Jordi L. Gutiérrez

Evolution and CNO yields of Z = 10-5 stars and possible effects on carbon-enhanced metal-poor production

Aims. Our main goals are to get a deeper insight into the evolution and final fates of intermediate-mass, extremely metal-poor (EMP) stars. We also aim to investigate the C, N, and O yields of these stars. Methods. Using the Monash University Stellar Evolution code MONSTAR we computed and analysed the evolution of stars of metallicity Z = 10-5 and masses between 4 and 9 M?, from their main sequence until the late thermally pulsing (super) asymptotic giant branch, TP-(S)AGB phase. Results. Our model stars experience a strong C, N, and O envelope enrichment either due to the second dredge-up process, the dredge-out phenomenon, or the third dredge-up early during the TP-(S)AGB phase. Their late evolution is therefore similar to that of higher metallicity objects. When using a standard prescription for the mass loss rates during the TP-(S)AGB phase, the computed stars are able to lose most of their envelopes before their cores reach the Chandrasekhar mass (mCh), so our standard models do not predict the occurrence of SNI1/2 for Z = 10-5 stars. However, we find that the reduction of only one order of magnitude in the mass-loss rates, which are particularly uncertain at this metallicity, would prevent the complete ejection of the envelope, allowing the stars to either explode as an SNI1/2 or become an electron-capture SN. Our calculations stop due to an instability near the base of the convective envelope that hampers further convergence and leaves remnant envelope masses between 0.25 M? for our 4 M? model and 1.5 M? for our 9 M? model. We present two sets of C, N, and O yields derived from our full calculations and computed under two different assumptions, namely, that the instability causes a practically instant loss of the remnant envelope or that the stars recover and proceed with further thermal pulses. Conclusions. Our results have implications for the early chemical evolution of the Universe and might provide another piece for the puzzle of the carbon-enhanced EMP star problem.

A probe of concepts for femto-satellites based on COTS

• It is possible to build a low cost, low weight and good enough performance Femto-Satellite • This Femto-Satellite built by the Wikisat team is based on Commercial-Of-The-Shelf and fulfills the N-Prize requirements • A list of subsystems and the preferred components were described

Terrene Meteorites on The Moon

The study of the origin of life on the Earth is impeded by the fact that very few ancient rocks from the era of the appearance of biological systems are preserved. The oldest sedimentary rock formations are about 3.9 billion years old, and even these show indications of the early emergence of life [1]. Impacts, tectonic activity and erosion have hopelessly destroyed all the information predating the aforementioned age. Nevertheless, here we show that the Moon could constitute an invaluable reservoir of very ancient terrestrial rocks, stripped off the surface of our planet during the great bombardment that took place shortly after the origin of the solar system. These rocks could store information about the origin of life on Earth that our own planet wiped aeons ago.

SIXE: An X-ray experiment for the MINISAT platform

SIXE (Spanish Italian X-ray Experiment) is an X-ray payload with geometric area of ~3200 cm2 , formed by four identical gas-filled Multiwire Proportional Counters devoted for a long term spectroscopy of selected X-ray sources in the energy range ~3-60 KeV. The spectral resolution of ~5% for E>35 KeV and ?E/E=60/E1/2 for E<35 KeV, the continuum sensitivity (3o in 105 s) of ~3•10-6ph/cm2 •KeV, the line detection sensitivity (3o in 105 s) of ~3.5•10-6ph /cm2 •KeV, the time accuracy of 0.1 ms, the experiment weight of ~90 Kg, the full dimensions including the electronic box of ~660x660x400 mm3, the power budget of -40 W, the telemetry rate of :=100 Kbit/s and on-board memory of ~2 Gbytes makes this experiment fully compatible for a minisatellite mission, such as for istance the spanish MINISAT 02. The main scientific goal of SIXE is the study of the short and long term spectral and intensity variabilities of few selected extragalactic and galactic X-ray sources, such as quasars, Seyfert galaxies, high and low mass X-ray binaries, etc. Since the sensitivity and the energy resolution of SIXE are rather good, it is possible to study the behaviour of the eventual Fe lines with respect to the continuum emission. This possibility of SIXE is unique for the present generation of X-ray experiments, since no one is dedicated to long term monitoring of X-ray sources.SIXE (Spanish Italian X-ray Experiment) is an X-ray detector withgeometric area of 2300 cm2, formed by four identical gas-filledMulticell Proportional Counters, and devoted to study the long termspectroscopy of selected X-ray sources in the energy range 3–50 keV. Themain characteristics of SIXE are: time accuracy of 1 microsecond,spectral resolution of 5% for E > 35 keV and 46/√E% for E <35 keV, continuum sensitivity (3σ in 105 s) of 2 ×10-6 ph cm-2 s-1 keV-1, and line sensitivity (3σin 105 s) of 8 × 10-6 ph cm-2 s-1. The size of theinstruments and the requirements of the payload (weight 103 kg, fulldimensions 660 × 660 × 450 mm3, power budget < 60 W,on-board memory 2 Gbits, telemetry rate < 100 kbps) make this experimentfully compatible with the MINISAT platform.The main scientific goal of SIXE is the study of short and long termvariability of some of the most important X-ray sources. To do that a fewselected extragalactic and galactic X-ray sources will be selected toperform a dedicated and extensive monitoring program. The mission willprovide in this way the unique opportunity for the study of X-ray sourceswith a temporal accuracy of 1 microsecond all through the time range10-5 :107 s.

Life Extinctions and the Gravitational Collapse of Onemg Electron-Degenerate Objects

Supernova explosions have been considered a possible (although improbable) thread to life on Earth. In 1987, a massive star exploded in the Large Magellanic Cloud and, coinciding with the arrival of the first photons of that event, several neutrino observatories detected a burst of neutrinos. This was the final evidence needed to validate the model of gravitational collapse supernovae.

SIXE: An X-ray experiment for a minisatellite

SIXE (Spanish Italian X-ray Experiment) is an X-ray detector with geometric area of 2300 cm2, formed by four identical gas-filled Multicell Proportional Counters, and devoted to study the long term spectroscopy of selected X-ray sources in the energy range 3–50 keV. The main characteristics of SIXE are: time accuracy of 1 microsecond, spectral resolution of 5% for E>35 keV and 46/E% for E<35 keV, continuum sensitivity (3σ in 105 s) of 2×10−6 ph/cm2⋅s−1⋅keV−1, and line sensitivity (3σ in 105 s) of 8×10−6 ph/cm2⋅s−1. The size of the instruments and the requirements of the payload (weight 103 kg, full dimensions 660×660×450 mm3, power budget <60 W, on-board memory 2 Gbits, telemetry rate <100 kbps) make this experiment fully compatible with a minisatellite mission. The experiment, whose feasibility study has just been finished, has been proposed for flying on the Spanish MINISAT-02 satellite, in a 3 years long mission starting about 2002–2004. The main scientific goal is the study of the short and long term ...