Physical processes leading to surface inhomogeneities: the case of rotation

In this lecture I discuss the bulk surface heterogeneity of rotating stars, namely gravity darkening. I especially detail the derivation of the omega-model of Espinosa Lara & Rieutord (2011), which gives the gravity darkening in early-type stars. I also discuss the problem of deriving gravity darkening in stars owning a convective envelope and in those that are members of a binary system.Comment: 23 pages, 11 figure, Lecture given to the school on the cartography of the Sun and the stars (May 2014 in Besan\c{c}on), to appear in LNP, Neiner and Rozelot edts V2: typos correcte

The giant radio galaxy 8C0821+695 and its environment

We present new VLA and Effelsberg observations of the radio galaxy 8C0821+695. We have obtained detailed images in total intensity and polarization of this 2 Mpc sized giant. The magnetic field has a configuration predominantly parallel to the source main axis. We observe Faraday rotation at low frequencies, most probably produced by an ionized medium external to the radio source. The spectral index distribution is that typical of FR II radio galaxies, with spectral indices gradually steepening from the source extremes towards the core. Modeling the spectrum in the lobes using standard synchrotron loss models yields the spectral age of the source and the mean velocity of the jet-head with respect to the lobe material. The existence of a possible backflow in the lobe is considered to relate spectral with dynamical determinations of the age and the velocity with respect to the external medium. Through a very simple model, we obtain a physical characterization of the jets and the external medium in which the radio galaxy expands. The results in 8C0821+695 are consistent with a relativistic jet nourishing the lobes which expand in a hot, low density halo. We infer a deceleration of the source expansion velocity which we explain through a progressive increase in the hot-spot size.Comment: 11 pages; 8 figures; accepted in A&

The Broad Line Radio Galaxy J2114+820

In the frame of the study of a new sample of large angular size radio galaxies selected from the NRAO VLA Sky Survey, we have made radio observations of J2114+820, a low power radio galaxy with an angular size of 6'. Its radio structure basically consists of a prominent core, a jet directed in north-west direction and two extended S-shaped lobes. We have also observed the optical counterpart of J2114+820, a bright elliptical galaxy with a strong unresolved central component. The optical spectrum shows broad emission lines. This fact, together with its low radio power and FR-I type morphology, renders J2114+820 a non-trivial object from the point of view of the current unification schemes of radio loud active galactic nuclei.Comment: 6 pages, 5 figures. To appear in the proceedings of EVN/JIVE Symposium No. 4, New Astronomy Reviews (eds. Garrett et al.

Parsec Scale Properties of Markarian 501

We present the results of a high angular resolution study of the BL Lac object Markarian 501 in the radio band. We consider data taken at 14 different epochs, ranging between 1.6 GHz and 22 GHz in frequency, and including new Space VLBI observations obtained on 2001 March 5 and 6 at 1.6 and 5 GHz. We study the kinematics of the parsec-scale jet and estimate its bulk velocity and orientation with respect to the line of sight. Limb brightened structure in the jet is clearly visible in our data and we discuss its possible origin in terms of velocity gradients in the jet. Quasi-simultaneous multi-wavelength observations allow us to map the spectral index distribution and to compare it to the jet morphology. Finally, we estimate the physical parameters of the parsec-scale jet.Comment: accepted for publication in ApJ; 24 pages with 17 figures (fig. 1 and fig. 2 available only as .jpg files

Searching for Milky Way twins: Radial abundance distribution as a strict criterion

We search for Milky Way-like galaxies among a sample of approximately 500 galaxies. The characteristics we considered of the candidate galaxies are the following: stellar mass M_star, optical radius R_25, rotation velocity V_rot, central oxygen abundance (O/H)_0, and abundance at the optical radius (O/H)_R25. If the values of R_25 and M_star of the galaxy were close to that of the Milky Way, then the galaxy was referred to as a structural Milky Way analogue (sMWA). The oxygen abundance at a given radius of a galaxy is defined by the evolution of that region, and we then assumed that the similarity of (O/H)_0 and (O/H)_R25 in two galaxies suggests a similarity in their evolution. If the values of (O/H)_0 and (O/H)_R25 in the galaxy were close to that of the Milky Way, then the galaxy was referred to as an evolutionary Milky Way analogue (eMWA). If the galaxy was simultaneously an eMWA and sMWA, then the galaxy was considered a Milky Way twin. We find that the position of the Milky Way on the (O/H)_0 - (O/H)_R25 diagram shows a large deviation from the general trend in the sense that the (O/H)_R25 in the Milky Way is appreciably lower than in other galaxies of similar (O/H)_0. This feature of the Milky Way evidences that its (chemical) evolution is not typical. We identify four galaxies (NGC~3521, NGC~4651, NGC~2903, and MaNGA galaxy M-8341-09101) that are simultaneously sMWA and eMWA and can therefore be considered as Milky Way twins. In previous studies, Milky Way-like galaxies were selected using structural and morphological characteristics, that is, sMWAs were selected. We find that the abundances at the centre and at the optical radius (evolutionary characteristics) provide a stricter criterion for selecting real Milky Way twinsComment: Accepted to Astronomy and Astrophysics, 28 pages, 13 figure

Amino acid content and nectar choice by forager honeybees (Apis mellifera L.)

Dual choice feeding tests were performed to determine a preference of forager honeybees for specific amino acids. Artificial nectar containing proline was preferred over those containing only sugars. Nectar containing alanine was preferred on the first day, but preference was no longer significant thereafter. On the contrary, a negative response was found for serine. When the bees were given the choice between two nectars enriched with different compounds, proline was preferred above both alanine and serine, and alanine above serine