NEW PHOTOMETRICALLY VARIABLE MAGNETIC CHEMICALLY PECULIAR STARS IN THE ASAS-3 ARCHIVE

The aim of the All Sky Automated Survey (ASAS) is the detection and investigation of any kind of photometric variability. To this end, ASAS constantly monitored the entire southern sky and part of the northern sky to about δ < +28°. The third phase of the project, ASAS-3, lasted from 2000 until 2009 (Pojmański 2002). The employed instrumentation, which was situated at the 10 inch astrograph dome of the Las Campanas Observatory in Chile, consisted of two wide-field telescopes equipped with f/2.8 200 mm Minolta lenses and 2048 × 2048 AP 10 Apogee detectors that covered a field of sky of 88 × 88. About 10⁷ sources brighter than V ≈ 14 mag were monitored in Johnson V. The achieved CCD resolution was about 148 pixel⁻¹, which led to an astrometric accuracy of around 3''–5'' for bright stars and up to 155 for fainter stars. As a result, photometry in crowded fields, as in star clusters, is rather uncertain. A field was typically observed every one, two, or three days (Pigulski 2014). This observing cadence results in strong daily aliasing and renders the interpretation of the resulting Fourier amplitude spectra ambiguous.

The ASAS-3 archive contains reasonable photometry for stars in the magnitude range of 7 ≲ V ≲ 14. However, the most accurate data were obtained for targets in the magnitude range of 8 ≲ V ≲ 10. Here, the typical scatter is about 0.01 mag (e.g., Pigulski 2014). However, because of the long time base of almost 10 years, ASAS-3 data allow for the detection of periodic signals with very small amplitudes. For instance, David et al. (2014) identified periodic variables with a range of variability of 0.01–0.02 mag in the magnitude range of 7 ≲ V ≲ 10. Pigulski (2014) estimated that periodic signals with amplitudes as low as about 5 millimag (mmag) can be detected.

Pojmański (2002) has shown that the zero-points of the ASAS-3 and Hipparcos photometry agree to within about ±0.015 mag for stars lying close to the frame center. However, flat-fielding issues, missing color information, and blending may result in much larger differences. We have investigated the agreement between mean ASAS-3 V magnitudes and V magnitudes given by Kharchenko (2001) for the stars of our final sample. The results are shown in Figure 1 and indicate very good general agreement between both sources. In most cases, unresolved close companions are responsible for the observed discrepancies.

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An intial list of target stars was created by selecting CP2 stars or CP2 star candidates and He-weak (CP4)/He-strong objects from the most recent version of the Catalog of Ap, HgMn, and Am stars (Renson & Manfroid 2009, RM09 hereafter). Objects in the RM09 catalog are not explicitly subdivided according to the classification established by Preston (1974). We therefore resorted to the listed spectral types to distinguish between the different groups of CP stars (mainly denoted as Si, Sr, Sr Eu Si, He weak, HgMn, and so on). The resulting list of stars was cross-matched with the Tycho-2 catalog (Høg et al. 2000); unlike our initial approach, where we defined a cut-off at V_T < 11 mag (see Paper 1, Section 2), no brightness limit was imposed.

In addition to that, a systematic investigation of early-type (spectral types B/A) variable stars of undetermined type in the AAVSO International Variable Star Index (VSX; Watson 2006) yielded additional ACV candidates, which were added to our target list.

We consulted the GCVS (Samus et al. 2007–2016), VSX, SIMBAD (Wenger et al. 2000), and VizieR (Ochsenbein et al. 2000) databases in order to check for an entry in variability catalogs and to collect literature information on our target stars. Known ACV variables with well-determined parameters were dropped from our sample; suspected or misclassified variables and variables of undetermined type were kept.

The light curves of our sample stars were downloaded from the ASAS-3 website.⁴ For the present investigation, a refined analysis approach was developed with the intention of discovering variable objects that might have been missed by the imposed criteria in our previous work (Paper 1). In order to retain as many objects as possible, no lower limit was imposed on the number of observations in the ASAS-3 archive. In Paper 1, we restricted our analysis to promising candidates in order to keep our sample down to a manageable size. As promising candidates, we defined stars showing a larger scatter than usually observed for apparently constant stars in the corresponding magnitude range with comparable instruments (Hartman et al. 2004). No such criteria were imposed in the present investigation; instead, every individual ASAS data set was roughly cleaned of outliers and searched for periodic signals in the frequency domain of 0 < f (cycles per day; c/d hereafter) <20 using Period04 (Lenz & Breger 2005).

Furthermore, the periodicity detection threshold was lowered significantly. Only objects with semi-amplitudes of ≳0.007 mag (as derived with Period04) were considered in Paper 1. In the present investigation, all objects exhibiting variability with a semi-amplitude of at least 0.004 mag were subjected to a more detailed analysis. This limit is an experiental value based on our own extensive experience in dealing with the ASAS-3 data and the results of David et al. (2014) and Pigulski (2014). It was chosen as a compromise between retaining variables with small amplitudes and eliminating spurious detections.

In the next step of the analysis, left-over data points with a quality flag of "D" (="worst data, probably useless") were rejected and remaining outliers were carefully removed by visual inspection. Furthermore, the data were checked for the presence of systematic trends. These were mostly due to strong blending effects, which might result in significant additional scatter due to the inclusion of part of a neighboring star's flux (Sitek & Pojmański 2014) or instrumental long-term trends that could introduce spurious signals into the data. Depending on the severity of artifacts, the affected data sets were either rejected or the trends were removed.

To refine the initial frequency analysis, the pretreated data sets were again searched for periodic signals in the frequency domain of 0 < f(c/d) < 10 with Period04. The data were folded on the resulting best fitting frequency and visually inspected. Objects exhibiting convincing phase plots were kept.

The light curves of CP2 stars can be well described by a sine wave and its first harmonic (North 1984; Mathys & Manfroid 1985; Heck et al. 1987; Bernhard et al. 2015b). We performed a least-squares fit to the data using Period04. Each light curve was fitted using a Fourier series consisting of the fundamental sine wave and its first harmonic, from which the light-curve parameters (semi-amplitudes ${A}_{1}$, ${A}_{2}$, and the corresponding phases ${\phi }_{1}$, ${\phi }_{2}$) were derived.

As pointed out, the light curves of most ACV variables are sinusoidal. In orientations where two photometric spots of overabundant optically active elements come into view during a single rotation cycle, the light curve becomes a double wave (Maitzen 1980). If the two spots are of similar extent and photometric properties, the resulting "maxima" will be of approximately the same height. Therefore, a twice longer (or shorter) rotation period cannot be excluded. This holds especially true for objects with very small amplitudes and/or significant scatter in their light curves.

In addition to that, alias periods cannot be totally excluded because of the strong daily aliasing inherent to ASAS-3 data (see Section 2.1). However, we have checked the period solution of all doubtful cases and are confident that we have come up with the period that fits ASAS-3 data best. This assumption is further corroborated by the generally very good agreement of our period solutions to those from the literature (see also Paper 1).

For the final classification, all available information (spectral type, color indices, period, shape of the light curve, and Fourier amplitude spectrum) was taken into account. Except for the eclipsing binary systems (see below), all stars in our final sample exhibit a variability pattern that is generally in accordance with rotational modulation caused by spots. HD 66051 (V414 Pup) is a special case in that it clearly shows both orbital (eclipses) and rotational modulation.

However, caution has to be taken because it is not straightforward to distinguish between variability induced by rotation and other sources such as, e.g., pulsation or orbital motion. This holds especially true when analyzing variable stars whose photometric amplitudes are near the detection limit of the employed data, as is the case for many of our targets.

Pulsation as the underlying mechanism of the observed variability can be ruled out for most objects of our sample on the following grounds. The vast majority of our sample stars is found between spectral types B7 to A5 (see Figure 2). Therefore, pulsators that are exclusively found among earlier spectral types, such as, e.g., β Cephei variables (GCVS-type BCEP, spectral types ∼O8–B6), or primarily among later spectral types, such as, e.g., the γ Doradus stars (GCVS-type GDOR, spectral types ∼A7–F7), are not expected to contribute much to our sample. Of course, inaccuracies/difficulties in spectral classification have to be considered, and the spectral types shown in Figure 2 might be uncertain by several subclasses.

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Furthermore, our target stars exhibit photometric periods longer than P > 0.5 days. We can thus exclude the presence of δ Scuti variables (GCVS-type DSCT) or other short period pulsators.

On the other hand, some types of pulsating variables partly overlap with ACV stars in respect to spectral type and period. The so-called slowly pulsating B (GCVS-type SPB) stars, for instance, are encountered down to spectral type B9 (Figure 2) and exhibit periods between about 0.4 and 5 days. The γ Doradus stars are found between spectral types A7 to F7; observed periods usually range from 0.3 to 3 days.

One way of distinguishing these types of variable stars is an investigation of their Fourier amplitude spectra. Many kinds of pulsators, such as, e.g., SPB and γ Doradus stars, show multiple periods and quite different frequency spectra from rotating variables. For instance, harmonics of pulsation modes are only expected to be present in frequency spectra when the amplitude is large. On the other hand, harmonics are a consequence of localized spots and a characteristic of the frequency spectra of rotating variables (Balona et al. 2015).

Spots form and decay in late-type, active stars, and differential rotation might led to the presence of multiple, closely spaced periods in these objects (Reinhold & Gizon 2015). However, the presence of starspots in stars with radiative envelopes, like B/A stars, is still a matter of some controversy. Recently, Balona and coworkers have collected evidence that A-type stars are active and show starspots in the same way as their cooler counterparts (e.g., Balona 2013). Nevertheless, the spots on CP2 stars are of a different nature (abundance patches) and constitute durable configurations that remain stable for decades, probably as a consequence of strong magnetic fields.

Differential rotation, however, plays an important role in A-type stars (Ammler-von Eiff & Reiners 2012; Szklarski & Arlt 2013; Balona & Abedigamba 2016). However, to our knowledge, no study of the possible effects of differential rotation on CP2 star light curves exists. Judging from the stability of the periods and light curves among ACV variables, we assume that these effects, if present, are generally small. However, it must not be dismissed that the presence of multiple, closely spaced frequencies in the Fourier amplitude spectra of early-type stars might be due to differential rotation and need not automatically imply pulsation. Apart from this special scenario, however, the presence of multiple periods is not to be expected in CP2 stars and interpreted by us as an indication of pulsation in a non-CP2 star as the underlying mechanism of the observed photometric variability.

Figure 3 shows the Fourier amplitude spectra of two B-type stars and illustrates the described differences in the frequency spectra between a multi-periodic, pulsating variable (NSV 24561, spectral type B3, likely an SPB star) and a rotating variable (HD 63204, spectral type B9pSi, a confirmed ACV variable, see Bernhard et al. 2015a). No harmonics are seen in the spectrum of NSV 24561, which exhibits two significant low frequencies. In contrast, only one frequency and its first harmonic are present in the frequency spectrum of HD 63204.

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It has to be kept in mind, though, that these assumptions are simplifications that do not represent nature with all its intricacies. For instance, recent evidence from Kepler data indicates that rotational frequencies might possibly be present in SPB variables and result in the presence of harmonics in the corresponding Fourier amplitude spectra (Balona et al. 2015).

Finally, and most importantly, the spectra of all these kinds of pulsating variables are not characterized by the abnormal abundance patterns of the CP2/4 stars, which are a confirmed characteristic of most of our target stars and are expected for the CP2 star candidates in our sample. Generally, pulsation is not to be expected in CP2 stars. The only proven form of pulsational variability among this type of CP stars is observed in the so-called rapidly oscillating Ap (roAp) stars (Kurtz 1982), which exhibit photometric variability in the period range of 5–20 minutes (high-overtone, low-degree, and non-radial pulsation modes). This is very different from what has been observed for our sample stars. We therefore feel confident in ruling out pulsation as the underlying cause of the observed photometric variability in most of our sample stars.

The discrimination between rotational modulation and variability induced by orbital motion (as observed in ellipsoidal variables, GCVS-type ELL, and eclipsing binaries) is more difficult, though. Generally, it is not possible to distinguish between both types of variations without additional spectroscopic information (Paper 1; Balona et al. 2015). For some CP stars, for instance, a double-wave structure of the photometric light curve has been observed (Maitzen 1980). The light curves of these "double-humped" ACVs are not to be distiguished from the light curves of ellipsoidal variables on grounds of single-passband photometric data alone. However, it has been shown that the incidence of ellipsoidal or eclipsing variables among CP2 stars is very low (Gerbaldi et al. 1985; North & Debernardi 2004; Hubrig et al. 2014) and even in a sample of some hundred stars, only very few ellipsoidal or eclipsing variable star candidates are to be expected (see Paper 1).

We have identified three eclipsing binary stars among our targets (CPD-20 1640, HD 66051, and HD 149334, see Section 4). While the system of HD 66051 (V414 Pup) definitely hosts a CP2 star, the CP classification of the other two objects is doubtful; thus, spectroscopic investigations are needed to confirm or reject the assumed presence of a CP2 star in these systems. Furthermore, with the available data, we are not able to distinguish between rotational and orbital modulation as the underlying cause of the photometric variability of the CP4 star HD 161733A. Section 4.2 provides a detailed discussion of these objects.

Before the background of the characteristic light variations and Fourier amplitude spectra, the confirmed CP2/4 nature of our targets, and the available spectral classifications, which go along well with the observed color indices, the most likely explanation of the observed light variations in the majority of our sample stars is the redistribution of flux in spots of overabundant optically active chemical elements. We are therefore confident that most of the confirmed CP2/4 stars in our sample are bona-fide ACV variables (N = 334). The few exceptions or special cases are commented on in Section 4.2.

This assumption is further corroborated by the fact that (with the exception of the eclipsing binaries) all light curves of our sample stars can be well represented by a sine wave and its first harmonic—a procedure which has been shown to adequately describe the light curves of ACV variables (see Section 3.1). The photometrically variable CP2 star candidates in our sample are here proposed as ACV variable candidates (type ACV: in Table 2; N = 23) on grounds of their periods and typical photometric variability but need spectroscopic confirmation of their CP status. The two CP4 objects and the He-strong star are also designated as ACV candidates, as other mechanisms beside rotational modulation might be at work in these objects (Section 4.2).

Employing the methodology outlined above (Sections 2 and 3), 360 stars exhibiting photometric variability in the accuracy limit of the ASAS-3 data were identified among the stars of our target list. We have ruled out pulsation as the underlying mechanism of the observed variability in most of our targets and are confident of the applicability of our classifications. Table 1 gives statistical information on the composition of the final sample.

We have searched the SIMBAD, VizieR, and VSX databases for previously published information on our targets. According to these sources, most of the investigated CP stars have never been the subject of a light variability analysis before and are presented here as variable stars for the first time. Some of our target stars have been previously investigated and found constant or probably constant; other objects have been identified as variable stars with or without a given period in the literature, but their variability types have not been determined or they have been misclassified.

Table 2 presents essential data and light-curve fit parameters for our sample stars and is organized as follows.

• 1.  
  Column 1: star name, HD number, or other conventional identification.
• 2.  
  Column 2: identification number from RM09.
• 3.  
  Column 3: R.A. (J2000; Tycho-2).
• 4.  
  Column 4: decl. (J2000; Tycho-2).
• 5.  
  Column 5: variability type, according to GCVS convention (ACV/ACV:/EA).
• 6.  
  Column 6: V magnitude range, as derived from the Fourier fit to the ASAS-3 data.
• 7.  
  Column 7: period (day).
• 8.  
  Column 8: epoch (HJD-2450000); time of maximum is indicated for ACV variables or candidates, time of minimum for the eclipsing binary systems.
• 9.  
  Column 9: semi-amplitude of the fundamental variation (${A}_{1}$).⁵
• 10.  
  Column 10: semi-amplitude of the first harmonic variation (${A}_{2}$).
• 11.  
  Column 11: phase of the fundamental variation (${\phi }_{1}$).⁶
• 12.  
  Column 12: phase of the first harmonic variation (${\phi }_{2}$).
• 13.  
  Column 13: Spectral classification, as listed in RM09; it is noteworthy that, as in the original catalog, the "p" denoting peculiarity has been omitted from the spectral classifications taken from RM09. For the five stars not included in this catalog, the spectral types have been gleaned from the VSX and verified using the VizieR and SIMBAD catalog services.
• 14.  
  Column 14: $(B-V)$ index, taken from Kharchenko (2001).
• 15.  
  Column 15: $(J-{K}_{{\rm{s}}})$ index, as derived from the 2MASS catalog (Skrutskie et al. 2006).

Table 2.  Essential Data for the Stars Identified As Photometrically Variable Chemically Peculiar Stars or Candidates in the Present Paper

Star	ID (RM09)	α (J2000)	δ (J2000)	Type	Range (V)	Period	Epoch (HJD)	${A}_{1}$	${A}_{2}$	${\phi }_{1}$	${\phi }_{2}$	Spectral Type	$(B-V)$	$(J-{K}_{{\rm{s}}})$
					(mag)	(day)	(day)	(mag)	(mag)	(rad)	(rad)		(mag)	(mag)
HD 2957	760	00 32 44.08	−13 29 13.5	ACV	8.48–8.51	4.6327(3)	4627.91(9)	0.011	0.002	0.846	0.750	B9 Cr Eu	+0.052	−0.017
HD 3885	1050	00 41 18.31	−19 51 45.9	ACV	9.79–9.81	1.81508(4)	2910.72(4)	0.007	0.009	0.348	0.449	B9 Si	−0.090	−0.079
HD 5823	1540	00 59 39.29	−11 56 01.2	ACV	9.95–9.97	1.24520(2)	3765.53(2)	0.007	0.004	0.723	0.646	F2 Sr Eu Cr	+0.304	+0.176
HD 8783	2110	01 24 00.43	−72 19 27.9	ACV	7.80–7.82	19.396(5)	3794.5(4)	0.009	0.001	0.102	0.715	A2 Sr Eu Cr	+0.150	+0.039
HD 12559	⋯	02 03 29.36	+18 19 39.4	ACV:	8.41–8.44	4.0358(3)	3338.62(8)	0.010	0.012	0.479	0.293	A2	+0.092	−0.034
HD 16145	4060	02 35 04.20	−17 17 22.3	ACV	7.64–7.67	2.23766(7)	4525.52(4)	0.011	0.002	0.342	0.873	A0 Cr Sr Eu	+0.117	−0.023
HD 20505	5120	03 15 03.18	−59 11 36.1	ACV	9.88–9.90	2.04401(5)	2666.49(4)	0.009	0.002	0.222	0.726	A2 Cr Sr	+0.120	+0.001
HD 22032	5540	03 33 11.64	+04 40 13.3	ACV	9.05–9.07	4.8589(3)	3031.57(9)	0.010	0.001	0.839	0.523	A3 Sr Eu Cr	+0.455	+0.056
HD 23509	6020	03 41 29.82	−66 28 37.9	ACV:	7.75–7.78	1.48786(3)	3010.64(3)	0.012	0.002	0.302	0.426	A3	+0.309	+0.167
HD 27210	6960	04 15 22.02	−51 44 27.1	ACV:	10.09–10.12	1.01438(1)	3447.55(2)	0.015	0.000	0.120	...	A0	+0.064	−0.046
HD 28238	7210	04 27 35.96	+06 36 43.2	ACV	9.11–9.12	24.743(7)	2676.5(5)	0.007	0.001	0.615	0.177	A0 Sr Cr Eu	+0.241	+0.053
HD 30374	7830	04 39 01.57	−75 06 10.1	ACV	10.02–10.04	1.55631(3)	3018.65(3)	0.008	0.003	0.097	0.580	A0 Sr Eu Cr	+0.105	+0.081
HD 240563	8310	05 04 57.34	+08 50 05.6	ACV	10.09–10.12	2.9447(1)	4399.78(6)	0.015	0.003	0.646	0.601	A3 Sr	+0.216	+0.078
HD 245155	9662	05 35 42.79	+25 16 29.4	ACV	9.67–9.69	0.705370(7)	3730.62(1)	0.009	0.001	0.809	0.251	B9 Si Sr	+0.080	+0.109
HD 38417	10330	05 38 55.39	−71 38 20.1	ACV	9.61–9.63	2.16619(6)	3086.56(4)	0.002	0.008	0.096	0.011	A0 Sr	+0.121	+0.044
HD 38912	10450	05 49 13.10	+01 27 30.2	ACV	9.46–9.49	1.46279(2)	2539.74(3)	0.013	0.003	0.608	0.148	B8 Si	+0.266	+0.106
HD 39082	10500	05 50 23.85	+04 57 24.3	ACV	7.41–7.42	0.764776(7)	4877.58(2)	0.007	0.001	0.045	0.341	B9 Sr Cr Eu	+0.039	−0.041
HD 40071	10680	05 56 06.12	−13 08 07.2	ACV	8.06–8.08	1.98735(5)	4477.82(4)	0.005	0.005	0.744	0.369	B9 Si	−0.042	−0.062
HD 40383	10780	05 58 37.50	+04 29 33.6	ACV	8.98–9.00	4.0364(3)	3644.86(8)	0.009	0.007	0.739	0.771	B9 Si	+0.215	+0.059
HD 40678	10876	06 01 29.21	+23 42 14.2	ACV	7.37–7.39	22.029(6)	2678.2(4)	0.012	0.001	0.238	0.541	A0 Si Sr	+0.158	−0.085

Only a portion of this table is shown here to demonstrate its form and content. A machine-readable version of the full table is available.

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The light curves of all objects, folded with the periods listed in Table 2, are presented in the Appendix (see Figure 8). Information from the literature and miscellaneous remarks on individual objects are listed in Table 3, which is organized as follows.

• 1.  
  Column 1: star name, HD number, or other conventional identification.
• 2.  
  Column 2: variable star designation from the literature.
• 3.  
  Column 3: variable star type from the literature.
• 4.  
  Column 4: period (day) from the literature.
• 5.  
  Column 5: period (day) from this work.
• 6.  
  Column 6: reference in which, to the best of our knowledge, the object has been announced as a variable star for the first time.
• 7.  
  Column 7: remarks/comments of a miscellaneous nature; an asterisk denotes stars whose status as CP objects is doubtful according to RM09.

Table 3.  Relevant Information on Single Objects from the Literature and Miscellaneous Remarks

Star	Var. Desig.	Var. Type	Period (day)	Period (day)	Reference	Remarks/Comments
	Literature	Literature	Literature	This work		Literature
HD 2957				4.6327(3)		Null result for roAp pulsations (Martinez & Kurtz 1994).
HD 3885	NSV 15149	VAR		1.81508(4)	Wesselius et al. (1982)
HD 5823				1.24520(2)		Null result for roAp pulsations (Kochukhov et al. 2013a).
HD 8783	SMC V2339	VAR:	21(or 1.05)? (GCVS)	19.396(5)	GCVS	Non-member of the SMC according to the GCVS. The given period
						values are derived from variations of the peculiarity index Δa.
HD 12559	HIP 9602	VAR	2.01833 (VSX); 2.01837 (R12)	4.0358(3)	Koen & Eyer (2002)	R12: SPB/ACV (prob: 0.24/0.51)
HD 16145			2.24(or 4.47)? (RM09)	2.23766(7)		Null result for roAp pulsations (Martinez & Kurtz 1994).
HD 23509	HIP 17239	VAR	1.48779 (VSX); 1.48765 (R12)	1.48786(3)	Koen & Eyer (2002)	R12: SPB/DSCTC (prob: 0.23/0.33)
HD 27210				1.01438(1)		*
HD 240563				2.9447(1)		*
HD 245155				0.705370(7)		Constant or quality of data prevented detection (W12).
HD 38417				2.16619(6)		*
HD 39082	NSV 16689	VAR	0.76484 (VSX)	0.764776(7)	Vogt & Faundez (1979)
HD 40678				22.029(6)		Constant or quality of data prevented detection (W12).
BD-06 1402	HIP 28864	VAR	1.13065 (VSX)	1.13063(2)	Koen & Eyer (2002)	R12: EB/SPB (prob: 0.15/0.57)
	ASAS J060540-0603.2	DCEP-FU/MISC	1.13058 (R12)			Richards et al. (2012): ACV (prob: 0.8109)
HD 41869				5.2350(4)		Constant or probably constant, blend? in STEREO data (W12).
HD 46105	NSV 16891	VAR		0.793263(8)	Rufener & Bartholdi (1982)
HD 46649				4.1792(3)		RM09: A0 Si Cr ? *
HD 49797				1.22649(2)		*
HD 50031				2.8743(1)		Null result for roAp pulsations (Martinez & Kurtz 1994).
HD 51342				1.43601(2)		*
HD 296343	GDS_J0705593-050617	VAR	n/a	9.8306(9)	Hackstein et al. (2015)
HD 57368				3.5286(2)		*
HD 57964A				0.676093(6)		The CP2 star may not be the A component (RM09). *
HD 61008	NSV 17517	VAR	1.33237 (VSX)	2.66482(9)	Koen & Eyer (2002)
HD 62821A	GDS_J0744549-250026	VAR	n/a	3.8347(2)	Hackstein et al. (2015)
GSC 08911-01572				5.5805(4)		*
HD 66051	V414 Pup	EA+ACV	4.74922 (Otero 2003)	4.74922(1)	Otero (2003)	Synchronous rotation. ACV and EA period are the same.
						Amp. of rot. var. = 0.05 mag (Otero 2003).
HD 67909				2.41433(8)		Null result for roAp pulsations (Martinez & Kurtz 1994).
HD 68250				0.841212(9)		*
HD 68322				1.76642(3)		*
HD 68781				3.2112(1)		Null result for roAp pulsations (Martinez & Kurtz 1994).
HD 69728				1.63779(3)		*
HD 71034A				5.3998(4)		RM09: uncertain, which component is (weakly) Ap
HD 72634	HIP 41667	VAR	0.93051 (VSX)	0.93062(1)	Koen & Eyer (2002)
HD 72976	HIP 41954	VAR	3.85654 (VSX); 3.85656 (R12)	3.8560(2)	Koen & Eyer (2002)	R12: SPB/ACV (prob: 0.31/0.40)
HD 72770	ASAS J083344-2808.1	ESD/EC	4.7930 (VSX)	4.7915(3)	Sitek & Pojmański (2014)	R12: BCEP/DSCT (prob: 0.30/0.49)
CD-38 4858	GDS_J0846444-383832	VAR	n/a	9.6457(9)	Hackstein et al. (2015)
HD 76759A				1.20648(2)		Null result for roAp pulsations (Martinez & Kurtz 1994).
HD 77809				2.37366(7)		Null result for roAp pulsations (Martinez & Kurtz 1994).
CPD-59 1669				3.8271(2)		*
HD 91825A				2.7634(1)		*
HD 92315				1.57651(3)		*
HD 92384				2.29382(7)		*
HD 303209				1.60624(3)		*
HD 96204				3.5745(2)		*
HD 102454	ASAS J114726-3115.3	ED/ESD/SR	4.1579 (Sitek & Pojmański 2014)	2.07906(5)	Sitek & Pojmański (2014)
HD 106204	NSV 19303	VAR		4.3572(3)	Rufener & Bartholdi (1982)
BD+01 2668				0.98410(1)		*
HD 109300				2.63189(9)		*
HD 110072				22.225(6)		Null result for roAp pulsations (e.g., Martinez & Kurtz 1994).
						$v\,\sin \,i$ = 3.3 ± 0.5; Teff = 7300 K; double-lined binary with
						peculiar lines of e.g., Nd, Pr and Eu (Freyhammer et al. 2008b).
HD 110274	ASAS J124131-5855.4	MISC	265.3 (Freyhammer et al. 2008a)	265.1(4)	Freyhammer et al. (2008a)
			310.0 (Sitek & Pojmański 2014)
HD 110568				9.6018(9)		*
HD 115398				0.720460(7)		*
HD 115226		roAp	10.86 minutes (Kochukhov et al. 2008)	2.9882(1)	Kochukhov et al. (2008)	Kochukhov et al. (2008) find ve sin i = 25–30 km s−1 and
						Prot ≤ 3.0–3.5 day. Surface abundance inhomogeneities established.
						No variability found in ASAS data but marginal variability
						with P = 3.61 day in Hipparcos data.
HD 115440				5.4421(4)		Null result for roAp pulsations (Martinez & Kurtz 1994).
HD 117096				2.12428(6)		*
HD 117692				3.2798(1)		*
HD 121142				1.69062(3)		*
HD 121661	ASAS J135842-6243.1	MISC	47.0 (Freyhammer et al. 2008a)	46.86(2)	Freyhammer et al. (2008a)	Null results for roAp pulsations (Martinez & Kurtz 1994).
			46.850 (Sitek & Pojmański 2014)
HD 121841				1.08529(2)		*
HD 122983		ACV	3.4 $\lt \,P\,\lt$ 3.8 (Paunzen et al. 2011)	3.6166(2)	Paunzen et al. (2011)
HD 123164				2.51961(8)		Null results for roAp pulsations (Martinez & Kurtz 1994).
HD 124455				0.606079(5)		*
HD 124437	HIP 69725	VAR	0.828705 (R12)	5.9563(4)	R12	R12: BE+GCAS/DSCT (prob: 0.23/0.59)
HD 127924		ACV	3.55 (Paunzen et al. 2011)	3.5487(2)	Paunzen et al. (2011)	*
HD 129934				2.17566(6)		*
HD 130382				1.66901(3)		*
HD 131505A			1.258 (RM09)	1.25794(2)
HD 133428	HIP 74294	VAR	0.758752 (R12)	1.51763(3)	R12	R12: DSCTC/DSCT (prob: 0.24/0.24)
	ASAS J151109-7657.0	EC/ACV/ESD	1.51765 (Sitek & Pojmański 2014)
HD 136357				1.92479(5)		*
HD 137309				2.19247(6)		*
HD 139149				1.64538(3)		*
HD 140532				1.07077(1)		*
HD 144748		ACV:	3.9815 (W12)	4.9549(3)	W12	blend?, weak signal (W12).
HD 144264A				1.25143(2)		*
CD-28 12149				1.35884(2)		Constant or probably constant (W12).
HD 149228				1.54043(3)		Constant or probably constant (W12).
HD 149334	ASAS J163524-3400.8	EA	3.5444 (Sitek & Pojmański 2014)	3.54420(6)	Sitek & Pojmański (2014)
HD 149769				8.2422(8)		Null result for roAp pulsations (Martinez & Kurtz 1994).
HD 150323	NSV 20737	VAR		5.3777(4)	Vogt & Faundez (1979)
HD 155188				3.3334(2)		Null result for roAp pulsations (Martinez & Kurtz 1994).
HD 158450	NSV 22273	VAR		8.5239(8)	Vogt & Faundez (1979)	Null result for roAp pulsations (Martinez & Kurtz 1994).
HD 167476				3.2895(1)		*
HD 170054	NSV 24444	VAR	1.043999 (R12)	0.97317(1)	Hrivnak (1977)	Blue straggler according to Hrivnak (1977);
						R12: BE+GCAS/SPB (prob: 0.27/0.48)
HD 169789				5.2315(4)		*
HD 170836		ACV	0.9? (Paunzen et al. 2011)	19.516(5)	Paunzen et al. (2011)
HD 170860A		ACV	"variable" (Paunzen et al. 2011)	1.38585(2)	Paunzen et al. (2011)	*
HD 173657	HIP 92215	VAR	1.93720 (VSX)	1.93789(5)	Koen & Eyer (2002)
HD 173361				0.831981(9)		*
HD 181549				22.871(6)		*
HD 193325			3.153 day? (RM09)	3.1529(1)
HD 198918	NP Del	ELL:	0.777813 (VSX); 0.388866 (Dubath et al. 2011)	0.777809(7)	van Leeuwen et al. (1997)
HD 200199				1.03512(1)		*
HD 205013	NSV 25655	VAR	1.57594 (VSX)	1.57624(3)	Kornilov et al. (1991)
HD 209605A				7.8132(7)		Null result for roAp pulsations (Martinez & Kurtz 1994).

Note. An asterisk in Column 7 ("Remarks/comments") denotes stars whose statuses as chemically peculiar objects are doubtful according to RM09. The following abbreviations are employed in Column 7: R12 = Rimoldini et al. (2012); W12 = Wraight et al. (2012).

Download table as:  ASCIITypeset images: 1 2 3 4

Table 2 is available in its entirety in machine-readable form. We are currently working on a statistical paper on the properties of ACV variables, which will include results from the literature as well as our own investigations (Paper 1; Bernhard et al. 2015b, this paper). Therefore, in the present work, we restrict ourselves to the discussion of interesting and unusual objects.

The following sections contain notes and literature information on several unusual and interesting objects.

4.2.1. CPD-20 1640 = NGC 2287 40

CPD-20 1640 is listed with a spectral type of A5pSiSr in the RM09 catalog. It has been identified with Cox 40 (=NGC 2287 40) and is likely a member of the intermediate-age open cluster NGC 2287 (Landstreet et al. 2007). However, its status as a CP2 star needs confirmation. While the listed spectral type is in accordance with this classification, it is not supported by the measured ${\rm{\Delta }}a$ and Z values and the non-detection of a magnetic field (see Landstreet et al. 2007, and references therein).

ASAS-3 data indicate that CPD-20 1640 is an eclipsing binary with a period of P = 2.43400(2) days. The primary minimum is sharp and suggestive of a detached or semi-detached system (see Figure 4). If proven that at least one component of this system is indeed a classical CP2 star, CPD-20 1640 would be of high interest, as the incidence of CP2 stars in eclipsing binaries is very low (see Section 3.2). RM09 list only five candidates for eclipsing CP2 stars; only one (AO Velorum) has been confirmed (González et al. 2006). Another confirmed eclipsing CP2 star (HD 66051) is presented in the following section. One good candidate (HD 70817) and three possible candidates were identified in Paper 1 but need spectroscopic confirmation. We therefore strongly encourage further studies of CPD-20 1640 in order to confirm or reject the assumed presence of a CP2 star in the system.

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4.2.2. HD 66051 = V414 Pup

HD 66051 is a confirmed CP2 star of the Silicon subgroup (Bidelman & MacConnell 1973; Houk & Smith-Moore 1988) and listed with a spectral type of A0pSi in the RM09 catalog. Its photometric variability was discovered in Hipparcos data (HIP 39229; van Leeuwen et al. 1997). The star was subsequently included in the GCVS as an ACV candidate (type ACV:); no period or epoch were given.

The star was discovered to be an eclipsing binary of Algol-type (GCVS-type EA) by Otero (2003), who derived an orbital period of P = 4.74922 days and a magnitude range of 8.79–9.12 mag (V) from a combination of Hipparcos and ASAS-3 data. Furthermore, the star was shown to exhibit additional variability with an amplitude of 0.05 mag and the same period, which was interpreted as being due to "ACV variations," i.e., rotationally induced variability caused by surface inhomogeneities on (at least) one of the system's components.

No further detailed studies of HD 66051 exist in the VizieR and SIMBAD databases. However, a high-resolution spectrum of the star is available in the archive of the "Variable Star One-shot Project" (Dall et al. 2007), which was taken with the HARPS instrument (Mayor et al. 2003) at the ESO La Silla Observatory in Chile. Details on the spectroscopic observation can be found in Dall et al. (2007). The spectrum confirms that HD 66051 harbours a CP2 Si star (see Figure 5). In addition to that, enhanced lines of other elements, such as, e.g., Sr, Cr, and Eu, are present. The spectrum was obtained on JD 2453827.518802, which—assuming the epoch of 2452167.867 as orbital phase φ = 0 (Otero 2003)—corresponds to φ_orb = 0.46. The spectrum does not confirm the proposed SB2 nature of the system (Dall et al. 2007), which is likely due to coverage at an "unfortunate" orbital phase.

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We have investigated the object using all available data and confirm the findings of Otero (2003). The longevity of the observed secondary variability in the light curve, which remains stable during the ∼9 years of ASAS-3 coverage (Figure 6), might be interpreted in terms of synchronous rotation, i.e., both stars are tidally locked.

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HD 66051 is of great astrophysical interest. First, the incidence of eclipsing binaries among CP2 stars is very low (see Section 3.2). Second, the system is quite unique in exhibiting both eclipses and obvious rotational variability due to abundance inhomogeneities, which opens up a lot of interesting possibilites for future research. We have already embarked on a detailed study of this star, the results of which will be presented in a future publication.

4.2.3. HD 115226

Using time-series spectroscopy, Kochukhov et al. (2008) identified HD 115226 as a rapidly oscillating Ap (roAp) star and inferred a pulsation period of 10.86 minutes from radial velocity variations in Pr III, Nd III, Dy III, and the narrow cores of the hydrogen lines. They found v_e sin i = 25–30 km⁻¹ and deduced a rotational period of P_rot ≤ 3.0–3.5 days. Furthermore, they established the presence of surface abundance inhomogeneities but did not detect any significant variability in the then available data from the ASAS-3 survey. However, marginal variability with P = 3.61 days and an amplitude below 0.01 mag was detected in Hipparcos data (van Leeuwen et al. 1997).

We have analyzed the available ASAS-3 data for HD 115226 and detect a clear signal at a frequency of f = 0.33465 c/d (P = 2.9882(1) days), which lies well above the noise level (Figure 7). The resulting phase plot shows a double wave, which is typical of ACV variables and consistent with both magnetic poles being visible over the rotation period (Figure 4). Furthermore, the derived period is in accordance with the above mentioned assumptions of Kochukhov et al. (2008).

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We have investigated Hipparcos data and confirm marginal variability with P = 3.61 days, as proposed by the aformentioned authors. However, this signal is not present at all in the ASAS-3 data, which boast a much longer time base (∼3000 days) and a greater number of observations (639 measurements) than Hipparcos data (∼1250 days; 116 measurements). We are therefore inclined to accept the period value derived from ASAS-3 data as real.

The pulsations of roAp stars are explained satisfactorily by the oblique pulsator model (Kurtz 1982; Saio 2005). Oblique pulsation results in frequency multiplets with components that are separated by the rotation frequency of the star (e.g., Takata & Shibahashi 1995). Thus, accurate knowledge of the rotation frequency is mandatory for the full interpretation of the frequency multiplets generated by the rotational modulation of the short period pulsations observed in roAp stars. The result of the present investigation will therefore provide a significant contribution to the deciphering of the frequency multiplet of the rapid, 10.86 minute oscillations observed in HD 115226.

4.2.4. HD 123884

4.2.5. HD 149334

4.2.6. HD 161733A = IC 4665 82

4.2.7. HD 186205