Climate forced atmospheric CO₂ variability in the early Holocene: A stomatal frequency reconstruction     

C.A. Jessen  M. Rundgren  S. Bjrck  R. Muscheler 《Global and Planetary Change》2007,57(3-4):247-260

The dynamic climate in the Northern Hemisphere during the early Holocene could be expected to have impacted on the global carbon cycle. Ice core studies however, show little variability in atmospheric CO₂. Resolving any possible centennial to decadal CO₂ changes is limited by gas diffusion through the firn layer during bubble enclosure. Here we apply the inverse relationship between stomatal index (measured on sub-fossil leaves) and atmospheric CO₂ to complement ice core records between 11,230 and 10,330 cal. yr BP. High-resolution sampling and radiocarbon dating of lake sediments from the Faroe Islands reconstruct a distinct CO₂ decrease centred on ca. 11,050 cal. yr BP, a consistent and steady decline between ca. 10,900 and 10,600 cal. yr BP and an increased instability after ca. 10,550 cal. yr BP. The earliest decline lasting ca. 150 yr is probably associated with the Preboreal Oscillation, an abrupt climatic cooling affecting much of the Northern Hemisphere a few hundred years after the end of the Younger Dryas. In the absence of known global climatic instability, the decline to ca. 10,600 cal. yr BP is possibly due to expanding vegetation in the Northern Hemisphere. The increasing instability in CO₂ after 10,600 cal. yr BP occurs during a period of increasing cooling of surface waters in the North Atlantic and some increased variability in proxy climate indicators in the region.The reconstructed CO₂ changes also show a distinct similarity to indicators of changing solar activity. This may suggest that at least the Northern Hemisphere was particularly sensitive to changes in solar activity during this time and that atmospheric CO₂ concentrations fluctuated via rapid responses in climate.  相似文献   

The effect of ground ice on the Martian seasonal CO₂ cycle     

Robert M. Haberle  Francois Forget  James Schaeffer  Nora J. Kelly 《Planetary and Space Science》2008,56(2):251-255

The mostly carbon dioxide (CO₂) atmosphere of Mars condenses and sublimes in the polar regions, giving rise to the familiar waxing and waning of its polar caps. The signature of this seasonal CO₂ cycle has been detected in surface pressure measurements from the Viking and Pathfinder landers. The amount of CO₂ that condenses during fall and winter is controlled by the net polar energy loss, which is dominated by emitted infrared radiation from the cap itself. However, models of the CO₂ cycle match the surface pressure data only if the emitted radiation is artificially suppressed suggesting that they are missing a heat source. Here we show that the missing heat source is the conducted energy coming from soil that contains water ice very close to the surface. The presence of ice significantly increases the thermal conductivity of the ground such that more of the solar energy absorbed at the surface during summer is conducted downward into the ground where it is stored and released back to the surface during fall and winter thereby retarding the CO₂ condensation rate. The reduction in the condensation rate is very sensitive to the depth of the soil/ice interface, which our models suggest is about 8 cm in the Northern Hemisphere and 11 cm in the Southern Hemisphere. This is consistent with the detection of significant amounts of polar ground ice by the Mars Odyssey Gamma Ray Spectrometer and provides an independent means for assessing how close to the surface the ice must be. Our results also provide an accurate determination of the global annual mean size of the atmosphere and cap CO₂ reservoirs, which are, respectively, 6.1 and 0.9 hPa. They also indicate that general circulation models will need to account for the effect of ground ice in their simulations of the seasonal CO₂ cycle.  相似文献   

Electronic Sputtering Analysis of Astrophysical Ices     

L. S. Farenzena  P. Iza  R. Martinez  F. A. Fernandez-Lima  E. Seperuelo Duarte  G. S. Faraudo  C. R. Ponciano  M. G. P. Homem  A. Naves de Brito  K. Wien  E. F. da Silveira 《Earth, Moon, and Planets》2005,97(3-4):311-329

Experimental results on fast ion collision with icy surfaces having astrophysical interest are presented. ²⁵²Cf fission fragments projectiles were used to induce ejection of ionized material from H₂O, CO₂, CO, NH₃, N₂, O₂ and Ar ices; the secondary ions were identified by time-of-flight mass spectrometry. It is observed that all the bombarded frozen gas targets emit cluster ions which have the structure X_nR^±, where X is the neutral ice molecule and R^± is either an atomic or a molecular ion. The shape of the positive or negative ion mass spectra is characterized by a decreasing yield as the emitted ion mass increases and is generally described by the sum of two exponential functions. The positive ion water ice spectrum is dominated by the series (H₂O)_nH₃O⁺ and the negative ion spectrum by the series (H₂O)_nOH⁻ and (H₂O)_nO⁻. The positive ion CO₂ ice spectrum is characterized by R⁺ = C⁺, O⁺, CO⁺, O₂⁺ or CO₂⁺ and the negative one by R⁻ = CO₃⁻. The dominant series for ammonia ice correspond to R⁺ = NH₄⁺ and to R⁻ = NH₂⁻. The oxygen series are better described by (O₃)_nO_m⁺ secondary ions where m = 1, 2 or 3. Two positive ion series exist for N₂ ice: (N₂)_nN₂⁺ and (N₂)_nN⁺. For argon positive secondary ions, only the (Ar)_nAr⁺ series was observed. Most of the detected molecular ions were formed by one-step reactions. Ice temperature was varied from ∼20 K to complete sublimation.  相似文献   

Tolerance of allogromiid Foraminifera to severely elevated carbon dioxide concentrations: Implications to future ecosystem functioning and paleoceanographic interpretations     

Joan M. Bernhard  Elizabeth Mollo-Christensen  Nadine Eisenkolb  Victoria R. Starczak 《Global and Planetary Change》2009,65(3-4):107-114

Increases in the partial pressure of carbon dioxide (pCO₂) in the atmosphere will significantly affect a wide variety of terrestrial fauna and flora. Because of tight atmospheric–oceanic coupling, shallow-water marine species are also expected to be affected by increases in atmospheric carbon dioxide concentrations. One proposed way to slow increases in atmospheric pCO₂ is to sequester CO₂ in the deep sea. Thus, over the next few centuries marine species will be exposed to changing seawater chemistry caused by ocean–atmospheric exchange and/or deep-ocean sequestration. This initial case study on one allogromiid foraminiferal species (Allogromia laticollaris) was conducted to begin to ascertain the effect of elevated pCO₂ on benthic Foraminifera, which are a major meiofaunal constituent of shallow- and deep-water marine communities. Cultures of this thecate foraminiferan protist were used for 10–14-day experiments. Experimental treatments were executed in an incubator that controlled CO₂ (15 000; 30 000; 60 000; 90 000; 200 000 ppm), temperature and humidity; atmospheric controls (i.e., ~ 375 ppm CO₂) were executed simultaneously. Although the experimental elevated pCO₂ values are far above foreseeable surface water pCO₂, they were selected to represent the spectrum of conditions expected for the benthos if deep-sea CO₂ sequestration becomes a reality. Survival was assessed in two independent ways: pseudopodial presence/absence and measurement of adenosine triphosphate (ATP), which is an indicator of cellular energy. Substantial proportions of A. laticollaris populations survived 200 000 ppm CO₂ although the mean of the median [ATP] of survivors was statistically lower for this treatment than for that of atmospheric control specimens. After individuals that had been incubated in 200 000 ppm CO₂ for 12 days were transferred to atmospheric conditions for ~ 24 h, the [ATP] of live specimens (survivors) approximated those of the comparable atmospheric control treatment. Incubation in 200 000 ppm CO₂ also resulted in reproduction by some individuals. Results suggest that certain Foraminifera are able to tolerate deep-sea CO₂ sequestration and perhaps thrive as a result of elevated pCO₂ that is predicted for the next few centuries, in a high-pCO₂ world. Thus, allogromiid foraminiferal “blooms” may result from climate change. Furthermore, because allogromiids consume a variety of prey, it is likely that they will be major players in ecosystem dynamics of future coastal sedimentary environments.  相似文献   

Numerical simulation of the winter polar wave clouds observed by Mars Global Surveyor Mars Orbiter Laser Altimeter     

G Tobie  F Forget  F Lott 《Icarus》2003,164(1):33-49

In 1998, the Mars Orbiter Laser Altimeter revealed the presence of isolated or quasi-periodic thick clouds during the martian polar night. They are believed to be composed of CO₂ ice particles and to be tilted against the wind direction, a feature characteristic of vertically propagating orographic gravity waves. To support that interpretation, we present here numerical simulations with a two-dimensional anelastic model of stratified shear flow that includes simple CO₂ ice microphysics. In some of the simulations presented, the orography is an idealized trough, with dimensions characteristic of the many troughs that shape the Mars polar cap. In others, it is near the real orography. In the polar night conditions, our model shows that gravity waves over the north polar cap are strong enough to induce adiabatic cooling below the CO₂ frost point. From this cooling, airborne heterogeneous nucleation of CO₂ ice particles occurs from the ground up to the altitude of the polar thermal inversion. Although the model predicts that clouds can be present above 15 km, only low altitude clouds can backscatter the Laser beams of MOLA at a detectable level. Accordingly, the shape of the Laser echoes is related to the shape of the clouds at low level, but do not necessarily coincide with the top of the clouds. The model helps to interpret the cloud patterns observed by MOLA. Above an isolated orographic trough, an isolated extended sloping cloud tilted against the wind is obtained. The model shows that the observed quasi-periodic clouds are due to the succession of small-scale topographic features, rather than to the presence of resonant trapped lee waves. Indeed, the CO₂ condensation greatly damps the buoyancy force, essential for the maintenance of gravity waves far from their sources. Simulations with realistic topography profiles show the cloud response is sensitive to the wind direction. When the wind is directed upslope of the polar cap, on the one hand, a large scale cloud, modulated by small-scale waves, forms just above the ground. On the other hand, when the wind is directed downslope, air is globally warmed, and periodic ice clouds induced by small-scale orography form at altitudes higher than 3-5 km above the ground. In both cases, a good agreement between the simulated echoes and the observed one is obtained. According to our model, we conclude that the observed clouds are quasi-stationary clouds made of moving ice particles that successively grow and sublimate by crossing cold and warm phases of orographic gravity waves generated by the successive polar troughs. We also find that the rate of ice precipitation is relatively weak, except when there is a large scale air dynamical cooling.  相似文献   

The natural latitudinal distribution of atmospheric CO₂     

John A. Taylor  James C. Orr 《Global and Planetary Change》2000,26(4)

Although poorly understood, the north–south distribution of the natural component of atmospheric CO₂ offers information essential to improving our understanding of the exchange of CO₂ between the atmosphere, oceans, and biosphere. The natural or unperturbed component is equivalent to that part of the atmospheric CO₂ distribution which is controlled by non-anthropogenic CO₂ fluxes from the ocean and terrestrial biosphere. Models should be able to reproduce the true north–south gradient in CO₂ due to the natural component before they can reliably estimate present-day CO₂ sources and sinks and predict future atmospheric CO₂. We have estimated the natural latitudinal distribution of atmospheric CO₂, relative to the South Pole, using measurements of atmospheric CO₂ during 1959–1991 and corresponding estimates of anthropogenic CO₂ emissions to the atmosphere. Key features of the natural latitudinal distribution include: (1) CO₂ concentrations in the northern hemisphere that are lower than those in the southern hemisphere; (2) CO₂ concentration differences that are higher in the tropics (associated with outgassing of the oceans) than those currently measured; and (3) CO₂ concentrations over the southern ocean that are relatively uniform. This natural latitudinal distribution and its sensitivity to increasing fossil fuel emissions both indicate that near-surface concentrations of atmospheric CO₂ in the northern hemisphere are naturally lower than those in the southern hemisphere. Models that find the contrary will also mismatch present-day CO₂ in the northern hemisphere and incorrectly ascribe that region as a large sink of anthropogenic CO₂.  相似文献   

Spatial distributions and seasonal variations of features related to a venting process at high southern latitudes observed by the MOC camera     

Jeng-Jong Jian  Wing-Huen Ip  Shin-Reu Sheu 《Planetary and Space Science》2009,57(7):797-803

A distinctive terrain named cryptic region which is characterized by regions of low albedo and low temperature has been identified on the Martian south polar cap. In this zone, many fan- and spider-shaped features of km-scale appeared following the sublimation of the CO₂ frost layer. These peculiar features were apparently caused by a wind-blown system of dust-laden jets. During the warming period starting at L_s∼180°, the seasonal ice cap regresses and fans and spiders appear in sequence. These surface features are repeatable events that tend to occupy the same areas from year to year. In this study, we use the Mars Orbiter camera (MOC) narrow-angle images to produce a statistical study of the time distributions of the fans and spiders as functions of L_s and as functions of the topography. The time variations and spatial distributions of these features are further correlated with the CO₂ ice coverage measured by the Mars Orbiter laser altimeter (MOLA) instrument. We have documented that most of the fans are found in the early spring with L_s<230° and the fans and spiders coexist at L_s=250°±20°. It is also found that there is a strong dependence on latitude and altitude with fans and spiders most often observed at high latitude (>83°S) and high altitude (>2500 m). Our statistical result also indicates that the occurrence of fans is highly correlated with the thickness of the CO₂ frost thus providing support for the venting model.  相似文献   

Sublimation kinetics of CO₂ ice on Mars     

David G. Blackburn  Kathryn L. Bryson  Vincent F. Chevrier  Krista F. White 《Planetary and Space Science》2010,58(5):780-791

Dynamic models of the martian polar caps are in abundance, but most rely on the assumption that the rate of sublimation of CO₂ ice can be calculated from heat transfer and lack experimental verification. We experimentally measured the sublimation rate of pure CO₂ ice under simulated martian conditions as a test of this assumption, developed a model based on our experimental results, and compared our model's predictions with observations from several martian missions (MRO, MGS, Viking). We show that sun irradiance is the primary control for the sublimation of CO₂ ice on the martian poles with the amount of radiation penetrating the surface being controlled by variations in the optical depth, ensuring the formation and sublimation of the seasonal cap. Our model confirmed by comparison of MGS-MOC and MRO-HiRISE images, separated by 2-3 martian years, shows that ∼0.4 m are currently being lost from the south perennial cap per martian year. At this rate, the ∼2.4-m-thick south CO₂ perennial cap will disappear in about 6-7 martian years, unless a short-scale climatic cycle alters this rate of retreat.  相似文献   

Oxidation of CO on surface hematite in high CO₂ atmospheres     

John Lee Grenfell  Joachim W. Stock  Stefanie Gebauer 《Planetary and Space Science》2010,58(10):1252-1257

We propose a mechanism for the oxidation of gaseous CO into CO₂ occurring on the surface mineral hematite (Fe₂O₃(s)) in hot, CO₂-rich planetary atmospheres, such as Venus. This mechanism is likely to constitute an important source of tropospheric CO₂ on Venus and could at least partly address the CO₂ stability problem in Venus’ stratosphere, since our results suggest that atmospheric CO₂ is produced from CO oxidation via surface hematite at a rate of 0.4 petagrammes (Pg) CO₂ per (Earth) year on Venus which is about 45% of the mass loss of CO₂ via photolysis in the Venusian stratosphere. We also investigated CO oxidation via the hematite mechanism for a range of planetary scenarios and found that modern Earth and Mars are probably too cold for the mechanism to be important because the rate-limiting step, involving CO(g) reacting onto the hematite surface, proceeds much slower at lower temperatures. The mechanism may feature on extrasolar planets such as Gliese 581c or CoRoT-7b assuming they can maintain solid surface hematite which, e.g. starts to melt above about 1200 K. The mechanism may also be important for hot Hadean-type environments and for the emerging class of hot Super-Earths with planetary surface temperatures between about 600 and 900 K.  相似文献   

Progressive Build Up Of Co 2 In The AtmosphereOf Venus Through Multiple Volcanic Resurfacing Events     

Lopez  Ivan  Oyarzun  Roberto  Marquez  Alvaro  Doblas-Reyes  Francisco  Laurrieta  Alejandro 《Earth, Moon, and Planets》1998,81(3):187-192

In absence of other mechanisms, the main input of CO₂into the Venusian atmosphere is via volcanic out gassing. Since Venus can be regarded as a planet-wide large igneous province, we can expect large quantities of CO₂ being transferred into its atmosphere via volcanic out gassing. We have quantified the maximum possible amount of CO₂ that can be out gassed via a single massive episode of resurfacing of the planet. This figure (5.6 × 10¹⁹ kg of CO₂) is about 8 times smaller than the total CO₂ present in the Venusian atmosphere (4.55 × 10²⁰ kg CO₂). The lack of planet-wide, efficient mechanisms for the recycling of CO₂ on Venus indicates that CO₂ has progressively accumulated in the atmosphere. Based on these considerations we suggest that the “equivalent” to eight global resurfacing episodes would be required to account for the present values of CO_{2 atmosphere}. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

An improvement to the volcano-scan algorithm for atmospheric correction of CRISM and OMEGA spectral data   总被引：1，自引：0，他引：1  

Patrick C. McGuire  Janice L. Bishop  Adrian J. Brown  Giuseppe A. Marzo  Scott L. Murchie  Mario Parente  Ted L. Roush  Michael D. Smith  Michael J. Wolff 《Planetary and Space Science》2009,57(7):809-815

The observations of Mars by the CRISM and OMEGA hyperspectral imaging spectrometers require correction for photometric, atmospheric and thermal effects prior to the interpretation of possible mineralogical features in the spectra. Here, we report on a simple, yet non-trivial, adaptation to the commonly-used volcano-scan correction technique for atmospheric CO₂, which allows for the improved detection of minerals with intrinsic absorption bands at wavelengths between 1.9 and 2.1 μm. This volcano-scan technique removes the absorption bands of CO₂ by ensuring that the Lambert albedo is the same at two wavelengths: 1.890 and 2.011 μm, with the first wavelength outside the CO₂ gas bands and the second wavelength deep inside the CO₂ gas bands. Our adaptation to the volcano-scan technique moves the first wavelength from 1.890 μm to be instead within the gas bands at 1.980 μm, and for CRISM data, our adaptation shifts the second wavelength slightly, to 2.007 μm. We also report on our efforts to account for a slight ∼0.001 μm shift in wavelengths due to thermal effects in the CRISM instrument.  相似文献   

Phytochemical changes in leaves of subtropical grasses and fynbos shrubs at elevated atmospheric CO₂ concentrations     

D. Hattas  W.D. Stock  W.T. Mabusela  I.R. Green 《Global and Planetary Change》2005,47(2-4):181

The effects of elevated atmospheric CO₂ concentrations on plant polyphenolic, tannin, nitrogen, phosphorus and total nonstructural carbohydrate concentrations were investigated in leaves of subtropical grass and fynbos shrub species. The hypothesis tested was that carbon-based secondary compounds would increase when carbon gain is in excess of growth requirements. This premise was tested in two ecosystems involving plants with different photosynthetic mechanisms and growth strategies. The first ecosystem comprised grasses from a C₄-dominated, subtropical grassland, where three plots were subjected to three different free air CO₂ enrichment treatments, i.e., elevated (600 to 800 μmol mol⁻¹), intermediate (400 μmol mol⁻¹) and ambient atmospheric CO₂. One of the seven grass species, Alloteropsis semialata, had a C₃ photosynthetic pathway while the other grasses were all C₄. The second ecosystem was simulated in a microcosm experiment where three fynbos species were grown in open-top chambers at ambient and 700 μmol mol⁻¹ atmospheric CO₂ in low nutrient acid sands typical of south western coastal and mountain fynbos ecosystems. Results showed that polyphenolics and tannins did not increase in the grass species under elevated CO₂ and only in Leucadendron laureolum among the fynbos species. Similarly, foliar nitrogen content of grasses was largely unaffected by elevated CO₂, and among the fynbos species, only L. laureolum and Leucadendron xanthoconus showed changes in foliar nitrogen content under elevated CO₂, but these were of different magnitude. The overall decrease in nitrogen and phosphorus and consequent increase in C:N and C:P ratio in both ecosystems, along with the increase in polyphenolics and tannins in L. laureolum in the fynbos ecosystem, may negatively affect forage quality and decomposition rates. It is concluded that fast growing grasses do not experience sink limitation and invest extra carbon into growth rather than polyphenolics and tannins and show small species-specific chemical changes at elevated atmospheric CO₂ concentrations. Responses of fynbos species are varied and were species-specific.  相似文献   

Simulated responses of Pinus halepensis forest productivity to climatic change and CO₂ increase using a statistical model     

Cyrille Rathgeber  Antoine Nicault  Joël Guiot  Thierry Keller  Frdric Guibal  Philip Roche 《Global and Planetary Change》2000,26(4)

Tree ring chronologies provide long-term records of growth in natural environmental conditions and may be used to evaluate impacts of climatic change and CO₂ increase on forest productivity. This study focuses on 21 Pinus halepensis forest stands in calcareous Provence (in the south-east of France). A chronology of net primary productivity (NPP) both for the 20th century and for each stand was estimated using tree ring data (width and density). The response of each stand to climate in terms of NPP was statistically modelled using response functions. Anomalies between estimated NPP and NPP reconstructed by response functions were calculated to evaluate the fertilising effect of CO₂ increase on tree growth. The changes in anomalies during the 20th century were attributed to the effect of CO₂ increase. A multiplying factor (β) linking CO₂ concentration and stand productivity was then calculated, on the basis of the trend observed during the 20th century. In this study, the value of the β factor obtained under natural conditions (β=0.50) is consistent with those from controlled CO₂ enrichment experiments. Both response functions and the β factor were used to predict NPP changes for a 2×CO₂ scenario. The 2×CO₂ climate was obtained using predictions from Météo France's ARPEGE atmospheric general circulation model (AGCM) downscaled to Marseilles meteorological station. NPP increased significantly for nine stands solely when the climatic effect was taken into account. The main factors responsible for this enhancement were increased winter and early spring temperatures. When the fertilising effect of the CO₂ increase was added, NPP was significantly enhanced for 14 stands (i.e. NPP enhancement ranged from 8% to 55%). Although the effects of global change were slightly detectable during the 20th century, their acceleration is likely to lead to great changes in the future productivity of P. halepensis forests.  相似文献   

Einstein A-coefficients for rotational transitions in cyclopropenylidene     

A. K. Sharma  Suresh Chandra 《Journal of Astrophysics and Astronomy》1996,17(1-2):41-52

Einstein A-values are given for the electric dipole transitions in the C₃ H₂-molecule between the rotational levels of the vibrational ground state up to 85cm^-1. The mean radiation life-times of the levels are calculated from the Einstein A-values. These values can be used as input parameters for analysing the spectra of C₃H₂  相似文献   

Bifurcation of Relative Equilibria in the Main Problem of Artificial Satellite Theory for a Prolate Body     

Cédric Langbort 《Celestial Mechanics and Dynamical Astronomy》2002,84(4):369-385

In this paper, we study circular orbits of the J ₂ problem that are confined to constant-z planes. They correspond to fixed points of the dynamics in a meridian plane. It turns out that, in the case of a prolate body, such orbits can exist that are not equatorial and branch from the equatorial one through a saddle-center bifurcation. A closed-form parametrization of these branching solutions is given and the bifurcation is studied in detail. We show both theoretically and numerically that, close to the bifurcation point, quasi-periodic orbits are created, along with two families of reversible orbits that are homoclinic to each one of them.  相似文献   

Jets And Arcs In The Coma Of Comet Hale-Bopp From August 1996 To April 1997     

LAFFONT  CÉLINE  ROUSSELOT  P.  CLAIREMIDI  J.  MOREELS  G.  BOICE  D. C. 《Earth, Moon, and Planets》1997,78(1-3):211-217

An observation program for measuring the activity of Comet Hale-Bopp was conducted at the Observatoire de Haute Provence from August 1996 to April 1997. Narrow band images were obtained from the 120 cm telescope. A set of four filters at 513, 516, 527 and 682 nm was used to measure the C₂ emission in the (1,1) and (0,0) band and the intensity of the dust-scattered continuum. The luminosity of the central part of the coma was measured in the continuum and C₂ emissions, as a function of heliocentric distance before perihelion. The activity of the comet considerably increased between October 1996 and February 1997. The images obtained in August, September and October 1996 show the presence of strong jets. In February, March and April 1997, series of roughly concentric arcs were observed in the sunward hemisphere of the coma. The arcs were also detected in the spatial distribution of the I(682 nm)/I(527 nm) red color ratio and the I(513 nm)/I(516 nm) C₂ emission ratio. Using the I(513 nm)/I(516 nm) ratio as a parameter to measure the degree of excitation of C₂ molecules, we can show that the local production of gas, probably resulting from dust fragmentation, should be taken into account. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Preliminary Analysis of Photometric Variations of the Central Star of the Planetary Nebula Sh 2-71     

Zdeněk MikulÁšek  Luboš Kohoutek  Miloslav Zejda  Ondřej Pejcha 《Astrophysics and Space Science》2005,296(1-4):465-468

We confirm the presence of regular UBV(RI)_C light variations of the object in the center of the planetary nebula Sh 2-71, with an improved period of P = 68.132 ± 0.005 days. The shapes and amplitudes of light curves, in particular colours, are briefly discussed.  相似文献   

Astrophysical properties of red giants in three open clusters older than the hyades     

J. J. Clariá  E. Lapasset 《Journal of Astrophysics and Astronomy》1983,4(2):117-134

Results fromCMT ₁T₂ 1T2 broad-band and DDO intermediate-band photometry are presented for G and K giants in the old open clusters NGC. 2482, NGC 3680, and IC 4651. Two independent photometric criteria have been used to separate red field stars from the physical members of the clusters. Recent calibrations of the DDO andCMT ₁T₂ systems have been used to derive reddening, distance moduli, metallicities, effective temperatures, and surface gravities. Rough estimates of masses have also been made. The giants of NGC 2482 and IC 4651 have CN strengths nearly identical to the Hyades giants, while those of NGC 3680 are slightly richer in CN than the nearby K giants.CMT1T2 abundance analysis in NGC 2482 and NGC 3680 yield [Fe/H]_MT = - 0.1 ± 0.1 as derived from the iron lines, while abundances derived from the CNO - contaminated (C - M) index are 0.4 dex higher. BothCMT ₁T₂ and DDO data support the conclusion that 1C 4651, with [Fe/H] = + 0.2 ± 0.1, is on the metalrich side of the distribution of intermediate and old open clusters. Finally, the mass results suggest that the clump stars in NGC 3680 and. IC 4651 could have undergone mass loss before reaching their helium core burning phase of evolution. Supported in part by the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) of Argentina. Visiting astronomer of Cerro Tololo Inter-American Observatory supported by the National Science Foundation under contract No. AST 74-04128.  相似文献   

Oxygen airglow emission on Venus and Mars as seen by VIRTIS/VEX and OMEGA/MEX imaging spectrometers     

A. Migliorini  F. Altieri  G. Piccioni  A. Cardesín Moinelo  E. D’Aversa  B. Gondet 《Planetary and Space Science》2011,59(10):981-987

Imaging spectrometers are highly effective instruments for investigation of planetary atmospheres. They present the advantage of coupling the compositional information to the spatial distribution, allowing simultaneous study of chemistry and dynamics in the atmospheres of Venus and Mars. In this work, we summarize recent results about the O₂(a¹Δ_g) night and day glows, respectively obtained by VIRTIS/Venus Express and OMEGA/Mars Express, the imaging spectrometers currently in orbit around Venus and Mars. The case of the O₂(a¹Δ_g - X³Σ_g⁻) IR emission at 1.27 μm on the night side of Venus and the day side of Mars is analyzed, pointing out dynamical aspects of these planets, like the detection of gravity waves in their atmospheres. The monitoring of seasonal and daily airglow variations provides hints about the photochemistry on these planets.  相似文献   

The possible response of life zones in China under global climate change   总被引：5，自引：0，他引：5  

Xiongwen Chen  Xin-Shi Zhang  Bai-Lian Li 《Global and Planetary Change》2003,38(3-4):327-337

The response of natural vegetation to climate change is of global concern. In this research, an aggregated Holdridge Life Zone System was used to study the possible response of life zones in China under doubled atmospheric CO₂ concentration with the input climatic parameters at 0.5×0.5° resolution of longitude and latitude from NCAR regional climate model 2 (RegCM2) coupled with the CSIRO global climate model. The results indicate that the latitudinal distribution of life zones would become irregular because of the complicated climate change. In particular, new life zones, such as subtropical desert (SD), tropical desert (TDE) and tropical thorn woodland (TTW), would appear. Subtropical evergreen broadleaved forest (SEBF), tropical rainforest and monsoon forest (TRF), SD, TDE and TTW zones would appear in the northeastern China. Cool-temperate mixed coniferous and broadleaved forest (CMC) and warm-temperate deciduous broadleaved forest (WDBF) zones would appear at latitudes 25–35°N. The temperate desert (TD) in the western China would become Tibetan high-cold plateau (THP), SEBF, WDBF and temperate steppe (TS), and a large part of THP would be replaced by TRF, TDE, SEBF, TS and TTW. The relative area (distribution area/total terrestrial area) of CMC, TRF, TDE and TTW zone would increase about 3%, 21%, 3% and 6%, respectively. However, the relative area of SEBF, TS, TD and THP would decrease about 5%, 3%, 19% and 4%, respectively. In all, the relative area of forests (CCF, CMC, WDBF, SEBF, TRF) would increase about 15%, but the relative area of desert (TD, SD, TDE, and TTW) and THP would decrease about 9% and 4%, respectively. Therefore, responses of different life zones in China to climate change would be dramatic, and nationwide corridors should be considered for the conservation of migrating species under climate change.  相似文献