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Search Results: 1 - 10 of 12486 matches for " for the EROS collaboration "
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Limits on Galactic Dark Matter with 5 Years of EROS SMC Data
EROS Collaboration
Physics , 2002,
Abstract: Five years of EROS data towards the Small Magellanic Cloud have been searched for gravitational microlensing events, using a new, more accurate method to assess the impact of stellar blending on the efficiency. Four long-duration candidates have been found which, if they are microlensing events, hint at a non-halo population of lenses. Combined with results from other EROS observation programs, this analysis yields strong limits on the amount of Galactic dark matter made of compact objects. Less than 25% of a standard halo can be composed of objects with a mass between 2 10^-7 Msol and 1 Msol at the 95% C.L.
Microlensing towards the Small Magellanic Cloud --- EROS 2 two-year analysis
EROS Collaboration
Physics , 1998,
Abstract: We present the analysis of the first two years of a search for microlensing of stars in the Small Magellanic Cloud with the EROS (Exp\'erience de Recherche d'Objets Sombres) project. A single event is detected, already present in the first year analysis. This low event rate allows us to put new constraints on the fraction of the Galactic Halo mass due to compact objects in the mass range [10^-2, 1] Msol. These limits, along with the fact that the two SMC events observed so far are probably due to SMC deflectors, suggest that LMC and SMC self-lensing may dominate the event rate.
Observation of Microlensing towards the Galactic Spiral Arms. EROS II 3 year survey
EROS Collaboration
Physics , 2000,
Abstract: We present an analysis of the light curves of 9.1 million stars observed during three seasons by EROS (Experience 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 tau = 0.45 +0.24 -0.11 x 10^-6. While this value is compatible with expectations from simple galactic models under reasonable assumptions on the target distances, we find an excess of events with short timescale towards the direction closest to the Galactic Centre.
EROS 2 intensive observation of the caustic crossing of microlensing event MACHO SMC-98-1
EROS collaboration
Physics , 1998,
Abstract: We report on intensive photometric monitoring on 18 June 1998 of MACHO SMC-98-1, a binary-lens microlensing event seen toward the Small Magellanic Cloud (SMC). The observations cover 5.3 hours (UT 5:17 -- 10:37), and show a sharp drop of 1.8 mag during the first 1.8 hours, followed by an abrupt flattening at UT 7:08 +- 0:02. We interpret the kink at 7:08 as the end of the second caustic crossing (when the source first moved completely outside the caustic). These results indicate that mu sin(phi) <~ 1.5 km/s/kpc at the 2 sigma level, where mu is the proper motion of the lens (relative to the line of sight to the source), and phi is the unknown (and so random) angle of the caustic crossing. Hence, the lens probably does not lie in either the Galactic halo or disk and so is most likely in the SMC itself. Our data can be combined with those of other groups to give more precise constraints on the proper motion (and hence the nature) of the lens.
EROS and MACHO Combined Limits on Planetary Mass Dark Matter in the Galactic Halo
EROS Collaboration,MACHO Collaboration
Physics , 1998, DOI: 10.1086/311355
Abstract: The EROS and MACHO collaborations have each published upper limits on the amount of planetary mass dark matter in the Galactic Halo obtained from gravitational microlensing searches. In this paper the two limits are combined to give a much stronger constraint on the abundance of low mass MACHOs.
EROS2 microlensing search towards the Magellanic Clouds
T. Lasserre,EROS Collaboration
Physics , 1999,
Abstract: EROS2 is a second generation microlensing experiment operating since mid-1996 at the European Southern Observatory (ESO) at La Silla (Chile). We present the two year analysis from our microlensing search towards the Small Magellanic Cloud (SMC) and report on the intensive observation of the caustic crossing event MACHO-SMC-98-1 and the limit derived on t he location of the lens. We also give preliminary results from our search towards the Large Magellanic Cloud (LMC); 25 square degrees are being analyzed and two candidates have been found. This allows us to set another limit on the halo mass fraction comprised of compact objects.
Not enough stellar Mass Machos in the Galactic Halo
T. Lasserre,EROS Collaboration
Physics , 2000,
Abstract: We combine new results from the search for microlensing towards the Large Magellanic Cloud (LMC) by EROS2 (Experience de Recherche d'Objets Sombres) with limits previously reported by EROS1 and EROS2 towards both Magellanic Clouds. The derived upper limit on the abundance of stellar mass MACHOs rules out such objects as an important component of the Galactic halo if their mass is smaller than 1 solar mass.
Eros 2 proper motion survey for halo white dwarfs
Bertrand Goldman,Eros Collaboration
Physics , 2000, DOI: 10.1016/S0920-5632(00)88933-1
Abstract: Since 1996 EROS 2 has surveyed 440 square degrees at high Galactic latitude in order to search for high proper motion stars in the Solar neighbourhood. We present here the analysis of 250 square degrees for which we have three years of data. No object with halo-like kinematics has been detected. Using a detailed Monte-Carlo simulation of the observations, we calculate our detection efficiency for this kind of object and place constraints on their contribution to various halo models. If 14 Gyr old, the halo cannot be made of more than 18% of hydrogen white dwarfs (95% C.L.).
Not enough stellar mass Machos in the Galactic halo
A. Milsztajn,T. Lasserre,for the EROS collaboration
Physics , 2000, DOI: 10.1016/S0920-5632(00)00970-1
Abstract: We present an update of results from the search for microlensing towards the Large Magellanic Cloud (LMC) by EROS (Experience de Recherche d'Objets Sombres). We have now monitored 25 million stars over three years. Because of the small number of observed microlensing candidates (four), our results are best presented as upper limits on the amount of dark compact objects in the halo of our Galaxy. We discuss critically the candidates and the possible location of the lenses, halo or LMC . We compare our results to those of the MACHO group. Finally, we combine these new results with those from our search towards the Small Magellanic Cloud as well as earlier ones from the EROS1 phase of our survey. The combined data is sensitive to compact objects in the broad mass range $ 10^{-7} - 10 $ solar masses. The derived upper limit on the abundance of stellar mass MACHOs rules out such objects as the dominant component of the Galactic halo if their mass is smaller than 2 solar masses.
Microlensing towards the Small Magellanic Cloud. EROS 2 first year survey
EROS collaboration,N. Palanque-Delabrouille et al
Physics , 1997,
Abstract: We present here an analysis of the light curves of 5.3 million stars in the Small Magellanic Cloud observed by EROS (Exp\'erience de Recherche d'Objets Sombres). One star exhibits a variation that is best interpreted as due to gravitational microlensing by an unseen object. This candidate was also reported by the MACHO collaboration. Once corrected for blending, the Einstein radius crossing time is 123 days, corresponding to lensing by a Halo object of $2.6^{+8.2}_{-2.3} M_{\odot}$. The maximum magnification is a factor of 2.6. The light curve also displays a periodic modulation with a 2.5% amplitude and a period of 5.1 days. Parallax analysis of the candidate indicates that a Halo lens would need to have a mass of at least $0.3 M_{\odot}$, although a lens in the SMC could have a mass as low as $0.07 M_{\odot}}$. We estimate the optical depth for microlensing towards the SMC due to this event to be $\sim 3.3 \times 10^{-7}$, with an uncertainty dominated by Poisson statistics. We show that this optical depth corresponds to about half that expected for a spherical isothermal Galactic Halo comprised solely of such objects, and that it is consistent with SMC self-lensing if the SMC is elongated along the line-of-sight by at least 5 kpc.
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