We studied orbital period changes in the non-eclipsing close binary HR 1099, one of the most brig... more We studied orbital period changes in the non-eclipsing close binary HR 1099, one of the most bright members of the RS CVn class of magnetically active binary systems. Intermediate-resolution optical spectroscopy and IUE archive spectra were used to build radial-velocity curves yielding epochs of superior conjunction with an accuracy of 0.01 days. The final database ranged from 1976 to 2002 and allowed us a better assessment of the amplitude of the orbital period variation and its timescale. (2 data files).
We observed in the optical range the strong infrared source IRAS F18187+6304 in the context of a ... more We observed in the optical range the strong infrared source IRAS F18187+6304 in the context of a program aimed to clarify the nature of the stellar objects of the Byurakan Infrared Source catalogue. The optical spectrum is characterized by continuum and absorption lines typical of early K-type giants plus a few permitted and forbidden emission lines. The sparse optical photometry did not put in evidence strong variations during the last 50 years. Our repeated observations indicate a substantial stability of the spectra and a monotonic increase of the luminosity in the BVR bands of about 0.4 magnitudes between Summer 2007 and Fall 2008. From a high resolution spectrum we measured a heliocentric radial velocity of -25 km/s and discovered a complex NaI-D structure resembling that of some T Tauri stars; the infrared CaII triplet is in absorption. A strong IR excess in the IRAS bands indicates a substantial quantity of circumstellar dust and gas. IRAS F18187+6304 is an isolated star at quite high galactic latitude, far from any star forming region. All these characteristics make this object an intriguing case of difficult interpretation. The preliminary results are discussed in the framework of the available synthetic energy distribution and accretion models.
Once mixed in the ambient galactic plane stellar population, young stars are virtually indiscerni... more Once mixed in the ambient galactic plane stellar population, young stars are virtually indiscernible because neither their global photometric properties nor the presence of nearby gas can help to disentangle them from older ones. Nevertheless, the study of the RasTyc sample revealed 4 lithium-rich field stars displaying the same space motion, which are located within a few degrees from each other on the celestial sphere near the Cepheus-Cassiopeia complex and at a similar distance from the Sun. Both physical and kinematical indicators show that all these stars are young, with ages in the range 10-30 Myr. Using multivariate analysis methods, we selected optical counterparts of ROSAT All-Sky Survey / XMM-Newton X-ray sources cross-identified with late-type stars around these 4 young stars. Recent spectroscopic observations of this sample allowed us to discover additional lithium-rich sources. Our preliminary results showed that some of them share the same space motion as the 4 young c...
Once mixed in the galactic plane stellar population, young stars are virtually indiscernible from... more Once mixed in the galactic plane stellar population, young stars are virtually indiscernible from older ones. In the RasTyc sample, we nevertheless discovered 4 lithium-rich field stars that are located within a few degrees from each other on the celestial sphere and near the Cepheus-Cassiopeia complex. They form a homogeneous group of T Tauri stars. To discover some new comoving companions, we selected optical counterparts of ROSAT All-Sky Survey X-ray sources cross-identified with late-type stars around these 4 young stars thanks to multivariate analysis methods. Our recent intermediate- and high-resolution spectroscopic observations of this sample allowed us to discover additional lithium-rich sources. From the analysis of their spectra, we found that 6 of our young star candidates have similar physical and kinematical properties as those of the 4 comoving T Tauri stars. Moreover they are all located inside or close to the CO Cepheus void. They have properties rather similar to t...
After mixing in the Galactic plane, young stars are barely discernible from old ones. Nonetheless... more After mixing in the Galactic plane, young stars are barely discernible from old ones. Nonetheless, the characterization of stars in the RasTyc} sample has ledto the discovery of several sources whose lithium content is higher than that of the Pleiades cluster members. In the locus of the CO Cepheus void, we identified four comoving T Tauri stars within a few degrees. They likely form a new young association. Looking for the presence of further members, we performed selections through multivariate analysis. We focused on the late-type stars in the field, which are identified as the optical and infrared counterparts of ROSAT All-Sky Survey/XMM-Newton X-ray sources and are in a 30^circ-wide region encompassing this new moving group. Based on our spectroscopic observations of this dataset, we identified two distinct populations of lithium-rich stars that are spatially and kinematically separated. While the sources having the same lithium content as the members of the Pleiades cluster ar...
After mixing in the Galactic plane, young stars are barely discernible from old ones. In the RasT... more After mixing in the Galactic plane, young stars are barely discernible from old ones. In the RasTyc sample we have identified several stars whose lithium content is higher than that of the Pleiades cluster members. Furthermore, four of them are concentrated, within a few degrees, inside the CO Cepheus void. They likely constitute a new young association. To discover further additional members, we used multivariate analysis methods for selecting optical and infrared counterparts of ROSAT All-Sky Survey/XMM-Newton X-ray sources cross-identified with late-type stars. From our spectroscopic observations, we distinguished two populations of lithium-rich stars that are spatially and kinematically separated. While the sources having the same lithium content as the members of the Pleiades cluster are mostly projected towards the Galactic plane, the youngest stars are mainly located in the sky area surrounding the CO Cepheus void and have an age of about 5 - 15 Myr. The latter stars have pro...
We present new spectroscopic observations of the early type, double-lined eclipsing binary V446\,... more We present new spectroscopic observations of the early type, double-lined eclipsing binary V446\,Cep. The radial velocities and the photometric data obtained by $Hipparcos$ were analysed for deriving the astrophysical parameters of the components. Masses and radii were determined as M$_p$=17.94$\pm$1.16 M$_{\odot}$ and R$_p$=8.33$\pm$0.29 R$_{\odot}$, M$_s$=2.64$\pm$0.30 M$_{\odot}$ and R$_s$=2.13$\pm$0.10 R$_{\odot}$ for the components of V446\,Cep. Our analyses show that V446\,Cep is a detached Algol-type system. Based on the position of the components plotted on the theoretical Hertzsprung-Russell diagram, we estimate that the age of V446\,Cep is about 10 Myr, neglecting the effects of mass-loss and mass exchange between the components. Using the UBVJHK magnitudes and interstellar absorption we estimated the mean distance to the system V446\,Cep as 1100$\pm$62\,pc.
We studied orbital period changes in the non-eclipsing close binary HR 1099, one of the most brig... more We studied orbital period changes in the non-eclipsing close binary HR 1099, one of the most bright members of the RS CVn class of magnetically active binary systems. Intermediate-resolution optical spectroscopy and IUE archive spectra were used to build radial-velocity curves yielding epochs of superior conjunction with an accuracy of 0.01 days. The final database ranged from 1976 to 2002 and allowed us a better assessment of the amplitude of the orbital period variation and its timescale. (2 data files).
We observed in the optical range the strong infrared source IRAS F18187+6304 in the context of a ... more We observed in the optical range the strong infrared source IRAS F18187+6304 in the context of a program aimed to clarify the nature of the stellar objects of the Byurakan Infrared Source catalogue. The optical spectrum is characterized by continuum and absorption lines typical of early K-type giants plus a few permitted and forbidden emission lines. The sparse optical photometry did not put in evidence strong variations during the last 50 years. Our repeated observations indicate a substantial stability of the spectra and a monotonic increase of the luminosity in the BVR bands of about 0.4 magnitudes between Summer 2007 and Fall 2008. From a high resolution spectrum we measured a heliocentric radial velocity of -25 km/s and discovered a complex NaI-D structure resembling that of some T Tauri stars; the infrared CaII triplet is in absorption. A strong IR excess in the IRAS bands indicates a substantial quantity of circumstellar dust and gas. IRAS F18187+6304 is an isolated star at quite high galactic latitude, far from any star forming region. All these characteristics make this object an intriguing case of difficult interpretation. The preliminary results are discussed in the framework of the available synthetic energy distribution and accretion models.
Once mixed in the ambient galactic plane stellar population, young stars are virtually indiscerni... more Once mixed in the ambient galactic plane stellar population, young stars are virtually indiscernible because neither their global photometric properties nor the presence of nearby gas can help to disentangle them from older ones. Nevertheless, the study of the RasTyc sample revealed 4 lithium-rich field stars displaying the same space motion, which are located within a few degrees from each other on the celestial sphere near the Cepheus-Cassiopeia complex and at a similar distance from the Sun. Both physical and kinematical indicators show that all these stars are young, with ages in the range 10-30 Myr. Using multivariate analysis methods, we selected optical counterparts of ROSAT All-Sky Survey / XMM-Newton X-ray sources cross-identified with late-type stars around these 4 young stars. Recent spectroscopic observations of this sample allowed us to discover additional lithium-rich sources. Our preliminary results showed that some of them share the same space motion as the 4 young c...
Once mixed in the galactic plane stellar population, young stars are virtually indiscernible from... more Once mixed in the galactic plane stellar population, young stars are virtually indiscernible from older ones. In the RasTyc sample, we nevertheless discovered 4 lithium-rich field stars that are located within a few degrees from each other on the celestial sphere and near the Cepheus-Cassiopeia complex. They form a homogeneous group of T Tauri stars. To discover some new comoving companions, we selected optical counterparts of ROSAT All-Sky Survey X-ray sources cross-identified with late-type stars around these 4 young stars thanks to multivariate analysis methods. Our recent intermediate- and high-resolution spectroscopic observations of this sample allowed us to discover additional lithium-rich sources. From the analysis of their spectra, we found that 6 of our young star candidates have similar physical and kinematical properties as those of the 4 comoving T Tauri stars. Moreover they are all located inside or close to the CO Cepheus void. They have properties rather similar to t...
After mixing in the Galactic plane, young stars are barely discernible from old ones. Nonetheless... more After mixing in the Galactic plane, young stars are barely discernible from old ones. Nonetheless, the characterization of stars in the RasTyc} sample has ledto the discovery of several sources whose lithium content is higher than that of the Pleiades cluster members. In the locus of the CO Cepheus void, we identified four comoving T Tauri stars within a few degrees. They likely form a new young association. Looking for the presence of further members, we performed selections through multivariate analysis. We focused on the late-type stars in the field, which are identified as the optical and infrared counterparts of ROSAT All-Sky Survey/XMM-Newton X-ray sources and are in a 30^circ-wide region encompassing this new moving group. Based on our spectroscopic observations of this dataset, we identified two distinct populations of lithium-rich stars that are spatially and kinematically separated. While the sources having the same lithium content as the members of the Pleiades cluster ar...
After mixing in the Galactic plane, young stars are barely discernible from old ones. In the RasT... more After mixing in the Galactic plane, young stars are barely discernible from old ones. In the RasTyc sample we have identified several stars whose lithium content is higher than that of the Pleiades cluster members. Furthermore, four of them are concentrated, within a few degrees, inside the CO Cepheus void. They likely constitute a new young association. To discover further additional members, we used multivariate analysis methods for selecting optical and infrared counterparts of ROSAT All-Sky Survey/XMM-Newton X-ray sources cross-identified with late-type stars. From our spectroscopic observations, we distinguished two populations of lithium-rich stars that are spatially and kinematically separated. While the sources having the same lithium content as the members of the Pleiades cluster are mostly projected towards the Galactic plane, the youngest stars are mainly located in the sky area surrounding the CO Cepheus void and have an age of about 5 - 15 Myr. The latter stars have pro...
We present new spectroscopic observations of the early type, double-lined eclipsing binary V446\,... more We present new spectroscopic observations of the early type, double-lined eclipsing binary V446\,Cep. The radial velocities and the photometric data obtained by $Hipparcos$ were analysed for deriving the astrophysical parameters of the components. Masses and radii were determined as M$_p$=17.94$\pm$1.16 M$_{\odot}$ and R$_p$=8.33$\pm$0.29 R$_{\odot}$, M$_s$=2.64$\pm$0.30 M$_{\odot}$ and R$_s$=2.13$\pm$0.10 R$_{\odot}$ for the components of V446\,Cep. Our analyses show that V446\,Cep is a detached Algol-type system. Based on the position of the components plotted on the theoretical Hertzsprung-Russell diagram, we estimate that the age of V446\,Cep is about 10 Myr, neglecting the effects of mass-loss and mass exchange between the components. Using the UBVJHK magnitudes and interstellar absorption we estimated the mean distance to the system V446\,Cep as 1100$\pm$62\,pc.
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Papers by Antonio Frasca