1,427 research outputs found
A balloon-borne 1 meter telescope for far-infrared astronomy
The flight of a balloon-borne one-meter telescope for infrared astronomy in the wavelength interval of 40 to 240 microns is discussed. The gyro-stabilized telescope mapped the intensity of the far infrared radiation from NGC 7538, Mars, the Orion Nebula, and W3 with a resolution of one minute and from selected regions of these sources with a resolution of 30 seconds. The infrared detection is described and its capabilities are analyzed. The instrumentation, orientation system, and modes of observation of the telescope are defined
The Case Against Cold, Dark Chromospheres
Is the solar chromosphere always hot, with relatively small temperature
variations (); or is it cold most of the time, with
temperature fluctuations that reach at the top of the
chromosphere? Or, equivalently: Is the chromosphere heated continually, or only
for a few seconds once every three minutes? Two types of empirical model, one
essentially time independent and always hot, the other highly time dependent
and mostly cold, come to fundamentally different conclusions. This paper
analyzes the time-dependent model of the quiet, nonmagnetic chromosphere by
Carlsson & Stein (1994: CS94) and shows that it predicts deep absorption lines,
none of which is observed; intensity fluctuations in the Lyman continuum that
are much larger than observed; and time-averaged emission that falls far short
of the observed emission. The paper concludes that the solar chromosphere,
while time dependent, is never cold and dark. The same conclusion applies for
stellar chromospheres.
A complete, time-dependent model of the nonmagnetic chromosphere must
describe two phenomena: (1) dynamics, like that modeled by CS94 for
chromospheric bright points but corrected for the geometrical properties of
shocks propagating in an upward-expanding channel; and (2) the energetically
more important general, sustained heating of the chromosphere, as described by
current time-independent empirical models, but modified in the upper
photosphere for the formation of molecular absorption lines of CO in a
dynamical medium. This model is always hot and, except for absorption features
caused by departures from local thermodynamic equilibrium, shows chromospheric
lines only in emission.Comment: 22 pages, 5 figures (in 6 files
A High-Eccentricity Low-Mass Companion to HD 89744
HD 89744 is an F7 V star with mass 1.4 M, effective temperature 6166 K, age
2.0 Gy and metallicity [Fe/H]= 0.18. The radial velocity of the star has been
monitored with the AFOE spectrograph at the Whipple Observatory since 1996, and
evidence has been found for a low mass companion. The data were complemented by
additional data from the Hamilton spectrograph at Lick Observatory during the
companion's periastron passage in fall 1999. As a result, we have determined
the star's orbital wobble to have period P = 256 d, orbital amplitude K = 257
m/s, and eccentricity e = 0.7. From the stellar mass we infer that the
companion has minimum mass m2 sin i = 7.2 MJup in an orbit with semi-major axis
a2 = 0.88 AU. The eccentricity of the orbit, among the highest known for
extra-solar planets, continues the trend that extra-solar planets with
semi-major axes greater than about 0.15 AU tend to have much higher
eccentricities than are found in our solar system. The high metallicity of the
parent star reinforces the trend that parent stars of extra-solar planets tend
to have high metallicityComment: AASTEX-LateX v5.0, 7 pages w/ 3 figures, to be published in ApJ
HAT-P-5b: A Jupiter-like hot Jupiter Transiting a Bright Star
We report the discovery of a planet transiting a moderately bright (V =
12.00) G star, with an orbital period of 2.788491 +/-0.000025 days. From the
transit light curve we determine that the radius of the planet is Rp = 1.257
+/- 0.053 RJup. HAT-P-5b has a mass of Mp = 1.06 +/- 0.11 MJup, similar to the
average mass of previously-known transiting exoplanets, and a density of rho =
0.66 +/- 0.11 g cm^-3 . We find that the center of transit is Tc =
2,454,241.77663 +/- 0.00022 (HJD), and the total transit duration is 0.1217 +/-
0.0012 days.Comment: 5 pages, submitted to APJ
Fine structure of the chromospheric activity in Solar-type stars - The Halpha Line
A calibration of H-alpha as both a chromospheric diagnostic and an age
indicator is presented, complementing the works previously done on this subject
(Herbig 1985, Pasquini & Pallavicini 1991. The chromospheric diagnostic was
built with a statistically significant sample, covering nine years of
observations, and including 175 solar neighborhood stars. Regarding the age
indicator, the presence of stars for which very accurate ages are determined,
such as those belonging to clusters and kinematic groups, lends confidence to
our analysis. We also investigate the possibility that stars of the same age
might have gone through different tracks of chromospheric decay, identifying -
within the same age range - effects of metallicity and mass. These parameters,
however, as well as age, seem to be significant only for dwarf stars, losing
their meaning when we analyze stars in the subgiant branch. This result
suggests that, in these evolved stars, the emission mechanism cannot be
magnetohydrodynamical in nature, in agreement with recent models (Fawzy et al.
2002c, and references therein). The Sun is found to be a typical star in its
H-alpha chromospheric flux, for its age, mass and metallicity. As a byproduct
of this work, we developed an automatic method to determine temperatures from
the wings of H-alpha, which means the suppression of the error inherent to the
visual procedure used in the literature.Comment: 10 pages, 10 figures, accepted for publication in Astronomy &
Astrophysics. Nature of replacement: match astro-ph and ADS title (greek
letter
Refined parameters of the planet orbiting HD 189733
We report on the BVRI multi-band follow-up photometry of the transiting
extrasolar planet HD 189733b. We revise the transit parameters and find
planetary radius RP = 1.154+/- 0.032RJ and inclination i_P = 85.79+/-0.24deg.
The new density (~ 1g cm-3) is significantly higher than the former estimate (~
0.75g cm-3); this shows that from the current sample of 9 transiting planets,
only HD 209458 (and possibly OGLE-10b) have anomalously large radii and low
densities. We note that due to the proximity of the parent star, HD 189733b
currently has one of the most precise radius determinations among extrasolar
planets. We calculate new ephemerides: P = 2.218573+/-0.000020 days, T0 =
2453629.39420+/-0.00024 (HJD), and estimate the timing offsets of the 11
distinct transits with respect to the predictions of a constant orbital period,
which can be used to reveal the presence of additional planets in the system.Comment: 10 pages, 4 figures, submitted to Ap
Dynamics of Magnetic Flux Elements in the Solar Photosphere
The interaction of magnetic fields and convection is investigated in the
context of the coronal heating problem. We study the motions of photospheric
magnetic elements using filtergrams obtained at the Swedish Vacuum Solar
Telescope at La Palma. We use potential-field modeling to extrapolate the
magnetic and velocity fields to larger height. We find that the velocity in the
chromosphere can be locally enhanced at the separatrix surfaces between
neighboring flux tubes. The predicted velocities are several km/s,
significantly larger than those of the photospheric flux tubes, which may have
important implications for coronal heating. sComment: submitted to ApJ, 21 pages, 10 figure
Super-recognizers: From the lab to the world and back again
The recent discovery of individuals with superior face processing ability has sparked considerable interest amongst cognitive scientists and practitioners alike. These ‘Super‐recognizers’ (SRs) offer clues to the underlying processes responsible for high levels of face processing ability. It has been claimed that they can help make societies safer and fairer by improving accuracy of facial identity processing in real‐world tasks, for example when identifying suspects from Closed Circuit Television or performing security‐critical identity verification tasks. Here, we argue that the current understanding of superior face processing does not justify widespread interest in SR deployment: There are relatively few studies of SRs and no evidence that high accuracy on laboratory‐based tests translates directly to operational deployment. Using simulated data, we show that modest accuracy benefits can be expected from deploying SRs on the basis of ideally calibrated laboratory tests. Attaining more substantial benefits will require greater levels of communication and collaboration between psychologists and practitioners. We propose that translational and reverse‐translational approaches to knowledge development are critical to advance current understanding and to enable optimal deployment of SRs in society. Finally, we outline knowledge gaps that this approach can help address
Search for very high energy gamma-rays from WIMP annihilations near the Sun with the Milagro Detector
The neutralino, the lightest stable supersymmetric particle, is a strong
theoretical candidate for the missing astronomical ``dark matter''. A profusion
of such neutralinos can accumulate near the Sun when they lose energy upon
scattering and are gravitationally captured. Pair-annihilations of those
neutralinos may produce very high energy (VHE, above ) gamma-rays.
Milagro is an air shower array which uses the water Cherenkov technique to
detect extensive air showers and is capable of observing VHE gamma-rays from
the direction of the Sun with an angular resolution of . Analysis
of Milagro data with an exposure to the Sun of 1165 hours presents the first
attempt to detect TeV gamma-rays produced by annihilating neutralinos captured
by the Solar system and shows no statistically significant signal. Resulting
limits that can be set on gamma-ray flux due to near-Solar neutralino
annihilations and on neutralino cross-section are presented
The Quiet-Sun Photosphere and Chromosphere
The overall structure and the fine structure of the solar photosphere outside
active regions are largely understood, except possibly important roles of a
turbulent near-surface dynamo at its bottom, internal gravity waves at its top,
and small-scale vorticity. Classical 1D static radiation-escape modelling has
been replaced by 3D time-dependent MHD simulations that come closer to reality.
The solar chromosphere, in contrast, remains ill-understood although its
pivotal role in coronal mass and energy loading makes it a principal research
area. Its fine structure defines its overall structure, so that hard-to-observe
and hard-to-model small-scale dynamical processes are the key to understanding.
However, both chromospheric observation and chromospheric simulation presently
mature towards the required sophistication. The open-field features seem of
greater interest than the easier-to-see closed-field features.Comment: Accepted for special issue "Astrophysical Processes on the Sun" of
Phil. Trans. Royal Soc. A, ed. C. Parnell. Note: clicking on the year in a
citation opens the corresponding ADS abstract page in the browse
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