Santo Catalano

Further identification of ROSAT all-sky survey sources in Orion

We report on the identification of 22 ROSAT All-Sky Survey (RASS) X-ray sources distributed in the general direc- tion of the Orion star-forming region. The X-ray sample contains sources from the ROSAT bright source catalogue and from previous detections. The optical identifications are based on intermediate-resolution spectroscopy and UBV Johnson photom- etry using a 1m-class telescope. The strengths of the Hα ,N a D2 and lithium lines for the stellar counterparts are evaluated applying the spectral subtraction technique, using templates of the same spectral type. Radial velocities of the optical coun- terparts are also reported. Thirteen of the optical counterparts show the lithium absorption line in their spectra and have radial velocities consistent with the Orion star forming region. Four of these objects can be classified as new bona-fide T Tauri stars.

ROTATION PERIODS OF OPEN-CLUSTER STARS. III

We present the results from a photometric monitoring program of 21 stars observed during 1992 in the Pleiades and Alpha Persei open clusters. Period determinations for 16 stars are given, 13 of which are the first periods reported for these stars. Brightness variations for an additional five cluster stars are also given. One K dwarf member of the Alpha Per cluster is observed to have a period of rotation of only 4.39 hrs, perhaps the shortest period currently known among BY Dra variables. The individual photometric measurements have been deposited with the NSSDC. Combining current X-ray flux determinations with known photometric periods, we illustrate the X-ray activity/rotation relation among Pleiades K dwarfs based on available data.

Long-term starspot evolution, activity cycle and orbital period variation of RT Lacertae

A sequence of V -band light curves of the active close binary RT Lacertae (G5+G9 IV), extending from 1965 to 2000, is presented and analysed to derive the spot distribution and evolution on the component stars. In our modelling approach, the Roche geometry and Kuruczs atmospheric models were adopted. The resulting maps of the spot surface distribution were regularized by means of the Maximum Entropy and Tikhonov criteria to take full advantage of the increased geometrical resolution during eclipses. By comparing the maps obtained with these two criteria, it was possible to discriminate between surface features actually required by the data and artifacts introduced by the regularization process. Satisfactory ts were obtained assuming spots on both components and the unspotted V -band luminosity ratio: LG5=LG9 IV =0 :65 0:05. The more massive G5 primary appears to be the most active star in the system and its spotted areas are mainly responsible for the light curve distortions. The yearly spot distributions on both components indicate that their spot patterns consist of two components, one uniformly and the other non-uniformly distributed in longitude, the latter suggesting the presence of preferential longitudes. In particular, spots are concentrated around the substellar points and their antipodes on both stars. The eclipse scanning reveals spots with diameters of40, or possibly smaller, on the hemisphere of the primary star being occulted. The primary shows clear evidence for a short-term activity cycle with a period of8: 5y r and a possible long-term cycle with a period of approximately 35 yr. The variation of the spot migration rate may be related with surface dierential rotation, with a lower limit of = 3:2 10 3 . The G9 IV secondary does not show evidence for an activity cycle, its spot coverage appearing rather constant at15 20% of its surface. The relative amplitude of its surface dierential rotation, as indicated by the variation of the spot migration rate, is = 2:7 10 3 . The variation of the orbital period shows a correlation with the activity level of the primary component. Specically, the decreases of the orbital period appear to be associated with minimum spottedness and sizeable changes of the surface spot distribution that may be related to increases of the rotation rate of the spot pattern. Conversely, an episode of increase of the orbital period was related to an increase of the spotted area on the primary star. Such results support the recently proposed models that connect the perturbations of the orbital dynamics with the variation of the gure of equilibrium of the active components, due to the operation of non-linear hydromagnetic dynamos in their extended convective envelopes.

Photospheric and Chromospheric Active Regions in Four Young Solar-Type Stars*

We present a photometric and spectroscopic study of four G-K dwarfs, namely HD 166, Eri, ?1 Ori, and ?1 Cet. In three cases, we find a clear spatial association between photospheric and chromospheric active regions. For ?1 Ori we do not find appreciable variations of photospheric temperature or chromospheric H? emission. We applied a spot/plage model to the observed rotational modulation of temperature and flux to derive spot/plage parameters and to reconstruct a rough three-dimensional map of the outer atmosphere of ?1 Cet, HD 166, and Eri.

A spectroscopic study of the Algol-type binaries S Equulei and KO Aquilae: absolute parameters and mass transfer

We present and analyse high-resolution optical spectra of two Algol binaries, namely S Equ and KO Aql, obtained with the echelle spectrograph at Catania Astrophysical Observatory. New accurate radial velocities (RVs) for the hotter primary components are obtained. Thanks to the cross-correlation procedure, we were able to measure, for the first time to our knowledge, RVs also for the cool secondary components of S Equ and KO Aql. By combining the parameters obtained from the solution of the RV curves with those obtained from the light-curve analysis, reliable absolute parameters of the systems have been derived. The rotational velocity of the hotter components of S Equ and KO Aql has been measured and it is found that the gainers of both systems rotate about 30 per cent faster than synchronously. This is likely due to mass transfer across the Lagrangian L1 point from the cooler to the hotter component. The lower luminosity of the mass-gaining components of these systems compared to normal mainsequence stars of the same mass can also be an effect of the mass transfer. The Hα profiles were analysed with the ‘synthesis and subtraction’ technique and reveal clear evidence of mass transfer and accretion structures. In both systems, especially before the primary eclipses and afterwards, we clearly observed extra absorption lines. From the integrated absorption and the RV variations of these features, we found that the mass accretion is very dense around the impact region of the hotter components. A double-peaked emission in the spectra of S Equ was seen outside the eclipses. One of these peaks is likely originated in a region between the centre of mass and the cooler component, which is occupied by the flowing matter. Furthermore, the Hα difference spectra of S Equ and KO Aql also display emission features, which should be arising from the magnetic activity of the cooler components.

Light curves of SZ Piscium for 1977 and 1978

We present a relatively completeV-band light curve of SZ Psc for 1978 and a partial light curve for 1977. From the 1978 light curve we derive a new time of primary minimum, JD⊙2443823.674±0.001, and a Russell-model solution,i=75°.8±0°.1,rh=0.096±0.003,rc=0.351±0.001, andLh=0.253±0.002. The hotter component of this system is a F5-8 main-sequence star, the cooler component a K3-4 star well above the main sequence. The system is detached with the larger component filling only 82% of its Roche lobe. The distortion wave in this RS CVn-type binary seems not to migrate regularly as do those in many other such systems, but rather seems to change phase and amplitude more erratically. Between 1977 and 1978 its phase stayed practically constant while its amplitude decreased by a factor of three. We discuss the implications of this behavior for the spot model of RS CVn-type activity. We find that the traditional comparison star for SZ Psc, HD 219018, is very likely a constant star contrary to a recent suggestion that it is variable. Its brightness and colors,V=7.705, (B-V)=0.628, and (V-I)c=0.688, are those of a G2V star.

Optical design of CAOS: a high-resolution spectropolarimeter for the Catania Astrophysical Observatory 0.91-m telescope

CAOS (Catania Astrophysical Observatory Spectrograph) is a high-resolution (R~60,000), fiber fed, bench-mounted, prism cross-dispersed, white-pupil R-4 echelle spectrograph with polarimetric capabilities, for the 0.91m telescope on Mt. Etna. Wavelengths from 390 to 710 nm are covered in one-shot with a 2Kx2K 13.5 micron CCD. Inherent high efficiency of the spectrograph and optimum matching between fibers and spectrograph will allow high throughput for the overall system. This instrument will replace the existing spectrograph, with a net gain in spectral resolution (about a factor 2) and in efficiency (about a factor 10), extending current studies undertaken by Catania Astrophysical Observatory in stellar physics.

Hα variations of the RS CVn type binary ER Vulpeculae

We present the results of spectroscopic observations of the active eclipsing binary ER Vul in the 5860-6700 A spec- tral range carried out at the Catania Astrophysical Observatory. Accurate measurements of radial velocities by using the cross- correlation technique have been made and a new orbital solution is given. All spectra display chromospheric emission which fills in the Hα absorption lines of both components. The equivalent width (EW )o f the Hα emission has been measured by subtraction of a synthetic spectrum built up with spectra of inactive standard stars. The EW of total Hα emission, arisen from both components, shows a phase-dependent variation. It reaches its maximum value just before the primary eclipse. We were able to separate the contributions to the Hα emission from the individual components at phases far from the eclipses. We have found that the secondary, cooler component is the most active and its Hα residual emission shows the same trend as the total Hα emission, along orbital phase. This Hα equivalent width variation can be due to plage-like structures on the chromosphere of secondary star. In addition, a decrease of the Hα EW around the ingress phase of the primary eclipse is apparent.

PG 1613+426: A new sdB pulsator

We report the detection of short period oscillations in the hot subdwarf B (sdB) star PG 1613+426 from time-series photometry carried out with the 91-cm Cassegrain telescope of the Catania Astrophysical Observatory. This star, which is brighter than the average of the presently known sdB pulsators, with B = 14.14 mag, has

Design Study of an Adaptive Optics Visual Echelle Spectrograph and Imager for the VLT

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