Heavy elements in peculiar stars

In a group of seven late-type peculiar stars a search was made for the heavy elements Os (76), Pt (78), Au (79) and U (92) previously identified in 73 Dra by Jaschek and Malaroda. The results are given in Table I.Asociación Argentina de Astronomí

Variaciones espectrales en estrellas Ap

Se obtuvieron alrededor de 450 espectros, en Cerro Tololo y La Plata, con una dispersión de 40 Å/mm de una lista de 30 estrellas Ap. En la mayoría de ellos se observan variaciones en la intensidad de líneas de elementos tales como el calcio, europio, silicio, estroncio y cromo y además variaciones en algunos perfiles tales como en la línea K del calcio ionizado. El trabajo completo, con la determinación de períodos, se publicará más adelante.Asociación Argentina de Astronomí

The symbiotic binary system RX Puppis: a possible recurrent nova with a Mira companion

We present an analysis of photometric and spectroscopic observations of the symbiotic binary system RX Pup with the aims of developing a reliable binary for the system and identifying mechanisms responsible for its spectacular activity. The binary is composed of a long-perod Mira variable surrounded by a thick dust shell and a hot white dwarf companion. The hot component produces practically all activity observed in the UV, optical and radio range, while variable obscuration of the Mira by circumstellar dust is responsible for long-term changes in the near-IR magnitudes. The observations show RX Pup underwent a nova-like eruption during the last three decades. The hot component contracted in radius at roughly constant luminosity from 1975 to 1986, and was the source of a strong stellar wind which prevented it from accreting material lost in the Mira wind. Around 1988/9 the hot component turned over in the HR diagram and by 1991 its luminosity had faded by a factor of about 30 with respect to the maximum plateau value and the hot wind had practically ceased. By 1995 the nova remnant started to accrete material from the Mira wind, as indicated by a general increase in intensity of the optical continuum and HI emission. The quiescent spectrum resembles the quiescent spectra of symbiotic recurrent novae, and its intensity indicates the hot component must accrete as much as about 1 per cent of the Mira wind, which is more or less the amount predicted by Bondi-Hoyle theory. The earliest observational records from the 1890s suggest that another nova-like eruption of RX Pup occurred around 1894.Comment: 23 pages, 12 figues, MNRAS - accepte

Velocidades radiales en sistemas múltiples tipo trapecio I. ADS 4241 (Sigma Orionis)

Las componentes del sistema ADS 4241 fueron observadas utilizando el telescopio de 36" del Observatorio Interamericano de Cerro Tololo. Se obtuvieron 55 espectrogramas con una dispersión de 63 Å/mm que fueron medidos con el microcomparador Grant del Observatorio Astronómico de La Plata, con el fin de analizar el comportamiento de las velocidades radiales y de tratar de determinar la posible presencia de compañeras espectroscópicas. El objetivo principal del trabajo es comparar las velocidades radiales medias de las componentes y verificar las características del movimiento relativo entre ellas. Como standards de velocidad radial fueron observadas las estrellas HD 44131 y B Leporis de las cuales se obtuvieron 14 y 18 espectrogramas, respectivamente. Los resultados obtenidos que se muestran en la Tabla I, parecen sugerir que las componentes del sistema a Ori se mueven en conjunto en el espacio, a pesar de la configuración aparentemente inestable que presentan (ver Tabla 1).Asociación Argentina de Astronomí

Linear polarization of a group of symbiotic systems

We report linear polarization measurements of a set of symbiotic stars, made at several epochs during the period 1994-1998. Evidence of intrinsic polarization is looked for from the wavelength dependence of the polarization degree and position angle in UBVRI bands. The results have also been analysed to search for temporal variability of polarization. Several objects have shown a polarization spectrum different from that produced by interstellar dust grains and/or polarimetric variations on time scales as short as several days or months, indicating the presence of polarization component of circumstellar origin.Facultad de Ciencias Astronómicas y Geofísica

Linear polarization of a group of symbiotic systems

We report linear polarization measurements of a set of symbiotic stars, made at several epochs during the period 1994-1998. Evidence of intrinsic polarization is looked for from the wavelength dependence of the polarization degree and position angle in UBVRI bands. The results have also been analysed to search for temporal variability of polarization. Several objects have shown a polarization spectrum different from that produced by interstellar dust grains and/or polarimetric variations on time scales as short as several days or months, indicating the presence of polarization component of circumstellar origin.Facultad de Ciencias Astronómicas y Geofísica

Spectroscopic orbits and variations of RS Ophiuchi

The aims of our study are to improve the orbital elements of the giant, and to derive the spectroscopic orbit for the white dwarf companion. Spectral variations related to the 2006 outburst are also studied. Methods. We performed an analysis of about seventy optical and near infrared spectra of RS Oph that were acquired between 1998 and June 2008. The spectroscopic orbits have been obtained by measuring the radial velocities of the cool component absorption lines and the broad Hα emission wings, which seem to be associated with the hot component. A set of cF-type absorption lines were also analyzed for a possible connection with the hot component motion. Results. A new period of 453.6 days, and a mass ratio, q = Mg/Mh = 0.59 ± 0.05, were determined. Assuming a massive white dwarf as the hot component (Mh = 1.2 − 1.4M⊙) the red giant mass is Mg = 0.68 − 0.80M⊙ and the orbit inclination, i = 49◦ − 52◦. The cF-type lines are not associated with either binary component, and are most likely formed in the material streaming towards the hot component. We also confirm the presence of the Li I doublet in RS Oph and its radial velocities fit very well the M-giant radial velocity curve. Regardless of the mechanism involved to produce lithium, its origin is most likely from within the cool giant rather than material captured by the giant at the time of the nova explosion. The quiescent spectra reveal a correlation of the HI and He I emission line fluxes with the monochromatic magnitudes at 4800 Å indicating that the hot component activity is responsible for those flux variations. We also discuss the spectral characteristics around 54–55 and 240 days after the 2006 outburst. In April 2006 most of the emission lines present a broad pedestal with a strong and narrow component at about -20 kms−1 and two other extended emission components at -200 and +150 kms−1. These components could originate in a bipolar gas outflow supporting the model of a bipolar shock-heated shell expanding through the cool component wind perpendicularly to the binary orbital plane. Our observations also indicate that the cF absorption system was disrupted during the outburst, and restored about 240 days after the outburst, which is consistent with the resumption of accretion.Facultad de Ciencias Astronómicas y Geofísica

KX Tra y He-127: dos estrellas simbióticas de alta excitación

These two high excitation symbiotic stars were included in the observing programme of spectroscopic research of southern symbiotic stars, carried out in CASLEO, with 2.15m telescope, during 1990 and 1991. The observed spectral region (~4400-7200 Å) showed several emission lines of allowed and forbidden transitions with a broad ionization range. The wavelength and flux calibrated images of both stars were analyzed in order to obtain radial velocities, equivalent widths and intensities of the emission features. The intensities of the red continuum and the molecular bands, allowed us to give the spectral type of the late type companion in these systems.Asociación Argentina de Astronomí

Spectroscopic orbits and variations of RS Ophiuchi

The aims of our study are to improve the orbital elements of the giant, and to derive the spectroscopic orbit for the white dwarf companion. Spectral variations related to the 2006 outburst are also studied. Methods. We performed an analysis of about seventy optical and near infrared spectra of RS Oph that were acquired between 1998 and June 2008. The spectroscopic orbits have been obtained by measuring the radial velocities of the cool component absorption lines and the broad Hα emission wings, which seem to be associated with the hot component. A set of cF-type absorption lines were also analyzed for a possible connection with the hot component motion. Results. A new period of 453.6 days, and a mass ratio, q = Mg/Mh = 0.59 ± 0.05, were determined. Assuming a massive white dwarf as the hot component (Mh = 1.2 − 1.4M⊙) the red giant mass is Mg = 0.68 − 0.80M⊙ and the orbit inclination, i = 49◦ − 52◦. The cF-type lines are not associated with either binary component, and are most likely formed in the material streaming towards the hot component. We also confirm the presence of the Li I doublet in RS Oph and its radial velocities fit very well the M-giant radial velocity curve. Regardless of the mechanism involved to produce lithium, its origin is most likely from within the cool giant rather than material captured by the giant at the time of the nova explosion. The quiescent spectra reveal a correlation of the HI and He I emission line fluxes with the monochromatic magnitudes at 4800 Å indicating that the hot component activity is responsible for those flux variations. We also discuss the spectral characteristics around 54–55 and 240 days after the 2006 outburst. In April 2006 most of the emission lines present a broad pedestal with a strong and narrow component at about -20 kms−1 and two other extended emission components at -200 and +150 kms−1. These components could originate in a bipolar gas outflow supporting the model of a bipolar shock-heated shell expanding through the cool component wind perpendicularly to the binary orbital plane. Our observations also indicate that the cF absorption system was disrupted during the outburst, and restored about 240 days after the outburst, which is consistent with the resumption of accretion.Facultad de Ciencias Astronómicas y Geofísica

The interacting eclipsing binary AU Monocerotis revisited

New spectrographic observations of the Algol binary AU Monocerotis have permitted the determination of the orbital elements of the two components of the system. They have further suggested that the image tube spectrograph that was attached to the CTIO 1m-reflecting telescope in 1978 and 1979 was not quite suitable for radial velocity work.Facultad de Ciencias Astronómicas y Geofísica