P-mode observations on Alpha Cen A

We have made a clear detection of p-mode oscillations in the nearest solar-like G2V star $\alpha$ Cen A with the CORALIE spectrograph on the 1.2-m Swiss telescope at the ESO La Silla Observatory. We report the 5 nights of observation on this star in May 2001 during which 1260 high precision radial velocity measurements were obtained. The power spectrum clearly shows several identifiable peaks between 1.7 and 3 mHz. The average large splitting of 105.7 $\mu$Hz and the amplitude of about 35 cm s$^{-1}$ of these modes are in agreement with theoretical expectations.Comment: 4 pages, 4 figures, A&A Letter accepte

Characteristics of solar-like oscillations in red giants observed in the CoRoT exoplanet field

Observations during the first long run (~150 days) in the exo-planet field of CoRoT increase the number of G-K giant stars for which solar-like oscillations are observed by a factor of 100. This opens the possibility to study the characteristics of their oscillations in a statistical sense. We aim to understand the statistical distribution of the frequencies of maximum oscillation power (nu_max) in red giants and to search for a possible correlation between nu_max and the large separation (delta_nu). The nu_max distribution shows a pronounced peak between 20 - 40 microHz. For about half of the stars we obtain delta_nu with at least two methods. The correlation between nu_max and delta_nu follows the same scaling relation as inferred for solar-like stars. The shape of the nu_max distribution can partly be explained by granulation at low frequencies and by white noise at high frequencies, but the population density of the observed stars turns out to be also an important factor. From the fact that the correlation between delta_nu and nu_max for red giants follows the same scaling relation as obtained for sun-like stars, we conclude that the sound travel time over the pressure scale height of the atmosphere scales with the sound travel time through the whole star irrespective of evolution.Comment: Accepted for publication in Astronomy and Astrophysics (CoRoT special issue), 5 pages, 7 figures and 1 tabl

Solar-like oscillations in the G9.5 subgiant beta Aquilae

An interesting asteroseismic target is the G9.5 IV solar-like star beta Aql. This is an ideal target for asteroseismic investigations, because precise astrometric measurements are available from Hipparcos that greatly help in constraining the theoretical interpretation of the results. The star was observed during six nights in August 2009 by means of the high-resolution \'echelle spectrograph SARG operating with the TNG 3.58 m Italian telescope on the Canary Islands, exploiting the iodine cell technique. We present the result and the detailed analysis of high-precision radial velocity measurements, where the possibility of detecting time individual p-mode frequencies for the first and deriving their corresponding asymptotic values will be discussed. The time-series analysis carried out from \sim 800 collected spectra shows the typical p-mode frequency pattern with a maximum centered at 416 \muHz. In the frequency range 300 - 600 \muHz we identified for the first time six high S/N (\gtrsim 3.5) modes with l = 0,2 and 11 < n < 16 and three possible candidates for mixed modes (l = 1), although the p-mode identification for this type of star appears to be quite difficult owing to a substantial presence of avoided crossings. The large frequency separation and the surface term from the set of identified modes by means of the asymptotic relation were derived for the first time. Their values are \Delta \nu = 29.56 \pm 0.10 \muHz and \epsilon = 1.29 \pm 0.04, consistent with expectations. The most likely value for the small separation is \delta\nu_{02} = 2.55 \pm 0.71 \muHz.Comment: 8 pages, 8 figures, 3 tables, accepted by A&

Solar-like oscillations in the metal-poor subgiant nu Indi: II. Acoustic spectrum and mode lifetime

Convection in stars excites resonant acoustic waves which depend on the sound speed inside the star, which in turn depends on properties of the stellar interior. Therefore, asteroseismology is an unrivaled method to probe the internal structure of a star. We made a seismic study of the metal-poor subgiant star nu Indi with the goal of constraining its interior structure. Our study is based on a time series of 1201 radial velocity measurements spread over 14 nights obtained from two sites, Siding Spring Observatory in Australia and ESO La Silla Observatory in Chile. The power spectrum of the high precision velocity time series clearly presents several identifiable peaks between 200 and 500 uHz showing regularity with a large and small spacing of 25.14 +- 0.09 uHz and 2.96 +- 0.22 uHz at 330 uHz. Thirteen individual modes have been identified with amplitudes in the range 53 to 173 cm/s. The mode damping time is estimated to be about 16 days (1-sigma range between 9 and 50 days), substantially longer than in other stars like the Sun, the alpha Cen system or the giant xi Hya.Comment: 5 pages, 7 figures, A&A accepte

Solar-like oscillations in the G8 V star tau Ceti

We used HARPS to measure oscillations in the low-mass star tau Cet. Although the data were compromised by instrumental noise, we have been able to extract the main features of the oscillations. We found tau Cet to oscillate with an amplitude that is about half that of the Sun, and with a mode lifetime that is slightly shorter than solar. The large frequency separation is 169 muHz, and we have identified modes with degrees 0, 1, 2, and 3. We used the frequencies to estimate the mean density of the star to an accuracy of 0.45% which, combined with the interferometric radius, gives a mass of 0.783 +/- 0.012 M_sun (1.6%).Comment: accepted for publication in A&

Characterizing temporary hydrological regimes at a European scale

Monthly duration curves have been constructed from climate data across Europe to help address the relative frequency of ecologically critical low flow stages in temporary rivers, when flow persists only in disconnected pools in the river bed. The hydrological model is 5 based on a partitioning of precipitation to estimate water available for evapotranspiration and plant growth and for residual runoff. The duration curve for monthly flows has then been analysed to give an estimate of bankfull flow based on recurrence interval. The corresponding frequency for pools is then based on the ratio of bank full discharge to pool flow, arguing from observed ratios of cross-sectional areas at flood 10 and low flows to estimate pool flow as 0.1% of bankfull flow, and so estimate the frequency of the pool conditions that constrain survival of river-dwelling arthropods and fish. The methodology has been applied across Europe at 15 km resolution, and can equally be applied under future climatic scenarios

Hot Electron Capture Dissociation Distinguishes Leucine from Isoleucine in a Novel Hemoglobin Variant, Hb Askew, β54(D5)Val→Ile

Population migration has led to the global dispersion of human hemoglobinopathies and has precipitated a need for their identification. An effective mass spectrometry-based procedure involves analysis of the intact α- and β-globin chains to determine their mass, followed by location of the variant amino acid residue by direct analysis of the enzymatically digested chains and low-energy collision induced dissociation of the variant peptide. Using this procedure, a variant was identified as either β54Val→Leu or β54Val→Ile, since the amino acids leucine and isoleucine cannot be distinguished using low-energy collisions. Here, we describe how hot electron capture dissociation on a Fourier transform-ion cyclotron resonance mass spectrometer was used to distinguish isoleucine from leucine and identify the mutation as β54(D5)Val→Ile. This is a novel variant, and we have named it Hb Askew