CDROM/APJ/V439/P983 UX Arietis (Elias+ 1995) ================================================================================ Correlations Between the Flaring Radio Emission and Starspot Distribution of UX Arietis Nicholas M. Elias II, Andreas Quirrenbach, Arno Witzel, Christian E. Naundorf, Ralf Wegner, Edward F. Guinan and George P. McCook <1995, ApJ, 439, 983> =1995ApJ...439..983E ================================================================================ Abstract: We have observed UX Arietis at C band (6 cm) for 3 weeks with four VLA antennas. The temporal coverage during the program was approximately three scans per day. A few days into the VLA program, UX Ari began a radio flaring period which lasted for at least 2 weeks. All the radio fluxes were above the system noise during this episode, but the largest values (up to 270 mJy) occurred close to 0.0 phase. This phasing is confirmed by the UX Ari radio observations of Neidhoefer, Massi, & Chiuderi-Drago (1993, A&A, 278, L51). Visible-band light curves of UX Ari were obtained both during and after our radio observations; the peak-to-peak variation in all filters was ~ 0.2 mag. The light curves indicate that the maximum starspot visibility occurred very close to 0.0 phase, the same phase as the radio maxima. Closer comparison of our radio and optical light curves indicates that they are almost perfectly anticorrelated. A similar radio/optical correlation has been found by Lim et al. (1992, ApJ, 388, 27) and Lim et al. (1994, ApJ, 430, 332) for the single K0 V star AB Dor. We make the following conclusions from our observations. First, the episodes of long-term (~hours to days) radio flaring were modulated by stellar eclipses. Second, the flares were located close to the starspot groups. Third, the sizes of the flares were comparable to sizes of the starspot groups, which is consistent with nonthermal emission of brightness temperature T_b ~ 10^10-10^13 K. Fourth, the radio emission arose only from the midlatitude starspot groups. Last, the radio flares emitted their radiation nearly normal to the stellar surface. Keywords: radio continuum: stars -- stars: flare -- stars: individual (UX Arietis) File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- radio.dat 19 42 UX Arietis C-band VLA observations optical.dat 31 418 UX Arietis visible-band photometry -------------------------------------------------------------------------------- Byte-by-byte Description of file: radio.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 8 F8.4 d HJD Heliocentric Julian Date (- 2448000) 9-15 F7.4 --- Phase Phase 16-19 I4 mJy Flux Radio flux -------------------------------------------------------------------------------- Byte-by-byte Description of file: optical.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1-10 F10.5 d HJD Heliocentric Julian Date (- 2440000) 11-18 F8.5 --- Phase Phase 19-24 F6.3 mag dMag *Differential magnitude, Var - Comp 25 1X --- --- Blank 26-27 A2 --- Filter *Filter: b', y, r 28 1X --- --- Blank 29-31 A3 --- Obs *Observatory, VUO or APT -------------------------------------------------------------------------------- Notes for file: optical.dat -------------------------------------------------------------------------------- dMag: Comparison star was 62 Ari (HR 1012, HD 20825; V = +5.52; B-V = +1.10; G5 III). Check star was HR 999 (HD 20644, V = +4.47, B-V = +1.54; K4 III). 62 Ari has been used previously in photometric studies of UX Ari and appears to be constant in light. Filter: Intermediate-band intererence filters: b' - lambda = 453 nm, FWHM = 15 nm y - Stromgren y, lambda = 550 nm, FWHM = 35 nm r - lambda = 660 nm, FWHM = 28 nm, also known as H-alpha I Obs: VUO - Villanova University Observatory, APT - Automatic Photometric Telescope, Mount Hopkins, Arizona -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 06-May-1995