COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 4094 Konkoly Observatory Budapest 30 September 1994 HU ISSN 0374 - 0676 MULTIPERIODIC PHOTOMETRIC VARIATIONS OF HD210111 AND SUSPECTED VARIABILITY OF HD210049 We present time series of our observations of a new variable lambda Boo star, HD210111 (m_V = 6.4), which is classified as kA2hA7mA2V lambda Boo by Gray and Corbally (1993). lambda Bootis stars are a group of metal poor PopulationI stars (Weiss et al. 1994) with broad and often shallow hydrogen lines, which are probably caused by a gas shell. There are indications for such a gas shell also for HD210111 (Sturenburg 1993). An abundance analysis for that star (Sturenburg 1993) gave a metal deficiency of about a factor of 10 compared to the Sun. Our observations were part of a survey for pulsation among lambda Boo stars (Paunzen, Weiss and North 1994, Kuschnig, Paunzen and Weiss 1994a,b), using the 70cm Swiss-telescope at ESO, La Silla with the Geneva photometer. When variability of HD210111 became evident in the raw data, it was decided to observe this lambda Boo type star as frequently as possible. PN and EP used HD210049 (m_V = 4.5, A1IVnn) as first comparison star during 8 nights distributed over 2 weeks, and in addition in one of these nights HD210302 (m_V = 4.9, F6V) as a second comparison. HD 210111: A quick look at the extinction corrected differential instrumental magnitudes (Fig.1) indicates already multiperiodic variations for this star. An amplitude spectrum computed with a single-frequency Fourier technique for unequally spaced data (program PERIOD, Breger 1990) indicates the presence of at least 2 pulsation frequencies (Fig.2, second panel). The frequencies with the largest amplitudes are = 27.99c/d and = 17.01c/d, which could be influenced by a 1c/d aliasing. In any case, this solution is rather formal and serves only as a guideline for the relevant frequency range. A simultaneous 4-frequency fit to the observations of HD210111, based on the lowest residuals after a step-by-step prewhitening, results in a scatter of 4.0mmag, which is almost twice the value for the extinction corrected observations of the comparison star HD210049. We thus conclude that probably several modes may be excited in HD210111. A problem for the frequency analysis is the poor duty cycle of only 7 of our single-site data. However, it is quite obvious that HD210111 is a promising candidate for an international photometric observing campaign. The calibration (Crawford 1979, Philip Relyea 1979, for [Fe/H] = -1) of uvbyHbeta photometry applied to the indices listed by Hauck & Mermilliod (1990) for HD210111 results in Mv = 1.65, Teff = 7900K, and log g = 3.95. These parameters give Q-values ranging from 0.014 to 0.022d, based on Q = -6.456 + log T_eff + 0.5 log g + 0.1 M_bol + log P According to pulsation models (Fitch 1981), such Q-values indicate pulsation in the second to fifth overtone. HD 210049: Our present analysis depends on the constancy of the primary comparison, HD210049, except for one night, where a second comparison star has been observed. [FIGURE 1] Figure 1. HD210111-HD210049 in Geneva-V, residuals to night-mean [FIGURE 2] Figure 2. Amplitude spectrum (bottom panel) and spectral window of the data of Fig. 1 [FIGURE 3] Figure 3. Amplitude spectrum of the extinction corrected Geneva-V photometry of HD210049 In order to demonstrate the validity of this assumption we show the amplitude spectrum of our extinction corrected instrumental data of HD210049 in Fig.3. The highest noise peaks for frequencies larger than 15c/d show amplitudes of 0.7mmag. However, a peak at 8.9c/d with an amplitude of 1.7mmag clearly exceeds the noise level. This peak also appears in the amplitude spectrum of the differential HD210111 - HD210049 data, but not in the HD210111 data alone. The differential magnitudes of the two comparison stars HD210049 - HD210302 have sigma=2.0mmag. We therefore cannot exclude variability of our primary comparison star, HD210049, with a period of about 2.7 hours, but cannot proof this claim with the second comparison star. However, it is quite safe to attribute the variability in the differential photometry of our lambda Boo star in the 15 to 30c/d frequency domain (Figs. 1 and 2) to HD210111, and not to the comparison star. Pulsation of HD210049 would be remarkable, because effective temperature and absolute magnitude (Teff = 9000K, Mv= 0.9), based on Stromgren photometry, locate this star outside the delta Scuti instability strip. On the other hand, the hot border of this instability strip is not very well defined and a shift towards hotter temperatures was recently proposed by Rodriguez et al. (1994). Conclusions: We discovered multi-periodic variability in the lambda Boo star HD210111 and cannot rule out variability of HD210049. The frequency spectrum of HD210111 is complicated and only a sufficiently long multi-site campaign (3 weeks or more) will allow a successful resolution. HD210111 is a promising candidate for applying asteroseismic techniques and thus to investigate the problem of the origin of lambda Bootis stars. Another interesting case is HD111786 (Kuschnig et al. 1994a). We also encourage further observations of HD210049. Acknowledgement: This research was supported by the Hochschuljubilaumsstiftung der Stadt Wien, and by the Swiss National Foundation for Scientific Research. E. PAUNZEN G. HANDLER W. W. WEISS Institut fur Astronomie Turkenschanzstr. 17 A-1180 Wien, Austria E-mail: LAST_NAME @ ASTRO.AST.UNIVIE.AC.AT P. NORTH Institut d'astronomie de l'Universite de Lausanne, CH-1290 Chavannes-des-Bois, Switzerland E-mail: NORTH@OBS.UNIGE.CH References: Breger, M., 1990, Communications in Asteroseismology 20, 1 (University of Vienna) Crawford, D. L., 1979, AJ, 84, 1858 [BIBCODE 1979AJ.....84.1858C ] Fitch, W. S., 1981, ApJ, 249, 218 [BIBCODE 1981ApJ...249..218F ] Gray R. O., Corbally C. 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