,
and R. We compare our photometry to previous studies. We provide cross
references to the stars confirmed as members by spectroscopy, and compare the
location of these to the complete set in color-magnitude diagrams. While
follow-up spectroscopy is needed for many projects, we demonstrate the success
of our photometry in being able to distinguish M31/M33 members from foreground
Galactic stars. We also present the results of newly obtained spectroscopy,
which identifies 34 newly confirmed members, including B-A supergiants, the
earliest O star known in M31, and two new Luminous Blue Variable candidates
whose spectra are similar to that of P Cygni.Comment: Accepted by the Astronomical Journal. A version with higher
resolution figures can be found at:
http://www.lowell.edu/users/massey/M3133.pdf.g
Ultraviolet Imagery of NGC 6752: A Test of Extreme Horizontal Branch Models
We present a 1620 A image of the nearby globular cluster NGC 6752 obtained
with the Ultraviolet Imaging Telescope (UIT) during the Astro-2 mission of the
Space Shuttle Endeavour in 1995 March. An ultraviolet-visible color-magnitude
diagram (CMD) is derived for 216 stars matched with the visible photometry of
Buonanno et al. (1986). This CMD provides a nearly complete census of the hot
horizontal branch (HB) population with good temperature and luminosity
discrimination for comparison with theoretical tracks. The observed data show
good agreement with the theoretical zero-age horizontal branch (ZAHB) of
Sweigart (1996) for an assumed reddening of E(B-V) = 0.05 and a distance
modulus of 13.05. The observed HB luminosity width is in excellent agreement
with the theoretical models and supports the single star scenario for the
origin of extreme horizontal branch (EHB) stars. However, only four stars can
be identified as post-EHB stars, whereas almost three times this many are
expected from the HB number counts. If this effect is not a statistical
anomaly, then some non-canonical effect may be decreasing the post-EHB
lifetime. The recent non-canonical models of Sweigart (1996), which have
helium-enriched envelopes due to mixing along the red giant branch, cannot
explain the deficit of post-EHB stars, but might be better able to explain
their luminosity distribution.Comment: 14 pages, AASTeX, includes 4 EPS figures ApJ Letters accepte
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