arXiv subjects

EROS collaboration

Publications and source records attributed to EROS collaboration.

4 recordsLinked to original sources

arXiv1998

EROS 2 intensive observation of the caustic crossing of microlensing event MACHO SMC-98-1

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.

astro-ph↗

arXiv1997

Microlensing towards the Small Magellanic Cloud. EROS 2 first year survey

We present here an analysis of the light curves of 5.3 million stars in the Small Magellanic Cloud observed by EROS (Expérience 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.

astro-ph↗

arXiv1997

Observational Limits on Machos in the Galactic Halo

We present final results from the first phase of the EROS search for gravitational microlensing of stars in the Magellanic Clouds by unseen deflectors (machos: MAssive Compact Halo Objects). The search is sensitive to events with time scales between 15 minutes and 200 days corresponding to deflector masses in the range 1.e-7 to a few solar masses. Two events were observed that are compatible with microlensing by objects of mass of about 0.1 Mo. By comparing the results with the expected number of events for various models of the Galaxy, we conclude that machos in the mass range [1.e-7, 0.02] Mo make up less than 20% (95% C.L.) of the Halo dark matter.

astro-ph↗

arXiv1995

SEARCH FOR VERY LOW MASS OBJECTS IN THE GALACTIC HALO

We present results from a search for gravitational microlensing of stars in the Large Magellanic Cloud by low mass objects in the Galactic Halo. The search uses the CCD light curves of about 82,000 stars with up to 46 measurements per night over a period of 10 months. No light curve exhibits a form that is consistent with a microlensing event of maximum amplification greater than 1.2. This null result makes it unlikely that the Halo is dominated by objects in the mass range $5 10^{-8}M_{\odot} < M <5 10^{-4}M_{\odot} $. keywords{Galaxy : Halo, kinematics and dynamics, stellar content -- Cosmology : dark matter, gravitational lensing}

astro-ph↗