SuperWASP observations of pulsating Am stars

c ESO 2011 Astronomy & Astrophysics manuscript no. Wasp˙Am July 4, 2011 SuperWASP observations of pulsating Am stars⋆ B. Smalley1 , D. W. Kurtz2 , A. M. S. Smith1 , L. Fossati3 , D. R. Anderson1 , S. C. C. Barros4 , O. W. Butters5 , A. Collier Cameron6 , D. J. Christian7 , B. Enoch6 , F. Faedi4 , C. A. Haswell3 , C. Hellier1 , S. Holmes3 , K. Horne6 , S. R. Kane8 , T. A. Lister9 , P. F. L. Maxted1 , A. J. Norton3 , N. Parley6 , D. Pollacco4 , E. K. Simpson4 , I. Skillen10 , J. Southworth1 , R. A. Street9 , R. G. West5 , P. J. Wheatley11 , P. L. Wood1 1 2 3 arXiv:1107.0246v1 [astro-ph.SR] 1 Jul 2011 4 5 6 7 8 9 10 11 Astrophysics Group, Keele University, Staffordshire, ST5 5BG, United Kingdom Jeremiah Horrocks Institute of Astrophysics, University of Central Lancashire, Preston PR1 2HE, UK Department of Physics & Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK Astrophysics Research Centre, Main Physics Building, School of Mathematics & Physics, Queen’s University, University Road, Belfast, BT7 1NN, UK Department of Physics & Astronomy, University of Leicester, Leicester, LE1 7RH, UK SUPA, School of Physics & Astronomy, University of St. Andrews, North Haugh, Fife, KY16 9SS, UK Department of Physics & Astronomy, California State University, Northridge, CA, 91330, USA NASA Exoplanet Science Institute, Caltech, MS 100-22, 770 South Wilson Avenue, Pasadena, CA, 91125, USA Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Goleta, CA, 93117, USA Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de la Palma, Tenerife, Spain Department of Physics, University of Warwick, Coventry, CV4 7AL, UK Received date / accepted date ABSTRACT We have studied over 1600 Am stars at a photometric precision of 1 mmag with SuperWASP photometric data. Contrary to previous belief, we find that around 200 Am stars are pulsating δ Sct and γ Dor stars, with low amplitudes that have been missed in previous, less extensive studies. While the amplitudes are generally low, the presence of pulsation in Am stars places a strong constraint on atmospheric convection, and may require the pulsation to be laminar. While some pulsating Am stars have been previously found to be δ Sct stars, the vast majority of Am stars known to pulsate are presented in this paper. They will form the basis of future statistical studies of pulsation in the presence of atomic diffusion. Key words. Asteroseismology – Stars: chemically peculiar – Stars: oscillations – Stars: variables: delta Scuti – Techniques: photom- etry 1. Introduction In the region of the Hertzsprung-Russell (HR) diagram where the Cepheid instability strip extends across the main sequence, there is a complex relationship between stellar pulsation and atmospheric abundance anomalies that is not fully understood. This region ranges from the early A stars to mid-F stars in spectral type, and from the zero age main sequence to the terminal age main sequence in luminosity. Found here are the strongly magnetic chemically peculiar Ap and Fp stars, the non-magnetic metallic-lined Am stars, the rarer metal-deficient λ Boo stars, the pulsating δ Sct stars, γ Dor stars and rapidly oscillating Ap (roAp) stars. Much has been written about these stars and their physics, which we briefly summarise here. For more detailed discussions see Joshi et al. (2006), Kurtz & Martinez (2000) and Kurtz (1989, 1978, 1976). Most stars in the main-sequence region of the instability strip are normal abundance δ Sct stars with relatively high rotational velocities – usually v sin i ≥ 100 km s−1 . A large fraction of A stars are Am stars, peaking at around 50 per cent at A8, but Am stars are believed either not to pulsate as δ Sct stars, or may do so ⋆ An extended version of Table 1 containing all the detected frequencies and amplitudes is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ with much smaller amplitudes than the normal abundance δ Sct stars. Am stars are mostly found in short period binary systems with orbital periods between 1 − 10 d, causing synchronous rotation with v sin i ≤ 120 km s−1 (Abt, 2009); a few single Am stars with similar slow rotation are known. The magnetic Ap stars are rarer, constituting less than 10 per cent of the A stars. They have very strong global magnetic fields and are often roAp stars with high overtone p mode pulsations with much shorter periods than the δ Sct stars. No Ap star is known to be a δ Sct star. Our physical understanding is that atomic diffusion – radiative levitation and gravitational settling – stabilises the slowly rotating Am and Ap stars so that low overtone p modes are not excited; particularly important in this context is the gravitational settling of helium from the He ii ionisation zone where the κ-mechanism drives the pulsation of δ Sct stars (see Aerts et al. 2010). Otherwise, the more rapidly rotating stars remain mixed because of turbulence induced by meridional circulation and are excited by the κ-mechanism (Turcotte et al., 2000). The understanding of the relationship of the long-established δ Sct stars to the more recently discovered γ Dor stars is currently in flux. Previously, the δ Sct stars were known as p mode pulsators, while the γ Dor stars were known as g mode pulsators. The instability strips for these classes of stars partially overlap, and some “hybrid” stars were discovered with pulsation in both 1 B. Smalley et al.: SuperWASP observations of pulsating Am stars p modes and g modes. A striking case is that of HD 8801, which is an Am star that shows both δ Sct and γ Dor p-mode and gmode pulsation (Henry & Fekel, 2005). Hybrid stars that show both p modes and g modes are of particular interest asteroseismically because the p modes characterise the conditions primarily in the outer part of the star, while the g modes test the core conditions. Now with data from the Kepler Mission, which is obtaining nearly continuous data for over 150 000 stars for 3.5 y, mostly with 30-min cadence, but for 512 stars with 1-min cadence (Gilliland et al., 2010), the Kepler Asteroseismic Science Consortium (KASC) is studying numbers of δ Sct stars and γ Dor stars at µmag precision. It is becoming clear that hybrid stars are common and may be the norm, so that the classes of δ Sct and γ Dor stars are merging (Grigahcène et al., 2010). Interestingly, the latter authors find a possible correlation among the hybrid stars and Am spectral classification. The Kepler Mission through KASC will model individual Am stars that are δ Sct pulsators with data of such high precision that new insight into the physics of the relationship between atomic diffusion and p mode pulsation will be obtained. But Kepler has a limited number of Am stars in its 105 deg2 field-of-view. Another complementary source of information is to look at the statistics of pulsation in Am stars over the entire sky. That is now possible with the highly successful SuperWASP planetary transit-finding programme (Pollacco et al., 2006) that has surveyed a large fraction of both the northern and southern skies. There now exists in the SuperWASP archive over 290 billion photometric measurements for more than 30 million stars. These light curves encompass many types of stars, including the A stars in general, and Am stars in particular. In this paper we have selected Am stars from the Renson & Manfroid (2009) catalogue of peculiar stars for which we have at least 1000 data points in SuperWASP light curves. While we do not detect pulsation in all of our programme stars, for around 200 metallic-lined stars out of over 1600 tested we find δ Sct pulsation. This is contrary to previous understanding that Am stars are constant in brightness. The reason we have gained this new understanding is that there has been no previous survey of so many Am stars, and previous studies have not all reached the SuperWASP detection threshold of only 1 mmag. Many Am stars therefore do pulsate, generally with lower amplitude than normal abundance δ Sct stars. This amplitude difference is still to be understood in terms of atomic diffusion reducing pulsation driving for the slowly rotating Am stars, but there is not a complete lack of pulsation. That, has implications for turbulence in the diffusive layers and may require that the pulsation be laminar. Some striking examples of metallic-lined stars with relatively high pulsation amplitude (these are rare) address this question further, such as HD 188136 (Kurtz 1980; Wegner 1981) and HD 40765 (Kurtz et al., 1995). More constraints on the physics of the interaction of pulsation and atomic diffusion may also be found in stars that show no δ Sct p modes or γ Dor g modes at precisions of µmag. Some such A stars are known in the CoRoT and Kepler data sets, but in-depth studies have not yet been made, hence discussions of these have yet to be published. The combination of the all-sky mmag precision of SuperWASP with the µmag precision of CoRoT and Kepler on selected stars, calls for new attempts to model the physics of the interaction of pulsation, rotation and atomic diffusion in the A stars. 2 2. Observations The WASP project is surveying the sky for transiting extrasolar planets (Pollacco et al., 2006) using two robotic telescopes, one at the Observatorio del Roque de los Muchachos on the island of La Palma in the Canary Islands, and the other at the Sutherland Station, South African Astronomical Observatory (SAAO). Both telescopes consist of an array of eight 200-mm, f/1.8 Canon telephoto lenses and Andor CCDs, giving a field of view of 7.8◦ × 7.8◦ and pixel size of around 14 ′′ . The observing strategy is such that each field is observed with a typical cadence of the order of 10 min. WASP provides good quality photometry with a precision exceeding 1 per cent per observation in the approximate magnitude range 9 ≤ V ≤ 12. The SuperWASP data reduction pipeline is described in detail in Pollacco et al. (2006). The aperture-extracted photometry from each camera on each night are corrected for primary and secondary extinction, instrumental colour response and system zero-point relative to a network of local secondary standards. The resultant pseudo-V magnitudes are comparable to Tycho V magnitudes. Additional systematic errors affecting all the stars are identified and removed using the SysRem algorithm of Tamuz et al. (2005). The final light curves are stored in the WASP project’s searchable archive (Butters et al., 2010). 3. Am star selection and analysis We have selected Am stars from the Renson & Manfroid (2009) catalogue of peculiar stars for which we have data in the WASP archive and when individual light curves have at least 1000 data points (i.e. for a single camera and during a single season). Any stars known, or found, to be eclipsing binary systems were excluded from the analysis. Stars were also rejected when two approximately equal brightness stars were within the 3.5-pixel (∼50 ′′ ) SuperWASP photometry aperture. However, unresolved ′′ close pairs in DSS images (separation < ∼2 ) and systems with > fainter companions (∼ 2 mag) were retained. For each individual light curve, periodograms were calculated using the fast computation of the Lomb periodogram method of Press & Rybicki (1989) as implemented in the Numerical Recipes fasper routine (Press et al., 1992). Spectral window functions were also calculated, in order to identify peaks which had arisen due to the gaps in the observations. The periodograms were examined for any evidence of variability. Stars were rejected if the false alarm probability of the strongest peaks exceeded 0.1 (Horne & Baliunas, 1986). The remaining stars were examined in more detail using the Period04 program (Lenz & Breger, 2005). For stars in which variability was confirmed, frequencies continued to be selected so long as their amplitude was > 4 times the average background of the prewhitened residuals (Breger et al., 1993). Formal uncertainties on frequencies and amplitudes were obtained from the least-squares fitting using the method of Montgomery & O’Donoghue (1999). Of the 1620 Am stars initially selected, a total of 227 (14% of the total) have been found to pulsate. The remaining 1393 stars were deemed as “not found to pulsate”, since low-level pulsation could be present below the SuperWASP detection limits. Table 1 provides a summary of the pulsating Am stars. The individual periodograms and phase-folded lightcurves are presented in Fig. 1. B. Smalley et al.: SuperWASP observations of pulsating Am stars Table 2. Am stars with both SuperWASP and Kepler data. KIC Ren ID 9204718 11445913 9272082 12253106 9764965 8881697 11402951 9349245 8703413 8323104 49340 49650 49840 50070 50230 50420 50670 51233 51640 52260 Max Amp (mmag) 0.13 2.5 <0.01 <0.01 1.0 1.9 1.2 <0.1 <0.1 <0.1 Ref Bal Cat,Bal Bal Cat,Bal Bal Bal Notes. The second column gives the identification number (Ren ID) from the Renson & Manfroid (2009) catalogue. Column 3 gives the amplitude (Max Amp) of the highest peak in the Kepler periodogram. Column 4 gives reference to published Kepler data: Cat: Catanzaro et al. (2011), Bal: Balona et al. (2011) 4. Stellar parameters To place stars on the HR diagram we require values of T eff and log L. For stars with uvbyβ photometry in the Hauck & Mermilliod (1998) catalogue, we used the uvbybeta code of Moon (1985) to obtain de-reddened indices, and the (b−y, c0 ) grids of Smalley & Kupka (1997) to determine T eff and log g. For stars with only uvby photometry the above procedure was used but without the de-reddening step. For stars without uvby photometry, Geveva photometry from Rufener (1988) was used and the calibration of Künzli et al. (1997) used to determine T eff and log g, assuming zero reddening. In all of the above cases, the Torres et al. (2010) relations were used to determine log L. For stars without suitable intermediate-band photometry, but with Hipparcos parallaxes (van Leeuwen, 2007), spectral energy distributions (SEDs) were constructed using literature broad-band photometry. Values of T eff were determined by fitting Kurucz flux distributions to the SEDs and log L determined from the bolometric flux at the earth ( f⊕ ) and the Hipparcos parallax. The typical uncertainties are estimated to be ±200 K in T eff (±0.01 in log T eff ) and ±0.25 in log L. The stellar parameters are given in Table 1. In total around a third of the Am stars investigated have stellar parameters determined. 5. Am stars in Kepler field The sky coverage of the SuperWASP survey overlaps with a large fraction of the Kepler field. For Am stars with light curves in both the Kepler Public archive and the SuperWASP database we have compared the frequencies and amplitudes. This allows us to evaluate the detection limits of SuperWASP. Of the 10 stars with both Kepler and SuperWASP data, four have clear pulsations with amplitudes > ∼ 1 mmag (Table 2), while the other six stars have amplitudes below the SuperWASP detectability limit. The period04 analysis (Table 3) shows good agreement above the nominal SuperWASP 1 mmag amplitude limit. There is a suggestion that the amplitudes found using SuperWASP lightcurves are slightly higher than those from Kepler. In addition, the SuperWASP frequency can differ from the ‘true’ frequency by a small integer number of 1 d−1 aliases. The comparison also shows that it is possible with SuperWASP data to detect frequencies slightly below the 1 mmag level (Figure 2). Naturally, the variable data quality of ground-based photometry means that not all stars with suitable variability will be detected. Table 3. Comparison between frequencies and amplitudes found in the Kepler and SuperWASP data for the four Am stars common to both. Kepler SuperWASP Freq. Amp.a Freq. Amp. (d−1 ) (mmag) (d−1 ) (mmag) Ren ID 49650 (KIC 11445913, 1SWASP J190540.61+491820.7) f1 31.5577 ± 0.0003 2.8 31.5577 ± 0.0001 3.2 ± 0.1 f2 25.3799 ± 0.0007 1.1 25.3769 ± 0.0001 1.2 ± 0.1 f3 22.1307 ± 0.0009 0.8 22.1306 ± 0.0002 1.0 ± 0.1 f4 37.8182 ± 0.0011 0.6 f5 29.7394 ± 0.0012 0.6 Ren ID 50230 (KIC 9764965, 1SWASP J191724.91+463535.2) f1 27.1777 ± 0.0001 1.1 27.1778 ± 0.0001 1.2 ± 0.1 f2 21.3819 ± 0.0002 0.6 22.3891 ± 0.0001 0.9 ± 0.1 f3 31.9895 ± 0.0002 0.4 31.9902 ± 0.0001 0.9 ± 0.1 f4 19.9579 ± 0.0004 0.2 Ren ID 50420 (KIC 8881697, 1SWASP J192136.03+450706.8) f1 16.5567 ± 0.0003 1.9 16.5565 ± 0.0005 2.1 ± 0.1 f2 32.0477 ± 0.0004 1.5 32.0481 ± 0.0006 1.6 ± 0.1 f3 25.2105 ± 0.0005 1.2 25.2064 ± 0.0008 1.2 ± 0.1 f4 30.0120 ± 0.0006 1.1 30.0111 ± 0.0009 1.1 ± 0.1 f5 34.3647 ± 0.0007 0.9 34.3661 ± 0.0009 1.0 ± 0.1 f6 30.6537 ± 0.0008 0.9 30.6569 ± 0.0010 0.9 ± 0.1 f7 28.8044 ± 0.0009 0.7 27.8049 ± 0.0011 0.8 ± 0.1 f8 34.0106 ± 0.0009 0.7 f9 27.4073 ± 0.0010 0.7 f10 16.0119 ± 0.0013 0.5 Ren ID 50670 (KIC 11402951, 1SWASP J192732.81+491523.5) f1 23.8493 ± 0.0004 1.3 23.8464 ± 0.0008 1.4 ± 0.2 f2 23.2770 ± 0.0004 1.1 23.2790 ± 0.0008 1.4 ± 0.2 f3 27.4616 ± 0.0007 0.7 27.4643 ± 0.0012 1.0 ± 0.2 f4 15.1001 ± 0.0007 0.7 f4 14.4967 ± 0.0009 0.5 Notes. (a) Uncertainties on Kepler Amplitudes are all < 0.05 mmag. 6. Discussion The pulsating Am stars (see Fig. 3) are concentrated within the fundamental radial mode red and blue edges of Dupret et al. (2005). This is in agreement with that found by Balona et al. (2011) for Am stars within the Kepler field. These studies show that pulsating Am stars are concentrated in the cooler region of the instability strip. Hot Am stars do not appear to pulsate at the precision of the Kepler data. The standard interpretation of the Am phenomenon is that atomic diffusion – radiative levitation and gravitational settling – in the outer stellar envelope gives rise to the observed atmospheric abundance anomalies. For a typical mid-A star, T eff ∼ 8000 K, there are two thin convection zones in the outer envelope. The atmosphere itself is a convection zone a few thousand km thick where ionisation of H drives the convection. Deeper in the atmosphere, at T ∼ 50 000 K, the ionisation of He ii also creates a thin convection zone, where the κ-mechanism drives δ Sct pulsation. It has long been clear that some Am stars and related types do pulsate, particularly the marginal Am stars (labelled spectroscopically as Am: stars), the evolved Am stars (δ Del or ρ Pup stars), and some more extreme cases, such as HD 188136 (Kurtz 1980; Wegner 1981) and HD 40765 (Kurtz et al., 1995). The pulsation modes that we observe in Am stars are low radial order, low spherical degree p modes. The surface of the star is an anti-node. With the low radial order, the vertical wavelength is long compared to the depth of the envelope above the 3 B. Smalley et al.: SuperWASP observations of pulsating Am stars Fig. 2. Comparison between the period04 periodograms from Kepler (left) and SuperWASP (right) for four Am stars with pulsations detected by SuperWASP (see Table 3 for details of frequencies identified). He ii ionisation zone. With the decrease in density with height in the atmosphere, conservation of kinetic energy density means that the pulsation amplitude increases with height in the atmosphere, or conversely, decreases with depth. In Am stars, the microturbulence velocity is also peculiar, as it is generally much higher than that of chemically normal stars. This high microturbulence arises from large velocity fields in the stellar atmosphere (Landstreet, 1998), which are even supersonic for some Am stars. We do not really know what causes these large velocity fields to develop exclusively in Am stars and how chemical peculiarities and velocity fields coexist. The results shown by Landstreet et al. (2009) suggest that there is a connection between T eff and the velocity fields, peaking at 4 around T eff ∼ 8000 K, although we do not know what happens for cooler Am stars. Atomic diffusion occurs in the radiative zone below the turbulent outer convective layer, which is far below the observable atmosphere. In this radiative layer there must be no turbulence at the diffusion velocity, which is of the order of 10−4 – 1 cm s−1 . The photometric amplitudes found in Am stars are consistent with atmospheric pulsation radial velocity amplitudes of a few km s−1 . Taking into account the decrease in pulsation amplitude with depth –largely because of the increase in density, but also because of the radial wave function – the pulsation velocity in the radiative layer where atomic diffusion is most important in Am stars is still of the order of a km s−1 . With such pulsations in B. Smalley et al.: SuperWASP observations of pulsating Am stars Fig. 3. HR diagram showing the location of Am stars. The filled circles are the Am stars which were found to pulsate, while the open circles are the Am stars which were not found to pulsate. The solid lines indicate the location of the ZAMS and the fundamental radial mode red and blue edges of the instability strip (Dupret et al., 2005). The large cross indicates the typical uncertainties in log T eff and log L. The dots are the δ Sct stars from the catalogue of Rodrı́guez et al. (2000). Fig. 4. Location of the pulsating Am stars in the HR diagram. The circles are pulsating Am stars, with the filled circles indicating those with spectral classification noted as δ Del. The crosses are the Fm δ Del stars which were not found to pulsate. The solid lines indicate the location of the ZAMS and the fundamental radial mode red and blue edges of the instability strip (Dupret et al., 2005). The large cross indicates the typical uncertainties in log T eff and log L a layer where atomic diffusion is operating at sub-cm s−1 velocities, it must be that the pulsation is laminar; i.e., producing no turbulence at the sub-cm s−1 level. With the results from the Kepler mission (Balona et al., 2011) and now our results from SuperWASP we conclude that the loss of helium by gravitational settling from the He ii ionisation zone reduces driving, but does not suppress it entirely. Thus Am stars can pulsate as δ Sct stars, but typically with relatively low amplitudes compared to normal abundance δ Sct stars. Some Am stars show no pulsation whatsoever at Kepler µmag precision. It has yet to be shown whether this lack of pulsation can also occur in the more rapidly rotating normal abundance stars in the δ Sct instability strip. Study of this question is in progress with Kepler data. As was concluded for the individual cases of HD 188136 and HD 40765, we may now state in general: in Am stars the pulsation must be laminar, not generating turbulence to mix away the observed effects of atomic diffusion in the outer atmosphere. The Fm δ Del subclass are evolved Am stars above the mainsequence, many of which have been found to show variability (Kurtz, 1976). Not unexpectedly, many stars classed as Fm δ Del are found to be pulsating in the WASP data, but clearly not all. Of the 227 Am stars that we found to be pulsating 55 are classed as Fm δ Del: 24% of the Am stars found to pulsate. This compares to a total of 186 Fm δ Del stars out of the 1620 Am stars investigated using WASP data, around 11% of the sample. Therefore, 30% of the Fm δ Del stars have been found to pulsate, compared to just 12% of other Am stars. Thus pulsation amplitude either grows in Am stars as they evolve, or some non-pulsating Am stars begin pulsating as they move off the main sequence. This is likely to be a consequence of the driving region moving deeper into the star where the helium abundance is higher than in the main sequence He ii ionisation zone (see Turcotte et al. 2000 for theoretical discussion). The location of the pulsating Fm δ Del stars in the HR diagram is shown in Fig. 4. There is a tendency for the pulsating Fm δ Del stars to be located toward the cooler (and/or) slightly Fig. 5. Frequency-amplitude diagram for pulsating Am stars shown as circles, with filled circles indicating those with spectral classification noted as δ Del. Note that in multi-periodic systems only the frequency of the highest amplitude is shown, as given in Table 1. The dots are the δ Sct stars from the catalogue of Rodrı́guez et al. (2000). more evolved parts of the instability strip, whereas the nonpulsating Fm δ Del stars are distributed more uniformly. The frequency–amplitude diagram (Fig. 5) shows that the Fm δ Del stars occupy the same regions as the other Am stars, but with an −1 absence of high-frequency (> ∼ 20 d ) pulsations; this is not surprising, given that they are cooler and more evolved than average δ Sct stars. Several factors are thought to play a role in the development of pulsating Am stars, but stellar rotation is probably one of the most important. Charbonneau & Michaud (1991) showed that Am chemical peculiarity develops in stars that rotate slower than 90 km s−1 and that the He ii ionisation zone deepens with decreasing rotation. This was later confirmed by more advanced diffusion model calculations by Talon et al. (2006) and obser5 B. Smalley et al.: SuperWASP observations of pulsating Am stars vationally by Fossati et al. (2008), who found a correlation between Am chemical peculiarities and v sin i in Am stars belonging to the Praesepe open cluster. The vast majority of the Am stars already known to pulsate have a rather large v sin i, between 40 and 90 km s−1 , thus avoiding the He ii ionisation zone sinking too deep into the star and therefore allowing the development of pulsation driven by the κ-mechanism. On the other hand, for the very slowly rotating pulsating Am stars, the pulsation could be laminar. It is therefore likely there are two different mechanisms driving pulsation in Am stars. Our results show a wide variety of pulsations, from singly periodic to complex multiperiodic, and also some examples of what appear to be hybrid γ Dor/δ Sct pulsators. This is similar to the range of behaviour seen in normal abundance δ Sct stars, as can be seen in the study of Kepler data by Grigahcène et al. (2010). Those authors reclassified pulsation types with the following scheme: δ Sct: frequencies above 5 d−1 ; δ Sct/γ Dor hybrid: most frequencies above 5 d−1 , but some low frequencies present; γ Dor: frequencies lower than 5 d−1 ; γ Dor/δ Sct hybrid: most frequencies lower than 5 d−1 , but some high frequencies present. Our results are summarized in Table 4 and the individual classes for each star are given in Table 1. The majority of the pulsators we found are δ Sct stars, with the remaining quarter split between γ Dor stars and mostly δ Sct/γ Dor hybrids. Given that the SuperWASP data are affected by daily aliases and systematics at low frequencies, the true number of stars with γ Dor pulsations may indeed be higher. However, given that Am stars are thought to be members of binary systems and tidal effects slow the stellar rotation rate, it is possible that some of the lowfrequency signatures found in the SuperWASP data are due to ellipsoidal effects in close binaries. Assuming a rotation limit −1 of v sin i < ∼ 120 km s for an Am star and a radius of 1.5 R⊙ , the shortest period for a binary system containing a tidallysynchronised Am star is ∼0.6 d. Close binary systems with dissimilar components have two maxima and minima per orbital period, and this value dominates over the orbital value in pe−1 riodograms. Hence, frequencies < ∼3.3 d may have arisen due to ellipsoidal variations in close binaries. Thus, we caution that some of the stars presented in Table 1 could have erroneously been classified as having γ Dor pulsations. In addition, it is possible that long-period pulsations in close binaries could be tidally excited (Handler et al., 2002). It is clear from examination of the Kepler data set that the δ Sct stars show frequencies ranging from nearly zero d−1 up to 100 d−1 ; some stars even show the full range, including frequencies between the g mode and p mode ranges seen in models. These intermediate frequencies are unexplained at present. It is clear that the δ Sct stars are complex pulsators that show g modes, p modes, mixed modes and many nonlinear cross terms. Whether there are differences between abnormal abundance, slowly rotating Am stars that are δ Sct stars and the more rapidly rotating, normal abundance δ Sct stars is yet to be determined. The objects we present here from SuperWASP greatly increases the number of pulsating Am stars for statistical study of this question. Acknowledgements. The WASP project is funded and operated by Queen’s University Belfast, the Universities of Keele, St. Andrews and Leicester, the Open University, the Isaac Newton Group, the Instituto de Astrofisica de Canarias, the South African Astronomical Observatory and by STFC. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, 6 Table 4. The number of pulsating Am stars and percentage in each of the four pulsation classes as defined by Grigahcène et al. (2010). Pulsation Class δ Sct δ Sct/γ Dor γ Dor γ Dor/δ Sct Number 169 23 30 5 Percentage 75 10 13 2 France. Some of the data presented in this paper were obtained from the Multimission Archive at the Space Telescope Science Institute (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. 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Type 10 110 113 140 210 355 500 1233 1790 1830 1920 1984 2060 2340 2370 2720 2920 3013 3340 3378 3550 3655 4413 4793 4885 5055 6044 6083 6295 6390 6368 6463 6527 6681 6663 8720 8711 8842 8898 8932 8951 8972 8974 8988 9084 9123 9144 9262 9269 9470 9375 9454 9685 9534 9581 9556 9653 9812 9868 10206 10259 10383 10423 10610 10448 10474 HD 154A HD 719 HD 728 HD 923 HD 1097 HD 1651 BD+40 77 A HD 4630 HD 7133 CD-22 422 TYC 5276-1653-1 HD 8043 HD 8457 BD-12 290 HD 9659 BD+58 304 HD 11490 TYC 2816-327-1 HD 12961 HD 13079 HD 13776 HD 14494 A9mF2 A3mF0 A m δ Del A6mF2 A4mF4 Sr A6mA9 A2mA7 Sr A3m δ Del A3 Sr or Am δ Del ? A6m A6m A2mF A2mF A2mA7 A1mA7 A7m A5m F1mF4 A5mF3 δ Del? F0m A0m A5mA9 A3m A3m δ Del A5mA8 A5mF0 A5m δ Del A2mF0 A3m A7m A5m δ Del? A2mA8 A1m A3mF0 A2mF0 A3mF2 A5m A5m A2m A5m A3m A5m A2m A2m A2m A3m A2m A7m A3m A6mF2 A5m A2m F0m δ Del? A3m A2m A0m A3m A3m A3m A5m A5m A7m A1m A5mF1 A0m A2m HD 19108 HD 19762 HD 20308 HD 23543 TYC 3729-775-1 TYC 3725-169-1 HD 25052 HD 24925 HD 25369 HD 25648 HD 26386 TYC 3726-618-1 HD 34296 HD 242159 HD 242632A HD 34841 HD 242938 HD 243010 HD 243093 HD 243112 HD 35236 HD 35467 HD 243542 HD 35531 HD 244020 BD-7 1108 TYC 2411-1663-1 HD 244698 HD 36887 HD 244810 HD 36681 BD+34 1091 HD 245063 HD 245303 TYC 1869-592-1 HD 246984 HD 247634 HD 247837 HD 39641 HD 248069 HD 248174 log T eff (K) 3.862 3.855 log L (L⊙ ) 0.89 1.01 Method a a 3.908 3.840 3.859 1.39 0.11 0.92 a a a 3.832 1.09 a 3.849 1.17 a 3.862 3.883 1.08 1.08 b c 3.859 3.832 0.96 0.83 a a 3.854 3.862 3.850 3.839 3.852 0.74 0.90 1.16 0.81 0.81 a d a a a 3.864 1.14 d 3.853 0.98 a 3.865 1.20 d 3.861 0.77 a 3.886 1.14 a 3.854 1.09 a 3.855 0.90 a 3.858 0.85 a 3.863 0.86 a Freq. (d−1 ) 4.7672 14.1368 14.9268 18.6684 15.5491 15.0600 32.3130 20.6497 14.8755 1.9041 1.6420 10.3662 16.5741 34.8219 17.6028 28.1912 6.1679 0.8838 4.0115 19.4090 4.4078 15.5855 21.3019 14.7306 16.9993 29.7634 7.1268 24.0686 28.1774 6.5758 18.2088 31.8867 1.3183 20.7307 22.3602 1.7424 8.7898 0.3043 11.4943 21.6154 16.4353 19.9969 44.9530 45.7112 33.0007 25.6983 21.4997 6.4681 9.7183 12.7088 21.9980 29.4675 0.7113 18.5025 20.8887 1.4571 11.0583 17.6418 0.6786 23.4739 20.7162 2.8538 0.2336 20.4628 3.7473 18.3207 Amp. (mmag) 22.4 3.2 2.8 2.2 2.0 1.9 2.6 1.4 4.1 6.2 6.8 3.6 1.9 2.0 17.1 4.0 1.2 13.9 4.0 7.0 15.2 4.2 1.6 3.2 1.4 2.1 3.3 2.1 4.1 3.0 0.9 1.7 9.7 4.3 2.6 6.0 3.4 3.8 2.3 1.8 2.0 3.4 1.4 1.6 2.7 1.7 3.6 5.5 3.6 73.6 2.4 1.7 4.6 3.6 1.7 5.8 3.6 3.6 9.9 3.1 6.6 7.4 13.0 2.2 10.6 1.9 nFreq. 2 10 2 1 2 8 10 1 8 4 5 1 7 6 8 6 7 2 7 5 2 10 7 5 1 4 3 1 2 7 1 4 1 7 1 9 8 1 4 3 2 6 2 2 3 2 5 2 2 4 5 2 2 4 1 1 1 5 3 1 3 3 2 8 2 1 ∆T (d) 1135 473 119 50 50 154 146 114 114 140 140 115 140 136 927 115 580 1246 563 480 563 910 511 121 145 521 521 94 1228 521 119 119 112 134 71 506 1233 924 139 902 927 1232 139 139 1233 1233 1232 1200 138 112 941 133 152 941 139 941 941 138 152 133 935 928 923 177 923 133 Class γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct γ Dor δ Sct/γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct γ Dor δ Sct/γ Dor δ Sct γ Dor δ Sct γ Dor/δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct/γ Dor δ Sct δ Sct γ Dor δ Sct δ Sct δ Sct/γ Dor δ Sct γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct γ Dor δ Sct δ Sct γ Dor δ Sct δ Sct γ Dor δ Sct δ Sct γ Dor γ Dor δ Sct/γ Dor γ Dor/δ Sct δ Sct 7 B. Smalley et al.: SuperWASP observations of pulsating Am stars Table 1. continued. 8 Ren ID Name Sp. Type 10482 10565 10554 10586 10602 10641 10855 11007 11022 11025 11032 11033 11135 11184 11182 11274 11265 11473 11820 12250 12820 12940 13550 14140 15423 16920 18657 18730 20143 20333 20485 20855 20908 21730 21920 22180 22404 22450 22685 23195 23410 23672 24920 24990 25160 25730 26360 26860 26880 27270 27405 27526 27610 28290 28340 28510 28610 28690 28850 29280 29310 29590 29800 30390 30453 30926 HD 248244 HD 248637 HD 248577 TYC 1867-814-1 HD 248874 HD 249278 TYC 1876-325-1 HD 251038 HD 251095 HD 251143 HD 251227 HD 251226 HD 251963 HD 252154 TYC 1889-117-1 HD 252679 HD 42155 TYC 1314-887-1 HD 44596 HD 45863 HD 47743 HD 48223 CP-60 704 HD 51319 HD 56484 HD 61659 HD 67518 HD 67911 HD 72658 HD 73144 HD 73675 HD 74626 HD 74784 HD 77105 HD 77532 HD 78325 HD 79034A HD 79111 HD 79787 HD 81729 HD 82396 HD 83049 HD 87118 HD 87360 HD 87869 BD+42 2113 HD 91616 HD 93038 HD 93137 HD 94479 HD 95192 HD 95562 HD 95856 HD 98009 HD 98299 HD 98946 HD 99302 HD 99729 HD 100376 BD+41 2224 HD 101717 HD 102594 HD 103318 HD 104957 BD+18 2569 HD 106832A A1m A2m A0m A5m A0m A5m A0m A0m A2m A3m A3m A5m A7m A5m A3m A3mF2 A2m A3mF2 A6mF2 A2mA8 A3mF0 A4m δ Del? F0m A2mA9 A2mF0 A5mF0 A3m δ Del F0mF4 F m δ Del? F m δ Del? A4m A5m δ Del A3mF2 δ Del? A3m Sr δ Del A5mF0 A2mA8 F0m δ Del A2mF2 A3mF2 A5m F0m δ Del F5m δ Del A4mF2 F0m δ Del A2m δ Del A mF A3mF3 A3m F5m δ Del A4mF0 A1mF0 A2mA9 F5m δ Del A3mF0 A3mA7 A5m A3mF1 F5m δ Del F0m δ Del? A0m A5m δ Del F2m δ Del A4m A3mF1 Am A1mA9 Hg log T eff (K) log L (L⊙ ) Method 3.847 3.879 3.863 1.04 0.81 0.80 a c a 3.876 3.874 3.841 3.834 1.22 0.93 0.98 1.07 a a a a 3.837 3.829 1.38 1.19 a d 3.850 3.847 1.24 1.29 d a 3.865 1.27 a 3.862 1.00 a 3.871 3.843 1.05 1.08 d a 3.887 3.882 3.825 1.40 0.95 0.93 a b d 3.867 3.847 0.87 0.75 a a Freq. (d−1 ) 49.2363 12.4952 11.3345 12.5497 0.1771 29.2307 9.9108 14.3993 7.3109 17.2563 3.8590 22.1084 10.1655 1.4525 6.6767 30.1049 22.0073 1.1943 11.9914 0.5209 18.3705 18.5331 14.5060 15.9002 14.8533 0.7136 5.1544 8.8671 8.6775 8.0629 33.6236 7.8486 7.5427 11.2579 19.5074 7.0172 14.3002 15.9320 20.9176 9.7198 9.3672 7.3912 0.5334 13.5113 13.8008 8.3255 0.4861 17.9074 6.6384 20.1477 19.0772 41.0464 17.4329 34.0300 13.0735 18.6186 39.1743 7.9438 1.2169 0.3505 18.3663 16.3003 16.3386 18.8594 16.8163 23.3836 Amp. (mmag) 1.1 2.8 3.2 28.5 9.5 1.6 8.8 3.1 11.0 1.9 3.9 2.7 4.9 13.1 2.5 1.5 2.3 6.7 3.8 1.3 3.9 3.1 3.0 1.9 5.7 5.5 4.0 31.1 4.9 2.6 1.3 8.6 25.8 3.0 1.6 2.5 6.1 4.6 2.9 6.6 21.6 14.2 5.1 8.0 3.8 8.1 3.6 4.0 37.2 4.8 1.9 1.8 5.6 1.4 1.5 5.1 2.6 8.4 22.9 11.6 2.8 2.3 1.7 11.3 1.8 2.0 nFreq. 1 5 1 5 1 1 1 3 6 3 4 2 4 5 1 2 4 1 15 1 3 13 9 5 3 1 2 3 1 1 4 10 12 6 4 5 2 1 4 4 6 3 1 2 7 2 1 7 7 3 2 1 6 5 2 3 2 9 3 2 2 9 2 6 5 1 ∆T (d) 138 133 1194 923 138 138 138 1915 1218 133 133 133 1218 919 133 138 133 138 177 1040 66 795 177 177 132 142 117 98 96 97 96 119 97 119 119 717 96 745 749 131 110 511 521 457 113 134 717 717 1090 123 478 144 510 510 144 1097 134 510 510 1108 142 414 132 409 1058 496 Class δ Sct δ Sct δ Sct δ Sct/γ Dor γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct/γ Dor δ Sct δ Sct δ Sct/γ Dor δ Sct δ Sct δ Sct γ Dor δ Sct γ Dor γ Dor/δ Sct δ Sct/γ Dor δ Sct δ Sct δ Sct γ Dor δ Sct/γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct/γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct γ Dor δ Sct δ Sct δ Sct γ Dor δ Sct/γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct γ Dor γ Dor δ Sct δ Sct δ Sct γ Dor/δ Sct δ Sct δ Sct B. Smalley et al.: SuperWASP observations of pulsating Am stars Table 1. continued. Ren ID Name Sp. Type 30970 31500 31560 31600 31680 31710 31800 31913 31950 32180 32340 32624 32870 32885 33220 33490 33555 33636 33940 34137 34076 34620 34930 34920 34996 35074 35450 35490 35650 35710 35776 36080 36330 36940 37513 37494 37884 38400 40280 40613 40675 40805 41030 41315 41640 43588 43590 45870 46050 49650 50230 50420 50670 50520 51760 52850 54150 54515 54656 54736 54970 55087 55094 55710 56159 56110 TYC 2530-1366-1 HD 108452 HD 108668 BD+37 2284 A2m A0m A3mF2 A7mF3 A5m F2m A2m A3m δ Del A3mF0 A6mF2 A3m A2m A3mF0 F0m δ Del A3m F5m δ Del F0m δ Del A2m F5m δ Del Am A3mF3 A2mA8 A4mF3 A2mA9 A4mF2 F0m δ Del F2m δ Del? F2m δ Del? A2mF2 A3m δ Del A4mF0 A5mF2 F5m δ Del A2mF0 A5mF0 A3mA9 A2m δ Del F5m δ Del A6m F0m δ Del A3 Sr or δ Del A3mF4 A5m δ Del A6mF3 A2mF3 A5m A2m A3m A3m A6mF5 A5m A5m A9mF5 A7m δ Del? A3mF0 A1mF2 A6m F2m δ Del A3mA9 A3m δ Del A5m A mF A2m δ Del? A4mF δ Del A5m A3mF0 HD 109306 TYC 2533-2112-1 HD 109957 HD 110056 BD+38 2361 BD+21 2457 HD 112340 HD 113221 HD 113385 HD 114839 HD 115800A HD 116276 HD 116635 HD 117682 BD+35 2465 HD 118209 HD 120054 HD 121352 HD 121290 HD 121698 HD 122370 HD 123937 HD 124028 HD 124467 HD 124891 HD 125296 HD 126685 HD 127832 HD 129570 HD 132092 HD 132054 HD 133489 HD 135306 HD 141976 HD 143439 HD 143517 HD 144033 HD 144768 HD 146053 HD 147400 HD 154225 HD 154226 BD+46 2371 BD+45 2607 HD 178327 HD 181206 BD+44 3115 HD 183489 HD 182684 HD 187698 HD 190242 HD 193981 HD 195638 HD 196100 HD 196414 HD 197105 HD 235334 HD 197778 HD 200057 BD+37 4187 HD 201150A log T eff (K) log L (L⊙ ) Method 3.879 3.874 3.836 1.17 1.04 1.04 a b a 3.839 3.847 3.864 3.847 3.936 3.854 3.842 3.863 0.60 0.60 1.22 1.05 1.10 0.89 0.66 0.80 d d a a a c a a 3.846 3.932 1.11 1.00 a a 3.897 0.83 a 3.849 0.94 a 3.862 0.89 a 3.852 1.10 a 3.779 2.72 b 3.820 3.879 3.861 1.30 1.33 0.89 b d a 3.859 0.90 b 3.855 1.07 b 3.854 0.92 c 3.811 1.14 d 3.838 3.856 0.88 0.79 d a 3.843 0.76 c Freq. (d−1 ) 10.0009 70.7600 23.2410 22.2298 2.1429 3.0068 24.6919 13.3080 16.4269 20.0646 13.1200 31.0376 25.5893 0.3905 0.9665 6.1654 10.6404 0.2997 13.9189 0.7607 17.6727 1.3539 15.4849 0.7363 0.5498 15.5955 6.8438 11.0526 26.8987 1.1567 20.2108 17.3456 8.4714 26.1936 18.3348 17.5428 9.6097 12.1156 22.3807 14.1303 14.0384 15.4669 16.9885 9.8533 12.2295 6.9346 0.6233 32.7894 13.7280 31.5577 27.1776 16.5565 23.8464 12.1003 0.5468 26.0473 24.8629 8.4041 27.7231 11.2288 7.5023 8.9589 15.2904 18.6734 12.9635 17.6571 Amp. (mmag) 2.2 4.7 1.4 9.9 7.8 9.8 3.5 4.1 5.8 4.4 18.3 5.3 1.3 10.1 4.7 4.4 4.4 5.0 6.6 7.9 2.3 3.7 6.4 8.0 3.2 5.3 42.8 2.2 5.4 6.0 2.0 4.0 5.4 2.2 3.1 1.8 4.0 4.0 2.2 2.8 7.6 1.3 6.0 3.5 1.8 20.0 9.2 1.4 1.7 3.3 1.2 2.1 1.4 4.0 7.8 1.0 2.0 9.9 3.4 2.2 13.1 5.3 4.8 6.6 2.2 2.3 nFreq. 1 7 1 8 4 3 1 2 10 3 8 3 2 5 9 1 6 2 11 1 7 2 2 1 1 2 11 1 5 2 2 3 5 3 4 1 8 7 4 5 18 2 2 14 6 4 1 5 4 3 3 7 3 12 1 2 8 1 2 3 2 3 4 10 6 2 ∆T (d) 1108 117 153 1123 1123 136 136 509 755 1123 136 779 713 483 1080 167 1141 136 713 1138 396 713 483 755 143 489 714 752 752 714 143 755 752 153 464 890 1178 753 167 1192 1192 391 657 1192 755 1047 127 126 126 456 128 128 1562 519 755 755 162 124 890 890 832 135 105 907 125 907 Class δ Sct δ Sct/γ Dor δ Sct δ Sct/γ Dor δ Sct/γ Dor δ Sct/γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct γ Dor δ Sct/γ Dor δ Sct δ Sct γ Dor δ Sct γ Dor δ Sct γ Dor/δ Sct δ Sct γ Dor γ Dor δ Sct δ Sct δ Sct δ Sct γ Dor δ Sct/γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct/γ Dor δ Sct δ Sct δ Sct/γ Dor δ Sct δ Sct γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct 9 B. Smalley et al.: SuperWASP observations of pulsating Am stars Table 1. continued. Ren ID Name Sp. Type 56275 56280 56770 56980 57020 57104 57300 57323 57696 57760 57764 58270 58440 58850 58870 59072 59020 59090 59500 59560 60696 60690 60740 61105 61320 61350 61356 61580 61756 BD+34 4321 HD 201816 HD 203880 HD 204620 HD 204806 HD 204972 HD 205651 HD 205813 TYC 3975-745-1 HD 207658 HD 207723 HD 209430A HD 209930 HD 212108 HD 212164 TYC 3611-1607-1 HD 212765 HD 213204 HD 215396 HD 215611 HD 221446 HD 221431 HD 221576 HD 222828 HD 223676 BD+44 4512 HD 223944 HD 224657 HD 225184 A7 Si Sr or A5m A3mF0 A5mA9 A9m A4mF1 A2mF2 A4mF3 δ Del? F0m δ Del A5m A5m δ Del? A1mF3 A2mF2 A3m δ Del A2m A1mA9 A3m A2mF2 F1m A2mF3 A8mF3 δ Del F2m δ Del A5m δ Del A2m F2m δ Del A2mA8 A2mF5 A7mF4 F0mF5 A2m δ Del log T eff (K) log L (L⊙ ) Method 3.874 3.848 0.36 0.95 d c 3.849 0.79 d 3.858 1.01 a 3.839 3.844 3.867 1.18 1.08 1.08 c a d 3.843 3.846 3.852 1.12 1.00 1.15 a c a 3.837 1.04 b 3.818 3.855 1.50 0.93 b c 3.847 1.23 b Freq. (d−1 ) 5.8258 22.2879 12.9823 10.3385 2.4913 13.8158 11.6332 16.4598 13.9770 19.3944 30.8011 22.9653 13.5892 19.4303 2.4622 4.4864 23.0318 9.1521 18.5845 6.3584 12.0775 0.6072 25.3063 8.5454 21.1612 3.3802 7.1976 20.3278 12.0588 Amp. (mmag) 13.9 3.5 1.9 5.6 4.4 2.9 3.6 1.8 2.2 4.0 2.8 2.3 3.7 1.2 3.4 9.9 6.7 10.1 1.8 13.8 4.1 9.1 1.4 7.1 1.1 2.3 21.4 3.7 1.6 nFreq. 7 3 4 3 4 4 13 4 5 8 4 5 1 4 5 2 8 4 5 4 3 2 1 2 1 1 6 2 7 ∆T (d) 125 179 179 537 536 1219 536 141 140 537 439 556 179 112 556 120 556 549 555 1218 141 563 506 546 563 140 154 140 520 Class δ Sct δ Sct δ Sct δ Sct δ Sct/γ Dor δ Sct δ Sct δ Sct/γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct δ Sct/γ Dor γ Dor δ Sct δ Sct δ Sct δ Sct δ Sct γ Dor δ Sct δ Sct δ Sct γ Dor δ Sct δ Sct δ Sct Notes. The first column gives the identification number (Ren ID) from the Renson & Manfroid (2009) catalogue. In column 6, the method of stellar parameter determination is given: a) uvbyβ photometry, b) uvby photometry c) Geneva photometry, d) spectral energy distribution and parallax. Freq. is the frequency of the highest amplitude (Amp.) and nFreq is the number of identified frequencies. ∆T is the time baseline of the SuperWASP photometry. Class is the pulsation class as defined by Grigahcène et al. (2010). 10