- ID:
- ivo://CDS.VizieR/J/ApJ/858/119
- Title:
- O_2_ laboratory atmosphere simulation experiments
- Short Name:
- J/ApJ/858/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous studies of haze formation in the atmosphere of the early Earth have focused on N_2_/CO_2_/CH_4_ atmospheres. Here, we experimentally investigate the effect of O_2_ on the formation and composition of aerosols to improve our understanding of haze formation on the Neoproterozoic Earth. We obtained in situ size, particle density, and composition measurements of aerosol particles produced from N_2_/CO_2_/CH_4_/O_2_ gas mixtures subjected to FUV radiation (115-400nm) for a range of initial CO_2_/CH_4_/O_2_ mixing ratios (O_2_ ranging from 2ppm to 0.2%). At the lowest O_2_ concentration (2ppm), the addition increased particle production for all but one gas mixture. At higher oxygen concentrations (20ppm and greater), particles are still produced, but the addition of O_2_ decreases the production rate. Both the particle size and number density decrease with increasing O_2_, indicating that O_2_ affects particle nucleation and growth. The particle density increases with increasing O_2_. The addition of CO_2_ and O_2_ not only increases the amount of oxygen in the aerosol, but it also increases the degree of nitrogen incorporation. In particular, the addition of O_2_ results in the formation of nitrate-bearing molecules. The fact that the presence of oxygen-bearing molecules increases the efficiency of nitrogen fixation has implications for the role of haze as a source of molecules required for the origin and evolution of life. The composition changes also likely affect the absorption and scattering behavior of these particles but optical property measurements are required to fully understand the implications for the effect on the planetary radiative energy balance and climate.
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- ID:
- ivo://CDS.VizieR/J/A+A/459/981
- Title:
- Precession-nutation procedures (IAU 2006)
- Short Name:
- J/A+A/459/981
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 2006 IAU General Assembly has adopted the P03 model of Capitaine et al. (2003A&A...412..567C) recommended by the WG on precession and the ecliptic (Hilton et al., 2006, Celest. Mech. Dyn. Astron. 94, 351) to replace the IAU 2000 model, which comprised the Lieske et al. (1977A&A....58....1L) model with adjusted rates. Practical implementations of this new "IAU 2006" model are therefore required, involving choices of procedures and algorithms. The purpose of this paper is to recommend IAU 2006 based precession-nutation computing procedures, suitable for different classes of application and achieving high standards of consistency.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A32
- Title:
- Precipitable water vapour at Cerro Armazones
- Short Name:
- J/A+A/588/A32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We studied the precipitable water vapour (PWV) content near Cerro Armazones and discuss the potential use of our technique of modelling the telluric absorption lines for the investigation of other molecular layers. The site is designated for the European Extremely Large Telescope (E-ELT) and the nearby planned site for the Cherenkov Telescope Array (CTA). Spectroscopic data from the Bochum Echelle Spectroscopic Observer (BESO) instrument were investigated by using line-by-line radiative transfer model (LBLRTM) radiative transfer models for the Earths atmosphere with the telluric absorption correction tool molecfit. All observations from the archive in the period from December 2008 to the end of 2014 were investigated. The dataset completely covers the El Nino event registered in the period 2009-2010. Models of the 3D Global Data Assimilation System (GDAS) were used for further comparison. Moreover, for those days with coincidence of data from a similar study with VLT/X-shooter and microwave radiometer LHATPRO data at Cerro Paranal, a direct comparison is presented. This analysis shows that the site has systematically lower PWV values, even after accounting for the decrease in PWV expected from the higher altitude of the site with respect to Cerro Paranal, using the average atmosphere found with radiosondes. We found that GDAS data are not a suitable method for predicting of local atmospheric conditions - they usually systematically overestimate the PWV values. Due to the large sample, we were furthermore able to characterize the site with respect to symmetry across the sky and variation with the years and within the seasons. This kind of technique of studying the atmospheric conditions is shown to be a promising step into a possible monitoring equipment for CTA.
- ID:
- ivo://CDS.VizieR/J/A+AS/127/1
- Title:
- 1997 reference of diffuse night sky brightness
- Short Name:
- J/A+AS/127/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the following we present material in tabular and graphical form, with the aim to allow the non-specialist to obtain a realistic estimate of the diffuse night sky brightness over a wide range of wavelengths from the far UV longward of Ly{alpha} to the far-infrared. At the same time the data are to provide a reference for cases in which background brightness has to be discussed, including the planning for space observations and the issue of protection of observatory sites. We try to give a critical presentation of the status at the beginning of 1997.
- ID:
- ivo://CDS.VizieR/J/AJ/114/2822
- Title:
- Seeing Tests for NPOI Project
- Short Name:
- J/AJ/114/2822
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper reports astronomical seeing measurements made at four sites in the western United States during 1991-92. This study was conducted as part of the site selection process for the Navy Prototype Optical Interferometer. An extensive series of observations were made at Chews Ridge and Anderson Ridge, CA (~36,000 equivalent FWHM seeing estimates). Observations made from Chews Ridge over 49 nights yield an average FWHM seeing value of ~1.1", while those made from Anderson Ridge over 34 nights yield an average FWHM seeing of ~1.4". However, observations made from Anderson Ridge at a location away from any nearby trees indicate that more open sites in that area may enjoy seeing comparable to that measured at Chews Ridge. Simultaneous free-air, ground-level observations at the U.S. Naval Observatory's Flagstaff Station and at Anderson Mesa, both near Flagstaff, AZ, yield similar seeing values to each other (<=0.1" difference).
- ID:
- ivo://CDS.VizieR/J/A+A/321/L33
- Title:
- Terrestrial impact cratering rate
- Short Name:
- J/A+A/321/L33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The most significant periodicities in the terrestrial impact crater record are due to the "human-signal": the bias of assigning integer values for the crater ages. This bias seems to have eluded the proponents and opponents of real periodicity in the occurrence of these events, as well as the theorists searching for an extraterrestrial explanation for such periodicity. The "human-signal" should be seriously considered by scientists in astronomy, geology and paleontology when searching for a connection between terrestrial major comet or asteroid impacts and mass extinctions of species.
- ID:
- ivo://CDS.VizieR/J/A+A/523/A57
- Title:
- The Earth as a transiting planet
- Short Name:
- J/A+A/523/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An important goal within the quest for detecting an Earth-like extrasolar planet, will be to identify atmospheric gaseous bio-signatures. Aims. Observations of the light transmitted through the Earth's atmosphere, as for an extrasolar planet, will be the first important step for future comparisons. We have completed observations of the Earth during a lunar eclipse, a unique situation similar to that of a transiting planet. We aim at showing what species could be detected in its atmosphere at optical wavelengths, where a lot of photons are available in the masked stellar light. We present observations of the 2008 August 16 Moon eclipse performed with the SOPHIE spectrograph at the Observatoire de Haute- Provence (France). Locating the spectrograph's fibers in the penumbra of the eclipse, the Moon irradiance is then a mix of direct, unabsorbed Sun light and solar light that has passed through the Earth's atmosphere. This mixture essentially reproduces what is recorded during the transit of an extrasolar planet. We report here the clear detection of several Earth atmospheric compounds in the transmission spectra, such as ozone, molecular oxygen, and neutral sodium as well as molecular nitrogen and oxygen through the Rayleigh signature. Moreover, we present a method that allows us to derive the thickness of the atmosphere versus the wavelength for penumbra eclipse observations. We quantitatively evaluate the altitude at which the atmosphere becomes transparent for important species like molecular oxygen and ozone, two species thought to be tightly linked to the presence of life. The molecular detections presented here are an encouraging first attempt, necessary to better prepare for the future of extremely-large telescopes and transiting Earth-like planets. Instruments like SOPHIE will be mandatory when characterizing the atmospheres of transiting Earth-like planets from the ground and searching for bio-marker signatures.
- ID:
- ivo://CDS.VizieR/J/A+A/408/387
- Title:
- Transformation between ICRS and ITRS
- Short Name:
- J/A+A/408/387
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on the current IAU hierarchy of the relativistic reference systems, practical formulae for the transformation between barycentric (BCRS) and geocentric (GCRS) celestial reference systems are derived. BCRS is used to refer to ICRS, International Celestial Reference System. This transformation is given in four versions, dependent on the time arguments used for BCRS (TCB or TDB) and for GCRS (TCG or TT). All quantities involved in these formulae have been tabulated with the use of the VSOP theories (IMCCE theories of motion of the major planets). In particular, these formulae may be applied to account for the indirect relativistic third-body perturbations in motion of Earth's satellites and Earth's rotation problem. We propose to use the SMART theory (IMCCE theory of Earth's rotation) in constructing the Newtonian three-dimensional spatial rotation transformation between GCRS and ITRS, the International Terrestrial Reference System. This transformation is compared with two other versions involving extra angular variables currently used by IERS, the International Earth Rotation Service. It is shown that the comparison of these three forms of the same transformation may be greatly simplified by using the proposed composite rotation formula.
- ID:
- ivo://CDS.VizieR/J/A+A/406/1135
- Title:
- UT1 definitions in IAU 2000
- Short Name:
- J/A+A/406/1135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper provides expressions to be used to implement the new definition of UT1 corresponding to the IAU 2000 resolutions either in the new (CEO-based) or classical (equinox-based) transformations between the International Terrestrial Reference System (ITRS) and the Geocentric Celestial Reference System (GCRS). The new expression for Greenwich Sidereal Time (GST) has to be in agreement at the micro-arcsecond level, for one century, with the IAU 2000 expressions for the Earth Rotation Angle (ERA) and for the quantity s positioning the Celestial Ephemeris Origin (CEO) on the equator of the CIP. The computations of the new expressions using the IAU 2000 precession-nutation model are performed in such a manner as to ensure that there is no discontinuity in UT1 on 1 January 2003 and that there is equivalence of the classical and new transformations between the ITRS and GCRS relative to the rotation about the axis of the CIP when these expressions are used. The equinox offset that is considered in the computations refers to the dynamical mean equinox of J2000.0. The resulting expressions have been included in the IERS Conventions 2000.
- ID:
- ivo://CDS.VizieR/J/ApJ/775/121
- Title:
- X-ray events in Earth's magnetosphere
- Short Name:
- J/ApJ/775/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We found 217 X-ray brightening events in Earth's magnetosphere. These events occur in the high-energy band (0.5-4{AA}) of the Geostationary Operational Environmental Satellite (GOES) X-ray light curves, although GOES X-ray light curves are frequently used as indices of solar flare magnitudes. We found that (1) brightening events are absent in the low-energy band (1-8{AA}), unlike those associated with solar flares; and (2) the peak fluxes, durations, and onset times of these events depend on the magnetic local time (MLT). The events were detected in 2006, 2010, and 2011 at around 19-10MLT, that is, from night to morning. They typically lasted for 2-3hr. Their peak fluxes are less than 3x10^-8^W/m^2^ in the 0.5-4{AA} band and are maximized around 0-5MLT. From these MLT dependencies, we constructed an MLT time profile of X-ray brightening events. Because 0.5-4 and 1-8{AA} fluxes were observed and had the same order of magnitude when GOES 14 passed through Earth's shadow, we expected that X-ray brightening events in the 1-8{AA} band are obscured by high-background X-ray fluxes coming from the Sun. We also found coincidence between X-ray brightening events and aurora substorms. In the majority of our events, the minimum geomagnetic field values (AL index) are below -400nT. From these results and consideration of the GOES satellite orbit, we expect that these X-ray brightening events occur in the magnetosphere. We cannot, however, clarify the radiative process of the observed X-ray brightening events.
