Lucio Paterno

Detection of Solar-like Oscillations in the G5 Subgiant μ Her

A clear detection of excess of power, providing a substantial evidence for solar-like oscillations in the G5 sub- giantHer, is presented. This star was observed over seven nights with the SARG echelle spectrograph operating withthe3.6m ItalianTNG Telescope,usinganiodineabsorptioncell asavelocityreference. Aclear excess of power centeredat1.2mHz, withpeakamplitudesof about0.9ms � 1 intheamplitudespectrum ispresent.Fitting theasymp- totic relation to the power spectrum, a mode identification for the l ¼ 0, 1, 2, 3 modes in the frequency range 900Y 1600 � Hz is derived.Themostlikely value for the largeseparationturns out to be56.5 � Hz, consistent with theoretical expectations. The mean amplitude per mode (l ¼ 0;1) at peak power results to be 0.63 ms � 1 , almost 3 times larger than the solar one. Subject headingg stars: individual (� Her) — stars: oscillations — techniques: radial velocities

CONVECTION IN A ROTATING DEEP COMPRESSIBLE SPHERICAL SHELL: APPLICATION TO THE SUN

In this paper we study the interaction of rotation with convection in a deep compressible spherical shell as the Suns convection zone. We examine how the energy transport and the large scale motions can be affected by rotation. In particular we study how a large scale meridional circulation can give rise to variations of angular velocity with latitude and depth.It is assumed that the energy transport is only due to convection and that the mixing-length theory gives an adequate representation of it. Furthermore we assume that rotation acts as a perturbation of the turbulent convective flux through its transport coefficient.The equations involved in the model are integrated numerically in the limit of large viscosity and slow rotation. After having expanded all physical quantities to the first order in terms of Legendre polynomials, the fitting with the observed solar differential rotation gives the expansion parameter, which represents the coupling constant between rotation and convection.The results show a three-cell circulation extending from the poles to the equator. The first one is located in the lower half of the convection zone with the fluid rising at the equator and sinking at the poles. In the second one the direction of the motion is reversed while the third one, located in a thin upper layer, shows the same characteristics of the first one. The meridional velocities at the surface are directed towards the poles and are about 20 cm s-1. In the other cells the meridional velocities are typically of a few cm s-1 while the radial velocities are of the order of a few tenths of cm s-1.The heat flux relative variation at the surface is about 10-4 (3 × 10-3 at the bottom) with a polar excess. The temperature variation at the surface is of the same order, with an equatorial excess however. The convection seems to be stabilized stronger at the equator. The angular velocity increases inwards and varies about 6% between the surface and the bottom of the convection zone.An attempt is made for explaining the picture which emerges. In particular the negligible flux and temperature variations at the surface are explained in terms of equalization by the particular structure of the latitudinal flow. This configuration of large scale circulation is attributed to the high stratification of the convection zone with depth.

Differential rotation set up by latitude-dependent heat transport

Abstract Models of differentially rotating compressible deep spherical shells are computed according to the method of Belvedere and Paterno (1977): the heat transport is entirely convective, small-scale motions are parametrized by a thermal diffusivity and a kinematic viscosity, and the limit of slow rotation and large viscosity is considered. In order to adapt the resulting differential rotation to the observed equatorial acceleration of the Sun, the heat transport must be more effective in the vicinity of the equator. In all models the latitude dependence of the transport coefficient induces meridional circulation in the form of a large cell, with rising material at high latitudes and sinking material near the equator. On top of this cell, one or two thin countercells develop in a minority of cases. Large pole-equator temperature differences and meridonal velocities at the surface are obtained when the Prandtl number is 1. But values of, say, 1/10 are sufficiently small to allow the models to be applied...

Asteroseismology of Procyon A with SARG at TNG

We present high precision radial velocity measurements on the F5 IV star α 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. 3m s −1 . 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 ∆ν0 = 56 ± 2 µHz, consistent with both theoretical estimates (Chaboyer et al. 1999) and previous observations (Martic et al. 2004).

Seismology of Procyon A: Determination of mode frequencies, amplitudes, lifetimes, and granulation noise

The F5 IV-V star Procyon A (

Optical remote sensing of atmospheric turbulence: a comparison with simultaneous thermal measurements

\alpha\!-\!\rm CMi

Seismic inference of differential rotation in Procyon A

) was observed in January 2001 by means of the high-resolution spectrograph SARG operating with the TNG

Daytime r(0) evaluated from vertical microthermal measurements.

3.5\,\rm m

Magnetic field amplification in proto-neutron stars - The role of the neutron-finger instability for dynamo excitation

Italian telescope (Telescopio Nazionale Galileo) in the Canary Islands, exploiting the iodine cell technique. The time series of about 950 spectra carried out during 6 observation nights and a preliminary data analysis [CITE] showed a significant power excess between 0.5 and

URSULA: a twin-beam multiband computer-controlled photometer for astronomical applications.

1.5\,\rm mHz