Publications of the Astronomical Society of the Pacific 105: 281-286, 1993 March The He I /16678 Emission Line of Phi Persei: New Evidence of the Companion Star Douglas R. Gibs, Chilinda Y. Willis, and Laura R. Penny Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303-3083 Electronic mail: [email protected], [email protected] David McDavid Division of Earth and Physical Sciences, University of Texas at San Antonio, 6900 North Loop 1604 West, San Antonio, Texas 78249-0663 Electronic mail: [email protected] Received 1992 November 2; accepted 1992 December 9 ABSTRACT. We present Ha and He I /16678 emission profiles for the Be binary system φ Persei. Both lines display orbital phase-related variations in radial velocity and equivalent width that can be used to associate the lines with emitting gas surrounding the Be star primary or undetected secondary. We find that one component of He I /16678 emission follows the He π /14686 radial-velocity curve given by Poeckert (1981) which indicates an origin in the circumstellar gas near the secondary. A second emission component probably forms between the stars in a gas flow directed toward the high-density portion of the primary's circumstellar disk that faces the secondary. 1. INTRODUCTION kms-1), double-peaked Hell /14686 emission line which displays anti-phase motion and is probably formed in a The Be star φ Persei is the more massive member of a disk surrounding the secondary, and (5) generally weak binary system in which the photosphere of the companion shell lines (seen in He I A/L4026, 4471) that follow the has yet to be detected. In a seminal paper, Poeckert ( 1981 ) motion of He π /14686 and thus probably form in the outer presented radial-velocity data for many line features, and part of the disk surrounding the secondary (where the gas he showed that the He II /14686 emission line originates in is cooler). The shell lines from the primary's disk (3) gas surrounding the secondary. Based on this association, strengthen significantly near primary superior conjunction, Poeckert estimated the masses to be 21.1 and 3.4 Mq for and for this and related reasons, Poeckert argues that the the primary and secondary, respectively. Poeckert argued density of the disk is enhanced in the direction of the sec- that the high excitation required to produce He II /14686 in ondary. emission indicates a high-temperature secondary, and he In the course of study of the polarimetric and photo- suggested that the secondary is the remnant He core of a spheric profile variations in φ Per (Gies and McDavid once more massive star. The period (127 days) and veloc- 1987), we discovered a weak emission feature in the He I ity curve of the primary have been confirmed more recently /16678 line which displays radial-velocity changes similar by Jarad et al. ( 1989), and variations in the Balmer profiles to those seen in He π /14686. This weak line has also been have been documented by Whitehome (1992). Although observed by Hendry ( 1977) and Hubert et al. ( 1988). The the system has a high inclination (estimated by Poeckert to ο ο He I /16678 emission offers important new clues about the be in the range 80 -88 ), eclipses are not seen (Brown distribution of circumstellar gas in the binary, and in this 1992) but fadings may occur near conjunctions due to the paper we describe its orbital variations and how they relate influence of circumstellar material. The maximum angular to Poeckert's model of the system. separation in the sky is approximately 0.04 arcsec, but the system has not been resolved by speckle interferometry 2. OBSERVATIONS (Hartkopf and McAllster 1984), presumably because of the large magnitude difference between components (AmB The spectra used in this study were obtained between > 1.9; Poeckert 1981). 1985 September 24 and 1988 July 24 at the University of Poeckert (1981) groups the spectral components into Texas McDonald Observatory using the 2.1-m telescope five categories: (1) broad absorption lines formed in the and coudé spectrograph. The spectra were made using a photosphere of the Be primary ( V sin /=447 km s_1), (2) 600 grooves mm-1 grating in first order with an OG515 emission lines (H Balmer, Fe il) which share the primary's filter to block higher orders, and they have a reciprocal motion and are formed mainly in the circumstellar disk dispersion of 9.7 A mm-1. The detector was a Reticon surrounding the primary, (3) narrow absorption features (RL1728H/20) consisting of a linear array of 1728 15 (mainly He I "shell'* lines) which follow the motion of the X 750 μτΆ pixels. The spectra generally have a S/N ratio of primary for most of the orbit (see Harmanec 1985) and 400 per pixel at the peak of Ha (although in some spectra which are probably formed in the outer region of the disk the Ha region was overexposed to increase the S/N ratio surrounding the primary, (4) a broad (full width of 570 at 6678 A), and they have a spectral resolution of 0.56 A 281 © 1993. Astronomical Society of the Pacific © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 282 GIES ET AL. Table 1 Emission Measurements 10% 0.0 Orbital HJD Κ (wings) Wx ^-(1) Vr{2) FWHM Wx Phase (2440000+) (km s-1) (Â) (km s -1) (km s ^ (km s-1) (Â) 0.0522 7158.6958 -1.0 -107.9 93 0.177 0.0523 7158.7120 -105.0 92 0.159 0.2180 6799.6166 4.0 -124.7 -63.6 67 0.181 0.2180 6799.6217 -124.5 -64.8 57 0.181 0.2254 6800.5592 2.6 -128.8 -58.7 51 0.160 0.2255 6800.5644 -128.4 -60.5 54 0.167 0.2492 6803.5661 -127.4 -51.2 63 0.194 0.2493 6803.5769 -125.9 -45.6 57 0.200 0.5 0.4394 6447.5747 -4.7 52.1 -32.8 177 0.272 LU 0.4398 6447.6235 -5.4 52.3 -27.4 178 0.273 CO 0.4406 6447.7249 -6.3 51.9 -26.8 179 0.306 < 0.4472 6448.5682 -6.3 52.8 -16.7 165 0.300 IE 0.4478 6448.6476 -8.1 52,1 -22.9 159 0.302 CL 0.4550 6449.5557 -5.4 52.7 -7.7 170 0.326 0.4557 6449.6483 53.7 -13.4 173 0.364 0.4631 6450.5753 53.0 -0.8 180 0.292 0.4637 6450.6518 -6.1 52.7 -1.0 172 0.302 CÛ 0.4713 6451.6209 -5.9 53.1 15.6 176 0.265 cr 1.0 0.4788 6452.5719 -7.0 52.7 20.7 161 0.257 O 0.4795 6452.6642 -6.9 53.0 23.1 172 0.253 0.4866 6453.5541 -9 5 52.2 33.3 164 0.282 0.5347 6332.9527 74.7 106 0.264 0.5348 6332.9739 -6.6 51.9 70.5 114 0.268 0.6957 7366.9188 -17.5 49.8 103.0 59 0.162 0.6957 7366.9248 105.7 51.8 59 0.156 0.7313 6484.5580 113.2 47.4 53 0.145 FWHM (equivalent to four pixels). The exposed part of the Reticon recorded the spectrum over the wavelength range 6500-6710 A. The heliocentric Julian dates and the orbital phases for each spectrum are listed in Table 1. The -600 -400 -200 0 200 400 600 1 typical exposure time was approximately 1 min. The or- VELOCITY (km s ) bital phase was calculated from the ephemeris of Hickok (1969) (Ρ= 126.696 days; T0=JO 2424473.500), and Fig. 1—Upper frame: He I A6678 spectra of φ Per (solid lines) plotted phase 0.46 corresponds to superior conjunction of the pri- against heliocentric radial velocity. The profiles are arranged in order of increasing orbital phase and each spectrum is placed in the y ordinate so mary. that the continuum equals the phase of observation (phase 0.46=primary The first step in the reduction was to remove irregular- superior conjunction). The bar in the upper right gives the spectrum ities in the Reticon detector by dividing the stellar spectra intensity scale relative to a unit continuum. Lower frame·. A gray-scale by an average flat-field exposure, made from all the flat representation of the observed profile variations shown above. Here each spectral intensity is assigned one of 16 gray levels based on its value fields taken during the night. The spectra were then recti- between the minimum (deepest-line core; depicted bright) and maximum fied to a unit continuum by fitting a straight line through (highest-emission peak; depicted dark) observed values. The spectrum at selected continuum points in order to correct for any slope each phase in the image is calculated by a linear interpolation between the and/or curvature in the data. Iron arc exposures were used closest observed phases. The spectral image for the first and last 20% of the orbit are reproduced at the bottom and top of the image, respectively, to make a wavelength calibration, and the spectra were to improve the sense of phase continuity. The white line in the gray-scale then transformed to a uniform, heliocentric velocity grid. image shows the secondary velocity curve from Poeckert (1981). The resulting spectra appear in Figs.