* Astronomy

Blobrana · L

RE: Delta Scorpii

Blobrana · L

Title: The 2011 Periastron Passage of the Be Binary delta Scorpii
Authors: A.S. Miroshnichenko, A.V. Pasechnik, N. Manset, A. C. Carciofi, Th. Rivinius, S. Stefl, V. V. Gvaramadze, J. Ribeiro, A. Fernando, T. Garrel, J. H. Knapen, C. Buil, B. Heathcote, E. Pollmann, B. Mauclaire, O. Thizy, J. Martin, S. V. Zharikov, A. T. Okazaki, T. L. Gandet, T. Eversberg, N. Reinecke

We describe the results of the world-wide observing campaign of the highly eccentric Be binary system delta Scorpii 2011 periastron passage which involved professional and amateur astronomers. Our spectroscopic observations provided a precise measurement of the system orbital period at 10.8092±0.0005 years. Fitting of the He II 4686A line radial velocity curve determined the periastron passage time on 2011 July 3, UT 9:20 with a 0.9--day uncertainty. Both these results are in a very good agreement with recent findings from interferometry. We also derived new evolutionary masses of the binary components (13 and 8.2 solar masses) and a new distance of 136 pc from the Sun, consistent with the HIPPARCOS parallax. The radial velocity and profile variations observed in the H_alpha line near the 2011 periastron reflected the interaction of the secondary component and the circumstellar disk around the primary component. Using these data, we estimated a disk radius of 150 solar radii. Our analysis of the radial velocity variations measured during the periastron passage time in 2000 and 2011 along with those measured during the 20th century, the high eccentricity of the system, and the presence of a bow shock-like structure around it suggest that delta Sco might be a runaway triple system. The third component should be external to the known binary and move on an elliptical orbit that is tilted by at least 40 degree with respect to the binary orbital plane for such a system to be stable and responsible for the observed long-term radial velocity variations.

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Blobrana · L

Title: Differential photometry of delta Scorpii during 2011 periastron
Authors: Costantino Sigismondi

Hundred observations of Delta Scorpii over 200 days, from April 2 to October 16, 2011, have been made for AAVSO visually and digitally from Rio de Janeiro, Rome and Paris. The three most luminous pixels either of the target star and the two reference stars are used to evaluate the magnitude through differential photometry. The main sources of errors are outlined. The system of Delta Scorpii, a spectroscopic double star, has experienced a close periastron in July 2011 within the outer atmospheres of the two giant components. The whole luminosity of Delta Scorpii system increased from about Mv=1.8 to 1.65 peaking around 5 to 15 July 2011, but there are significant rapid fluctuations of 0.2 - 0.3 magnitudes occurring in 20 days that seem to be real, rather than a consequence of systematic errors due to the changes of reference stars and observing conditions. This method is promising for being applied to other bright variable stars like Betelgeuse and Antares. After August the magnitude remained constant at Mv=1.8 until the last observation on October 16 made in twilight from Rome.

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Blobrana · L

Title: Delta Scorpii 2011 periastron: visual and digital photometric campaign
Authors: Leonid N Georgiev, Gloria Koenigsberger, D John Hillier, Nidia Morrell, Rodolfo Costantino Sigismondi

Hundred observations of Delta Scorpii, from April to September 2011, made for AAVSO visually and digitally with a commercial CMOS camera have been plotted. The three most luminous pixels either of the target star and the two reference stars are used to evaluate the magnitude through differential photometry. The main sources of errors are outlined. The system of Delta Scorpii, a spectroscopic double star, has experienced a close periastron in July 2011 within the outer atmospheres of the two giant components. The whole luminosity of Delta Scorpii increased from about Mv=1.8 to 1.65 peaking around 5 to 15 July 2011, but there are significant rapid fluctuations of 0.2-0.3 magnitudes occurring in 20 days that seem to be real, rather than a consequence of systematic errors due to the changes of reference stars and observing conditions. This method is promising for being applied to other bright variable stars like Betelgeuse and Antares.

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Blobrana · L

Occultation of Delta Scorpii

Occultation of Delta Scorpii on the morning of the 25th February 2011 from Australia.

Blobrana · L

Title: Delta Scorpii 2011 periastron: worldwide observational campaign and preliminary photometric analysis
Authors: Costantino Sigismondi

Delta Scorpii is a double giant Be star in the forefront of the Scorpio, well visible to the naked eye, being normally of magnitude 2.3. In the year 2000 its luminosity rose up suddenly to the magnitude 1.6, changing the usual aspect of the constellation of Scorpio. This phenomenon has been associated to the close periastron of the companion, orbiting on a elongate ellipse with a period of about 11 years. The periastron, on basis of high precision astrometry, is expected to occur in the first decade of July 2011, and the second star of the system is approaching the atmosphere of the primary, whose circumstellar disk has a H-alpha diameter of 5 milliarcsec, comparable with the periastron distance. The preliminary results of a photometric campaign, here presented in the very days of the periastron, show an irregular behaviour of the star's luminosity, which can reflect some shocks between material around the two stars. The small luminosity increasement detected in the observation of 5 of July 2011 at 20 UT may suggest that the periastron phenomena are now going to start.

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