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Post Info TOPIC: Delta Scuti stars
Blobrana


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RE: Delta Scuti stars
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Title: Understanding the dynamical structure of pulsating stars: The Baade-Wesselink projection factor of the delta Scuti stars AI Vel and beta Cas
Authors: G. Guiglion, N. Nardetto, P. Mathias, A. Domiciano de Souza, E. Poretti, M. Rainer, A. Fokin, D. Mourard, W.Gieren

Aims. The Baade-Wesselink method of distance determination is based on the oscillations of pulsating stars. The key parameter of this method is the projection factor used to convert the radial velocity into the pulsation velocity. Our analysis was aimed at deriving for the first time the projection factor of delta Scuti stars, using high-resolution spectra of the high-amplitude pulsator AI Vel and of the fast rotator beta Cas. Methods. The geometric component of the projection factor (i.e. p0) was calculated using a limb-darkening model of the intensity distribution for AI Vel, and a fast-rotator model for beta Cas. Then, using SOPHIE/OHP data for beta Cas and HARPS/ESO data for AI Vel, we compared the radial velocity curves of several spectral lines forming at different levels in the atmosphere and derived the velocity gradient associated to the spectral-line-forming regions in the atmosphere of the star. This velocity gradient was used to derive a dynamical projection factor p. Results. We find a flat velocity gradient for both stars and finally p = p0 = 1.44 for AI Vel and p = p0 = 1.41 for beta Cas. By comparing Cepheids and delta Scuti stars, these results bring valuable insights into the dynamical structure of pulsating star atmospheres. They suggest that the period-projection factor relation derived for Cepheids is also applicable to delta Scuti stars pulsating in a dominant radial mode.

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Blobrana


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Title: Regularities in frequency spacings of Delta Scuti stars: The Kepler star KIC 9700322
Authors: M. Breger, L. Balona, P. Lenz, J. K. Hollek, D. W. Kurtz, G. Catanzaro, M. Marconi, A. A. Pamyatnykh, B. Smalley, J. C. Suarez, R. Szabo, K. Uytterhoeven, V. Ripepi, J. Christensen-Dalsgaard, H. Kjeldsen, M. N. Fanelli, K. A. Ibrahim, K. Uddin

In the faint star KIC 9700322 observed by the Kepler satellite, 76 frequencies with amplitudes from 14 to 29000 ppm were detected. The two dominant frequencies at 9.79 and 12.57 c/d (113.3 and 145.5 \mu Hz), interpreted to be radial modes, are accompanied by a large number of combination frequencies. A small additional modulation with a 0.16 c/d frequency is also seen; this is interpreted to be the rotation frequency of the star. The corresponding prediction of slow rotation is confirmed by a spectrum from which v sin i = 19 ±1 km/s is obtained. The analysis of the spectrum shows that the star is one of the coolest {\delta} Sct variables. We also determine Teff = 6700 ±100 K and log g = 3.7 ±0.1, compatible with the observed frequencies of the radial modes. Normal solar abundances are found. An \ell = 2 frequency quintuplet is also detected with a frequency separation consistent with predictions from the measured rotation rate. A remarkable result is the absence of additional independent frequencies down to an amplitude limit near 14 ppm, suggesting that the star is stable against most forms of nonradial pulsation. The frequency spectrum of this star emphasizes the need for caution in interpreting low frequencies in {\delta} Sct stars as independent gravity modes. A low frequency peak at 2.7763 c/d in KIC 9700322 is, in fact, the frequency difference between the two dominant modes and is repeated over and over in various frequency combinations involving the two dominant modes. The relative phases of the combination frequencies show a strong correlation with frequency, but the physical significance of this result is not clear.

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Blobrana


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Title: HD 207331 a new delta Scuti star in the Cygnus field: discovery and follow-up observations
Authors: L. Fox-Machado, W.J. Schuster, C. Zurita, J.S. Silva, R. Michel
(Version v2)

Preliminary results on the discovery and follow-up observations of a new delta Scuti pulsator in the Cygnus field are presented. The variability of the star HD 207331 was detected while testing a Stromgren spectrophotometer attached to the H.L. Johnson 1.5-m telescope at the San Pedro Martir observatory, Mexico. CCD photometric data acquired soon after confirmed its variability. A few hours of uvby differential photoelectric photometry during three nights revealed at least two beating periods. A two-site observational campaign carried out during one week in 2009 confirms the multi-periodic nature of this new delta Scuti pulsator.

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Blobrana


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Posts: 131433
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HD 207331
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Title: HD 207331 a new delta Scuti star in the Cygnus field: discovery and follow-up observations
Authors: L. Fox-Machado, W.J. Schuster, C. Zurita, J.S. Silva, R. Michel

Preliminary results on the discovery and follow-up observations of a new delta Scuti pulsator in the Cygnus field are presented. The variability of the star HD 207331 was detected while testing a Stromgren spectrophotometer attached to the H.L. Johnson 1.5-m telescope at the San Pedro Martir observatory, Mexico. CCD photometric data acquired soon after confirmed its variability. A few hours of uvby differential photoelectric photometry during three nights revealed at least two beating periods. A two-site observational campaign carried out during one week in 2009 confirms the multi-periodic nature of this new delta Scuti pulsator.

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Blobrana


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Posts: 131433
Date:
RE: Delta Scuti stars
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Title: On the nature of HD 207331: a new Delta Scuti variable
Authors: L. Fox Machado, W.J. Schuster, C. Zurita, J.L. Ochoa, J.S. Silva

While testing a Stromgren spectrophotometer attached to the 1.5-m telescope at the San Pedro Martir observatory, Mexico, some A-type stars were observed, one of which, HD 207331, presented clear indications of photometric variability. CCD photometric data acquired soon after that, confirmed its variability. In order to determine its pulsation behaviour more accurately, uvby differential photoelectric photometry was carried out for three nights. As a result of the period analysis of the light curves we have found a dominant pulsation mode at 21.1 c/d with an amplitude of 6 mag which suggests strongly that HD 207331 is a new Delta Scuti-type pulsating star.

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Blobrana


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Title: New multisite observations of Delta Scuti stars V624 Tauri and HD 23194
Authors: L. Fox Machado, E. Michel, M. Chevreton, M. Alvarez, Z.P. Li, J.A. Belmonte, A. Fernandez, L. Parrao, M. Rabus, J Lochard, F. Perez Hernandez, J.H. Pena, S. Pau

The preliminary results of STEPHI 2006 campaign are reported.

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Blobrana


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Title: CCD Photometry of Delta Scuti stars 7 Aql and 8 Aql
Authors: L. Fox Machado, R. Michel, M. Alvarez, L. Parrao, A. Castro, J.H. Pena
(Version v2)

As a continuation of the study of the Delta Scuti stars 7 Aql and 8 Aql; new CCD photometric data were acquired in 2007. We present a period analysis on these data that confirm the dominant modes detected in each star in the framework of the STEPHI XII campaign in 2003.

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Blobrana


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Posts: 131433
Date:
UNSW-V-500
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Title: The first high-amplitude delta Scuti star in an eclipsing binary system
Authors: J. L. Christiansen (1), A. Derekas (2), M. C. B. Ashley (1), J. K. Webb (1), M. G. Hidas (3 and 4), D. W. Hamacher (1), L. L. Kiss (2) ((1) University of NSW, Australia, (2) University of Sydney, Australia, (3) Las Cumbres Observatory Global Telescope, US, (4) University of California, US)
(Version v2)

We report the discovery of the first high-amplitude delta Scuti star in an eclipsing binary, which we have designated UNSW-V-500. The system is an Algol-type semi-detached eclipsing binary of maximum brightness V = 12.52 mag. A best-fitting solution to the binary light curve and two radial velocity curves is derived using the Wilson-Devinney code. We identify a late A spectral type primary component of mass 1.49 ±0.02 M_sun and a late K spectral type secondary of mass 0.33 ±0.02 M_sun, with an inclination of 86.5 ±1.0 degrees, and a period of 5.3504751 ±0.0000006 d. A Fourier analysis of the residuals from this solution is performed using PERIOD04 to investigate the delta Scuti pulsations. We detect a single pulsation frequency of f_1 = 13.621 ±0.015 c/d, and it appears this is the first overtone radial mode frequency. This system provides the first opportunity to measure the dynamical mass for a star of this variable type; previously, masses have been derived from stellar evolution and pulsation models.

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Blobrana


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Posts: 131433
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HD 114839
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Title: HD 114839 - An Am star showing both delta Scuti and gamma Dor pulsations discovered through MOST photometry
Authors: H. King, J.M. Matthews, J.F. Rowe, C.Cameron, R.Kuschnig, D.B. Guenther, A.F.J. Moffat, S.M. Rucinski, D. Sasselov, G.A.H. Walker, W.W. Weiss

Using MOST (Microvariability and Oscillations of STars) satellite guide star photometry, we have discovered a metallic A star showing hybrid p- and g-mode pulsations. HD 114839 was observed nearly continuously for 10 days in March, 2005. We identify frequencies in three groups: the first centred near 2 cycles/day, in the gamma Dor pulsation range, and two others near 8 and 20, both in the delta Scuti range. This is only the fourth known such hybrid pulsator, including another MOST discovery.

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Blobrana


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Posts: 131433
Date:
Delta Scuti stars
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Title: Multi-site observations of Delta Scuti stars 7 Aql and 8 Aql (a new Delta Scuti variable): The twelfth STEPHI campaign in 2003
Authors: L. Fox Machado, E. Michel, F. Perez Hernandez, J.H. Pena, Z.P. Li, M. Chevreton, J.A. Belmonte, M. Alvarez, L. Parrao, M.-A. Dupret, S. Pau, A. Fernandez, J.P. Michel, R. Michel, A. Pani

We present an analysis of the pulsation behaviour of the Delta Scuti stars 7 Aql (HD 174532) and 8 Aql (HD 174589) -- a new variable star -- observed in the framework of STEPHI XII campaign during 2003 June--July. 183 hours of high precision photometry were acquired by using four-channel photometers at three sites on three continents during 21 days. The light curves and amplitude spectra were obtained following a classical scheme of multi-channel photometry. Observations in different filters were also obtained and analysed. Six and three frequencies have been unambiguously detected above a 99% confidence level in the range 0.090 mHz--0.300 mHz and 0.100 mHz-- 0.145 mHz in 7 Aql and 8 Aql respectively. A comparison of observed and theoretical frequencies shows that 7 Aql and 8 Aql may oscillate with p modes of low radial orders, typical among Delta Scuti stars. In terms of radial oscillations the range of 8 Aql goes from n=1 to n=3 while for 7 Aql the range spans from n=4 to n=7. Non-radial oscillations have to be present in both stars as well. The expected range of excited modes according to a non adiabatic analysis goes from n=1 to n=6 in both stars.

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