MONITORING THREE LESS-STUDIED SCUTI VARIABLES: GW URSAE MAJORIS, BO LYNCIS, AND AN LYNCIS

The Astronomical Journal, 130:2876 2883, 2005 December # 2005. The American Astronomical Society. All rights reserved. Printed in U.S.A. MONITORING THREE LESS-STUDIED SCUTI VARIABLES: GW URSAE MAJORIS, BO LYNCIS, AND AN LYNCIS Eric G. Hintz, 1 Tabitha C. Bush, 1 and Michael B. Rose 1 Department of Physics and Astronomy, Brigham Young University, N283 ESC, Provo, UT 84602; doctor@tardis.byu.edu, tabitha.bush@gmail.com, shenpei@hotmail.com Received 2005 August 9; accepted 2005 August 22 ABSTRACT We present results from monitoring three Scuti variables. GW UMa is found to be a stable, monoperiodic, highamplitude Scuti variable with a revised period of 0.20319389 days. We also report a full radial velocity curve, a near-solar metal content, and a rotational velocity of 15 5kms 1. From a very short time line we find that BO Lyn has a constant period change of 1:5 ; 10 10 days day 1. We also find two potential secondary frequencies of f 2 ¼ 15:81 and f 3 ¼ 13:60 cycles day 1. Finally, we report some unusual results for AN Lyn. We show that the period and amplitude are changing in phase and that this change is related to a binary companion. Key words: Scuti stars: individual (GW Ursae Majoris, BO Lyncis, AN Lyncis) 1. INTRODUCTION The theoretical and observational aims of monitoring highamplitude Scuti variable stars ( HADSs) are eloquently discussed by Kiss et al. (2002). As part of our monitoring program we have examined three medium- to high-amplitude Scuti variables: GW Ursae Majoris, BO Lyncis, and AN Lyncis. These stars have each been monitored for a relatively short period of time compared to other HADSs. The variability of GW UMa (GSC 03011-02418; 2000 ¼ 10 h 44 m 11: s 2, 2000 ¼þ44 40 0 43 00, hv i¼ 9:60, V ¼ 0:51) was discovered by the Hipparcos satellite. GW UMa appears to be just on the boundary between the Scuti classification and the RR Lyrae stars ( Poretti 2001). This star was studied by Derekas et al. (2003) and reported as monoperiodic with an ephemeris given in equation (1). Because of the high Galactic latitude (+59N14) and high velocity ( 81 km s 1 ), Derekas et al. (2003) classified GW UMa as an SX Phe star. The short baseline of observations makes this an interesting target for further monitoring; HJD max ¼ 2;448;500:1160 þ 0:20319367E: BO Lyn (GSC 02985-01044; 2000 ¼ 08 h 43 m 01: s 2, 2000 ¼ þ40 59 0 51 00, hv i ¼ 11:95, V ¼ 0:25) is a HADS that was part of the Case photometric and spectroscopic survey of AF stars published by Pesch & Sanduleak (1989). The photometric variations of this star were examined by Kinman (1998), and the ephemeris given in equation (2) was calculated. Kinman (1998) also reported that the maxima with earlier phases are brighter than those with later phases. It was postulated that this was due to modulations of the light curve by a second pulsational frequency. In addition to photometric information, Kinman (1998) also gave a mean radial velocity of +30 2kms 1. Since the observations reported in Kinman (1998), this star has received little attention; HJD max ¼ 2;438;788:0355 þ 0:0933584E: AN Lyn (GSC 02990-00019; 2000 ¼ 09 h 14 m 29: s 0, 2000 ¼ þ42 45 0 45 00, hv i ¼ 10:70, V ¼ 0:18) is a medium-amplitude 1 Guest investigator, Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada. Observations were made with the 1.85 m Plaskett Telescope and the 1.22 m McKellar Telescope. ð1þ ð2þ 2876 Scuti star that was discovered by Yamasaki et al. (1981). From photometric data Yamasaki et al. (1981) found a period of 0.0982747 days and determined that the star was monoperiodic. They also estimated a distance of 700 pc. From spectroscopic observations Yamasaki et al. (1981) classified AN Lyn as an A7 IV V star. In the following years a number of groups (Agerer et al. 1983; Yamasaki et al. 1983; Costa et al. 1984) added additional times of maximum light and debated the correct period value for AN Lyn. These papers also reported AN Lyn to be a monoperiodic star. A pair of papers from Rodriguez et al. (Rodriguez et al. 1997a, 1997b) gave more detailed analysis of AN Lyn. The light curve of AN Lyn was found to have a steeper descending branch and to have amplitude variations from cycle to cycle. From a Fourier analysis Rodriguez et al. (1997b) found three independent frequencies ( f 1 ¼ 10:1756, f 2 ¼ 18:1309, and f 3 ¼ 9:5598 cycles day 1 ). This refuted earlier claims that AN Lyn was monoperiodic. Additional information was reported in the two Rodriguez et al. papers. They found that AN Lyn has an approximately solar metal abundance. The near-solar metal abundance was supported by Strömgren observations reported by Balona & Evers (1999). Rodriguez et al. (1997b) also determined that the period of AN Lyn is decreasing over time at a rate of dp/dt ¼ 5 ; 10 7 yr 1. However, neither the linear nor the quadratic fit were satisfactory for the (O C ) residuals. Finally, they reported that the amplitude was decreasing over time. LaCluyzé et al. (2001) reported that the amplitude of AN Lyn was now rising. This was followed by another extensive study reported by Zhou (2002). Zhou (2002) confirmed that the amplitude was continuing to rise and that the variations seemed sinusoidal. He also found frequencies similar to those found by Rodriguez et al. (1997b) of f 1 ¼10:1756 and f 2 ¼18:1310 cycles day 1. However, he did not find the third frequency. Finally, Zhou (2002) claimed that the morphology of the (O C ) residuals was not explainable. The unexplained (O C ) curve makes AN Lyn a very interesting target for monitoring. 2. PHOTOMETRIC AND SPECTROSCOPIC OBSERVATIONS Photometric observations of the three stars were secured between 2000 March and 2005 May. A total of 13 nights of data were obtained for AN Lyn, 12 nights for BO Lyn, and 19 nights for GW UMa. All photometric data were obtained using the

MONITORING THREE SCUTI VARIABLES 2877 TABLE 1 DDT Telescope and CCD Specifications Focus CCD Pixel Size ( m) Plate Scale (arcsec pixel 1 ) Array Size ( pixels) Years Cassegrain... Apogee Ap8p 24 0.76 1024 ; 1024 2001 2002 Newtonian... Apogee Ap47p 13 1.32 1024 ; 1024 2004 Newtonian... Meade Pictor 416 9 0.91 768 ; 512 2000 2001 Newtonian... Meade Pictor 1616 9 0.91 1536 ; 1024 2000 2003 Cassegrain... SBIG ST-1001 24 0.76 1024 ; 1024 2005 0.4 m David Derrick Telescope (DDT) of the Orson Pratt Observatory. A variety of telescope focus/ccd combinations was used throughout the course of the observations. A summary of these configurations is given in Table 1. Most observations were obtained through a standard Johnson V filter, with a few additional observations in the Johnson B filter. All observations were reduced using standard IRAF procedures. Spectroscopic data were secured in 2003 February and 2004 April at the Dominion Astrophysical Observatory ( DAO). Observations in the region of H were obtained with the 1.8 m Plaskett Telescope using the Cassegrain spectrograph and the 21121B grating. This grating is blazed at 4100 8 and yields 15 8 mm 1. Using the Site2 CCD with 15 m pixels results in 0.23 8 pixel 1. The grating was set to give a central wavelength of 4773 8 with coverage from 4570 to 4970 8. All spectra were processed with the DOSLIT package in IRAF with wavelength calibration being done with a FeAr comparison arc. A few additional observations were obtained in the spectral region from Ca ii H and K to H using the 1.2 m McKellar Telescope at DAO. These observations were taken with the coudé spectrograph using the 32121 grating. The grating is blazed at 5000 8 and yields 10.1 8 mm 1. Using the Site4 CCD with 15 m pixels gives 0.15 8 pixel 1. The grating was set to give a central wavelength of 4128 8 with coverage from 3810 to 4440 8. Once again the spectra were processed with standard IRAF techniques. Finally, a number of radial velocities were measured in 2001 with the radial velocity speedometer (RVS) on the 1.2 m telescope. 3. SPECTROSCOPIC AND PHOTOMETRIC ANALYSIS 3.1. Spectroscopy Although spectra were obtained on all three stars, only those for AN Lyn and GW UMa were found to provide satisfactory results. The first information gathered from the spectral data was radial velocities. For both AN Lyn and GW UMa we obtained spectral observations in both 2003 and 2004. These spectra were examined using the RVIDLINES package in IRAF. The radial TABLE 2 Radial Velocity Measurements for GW Ursae Majoris and AN Lyncis HJD 2,400,000.0+ GW UMa RV (km s 1 ) Instrument HJD 2,400,000.0+ AN Lyn RV (km s 1 ) Instrument 52,025.7103... 93.3 RVS 52,694.8091 14.0 Spec. 52,025.7260... 92.2 RVS 52,694.8161 11.2 Spec. 52,025.7333... 95.9 RVS 52,694.8232 8.3 Spec. 52,025.7429... 98.3 RVS 53,124.7175 41.9 Spec. 52,025.7522... 99.6 RVS 53,124.7249 38.3 Spec. 52,031.7612... 60.2 RVS 53,124.7322 34.2 Spec. 52,692.9510... 56.4 Spec. 53,124.7417 31.9 Spec. 52,692.9582... 51.2 Spec. 53,124.7502 31.9 Spec. 52,692.9653... 51.1 Spec. 53,124.7590 34.5 Spec. 52,692.9739... 50.1 Spec. 53,124.7689 35.8 Spec. 52,692.9812... 58.9 Spec. 53,124.7774 34.1 Spec. 52,692.9885... 71.6 Spec. 53,124.7863 37.3 Spec. 53,121.7598... 95.5 Spec. 53,124.7949 39.2 Spec. 53,121.7670... 94.3 Spec. 53,124.8048 41.8 Spec. 53,121.7740... 93.8 Spec. 53,124.8135 40.2 Spec. 53,121.7837... 94.4 Spec.......... 53,121.7907... 92.7 Spec.......... 53,121.7978... 90.5 Spec.......... 53,121.8068... 88.8 Spec.......... 53,121.8138... 85.0 Spec.......... 53,121.8208... 84.2 Spec.......... 53,121.8301... 79.3 Spec.......... 53,121.8372... 78.6 Spec.......... 53,122.7621... 90.8 Spec.......... 53,122.7714... 94.0 Spec.......... 53,122.7821... 97.7 Spec.......... 53,122.7955... 96.1 Spec.......... 53,122.8061... 93.0 Spec.......... 53,122.8167... 91.7 Spec..........

2878 HINTZ, BUSH, & ROSE Vol. 130 Fig. 1. Continuum-corrected spectra of AN Lyn and GW UMa in the region of H. For comparison, the spectrum of BD Cap is included. velocities determined are reported in Table 2. From the line-toline errors we determined an average error in the radial velocity determination of about 1.5 km s 1. For GW UMa we also obtained six radial velocities from the RVS system. These observations were calibrated against the FeAr arc and a number of radial velocity standards. All values are collected in Table 2. For the RVS observations, the error for the radial velocity standards was 0.6 km s 1 ; however, GW UMa was substantially fainter, and we estimate the error to be 1.5 km s 1. We discuss the radial velocity values, in conjunction with the photometry, in x 3.2. From the spectroscopy we also determined spectral types, estimated metal contents, and determined a rotational velocity for GW UMa. In comparing our spectra with digital spectra from Bagnulo et al. (2003), we classify both AN Lyn and GW UMa as A8 IV stars. Our spectral type for AN Lyn is similar to the A7 IV V from Yamasaki et al. (1981). In Figure 1 we show the spectra of AN Lyn, GW UMa, and BD Cap (Bagnulo et al. 2003) in the region of H. The third star included in Figure 1, BD Cap, has a published metal content of ½Fe/HŠ ¼ 0:03 (Nordström et al. 2004) and a spectral type of A9 III (Bagnulo et al. 2003), and, as reported earlier, AN Lyn has a near-solar metal content. The spectra of GW UMa, AN Lyn, and BD Cap imply that the metal content of all three stars is quite similar, as they show the same spectral features with similar strengths. This is a little surprising for GW UMa, since it had previously been considered an SX Phe star. Finally, for GW UMa, our spectrum in the region of Ca ii H and K (see Fig. 2) was sufficient to examine the rotational velocity. We measured the average intrinsic FWHM of metal lines near 4500 8. Using the equation in Fekel (2003), we determined a rotational velocity of 15 5kms 1 for GW UMa. This corresponds with the rotational velocities of other HADSs. From a comparison of spectra in Figure 1 we would estimate that AN Lyn has a slightly higher rotational rate, but the quality of the Ca ii spectra was not sufficient to determine a numerical value. 3.2. Photometry For each star the observed fields were centered to provide comparison stars of reasonably similar brightness. These ensembles of comparison stars were then used to obtain differential magnitudes using the methods detailed in Hintz et al. (1997). The differential magnitudes were then combined with the HJD to generate the light curves. In Figure 3 we show representative light curves for each of the three stars on four separate nights. Both AN Lyn and BO Lyn clearly show shape variations during the nights presented. For GW UMa the curves appear to be quite consistent. 3.2.1. GW Ursae Majoris GW UMa had three previously reported times of maximum light in the V filter. To this we add nine new times of maximum Fig. 2. Continuum-corrected spectrum of GW UMa ranging from the Ca ii HandKregiontoH. The major features are labeled. For comparison, the spectrum of BD Cap is included.

No. 6, 2005 MONITORING THREE SCUTI VARIABLES 2879 Fig. 3. Representative light curves for AN Lyn, BO Lyn, and GW UMa on four nights. light, and all times are collected in Table 3. Our new times of maximum light bracket those reported by Derekas et al. (2003). Using the 12 times of maximum light, we find the ephemeris given in equation (3), with the error in the last digit being given in parentheses: HJD max ¼ 2;451;999:9227(3) þ 0:20319389(6)E: ð3þ There is no pattern to the (O C ) diagram, and all values are smaller than 0.0015. From this we conclude that the period of GW UMa has remained constant over the last 5 yr. For three TABLE 3 Times of Maximum Light for GW Ursae Majoris HJD 2,400,000.0+ Obs. a Cycle 51,999.9226... BYU 0 52,037.7160... BYU 186 52,041.7810... BYU 206 52,065.7578... BYU 324 52,075.7141... BYU 373 52,395.5408... Derekas 1947 52,396.5584... Derekas 1952 52,398.3850... Derekas 1961 53,085.7914... BYU 5344 53,473.8904... BYU 7254 53,475.7200... BYU 7263 53,476.7361... BYU 7268 a Derekas: Derekas et al. (2003); BYU: this paper. Fig. 4. Phased radial velocity curve and light curve for GW UMa from 2004 data.

2880 HINTZ, BUSH, & ROSE Vol. 130 TABLE 4 Times of Maximum Light for BO Lyncis HJD 2,400,000.0+ Obs. a Cycle HJD 2,400,000.0+ Obs. a Cycle 47,933.7964... Kin. 0 52,288.7455... BYU 46648 47,938.7478... Kin. 53 52,288.8399... BYU 46649 48,577.9691... Kin. 6900 52,310.6849... BYU 46883 52,252.8044... BYU 46263 52,331.7861... BYU 47109 52,252.8993... BYU 46264 53,075.7484... BYU 55078 52,264.7545... BYU 46391 53,075.8406... BYU 55079 52,264.8459... BYU 46392 53,083.7767... BYU 55164 52,266.7141... BYU 46412 53,427.7978... BYU 58849 52,266.8091... BYU 46413 53,429.7592... BYU 58870 52,288.6538... BYU 46647 53,487.7356... BYU 59491 a Kin.: Kinman (1998); BYU: this paper. epochs we have sufficient data to run a Fourier analysis. For all three epochs we find only the primary frequency and its multiples. In addition, the amplitude of the first term of the Fourier series has remained constant at 0.38 mag. All evidence points to GW UMa being a monoperiodic star with constant period, although the time line is extremely short. From our radial velocity values we find a well-defined curve with an average velocity of 72 km s 1 and a full amplitude of 47 km s 1. Our average radial velocity differs from the published 81 km s 1 but is based on the entire curve instead of isolated observations. In Figure 4 we show the phased light curve and the phased radial velocity curve for GW UMa. This shows the normal inverted curve we expect for a pulsating star. 3.2.2. BO Lyncis From the original Kinman (1998) paper we determined three times of maximum light. To this we have added 17 new times of maximum light and 15 yr of time line. All times of maximum light are gathered in Table 4. Using all times of maximum light, we find the ephemeris given in equation (4): HJD max ¼ 2;447;933:8007 þ 0:09335759(2)E: The (O C ) diagram resulting from equation (4) shows a distinct parabolic shape, as shown in Figure 5. Using only our ð4þ own data set we find the ephemeris given in equation (5). However, this equation has more than double the error and does not yield a flat (O C ) diagram: HJD max ¼ 2;447;933:8183 þ 0:09335724(5)E: ð5þ Using a parabolic fit we find equation (6), which provides a period change of 1:5 ; 10 10 days day 1 : HJD max ¼ 2;447;933:7988 þ 0:09335800(5)E 7:2(1:0) ; 10 12 E 2 : Our data set in each epoch is fairly small and does not produce a detailed Fourier analysis. However, we can report that the amplitude of the primary frequency has remained constant over our entire data set. The shape of the light curves also suggests that there are likely additional frequencies in the data. From our limited data set we find two potential frequencies: f 2 ¼ 15:81 and f 3 ¼ 13:60 cycles day 1. Both frequencies change amplitude from epoch to epoch. The overall time line for this star is still relatively short at 15 yr. In addition, a single-epoch data set of sufficient size to do a detailed Fourier analysis has not yet been obtained. To gain a better understanding of this star, a large single-epoch data set is needed, along with continued long-term monitoring. ð6þ 3.2.3. AN Lyncis Of the three stars reported in this paper, AN Lyn is the most intriguing and by far the most studied. We report 17 new times of maximum light that are gathered in Table 5 along with previously published times. Our new times are mixed with those of Zhou (2002) and extend the overall time line by 5 yr. Taking a total linear fit through all the data provides the ephemeris given in equation (7). From this equation we generate the unusual (O C ) diagram shown in Figure 6: HJD max ¼ 2;444;291:0326 þ 0:09827292(3)E: ð7þ Fig. 5. The (O C ) diagram for BO Lyn generated using eq. (4). An examination of Figure 6 does not provide an obvious solution. There is not a clear sinusoidal shape, and the parabolic shape can only be defined starting with the Rodriguez et al. (1997b) data. If we only include the data after Rodriguez et al. (1997b), we find the parabolic fit that yields a period change of

No. 6, 2005 MONITORING THREE SCUTI VARIABLES 2881 TABLE 5 Times of Maximum Light for AN Lyncis HJD 2,400,000.0+ Obs. a Cycle HJD 2,400,000.0+ Obs. a Cycle HJD 2,400,000.0+ Obs. a Cycle 44,291.0340... Costa 0 49,701.0376... Rod. 55051 51,597.3267... Zhou 74347 44,291.1250... Costa 1 49,702.0202... Rod. 55061 51,598.0147... Zhou 74354 44,291.2220... Costa 2 49,703.0036... Rod. 55071 51,598.1120... Zhou 74355 44,292.1110... Costa 11 49,704.9687... Rod. 55091 51,598.2112... Zhou 74356 44,292.2110... Costa 12 49,706.9355... Rod. 55111 51,598.3076... Zhou 74357 44,300.1650... Costa 93 49,707.0329... Rod. 55112 51,598.9944... Zhou 74364 44,300.9600... Costa 101 49,707.0329... Rod. 55112 51,599.0965... Zhou 74365 44,301.0600... Costa 102 49,737.3999... Rod. 55421 51,599.1914... Zhou 74366 44,349.0110... Costa 590 49,737.4960... Rod. 55422 51,599.9823... Zhou 74374 44,349.1050... Costa 591 49,739.4630... Rod. 55442 51,600.0785... Zhou 74375 45,043.4150... Costa 7656 49,740.5447... Rod. 55453 51,600.1771... Zhou 74376 45,044.7940... Costa 7670 49,741.5269... Rod. 55463 51,605.0888... Zhou 74426 45,044.8840... Costa 7671 49,742.4109... Rod. 55472 51,608.7259... BYU 74463 45,045.3800... Costa 7676 51,583.0750... Zhou 74202 51,608.8244... BYU 74464 45,045.5750... Costa 7678 51,583.1763... Zhou 74203 51,619.6344... BYU 74574 45,045.7690... Costa 7680 51,583.2752... Zhou 74204 51,619.8318... BYU 74576 45,045.8700... Costa 7681 51,583.3708... Zhou 74205 51,632.0216... Zhou 74700 45,046.4640... Costa 7687 51,584.3568... Zhou 74215 51,632.1131... Zhou 74701 45,046.5580... Costa 7688 51,585.3378... Zhou 74225 51,632.2136... Zhou 74702 45,046.9530... Costa 7692 51,586.0242... Zhou 74232 51,633.0008... Zhou 74710 45,048.7170... Costa 7710 51,586.1217... Zhou 74233 51,633.0963... Zhou 74711 45,074.7610... Costa 7975 51,586.2228... Zhou 74234 51,633.1928... Zhou 74712 45,075.7440... Costa 7985 51,586.3221... Zhou 74235 51,634.0824... Zhou 74721 45,076.7320... Costa 7995 51,587.0077... Zhou 74242 51,634.1838... Zhou 74722 45,077.0230... Costa 7998 51,587.1062... Zhou 74243 51,639.0913... Zhou 74772 45,077.1190... Costa 7999 51,587.2020... Zhou 74244 51,644.1036... Zhou 74823 45,092.6540... Costa 8157 51,592.0186... Zhou 74293 51,645.0865... Zhou 74833 45,092.7510... Costa 8158 51,592.1161... Zhou 74294 51,662.6806... BYU 75012 45,347.3827... AFF 10749 51,592.2171... Zhou 74295 51,669.6569... BYU 75083 45,347.4743... AFF 10750 51,593.9861... Zhou 74313 51,669.7548... BYU 75084 45,347.5771... AFF 10751 51,594.0885... Zhou 74314 51,669.8516... BYU 75085 45,379.3174... AFF 11074 51,594.1785... Zhou 74315 51,992.6859... BYU 78370 45,379.4243... AFF 11075 51,594.2761... Zhou 74316 51,992.7806... BYU 78371 45,382.3630... AFF 11105 51,594.3813... Zhou 74317 52,342.3455... AH 81928 45,406.3395... AFF 11349 51,595.0648... Zhou 74324 53,076.7621... BYU 89401 45,406.3437... AFF 11349 51,595.1639... Zhou 74325 53,076.8573... BYU 89402 45,406.4367... AFF 11350 51,595.2657... Zhou 74326 53,429.8621... BYU 92994 45,406.4423... AFF 11350 51,595.3675... Zhou 74327 53,439.7888... BYU 93095 45,406.5367... AFF 11351 51,596.0480... Zhou 74334 53,439.8886... BYU 93096 45,472.3708... AFF 12021 51,596.1443... Zhou 74335 53,473.6946... BYU 93440 49,398.7497... Rod. 51975 51,597.0332... Zhou 74344 53,476.8380... BYU 93472 49,398.8478... Rod. 51976 51,597.1288... Zhou 74345......... 49,398.9439... Rod. 51977 51,597.2311... Zhou 74346......... a AH: Agerer & Hübscher (2003); AFF: Agerer et al. (1983); Costa: Costa et al. (1984); Rod.: Rodriguez et al. (1997b); Zhou: Zhou (2002); BYU: this paper. Fig. 6. The (O C ) diagram for AN Lyn generated using eq. (7). +7:9 ; 10 10 days day 1. However, this result totally excludes a large portion of the data set. The radial velocity data detailed earlier provide some insight into the problem. The data from 2004 have an average value of 36.8 km s 1 and phase well with the V photometry. It is interesting to note that AN Lyn is known for the slow rise and sharp fall in its light curve. This is also evident in the shape of the radial velocity curve, as shown in Figure 7. The data from 2003 have an average value of 11.4 km s 1 and do not phase with the 2004 data. However, this rapid change in radial velocity matches the time of maximum change in the (O C ) diagram. From 2003 to 2004 AN Lyn s velocity toward us has increased. If this is orbital motion, this change corresponds to earlier observed maxima and therefore more positive (O C ) values. The combination of the (O C ) values with radial velocities clearly shows that AN Lyn is a binary system. We estimate an orbital period of approximately 22 yr.

2882 HINTZ, BUSH, & ROSE Vol. 130 Fig. 7. Phased radial velocity curve and light curve for AN Lyn from 2004 data. To further investigate the nature of AN Lyn we examined the amplitude change as suggested by Zhou (2002) and LaCluyzé et al. (2001). In Table 6 we gather the published Fourier amplitudes by year and add four epochs from our own data. Due to the more limited data sets, our amplitudes have larger errors than those of Zhou (2002). In Figure 8 we show the average (O C ) values, the Fourier amplitude, and the radial velocity averaged for each year. Amazingly, the amplitude is changing in phase with the period. It is mysterious why the amplitude is changing in sync with the orbital motion. Something interesting is taking place in this system. 4. CONCLUSION For the relatively newly discovered high-amplitude Scuti variable GW UMa, we find a revised period of 0.20319389 days. We also find that GW UMa is best defined as a monoperiodic star of constant period. In addition, we find an average radial velocity TABLE 6 Fourier Amplitude for AN Lyncis Year Amplitude Source 1980... 0.079 1 1982... 0.089 1 1983... 0.091 1 1994... 0.067 1 1995... 0.068 1 1996... 0.072 1 2000... 0.081 2 2000... 0.086 3 2001... 0.092 4 2001... 0.087 3 2004... 0.097 3 2005... 0.094 3 References. (1) Rodriguez et al. 1997b; (2) Zhou 2002; (3) this paper; (4) LaCluyzé et al. 2001. Fig. 8. Radial velocity, (O C ), and amplitude averages by year for AN Lyn. of 72 km s 1 over a full curve. With its high Galactic latitude and high radial velocity, it had been concluded (Derekas et al. 2003) that GW UMa is an SX Phe star. However, our spectral observations show that GW UMa has near-solar metal content. The results make GW UMa an interesting target for further study. For the relatively unstudied Scuti variable BO Lyn we find a constant period change of 1:5 ; 10 10 days day 1 over a 15 yr period. This is a short time span, and further observations are needed to confirm this result. From Fourier analysis we find two potential secondary frequencies in BO Lyn, f 2 ¼ 15:81 and f 3 ¼ 13:60 cycles day 1. Again, a large data set is needed to confirm the secondary frequencies. Longer monitoring is needed to confirm the period change. The most interesting star examined in this paper is AN Lyn. We conclude that AN Lyn is a member of a binary system and that the variation seen in the (O C ) diagram can be traced to this. What is most interesting is that the amplitude of pulsation is changing in phase with the orbital motion. This star clearly needs follow-up observing campaigns over the next few years. It appears we are reaching a maximum point in the orbit, and the amplitude change and (O C ) value are expected to go back down in the next 2 yr.

No. 6, 2005 MONITORING THREE SCUTI VARIABLES 2883 We acknowledge the Brigham Young University ( BYU) Department of Physics and Astronomy for their continued support of our research efforts. We wish to thank A.-Y. Zhou for providing unpublished times of maximum light for AN Lyn. We express gratitude for a grant from the Theodore Dunham, Jr., Grant for Research in Astronomy and an AAS small research grant, which have been used to further equip the BYU campus observatory. We acknowledge the use of the 1.85 m Plaskett Telescope and1.22mmckellartelescopeat the Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada. Finally, we acknowledge the use of the online Library of High-Resolution Spectra of Stars across the H-R Diagram of the UVES Paranal Observatory Project ( ESO DDT program ID 266.D-5655). Agerer, F., Fernandes, M., & Frank, P. 1983, Inf. Bull. Variable Stars, 2370, 1 Agerer, F., & Hübscher, J. 2003, Inf. Bull. Variable Stars, 5485, 1 Bagnulo, S., Jehin, E., Ledoux, C., Cabanac, R., Melo, C., & Gilmozzi, R. 2003, Messenger, 114, 10 Balona, L. A., & Evers, E. A. 1999, MNRAS, 302, 349 Costa, V., Garrido, R., Lopez de Coca, P., Quintana, J. M., Rolland, A., Peniche, R., & Pena, J. H. 1984, A&AS, 57, 233 Derekas, A., et al. 2003, A&A, 402, 733 Fekel, F. C. 2003, PASP, 115, 807 Hintz, E. G., Joner, M. D., McNamara, D. H., Nelson, K. A., Moody, J. W., & Kim, C. 1997, PASP, 109, 15 Kinman, T. D. 1998, PASP, 110, 1277 REFERENCES Kiss, L. L., Derekas, A., Mészáros, Sz., & Székely, P. 2002, A&A, 394, 943 LaCluyzé, A., et al. 2001, Inf. Bull. Variable Stars, 5180, 1 Nordström, B., et al. 2004, A&A, 418, 989 Pesch, P., & Sanduleak, N. 1989, ApJS, 71, 549 Poretti, E. 2001, A&A, 371, 986 Rodriguez, E., Gonzalez-Bedolla, S. F., Rolland, A., Costa, V., & Lopez de Coca, P. 1997a, A&A, 324, 959 Rodriguez, E., Gonzalez-Bedolla, S. F., Rolland, A., Costa, V., Lopez-Gonzalez, M. J., & Lopez de Coca, P. 1997b, A&A, 328, 235 Yamasaki, A., Gonzalez, S. F., Peniche, R., & Pena, J. H. 1983, PASP, 95, 447 Yamasaki, A., Okazaki, A., & Kitamura, M. 1981, PASP, 93, 77 Zhou, A.-Y. 2002, A&A, 385, 503