[show abstract][hide abstract] ABSTRACT: In this paper we present the results of multisite photometric and spectroscopic campaigns, carried out during the years 1995 and 1996, to study the pulsations of a typical lambda Bootis star, 29 Cyg. During the 1995 campaign we found well-defined multiperiodicity in 29 Cyg, which was studied in detail during a multilongitude campaign covering a 65 day time interval in 1996. The frequency analysis of the 1996 campaign's data easily revealed 11 excited low ell degree modes with frequencies of oscillation ranging from 20.3 to 37.4 cycles day-1 and mean photometric amplitudes ranging from 10.65 to 0.96 mmag in the V filter. After removing the well-identified frequencies, the discrete Fourier transform of the residuals showed excess power in the 20-40 cycle day-1 domain, which indicates the probable existence of unresolved rich p-mode spectra with photometric V amplitudes below 0.5 mmag. We found a regular spacing of 2.41 cycles day-1 within the modes of 29 Cyg, which was interpreted as the spacing of consecutive even and odd ell-values. The asteroseismic luminosity log L/Lodot = 1.12, calculated from the frequency spacing, is in good agreement with the Hipparcos luminosity log L/Lodot = 1.16 and with luminosities from photometric and spectroscopic calibrations. Using our multicolor photometry we tentatively identified the dominant f1 = 37.425 cycle day-1 mode as an ell = 2, n = 5 mode, and made radial overtone identification for all frequencies. These ranged from n = 2 to 5. Analysis of the photometric data shows the long-term (years) and probable short-term (days) variability of amplitudes for all of these modes in 29 Cyg. Using our multicolor WBVR filter photometry, we found the wavelength dependence of the pulsation amplitudes for the five highest amplitude modes. Based on the Halpha line radial velocity observations of 29 Cyg, we detected multiperiodic radial velocity variations with frequencies of 38.36 and 29.99 cycles day-1 and semiamplitudes of 1.0 and 0.8 km s-1, respectively. These frequencies coincide within the errors with the photometric frequencies of the two highest amplitude modes, 37.425 and 29.775 cycles day-1. For the highest amplitude ell = 2, n = 5 mode (37.425 cycles day-1), the radial velocity-to-light amplitude ratio and velocity-to-light phase shift are equal to 2K(Halpha)/DeltaV = 94 km mag-1 s-1 and Phif1 = phi - phiV = +0.08 ± 0.01, respectively, and are in good agreement with values for delta Scuti stars. The rich multiperiodic spectrum makes 29 Cyg a promising target for future multisite campaigns.
The Astronomical Journal 01/2007; 134. · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: We undertook a multisite photometric campaign for the Beta Cephei star Nu Eridani. More than 600 hours of differential photoelectric uvyV photometry were obtained with 11 telescopes during 148 clear nights. The frequency analysis of our measurements shows that the variability of Nu Eri can be decomposed into 23 sinusoidal components, eight of which correspond to independent pulsation frequencies between 5 - 8 c/d. Some of these are arranged in multiplets, which suggests rotational m-mode splitting of nonradial pulsation modes as the cause. If so, the rotation period of the star must be between 30 - 60 d. One of the signals in the light curves of Nu Eri has a very low frequency of 0.432 c/d. It can be a high-order combination frequency or, more likely, an independent pulsation mode. In the latter case Nu Eri would be both a Beta Cephei star and a slowly pulsating B (SPB) star. The photometric amplitudes of the individual pulsation modes of Nu Eri appear to have increased by about 20 per cent over the last 40 years. So do the amplitudes of the dominant combination frequencies of the star. Among the latter, we only could identify sum frequencies with certainty, not difference frequencies, which suggests that neither light-curve distortion in its simplest form nor resonant mode coupling are their single cause. One of our comparison stars, Mu Eridani, turned out to be variable with a dominant time scale of 1.62 d. We believe that it is either an SPB star just leaving its instability strip or that its variations are of rotational origin. Comment: 10 pages, 5 figures
Monthly Notices of the Royal Astronomical Society 01/2005; · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: We discuss new photometric data collected on the gamma Dor variables HD 224945 and HD 224638. Multiperiodicity was detected in both stars, thanks to the clear spectral window of a multisite campaign that involved five observatories. HD 224945 shows the shortest period among the gamma Dor stars, i.e., 0.3330 d. The pulsation behaviour is very different: HD 224945 displays a set of frequencies spread over an interval much wider than that of HD 224638. We clearly found evidence for amplitude variations in the excited modes by comparing data from different years. HD 224945 and HD 224638 are among the best examples of $\gamma$ Dor stars that show multimode pulsations, which make them very interesting from an asteroseismological point of view. Comment: 8 pages (in A&A style), 3 eps figures. Accepted for A&A Main Journal
[show abstract][hide abstract] ABSTRACT: In this contribution we describe a new class of pulsating stars, the
prototype of which is the bright, early F-type dwarf, γ Doradus.
These stars typically have between 1 and 5 periods ranging from 0.4 to 3
d with photometric amplitudes up to 0.1m in Johnson V. The mechanism for
these observed variations is high-order, low-degree, nonradial,
gravity-mode pulsation. A recent theoretical development describing a
proposed driving mechanism for these new variables is discussed.
[show abstract][hide abstract] ABSTRACT: In this paper, we present the results of a multisite photometric campaign devoted to the Doradus type variable HR 8799. From Johnson and Strömgren data, we were able to identify three independent frequencies (f1= 1.9791 cycle d-1, f2=1.7268 cycle d-1 and f3=1.6498 cycle d-1) as well as another signal, which we are able to identify as the coupling term between two of the frequencies (f4=f1-f2=0.2479 cycle d-1). These four frequencies are able to account for all of the observed variations down to the 1σ significance level. We discuss another possible interpretation of these frequencies using a model of quasi-stochastic amplitude modulation. In this scenario, we are able to show that HR 8799 might be pulsating with two independent frequencies, one of which undergoes amplitude modulation similar to other Dor objects. In addition, we discuss a preliminary mode identification based on the observed colour curves. Finally, 18 simultaneous, high-resolution echelle spectra were collected on two nights and we qualitatively compare the radial velocities from these data with our photometry.
Monthly Notices of the Royal Astronomical Society 02/1999; 303(2):275 - 283. · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: HD 163151 is discovered to be a new variable as a part of a W UMa
system. In this paper we present complete uvby light curves. Additional
Crawford H_β and Johnson BV data are also obtained. A detailed
photometric analysis based on these observations is presented using the
WD code. Several tests have been carried out concerning mass ratio and
effective temperatures. The best fitting was achieved with q = 0.27 and
T_1=6450 K (fixed) and T_2 = 6130 K. Moreover, the light curves show
evidences of spots in one of the components. Tables 2 to 5 will be
accessible only in electronic form at the CDS
Astronomy and Astrophysics 07/1998; 336:920-924. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: The preliminary results of a 1996 multisite campaign on the pulsating lambda Bootis star 29 Cyg are presented. This campaign, initiated by the Central Asian Network (CAN), allowed to collect data during 48 photometric and 2 spectroscopic nights at observatories of Ukraine, Kazakhstan, Turkey, Hungary, Canada and USA. The multiplicity of excited modes is confirmed in both spectroscopy and photometry. The analysis of all 1995 and 1996 data, combined with new CAN observations made in July-October 1997, is under way.
[show abstract][hide abstract] ABSTRACT: We present the results from a multisite photometric campaign devoted to
the Gamma Dor variable HD 164615. During the campaign, data were
collected in the Johnson and Stromgren photometric systems. A first
search for sinusoidal periodicities yielded a three-term solution with
frequencies f1 = 1.2328, f2 = 1.0899, and f3 = 2.3501/d, and a long-term
trend f4 = 0.1301/d. The star may therefore be multiperiodic with each
frequency related to a pulsation mode. However, a further examination of
the curve provided evidence that the amplitude at the instant of maximum
brightness is modulated. Alternatively, HD 164615 may be a monoperiodic
variable with frequency f1 = 1.2321/d, showing amplitude modulation with
frequency f4 = 0.1301/d. The presence in the power spectra of the
coupling terms f2 = f1 - f4 and f3 = f1 + f4 - 1 supports the latter
interpretation. In the monoperiodic case the previously given
interpretation based on a spot carried through the visible disk by
rotation still holds, provided that the spot is bright and evolves on a
time scale of a few days. However, similarities with other Gamma Dor
stars provide indirect indication in favor of the existence of a
nonradial pulsation interpretation.
Monthly Notices of the Royal Astronomical Society 10/1997; 292:43. · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present the results of a multi-longitude coordinated photometric
campaign on the gamma Dor variable 9 Aur. Three frequencies can be
determined from the data (f_1=0.7948, f_3=0.7679, f_5=0.3429 d^-1) two
of them have already been recognized in past seasons while the third
frequency is reported for the first time. Analysis shows that the third
was `turned off' or present with an amplitude below the limits of
detection during previous observing seasons. This evidence, together
with consistent amplitude changes in the two previously recognized
signals, suggests that the stellar structure responsible for 9 Aur's
variability is extremely dynamic. Intermediate-resolution spectra and
CORAVEL radial velocities collected simultaneously show variability on
time-scales commensurable with the photometry. The only sensible
explanation appears to be a non-radial pulsation (NRP) model. However,
results obtained reveal a number of features that deviate from classical
NRP behaviour. Such features are emphasized in this paper in support of
the future development of a specific NRP model - a model which has yet
to be elucidated for gamma Dor-type variables.
Monthly Notices of the Royal Astronomical Society 08/1997; 290:401-410. · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: A multisite campaign involving five observatories allowed us to solve the light curve of the Gamma Doradus star HD 224945. The multiperiodic content, the high frequency term at 3.00 c/d and the frequency spacing between the observed terms strongly support its pulsational nature. Considering the low frequency terms observed in Gamma Dor stars, it seems that g--mode pulsators can be found near the cold border of the instability strip.
[show abstract][hide abstract] ABSTRACT: We report a frequency analysis of the δ Scuti star CD-24 7599 and
the discovery that it pulsates nonradially with at least 7 frequencies
between 27.01 and 38.11 cycles per day (312 to 441 μHz). These
results are based on 116.7 hours of photometric data obtained with the
Whole Earth Telescope network. New uvbyβ photometry implies that
the star is unevolved and located near the observed hot border of the
classical instability strip. We give arguments for interpreting the
pulsation periods in terms of low-order low-degree nonradial p-modes.
Rotational m-mode splitting is likely. Few radial modes could also be
present. The rich modal content and unevolved state of CD-24 7599
emphasize its importance for δ Scuti star asteroseismology. We
detect linear combination frequencies of the pulsation modes with the
highest photometric amplitudes and suggest they are not normal modes
excited by resonance.
Astronomy and Astrophysics 02/1996; 307:529-538. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report a frequency analysis of the delta Scuti star CD-24 7599 and the discovery that it pulsates nonradially with at least 7 frequencies between 27.01 and 38.11 cycles per day (312 to 441 muHz). These results are based on 116.7 hours of photometric data obtained with the Whole Earth Telescope network. New uvbybeta photometry implies that the star is unevolved and located near the observed hot border of the classical instability strip. We give arguments for interpreting the pulsation periods in terms of low-order low-degree nonradial p-modes. Rotational m-mode splitting is likely. Few radial modes could also be present. The rich modal content and unevolved state of CD-24 7599 emphasize its importance for delta Scuti star asteroseismology. We detect linear combination frequencies of the pulsation modes with the highest photometric amplitudes and suggest they are not normal modes excited by resonance.
[show abstract][hide abstract] ABSTRACT: We observed G226-29 for 121 hr in 1992 February and confirm the presence
of the three previously identified frequencies close to 109 s. We find
no evidence of other pulsation periods down to our noise level of about
0.35 millimodulation amplitudes. The presence of only one triplet
pulsation mode in G226-29 and its effective temperature near the blue
edge of the instability strip identify the observed triplet of modes
near 109 s as rotationally split components of the k = 1, l = 1 mode.
With the mode identification, we derived a rotation period of 8.9 hr and
an inclination of the pulsation axis of 70°-75° to our line of
The Astrophysical Journal 06/1995; 447:874. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: IUE observations are proposed for the 14.6 year binary system tau Per, which may be another zeta Aur-like eclipsing system. Optically this object is classified as a G8III + A3 system, although we find the IUE data indicates that the secondary is of earlier type, Al. An astrometric orbit from speckle-interferometric observations has been determined by McAlister (1982), and coupled with the spectroscopic orbit, Popper and McAlister (1987) find the inclination to be near 90' and predict an atmospheric eclipse to occur in November 1990. The components of the system also appear to be overluminous and cannot be fit simultaneously to evolutionary tracks appropriate for their masses. Based on its similarity to the eclipsing systern tau Per, we expect the eclipse to show a curious wavelength dependence unlike the other zeta Aur systems and much like the peculiar binary epsilon Aur, where the eclipse depth increases with decreasing wavelength to ~ 1600 and then becomes shallower down to ~ 1200. As in systems of this type, strong absorption lines in the far and mid-UV should be seen superimposed on the secondary's spectrum during these phases. UV observations are needed at various times near eclipse to map out the extent and homogeneity of mass flow from the primary star and investigate the wavelength dependent nature of the eclipse. Of the other zeta Aur-like systems, tau Per will join 22 Vul, HR 2554, and tau Per as the only ones with primaries of G-type.
International Amateur-Professional Photoelectric Photometry Communications. 08/1994; 57:31.