7,749 research outputs found
Far-Ultraviolet Dust Albedo Measurements in the Upper Scorpius Cloud Using the SPINR Sounding Rocket Experiment
The Spectrograph for Photometric Imaging with Numeric Reconstruction (SPINR)
sounding rocket experiment was launched on 2000 August 4 to record
far-ultraviolet (912-1450 A) spectral and spatial information for the giant
reflection nebula in the Upper Scorpius region. The data were divided into
three arbitrary bandpasses (912-1029 A, 1030-1200 A, and 1235-1450 A) for which
stellar and nebular flux levels were derived. These flux measurements were used
to constrain a radiative transfer model and to determine the dust albedo for
the Upper Scorpius region. The resulting albedos were 0.28+/-0.07 for the
912-1029 A bandpass, 0.33+/-0.07 for the 1030-1200 A bandpass, and 0.77+/-0.13
for the 1235-1450 A bandpass
Phase-Dependent Properties of Extrasolar Planet Atmospheres
Recently the Spitzer Space Telescope observed the transiting extrasolar
planets, TrES-1 and HD209458b. These observations have provided the first
estimates of the day side thermal flux from two extrasolar planets orbiting
Sun-like stars. In this paper, synthetic spectra from atmospheric models are
compared to these observations. The day-night temperature difference is
explored and phase-dependent flux densities are predicted for both planets. For
HD209458b and TrES-1, models with significant day-to-night energy
redistribution are required to reproduce the observations. However, the
observational error bars are large and a range of models remains viable.Comment: 8 pages, 7 figures, accepted for publication in the Astrophysical
Journa
Diagnosis of Helicobacter pylori by carbon-13 urea breath test using a portable mass spectrometer
CONTEXT: In the non-invasive detection of markers of disease, mass spectrometry is able to detect small quantities of volatile markers in exhaled air. However, the problem of size, expense and immobility of conventional mass spectrometry equipment has restricted its use. Now, a smaller, less expensive, portable quadrupole mass spectrometer system has been developed. Helicobacter pylori has been implicated in the development of chronic gastritis, gastric and duodenal ulcers and gastric cancer. OBJECTIVES: To compare the results obtained from the presence of H. pylori by a carbon-13 urea test using a portable quadrupole mass spectrometer system with those from a fixed mass spectrometer in a hospital-based clinical trial. METHODS: Following ethical approval, 45 patients attending a gastroenterology clinic at the Royal Liverpool University Hospital exhaled a breath sample into a Tedlar gas sampling bag. They then drank an orange juice containing urea radiolabelled with carbon and 30 min later gave a second breath sample. The carbon-13 content of both samples was measured using both quadrupole mass spectrometer systems. If the post-drink level exceeded the pre-drink level by 3% or more, a positive diagnosis for the presence of H. pylori was made. RESULTS: The findings were compared to the results using conventional isotope ratio mass spectrometry using a laboratory-based magnetic sector instrument off-site. The results showed agreement in 39 of the 45 patients. CONCLUSIONS: This study suggests that a portable quadrupole mass spectrometer is a potential alternative to the conventional centralised testing equipment. Future development of the portable quadrupole mass spectrometer to reduce further its size and cost is indicated, together with further work to validate this new equipment and to enhance its use in mass spectrometry diagnosis of other medical conditions
Far-Ultraviolet Activity Levels of F, G, K, and M dwarf Exoplanet Host Stars
We present a survey of far-ultraviolet (FUV; 1150 - 1450 Ang) emission line
spectra from 71 planet-hosting and 33 non-planet-hosting F, G, K, and M dwarfs
with the goals of characterizing their range of FUV activity levels,
calibrating the FUV activity level to the 90 - 360 Ang extreme-ultraviolet
(EUV) stellar flux, and investigating the potential for FUV emission lines to
probe star-planet interactions (SPIs). We build this emission line sample from
a combination of new and archival observations with the Hubble Space
Telescope-COS and -STIS instruments, targeting the chromospheric and transition
region emission lines of Si III, N V, C II, and Si IV.
We find that the exoplanet host stars, on average, display factors of 5 - 10
lower UV activity levels compared with the non-planet hosting sample; this is
explained by a combination of observational and astrophysical biases in the
selection of stars for radial-velocity planet searches. We demonstrate that UV
activity-rotation relation in the full F - M star sample is characterized by a
power-law decline (with index ~ -1.1), starting at rotation periods
>~3.5 days. Using N V or Si IV spectra and a knowledge of the star's bolometric
flux, we present a new analytic relationship to estimate the intrinsic stellar
EUV irradiance in the 90 - 360 Ang band with an accuracy of roughly a factor of
~2. Finally, we study the correlation between SPI strength and UV activity in
the context of a principal component analysis that controls for the sample
biases. We find that SPIs are not a statistically significant contributor to
the observed UV activity levels.Comment: ApJS, accepted. 33 pages in emulateapj, 13 figures, 10 table
X-ray to NIR emission from AA Tauri during the dim state - Occultation of the inner disk and gas-to-dust ratio of the absorber
AA Tau is a well-studied, nearby classical T Tauri star, which is viewed
almost edge-on. A warp in its inner disk periodically eclipses the central
star, causing a clear modulation of its optical light curve. The system
underwent a major dimming event beginning in 2011 caused by an extra absorber,
which is most likely associated with additional disk material in the line of
sight toward the central source. We present new XMM-Newton X-ray, Hubble Space
Telescope FUV, and ground based optical and near-infrared data of the system
obtained in 2013 during the long-lasting dim phase. The line width decrease of
the fluorescent H disk emission shows that the extra absorber is located at
au. Comparison of X-ray absorption () with dust extinction (),
as derived from measurements obtained one inner disk orbit (eight days) after
the X-ray measurement, indicates that the gas-to-dust ratio as probed by the
to ratio of the extra absorber is compatible with the ISM ratio.
Combining both results suggests that the extra absorber, i.e., material at
au, has no significant gas excess in contrast to the elevated
gas-to-dust ratio previously derived for material in the inner region
(au).Comment: 16 pages, 12 figures, accepted by A&
On the Significance of Absorption Features in HST/COS Data
We present empirical scaling relations for the significance of absorption
features detected in medium resolution, far-UV spectra obtained with the Cosmic
Origins Spectrograph (COS). These relations properly account for both the
extended wings of the COS line spread function and the non-Poissonian noise
properties of the data, which we characterize for the first time, and predict
limiting equivalent widths that deviate from the empirical behavior by \leq 5%
when the wavelength and Doppler parameter are in the ranges \lambda = 1150-1750
A and b > 10 km/s. We have tested a number of coaddition algorithms and find
the noise properties of individual exposures to be closer to the Poissonian
ideal than coadded data in all cases. For unresolved absorption lines, limiting
equivalent widths for coadded data are 6% larger than limiting equivalent
widths derived from individual exposures with the same signal-to-noise. This
ratio scales with b-value for resolved absorption lines, with coadded data
having a limiting equivalent width that is 25% larger than individual exposures
when b \approx 150 km/s.Comment: 25 pages, 3 tables, 7 figures, accepted for publication in PAS
Probing UV-sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope
The UV radiation field is a critical regulator of gas-phase chemistry in surface layers of disks around young stars. In an effort to understand the relationship between photocatalyzing UV radiation fields and gas emission observed at infrared and submillimeter wavelengths, we present an analysis of new and archival Hubble Space Telescope (HST), Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupus cloud complex and 14 systems in Taurus-Auriga. The HST spectra were used to measure Lyα and far-UV (FUV) continuum fluxes reaching the disk surface, which are responsible for dissociating relevant molecular species (e.g., HCN, N₂). Semi-forbidden C II] λ2325 and UV-fluorescent H₂ emission were also measured to constrain inner disk populations of C⁺ and vibrationally excited H2. We find a significant positive correlation between 14 μm HCN emission and fluxes from the FUV continuum and C II] λ2325, consistent with model predictions requiring N₂ photodissociation and carbon ionization to trigger the main CN/HCN formation pathways. We also report significant negative correlations between submillimeter CN emission and both C II] and FUV continuum fluxes, implying that CN is also more readily dissociated in disks with stronger FUV irradiation. No clear relationships are detected between either CN or HCN and Lyα or UV-H₂ emission. This is attributed to the spatial stratification of the various molecular species, which span several vertical layers and radii across the inner and outer disk. We expect that future observations with the James Webb Space Telescope will build on this work by enabling more sensitive IR surveys than were possible with Spitzer
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