The atmospheres of M dwarfs: Observations

After presenting global properties of M dwarfs, the principal diagnostic of activity phenomena occurring in their atmosphere from the geometrical, energetic, and temporal points of view is stressed. Observations of sunspots, plages, flares, and activity cycles are presented. The major sources of activity are discussed with particular emphasis on the generation, intensification, and measurements of stellar magnetic fields

Doppler imaging of AR Lacertae at three epochs

Observations from IUE were used to study the structure of the lower chromosphere of AR Lacertae in the light of Mg II k. Sequences of LWR/P-HI images distributed around the binary period at three epochs were obtained. Discrete plage-like regions of enhanced Mg II surface flux in this system are identified. There are temporal variations in the Mg II flux on timescales of hours as well as substantial changes in chromospheric morphology on timescales of years. Even with the limited S/N attainable with the IUE, one can map the gross structures of active stellar atmospheres. With such information, one can begin to study the true 3-D structure of the atmospheres of late-type stars

Close Binaries with Infrared Excess: Destroyers of Worlds?

We present the results of a Spitzer photometric investigation into the IR excesses of close binary systems. In a sample of 10 objects, excesses in IRAC and MIPS24 bands implying the presence of warm dust are found for 3. For 2 objects we do not find excesses reported in earlier IRAS studies. We discuss the results in the context of the scenario suggested by Rhee and co-workers, in which warm dust is continuously created by destructive collisions between planetary bodies. A simple numerical model for the steady-state distribution of dust in one IR excess system shows a central clearing of radius 0.22 AU caused by dynamical perturbations from the binary star. This is consistent with the size of the central clearing derived from the Spitzer spectral energy distribution. We conclude that close binaries could be efficient "destroyers of worlds", lead to destabilize the orbits of their planetary progeny by magnetically-driven angular momentum loss and secular shrinkage of the binary separation.Comment: Accepted by The Astrophysical Journa

A Tentative Detection of a Starspot During Consecutive Transits of an Extrasolar Planet from the Ground: No Evidence of a Double Transiting Planet System Around TrES-1

There have been numerous reports of anomalies during transits of the planet TrES-1b. Recently, Rabus and coworkers' analysis of HST observations lead them to claim brightening anomalies during transit might be caused by either a second transiting planet or a cool starspot. Observations of two consecutive transits are presented here from the University of Arizona's 61-inch Kuiper Telescope on May 12 and May 15, 2008 UT. A 5.4 +/- 1.7 mmag (0.54 +/- 0.17%) brightening anomaly was detected during the first half of the transit on May 12 and again in the second half of the transit on May 15th. We conclude that this is a tentative detection of a r greater than or equal to 6 earth radii starspot rotating on the surface of the star. We suggest that all evidence to date suggest TrES-1 has a spotty surface and there is no need to introduce a second transiting planet in this system to explain these anomalies. We are only able to constrain the rotational period of the star to 40.2 +22.9 -14.6 days, due to previous errors in measuring the alignment of the stellar spin axis with the planetary orbital axis. This is consistent with the previously observed P_obs = 33.2 +22.3 -14.3 day period. We note that this technique could be applied to other transiting systems for which starspots exist on the star in the transit path of the planet in order to constrain the rotation rate of the star. (abridged)Comment: 21 pages, 3 tables, 6 figures, Accepted to Ap

La durabilit\ue0 dei componenti edilizi

La pubblicazione riporta una sintesi dei risultati della ricerca scientifica nazionale (PRIN-2003) su \u201cMetodologie di progettazione e di valutazione della durabilit\ue0 dei componenti edilizi in processi di produzione sostenibili, finalizzate alla programmazione della manutenzione degli edifici\u201d delle sei unit\ue0 di ricerca (Politecnico di Milano, Politecnico di Torino, Universit\ue0 degli Studi Federico II di Napoli, Universit\ue0 degli Studi di Palermo, Universit\ue0 degli Studi di Catania, Universit\ue0 degli Studi di Brescia). La ricerca \ue8 condotta in coerenza con quanto si sta sviluppando a livello internazionale nell\u2019ambito dell\u2019International Council for Research and Innovation in Buiding and Construction (CIB), in particolare nella Commissione CIB W80 Prediction of Service Life of Building Materials and Components, nonch\ue9 nei correlati lavori dell\u2019ISO TC 59 SC14 per l\u2019elaborazione delle varie parti della norma ISO 15686 \u201cService life planning\u201d. Il lavoro ha portato nel 2006 alla uscita della prima norma italiana UNI 11156 \u201cValutazione della durabilit\ue0 dei componenti edilizi\u201d articolata in tre parti: \u201cTerminologia e definizione dei parametri di valutazione\u201d, \u201dMetodi per la valutazione della propensione all\u2019affidabilit\ue0\u201d, \u201dMetodi per la valutazione della durata\u201d. I risultati finora acquisiti costituiscono gi\ue0 un significativo riferimento per gli operatori di committenza pubblica e privata in interventi edilizi di nuova costruzione ai fini di organizzare per essi una manutenzione programmata atta ad assicurare nel tempo il mantenimento di un livello di qualit\ue0 tecnologica adeguato, con benefico effetto di riduzione dei costi di gestione degli edifici. Ci\uf2 potr\ue0 essere perseguito attraverso la conoscenza della qualit\ue0 tecnologica utile dei componenti edilizi dei componenti edilizi richiedibile attraverso le specifiche di durabilit\ue0 direttamente imponibili da parte dei progettisti nei capitolati speciali d\u2019appalto secondo i dettati della sopra citata norma UNI 11156

Mass Transfer in Binary Stars using SPH. I. Numerical Method

Close interactions and mass transfer in binary stars can lead to the formation of many different exotic stellar populations, but detailed modeling of mass transfer is a computationally challenging problem. Here, we present an alternate Smoothed Particle Hydrodynamics approach to the modeling of mass transfer in binary systems that allows a better resolution of the flow of matter between main-sequence stars. Our approach consists of modeling only the outermost layers of the stars using appropriate boundary conditions and ghost particles. We arbitrarily set the radius of the boundary and find that our boundary treatment behaves physically and conserves energy well. In particular, when used with our binary relaxation procedure, our treatment of boundary conditions is also shown to evolve circular binaries properly for many orbits. The results of our first simulation of mass transfer are also discussed and used to assess the strengths and limitations of our method. We conclude that it is well suited for the modeling of interacting binary stars. The method presented here represents a convenient alternative to previous hydrodynamical techniques aimed at modeling mass transfer in binary systems since it can be used to model both the donor and the accretor while maintaining the density profiles taken from realistic stellar models.Comment: 10 pages, 10 figures. Accepted for publication in The Astrophysical Journa

Long-Term V-Band Monitoring of the Bright Stars of M33 at the Wise Observatory

We have conducted a long-term V-band photometric monitoring of M33 on 95 nights during four observing seasons (2000 - 2003). A total number of 6418 lightcurves of bright objects in the range of 14 - 21 mag have been obtained. All measurements are publicly available. A total of 127 new variables were detected, of which 28 are periodic. Ten previously known non-periodic variables were identified as periodic, 3 of which are Cepheids, and another previously known periodic variable was identified as an eclipsing binary. Our derived periods range from 2.11 to almost 300 days. For 50 variables we have combined our observations with those of the DIRECT project, obtaining lightcurves of up to 500 measurements, with a time-span of ~7 years. We have detected a few interesting variables, including a 99.3 day periodic variable with a 0.04 mag amplitude, at the position of SNR 19.Comment: 29 pages, accepted for publication in MNRAS. Additional material is available at http://wise-obs.tau.ac.il/~shporer/m33

The Coronae of AR Lac

We observed the coronally active eclipsing binary, AR Lac, with the High Energy Transmission Grating on Chandra for a total of 97 ks, spaced over five orbits, at quadratures and conjunctions. Contemporaneous and simultaneous EUV spectra and photometry were also obtained with the Extreme Ultraviolet Explorer. Significant variability in both X-ray and EUV fluxes were observed, dominated by at least one X-ray flare and one EUV flare. We saw no evidence of primary or secondary eclipses. X-ray flux modulation was largest at high temperature, indicative of flare heating of coronal plasma. Line widths interpreted in terms of Doppler broadening suggest that both binary stellar components are active. From line fluxes obtained from total integrated spectra, we have modeled the emission measure and abundance distributions. A strong maximum was found in the differential emission measure, characterized by peaks at log T = 6.9 and 7.4, together with a weak but significant cooler maximum near log T=6.2, and a moderately strong hot tail from log T= 7.6-8.2. Coronal abundances have a broad distribution and show no simple correlation with first ionization potential. While the resulting model spectrum generally agrees very well with the observed spectrum, there are some significant discrepancies, especially among the many Fe L-lines. Both the emission measure and abundance distributions are qualitatively similar to prior determinations from other X-ray and ultraviolet spectra, indicating some long-term stability in the overall coronal structure.Comment: 31 pages, 8 figures, 3 tables; Accepted for publication in the Astrophysical Journal (tentatively October 1, 2003