Delta Scuti Star Newsletter

Issue 7, March 1994


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Delta Scuti Stars: continuously in progress

by: E.Rodriguez, P.Lopez de Coca, A.Rolland, R.Garrido, V.Costa

In the past few years much progress has been made in the study of Delta Scuti stars, specially from an observational point of view. The number of these variables is continuously increasing as a result of discoveries of new members. Furthermore, new observations of stars previously regarded as constant, in the lower part of the instability strip, have been shown to be new variables with very small amplitudes. An immense effort has also been expended to study a number of Delta Scuti stars with complex pulsation frequency spectra by means of internationally coordinated observing campaigns covering individual stars, which have given very interesting and definitive results. Global frequency spectra have been satisfactorily resolved in some stars; new frequencies have been identif1ed in others; several variables have been found to pulsate in a large number of simultaneously excited nonradial p-modes; nonradial pulsation has also been found in several of these stars where only one pulsation frequency had been previously identified. Some o Scuti variables have shown to exhibit variable amplitudes whereas others show constant both frequencies and amplitudes. New periods and period changes have also been recently determined for a number of these variables which have been compared with those expected from stellar evolutionary tracks inside the lower instability strip. Insummary,our knowledge about Delta Scuti stars is continuously increasing in almost all respects; both literature and the number of these stars are growing every day.

Fig.1: Position of the Delta Scuti stars in the H-R diagram.

In this way, we have compiled a new revised and up to date list of Delta Scuti stars. This catalogue is intended to be a comprehensive review of observational characteristics of all the Delta Scuti stars known until now, including stars contained in earlier catalogues together with other new discovered variables, covering information published until November 1993. The full text together with the list of stars, their most significant parameters, references to studies of individual stars and notes has been submitted to Astronomy and Astrophysics Supplement Series and can be requested from the authors. Communication by e-mail is also possible (16488::eloy, <eloy@iaa.es>).

Fig.2: Distribution of the stars in the catalogue (N) as function of the visual amplitude (dV).

Fig.3: Distribution of the stars in the catalogue (N) as function of the period (P).

In total, 369 stars have been analysed. However,71 of these were rejected mainly because either time scales of variation or signal/noise ratio of their light curves do not allow us to definitively classify them as Delta Scuti variables. They are not listed in our catalogue. In fact, most of them have been previously considered only as suspected Delta Scuti variables by earlier authors.The main source of information has been the 4th Edition of the General Catalogue of Variable Stars Vol. I, II, III, IV and the Name Lists Nrs.67, 68, 69, 70 and 71. In addition, the lists of Breger(1979), Eggen(1979), Halprin & Moon(1983), Garcia et al. (1988), Petit(1990), Lopez de Coca et al. (1990) and Garcia et al.(1993) have also been taken into account, together with all the available bibliography in the last few years. Special mention must be made of the Simbad database operated at the Centre de Donnees Astronomiques de Strasbourg (CDS). This database has been very useful for this research. Insummary, our newlist contains 298 stars, 207 have homogeneous photometric information in the uvby Beta system,14 more in uvby and 1 in Beta.

Fig.4: Distribution of the stars in the catalogue (N) as function of the visual magnitude (V).

Figure 1 shows the position in the H-R diagram of all the Delta Scuti stars in our catalogue, with available uvby photometry. In the figure are also drawn the ZAMS line (from Philip & Egret 1980) and the observational edges obtained for the instability strip in the Delta Scuti region. The cold edge is the same as that found by Breger (1979), however the hot edge is shifted blueward by about 100 K with respect to the Breger's adopted hot border. Four stars have suggested this shift: HD 16439, HD 19279, HD90386 and HD153747 (the four bluest stars inside our defined instability strip). In all the four cases, the variability of the star is reliable and its position in the H-R diagram seems well defined according to earlier papers available for pulsation and Stromgren photometry of these stars from different authors. Figures 2, 3, 4 and 5 show the corresponding distributions of the stars in the catalogue as functions of the visual amplitude, period, visual magnitude and rotational velocity (when available), respectively.

Acknowledgements:

This research has made use of the Simbad database, operated at CDS, Strasbourg, France. Acknowledgements are also specially made to M. C. Romero for making available a large number of papers used in this investigation and to V.G. Brown for proof reading. This research was supported by the Junta de Andalucia and the Direccion General de Investigacion Cientifica y Tecnica(DGICYT) under project PB90-0113.

Fig.5: Distribution of the stars in the catalogue (N) as function of the rotational velocity (v sin i).


References:

  1. Breger M. 1979, PASP 91, 5
  2. Eggen O.J. 1979,ApJS 41, 413
  3. Garcia J.R., Cebral J.R., Di Giorgio F. et al. 1988, Bull. Infor CDS 34, 67
  4. Garcia J.R., Cebral J.R., Scoccimarro E.R. et al. 1993, Delta Scuti Star Newsletter 6, 14
  5. Halprin L., Moon T.T. 1983, Ap&SS 91, 43
  6. Lopez de Coca P., Rolland A., Rodriguez E., Garrido R. l990,A&AS 83, 51
  7. Petit M. 1990, A &AS 85,971
  8. Philip A.G.D., Egret D. 1980,A&A 40, 199

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