59 research outputs found
Radiolysis of ammonia-containing ices by energetic, heavy and highly charged ions inside dense astrophysical environments
Deeply inside dense molecular clouds and protostellar disks, the interstellar
ices are protected from stellar energetic UV photons. However, X-rays and
energetic cosmic rays can penetrate inside these regions triggering chemical
reactions, molecular dissociation and evaporation processes. We present
experimental studies on the interaction of heavy, highly charged and energetic
ions (46 MeV Ni^13+) with ammonia-containing ices in an attempt to simulate the
physical chemistry induced by heavy ion cosmic rays inside dense astrophysical
environments. The measurements were performed inside a high vacuum chamber
coupled to the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions
Lourds) in Caen, France.\textit{In-situ} analysis is performed by a Fourier
transform infrared spectrometer (FTIR) at different fluences. The averaged
values for the dissociation cross section of water, ammonia and carbon monoxide
due to heavy cosmic ray ion analogs are ~2x10^{-13}, 1.4x10^{-13} and
1.9x10^{-13} cm, respectively. In the presence of a typical heavy cosmic
ray field, the estimated half life for the studied species is 2-3x10^6 years.
The ice compaction (micropore collapse) due to heavy cosmic rays seems to be at
least 3 orders of magnitude higher than the one promoted by (0.8 MeV) protons .
In the case of the irradiated H2O:NH3:CO ice, the infrared spectrum at room
temperature reveals five bands that were tentatively assigned to vibration
modes of the zwitterionic glycine (+NH3CH2COO-).Comment: Accepted to be published in Astronomy and Astrophysics; Number of
pages: 12; Number of Figures: 7; Number of Tables:
Variabilidade espectral de estrelas T Tauri: GQ Lupi
Bolsa de Iniciação cientĂfica CNPQApresentamos a sĂ©rie temporal de observações de baixa resolução da estrela GQ Lupi, uma estrela T Tauri que apresenta fortes indĂcios de um disco de acresção circunstelar. Nosso conjunto de dados consiste em 18 observações realizadas durante 18 noites consecutivas no mĂŞs de Fevereiro de 1999. Medimos a distribuição do excesso de contĂnuo (velamento) e determinamos o velamento mĂ©dio para cada noite de observação. A sĂ©rie temporal do velamento apresentou um comportamento senoidal com um perĂodo de aproximadamente 13 dias. Acreditamos que uma mancha quente na superfĂcie estelar que rotacional junto com a estrela Ă© a responsável por esse comportamento do velamento. A Fotometria da Gq Lupi encontrada na literatura e nossas observações espectrofotomĂ©tricas de 1998 confirmam este perĂodo encontrado para o velamento. A sĂ©rie temporal do velamento nĂŁo apresentou uma boa correlação com as linhas de emissĂŁo. PorĂ©m, correlações entre as linhas de emissĂŁo indicam uma regiĂŁo comum de formação ou um mecanismo fĂsico governando suas luminosidades ao mesmo tempo. Os perfis P Cygni invertido praticamente desapareceram em relação aos dados de 1998. As observações foram realizadas no European Southern Observatory, La Silla, Chile sob o acordo ESO-ON
Exploring Kepler Giant Planets in the Habitable Zone
The Kepler mission found hundreds of planet candidates within the habitable
zones (HZ) of their host star, including over 70 candidates with radii larger
than 3 Earth radii () within the optimistic habitable zone (OHZ)
(Kane et al. 2016). These giant planets are potential hosts to large
terrestrial satellites (or exomoons) which would also exist in the HZ. We
calculate the occurrence rates of giant planets (~3.0--25~) in
the OHZ and find a frequency of for G stars, for K stars, and for M stars. We compare this with
previously estimated occurrence rates of terrestrial planets in the HZ of G, K
and M stars and find that if each giant planet has one large terrestrial moon
then these moons are less likely to exist in the HZ than terrestrial planets.
However, if each giant planet holds more than one moon, then the occurrence
rates of moons in the HZ would be comparable to that of terrestrial planets,
and could potentially exceed them. We estimate the mass of each planet
candidate using the mass-radius relationship developed by Chen & Kipping
(2016). We calculate the Hill radius of each planet to determine the area of
influence of the planet in which any attached moon may reside, then calculate
the estimated angular separation of the moon and planet for future imaging
missions. Finally, we estimate the radial velocity semi-amplitudes of each
planet for use in follow up observations.Comment: 19 Pages, 16 Figures, 5 Table
Como seria trabalhar astrobiologia na sala de aula?
Neste trabalho sĂŁo apresentados os resultados preliminares de uma aula experimental vi¬sando conhecer os subsunçores dos alunos de ensino mĂ©dio a respeito da Astrobiologia. Este tema foi escolhido de modo a potencializar a aprendizagem significativa devido a sua natureza interdisciplinar. A aula foi aplicada em uma turma de terceiro perĂodo do curso mĂ©dio tĂ©cnico em controle ambien¬tal em uma escola pĂşblica do municĂpio de NilĂłpolis. Os subsunçores expressos, por intermĂ©dio de um questionário com perguntas abertas e fechadas, versavam sobre a definição de Astrobiologia e da relacionabilidade entre as disciplinas no ensino mĂ©dio. A partir dos dados coletados definiram-se os descritores dos grupos de respostas similares. Os resultados mostraram que muitos ainda desconhecem o tema abordado, porĂ©m possuem concepções prĂ©vias a respeito de vida extraterrestre, possivelmente devido Ă s influĂŞncias de filmes de ficção cientĂfica. AlĂ©m disso, foram encontrados muitos elementos de interdisciplinaridade nas respostas dos alunos o que indica a relevância do tema para promover a aprendizagem significativa
Production of Oxidants by Ion Bombardment of Icy Moons in the Outer Solar System
Our groups in Brazil, France and Italy have been active, among others in the world, in performing experiments on physical-chemical effects induced by fast ions colliding with solids (frozen gases, carbonaceous and organic materials, silicates, etc.) of astrophysical interest. The used ions span a very large range of energies, from a few keV to hundreds MeV. Here we present a summary of the results obtained so far on the formation of oxidants (hydrogen peroxide and ozone) after ion irradiation of frozen water, carbon dioxide and their mixtures. Irradiation of pure water ice produces hydrogen peroxide whatever is the used ion and at different temperatures. Irradiation of carbon dioxide and water frozen mixtures result in the production of molecules among which hydrogen peroxide and ozone. The experimental results are discussed in the light of the relevance they have to support the presence of an energy source for biosphere on Europa and other icy moons in the outer Solar System.This research has been supported by the European COST Action CM0805: The Chemical Cosmos.Boduch, P.; Da Silveira, EF.; Domaracka, A.; Gomis Hilario, O.; Lv, XY.; Palumbo, ME.; Pilling, S.... (2011). Production of Oxidants by Ion Bombardment of Icy Moons in the Outer Solar System. Advances in Astronomy. 1-10. doi:10.1155/2011/327641S11
Magnetometry of the classical T Tauri star GQ Lup: non-stationary dynamos & spin evolution of young Suns
We report here results of spectropolarimetric observations of the classical T
Tauri star (cTTS) GQ Lup carried out with ESPaDOnS at the Canada-France-Hawaii
Telescope (CFHT) in the framework of the "Magnetic Protostars and Planets"
(MaPP) programme, and obtained at 2 different epochs (2009 July & 2011 June).
From these observations, we first infer that GQ Lup has a photospheric
temperature of 4,300+-50\^A K and a rotation period of 8.4+-0.3 d; it implies
that it is a 1.05+-0.07 Msun star viewed at an inclination of ~30deg, with an
age of 2-5 Myr, a radius of 1.7+-0.2 Rsun, and has just started to develop a
radiative core.
Large Zeeman signatures are clearly detected at all times, both in
photospheric lines & in accretion-powered emission lines, probing longitudinal
fields of up to 6 kG and hence making GQ Lup the cTTS with the strongest
large-scale fields known as of today. Rotational modulation of Zeeman
signatures is clearly different between our 2 runs, demonstrating that
large-scale fields of cTTSs are evolving with time and are likely produced by
non-stationary dynamo processes.
Using tomographic imaging, we reconstruct maps of the large-scale field, of
the photospheric brightness & of the accretion-powered emission of GQ Lup. We
find that the magnetic topology is mostly poloidal & axisymmetric; moreover,
the octupolar component of the large-scale field (of strength 2.4 & 1.6 kG in
2009 & 2011) dominates the dipolar component (of strength ~1 kG) by a factor of
~2, consistent with the fact that GQ Lup is no longer fully-convective.
GQ Lup also features dominantly poleward magnetospheric accretion at both
epochs. The large-scale dipole of GQ Lup is however not strong enough to
disrupt the surrounding accretion disc further than about half-way to the
corotation radius, suggesting that GQ Lup should rapidly spin up like other
similar partly-convective cTTSs (abridged).Comment: MNRAS, in press (17 pages, 10 figures, 1 table
Formation of unsaturated hydrocarbons in interstellar ice analogs by cosmic rays
The formation of double and triple C-C bonds from the processing of pure
c-C6H12 (cyclohexane) and mixed H2O:NH3:c-C6H12 (1:0.3:0.7) ices by
highly-charged, and energetic ions (219 MeV O^{7+} and 632 MeV Ni^{24+}) is
studied. The experiments simulate the physical chemistry induced by medium-mass
and heavy-ion cosmic rays in interstellar ices analogs. The measurements were
performed inside a high vacuum chamber at the heavy-ion accelerator GANIL
(Grand Accel\'erat\'eur National d'Ions Lourds) in Caen, France. The gas
samples were deposited onto a polished CsI substrate previously cooled to 13 K.
In-situ analysis was performed by a Fourier transform infrared (FTIR)
spectrometry at different ion fluences. Dissociation cross section of
cyclohexane and its half-life in astrophysical environments were determined. A
comparison between spectra of bombarded ices and young stellar sources
indicates that the initial composition of grains in theses environments should
contain a mixture of H2O, NH3, CO (or CO2), simple alkanes, and CH3OH. Several
species containing double or triple bounds were identified in the radiochemical
products, such as hexene, cyclohexene, benzene, OCN-, CO, CO2, as well as
several aliphatic and aromatic alkenes and alkynes. The results suggest an
alternative scenario for the production of unsaturated hydrocarbons and
possibly aromatic rings (via dehydrogenation processes) in interstellar ices
induced by cosmic ray bombardment.Comment: 14 pages, 10 figures, 4 tables. Accepted to be published in MNRA
Exploring Kepler Giant Planets in the Habitable Zone
The Kepler mission found hundreds of planet candidates within the Habitable Zones (HZ) of their host star, including over 70 candidates with radii larger than three Earth radii (R⊕) within the optimistic HZ (OHZ). These giant planets are potential hosts to large terrestrial satellites (or exomoons) which would also exist in the HZ. We calculate the occurrence rates of giant planets (R_p = 3.0–25 R⊕) in the OHZ, and find a frequency of (6.5 ± 1.9)% for G stars, (11.5 ± 3.1)% for K stars, and (6 ± 6)% for M stars. We compare this with previously estimated occurrence rates of terrestrial planets in the HZ of G, K, and M stars and find that if each giant planet has one large terrestrial moon then these moons are less likely to exist in the HZ than terrestrial planets. However, if each giant planet holds more than one moon, then the occurrence rates of moons in the HZ would be comparable to that of terrestrial planets, and could potentially exceed them. We estimate the mass of each planet candidate using the mass–radius relationship developed by Chen & Kipping. We calculate the Hill radius of each planet to determine the area of influence of the planet in which any attached moon may reside, then calculate the estimated angular separation of the moon and planet for future imaging missions. Finally, we estimate the radial velocity semi-amplitudes of each planet for use in follow-up observations
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