2,165 research outputs found
Quasi-molecular lines in Lyman wings of cool DA white dwarfs; Application to FUSE observations of G231-40
We present new theoretical calculations of the total line profiles of Lyman
alpha and Lyman beta which include perturbations by both neutral hydrogen AND
protons and all possible quasi-molecular states of H_2 and H_2^+. They are used
to improve theoretical modeling of synthetic spectra for cool DA white dwarfs.
We compare them with FUSE observation of G231-40. The appearance of the line
wings between Lyman alpha and Lyman beta is shown to be sensitive to the
relative abundance of hydrogen ions and neutral atoms, and thereby to provide a
temperature diagnostic for stellar atmospheres and laboratory plasmas.Comment: 6 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Largest eigenvalue distribution in the double scaling limit of matrix models: A Coulomb fluid approach
Using thermodynamic arguments we find that the probability that there are no
eigenvalues in the interval (-s,\infty) in the double scaling limit of
Hermitean matrix models is O(exp(-s^{2m+1})) as s\to+\infty.Here m=1,2,3..
determine the m^{th} multi-critical point of the level density:\sigma(x)\sim
b[1-(x/b)^2]^{m-1/2} and b^2\sim N.Furthermore,the size of the transition zone
where the eigenvalue density becomes vanishingly small at the tail of the
spectrum is \sim N^{(m-3/2)/(2m+1)} in agreement with earlier work based on the
string equation.Comment: 10 pages, no figures, to appear in J.Phys. A Lett. 199
Quasi-molecular Satellites of Lyman Beta in the Spectrum of the DA White Dwarf WOLF 1346
We present new FUV/UV observations of the DA white dwarf Wolf 1346 obtained
with the Hopkins Ultraviolet Telescope. The atmospheric parameters of this
object are estimated from a fit of model atmospheres to several optical spectra
to be Teff = 20000 K, log g = 7.90. From the optical spectrum this star is a
normal DA without any indications for chemical elements other than hydrogen.
The hydrogen line L beta, however, shows a very unusual shape, with a steep red
wing and two absorption features on this wing. The shape is reminiscent of the
effects of quasi-molecular line broadening, as observed in L alpha in cooler DA
white dwarfs. We show that this is indeed the correct explanation, by
identifying 4 quasi-molecular satellites caused through perturbations by the H+
ion (H2+ quasi-molecule). The steep red wing is caused by the exponential
decline of the line profile beyond the satellite most distant from the line
center at 1078 A.Comment: 11 pages Latex with aaspp4 style, 4 postscript figures, as compressed
tar file, ApJ Letters, in pres
K-H_2 Quasi-molecular absorption detected in the T-dwarf epsilon Indi Ba
T-type dwarfs present a broad and shallow absorption feature centred around
6950 A in the blue wing of the K doublet at 0.77 micron which resembles in
depth and shape the satellite absorption predicted by detailed collisional
broadening profiles. In our previous work, the predicted line satellite
position was however somewhat too blue compared to the observed feature. In
this paper we investigate whether new calculations of the energy surfaces of
the potentials in the K-H_2 system, including spin-orbit coupling, result in a
closer coincidence of the satellite with the observed position. We also
investigate the extent to which CaH absorption bands contribute to the feature.
We present model atmospheres and synthetic spectra, including gravitational
settling for an improved description of depth-dependent abundances of
refractory elements, and based on new K-H_2 line profiles using improved
interaction potentials. By comparison with a high signal-to-noise optical
spectrum of the T1 dwarf epsilon Indi Ba, we find that these new models do
reproduce the observed feature, while CaH does not contribute for the
atmospheric parameters considered. We also find that CaH is settled out so deep
into the atmosphere that even turbulent vertical mixing would appear
insufficient to bring significant amounts of CaH to the photosphere in dwarfs
later than ~L5. We conclude that previous identification of the feature at this
location in T and late L dwarf spectra with CaH was erroneous, as expected on
physical grounds: calcium condenses onto grains in early L dwarfs and thus
should have settled out of the photosphere in cooler brown dwarfs. This finding
revokes one observational verification for the cloud-clearing theory: a gradual
clearing of the cloud cover in early T dwarfs.Comment: accepted for publication by Astronomy & Astrophysics Letters, 4
pages, 3 colour figure
FUSE observations of G226-29: First detection of the H_2 quasi-molecular satellite at 1150A
We present new FUV observations of the pulsating DA white dwarf G226-29
obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). This ZZ Ceti
star is the brightest one of its class and the coolest white dwarf observed by
FUSE. We report the first detection of the broad quasi-molecular
collision-induced satellite of Ly-beta at 1150 A, an absorption feature that is
due to transitions which take place during close collisions of hydrogen atoms.
The physical interpretation of this feature is based on recent progress of the
line broadening theory of the far wing of Ly-beta. This predicted feature had
never been observed before, even in laboratory spectra.Comment: Accepted for publication in ApJ Letters; 6 pages, 3 figure
Metallicity of M dwarfs III. Planet-metallicity and planet-stellar mass correlations of the HARPS GTO M dwarf sample
Aims. The aim of this work is the study of the planet-metallicity and the
planet-stellar mass correlations for M dwarfs from the HARPS GTO M dwarf
subsample
Methods. We use a new method that takes advantage of the HARPS
high-resolution spectra to increase the precision of metallicity, using
previous photometric calibrations of [Fe/H] and effective temperature as
starting values.
Results. In this work we use our new calibration (rms = 0.08 dex) to study
the planet-metallicity relation of our sample. The well-known correlation for
Giant planet FGKM hosts with metallicity is present. Regarding Neptunians and
smaller hosts no correlation is found but there is a hint that an
anti-correlation with [Fe/H] may exist. We combined our sample with the
California Planet Survey late-K and M-type dwarf sample to increase our
statistics but found no new trends. We fitted a power law to the frequency
histogram of the Jovian hosts for our sample and for the combined sample, f_p =
C10^\alpha[Fe/H], using two different approaches: a direct bin fitting and a
bayesian fitting procedure. We obtained a value for C between 0.02 and 0.04 and
for \alpha between 1.26 and 2.94.
Regarding stellar mass, an hypothetical correlation with planets was
discovered, but was found to be the result of a detection bias.Comment: Accepted for publication in A&A. 18 pages, 11 Figures, 12 Table
Metallicity of M dwarfs IV. A high-precision [Fe/H] and Teff technique from high-resolution optical spectra for M dwarfs
Aims. In this work we develop a technique to obtain high precision
determinations of both metallicity and effective temperature of M dwarfs in the
optical.
Methods. A new method is presented that makes use of the information of 4104
lines in the 530-690 nm spectral region. It consists in the measurement of
pseudo equivalent widths and their correlation with established scales of
[Fe/H] and .
Results. Our technique achieves a of 0.080.01 for [Fe/H],
9113 K for , and is valid in the (-0.85, 0.26 dex), (2800, 4100
K), and (M0.0, M5.0) intervals for [Fe/H], and spectral type
respectively. We also calculated the RMSE which estimates uncertainties
of the order of 0.12 dex for the metallicity and of 293 K for the effective
temperature. The technique has an activity limit and should only be used for
stars with . Our method is available
online at \url{http://www.astro.up.pt/resources/mcal}.Comment: Accepted in Astronomy and Astrophysics. Updated one important
reference in the introduction. Some typos correcte
LP 400-22, A very low-mass and high-velocity white dwarf
We report the identification of LP 400-22 (WD 2234+222) as a very low-mass
and high-velocity white dwarf. The ultraviolet GALEX and optical photometric
colors and a spectral line analysis of LP 400-22 show this star to have an
effective temperature of 11080+/-140 K and a surface gravity of log g =
6.32+/-0.08. Therefore, this is a helium core white dwarf with a mass of 0.17
M_solar. The tangential velocity of this white dwarf is 414+/-43 km/s, making
it one of the fastest moving white dwarfs known. We discuss probable
evolutionary scenarios for this remarkable object.Comment: accepted for publication in ApJ Letters, made minor correction
FUSE Observation of the Ultramassive White Dwarf PG1658+441
We present an analysis of the Far Ultraviolet Spectroscopic Explorer (FUSE)
spectrum of the ultramassive (M = 1.31 solar mass), magnetic (B_s = 2.3 MG)
white dwarf PG 1658+441. The far ultraviolet (FUV) spectrum exhibits very broad
Lyman lines and quasi-molecular Lyman beta satellites, but weak Lyman gamma
satellites may also be present. PG 1658+441 is the hottest white dwarf known to
show these satellite features. We fit the Lyman lines with stellar models and
obtain atmospheric parameters consistent with a published analysis of the
Balmer lines. By averaging results obtained for the different FUSE segments, we
determine Teff = 29,620 +/- 500K and log g = 9.31 +/- 0.07. The models match
the data over large portions of the spectrum but discrepancies remain near the
satellite features. Finally, no trace elements have been identified in the FUV
spectrum, and we provide abundance upper limits for C, N, Si, and P.Comment: 17 pages, 4 figure
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