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Papers by Juan Fabregat

Astronomy and Astrophysics, 2009

1 GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudo... more 1 GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France e-mail: anne-laure.huat@obspm.fr 2 Institut d'Astrophysique Spatiale (IAS), Bâtiment 121, 91405 Orsay Cedex, France 3 Royal Observatory of Belgium, 3 avenue ...

Earth Moon and Planets, 2002

Photographic multi-station observations of 18 Leonid meteors obtained by the Spanish Photographic... more Photographic multi-station observations of 18 Leonid meteors obtained by the Spanish Photographic Meteor Network are presented. For each meteoroid the radiant position, trajectory data and orbital parameters are discussed and compared to theoretical radiant positions and orbital elements of particles ejected from 55P/Tempel-Tuttle in 1899. We discuss the role of mean velocity imprecision in the dispersion of some orbital parameters, specially the semimajor axis. Finally, by applying the dust trail theory we have adjusted the1999 Leonid storm orbits to a defined semimajor axis value to test the quality of photographic observations.

Monthly Notices of The Royal Astronomical Society, 2004

Meteoritics & Planetary Science, 2003

Abstract— Relative chemical abundances of 13 meteoroids were determined by averaging the composit... more Abstract— Relative chemical abundances of 13 meteoroids were determined by averaging the composition of the radiating gas along the fireball path that originated during their penetration into the Earth's atmosphere. Mg, Fe, Ni, Cr, Mn, and Co abundances, relative to Si, are similar to those reported for CI and CM carbonaceous chondrites and interplanetary dust particles. In contrast, relative abundances of Ca and Ti in meteor spectra indicate that these elements suffer incomplete evaporation processes. The chemical composition of all meteoroids studied in this work differs from that of 1P/Halley dust.

Earth Moon and Planets, 2004

We have developed an all-sky charge coupled devices (CCD) automatic system for detecting meteors ... more We have developed an all-sky charge coupled devices (CCD) automatic system for detecting meteors and fireballs that will be operative in four stations in Spain during 2005. The cameras were developed following the BOOTES-1 prototype installed at the El Arenosillo Observatory in 2002, which is based on a CCD detector of 4096 × 4096 pixels with a fish-eye lens that provides an all-sky image with enough resolution to make accurate astrometric measurements. Since late 2004, a couple of cameras at two of the four stations operate for 30 s in alternate exposures, allowing 100% time coverage. The stellar limiting magnitude of the images is +10 in the zenith, and +8 below ~ 65° of zenithal angle. As a result, the images provide enough comparison stars to make astrometric measurements of faint meteors and fireballs with an accuracy of ~ 2°arcminutes. Using this prototype, four automatic all-sky CCD stations have been developed, two in Andalusia and two in the Valencian Community, to start full operation of the Spanish Fireball Network. In addition to all-sky coverage, we are developing a fireball spectroscopy program using medium field lenses with additional CCD cameras. Here we present the first images obtained from the El Arenosillo and La Mayora stations in Andalusia during their first months of activity. The detection of the Jan 27, 2003 superbolide of ± 17 ± 1 absolute magnitude that overflew Algeria and Morocco is an example of the detection capability of our prototype.

Monthly Notices of The Royal Astronomical Society, 1998

The results of a 7-yr optical and UV spectroscopic study of the high-mass X-ray binary A 0535ǹ26 ... more The results of a 7-yr optical and UV spectroscopic study of the high-mass X-ray binary A 0535ǹ26 are presented. It was found that throughout the period of the observations the line profile of H showed considerable variability. A correlation between the equivalent width of H and both V-band magnitude and (B 2V ) colour excess was observed, albeit with considerable scatter present in the data set. A giant X-ray flare in early 1994 was accompanied by a fading in optical and infrared photometric bands, and a reduction in the equivalent width of H . When the star was observed in 1994 September, it was found to have developed a double-peaked H profile, and further observations saw the V /R peak ratio vary cyclically, with a period of #1 yr. If this is identified as a global one-armed oscillation, it becomes the shortest period ever observed in a Be star. The accompanying photometric and spectroscopic observations provide a test of any theory seeking to describe the onset and behaviour of such a density wave. Table 1. Summary of the H observations of A 0535ǹ262. 168 J. S. Clark et al. © 1998 R AS, MNR AS 294, 165-176

Astronomy & Astrophysics, 2001

The bright star δ Sco has been considered a typical B0-type object for many years. Spectra of the... more The bright star δ Sco has been considered a typical B0-type object for many years. Spectra of the star published prior to 1990 showed no evidence of emission, but only of short-term line profile variations attributed to nonradial pulsations. Speckle interferometric observations show that δ Sco is a binary system with a highlyeccentric orbit and a period of ∼10.6 years. Weak emission in the Hα line was detected in its spectrum for the first time during a periastron passage in 1990. Shortly before the next periastron passage in the summer of 2000, the binary entered a strong Hα emission and enhanced mass-loss phase. We monitored the spectroscopic development of the Be outburst from July 2000 through March 2001. In this paper we present results from our spectroscopy, refine elements of the binary orbit, and discuss possible mechanisms for the mass loss.

Monthly Notices of The Royal Astronomical Society, 1999

We present optical and infrared observations of BQ Cam, the optical counterpart to the Be/X-ray t... more We present optical and infrared observations of BQ Cam, the optical counterpart to the Be/X-ray transient system V0332+53. BQ Cam is shown to be an O8 -9Ve star, which places V0332+53 at a distance of ∼ 7 kpc. Hα spectroscopy and infrared photometry are used to discuss the evolution of the circumstellar envelope. Due to the low inclination of the system, parameters are strongly constrained. We find strong evidence for a tilt of the orbital plane with respect to the circumstellar disc (pressumably on the equatorial plane). Even though the periastron distance is only ≈ 10R * , during the present quiescent state the circumstellar disc does not extend to the distance of periastron passage. Under these conditions, X-ray emission is effectively prevented by centrifugal inhibition of accretion. The circumstellar disc is shown to be optically dense at optical and infrared wavelengths, which together with its small size, is taken as an indication of tidal truncation.

Astrophysical Journal, 2002

Using BATSE and RXTE observations from 1991 April to 2001 August we have detected 71 outbursts fr... more Using BATSE and RXTE observations from 1991 April to 2001 August we have detected 71 outbursts from 82 periastron passages of EXO 2030+375, a 42-second transient X-ray pulsar with a Be star companion, including several outbursts from 1993 August to 1996 April when the source was previously believed to be quiescent. Combining BATSE, RXTE, and EXOSAT data we have derived an improved orbital solution. Applying this solution results in a smooth profile for the spin-up rate during the giant outburst and results in evidence for a correlation between the spin-up rate and observed flux in the brighter BATSE outbursts. Infrared and Hα measurements show a decline in the density of the circumstellar disk around the Be star. This decline is followed by a sudden drop in the X-ray flux and a turn-over from a spin-up trend to spin-down in the frequency history. This is the first Be/X-ray binary which shows an extended interval, about 2.5 years, where the global trend is spin-down, but the outbursts continue. In 1995 the orbital phase of EXO 2030+375's outbursts shifted from peaking about 6 days after periastron to peaking before periastron. The outburst phase slowly recovered to peaking at about 2.5 days after periastron. We interpret this shift in orbital phase followed by a slow recovery as evidence for a global one-armed oscillation propagating in the Be disk. This is further supported by changes in the shape of the Hα profile which are commonly believed to be produced by a reconfiguration of the Be disk. The truncated viscous decretion disk model provides an explanation for the long series of normal outbursts and the evidence for an accretion disk in the brighter normal outbursts. Long-term multi-wavelength observations such as these clearly add considerably to our knowledge of Be/X-ray binaries and the relationship between optical, infrared and X-ray observations.

Papers | Astronomy by Juan Fabregat

Stellar pulsations in main-sequence B-type stars are driven by the kappa\kappakappa-mechanism due to the ... more Stellar pulsations in main-sequence B-type stars are driven by the kappa\kappakappa-mechanism due to the Fe-group opacity bump. The current models do not predict the presence of instability strips in the B spectral domain at very low metallicities. As the metallicity of the Magellanic Clouds has been measured to be around Z=0.002Z=0.002Z=0.002 for the SMC and Z=0.007Z=0.007Z=0.007 for the LMC, they constitute a very suitable objects to test these predictions.

Book Chapters by Juan Fabregat

Stellar pulsations in main-sequence B-type stars are driven by the kappa-mechanism due to the Fe-... more Stellar pulsations in main-sequence B-type stars are driven by the kappa-mechanism due to the Fe-group opacity bump. The current models do not predict the presence of instability strips in the B spectral domain at very low metallicities. As the metallicity of the Magellanic Clouds (MC) has been measured to be around Z = 0. 002 for the Small Magellanic Cloud (SMC) and Z = 0. 007 for the Large Magellanic Cloud (LMC), they constitute a very suitable objects to test these predictions. The aim of this work is to investigate the existence of B-type pulsators at low metallicities, searching for short-term periodic variability in a large sample of B and Be stars from the MC with accurately determined fundamental astrophysical parameters.

Arxiv preprint arXiv: …, 2008

Abstract: To study the variability of the 523 B and Be stars observed in the Magellanic clouds wi... more Abstract: To study the variability of the 523 B and Be stars observed in the Magellanic clouds with the VLT-FLAMES, we cross-matched the stars of our sample with the photometric database MACHO, which provides for each star an 8 years lightcurve. We searched for ...