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Simultaneous Observations of Variability at All Atmospheric Levels of V824 Arae (HD 155555)
We conducted a multiwavelength campaign observing V824 Ara (HD 155555,G5 IV+K0 IV-V) continuously throughout one complete orbital cycle (~1.7days) in early May of 1996. At the core of this campaign wereobservations using the GHRS on the Hubble Space Telescope (HST). In all,about 48,000 spectra, many in rapid readout mode, were obtained with theGHRS covering the C IV, Mg II, and Fe XXI wavelength regions at 11-15separate phases. Simultaneous observations were made with the ExtremeUltraviolet Explorer (EUVE). Radio observations (3.5 and 6 cm) wereconducted at the Australian Telescope, while ground-based visualspectroscopic and photometric observations were made at EuropeanSouthern Observatory, Cerro Tololo Inter-American Observatory, theAnglo-Australian Telescope, and South African Astronomical Observatory.Additional ground-based observations were obtained before, during, andafter the campaign. Our primary intent was to obtain a three-dimensionalmodel of the atmosphere extending from the photosphere to the corona.Variability was clearly detected, including several flares observed inthe HST, EUVE, and radio data. We present results from modeling theultraviolet transition region lines using an anisotropic macroturbulencemodel. Previous studies of transition region lines in late-type activestars have used multiple Gaussians to fit the observed line profiles,adding broad components to account for the extended wings observed inseveral active systems, including V711 Tau (HR 1099). This broadcomponent has been interpreted as arising from the continuous presenceof microflaring. We demonstrate that anisotropic macroturbulence modelscan also explain the observed Mg II profiles. Based on observations withthe NASA/ESA Hubble Space Telescope, obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555.
| Doppler imaging of stellar surface structure --- XIV. The double-lined pre-main-sequence binary V 824 Arae = HD 155555
Photospheric Doppler images for both stellar components of thedouble-lined pre-main-sequence binary V 824 Ara reveal surfacetemperature inhomogeneities of up to 1800 K on both stars. The spotgeometry on the hotter primary is dominated by an elongated, tilted,equatorial feature but our maps from two spectral regions consistentlyalso show a polar spot cooler by 1700 K. The secondary star has spotsmainly at low and very high latitudes but not a full-sized polar cap. Aflux-tube simulation with appropriate stellar models for V 824 Arasuggests that any polar or high-latitude spot must have formed afterflux-tube emergence. Generally, the low-latitude spots on both stellarcomponents appear to be mostly concentrated on the hemispheres turnedaway from each other while the asymmetry of the polar spot on theprimary points in the direction of the orbital motion. We present newradial velocities and use them to re- evaluate the orbital elements andto derive absolute parameters for both stellar components. The absolutebrightness and mass of the two stars suggest that they are very close tothe main sequence - but not yet on the ZAMS - if an inclination of theorbital plane (and rotational axes) of 52̂ is adopted as suggestedby the Doppler imaging. Since both stars are active, we solve for theinclinations of both stellar components separately and find that thevalues agree to within their uncertainties. Based on observationscollected at the European Southern Observatory
| Long-term monitoring of active stars. VII. UBV(RI)_c photometry collected in March 1991
In the framework of an extensive program focusing on the globalproperties and evolution of active stars, high-precision UBV(RI)_cphotometry of 19 selected stars, collected at the European SouthernObservatory over the 15-31 March 1991 interval is presented. Significantevolution of the light curves, period variations and evidence forlong-term variability of the global degree of spottedness are found.Most of the spectral classifications are discussed. A flare event wasdetected for the star HD 127535 = V 841 Cen. These observationscontribute to the establishment of a time-extended photometric databasewhich can give important clues on topics such as the stability ofspotted areas, differential rotation, solar-like cycles and thecorrelation between inhomogeneities at different atmospheric levelsFigure 1 to 24 are only available on the on-line version of A&A athttp://www.ed-phys.fr}. based on data collected at the European SouthernObservatory, La Silla, Chile. Tables and the complete data set are alsoavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr or via http://cdsweb.u-strasbg.fr/Abstract.html
| Long-term monitoring of active stars. VI. UBV(RI)_c observations collected in Sep.-Oct. 1990
In the framework of an extensive program focusing on the globalproperties and evolution of active stars, high-precision UBV(RI)_cphotometry of 9 selected stars, collected at the European SouthernObservatory over the intervals 7-17 September and 30 September - 10October 1990, is presented. Significant evolution of the light curves,period variations and evidence for long-term variability of the globaldegree of spottedness are found. Some of the spectral classificationsare discussed. These observations contribute to the establishment of atime-extended photometric database which can give important clues ontopics such as the stability of the spotted areas, differentialrotation, solar-like cycles and the correlation between inhomogeneitiesat different atmospheric levels. Based on data collected at the EuropeanSouthern Observatory, La Silla, Chile. Tables and the complete data setare also available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr or via http://cdsweb.u-strasbg.fr/Abstract.html
| Long-term monitoring of active stars. V. UBV(RI)_ c_ photometry collected in Feb.-Mar. 1990.
High-precision UBV(RI)_c_ photometry of 12 selected active stars,collected at the European Southern Observatory (La Silla, Chile) overthe period February - March 1990, is presented. Significant evolution ofthe light curves, period variations and, in most cases, evidence forlong-term variability of the global degree of spottedness are found.Some of the spectral classifications are discussed. This paper is partof a more extensive program focusing on the global properties andevolution of active stars and is aimed at establishing a time-extendedphotometric database which can give important clues on topics such asthe stability of the spotted areas, differential rotation and solar-likecycles.
| Longterm Monitoring of Active Stars - Part Three - UBV Ri/c Photometry of 14 Southern Hemisphere Variables
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102..655C&db_key=AST
| UBVRI Observations of the Chromospherically Active Star HD 155555 (V824 Ara) in 1986 and 1987
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Oltár |
| Rektaszcenzió: | 17h12m25.28s |
| Deklináció: | -66°36'34.7" |
| Vizuális fényesség: | 7.599 |
| Távolság: | 418.41 parszek |
| RA sajátmozgás: | -1.6 |
| Dec sajátmozgás: | -18.5 |
| B-T magnitude: | 9.689 |
| V-T magnitude: | 7.772 |
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