426 research outputs found
Subjective and metrical depth of the suborbital fossa
Thesis (M.A.)--University of Kansas, Sociology and Anthropology, 1963
Evidence against a strong thermal inversion in HD 209458 b from high-dispersion spectroscopy
Broadband secondary-eclipse measurements of hot Jupiters have indicated the
existence of atmospheric thermal inversions, but their presence is difficult to
determine from broadband measurements because of degeneracies between molecular
abundances and temperature structure. We apply high-resolution (R = 100 000)
infrared spectroscopy to probe the temperature-pressure profile of HD 209458 b.
This bright, transiting hot-Jupiter has long been considered the gold standard
for a hot Jupiter with an inversion layer, but this has been challenged in
recent publications. We observed the thermal dayside emission of HD 209458 b
with CRIRES / VLT during three nights, targeting the carbon monoxide band at
2.3 microns. Thermal inversions give rise to emission features, which means
that detecting emission lines in the planetary spectrum, as opposed to
absorption lines, would be direct evidence of a region in which the temperature
increases with altitude.
We do not detect any significant absorption or emission of CO in the dayside
spectrum of HD 209458 b, although cross-correlation with template spectra
either with CO absorption lines or with weak emission at the core of the lines
show a low-significance correlation signal with a signal-to-noise ratio of 3 -
3.5. Models with strong CO emission lines show a weak anti-correlation with
similar or lower significance levels. Furthermore, we found no evidence of
absorption or emission from H2O at these wavelengths.
The non-detection of CO in the dayside spectrum of HD 209458 b is interesting
in light of a previous CO detection in the transmission spectrum. That there is
no signal indicates that HD 209458 b either has a nearly isothermal atmosphere
or that the signal is heavily muted. Assuming a clear atmosphere, we can rule
out a full-disc dayside inversion layer in the pressure range 1 bar to 1 mbar.Comment: 11 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
Finding extraterrestrial life using ground-based high-resolution spectroscopy
Exoplanet observations promise one day to unveil the presence of
extraterrestrial life. Atmospheric compounds in strong chemical disequilibrium
would point to large-scale biological activity just as oxygen and methane do in
the Earth's atmosphere. The cancellation of both the Terrestrial Planet Finder
and Darwin missions means that it is unlikely that a dedicated space telescope
to search for biomarker gases in exoplanet atmospheres will be launched within
the next 25 years. Here we show that ground-based telescopes provide a strong
alternative for finding biomarkers in exoplanet atmospheres through transit
observations. Recent results on hot Jupiters show the enormous potential of
high-dispersion spectroscopy to separate the extraterrestrial and telluric
signals making use of the Doppler shift of the planet. The transmission signal
of oxygen from an Earth-twin orbiting a small red dwarf star is only a factor 3
smaller than that of carbon monoxide recently detected in the hot Jupiter tau
Bootis b, albeit such a star will be orders of magnitude fainter. We show that
if Earth-like planets are common, the planned extremely large telescopes can
detect oxygen within a few dozen transits. Ultimately, large arrays of
dedicated flux collector telescopes equipped with high-dispersion spectrographs
can provide the large collecting area needed to perform a statistical study of
life-bearing planets in the solar neighborhood.Comment: 22 pages, 3 figures; published in Ap
Low-mass eclipsing binaries in the WFCAM Transit Survey : The persistence of the M-dwarf radius inflation problem
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present the characterization of five new short-period low-mass eclipsing binaries (LMEBs) from the WFCAM Transit Survey. The analysis was performed by using the photometric WFCAM J-mag data and additional low- and intermediate-resolution spectroscopic data to obtain both orbital and physical properties of the studied sample. The light curves and the measured radial velocity curves were modelled simultaneously with the JKTEBOP code, with Markov chain MonteCarlo simulations for the error estimates. The best-model fit have revealed that the investigated detached binaries are in very close orbits, with orbital separations of 2.9 ≤ a ≤ 6.7R⊙ and short periods of 0.59 ≤ Porb ≤ 1.72 d, approximately. We have derived stellar masses between 0.24 and 0.72M⊙ and radii ranging from 0.42 to 0.67 R⊙. The great majority of the LMEBs in our sample has an estimated radius far from the predicted values according to evolutionary models. The components with derived masses of M < 0.6M⊙ present a radius inflation of ~9 per cent or more. This general behaviour follows the trend of inflation for partially radiative stars proposed previously. These systems add to the increasing sample of low-mass stellar radii that are not well-reproduced by stellarmodels. They further highlight the need to understand the magnetic activity and physical state of small stars. Missions like TESS will provide many such systems to perform high-precision radius measurements to tightly constrain low-mass stellar evolution models.Peer reviewe
Numerical predictions of turbulent underexpanded sonic jets using a pressure-based methodology
The objective of this work is to model underexpanded turbulent sonic jets. A pressure-based
computational fluid dynamics methodology has been employed, incorporating extensions to handle high
speed flows. A standard two-equation turbulence model is used, with an optional compressibility
correction. Comparison with experimental jet centre-line Mach number showed the correct shock cell
wavelength but a too rapid decay. The compressibility correction had no effect on the shock cell decay but
increased the potential core length to give better agreement with experiment. Calculations for nozzle
pressure ratios up to 30 showed the variation of Mach disc location in good agreement with experiment.
For nozzle pressure ratios above 6, unsteady solutions were observed, emanating from the intersection of
the Mach disc with the shear layer. Experimental work has identified similar large-scale instabilities; the
peak mode of the prediction had a Strouhal number of 0.16, close to experimental values
Book Reviews
Law and Politics in the Supreme Court By Martin Shapiro New York: Free Press of Glencoe, 1964. Pp. 333. $6.95.
reviewer: Robert H. Birkby
======================
Lives of the Lord Chancellors, 1885-1940 By R. F. V. Heuston Oxford: Clarendon Press, 1964, Pp. xxiii, 632.
reviewer: Elliot E. Cheatha
Carbon monoxide and water vapor in the atmosphere of the non-transiting exoplanet HD 179949 b
(Abridged) In recent years, ground-based high-resolution spectroscopy has
become a powerful tool for investigating exoplanet atmospheres. It allows the
robust identification of molecular species, and it can be applied to both
transiting and non-transiting planets. Radial-velocity measurements of the star
HD 179949 indicate the presence of a giant planet companion in a close-in
orbit. Here we present the analysis of spectra of the system at 2.3 micron,
obtained at a resolution of R~100,000, during three nights of observations with
CRIRES at the VLT. We targeted the system while the exoplanet was near superior
conjunction, aiming to detect the planet's thermal spectrum and the radial
component of its orbital velocity. We detect molecular absorption from carbon
monoxide and water vapor with a combined S/N of 6.3, at a projected planet
orbital velocity of K_P = (142.8 +- 3.4) km/s, which translates into a planet
mass of M_P = (0.98 +- 0.04) Jupiter masses, and an orbital inclination of i =
(67.7 +- 4.3) degrees, using the known stellar radial velocity and stellar
mass. The detection of absorption features rather than emission means that,
despite being highly irradiated, HD 179949 b does not have an atmospheric
temperature inversion in the probed range of pressures and temperatures. Since
the host star is active (R_HK > -4.9), this is in line with the hypothesis that
stellar activity damps the onset of thermal inversion layers owing to UV flux
photo-dissociating high-altitude, optical absorbers. Finally, our analysis
favors an oxygen-rich atmosphere for HD 179949 b, although a carbon-rich planet
cannot be statistically ruled out based on these data alone.Comment: 10 pages, 9 figures. Accepted for publication in Astronomy and
Astrophysic
Detection of the secondary eclipse of Qatar-1b in the Ks band
Qatar-1b is a close-orbiting hot Jupiter ( , ) around a metal-rich K-dwarf, with orbital separation and period of
0.023 AU and 1.42 days. We have observed the secondary eclipse of this
exoplanet in the Ks band with the objective of deriving a brightness
temperature for the planet and providing further constraints to the orbital
configuration of the system. We obtained near-infrared photometric data from
the ground by using the OMEGA2000 instrument at the 3.5 m telescope at Calar
Alto (Spain) in staring mode, with the telescope defocused. We have used
principal component analysis (PCA) to identify correlated systematic trends in
the data. A Markov chain Monte Carlo analysis was performed to model the
correlated systematics and fit for the secondary eclipse of Qatar-1b using a
previously developed occultation model. We adopted the prayer bead method to
assess the effect of red noise on the derived parameters. We measured a
secondary eclipse depth of , which indicates a
brightness temperature in the Ks band for the planet of K.
We also measured a small deviation in the central phase of the secondary
eclipse of , which leads to a value for
of . However, this last result
needs to be confirmed with more data.Comment: 6 pages, 6 figures, accepted for publication in A&
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