Liliana Formiggini

Modeling RR Telescopii through the Evolution of the Spectra

We investigate the evolution of RR Tel after the outburst by fitting the emission spectra in two epochs. The first one (1978) is characterized by large fluctuations in the light curve, and the second one (1993) by a slow fading trend. In the frame of a colliding wind model, two shocks are present: the reverse shock propagates in the direction of the white dwarf, while the other one expands toward or beyond the giant. The results of our modeling show that in 1993, the expanding shock has overcome the system and is propagating in the nearby ISM. The large fluctuations observed in the 1978 light curve result from line intensity rather than from continuum variation. These variations are explained by fragmentation of matter at the time of head-on collision of the winds from the two stars. A high-velocity (500 km s-1) wind component is revealed from the fit of the SED of the continuum in the X-ray range in 1978, but is quite unobservable in the line profiles. The geometrical thickness of the emitting clumps is the critical parameter that can explain the short-timescale variabilities of the spectrum and the trend of slow line intensity decrease.

Multiperiodic variations in the last 104-yr light curve of the symbiotic star BF Cyg

We analyse a light curve (LC) of the symbiotic star BF Cyg, covering 114 yr of its photometric history. The star had a major outburst around the year 1894. Since then the mean optical brightness of the system is in steady decline, reaching only in the last few years its pre-outburst value. Superposed on this general decline are some six less intense outbursts of 1‐2 mag and duration of 2000‐5000 d. We find a cycle of 6376 d, or possibly twice this period, in the occurrence of these outbursts. We suggest that the origin of the system outbursts is in some magnetic cycle in the outer layers of the giant star of the system, akin to the less intense 8000-d magnetic cycle of our Sun. We further find, that in addition to its well-known binary period of 757.3 d, BF Cyg possesses also another photometric period of 798.8 d. This could be the rotation period of the giant star of the system. If it is, the beat period of these two periodicities, 14 580 d, is the rotation period of a tidal wave on the surface of the giant. A fourth period of 4436 d, the beat period of the 14 580-d and the 6376-d cycles is possibly also present in the LC. We predict that BF Cyg will be at the peak of its next outburst around the month of May in the year 2007. The newly discovered 798.8-d period explains the disappearance of the orbital modulation at some epochs in the LC. The 757.3-d oscillations will be damped again around the year 2013.

Activity cycle of the giant star of Z Andromedae and its spin period

We have re-analysed the long-term optical light curve (LC) of the symbiotic star Z Andromedae, covering 112 yr of mostly visual observations. Two strictly periodic cycles and one quasiperiodic cycle can be identified in this LC. A P1 = 7550 d quasi-periodicity characterizes the repetition time of the outburst episodes of this symbiotic star. Six such events have been recorded so far. During quiescence states of the system, that is, in time-intervals between outbursts, the LC is clearly modulated by a stable coherent period of P2 = 759.1 d. This is the well-known orbital period of the Z Andromedae binary system that has been measured also spectroscopically. A third coherent period of P3 = 658.4 d is modulating the intense fluctuations in the optical brightness of the system during outbursts. We attribute the trigger of the outburst phenomenon and the clock that drives it, to a solar-type magnetic dynamo cycle that operates in the convection and the outer layers of the giant star of the system. We suggest that the intense surface activity of the giant star during maximum phases of its magnetic cycle is especially enhanced in one or two antipode regions, fixed in the atmosphere of the star and rotating with it. Such spots could be active regions around the North Pole and the South Pole of a general magnetic dipole field of the star. The P3 periodicity is half the beat of the binary orbital period of the system and the spin period of the giant. The latter is then either 482 or 1790 d. If only one pole is active on the surface of the giant, P3 is the beat period itself, and the spin period is 352 d. It could also be 5000 d if the giant is rotating in a retrograde direction. We briefly compare these findings in the LC of Z Andromedae to similar modulations that were identified in the LC of two other prototype symbiotics, BF Cyg and YY Her.

The rapidly pulsating subdwarf B star PG 1325+101 - I. Oscillation modes from multisite observations

In this article we present the results of 215 h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (T_eff = 35 000 K, log g = 5.8, log N(He)/N(H) = -1.7), obtained during 25 days of observation in Spring 2003 from nine different sites. As in previous observations, the temporal spectrum is dominated by the main peak at 7255.55 ?Hz, with an amplitude of about 2.7% which, however, is dropped to about 1.7% in February 2005. No secondary peaks close to the dominant pulsation mode are clearly detected. In addition, at least fourteen more pulsation frequencies are found: three of them at 7704.92, 9380.17 and 14511.10 ?Hz were already present in the discovery run with small differences in frequency, probably due to 1-day aliasing effects. The peak at 7704.92 ?Hz belongs to a triplet of almost equally spaced frequencies that could be due to rotational splitting and would imply a rotational period of about 1.6 days. Based on the results of this article, a detailed asteroseismic analysis of PG 1325+101 is presented in a separate paper (Charpinet et al. 2006b, A&A, 459, 565, Paper II).

R Aquarii spectra revisited by SUMA

We analyse the optical spectra and the ultraviolet (UV) spectral evolution of the jets and of the H II region inside the R Aquarii binary system using the code SUMA, which accounts for shock and photoionization consistently. The temperature of the hot star is 80 000 K as for a white dwarf. We find that the shock velocity in the NE jet increased between 1983 and 1989. The spectral evolution between 1989 and 1991 of the SW jet indicates that a larger contribution from low-density-velocity matter affects the 1991 spectra. The evolution of the UV spectra from 1980 November 8 to 1991 May 26 in the H II region indicates that the reverse shock is actually a standing shock. The results obtained by modelling the line spectra are cross-checked against the fit of the continuum spectral energy distribution. It is found that a blackbody temperature of 2800 K reproduces the radiation from the red giant. A blackbody emission component corresponding to 1000 K is emitted by dust in the surroundings of the red giant. Model calculations confirm that the radio emission is of thermal origin. We found that the NE jet bulk emission is at a distance of approximately 2 x 10 1 5 cm from the internal system, while the distance of the SW jet bulk is ∼6 x 10 1 4 cm. The distance of the reverse shock from the hot source in the internal region is ≤9 × 10 1 3 cm.

The giant star of the symbiotic system YY Her: rotation, tidal wave, solar-type cycle and spots

We analyze the historical light curve of the symbiotic star YY Her, from 1890 up to December 2005. A secular declining trend is detected, at a rate of �.01 magn in 1000 d, suggesting that the system could belong to the sub-class of symbiotic novae. Several outburst events are superposed on this slow decline. Three independent periodicities are identified in the light curve. A quasi-periodicity of 4650.7 d is detected for the outburst occurrence. We suggest that it is a signature of a solar-type magnetic dynamo cycle in the giant component. A period of 593.2 d modulates the quiescent light curve and it is identified as the binary period of the system. During outburst events the system shows a stable periodic oscillation of 551.4 d. We suggest that it is the rotation period of the giant.The secondary minima detected at some epochs of quiescence are probably due to dark spots on the surface of the rotating giant. The difference between the frequencies of these two last periods is the frequency of a tidal wave in the outer layers of the giant. A period which is a beat between the magnetic cycle and the tidal wave period is also apparent in the light curve. YY Her is a third symbiotic system exhibiting these cycles in their light curve, suggesting that a magnetic dynamo process is prevalent in the giant components of symbiotic stars, playing an important role in the outburst mechanism of some of these systems.

FAUST Observations of Ultraviolet Sources toward the Virgo Cluster

We analyze three UV images covering a ~100 square degree field toward the Virgo cluster, obtained by the FAUST space experiment. We detect 191 sources to a signal-to-noise ratio of 4.4 and identify 94% of them. Most sources have optical counterparts in existing catalogs, and about half are identified as galaxies. Some sources with no listed counterpart were observed at the Wise Observatory. We present the results of low-resolution visible spectrophotometry and discuss the foreground 101 stellar sources and the 76 detected galaxies, both in the cluster and in the foreground or background. We derive conclusions on star formation properties of galaxies and on the total UV flux from discrete and diffuse sources in the cluster. We test for the presence of intracluster dust, determine the clustering properties of UV emitting galaxies, and derive the UV luminosity function of Virgo galaxies.

Period switching in the symbiotic star BX Mon

ABSTRACT We report on a detailed analysis of the optical light curve of the symbiotic system BXMon, the data of which were gathered from the literature. The light curve covers theperiod December 1889 March 2009, with a gap of no observations between March 1940and February 1972. The light curve is characterized by strong oscillations of peak topeak amplitude of 2 to more than 3 magnitudes. Before the gap the fluctuations weremodulated mainly by a period P a =1373±4 d. After the gap the dominant periodicityis P b =1256±16. Higher harmonics as well as a few beats of the two major periodicitiescan also be identified in the light curve. We identify one of the beat periods, P r =656d, as the sidereal rotation period of the giant component of the system . The periodswitching that took place during the gap in the observations was possibly associatedwith a certain cataclysmic event, hints of which may be recognized in the LC in thefirst 11 years after the gap.We suggest that the origin of the major oscillations is in periodic episodes of massaccretion from the M giant onto the hot component of the system. After the gap theyare correlated with the periastron passage of the system, and therefore appear withthe binary period. Before the gap the oscillations appeared with the diurnal cycle ofan observer on the surface of the rotating M giant, whose sun is the hot component.The event of the period switching is possibly related to an intensive magnetic activityin the outer layers of the giant star.Keywords: binaries: symbiotic – stars: individual: BX Mon – stars: magnetic fields– stars: rotation.

Principal component analysis of IUE galaxy spectra

We analyse the UV spectral energy distribution of a sample of normal galaxies listed in the IUE INES Guide No. 2-Normal Galaxies (Formiggini & Brosch, 2000) using a Principal Component Analysis. The sample consists of the IUE-SW spectra of the central regions of 118 galaxies, where the IUE aperture included more than 1 per cent of the galaxy size. The principal components are associated with the main components observed in the UV spectra of galaxies. The first component, accounting for the largest source of diversity, can be associated with the UV continuum emission. The second component represents the UV contribution of an underlying evolved stellar population. The third component is sensitive to the amount of activity in the central regions of galaxies and measures the strength of star formation events. In all the samples analysed here the principal component representative of starforming activity accounts for a significant percentage of the variance. The fractional contribution to the SED by the evolved stars and by the young population are similar. Projecting the SEDs onto their eigenspectra, we find that none of the coefficients of the principal components can outline an internal correlation or can correlate with the optical morphological types. In a sub-sample of 43 galaxies, consisting of almost only compact and BCD galaxies, the third principal component defines a sequence related to the degree of starburst activity of the galaxy.

Principal component analysis of International Ultraviolet Explorer galaxy spectra

We analyse the UV spectral energy distribution of a sample of normal galaxies listed in the IUE INES Guide No. 2-Normal Galaxies (Formiggini & Brosch, 2000) using a Principal Component Analysis. The sample consists of the IUE-SW spectra of the central regions of 118 galaxies, where the IUE aperture included more than 1 per cent of the galaxy size. The principal components are associated with the main components observed in the UV spectra of galaxies. The first component, accounting for the largest source of diversity, can be associated with the UV continuum emission. The second component represents the UV contribution of an underlying evolved stellar population. The third component is sensitive to the amount of activity in the central regions of galaxies and measures the strength of star formation events. In all the samples analysed here the principal component representative of starforming activity accounts for a significant percentage of the variance. The fractional contribution to the SED by the evolved stars and by the young population are similar. Projecting the SEDs onto their eigenspectra, we find that none of the coefficients of the principal components can outline an internal correlation or can correlate with the optical morphological types. In a sub-sample of 43 galaxies, consisting of almost only compact and BCD galaxies, the third principal component defines a sequence related to the degree of starburst activity of the galaxy.