Spectroscopic observations in the range 6500-6700 Å and BVRI photometry of the eclipsing short-period RS CVn-star RT And are presented. We determined $K_1=130$ km s-1 and $K_2=175.8$ km s-1 by ...measurement of the double profiles of the lines Hα and FeI 6678, and obtained the mass ratio $q=0.74$ and masses of the star components $M_1=1.23$ $M_{\odot}$ and $M_2=0.91$ $M_{\odot}$. It was established that the emission activity of RT And is associated with its secondary component. The relative contribution of the secondary star is stronger in the FeI 6678 line than in Hα. A strong emission feature between the two profiles of FeI 6678 at phase 0.73 was detected that is probably due to the appearance of extended emitting structure. The multicolor light curve of RT And is fitted by two cool spots on the primary star with equal sizes 21° and temperatures 4980 K and located at middle latitudes and longitudes symmetrical to the line connecting the star centers. Both spectral and photometric data lead to the conclusion that the secondary star of RT And is oversized for its mass.
The everchanging pulsating white dwarf GD358 Kepler, S. O.; Nather, R. E.; Winget, D. E. ...
Astronomy and astrophysics (Berlin),
04/2003, Letnik:
401, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We report 323 hours of nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23rd to June 8th, 2000. We acquired ...more than 232 000 independent measurements. We also report on 48 hours of time-series photometric observations in Aug 1996. We detected the non-radial g-modes consistent with degree $\ell=1$ and radial order 8 to 20 and their linear combinations up to 6th order. We also detect, for the first time, a high amplitude $\ell=2$ mode, with a period of 796 s. In the 2000 WET data, the largest amplitude modes are similar to those detected with the WET observations of 1990 and 1994, but the highest combination order previously detected was 4th order. At one point during the 1996 observations, most of the pulsation energy was transferred into the radial order $k=8$ mode, which displayed a sinusoidal pulse shape in spite of the large amplitude. The multiplet structure of the individual modes changes from year to year, and during the 2000 observations only the $k=9$ mode displays clear normal triplet structure. Even though the pulsation amplitudes change on timescales of days and years, the eigenfrequencies remain essentially the same, showing the stellar structure is not changing on any dynamical timescale.
We report on an analysis of 308.3 hr of high-speed photometry targeting the pulsating DA white dwarf EC14012-1446. The data were acquired with the Whole Earth Telescope during the 2008 international ...observing run XCOV26. The Fourier transform of the light curve contains 19 independent frequencies and numerous combination frequencies. The dominant peaks are 1633.907, 1887.404, and 2504.897 mu Hz. Our analysis of the combination amplitudes reveals that the parent frequencies are consistent with modes of spherical degree l = 1. The combination amplitudes also provide m identifications for the largest amplitude parent frequencies. Our seismology analysis, which includes 2004-2007 archival data, confirms these identifications, provides constraints on additional frequencies, and finds an average period spacing of 41 s. Building on this foundation, we present nonlinear fits to high signal-to-noise light curves from the SOAR 4.1 m, McDonald 2.1 m, and KPNO 2 m telescopes. The fits indicate a time-averaged convective response timescale of tau sub(0) = 99.4 + or - 17 s, a temperature exponent N = 85 + or - 6.2, and an inclination angle of theta sub(i) = 32degrees.9 + or - 3degrees.2. We present our current empirical map of the convective response timescale across the DA instability strip.
We present the results of a statistical investigation of the period-color and period-bolometric magnitude relations using a carefully selected sample of 120 contact systems with known physical ...parameters.
Preliminary XCOV26 results for EC14012-1446 Provencal, J L; Thompson, S; Montgomery, M ...
Journal of physics. Conference series,
06/2009, Letnik:
172, Številka:
1
Journal Article
Recenzirano
Odprti dostop
EC14012-1446 is a hydrogen atmosphere (DA) white dwarf pulsator. Its rich pulsation spectrum displays a range of excited modes with complex multiplet structure, in addition to numerous combination ...frequencies. In April 2008, EC14012-1446 was the primary target of XCOV26. We obtained over 300 hrs of nearly continuous high speed photometry with the goal of using the nonlinear pulse shapes to empirically determine the parameters of the convection zone. The Fourier transform (FT) of the light curve contains power between 1000 to 4000 μHz, with the dominant peak at 1234 μHz. We find 13 independent frequencies distributed in 8 modes, as well as a myriad of combination frequencies. In the following, we present preliminary results and lay the groundwork for future investigation leading to light curve fitting of EC14012-1446.
Constraining the Evolution of ZZ Ceti Mukadam, Anjum S; Kepler, S. O; Winget, D. E ...
The Astrophysical journal,
09/2003, Letnik:
594, Številka:
2
Journal Article
We present results from a multisite (‘Whole Earth Telescope’) photometric campaign on PG 1336−018, the close eclipsing binary system containing a pulsating subdwarf B (sdB) star. The main part of the ...campaign (1999 April) resulted in ∼172 h of observations, representing a coverage of about 47 per cent, and additional data were obtained outside the core campaign. Periodogram analysis shows that the light variations are dominated by three frequencies near 5757, 5585 and 5369 μHz (∼174, 179 and 186 s, respectively), although many frequencies are present, particularly in the range 5000–6000 μHz (∼200–170 s). We identify, with some confidence, 28 frequencies down to a semi-amplitude of 0.0005 in fractional intensity (equivalent to about 0.5 mmag). It is clear that the pulsation frequencies of PG 1336−018 have changed substantially since the 1996 discovery observations were made, and that amplitude changes occur, at least in the dominant three frequencies, on relatively short time-scales (of the order of a day). On the assumption that the pulsating star is phase-locked in the binary system, we have searched for rotational splitting of frequencies near the orbital and half of the orbital period, but the results are confused by aliasing at those frequencies (due to the data gaps caused by the eclipses). A preliminary model qualitatively matches the distribution of frequencies in PG 1336−018, with some good individual correspondences, but cannot be considered adequate because geometric cancellation should hide some of the modes which are apparently detected. Analysis of the pulsations during eclipse recovers three of the strongest modes, but the limited eclipse data — which can, at best, be only about 9 per cent of the total — do not allow mode identification at this stage. Simulations indicate that an overall coverage of about 80 per cent would be required for this to be viable. An attempt was made to determine phase shifts in the pulsation frequencies as a way of directly measuring the size of the binary orbit, but the uncertainties in the method are comparable to the light travel time across the orbit (probably less than a second).
Radial velocity measurements and sine-curve fits to orbital velocity variations are presented for the ninth set of 10 close binary systems: V395 And, HS Aqr, V449 Aur, FP Boo, SW Lac, KS Peg, IW Per, ...V592 Per, TU UMi, and FO Vir. The first three are very close, possibly detached, early-type binaries, and all three require further investigation. Particularly interesting is V395 And, whose spectral type is as early as B7/8 for a 0.685 day orbit binary. KS Peg and IW Per are single-line binaries, with the former probably hosting a very low mass star. We have detected a low-mass secondary in an important semidetached system, FO Vir, at q = 0.125 ± 0.005. The contact binary FP Boo is also a very small mass ratio system, q = 0.106 ± 0.005. The other contact binaries in this group are V592 Per, TU UMi, and the well-known SW Lac. V592 Per and TU UMi have bright tertiary companions; for these binaries, and for V395 And, we used a novel technique of arranging the broadening functions into a two-dimensional image in phase. The case of TU UMi turned out to be intractable even using this approach, and we have not been able to derive a firm radial velocity orbit for this binary. Three systems of this group were observed spectroscopically before: HS Aqr, SW Lac, and KS Peg.
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