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19 6 6Apj. . .14 6. .743D the VARIABILITY of RHO PUPPIS* I. J .743D 6. .14 THE VARIABILITY OF RHO PUPPIS* . I. J. Danziger and L. V. Kumf 6ApJ. Mount Wilson and Palomar Observatories 6 19 Carnegie Institution of Washington, California Institute of Technology Received April 30, 1966 ABSTRACT The results of simultaneous spectrophotometric and spectral observations of the short-period variable star, p Puppis, are reported. The amplitudes of radial-velocity, light, and temperature variations are 11 km/sec, 0.15 mag., and 280° K, respectively. The relative phases differ from those observed in cluster- type c variables. Estimates of the absolute luminosity and mass from the observed gravity and the Py/(p/po) — Q relationship indicate that either p Puppis is pulsating in a higher-order harmonic mode than the first or the theory of its pulsation is not understood. I. INTRODUCTION The bright star p Puppis, classified in the MKK system as type F6II, was first shown to be variable in light (period 0.141 days) by Eggen (1956) who measured a total ampli- tude of 0.15 mag. Struve, Sahade, and Zebergs (1956) showed that there is an associated variation in radial velocity with a total amplitude of 10 km/sec and that maximum brightness occurs approximately 0.02 days later than minimum radial velocity. Bappu (1959) reported that two-color measurements indicate a variation in temperature of 300° K. An intrinsic luminosity of p Puppis, MPg = +2.4, was obtained by Kinman (1959). He assumed it fitted the observed period-luminosity relation of cluster-type c variables in order to use an observed period-luminosity relation. Strömgren’s c-l sys- tem indices were measured by McNamara and Augason (1962) to derive Mpg = +1.7 and a mass 9J£ = 3.2 $)îo from the period-density law with the pulsation constant Q ~ 0-041* It is of interest to note that, although p Puppis has been classified as a ô Scuti star, none of the multiple-period characteristics associated with such stars has been found to apply to it. For example, the amplitudes of both light and radial-velocity variations remain constant, and there is no evidence for the existence of a secondary period. Rlio Puppis has the lowest temperature of all known ô Scuti stars, and a significantly greater space velocity. Greenstein’s (1948) abundance analysis of this star showed that the heavy elements are relatively more abundant than the lighter elements compared to the Sun, in the manner of Am stars. McNamara and Augason (1962) reported that the K-line (Ca n) photoelectric index is weak for its spectral type. The observations reported below were made to provide greater insight into the vari- ability and evolutionary role of such stars. II. OBSERVATIONS Simultaneous high-dispersion spectra and spectrophotometric continuum observa- tions were obtained for the duration of a complete cycle on the night of January 22-23, 1965. The continuum observations were made with the Cassegrain photoelectric spec- trum scanner (used with a refrigerated 1P21 photomultiplier) on the 60-inch reflector at Mount Wilson. The intensities at sixteen discrete wavelengths (selected by Oke [1964] * This research was supported in part by the United States Air Force under contract AF 49(638)-1323, monitored by the Air Force Office of Scientific Research of the Office of Aerospace Research. f Presently at the Berkeley Astronomical Department, University of California. 743 © American Astronomical Society • Provided by the NASA Astrophysics Data System .743D 6. 744 I. J. DANZIGER AND L. V. KUHI .14 . to be relatively free of lines) were measured with an exit slit of SO Â, and corrected for 6ApJ. atmospheric extinction by using mean extinction coefficients for Mount Wilson. A nearby 6 secondary standard, 16 Puppis, was observed intermittently during the cycle and was 19 tied to Oke’s system of absolute standards by observing € Ori and a Leo on the same night. A check on the validity of the mean extinction coefficients was also provided by the observations of 16 Pup at different zenith distances. No deviations of individual fluxes greater than 1 or 2 per cent or gross variations in extinction during the course of the observations were detected. Since the observed continuum of 16 Pup is also in good agreement with that expected from its spectral type it is reasonable to conclude that the extinction corrections are not in error. Coudé spectra of the violet and blue regions were taken on baked IlaO plates with a dispersion of 4.5 Â/mm with the 32-inch camera of the 100-inch telescope. These spectra Fig. 1.—Radial velocity, light, and temperature of p Pup plotted as a function of Pacific Standard Time. Radial velocity measurements are relative, not absolute. were used to define the radial-velocity variation of p Pup and to provide line-blanketing corrections to the continuum observations. Additional plates of the visual and far-ultra- violet regions were obtained at a few phases to complete the blanketing corrections. The uncorrected continuum fluxes expressed in magnitudes per unit frequency inter- val around the cycle are given in Table 1, together with the continuum measures of 16 Pup and the blanketing corrections which are effectively the same at all phases. The corrections, obtained by measuring the energy absorbed by the line spectrum from the smooth continuum, are similar to those in Hyades stars of the same temperature (Oke and Conti 1966). In particular, because the size of the Balmer jump is sensitive to the surface gravity, we were concerned with the corrections shortward of the Balmer jump where it is difficult to judge the position of the continuum. Because Oke and Conti obtained gravities which appeared to be reasonable for the Hyades stars, it seems likely that the gravities obtained here for p Pup are not subject to large errors. An effective temperature and gravity at each phase was obtained by fitting the continuum measures corrected for blanketing to theoretical models computed with the program of Mihalas (1965). A more detailed discussion of the method has been given by Oke (1965). In Figure 1 the radial-velocity, light, and temperature variations are plotted © American Astronomical Society • Provided by the NASA Astrophysics Data System .743D 6. t'* V© ^ !>• © i-t 04 CN CM 00 © 00 © OO CM .14 C<5 CO ^ ^ LO lO lO »O lO ^ CO ^ CO . On © ©\ ^ »O v© 00 O rt< CM co O- 6ApJ. 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N© !>.to vo NOOn N©On NOOn CO00 CM CM CM CM CM CM CM CM CM CM CM CM oO bo 0 v© CM © CM i-ii © 00 NO VO 1—1 CM ’rfl i-HI©©CO’^»OVO©tH©i-HIO 3a '■g ¿ CMCMCOCOCOCOCO©© (P •äl S CM CM CM CM CM CM CM CM © © © © © v© cj P Pi pq © American Astronomical Society Provided by the NASA Astrophysics Data System .743D 6. 746 I. J. DANZIGER AND L. V. KUHI Vol. 146 .14 . as a function of time. The light variations are those measured at 4566 Â. Changes in the 6ApJ. gravity are not shown since the amplitude of the expected variations is smaller than the 6 error in an individual determination, i.e., ±0.2 in the logarithm. Only relative radial 19 velocities are plotted. It can be seen that the amplitudes of the radial-velocity, light, and temperature varia- tions are 11 km/sec, 0.15 mag., and 280° K, respectively, in good agreement with previous determinations quoted above. However, the relative phases of light and radial velocity are different. Minimum light occurs approximately 0.08 P before maximum radial velocity. Minimum temperature seems to occur closer to maximum radial velocity than to minimum light, a conclusion supported by effective temperatures derived from Hy profiles, by the method of Searle and Oke (1962).
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