scholarly journals Oxygen in Unevolved Starss

2002 ◽  
Vol 12 ◽  
pp. 416-419
Author(s):  
Ann Merchant Boesgaard
Keyword(s):  
Spectral Resolution ◽  
Linear Relation ◽  
Spectral Region ◽  
High Spectral Resolution ◽  
High Signal ◽  
Signal To Noise ◽  
Spectrum Synthesis ◽  
Ultraviolet Spectral Region

AbstractWe have made observations of 24unevolvedstars of the OH lines in the ultraviolet spectral region at high spectral resolution and high signal-to-noise, typically 60 − 110 with Keck + HIRES. The O abundances have been computed by spectrum synthesis. For these cool, unevolved stars there is a linear relation between [O/H] and [Fe/H] over three orders of magnitude with very little scatter and a slope of +0.66 ±0.02. The relation between [O/Fe] and [Fe/H] is robustly linear with [O/Fe] = −0.35 (±0.03) [Fe/H]. There is no sign of a break at metallicities between −1.0 and −2.0.

scholarly journals Ionisation Structure of NGC 6543

1997 ◽  
Vol 180 ◽  
pp. 270-270
Author(s):  
E. Pérez ◽  
L. Cuesta ◽  
D. Axon ◽  
A. Robinson
Keyword(s):  
Chemical Composition ◽  
Spectral Resolution ◽  
Signal To Noise Ratio ◽  
Planetary Nebulae ◽  
High Spectral Resolution ◽  
High Signal ◽  
Signal To Noise ◽  
Physical Conditions ◽  
Noise Ratio ◽  
Effects Of Radiation

We have obtained high spectral resolution, high signal-to-noise ratio longslit spectra of a sample of Planetary Nebulae with the purpose of studying their physical conditions, chemical composition and ionisation structure. In particular, we are interested in disentangling the effects of radiation and shock ionisation.

scholarly journals Goals for the Application of High-Resolution X-ray Spectroscopy to the Diagnosis of Stellar Coronal Plasmas

1990 ◽  
Vol 115 ◽  
pp. 94-109 ◽  
Author(s):  
Jeffrey L. Linsky
Keyword(s):  
High Resolution ◽  
Spectral Resolution ◽  
Transient Flow ◽  
Emission Measure ◽  
Active Regions ◽  
High Sensitivity ◽  
High Spectral Resolution ◽  
Spectral Features ◽  
Signal To Noise ◽  
X Ray

AbstractI provide examples of how high-resolution x-ray spectra may be used to determine the temperature and emission measure distributions, electron densities, steady and transient flow velocities, and location of active regions in stellar coronae. For each type of measurement I estimate the minimum spectral resolution required to resolve the most useful spectral features. In general, high sensitivity is required to obtain sufficient signal-to-noise to exploit the high spectral resolution. Although difficult, each measurement should be achievable with the instrumentation proposed for AXAF.

scholarly journals Global monitoring of terrestrial chlorophyll fluorescence from moderate spectral resolution near-infrared satellite measurements: methodology, simulations, and application to GOME-2

2013 ◽  
Vol 6 (2) ◽  
pp. 3883-3930 ◽  
Author(s):  
J. Joiner ◽  
L. Guanter ◽  
R. Lindstrot ◽  
M. Voigt ◽  
A. P. Vasilkov ◽  
...  
Keyword(s):  
Chlorophyll Fluorescence ◽  
Spectral Resolution ◽  
Near Infrared ◽  
High Spectral Resolution ◽  
High Signal ◽  
Good Precision ◽  
Atmospheric Absorption ◽  
Red Fluorescence ◽  
Fluorescence Measurements ◽  
Global Mapping

Abstract. Globally mapped terrestrial chlorophyll fluorescence retrievals are of high interest because they can provide information on the functional status of vegetation including light-use efficiency and global primary productivity that can be used for global carbon cycle modeling and agricultural applications. In addition, fluorescence can contaminate photon path estimates from the O2 A-band that has become an integral part of missions to accurately measure greenhouse gas concentrations. Global mapping of far-red (~ 755–770 nm) terrestrial vegetation solar-induced fluorescence from space has been accomplished using the high spectral resolution (ν/Δ ν > 35 000) interferometer on the Japanese Greenhouse gases Observing SATellite (GOSAT). These satellite retrievals of fluorescence rely solely upon the filling-in of solar Fraunhofer lines that are not significantly affected by atmospheric absorption. Although these measurements provide near global coverage on a monthly basis, they suffer from relatively low precision and sparse spatial sampling. Here, we describe a new methodology to retrieve global far-red fluorescence information; we use hyperspectral data to disentangle the spectral signatures of three basic components in and surrounding the O2 A-band: atmospheric absorption, surface reflectance, and fluorescence radiance. Through detailed simulations, we demonstrate the feasibility of the approach and show that moderate spectral resolution measurements with a relatively high signal-to-noise ratio within and outside the O2 A-band can be used to retrieve far-red fluorescence information with good precision and accuracy. The method is then applied to data from the Global Ozone Monitoring Instrument 2 (GOME-2). The GOME-2 fluorescence retrievals display similar spatial structure as compared with GOSAT. GOME-2 enables global mapping of far-red fluorescence with higher precision over smaller spatial and temporal scales than is possible with GOSAT. It should be noted that both GOME-2 and GOSAT were designed to make atmospheric trace gas measurements and were not optimized for fluorescence measurements. Our approach can be applied to other existing and future space-based instruments that provide moderate spectral resolution observations in the near-infrared region.

scholarly journals Analysis of ACAM Data for Trace Gas Retrievals during the 2011 DISCOVER-AQ Campaign

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
C. Liu ◽  
X. Liu ◽  
M. G. Kowalewski ◽  
S. J. Janz ◽  
G. González Abad ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
Spectral Region ◽  
Total Ozone ◽  
Signal To Noise Ratio ◽  
Trace Gas ◽  
System Throughput ◽  
Signal To Noise ◽  
Ozone Profile ◽  
Blue Spectral Region ◽  
Large Wavelength

To improve the trace gas retrieval from Airborne Compact Atmospheric Mapper (ACAM) during the DSICOVER-AQ campaigns, we characterize the signal to noise ratio (SNR) of the ACAM measurement. From the standard deviations of the fitting residuals, the SNRs of ACAM nadir measurements are estimated to vary from ~300 at 310 nm to ~1000 in the blue spectral region; the zenith data are noisier due to reduced levels of illumination and lower system throughput and also show many more pixels with abrupt anomalous values; therefore, a new method is developed to derive a solar irradiance reference at the top of the atmosphere (TOA) from average nadir measurements, at instrument spectral resolution and including instrument calibration characteristics. Using this reference can significantly reduce fitting residuals and improve the retrievals. This approach derives an absolute reference for direct fitting algorithms involving radiative transfer calculations and thus can be applied to both aircraft and ground-based measurements. The comparison of ACAM radiance with simulations using coincident ozonesonde and OMI data shows large wavelength-dependent biases in ACAM data, varying from ~−19% at 310 nm to 5% at 360 nm. Correcting ACAM radiance in direct-fitting based ozone profile algorithm significantly improves the consistency with OMI total ozone.

scholarly journals Tracing the 107 K warm–hot intergalactic medium with UV absorption lines

2020 ◽  
Vol 499 (4) ◽  
pp. 5230-5240
Author(s):  
A Y Fresco ◽  
C Péroux ◽  
A Merloni ◽  
A Hamanowicz ◽  
R Szakacs
Keyword(s):  
Galaxy Formation ◽  
Spectral Resolution ◽  
Column Density ◽  
Intergalactic Medium ◽  
High Spectral Resolution ◽  
High Signal ◽  
Gas Temperature ◽  
X Ray ◽  
Quasar Spectra ◽  
Hydrodynamical Simulations

ABSTRACT Today, the majority of the cosmic baryons in the Universe are not observed directly, leading to an issue of ‘missing baryons’ at low redshift. Cosmological hydrodynamical simulations have indicated that a significant portion of them will be converted into the so-called warm–hot intergalactic medium (WHIM), with gas temperature ranging between 105 and 107 K. While the cooler phase of this gas has been observed using O vi and Ne viii absorbers at ultraviolet (UV) wavelengths, the hotter fraction detection relies mostly on observations of O vii and O viii at X-ray wavelengths. Here, we target the forbidden line of [Fe xxi] λ 1354 Å which traces 107 K gas at UV wavelengths, using more than 100 high-spectral resolution ($R\sim 49\, 000$) and high signal to noise VLT/UVES quasar spectra, corresponding to over 600 h of VLT time observations. A stack of these at the position of known Ly α absorbers lead to a 5σ limit of $\log [N\mathrm{([Fe\,{\small XXI}])]\lt }$17.4 (EWrest < 22 mÅ), three orders of magnitude higher than the expected column density of the WHIM $\log [N\mathrm{([Fe\,{\small XXI}])]\lt }$14.5. This work proposes an alternative to X-ray detected 107 K WHIM tracers, by targeting faint lines at UV wavelengths from the ground benefiting from higher instrumental throughput, enhanced spectral resolution, longer exposure times, and increased number of targets. The number of quasar spectra required to reach this theoretical column density with future facilities including 4MOST, ELT/HIRES, MSE, and the Spectroscopic Telescope appears challenging at present. Probing the missing baryons is essential to constrain the accretion and feedback processes that are fundamental to galaxy formation.

scholarly journals Photospheric molecular line profiles in cool stars

1981 ◽  
Vol 59 ◽  
pp. 119-124
Author(s):  
S.T. Ridgway ◽  
E.D. Friel
Keyword(s):  
Spectral Lines ◽  
High Spectral Resolution ◽  
High Signal ◽  
Line Profiles ◽  
Signal To Noise ◽  
Molecular Line ◽  
Ejection Process ◽  
Cool Stars ◽  
Mass Ejection ◽  
Selection Of

AbstractSpectral lines of the ΔV=2 rotation vibration bands of CO are well suited for study of photospheric motions and the mass ejection process in cool stars. We have obtained high spectral resolution (1.8 km/sec) and high signal-to-noise (>102) line profiles for a selection of K and M giants. These profiles are being studied for evidence of gas motions in the photosphere and near circumstellar regions.

scholarly journals A Monolithic Spatial Heterodyne Raman Spectrometer: Initial Tests

2020 ◽  
Vol 75 (1) ◽  
pp. 57-69
Author(s):  
Abigail Waldron ◽  
Ashley Allen ◽  
Arelis Colón ◽  
J. Chance Carter ◽  
S. Michael Angel
Keyword(s):  
Spectral Range ◽  
Spectral Resolution ◽  
Signal To Noise Ratio ◽  
Focal Length ◽  
High Spectral Resolution ◽  
Signal To Noise ◽  
Free Standing ◽  
Raman Spectrometer ◽  
Construction Techniques ◽  
The Stability

A monolithic spatial heterodyne Raman spectrometer (mSHRS) is described, where the optical components of the spectrometer are bonded to make a small, stable, one-piece structure. This builds on previous work, where we described bench top spatial heterodyne Raman spectrometers (SHRS), developed for planetary spacecraft and rovers. The SHRS is based on a fixed grating spatial heterodyne spectrometer (SHS) that offers high spectral resolution and high light throughput in a small footprint. The resolution of the SHS is not dependent on a slit, and high resolution can be realized without using long focal length dispersing optics since it is not a dispersive device. Thus, the SHS can be used as a component in a compact Raman spectrometer with high spectral resolution and a large spectral range using a standard 1024 element charge-coupled device. Since the resolution of the SHRS is not dependent on a long optical path, it is amenable to the use of monolithic construction techniques to make a compact and robust device. In this paper, we describe the use of two different monolithic SHSs (mSHSs), with Littrow wavelengths of 531.6 nm and 541.05 nm, each about 3.5 × 3.5 × 2.5 cm in size and weighing about 80 g, in a Raman spectrometer that provides ∼3500 cm−1 spectral range with 4–5 cm−1 and 8–9 cm−1 resolution, for 600 grooves/mm and 150 grooves/mm grating-based mSHS devices, respectively. In this proof of concept paper, the stability, spectral resolution, spectral range, and signal-to-noise ratio of the mSHRS spectrometers are compared to our bench top SHRS that uses free-standing optics, and signal to noise comparisons are also made to a Kaiser Holospec f/1.8 Raman spectrometer.

scholarly journals NGC 6302: high-ionization permitted lines. Applying X-SSN synthesis to VLT-UVES spectra

2011 ◽  
Vol 7 (S283) ◽  
pp. 470-471
Author(s):  
Daniel Péquignot ◽  
Christophe Morisset ◽  
Simon Casassus
Keyword(s):  
High Signal ◽  
Signal To Noise ◽  
High Ionization ◽  
Spectrum Synthesis ◽  
First Time

AbstractA preliminary VLT-UVES spectrum of NGC 6302 (Casassus et al. 2002, MN), which hosts one of the hottest PN nuclei known (Teff ~ 220000 K; Wright et al. 2011, MN), has been recently analysed by means of X-SSN, a spectrum synthesis code for nebulae (Morisset and Péquignot). Permitted recombination lines from highly-ionized species are detected/identified for the first time in a PN, and some of them probably for the first time in (astro)physics. The need for a homogeneous, high signal-to-noise UVES spectrum for NGC 6302 is advocated.

scholarly journals Beryllium abundances along the evolutionary sequence of the open cluster IC 4651

2009 ◽  
Vol 5 (S268) ◽  
pp. 357-358 ◽  
Author(s):  
Rodolfo Smiljanic ◽  
L. Pasquini ◽  
C. Charbonnel ◽  
N. Lagarde
Keyword(s):  
Main Sequence ◽  
Open Cluster ◽  
High Signal ◽  
Evolutionary Sequence ◽  
Main Sequence Stars ◽  
Signal To Noise ◽  
Mixing Processes ◽  
Hydrodynamical Models ◽  
Spectrum Synthesis ◽  
Hertzsprung Gap

AbstractThe simultaneous investigation of Li and Be in stars is a powerful tool in the study of the evolutionary mixing processes. Here, we present beryllium abundances in stars along the whole evolutionary sequence of the open cluster IC 4651. This cluster has a metallicity of [Fe/H] = +0.11 and an age of 1.2 or 1.7 Gyr. Abundances have been determined from high-resolution, high signal-to-noise UVES spectra using spectrum synthesis and model atmospheres. Lithium abundances for the same stars were determined in a previous work. Confirming previous results, we find that the Li dip is also a Be dip. For post-main-sequence stars, the Be dilution starts earlier within the Hertzsprung gap than expected from classical predictions, as does the Li dilution. Theoretical hydrodynamical models are able to reproduce well all the observed features.

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