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ABSTRACT: At the current time, there are 12 white dwarfs in cataclysmic variables
that have shown evidence for pulsations. We are investigating how their
pulsation properties could be different than for single, non-accreting
white dwarfs due to their presence in these accreting close binaries.
Our work includes results from coordinated HST ultraviolet and
ground-based optical observations to determine the temperatures of the
white dwarfs and their location in an instability strip, as well as a
coordinated campaign on SDSS1610-01 and an observing program on GW Lib
and V455 And after both systems underwent dwarf nova outbursts in 2007.
07/2009; 404:229.
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S. J. Kleinman,
Hugh C. Harris,
Daniel J. Eisenstein,
James Liebert,
Atsuko Nitta,
Jurek Krzesiński,
Jeffrey A. Munn,
Conard C. Dahn,
Suzanne L. Hawley,
Jeffrey R. Pier, [......],
Matthew J. Collinge, A. S. Mukadam,
D. Koester,
Alan Uomoto,
D. J. Schlegel,
Scott F. Anderson,
J. Brinkmann,
D. Q. Lamb,
Donald P. Schneider,
and Donald G. York
[show abstract]
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ABSTRACT: We present the full spectroscopic white dwarf and hot subdwarf sample from the Sloan Digital Sky Survey (SDSS) first data release, DR1. We find 2551 white dwarf stars of various types, 240 hot subdwarf stars, and an additional 144 objects we have identified as uncertain white dwarf stars. Of the white dwarf stars, 1888 are nonmagnetic DA types and 171 are nonmagnetic DBs. The remaining (492) objects consist of all different types of white dwarf stars: DO, DQ, DC, DH, DZ, hybrid stars such as DAB, etc., and those with nondegenerate companions. We fit the DA and DB spectra with a grid of models to determine the Teff and log g for each object. For all objects, we provide coordinates, proper motions, SDSS photometric magnitudes, and enough information to retrieve the spectrum/image from the SDSS public database. This catalog nearly doubles the known sample of spectroscopically identified white dwarf stars. In the DR1 imaged area of the sky, we increase the known sample of white dwarf stars by a factor of 8.5. We also comment on several particularly interesting objects in this sample.
The Astrophysical Journal 12/2008; 607(1):426. · 6.02 Impact Factor
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S. F. Anderson,
A. C. Becker,
D. Haggard,
J. L. Prieto,
G. R. Knapp,
M. Sako,
K. B. Halford,
S. Jha,
B. Martin,
J. Holtzman, [......],
P. M. Garnavich,
S. Hayward,
Z. Ivezic, A. S. Mukadam,
B. Sesar,
P. Szkody,
V. Malanushenko,
M. W. Richmond,
D. P. Schneider,
D. G. York
[show abstract]
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ABSTRACT: AM CVn systems are a select group of ultracompact binaries with the shortest orbital periods of any known binary subclass; mass-transfer is likely from a low-mass (partially-)degenerate secondary onto a white dwarf primary, driven by gravitational radiation. In the past few years, the Sloan Digital Sky Survey (SDSS) has provided five new AM CVns. Here we report on two further candidates selected from more recent SDSS data. SDSS J1208+3550 is similar to the earlier SDSS discoveries, recognized as an AM CVn via its distinctive spectrum which is dominated by helium emission. From the expanded SDSS Data Release 6 (DR6) spectroscopic area, we provide an updated surface density estimate for such AM CVns of order 10^{-3.1} to 10^{-2.5} per deg^2 for 15<g<20.5. In addition, we present another new candidate AM CVn, SDSS J2047+0008, that was discovered in the course of followup of SDSS-II supernova candidates. It shows nova-like outbursts in multi-epoch imaging data; in contrast to the other SDSS AM CVn discoveries, its (outburst) spectrum is dominated by helium absorption lines, reminiscent of KL Dra and 2003aw. The variability selection of SDSS J2047+0008 from the 300 deg^2 of SDSS Stripe 82 presages further AM CVn discoveries in future deep, multicolor, and time-domain surveys such as LSST. The new additions bring the total SDSS yield to seven AM CVns thus far, a substantial contribution to this rare subclass, versus the dozen previously known.
03/2008;
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J E S Costa,
S O Kepler,
D E Winget,
M S O 'brien,
S D Kawaler,
A F M Costa,
O Giovannini,
A Kanaan, A S Mukadam,
F Mullally, [......],
J L Provençal,
H Shipman,
M A Wood,
T J Ahrens,
A Grauer,
M Kilic,
P A Bradley,
K Sekiguchi,
R Crowe,
X J Jiang
[show abstract]
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ABSTRACT: Context. PG 1159-035, a pre-white dwarf with T eff ≃ 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters. Methods. We used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods. Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M ⊙ = 0.59 ± 0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r c /R ⋆ = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period P rot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for ℓ = 1 modes and less than 50% for ℓ = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.
J. Krzesinski E. Klumpe J. Larrison T. Lawrence E. Meištas R. E. Nather J.-N. Fu E. Pakštien˙ e R. Rosen E. Romero-Colmenero. 01/2008; 25252728434646(45).
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J. E. S. Costa,
S. O. Kepler,
D. E. Winget,
M. S. O'Brien,
S. D. Kawaler,
A. F. M. Costa,
O. Giovannini,
A. Kanaan, A. S. Mukadam,
F. Mullally, [......],
E. Romero-Colmenero,
R. Riddle,
S. Seetha,
N. M. Silvestri,
M. Vučković,
B. Warner,
S. Zola,
L. G. Althaus,
A. H. Córsico,
M. H. Montgomery
[show abstract]
[hide abstract]
ABSTRACT: PG 1159-035, a pre-white dwarf with T_eff=140,000 K, is the prototype of both two classes: the PG1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. In this work, we used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods and identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M = 0.59 +/- 0.02 solar masses for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r_c = 0.83 +/- 0.05 stellar radius. From the multiplet splitting, we calculated the rotational period P_rot = 1.3920 +/- 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for l=1 modes and less than 50% for l=2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.
12/2007;
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G. Vauclair,
J.-E. Solheim,
J.-N. Fu,
M. Chevreton,
N. Dolez,
M. S. O'Brien, A. S. Mukadam,
S.-L. Kim,
B.-G. Park,
G. Handler, [......],
J. L. Provencal,
S. Dreizler,
S. Schuh,
E. M. Leibowitz,
Y. Lipkin,
X.-B. Zhang,
M. Paparo,
B. Szeidl,
G. Virághalmy,
D. Zsuffa
[show abstract]
[hide abstract]
ABSTRACT: While Abell 43 is entering the PG 1159 instability strip, in fact as an
"hybrid-PG 1159" nucleus of a planetary nebula, PG 0122+200 presently
defines its red edge. So these two stars define the limits of the
instability strip along the evolutionary sequence from the planetary
nebula nuclei to the pre-white dwarf PG 1159 stars. We describe the new
observations that have been obtained recently on these two extreme PG
1159 pulsators. Abell 43, the second discovered "hybrid-PG 1159"
pulsator after HS 2324+3944, is a multi-periodic low amplitude pulsator
with the longest period observed so far in PG 1159 pulsators. As it
shows amplitude variations, follow-up observations are needed to obtain
a sufficient number of frequencies to start an asteroseismological
analysis. We summarize the status of the presently available data. On PG
0122+200, new observations were obtained in 2001 and 2002. Together with
previous data, they allow us to detect 23 frequencies, including seven
triplets and two single frequencies. We interpret the triplets as
ℓ=1 modes split by rotation and confirm an average rotation period
of 1.55 days. From the up-dated average period spacing of 22.9 s, we
derive a mass of 0.59 ± 0.02 Msun, in better
agreement with the spectroscopically derived mass than from previous
estimates, and a luminosity log(L/Lsun)= 1.3 ± 0.5.
The uncertainty on the luminosity is dominated by the poorly determined
surface gravity. We discuss the impact of that new mass determination on
the predicted neutrino luminosity.
08/2007; 372:641.
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[show abstract]
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ABSTRACT: Based on 24h high speed photometry of the hybrid PG 1159 star Abell 43, we have detected 6 sighificant pulsations with periods between 2380 s and 6075 s. A short (4h) run on the almost spectroscopic twin NGC 7094 central star resulted in detection of 3 low amplitude pulsations with periods between 2000 s and 5000 s. The results are close to predictions for g-mode pulsations driven by the kappa-mechanism induced by the partial ionization of carbon and oxygen. Comment: 5 pages, 5 figures, to be published in Astronomy and Astrophysics
05/2007;
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[show abstract]
[hide abstract]
ABSTRACT: We use the new ZZ Ceti stars (hydrogen atmosphere white dwarf variables;
DAVs) discovered within the Sloan Digital Sky Survey (Mukadam et al.
2004a) to re-define the empirical ZZ Ceti instability strip. This is
the first time since the discovery of white dwarf variables in 1968 that
we have a statistically significant set of homogeneous spectra of ZZ
Ceti stars, acquired using the same detection system and with consistent
data reductions. The homogeneity of the spectra reduces the scatter in
the spectroscopic temperatures and we find a narrow instability strip of
width ˜ 950 K, from 10850-11800 K. We question the purity of the
instability strip as we find several non-variables within.
06/2005; 334:459.
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G. Handler,
D. O'Donoghue,
M. Müller,
J.-E. Solheim,
J. M. Gonzalez-Perez,
F. Johannessen,
M. Paparo,
B. Szeidl,
G. Viraghalmy,
R. Silvotti, [......],
R. Janulis,
R. Kalytis,
D. Ališauskas,
S. K. Anguma,
P. C. Kalebwe,
P. Moskalik,
W. Ogloza,
G. Stachowski,
G. Pajdosz,
S. Zola
[show abstract]
[hide abstract]
ABSTRACT: We have acquired new time series photometry of the two pulsating DB white dwarf stars KUV 05134+2605 and PG 1654+160 with the Whole Earth Telescope. Additional single-site photometry is also presented. We use all these data plus all available archival measurements to study the temporal behaviour of the pulsational amplitudes and frequencies of these stars for the first time.We demonstrate that both KUV 05134+2605 and PG 1654+160 pulsate in many modes, the amplitudes of which are variable in time; some frequency variability of PG 1654+160 is also indicated. Beating of multiple pulsation modes cannot explain our observations; the amplitude variability must therefore be intrinsic. We cannot find stable modes to be used for determinations of the evolutionary period changes of the stars. Some of the modes of PG 1654+160 appear at the same periods whenever detected. The mean spacing of these periods (≈40 s) suggests that they are probably caused by non-radial gravity-mode pulsations of spherical degree ℓ= 1. If so, PG 1654+160 has a mass around 0.6 M⊙.The time-scales of the amplitude variability of both stars (down to two weeks) are consistent with theoretical predictions of resonant mode coupling, a conclusion which might however be affected by the temporal distribution of our data.
Monthly Notices of the Royal Astronomical Society 03/2003; 340(3):1031 - 1038. · 4.90 Impact Factor
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226:337.
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S. O. Kepler,
E. R. Nather,
D. E. Winget,
A. Nitta,
S. J. Kleinman,
T. Metcalfe,
K. Sekiguchi,
Xiaojun Jiang,
D. Sullivan,
T. Sullivan, [......],
A. E. Collins,
M. Boyer,
J. S. Shaw, A. S. Mukadam,
E. W. Klumpe,
J. Larrison,
S. D. Kawaler,
R. L. Riddle,
A. Ulla,
P. Bradley
[show abstract]
[hide abstract]
ABSTRACT: We report on the 323 hours of nearly uninterrupted time series
photometric observations of the DBV star GD 358 acquired with the Whole
Earth Telescope (WET) during May 23 to June 8, 2000. We acquired more
than 232000 independent measurements and detected the non-radial g-modes
consistent with degree l=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 l=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.
Baltic Astronomy. 12:45-53.
