A. Talavera

The INES system - II. Ripple correction and absolute calibration for IUE high resolution spectra

In this paper we document the results of the study which led to the ripple correction and absolute cal- ibration algorithms applied to the high resolution spec- tra processed with the NEWSIPS software for the Final Archive of the IUE Project. In this analysis, based on a very large number of spectra, we nd that both the K and parameters (not only the former as previously be- lieved) vary with order number. This fact, together with the nding that the central peaks of the blaze function vary also as a function of the THDA temperature (for the SWP camera) and of the date of observations (for the LWP and LWR cameras), makes the ripple correction algorithm more complex than previously considered but, at the same time, considerably more reliable. As for the high resolution absolute calibration, the method followed is similar to the one implemented in IUESIPS .T he in- ternal accuracy of the high resolution calibration is about 4%. We note that the ripple correction and absolute cali- bration algorithms here described apply also to IUE data processed and distributed with the INES system.

STELLAR WINDS AND MASS LOSS IN A-TYPE SUPERGIANTS

We examine the relationship between the surface escape velocities and wind terminal velocities of A-type supergiants according to the radiation-driven wind theory.

INES: The IUE Archive in Spain

INES (IUE Newly Extracted Spectra) is both a complete archive, which contains more than 110000 ultraviolet spectra obtained by the International Ultraviolet Explorer (IUE) during its 17.5 years of operations, and the associated data distribution system. In March 2000, the European Space Agency delivered the IUE archive to the international scientific community. LAEFF has become now the full responsible for the maintenance and development of the IUE archive and the INES system. LAEFF will be therefore in the coming years, the repository of the largest and most complete set of data in the ultraviolet domain. The INES system can be reached through the Principal Centre Home Page at the URL http://ines.vilspa.esa.es.

The Science Operations Centre of Minisat-01

The Scientific Operations Centre (C.O.C.) takes care of all aspects of theMinisat-01 Mission related to the payload and its scientific instruments. Operations planning, preparation of commands, monitoring of the scientific instruments and data processing and distribution are the daily tasks carried out at the COC. We review these tasks along the operational life of Minisat-01 and we present a summary of the science operations andsome statistics on the usage of the satellite.

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 ...

Variability and Evidence of Non-spherical Stellar Winds in A-Type Supergiants

The profiles of the Hα and uv lines and the observed variability suggest deviations from spherical symmetry for the envelope of A-type supergiants.

Understanding A-Type Supergiants: Visible and Ultraviolet Spectral Variability

We have performed an extensive spectroscopic analysis of high-resolution visible (Balmer lines, Na I D lines, Ca II H and K lines, and Mg II λ4481) and ultraviolet (IUE LWP spectra) observations for 43 A-type supergiants. Our study shows that A-type supergiants can be divided into two groups that depend on the strength of mass-loss indicators, which are correlated with stellar luminosity. Group I contains the A supergiants with luminosity class Ib, which only show weak signs of stellar winds in the Mg II resonance lines, while Group II contains the most luminous stars, which show strong evidence for winds and mass loss in the visible and ultraviolet spectral ranges. Moreover, the analysis of spectral variability shows:

Stellar winds in a-type supergiants

The contribution of A supergiant stars to the return of mass and energy to the interstellar medium is not very important. Abbott (1982) analised a sample of early stars and concluded that B and A supergiants provided less than 8 % of the mass input to the ISM by stellar winds. However, A-type supergiants are important in the framework of the stellar winds-mass loss phenomenology since they are located at the boundary between hot and cool stars, where radiative acceleration may not be sufficiently efficient to drive the wind.