Kinetics of the Reaction of N-Ethylmalemide with Cysteine and Some Congeners

Physical Chemistr

Solar-like oscillations of semiregular variables

Oscillations of the Sun and solar-like stars are believed to be excited stochastically by convection near the stellar surface. Theoretical modeling predicts that the resulting amplitude increases rapidly with the luminosity of the star. Thus one might expect oscillations of substantial amplitudes in red giants with high luminosities and vigorous convection. Here we present evidence that such oscillations may in fact have been detected in the so-called semiregular variables, extensive observations of which have been made by amateur astronomers in the American Association for Variable Star Observers (AAVSO). This may offer a new opportunity for studying the physical processes that give rise to the oscillations, possibly leading to further information about the properties of convection in these stars.Comment: Astrophys. J. Lett., in the press. Processed with aastex and emulateap

Asteroseismology of Procyon A with SARG at TNG

We present high precision radial velocity measurements on the F5 IV star alpha CMi obtained by the SARG spectrograph at TNG (Telescopio Nazionale Galileo) exploiting the iodine cell technique. The time series of about 950 spectra of Procyon A taken during 6 observation nights are affected by an individual error of 1.3 m/s. Thanks to the iodine cell technique, the spectrograph contribution to the Doppler shift measurement error is quite negligible and our error is dominated by the photon statistics Brown et al 1994. An excess of power between 0.5 and 1.5 mHz, detected also by Martic et al. 2004 has been found. We determined a large separation frequency Delta nu0 = 56\pm 2 microHz, consistent with both theoretical estimates Chaboyer et al. 1999 and previous observations Martic et al. 2004.Comment: 4 pages, 5 figures, accepted to be published in A&A Letter

Precise radial velocities of giant stars. IV. A correlation between surface gravity and radial velocity variation and a statistical investigation of companion properties

Since 1999, we have been conducting a radial velocity survey of 179 K giants using the CAT at UCO/Lick observatory. At present ~20-100 measurements have been collected per star with a precision of 5 to 8 m/s. Of the stars monitored, 145 (80%) show radial velocity (RV) variations at a level >20 m/s, of which 43 exhibit significant periodicities. Our aim is to investigate possible mechanism(s) that cause these observed RV variations. We intend to test whether these variations are intrinsic in nature, or possibly induced by companions, or both. In addition, we aim to characterise the parameters of these companions. A relation between log g and the amplitude of the RV variations is investigated for all stars in the sample. Furthermore, the hypothesis that all periodic RV variations are caused by companions is investigated by comparing their inferred orbital statistics with the statistics of companions around main sequence stars. A strong relation is found between the amplitude of the RV variations and log g in K giant stars, as suggested earlier by Hatzes & Cochran (1998). However, most of the stars exhibiting periodic variations are located above this relation. These RV variations can be split in a periodic component which is not correlated with log g and a random residual part which does correlate with log g. Compared to main-sequence stars, K giants frequently exhibit periodic RV variations. Interpreting these RV variations as being caused by companions, the orbital param eters are different from the companions orbiting dwarfs. Intrinsic mechanisms play an important role in producing RV variations in K giants stars, as suggested by their dependence on log g. However, it appears that periodic RV variations are additional to these intrinsic variations, consistent with them being caused by companions.Comment: 10 pages, accepted by A&

Solar-like oscillations in Procyon A

The F5 subgiant Procyon A (alpha CMi, HR 2943) was observed with the Coralie fiber-fed echelle spectrograph on the 1.2-m Swiss telescope at La Silla in February 1999. The resulting 908 high-accuracy radial velocities exhibit a mean noise level in the amplitude spectrum of 0.11 m s^-1 at high frequency. These measurements show significant excess in the power spectrum between 0.6-1.6 mHz with 0.60 m s^-1 peak amplitude. An average large spacing of 55.5 uHz has been determined and twenty-three individual frequencies have been identified.Comment: A&A accepte

Asteroseismology of Procyon with SOPHIE

This paper reports a 9-night asteroseismic observation program conducted in January 2007 with the new spectrometer Sophie at the OHP 193-cm telescope, on the F5 IV-V target Procyon A. This first asteroseismic program with Sophie was intended to test the performance of the instrument with a bright but demanding asteroseismic target and was part of a multisite network. The Sophie spectra have been reduced with the data reduction software provided by OHP. The Procyon asteroseismic data were then analyzed with statistical tools. The asymptotic analysis has been conducted considering possible curvature in the echelle diagram analysis. These observations have proven the efficient performance of Sophie used as an asteroseismometer, and succeed in a clear detection of the large spacing. An \'echelle diagram based on the 54-$\mu$Hz spacing shows clear ridges. Identification of the peaks exhibits large spacings varying from about 52 $\mu$Hz to 56 $\mu$Hz.Comment: 7 pages, 7 figure

Seismic inference of differential rotation in Procyon A

The differential rotation of the F5V-IV star Procyon A is computed for a class of models which are consistent with recent astrometric and asteroseismic data. The rotation pattern is determined by solving the Reynolds equation for motion, including the convective energy transport, where the latter is anisotropic owing to the Coriolis force action which produces a horizontal temperature gradient between the poles and the equator. All the models show a decrease of the rotation rate with increasing radius and solar-type isorotation surfaces with the equator rotating faster than the poles, the horizontal rotational shear being much smaller for models with a less extended convective envelope. The meridional flow circulation can be either clockwise or counter-clockwise, and in some cases a double latitudinal cell appears. The rotational splittings are calculated for low degree $p$-modes with $l=1, m=1$ and $l=2, m=1,2$, and it is shown that, for modes with $m=1$, the stronger is the horizontal differential rotation shear the weaker the effect on the average rotational splitting expected, whilst the opposite happens for the mode with $m=2$. On the basis of the present study, a resolution of $10 \rm nHz$ in individual oscillation frequencies seems to be necessary to test the different dynamical behaviour of the proposed models, that appears barely achievable even in the forthcoming space missions. However, the average over several observed splittings could produce the required accuracy.Comment: 9 pages, 7 figures, A&A to appea

Empirical Constraints on Convective Core Overshoot

In stellar evolution calculations, the local pressure scale height is often used to empirically constrain the amount of convective core overshoot. However, this method brings unsatisfactory results for low-mass stars (< 1.1 -1.2 Mo for Z= \Zs) which have very small cores or no convective core at all. Following Roxburgh's integral constraint,we implemented an upper limit of overshoot within the conventional method of alpha parameterization in order to remove an overly large overshoot effect on low-mass stars. The erroneously large effect of core overshoot due to the failure of alpha parameterization can be effectively corrected by limiting the amount of overshoot to < 15 % of the core radius. 15 % of the core radius would be a proper limit of overshoot which can be implemented in a stellar evolution code for intermediate to low mass stars. The temperature structure of the overshoot region does not play a crucial role in stellar evolution since this transition region is very thin.Comment: 15 pages, 5 figures, accepted for A

SOPHIE+: First results of an octagonal-section fiber for high-precision radial velocity measurements

High-precision spectrographs play a key role in exoplanet searches and Doppler asteroseismology using the radial velocity technique. The 1 m/s level of precision requires very high stability and uniformity of the illumination of the spectrograph. In fiber-fed spectrographs such as SOPHIE, the fiber-link scrambling properties are one of the main conditions for high precision. To significantly improve the radial velocity precision of the SOPHIE spectrograph, which was limited to 5-6 m/s, we implemented a piece of octagonal-section fiber in the fiber link. We present here the scientific validation of the upgrade of this instrument, demonstrating a real improvement. The upgraded instrument, renamed SOPHIE+, reaches radial velocity precision in the range of 1-2 m/s. It is now fully efficient for the detection of low-mass exoplanets down to 5-10 Earth mass and for the identification of acoustic modes down to a few tens of cm/s.Comment: 12 pages, 11 figures, accepted in Astronomy and Astrophysic