The background, and historical characterizations, of the individual RS CVn systems are critical to understand the general nature of the RS CVn phenomena. The observations and analysis of previous works can be examined for consistency, compared and correlated with the results of the analysis in this dissertation.
This chapter briefly reviews the of characteristics all thirty-six sources. The spectral types, luminosity classifications, orbital periods and eccentricities are taken from the Catalog of Chromospherically Active Binary Stars (Strassmeier et al. 1988) unless otherwise indicated.
Observations other than photometry are important in characterizing the activity levels of the systems. Radio emission, for example, has been detected in most RS CVn systems but is not, in general, correlated with orbital phase. Ultraviolet emission is characteristic of the transition region between the chromosphere and photosphere and X-ray observations are considered a good indicator of the overall coronal activity level. Infrared (IR) observations are just mentioned here because they can only be used for identifying spectral types and searching for circumstellar dust emission since these two effects would swamp any spot activity at IR wavelengths (Berriman et al. 1983).
33 Psc (HR 3, HD 28, BD -06° 6357, SAO 128572) is a long period (P = 72.93d), non-eclipsing, single-line spectral system classified as K0 III. It was first identified has having very weak Ca II H and K emission by Wilson (1976), however Koniges (1977) and Lloyd Evans (1977) found very strong emission. The system is highly eccentric (e = 0.27) and was found by Barksdale et al. (1985a) to have a photometric period of 36.51 ± 0.12 days (DV = 0.007m) which was attributed to ellipticity.
Walter (1985) identified the system as a weak X-ray source with activity levels 100 times lower than the least active known long period systems (z And and e UMa), and he suggests that this system may not be an RS CVn at all because of the lack of activity. The fact that radio emission has not been observed (Mutel and Lestrade 1985) is also indicative of low activity levels.
13 Cet (A) (HR 142, HD 3196, BD -04° 62, SAO 128839) is the active component of the visual binary ADS 490, which comprises a triple system. It is a regular period (P = 2.08200d), non-eclipsing, single-lined spectroscopic binary classified as F7 V with the B component of the visual system classified as G4 V. Very little has been published about this system and a photometric period has not been previously identified. The system has been observed, but not detected down to 0.9 mJy, at radio frequencies (Mutel and Lestrade 1985).
z And (34 And, HR 215, HD 4502, BD +23° 106, SAO 074267) is a long period (P = 17.7692d), possibly partially-eclipsing, single-line spectroscopic binary classified as K1 II. The Ca II H and K emission is strong and Hendry (1980) found variable emission with a general increase in the three year period from 1977 to 1980, which suggests a possible long term periodicity. The presence of a distortion wave has not been detected, but Herbst (1973) reported a photometric period with a full amplitude of 0.14m which he attributed to the ellipticity effect. This system has not been observed at radio frequencies, but it was found by Walter and Bowyer (1981) to be a moderately strong X-ray source (Lx = 1.4x1023 watts).
AY Cet (39 Cet, HR 373, HD 7672, BD -03° 172,SAO 129204) is a long period (P = 56.815d), non-eclipsing, single-line (G5 III) spectroscopic V471 Tau-type RS CVn system with a weakly eccentric (e = 0.04) orbit. It was labeled as a suspected variable by Cousins (1962) and the variability was later verified by Olsen (1974). The presence of weak to moderate Ca II emission was noted by Cowley and Bidelman (1979).
IUE and radio observations, showing variable emission (~15 mJy), by Simon et al. (1985) indicate the presence of a white dwarf companion. X-rays (Lx»1.5x1024) were also observed from the cooler companion, but no evidence for mass transfer was observed. Verm, Iyengar and Rengarajan (1987) found and IR excess from IRAS6 data and attributed it to circumstellar dust emission.
Eaton et al. (1983a) classified this system as a suspected RS CVn binary and found a photometric period of 77.65 days (DV = 0.18m), which differs greatly from the cited orbital period of 57.1 days. The effect was identified as an example of pseudosynchronous rotation caused by an eccentric orbit (Hut 1981) which was cited as e = 0.1. l And (e = 0.04, Pphtm/Porb = 2.63) and 54 Cam (e = 0.11, Pphtm/Porb = 0.92) were also cited as examples of the same phenomena.
Poretti et al. (1986) observed a clear trend in decreasing amplitude and increasing brightness from 1984 to 1986. Periods of 77.22 days (DV = 0.06m), 79.36 days (DV=0.03m), and 1820 days (DV=0.07m) were identified by a three term truncated Fourier series. A shrinking starspot group was used to explain the decreasing amplitude and increasing mean brightness. The other periods were considered as evidence for different activity cycles. The possibility that the observations were of multiple spot groups on a differentially rotating star was discarded since they state that the effect would hardly be detectable and that the modeling requires more free parameters than multiple activity cycles.
AR Psc (HD 8357, BD +06° 211, SAO 109841) is a long period (P = 14.300d), non-eclipsing, double-lined spectroscopic binary with an eccentric orbit (e = 0.19). The cooler star has been classified as G8 IV. Attention was first drawn to the system when Garcia et al. (1980) identified it as the optical counterpart to an X-ray source detected by HEAO 1. Their spectra showed very strong Ca II H and K emission and double absorption lines. Ambruster, Snyder and Wood (1984) observed X-ray flares (Lx»1.5x1025 watts) and variable low-level quiescent emission from the HEAO 1 A-1 Sky Survey data, while Xuefu and Huisong (1984) observed changes in both emission and absorption in Ha similar to that observed in UX Ari.
Very little optical information is available on this system, but Hall, Henry and Louth (1982) did discover V-band variability (DV = 0.08m ± 0.003) with a period of 12.3 ± 0.01 days and a minimum at 0.205p ± 0.006. Fekel, Moffett and Henry (1986) note that it is one of the few RS CVn systems, possibly along with AE Lyn, with a sub-giant or giant component with such a short period and high eccentricity.
TZ Tri (i Tri, 6 Tri, HR 642, HD 13480, BD +29° 371, SAO 055347) is the A-component of the visual binary ADS 1697. It is a long period (P = 14.732d), non-eclipsing, double-lined spectroscopic binary consisting of a pair of G5 III sub-giants in a slightly eccentric orbit (e = 0.04).
This system has very few optical observations and a photometric wave has not been detected. Hall et al. (1980) observed the system on 34 nights from 1979-80 and noted that the light curve showed two maxima of equal height and two minima of unequal depth with a maximum full amplitude of DV=0.037m ± 0.004. They concluded that the distortion arises from a superposition of the ellipticity and reflection effects. They also suggest that a long period (~100 day) variation may be present. The lack of an observed distortion wave is consistent with the lack of radio emission observed by Spangler, Owen and Hulse (1977) which implies low activity levels.
The system is a known X-ray source (Majer et al. 1986) and an infrared excess has been reported by Verm, Iyengar and Rengarajan (1987), which they attributed to circumstellar dust emission.
UX Ari (HD 21242, BD +28° 532, SAO 075927) is a regular period (P = 6.43791d), non-eclipsing, double-lined spectroscopic binary that Pye and McHardy (1983) associated with the fast X-ray transient AT 0318+220 from the Ariel V survey. The stars are classified as G5 V and K0 IV.
This system, along with V711 Tau, is one of the most extensively observed of the RS CVn binaries (Hall 1977; Bopp and Talcott 1978; Landis et al. 1978; Mutel and Weisberg 1978; Owen and Gibson 1978; Weiler et al. 1978; Simon and Linsky 1980; Simon, Linsky and Schiffer 1980; Guinan et al. 1981; Walter and Bowyer 1981; Zeilik et al. 1981; Sarma et al. 1983; Pye and McHardy 1983; Mutel et al. 1984; Johnston et al. 1985; Wacker et al. 1986; Willson and Lang 1987). The system is visible from radio up to X-ray wavelengths. The light of UX Ari is known to be variable on a variety of time scales (Hall 1977) with variations observed in the mean amplitude and distortion wave amplitude. Zeilik et al. (1981) considered the behavior of the system erratic, but Sarma et al. (1983) suggested that the variations may be systematic with a cycle length from 5 to 6 years. It is interesting that both Guinan et al. (1981) and Zeilik et al. (1981) reported a minimum at 0.97p, which would indicate that the phase of the system was stable for a period of at least one year.
Nominally, the photometric period has been found to be on the order of the orbital period (DV=0.15m). Landis et al. (1978) point out that even though this is one of the most widely observed RS CVn systems, the light curve needs to be observed continuously, for a long interval of time, before the characteristics of the distortion wave can be defined.
Weiler (1978) found broad Lya l1215.67 emission, which was variable, and seemed correlated with orbital phase. Mg II H and K emissions were also variable and matched the velocity of the more active, cooler star. Evidence for high velocity gas motions were observed. Highly active and variable chromospheric phenomena in the form of plage-like activity was found to be the most consistent explanation.
IUE observations by Simon, Linsky and Schiffer (1980) showed a flare in the chromospheric and emission-lines fluxes about 2.5 and 5.5 times brighter than the quiescent levels, respectively. The observed Mg II emission wings were interpreted as mass flow from the K0 IV to the G5 V star via gas streams from connected flux tubes, which is consistent with the high velocity gas motions observed by Weiler (1978). Simon, Linsky and Schiffer postulate that large corotating flux tubes that interact through magnetic reconnection may provide the energy needed for the radio, UV and X-ray flares. This model is consistent with the observations of Rhombs and Fix (1977) who concluded that free-free emission of hydrogen from a hot circumstellar gas best describes the UV emission. Simon and Linsky (1980) found no correlation between UV emission line flux and orbital phase and that the K star is the emitter of the Mg II lines at levels 25 times that of the sun implying coronal loop structures 5 to 25 solar radii in height.
Mutel et al. (1984) found a sub-milliarcsecond radio component consistent with gyrosynchrotron emission from a power-law energy distribution of electrons in a magnetic field of 6 Gauss. Willson and Lang (1987) found variability from 6.6 seconds to 1 hour at 4835 MHz and 1415 MHz and suggested absorption by a thermal plasma between the stars, while Pallavicini, Willson and Lang (1985) Observations a 6cm indicate an extended halo of radio emission.
V711 Tau (HR 1099, HD 22468, BD +00° 616, SAO 111291) is the A-component of the visual binary ADS 2644. It is a regular period (P = 2.83774d), non-eclipsing, double-lined spectroscopic binary. The stars are classified as G5 IV and K1 IV. The system is a strong X-ray source (Walter and Bowyer 1981) and Pye and McHardy (1983) associated it with the fast X-ray transient AT 0339+063 from the Ariel V survey.
V711 Tau is the single most heavily observed of the RS CVn systems, particularly at radio frequencies. Its radio emission, and spectral line characteristics are well described by a series of papers in 1978 as well as more recent works (Aller, Rugare and Hodge 1978; Brown and Crane 1978; Bopp and Talcott et al. 1978; Epstein and Briggs 1978; Fekel 1983; Feldman et al. 1978; Furenlid and Young 1978; Fraquelli 1978; Gibson, Hicks and Owen 1978; Hearnshaw 1978; Hobbs, Kondo and Feibelman 1978; Landis et al. 1978; Mutel and Weisberg 1978; Owen and Gibson 1978; Popper 1978; Weiler 1978; Weiler et al. 1978; Pallavicini, Ramsey and Nations 1980; Lestrade et al. 1984a; Mutel et al. 1984; Johnston et al. 1985; Willson and Lang 1985; Gondoin, Ph. 1986; Willson and Lang 1987).
The optical variability of the system was first suspected by Cousins (1963) and was later confirmed by Landis and Hall (1976) who found a quasisinusoidal light variation with a period of 2.84 days and a full V-band amplitude of 0.11 magnitude. Ca II and Ha emissions were discovered by Bopp and Fekel (1976) who identified it as an RS CVn type system. Further photoelectric studies show a clear photometric wave, with a period near that found by spectroscopy. The wave is variable in mean magnitude, amplitude, frequency and symmetry (Bopp et al. 1977a; Bartolini et al. 1978; Chambliss et al. 1978; Landis et al. 1978; Chambliss and Detterline 1979; Guinan and McCook 1979; Antonopoulou 1980; Guinan et al. 1980; Sarma and Ausekar 1980; Blanco et al. 1981; Dorren et al. 1981; Parthasaratny, Raveendran and Mekkaden 1981; Dorren and Guinan 1982; Mekkaden et al. 1982; Mohin, Raveendran and Mekkaden 1982; Olsen 1982; Nha and Oh 1983; Sarma et al. 1985; Wacker and Guinan 1986).
The most widely used model to describe the observed variations is a pair of starspots that are some 1800K cooler than the surrounding photosphere and cover from 14% to 20% of the stellar surface of the cooler component, although IUE observations by Bennet and Ayres (1986) indicate activity on both components and Mekkaden, Raveendran and Mohin (1982) found that a simple two spot model was inadequate to describe their observations. Their light curve was highly asymmetric showing two unequal flat-topped maxima. They noted that the maxima of the light curve increased as the wave amplitude increased, but the minima did not change. They interpreted this behavior as evidence that one hemisphere of the active component is "saturated" with starspots. Doppler imaging performed by Vogt and Penrod (1983) indicate the presence of structures that resemble X-ray images of solar coronal holes, and they suggest that the starspots are scaled-up stellar analogs of solar complexes when they first appear at low latitudes and more closely resemble coronal holes as they move poleward.
Weiler (1978) found broad, variable Lya l1215.67 emission which seemed correlated with orbital phase. Mg II H and K emission was also found to be variable and matched the velocity of the more active, cooler component. Evidence for high velocity gas motions was also found. As was the case for UX Ari, highly active and variable chromospheric phenomena in the form of plage-like activity was found to be the most consistent explanation.
Ramsey and Nations (1980) found that TiO emission lines strengthen greatly at phases where starspots were predicted from photometric observations. Fraquelli (1982) found that a localized region in the chromosphere is responsible for the observed enhanced Ha emission during flares, and Fekel (1983) interpreted asymmetries in absorption lines, that are correlated with the distortion wave, as being caused by starspots.
IUE observations by Rodono et al. (1987) showed stellar line fluxes hundred of times the solar values, and activity was seen on both components. Although the G star showed stronger Mg II emission lines than the K star, the K star dominates the emission at UV wavelengths.
HD 22403 (BD +25° 580) is a regular period (P = 1.9299395d), non-eclipsing, double-lined spectroscopic binary consisting of a G2 V and K V sub-dwarf. The orbit is moderately eccentric (e = 0.035) and a photometric period of 1.9 days with DV = 0.09m has been observed by Raveendran, Mohin and Mekkaden (1985) who concluded that the distortion was caused by some form of chromospheric activity. Very little has been published on the photometric properties of this system, although a detailed spectral study by Carquillat et al. (1979) showed strong Ca II emission from the hotter star.
EI Eri (HD 26337, BD -08° 801, SAO 130994) is a regular period (P = 1.94722d), non-eclipsing, single-lined (G5 IV) spectroscopic binary. It was classified as a single-lined spectroscopic low amplitude light variable by Fekel et al. (1982) who also observed moderately strong Ca II H and K emission and reported an orbital period of 2.04414 days and a photometric period of 2.038 days (DV=0.19m). Fekel, Moffett and Henry (1986), however, found an orbital period of 1.94722 days and concluded that the 2.04414 day period cited by Fekel et al. (1982) was an alias. Fekel et al. (1982) reported a photometric period of 2.038 days (DV = 0.16m), which is 4.6% longer than the orbital period. Photometric observations by Bopp et al. (1983) indicated a slightly longer period of 2.049 days, while those of Hall et al. (1987) indicate a period of 1945 days (DV = 0.20m) and included the data used in this work. Hall et al. also concluded that the photometric period was intrinsically variable by about one percent on a time scale of one year.
Baliunas, Blair and Guinan (1983) reported that IUE observations of the Mg II H and K emission lines showing strong variability. They interpreted these variations as evidence of poleward migrating starspots. Mutel and Lestrade (1985) also note that EI Eri is a moderately strong (4 mJy) radio source.
RZ Eri (HD 30050, BD -10° 993, SAO 149847) is a long period (P = 39.2826d), totally-eclipsing, double-lined spectroscopic binary consisting of an Am star and a K0 IV dwarf. The orbit is highly eccentric (e = 0.36) and the system is a moderate radio source (4 mJy) and a strong X-ray emitter (2.1 × 1024 watts).
Caton and Oliver (1979) found no evidence for a distortion wave while Caton (1986), using a truncated Fourier series for the outside-of-eclipse data, found a small amplitude wave (DV = 0.068m). Hall (1986) has reported a photometric period of 21.6 days. The observations by both Caton and Hall represent the most extensive optical work on this system to date, but it amounts to little more than a statement of the detection of the photometric wave.
BM Cam (12 Cam, HR 1623, HD 32357, BD +58° 805, SAO 025003) is a long period (P = 80.174469d), non-eclipsing, single-lined (K0 III) spectroscopic binary. The variability of this highly eccentric system (e = 0.35) system was discovered by Eaton et al. (1980) who found a photometric period near 80 days. They attributed the variability to an uneven darkening of the K0 star by starspots and concluded that the rotation was synchronized with the orbital motion to within a few percent. BM Cam is still the longest period, chromospherically active binary in which synchronous rotation has been established.
Hall and Osborn (1986) noted that the light curve changed dramatically from 1979 to 1985 where the photometric period changed from 80.94 days, similar to that observed by Eaton et al. (1980), to on the order of 40 days. They also noted that this variation was associated with changes in the mean brightness (+0.04m in 1981 to -0.04m in 1985) and amplitude (variable from 0.18m to 0.04m). They interpreted these variations as being caused by two migrating spot groups on a synchronously rotating star. Using a linear least squares fit to graphically determined times of minima, they determined spot rotation periods of 80.94 ± 0.15 days and 79.94 ± 0.12 days.
HD 37824 (BD +03° 1007) is a long period (P = 53.580d), non-eclipsing, slightly eccentric (e = 0.03), single-lined spectroscopic binary. The system is classified as an F star with a K1 III companion. Hall et al. (1983) found a 52.6 day photometric period (DV = 0.11m.). A 26 day period was also possible, but it was considered unlikely because of the high eccentricity needed for such an orbit. Fekel, Moffett and Henry (1986) found an orbital period of 53.5 days which differs slightly from the value cited above.
s Gem (75 Gem, HR 2973, HD 62044, BD +29° 1590, SAO 079638) is a long period (P = 19.60458d), non-eclipsing, single-lined system (K1 III) with very strong Ca II H and K reversals. Walter and Bowyer (1981) found it to be a strong X-ray source (Lx = 2.0x1024 watts) and Pye and McHardy (1983) associated it with the fast X-ray transient AT 0737+270 from the Ariel V survey.
Fried et al. (1983), using 5 years of V-band photometry from 13 observatories, found a photometric period of 19.423 days. They noted that the photometric wave showed two distinct minima, except in 1979. They also noted phase shifts in the times of minima and variations in the relative depths of the two minima. A photometric wave (DV = 0.15m) with a similar period of 19.410 days has been reported by Strassmeier et al. (1988).
IUE observations by Ayres, Simon and Linsky (1984) showed no evidence for circumstellar material, but significant changes in the profiles of high-excitation species suggest rotation, off the visible hemisphere of the primary, of a large-scale magnetic active region.
AE Lyn (54 Cam, HR 3119, HD 65626, BD +57° 1118, SAO 026634) is a regular period (P = 11.0764d), non-eclipsing, double-lined spectroscopic binary with an eccentric orbit (e = 0.107). The two components of the system are similar in spectral type (K9 IV) as well as brightness and mass. It is a weak X-ray emitter (Lx=5x1022 watts) and has been detected at radio frequencies by Spangler, Owen and Hulse (1977) at the 15 mJy level, but it was not detected by Mutel and Lestrade (1985) which suggests the possibility of radio variability.
Eaton et al. (1981) observed photometric variability in V-band with a period of 10.163 days and a minimum near the time of conjunction. This period is 9% shorter than the orbital period. They also noted that the amplitude of the signal has increased monotonically (0.03m to 0.06m) from 1979.19 to 1980.82 while the mean brightness has been decreasing.
Young and Koniges (1977) noted that the velocities of the absorption lines are different from the Ca II emission lines by 22 km/s. This difference suggests that the emission may not be chromospheric in nature.
53 UMa (n UMa (B), HR 4374, HD 98230, BD +32° 2132) is a regular period (P = 3.9805d), non-eclipsing, single-lined spectroscopic binary (G5 V). It forms a visual binary with HD 98231 (the A-component of the visual binary ADS 8119) which is 3" distant and slightly brighter. It is known to be a weak X-ray source (Lx » 1x1022 watts) and non-detections of a distortion wave have been reported by Percy and Welch (1982) and Hall, Kirkpatrick and Seufert (1986). Percy and Welch (1982) obtained 31 observations over 762 days. Although they did not detect a distortion wave, they did suggest variability on the order of 500 days which may be caused by the possible intrinsic variability of the optical companion HD 98231 which is a known 670 day spectroscopic binary.
DQ Leo (93 Leo, HR 4527, HD 102509, BD +21° 2358, SAO 081998) is a long period (P = 71.6900d), non-eclipsing, double-lined spectroscopic binary with the stars classified as A6 V and G5 IV-III. It is a moderate X-ray source (Lx = 1.3x1023 watts) and has not been detected at radio frequencies (Spangler, Owen and Hulse 1977).
Hall et al. (1980) found a distortion wave with a photometric period near that of the orbital period. The wave showed a V-band amplitude of 0.028m ± 0.005 and a minimum at 0.452p ± 0.034. They concluded that the wave was also present in 1976 and noted that the mean light level had risen by 0.03m from 1976 to 1979. The differential reflection effect was not considered a viable cause of the distortions because: of the length of the period of the system, the possibility of a variable amplitude of the photometric wave and the fact that the observed phase was inappropriate for reflection.
DK Dra (HR 4665, HD 106677, BD +73° 549, SAO 007533) is a long period (P = 64.44d), non-eclipsing, double-lined spectroscopic binary with two nearly identical components classified as K1 III. The optical variability of this system was first described by Bopp et al. (1977) who found a photometric period between 60-70 days and a V-band amplitude variation of 0.08m. Chambliss (1978) refined the period to 64 days and found an amplitude of 0.15m. Eaton et al. (1982) derived a period of 63.75 ± 0.16 days and found the light curve symmetrical and roughly sinusoidal in 1979-80 but asymmetrical in 1977-78 with a mean magnitude ranging from 6.07m to 6.35m.
DK Dra is a weak radio emitter (Mutel and Lestrade 1985) and soft X-ray source (Walter et al. 1980). It has strong emission-line features of high temperature species such as C IV, Si IV and N V in the far UV (Hartmann et al. 1982). The X-ray emission is most likely from the stellar corona while the UV features are associated with corona-chromosphere transition regions.
Guinan et al. (1982) observed Ha and the O I l7774 triplet and found a quasisinusoidal period of 64.6 ± 0.4 days with amplitudes of 0.12m and 0.11m respectively. This period equals the orbital period within the errors. No emission in either line was found. A pair of starspots, covering 8% of the star, was suggested to account for the variations.
BH CVn (HR 5110, HD 118216, BD +37° 2426, SAO 063623) is a regular period (P = 2.6131738d), non-eclipsing, double-lined spectroscopic binary with the stars classified as F2 IV and K2 IV. The system was studied extensively by Conti (1967) where he noted that, even though it does not eclipse, it shows a photometric variation on the time scale of the orbital period. BH CVn is also a known X-ray (Walter and Bowyer 1981) and non-thermal radio source (Mutel and Lestrade 1985 and Lestrade et al. 1984b).
Hall et al. (1978) and Burke et al. (1980) observed the system photometrically (the observations of Burke et al. encompassed a radio outburst), Dorren and Guinan (1980) observed in Ha and yu and Barbour and Kemp (1981) observed the system in polarized light. All four papers conclude that the light variations, with a full amplitude of DV ~ 0.01m, are a result of the differential reflection effect.
There is some disagreement, however as to the classification of the system and the cause of the light variations. Little-Marenin et al. (1986) state that BH CVn is also an Algol type system since: the primary is cool (F2 IV), the secondary fills its Roche lobe (the system is semidetached), there is no apparent emission from an accretion disk (although Eker (1985) suggests a thin accretion disk to explain a narrow peak in the Ha profile), the mass ratio is about 0.28 (RS CVns are typically near 1), there is evidence for gas streams and no photometric wave has been observed. They also noted that velocity shifts in the UV spectra show unambiguously that the active star is the K dwarf and not the F2 star. Shore and Adelman (1984), on the other hand, suggest that the light variations are caused by a dark wave and not reflection. They propose that the system is detached, not semi-detached, and that the temperature of the secondary is 6000K, not 4000K, so it cannot be a K star. These conjectures remove the possibility of an Algol classification of system as suggested by Little-Marenin et al. (1986), and change dramatically the expected long term photometric characteristics of the system.
HD 136901 (BD +26° 2685) is a long period (P = 18.670d), single-lined spectroscopic binary (K1 III) with an eccentric orbit (e = 0.066). Its has not yet been determined whether or not the system is eclipsing.
Boyed, Genet and Hall (1984) found light variations with a period of 9.63 days (DV = 0.16m). Fekel, Moffett and Henry (1986) found a spectroscopic period of 18.68 days and concluded that the light variations observed by Boyed, Genet and Hall (1984) may be due primarily to ellipticity effects.
TZ CrB (s2 CrB, 17 CrB, HR 6063, HD 146361, BD +34° 2750, SAO 065165) is a regular period (P = 1.1397912d), non-eclipsing, double-lined spectroscopic binary with a slightly eccentric orbit (e = 0.022). The components are classified as F6 V and G0 V. It is the brighter component of the visual binary ADS 9979 (s CrB). It shows intense chromospheric, transition region and coronal activity as seen in the optical, UV and X-ray bands (Young and Koniges 1977; Agrawal et al. 1980, 1985; Tarafdar and Agrawal 1984; Schrijver and Mewe 1986). It is also a known radio source (Spangler, Owen and Hulse 1977; Mutel and Lestrade 1985).
Skillman and Hall (1978) found the presence of a distortion wave (DV = 0.05m) with a minimum at 0.4p with a period of 1.14 days. They concluded that the distortion was the result of neither ellipticity effects, because of the phase, nor reflection, because of the amplitude. They also found evidence of short term variability (0.1 days with an amplitude of 0.12m) similar to that observed in d Scuti stars.
Bakos (1984) also found a photometric period near the orbital, but the d Scuti-type variations, reported by Skillman and Hall (1978), were not observed. Vivenkanada Rao et al. (1985), however found no evidence for any type of variability. Gimenez et al. (1985) also failed to find any d Scuti-type changes in ubvy, however Gimenez et al. (1986) did find a small amplitude distortion (DV = 0.012m) in y with a maximum light at 0.75p.
HR 6469 (HD 157482, BD +40° 3136, SAO 046664) is a single-line, eclipsing triple system with the spectral classes being identified as F2 V, G0 V and G5 IV. It was resolved as a triple system by McAlister et al. (1983) using speckle interferometry, and was found to have a 5.53 year orbital period for the third component (McAlister et al. 1984). It was discovered to be eclipsing by Boyd et al. (1985), using the first two years of APT data, with a period of 2.2299 days and a time of conjunction of JD 2445839.813. They also reported the presence of a distortion wave with an 83.2 day period and were later quoted by Fekel, Moffett and Henry (1986).
DR Dra (29 Dra, HD 160538, BD +74° 717, SAO 008842) is a long period (P = 39 days), non-eclipsing, single-lined (K0-2 III) spectroscopic V471 Tau-type RS CVn system. Very little is known about this system; in fact, it is one of the few RS CVn's where the time of conjunction has yet to be determined.
Short-wavelength UV spectra by Fekel and Simon (1985) show a hot stellar continua and La absorption which indicates that the companion is a white dwarf with an effective temperature of Teff = 30,000K. This system is very similar to AY Cet, in that the masses and radii of the white dwarf companions are the same.
Hall et al. (1982), who identified the system as a new variable star, found a photometric period of 31.5 ± 1 days with DV = 0.12m and a minimum at 2,444,445.0. A long term brightening trend was observed with their 47 nights of observations taken over a 260 day period in 1980. Spectroscopic work by Fekel, Moffett and Henry (1986) confirm the presence of the white dwarf but they found no spectral periodicity near the photometric period of Hall et al.
Z Her (HD 163930, BD +15° 3311, SAO 103254) is a regular period (P = 3.9928012d), partially eclipsing, double-lined spectroscopic binary. The stars are classified as F4 V-IV and K0 IV. The system is a moderate X-ray source (Walter and Bowyer 1981), but has not been detected at radio wavelengths (Spangler, Owen and Hulse 1977). A distortion wave (DV = 0.0380m) with a period of 3.962 days has been reported by Evren et al. (1982) with B and V data from 1978 to 1981. They note that the distortion wave was symmetrical in 1980 and asymmetrical in 1981. The system has also been observed by Bopp and Talcott (1980) who found Ha absorption of constant equivalent width and Eggen (1984) who reported that the spectra of the system show variable emission lines of Ca II H and K, as well as Ha.
V815 Her (HD 166181, BD +29° 3187, SAO 085767) is a regular period (P = 1.8098368d), non-eclipsing, single-lined (G5 V) spectroscopic binary with an eccentric orbit (e = 0.029). Nadel et al. (1974) initially determined an orbital period of 1.81 days while Mekkaden, Raveendran and Mohin (1980) have reported a photometric period of 1.8 days (DV = 0.10m).
Gimenez et al. (1985) state that the system resembles a metal-deficient dwarf star in its photometric properties and Fekel, Moffett and Henry (1986) observed a strong Li line in the 6700Å region. Such a strong line in a late-type dwarf indicates that the star is very young, but further spectral work is needed to verify that a blend is not being observed as was the case with II Peg (Vogt 1979, 1981).
47 Dra (o Dra, HR 7125, HD 175306, BD +59° 1925, SAO 031218) is the A-component of the visual binary ADS 11799. It is a non-eclipsing, single-lined (G9 III), long period (P = 138.420d) binary with a highly eccentric orbit (e = 0.114). Very little has been published on this system, but Hall and Persinger (1986) report no evidence for ellipticity or reflection effects, but a possible 54.6 day variation (DV = 0.034m) is attributed to starspots on the giant star. They also state that measurable spot activity was absent prior to 1984.
V478 Lyr (HD 178450, BD +30° 3425, SAO 067836) is a regular period (P = 2.310541d), non-eclipsing, single-lined (G8 V) spectroscopic binary. The only published photometric observations are those of Henry (1981) who found V-band variations of 0.033m with a photometric period of 2.185 days. Ca II H and K emission lines were observed by Fekel, Moffett and Henry (1986). Their UV observations show emission lines typical of chromospherically active stars and no evidence of a hot companion. They found a period of 2.310541 days which is misprinted by Strassmeier et al. (1988) as 2.130541 days.
HR 7428 (HD 184398, BD +55° 2215, SAO 031741) is a long-period (P = 108.5707d), non-eclipsing, single-lined spectroscopic binary with a mildly eccentric (e = 0.05) orbit. The stars are classified as A0 V and K2 III-II. Moderate X-ray emission has been reported by Charles (1983).
V-band photometric observations by Barksdale et al. (1985b) indicates the presence of two periods. The shorter, near 55 days (DV = 0.05m), was attributed to the ellipticity effect while the longer, with a period of 108.85 ± 1.15 days, was attributed to differential reflection. They also suggest the possibility of the presence of a low level distortion wave.
Xuefu and Huisong (1984) observed double emission in Ha, with the red element being stronger than the blue, and they suggest there may be a phase relation. Verm, Iyengar and Rengarajan (1987) found and IR excess from IRAS data and attributed it to circumstellar dust emission.
V1764 Cyg (HD 185151, BD +27° 3444, SAO 087451) is a long period (P = 40.1425d), non-eclipsing, single-line (K1 III) spectroscopic binary. Bopp et al. (1982) showed this system to be a single-lined binary with an orbital period of 40.13 days. They observed a distortion wave with a period near 20 days and an amplitude of DV = 0.15m. The source of the distortion was attributed to starspots. Two peaks were found in the spectral analysis of the light curve. It was noted that a double sine light curve had only been previously observed in II Peg (Nations and Ramsey 1981) and HR 1099 (Blanco et al. 1981).
Lines et al. (1987) applied a truncated Fourier series to V-band data and found a photometric period of 20.0665 ± 0.0044 days (DV = 0.125m ± 0.004). The wave had a minimum at the time of conjunction and so it was attributed to the ellipticity effect. They also found a variable amplitude distortion wave with DV ranging from 0.022m to 0.092m. The period of the wave, which was attributed to starspots, was determined to be 39.878 ± 0.036 days.
ER Vul (HD 200391, BD +27° 3952, SAO 089396) is a short period (P = 0.69809510d), partially eclipsing, double-lined spectroscopic binary with an eccentric orbit (e = 0.02). The stars have been classified as G0 V and G5 V. The system is a known X-ray source (Walter and Bowyer 1981; Charles 1983; Vilhu and Heise 1986) and has been observed in the ultraviolet (Budding and Kadouri 1982; Vilhu and Heise 1986).
The system was discovered spectroscopically by Northcott and Bakos (1956). The irregular light curve variations were identified by Al-Naimiy (1978) and the times of minima have been monitored by Ibanoglu, Akan and Evren (1985) from 1981 to 1985. Photometric observations by Zeilik et al. (1981) indicated variations on the scale of 1 week and observations by Kadouri (1981) showed no intrinsic variations of color with orbital phase. Zeilik et al. (1982) acquired a complete light curve, in a one week period, in U, B, V and R bands. Their observations indicated a clear decrease in mean magnitude in all four colors (0.05m in U and B, 0.03m in V and R). Starspot Analysis by Zeilik and Budding (1986) indicates that two spots are needed to adequately describe the light variations and observations by Akan et al. (1987) indicate a photometric wave migration rate on the order of eight months.
HK Lac (HD 209813, BD +46° 3572, SAO 051628) is a long period (P = 24.4284d), non-eclipsing, single-lined spectroscopic binary with an eccentric orbit (e = 0.01). The stars have been classified as F1 V and K0 III and the system is a known X-ray (Walter and Bowyer 1981) and radio source (Spangler, Owen and Hulse 1977).
The system was discovered to be variable by Blanco and Catalano (1968). Blanco and Catalano (1970) reported a photometric period of 25.3 days, while Hall (1980b) reported a period of 24.0026 days. Bopp and Talcott (1980) reported sporadic Ha emission indicating high-velocity ejection of material presumably in the form of large active prominences.
Olah (1983) first reported observations from 1976 to 1981. She noted that: none of the observed light curves were symmetrical, the median brightness of the system was strongly varying and that no single photometric period could fit all the data. Further work by Olah et al. (1985) interpreted the distortion wave as being caused by two large spots that have maintained their individuality for 15 years. The motions of the spots were found to be 0.025% faster and 0.08% slower than the orbital period. They again noted that no constant photometric period can satisfy the light curve but the average period is near 24.461 days (DV = 0.25m). More recent work by Olah et al. (1986) indicates that the median brightness variations reported in 1983 and 1985 may have a cyclic variation on the order of seven years. They also note that the spot groups identified in 1985 were still present. They suggest that this apparent long term stability of the spot groups may be caused by the presence of active longitude belts that are maintained by magnetic interconnection between the stars.
AR Lac (HR 8448, HD 210334, BD +45° 3813, SAO 051684) is a regular period (P = 1.98322195d), totally eclipsing, double-lined spectroscopic binary. It is a known X-ray source (Walter and Bowyer 1981) and the stars are classified as G2 IV and K0 IV. This system has been observed for over half a century and a detailed account of its early history is given by Chambliss (1976). It was for this system that Kron (1947) first proposed the starspot model to account for the outside-of-eclipse light variations.
Analysis of 18 light curves from 1926 to 1974 by Hall, Richardson and Chambliss (1976) showed a wave like distortion with a migration rate that varied from 50-60 yr/cycle in 1930-40 to 10-15 yr/cycle in 1970. Variations in the times of conjunction were also observed, indicating a decrease in the orbital period. B and V observations by Kurutac et al. (1981) and Ertan et al. (1982) confirmed that the period is decreasing at a rate of 14.6 s/century. Kurutac et al. (1981) also noted a distortion wave migration period of 2.5 years. Ertan et al. (1982) noted that the outside-of-eclipse distortion showed two maxima and that the wave was relatively constant in shape from 1980 to 1981. The distortion wave was also observed by Nha et al. (1985) who acquired a complete light curve, in three colors, from 1980-82.
U, B and V observations by Srivastava (1983, 1984, 1985, 1986) indicate that AR Lac shows flare activity on both components. This conclusion is consistent with the IUE observations by Kiziloglu et al. (1983) and Rodono et al. (1987) which indicate chromospheric activity at roughly equal levels for each star. Srivastava's analysis indicates that: 1) the secondary component is away from the main sequence while the primary lies nearly on the main sequence, 2) AR Lac may be a semi-detached system, 3) the secondary component is approaching to fill its Roche lobe, or it has already done so and is shrinking, 4) there is evidence that the secondary is losing mass to the primary, and thereby producing changes in the period, 5) the spectral-luminosity class is G9 V-IV which supports the conclusion that it is on the sub-giant branch. His observations indicate that the distortion wave could not be caused by gas streaming, stellar pulsations (both of which were proposed by Theokas (1977)), or extended atmospheres. He concludes that starspots, on both components of the system, is the only consistent explanation. Srivastava did not investigate the possibility of third light as the source of the distortion, however observations by Van Buren (1986) ruled out this possibility.
Lee (1986) observed the system in y and b in 1982-83. His observations clearly show a distortion wave, while V-band observations by Caton (1986), who used truncated Fourier series for the outside-of-eclipse data, showed no evidence for a wave.
AR Lac is a variable, flaring radio source (Hjellming and Blankenship 1973; Gibson and Hjellming 1974; Spangler et al. 1977; Feldman 1978; Owen and Gibson 1978; Watler et al. 1978). Owen and Spangler (1977) observed 3 eclipse cycles at 4585MHz and saw no dependence, which indicated that the radio emitting region is in the form of an extended shell or disk. Doiron and Mutel (1984) also failed to observe an eclipse at 1.5 and 4.9GHz. These observations are consistent with the UV spectrophotometry work of Rhombs and Fix (1977), who concluded that the observed excesses were best described by free-free emission of hydrogen from a hot circumstellar gas. A spectroscopic study by Naftilan and Drake (1977) indicated a disk or shell around the secondary (G2 IV) which is moderately under-abundant in metals while the primary is solar like.
V350 Lac (HR 8575, HD 213389, BD +48° 3747, SAO 052073) is a long period (P = 17.755d), non-eclipsing, single-lined (K2 III) spectroscopic binary with a slightly eccentric orbit (e = 0.02). The system is not well observed, but it is a known X-ray (Charles 1983) and radio (Mutal and Lestrade 1985) source.
Photometric variability was first detected by Herbst (1973). He found a photometric period of one-half the orbital, using observations over 12 orbital periods, and attributed the distortion (DV = 0.1m) to the ellipticity effect. Percy and Welch (1982) also found similar photometric variability, near one-half the orbital period, and concluded that the variation may be caused by ellipticity or possibly starspots.
IM Peg (HR 8703, HD 216489, BD +16° 4831, SAO 108231) is a long period (P = 24.649d), non-eclipsing, single-lined (K2 III-II) spectroscopic binary that has been identified as the optical counter part to the X-ray source 4U225218 (Walter et al. 1980 and Walter and Bowyer 1981). IM Peg is also a known radio binary (Spangler, Owen and Hulse 1977).
Herbst (1971) was the first to discover the photometric variability of the system. Percy and Welch (1982), using 17 nights of V-band data in 1979, derived a photometric period of 24.3 ± 0.3 days. Eaton et al. (1983b), using a truncated Fourier series, found a photometric period of 24.39 ± 0.03 days with observations from 1978 to 1981. They noted that the amplitude of the wave changed from DV=0.20m in 1978-79 to 0.13m in 1980-81 and that there were corresponding variations in the symmetry of the light curve.
l And (16 And, HR 8961, HD 222107, BD +45° 4283, SAO 053204) is a long period (P = 20.5212d), non-eclipsing, single-lined (G8 IV-III) spectroscopic binary with an eccentric orbit (e = 0.04). The optical variability of the system was discovered by Calder (1938) who found quasisinusoidal light variations with a period near 54 days. Subsequent photometry by Archer (1960), Landis et al. (1978) and Dorren, Guinan and Paczkowski (1982) indicated that the light curve is variable in amplitude, mean brightness and shape. Bopp and Noah (1980) and Dorren, Guinan and Paczkowski (1982), using classical spot modeling on selected light curves, found strong evidence in support of the canonical two component starspot model.
The system has been detected at radio (Spangler, Owen and Hulse 1977; Pallavicini, Willson and Lang 1985), ultraviolet (Baliunas and Dupree 1982) and X-ray (Walter and Bowyer 1981; Mewe and Schrijver 1986) wavelengths. It has been observed in Ha by Guinan and Wacker (1985) who found no correlation between emission and orbital phase, unlike the phase correlation found by Baliunas and Dupree (1982) for the UV transition-region lines and Ca II H and K emission. The system has also been observed for Zeeman broadening by Marcy and Bruning (1984) who found a null detection indicating a magnetic field strength less than 1000 Gauss, but a positive detection at 1290 ± 50 Gauss has been reported by Giampapa and Worden (1983), who used a magnetically sensitive spectral line comparison technique.
Boyd et al. (1983), using V-band photometry from 1977 thorough 1981 from 14 observatories, derived and ephemeris of 2443829.2 + 53.95d ± 0.07 E. They noted that the shape of the light curve is highly variable in both amplitude and mean magnitude. Fourier analysis of V-band observations by Scaltriti et al. (1984) confirms the photometric period of Boyed et al. (1983). They observed the same general variations in the shape and amplitude of the light curve. In particular, they noted that the maximum amplitude has been diminishing since 1976-77 and that the mean V magnitude is fainter in 1981-82 by 0.07m as compared to 1976-77. They suggest that the observed photometric period is actually the mean value of a complex quasi-periodic distortion, with a period near nine years. They conclude that the light curve is consistent with a spotted surface in which spots are spread in latitude on a differentially rotating star.
II Peg (HD 224085, BD +27° 4642, SAO 091578) is a regular period (P = 6.724183d), non-eclipsing, single-lined (K2-3 V-IV) spectroscopic binary and has been identified with the fast X-ray transient A0000 + 28 (3A2355 + 284) (Walter et al. 1980; Pye and McHardy 1983; Schwartz et al. 1984). II Peg is also an active radio source (Spangler, Owen and Hulse 1977) and a radio source at centimeter wavelengths (Owen and Gibson 1978).
Its photometric variability was discovered by Chugainov (1976) who noted variations at V-band and tentatively classified the star as a BY Draconis-type variable. Rucinski (1977) concluded that the star more closely resembled an RS CVn-type system, but that it also exhibited the characteristics of the post-T Tauri star FK Ser (rapid rotation, Ca II H and K emission, Ha and Li I l6707 emission and a spectral type of K2-3 VI-V). Vogt (1979, 1981), however, found that the Li I l6707 line found by Rucinski (1977) is actually a blend of Fe VI and Fe I lines, which invalidated the possible post-T Tauri classification.
Rucinski (1977) found amplitude variations amounting to about 0.25m at V-band and suggested starspots, distributed non-uniformly in longitude, as the cause of the light changes. Vogt (1979, 1981) found a 0.43m V-band variation and a 0.60m V-R variation which he attributed to a large (35% of the stellar surface) cool (3300K) spot or spot group (M6 equivalent spectral type). He observed a flat-topped lightcurve and concluded that the proposed spot group passed completely out of view. He also concluded that the observed variations in the light curve implied evolutionary time scales less than one year while Cano et al. (1987) observed a rapid change in amplitude (0.5m to 0.15m) on a time scale of a few months. Byrne (1986) also observed large variations in the amplitude of the light curve and interpreted them as evidence for large amplitude spot variations.
Nations and Ramsey (1981) found two unequal maxima, separated by 0.55 in orbital phase, which were interpreted as starspots that cover 27% of the visible disk at a temperature 1100K cooler than the surrounding photosphere. Amplitudes of the light curves decreased at longer wavelengths and the star was reddest at minimum light. The light curves did not show a flat maximum, as was observed by Vogt (1981), and the two peaks were widely separated in phase which was interpreted as a nearly continuous longitudinal spot distribution. Arevalo, Lazaro and Fuensal (1985) also found a light curve with two minima at 0.26p and 0.97p (DV = 0.15m). Observations by Wacker and Guinan (1986) identified two maxima, and minima, of unequal brightness. The minima were separated by about 0.5 in orbital phase. Two minima have also been observed by Boyd et al. (1987) at 0.18p and 0.85p in orbital phase. Raveendran, Mohin and Mekkaden (1981) found Pphot = 6.7026 ± 0.0034 days in B and V-bands with amplitudes of 0.15m in both colors using least squares times of maximum over 10 orbital periods.
Hartmann, Londono and Phillips (1979) used Harvard photographic plates to study the long term variability of the system. They found that the mean light level was constant for 40 years before exhibiting a change of 0.3m in 1945. This lack of variability suggests long term periods of inactivity similar to the solar Maunder minimum.
Bopp and Noah (1980) found that the Ha equivalent width varies, by a factor of 10 over several days, in phase with rotation. These variations were attributed to a strong localization of the emitting regions.
IUE observations by Udalski and Rucinski (1982) indicate strong emission (20-120 times the quiet sun) from the primary. IUE observations by Rodono et al. (1987) also show stellar line fluxes hundreds of times the solar values and activity was seen only on the visible component of the system.
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Copyright (c) 1988-1997, Eric R. Nelson, Ph.D.