260 research outputs found
Multiwavelength Observations of the Hot DB Star PG 0112+104
We present a comprehensive multiwavelength analysis of the hot DB white dwarf
PG 0112+104. Our analysis relies on newly-acquired FUSE observations, on
medium-resolution FOS and GHRS data, on archival high-resolution GHRS
observations, on optical spectrophotometry both in the blue and around Halpha,
as well as on time-resolved photometry. From the optical data, we derive a
self-consistent effective temperature of 31,300+-500 K, a surface gravity of
log g = 7.8 +- 0.1 (M=0.52 Msun), and a hydrogen abundance of log N(H)/N(He) <
-4.0. The FUSE spectra reveal the presence of CII and CIII lines that
complement the previous detection of CII transitions with the GHRS. The
improved carbon abundance in this hot object is log N(C)/N(He) = -6.15 +- 0.23.
No photospheric features associated with other heavy elements are detected. We
reconsider the role of PG 0112+104 in the definition of the blue edge of the
V777 Her instability strip in light of our high-speed photometry, and contrast
our results with those of previous observations carried out at the McDonald
Observatory.Comment: 10 pages in emulateapj, 9 figures, accepted for publication in Ap
Characterizing the pulsations of the ZZ Ceti star KUV 02464+3239
We present the results on period search and modeling 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 6 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-fit models resulting from a grid search, we selected 3
that gave l=1 solutions for the largest amplitude modes. These models had
masses of 0.645, 0.650 and 0.680 M_Sun. The 3 `favoured' models have M_H
between 2.5x10^-5 - 6.3x10^-6 M_* and give 14.2 - 14.8 mas seismological
parallax. The 0.645 M_Sun (11400 K) model also matches the spectroscopic log g
and T_eff within 1 sigma. We investigated the possibility of mode trapping and
concluded that while it can explain high amplitude modes, it is not required.Comment: 11 pages, 8 figures, accepted for publication in MNRA
Precursor flares in OJ 287
We have studied three most recent precursor flares in the light curve of the
blazar OJ 287 while invoking the presence of a precessing binary black hole in
the system to explain the nature of these flares. Precursor flare timings from
the historical light curves are compared with theoretical predictions from our
model that incorporate effects of an accretion disk and post-Newtonian
description for the binary black hole orbit. We find that the precursor flares
coincide with the secondary black hole descending towards the accretion disk of
the primary black hole from the observed side, with a mean z-component of
approximately z_c = 4000 AU. We use this model of precursor flares to predict
that precursor flare of similar nature should happen around 2020.96 before the
next major outburst in 2022.Comment: to appear in the Astrophysical Journa
Pulsational Mapping of Calcium Across the Surface of a White Dwarf
We constrain the distribution of calcium across the surface of the white
dwarf star G29-38 by combining time series spectroscopy from Gemini-North with
global time series photometry from the Whole Earth Telescope. G29-38 is
actively accreting metals from a known debris disk. Since the metals sink
significantly faster than they mix across the surface, any inhomogeneity in the
accretion process will appear as an inhomogeneity of the metals on the surface
of the star. We measure the flux amplitudes and the calcium equivalent width
amplitudes for two large pulsations excited on G29-38 in 2008. The ratio of
these amplitudes best fits a model for polar accretion of calcium and rules out
equatorial accretion.Comment: Accepted to the Astrophysical Journal. 16 pages, 10 figures
A precision study of two eclipsing white dwarf plus M dwarf binaries
We use a combination of X-shooter spectroscopy, ULTRACAM high-speed
photometry and SOFI near-infrared photometry to measure the masses and radii of
both components of the eclipsing post common envelope binaries SDSS J1212-0123
and GK Vir. For both systems we measure the gravitational redshift of the white
dwarf and combine it with light curve model fits to determine the inclinations,
masses and radii. For SDSS J1212-0123 we find a white dwarf mass and radius of
0.439 +/- 0.002 Msun and 0.0168 +/- 0.0003 Rsun, and a secondary star mass and
radius of 0.273 +/- 0.002 Msun and 0.306 +/- 0.007 Rsun. For GK Vir we find a
white dwarf mass and radius of 0.564 +/- 0.014 Msun and 0.0170 +/- 0.0004 Rsun,
and a secondary star mass and radius of 0.116 +/- 0.003 Msun and 0.155 +/-
0.003 Rsun. The mass and radius of the white dwarf in GK Vir are consistent
with evolutionary models for a 50,000K carbon-oxygen core white dwarf. Although
the mass and radius of the white dwarf in SDSS J1212-0123 are consistent with
carbon-oxygen core models, evolutionary models imply that a white dwarf with
such a low mass and in a short period binary must have a helium core. The mass
and radius measurements are consistent with helium core models but only if the
white dwarf has a very thin hydrogen envelope, which has not been predicted by
evolutionary models. The mass and radius of the secondary star in GK Vir are
consistent with evolutionary models after correcting for the effects of
irradiation by the white dwarf. The secondary star in SDSS J1212-0123 has a
radius ~9 per cent larger than predicted.Comment: 21 pages, 14 Figures and 11 Tables. Accepted for publication in MNRA
Interstellar detection of CCC and high-precision laboratory measurements near 2THz
ABSTRACT We describe more fully our original tentative interstellar detection of the triatomic pure carbon chain molecule, CCC, in absorption toward the Galactic center source Sgr B2
Vertically resolved aerosol optical properties over the ARM SGP site
We will present an overview of early airborne results obtained aboard the Center for Interdisciplinary Remotely-Piloted
Aircraft Studies (CIRP AS) Twin Otter aircraft during the Atmospheric Radiation Measurement (ARM) program aerosol
intensive observation period in May 2003
Whole Earth Telescope observations of the pulsating subdwarf B star PG 0014+067
PG 0014+067 is one of the most promising pulsating subdwarf B stars for
seismic analysis, as it has a rich pulsation spectrum. The richness of its
pulsations, however, poses a fundamental challenge to understanding the
pulsations of these stars, as the mode density is too complex to be explained
only with radial and nonradial low degree (l < 3) p-modes without rotational
splittings. One proposed solution, for the case of PG 0014+067 in particular,
assigns some modes with high degree (l=3). On the other hand, theoretical
models of sdB stars suggest that they may retain rapidly rotating cores, and so
the high mode density may result from the presence of a few rotationally-split
triplet (l=1), quintuplet (l=2) modes, along with radial (l=0) p-modes. To
examine alternative theoretical models for these stars, we need better
frequency resolution and denser longitude coverage. Therefore, we observed this
star with the Whole Earth Telescope for two weeks in October 2004. In this
paper we report the results of Whole Earth Telescope observations of the
pulsating subdwarf B star PG 0014+067. We find that the frequencies seen in PG
0014+067 do not appear to fit any theoretical model currently available;
however, we find a simple empirical relation that is able to match all of the
well-determined frequencies in this star.Comment: 19 pages, preprint of paper accepted for publication in The
Astrophysical Journa
Resolving Sirius-like binaries with the Hubble Space Telescope
We have imaged seventeen recently discovered Sirius-like binary systems with
HST/WFPC2 and resolved the white dwarf secondary in eight cases. Most of the
implied orbital periods are of order several hundred years, but in three cases
(56 Per, Zeta Cygni and REJ1925-566) the periods are short enough that it may
be possible to detect orbital motion within a few years. It will then be
possible to derive dynamically determined masses for the white dwarfs, and
potentially these stars could be used as stringent tests of the mass-radius
relation and initial-final mass relation.Comment: To appear in Proceedings of the 12th European Workshop on White
Dwarfs, eds. H. Shipman and J. Provenca
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