Search Publications
Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images II. Lithium abundances
Tagliaferri, G.; Pasquini, L.; Pallavicini, R. +2 more
We present high-resolution spectra in the Li I 6708 A region, and multicolor photometry, for a sample of active stars detected serendipitously by the EXOSAT satellite. We analyse the spectral data with a spectral synthesis code and derive Li abundances, rotation rates and metallicities. We use our multicolor photometry to infer the spectral classi…
Sub-arcsecond 2D photometry and spectroscopy of the nucleus of M 31 : the supermassive black hole revisited.
Emsellem, E.; Bacon, R.; Monnet, G. +1 more
Sub-arcsecond imagery (HRCAM, 0.35" - 0.57" FWHM) and two- dimensional spectrography (TIGER, 0.9" FWHM) of the central nucleus of M 31 have been obtained at CFHT. The photometric data clearly show the double-peaked nucleus, in excellent agreement with a recent HST image by Lauer et al. (1993). We built deconvolved surface brightness models, using …
Methanol and hydrogen sulfide in comet P/Halley.
Eberhardt, P.; Meier, R.; Krankowsky, D. +1 more
The Neutral Mass Spectrometer on the Giotto spacecraft measured the gas and ion composition in the coma of comet P/Halley. A detailed model of the ion chemistry inside the contact surface located at 4660 km is used to interpret the measured ion density profiles in the 32 to 35 amu/e mass range. The masses 33 and 35 amu/e are dominated by the proto…
Multi-wavelength monitoring of the BL Lacertae Object PKS 2155-304 II. The ROSAT Observations
Maraschi, L.; Treves, A.; Brinkmann, W. +7 more
Extensive ROSAT PSPC observations of the BL Lac object PKS 2155-304 carried out between November 12 and November 15, 1991 revealed the source to be in a bright state with a soft X-ray flux of F_x_(0.1-2.4keV)=~7x10^-10^erg/cm^2^/s. Rapid variations in the X-ray flux of up to 30% within a day were apparent but at the sampling rate of ~96 min all of…
Systematic study of the ultraviolet variability of active galactic nuclei.
Paltani, S.; Courvoisier, T. J. -L.
We have analysed all spectra of all active galactic nuclei (AGN) observed with the IUE satellite during the period 1978-1991. 90% of the 93 objects for which an estimate of the variability can be obtained have varied by more than 15% in the ultraviolet domain. In almost all objects the flux variations are more important at 1200 A (mean of 39%) tha…
FOS observations of G117-B15A and the blue edge of the ZZ Ceti instability strip.
Koester, D.; Vauclair, G.; Allard, N. F.
From an analysis of FOS observations of G117-B15A, one of the hottest members of the ZZ Ceti class, we derive an effective temperature of 12250+/-125K. Since several other DA near the blue edge of the instability strip must have very similar temperatures according to their UV spectra, it is likely that the blue edge is lower than assumed until now…
ROSAT X-ray observations of ten cataclysmic variables.
Verbunt, Frank; van Teeseling, Andre
Ten cataclysmic variables have been observed with the ROSAT PSPC. The x-ray spectra can be fitted with optically thin spectra, but several spectra require more than one component. The high emission measures indicate that the emitting plasma is optically thick in strong resonance lines. Variability in the count rate is discovered in seven systems; …
The hot wind in the symbiotic nova AG Pegasi.
Vogel, M.; Nussbaumer, H.
The nature of the hot radiation source in symbiotic systems is still controversial. In AG Peg, the hot component went into a thermonuclear outburst after a probably long phase of mass accretion from the cool giant companion. This outburst has been lasting for more than 150 years. During most of this phase the hot compact component has been losing …
A model for the X-ray spectrum of the symbiotic nova RR Telescopii.
Werner, K.; Jordan, S.; Murset, U.
Pointed ROSAT position sensitive proportional counter (PSPC) observations of the symbiotic nova RR Tel are presented. The PSPC pulse height distribution exhibits a rather soft energy distribution plus few, but significant counts at higher energies. We interprete this as superposition of photospheric flux from the hot component of the symbiotic bin…
Analysis of BD+33 2642: a newly detected planetary nebula in the galactic halo and its central star.
Heber, U.; Napiwotzki, R.; Koeppen, J.
The spectra of the star BD+33 2642 and its surrounding planetary nebula (PN) are analyzed. The stellar parameters are found to be T_eff_=20200K, logg=2.9; the stellar mass is 0.560Msun_. In the stellar atmosphere, He is solar, C, N, O, Mg, Si are depleted by about 1dex, and Fe is depleted by 2dex relative to the sun. This abundance patt…