Coude-feed stellar spectral library - atmospheric parameters

Context: Empirical libraries of stellar spectra play an important role in different fields. For example, they are used as reference for the automatic determination of atmospheric parameters, or for building synthetic stellar populations to study galaxies. The CFLIB (Coude-feed library, Indo-US) database is at present one of the most complete libraries, in terms of its coverage of the atmospheric parameters space (Teff, log g and [Fe/H]) and wavelength coverage 3460 - 9464 A at a resolution of 1 A FWHM. Although the atmospheric parameters of most of the stars were determined from detailed analyses of high-resolution spectra, for nearly 300 of the 1273 stars of the library at least one of the three parameters is missing. For the others, the measurements, compiled from the literature, are inhomogeneous. Aims: In this paper, we re-determine the atmospheric parameters, directly using the CFLIB spectra, and compare them to the previous studies. Methods: We use the ULySS program to derive the atmospheric parameters, using the ELODIE library as a reference. Results: Based on comparisons with several previous studies we conclude that our determinations are unbiased. For the 958 F,G, and K type stars the precision on Teff, log g, and [Fe/H] is respectively 43 K, 0.13 dex and 0.05 dex. For the 53 M stars they are 82 K, 0.22 dex and 0.28 dex. And, for the 260 OBA type stars the relative precision on Teff is 5.1%, and on log g, and [Fe/H] the precision is respectively 0.19 dex and 0.16 dex. These parameters will be used to re-calibrate the CFLIB fluxes and to produce synthetic spectra of stellar populations.Comment: 51 pages, accepted for publication in Astronomy and Astrophysic

The MVGC multivariate Granger causality toolbox: a new approach to Granger-causal inference

Background: Wiener-Granger causality (“G-causality”) is a statistical notion of causality applicable to time series data, whereby cause precedes, and helps predict, effect. It is defined in both time and frequency domains, and allows for the conditioning out of common causal influences. Originally developed in the context of econometric theory, it has since achieved broad application in the neurosciences and beyond. Prediction in the G-causality formalism is based on VAR (Vector AutoRegressive) modelling. New Method: The MVGC Matlab c Toolbox approach to G-causal inference is based on multiple equivalent representations of a VAR model by (i) regression parameters, (ii) the autocovariance sequence and (iii) the cross-power spectral density of the underlying process. It features a variety of algorithms for moving between these representations, enabling selection of the most suitable algorithms with regard to computational efficiency and numerical accuracy. Results: In this paper we explain the theoretical basis, computational strategy and application to empirical G-causal inference of the MVGC Toolbox. We also show via numerical simulations the advantages of our Toolbox over previous methods in terms of computational accuracy and statistical inference. Comparison with Existing Method(s): The standard method of computing G-causality involves estimation of parameters for both a full and a nested (reduced) VAR model. The MVGC approach, by contrast, avoids explicit estimation of the reduced model, thus eliminating a source of estimation error and improving statistical power, and in addition facilitates fast and accurate estimation of the computationally awkward case of conditional G-causality in the frequency domain. Conclusions: The MVGC Toolbox implements a flexible, powerful and efficient approach to G-causal inference. Keywords: Granger causality, vector autoregressive modelling, time series analysi

Automatic Determination of Stellar Atmospheric Parameters and Construction of Stellar Spectral Templates of the Guoshoujing Telescope (LAMOST)

A number of spectroscopic surveys have been carried out or are planned to study the origin of the Milky Way. Their exploitation requires reliable automated methods and softwares to measure the fundamental parameters of the stars. Adopting the ULySS package, we have tested the effect of different resolutions and signal-to-noise ratios (SNR) on the measurement of the stellar atmospheric parameters (effective temperature Teff, surface gravity log g, and metallicity [Fe/H]). We show that ULySS is reliable to determine these parameters with medium-resolution spectra (R~2000). Then, we applied the method to measure the parameters of 771 stars selected in the commissioning database of the Guoshoujing Telescope (GSJT). The results were compared with the SDSS/SEGUE Stellar Parameter Pipeline (SSPP), and we derived precisions of 167 K, 0.34 dex, and 0.16 dex for Teff, log g and [Fe/H] respectively. Furthermore, 120 of these stars are selected to construct the primary stellar spectra template library (Version 1.0) of GSJT, and will be deployed as basic ingredients for the GSJT automated parametrization pipeline.Comment: 23 pages, 15 figures, accepted by RA

Discovery of a new PG1159 (GW Vir) Pulsator

We report the discovery of pulsations in the spectroscopic PG 1159 type pre-white dwarf SDSS J075415.12+085232.18. Analysis of the spectrum by Werner, Rauch and Kepler (2014) indicated Teff=120 000+/-10 000 K, log g=7.0+/-0.3, mass M=0.52+/-0.02 Msun, C/He=0.33 by number. We obtained time-series images with the SOAR 4.1 m telescope and 2.1 m Otto Struve telescope at McDonald Observatory and show the star is also a variable PG 1159 type star, with dominant period of 525 s.Comment: 5 pages, 3 figure

Exotic energy injection with ExoCLASS: Application to the Higgs portal model and evaporating black holes

We devise a new user-friendly tool interfaced with the Boltzmann code CLASS to deal with any kind of exotic electromagnetic energy injection in the universe and its impact on anisotropies of the Cosmic Microwave Background. It makes use of the results from standard electromagnetic cascade calculations develop in the context of WIMP annihilation, generalized to incorporate any injection history. We first validate it on a specific WIMP scenario, the Higgs Portal model, confirming that the standard effective on-the-spot treatment is accurate enough. We then analyze the more involved example of evaporating Primordial Black Holes (PBHs) with masses in the range $[3\times10^{13},5\times10^{16}]$g, for which the standard approximations break down. We derive robust CMB bounds on the relic density of evaporating PBHs, ruling out the possibility for PBHs with a monochromatic distribution of masses in the range $[3\times10^{13},2.5\times10^{16}]$g to represent all of the Dark Matter in our Universe. Remarkably, we confirm with an accurate study that the CMB bounds are several orders of magnitude stronger than those from the galactic gamma-ray background in the range $[3\times10^{13},3\times10^{14}]$g. A future CMB experiment like CORE+, or an experiment attempting at measuring the 21 cm signal from the Dark Ages could greatly improve the sensitivity to these models.Comment: 29 pages, 10 figures. Comments welcom

Stable isotope (δ18O and δ13C) sclerochronology of Callovian (Middle Jurassic) bivalves (Gryphaea (Bilobissa) dilobotes) and belemnites (Cylindroteuthis puzosiana) from the Peterborough Member of the Oxford Clay Formation (Cambridgeshire, England): Evidence of palaeoclimate, water depth and belemnite behaviour

Incremental δ18O and δ13C signals were obtained from three well-preserved specimens of Cylindroteuthis puzosiana and from three well-preserved specimens of Gryphaea (Bilobissa) dilobotes from the Peterborough Member of the Oxford Clay Formation (Cambridgeshire, England). Through-ontogeny (sclerochronological) δ18O data from G. (B.) dilobotes appear to faithfully record seasonal temperature variations in benthic Callovian waters of the study area, which range from c. 14 °C to c. 17 °C (arithmetic mean temperature c. 15 °C). Water depth is estimated to have been in the region of c. 50 m, based upon comparisons between these data, previously published non-incremental sea surface δ18O values, and a modern analogue situation. Productivity in Callovian waters was comparable with that in modern seas, based upon δ13C data from G. (B.)dilobotes, with 13C depletion occurring during warmer periods, possibly related to an interaction between plankton blooms and intra-annual variations in mixing across a thermocline. Incremental δ18O data from C.puzosiana provide temperature minima of c.11 °C for all specimens but with maxima varying between c.14 °C and c.16 °C for different individuals (arithmetic mean values c. 13 °C). Temperatures for late ontogeny, when the C. puzosiana individuals must have been living close to the study site and hence the analysed specimens of G. (B.) dilobotes, are closely comparable to those indicated by the latter. However, for significant portions of ontogeny C. puzosiana experienced temperatures between c. 2 °C and c. 3 °C cooler than the winter minimum as recorded by co-occurring G. (B.) dilobotes. Comparisons with modern seas suggest that descent to a depth of c. 1000 m would be necessary to explain such cool minimum temperatures. This can be discounted due to the lack of deep waters locally and due to estimates of the depth tolerance of belemnites. The most likely cause of cool δ18O signals from C. puzosiana is a cosmopolitan lifestyle including migration to more northerly latitudes. Mean δ13C values from C. puzosiana are comparable with those from G.(B.)dilobotes. However, the incrementally acquired data are highly variable and probably influenced by metabolic effects.The probable identification of migratory behaviour in C. puzosiana calls into question the reliability of some belemnite species as place-specific palaeoenvironmental archives and highlights the benefits of adopting a sclerochronological approach

The effect of soil compaction on conventional tilled soil and permanent grasslands : a field study

Att gårdar blir större är en tydlig trend inom det svenska lantbruket. Med det följer även en större efterfrågan på större maskiner och redskap. Denna rationalisering medför en ökad risk för att åkermarken blir kraftigt packad och därigenom skadad, vilket på sikt kan leda till försämrad bördighet. I detta arbete har två identiska jordbearbetningsförsök legat till grund för arbetets mätningar. Eftersom jordarten skiljde på de två försöksplatserna kunde även den skillnaden jämföras. På respektive försöksplats har två olika odlingssystem jämförts och undersökts hur de påverkas av kompaktion. Det ena odlingssystemet som jämförts var konventionell jordbearbetning med årlig plöjning. Det andra var ett odlingssystem bevuxen med ett permanent växttäcke med vall. Permanent vall användes i jämförelsen för att simulera ett direkt sått odlingssystem. Det för att markstrukturen i ett direkt sått odlingssystem och permanent bevuxen gräsmark med vall ska i teorin ha en liknande struktur. Både hållfasthet och tryckutbredning i marken i respektive jord och odlingssystem testats. För att testa hållfastheten togs sammanlagd 108 cylinderprover. Orörda markstrukturprover togs ifrån tre olika djup för varje markprofil, för att sedan testa provernas hållfasthet på labb med hjälp av en kompakteringsmaskin. Tryckutbredning testades genom att nergrävda trycksensorer passerades av en tung traktor med högt ringtryck. Sensorerna var placerade på tre olika djup i alla av försöksleden. Även här togs sammanlagd 108 cylinderprover före och efter överfarterna med traktorn för att undersöka skrymdensitet. Dessa prover analyserades också i labb. I samband med överfarterna mättes även spårdjupen som orsakats av traktorn. Resultaten visar att markens bindningstryck dvs fuktighet är det som påverkar hållfastheten mest,till skillnad från struktur och textur. Av struktur och textur så var texturen mer bidragande till provernas hållfasthet. Strukturen i proven bidrog alltså minst till hållfastheten. Den permanenta vallen hade högre hållfasthet än det plöjda ledet för den styva lerjorden. I det fallet hade alltså strukturen en avgörande roll för hållfastheten på alla djup som testades. I proven som togs i den lättare jorden sågs ingen skillnad i hållfasthet mellan vall ledet och det plöjda ledet. Däremot vad gäller tryckutbredning som testades i fält fanns tydliga skillnader mellan leden i den lättare jorden. Trycket som uppmättes var lägre för ledet med permanent vall jämfört med ledet som plöjs årligen. Marken med ett permanent växttäcke kan alltså fördela trycket bättre med hjälp av strukturen som ett välutvecklat rotsystem ger. Gällande tryckutbredning i jorden med styv lera sågs ingen skillnad mellan leden. Den potentiella skillnaden i struktur var alltså inte avgörande för tryckutbredningen i markprofilen. Jordens fysikaliska egenskaper som textur och bindningstryck var det som påverkade truckutbredningen mest. Såvida stämmer den äldre tesen om att styva leror är mera packningsbenägna än lättare jordar. Att en god struktur skapad av rotsystem hade störst effekt på den lättare jorden var väntat, men att det inte fanns någon skillnad på den styvare jorden var oväntat. En potentiell bieffekt av det permanenta växttäcket är att det välutvecklade rotsystemet har en uttorkande effekt på jorden vid fuktiga förhållanden, då markfukten respireras bort eller hålls i rotsystem och i växterna. Det samma gäller torra förhållanden. Rötterna håller fukten då den andra jorden, som är mera homogen i sin struktur snabbt torkar ur. Denna vattenbuffrande effekt som rotsystemen ger i ett orört odlingssystem med permanent växttäcke är det som till störst del svarar för hur påfrestningarna den utsätts för.Farms getting bigger is a clear trend in Swedish agriculture. With that comes a demand for larger machines and implements. This rationalization entails an increased risk that the arable land will be heavily compacted and thereby damaged, which in the long run may lead to reduced soil fertility. In this thesis, two identical tillage field trials have formed the basis for the thesis. Since the soil type differed at the two experimental sites, the soil differences could also be compared. At each field trial site, two different cultivation systems have been compared and investigated on how they are affected by compaction. One of the cultivation systems was conventional tillage with annual mouldboard ploughing. The other cultivation system consisted of a permanent grassland. The permanent grassland was used in the comparison to simulate a directly sown cultivation system. This is because the soil structure in a directly sown cultivation system and permanent grassland should in theory have a similar structure. Both tension strength and pressure distribution where tested and compered. To test the strength, a total of 108-cylinder samples was taken. Intact soil structure samples were taken from three different depths for each soil profile. Samples where then tested to determine strength in lab using a compaction machine. Pressure propagation was tested by passing over buried pressure sensors in each field trial lot, with a heavy tractor with high tire pressure. The sensors were placed at three different depths in each of the experimental test lot. Another batch 108-cylinder samples were taken before and after the crossings with the tractor to examine bulk density changes, before and after the passes. These samples were analysed in the lab. In connection with the crossings, even the track depths were measured. The results show that the tension pressure of the soil, is what affects the strength the most, in contrast to structure and texture. Texture was more contributing to the strength of the samples. The structure of the samples contributed the least to the strength. The permanent grassland had higher strength than the annually tilled soil, for the heavy clay soil. In that case, the structure played a decisive role in the strength at all the depths tested. In the samples taken in the silty soil, no difference in strength were seen between the grass lot and the ploughed lot. However, in terms of pressure propagation tested in the field, there were clear differences between the slots in the silt soil. The pressure measured was lower for the joint with permanent grass compared to the lot that is ploughed annually. The soil with a permanent grass cover can distribute the pressure better with the help of the structure, which the well-developed root system provides. Regarding pressure distribution in the soil with heavy clay, no difference was seen between the plots. The potential difference in structure was not decisive for the pressure distribution in the soil profile. The soil profiles physical properties such as texture and tension strength affected the pressure distribution the most. Old results stating that heavy clays are more prone to compaction than lighter soils are conforms with the findings from this thesis. It was expected that a good structure created by root systems would have a greater effect on the lighter soil. However, it was unexpected that there was no difference in this matter in the heavy soil. A potential side effect of the permanent grass lots is that the well-developed root system had a drying effect on the soil in wet conditions. Whereas soil moisture is respirated by the grass or kept in the root system of the plants. It’s the same in dry conditions, the roots will retain moisture, while a tilled soil which is more homogeneous in its structure, dries out more quickly. This water-buffering effect that the root systems provide in an undisturbed cultivation system responds for how the stress propagation will be distributed

Transient simulations of the carbon and nitrogen dynamics in northern peatlands: from the Last Glacial Maximum to the 21st century

The development of northern high-latitude peatlands played an important role in the carbon (C) balance of the land biosphere since the Last Glacial Maximum (LGM). At present, carbon storage in northern peatlands is substantial and estimated to be 500 ± 100 Pg C (1 Pg C = 1015 g C). Here, we develop and apply a peatland module embedded in a dynamic global vegetation and land surface process model (LPX-Bern 1.0). The peatland module features a dynamic nitrogen cycle, a dynamic C transfer between peatland acrotelm (upper oxic layer) and catotelm (deep anoxic layer), hydrology- and temperature-dependent respiration rates, and peatland specific plant functional types. Nitrogen limitation down-regulates average modern net primary productivity over peatlands by about half. Decadal acrotelm-to-catotelm C fluxes vary between −20 and +50 g C m−2 yr−1 over the Holocene. Key model parameters are calibrated with reconstructed peat accumulation rates from peat-core data. The model reproduces the major features of the peat core data and of the observation-based modern circumpolar soil carbon distribution. Results from a set of simulations for possible evolutions of northern peat development and areal extent show that soil C stocks in modern peatlands increased by 365–550 Pg C since the LGM, of which 175–272 Pg C accumulated between 11 and 5 kyr BP. Furthermore, our simulations suggest a persistent C sequestration rate of 35–50 Pg C per 1000 yr in present-day peatlands under current climate conditions, and that this C sink could either sustain or turn towards a source by 2100 AD depending on climate trajectories as projected for different representative greenhouse gas concentration pathways