COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3893 Konkoly Observatory Budapest 10 June 1993 HU ISSN 0374 - 0676 SERENDIPITOUS DISCOVERY OF DELTA SCUTI PULSATION IN THE EARLY A STAR HD 127269 The Edinburgh-Cape Survey is a search for blue stellar and quasi-stellar objects lying at high galactic latitude in the southern hemisphere. On 24/25 February 1993 while testing the white dwarf EC 14276-2508 for pulsational light variations, we serendipitously found delta Scuti variations in an early A star, HD 127269. HD 127269 is classified A2 in the HD catalogue; Houk & Smith-Moore (1988) classify it A3V. It has V = 7.8 and B = 7.9, consistent with its early A spectral type. We monitored the brightness of HD 127269 in the second channel of the two-channel University of Cape Town photometer attached to the 1-m telescope at the Sutherland observing station of the South African Astronomical Observatory. This star was selected because of its proximity to the target white dwarf and its apparent brightness. Observations were made through a Johnson B filter using continuous 10-s integrations with interruptions for guiding and sky measurements. The observations were corrected for coincidence losses, sky background and extinction. The times were corrected to Heliocentric Julian Date to an accuracy 10^-5 d. We then averaged groups of 6 observations to give 60-s integrations. Table 1 gives the HJD and magnitudes normalized in the mean to zero for HD 127269. Fig. 1 shows the 2.5-hr long light curve. While high-speed photometry is not the best way to observe delta Scuti stars, on good photometric nights, it can detect even small light variations with confidence. We judge the night of 24/25 February 1993 to have been good enough for this at Sutherland. We thus claim that the variations seen in Fig. 1 are not atmospheric in origin, but are characteristic of HD 127269. The observations of EC 14276-2508 obtained in channel 1 cannot be used to verify this; that star is so faint that the photon statistics give the observations much more scatter than the amplitude of HD 127269. We performed a Discrete Fourier Transform on the data listed in Table 1 which shows a clear peak at 30 d^-1. A least-squares fit of that frequency to the data, and then a non-linear least-squares optimization give: f = 29.93 +- 0.15 d^-1 (P = 48.1 +- 0.2 minutes); A = 4.92 +- 0.14 mmag; phi = -2.774 +- 0.059 radians; and a = 1.06 mmag per 60-s observation, where these parameters fit the relation Delta B = A cos (2 pi f(t-t_0) + phi ) where t0 = 9043.50000. The solid line fitted to the data in Fig. 1 has those parameters. [FIGURE 1] Fig. 1. The light curve of HD 127269. The plotted points are given in Table 1; the fitted curve is constructed from the parameters given in this note. Table 1. Johnson B observations of HD 127269 normalized in the mean to zero. HJD B HJD B HJD B HJD B 9043.49179 -0.0040 9043.52142 0.0014 9043.55059 0.0071 9043.57525 0.0008 9043.49249 -0.0031 9043.52212 0.0009 9043.55129 0.0042 9043.57594 0.0016 9043.49318 -0.0055 9043.52281 -0.0012 9043.55198 0.0044 9043.57664 0.0023 9043.49388 -0.0042 9043.52351 0.0005 9043.55268 0.0035 9043.57733 0.0027 9043.49461 -0.0050 9043.52428 -0.0014 9043.55337 0.0036 9043.57803 0.0022 9043.49538 -0.0058 9043.52501 -0.0007 9043.55407 0.0020 9043.57888 0.0024 9043.49608 -0.0046 9043.53207 -0.0046 9043.55476 0.0020 9043.57965 0.0030 9043.49677 -0.0061 9043.53277 -0.0054 9043.55545 0.0022 9043.58034 0.0036 9043.49746 -0.0023 9043.53346 -0.0042 9043.55904 -0.0024 9043.58104 0.0033 9043.49816 -0.0042 9043.53416 -0.0042 9043.55974 -0.0037 9043.58173 0.0040 9043.49885 -0.0044 9043.53485 -0.0052 9043.56043 -0.0038 9043.58242 0.0035 9043.49955 -0.0037 9043.53558 -0.0030 9043.56113 -0.0032 9043.58312 0.0048 9043.50036 -0.0044 9043.53636 -0.0047 9043.56182 -0.0041 9043.58381 0.0030 9043.50105 -0.0031 9043.53707 -0.0037 9043.56251 -0.0037 9043.58451 0.0019 9043.50175 -0.0031 9043.53786 -0.0025 9043.56321 -0.0039 9043.58520 0.0035 9043.50244 -0.0036 9043.53856 -0.0013 9043.56390 -0.0041 9043.58590 0.0021 9043.51089 0.0034 9043.53925 -0.0015 9043.56460 -0.0040 9043.58659 0.0010 9043.51159 0.0047 9043.53994 -0.0006 9043.56529 -0.0048 9043.58733 0.0010 9043.51228 0.0052 9043.54064 -0.0001 9043.56599 -0.0044 9043.58810 -0.0003 9043.51297 0.0053 9043.54133 0.0019 9043.56680 -0.0039 9043.58879 0.0004 9043.51367 0.0053 9043.54203 0.0012 9043.56761 -0.0047 9043.58949 -0.0009 9043.51436 0.0059 9043.54272 0.0030 9043.56830 -0.0027 9043.59018 -0.0006 9043.51506 0.0060 9043.54342 0.0048 9043.56900 -0.0036 9043.59087 -0.0029 9043.51575 0.0054 9043.54411 0.0032 9043.56969 -0.0034 9043.59157 -0.0022 9043.51645 0.0062 9043.54481 0.0038 9043.57039 -0.0026 9043.59226 -0.0024 9043.51714 0.0040 9043.54550 0.0047 9043.57108 -0.0035 9043.59296 -0.0030 9043.51783 0.0056 9043.54666 0.0060 9043.57178 -0.0020 9043.59365 -0.0030 9043.51855 0.0072 9043.54781 0.0050 9043.57247 -0.0007 9043.59435 -0.0046 9043.51934 0.0037 9043.54851 0.0035 9043.57317 -0.0012 9043.59481 -0.0037 9043.52003 0.0029 9043.54921 0.0063 9043.57386 0.0000 9043.52073 0.0019 9043.54990 0.0058 9043.57456 0.0014 An A3V star has beta = 2.871 and M_v = 2.4 (Crawford 1979). It is easy to rearrange the pulsation equation P(P/P_sun)^1/2 = Q to log Q = -6.454 + log P + 55 log g + 0.1 M_bol + log T_eff, where P is measured in days, g is in cgs units and T_eff in K. The beta index implies T_eff = 8800 K; the luminosity class implies log g ~= 4. Applying the above equation gives Q = 0.018 for T_eff = 8800 K and log g = 4.0, or Q = 0.027 for T_eff = 9000 K and log g = 4.3. These Q-values indicate pulsation in a low overtone - probably not the fundamental mode. That they are reasonable for an early A star supports the contention that Fig. 1 does demonstrate light variability in HD 127269 and is not an artifact. This star lies near the observed blue border of the delta Scuti instability strip where there is a tendency for the stars to pulsate in overtones higher than the fundamental (see Breger 1979). As the reader has probably guessed, we did not expect to find delta Scuti pulsation in our comparison star. We selected it at the eyepiece of the telescope (in lazy ignorance) as the brightest convenient guide and comparison star for the program star. In retrospect, it is no surprise that we found such variability in an A3V star, since delta Scuti variability is extremely common in the instability strip. It would be interesting to know what fraction of stars in the instability strip with normal spectra do not show variability when observed with the accuracy of the HD 127269 data presented here. D. O'Donoghue and D. W. Kurtz Department of Astronomy University of Cape Town Rondebosch 7700 South Africa email: dod@uctvax.uct.ac.za and dkurtz@uctvax.uct.ac.za References Breger, M., 1979. PASP, 91, 5 [BIBCODE 1979PASP...91....5B ] Crawford, D. L., 1979. AJ, 84,1858 [BIBCODE 1979AJ.....84.1858C ] Houk, N. & Smith-Moore, M., 1988. Michigan Spectral Catalogue, vol. 4, Department of Astronomy, University of Michigan, Ann Arbor [BIBCODE 1988mcts.book.....H ]