>H CMLO i Publications OFTHE Astronomical Society of the Pacific CTi 99:425-438, May 1987 S< THE SPECTRAL VARIATIONS OF THE DELTA SCUTI STAR RHO PUPPIS r-cu \—Is s. YANG,* G. A. H. WALKER,* AND P. BENNETT Department of Geophysics and Astronomy, University of British Columbia, Vancouver, BC V6T 1W5, Canada Received 1986 December 12, revised 1987 February 9 ABSTRACT Precise differential radial velocities of the sharp-lined (υ sin ί = 14 km s _1) δ Scuti variable ρ Pup (P = 3.37 hours) with a time resolution < P/15givea2Kamplitude of 9.08 km s_1for Ca II λ8662 and 8.35 km s-1 for Η ΐλ8750. The amplitudes for the Fe I, Si I, and S I velocities are 9.46, 9.23, and 9.41 -1 1 -1 km s , respectively. The 2 Κ/Διηυ value of 93 km s mag is typical of a radial pulsator. The line intensities of the stellar lines vary out of phase with the observed radial velocities but closer in phase with the light curve. The amplitudes of the variations are between 0.3% and 1% of the continuum. Most lines are weaker near light maximum (temperature maximum) and stronger near light minimum (temperature minimum). The variations correspond to the changes in spectral type associated with the variations of eifective temperature over the pulsation cycle. A simple linear theory is developed in which the temperature dependence of both the stellar continuum opacity and line opacity are calculated. Key words: δ Scuti variable-radial velocities-equivalent widths I. Introduction metric data and derived a period of 0^14088141 (3.3712 The star ρ Puppis (HR 3185, HD 67523) is a small-am- hours) and a blue-light amplitude of 0.126 mag. The light plitude, sharp-lined {v sin ¿ = 14 km s ^), δ Scuti variable curve was found to be nearly sinusoidal with the maxi- with a spectral type of F5 Hp (Morgan and Abt 1972). The mum slightly sharper than the minimum. Both the rising star is similar to the proto-Am (δ Delphini-type) stars and descending branches of the curve are equally steep. which show anomalous metal abundances. The enhanced Bappu (1959) measured a light amplitude of 0.16 mag at metal abundance in ρ Pup has been confirmed by Green- λ4050 together with a 300 Κ change in the color tempera- stein (1948), Bessell (1969), Breger (1970), and Kurtz ture. The simultaneous photometric and spectroscopic (1976). A value of 0.54 dex has been determined for observations by Danziger and Kuhi (1966) give a 2 Κ value -1 [Fe/H] by Kurtz (1976) who also found deficiencies in of 11 km s , a light amplitude of 0.15 mag at λ4566, and Ca i, Se II, Ti π, and V π. Meanwhile, Bidelman (1951), an effective-temperature variation of ± 140 K. Minimum McNamara and Augason (1962), and Morgan and Abt light was found to occur at about 0.08 of a period before (1972) have all pointed out that Ca π is weak in ρ Pup maximum radial velocity. when compared to stars of similar spectral type. Bessell (1969), using simultaneous radial-velocity and The star ρ Pup was first reported to exhibit variable photoelectric spectrum-scanner observations of the con- radial velocities by Reese (1903) and Campbell and Moore tinuum, measured a light amplitude of 0.130 mag at (1928). These early Lick velocities suggested a 2 Κ value X4255 and a 2 Κ value of 9.5 km s_1. One can measure (the peak-to-peak radial-velocity amplitude) of 8.4 km s_1. from his data that the radial-velocity minimum lags the Meanwhile, Spencer Jones (1928) derived a 2 Κ value of light maximum by about 0.075 in phase. Bessell (1969) has 11.6 km s-1 from Cape observations. The data from also reported a temperature variation of ± 65 Κ and a Struve, Sahade, and Zebergs (1956) has a 2 Κ amplitude of radius variation, AR, of ± 8 X 103 km. Thulasi Doss 9.7 km s-1 and a period of 0?1409. Additional radial-veloc- (1969) observed the photometric variations in the narrow ity measurements were also reported by Buscombe passbands at λ3858, λ4310, λ4720, and λ5875. The corre- (1957). Photometric variations were first reported by sponding amplitudes were given as 0.17, 0.14, 0.12, and Cousins (1951) and Eggen (1956, 1957). Ponsen (1963) 0.09 mag, respectively. An effective-temperature varia- reanalyzed all the early data together with his own photo- tion of ± 160 Κ and a period of 0^14088667 were also derived. Trodahl and Sullivan (1977) measured a light *Visiting Astronomer, Canada-France-Hawaii Telescope, which is amplitude of 0.105 mag at X4850 and an effective-temper- operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of ature variation of ± 90 K. A corresponding amplitude of Hawaii. about 0.033 was given for AR/R, the relative radius varia- 425 © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 426 YANG, WALKER, AND BENNETT tion. Dravins, Lind, and Sarg (1977), with simultaneous period of 0^141 (3.37 hours), respectively. Period cover- radial-velocity and photometric observations, have mea- age on the three nights was 83%, 112%, and 69%, respec- sured a phase lag of 0.06 between the radial-velocity tively. The mean S/N per diode (pixel) in the continuum of minimum and the light maximum. A temperature of ± each spectrum is 690, 800, and 400 for the three respec- 80 Κ was measured from the loop traveled by ρ Pup in the tive nights of observations. The midexposure time (in {c^ (b—y)) diagram over the pulsation cycle. Dravins et barycentric Julian day) of each observation is listed in al. (1977) also reported emission in the blue wing of the Table I. Ca π Κ line profile at about 0.28 in phase before maximum A spectrum of ρ Pup without the imposed HF lines is light. It has been suggested that the emission was caused shown in Figure 1. Lines from the same atomic or ionic by a shock wave propagating through the stellar atmo- species are indicated with the same number and are sphere (Dravins et al. 1977; Hill 1977; Smith 1982). identified in the caption. Simultaneous photometry and photoelectric radial veloc- The data reduction was performed using the program ities have also been given by Balona and Stobie (1983). RETICENT (Pritchet, Mochnacki, and Yang 1982). The With a Reticon detector, Campos and Smith (1980) mea- technique of preprocessing the Reticon spectra to obtain sured a 2 Κ value of 11.5 km s-1 from the Fe I λ4476 and the optimum S/N has been described in Walker et al. Fe π λ4508 lines. No line width or line-profile variation (1985). The procedure to measure radial velocities from greater than 5% of the continuum was detected. the stellar + HF spectra has been described in Yang et al. Smith (1982) adopted, for ρ Pup, a Δτη^ value (the peak- (1982) and Yang and Walker (1986α,&). The same stan- to-peak light amplitude in V) of 0.102 mag and a phase dard stellar and lamp + HF spectra were used to measure difference of 0.08 between the light maximum and the the radial velocities from all of the spectra. This ensures radial-velocity minimum. Reay, Hicks, and Atherton internal consistency for the measured velocities between (1983) used a servo-controlled Fabry-Perot-radial-veloc- the three time series. ity spectrometer to measure the radial-velocity variations TABLE I of Pup with a precision of ± 20 m s_1. From 226 minutes ρ Relative Radial Velocities of ρ Puppis (3.76 hours) of observations, there was no evidence of periodicity other than the period of 0^141. Fracassini et Mid-exposure Ca II mean mean mean time λ8662 Fe I Si I S I al. (1983) have reported a time series of IUE high-disper- BJD2445356+ (kms"1) (kms"1) (kms"1) (kms-1) sion observations of the Mg π H and Κ lines. Emission in 0.90112 -1.118 -1.119 -0.855 -0.950 the cores of the lines was found to be present over the 0.90839 +0.245 +0.211 +0.341 +0.462 0.91564 +1.484 +1.508 +1.715 +1.846 entire pulsation cycle. These emissions increased with 0.92289 +2.590 +2.694 +2.956 +3.056 increasing luminosity of the star. 0.93021 +3.702 +3.824 +3.968 +4.007 0.93748 +4.525 +4.600 +4.695 +4.793 Because it is so bright (V = 2.82 mag), ρ Pup offers a 0.94473 +4.771 +4.860 +4.976 +5.002 0.95197 +4.758 +4.655 +4.871 +4.767 rather unique opportunity to apply high S/N spectra to 0.95921 +4.079 +3.866 +4.107 +4.017 0.96646 +2.898 +2.793 +2.713 +2.803 the study of δ S cuti pulsation. In this paper, we report the 0.97372 +1.521 +1.162 + 1 .309 + 1 .244 results obtained with spectra having S/N in the range 400 0.98097 -0.213 -0.571 -0.651 -0.603 0.98821 -1.948 -2.384 -2.234 -2.332 to 800 per pixel. Radial velocities of ρ Pup were measured 0.99545 -3.220 -3.674 -3.447 -3.663 1.00271 -4.105 -4.526 -4.310 -4.518 using the hydrogen fluoride (HF) absorption-cell tech- 1.00996 -4.361 -4.761 -4.629 -4.799 nique (Campbell and Walker 1979; Yang and Walker 1.01844 -4.137 -4.544 -4.256 -4.629 2.84152 -4.644 -4.772 -4.768 -4.686 1986a).