Search

Aims. The EROS-2 project has been designed to search for microlensing events towards any dense stellar field. The densest parts of the Galactic spiral arms have been monitored to maximize the microlensing signal expected from the stars of the Galactic disk and bulge.

Context. A number of microlensing dark-matter surveys have produced tens of millions of light curves of individual background stars. These data provide an unprecedented opportunity for systematic studies of whole classes of variable stars and their host galaxies.

We present the results of a massive variability search based on a photometric survey of a six square degree region along the Galactic plane at ($l = 305^\circ$, $b = -0.8^\circ$) and ($l = 330^\circ$, $b = -2.5^\circ$). This survey was performed in the framework of the EROS II(Expérience de Recherche d'Objets Sombres) microlensing program. The variable stars were found among 1 913 576 stars that were monitored between April and June 1998 in two passbands, with an average of 60 measurements. A new period-search technique is proposed which makes use of a statistical variable that characterizes the overall regularity of the flux versus phase diagram. This method is well suited when the photometric data are unevenly distributed in time, as is our case. 1362 objects whose luminosity varies were selected. Among them we identified 9 Cepheids, 19 RR Lyræ, 34 Miras, 176 eclipsing binaries and 266 Semi-Regular stars. Most of them are newly identified objects. The cross-identification with known catalogues has been performed. The mean distance of the RR Lyræ is estimated to be ~$ 4.9 \pm 0.3$kpc undergoing an average absorption of ~$ 3.4 \pm 0.2$mag. This distance is in good agreement with that of disc stars that contribute to the microlensing source star population. Our catalogue and light curves are available electronically from the CDS, Strasbourg and from our Web site.

We are conducting a $377^{\circ 2}$proper motion survey in the ~Vand Ibands in order to determine the cool white dwarf contribution to the Galactic dark matter. Using the $250^{\circ 2}$for which we possess three epochs, and applying selection criteria designed to isolate halo-type objects, we find no candidates in a $5500\,{\rm pc}^3$effective volume for old, fast MV=17 white dwarfs. We check the detection efficiency by cross-matching our catalogue with Luyten's NLTT catalogue. The halo white dwarf contribution cannot exceed 5% (95% C.L.) for objects with and . The same conclusion applies to a 14 Gyr halo composed of white dwarfs with hydrogen atmosphere, as modeled by Chabrier.

We apply EROS photometric data to interpret previously published Keck and VLT spectra of the binary-microlens caustic-crossing event EROS-BLG-2000-5. We show that the VLT data imply that the outer ${\sim} 4\%$of the limb of the K3-giant source is strongly in emission in Hα, in contradiction to available models of the photosphere. This conflict could be resolved if the integrated Hαemission from the chromosphere were equal to 8% of the integrated Hαabsorption from the source as a whole. These conclusions regarding the extreme limb are almost completely model-independent. We also present a general method for using the photometric data to facilitate direct comparison between the atmospheric model and the spectroscopic data. While this method has some model-dependent features, it is fairly robust and can serve to guide the analysis of spectra while more detailed models of the lens geometry are being developed. In addition, we find that the color of the limb of the source (outer 5.5% by radius) is $\Delta(V-I)\sim 0.37$redder than the source as a whole, so that it has the color of a M0 giant.

We present an analysis of the light curves of 9.1 million stars observed during three seasons by EROS(Expérience de Recherche d'Objets Sombres), in the Galactic plane away from the bulge. Seven stars exhibit luminosity variations compatible with gravitational microlensing effects due to unseen objects. The corresponding optical depth, averaged over four directions, is $\bar\tau = 0.43 \pm 0.2 \times 10^{-6}$. While this value is compatible with expectations from simple Galactic models under reasonable assumptions on the target star distances, we find an excess of events with short timescales toward the direction closest to the Galactic centre. We discuss a possible interpretation involving the contribution of an elongated bar.

This paper reports a complete analysis of data taken at DCI to measure lepton and pion pair production close to the threshold in two-photon processes: e+e−→ e+e−(e+e−, μ+μ−, π+π−). Preliminary results have been previously published including one-half of the total statistics. Final results presented here are in good agreement with QED for lepton pair production. The measured cross section for pion pair production is twice as large as that expected from Born terms only — a two standard deviation effect.

Abstract: The three reactionse +e−→e +e−e+e−,e + e -→e + e -μ+μ- ande + e -→μ+μ-μ+ μ- have been studied using the CELLO detector at PETRA. The data correspond to 130 pb−1 collected at energies ranging from 35 GeV to 46.8 GeV. A detailed analysis of the distribution of the observed events in phase space shows good agreement with QED to order α4.

The longitudinal equilibrium distribution of electrons stored in a ring is computed in the general case of a nonlinear accelerating field. From this is derived an equation which gives the exact longitudinal density in the presence of longitudinal fields generated by the circulating particles. A method for solving numerically this equation is given and the exact solution is compared to the lowest-approximation solution when self-fields are proportional to the derivative of the bunch density. Si calcola la distribuzione di equilibrio longitudinale degli elettroni immagazzinati in un anello nel caso generale di un campo accelerators non lineare. Da ciò si deduce un’equazione che dà l’esatta densità longitudinale in presenza di campi longitudinali generati dalle particelle circolanti. Si espone un metodo per risolvere numericamente questa equazione e si confronta la soluzione esatta con la soluzione di minima approssimazione quando gli autocampi sono proporzionali alla derivata della densità del pacchetto. В общем случае нелине йного ускоряющего поля вычисляется про дольное равновесное распределение элект ронов, накопленных в к ольце. И распределение элект ронов, накопленных в к ольце. Из этого выводи тся уравнение, которо е дает точную продоль ную плотность при нал ичии продольны этого выводится урав нение, которое дает то чную продольную плот ность при наличии про дольных полей, образо ванных вращающимися частицами. Приводитс я метод для численног о решения этого уравн продольную плотност ь при наличии продоль ных полей, образованн ых вращающимися част ицами. Приводится мет од для численного реш ения этого уравнения. Точное решение сравн ивается с приближенн ым решением, когда соб ственные поля пропор циональны образованных вращаю щимися частицами. При водится метод для чис ленного решения этог о уравнения. Точное ре шение сравнивается с приближенным решени ем, когда собственные поля пропорциональн ы производной от плот ности сгустка. метод для численного решения этого уравне ния. Точное решение ср авнивается с приближ енным решением, когда собственные поля про порциональны произв одной от плотности сг устка. решение сравниваетс я с приближенным реше нием, когда собственн ые поля пропорционал ьны производной от пл отности сгустка. собственные поля про порциональны произв одной от плотности сг устка. плотности сгустка.

The High Frequency Instrument of Planckwill map the entire sky in the millimeter and sub-millimeter domain from 100 to 857 GHz with unprecedented sensitivity to polarization (ΔP/Tcmb~ 4 × 10-6for Peither Qor Uand Tcmb$\simeq$2.7 K) at 100, 143, 217 and 353 GHz. It will lead to major improvements in our understanding of the cosmic microwave background anisotropies and polarized foreground signals. Planckwill make high resolution measurements of the E-mode spectrum (up to $\ell$~ 1500) and will also play a prominent role in the search for the faint imprint of primordial gravitational waves on the CMB polarization. This paper addresses the effects of calibration of both temperature (gain) and polarization (polarization efficiency and detector orientation) on polarization measurements. The specific requirements on the polarization parameters of the instrument are set and we report on their pre-flight measurement on HFI bolometers. We present a semi-analytical method that exactly accounts for the scanning strategy of the instrument as well as the combination of different detectors. We use this method to propagate errors through to the CMB angular power spectra in the particular case of Planck-HFI, and to derive constraints on polarization parameters. We show that in order to limit the systematic error to 10% of the cosmic variance of the E-mode power spectrum, uncertainties in gain, polarization efficiency and detector orientation must be below 0.15%, 0.3% and 1° respectively. Pre-launch ground measurements reported in this paper already fulfill these requirements.

The High Frequency Instrument of Planckwill map the entire sky in the millimeter and sub-millimeter domain from 100 to 857 GHz with unprecedented sensitivity to polarization (ΔP/Tcmb~ 4 × 10-6for Peither Qor Uand Tcmb$\simeq$2.7 K) at 100, 143, 217 and 353 GHz. It will lead to major improvements in our understanding of the cosmic microwave background anisotropies and polarized foreground signals. Planckwill make high resolution measurements of the E-mode spectrum (up to $\ell$~ 1500) and will also play a prominent role in the search for the faint imprint of primordial gravitational waves on the CMB polarization. This paper addresses the effects of calibration of both temperature (gain) and polarization (polarization efficiency and detector orientation) on polarization measurements. The specific requirements on the polarization parameters of the instrument are set and we report on their pre-flight measurement on HFI bolometers. We present a semi-analytical method that exactly accounts for the scanning strategy of the instrument as well as the combination of different detectors. We use this method to propagate errors through to the CMB angular power spectra in the particular case of Planck-HFI, and to derive constraints on polarization parameters. We show that in order to limit the systematic error to 10% of the cosmic variance of the E-mode power spectrum, uncertainties in gain, polarization efficiency and detector orientation must be below 0.15%, 0.3% and 1° respectively. Pre-launch ground measurements reported in this paper already fulfill these requirements.