HD 170714

1. 5th COROT WEEK, BERLIN 10-12 DECEMBER 2003 PHOTOMETRY OF BRIGHT Be STARS IN THE CONES OF COROT J. Gutiérrez-Soto1, J. Fabregat1, J. Suso2, A.M. Hubert3, M. Floquet3, C. Neiner3, E. Janot-Pacheco4 and R. Garrido5 1Observatori Astronòmic, Universitat de València, 2Instituto Ciencia de los Materiales, Universitat de València, 3GEPI, Observatoire de Paris-Meudon, 4IAG, Universidade de São Paulo, 5Instituto de Astrofísica de Andalucía Abstract: We present differential photometry of bright Be stars in the cones of COROT. Several stars are found to be short period variables and two of them multiperiodic variables with high amplitude. Introduction The observation of classical Be stars by COROT will provide important keys to understand the physics of these objects and the nature of the Be phenomenon. In particular, the detection of photospheric multiperiodicity will confirm the presence of non radial pulsations (nrp) as the origin of the short term variability. COROT observations will allow the study of the beat phenomenon of nrp modes and its relation with the recurrent outburst and the building of the circumstellar disc. Our group is proposing the observation of Be stars as secondary targets in the asteroseismology fields. The first results of our search were presented at CW4 (Gutierrez-Soto et al 2003). Now we are extending our photometric search to bright Be stars, in order to find likely candidates to be proposed as primary targets in the asteroseismolgy fields for the short runs. In this paper we present the results of our first observing campaigns. Observations and data analysis Observations were done at the 0.9 m telescope of the Observatorio de Sierra Nevada (Granada, Spain). The instrument used was the automatic six-channel spectrophotometer which allows simultaneous observations through the four uvby filters of the Strömgren system. Differential photometry of eight Be stars in the galactic center direction was obtained in the period 1 to 12 of July 2003. The observing strategy was to observe all eight stars every night. We chose a comparison and a check star which were constant for each target and observed these set of stars every night. Fortunately, we have 9 consecutive photometric days, from 1 to 9 of July. The period analysis was performed by means of standard Fourier-analysis with subsequent prewhitening steps. For this we have used Scargle (1982) and PDM (Stellingwerf 1978) techniquesandmultifrequency least squares to fit the parameters. Phase curves at the detected frequencies were made. Notes on individual stars HD 168797 This star has been studied by Hubert et al (1998) using Hipparcos data. A period of 0.488 days is proposed. Percy et al (1999) found two possible periods: 0.46d and 5.5d from both the Hipparcos and ground-based data. Pavlovski et al (1997) noted that the amplitude varies from season to season. Our 9-days light curve shows a variation in amplitude in a short lenght of time which can be caused by the beat of two close frequencies. The periodogram analysis gives 4 short periods: 1.5835 d ,0.694 d, 0.4537 d, 0.4427 d. Moreover there is a long term variation which is compatible with the 5.5d period given by Percy. HD 170714 This star is found periodic. The possible period is 0.359 days. We present the phase curve with this period. HD 171219 This star is not variable at our detection level. In Gutierrez-Soto et al (2003) we also found this star constant. HD 173637 Short term variability is found. The periodogram analysis shows a significant peak in 3.01 c/d and in its aliases caused by the spectral window. The frequency too close to an entire fraction of a day makes difficult to distinguish the actual frequency from the aliases. We present the phase curve with the 0.33 days period, which we consider the most likely one. The determination of the actual period would need more observational work. HD 181231 This star is not variable at our detection level. The same conclusions has been reached from the observations by Poretti et al (2003), presented at this meeting. HD 181367 That star is not variable at our detection level. HD 173817 This star is found variable with a 0.2849 d. period. We present the phase curve with this period. HD 179405 This star presents short term variability. The variation of amplitude implies the existence of at least two frequencies. 2.024 d, 0.56 d, 0.3879 d, 0.3634 d are the most likely periods we have found in our analysis. The two shorter periods are so close that their precise determination would need a longer photometric study. Conclusions Our observations confirm that stars HD 168797, HD 170714, HD 173637, HD 173817 and HD 179405 are periodic variables, with the periods given in Table 1. HD 171219, HD 181231 and 181367 appear as no variables in our data. All results are summarized in Table 1. Among them, HD 168797 and HD 179405 are multiperiodic variables. We consider them as suitable candidates for the COROT short runs. A more detailed description of the variablity of these stars is presented at this meeting (Fabregat et al 2003). TABLE 1 • References • Fabregat et al. 2003, 5th COROT Week, Berlin. • Gutierrez-Soto et al. 2003, 4th COROT Week, Marseille. • Hubert, A.M. et al. 1998, A&A, 335, 565-572 • Pavlovski et al. 1997, A&AS, 125,75 • Percy J. R. et al. 1999, A&A, 348, 553-556 • Poretti et al. 2003, 5th COROT Week, Berlin. • Scargle, J.D. 1982, ApJ, 263, 835 • Stellingwerf, R. F. 1978, ApJ, 224, 953S