Jens Biele, Matthias Grott, Michael E. Zolensky
et al.
We provide detailed background, theoretical and practical, on the specific heat cp of minerals and mixtures thereof, 'astro-materials', as well as background information on common minerals and other relevant solid substances found on the surfaces of solar system bodies. Furthermore, we demonstrate how to use specific heat and composition data for lunar samples and meteorites as well as a new database of endmember mineral heat capacities (the result of an extensive literature review) to construct reference models for the isobaric specific heat cP as a function of temperature for common solar system materials. Using a (generally linear) mixing model for the specific heat of minerals allows extrapolation of the available data to very low and very high temperatures, such that models cover the temperature range between 10 and 1000 K at least (and pressures from zero up to several kbars). We describe a procedure to estimate cp(T) for virtually any solid solar system material with a known mineral composition, e.g., model specific heat as a function of temperature for a number of typical meteorite classes with known mineralogical compositions. We present, as examples, the cp(T) curves of a number of well-described laboratory regolith analogues, as well as for planetary ices and 'tholins' in the outer solar system. Part II will review and present the heat capacity database for minerals and compounds and part III is going to cover applications, standard reference compositions, cp(T) curves and a comparison with new and literature experimental data.
Context. Sulfur (S) is of prime interest in the context of (astro)chemical evolution and habitability. However, the origin of S-bearing organic compounds in the Solar System is still not well constrained. Aims. We carried out laboratory experiments to test whether complex organosulfur compounds can be formed when surfaces of icy Solar System bodies are subject to high-energy S ions. Methods. Non-S-bearing organic residues, formed during the processing of astrophysical H 2 O:CH 3 OH:NH 3 -bearing ice analogs, were irradiated with 105 keV-S 7 + ions at 10 K and analyzed by high-resolving FT-ICR-MS. The resulting data were comprehensively analyzed, including network analysis tools. Results. Out of several thousands of detected compounds, 16% contain at least one sulfur atom (organosulfur (CHNOS) compounds), as verified via isotopic fine structures. These residue-related organosulfur compounds are different from those formed during the S ion irradiation of ices at 10 K. Furthermore, insoluble, apolar material was formed during the sulfur irradiation of residues. Potential organosulfur precursors (CHNO molecules) were identified by means of molecular networks. Conclusions. This evidence of organosulfur compounds formed by sulfur irradiation of organic residues sheds new light onto the rich and complex scope of pristine organosulfur chemistry in the Solar System, presented in the context of current and future space missions. These results indicate that the space weathering of Solar System bodies may lead to the formation of organosulfur compounds.
In this chapter, authors have discussed few machine learning techniques and their application to perform the supernovae classification. Supernovae has various types, mainly categorized into two important types. Here, focus is given on the classification of Type-Ia supernova. Astronomers use Type-Ia supernovae as “standard candles” to measure distances in the Universe. Classification of supernovae is mainly a matter of concern for the astronomers in the absence of spectra. Through the application of different machine learning techniques on the data set authors have tried to check how well classification of supernovae can be performed using these techniques. Data set used is available at Riess et al. (2007) (astro-ph/0611572).
A primeira formulação de uma física completa, do ponto de vista lógico, foi feita por Aristóteles no século IV a.c. A física aristotélica dominou o pensamento ocidental por quase dois mil anos. Tentarei mostrar neste texto que as teses aristotélicas contêm um primeiro protótipo de teoria gravitacional, inteiramente refutada a partir dos conhecimentos atuais, mas mesmo assim importante pelo contexto em que surge e por suas diversas implicações.
Apresentamos aqui uma breve e não-técnica introdução à teoria da relatividade geral, começando pelo conceito de espaço-tempo, passando pelo princípio de equivalência, e chegando nos testes clássicos que consagraram a teoria como uma das mais bonitas e bem-sucedidas da física.
Há mais de 2500 anos, o filósofo grego Tales de Mileto descobriu um teorema geométrico que lhe permitiu avaliar a altura da Grande Pirâmide no Egito comparando o comprimento de sua sombra com o comprimento da sombra projetada pelo bastão vertical ao mesmo tempo. Ao fazer isso, Tales estava usando três definições independentes de linha, e geometria em geral, provenientes de três reinos da física: gravidade, física quântica e atômica, e ótica. No presente trabalho analisamos as implicações físicas e filosóficas da coincidência entre três definições de espaço físico e sua geometria.
We demonstrate a compact 29.3 GHz visible astro-comb covering the spectrum from 560nm to 700nm. A 837 MHz Yb:fiber laser frequency comb phase locked to a Rb clock served as the seed comb to ensure the frequency stability and high side mode suppression ratio. After the visible super-continuum generation, a cavity-length-fixed Fabry-Perot cavity made by ultra-low expansion glass was utilized to filter the comb teeth for eliminating the rapid active dithering. The mirrors were home-made complementary chirped mirrors pair with zero dispersion and high reflection to guarantee no mode skipping. These filtered comb teeth were clearly resolved in an astronomical spectrograph of 49,000 resolution, exhibiting sharp linetype, zero noise floor, and uniform exposure amplitude.
Joshua Krissansen-Totton, Giada N. Arney, David C. Catling
The early Earth's environment is controversial. Climatic estimates range from hot to glacial, and inferred marine pH spans strongly alkaline to acidic. Better understanding of early climate and ocean chemistry would improve our knowledge of the origin of life and its coevolution with the environment. Here, we use a geological carbon cycle model with ocean chemistry to calculate self-consistent histories of climate and ocean pH. Our carbon cycle model includes an empirically justified temperature and pH dependence of seafloor weathering, allowing the relative importance of continental and seafloor weathering to be evaluated. We find that the Archean climate was likely temperate (0-50 °C) due to the combined negative feedbacks of continental and seafloor weathering. Ocean pH evolves monotonically from 6.6 (+0.6,-0.4) (2σ) at 4.0 Ga to 7.0 (+0.7,-0.5) (2σ) at the Archean-Proterozoic boundary, and to 7.9 (+0.1,-0.2) (2σ) at the Proterozoic-Phanerozoic boundary. This evolution is driven by the secular decline of pCO2, which in turn is a consequence of increasing solar luminosity, but is moderated by carbonate alkalinity delivered from continental and seafloor weathering. Archean seafloor weathering may have been a comparable carbon sink to continental weathering, but is less dominant than previously assumed, and would not have induced global glaciation. We show how these conclusions are robust to a wide range of scenarios for continental growth, internal heat flow evolution and outgassing history, greenhouse gas abundances, and changes in the biotic enhancement of weathering.
The present material covers the features of large scale ring dynamics in perturbed flows that were not addressed in part 1 (astro-ph/1606.00759); this includes an extensive coverage of all kinds of ring modes dynamics (except density waves which have been covered in part 1), the origin of ring eccentricities and mode amplitudes, and the issue of ring/gap confinement. This still leaves aside a number of important dynamical issues relating to the ring small scale structure, most notably the dynamics of self-gravitational wakes, of local viscous overstabilities and of ballistic transport processes. As this material is designed to be self-contained, there is some 30% overlap with part 1. This work constitutes a preprint of Chapter 11 of the forthcoming Cambridge University book on rings (Planetary Ring Systems, Matt Tiscareno and Carl Murray, eds).
In this paper, we discuss limits on various astro-particle scenarios if the scale \textit{and} the reheat temperature of the last relevant inflation were very high. While the observed "B" like pattern of polarizations of the CMB suggest a very high ($\ge 10^{16}\ GeV$) scale of a primordial (which motivated this work initially) and may reflect effects of dust, we believe that addressing these issues is nonetheless very useful. We recall the potential difficulties with various topological defects - monopoles, strings and domain walls generated at the SSB (spontaneous symmetry breaking) of various gauge symmetries. The main part of the paper is devoted to discussing difficulties with long-lived heavy particles, which could be dark matter but cannot efficiently annihilate to the required residual density because of basic S-Matrix unitarity/analyticity limits. We indicate in simple terms yet in some detail how the WIMP miracle occurs at $M(X)\sim{TeV}$ and how the axiomatic upper bound presently updated to $M(X) \le{110 TeV}$ was originally derived by Greist and Kamionokowski. We also argue that generically we expect the stronger $M(X)\le{20\ GeV}$ bound to hold. We then elaborate on the pure particle physics approaches aiming to enhance the annihilation and evade the bounds. We find that the only and in fact very satisfactory way of doing this requires endowing the particles with gauge interactions with a confinement scale lower than $M(X)$. We also comment on models with light $O(KeV)$ dark matter, which was supposed to be frozen in via out-of equilibrium processes so as to have the right relic densities pointing out that in many such cases \textit{very} low reheat temperatures are indeed required and speculate on the large desert scenario of particle physics. Most of what we discuss is not new but was not presented in a coherent fashion.
Abstract Because of an old quasar APM 08279 + 5255 at z = 3.91 , some dark energy models face the challenge of the cosmic age problem. It has been shown by Wei and Zhang [H. Wei, S.N. Zhang, Phys. Rev. D 76 (2007) 063003, arXiv:0707.2129 [astro-ph] ] that the holographic dark energy model is also troubled with such a cosmic age problem. In order to accommodate this old quasar and solve the age problem, we propose in this Letter to consider the interacting holographic dark energy in a non-flat universe. We show that the cosmic age problem can be eliminated when the interaction and spatial curvature are both involved in the holographic dark energy model.
Improved wavelength calibrators for high-resolution astrophysical spectrographs will be essential for precision radial velocity (RV) detection of Earth-like exoplanets and direct observation of cosmological deceleration. The astro-comb is a combination of an octave-spanning femtosecond laser frequency comb and a Fabry-Pérot cavity used to achieve calibrator line spacings that can be resolved by an astrophysical spectrograph. Systematic spectral shifts associated with the cavity can be 0.1-1 MHz, corresponding to RV errors of 10-100 cm/s, due to the dispersive properties of the cavity mirrors over broad spectral widths. Although these systematic shifts are very stable, their correction is crucial to high accuracy astrophysical spectroscopy. Here, we demonstrate an \emph{in-situ} technique to determine the systematic shifts of astro-comb lines due to finite Fabry-Pérot cavity dispersion. The technique is practical for implementation at a telescope-based spectrograph to enable wavelength calibration accuracy better than 10 cm/s.
In this Letter, we extend our previous work [H. Wei, S.N. Zhang, Phys. Lett. B 644 (2007) 7, astro-ph/0609597], and compare eleven interacting dark energy models with different couplings to the observational H(z) data. However, none of these models is better than the simplest ACDM model. This implies that either more exotic couplings are needed in the cosmological models with interaction between dark energy and dust matter, or there is no interaction at all. We consider that this result is disadvantageous to the interacting dark energy models studied extensively in the literature. (c) 2007 Elsevier B.V. All rights reserved.
Comments to the review "Nonthermal Phenomena in Clusters of Galaxies" by Y.Rephaeli et al. (arXiv:0801.0982 [astro-ph]) that regard the presence of a hard X-ray excess in the Coma cluster, A2199, A2163 and the Bullet cluster.
We have used data from ADS, AAS, and astro-ph, to study the publishing, preprint posting, and citation patterns for papers published in the ApJ in 1999 and 2002. This allowed us to track statistical trends in author demographics, preprint posting habits, and citation rates for ApJ papers as a whole and across various subgroups and types of ApJ papers. The most interesting results are the frequencies of use of the astro-ph server across various subdisciplines of astronomy, and the impact that such posting has on the citation history of the subsequent ApJ papers. By 2002 72% of ApJ papers were posted as astro-ph preprints, but this fraction varies from 22-95% among the subfields studied. A majority of these preprints (61%) were posted after the papers were accepted at ApJ, and 88% were posted or updated after acceptance. On average, ApJ papers posted on astro-ph are cited more than twice as often as those that are not posted on astro-ph. This difference can account for a number of other, secondary citation trends, including some of the differences in citation rates between journals and different subdisciplines. Preprints clearly have supplanted the journals as the primary means for initially becoming aware of papers, at least for a large fraction of the ApJ author community. Publication in a widely-recognized peer-reviewed journal remains as the primary determinant of the impact of a paper, however. For example, conference proceedings papers posted on astro-ph are also cited twice as frequently as those that are not posted, but overall such papers are still cited 20 times less often than the average ApJ paper. These results provide insights into how astronomical research is currently disseminated by authors and ingested by readers.
15 pages, 9 figures.-- arXiv:0503320 astro-ph pre-print supplied.-- Version with high-resolution images can be found at: ftp://ftp.astro.su.se/matthew/papers/lya_e338.pdf.-- Final full-text version of the paper available at: http://dx.doi.org/10.1051/0004-6361:20052702.
Papers that are posted to a digital preprint archive are typically cited twice as often as papers that are not posted. This has been demonstrated for papers published in a wide variety of journals, and in many different subfields of astronomy. Most astronomers now use the arXiv.org server (astro-ph) to distribute preprints, but the solar physics community has an independent archive hosted at Montana State University. For several samples of solar physics papers published in 2003, I quantify the boost in citation rates for preprints posted to each of these servers. I show that papers on the MSU archive typically have citation rates 1.7 times higher than the average of similar papers that are not posted as preprints, while those posted to astro-ph get 2.6 times the average. A comparable boost is found for papers published in conference proceedings, suggesting that the higher citation rates are not the result of self-selection of above-average papers.