Stellar activity and planetary atmosphere evolution in tight binary star systems

Context. In tight binary star systems, tidal interactions can significantly influence the rotational and orbital evolution of both stars, and therefore their activity evolution. This can have strong effects on the atmospheric evolution of planets that are orbiting the two stars. Aims. In this paper, we aim to study the evolution of stellar rotation and of X-ray and ultraviolet (XUV) radiation in tight binary systems consisting of two solar mass stars and use our results to study planetary atmosphere evolution in the habitable zones of these systems. Methods. We have applied a rotation model developed for single stars to binary systems, taking into account the effects of tidal interactions on the rotational and orbital evolution of both stars. We used empirical rotation-activity relations to predict XUV evolution tracks for the stars, which we used to model hydrodynamic escape of hydrogen dominated atmospheres. Results. When significant, tidal interactions increase the total amount of XUV energy emitted, and in the most extreme cases by up to factor of $\sim$50. We find that in the systems that we study, habitable zone planets with masses of 1~M$_\oplus$ can lose huge hydrogen atmospheres due to the extended high levels of XUV emission, and the time that is needed to lose these atmospheres depends on the binary orbital separation.For some orbital separations, and when the stars are born as rapid rotators, it is also possible for tidal interactions to protect atmospheres from erosion by quickly spinning down the stars. For very small orbital separations, the loss of orbital angular momentum by stellar winds causes the two stars to merge. We suggest that the merging of the two stars could cause previously frozen planets to become habitable due to the habitable zone boundaries moving outwards.Comment: Accepted for publication by A&

Interaction of infalling solid bodies with primordial atmospheres of disk-embedded planets

Planets that form early enough to be embedded in the circumstellar gas disk accumulate thick atmospheres of nebular gas. Models of these atmospheres need to specify the surface luminosity (i.e. energy loss rate) of the planet. This luminosity is usually associated with a continuous inflow of solid bodies, where the gravitational energy released from these bodies is the source of energy. However, if these bodies release energy in the atmosphere instead of at the surface, this assumption might not be justified. Our aim is to explore the interactions of infalling planetesimals with primordial atmospheres at an embedded phase of evolution. We investigate effects of atmospheric interaction on the planetesimals (mass loss) and the atmosphere (heating/cooling). We used atmospheric parameters from a snapshot of time-dependent evolution simulations for embedded atmospheres and simulated purely radial, infall events of siliceous planetesimals in a 1D, explicit code. We implemented energy transfer between friction, radiation transfer by the atmosphere and the body and thermal ablation; this gives us the possibility to examine the effects on the planetesimals and the atmosphere. We find that a significant amount of gravitational energy is indeed dissipated into the atmosphere, especially for larger planetary cores, which consequently cannot contribute to the atmospheric planetary luminosity. Furthermore, we examine that planetesimal infall events for cores, $M_\mathrm{C} > 2$M$_{\oplus}$, which actually result in a local cooling of the atmosphere; this is totally in contradiction with the classical model

The role of pollinator attracting scent in the sexually deceptive orchids Ophrys chestermanii, O. normanii and O. tenthredinifera

Sexual deception of male bees is one of the most remarkable mechanisms of pollination (Ackermann 1986, Proctor & al. 1996). Flowers of the orchid genus Ophrys mimic females of their pollinator species, usually bees and wasps, to attract males, which try to copulate with the flowers. During this so-called “pseudocopulation” the male removes the pollinia and transfers them to another flower to ensure pollination. Apart from visual and tactile cues, floral scent was shown to be most important for eliciting mating behaviour in males (Kullenberg 1961, Schiestl & al. 1999, Ayasse & al. 2003). Pollination in Ophrys is highly specific and usually each Ophrys species attracts only one pollinator species (Paulus & Gack 1990). The high degree of specialization provides the means of reproductive isolation between the intercrossable Ophrys-species (Ehrendorfer 1980). The complex odour-bouquets released by the flowers are species-specific and often consist of more than 100 different chemical compounds (Borg-Karlson & al. 1985, Ayasse 2006). Speciation in Ophrys-orchids may be brought about by changes in the pollinator attracting floral scent. The attraction of a new pollinator may act as a pre-zygotic isolation barrier (Stebbins 1970, Paulus & Gack 1990, Soliva & al. 2001). We investigated three sympatrically occuring Ophrys-species on Sardinia. O. chestermanii and O. normanii are endemic and are both pollinated by males of the bumblebee B. vestalis. O. tenthredinifera is pollinated by Eucera nigrilabris. There are different opinions concerning the taxonomic status of O. normanii. It has been described as an actual hybrid between O. chestermanii and O. tenthredinifera (Wood 1983). Paulus & Gack (1995) suggested that it is an own species, that either has developed from a hybrid between O. chestermanii and O. normanii or that has evolved by radiation from O. tenthredinifera. By conducting behavioural-tests with B. vestalis males, performing gas chromatographic analyses and electrophysiological studies we wanted to identify pollinator attracting scent and to clarify the taxonomic status of O. normanii.Sexualtäuschorchideen der Gattung Ophrys (Orchidaceae) imitieren die Weibchen ihrer Bestäuber in Duft, Form und Farbe. Insektenmännchen versuchen mit dem Labellum der Blüte zu kopulieren und transportieren den Pollen von Blüte zu Blüte, wodurch die Orchidee bestäubt wird. In dieser Arbeit untersuchten wir die Bestäuber anlockenden Duftstoffe der beiden endemisch auf Sardinien vorkommenden Arten O. normanii und O. chestermanii, die beide von Bombus vestalis Männchen (Hymenoptera: Apidae) bestäubt werden und von O. tenthredinifera, die Eucera nigrilabris (Hymenoptera: Apidae) zur Bestäubung anlockt. O. normanii wurde von Wood (1983) als Primärhybride beschrieben. Nach Paulus und Gack (1995) handelt es sich um eine hybridogene Art oder um eine Art die durch Abspaltung von O. tenthredinifera entstanden ist. Das Ziel der Untersuchungen war die Identifizierung Männchen-anlockender Verbindungen. Die Attraktivität der drei Arten für B. vestalis Männchen sollte Hinweise auf den Artstatus von O. normanii geben. In Biotests mit B. vestalis-Männchen lösten Blütenextrakte von O. normanii und O. chestermanii ebenso wie B. vestalis-Weibchen Kopulationsverhalten der Männchen aus, nicht jedoch Extrakte von O. tenthredinifera. Folglich handelt es sich bei O. normanii nicht um einen aktuellen Hybriden zwischen O. chestermanii und O. tenthredinifera. Ein Vergleich der GC-EAD-aktiven Duftbouquets mittels Diskriminanzanalyse ergab große Ähnlichkeiten zwischen O. normanii und O. chestermanii für die Substanzklassen der Ester, Alkohole und Fettsäuren, die daher vermutlich eine Schlüsselfunktion bei der Bestäuberanlockung haben

Below ground efficiency of a parasitic wasp for Drosophila suzukii biocontrol in different soil types

The parasitoid wasp Trichopria drosophilae is promising as a biocontrol agent for controlling the ubiquitous pest Drosophila suzukii (Matsumura). Crucial for the successful implementation of any biocontrol agent is a high parasitisation rate by the parasitoid. Most studies investigating the parasitisation rate of D. suzukii pupae have focused on parasitisation in the fruit or in a petri dish. However, the predominant pupation site of D. suzukii in the field is the soil. Unfortunately, little is known on how well parasitoid wasps can detect and parasitise pupae of D. suzukii buried in the soil. Therefore, we conducted soil parasitisation experiments of T. drosophilae on D. suzukii pupae using two pupation depths in three different soil types (loamy sand, loam, and clay). In all three soil types, we found generally low D. suzukii pupae parasitisation rate by T. drosophilae, independent of the pupation depth. The pupation behaviour of D. suzukii and the parasitisation behaviour of T. drosophilae are discussed in detail. For pest control in most soil types, our results mean that the number of D. suzukii larvae pupating in the soil should be reduced, e.g., by adding a layer of sandy soil or covering the soil with plastic mulch. This might increase the probability of success when using T. drosophilae as a biocontrol agent