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 $T_{eff}$. Results. Our technique achieves a $rms$ of 0.08$\pm$0.01 for [Fe/H], 91$\pm$13 K for $T_{eff}$, and is valid in the (-0.85, 0.26 dex), (2800, 4100 K), and (M0.0, M5.0) intervals for [Fe/H], $T_{eff}$ and spectral type respectively. We also calculated the RMSE$_{V}$ 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 $\log{L_{H_{\alpha}}/L_{bol}} < -4.0$. 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