Simultaneous optical and X-ray observations of flares and rotational modulation on the RS CVn binary HR 1099 (V711 Tau) from the MUSICOS 1998 campaignD. Garcia-Alvarez, et al., 2003, A&A, 397, 2852004/05/19 Plasma seminar

1. IntroductionRS CVn binary: chromospherically active evolved star + main sequence (or sub-giant) tidally locked co-rotating binary (Porb = Prot = 1 - a few ten days) energetic flares (logE =34-36 (erg)) large dark spots (photometry, spectroscopy)V711 Tau: one of the brightest and most active RS CVns (V=5.64) d = 29 pc, K1 IV primary + G5 V secondary Porb = 2.84 days long-lived (>11yr) polar spot + transient (

MUSICOS (Multi-Site Continuous Spectroscopy) campaign held in 1989 (Foing et al. 1994) and 1989

9 telescopes (0.9m 2.5m) at the below 8 sites were used 1998 Nov. 21 Dec. 13 2. Observations

Rossi X-ray Timing Explorer (RXTE): all-sky monitor detector (ASM) 4 energy bands: A(1.3-3.0 keV), B(3.0-4.8 keV) C(4.8-12.2 keV), S(1.3-12.2 keV)Optical photometry: 0.8-m tel. of Catania Astrophysical Obs., Italy 0.25-m tel. of Fairborn Obs., USA

3. Photometry and spot modellingSpot modelling by two methods (maximum entropy & Tikhonov criterion) for the orbital light curve. K1IV G5VTeff 4750K 5500KSpot 3750K 4500K

4. Spectroscopy4.1 radial velocity and orbital solutionAnalysis of the radial velocity variations of photospheric lines Fe I 6430.84A and Ca I 6439.07A, using a two-Gaussian fitting.Kpri 49.660.34 km/sKsec 62.880.70 km/sPorb 2.83774 days Assuming i=33deg,M1 1.45MsolM2 1.14MsolH velocity during flares

4.2 chromospheric activity indicatorsNa I D1, D2 doublet (formed in the upper photosphere)Ca II H & K (lower chromosphere)He I D3 (upper chromosphere)Rotational behavior (see Fig. 9)The EWs of He I D3 and Na I D are enhanced between = 0.5 and 1.0. (pumping of the chromospheric emission by coronal X-rays from an overlying active region)That of H is also increased between = 0.7 and 1.0.But those of H and Ca II H&K do NOT show any rotational modulation behavior.

Time series of H line. The vertical scale indicates the accumulative orbital phse.Time series of Na I D doublet and He I D3.

Time series of HTime series of Ca II H & K

Variations of EW. H, Na I D, He I D3, H, Ca II H, Ca II K, from top to bottom.The abscissa of the left panels is Jurian Day, and that of the right panels is the orbital phase.Two flares are obvious about JD 2451145 and JD 2451151.

5.Flares analysisTwo optical flares: at JD 2451145.51 (28/11/98) lasting about 0.63 days at JD 2451151.07 (03/12/98) 1.1 days5.1 hydrogen linesH: EW increase by a factor of 2 broad component (FWHM =2.87=131 km/s at =0.7923; 4.52=207 km/s at =0.7981; 3.47=159 km/s at =0.8571) noticeable blue wing excess during a rising phase narrow absorption feature in the red partMax EW During the first flare

Profile variations during the first optical flare

Profile variations during the second optical flare

During the second flare H: EW increase by a factor of 4 line broadenings similar to those during the first flare blue wing excess during the rising phase, but symmetrical profile around the maximum at =0.8141 base width for the blue and red winds of 6.25 (286 km/s) at the maximum narrow absorption component during the rise phaseOther than these two flares EW enhancements were sometimes seen in H around JD 2451143.0, 2451156.5, and 2451157.3, and in H around JD 2451155.0, and 2451157.3. referred as `flare-like, hereafter

5.2 the Na I D1, D2 doublet (5895.92, 5889.95)During both flares, these lines showed a filling-in.There is a `flare-like event happened at around JD 2451155.0.5.3 the He I D3 line (5876)This line turns into emission during the second optical flare, but not during the first one. It peaks before the Balmer lines.Three `flare-like events around JD 2451148.0, 2451156.5, and 2451159.6 (=0.8-0.9)

5.4 the Ca II H & K lines Small increase in flux around the flare maximum.These lines peaked later than the Balmer lines.5.5 flare locationSlight displacement of RV compared to the center of gravity of the primary. flares took place off the disk of the primary.Both flares took place around the same phase 0.85 a link to the active region complexDuring the MUSICOS 89, a flare occurred at a similar phase 0.87. long-lived active region

5.6 energy releasedExcess EW (EW(flare)-EW(quiescence)) flare energy 1.3 x 10**34 erg for the first flare 5.5 x 10**34 erg for the second

6. X-ray dataFlare and flare-like eventAll events are detected in the S and A band, but not in the B and C band. These X-ray events were soft.

6.1 X-ray and optical flare correlationThe X-ray event at JD 2451151.07 corresponds to the second optical flare.Flare-like events at JD 2451143.02, 245155.24, 2451156.74, and 2451157.24 have relevant EW increases of some lines.However, the first optical flare at JD 2451145.51 was not observed in any of the X-ray bands.6.2 flare periodicityMost of the X-ray flares and flare-like events took place at 0.31 (JD 2451149.63, 2451152.54, and 2451155.24), or at 0.91 (JD 2451143.02, 2451151.23, 2451157.24, and 2451159.64) there were two active regions!

There are 3 possible explanations for the periodicity.Rotational variability of two very large flares which lasted more than 8 days.Occultation of the flaring regionPeriodic flaringAs for 1), one would expect an exponential decay in the X-ray flux. As for 2), the light curve should have an on-off fashion. The authors believe 3) in that the two active regions, flaring at the same epoch, are responsible for the observed behavior of the X-ray light curve.