For each light curve a least square fit of all the data has been performed with a function of the type:

In this relation

is the magnitude difference in each filter between the CP star and the comparison star, t is the JD date, t₀ is the assumed initial epoch, P is the period in days. This procedure can be partially accounted for by considering that within the accuracy of the measurements a sine wave and its first harmonic appear to be generally adequate to describe the light curves (North 1984; Mathys & Manfroid 1985) and the magnetic field variations (Borra & Landstreet 1980; Bohlender et al. 1993).

In the figures, where the infrared variations are plotted, open squares do represent the data collected in the 1986 run (i.e. the data with an accuracy lower than 0.01 mag), while the other symbols, listed in Table 2 (click here), represent the observations of the successive runs, having a better accuracy. In the same figures, the continuous line represents the fit to the observations obtained by means of Eq. (1) and which has to be considered only as indicative, just to evidentiate the observed variations. For most of the stars the individual fit of the differential J, H, and K variations did show very similar behavior although with different amplitudes.

Indeed in the fits performed by means of (1), whose A₁ and A₂ coefficients and

are given in the last three columns of Table 3 (click here), the second harmonic was not retained for the stars HD 72968 and HD 126515, because of a too small number of observations (HD 72968) and of a very poor phase coverage (HD 126515).

**Table 3:** Ephemeris elements used to compute the phases of the variations, coefficients of the fits and their errors

HD	JD()	Instant of	P(days)	coeff.	J	H	K


3980		v min.	3.9516	A₁	-0.0114	-0.0138	-0.0126
				A₂	0.0116	0.0125	0.0135
					0.0130	0.0105	0.0136
24712		pos. extr.	12.4610	A₁	-0.0031	-0.0027	0.0076
				A₂	-0.0095	0.0059	-0.0077
					0.0093	0.0052	0.0058
49976		uvby max	2.97666	A₁	0.0090	0.0107	0.0080
				A₂	0.0088	0.0055	0.0035
					0.0137	0.0089	0.0072
72968		max.	11.305	A₁	-0.0073	0.0002	0.0069
				A₂	--	--	--
					0.0047	0.0037	0.0033
83368		neg. extr.	2.851982	A₁	0.0021	-0.0021	0.0017
				A₂	0.0075	0.0043	-0.0045
					0.0072	0.0069	0.0088
96616		uvby max.	2.4394	A₁	0.0122	0.0086	0.0098
				A₂	-0.0056	-0.0064	-0.0079
					0.0040	0.0032	0.0067
98088		periastron	5.905130	A₁	-0.0084	0.0054	-0.0100
				A₂	-0.0136	-0.0094	0.0107
					0.0109	0.0095	0.0124
101065		--	7.593	A₁	-0.0110	0.0039	0.0033
				A₂	0.0016	-0.0029	-0.0047
					0.0098	0.0089	0.0087
111133		uvby max.	16.30720	A₁	0.0035	0.0054	0.0047
				A₂	-0.0091	0.0087	-0.0069
					0.0046	0.0059	0.0050
118022		y max.	3.722084	A₁	0.0125	0.0096	-0.0028
				A₂	0.0064	0.0049	-0.0025
					0.0065	0.0094	0.0074
125248		u max.	9.295710	A₁	-0.0062	-0.0092	0.0051
				A₂	-0.0110	0.0096	0.0105
					0.0062	0.0041	0.0046
126515		max.	129.99	A₁	0.0157	0.0080	-0.0137
				A₂	--	--	--
					0.0103	0.0077	0.0063
148898		--	0.7462	A₁	0.0041	0.0025	0.0017
				A₂	0.0068	-0.0026	0.0049
					0.0059	0.0049	0.0056
153882		pos. crossover	6.00890	A₁	-0.0109	-0.0101	-0.0109
				A₂	0.0104	0.0140	-0.0155
					0.0038	0.0133	0.0069
164258		uvby min.	0.829	A₁	-0.0052	-0.0046	-0.0053
				A₂	-0.0058	-0.0053	-0.0032
					0.0073	0.0048	0.0056
203006		uvby I max.	2.1224	A₁	-0.0029	0.0045	-0.0048
				A₂	0.0072	-0.0141	-0.0106
					0.0137	0.0111	0.0095
206088		--	2.78	A₁	0.0094	0.0054	0.0022
				A₂	-0.0040	0.0025	-0.0039
					0.0103	0.0099	0.0053
220825			1.418	A₁	-0.0061	0.0038	0.0109
				A₂	0.0024	-0.0036	-0.0005
					0.0063	0.0057	0.0082
221760		uvby max.	12.45	A₁	0.0098	0.0075	0.0052
				A₂	0.0032	0.0019	-0.0008
					0.0048	0.0065	0.0074

HD 3980 A = HR 183 A =

Phe A

An analysis of the photometric and magnetic variability of the late type CP2 star HD 3980 has been carried out by Maitzen et al. (1980) who found the period to be 3.9516 (

) days. The visible light curves show a double wave with different amplitudes, the maximum amplitude occurring in the v filter, where it amounts to 0.13 mag peak to peak. A well defined double-wave variation with the same period is indeed shown by the peculiarity index

(Maitzen & Vogt 1983).

Figure 1: Differential infrared light curves of HD 3980. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

The infrared variability of HD 3980 was discovered by CKL. However further infrared observations have been carried out which are here reported. The infrared differential light curves, displayed in Fig. 1 (click here), are plotted versus the phase computed by means of Maitzen et al.'s ephemeris elements reported in Table 3 (click here). From Fig. 1 (click here) a double wave variation is quite evident with the same amplitude (of the order of 0.03 mag peak to peak) in all three filters, although it looks better defined in the H and K filters.

HD 24712 = HR 1217 = DO Eri

The cool magnetic star HD 24712 has had many studies made since the measurements of the magnetic field strength, of the radial velocity and of the line strengths of Mg and Eu carried out by Preston (1972), who found all of these to vary with a period of 12.448 days.

HD 24712 has been extensively studied by Kurtz and coworkers, with the aim of investigating the short period oscillations of the cool magnetic SrCrEu stars which have been successfully interpreted as high-overtone p-modes with the pulsation axis aligned with the magnetic axis of the star which is itself oblique to the rotation axis (the oblique pulsator model: Kurtz 1982; Kurtz & Marang 1987; Kurtz et al. 1992, and references therein).

Figure 2: Differential infrared light curves of HD 24712. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

The infrared variability of HD 24712 was also discovered by CKL, however some more infrared observations have been carried out which are here reported. The infrared differential light curves are plotted in Fig. 2 (click here) versus the phase computed by means of the above cited ephemeris elements. From this figure a double-wave variation in all three filters seems evident, with an amplitude of the order of 0.03 mag.

HD 49976 = HR 2534 = V592 Mon

A rather strong magnetic field was measured in HD 49976 by Babcock (1958a) who also found evidence of an extraordinary range of variation of the SrII lines.

Figure 3: Differential infrared light curves of HD 49976. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

The infrared differential light curves of HD 49976 are plotted in Fig. 3 (click here) versus the phase computed by means of the ephemeris elements reported in Table 3 (click here), where the assumed initial epoch is the actual time of maximum visible light as taken from the observations of Pilachowski et al. (1974). The infrared light variations are in phase with each other, and show quite the same amplitude, of the order of 0.03 mag peak to peak, in all three filters.

HD 72968 = HR 3398 = 3 Hya = HV Hya

HD 72968 is the first star for which an estimate of the surface magnetic field intensity has been carried out on the basis of the study of the Zeeman intensification of spectral lines on the saturated part of the curve of growth (Hensberge & de Loore 1974).

Figure 4: Differential infrared light curves of HD 72968. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

The infrared differential light curves of HD 72968 are plotted in Fig. 4 (click here) versus the phase computed on the basis of Maitzen et al. (1978) ephemeris elements reported in Table 3 (click here). From Fig. 4 (click here) a slight variability is better evident in the K filter, with an amplitude of the order of 0.02 mag.

HD 83368 = HR 3831 = IM Vel

The late type CP2 star HD 83368 is a visual double with a magnitude difference

= 2.85 and a separation of 3.3 arcsec, which implies that both components are measured in the photometric observations.

The photometric variability of HD 83368 has been detected by Renson & Manfroid (1978). Thompson (1983) measured a magnetic field symmetrically variable from +800 to -800 gauss within a period of 2.857 d. Kurtz (1982) discovered that HD 83368 shows pulsations with periods of

6 and 12 min modulated within a period of about 2.85 d. More recently Kurtz et al. (1992) have shown that the period of the pulsation amplitude modulation is equal to the period of the mean-light variation and have refined the rotation period to the value 2.851982

0.000005 d. This value of the period has been confirmed by Mathys & Manfroid (1985), Heck et al. (1987), Kurtz & Marang (1988), and Catalano & Leone (1994), and represents quite well also the magnetic observations of Mathys (1994) and Mathys & Hubrig (1997).

The infrared differential light curves of HD 83368 are plotted in Fig. 5 (click here) versus the phase computed by means of Mathys & Hubrig (1997) ephemeris elements reported in Table 3 (click here). From Fig. 5 (click here) we see that the HD 83368 shows a small amplitude double-wave variation, although with a quite large dispersion of the data, which could be due to the light dilution due to the presence of the close companion (Renson et al. 1984).

Figure 5: Differential infrared light curves of HD 83368. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

HD 96616 = HR 4327 = 4G. Cen = V815 Cen

HD 96616 is a visual double with a secondary component 2.6 mag fainter than the primary and separated only by 2 arcsec.

Figure 6: Differential infrared light curves of HD 96616. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

Only one measurement of the magnetic field of HD 96616 has been made by Borra & Landstreet (1975) but no field significantly different from zero was measured.

Our infrared differential observations of HD 96616 are plotted in Fig. 6 (click here) versus the phase computed by means of the ephemeris elements reported in Table 3 (click here). The infrared variation of HD 96616 is clearly evident in all three filters and amounts to about 0.03 mag peak to peak.

HD 98088 = HR 4369 = SV Crt

HD 98088 is the brightest component of a visual binary (ADS 8115) whose components are separated by 57.2 arcsec and the secondary is 3.8 mag fainter. It is also a double-lined spectroscopic binary with a known orbit (Abt 1953; Abt et al. 1968; Wolff 1974) and a period of 5.90513 d.

The magnetic field of HD 98088 has been measured by Babcock (1958a,b), who showed it to vary with the same period as the orbital motion.

The light variations of HD 98088 have been studied by Maitzen (1973), Wolff & Morrison (1975), and Catalano & Leone (1994). From all these data it appears that the period of this star is very well defined and still adequately represents observations carried out many years apart.

Figure 7: Differential infrared light curves of HD 98088. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

The infrared differential observations of HD 98088 are plotted in Fig. 7 (click here) versus the phase computed by means of Abt et al. (1968) ephemeris elements reported in Table 3 (click here). The infrared light variation of HD 98088 is double-waved in all three filters, with amplitudes of the order of 0.03 mag.

HD 101065 = CoD

7232 = V816 Cen

HD 101065, also known as Przybylski's star, is one of the most peculiar stars known: its visible spectrum is strongly dominated by the rare earth lines (Przybylski 1961, 1963, 1966; Cowley et al. 1977) whose abundances are estimated as high as five orders of magnitude if compared to cosmic abundances (Wegner & Petford 1974). The iron peak elements, formerly considered to be underabundant in the visible spectrum, have been found to be strongly represented in the ultraviolet region 1900 - 3200 Å\ (Wegner et al. 1983).

HD 101065 is an extremely highly blanketed star, so much that no available model atmosphere can fit the entire energy distribution as deduced from low resolution IUE spectra and visible and infrared photometry (Wegner et al. 1983). This fact can explain the difficulty in obtaining a reliable value of the effective temperature: values as low as

K have been proposed (Przybylski 1977a).

In spite of the several spectroscopic studies carried out, no clear evidence of variations of HD 101065 has been found so far in the line spectrum (Wolff & Hagen 1976; Cowley et al. 1977) nor in the -2200 gauss magnetic field measured by Wolff & Hagen (1976).

Photometric observations of HD 101065 aimed at detecting light variations have been carried out in the past by several authors. The most extensive photometric work has been done from 1969 to 1977 by Przybylski (1977b) who reported possible small amplitude long-period brightness variations of the order of two to three hundredths of a magnitude in Johnson V. However uvby observations appear to exclude systematic variations on a time scale of a week (Heck et al. 1976; Renson et al. 1976; Heck et al. 1987).

The only kind of variability so far detected to occur in HD 101065 is the rapid light variation with P = 12.14 min. (Kurtz 1978; Kurtz & Wegner 1979; Kurtz 1980, 1981). Kurtz (1982) discovered HD 101065 to show pulsations with periods of

12 min modulated within a period of about 2.85 d and interpreted this result within the context of the oblique rotator model, suggesting the presence of a polarity reversing magnetic field.

Near infrared photometric observations have been carried out by several authors and some discrepancies are evident from these data (Hyland et al. 1975; Glass 1982). For this and on the basis of the fact that from Przybylski's (1977b) photometric observations some evidence of light variability could be present at the longer wavelengths, we decided to observe HD 101065 for variability in the near infrared.

According to our observations spanning several runs, HD 101065 is quite clearly variable in the J filter, although some hint of variability seems to be present in the other filters. Period search led to the value 7.596

0.005 d, which was found to represent quite well the observations. Other possible period values are 0.858 and 1.827 d, which however should be excluded if the rotational velocity

is lower than 7 km s^-1, as suggested by Wegner (1979) and Martinez & Kurtz (1990).

The infrared differential observations of HD 101065 are plotted in Fig. 8 (click here) versus the phase computed by means of the ephemeris elements reported in Table 3 (click here).

Figure 8: Differential infrared light curves of HD 101065. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

HD 111133 = HR 4854 = EP Vir

The presence of a fairly strong magnetic field in HD 111133 has been revealed by Babcock (1958a).

The magnetic variation has been studied by Wolff & Wolff (1972), who found it occurring within a period of 16.31 d. The same period was found for the spectral line intensity of CrI, CrII, FeI, and FeII, and the light variations. Further magnetic field measurements have been carried out by Glagolevsky et al. (1982).

Figure 9: Differential infrared light curves of HD 111133. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

The spectrum variations have been studied by Engin (1974), while the

peculiarity index and b-y variations have been studied by Buchholz & Maitzen (1979).

Recent photometric observations of HD 111133 have been carried out by Adelman et al. (1992), Catalano & Leone (1994) and North & Adelman (1995). The best representation of all photometric observations was obtained by North & Adelman (1995) whose ephemeris elements reported in Table 3 (click here), we have assumed in Fig. 9 (click here) to plot our infrared differential observations. From this figure it appears that the infrared light curves of HD 111133 show constant amplitudes of about 0.03 mag and are in phase with each other.

HD 118022 = HR 5105 = 78 Vir = CW Vir

HD 118022 is the first star in which a magnetic field has been detected (Babcock 1947). The magnetic field variation has been subsequently studied by Preston (1969), who first determined the correct period to be 3.7220 d from the analysis of the crossover effect. Several authors have provided further magnetic measurements (Wolff & Wolff 1971; Wolff & Bonsack 1972; Wolff 1978; Borra 1980; Borra & Landstreet 1980; Leroy 1995), all of them confirming the period found by Preston.

Figure 10: Differential infrared light curves of HD 118022. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

The infrared differential observations of HD 118022 are plotted in Fig. 10 (click here) with the ephemeris elements reported in Table 3 (click here). As it is evident from Fig. 10 (click here), HD 118022 is variable in J and H, with light curves which are essentially single-waved and have amplitudes of about 0.04 mag, while it is almost constant in the K filter.

HD 125248 = HR 5355 = 236G. Vir = CS Vir

HD 125248 is an outstanding magnetic, spectroscopic and light variable and is the first star for which an oblique rotator model has been put forward in order to describe the observed variations (Stibbs 1950). HD 125248 is also the first star for which Deutsch (1958) carried out a spherical harmonics analysis aimed at synthesizing a surface map of the abundance anomalies and of the magnetic field, based on his own spectroscopic observations (Deutsch 1947) and the magnetic field measurements of Babcock (1951). A lot of observational work has been devoted to HD 125248 (see Catalano & Renson 1984, 1988, 1987, and Catalano et al. 1991, 1993 for references).

Figure 11: Differential infrared light curves of HD 125248. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

HD 125248 has been found to be variable in the near infrared by Catalano et al. (1992) with the same period as the visible light, spectrum and magnetic field variations. The infrared differential observations of HD 125248 are plotted in Fig. 11 (click here) versus the phase computed by means of the ephemeris elements reported in Table 3 (click here). The infrared variations do show a nearly constant amplitude larger than 0.03 mag peak-to-peak and look almost unchanged in all filters. All three light curves are in phase with each other, presenting a more pronounced double wave behavior than the visible light curves.

HD 126515 = GC 19462 = FF Vir

The star HD 126515 is the first star in which the spectral lines split in the Zeeman components have been observed. This fact allowed Preston (1970) to succeed in measuring the average surface field

which resulted to vary between 10 and 17 kG with a periodicity of 130 d. Preston also observed spectral line intensity variations of the lines of such elements as Si, Cr, Fe, Ti, Sr, and Eu with the same period of the magnetic field and in phase with the magnetic variations.

From the

study of the

continuum depression carried out by Hensberge et al. (1986) it was inferred that the surface region, in which the high peculiarity values originate, are associated with the regions of enhanced spectral line strength, rather than with the local magnetic field.

Figure 12: Differential infrared light curves of HD 126515. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

Photoelectric observations of HD 126515 have been carried out by Catalano & Leone (1990) and North & Adelman (1995). The latter authors refined the period to the value 129.99 d. This value of the period has recently been confirmed by Mathys et al. (1997), from magnetic field observations.

The infrared differential observations of HD 126515 are plotted in Fig. 12 (click here) versus the phase computed by means of Mathys et al. (1997) ephemeris elements reported in Table 3 (click here). As it is evident from Fig. 12 (click here), due to the incomplete coverage of the light curves of HD 126515, nothing can be said about the amplitude of the variability.

HD 137949 =

Lib = GZ Lib

The unusual strength of the lines of SrII in the spectrum of HD 137949 has been noted by Adams et al. (1935). Babcock (1958a) also noted the unusual intensity of the EuII lines and found evidence of a rather strong magnetic field (

1 kgauss). Further magnetic measurements were carried out by van den Heuvel (1971), who suggested that the magnetic field variation occurs within 18.4 d. This value of the period was not confirmed by Wolff (1975), who instead supported evidence of a magnetic variation occurring within a period of 23.26 d, but did not detect light variations larger than 0.01 mag. Further magnetic observations have been carried out by Mathys et al. (1997), who have pointed out the possibility of a very long period (

years).

From photometric observations Kurtz (1982) suggested that the rotation period of HD 137949 could be 7.194 d. However, the light variability of this late CP star, if ever exists, is controversial. Essentially, no variability was evident from photometric observations carried out by Wolff (1975), Deul & van Genderen (1983), and Catalano & Leone (1994). No variations have also been found in the UV by van Dijk et al. (1978).

Our infrared observations are consistent with no light variation in excess of 0.01 mag.

HD 148898 = HR 6153 =

Oph

The spectrum variability of HD 148898 has been discovered by Morgan (1932) who noted that maxima and minima of the spectral line intensity of

4215(SrII) occurred within a few days. Deutsch estimated the period to be of the order of 2 d (Bowen 1952). The existence of a polarity reversing magnetic field has been inferred by Babcock (1958a), but not measured because of the large spectral line width. Four measurements of the magnetic field intensity have been carried out by Borra & Landstreet (1980) with low values inside the 3

level.

Figure 13: Differential infrared light curves of HD 148898. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

HD 148898 has been found to be a low amplitude light variable with several possible values of the period such as 0.7462

0.0002, 1.4922

0.0004, and 2.968

0.003 d or nearby values (Renson & Maitzen 1978). Subsequent uvby observations led to the most probable periodicities 1.79 (

0.02) d, 4.67 (

0.08) d or, less probably, 2.33 (

) d (Manfroid & Mathys 1985; Mathys & Manfroid 1985).

Among the above mentioned possible values, we have found that the best representation of our infrared differential observations was obtained with the period of 0.7462 d, hence the infrared light curves of HD 148898 are plotted in Fig. 13 (click here) versus the phase computed by means of the ephemeris elements reported in Table 3 (click here). As it is evident from Fig. 13 (click here) the infrared variations of HD 148898 show an essentially single-waved trend and are in phase with each other, with very low amplitudes.

HD 153882 = HR 6326 = V451 Her

Taking into account all magnetic data, relative to a time interval of more than forty years, Mathys (1991) refined the value of the period to 6.00890(

0.000015) d. Mathys also confirmed the quite sinusoidal character with polarity reversal of the magnetic variation, occurring with the same period as the photometric one, and extrema in the range -1600 to +1600 gauss. Moreover Mathys studied the equivalent width of the FeII

5961 line and found large anharmonic variations whose extrema coincide in phase with the light variations but show no simple phase relation with the extrema of the magnetic field.

The infrared differential observations of HD 153882 are shown in Fig. 14 (click here), where they are plotted versus the phase computed by means of the ephemeris elements reported in Table 3 (click here). From Fig. 14 (click here) we see that HD 153882 is slightly variable in the infrared with an amplitude of the order of 0.04 mag peak to peak.

Figure 14: Differential infrared light curves of HD 153882. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

HD 164258 = HR 6709 = V2126 Oph

Babcock (1958a) included HD 164258 in the list of the stars with probable magnetic fields and noted the unusual strength of the SrII lines. Bonsack (1974) found indication of variability in the lines of EuII but did not determined any period.

HD 164258 has been found to be variable by Renson & Manfroid (1980) who gave indication of a period of about 2.41 d. However, Manfroid & Mathys (1985) suggested shorter periods such as 0.719 or 0.359 d. On the basis of new uvby observations Catalano & Leone (1994) have found a period of 0.829(

0.005) d, which gives quite a good representation of the observations.

Figure 15: Differential infrared light curves of HD 164250. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

The infrared differential observations of HD 164258 are shown in Fig. 15 (click here), where they are plotted versus the phase computed by means of the ephemeris elements reported in Table 3 (click here). From Fig. 15 (click here) we see that HD 164258 shows a very small single-waved variation, better evident in J where it has an amplitude of the order of 0.02 mag.

HD 203006 = HR 8151 =

Mic

HD 203006 has been found by Babcock (1958a) to be both spectrum and magnetic variable, on the basis of the fact that the magnetic field polarity appeared to reverse polarity in one day while lines of EuII and of SrII showed intensity variations of opposite sign.

The first determination of the period has been performed by Morrison & Wolff (1971); from uvby observations these authors found HD 203006 to vary within 1.062

0.001 d. Maitzen et al. (1974) found a double wave in their UBV and uvby observations and stated the correct period to be 2.1219 d. From more recent photoelectric observations Deul & van Genderen (1983), have argued for a slightly shorter period, i.e. 2.1215

0.0001, while from spectroscopic measurements Brandi & Ziznovský (1990) favoured a slightly longer one, i.e. 2.1221

0.0002 d, although both values are very near to Maitzen et al.'s value.

Figure 16: Differential infrared light curves of HD 203006. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

Our infrared differential observations of HD 203006, phased with all of these period values, do show too large a dispersion, in fact they are better represented with a slightly longer period value, i.e. 2.1224 d, which is just outside of the error bar. The resulting light curves are shown in Fig. 16 (click here), where they are plotted versus the phase computed by means of the ephemeris elements reported in Table 3 (click here). As it is evident from Fig. 16 (click here) the light curves of HD 203006 show essentially the same high dispersion double-waved variations, in phase with each other, as in the uvby, with amplitudes of about 0.04 mag.

HD 206088 = HR 8278 =

Cap

HD 206088 was initially used as a standard, however, since we noted an anomalous scatter of the observations, it was included among the programme stars to look for variability.

The spectral type of HD 206088 is given as A8-F4 Sr in the General Catalogue of Ap and Am Stars (Renson et al. 1991), so it would be intermediate between late Ap stars and Am stars. No photometric nor spectroscopic studies of this star are available in the literature.

Figure 17: Differential infrared light curves of HD 206088. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

Period search led to the most probable value of the period of 2.78 d, although many other nearby values are possible. However the number of the observed points is too small to allow a better determination. The infrared differential light curves of HD 206088 are shown in Fig. 17 (click here), where they are plotted versus the phase computed by means of the ephemeris elements reported in Table 3 (click here). As it is evident from Fig. 17 (click here), of HD 206088 might be variable, at least in the J filter, but the period is too poorly defined to be fully reliable: it has to be considered as a trial value and needs to be confirmed.

HD 220825 = HR 8911 =

Psc

A lot of photometric and spectroscopic studies of the SrCr star HD 220825 have been performed since Rakosch (1962) discovery of its variability with a period of 0.5805 d. Recent studies have allowed to determine the period to be 1.418 d (Ryabchikova et al. 1996, and references therein). A small amplitude magnetic field variation (Borra & Landstreet 1980) is also consistent with this period.

Figure 18: Differential infrared light curves of HD 220825. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text

The infrared differential light curves of HD 220825 are shown in Fig. 18 (click here), where they are plotted versus the phase computed by means of the ephemeris elements reported in Table 3 (click here). As it is evident from Fig. 18 (click here), HD 220825 appears to be slightly variable in K with an amplitude of the order of 0.03 mag.

HD 221760 = HR 8949 =

Phe

Babcock (1958a) found the SrII, CrI and CrII lines to be particularly prominent in the spectrum of HD 221760, and supported evidence for a rather weak magnetic field of positive polarity. Further magnetic field measurements by Borra & Landstreet (1980) confirmed the weakness of the field (

0).

The only available photometric observations of this star are those by van Genderen (1971), who discovered HD 221760 to be variable in light with a period of 12.5 d.

HD 221760 was found to be variable in the infrared, at least in the J filter, and period search led to a number of values as 12.016, 12.224, 12.450, 12.655, and 12.886 days. We have preferred the value 12.45 days, which gives the minimum dispersion, but it has to be considered only as preliminary and should be confirmed. Our infrared differential observations of HD 221760 are plotted in Fig. 19 (click here) versus the phase computed by means of the ephemeris elements reported in Table 3 (click here). From Fig. 19 (click here) we see that HD 221760 might be variable in J with an amplitude of the order of 0.02 mag. However, the period should be confirmed.

Figure 19: Differential infrared light curves of HD 221760. The phases are computed according to the ephemeris elements in Table 3 (click here). The solid line is a least-square fit of the observations by Eq. (1) as described in the text