The on-ground calibration of the flight model of the HPGSPC onboard the SAX satellite: Calibration set-up and preliminary results

The High Pressure Gas Scintillation Proportional Counter (HPGSPC) is one of the Narrow Field Instruments of the Italian-Dutch X-ray astronomy satellite SAX. Sensitive in the hard X-ray band (4–120 keV), with a very good energy resolution, the HPGSPC is well suited for studying in detail the cyclotron features present in the hard X-ray spectrum of some celestial sources. The scientific calibration of the flight model of the HPGSPC took place at the LABEN premises(Vimodrone-Milano) during October and November 1994. In this paper we briefly describe the on-ground instrument calibration system and we report some preliminary results that show the performances of both single/double event and position reconstruction/energy correction onboard processing. Preliminary results concerning the energy resolution and energy linearity are reported too

BeppoSAX Observations of the TeV Blazar Mkn 421

The blazar Mkn 421 has been observed, as part of the AO1 Core Program, five times from 2 to 7 May 1997. In the LECS+MECS energy band the spectrum shows convex curvature, well represented by a broken power--law. Flux variability (more than a factor 2) has been detected over the entire 0.1--10 keV range, accompanying which the spectrum steepens with the decrease in intensity. Mkn 421 has also been detected with the PDS instrument. Our preliminary analysis indicates that the PDS spectrum lies significantly above the extrapolation from the MECS, suggesting a contribution from a flatter high energy component.Comment: 4 pages, 4 Postscript figures, uses espcrc2.sty and psfig.sty (both included). To appear in "The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE", Rome, Italy, 21-24 October, 1997. Eds.: L. Scarsi, H. Bradt, P. Giommi and F. Fior

BeppoSAX observations of PKS 0528+134

We report on the BeppoSAX observations of the gamma-ray blazar PKS 0528+134 performed in Feb and Mar 1997, during a multiwavelength campaign involving EGRET and ground based telescopes. The source was in a faint and hard state, with energy spectral index alpha=0.48+-0.04 between 0.1 and 10 keV, and [2-10] keV flux of 2.7E-12 erg/cm2/s. No significant variability was observed. The source was detected in the 20-120 keV band by the PDS, with a flux lying slightly above the extrapolation from lower X-ray energies. Comparing this low state with previous higher states of the source, there is an indication that the X-ray spectrum hardens and the gamma-ray spectrum steepens when the source is fainter.Comment: 4 pages, LateX, 5 figures (included). Uses espcrc2.sty and epsf.sty (included). To appear in The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE, Rome, Italy, 21-24 October, 1997. Eds.: L. Scarsi, H. Bradt, P. Giommi and F. Fior

Spectroscopic study of the HgMn star HD 49606: the quest for binarity, abundance stratifications and magnetic field

In this paper, we present a multi-instrument analysis of the mercury-manganese star HD 49606. New spectroscopic observations have been obtained by us with Catania Astrophysical Observatory Spectropolarimeter (CAOS@OAC) and High Accuracy Radial Velocity Planet Searcher-North@Telescopio Nazionale Galileo (HARPS-N@TNG). Combining these observations with archive data coming from other instruments, we performed a comprehensive analysis of this star. We highlight the motion around the centre of mass of a binary system of SB1 type, and we calculate the fundamental parameters characterizing its orbit. We also speculate on the nature of the unseen component. From the fit of H β and H γ, we determined the effective temperature and gravity, while from a number of metal lines, we derive the rotational and microturbulent velocities. Regarding chemical composition, we found underabundances of helium, oxygen, magnesium, sulfur and nickel, solar composition for carbon and overabundances for all the other elements. In particular, mercury abundance is derived taking into account an isotopic mixture different from the terrestrial one. As to magnesium, silicon and phosphorus, we found a non-constant abundance with the optical depth, a result currently considered an evidence of stratification. Spectropolarimetric observations have been performed in the attempt to highlight the presence of a magnetic field, but no detection has been found

Comprehensive spectroscopic and photometric study of pulsating eclipsing binary star AI Hya

The pulsating eclipsing binaries are remarkable systems that provide an opportunity to probe the stellar interior and to determine the fundamental stellar parameters precisely. Especially the detached eclipsing binary systems with (a) pulsating component(s) are significant objects to understand the nature of the oscillations since the binary effects in these systems are negligible. Recent studies based on space data have shown that the pulsation mechanisms of some oscillating stars are not completely understood. Hence, comprehensive studies of a number of pulsating stars within detached eclipsing binaries are important. In this study, we present a detailed analysis of the pulsating detached eclipsing binary system AI Hya which was studied by two independent groups with different methods. We carried out a spectroscopic survey to estimate the orbital parameters via radial velocity measurements and the atmospheric parameters of each binary component using the composite and/or disentangled spectra. We found that the more luminous component of the system is a massive, cool and chemically normal star while the hotter binary component is a slightly metal-rich object. The fundamental parameters of AI Hya were determined by the analysis of binary variations and subsequently used in the evolutionary modelling. Consequently, we obtained the age of the system as 850 $\pm$ 20 Myr and found that both binary components are situated in the Delta Scuti instability strip. The frequency analysis revealed pulsation frequencies between the 5.5 - 13.0 d$^{-1}$ and we tried to estimate which binary component is the pulsating one. However, it turned out that those frequencies could originate from both binary components.Comment: Accepted for publication in MNRA

BeppoSAX observations of 3C 273

We present preliminary results of BeppoSAX AO1 observations of 3C 273 performed in January 1997. We also present a close comparison with data obtained during the satellite SVP, in July 1996. On average, the AO1 flux is about a factor 2 higher than the flux detected during the SVP, and roughly on the middle of the historical X-ray flux range. Power law fits with galactic absorption to all observations yield spectral indices in the range 1.53-1.6, with the spectrum extending from 0.2 to at least up to 200 keV without any significant slope change. The broad band spectrum appears basically featureless, marking a clear difference from the SVP data, where an absorption feature at low energy and a fluorescence iron emission line are present. The lack of cold/warm matter signatures in our data may indicate that, at this "high" level of luminosity, the featureless continuum produced in a relativistic jet overwhelms any thermal and/or reprocessing component, while the two components were at least comparable during the "low" state of July 1996.Comment: 1+4 pages, 3 ps inlined figures, espcrc2.sty. Proc. of the Conf. "The Active X-Ray Sky: Results from BeppoSAX and Rossi-XTE", Rome 21-24 October 199

KIC 7599132: an ellipsoidal variable in a close SB1 system

In this paper, we present a spectroscopic and photometric analysis of the suspected ellipsoidal variable star KIC 7599132. New spectroscopic observations have been obtained with Catania Astrophysical Observatory Spectropolarimeter. From the fit of Hα and Hβ, we determined the effective temperature and gravity of the primary component, Teff = 10200 ± 150 K and log g = 4.1 ± 0.1, while from a number of metal lines, we derive the rotational velocity, v esin i = 60 ± 2 km s-1. We found almost solar abundances with the exception of silicon (0.50 dex) overabundance. A Bayesian analysis, based on the comparison between observational data and theoretical predictions of PROSECCO evolutionary models, allows us to estimate the mass and the age of the primary. We obtained M1 = 2.4 ± 0.2 M☉ and τs = 3.8 _{-0.7}^{+0.9} Myr. A new model for the system was obtained combining Kepler photometric time series (Q0-Q17) and our radial velocities by using the code PHOEBE. As a result, the system appears to be a detached binary system with a mass ratio q = 0.30 ± 0.01, a semimajor axis a = 7.3 ± 0.1 R☉ and an inclination angle i = 35° ± 2°. This modelling allowed us to derive: M2 = 0.7 ± 0.1 M☉, R1 = 3.0 ± 0.2 R☉, and R2 = 1.5 ± 0.2 R☉. Numerical simulations show that if the secondary star had been hotter than 4000 K, we would have observed its spectral features in our spectra