Infrared Polarimetry Of Very Young Objects Including Becklin-Neugebauer Source

NSFAstronom

Effects of gravitational darkening on the determination of fundamental parameters in fast rotating B-type stars

In this paper we develop a calculation code to account for the effects carried by fast rotation on the observed spectra of early-type stars. Stars are assumed to be in rigid rotation and the grid of plane-parallel model atmospheres used to represent the gravitational darkening are calculated by means of a non-LTE approach. Attention is paid on the relation between the apparent and parent non-rotating counterpart stellar fundamental parameters and apparent and true vsini parameters as a function of the rotation rate Omega/Omega_c, stellar mass and inclination angle. It is shown that omission of gravitational darkening in the analysis of chemical abundances of CNO elements can produce systematic overestimation or underestimation, depending on the lines used, rotational rate and inclination angle. The proximity of Be stars to the critical rotation is re-discussed by correcting not only the vsini of 130 Be stars, but also their effective temperature and gravity to account for stellar rotationally induced geometrical distortion and for the concomitant gravitational darkening effect. We concluded that the increase of the vsini estimate is accompanied by an even higher value of the stellar equatorial critical velocity, so that the most probable average rate of angular velocity of Be stars attains Omega/Omega_c ~ 0.88.Comment: 20 pages, 16 figures. Submitted for publication in A&

On the two approaches to the data analysis of the Cassini interplanetary relativity experiment

We compare two theoretical approaches to the data analysis of the Cassini relativity experiment based on the Doppler tracking and the time delay technique that were published correspondingly by Kopeikin et al in Phys. Lett. A 367, 276 (2007) and by Bertotti et al in Class. Quant. Grav. 25, 045013 (2008). Bertotti et al believed that they found a discrepancy with our paper and claimed that our analysis was erroneous. The present paper elucidates, however, that the discrepancy is illusory and does not exist. The two techniques give the same result making it evident that the numerical value of the PPN parameter 'gamma' measured in the Cassini experiment is indeed affected by the orbital motion of the Sun around the barycenter of the solar system.Comment: 6 pages, no figures. Accepted for publication to Physics Letters

Wettbewerb in der Restmüllerfassung: Eine empirische Analyse der Anbieterstruktur

Der vorliegende Beitrag ermittelt das aktuelle Ausmaß kommunaler Betätigung in der Abfallwirtschaft auf Basis von 9.248 deutschen Gemeinden und Städten. Vor allem in Großstädten mit über 100.000 Einwohnern haben Kommunen fast vollständig die Restmüllsammlung übernommen. Insgesamt wird über alle Kommunen zwar nur für knapp 34 % der Gebiete die Erfassung durch kommunale Unternehmen vorgenommen. Gewichtet man die jeweiligen Gebiete jedoch mit der Einwohneranzahl, entfällt insgesamt knapp 62 % der Restmüllerfassung auf kommunale Entsorgungsunternehmen. In Großstädten über 100.000 Einwohner haben sich kommunale Unternehmen sogar 94 % des Marktes gesichert. Private Entsorger dominieren hingegen vor allem im ländlichen Raum. Diese Befunde deuten auf eine Rosinenpickerei der Kommunen hin, die sich insbesondere die dicht besiedelten profitablen Gebiete herausgesucht haben. Im Vergleich zu bisher verfügbaren Statistiken über kommunale Aktivitäten in der Abfallwirtschaft (vgl. etwa Monopolkommission, 2014) zeigt sich eine weitere Zunahme der Rekommunalisierung. Sollten die Wettbewerbsbedingungen nunmehr auch in anderen Bereichen der Abfallwirtschaft, wie etwa bei Wertstoffen, zugunsten der Kommunen verzerrt werden, ist hier mit ähnlichen Rekommunalisierungstendenzen und einer Verdrängung privater Wettbewerber zu rechnen

The effects of inclination, gravity darkening and differential rotation on absorption profiles of fast rotators

Mechanisms influencing absorption line profiles of fast rotating stars can be sorted into two groups; (i) intrinsic variations sensitive to temperature and pressure, and (ii) global effects common to all spectral lines. I present a detailed study on the latter effects focusing on gravity darkening and inclination for various rotational velocities and spectral types. It is shown that the line shapes of rapidly and rigidly rotating stars mainly depend on the equatorial velocity $v_{\rm e}$, not on the projected rotational velocity $v \sin{i}$ which determines the lines width. The influence of gravity darkening and spectral type on the line profiles is shown. The results demonstrate the possibility of determining the inclination angle $i$ of single fast rotators, and they show that constraints on gravity darkening can be drawn for stellar samples. While significant line profile deformation occurs in stars rotating as fast as v_{\rm e} \ga 200 km s$^{-1}$, for slower rotators profile distortion are marginal. In these cases spectral signatures induced by, e.g., differential rotation are not affected by gravity darkening and the methods applicable to slow rotators can be applied to these faster rotators, too.Comment: 7 pages, accepted by A&

Photometry of comet 9P/Tempel 1 during the 2004/2005 approach and the Deep Impact module impact

The results of the 9P/Tempel 1 CARA (Cometary Archive for Amateur Astronomers) observing campaign is presented. The main goal was to perform an extended survey of the comet as a support to the Deep Impact (DI) Mission. CCD R, I and narrowband aperture photometries were used to monitor the $Af\rho$ quantity. The observed behaviour showed a peak of 310 cm 83 days before perihelion, but we argue that it could be distorted by the phase effect, too. The phase effect is roughly estimated around 0.0275 mag/degree, but we had no chance for direct determination because of the very similar geometry of the observed apparitions. The log-slope of $Af\rho$ was around -0.5 between about 180--100 days before the impact but evolved near the steady-state like 0 value by the impact time. The DI module impact caused an about 60%{} increase in the value of $Af\rho$ and a cloud feature in the coma profile which was observed just after the event. The expansion of the ejecta cloud was consistent with a fountain model with initial projected velocity of 0.2 km/s and $\beta$=0.73. Referring to a 25~000 km radius area centered on the nucleus, the total cross section of the ejected dust was 8.2/$A$ km$^2$ 0.06 days after the impact, and 1.2/$A$ km$^2$ 1.93 days after the impact ($A$ is the dust albedo). 5 days after the event no signs of the impact were detected nor deviations from the expected activity referring both to the average pre-impact behaviour and to the previous apparitions ones.Comment: 25 pages (including cover pages), 9 figures, 1 table, accepted by Icarus DI Special Issu

Rotational velocities of A-type stars I. Measurement of vsini in the southern hemisphere

Within the scope of a Key Programme determining fundamental parameters of stars observed by HIPPARCOS, spectra of 525 B8 to F2-type stars brighter than V=8 have been collected at ESO. Fourier transforms of several line profiles in the range 4200-4500 A are used to derive vsini from the frequency of the first zero. Statistical analysis of the sample indicates that measurement error is a function of vsini and this relative error of the rotational velocity is found to be about 6% on average. The results obtained are compared with data from the literature. There is a systematic shift from standard values from Slettebak et al. (1975), which are 10 to 12% lower than our findings. Comparisons with other independent vsini values tend to prove that those from Slettebak et al. are underestimated. This effect is attributed to the presence of binaries in the standard sample of Slettebak et al., and to the model atmosphere they used.Comment: 17 pages, includes 18 figures, accepted in A&

AVAST Survey 0.4-1.0 {\mu}m Spectroscopy of Igneous Asteroids in the Inner and Middle Main Belt

We present the spectra of 60 asteroids, including 47 V-types observed during the first phase of the Adler V-Type Asteroid (AVAST) Survey. SDSS photometry was used to select candidate V-type asteroids for follow up by nature of their very blue $i-z$ color. 47 of the 61 observed candidates were positively classified as V-type asteroids, while an additional six show indications of a 0.9 $\mu$m feature consistent with V-type spectra, but not sufficient for formal classification. Four asteroids were found to be S-type, all of which had $i-z$ values very near the adopted AVAST selection criteria of $i-z \le -0.2$, including one candidate observed well outside the cut (at a mean $i-z$ of -0.11). Three A-type asteroids were also identified. Six V-type asteroids were observed beyond the 3:1 mean motion resonance with Jupiter, including the identification of two new V-type asteroids (63085 and 105041) at this distance. Six V-type asteroids were observed with low ($<5\deg$) orbital inclination, outside of the normal dynamical range of classic Vestoids, and are suggestive of a non-Vesta origin for at least some of the population.Comment: 1 table, 3 figures, To appear to Icaru

M67-1194, an unusually Sun-like solar twin in M67

The rich open cluster M67 is known to have a chemical composition close to solar, and an age around 4Gyr. It thus offers the opportunity to check our understanding of the physics and the evolution of solar-type stars in a cluster environment. We present the first spectroscopic study at high resolution, R~50,000, of the potentially best solar twin, M67-1194, identified among solar-like stars in M67. Based on a pre-selection of solar-twin candidates performed at medium resolution by Pasquini et al. (2008), we explore the chemical-abundance similarities and differences between M67-1194 and the Sun, using VLT/FLAMES-UVES. Working with a solar twin in the framework of a differential analysis, we minimize systematic model errors in the abundance analysis compared to previous studies which utilized more evolved stars to determine the metallicity of M67. We find M67-1194 to have stellar parameters indistinguishable from the solar values, with the exception of the overall metallicity which is slightly super-solar ([Fe/H]=0.023 +/- 0.015). An age determination based on evolutionary tracks yields 4.2 +/- 1.6Gyr. Most surprisingly, we find the chemical abundance pattern to closely resemble the solar one, in contrast to most known solar twins in the solar neighbourhood. We confirm the solar-twin nature of M67-1194, the first solar twin known to belong to a stellar association. This fact allows us to put some constraints on the physical reasons for the seemingly systematic departure of M67-1194 and the Sun from most known solar twins regarding chemical composition. We find that radiative dust cleansing by nearby luminous stars may be the explanation for the peculiar composition of both the Sun and M67-1194, but alternative explanations are also possible. The chemical similarity between the Sun and M67-1194 also suggests that the Sun once formed in a cluster like M67

The Top Ten solar analogs in the ELODIE library

Several solar analogs have been identified in the library of high resolution stellar spectra taken with the echelle spectrograph ELODIE. A purely differential method has been used, based on the chi2 comparison of a large number of G dwarf spectra to 8 spectra of the Sun, taken on the Moon and Ceres. HD 146233 keeps its status of closest ever solar twin (Porto de Mello & da Silva 1997). Some other spectroscopic analogs have never been studied before, while the two planet-host stars HD095128 and HD186427 are also part of the selection. The fundamental parameters found in the literature for these stars show a surprising dispersion, partly due to the uncertainties which affect them. We discuss the advantages and drawbacks of photometric and spectroscopic methods to search for solar analogs and conclude that they have to be used jointly to find real solar twins.Comment: 12 pages, accepted in A&