210 research outputs found
The origin of the supersoft X-ray--optical/UV flux anticorrelation in the symbiotic binary AG Draconis
AG Draconis produces a strong supersoft X-ray emission.The X-ray and
optical/UV fluxes are in a strict anticorrelation throughout the active and
quiescent phases. The aim of this contribution is to identify the source of the
X-ray emission and reveal the nature of the observed flux anticorrelation. For
this purpose we model the X-ray and UV observations with XMM-Newton, far-UV
spectroscopy from FUSE, low- and high-resolution IUE spectra and
optical/near-IR spectroscopic and/or photometric observations. Our analysis
showed that the supersoft X-ray emission is produced by the white dwarf
photosphere. The X-ray and far-UV fluxes make it possible to determine its
temperature unambiguously. The supersoft X-ray--optical/UV flux anticorrelation
is caused by the variable wind from the hot star. The enhanced hot star wind
gives rise to the optical bursts by reprocessing high-energy photons from the
Lyman continuum to the optical/UV.Comment: 9 pages, 2 figures, 3 tables. Submitted to AA on 25/11/2008, revised
on 27/05/200
A study of the expanding envelope of Nova V1974 Cyg 1992 based on IUE high resolution spectroscopy
We have carried out a detailed analysis of the IUE archival high resolution
spectra of the classical nova V1974 Cyg 1992. In addition to the P Cygni and
emission lines, two shortward shifted absorption systems are present. Evidence
is given that these absorptions originate in two separate expanding shells,
outside the wind layers where the emission lines are formed. The outer main
shell, containing most of the matter ejected at outburst, produces the
so-called ``principal absorption line system'', and the inner faster moving
second shell produces the so-called ``diffuse--enhanced absorption line
system''. The outflow velocity of the two shells increases exponentially with
time reaching a value of about 1750 km/s and 2900 km/s, respectively. We
suggest that the acceleration of the shells is the result of increasing
line-radiation pressure due to the UV-brightening of the star as the effective
radius decreases. Around day 60 the second shell has overtaken the slower
moving principal system shell, and merged with it. This explains: the sudden
disappearance of the diffuse line system near that date, the upward jump of 240
km/s in velocity of the principal system and the first detection of hard X-ray
emission on day 63. This velocity jump indicates that the main shell is about 4
times more massive than the second shell. The deceleration suffered by the
diffuse-enhanced system after the shock provides a shock temperature of about
1.6 KeV, in fairly good agreement with the temperature of the observed hard
X-ray emission.Comment: 19 pages, 11 figure
The SSS phase of RS Ophiuchi observed with Chandra and XMM-Newton I.: Data and preliminary Modeling
The phase of Super-Soft-Source (SSS) emission of the sixth recorded outburst
of the recurrent nova RS Oph was observed twice with Chandra and once with
XMM-Newton. The observations were taken on days 39.7, 54.0, and 66.9 after
outburst. We confirm a 35-sec period on day 54.0 and found that it originates
from the SSS emission and not from the shock. We discus the bound-free
absorption by neutral elements in the line of sight, resonance absorption lines
plus self-absorbed emission line components, collisionally excited emission
lines from the shock, He-like intersystem lines, and spectral changes during an
episode of high-amplitude variability. We find a decrease of the oxygen K-shell
absorption edge that can be explained by photoionization of oxygen. The
absorption component has average velocities of -1286+-267 km/s on day 39.7 and
of -771+-65 km/s on day 66.9. The wavelengths of the emission line components
are consistent with their rest wavelengths as confirmed by measurements of
non-self absorbed He-like intersystem lines. We have evidence that these lines
originate from the shock rather than the outer layers of the outflow and may be
photoexcited in addition to collisional excitations. We found collisionally
excited emission lines that are fading at wavelengths shorter than 15A that
originate from the radiatively cooling shock. On day 39.5 we find a systematic
blue shift of -526+-114 km/s from these lines. We found anomalous He-like f/i
ratios which indicates either high densities or significant UV radiation near
the plasma where the emission lines are formed. During the phase of strong
variability the spectral hardness light curve overlies the total light curve
when shifted by 1000sec. This can be explained by photoionization of neutral
oxygen in the line of sight if the densities of order 10^{10}-10^{11} cm^{-3}.Comment: 16 pages, 10 figures, 4 tables. Accepted by ApJ; v2: Co-author
Woodward adde
Harpagifer bispinis
This rocky, intertidal species has a relatively small range, but is common and abundant. There are no known major threats at this time; therefore, it is listed as Least Concern.Fil: Buratti, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Hüne, M.. Universidad Austral de Chile; ChileFil: Irigoyen, A.. No especifíca;Fil: Landaeta, M.. Universidad de Valparaíso; ChileFil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Vieira, J.P.. Universidade Federal Do Rio Grande.; Brasi
Patagonotothen tessellata
This demersal species inhabits nearshore rocky reefs and kelp forests in southern Chile and Argentina and has an estimated generation length of 5 years. The global-level center of its abundance is in the straits of southern Chile. Invasive Chinook salmon now occur throughout the straits of Chile, and this represents a potential major threat, including impacts from competition, predation and disease introduction. The invasion is expected to expand into other parts of its range (i.e. Argentina). The Chilean salmon aquaculture industry, which is the source of escaped individuals, is expected to expand in the near future. The centre, or the major proportion of its global population is concentrated in the area where this threat is greatest. This threat has been increasing over time, but probably began about 30 years ago. There are no data to quantify population trends at this time; and considering this major threat and the lack of understanding for the likely direct impact, it is listed as Data Deficient. It is highly recommended to conduct studies on population trends as well as the impacts from the invasive salmon. Recommended conservation actions include the continued protection of kelp forests from harvest and to improve management of invasive salmon and prevention of escapes.Fil: Hüne, M.. Universidad Austral de Chile; ChileFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Landaeta, M.. Universidad de Valparaíso; ChileFil: Buratti, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Irigoyen, A.. No especifíca;Fil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Vieira, J.P.. Universidade Federal Do Rio Grande.; Brasi
Paralichthys isosceles
This demersal species occurs from southern Brazil to Argentina and is taken in multi-species commercial´s fisheries that target demersal fishes through much of its range. It is a relatively minor component of the catch of Paralichthys species as compared to catch of the sympatric P. patagonicus. For purposes of this assessment, half of the global population is considered to occur in Brazil and the other half in Uruguay and Argentina. According to landings and catch per unit effort data, the demersal fish stocks of Brazil are inferred to have declined by at least 30% and possibly to 50%. Due to the lack of specific data for this species, an estimate for population decline is not available or cannot be suspected at this time. According to stock assessment and fisheries data, there is no decline detected in the demersal stock in Argentina and Uruguay and abundance indices show an increase in recent years (since 2014). Fishing effort continues at an unsustainable level in Brazil, the fishery is not well-monitored and conservation measures are insufficient. Conservation measures in Argentina and Uruguay include a total allowable catch limit and regular monitoring of stock status. Based on the potential major threat from overfishing in at least half of its global population, but lack of quantified data, it is listed as Data Deficient with a recommendation to improve fisheries monitoring, including the collection of species-specific data, as" "well as implement conservation measures to reduce effort in Brazilian fisheries.Fil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Vieira, J. P.. Universidade Federal do Rio Grande do Sul; BrasilFil: Buratti, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Irigoyen, A.. No especifíca;Fil: Landaeta, M.. Universidad de Valparaíso; ChileFil: Hüne, M.. Universidad Austral de Chile; Chil
Champsocephalus esox, Pike Icefish
This demersal species is endemic to the southern Patagonia Sea region where it occurs in kelp forests and fjords. Its physiology restricts it to waters of high oxygen concentration and low temperature, and its survivability is reduced when these conditions fluctuate. Based on survey data and observations of fishers catch, this species has declined by 80% since the 1980s in at least half of its range (the Chilean coast). The status of its population in the other half of its range (Argentina) is poorly understood due to the lack of surveys. Considering the uncertainty regarding its status in the other half of its range, it is conservatively suspected to have declined overall by 30% over the past three generation lengths (12-18 years). Threats include climate change (warming water temperatures), mortality as bycatch in artisanal fisheries and invasive salmon. It is listed as Vulnerable A2bcde. Additional survey work is needed to monitor and understand its population throughout its range. Research is needed on its life history and response to heat shock.Fil: Buratti, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Hüne, M.. Universidad Austral de Chile; ChileFil: Irigoyen, A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Landaeta, M.. Universidad de Valparaíso; ChileFil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Vieira, J.P.. Universidade Federal Do Rio Grande.; Brasi
Patagonotothen ramsayi
This species has a relatively small range on the continental shelf and slope of the southern part of the Patagonia Sea where it plays an important ecological role as a prey item for larger marine species. The majority of its global population is concentrated in southern Argentina, including the Malvinas Islands, where the main fishing ground is located. One generation length is estimated as 10 years. It is relatively slow-growing and late to maturity with relatively low fecundity, which may cause it to be susceptible to declines when facing heavy fishing pressure. Previous to 2006, it was mostly discarded as bycatch in large quantities beginning in the 1980s. A large-scale, commercial fishery began in 2007 in the Malvinas area. In areas outside the Malvinas closer to the Argentine mainland, it is taken in fisheries in relatively small amounts. According to stock assessment models based on catch per unit effort data and fishery independent trawl surveys, the estimated biomass for the period of 2005 to 2018 was highest in 2005 and then declined by 79% to a low in 2018. According to the 2019 and 2020 survey results, biomass has continued to decline. Biomass trends prior to 2005 are poorly understood, but based on these data, it is suspected that its population has declined by 40-50% on a global-level over the past one and a half generation lengths, or 15 years. In addition, declines in length at maturity and average length of individuals in the survey catch have also occurred. The cause of decline is poorly understood, but may be attributed in part to fishing activity or a shift in the spatial distribution of its abundance to areas adjacent to the Malvinas. Several fishery management measures are in place, catches have been at a relatively low level and it is not considered overfished. Due to the uncertainty associated with the cause of decline and lack of data prior to 2005, it is not possible to estimate the population trend to cover a three generation length period (either in the past or into the future) at this time. It is listed as Data Deficient with a strong recommendation to conduct studies to improve the understanding of this decline both within the Malvinas area and areas adjacent to it.Fil: Buratti, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Hüne, M.. Universidad Austral de Chile; ChileFil: Irigoyen, A.. No especifíca;Fil: Landaeta, M.. Universidad de Valparaíso; ChileFil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Vieira, J. P.. Universidade Federal Do Rio Grande.; Brasi
Cottoperca trigloides, Frogmouth
This widely distributed, demersal species is associated with rocky bottoms and kelp forests. It is discarded as bycatch in trawl fisheries, but this is not expected to be driving population declines approaching a Near Threatened or threatened level at this time; therefore, it is listed as Least Concern.Fil: Buratti, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Hüne, M.. Universidad Austral de Chile; ChileFil: Irigoyen, A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Landaeta, M.. Universidad de Valparaíso; ChileFil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Vieira, J. P.. Universidade Federal Do Rio Grande.; Brasi
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