Papers by E. Janot-pacheco
Proceedings of the International Astronomical Union, 2018
If biologically complex molecules as DNA were present in the extraterrestrial targets, their spec... more If biologically complex molecules as DNA were present in the extraterrestrial targets, their spectral signatures would be rather difficult to be unambiguously identified. As a matter of fact, the molecular array of a single nucleobasis will generate a tangled spectral signature. On the other hand, a part of it, e.g. bands due to the group of HNCO of guanine may have been detected but associated to smaller molecules, e.g. isocianic acid (HNCO). However, if comprised in a nucleobasis, its detection would be misinterpreted. Five key transitions were preliminarly selected for either purines and pyrimidines that should be observed together in the same target. If this happens, it may be that we are detecting the whole from its parts.
International Astronomical Union Colloquium, 2000
The Be shell star EW Lac was observed in September 1993 during a multi-site campaign. Results fro... more The Be shell star EW Lac was observed in September 1993 during a multi-site campaign. Results from visual spectroscopy and polarimetry are summarized here. He I 6678 profiles have been compared to previous observations held in 1989 and show an additional complex and highly variable circumstellar component which can due to material expelled from the star just prior to these observations. Two groups of frequencies are found again in 1993 observations compared with 1989 ones. In the frame of nrp, they could be associated to low degree g-modes.
Environmental Research Letters, 2018
Human beings are constantly exposed to many kinds of environmental agents which affect their heal... more Human beings are constantly exposed to many kinds of environmental agents which affect their health and lifespan. Galactic cosmic rays (GCRs) are the main source of ionizing radiation in the lower troposphere, in which secondary products can penetrate the ground and underground layers. GCRs affect the physical-chemical properties of the terrestrial atmosphere, as well as the biosphere. GCRs are modulated by solar activity and latitudinal geomagnetic field distribution. In our ecological/populational retrospective study, we analyzed the correlation between the annual flux of local secondary GCR-induced ionization (CRII) and mortality rates in the city of Sao Paulo, Brazil, between 1951-2012. The multivariate linear regression analyses adjusted by demographic and weather parameters showed that CRII are significantly correlated with total mortality, infectious disease mortality, maternal mortality, and perinatal mortality rates (p < 0.001). The underlying mechanisms are still unclear. Further cross-sectional and experimental cohort studies are necessary to understand the biophysical mechanisms of the association found here.
International Astronomical Union Colloquium, 2000
In addition to the common applications (temperature, magnetic field, abundance distributions) the... more In addition to the common applications (temperature, magnetic field, abundance distributions) the Doppler Imaging technique can also be applied to non-radial stellar pulsations (NRP). Due to their rapid rotation, the Be stars are ideal candidates for Doppler Imaging. However, for the stars for which the periodic temporal line profile variability is produced by multiple mode NRP, the classical Doppler image in not an appropriate representation. When the corotating frequencies of existing pulsation modes are non-zero, the reference frame in which the resulting NRP is quasi-stationary cannot be defined. The technique can be applied “mode-by-mode”, which is illustrated in time-wavelength and Fourier frequency domain, using the time-resolved sequence of high resolution, high signal-to-noise ratio spectra of the Be star ζ Oph.
Pulsation, Rotation and Mass Loss in Early-Type Stars, 1994
A New Paradigm for Habitability in Planetary Systems: the Extremophilic Zone
Arxiv preprint arXiv:0811.1080, 2008
We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The develop... more We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working Group. With a few illustrative examples, we show how CoRoT data will help to address various problems associated with present open questions of stellar structure and evolution.
The Astronomical Journal, 2005
Its intention is to make the ground-based observations obtained in preparation of the asteroseism... more Its intention is to make the ground-based observations obtained in preparation of the asteroseismology program available in a simple and efficient way. It contains spectroscopic and photometric data together with inferred physical parameters for more than 1500 objects gathered since 1998 January 1998 in 6 years of observational campaigns. In this paper, the main functions and characteristics of the system are described.
Communications in Asteroseismology, 2009
About one year after the end of the first observational run and six months after the first CoRoT ... more About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first results to illustrate how these data of unprecedented quality shed a new light on the field of stellar seismology.
Astronomy & Astrophysics, 2013
Context. To date, the CoRoT space mission has produced more than 124 471 light curves. Classifyin... more Context. To date, the CoRoT space mission has produced more than 124 471 light curves. Classifying these curves in terms of unambiguous variability behavior is mandatory for obtaining an unbiased statistical view on their controlling root-causes. Aims. The present study provides an overview of semi-sinusoidal light curves observed by the CoRoT exo-field CCDs. Methods. We selected a sample of 4206 light curves presenting well-defined semi-sinusoidal signatures. The variability periods were computed based on Lomb-Scargle periodograms, harmonic fits, and visual inspection. Results. Color-period diagrams for the present sample show the trend of an increase of the variability periods as long as the stars evolve. This evolutionary behavior is also noticed when comparing the period distribution in the Galactic center and anti-center directions. These aspects indicate a compatibility with stellar rotation, although more information is needed to confirm their rootcauses. Considering this possibility, we identified a subset of three Sun-like candidates by their photometric period. Finally, the variability period versus color diagram behavior was found to be highly dependent on the reddening correction.
Astronomy & Astrophysics, 2009
The relatively large number of nearby radio-quiet and thermally emitting isolated neutron stars (... more The relatively large number of nearby radio-quiet and thermally emitting isolated neutron stars (INSs) discovered in the ROSAT All-Sky Survey, dubbed the "Magnificent Seven", suggests that they belong to a formerly neglected major component of the overall INS population. So far, attempts to discover similar INSs beyond the solar vicinity failed to confirm any reliable candidate. The good positional accuracy and soft X-ray sensitivity of the EPIC cameras onboard the XMM-Newton satellite allow us to efficiently search for new thermally emitting INSs. We used the 2XMMp catalogue to select sources with no catalogued candidate counterparts and with X-ray spectra similar to those of the Magnificent Seven, but seen at greater distances and thus undergoing higher interstellar absorptions. Identifications in more than 170 astronomical catalogues and visual screening allowed us to select fewer than 30 good INS candidates. In order to rule out alternative identifications, we obtained deep ESO-VLT and SOAR optical imaging for the X-ray brightest candidates. We report here on the optical follow-up results of our search and discuss the possible nature of 8 of our candidates. A high X-ray-to-optical flux ratio together with a stable flux and soft X-ray spectrum make the brightest source of our sample, 2XMM J104608.7-594306, a newly discovered thermally emitting INS. The X-ray source 2XMM J010642.3+005032 has no evident optical counterpart and should be further investigated. The remaining X-ray sources are most probably identified with cataclysmic variables and active galactic nuclei, as inferred from the colours and flux ratios of their likely optical counterparts. Beyond the finding of new thermally emitting INSs, our study aims at constraining the space density of this Galactic population at great distances and at determining whether their apparently high density is a local anomaly or not.
Astronomy & Astrophysics, 2007
Context. LS 5039 has been observed with several X-ray instruments so far showing quite steady emi... more Context. LS 5039 has been observed with several X-ray instruments so far showing quite steady emission in the long term and no signatures of accretion disk. The source also presents X-ray variability at orbital timescales in flux and photon index. The system harbors an O-type main sequence star with moderate mass-loss. At present, the link between the X-rays and the stellar wind is unclear. Aims. We study the X-ray fluxes, spectra, and absorption properties of LS 5039 at apastron and periastron passages during an epoch of enhanced stellar mass-loss, and the long term evolution of the latter in connection with the X-ray fluxes. Methods. New XMM-Newton observations were performed around periastron and apastron passages in September 2005, when the stellar wind activity was apparently higher. April 2005 Chandra observations on LS 5039 were revisited. Moreover, a compilation of Hα EW data obtained since 1992, from which the stellar mass-loss evolution can be approximately inferred, was carried out. Results. XMM-Newton observations show higher and harder emission around apastron than around periastron. No signatures of thermal emission or a reflection iron line indicating the presence of an accretion disk are found in the spectrum, and the hydrogen column density (N H) is compatible with being the same in both observations and consistent with the interstellar value. 2005 Chandra observations show a hard X-ray spectrum, and possibly high fluxes, although pileup effects preclude conclusive results from being obtained. The Hα EW shows yearly variations of ∼10%, and does not seem to be correlated with X-ray fluxes obtained at similar phases, unlike what is expected in the wind accretion scenario. Conclusions. 2005 XMM-Newton and Chandra observations are consistent with 2003 RXTE/PCA results, namely moderate flux and spectral variability at different orbital phases. The constancy of the N H seems to imply that either the X-ray emitter is located at > ∼ 10 12 cm from the compact object, or the density in the system is 3 to 27 times smaller than that predicted by a spherical symmetric wind model. We suggest that the multiwavelength non-thermal emission of LS 5039 is related to the observed extended radio jets and is unlikely to be produced inside the binary system.
Astronomy & Astrophysics, 2002
66 Oph is a Be star seen under a moderate inclination angle that shows strong variability from UV... more 66 Oph is a Be star seen under a moderate inclination angle that shows strong variability from UV to IR wavelengths. A concise review of long-term variability history is given. High resolution, high S /N spectroscopic observations obtained in 1997, 1998 and 2001 and spectropolarimetric observations obtained in 2000 are presented. These observations occurred during a long-term decrease of Hα intensity. Fundamental parameters of the star have been revisited from Barbier-Chalonge-Divan (BCD) calibrations. New V sin i values are obtained using Fourier transforms applied to observed helium lines and a rotational frequency f rot = 1.29 c d −1 is determined. Time series analysis and Fourier Doppler Imaging (FDI) of He i lines (4713, 4921, 5876 and 6678 Å) lead for the first time to the detection of multi-periodicity in 66 Oph. The two main frequencies found are f = 2.22 c d −1 and f = 4.05 c d −1. They are attributed to non-radial pulsations and can be associated with mode degree = 2 and = 3, respectively. Inspection of Stokes V profiles suggests the presence of a weak Zeeman signature but further observations are needed to confirm the detection of a magnetic field in 66 Oph.
Astronomy and Astrophysics, 2004
Differential interferometry (DI) is a technique that combines high spectral resolution with high ... more Differential interferometry (DI) is a technique that combines high spectral resolution with high spatial resolution. It is particularly suited to probe mechanisms that induce chromatic signatures, such as large scale mass motions. We thus investigate the use of DI combined with the Fourier transform method to study the stellar surface differential rotation. We show that, compared to spectroscopy, DI has the double advantage of allowing the use of all available Fourier frequencies as well as of disentangling the stellar differential rotation rate and the inclination angle. We derive some reference analytical expressions of DI observables. It is shown that the foreseen instrumental performances of the spectro-interferometer VLTI/AMBER are high enough to study the stellar differential rotation.
Astronomy & Astrophysics, 2003
Line profile variations (lpv) in He , Fe , Mg and Si transitions were detected in the Be... more Line profile variations (lpv) in He , Fe , Mg and Si transitions were detected in the Be star η Cen (HD 127972) by means of high resolution and S /N spectroscopic observations obtained in six epochs from May 1996 to April 2001. They were interpreted in terms of nonradial pulsations (NRPs). Time analysis was performed using Cleanest algorithm and showed the following frequencies with high order of significance: 0.61 c/d, 1.48 c/d, 3.81 c/d, 5.31 c/d, 9.24 c/d and 10.35 c/d. From phase variation diagrams we estimated mode degrees in the range 3-8. If the 10.35 c/d frequency is considered the first harmonic of 5.31 c/d, the corresponding azimuthal number of the mode is |m| = 4 ± 2. Except for 0.61 c/d, all other frequencies are compatible with NRPs. During the period of progressive activity enhancement in the He 6678 line, a strengthening of Balmer emission lines was observed. From Mar. 12 to Mar. 23, 2000, we noticed rapid variations of both Hα peak separation and V/R ratios. Using a simple model for the Hα line emission formation, we outlined an explanation for the season-averaged Hα emission variation in terms of changes of the mass density in the circumstellar envelope. The fundamental parameters of η Cen were analyzed using several methods. The adopted ones account for the stellar fast rotation, which helped us not only to estimate the stellar rotational frequency, but also to show that the star is in the middle of its main sequence life span.
Astronomy & Astrophysics, 2006
A growing number of early Be stars exhibit X-ray luminosities that are intermediate between those... more A growing number of early Be stars exhibit X-ray luminosities that are intermediate between those typical of early type stars and those emitted by most Be/X-ray binaries in quiescence. We report on XMM-Newton observations of two such Be stars, SAO 49725 and HD 161103, which were originally discovered in a systematic cross-correlation between the ROSAT all-sky survey and SIMBAD. The new observations confirm the X-ray luminosity excess (L X ∼ 10 32−33 erg s −1) and the hardness of their X-ray spectra, which are both unusual for normal early type stars. An iron Kα complex is clearly detected in HD 161103 in which the H-like, He-like, and fluorescent components are resolved, while strong evidences also exist for the presence of similar features in SAO 49725. X-ray spectra can be equally well-fitted by a thermal plasma (mekal) with T ∼ 10 8 K and solar abundances or by a power law + iron line model with photon index ∼1.5-1.8, both with a soft thermal component with T ∼ 10 7 K. The intensity of the fluorescence 6.4 keV line reflects the presence of large amounts of cold material close to the X-ray sources and strongly argues against accretion onto a companion neutron star in a large orbit. On the other hand, the probable thermal origin of the X-ray emission, as supported by the ionised iron lines, disagrees with those observed in all known Be/X-ray binaries, in which a non-thermal component is always required. Remarkably, the X-ray features are similar to those of white dwarves in several cataclysmic variables. There is no evidence of high frequency pulsations in neither of the two systems. However, a large oscillation in the light curve of HD 161103 with P ∼ 3200 s is readily detected. The X-ray light curve of SAO 49725 exhibits clear variability by ∼80% on time scales as short as ∼1000 s. New optical observations provide updated spectral types (B0.5 III-Ve) and disclose a dense, large, and apparently stable circumstellar disc for both stars. The nature of the excess X-ray emission is discussed in light of the models proposed for γ Cas, magnetic disc-star interaction, or accretion onto a compact companion object-whether neutron star or white dwarf. These two new objects, added to similar cases discovered in XMM-Newton surveys, point to the emergence of a new class of γ Cas analogs.
Astronomy & Astrophysics, 2009
Context. The origin of the short-term variability in Be stars remains a matter of controversy. Pu... more Context. The origin of the short-term variability in Be stars remains a matter of controversy. Pulsations and rotational modulation are the components of the favored hypothesis. Aims. We present our analysis of CoRoT data of the B8IIIe star HD 175869 observed during the first short run in the center direction (SRC1). Methods. We review both the instrumental effects visible in the CoRoT light curve and the analysis methods used by the CoRoT Be team. We applied these methods to the CoRoT light curve of the star HD 175869. A search for line-profile variations in the spectroscopic data was also performed. We also searched for a magnetic field, by applying the LSD technique to spectropolarimetric data. Results. The light curve exhibits low-amplitude variations of the order of 300 μmag with a double wave shape. A frequency within the range determined for the rotational frequency and 6 of its harmonics are detected. The main frequency and its first harmonic exhibit amplitude variations of a few days. Other significant frequencies of low-amplitude from 25 to a few μmag are also found. The analysis of line profiles from ground-based spectroscopic data does not detect any variation. In addition, no Zeeman signature was found. Conclusions. Inhomogeneities caused by stellar activity in or just above the photosphere are proposed to produce the photometric variability detected by CoRoT in the Be star HD 175869. The hypothesis that non-radial pulsations are the origin of these variations cannot be excluded.
Astronomy & Astrophysics, 2006
In preparation for the COROT space mission, we determined the fundamental parameters (spectral ty... more In preparation for the COROT space mission, we determined the fundamental parameters (spectral type, temperature, gravity, V sin i) of the Be stars observable by COROT in its seismology fields (64 Be stars). We applied a careful and detailed modeling of the stellar spectra, taking into account the veiling caused by the envelope, as well as the gravitational darkening and stellar flattening due to rapid rotation. Evolutionary tracks for fast rotators were used to derive stellar masses and ages. The derived parameters will be used to select Be stars as secondary targets (i.e. observed for 5 consecutive months) and short-run targets of the COROT mission. Furthermore, we note that the main part of our stellar sample falls in the second half of the main sequence life time, and that in most cases the luminosity class of Be stars is inaccurate in characterizing their evolutionary status.
Astrobiology, 2011
In this experimental study, cells of the radiation-resistant bacterium Deinococcus radiodurans we... more In this experimental study, cells of the radiation-resistant bacterium Deinococcus radiodurans were exposed to several different sources of radiation chosen to replicate the charged particles found in the solar wind. Naked cells or cells mixed with dust grains (basalt or sandstone) differing in elemental composition were exposed to electrons, protons, and ions to determine the probability of cell survival after irradiation. Doses necessary to reduce the viability of cell population to 10% (LD 10) were determined under different experimental conditions. The results of this study indicate that low-energy particle radiation (2-4 keV), typically present in the slow component of the solar wind, had no effect on dehydrated cells, even if exposed at fluences only reached in more than 1000 years at Sun-Earth distance (1 AU). Higher-energy ions (200 keV) found in solar flares would inactivate 90% of exposed cells after several events in less than 1 year at 1 AU. When mixed with dust grains, LD 10 increases about 10-fold. These results show that, compared to the highly deleterious effects of UV radiation, solar wind charged particles are relatively benign, and organisms protected under grains from UV radiation would also be protected from the charged particles considered in this study.
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Papers by E. Janot-pacheco