.167B .18. The Astrophysical Journal Supplement Series No. 160, Vol. 18 (c) 1969. The University of Chicago. All rights reserved. Printed in U.S.A. 9ApJS. 6 19 AN INVESTIGATION OF SHORT-PERIOD VARIABLE STARS - I. THE DELTA SCUTI STARS M. S. Bessell* Mount Stromlo and Siding Spring Observatories, Research School of Physical Sciences, Australian National University Received Jidy 24> 1968; revised September 30y 1968 ABSTRACT Photoelectric continuum observations between 3390 and 10400 Â have been obtained for the MKK standard stars rj Lep F0 V and a CMi F5 IV (Procyon) and for the Delta Scuti stars p Pup, 5 Set, and ô Del over complete cycles. Coudé spectra covering from 3390 to 6700 Â were obtained to measure the Hy profile and to correct the observed fluxes for line blanketing. The resultant energy distributions and profiles were compared with the model-atmosphere computations of Mihalas and of Searle and Oke to derive the effective temperatures and gravities. For each star the same value of the effective temperature was derived from both the Hy profile and the energy distribution. From a fitting of the continuum of Procyon to the Mihalas computations it was found that the true gravity of Procyon could only be derived by adopting the solar value of He/H = 0.11 for the model composition, instead of the value of 0.15 used by Mihalas. Large anomalous line blanketing in the blue-violet region was found for p Pup and 8 Set, and curve-of-growth analyses relative to 77 Lep showed that the line strengthening in these stars was due to high microturbulence and an apparent overabundance of the iron-group elements. These peculiarities and the low Ca/Fe and Sc/Fe ratios also found for 8 Set, 8 Del, and p Pup are similar to the properties of metallic-line stars. The masses of the Delta Scuti stars determined from the observed temperatures and gravities are consistent with normal left-to-right evolution in the HR diagram for stars of about 1.9 Af o. The space motions of all the known Delta Scuti stars support the interpretation of their being old A stars. INTRODUCTION Recent investigations of Delta Scuti stars have resulted in low temperatures, low gravities, and unexpectedly low masses being derived for many of these stars (Danziger and Kuhi 1966; Kuhi and Danziger 1967; Dickens 1967; Danziger and Dickens 1967). An independent investigation of short-period variable F stars made at this observatory from 1964 to 1966 obtained values of 6e and log g for the Delta Scuti stars p Pup, d Set, and d Del which were not in agreement with those derived by the above authors. A brief out- line of the probable reasons for the differences has been given previously (Bessell 1967), and additional observations and a fuller discussion given here strengthen both the conclusion made in that paper and the proposition that the Delta Scuti stars are Popula- tion I stars of about 1.5-2 Mo evolving from the main sequence. In this paper, spectrophotometric observations of the variable stars p Pup, ô Set, and 6 Del and the non-variable stars r) Lep and a CMi are presented. The bright, sharp-lined MKK standards rj Lep F0 V and a CMi F5 IV, having colors bracketing those of the variable stars, were chosen as comparison stars for both the observational and reduction procedures and for the curve-of-growth analyses. In addition, because a CMi has an accurate parallax (0''288) and mass (1.8 Mo), it was possible to compare for the first time the actual log g (where g is the gravitational acceleration) with that derived by fitting the continuum flux to model-atmosphere computations. OBSERVATIONS Continuum observations with the Cassegrain photoelectric spectrum scanner on the 50-inch telescope at Mount Stromlo were made covering four periods for p Pup and one * Present address: Yerkes Observatory, Wilfiams Bay, Wisconsin. 167 © American Astronomical Society • Provided by the NASA Astrophysics Data System .167B .18. 168 M. S. BESSELL complete cycle for d Set and 8 Del. Blue (3390-5700 Â) and red (5000-10000 Â) scans 9ApJS. 6 were made on different cycles for p Pup, but consecutively on the same cycle for 8 Del. 19 Extinction was determined each night, and the energy distributions were placed on an absolute scale by using Oke standards modified as described by Bessell (1967). The red and blue observations were combined by best fitting the overlapping points. The un- corrected fluxes at many phases, expressed in magnitudes per unit frequency interval, are given for p Pup in Table 1 and for ô Del and 8 Set in Table 2. Instantaneous energy TABLE 1 Absolute Energy Distributions (-2.5 log Fy+const.) for Various Phases p Pup Epoch JDq 2435560.756, Period 0.14088143 1A 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 3.03. 4.759 4.718 4.675 4.636 4.626 4.659 4.694 4.729 4.760 4.774 2.95. 4.641 4.613 4.571 4.528 4.526 4.551 4.586 4.621 4.639 4.651 2.90. 4.566 4.529 4.489 4.448 4.441 4.467 4.501 4.533 4.569 4.583 2.85. 4.574 4.541 4.496 4.457 4.449 4.479 4.513 4.541 4.569 4.586 2.80. 4.456 4.432 4.397 4.349 4.344 4.366 4.388 4.415 4.446 4.466 2.75. 4.386 4.354 4.318 4.280 4.262 4.286 4.316 4.344 4.371 4.391 2.48. 3.256 3.234 3.193 3.144 3.116 3.136 3.167 3.206 3.242 3.258 2.40. 3.196 3.164 3.125 3.083 3.063 3.072 3.102 3.138 3.176 3.198 2.35. 3.106 3.084 3.039 3.001 2.980 2.994 3.021 3.056 3.091 3.111 2.24. 3.071 3.049 3.002 2.966 2.948 2.971 2.996 3.027 3.056 3.079 2.19. 2.994 2.965 2.926 2.886 2.873 2.891 2.916 2.941 2.975 2.998 2.09. 2.873 2.853 2.816 2.784 2.766 2.781 2.802 2.828 2.861 2.881 2.00. 2.923 2.902 2.874 2.842 2.826 2.832 2.853 2.879 2.909 2.930 1.95. 2.869 2.848 2.818 2.791 2.774 2.777 2.798 2.827 2.858 2.878 1.90. 2.868 2.845 2.813 2.787 2.776 2.785 2.805 2.830 2.855 2.875 1.85. 2.801 2.776 2.741 2.716 2.713 2.806 2.731 2.756 784 2.803 1.80. 2.781 2.761 2.736 2.703 2.691 2.711 2.736 2.758 769 2.778 1.72. 2.701 2.689 2.674 2.651 2.640 2.646 2.663 2.681 696 2.706 1.65. 2.689 2.684 2.668 2.644 2.636 2.640 2.651 2.664 673 2.682 1.57. 2.708 2.696 2.676 2.655 2.644 2.651 2.668 2.681 691 2.701 1.47. 2.694 2.684 2.668 2.642 2.631 2.636 2.652 2.668 2.684 2.694 1.41. 2.696 2.681 2.661 2.646 2.639 2.642 2.661 2.678 2.692 2.696 1.33. 2.713 2.699 2.681 2.666 2.662 2.668 2.686 2.699 2.711 2.716 1.27. 2.703 2.699 2.686 2.669 2.664 2.671 2.683 2.692 2.698 2.704 1.24. 2.713 2.705 2.688 2.661 2.651 2.658 2.669 2.683 2.699 2.711 1.19. 2.668 2.653 2.636 2.615 2.606 2.610 2.624 2.638 2.655 2.671 1.14. 2.530 2.521 2.506 2.494 2.480 2.477 2.486 2.500 2.514 2.526 1.03. 2.726 2.714 2.706 2.694 2.683 2.681 2.689 2.700 2.711 2.706 1.01. 2.703 2.693 2.676 2.660 2.661 2.672 2.686 2.696 2.704 2.708 0.98. 2.719 2.713 2.697 2.674 2.651 2.651 2.671 2.688 2.701 2.716 0.96. 2.748 2.729 2.712 2.701 2.693 2.689 2.695 2.698 2.706 2.716 distributions were read from monochromatic light curves derived from the observations of p Pup, while for ô Del and 8 Set the listed distributions are discrete scans, the phase referring to the midpoint of the scan. Table 2 also contains the energy distribution of r¡ Lep and a CMi. In order to correct for line blanketing and to measure the hydrogen-line profile and the radial velocity, coudé spectra simultaneous with the scans were taken covering the spectral range 3300-6700 Â. The dispersions obtained were 6.7 Â mm“1 in the blue, and 10 Â mm-1 in the ultraviolet, visual, and red.