Communications in Asteroseismology

Volume 142 December, 2002

16th Delta Scuti Star Newsletter for Delta Scuti, Gamma Dor and SX Phe stars

Editor: Michel Breger, Turk¨ enschanzstraße 17, A - 1180 Wien, Austria Layout and Production: Wolfgang Zima Editorial Board: Gerald Handler, Don Kurtz, Jaymie Matthews, Ennio Poretti http://www.deltascuti.net

COVER ILLUSTRATION: Instability domains in the upper part of the Hertzsprung-Russel Diagram. Slowly Pulsating B stars are unstable only to nonradial high-order gravity modes. A similar instability was found for massive stars in addition to the β Cep–type instability. For the classical instability strip, only the Blue Edge is shown. A few evolutionary tracks for the indicated values of M/M¯ are shown. The location of γ Dor variables and of stars with solar-like oscillation is also shown. The position of the present Sun is marked by the symbol ¯. For more information please see the article by A. A. Pamyatnykh on p. 10.

British Library Cataloguing in Publication data. A Catalogue record for this book is available from the British Library. All rights reserved ISBN 3-7001-3137-2 ISSN 1021-2043 Copyright °c 2002 by Austrian Academy of Sciences Vienna Contents

Editorial 4 First results from a multisite campaign on AV Cet by T. H. Dall, G. Handler, and M. B. Moalusi 6 Comments on the upper main-sequence instability domains by A. A. Pamyatnykh 10 A ﬁve-month multitechnique, multisite campaign on the β Cephei star ν Eridani by G. Handler & C. Aerts 20 1994 multisite photometry of the δ Scuti star θ2 Tau by M. Breger, W. Zima, R. Garrido, G. Handler, P. Reegen, R. Zechner 25 Solar-like oscillations in δ Scuti stars by R. Samadi, M.-J. Goupil, and G. Houdek 37 NOTES

Fishing for Delta Scuti stars in the Hipparcos photometric database by J. R. Percy & G. Gilmour-Taylor 48 Discovery of pulsation in the Am Star HD 102480 by S. Joshi, V. Girish, R. Sagar, D. W. Kurtz, P. Martinez, and S. Seetha 50 Multiperiodicity of V350 Peg by J. Vidal-S´ainz, P. Wils, P. Lampens, and E. Garc´ıa-Melendo 52 The High Amplitude δ Scuti Variable Star GSC 3109-00162 by P. Wils, P. Van Cauteren, and R. Groenendaels 54 Is TU UMi a W UMa-type system? by A. Rolland, V. Costa, E. Rodr´ıguez, P.J. Amado, J.M. Garc´ıa-Pelayo, P. L´opez de Coca, and I. Olivares 57 CCD photometry of XX Cyg by S. N. Udovichenko 61 Comm. in Asteroseismology Vol. 142, 2002

Editorial

This is no empty bag! During the last decade, Asteroseismology has grown to a level where the customary, wonderful informal contacts between different workers in a small field are no longer enough to stay organized. So, why not bundle our expertise in a more organized way, apply for financial assistance that individuals could only dream about, and use some of these funds to support young scientists and allow them to move between different groups? And to be a bit selfish, why should you have to reinvent the wheel in your own country in your attempts to try to persuade the various funding agencies that asteroseismology is an important astronomical field? The supporting scientific arguments used in your proposal have already been written down several times by your colleagues in other countries. It appears that a loose association of asteroseismologists needs to be formed to support these and many other common interests. Enter BAG, the Belgian Asteroseismology Group. Do not be misled by the unassuming name! Under the leadership of Conny Aerts, in October, this group invited representatives from different institutions to Leuven in order to plan an Asteroseismology Society and to write a joint proposal to the EU to establish a European Network of Excellence in Asteroseismology (ENEAS). The meeting was a smashing success with a high level of science. The discussions on details of new committees and offices and how the offices are to be filled were kept to a minimum. Such (necessary) discussions make people like me turn and run away fast. Conny divided the time beautifully. Since the chances of obtaining EU financing for the ENEAS proposal to the EU regrettably are small, the formation of an asteroseismological society to assist the scientists may turn out to have the largest long-term impact. What does this editorial on the organization of the asteroseismologists have to do with a Delta Scuti Newsletter? I may be biased in this matter, I admit. But the growth in our knowledge of the behaviour of Delta Scuti and related stars has been almost exponential during the last decades. Due to this work, Delta Scuti stars form one of the main areas in asteroseismology. Furthermore, it appears that every discovery of a new type of pulsating variable in the end leads to the same unsolved astrophysical questions such as mode selection, amplitude and period variability. The answers to these scientific questions may Editorial 5 come from selecting the suitable pieces of the puzzle from many different types of stars. Successful asteroseismology means many types of stars, from solar-type all the way to the hot PG 1159 stars...... We hope that you find this issue of the newsletter interesting. The next volume of the Communications will again be devoted to all aspects of asteroseismology. So keep the news and articles coming!

Michel Breger Editor Comm. in Asteroseismology Vol. 142, 2002

First results from a multisite campaign on AV Cet

T. H. Dall1, G. Handler2,3, M. B. Moalusi4

1 European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago, Chile 2 Institut fur¨ Astronomie, Turk¨ enschanzstrasse 17, 1180 Vienna, Austria 3 South African Astronomical Observatory, P.O. Box 9, Observatory 7935, South Africa 4 Department of Physics, University of the North-West, Private Bag X2046, Mmabatho 2735, South Africa

Abstract

We present the first results from an international observing campaign on the δ Scuti star AV Cet. From more than 80 hours of Strömgren photometry, not yet fully analysed, we find 8 frequencies between 14 d−1 and 31 d−1, with amplitudes between 4.4 mmag and 1.6 mmag. Among the detected frequencies are the three that were found in previous studies. Results from simultaneous spectroscopy will be used in a later paper to attempt mode identification of the strongest modes of AV Cet.

Introduction

Little work has been done on the star AV Cet (HD 8511, V=6.21, F0V) since it was recognized as a δ Scuti pulsator by Jørgensen et al. (1971). Based on four nights of photoelectric observations Gonzalez-Bedolla (1990) and Gonzalez- Bedolla et al. (1990) found one dominant frequency of 14.59 d−1 and a suspected second frequency of 19.19 d−1. Later Dall & Frandsen (2002) veriﬁed the frequencies and found evidence for an additional frequency around 33 d−1 in the line indices of the Balmer lines, based on only four hours of spectroscopy. In order to verify this star as a multimode pulsator and to clarify its pulsational content an international photometric campaign was launched in October 2001, involving sites in Chile, South Africa and Australia. Regrettably we were unable to obtain data from Australia due to dome repair works that took much longer than expected. The observing log is presented in Table 1. T. H. Dall, G. Handler, and M. B. Moalusi 7

Observatory Telescope Str¨omgren hours HJD – 52200 ﬁlters observed ESO, La Silla 0.5m SAT uvby 41.5 8,11,12,13,14,15 SAAO 0.5m vby 42.2 8,9,12,13,14,15,16,18

Table 1: The participating sites and the amount of time used.

Alongside the photometric campaign, spectroscopy was done with the Dan- ish 1.54m at La Silla, Chile. We will attempt mode identiﬁcation by comparing the same modes in photometry and Balmer-line-indices, as has been done for FG Vir (Viskum et al. 1998) and BN Cnc (Dall et al. 2002). The spectroscopic data and part of the photometric data are still undergoing analysis, so here we will only present preliminary results of the photometric campaign.

Data analysis and results

The raw data from La Silla was fed through the standard reduction pipeline developed by E. H. Olsen et al. at the Copenhagen University Observatory, while the data from South Africa was locally reduced in the standard way. So far, only the Str¨omgren y data has undergone frequency analysis. The data set was assigned statistical weights based on the local scatter in the time series with each sub-series, deﬁned by observatory and date, treated individually. The frequency analysis was done using Period98 (Sperl 1998), which yielded the amplitude spectrum of the combined y data set shown in Fig. 1. The frequency content of AV Cet is given in Table 2.

mode frequency amplitude S/N [d−1] [mmag] f1 15.90 4.4 19 f2 14.59 2.6 11 f3 28.16 2.1 8.9 f4 25.95 2.0 8.5 f5 30.83 1.7 7.2 f6 29.39 1.6 6.8 f7 16.36 1.6 6.8 f8 21.20 1.6 6.8

Table 2: The frequencies found in the combined Str¨omgren y data set of AV Cet. The frequency spectrum after prewhitening with f1–f8 shows excess power, but we prefer not to present any more frequencies before the full data set has been analysed. 8 First results from a multisite campaign on AV Cet

Figure 1: The amplitude spectrum of the combined y data set is shown in the bottom panel, with the window shown in the top panel.

Discussion

Our preliminary analysis shows already that AV Cet has many pulsational modes excited. In this respect it resembles other extensively studied δ Scuti stars of low amplitude. We ﬁnd that the mode f2 reported to be the dominant by Gonzalez-Bedolla is exceeded by another mode close by, while the mode −1 reported at 19.19 d might be explained by our f8 mode, whose frequency is diﬀerent by 2.01 d−1, or by a combination of closely spaced frequencies, which are present around 20 d−1. The variation around 33 d−1 reported by Dall & Frandsen from only four hours of observations is found to consist of several close frequencies. The low amplitudes of these signals makes it likely that they are not detectable in the old data of Gonzalez-Bedolla. On the other hand, this region shows larger excess power than the region around 20 d−1, so the possibility of amplitude variations or even excitation of new modes cannot be ruled out. In a later paper we will present a detailed analysis of the photometric and spectroscopic data, and we will also compare with the data of Gonzalez-Bedolla to check for possible period or amplitude changes. T. H. Dall, G. Handler, and M. B. Moalusi 9

References Dall T. H., Frandsen S., Lehmann H., Anupama G. C., Kambe E., Handler G., Kawanomoto S., Watanabe E., Fukata M., Nagae T., Horner S. 2002, A&A 385, 921 Dall T. H., Frandsen S. 2002, A&A 386, 964 Gonzalez-Bedolla S. 1990, Rev. Mex. A&A 21, 401 Gonzalez-Bedolla S., Rolland A., Rodriguez E., Lopez de Coca P. 1990, IBVS 3533 Jørgensen H. E., Johansen K. T., Olsen E. H. 1971, A&A 12, 223 Sperl M. 1998, Comm. in Asteroseismology 111, 1 Viskum M., Kjeldsen H., Bedding T. R., Dall T. H., Baldry I. K., Bruntt H., Frandsen S. 1998, A&A 335, 549 Comm. in Asteroseismology Vol. 142, 2002

Comments on the upper main-sequence instability domains

A. A. Pamyatnykh 1,2,3

1 Institute of Astronomy, University of Vienna, Turk¨ enschanzstr.17, A-1180 Vienna, Austria 2 Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland 3 Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya Str. 48, 109017 Moscow, Russia

Abstract

Some results of theoretical studies of the instability domains in the upper main sequence are outlined. Using the frequency – log Teﬀ diagram for models of the Slowly Pulsating B-stars, we show that a recently detected tendency for the coolest SPBs to oscillate with higher frequencies than those for hotter SPB stars, may agree with the theoretical expectations.

Introduction

In this note I will outline some features of the instability domains in the upper main sequence and comment recent observational and theoretical data of other authors which were declared to be in a disagreement with our results or expectations. The numerical results I will present were obtained in Wojtek Dziembowski’s group in Warsaw and in Mike Breger’s group in Vienna. The note can be considered as an addition to and, partly, shortened exposition of reviews on pulsational instability domains on the main sequence (Pamyatnykh 1999, 2000, 2003 - hereafter, Papers I, II, III, correspondingly). The stellar models were computed without taking into account the eﬀects of rotation and convective overshooting. An initial hydrogen abundance of X = 0.70 and a heavy element abundance Z = 0.02 were assumed, and the heavy element mixture was that of Grevesse & Noels (1993). In the stellar envelope, the standard mixing-length theory of convection with the mixing- length parameter α = 1.0 was used. For opacities, we used the most recent A. A. Pamyatnykh 11 version of the OPAL data (Iglesias & Rogers 1996), supplemented with the low–temperature data of Alexander & Ferguson (1994). Other details of computations are given in Papers I and II.

The updated HR diagram

In Fig. 1 we present the location of the instability domains in the HR diagram. This plot is an updated version of Fig. 3 in Paper I. The observed domain of γ Dor variables is shown in the lower part of the diagram by two approximately vertical lines (G. Handler, private communication). Also the position of stars with solar-like oscillations is shown. The present Sun is located outside the evolutionary track of 1 M¯, even slightly to the left of the ZAMS because our standard parameters of the chemical composition and of the convective mixing-length don’t fit appropriate solar values. An important feature of the stability analysis is an extension of the high- gravity mode instability domain (the SPB domain) to larger masses and luminosities, as was for the first time mentioned by Pamyatnykh (1998). We discuss this feature in the next subsection. This extension is continuous if we use OP opacities (Seaton 1996, see Paper I). For the SPB domain and its extension, the low temperature boundary coincides with the TAMS due to strong damping of the high-order gravity modes for more evolved models. The TAMS line can be considered also as an effective Red Edge for the β Cep domain because of very fast post-MS evolution of massive stars. Almost all observed β Cep and SPB stars lie within the instability domains. However, the β Cep variables in NGC 6231 fall outside the instability region. An increase in heavy element abundance may solve this problem. The β Cep instability region extends to high luminosities where no observed variables of this type were found, in spite of the fact that the instability strip becomes wider at high luminosities. We have no satisfactory explanation of this discrepancy. It is possible that some additional factors like mass-loss or fast rotation influence the instability at high luminosities. Kiriakidis et al. (1993) noted that the low-amplitude variability of blue supergiants may be connected with the same κ-mechanism acting in the Z opacity bump region inside the star. For δ Sct variables, we chose 329 stars with available uvbyβ photometry from the catalogue of Rodriguez et al. (2000). The photometric data were transformed to effective temperature, Teff , and to luminosity, L, in the same way as in Paper II (an older version of the Rodriguez catalogue was used in that paper). Our comparison with the observations is rather illustrative. We do not discuss here the errors of calibrations, the positions of individual stars and we do not try to correct some data using additional information (like distances for the members of open clusters or according to the HIPPARCOS data). For 12 Comments on the upper main-sequence instability domains

Figure 1: Instability domains in the upper main sequence. Slowly Pulsating B stars are unstable only to nonradial high-order gravity modes. A similar instability was found for massive stars in addition to the β Cep–type instability. For the classical instability strip, only the Blue Edge is shown. A few evolutionary tracks for the indicated values of M/M¯ are shown. Observational data are taken from Balona (1994, NGC 3293), Balona & Koen (1994, NGC 4755), Balona & Laney (1995, NGC 6231), Sterken & Jerzykiewicz (1993, β Cep in field), North & Paltani (1994, SPB), Waelkens et al. (1998, SPB discovered by Hipparcos), and Rodriguez et al. (2000, δ Sct). The location of γ Dor variables and of stars with solar-like oscillation is also shown. The position of the present Sun is marked by the symbol ¯. the theoretical instability domain, only the Blue Edge of the instability strip is shown, because the Red Edge is not determined in our computations in which A. A. Pamyatnykh 13 we neglected variations of the convective flux during the pulsation cycle. The independence of the driving on the spherical harmonic degree, `, is a typical feature of modes excited by the κ-mechanism. Therefore the Blue Edge was computed for radial pulsations. Near the ZAMS, the hottest unstable model is pulsating in the seventh overtone, p8, changing to the fourth overtone, p5, at log L/L¯ ≈ 2.0, and to the fundamental mode, p1 at high luminosities, log L/L¯ ≈ 5.0. Recently, Deng & Xiong (2001) also determined the instability domain of the β Cep variables. There exists a significant quantitative disagreement of their results with ours. For example, for a standard heavy element abundance (Z = 0.02) they did not find any instability on the main sequence for stellar masses larger than, approximately, 20 M¯. In all our computations (Fig. 1, Paper I, see also earlier studies by Moskalik & Dziembowski 1992, Dziembowski & Pamyatnykh 1993) no upper limit for the instability was found in the studied mass range of M ≤ 40M¯. The disagreement may be due to the fact that Deng & Xiong used an analytical approximation to the opacity tables whereas we used elaborate subroutines of spline interpolation in the tables. We used new versions of the OPAL and 3 OP tables. These tables are fine-zoned in log T and in log R = log ρ/T6 where 6 T6 ≡ T/10 (additionally, we used even more fine-zoned tables which were constructed using spline interpolation). Together with the opacity tables, we used beforehand prepared tables for the opacity derivatives, these tables were constructed also with using the splines. We performed a lot of tests to guarantee the smoothness of the opacity and the derivatives. We are not sure whether an analytical approximation for the opacity can give more reliable results on the instability than our results, because even a good approximation for the opacity may not guarantee the adequate representation of the opacity derivatives which are most important in the instability studies (see Paper I). Recently, Pigulski & Kolaczkowski (2002) found a high-luminosity β Cep variable in the LMC which may be inconsistent with results by Deng & Xiong. Moreover, variability of some Luminous Blue Variables can be also caused by pulsation (see, for example, Dorfi & Gautschy 2002).

The extension of high-gravity mode instability domain

Let’s consider the instability of massive stars in more detail. There are two distinct ranges of unstable periods for these models. Shorter periods correspond to low-order mode (β Cep–type) instability, longer periods correspond to an extension of the SPB–type instability. Such a high-gravity mode instability occurs only in the evolved MS-models close to the TAMS, as can be seen from Fig. 1. 14 Comments on the upper main-sequence instability domains

Figure 2: Upper panels: Dimensionless frequencies, σ = ω/ 4πGhρi, and periods of quadrupole modes for a 30M¯ star in its MS evolution (frompthe left to the right). The small and large dots correspond to stable and unstable modes, respectively. Open circles at log Teﬀ ≈ 4.44 mark modes shown in the lower panels. Lower panels: The diﬀerential work integral, dW/dr, and the pressure eigenfunction, δP/P (both in arbitrary units), for three selected modes. Zero-lines for the variables are shifted with respect to each other. The metal opacity bump is located at r/R ≈ 0.916 (from Pamyatnykh 1999). A. A. Pamyatnykh 15

In Fig. 2, the behavior of the eigenfunction δP/P and of the work integral in three quadrupole modes of a 30M¯ model near the TAMS is shown. The evolution of the frequency spectrum from the ZAMS to the TAMS is shown in the upper panels. Three modes chosen for analysis are marked by open circles. The mode with a period of 0.62 days is formally the g3-mode according to the evolution of the frequency spectrum, see upper left panel (σ ≈ 2 for this mode). But during the evolution from the ZAMS a coupling between this mode g3 and the mode p0 occurred via an avoided crossing. Therefore, this mode is now similar to the acoustic mode p0 according to it’s kinetic energy, which is conﬁned mainly in the envelope. The behavior of the pressure eigenfunction also mimics that of the lowest-order acoustic mode. That is why we classify this mode as p0. The opacity mechanism will work eﬀectively if, in the driving region, δP/P is large and does not vary rapidly. That is true both for p0 and for g16. At intermediate periods the amplitude of the pressure variations is relatively small in the potentially driving region, so the damping in the interiors exceeds the driving in the envelope.

Period – log Teﬀ and Frequency – log Teﬀ diagrams

In Fig. 3, the periods of unstable modes are shown separately for ` = 0, 1 and 2. This ﬁgure is similar to Fig. 6 in Paper II, only the OPAL opacities have been used in the present case. Note two distinct ranges of unstable periods for massive stars. For clarity, the unstable modes of the MS models with masses 4 and 12 M¯ are marked by heavy symbols. Here, the leftmost points correspond to the ZAMS model, and the rightmost ones - to the TAMS model. For the ZAMS 4 M¯ model, the high-order gravity modes g9 to g16 of ` = 1 and g9 to g21 of ` = 2 are excited. For the TAMS 4 M¯ model, the high-order gravity modes g36 to g81 of ` = 1 and g43 to g85 of ` = 2 are excited (see Fig. 2 in Paper III for more details). The jagged appearance of the instability domains is due to considering discrete values of stellar masses. Quite recently, Peter De Cat & Conny Aerts published very interesting results of a study of bright southern SPB stars (De Cat & Aerts 2002). They found that ”the observed frequencies of the coolest SPB stars tend to be higher than those of the hotter stars, although the trend is only marginal” (see Fig. 18 in their paper). In the author’s opinion, ”such a temperature-frequency relation is not expected from theoretical excitation studies”. However, we are not sure, whether such a disagreement between theory and observations does exist. In Fig. 4 we plot frequencies of unstable modes versus eﬀective temperature both for β Cep and SPB type variables. Nonradial acoustic modes in the β Cep domain are not shown, their frequencies lie outside the corresponding boxes because for ` = 1 and ` = 2 we used frequency range similar to that in 16 Comments on the upper main-sequence instability domains

Figure 3: Periods of unstable modes in β Cep and SPB domains shown in Fig. 1. For the clarity, the results for two ﬁxed values of stellar mass are marked by heavy symbols. Left and right edges of 4M¯ sequence correspond to the model on ZAMS and TAMS, correspondingly. Note two distinct ranges of unstable periods for massive stars. Shorter periods correspond to low-order mode (β Cep–type) instability, long periods correspond to extension of the SPB–type instability.

Fig. 18 in De Cat & Aerts (2002). The observed domain from that ﬁgure is approximated by thin solid lines.

Indeed, for a given stellar mass, say, 4 M¯, unstable frequencies of the cooler models tend to be lower than those of the hotter models. This is because the local thermal time-scale in the driving zone at the metal opacity bump is larger for cooler models (and optimal conditions for excitation of oscillations are fulﬁlled for longer periods, i.e. for lower frequencies). This tendency is A. A. Pamyatnykh 17

Figure 4: Frequencies of unstable modes in β Cep and SPB domains. The same data as in Fig. 3 are used. Nonradial acoustic high-frequency modes in the β Cep domain are not shown, their frequencies lie outside the corresponding boxes. Thin solid lines approximate the observed domain of bright SPB stars (Fig. 18 in De Cat & Aerts 2002). opposite to the trend found by De Cat & Aerts. However, for diﬀerent masses inside the SPB domain along the main sequence, we have a more complicate interplay between opacity and requirements concerning both the shape of the eigenfunctions and the ratio of oscillation period to thermal time-scale. As a consequence, the above mentioned tendency does not exist in this relatively narrow range of periods or frequencies in the SPB domain, as can be seen in Fig. 4. Moreover, for ` = 1 we have the same marginal trend as it is observed, and the observed and theoretical domains are in a quite good agreement. The 18 Comments on the upper main-sequence instability domains only problem may arise for the lowest observed frequencies (longest periods) - all models are stable at these frequencies. It is possible that models with convective overshooting may solve this problem too - if in the HR diagram these stars are located slightly to the right of the MS band computed without overshooting. To conclude, at present we don’t see any signiﬁcant disagreement between observed results for the SPB variables and theoretical expectations. It is possible, that a disagreement still exists. However, for such a suggestion it is necessary to compare the observed data and theoretical results in more details, taking into account exact location of the stars inside the SBB domain in the HR diagram.

Acknowledgments. This note was written during my stay at the Institute of Astronomy of the University Vienna. I would like to thank Mike Breger and all members of his group for fruitful discussions. All numerical results presented here were obtained in the Wojtek Dziembowski’s group in Warsaw and in the Mike Breger’s group in Vienna. The investigation has been partly supported by Polish KBN grant No. 5 P03D 012 20 and by the Austrian Fonds zur F¨orderung der wissenschaftlichen Forschung under project number P14546-PHY.

References Alexander, D. R., Ferguson, J. W. 1994, ApJ 437, 879 Balona, L. A. 1994, MNRAS 267, 1060 Balona, L. A., Koen, C. 1994, MNRAS 267, 1071 Balona, L. A., Laney, C. D. 1995, MNRAS 276, 627 De Cat, P., Aerts, C. 2002, A&A 393, 965 Deng, L., Xiong, D. R. 2001, MNRAS 327, 881 Dorﬁ, E. A., Gautschy, A. 2002, Comm. in Asteroseismology, 141 ,57 Dziembowski, W. A., Moskalik, P., Pamyatnykh, A. A. 1993, MNRAS 265, 588 Dziembowski, W. A., Pamyatnykh, A. A. 1993, MNRAS 262, 204 Grevesse, N., Noels, A. 1993, in Origin and Evolution of the Elements, eds. Pratzo N., Vangioni-Flam E., Casse M., Cambridge Univ. Press, p. 15 Iglesias, C. A., Rogers, F. J. 1996, ApJ 464, 943 Kiriakidis, M., Fricke, K. J., Glatzel, W. 1993, MNRAS 264, 50 Moskalik, P., Dziembowski, W. A. 1992, A&A 256, L5 North, P., Paltani, S. 1994, A&A 288, 155 Pamyatnykh, A. A. 1998, in A Half-Century of Stellar Pulsation Interpretations, eds. Bradley P. A., Guzik J. A., ASP Conf. Ser., vol. 135, p. 268 Pamyatnykh, A. A. 1999, Acta Astr. 49, 119 (Paper I) Pamyatnykh, A. A. 2000, in Delta Scuti and Related Stars, eds. Breger M., Montgomery M. H., ASP Conf. Ser., Vol. 210, p. 215 (Paper II) Pamyatnykh, A. A. 2003, in Asteroseismology Across the HR Diagram, eds. A. A. Pamyatnykh 19

Thompson M. J., Cunha M., Monteiro M. J. P. F. G., Kluwer, in press (Paper III) Pigulski, A., KoÃlaczkowski, Z. 2002, A&A 388, 88 Rodriguez, E., López–González, M. J., López de Coca, P. 2000, in Delta Scuti and Related Stars, eds. Breger M., Montgomery M. H., ASP Conf. Ser., Vol. 210, p. 499 Seaton, M. J. 1996, MNRAS 279, 95 Sterken, C., Jerzykiewicz, M. 1993, Space Sci. Rev. 62, 95 Waelkens, C. 1991, A&A 246, 453 Waelkens, C., Aerts C., Kestens E., Grenon M., Eyer L. 1998, A&A 330, 215 Comm. in Asteroseismology Vol. 142, 2002

A ﬁve-month multitechnique, multisite campaign on the β Cephei star ν Eridani

G. Handler1, C. Aerts2

1 Institut fur¨ Astronomie, Turk¨ enschanzstrasse 17, 1180 Vienna, Austria 2 Instituut voor Sterrenkunde, Celestijnenlaan 200B, 3001 Leuven, Belgium

Abstract

We have organised the largest ever observing campaign for a β Cephei star. Its target star is ν Eridani. We brieﬂy discuss the prospects and problems for asteroseismology of B-type main sequence pulsators and we describe the layout of the campaign based on our scientiﬁc goals. Finally, we invite all interested colleagues who have not already done so to join our team.

Introduction

There is no doubt that the advent of multisite campaigns has improved our understanding of the pulsational behaviour of δ Scuti and γ Doradus stars enormously. Not only can pulsational mode frequencies be determined unambiguously because of the elimination of the aliasing problem, but the large amounts of data – sometimes even more than 1000 hr of observation (Breger et al. 2002) – also allow the detection of signals of very low amplitude. Such projects have led to determinations of up to 22 independent mode frequencies (Handler et al. 2000) for individual stars plus a number of combination signals. Consequently, it is expected that asteroseismology of massive stars, such as β Cephei stars and SPB stars, will also benefit from large multisite campaigns. The prospects and problems these stars pose are somewhat different from those for δ Scuti stars. Probably the greatest advantage for studying B-type pulsators is that the complicating effects of a surface convection zone as present in A/F stars do not exist, which should ease the tasks of mode identification and seismological modelling considerably. On the other hand, the beat periods of the multiple modes in these stars can be very long which requires measurements over a long G. Handler & C. Aerts 21 time base to be resolved. This difficulty effectively eliminates the SPB stars (where beat periods can be of the order of years) as prime asteroseismological targets, at least for the time being. This leaves the β Cephei stars as the objects of prime interest for multisite campaigns on massive pulsators. They have multiple pulsation periods of the order of a few hours, large light amplitudes, readily detectable line-profile variations and comparatively simple theoretically predicted pulsational mode spectra. In addition, many of these stars are quite bright, making them ideally suited for high-resolution spectroscopic studies. Consequently, we have organised for the first time an extensive multisite campaign on a β Cephei star, using both spectroscopic and photometric observing methods.

The target star

We have carefully selected the most promising β Cephei star for our campaign from the literature, ν Eri (RA (2000): 04:36:19, Dec (2000): −03:21:09, V = 3.92, B2 III). It has four well known pulsation frequencies (Cuypers & Goossens 1981), three of which have been claimed to form a triplet. Such a multiplet structure makes this star particularly interesting, as detecting several multiplets would allow us to derive the internal as well as external rotation rate with very high precision. In addition, the remaining mode is known to be radial which severely constrains the physical parameters of ν Eri. Clear pulsational line-profile variability, superposed to the moderate rotational broadening (v sin i < 25 km/s) was already detected by Aerts et al. (1994). Therefore, being visible from both hemispheres (accessible to large numbers of telescopes), being a slow rotator, and being bright enough for effective acquisition of high- resolution spectra yet not being too bright for most photoelectric photometers, ν Eri is an ideal candidate of a massive pulsator to be studied with multisite asteroseismology techniques. The only small difficulty for the organisation of our project was the close frequency splitting of the mode triplet, causing a beat period of 62 days that needs to be resolved with our measurements. It is important to note that the beat period of the outer two components of the triplet then has a beat period of about 31 days, which would interfere with a possible monthly alias if not being taken care of. It is, of course, impossible to get such long allocations on the large telescopes required for spectroscopy. We have therefore applied for block allocations of the order of one week at many different sites, suitably spreading them over a three-month interval (photometry will even be obtained during at least five months) to resolve the triplet (and possible additional ones!) cleanly in the combined data set. We have also asked for dark time at some sites to suppress the monthly alias. 22 A multisite campaign on the β Cep star ν Eri

Consequently, we hope that we have fulfilled all the necessary conditions to acquire the observational material sufficient to perform for the first time a detailed asteroseismological analysis of a massive main-sequence star with a large convective core. An overview of present telescope allocations is listed in Table 1 and shown in Fig. 1.

Figure 1: Graphical overview of telescope allocations. Upper panel: spectroscopy. Lower panel: photometry. The full lines are granted times of observation whereas the dashed-dotted lines are pending applications. Negative day numbers are due to a site starting earlier than planned.

So far, we have been allocated a total of 121 nights for spectroscopy at 10 telescopes up to 3.5 metres aperture on four continents spanning a total baseline of ∼ 105 days. We hope to obtain another ∼ 30 nights to extend our coverage. For the photometric measurements we have so far been awarded 166 nights with a time base of 94 days and we hope for ∼> 80 nights more. However, measurements have already been obtained at Siding Spring Observatory from early September on, which means that our ﬁnal time base is expected to be about 5 months. G. Handler & C. Aerts 23

Telescope Contact or Observer (desired) allocation status Spectroscopy APO 3.5m Krzesinski 3 nights granted NOT 2.6m Uytterhoeven/Telting 4 nights granted McDonald 2.1m Heiter 8 nights granted SAAO 1.9m Balona/Romero 2 × 7 nights granted MSSSO 1.9m James 2 × 7 nights granted OHP 1.9m Mathias/Aerts 2 × 8 nights granted ESO Swiss 1.2m Aerts/Maas/Groenewegen 2 × 14 nights granted Tautenburg 2.0m Lehmann 4 × 7 nights granted LNA 1.6m Bruch 2 × 3 nights granted Ondrejov 2.0m Steﬂ et al. whenever possible granted Mt. John 1.0m Cottrell/Wright 2 × 7 nights applied Calar Alto 2.2m Dreizler 10 half nights applied McDonald 2.1m De Cat/Uytterhoeven 10 nights applied Photometry SAAO 0.5m Handler/Tshenye 3 × 14 nights granted SSO 0.6m Shobbrook 30 nights granted Fairborn 0.75m APT 31 nights granted OSN 0.9m Rodriguez 14 nights granted Lowell 0.8m Jerzykiewicz 21 nights granted MDE 0.8m Dorokhova 2 × 14 nights granted SPM 1.5m Arellano Ferro 14 nights 2 hr/night Hungary 0.5m Paparo 14 nights applied MJUO 0.6m Cottrell/Wright whenever possible applied SAAO 0.5m Medupe/Ramokgali 21 half nights applied Leicester 0.4m Burleigh possible CTIO 0.6m Krisciunas 10 nights possible BAO 0.85m Zhou 4 + 16 nights possible La Luz 0.6m Eenens possible Mauna Kea 0.6m Crowe possible Perth 0.6m Birch possible

Table 1: The participating sites. 24 A multisite campaign on the β Cep star ν Eri

Call for participation

Although the campaign is already running, it may not be too late for additional interested researchers to join in. As the outcome of this project will largely determine future strategies for asteroseismology of β Cephei stars and possibly of opacity-driven main sequence pulsators in general, we are interested to obtain the best results possible. Observational requirements for spectroscopy is the ability to acquire high- resolution (R > 30000), high signal-to-noise (S/N ∼> 200) spectra of the stellar Si III absorption lines triplet near 4560 A˚ with a sampling interval no longer than 15 minutes. Photometric measurements are best acquired with photoelectric photometers and Strømgren uvy filters and a light neutral density filter, although Johnson (B)V photometry would also suffice. The photometric precision per differential target star measurement must be better than 5 mmag rms. CCD photometry would only be useful if heavy neutral density filters are available and if the field of view is larger than 20 arcminutes for acquisition of a sufficiently bright comparison star in the same field. Interested colleagues are invited to contact the authors of this article for more information. The spectroscopic part of the campaign is led by CA who can be reached at [email protected], whereas photometrists are requested to email GH at [email protected].

Acknowledgments. This project and GH are supported by the Austrian Fonds zur F¨orderung der wissenschaftlichen Forschung under grant R12. CA acknowledges the support of the Fund for Scientiﬁc Research of Flanders under grant G.0178.02. References Aerts, C., Waelkens, C., De Pauw, M. 1994, A&A 286, 136 Breger M., et al., 2002 MNRAS 329, 531 Cuypers J., Goossens M. 1981, A&AS 45, 487 Handler G., et al. 2000, MNRAS 318, 511 Comm. in Asteroseismology Vol. 142, 2002

1994 multisite photometry of the δ Scuti star θ2 Tau

M. Breger1, W. Zima1, R. Garrido2, G. Handler1, P. Reegen1, R. Zechner1

1 Institut fur¨ Astronomie, Turk¨ enschanzstrasse 17, 1180 Vienna, Austria 2 Instituto de Astrof´isica de Andalucia, SCIC, Apdo. 3004, E-18080 Granada, Spain

Abstract

The 1994 multisite photometry of the δ Scuti star θ2 Tau, obtained by the Delta Scuti Network, is presented. During 1994 November and December, a multisite photometric campaign to study θ2 Tau was organized utilizing the Delta Scuti Network. θ2 Tau was measured photometrically with the Three-Star-Technique at a number of observatories spaced around the globe. 152 hours of photometry at four observatories could be used. The telescopes used were: the 0.8m reflector at Lowell Observatory (USA), the 0.9m telescope at McDonald Observatory (USA), the 0.9m telescope at Sierra Nevada Observatory (Spain), and the 0.6m reflector at the XingLong station of Beijing Astronomical Observatory (China). Details of the observations as well as the astrophysical results obtained from these measurements can be found in Breger et al. (2002). This article presents the table of measurements used in the analysis in order to preserve the data for the future. At the present time, the data can also be obtained from the first author electronically. This investigation has been supported by the Austrian Fonds zur Förderung der wissenschaftlichen Forschung under project number P14546-PHY. References Breger, M., Pamyatnykh, A.A., Zima, W., Garrido, R., Handler, G., Reegen, P. 2002, MNRAS 336, 249 26 1994 multisite photometry of the δ Scuti star θ2 Tau

Table 1: The frequency spectrum of θ2 Tau

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 67.18854 -7.7 71.02082 -3.9 0.9 74.23331 -9.8 67.19080 -8.9 71.68329 -12.9 74.23746 -12.3 67.19470 -5.3 71.69274 -9.9 74.23954 -7.6 67.19721 -9.7 71.69957 -8.2 74.24295 -20.3 67.20404 -9.5 71.70548 -7.3 -6.9 74.24491 -20.6 67.21839 -7.8 71.71145 -4.9 -2.8 74.24869 -12.9 67.22052 -3.0 71.71817 -4.7 -3.1 74.25040 -15.0 67.22595 -2.3 71.72569 -4.4 -1.8 74.25565 -23.3 70.70247 -6.1 -6.1 71.73195 -5.5 -5.3 74.25791 -7.4 70.71172 -6.7 -4.2 71.73868 -8.6 -9.9 74.26163 -9.6 70.72368 -3.4 0.6 71.74501 -9.8 -12.3 74.26810 -12.4 70.73017 -7.3 -5.5 71.75139 -14.1 -15.0 74.27280 -6.6 70.73723 -6.4 -6.5 71.75801 -16.0 -14.8 74.27500 -4.6 70.74449 -13.4 -14.1 71.76369 -16.7 -16.4 74.27872 0.4 70.75125 -15.3 -18.9 71.76946 -16.1 -15.6 74.28379 1.6 70.76972 -18.8 -24.7 71.77498 -12.9 -13.4 74.28781 -0.7 70.77811 -10.1 -11.3 71.78204 -8.9 -6.2 74.29361 -1.0 70.78416 -4.3 -4.2 71.79199 -7.8 -2.7 74.30149 1.2 70.78986 0.6 1.3 71.79829 -7.5 -2.6 74.30503 0.4 70.79550 0.0 4.0 71.82142 -10.5 -8.2 74.31052 -10.6 70.80196 -1.2 1.1 71.82727 -13.4 -12.1 74.31308 -19.8 70.80832 -6.3 -4.2 71.83300 -14.4 -13.9 74.31821 -21.5 70.81548 -11.2 -11.8 71.83863 -14.7 -16.8 74.32144 -19.9 70.82334 -19.0 -20.6 71.84459 -12.7 -15.1 74.32321 -17.2 70.82996 -23.4 -27.8 71.85051 -12.6 -10.7 74.32645 -16.0 70.83670 -21.2 -29.9 71.85752 -11.1 -10.8 74.32846 -19.1 70.84268 -19.1 -23.9 71.86410 -10.5 -8.3 74.33200 -13.8 70.85603 -6.2 -8.7 71.87001 -9.9 -9.9 74.33390 -19.5 70.86215 -1.2 1.6 71.87655 -8.8 -8.9 74.33744 -8.3 70.86803 3.0 7.2 71.88276 -7.5 -6.1 74.33982 -7.6 70.88740 -4.6 -3.0 71.88835 -5.7 -3.8 74.34342 -10.3 70.89326 -12.7 -14.9 71.89447 -6.4 -2.4 74.34629 -4.9 70.89898 -16.6 -20.6 71.90044 -10.0 -6.2 78.78122 -16.4 70.90477 -21.5 -26.0 71.92049 -13.6 -13.8 78.78470 -16.6 70.91060 -23.0 -32.0 71.92682 -12.3 -12.9 78.78828 -16.8 70.91743 -18.6 -24.8 71.93375 -11.6 -12.4 78.79066 -14.5 70.92588 -6.6 -12.6 71.94042 -11.5 -14.2 78.79395 -15.2 70.93224 -2.8 -3.3 71.95371 -10.4 -9.5 78.79754 -15.5 70.93846 -1.3 3.6 71.98089 -9.6 -11.3 78.80148 -14.1 70.94488 1.4 6.0 71.98655 -12.1 -11.7 78.80495 -10.8 70.95118 -1.2 1.6 71.99343 -15.0 -16.5 78.80848 -11.0 70.96898 -14.0 -17.8 71.99911 -14.8 -17.8 79.64182 -9.4 70.97549 -18.4 -23.1 72.00622 -12.9 -21.3 79.64882 -11.5 70.98204 -21.2 -25.8 72.01275 -13.1 -14.8 79.65640 -10.0 70.98864 -18.7 -22.9 72.01846 -12.7 -12.5 79.67209 -7.9 70.99837 -16.0 -14.4 74.22415 -3.0 79.67978 -7.8 71.00474 -11.3 74.22654 -3.2 79.68748 -6.5 71.01217 0.6 3.9 74.23099 -13.2 79.69523 -8.9 M. Breger et al. 27

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 79.70287 -6.9 80.66129 -4.7 -5.5 81.17966 -22.3 79.82006 -8.2 80.66383 -8.6 -14.9 81.18613 -18.4 79.82510 -5.2 80.66617 -12.9 -18.4 81.19101 -20.9 79.82949 -9.3 80.66907 -17.5 -23.0 81.19577 -19.5 79.83337 -11.3 80.67124 -20.5 -20.0 81.20340 -15.5 79.84384 -13.5 80.67394 -19.7 -17.7 81.21048 -20.6 79.84807 -12.7 80.67710 -23.9 -19.9 81.21280 -6.5 79.85201 -15.5 80.68011 -25.6 -20.8 81.21744 -3.5 79.85594 -16.0 80.68255 -29.6 -23.2 81.22031 -3.4 79.86173 -18.3 80.68482 -39.3 81.22477 -6.8 79.86861 -13.4 80.68799 -31.4 81.22733 -4.7 79.87533 -14.7 80.69031 -31.7 -22.9 81.23203 -2.4 79.88210 -14.5 80.69206 -20.8 -15.1 81.25003 -8.8 80.56641 -7.6 -2.6 80.69513 -23.9 -21.0 81.25180 -10.2 80.56933 -7.7 -7.1 80.69718 -22.9 -18.9 81.25693 -16.0 80.57142 -6.3 -5.2 80.69897 -24.2 -17.9 81.26023 -18.4 80.57374 -5.2 -6.3 80.70126 -16.7 -17.7 81.26200 -13.4 80.57624 -8.3 -9.8 80.70312 -12.1 -13.2 81.26511 -19.4 80.57903 -7.2 -9.0 80.70478 -4.2 -9.3 81.27024 -10.7 80.58160 -8.4 -11.4 80.70790 2.6 -3.2 81.28128 -8.5 80.58406 -10.0 -10.0 80.71036 2.5 -2.9 81.28312 -17.7 80.58636 -11.4 -10.4 80.71216 6.1 -0.4 81.28605 -2.4 80.58882 -13.3 -13.8 80.71460 4.1 -1.7 81.28775 -2.6 80.59164 -12.5 -14.4 80.71708 2.7 -4.9 81.30082 -1.4 80.59455 -13.3 -15.3 80.71917 10.8 -2.1 81.30289 -9.4 80.59781 -18.7 -17.2 80.72249 16.7 81.30607 2.0 80.59997 -18.4 -17.8 80.96167 -13.6 81.30808 -6.2 80.60283 -20.8 -19.9 80.96765 -17.8 81.31180 4.2 80.60642 -21.3 -20.4 80.97376 -23.6 81.31376 1.0 80.60905 -24.0 -19.1 80.97770 -21.9 81.31693 -3.8 80.61125 -24.3 -19.8 80.98175 -23.2 81.32218 -1.3 80.61441 -24.8 -20.3 80.98569 -23.2 81.32407 -2.8 80.61753 -20.9 -16.6 80.98950 -19.0 81.32718 -20.8 80.61982 -23.6 -16.5 80.99344 -12.0 81.33280 -7.5 80.62247 -21.6 -16.3 80.99732 -8.3 81.33335 -9.1 -11.0 80.62501 -12.8 -14.3 81.10306 -17.4 81.33457 -19.6 80.62708 -6.2 -9.4 81.10740 -12.2 81.33841 -24.9 80.63110 -3.3 -5.8 81.11142 -15.9 81.33955 -21.3 -21.8 80.63385 -3.7 -4.1 81.11411 -18.1 81.34269 -19.1 -15.6 80.63596 0.2 -3.0 81.11972 -15.3 81.34519 -19.3 -16.8 80.63876 0.3 -0.1 81.12302 -17.3 81.34821 -18.9 -14.9 80.64078 4.1 0.3 81.13987 -11.7 81.35229 -21.0 -18.7 80.64314 6.0 1.9 81.14280 -14.8 81.35587 -18.8 -18.9 80.64565 5.0 1.8 81.14768 -7.3 81.35983 -10.8 -11.5 80.64853 3.6 0.2 81.15061 -5.4 81.36274 -11.4 -9.3 80.65061 4.9 2.5 81.15586 -4.9 81.38191 -0.3 -6.6 80.65250 9.5 -0.2 81.15848 -0.3 81.38479 1.0 -1.4 80.65492 6.4 -0.5 81.16593 -1.4 81.38793 -1.4 -3.5 80.65691 3.0 -2.5 81.16837 -1.7 81.39048 2.2 -0.4 80.65924 -1.6 -2.2 81.17258 -11.4 81.39310 -3.0 -3.3 28 1994 multisite photometry of the δ Scuti star θ2 Tau

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 81.39842 -5.1 -6.0 81.64000 -21.6 -19.1 82.41036 -1.4 -0.5 81.40149 -6.4 -7.7 81.64264 -21.5 -20.2 82.41280 2.5 -0.6 81.40437 -12.1 -11.7 81.64545 -25.5 -23.0 82.41437 -3.7 -3.2 81.40707 -13.1 -13.6 81.64831 -23.4 -22.5 82.41648 -2.7 -4.5 81.41011 -12.7 -12.1 81.65223 -21.7 -18.2 82.41977 -1.7 -7.4 81.50672 -21.0 81.65501 -24.2 -21.7 82.42189 -2.6 -5.8 81.51035 -17.8 -16.3 81.65818 -20.5 -14.7 82.42372 -7.9 -7.6 81.51293 -19.3 -13.6 81.66123 -15.9 -13.8 82.42612 -9.0 -10.7 81.51541 -15.8 -12.6 81.66397 -15.5 -16.6 82.42785 -11.6 -10.7 81.51758 -12.4 -11.1 81.66715 -10.6 -17.6 82.43028 -12.7 -10.1 81.51975 -10.8 -11.3 81.66960 -7.1 -11.5 82.43246 -13.4 -14.5 81.52239 -9.0 -6.2 81.67211 -5.9 -9.8 82.43432 -20.6 -20.6 81.52433 -7.5 -4.9 81.67426 -5.1 -5.8 82.43601 -19.5 -20.1 81.52664 -9.1 -6.0 81.67736 0.0 -7.9 82.43823 -20.0 -15.2 81.53031 -4.9 -5.9 81.68093 1.5 -3.7 82.43986 -23.4 -19.0 81.53272 -1.9 -4.3 81.68326 6.2 -0.2 82.44170 -22.4 -18.9 81.53526 -2.1 -7.4 81.68592 10.2 0.5 82.44521 -25.7 -19.6 81.53730 -0.8 -5.2 81.68901 7.0 -0.2 82.44737 -18.4 -12.3 81.54130 1.8 -2.3 81.69222 2.0 -0.2 82.45021 -21.3 -14.8 81.54957 -1.3 -4.6 81.69492 3.4 -3.4 82.45281 -18.3 -14.2 81.55367 -2.1 -9.9 81.69744 1.5 -3.7 82.45696 -15.6 -15.8 81.55749 -10.6 -10.4 81.69997 -1.7 -4.9 82.45934 -17.5 -16.9 81.56068 -13.3 -10.0 81.70268 -2.4 -6.0 82.46204 -15.7 -17.8 81.56325 -15.4 -14.7 81.70507 -7.6 -11.8 82.46426 -13.2 -12.0 81.56631 -19.1 -16.9 81.70742 -15.5 -17.7 82.46698 -10.9 -11.3 81.57155 -21.0 -23.2 81.70968 -16.3 -15.6 82.47094 -10.5 -9.3 81.57402 -23.5 -20.7 81.71220 -21.9 -21.6 82.47548 -8.3 -6.8 81.57601 -24.1 -20.0 81.71528 -24.6 -20.2 82.47870 -3.8 -5.6 81.57881 -23.9 -18.7 81.71815 -22.2 -20.6 82.48192 -6.9 -3.6 81.58153 -22.9 -19.2 81.72151 -22.0 -20.8 82.48394 -5.1 -1.3 81.58534 -20.0 -17.7 82.35204 -12.6 -12.3 82.48602 -5.9 -5.2 81.58794 -17.5 -12.5 82.35531 -16.8 -16.1 82.48870 -5.8 -6.8 81.59006 -15.2 -17.6 82.36085 -21.6 -17.7 82.49131 -5.6 -5.2 81.59220 -14.2 -15.1 82.36455 -20.0 -18.2 82.49412 -1.9 -5.9 81.59508 -9.3 -12.9 82.36689 -20.8 -15.9 82.49889 -5.7 -7.2 81.59703 -9.8 -11.7 82.37213 -24.3 82.50118 -6.6 -6.9 81.59890 -10.6 -13.0 82.37902 -13.6 -14.5 82.50331 -7.9 -7.3 81.60197 -9.6 -8.0 82.38161 -16.3 -13.7 82.50629 -10.9 81.60462 -6.6 -7.4 82.38388 -11.5 -9.8 82.50850 -11.8 -10.7 81.60714 -3.9 -6.6 82.38846 -10.5 -13.3 82.53012 -14.9 -11.1 81.61396 -0.7 -2.2 82.39031 -11.6 -12.0 82.53301 -14.5 -13.0 81.61699 0.4 -3.3 82.39206 -14.3 -11.7 82.53516 -16.9 -14.5 81.61964 1.0 -4.0 82.39470 -5.0 -10.1 82.53728 -15.7 -14.2 81.62219 0.8 -4.2 82.39728 0.9 -3.0 82.54008 -10.0 -6.5 81.62516 -3.8 -5.8 82.39926 -5.3 -6.2 82.54214 -11.4 -9.8 81.62730 -4.3 -7.5 82.40139 -5.9 -7.3 82.54467 -13.2 -9.5 81.62938 -8.2 -8.0 82.40297 -1.5 82.54728 -13.5 -11.4 81.63227 -7.2 -10.9 82.40471 0.5 -1.1 82.54971 -12.7 -14.1 81.63434 -9.6 -14.5 82.40701 7.6 82.55315 -15.4 -12.8 81.63631 -16.5 -18.1 82.40869 -2.1 -0.7 82.55687 -12.4 -10.0 M. Breger et al. 29

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 82.55956 -12.5 -10.9 82.69439 -8.6 -9.1 83.43831 -7.6 -7.1 82.56262 -12.8 -14.0 82.69647 -6.6 -9.2 83.44073 -8.5 -8.3 82.56648 -13.5 -10.7 82.69956 -17.2 -14.1 83.44274 -9.3 -6.1 82.56901 -9.3 -8.3 82.70217 -9.8 -11.5 83.44447 -7.5 -9.0 82.57144 -11.9 -10.5 82.70418 -16.1 -15.5 83.44684 -9.1 -8.5 82.57419 -5.5 -7.1 82.70624 -20.1 -18.0 83.44915 -11.7 -10.3 82.57639 -6.7 -7.2 82.70858 -22.1 -20.4 83.45110 -12.0 -11.0 82.57939 -5.7 -6.9 82.71173 -20.8 83.45336 -12.4 -11.2 82.58204 -9.0 -5.4 82.71476 -22.9 83.45544 -13.2 -8.8 82.58452 -5.8 -3.5 82.71713 -16.8 83.45803 -12.8 -9.5 82.58700 -3.9 -2.2 83.34169 -11.8 -10.5 83.46046 -13.9 -13.4 82.59056 -5.0 -7.4 83.34448 -7.5 -5.2 83.46244 -11.8 -10.7 82.59328 -6.7 -7.0 83.34686 -5.3 -6.8 83.46631 -17.5 -14.6 82.59543 -8.8 -8.7 83.34928 -5.2 -10.4 83.46831 -15.7 -10.4 82.59747 -10.3 -9.8 83.35136 -7.1 -6.9 83.47026 -18.0 -10.8 82.60053 -8.9 -10.6 83.35361 -12.4 -10.8 83.47206 -19.6 -14.8 82.60324 -10.8 -12.9 83.35661 -9.4 -9.9 83.47388 -20.0 -17.3 82.60677 -8.1 -11.1 83.35887 -5.3 -7.4 83.47609 -17.8 -13.9 82.60937 -13.0 -14.4 83.36140 -5.4 -5.4 83.47903 -17.2 -10.7 82.61193 -12.2 -11.5 83.36361 -2.1 -5.1 83.48084 -15.8 -13.7 82.61582 -16.8 -13.8 83.36621 -8.4 -12.0 83.48272 -15.4 -14.9 82.61842 -18.5 -14.6 83.36810 -4.7 -9.9 83.48512 -14.0 -12.1 82.62092 -15.7 -12.2 83.37090 -7.6 -10.8 83.48758 -12.9 -11.4 82.62460 -18.3 -16.7 83.37306 -9.2 -9.8 83.49027 -10.5 -9.7 82.62681 -19.7 -18.1 83.37486 -11.6 -12.0 83.49203 -11.2 -11.5 82.62894 -21.0 -21.0 83.37750 -7.6 -8.1 83.49384 -8.3 -10.1 82.63217 -20.5 -19.7 83.37940 -8.0 -7.3 83.49786 -5.9 -4.5 82.63442 -21.5 -19.3 83.38132 -11.4 -7.6 83.50002 -6.4 -8.1 82.63771 -19.6 -18.0 83.38342 -11.1 -8.0 83.50180 -3.6 -4.5 82.64082 -17.2 -16.8 83.38565 -14.3 -12.6 83.50487 -1.8 -5.0 82.64267 -14.7 -16.8 83.38866 -13.4 -13.2 83.50924 -5.2 -6.2 82.64501 -14.5 -16.6 83.39129 -13.0 -12.4 83.51229 -6.4 -7.5 82.64785 -16.6 -14.7 83.39355 -13.2 -10.1 83.51799 -1.1 -4.0 82.64977 -10.5 -7.5 83.39602 -12.6 -10.5 83.52257 -5.4 -8.8 82.65206 -12.8 -10.2 83.39818 -17.1 -16.1 83.52692 -9.7 -7.9 82.65539 -9.1 -9.5 83.40080 -19.0 -15.0 83.52967 -15.7 -12.9 82.65843 -3.1 -4.6 83.40478 -15.4 -12.1 83.53152 -13.4 -11.0 82.66110 -3.1 -5.4 83.40721 -16.2 -13.0 83.53417 -17.8 -10.6 82.66339 -4.9 -6.1 83.41084 -18.5 -14.0 83.53632 -18.0 -14.7 82.66601 -4.6 -6.0 83.41364 -14.6 -13.4 83.53844 -20.6 -16.8 82.66832 -5.0 -5.4 83.41585 -13.0 -11.8 83.54169 -18.5 -15.9 82.67158 3.1 -1.0 83.41847 -10.2 -9.8 83.54382 -18.3 -14.8 82.67367 0.4 -4.4 83.42111 -9.8 -9.5 83.54599 -19.9 -17.9 82.67616 -2.3 -6.5 83.42277 -8.4 -4.0 83.54915 -20.9 -17.0 82.67894 0.3 -6.5 83.42496 -7.4 -6.7 83.55137 -21.6 -18.5 82.68163 -2.4 -6.9 83.42705 -7.4 -8.7 83.55417 -18.1 -13.6 82.68405 -5.1 -4.7 83.42899 -5.4 -6.6 83.55675 -15.6 -13.1 82.68715 -9.7 -11.9 83.43059 -4.0 -4.0 83.55942 -16.3 -13.4 82.68949 -10.8 -12.4 83.43428 -3.5 -5.9 83.56269 -12.2 -12.3 82.69174 -8.6 -9.8 83.43625 -6.8 -6.6 83.56561 -13.1 -11.7 30 1994 multisite photometry of the δ Scuti star θ2 Tau

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 83.56770 -8.2 -7.3 83.69877 -16.8 -18.1 84.42062 2.5 -1.3 83.56986 -9.4 -6.6 83.70159 -11.6 -14.5 84.42267 0.7 1.7 83.57361 -7.8 -7.8 83.70418 -11.4 -12.3 84.42470 4.1 1.0 83.57656 -5.7 -7.3 83.70616 -12.4 -11.0 84.42664 -0.4 -2.8 83.57942 -4.6 -7.3 83.70846 -7.1 -7.2 84.42855 4.3 1.1 83.58257 -5.2 -3.3 83.71002 -11.0 -13.5 84.43139 4.1 -0.1 83.58520 -5.1 -5.2 83.71186 -3.7 -6.6 84.43361 7.6 3.0 83.58740 -2.7 -5.4 83.71409 -4.3 -5.0 84.43576 3.3 1.8 83.58953 -2.9 -2.6 83.71599 -10.1 -15.1 84.43804 -1.1 -2.4 83.59221 -8.7 -5.0 83.71776 -1.2 84.44059 -1.0 -2.5 83.59491 -7.9 -9.2 83.71970 -2.2 -7.6 84.44267 -5.3 -5.5 83.59710 -6.8 -6.0 83.72163 -0.2 -4.8 84.44536 -8.6 -7.0 83.59917 -9.8 -11.4 84.26471 -14.5 84.44746 -9.5 -7.7 83.60114 -11.3 -11.3 84.26935 -9.5 84.45032 -10.8 -10.2 83.60416 -11.1 -11.0 84.27228 -8.5 84.45260 -15.1 -12.7 83.60689 -10.4 -12.8 84.27637 -10.7 84.45480 -20.5 -13.0 83.60932 -10.6 -11.2 84.27906 -6.9 84.45739 -14.1 -11.7 83.61301 -19.4 -18.6 84.29352 -7.0 84.45955 -21.6 -17.2 83.61605 -16.4 -16.0 84.29719 -9.0 84.46278 -27.7 -23.7 83.61844 -16.5 -15.8 84.30390 -12.4 84.46487 -27.5 -17.0 83.62043 -18.7 -14.9 84.31269 -15.7 84.46702 -30.7 -20.3 83.62322 -18.5 -16.7 84.33980 -6.1 -6.5 84.46929 -28.2 -21.9 83.62621 -20.5 -16.5 84.34195 -7.4 -4.3 84.47239 -23.6 -17.0 83.62825 -21.5 -17.8 84.34640 -5.1 -3.5 84.47442 -24.4 -18.0 83.63070 -17.6 -16.4 84.34971 4.4 3.2 84.47858 -21.8 -16.5 83.63274 -13.3 -17.4 84.35171 0.8 -4.5 84.48087 -18.4 -16.7 83.63468 -12.4 -13.1 84.35372 4.2 4.6 84.48277 -15.5 -14.4 83.63725 -14.7 -10.8 84.35721 3.1 2.1 84.48698 -7.3 -8.0 83.63935 -13.0 -14.6 84.35996 5.8 0.7 84.48915 -4.1 -7.5 83.64196 -9.6 -8.1 84.36212 -4.1 -5.3 84.49104 -2.2 -3.6 83.64477 -10.7 -9.6 84.36453 -1.7 -6.1 84.49355 0.3 -1.9 83.64715 -7.6 -8.7 84.36812 -2.7 84.49599 0.0 -5.6 83.65015 -5.6 -8.3 84.37065 -1.5 -4.5 84.49847 3.0 -4.5 83.65302 -6.3 -5.8 84.37362 -9.0 -8.6 84.50129 4.4 -2.1 83.65519 -2.4 -3.6 84.37558 -5.3 -3.8 84.50400 5.6 1.0 83.65750 -6.1 -10.1 84.37844 -18.2 -14.0 84.50807 4.3 -1.4 83.65962 -3.9 -7.9 84.38151 -22.3 -17.5 84.51038 2.3 -1.4 83.66262 -7.8 -8.0 84.38380 -15.8 -13.0 84.51311 -1.7 -3.9 83.66580 -8.2 -8.4 84.38572 -13.0 -13.6 84.51535 -3.7 -5.2 83.66864 -9.8 -14.0 84.38964 -24.0 -17.3 84.51786 -2.9 -4.4 83.67107 -7.2 -10.3 84.39270 -21.7 -13.0 84.52023 -6.6 -6.4 83.67316 -8.4 -8.9 84.39489 -25.1 -20.1 84.52392 -10.1 -13.6 83.67627 -15.4 -18.4 84.39855 -25.0 -21.4 84.52673 -15.2 -14.0 83.67861 -9.8 -13.2 84.40144 -21.6 -18.9 84.52894 -14.0 -13.1 83.68232 -16.9 84.40466 -18.7 -17.6 84.53290 -18.1 -17.1 83.68529 -16.5 -16.1 84.40825 -11.5 -6.8 84.53587 -19.4 -18.0 83.68777 -17.9 -15.2 84.41042 -14.1 -12.2 84.53856 -19.8 -18.1 83.68979 -21.4 -15.1 84.41329 -9.3 -6.6 84.54407 -22.2 -17.7 83.69405 -17.7 -15.0 84.41553 -3.3 -2.9 84.54664 -25.2 -17.1 83.69644 -20.7 -17.9 84.41762 -1.6 0.2 84.54915 -21.0 -16.2 M. Breger et al. 31

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 84.55166 -17.5 -16.9 84.68631 -19.6 -17.3 85.06666 -3.9 84.55533 -9.6 -12.5 84.68711 -14.8 85.06904 -10.9 84.55809 -9.3 -11.3 84.68793 -12.8 -17.5 85.07319 -13.5 84.56061 -7.4 -9.6 84.69014 -8.8 85.07526 -4.9 84.56326 -2.3 -7.5 84.69058 -14.2 85.07941 -10.9 84.56685 3.6 -4.0 84.69293 -7.7 85.08173 -14.3 84.56977 2.8 -2.1 84.69406 -14.4 85.08564 -8.5 84.57251 2.8 2.7 84.69547 -15.0 -14.1 85.08777 -8.3 84.57530 0.4 -5.5 84.69550 -13.1 -17.1 85.09137 -1.2 84.57912 6.1 0.0 84.69753 -13.5 85.09363 -4.4 84.58225 3.1 -2.3 84.69811 -12.0 -8.4 85.09937 -11.2 84.58489 2.4 -1.0 84.70074 -6.1 -5.5 85.10175 -10.6 84.58871 4.5 1.9 84.70100 -10.8 85.10560 -1.4 84.59178 0.8 1.2 84.70355 -7.7 -11.7 85.10767 -0.5 84.59439 -3.3 -5.3 84.70447 -10.8 85.11115 -5.3 84.59822 -6.0 -13.9 84.70654 -9.9 -9.9 85.11652 -3.4 84.60068 -10.4 -13.2 84.70771 -9.3 85.11835 -12.6 84.60309 -12.6 -16.0 84.70841 -4.9 -13.6 85.12616 -8.7 84.60664 -15.8 -15.3 84.71104 -0.5 -5.7 85.13050 -14.4 84.60998 -18.7 -18.9 84.71355 -6.9 -5.4 85.13251 -8.1 84.61242 -15.8 -18.4 84.71357 -5.7 -10.2 85.13575 -13.2 84.61620 -12.1 -19.0 84.71454 -6.6 85.13788 -21.2 84.61865 -17.3 -18.0 84.71801 -6.5 85.14124 -12.9 84.62113 -16.4 -15.1 84.72046 -5.4 -4.3 85.14350 -9.6 84.62458 -11.5 -15.9 84.72755 -6.4 -4.0 85.14679 -15.8 84.62717 -12.7 -12.8 84.73472 -7.4 -6.8 85.14881 -4.3 84.63024 -7.9 -13.0 84.74208 -10.0 -8.2 85.15217 -10.1 84.63373 -0.3 -7.4 84.74867 -12.0 -15.3 85.15387 -20.3 84.63631 -4.1 -7.0 84.75655 -16.8 -16.6 85.15833 -5.2 84.63901 -2.8 -7.6 84.84933 -12.8 -15.4 85.16077 -1.1 84.64637 5.9 -1.2 84.85547 -14.6 -13.2 85.16407 -15.4 84.65632 -6.7 84.86181 -10.7 -11.8 85.16602 -1.6 84.65660 -1.8 -3.8 84.86799 -9.2 -7.6 85.16938 -4.0 84.65923 -2.8 -4.7 84.87447 -6.1 -5.9 85.17133 5.7 84.65980 -7.8 84.88252 -4.9 -7.2 85.17475 6.2 84.66275 1.0 -4.8 84.88855 -4.0 -7.4 85.17658 3.1 84.66327 -8.9 84.89512 -7.4 -5.0 85.17969 2.3 84.66533 -8.5 -12.1 84.90141 -8.3 -4.9 85.18177 0.2 84.66639 -8.9 84.90783 -13.5 -8.3 85.18494 -1.8 84.66786 -5.8 -11.8 84.91429 -14.1 -13.5 85.18720 -5.5 84.67203 -2.8 -9.2 84.92019 -17.5 -15.6 85.19031 -6.1 84.67322 -12.2 84.93795 -13.5 -14.9 85.19239 -5.8 84.67473 -10.2 -14.5 84.94487 -9.0 -9.5 85.19556 -13.9 84.67584 -14.9 84.95128 -7.0 -4.9 85.19751 -18.1 84.67670 -15.7 84.95805 -5.0 -4.1 85.20215 -22.2 84.67761 -14.1 -17.5 84.96480 -6.7 -6.9 85.20411 -9.3 84.68017 -15.8 84.97154 -6.6 -3.2 85.20752 -18.2 84.68032 -11.4 -13.6 84.97832 -5.4 -5.2 85.20966 -20.0 84.68310 -17.2 -17.0 84.98491 -10.1 -3.5 85.21296 -15.4 84.68364 -14.6 84.99092 -11.0 -7.8 85.21497 -11.5 32 1994 multisite photometry of the δ Scuti star θ2 Tau

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 85.21869 -20.4 85.74389 -14.0 -15.9 86.74334 -12.9 -13.6 85.22156 -16.4 85.74946 -13.1 -13.3 86.74889 -10.6 -15.6 85.22480 -14.7 85.75555 -10.4 -8.7 86.75447 -12.5 -13.3 85.22663 -5.1 85.76136 -8.5 -9.2 86.76055 -9.3 -13.3 85.22980 -10.0 85.76709 -6.5 -8.9 86.76665 -8.8 -6.6 85.23145 -16.5 85.78848 -12.4 -14.8 86.77223 -7.4 -6.0 85.23426 2.4 85.79483 -9.3 -11.9 86.77766 -7.7 -9.7 85.23633 -0.6 85.80442 -14.6 -11.8 86.78336 -6.9 -12.6 85.23963 -1.3 85.81032 -12.0 -15.5 86.78399 -7.5 85.24146 0.9 85.81604 -11.4 -16.6 86.78874 -9.5 85.24445 4.7 85.82209 -8.6 -12.6 86.78884 -9.9 -11.5 85.24616 -4.3 85.82838 -7.7 -6.6 86.79443 -9.5 -15.1 85.24927 3.1 85.83909 -8.9 -9.1 86.79846 -9.9 85.25116 -1.9 85.84493 -11.6 -7.1 86.80009 -12.1 -13.6 85.25489 3.8 85.85136 -13.0 -15.7 86.80332 -13.6 85.25654 6.5 85.85756 -14.0 -12.3 86.80620 -14.1 -8.4 85.26008 0.2 85.86341 -15.1 -17.2 86.80772 -16.7 85.26612 -12.0 85.87003 -15.4 -12.9 86.81166 -15.3 -13.8 85.26771 -8.0 85.87608 -13.0 -16.3 86.81235 -15.3 85.27240 -14.7 85.88179 -9.7 -13.6 86.81675 -16.3 85.27820 -12.3 85.88857 -8.7 -11.1 86.81699 -13.8 -16.9 85.28132 -26.6 85.89509 -5.0 -7.2 86.82161 -18.3 85.28284 -24.1 85.90106 -3.3 -4.0 86.82248 -13.6 -12.4 85.28577 -29.8 85.90778 -3.2 -2.2 86.82601 -10.9 85.28730 -16.6 85.91439 -7.2 -6.7 86.82794 -10.3 -14.4 85.29572 -11.8 85.93461 -16.2 -19.6 86.83363 -13.9 -13.3 85.29743 -28.2 85.94084 -16.0 -15.4 86.84101 -9.3 -8.3 85.30567 -7.1 85.94688 -17.4 -18.4 86.84163 -5.8 85.30719 -1.0 85.95389 -17.4 -18.2 86.84641 -6.2 -4.5 85.31104 -5.4 85.95998 -7.4 -14.8 86.84649 -6.0 85.31562 -4.2 85.96624 -8.0 -7.9 86.85089 -7.1 85.31733 5.6 85.97263 -7.3 -0.3 86.85575 0.0 85.32203 10.0 85.97891 -0.5 5.5 86.86501 -8.5 85.32520 -0.3 85.98543 -2.4 86.87011 -8.5 85.32679 11.1 85.99176 -1.0 86.87292 -13.2 -13.4 85.33136 9.5 86.64481 -11.1 86.87856 -13.9 -17.6 85.65391 -21.5 86.65133 -10.7 -11.3 86.87971 -16.9 85.66289 -20.2 -25.2 86.65865 -14.7 -12.4 86.88402 -17.8 -20.0 85.67053 -16.4 -20.0 86.66517 -9.8 -8.4 86.88446 -18.9 85.67669 -12.5 -14.7 86.67207 -10.8 -4.6 86.88937 -18.8 -21.4 85.68324 -3.4 -4.1 86.67865 -8.9 -7.1 86.88967 -16.5 85.68966 -0.7 0.9 86.68440 -8.2 -7.8 86.89418 -17.9 85.69577 -2.4 1.7 86.69105 -11.5 -8.8 86.89534 -18.3 -20.3 85.70210 -5.4 -0.9 86.69851 -10.4 -7.9 86.89858 -17.4 85.70822 -3.8 -7.3 86.70435 -11.3 -9.5 86.90130 -15.3 -11.7 85.71402 -8.9 -9.0 86.71015 -12.3 -13.3 86.90344 -11.7 85.72011 -11.0 -12.8 86.72010 -11.1 -10.1 86.90715 -10.5 -9.1 85.72616 -15.3 -15.1 86.72587 -13.1 -12.0 86.90830 -10.9 85.73207 -14.2 -15.3 86.73160 -13.6 -12.8 86.91339 -9.2 85.73810 -14.1 -16.6 86.73724 -12.9 -12.9 86.91396 -9.1 -6.9 M. Breger et al. 33

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 86.91779 -5.7 87.86698 -15.9 89.02298 0.2 86.91992 -3.6 -6.1 87.87115 -15.5 89.02499 -7.4 86.92265 -5.4 87.87554 -13.8 89.02865 -4.3 86.92540 -0.1 5.0 87.87994 -14.8 89.03414 -4.2 86.92728 0.4 87.88480 -13.2 89.03591 2.8 86.93120 -3.6 -1.0 87.88897 -5.8 89.03921 -0.7 86.93214 -5.8 87.89360 -8.1 89.04116 10.4 86.93674 -3.9 -4.0 87.89777 -5.6 89.04623 1.1 86.93700 -1.2 87.90448 -4.5 89.04830 3.8 86.94210 -7.4 87.91119 -3.3 89.05276 -10.4 86.94297 -8.6 -6.4 87.91748 -6.1 89.05471 -15.6 86.94719 -5.4 87.92392 -9.5 89.05813 -17.2 86.94870 -11.8 -8.6 87.92832 -8.3 89.06021 -25.4 86.95205 -15.5 87.93249 -15.6 89.06344 -27.6 86.95453 -15.5 -16.6 87.93781 -18.6 89.06570 -23.3 86.95645 -20.5 87.94198 -18.4 89.07083 -22.2 86.96041 -18.2 -20.4 87.94661 -16.8 89.07260 -24.0 86.96177 -20.6 87.95101 -15.5 89.07565 -29.6 86.96604 -19.6 -19.7 87.95564 -11.9 89.07742 -28.4 86.96652 -22.3 87.96038 -9.7 89.08059 -27.8 86.97173 -19.1 87.96548 -10.3 89.08230 -19.6 86.97186 -16.2 -25.1 87.97034 -8.2 89.08566 -12.1 86.97636 -16.6 88.24545 -16.7 89.08755 -14.7 86.97802 -16.8 -22.2 88.25497 -10.4 89.09042 -8.5 86.98398 -18.0 -12.9 88.25839 -13.3 89.09219 -10.4 86.98983 -9.1 -1.7 88.26028 -11.8 89.09573 -11.2 86.99605 -8.8 2.1 88.26382 -11.0 89.09787 1.8 87.76559 -13.4 88.26950 -12.0 89.10134 2.6 87.77022 -12.0 88.27694 -11.9 89.10330 5.2 87.77508 -11.7 88.28073 -12.6 89.10653 -2.3 87.77948 -13.5 88.92361 -22.9 89.10836 2.4 87.78411 -14.5 88.92569 -21.8 89.11392 3.8 87.78828 -13.8 88.92870 -19.3 89.11734 0.3 87.79291 -13.0 88.93148 -16.7 89.11911 1.6 87.79703 -10.5 88.93449 -12.5 89.12252 -10.7 87.80147 -1.4 88.93726 -6.1 89.12429 -12.7 87.80564 -6.1 88.95127 -0.8 89.12857 -4.8 87.81004 -9.7 88.95428 -2.4 89.13034 -5.8 87.81443 -3.8 88.95729 1.4 89.13357 -16.4 87.81883 -7.0 88.96041 -1.9 89.13565 -7.2 87.82300 -6.9 88.96342 1.0 89.13888 -11.2 87.82763 -10.4 88.96620 -0.2 89.14065 -17.5 87.83179 -8.7 88.98812 -16.5 89.14498 -16.6 87.83642 -6.8 88.98904 -25.7 89.14736 -22.5 87.84082 -6.5 88.99154 -25.1 89.15078 -27.6 87.84545 -6.3 89.00155 -29.3 89.15280 -22.9 87.84985 -2.5 89.00625 -27.0 89.16427 -11.6 87.85402 -13.6 89.00845 -25.1 89.16738 -16.1 87.85842 -11.9 89.01205 -12.3 89.17147 -15.6 87.86258 -16.7 89.01950 -8.1 89.17410 -5.8 34 1994 multisite photometry of the δ Scuti star θ2 Tau

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 89.17825 -6.6 89.85225 -8.0 90.50311 -6.9 -6.2 89.18112 -6.8 89.85642 -4.5 90.50652 -6.3 -5.7 89.18716 -3.5 89.86082 -2.8 90.50861 -4.1 -3.6 89.18966 4.1 89.86498 -9.4 90.51094 -3.7 89.19387 -1.7 89.86961 -12.4 90.51452 -8.6 89.19668 -0.7 89.87378 -13.0 90.51663 -8.3 -10.3 89.20047 -4.2 89.87841 -7.7 90.51901 -10.2 -9.9 89.20303 -1.2 89.88258 -12.6 90.52262 -13.3 -13.9 89.20712 -13.7 89.88721 -17.8 90.52555 -14.1 -13.0 89.20944 -14.7 89.89160 -20.9 90.52834 -14.0 -12.4 89.21389 -18.8 89.89693 -18.6 90.53173 -12.3 -12.8 89.21633 -17.6 89.90109 -13.7 90.53514 -16.7 -16.2 89.22006 -23.2 89.90549 -13.6 90.53744 -18.6 -15.5 89.22256 -22.6 89.90966 -12.2 90.54093 -19.7 -17.4 89.22683 -19.2 89.91417 -9.9 90.54342 -21.1 -17.5 89.22933 -15.4 89.91846 -8.5 90.55871 -11.2 89.23355 -8.5 89.92309 -8.7 90.56189 -10.9 89.23593 -12.6 90.00064 -5.6 90.56452 -7.9 89.24069 -12.0 90.00253 -4.6 90.57661 -6.0 89.24313 -11.2 90.00692 -0.6 90.57880 -1.1 89.24685 -16.9 90.00875 -8.8 90.58232 -0.5 -5.1 89.24905 -6.3 90.01596 -5.1 90.58531 -4.3 -4.7 89.25271 -5.0 90.01779 -15.9 90.58752 -4.6 -5.8 89.25497 -5.6 90.02883 -22.8 90.58971 -1.9 -6.2 89.26876 -3.6 90.43075 -13.0 -12.0 90.59198 -4.4 -5.2 89.27127 -6.2 90.43450 -10.9 -7.1 90.59560 -9.0 -5.5 89.27578 -7.9 90.43795 -13.2 -12.3 90.59817 -10.8 -11.6 89.27804 -15.1 90.44065 -8.1 -6.5 90.60044 -12.6 -13.2 89.28128 -11.6 90.44329 -10.6 -10.0 90.60297 -13.2 -10.2 89.28366 -6.3 90.44570 -7.9 -8.3 90.60511 -10.0 -7.7 89.28726 -13.4 90.44795 -4.5 -6.6 90.60827 -15.3 -11.0 89.28921 -13.1 90.45107 -7.7 -6.9 90.61074 -17.6 -16.6 89.29275 -24.6 90.45434 -9.4 -4.8 90.61432 -18.7 -15.2 89.30130 -11.3 90.45681 -10.7 -10.0 90.61825 -20.9 -17.4 89.30514 -11.6 90.45927 -11.3 -10.1 90.62059 -24.0 -19.2 89.30728 -16.3 90.46170 -11.9 -9.2 90.62694 -17.1 -12.7 89.31124 -18.7 90.46395 -9.1 -10.5 90.62933 -19.3 -13.8 89.31839 -14.4 90.46758 -11.7 -12.4 90.63295 -11.9 -8.4 89.32064 -5.8 90.47058 -11.3 -13.1 90.63675 -10.0 -9.7 89.32821 -6.6 90.47321 -10.8 -9.0 90.63979 -10.2 -10.6 89.33029 -11.8 90.47614 -10.1 -8.7 90.64239 -4.8 -5.3 89.33578 -4.6 90.47894 -11.3 -13.6 90.64705 -3.9 -4.4 89.33773 -1.4 90.48289 -10.0 -9.1 90.64940 -1.8 89.82123 -16.3 90.48523 -11.6 -9.4 90.65208 1.1 89.82540 -12.7 90.48781 -11.0 -9.5 90.65552 3.0 89.83003 -15.8 90.49115 -9.3 -10.0 90.65824 -1.4 -4.4 89.83443 -7.0 90.49329 -9.8 -8.6 90.66156 -5.4 -6.3 89.83906 -8.4 90.49564 -9.8 -5.3 90.66611 -6.1 -7.2 89.84346 -5.2 90.49886 -8.5 -7.8 90.66844 -5.2 -6.3 89.84762 -4.3 90.50099 -4.1 -5.5 90.67095 -9.1 -9.3 M. Breger et al. 35

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 90.67424 -10.0 -8.5 91.17433 -13.3 91.62399 -8.2 90.67682 -14.1 -12.3 91.17794 -10.8 91.64099 -23.1 90.67900 -16.6 91.17989 -15.7 91.64562 -21.5 90.68247 -19.3 -14.1 91.18361 -14.6 91.64956 -25.2 90.68472 -20.6 -18.4 91.18581 -13.2 91.65395 -22.9 90.68723 -22.5 -18.4 91.19063 -14.5 91.65816 -12.8 90.68954 -20.3 91.19252 -9.3 91.66275 -9.8 90.69283 -19.6 91.19594 -9.4 91.66692 -7.2 90.69643 -20.4 91.19795 -11.8 91.67131 0.9 91.01985 -17.8 91.20259 -10.6 91.67618 0.5 91.02730 -14.8 91.20436 -6.2 91.68011 7.2 91.03127 -12.6 91.20845 -7.0 91.68451 7.4 91.03353 -11.1 91.21041 -4.9 91.68879 6.6 91.03768 -10.4 91.21376 -6.7 91.69307 0.5 91.04366 -13.5 91.21572 -4.9 91.69747 -3.7 91.04732 -14.5 91.22072 -8.1 92.30385 -17.3 -15.5 91.05300 -15.0 91.22316 -11.0 92.30719 -20.8 -17.5 91.05696 -10.9 91.22646 -12.7 92.30951 -20.6 -15.0 91.06771 -11.8 91.22896 -10.1 92.31147 -18.2 -16.3 91.06996 -10.9 91.23281 -10.9 92.31359 -9.8 -8.2 91.07332 -13.5 91.23494 -15.1 92.31651 -14.2 -12.3 91.07765 -20.0 91.23989 -13.2 92.31861 -14.3 -13.5 91.08126 -18.9 91.24575 -17.4 92.32052 -15.9 -13.4 91.08406 -17.4 91.24892 -11.7 92.32273 -8.4 -9.9 91.08815 -20.2 91.25118 -10.0 92.32496 -8.0 -8.7 91.09023 -20.3 91.25698 -8.1 92.32711 -8.7 -10.9 91.09371 -13.0 91.26064 -15.1 92.33072 -2.1 -6.0 91.09664 -21.0 91.26259 -9.0 92.33296 -2.9 -6.4 91.09987 -21.4 91.26564 -12.1 92.33518 -4.7 -6.5 91.10201 -22.5 91.26802 -17.1 92.33793 -5.5 -6.5 91.10640 -13.2 91.27437 -10.8 92.34018 -0.4 -1.3 91.10927 -17.8 91.27834 -16.1 92.34354 1.2 -1.3 91.11269 -12.3 91.28005 -12.4 92.34579 0.7 -2.9 91.11470 -15.1 91.29262 -11.4 92.34799 -2.9 -5.5 91.11806 -13.8 91.29494 -13.9 92.35024 -1.9 -3.8 91.11995 -9.5 91.29854 -12.2 92.35254 -2.5 -8.5 91.12526 -7.0 91.30074 -12.8 92.35472 -1.8 -7.7 91.12740 -8.4 91.30544 -11.8 92.35804 -5.5 -4.7 91.13344 -3.1 91.31380 -17.5 92.36045 -5.9 -2.3 91.13973 -5.6 91.31752 -11.8 92.36317 -9.0 -7.0 91.14241 -11.5 91.31972 -15.8 92.36600 -9.5 -9.9 91.14650 -7.0 91.32509 -7.2 92.36811 -15.3 -10.9 91.14907 -11.8 91.32723 -11.7 92.37144 -12.8 -14.2 91.15261 -15.9 91.59475 -5.0 92.37363 -12.3 -12.1 91.15474 -9.9 91.59788 0.1 92.37587 -17.0 -12.3 91.15859 -15.6 91.60083 2.2 92.37846 -18.4 -14.1 91.16078 -11.8 91.60401 4.8 92.38103 -20.2 -14.6 91.16432 -19.0 91.60702 5.5 92.38496 -17.2 -16.7 91.16768 -15.1 91.61003 5.8 92.38740 -22.8 -15.2 91.17177 -14.8 91.61281 7.2 92.38979 -24.0 -19.1 36 1994 multisite photometry of the δ Scuti star θ2 Tau

HJD ∆v ∆y HJD ∆v ∆y HJD ∆v ∆y 244 9600+ mmag mmag 244 9600+ mmag mmag 244 9600+ mmag mmag 92.39214 -24.3 -17.0 92.42427 0.8 -3.4 92.45946 -16.7 -15.5 92.39511 -18.7 -15.7 92.42754 0.7 -2.3 92.46164 -20.1 -15.5 92.39895 -16.7 -11.0 92.43148 2.2 -0.3 92.46481 -21.0 -17.9 92.40208 -15.9 -12.1 92.43772 8.6 1.4 92.46753 -20.9 -16.8 92.40473 -14.6 -13.3 92.44074 -4.2 -9.7 92.47043 -21.2 -22.3 92.40897 -10.5 -11.0 92.44431 -6.0 -7.3 92.47377 -22.7 -22.6 92.41199 -7.1 -7.2 92.44754 -7.6 -6.9 92.47751 -18.8 -18.3 92.41509 -5.9 -4.7 92.44990 -8.4 -8.7 92.48003 -20.7 -16.1 92.41900 -4.9 -5.9 92.45209 -10.3 -8.3 92.48363 -16.3 -11.4 92.42209 -1.1 -4.4 92.45549 -14.5 -12.1 Comm. in Asteroseismology Vol. 142, 2002

Solar-like oscillations in δ Scuti stars†

R. Samadi1,2, M.-J. Goupil2, G. Houdek3

1 Astronomy Unit, Queen Mary, University of London, London E14NS, UK 2 Observatoire de Paris, LESIA, CNRS FRE 2461, 92195 Meudon, France 3 Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK

Abstract

Model computations of δ Scuti stars, located in the vicinity of the red edge of the classical instability strip, suggest amplitudes of solar-like oscillations larger than in cooler models located outside the instability strip. Solar-like amplitudes in our δ Scuti models are found to be large enough to be detectable with ground-based instruments provided they can be distinguished from the opacity- driven large-amplitude pulsations. We anticipate their possible detection in the context of the planned asteroseismic space missions, such as the French mission COROT (COnvection ROtation and planetary Transits). We propose known δ Scuti stars as potential candidates for the target selection of these upcoming space missions.

Introduction

The δ Scuti stars are in general main sequence stars with masses between 1.5 M¯ and 2.5 M¯. They are located inside the classical instability strip (IS hereafter) where the κ-mechanism drives low-order radial and nonradial modes of low degree to measurable amplitudes (opacity-driven unstable modes). Only a small number of opacity-driven modes are observed in δ Scuti stars (for a review see e.g. Gautschy & Saio 1996), but their amplitudes, which are limited by nonlinear processes, are much larger than stochastically driven intrinsically stable solar-like p modes. For main-sequence stars with surface convection zones, located outside the IS, model computations suggest all modes to be intrinsically stable but excited

†This article is an abridged version of a paper with the same title published first in A&A (2002). 38 Solar-like oscillations in δ Scuti stars stochastically by turbulent convection; for models located near the red edge of the IS the predicted velocity amplitudes become as large as 15 times the solar value (Houdek et al. 1999). Moreover, these computations suggest that models located inside the IS can pulsate simultaneously with modes excited both by the κ-mechanism and by the turbulent velocity field. Although it is possible from Fig. (13) of Houdek et al. (1999) to conclude that both types of modes can be excited simultaneously in the same star, amplitudes of stochastically excited modes for stars located inside the instability strip were not explicitly carried out by Houdek et al. (1999) and their possible detection were not addressed. The aim of this paper is to demonstrate that models of stars, located inside the IS and near the red edge, can exhibit both opacity driven modes and solar- like oscillations with sufficiently large amplitudes to be detectable with today’s ground-based instruments. Consequently the planned asteroseismology space missions, such as COROT (COnvection ROtation and planetary Transits, Baglin & The Corot Team 1998) or Eddington (Favata et al. 2000), will detect these oscillations even more easily.

The stellar models

Equilibrium envelope models are computed in the manner of Houdek et al. (1999) using the nonlocal formulation for convection by Gough (1976, 1977, hereafter G’MLT). Integration starts at an optical depth of τ = 10−4 and ends at a radius fraction 0.2. Radiation is treated in the Eddington approximation and the atmosphere is assumed to be gray and plane parallel. In G’MLT formulation two more parameters, a and b, are introduced which control the spatial coher- ence of the ensemble of eddies contributing to the total heat and momentum fluxes (a), and the degree to which the turbulent fluxes are coupled to the local stratification (b). In this paper we choose a2 = 900 and b2 = 2000 in order to obtain stable modes in the frequency range in which the damping rates exhibit a local minimum. The mixing-length parameter α has been calibrated to a solar model to obtain the helioseismically inferred depth of the convection zone of 0.287 of the solar radius (Christensen-Dalsgaard, Gough & Thompson 1991). All models assume solar chemical composition and have mass M = 1.68 M¯ and luminosity L = 11.3 L¯, but differ in effective temperature Teff , and whether or not acoustic radiation is included in the equilibrium computations. Table 1 lists the fundamental stellar parameters of these models. The models A1, A2 , B1 and B2 are hotter than model C and are located inside the IS and close to the red edge. Models A1 and A2 differ from models B1 and R. Samadi, M.-J. Goupil and G. Houdek 39

Table 1: Stellar parameters for the envelope models A1, A2, B1, B2 and C; R is the stellar radius at the photosphere (T = Teﬀ ), and νc is the acoustic cut-oﬀ frequency.

Model Teﬀ (b − y)0 R νc acoustic [K] [R¯] [mHz] radiation A1 , A2 6839 0.235 2.40 1.4 included B1 , B2 6839 0.235 2.40 1.4 neglected C 6650 0.262 2.54 1.3 neglected

Table 2: Acoustic emissivity coeﬃcient Λ and Mach-number dependence Γ assumed in the acoustic radiation model for the stellar models A1 and A2. Model Λ Γ A1 100 5 A2 2000 7.5

B2 by the inclusion of acoustic radiation by turbulence in the envelope cal- culations (Houdek & Gough 1998). In this model for acoustic radiation in the equilibrium model two more parameters are introduced (Houdek & Gough, 1998): the emissivity coefficient Λ and the parameter Γ which describes the power-law dependence of the acoustic power emission on the turbulent Mach number. A Mach-number dependence of Γ = 5 assumes that acoustic emission is dominated by the energy-bearing eddies ; if acoustic emission is predominantly emitted by inertial-range eddies Γ has the value 7.5. Table 2 lists the values of Λ and Γ that are assumed in the models A1 and A2. The values for Λ provide for a solar model a similar value for the acoustic flux Fac as the estimates of Stein (1968) and Musielak et al. (1994). For all the models, except for model B2, we assume for the mixing-length parameter the calibrated solar value α = 2.037; for model B2 the value α = 1.5 is assumed. Fig. 1 displays the locations of these models in the colour-magnitude diagram. Evolutionary tracks (dashed curves) are shown for models with various masses and are obtained with the CESAM code by Morel (1997) as described by Samadi et al. (2001a). The transformation from luminosity, effective temperature and surface gravity to absolute magnitude Mv and dereddened colour indices (b − y)o are obtained from the Basel Stellar Library (Lejeune, Cuisinier & Buser, 1998). The blue and red edges of the fundamental radial modes (solid curves) are calculated in the manner of Houdek et al. (1999). The positions of the observed δ Scuti stars (filled circles) are taken from Rodriguez et al. (2000): 40 Solar-like oscillations in δ Scuti stars

Figure 1: Colour-magnitude diagram: ﬁlled circles display the positions of observed δ Scuti stars from the Rodriguez et al. (2000) catalogue. Squares indicate the positions of the models A1, A2, B1 ,B2 and C (see Tab. 1). Dashed curves show evolutionary tracks for models with masses 1.5 M¯, 1.7 M¯ and 1.8 M¯. Solid curves display theoretical locations of the blue and red edges for the fundamental radial modes according to Houdek et al. (1999). Numbers associated with the symbols indicate apparent magnitudes V for selected observed δ Scuti stars.

absolute magnitudes, derived from Hipparcos distances and dereddened colour indices were kindly supplied by E. Rodr´iguez (2001, personal communication; see Rodriguez & Breger 2001, for details). R. Samadi, M.-J. Goupil and G. Houdek 41

Table 3: Frequency ν, damping/growth rate η and stability coeﬃcient ωi/ωr for all overstable radial p modes predicted for the models A1, A2 and B2.

Model n ν η ωi/ωr [µHz] [nHz] ×10−6 1 123 -0.03 0.25 A1 2 161 -0.31 1.92 3 202 -4.14 20.48 4 244 -3.90 15.97 1 124 -0.04 0.36 A2 2 162 -0.40 2.47 3 203 -1.27 6.25 1 124 -0.04 0.34 B2 2 161 -0.31 1.95 3 203 -0.83 4.09

Stability analysis

The stability computations are as described in Houdek (2000, and references therein). In particular they include the Lagrangian perturbations of the turbulent fluxes (heat and momentum) according to Gough’s (1976, 1977) nonlocal time-dependent formulation. Assuming a temporal dependence, exp(−iωt), for the pulsations, the complex eigenfrequencies of the modes can be written as ω = ωr + iωi, which defines the cyclic pulsation frequency ν = ωr/2π and the damping/growth rate η = −ωi/2π. The outer boundary conditions are applied at the temperature minimum, the mechanical boundary condition being consistent with a perfectly reflecting surface; at the base of the envelope, conditions of adiabaticity and vanishing displacement are imposed. In this paper only radial p modes are considered. For model C all the modes are found to be linearly stable (i.e., η > 0) as is expected for models lying well outside the IS. This is also found for the hotter model B1. For the model A1 (resp. A2) the first four (resp. three) radial modes, n=1,...,4 (resp. n=1,2,3), are found to be overstable. With the inclusion of a model for the acoustic radiation in the equilibrium structure the efficacy with which convection transports the turbulent fluxes is decreased (see Houdek & Gough 1998). This leads to a decrease in the turbulent Mach number and to a consequent reduction of the stabilizing influence of the perturbed momentum flux on the mode damping. The driving eventually dominates over the damping leading to overstable modes. Reducing α has a similar effect on mode stability 42 Solar-like oscillations in δ Scuti stars than the inclusion of acoustic radiation in the equilibrium model (see Houdek & Gough 1998, Michel et al. 1999, Houdek 2000). The model B2 was computed with the smaller mixing-length parameter α = 1.5, leading to overstable modes with radial orders n =1,2,3. Table 3 displays the frequency ν and damping/growth rate η for all overstable radial modes (η < 0) found in the models A1, A2 and B2.

Excitation rate and amplitude spectrum

Amplitudes of solar-like oscillations result from the balance between damping and stochastic driving by turbulence. The rate at which the turbulence injects energy into the p modes is estimated in the manner of Samadi & Goupil (2001, Paper I hereafter). The rms value of the mode surface velocity, vs, is related to the damping rate, η, and to the rate at which energy is injected into the mode (excitation rate), P , by P v2 = ξ2(r ) , (1) s r s 2 η I where ξr is the radial displacement eigenfunction, rs is the radius at which the surface velocities are measured and which we assume to be 200 km above Teﬀ , and I is the mode inertia. The rate of energy injected into a mode is computed according to Paper I and is proportional to

M dξ 2 P (ω) ∝ ρ w3 `4 r S(ω, m) dm , (2) Z0 µ dr ¶ where ρ is the density, ` is the mixing length, and w is the vertical component of the rms velocity of the convective elements. The function S(ω, m) describes approximately contributions from eddies with diﬀerent sizes to the excitation rate P . Detailed expressions for S(ω, m) were given in Paper I. Results for the estimated excitation rate P are depicted in the upper panel of Fig. 2. For the models A1, A2 and B1 the excitation rate P is about one magnitude larger than for model C. This is a result of the larger convective velocities in the superadiabatic boundary layers of the models A1, A2 and B1, which are all hotter than model C. For the models A2 and B2 the eﬃcacy of convection has been reduced severely by either including acoustic radiation in the equilibrium model (A2) or by reducing the mixing-length parameter α to a value much smaller than the calibrated value for a solar model (B2). This results in shallower superadiabatic regions and in larger superadiabatic temperature gradients; pulsation modes in A2 and B2 are therefore predominantly excited at the very top of the convection zone, whereas in the models A1 and B1 the modes are excited over a larger driving region. R. Samadi, M.-J. Goupil and G. Houdek 43

Figure 2: Excitation rate P (upper panel) and estimated velocity amplitudes (lower panel) as a function of frequency for all stellar models. 44 Solar-like oscillations in δ Scuti stars

Table 4: Maximum values of the estimated velocity, vs, and luminosity, δL/L, amplitudes.

Model vs δL/L [ ms−1] [ppm] A2 8.6 150 A1 7.9 97 B1 4.9 101 B2 5.5 98 C 2.0 84

In the lower panel of Fig. 2 the surface velocity amplitudes vs are depicted for all stellar models, computed according to Eq.(1). In the models A1, A2, B1 and B2 the amplitudes of stochastically excited p modes are larger (∼ 5 − 9 ms−1) than in model C (∼ 2 ms−1). The velocity amplitudes are computed 200 km above the photosphere (T = Teﬀ ) and do increase by a factor of about two at the outermost meshpoint of the model, i.e. at an optical depth τ = 10−4. For estimating the luminosity amplitudes the full nonadiabatic luminosity eigenfunctions have to be used. The relative luminosity amplitudes, δL/L, are linearly related to the velocity amplitudes, i.e. they are proportional to the ratio of the luminosity eigenfunction over the displacement eigenfunction. This ratio is determined by the solution of the nonadiabatic pulsation equations and is independent of a stochastic excitation model (see Houdek et al. 1999). We predict a maximum value of the luminosity amplitude δL/L ∼ 97 ppm for model A1, δL/L ∼ 150 ppm for model A2, δL/L ∼ 101 ppm for model B1 , δL/L ∼ 98 ppm for model B2 and δL/L ∼ 84 ppm for model C. These results are summarized in Table 4.

Observational constraints for detecting solar-type oscillations

There have been recent reports on the possible detection of solar-type oscillations in α Cen (HD 128620) by Bouchy & Carrier (2001), in β Hydri (HD 2151) by Bedding et al. (2001) and in Procyon A (HD 61421) by Martic et al. (1999, see also Barban et al. 1999), who obtained spectroscopic surface velocity measurements of these bright stars (the apparent magnitude V = 2.80 for β Hydri, V = 0.34 for Procyon and V = −0.1 for α Cen) from the ground. The maximum values of the observed peak-velocity amplitudes are of the order ∼ 35 cms−1 for α Cen, ∼ 50 cms−1 for β Hydri and ∼ 50 cms−1 for Procyon. Current ground-based instruments are able to detect oscillations with velocity R. Samadi, M.-J. Goupil and G. Houdek 45 amplitudes of the order predicted for our models A1, A2 and B1, B2, but only for stars with an apparent magnitude V of less than ∼ 3 − 4 (Bouchy, personal communication). The HARPS (High-Accuracy Radial-velocity Planetary Search) project (Bouchy & Carrier 2001), for example, will be able to detect oscillations with our predicted velocity amplitudes for stars with an apparent magnitude smaller than ∼ 4 − 5. This detection threshold is still too small for detecting solar-type oscillations in currently known δ Scuti stars located near the red edge of the IS, particularly in view of the fact that most of the currently known δ Scuti stars are even fainter. For example, the apparent magnitudes of known δ Scuti stars located nearest to the red edge (see Fig. 1) are between V = 5.7 and V = 9.3. Future space missions with instruments dedicated to asteroseismology, however, will be able to detect solar-like oscillations in δ Scuti stars: the forthcoming space project COROT (Baglin & The Corot Team 1998), for example, will reach a noise level of 0.7 ppm (Auvergne & The Corot Team 2000) for a star with an apparent magnitude of V = 6, using photometric measurements. There- fore, in stars with similar magnitudes, COROT will be able to detect oscillation amplitudes as small as ∼ 3 ppm, a value which is similar to that measured in the Sun. The instrument on COROT will be limited by the photon noise only for stars with magnitudes larger than V ' 9: i.e., for a star with magnitude V ' 8 the detection threshold will be ∼ 5 ppm. This threshold is small enough to detect and measure many solar-like oscillations in δ Scuti stars which are similar to the δ Scuti models considered in this paper.

Conclusion

We studied oscillation properties in δ Scuti stars located near the observed red edge of the classical instability strip. Such stars can pulsate with both opacity-driven modes and intrinsically stable stochastically driven (solar-like) modes. The estimated velocity amplitudes of the stochastically driven modes in our δ Scuti models are found to be larger than in cooler and pulsationally stable models lying outside the IS. This result supports the idea that solar-like oscillations in δ Scuti stars may be detected. Including a model for the acoustic radiation in the equilibrium model results in a cooler red edge and does effect the properties of the excitation rate of p modes (see also Houdek & Gough 1998, Houdek 2000); in particular the pulsation amplitudes become larger and are predicted to be largest for a model with the largest acoustic flux Fac (i.e., model A2). Moreover, for the δ Scuti models considered in this paper, overstable modes were predicted only if either acoustic emission in the mean stratification was included or if the mixing-length parameter was reduced to a value smaller than suggested by a calibrated solar 46 Solar-like oscillations in δ Scuti stars model. A potential target star should neither be too cool (i.e., no opacity-driven modes) nor too hot (i.e., stochastically excited modes with amplitudes too small to be detectable). We quantify this with the illustrative case of our δ Scuti models with a mass M = 1.68 M¯ and we identify the following δ Scuti stars from the Rodriguez et al. (2000) catalogue, located near the red edge, as potential candidates for the target selection of upcoming observing campaigns: HD57167, HD14147, HD208999 and HD105513. Although the amplitudes of the solar-type oscillations, predicted in our δ Scuti models, are large enough to be detected from ground, today’s ground- based instruments will detect such oscillations only in brighter δ Scuti stars with an apparent magnitude of up to V ∼ 3 − 4 (Bouchy 2001, personal communication). However, new ground-based observing campaigns, such as the HARPS project (Bouchy & Carrier 2001) will be able to detect stochastically excited oscillations in δ Scuti stars with an apparent magnitude of up to V ∼ 4 − 5. Unfortunately, there are no such bright stars in the Rodriguez et al. (2000) catalogue which are located near the red edge, although some bright stars near the red edge may have opacity-driven modes with amplitudes too small to be detectable with today’s ground-based instruments and are therefore not classified as δ Scuti stars. The forthcoming space missions for asteroseismology, such as COROT and Eddington will be able to detect solar-like oscillations in faint δ Scuti stars. The large instrument on the Eddington spacecraft will measure stellar oscillations with amplitudes as small as 1.5 ppm in stars with an apparent magnitude of V ' 11 assuming an observing period of 30 days. Moreover, Eddington’s large field of view will allow it to monitor a large number of stars simultaneously. This will be helpful for detecting and classifying new δ Scuti stars and for measuring the location of the red edge of the IS with greater precision than it was possible before.

Acknowledgments. We thank E. Rodr´iguez for providing the δ Scuti data set in a convenient and immediate usable form, T. Lejeune for allowing us to use the Basel library and D. Cordier for providing it on the Internet. We thank A. Baglin for useful discussions on the COROT speciﬁcations, F. Bouchy for providing valuable information on the HARPS project and related experiments, and C. Catala and E. Michel for useful discussions on the possibilities of detecting new δ Scuti stars. We are grateful to Douglas Gough for very helpful discussions on stochastic mode excitation and to Mike Montgomery for improv- ing the English. GH and RS acknowledge support by the Particle Physics and Astronomy Research Council of the UK. RS’s work has been supported under the grant PPA/G/O/1998/00576. R. Samadi, M.-J. Goupil and G. Houdek 47

References

Auvergne, M. & The COROT Team. 2000, in The Third MONS Workshop : Science Preparation and Target Selection, eds. T.C. Teixeira, T. Bedding, (Aarhus University: Aarhus), p. 135 Baglin, A. & The Corot Team. 1998, in IAU Symp. 185: New Eyes to See Inside the Sun and Stars, eds. F.-L. Deubner, J. Christensen-Dalsgaard, & D.W. Kurtz, (Kluwer: Dordrecht), Vol. 185, p. 301 Barban, C., Michel, E., Martic, M., Schmitt, J., Lebrun, J. C., Baglin, A., & Bertaux, J. L. 1999, A&A 350, 617 Bedding, T. R., Butler, R., Kjeldsen, H., Baldry, I. K., O’Toole, S., Tinney, C., Marcy, G. W., Kienzle, F., & Carrier, F. 2001, ApJ 549, L105 Bouchy, F. & Carrier, F. 2001, A&A 374, L5 Christensen-Dalsgaard, J., Gough, D. O., & Thompson, M. J. 1991, ApJ 378, 413 Favata, F., Roxburgh, I., & Christensen-Dalsgaard, J. 2000, in The Third MONS Workshop : Science Preparation and Target Selection, eds. T.C. Teixeira, T. Bedding, (Aarhus University: Aarhus), p. 49 Gautschy, A. & Saio, H. 1996, ARA&A 34, 551 Gough, D. 1976, in Lecture notes in physics, Vol. 71, Problems of stellar convection, eds. E. Spiegel & J.-P. Zahn (Springer: Berlin), p. 15 Gough, D. O. 1977, ApJ 214, 196 Houdek, G. 2000, in Delta Scuti and Related Stars, ASP Conference Series, Vol. 210, eds. M. Breger & M.H. Montgomery, (ASP: San Francisco), p. 454 Houdek, G., Gough, D.O., 1998, in: Proc. SOHO 6/GONG 98 Workshop, Structure and dynamics of the interior of the Sun and Sun-like stars, eds. S.G. Korzennik & A. Wilson (ESTEC: Noordwijk), ESA SP-418, vol. 2, p. 479 Houdek, G., Balmforth, N. J., Christensen-Dalsgaard, J., & Gough, D. O. 1999, A&A 351, 582 Lejeune, T., Cuisinier, F., & Buser, R. 1998, A&AS 130, 65 Martic, M., Schmitt, J., Lebrun, J.-C., Barban, C., Connes, P., Bouchy, F., Michel, E., Baglin, A., Appourchaux, T., & Bertaux, J.-L. 1999, A&A 351, 993 Michel, E., Hernández, M.M., Houdek, G., Goupil, M.J., Lebreton, Y., Hernández, F.Pérez, Baglin, A., Belmonte, J.A., & Soufi, F., 1999, A&A 342, 153 Morel, P. 1997, A&AS 124, 597 Musielak, Z. E., Rosner, R., Stein, R. F., & Ulmschneider, P. 1994, ApJ 423, 474 Rodríguez, E. & Breger, M. 2001, A&A 366, 178 Rodríguez, E., López-González, M. J., & López de Coca, P. 2000, A&AS 144, 469 Samadi, R. & Goupil, M.-J. 2001, A&A 370, 136 Samadi, R., Goupil, M.-J., & Lebreton, Y. 2001a, A&A 370, 147 Stein, R. F. 1968, ApJ 154, 297 Comm. in Asteroseismology Vol. 142, 2002

NOTES

Fishing for Delta Scuti stars in the Hipparcos photometric database

John R. Percy & Geoﬀrey Gilmour-Taylor Department of Astronomy, University of Toronto Mississauga ON Canada L5L 1C6 E-mail: [email protected]

Abstract

Our group has recently used a form of autocorrelation analysis to identify and study short-period variability in A and B type stars, using Hipparcos epoch photometry (Percy and Wilson 2000, Percy et al. 2002). Our method cal- culates, for all pairs of measurements (m,t), the difference in magnitude and the difference in time. The delta m’s are binned in time, and averaged, and then plotted against the average delta t’s. Minima occur at integral multiples of the period. Maxima occur halfway between. Our method determines the cycle-to-cycle behaviour of the star, averaged over all the data. The Hipparcos epoch photometry measurements are distributed in non- random fashion. Measurements are made 0.0143 days apart, then 0.0746, then 0.0143 and so forth, for several hours. These ”clusters” are separated by 20-30 days. Jerzykiewicz and Pamyatnykh (2000) have discussed the aliasing properties of Hipparcos measurements, as they apply to Fourier analysis of Delta Scuti stars. Our algorithm is quite different from Fourier analysis, but the distribution of the measurements produces gaps in our delta m versus delta t plots, between 0.0143 and 0.0746 days, between 0.1032 and 0.1635 days etc. These gaps make it difficult to interpret data on Delta Scuti stars, since they have periods of this order. We began by analyzing Hipparcos epoch photometry of a sample of known Delta Scuti stars with a range of mean magnitude, amplitude, period, and degree of multiperiodicity. Factors which made detection difficult were: amplitude J. R. Percy & G. Gilmour-Taylor 49 less than 0.03; mean magnitude fainter than 8.0; period less than 0.10 days; and appreciable multiperiodicity. We then examined a sample of 72 stars with spectral type A5-F2, parallaxes larger than 10 mas (to eliminate supergiants), and ”unsolved variables” according to the Hipparcos Catalogue. We found five possible Delta Scuti star candidates: HIP 1073, 9807, 30878, 63041 and 65208, and several marginal candidates. There were also two stars with longer periods: HIP 31075 and 63951. Among these, we wish to call attention to three interesting stars. Intensive ground-based photometry of these would be useful to confirm their variability. HIP 30878 (HD 45191, V455 Aur, V = 7.25, F2) is an eclipsing binary of the Algol type. From light curve and autocorrelation analysis, we suspect that it may be a Delta Scuti star with a period of 0.11 days and a full amplitude of 0.01 magnitude. HIP 31075 (HD 46169, V = 7.66, F0V), from light curve and autocorrelation analysis, has a suspected period of 0.55 days and a full amplitude of 0.02. HIP 63951 (HD 113867, V = 6.83, F0), from light curve and autocorrelation analysis, has a period of 1.1 days and a full amplitude of 0.02. The period in the Hipparcos Catalogue is 1.0731 days, which we confirm.

References Jerzykiewicz, M., Pamyatnykh, A. 2000, PASP 112, 776 Percy, J.R., Wilson, J.B. 2000, PASP 112, 846 Percy, J.R., AuYong, K., Gilmour-Taylor, G., Hosick, J., Kincaide, H., Pang, C., Wilson, J.B. 2002, in Observational Aspects of Pulsating B and A Stars, ed. C. Sterken, D.W. Kurtz, ASP Conf. Series 256, 99 Comm. in Asteroseismology Vol. 142, 2002

Discovery of pulsation in the Am Star HD 102480

S. Joshi1, V. Girish2, R. Sagar1, D. W. Kurtz3, P. Martinez 4 and S. Seetha2

1State Observatory, Manora Peak, Naini Tal-263 129, India, [email protected] 2ISRO Satellite Centre, Air Port Road Bangalore-560 034, India 3Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE UK 4South African Astronomical Observatory, P. O. Box 9, Observatory 7935, South Africa

We report the discovery of pulsation in the marginally chemically peculiar Am star HD 102480. This star was discovered during the “Naini Tal-Cape Survey for Pulsations in Chemically Peculiar Stars” (Martinez et al. 2001). 0 h m s o 00 HD 102480 (V = 8.45, α2000 = 11 47 52 , δ2000 = 53 00 54 ) is a cool Am star of spectral type Am (F2/F4/F4) (Abt 1984), where the types in brackets are the Ca II K-line type, Balmer line type and metal line type, respectively. It has Strömgren indices corresponding to the marginally enhanced metallicity indicated by its spectral type, viz. b − y = 0.211, m1 = 0.204, c1 = 0.732 (Olsen 1983); δm1 = −0.025 and δc1 = 0.087 using Crawford’s calibrations of the Strömgren indices for A stars (Crawford 1979). On the basis of these peculiar colours, we decided to search for pulsation in HD 102480 on the night of 19 January 2000 (HJD 2451563). The data were acquired as continuous 10-s integrations through a Johnson B filter with a high-speed photometer attached to the 104-cm Sampurnand telescope of State Observatory, Naini Tal (Gupta et al. 2001). A variation of 0.05 mag was observed in the star on this night, indicative of δ Sct pulsation. Fig. 1 shows the discovery light curve obtained on JD 2451563, and the confirming light curve obtained on night JD 2451598 using the same telescope/instrument combination. The light curves are corrected for coincidence counting losses, sky background and mean atmospheric extinction. From the light curves it can be seen that the amplitude of the pulsation is modulated with a maximum peak-to-peak variation of ≈ 0.08 mag. The corrected data were Fourier analysed to identify the dominant periodic- ities using a fast algorithm based on Deeming’s (1975) Discrete Fourier Trans- form (DFT). The amplitude spectra show two strong peaks at 0.10 § 0.02 mHz (2.78 § 0.56 hr) and 0.19 § 0.02 mHz (1.46 § 0.15 hr). On the basis of the periods, the shape of the light curve and the amplitude variation during our S. Joshi et al. 51

Figure 1: The light curves of HD 102480 on HJD 2451563 and HJD 2451598. observations, we announce that HD 102480 is a new δ Scuti star with marginal Am peculiarities (indicated by both its spectral type and Str¨omgren indices). References Abt, H. A. 1984, ApJ 285, 247 Crawford, D. 1979, AJ 84, 1858 Deeming, T. J. 1975, Ap&SS 36, 137 Gupta, S. K., Sagar, R., Joshi, S., Ashoka, B. N., Babu, V. C, Seetha, S., Girish, V. 2001, BASI 29, 479 Martinez, P., Kurtz, D. W., Ashoka, B. N., Chaubey, U. S., Girish, V., Gupta, S. K., Joshi, S., Kasturirangan, K., Sagar, R., Seetha S. 2001, A&A 371, 1048 Olsen, E.H. 1983 A&AS 54, 55 Comm. in Asteroseismology Vol. 142, 2002

Multiperiodicity of V350 Peg

J. Vidal-S´ainz 1, P. Wils 2, P. Lampens 3, and E. Garc´ıa-Melendo 4

1 Grup d’Estudis Astronomics, Apdo. 9481, 08080 Barcelona, Spain 2 Vereniging Voor Sterrenkunde, Belgium 3 Koninklijke Sterrenwacht van Belgi¨e, Ringlaan 3, 1180 Uccle, Belgium 4 Esteve Duran Observatory Foundation, Montseny 46 – Urb. El Montanya, 08553 Seva, Spain

Abstract

We report on the variability of V350 Peg, a δ Scuti star newly discovered by Hipparcos. Based on observations acquired during 35 nights at two private observatories in Spain, we could show that this star pulsates in a close doublet of frequencies (∆ f/f=3%). The period as listed in the Hipparcos Catalogue is not conﬁrmed.

V350 Peg (= HIP 115563) is a small-amplitude variable star assigned to the δ Scuti class of pulsating stars with a period of 0.2012 days and a total amplitude of 0.05 mag (ESA 1997). During 35 nights between July 1997 and December 2001 some 7500 CCD diﬀerential observations in the V band were acquired at the Monegrillo and Esteve Duran observatories in Northern Spain. HD 220538 (= HIP 115545) served as a comparison star.

A Fourier analysis of the new data revealed two significant frequencies separated by 0.17 c/d and with very similar amplitudes: one at 5.840 c/d (0.1712 d; semi-amp. 27 mmag) and one at 5.668 c/d (0.1764 d; semi-amp. 24 mmag). The result is an obvious beat phenomenon with a period of 5.81 days. But a fit with only two frequencies explains only half of the total variation (Fig. 1). The ratio of the most dominant frequencies (f2/f1 = 0.97) indicates non-radial pulsation for at least one of the modes. More frequencies are obviously excited. Though we have been searching for them, we cannot be confident about their correct identification due to various kinds of aliasing effects. The detailed anal- J. Vidal-Sáinz, P. Wils, P. Lampens, and E. Garc´ıa-Melendo 53 ysis will soon be available (Vidal-Sáinz et al. 2002).

The multiperiodicity combined with the short beat period and the fact that several non-radial modes are possibly excited, make this star a worthwhile target for a follow-up study in the context of a multisite campaign.

-0.95

-0.90

V -0.85 ∆

-0.80

-0.75 25.0 26.0 27.0 HJD (2450700+)

Figure 1: CCD data of V350 Peg on consecutive nights, and two-frequency ﬁt

References ESA 1997, The Hipparcos and Tycho Catalogues, ESA SP–1200 Vidal-S´ainz J., Wils P., Lampens P., Garc´ıa-Melendo E., A&A, accepted for publication Comm. in Asteroseismology Vol. 142, 2002

The High Amplitude δ Scuti Variable Star GSC 3109-00162

P. Wils1, P. Van Cauteren2,1, and R. Groenendaels3

1Vereniging Voor Sterrenkunde, Belgium ([email protected]) 2Beersel Hills Observatory, Laarheidestraat, 166, 1650 Beersel, Belgium ([email protected]) 3Email: ([email protected])

The ROTSE1 (Robotic Optical Transient Search Experiment 1) survey (Ak- erlof et al. 2000) found ROTSE1 J183206.54+403555.9 (= GSC 3109-00162; h m s ◦ 0 α2000 = 18 32 06 ; δ2000 = +40 35.9) to be a δ Scuti variable with a period of 0d. 102145 in the approximate magnitude range 12.4-12.9.

We observed the star on seven nights between June and August 2001, obtaining 1045 data points, totaling 18.2 hours of photometry. The instruments used were a 0.40-m telescope, equipped with a ST7E CCD camera (PVC: 16.1 hours of photometry), and a 0.30-m telescope, equipped with a Hisis24 CCD camera (RG: 2.1 hours). No ﬁlter was used. The exposure times varied between 50 and 60 seconds. The images were reduced with the aperture photometry procedure of the Mira AP software package (produced by Axiom Research Inc.).

The brightness of the variable was measured with respect to GSC 3109- 02150, while GSC 3109-01092 served as check star. To determine the best comparison star we also collected some images in B and V light, using a filterset following Bessell’s specifications. From these we derived instrumental ∆(B−V ) values with respect to the variable star. Our comparison star was chosen on basis of the smallest possible colour difference (in this case ∆(B − V )= 0.09 mag for the comparison star and ∆(B − V )= 0.26 mag for the check star) in order to reduce the influence of the differential colour term coupled to the second order extinction coefficient. The standard deviation of the differential magnitudes between the comparison and check star was of the order of 0m. 006 (with nightly variations between 0m. 004 and 0m. 009 depending on sky conditions). P. Wils, P. Van Cauteren, and R. Groenendaels 55

Table 1: Times of maxima from the CCD observations

JD Hel. E O-C Observer

2451243.6018 -8232 0.0006 ROTSE1 2452084.4973 0 -0.0002 PVC 2452085.4158 9 -0.0010 PVC 2452132.4054 469 -0.0003 PVC 2452132.5081 470 0.0002 PVC 2452136.4919 509 0.0002 RG 2452138.4320 528 -0.0005 PVC 2452145.4814 597 0.0005 PVC 2452150.3847 645 0.0006 PVC

In Table 1 we list the times of maxima that were determined from the new observations ((O-C) values are listed with respect to the ephemeris derived below). The table also contains one time of maximum derived from a phase diagram of the ROTSE1 data (available through http://www.umich.edu/˜rotse). The number of cycles between the ROTSE1 maximum and our data can be determined unambiguously, leading to the improved ephemeris: Max. = HJD 2452084.4974 + 0d. 1021497 × E. § 0.0003 § 0.0000002 Figure 1 shows the phased light curve from the data obtained by PVC.

Our results thus confirm that GSC 3109-00162 is a high amplitude δ Scuti star (HADS) with an unfiltered CCD amplitude of 0.55 mag. The rise from minimum to maximum (M-m) takes 0.31 cycles. No trace of multiperiodicity was found, although there may be small differences in the height of the maxima.

Acknowledgments. We thank Dr. Patricia Lampens, Koninklijke Ster- renwacht van Belgi¨e, for helpful comments. P. Van Cauteren is grateful to the Royal Observatory of Belgium for putting at his disposal material acquired by project G.0265.97 of the Fund for Scientiﬁc Research (FWO) - Flanders (Belgium). 56 The High Amplitude δ Scuti Variable Star GSC 3109-00162

Figure 1: Phase diagram for GSC 3109-00162.

References Akerlof, C., Amrose, S., Balsano, R., Bloch, J., Casperson, D., Fletcher, S., Gisler, G., Hills, J., Kehoe, R., Lee, B., Marshall, S., McKay, T., Pawl, A., Schaefer, J., Szymanski, J., Wren, J. 2000, AJ 119, 1901 Comm. in Asteroseismology Vol. 142, 2002

Is TU UMi a W UMa-type system?

A. Rolland, V. Costa, E. Rodr´ıguez, P.J. Amado, J.M. Garc´ıa-Pelayo, P. L´opez de Coca and I. Olivares

Instituto de Astrof´ısica de Andaluc´ıa-CSIC. P.O. Box 3004, 18080, Granada, Spain

Abstract

TU UMi was discovered as a variable star by Hipparcos satellite (ESA 1997) and catalogued as a δ Sct star by Kazarovets et al. (1999). Analysis of new photometric observations carried through the years 2001 and 2002 is presented. The frequency obtained is in good agreement with that given by the Hipparcos Catalogue. Using the derived uvbyβ indices we propose that this star could be a W UMa-type eclipsing binary system.

Introduction

m TU UMi (SAO 8123, mv = 8. 76) was found to be a variable star by the HIPPARCOS satellite. The Variability Annex of the Hipparcos Catalogue (ESA 1997) reports TU UMi to have a period of 0d. 188546 with Hp magnitudes ranging between 8m. 837 to 8m. 893 and the spectral type is listed as F2. Later Duerbeck (1997) suggested that this star can be a contact binary star (EW) or a pulsating star. In Kazarovets et al. (1999) it is considered as a DSCTC and Rodr´ıguez et al. (2000), on the basis of the preceding information, considered it as a δ Scuti-type variable. With these additional observations in the Str¨omgren photometric system, it should be possible to deﬁne the nature of this star.

Observations

The observations were carried out on three nights in April 2001 and ﬁve nights in March 2002, using the 90 cm telescope at Sierra Nevada Observatory, Spain. This telescope is equipped with a six channel uvbyβ photometer for simultaneous measurements in uvby or in the Hβ channels respectively (Nielsen 1983). The data consist of 684 measurements in Str¨omgren uvby colours collected 58 Is TU UMi a W UMa-type system? over 8 nights of observation and a time span of 332 days. Additionally, in one night Hβ data were also obtained. The comparison stars were C1 = SAO 8087 and C2 = SAO 8171.

Figure 1: δ Sct-type pulsators in the H-R diagram. The borders of the instability strip are shown (continuous for δ Sct stars and dashed for γ Dor). The position of the TU UMi star is shown with the symbol ?.

Results

Looking at the light curves of the data in (b-y) and c1 no variations were found. That suggests no pulsational nature of the variations of this star. Table 1: uvbyβ indices obtained for TU UMi and C1 comparison star. Indices for C2 are taken from Hauck & Mermillod (1998).

Object V b-y m1 c1 β TU UMi 8.76 0.292 0.145 0.449 2.643 C1 = SAO 8087 7.38 0.127 0.192 0.867 2.821 C2 = SAO 8171 8.29 0.084 0.189 0.965 2.867

In the catalogues there is only Str¨omgren photometry for the C2 comparison star, the indices were taken from Hauck & Mermillod (1998). The Johnson V A. Rolland et al. 59

Figure 2: Light-curve and colour-index of TU UMi over the cycle variation. magnitude for the C2 was derived from the Tycho catalogue. From the magnitude and index differences of the stars obtained by us, we derived the values 60 Is TU UMi a W UMa-type system? for the other stars. The results are given in Table 1. Using the above colour indices, we dereddened them making use of Crawford’s (1979) calibration. We derived a null colour excess, (b-y)0 = 0.292 and Mv = 3.22. Figure 1 shows the position of TU UMi in the colour-magnitude diagram. The position of the star in the H-R diagram is clearly outside the δ Sct and γ Dor instability strip borders. The analysis of this star was carried out by means of the Fourier Transform method and we obtained a period of P = 0d. 188544, in good agreement with that given in the Hipparcos catalogue. Figure 2 shows the light curve of the observed data in the v filter and colour index (b-y) and c1 along the period of 0d. 377088, the magnitude differences being made with respect to the C1 star.

Acknowledgments. This research was supported by the Junta de Andaluc´ıa and the Dirección General de Investigación (DGI) under project AYA2000-1580. PJA acknowledges support at the IAA-CSIC by an I3P contract (I3P-PC2001-1) funded by the European Social Fund. References Crawford, D.L. 1979, AJ 84, 1858 Duerbeck, H.W. 1997, IBVS 4513 ESA, 1997, The Hipparcos and Tycho Catalogues, ESA, SP-1200 Hauck, B., Mermilliod, M. 1998, A&AS 129, 431 Kazarovets, A.V., Samus, N.N., Durlevich, O.V., et al. 1999, IBVS 4659 Nielsen, R.F. 1983, Inst. Theor. Astrophys. Oslo Report, No. 59, ed. O. Hauge, 141 Rodr´ıguez, E., López-González, M.J., López de Coca, P. 2000, A&AS 144, 469 Comm. in Asteroseismology Vol. 142, 2002

CCD photometry of XX Cyg

S. N. Udovichenko Astronomical Observatory, Odessa National University, Shevchenko Park, 65014, Odessa, Ukraine XX Cyg (α=20h 02m 17s, δ=58 48’ 44”(1950), V=12 mag, A5) is well known as metal-poor, high-velocity SX Phe star (McNamara & Feltz, 1980). It shows a period of light variation of 0.13486507 d, and an amplitude up to 1 mag (from the General Catalog of Variable Stars). The photometric observation of XX Cyg in diﬀerent years show the variation of amplitude and period during a long time (Zhou et al., 2002). New observations of XX Cyg were made in 7

Figure 1: The light curve of XX Cyg (V) 25-26 October 2001. nights of October 2001 and were continued in 2002 using the 48 cm reﬂector at the Astronomical Observatory of Odessa National University. One star (α=20h 02m 24s, δ=58 51’ 43”) was used as a comparison star and monitored in the frame simultaneously. The CCD photometer was created using a chip ISD015 (520x580 pixels), vacuum housing and thermoelectric (Peltier) cooler. In the observations the V ﬁlter of the UBV system was used. 62 CCD photometry of XX Cyg

A typical observed light curve of XX Cyg is shown in Figure 1. A preliminary analysis of the light curve shows a total light range of 0.8 mag in the ﬁlter V. Possibly, the light curve shows, besides the primary maximum, a small bump of an amplitude of approximately 0.1 mag. The light variation of XX Cyg can be ﬁt with a single pulsation frequency, but an analysis on multiple mode pulsation is being carried out. References Zhou, Ai-Ying, Jiang, Shi-Yang, Chayan, B., Du, Bai-Tian 2002, Ap&SS 281(4) McNamara, D. H., Feltz, K. A., Jr. 1980, PASP 92