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1.
We present the results of a three-year Johnson V and Strömgren uvby H β photometric study of the δ Scuti star BR Cancri (BR Cnc). Our data sets consist of 1293 discrete differential magnitudes in Johnson V and yellow y filters, 883 in Strömgren v and 239 in ub filters. The Fourier analysis of the data suggests four pulsation frequencies for the variable: f 1=24.978, f 2=11.358, f 3=11.808 and f 4=27.914 cycle d−1. During the three observing years, the main frequency f 1 kept its V ( y ) amplitude constant at about 6 mmag but its v amplitude seems to be changing. Amplitude variations for all the three other frequencies are also claimed. The pulsation modes of the frequencies are discussed based on the colour data. Using uvbyβ data and calibrations in the literature, we derive the physical parameters for BR Cnc.  相似文献   

2.
The pulsating DA white dwarfs are the coolest degenerate stars that undergo self-driven oscillations. Understanding their interior structure will help us to understand the previous evolution of the star. To this end, we report the analysis of more than 200 h of time-resolved CCD photometry of the pulsating DA white dwarf star EC 14012−1446 acquired during four observing epochs in three different years, including a coordinated three-site campaign. A total of 19 independent frequencies in the star's light variations together with 148 combination signals up to fifth order could be detected. We are unable to obtain the period spacing of the normal modes and therefore a mass estimate of the star, but we infer a fairly short rotation period of  0.61 ±0.03 d  , assuming the rotationally split modes are  ℓ= 1  . The pulsation modes of the star undergo amplitude and frequency variations, in the sense that modes with higher radial overtone show more pronounced variability and that amplitude changes are always accompanied by frequency variations. Most of the second-order combination frequencies detected have amplitudes that are a function of their parent mode amplitudes, but we found a few cases of possible resonantly excited modes. We point out the complications in the analysis and interpretation of data sets of pulsating white dwarfs that are affected by combination frequencies of the form   f A + f B − f C   intruding into the frequency range of the independent modes.  相似文献   

3.
Recent multisite campaigns of the Delta Scuti Network have revealed 34 frequencies of pulsation for the star 4 CVn. Our present knowledge of the frequencies makes it possible to reanalyse the shorter data sets in the literature, photometric observations from 1966 to 1997.
4 CVn shows strong amplitude variability with time-scales of ten years or longer, although for neighbouring years the amplitudes usually are similar. Seven of the eight dominant modes show annual variability of ∼12 per cent. The variability increases to ∼40 per cent over a decade. The formally derived time-scale of variation of 30 years can only be a rough estimate, since this is also the length of the available data span. The variability is compared with that of FG Vir, which shows lower amplitude variability.
The cyclic behaviour of the amplitude variations excludes an evolutionary origin. There exists some evidence that a mode at 6.12 d−1, which appeared during 1996 and 1997, may have been present with small amplitudes in the 1976–1978 time period.
The pulsation mode at 7.375 d−1 exhibited the most rapid decrease found so far: the V amplitude dropped from the highest known value of 15 mmag in 1974 to 4 mmag in 1976 and 1 mmag in 1977. After that the mode has been increasing in amplitude. There exists a phase jump between 1976 and 1977, suggesting the growth of a new mode. It is interesting to note that this mode also has the strongest coupling with other modes with combination frequencies, f i ± f j . The amplitudes of these combination frequencies are also strongly variable from year to year. We speculate that power is transferred between the modes through mode-coupling.  相似文献   

4.
We analyse 147 h of single-site CCD time series photometry of the multiperiodic low-amplitude δ Scuti star XX Pyx with the aim of investigating variability at low frequencies. Part of the data were obtained in the context of the 1998 multisite campaign on XX Pyx, the results of which were described by Handler et al. We find that periodic low-frequency variations are present in the XX Pyx light curves, and we detect two frequencies at f A=0.8695 cycle d−1 and f B=1.7352 cycle d−1 , respectively, with amplitudes of 4.5 and 5.4 mmag. The low-frequency variability is intrinsic to XX Pyx, and cannot be attributed to instrumental or atmospheric effects. The near 2:1 ratio of the frequencies leads us to suggest that XX Pyx is a δ Scuti star in a binary system, with a possible binary period of 27.6 h. This is strongly supported by the detection of radial velocity variations from the re-analysis of echelle spectra obtained by Handler et al. However, in the absence of a spectroscopic period, alternative explanations of the photometric variability involving pulsation are also possible; the variations occur close to possible combination frequencies of the short-period ( δ Scuti) variations, but high Q values of 0.57 and 0.28 d suggest that the variations are not a result of normal (p-)modes. They could possibly be due to g-modes excited to observable amplitudes as a result of resonance effects. Surface features (spots) are unlikely to be the cause of the variations.
We searched for combination frequencies (  f i − f j ) , f being the normal δ Scuti frequencies detected by Handler et al., but failed to detect any.  相似文献   

5.
A multifrequency analysis of the SX Phoenicis star BL Camelopardalis is presented on the basis of new high-speed photometry, along with fitting a total of 136 maxima. BL Cam is a multiple periodic pulsator. We find f 0=25.5768, f 1=25.2982, f 2=25.8622, f 3=31.5912, f 4=25.1065, f 5=25.5147 and f 6=25.6188 cycle d−1 together with the harmonics 51.1513 and 76.7268 cycle d−1 and combination frequencies f 0+ f 1, f 0+ f 2 and f 0+ f 3. The new frequency solution represents the light curves of BL Cam quite well. The observed minus calculated (O-C) analysis indicates that the fundamental frequency is in good agreement with the results of Fourier analysis.  相似文献   

6.
We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with eight different telescopes in a time span of 11 months. In addition, we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the slowly pulsating B-stars (SPB)-like g -mode with frequency 0.3428 d−1 reported before is detected in our spectroscopy. We identify the four main modes as  (ℓ1, m 1) = (1, 1), (ℓ2, m 2) = (0, 0), (ℓ3, m 3) = (1, 0)  and  (ℓ4, m 4) = (2, 1)  for   f 1= 5.178 964 d−1, f 2= 5.334 224 d−1, f 3= 5.066 316 d−1  and   f 4= 5.490 133 d−1  , respectively. Our seismic modelling shows that f 2 is likely the radial first overtone and that the core overshooting parameter  αov  is lower than 0.4 local pressure scale heights.  相似文献   

7.
We obtained CCD photometric observations of the Algol-type semidetached binary XX Cephei (XX Cep) during 15 nights from 2002 September 17 to 2003 February 2, and also on 2005 January 21. Except for those data taken on the last night of the concentrated observing season, the 3881 measurements were obtained over an interval of only 106 nights. From these data, four new times of minimum light were calculated. The  (O− C)  diagram formed from all available timings, and thus the orbital period of the system, can be partly represented as a beat effect between two cyclical variations with different periods (      yr,      yr) and amplitudes  ( K 1=0.015 d, K 2=0.103 d)  , respectively. Both physical and non-physical interpretations of these cycles were investigated. The long-term sinusoidal variation is too long for magnetic cycling in solar-type single and close binary stars. In addition, we have studied the effect of a possible secular period variation. By analysing the residuals from our Wilson–Devinney (WD) binary model, we found small light variations with a period of 5.99 d with amplitudes growing toward longer wavelengths. We think that these oscillations may be produced by instabilities at the systemic L 1 point (also occupied by the point of the cool star) and that these instabilities are, in turn, caused by non-uniform and sporadic convection. There is also a short-period oscillation of about 45 min in the WD light residuals that is attributed to accretion on to the mass-gaining primary component from a feeble gas stream originating on the cool donor star.  相似文献   

8.
We present the results of a CCD Johnson V and photoelectric Strömgren uvbyβ photometric study of the recently discovered multiperiodic δ Sct star GSC 2683-3076. Our data set mainly consists of 2874 differential measurements in V together with a few data collected into the uvbyβ system. Additional unfiltered CCD measurements were also carried out. A set of seven best-fitting pulsation frequencies representing the light variations of the variable has been detected. The spectral type of the variable is found to be A9V or F0V. Using the uvbyβ indices the following main physical parameters for the variable have been derived: T eff=7230 K , M V =1.95 mag , log  g =3.90 , M =1.85 M⊙ , R =2.30 R⊙ , ρ =0.16  ρ ⊙ , age =1.0 Gyr , metal abundance [Me/H]=0.16 and distance modulus =8.4 mag . GSC 2683-3076 is found to be a Population I δ Sct star, slightly metal-enriched, evolving on its main-sequence stage. A mixture of radial and non-radial modes seems to be present in the pulsation of this variable. This star is also known as H133 in the young open cluster NGC 6871, however arguments are given that address this star as a non-member of the cluster. The uvbyβ photometry available in the literature for NGC 6871 is also discussed.  相似文献   

9.
We present an analysis of high-speed spectroscopy of the pulsating subdwarf B star PG 1605+072. Periodic radial motions are detected at frequencies similar to those reported for photometric variations in the star, with amplitudes of up to 6 km s−1. Differences between relative strengths for given frequency peaks for our velocity data and previously measured photometry are probably a result of shifting of power between modes over time. Small differences in the detected frequencies may also indicate mode-shifting. We report the detection of line-shape variations using the moments of the cross-correlation function profiles. It may be possible to use the moments to identify the pulsation modes of the star.  相似文献   

10.
We present the results on period search and modelling of the cool DAV star KUV 02464+3239. Our observations resolved the multiperiodic pulsational behaviour of the star. In agreement with its position near the red edge of the DAV instability strip, it shows large amplitude, long-period pulsation modes, and has a strongly non-sinusoidal light curve. We determined six frequencies as normal modes and revealed remarkable short-term amplitude variations. A rigorous test was performed for the possible source of amplitude variation: beating of modes, effect of noise, unresolved frequencies or rotational triplets. Among the best-fitting models resulting from a grid search, we selected three that gave   l = 1  solutions for the largest amplitude modes. These models had masses of 0.645, 0.650 and  0.680  M ⊙  . The three 'favoured' models have   M H  between  2.5 × 10−5 and 6.3 × 10−6  M *  and give 14.2–14.8 mas seismological parallax. The  0.645  M ⊙  (11 400 K) model also matches the spectroscopic  log  g   and   T eff  within 1σ. We investigated the possibility of mode trapping and concluded that while it can explain high amplitude modes, it is not required.  相似文献   

11.
Simultaneous spectroscopic and photometric observations of the Z Cam type dwarf nova SY Cancri were used to obtain absolute flux calibrations. A comparison of the photometric calibration with a wide-slit spectrophotometric calibration showed that either method is equally satisfactory. A radial velocity study of the secondary star, made using the far-red Na  i doublet, yielded a semi-amplitude of   K 2= 127 ± 23 km s−1  . Taking the published value of  86 ± 9 km s−1  for K 1 gives a mass ratio of   q = M 2/ M 1= 0.68 ± 0.14  ; this is very different from the value of  1.13 ± 0.35  quoted in the literature. Using the new lower mass ratio, and constraining the mass of the white dwarf to be within reasonable limits, then leads to a mass for the secondary star that is substantially less than would be expected for its orbital period if it satisfied a main-sequence mass–radius relationship. We find a spectral type of M0 that is consistent with that expected for a main-sequence star of the low mass we have found. However, in order to fill its Roche lobe, the secondary must be significantly larger than a main-sequence star of that mass and spectral type. The secondary is definitely not a normal main-sequence star.  相似文献   

12.
We used the detected pulsation modes and adiabatic pulsation models to do seismology of the class of ZZ Ceti stars and measure the H layer mass for 83 stars. We found the surface hydrogen layer to be within the range  10−9.5≥ M H/ M *≥ 10−4  , with an average of   M H/ M *= 10−6.3  , which is thinner than the predicted value of   M H/ M *= 10−4  , indicating that the stars lose more mass during their evolution than previously expected. These results are preliminary and do not include the possible effects of realistic C/O profiles on the fits.  相似文献   

13.
We carried out a multicolour time-series photometric study of six stars claimed as 'hybrid' p and g mode pulsators in the literature. γ Peg was confirmed to show short-period oscillations of the β Cep type and simultaneous long-period pulsations typical of Slowly Pulsating B (SPB) stars. From the measured amplitude ratios in the Strömgren uvy passbands, the stronger of the two short period pulsation modes was identified as radial; the second is  ℓ= 1  . Three of the four SPB-type modes are most likely  ℓ= 1  or 2. Comparison with theoretical model calculations suggests that γ Peg is either a  ∼8.5 M⊙  radial fundamental mode pulsator or a  ∼9.6 M⊙  first radial overtone pulsator. HD 8801 was corroborated as a 'hybrid'δ Sct/γ Dor star; four pulsation modes of the γ Dor type were detected, and two modes of the δ Sct type were confirmed. Two pulsational signals between the frequency domains of these two known classes of variables were confirmed and another was newly detected. These are either previously unknown types of pulsation or do not originate from HD 8801. The O-type star HD 13745 showed small-amplitude slow variability on a time-scale of 3.2 d. This object may be related to the suspected new type of supergiant SPB stars, but a rotational origin of its light variations cannot be ruled out at this point. 53 Psc is an SPB star for which two pulsation frequencies were determined and identified with low spherical degree. Small-amplitude variability was formally detected for 53 Ari but is suspected not to be intrinsic. The behaviour of ι Her is consistent with non-variability during our observations, and we could not confirm light variations of the comparison star 34 Psc previously suspected. The use of signal-to-noise criteria in the analysis of data sets with strong aliasing is critically discussed.  相似文献   

14.
We undertook a time-series photometric multisite campaign for the rapidly oscillating Ap (roAp) star HD 99563 and also acquired mean light observations over four seasons. The pulsations of the star, which show flatter light maxima than minima, can be described with a frequency quintuplet centred on 1557.653 μHz and some first harmonics of it. The amplitude of the pulsation is modulated with the rotation period of the star that we determine with 2.91179 ± 0.00007 d from the analysis of the stellar pulsation spectrum and of the mean light data. We break up the distorted oscillation mode into its pure spherical harmonic components and find it is dominated by the ℓ= 1 pulsation, and also has a notable ℓ= 3 contribution, with weak ℓ= 0 and 2 components. The geometrical configuration of the star allows us to see both pulsation poles for about the same amount of time; HD 99563 is only the fourth roAp star for which both pulsation poles are seen and only the third where the distortion of the pulsation modes has been modelled. We point out that HD 99563 is very similar to the well-studied roAp star HR 3831. Finally, we note that the visual companion of HD 99563 is located in the δ Scuti instability strip and may thus show pulsation. We show that if the companion was physical, the roAp star would be a 2.03-M⊙, object, seen at a rotational inclination of 44°, which then predicts a magnetic obliquity     .  相似文献   

15.
We have performed high-speed UBV photometric observations on the peculiar binary V Sagittae. Using three new eclipse timings we update the orbital ephemeris and convert it to a dynamical time-scale (TDB). We also searched for quasi-periodic oscillations but did not detect them. Using the Wilson–Devinney algorithm we have modelled the light curve to find the stellar parameters of V Sge. We find that the system is a detached binary but that the primary star is very close to filling its Roche lobe, while the secondary star fills 90 per cent of its Roche lobe volume. We find temperatures of the primary and the secondary star to be T 1=41 000 K and T 2=22 000 K. We find i =72° and masses of 0.8 M⊙ and 3.3 M⊙ for the primary and secondary stars respectively. De-archived Hubble Space Telescope ( HST ) spectroscopy of V Sge shows evidence of mass loss via a wind or winds. In addition we report radio observations of V Sge during an optical high state at 2 cm, 3.6 cm and 6 cm wavelengths. The 3.6 cm emission is increased by a factor of more than six compared with an earlier detection in a previous optical high state.  相似文献   

16.
A multisite campaign of BI CMi was carried out with excellent frequency resolution and high photometric accuracy from 1997 to 2000, including two long observing seasons. 29 pulsation frequencies could be extracted from the 1024 h (177 nights) of photometry used. The detected frequencies include 20 pulsation modes in the main pulsation frequency range from 4.8 to 13.0 cycle d−1 (55 to 150 μHz), eight linear combinations of these frequencies, and a very low frequency at 1.66 cycle d−1. Since the value of the low frequency at 1.66 cycle d−1 cannot be identified with a linear combination of other frequencies, g-mode pulsation is suspected, but rotational modulation of abundance spots cannot be ruled out. BI CMi, which is situated near the cool edge of the classical instability strip, may be both a δ Scuti and a γ Doradus star. Another outstanding property of BI CMi is the presence of a number of close frequency pairs in the power spectrum with separations as small as 0.01 cycle d−1.
A rotational velocity of     was determined from a high-dispersion spectrum. From phase differences, the dominant modes can be identified with ℓ values from 0 to 2. The spectral type and evolutionary status of BI CMi are examined.  相似文献   

17.
We present spectroscopic and multisite time series photometric observations of the star HD 105759 which confirm that this is a new pulsating λ Bootis star. Our spectroscopy indicates an overall metallicity of [Z] = log Z − log Z⊙ = −1 and that T eff = 8000 ± 300 K and log  g  = 4.0 ± 0.2. The photometric data reveal that this star pulsates with at least five frequencies: 8.62, 12.69, 20.15, 21.27 and 23.66 d−1. These frequencies do not all match those found in an earlier single-site study, indicating that the pulsation spectrum changes with time.  相似文献   

18.
High-resolution spectroscopic observations around the Hα line and BVRI photometry of the eclipsing short-period RS CVn star UV Leo are presented. The simultaneous light-curve solution and radial velocity-curve solution led to the following values of the global parameters of the binary: temperatures   T 1= 6000 ± 100 K  and   T 2= 5970 ± 20 K  ; masses   M 1= 0.976 ± 0.067 M⊙  and   M 2= 0.931 ± 0.052 M⊙  ; separation   a = 3.716 ± 0.048 R⊙  ; orbital inclination     ; radii   R 1= 1.115 ± 0.052 R⊙  and   R 2= 1.078 ± 0.051 R⊙  ; equatorial velocities   V 1= 98.8 ± 2.3 km s−1  and   V 2= 89.6 ± 2.7 km s−1  . These results lead to the conclusion that the two components of UV Leo are slightly oversized for their masses and lie within the main-sequence band on the mass–radius diagram, close to the isochrone 9 × 1010 yr.  相似文献   

19.
We have carried out a three-site photometric campaign for the β Cephei star θ Oph from 2003 April to August. 245 h of differential photoelectric u v y photometry were obtained during 77 clear nights. The frequency analysis of our measurements has resulted in the detection of seven pulsation modes within a narrow frequency interval between 7.116 and 7.973 c d−1. No combination or harmonic frequencies have been found. We have performed a mode identification of the individual pulsations from our colour photometry that shows the presence of one radial mode, one rotationally split  ℓ= 1  triplet and possibly three components of a rotationally split  ℓ= 2  quintuplet. We discuss the implications of our findings and point out the similarity of the pulsation spectrum of θ Oph to that of another β Cephei star, V836 Cen.  相似文献   

20.
High-speed spectroscopy of two pulsating subdwarf B stars, KPD 2109+4401 and PB 8783, is presented. Radial motions are detected with the same frequencies as reported from photometric observations and with amplitudes of ∼2 km s−1 in two or more independent modes. These represent the first direct observations of surface motion arising from multimode non-radial oscillations in subdwarf B stars. In the case of the sdB+F binary PB 8783, the velocities of both components are resolved; high-frequency oscillations are found only in the sdB star and not the F star. There also appears to be evidence for mutual motion of the binary components. If confirmed, it implies that the F-type companion is ≳1.2 times more massive than the sdB star, while the amplitude of the F-star acceleration over 4 h would constrain the orbital period to lie between 0.5 and 3.2 d.  相似文献   

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