1,478 research outputs found
The Deuterium, Oxygen, and Nitrogen Abundance Toward LSE 44
We present measurements of the column densities of interstellar DI, OI, NI,
and H2 made with FUSE, and of HI made with IUE toward the sdO star LSE 44, at a
distance of 554+/-66 pc. This target is among the seven most distant Galactic
sight lines for which these abundance ratios have been measured. The column
densities were estimated by profile fitting and curve of growth analyses. We
find D/H = (2.24 +1.39 -1.32)E-5, D/O = (1.99 +1.30 -0.67)E-2, D/N = (2.75
+1.19 -0.89)E-1, and O/H = (1.13 +0.96 -0.71)E-3 (2 sigma). Of the most distant
Galactic sight lines for which the deuterium abundance has been measured LSE 44
is one of the few with D/H higher than the Local Bubble value, but D/O toward
all these targets is below the Local Bubble value and more uniform than the D/H
distribution. (Abstract abridged.)Comment: 20 pages, including 9 figures. Accepted for publication in Ap
Close binary EHB stars from SPY
We present the results of a radial velocity (RV) survey of 46 subdwarf B
(sdB) and 23 helium-rich subdwarf O (He-sdO) stars. We detected 18 (39%) new
sdB binary systems, but only one (4%) He-sdO binary. Orbital parameters of nine
sdB and sdO binaries, derived from follow-up spectroscopy, are presented. Our
results are compared with evolutionary scenarios and previous observational
investigations.Comment: To appear in "Extreme Horizontal Branch Stars and Related Objects",
Astrophysics and Space Science, Kluver Academic Publishers, edited by P.F.L.
Maxte
Striking Photospheric Abundance Anomalies in Blue Horizontal-Branch Stars in Globular Cluster M13
High-resolution optical spectra of thirteen blue horizontal-branch (BHB)
stars in the globular cluster M13 show enormous deviations in element
abundances from the expected cluster metallicity. In the hotter stars (T_eff >
12000 K), helium is depleted by factors of 10 to 100 below solar, while iron is
enhanced to three times the solar abundance, two orders of magnitude above the
canonical metallicity [Fe/H] ~= -1.5 dex for this globular cluster. Nitrogen,
phosphorus, and chromium exhibit even more pronounced enhancements, and other
metals are also mildly overabundant, with the exception of magnesium, which
stays very near the expected cluster metallicity. These photospheric anomalies
are most likely due to diffusion --- gravitational settling of helium, and
radiative levitation of the other elements --- in the stable radiative
atmospheres of these hot stars. The effects of these mechanisms may have some
impact on the photometric morphology of the cluster's horizontal branch and on
estimates of its age and distance.Comment: 11 pages, 1 Postscript figure, uses aaspp4.sty, accepted for
publication in ApJ Letter
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Noble gases from the interstellar medium trapped on the MIR space station and analyzed by in vacuo etching
Introduction: The composition of the present interstellar medium (ISM) provides an important benchmark in cosmochemistry. It serves as a reference for galactic chemical evolution (GCE) models, solar mixing predictions and provides information for understanding Big Bang nucleosynthesis. The present-day ISM 3He abundance allows, combined with the protosolar 3He, deduced from the Jovian atmosphere or meteorites [1,2], tracing the GCE over the past 4.56 Ga. 3He/4He = (2.5 0.6) x 10-4 has been determined for the local ISM [3]. However, the uncertainty is too large to better constrain GCE models and - in combination with the present-day solar wind value - the protosolar D/H [4]
First Kepler results on compact pulsators II: KIC 010139564, a new pulsating subdwarf B (V361 Hya) star with an additional low-frequency mode
We present the discovery of nonradial pulsations in a hot subdwarf B star
based on 30.5 days of nearly continuous time-series photometry using the
\emph{Kepler} spacecraft. KIC 010139564 is found to be a short-period pulsator
of the V361 Hya (EC 14026) class with more than 10 independent pulsation modes
whose periods range from 130 to 190 seconds. It also shows one periodicity at a
period of 3165 seconds. If this periodicity is a high order g-mode, then this
star may be the hottest member of the hybrid DW Lyn stars. In addition to the
resolved pulsation frequencies, additional periodic variations in the light
curve suggest that a significant number of additional pulsation frequencies may
be present. The long duration of the run, the extremely high duty cycle, and
the well-behaved noise properties allow us to explore the stability of the
periodic variations, and to place strong constraints on how many of them are
independent stellar oscillation modes. We find that most of the identified
periodicities are indeed stable in phase and amplitude, suggesting a rotation
period of 2-3 weeks for this star, but further observations are needed to
confirm this suspicion.Comment: 10 pages, accepted for publication in MNRA
HE 0437-5439 -- an unbound hyper-velocity main-sequence B-type star
We report the discovery of a 16th magnitude star, HE0437-5439, with a
heliocentric radial velocity of +723+-3km/s. A quantitative spectral analysis
of high-resolution optical spectra obtained with the VLT and the UVES
spectrograph shows that HE0437-5439 is a main sequence B-type star with
Teff=20350K, log g=3.77, solar within a factor of a few helium abundance and
metal content, rotating at v sin i=54km/s. Using appropriate evolutionary
tracks we derive a mass of 8 Msun and a corresponding distance of 61 kpc. Its
galactic rest frame velocity is at least 563km/s, almost twice the local
Galactic escape velocity, indicating that the star is unbound to the Galaxy.
Numerical kinematical experiments are carried out to constrain its place of
birth. It has been suggested that such hyper-velocity stars can be formed by
the tidal disruption of a binary through interaction with the super-massive
black hole at the Galactic center (GC). HE0437-5439 needs about 100Myrs to
travel from the GC to its presentposition, much longer than its main sequence
lifetime of 25Myrs. This can only be reconciled if HE0437-5439 is a blue
straggler star. In this case, the predicted proper motion is so small that it
can only be measured by future space missions. Since the star is much closer to
the Large Magellanic Cloud (LMC, 18kpc) than to the GC, it can reach its
position from the center of the LMC. The proper motion predicted in this case
is about 2mas/y (relative to the LMC), large enough to be measurable with
conventional techniques from the ground. The LMC origin could also be tested by
a high-precision abundance analysis.Comment: 13 pages, 4 figures. Astrophysical Journal Letters, accepte
PG 1613+426: a new sdB pulsator
We report the detection of short period oscillations in the hot subdwarf B
(sdB) star PG 1613+426 from time-series photometry carried out with the 91-cm
Cassegrain telescope of the Catania Astrophysical Observatory. This star, which
is brighter than the average of the presently known sdB pulsators, with B =
14.14 mag, has and , its position
is near the hot end of the sdB instability strip, and it is a pulsator with a
well observed peak in the power spectrum at . This star
seems to be well suited for high precision measurements, which could detect a
possible multi-mode pulsation behaviourComment: 3 pages, 4 figures. to appear on A&
A Quantitative Analysis of the Available Multicolor Photometry for Rapidly Pulsating Hot B Subdwarfs
We present a quantitative and homogeneous analysis of the broadband
multicolor photometric data sets gathered so far on rapidly pulsating hot B
subdwarf stars. This concerns seven distinct data sets related to six different
stars. Our analysis is carried out within the theoretical framework developed
by Randall et al., which includes full nonadiabatic effects. The goal of this
analysis is partial mode identification, i.e., the determination of the degree
index l of each of the observed pulsation modes. We assume possible values of l
from 0 to 5 in our calculations. For each target star, we compute a specific
model atmosphere and a specific pulsation model using estimates of the
atmospheric parameters coming from time-averaged optical spectroscopy. For
every assumed value of l, we use a formal chi-squared approach to model the
observed amplitude-wavelength distribution of each mode, and we compute a
quality-of-fit Q probability to quantify the derived fit and to discriminate
objectively between the various solutions. We find that no completely
convincing and unambiguous l identification is possible on the basis of the
available data, although partial mode discrimination has been reached for 25
out of the 41 modes studied. A brief statistical study of these results
suggests that a majority of the modes must have l values of 0, 1, and 2, but
also that modes with l = 4 could very well be present while modes with l = 3
appear to be rarer. This is in line with recent results showing that l = 4
modes in rapidly pulsating B subdwarfs have a higher visibility in the optical
domain than modes with l = 3. Although somewhat disappointing in terms of mode
discrimination, our results still suggest that the full potential of multicolor
photometry for l identification in pulsating subdwarfs is within reach.Comment: 59 pages, 18 figures, accepted for publication in the Astrophysical
Journal Supplement Serie
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