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27 results on '"Kat, J."'

1. Discovery of a peculiar Cepheid-like star towards the northern edge of the Small Magellanic Cloud

Author

Marquette, J. B., Tisserand, P., Francois, P., Beaulieu, J. P., Doublier, V., Lesquoy, E., Milsztajn, A., Pritchard, J., Schwarzenberg-Czerny, A., Afonso, C., Albert, J. N., Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Charlot, X., Coutures, C., Ferlet, R., Fouque, P., Glicenstein, J. F., Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., Hamadache, C., de Kat, J., Guillou, L. Le, Loup, C., Magneville, C., Maurice, E., Maury, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Rahal, Y. R., Rich, J., Spiro, M., Vidal-Madjar, A., and Zylberajch, S.

Subjects
Astrophysics
Abstract

For seven years, the EROS-2 project obtained a mass of photometric data on variable stars. We present a peculiar Cepheid-like star, in the direction of the Small Magellanic Cloud, which demonstrates unusual photometric behaviour over a short time interval. We report on data of the photometry acquired by the MARLY telescope and spectroscopy from the EFOSC instrument for this star, called EROS2 J005135-714459(sm0060n13842), which resembles the unusual Cepheid HR 7308. The light curve of our target is analysed using the Analysis of Variance method to determine a pulsational period of 5.5675 days. A fit of time-dependent Fourier coefficients is performed and a search for proper motion is conducted. The light curve exhibits a previously unobserved and spectacular change in both mean magnitude and amplitude, which has no clear theoretical explanation. Our analysis of the spectrum implies a radial velocity of 104 km s$^{-1}$ and a metallicity of -0.4$\pm$0.2 dex. In the direction of right ascension, we measure a proper motion of 17.4$\pm$6.0 mas yr$^{-1}$ using EROS astrometry, which is compatible with data from the NOMAD catalogue. The nature of EROS2 J005135-714459(sm0060n13842) remains unclear. For this star, we may have detected a non-zero proper motion for this star, which would imply that it is a foreground object. Its radial velocity, pulsational characteristics, and photometric data, however, suggest that it is instead a Cepheid-like object located in the SMC. In such a case, it would present a challenge to conventional Cepheid models., Comment: Correction of typos in the abstract

Published
2008
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2. R Coronae Borealis stars in the Galactic Bulge discovered by EROS-2

Author

Tisserand, P., Marquette, J. B., Wood, P. R., Lesquoy, E., Beaulieu, J. P., Milsztajn, A., Hamadache, C., Afonso, C., Albert, J. N., Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Charlot, X., Coutures, C., Ferlet, R., Fouqué, P., Glicenstein, J. F., Goldman, B., Gould, A., Gros, M., Haissinski, J., de Kat, J., Guillou, L. Le, Loup, C., Magneville, C., Maurice, E., Maury, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Rahal, Y., Rich, J., Spiro, M., Vidal-Madjar, A., and Zylberajch, S.

Subjects
Astrophysics
Abstract

Rare types of variable star may give unique insight into short-lived stages of stellar evolution. The systematic monitoring of millions of stars and advanced light curve analysis techniques of microlensing surveys make them ideal for discovering also such rare variable stars. One example is the R Coronae Borealis (RCB) stars, a rare type of evolved carbon-rich supergiant. We have conducted a systematic search of the EROS-2 database for the Galactic catalogue Bulge and spiral arms to find Galactic RCB stars. The light curves of $\sim$100 million stars, monitored for 6.7 years (from July 1996 to February 2003), have been analysed to search for the main signature of RCB stars, large and rapid drops in luminosity. Follow-up spectroscopy has been used to confirm the photometric candidates. We have discovered 14 new RCB stars, all in the direction of the Galactic Bulge, bringing the total number of confirmed Galactic RCB stars to about 51. After reddening correction, the colours and absolute magnitudes of at least 9 of the stars are similar to those of Magellanic RCB stars. This suggests that these stars are in fact located in the Galactic Bulge, making them the first RCB stars discovered in the Bulge. The localisation of the 5 remaining RCBs is more uncertain: 4 are either located behind the Bulge at an estimated maximum distance of 14 kpc or have an unusual thick circumstellar shell; the other is a DY Per RCB which may be located in the Bulge, even if it is fainter than the known Magellanic DY Per. From the small scale height found using the 9 new Bulge RCBs, $61

Published
2008
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3. Limits on the Macho Content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds

Author

Tisserand, P., Guillou, L. Le, Afonso, C., Albert, J. N., Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Beaulieu, J. P., Charlot, X., Coutures, C., Ferlet, R., Fouqué, P., Glicenstein, J. F., Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., Hamadache, C., de Kat, J., Lasserre, T., Lesquoy, E., Loup, C., Magneville, C., Marquette, J. B., Maurice, E., Maury, A., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Rahal, Y. R., Rich, J., Spiro, M., Vidal-Madjar, A., Vigroux, L., and Zylberajch, S.

Subjects
Astrophysics
Abstract

The EROS-2 project was designed to test the hypothesis that massive compact halo objects (the so-called ``machos'') could be a major component of the dark matter halo of the Milky Way galaxy. To this end, EROS-2 monitored over 6.7 years $33\times10^6$ stars in the Magellanic clouds for microlensing events caused by such objects. In this work, we use only a subsample of $7\times10^6$ bright stars spread over $84 \deg^2$ of the LMC and $9 \deg^2$ of the SMC. The strategy of using only bright stars helps to discriminate against background events due to variable stars and allows a simple determination of the effects of source confusion (blending). The use of a large solid angle makes the survey relatively insensitive to effects that could make the optical depth strongly direction dependent. Using this sample of bright stars, only one candidate event was found, whereas $\sim39$ events would have been expected if the Halo were entirely populated by objects of mass $M\sim0.4M_{\odot}$. Combined with the results of EROS-1, this implies that the optical depth toward the Large Magellanic Cloud (\object{LMC}) due to such lenses is $\tau<0.36\times10^{-7}$ (95%CL), corresponding to a fraction of the halo mass of less than 8%. This optical depth is considerably less than that measured by the MACHO collaboration in the central region of the LMC. More generally, machos in the mass range $0.6\times10^{-7}M_\odot

Published
2006
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4. Galactic Bulge Microlensing Optical Depth from EROS-2

Author

Hamadache, C., Guillou, L. Le, Tisserand, P., Afonso, C., Albert, J. N., Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Beaulieu, J. P., Charlot, X., Coutures, C., Ferlet, R., Fouqué, P., Glicenstein, J. F., Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., de Kat, J., Lesquoy, E., Loup, C., Magneville, C., Marquette, J. B., Maurice, E., Maury, A., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Rahal, Y. R., Rich, J., Spiro, M., Vidal-Madjar, A., Vigroux, L., and Zylberajch, S.

Subjects
Astrophysics
Abstract

We present a new EROS-2 measurement of the microlensing optical depth toward the Galactic Bulge. Light curves of $5.6\times 10^{6}$ clump-giant stars distributed over $66 \deg^2$ of the Bulge were monitored during seven Bulge seasons. 120 events were found with apparent amplifications greater than 1.6 and Einstein radius crossing times in the range $5 {\rm d}

Published
2006
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5. Type Ia supernova rate at $z \sim 0.1$

Author

Hardin, D., Afonso, C., Alard, C., Albert, J. N., Amadon, A., Andersen, J., Ansari, R., Aubourg, É., Bareyre, P., Bauer, F., Beaulieu, J. P., Blanc, G., Bouquet, A., Char, S., Charlot, X., Couchot, F., Coutures, C., Derue, F., Ferlet, R., Glicenstein, J. F., Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., Hamilton, J. C., de Kat, J., Kim, A., Lasserre, T., Lesquoy, É., Loup, C., Magneville, C., Mansoux, B., Marquette, J. B., Maurice, É., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prévot, L., Regnault, N., Rich, J., Spiro, M., Vidal-Madjar, A., Vigroux, L., Zylberajch, S., and collaboration, The EROS

Subjects
Astrophysics
Abstract

We present the EROS nearby supernova ($z \sim 0.02 - 0.2$) search and the analysis of the first year of data (1997). A total of 80 square degrees were surveyed. Eight supernov{\ae} were detected, four of which were spectroscopically identified as type Ia supernov{\ae}. The search efficiency was determined with a Monte-Carlo simulation taking into account the efficiencies for both supernova detection and host galaxy identification. Assuming that for a given galaxy the supernova rate is proportional to the galactic luminosity, we compute a type Ia supernova explosion rate of: ${\cal R} = 0.44 {}_{-0.21}^{+0.35} {}_{-0.07}^{+0.13} h^2: / 10^{10} \lbsun / 100 {\rm yrs}$ at an average redshift of $\sim 0.1$ where the errors are respectively statistical and systematic (type misidentification included)., Comment: 8 pages, 6 figures, accepted in A&A

Published
2000

6. EROS Variable Stars : Discovery of Beat Cepheids in the Small Magellanic Cloud and the effect of metallicity on pulsation

Author

Beaulieu, J. P., Krockenberger, M., Sasselov, D. D., Renault, C., Ferlet, R., Vidal-Madjar, A., Maurice, E., Prévot, L., Aubourg, E., Bareyre, P., Brehin, S., Coutures, C., Delabrouille, N., de Kat, J., Gros, M., Laurent, B., Lachièze-Rey, M., Lesquoy, E., Magneville, C., Milsztajn, A., Moscoso, L., Queinnec, F., Rich, J., Spiro, M., Vigroux, L., Zylberajch, S., Ansari, R., Cavalier, F., Moniez, M., and Gry., C.

Subjects
Astrophysics
Abstract

We report the discovery of eleven beat Cepheids in the Small Magellanic Cloud, using data obtained by the EROS microlensing survey. Four stars are beating in the fundamental and first overtone mode (F/1OT), seven are beating in the first and second overtone (1OT/2OT). The SMC F/1OT ratio is systematically higher than the LMC F/1OT, while the 1OT/2OT period ratio in the SMC Cepheids is the same as the LMC one., Comment: 4 pages, Latex file with 4 .ps figures. accepted for publication in A A Letters

Published
1997

7. The effect of metallicity on the Cepheid distance scale and its implications for the Hubble constant ($H_0$) determination

Author

Beaulieu, J. P., Sasselov, D. D., Renault, C., Grison, P., Ferlet, R., Vidal-Madjar, A., Maurice, E., Prévot, L., Aubourg, E., Bareyre, P., Brehin, S., Coutures, C., Delabrouille, N., de Kat, J., Gros, M., Laurent, B., Lachièze-Rey, M., Lesquoy, E., Magneville, C., Milsztajn, A., Moscoso, L., Queinnec, F., Rich, J., Spiro, M., Vigroux, L., Zylberajch, S., Ansari, R., Cavalier, F., Moniez, M., Gry, C., Guibert, J., Moreau, O., and Tajhmady, F.

Subjects
Astrophysics
Abstract

Recent HST determinations of the expansion's rate of the Universe (the Hubble constant, H_0) assumed that the Cepheid Period-Luminosity relation at V and I are independent of metallicity (Freedman, et al., 1996, Saha et al., 1996, Tanvir et al., 1995). The three groups obtain different vales for H_0. We note that most of this discrepancy stems from the asumption (by both groups) that the Period-Luminosity relation is independent of metallicity. We come to this conclusion as a result of our study of the Period-Luminosity relation of 481 Cepheids with 3 millions two colour measurements in the Large Magellanic Cloud and the Small Magellanic Cloud obtained as a by-product of the EROS microlensing survey. We find that the derived interstellar absorption corrections are particularly sensitive to the metallicity and when our result is applied to recent estimates based on HST Cepheids observations it makes the low-H_0 values higher and the high-H_0 value lower, bringing those discrepant estimates into agrement around $H_0 \approx 70 km/s Mpc^{-1}$., Comment: 4 pages, Latex, with 2 .ps accepted for publication astronomy and astrophysics Letters

Published
1996

8. Metallicity Effects on the Cepheid Extragalactic Distance Scale from EROS photometry in LMC and SMC

Author

Sasselov, D. D., Beaulieu, J. P., Renault, C., Grison, P., Ferlet, R., Vidal-Madjar, A., Maurice, E., Prévot, L., Aubourg, E., Bareyre, P., Brehin, S., Coutures, C., Delabrouille, N., de Kat, J., Gros, M., Laurent, B., Lachièze-Rey, M., Lesquoy, E., Magneville, C., Milsztajn, A., Moscoso, L., Queinnec, F., Rich, J., Spiro, M., Vigroux, L., Zylberajch, S., Ansari, R., Cavalier, F., Moniez, M., Gry, C., Guibert, J., Moreau, O., and Tajhmady, F.

Subjects
Astrophysics
Abstract

This is an investigation of the period-luminosity relation of classical Cepheids in samples of different metallicity. It is based on 481 Cepheids in the Large and Small Magellanic Clouds from the blue and red filter CCD observations (most similar to V_J & R_J) of the French EROS microlensing project. The data-set is complete and provides an excellent basis for a differential analysis between LMC and SMC. In comparison to previous studies of effects on the PL-relation, the EROS data-set offers extremely well-sampled light curves and well-filled instability strips. This allows reliable separation of Cepheids pulsating in the fundamental and the first overtone mode and derivation of differential reddening. Our main result concerns the determination of distances to galaxies which are inferred by using the LMC as a base and using two color photometry to establish the amount of reddening. We find a zero-point offset between SMC and LMC which amounts to a difference between inferred and true distance modulus of 0.14 \pm 0.06 mag in the VI_c system. The offset is exactly the same in both sets of PL-relations - of the fundamental and of the first overtone mode Cepheids. No effect is seen on the slopes of the PL-relations, although the fundamental and the first overtone mode Cepheids have different PL slopes. We attribute the color and the zero-point offset to the difference in metallicity between the SMC and LMC Cepheids. A metallicity effect of that small magnitude still has important consequencies for the inferred Cepheid distances and the determination of H_0. When applied to recent estimates based on HST Cepheid observations, our metallicity dependence makes the low-H_0 values (Sandage et al. 1994) higher and the high-H_0 values (Freedman et al. 1994b) lower, thus bringing those, Comment: 14 pages, Latex, with 8 .ps accepted for publication in astronomy and astrophysics

Published
1996

9. Observational Limits on Machos in the Galactic Halo

Author

EROS collaboration, Renault, C., Afonso, C., Aubourg, E., Bareyre, P., Bauer, F., Brehin, S., Coutures, C., Gaucherel, C., Glicenstein, J. F., Goldman, B., Gros, M., Hardin, D., de Kat, J., Lachieze-Rey, M., Laurent, B., Lesquoy, E., Magneville, C., Milsztajn, A., Moscoso, L., Palanque-Delabrouille, N., Queinnec, F., Rich, J., Spiro, M., Vigroux, L., Zylberajch, S., Ansari, R., Cavalier, F., Couchot, F., Mansoux, B., Moniez, M., Perdereau, O., Beaulieu, J. -Ph., Ferlet, R., Grison, Ph., Vidal-Madjar, A., Guibert, J., Moreau, O., Maurice, E., Prevot, L., Gry, C., Char, S., and Fernandez, J.

Subjects
Astrophysics
Abstract

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., Comment: 4 pages, 3 Postscript figures, to be published in Astronomy & Astrophysics

Published
1996

10. Combined analysis of the binary lens caustic-crossing event MACHO 98-SMC-1

Author

Afonso, C, Alard, C, Albert, J N, Andersen, J, Ansari, R, Aubourg, E, Bareyre, P, Bauer, F, Beaulieu, J P, Bouquet, A, Char, S, Charlot, X, Couchot, F, Coutures, C, Derue, F, Ferlet, R, Glicenstein, J F, Goldman, B, Gould, A, Graff, D, Gros, M, Haissinski, J, Hamilton, J C, Hardin, D, de Kat, J, Kim, A, Lasserre, T, Lesquoy, E, Loup, C, Magneville, C, Marquette, J B, Maurice, E, Milsztajn, A, Moniez, M, Palanque-Delabrouille, N, Perdereau, O, Prevot, L, Regnault, N, Rich, J, Spiro, M, Vidal-Madjar, A, Vigroux, L, Zylberajch, S, Alcock, C, Allsman, R A, Alves, D, Axelrod, TS, Becker, A C, Peterson, B A, Szymanski, M, Dominik, Martin, Naber, R M, Sackett, Penny D, Kapteyn Astronomical Institute, and Astronomy

Subjects
Lens (geometry), Physics, Proper motion, MICROLENSING EVENT, 010308 nuclear & particles physics, Astrophysics (astro-ph), gravitational lensing, FOS: Physical sciences, Binary number, Astronomy and Astrophysics, Astrophysics, Mass ratio, Gravitational microlensing, 01 natural sciences, dark matter, Einstein radius, Space and Planetary Science, Limb darkening, 0103 physical sciences, Magellanic Clouds, astrometry, PHOTOMETRY, Small Magellanic Cloud, 010303 astronomy & astrophysics
Abstract

We fit the data for the binary-lens microlensing event MACHO 98-SMC-1 from 5 different microlensing collaborations and find two distinct solutions characterized by binary separation d and mass ratio q: (d,q)=(0.54,0.50) and (d,q)=(3.65,0.36), where d is in units of the Einstein radius. However, the relative proper motion of the lens is very similar in the two solutions, 1.30 km/s/kpc and 1.48 km/s/kpc, thus confirming that the lens is in the Small Magellanic Cloud. The close binary can be either rotating or approximately static but the wide binary must be rotating at close its maximum allowed rate to be consistent with all the data. We measure limb-darkening coefficients for five bands ranging from I to V. As expected, these progressively decrease with rising wavelength. This is the first measurement of limb darkening for a metal-poor A star., 29 pages + 9 figures + 2 tables, submitted to ApJ

Published
2000

11. Removing the Microlensing Blending-Parallax Degeneracy Using Source Variability

Author

Assef, R.J., Gould, A., Afonso, C., Albert, J.N., Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Beaulieu, J.P., Charlot, X., Coutures, C., Ferlet, R., Fouqué, P., Glicenstein, J.F., Goldman, B., Graff, D., Gros, M., Haissinski, J., Hamadache, C., De Kat, J., Le Guillou, L., Lesquoy, E., Loup, C., Magneville, C., Marquette, J.B., Maurice, E., Maury, A., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Rahal, Y.R., Rich, J., Spiro, M., Tisserand, P., Vidal-Madjar, A., Vigroux, L., Zylberajch, S., Bennett, D.P., C. Becker, A., Griest, K., Vandehei, T., Welch, D.L., Udalski, A., Szymanski, M.K., Kubiak, M., Pietrzynski, G., Soszynski, I., Szewczyk, O., Wyrzykowski, L., Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), and EROS

Subjects
Event (relativity), FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Lambda, Gravitational microlensing, 01 natural sciences, law.invention, [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], law, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010308 nuclear & particles physics, Astrophysics (astro-ph), Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Lens (optics), Space and Planetary Science, Halo, Astrophysics::Earth and Planetary Astrophysics, Variable star, Degeneracy (mathematics), Parallax
Abstract

Microlensing event MACHO 97-SMC-1 is one of the rare microlensing events for which the source is a variable star, simply because most variable stars are systematically eliminated from microlensing studies. Using observational data for this event, we show that the intrinsic variability of a microlensed star is a powerful tool to constrain the nature of the lens by breaking the degeneracy between the microlens parallax and the blended light. We also present a statistical test for discriminating the location of the lens based on the \chi^2 contours of the vector \Lambda, the inverse of the projected velocity. We find that while SMC self lensing is somewhat favored over halo lensing, neither location can be ruled out with good confidence., Comment: 15 text pages + 2 tables + 7 figures. Published in the Astrophysical Journal

Published
2006

12. Bulge Microlensing Optical Depth from EROS 2 observations

Author

Afonso, C., Albert, J N., Alard, C., Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Bauer, F., Beaulieu, J-P., Blanc, G., Bouquet, A., Char, S., Charlot, X., Couchot, F., Coutures, C., Derue, F., Ferlet, R., Fouque, P., Glicenstein, J-F., Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., Hamache, C., Hamilton, J-C., Hardin, Doug, de Kat, J., Kim, A., Lasserre, T., Le Guillou, L., Lesquoy, E., Loup, C., Magneville, C., Mansoux, B., Marquette, J-B., Maurice, E., Maury, A., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prevot, L., Regnault, N., Rich, J., Spiro, M., Tisserand, P., Vidal-Madjar, A., Vogroux, L., Zylberajch, S., Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée (DAPNIA), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Departement d'Astrophysique Stellaire et Galactique (DASGAL), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut d'Astrophysique de Paris (IAP), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), EROS, Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), and Departement de recherche SPAtiale (DESPA)

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

We present a measurement of the microlensing optical depth toward the Galactic bulge based on the analysis of 15 contiguous1 square degrees fields centered on (l=2.5 deg, b=-4.0 deg) and containing 1.42 million clump-giant stars (belonging to the extended clump area) monitored during almost three bulge seasons by EROS (Experience de Recherche d'Objets Sombres). We find a microlensing optical depth towards the bulge tau_bulge=0.94 +/- 0.29 10^-6 averaged over all fields, based on 16 microlensing events with clump giants as sources. This value is substantially below several other determinations by the MACHO and OGLE groups and is more in agreement with what is expected from axisymmetric and non-axisymmetric bulge models., 18 pages, 15 images, accepted for publication in A&A

Published
2003
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13. Discovery and photometry of the binary-lensing caustic-crossing event EROS-BLG-2000-5

Author

Jung, J.M, Albert, J.N., Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Blanc, G., Charlot, X., Couchot, F., Coutures, C., Ferlet, R., Fields, D., Fouque, P., Glicenstein, J.F., Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., Hamadache, C., De Kat, J., LeGuillou, L., Lesquoy, E., Loup, C., Magneville, C., Marquette, J.B., Maurice, E., Maury, A., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prevot, L., Rahal, Y., Rich, J., Spiro, M., Tisserand, P., Vidal-Madjar, A., Vigroux, L., Zylberajch, S., Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), and EROS

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics
Abstract

The EROS collaboration has developed a real time alert system, which was operational in 1999 and 2000. A very long binary-lensing caustic crossing event, EROS-BLG-2000-5, was found in the 2000 season and monitored by EROS. EROS photometric data for this event are presented. The data are well fitted by the model of An et al. 2002 based on a completely different dataset. However, parameters of the model such as the mass ratio or the binary rotation rate are not very well constrained by EROS data., Comment: 10 pages, 6 figures

Published
2003
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14. EROS 2 proper motion survey : Constraints on the halo white dwarfs

Author

Goldman, B., Afonso, C., Alard, C., N Albert, J., Amadon, A., Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Bauer, F., P Beaulieu, J., Blanc, G., Bouquet, A., Char, S., Charlot, X., Couchot, F., Coutures, C., Derue, F., Ferlet, R., Fouque, P., F Glicenstein, J., Gould, A., Graff, D., Gros, M., Haissinski, J., Hamadache, C., C Hamilton, J., Hardin, D., Kat, J., Kim, A., Lasserre, T., Le Guillou, L., Lesquoy, E., Loup, C., Magneville, C., Mansoux, B., Jean-Baptiste Marquette, Maurice, E., Maury, A., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prevot, L., Regnault, N., Rich, J., Spiro, M., Tisserand, P., Vidal-Madjar, A., Vigroux, L., Zylberajch, S., Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Pierre et Marie Curie - Paris 6 (UPMC), EROS, Departement de recherche SPAtiale (DESPA), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Fouqué, Pascal, Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), and Kerec, Hélène

Subjects
Physics, Proper motion, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010308 nuclear & particles physics, Astrophysics (astro-ph), Dark matter, FOS: Physical sciences, White dwarf, Astronomy and Astrophysics, Astrophysics, [SDU.ASTR] Sciences of the Universe [physics]/Astrophysics [astro-ph], 01 natural sciences, Hydrogen atmosphere, [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Space and Planetary Science, [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], 0103 physical sciences, Halo, 10. No inequality, Effective volume, 010303 astronomy & astrophysics
Abstract

We are conducting a 377-square-degree proper motion survey in the ~V and I bands in order to determine the cool white dwarf contribution to the Galactic dark matter. Using the 250 square degrees for which we possess three epochs, and applying selection criteria designed to isolate halo-type objects, we find no candidates in a 5500 pc^3 effective volume for old, fast M_V=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 M_V=17 and 1, Comment: 5 pages, 2 postscript figures, accepted for publication in A&A. Requires aa,epsfig,slashbox,natbib

Published
2002

15. Photometric constraints on microlens spectroscopy of EROS-BLG-2000-5

Author

Alfonso, C., Albert, J. N., Andersen, J., Ansari, R., Aubourg, É, Bareyre, P., Bauer, F., Blanc, G., Bouquet, A., Char, S., Charlot, X., Couchot, F., Coutures, C., Derue, F., Ferlet, R., Fouqué, P., Glicenstein, J. F., Goldman, B., Gould, A., Graff, D., Gros, M., Haïssinski, J., Hamilton, J. C., Hardin, D., Kat, J., Kim, A., Lasserre, T., Leguillou, L., Lesquoy, É, Loup, C., Magneville, C., Mansoux, B., Marquette, J. B., Maurice, É, Milsztajn, A., Moniez, M., Nathalie Palanque-Delabrouille, Perdereau, O., Prévot, L., Regnault, N., Rich, J., Spiro, M., Vidal-Madjar, A., Vigroux, L., Zylberajch, S., Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée (DAPNIA), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Institut d'Astrophysique de Paris (IAP), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Departement de recherche SPAtiale (DESPA), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), EROS, Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), and Fouqué, Pascal

Subjects
Physics, Microlens, Photosphere, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010308 nuclear & particles physics, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Radius, Atmospheric model, [SDU.ASTR] Sciences of the Universe [physics]/Astrophysics [astro-ph], 01 natural sciences, Spectral line, [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], 13. Climate action, Space and Planetary Science, [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], 0103 physical sciences, Absorption (electromagnetic radiation), Spectroscopy, 010303 astronomy & astrophysics, Chromosphere
Abstract

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 4 % of the limb of the K3-giant source is strongly in emission in Halpha, in contradiction to available models of the photosphere. This conflict could be resolved if the integrated Halpha emission from the chromosphere were equal to 8 % of the integrated Halpha absorption 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) = 0.37 redder than the source as a whole, so that it has the color of a M0 giant., Comment: 7 figures, 1 table

Published
2001
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16. Not enough stellar Mass Machos in the Galactic Halo

Author

Lasserre, T., Afonso, C., J-N, Albert, Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Bauer, F., J-P, Beaulieu, Blanc, G., Bouquet, A., Char, S., Charlot, X., Couchot, F., Coutures, C., Derue, F., Ferlet, R., J-F, Glicenstein, Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., J-C, Hamilton, Hardin, D., Kat, J., Kim, A., Lesquoy, E., Loup, C., Magneville, C., Mansoux, B., Jean-Baptiste Marquette, Maurice, E., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prevot, L., Regnault, N., Renault, C., Rich, J., Spiro, M., Vidal-Madjar, A., Vigrou, L., Zylberajch, S., Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Physique Corpusculaire et Cosmologie - Collège de France (PCC), and Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics
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., 4 pages, 2 figures, Accepted by A&A Letters Feb 23, 2000 (minor modifications in section 6)

Published
2000

17. EROS 2 proper motion survey for halo white dwarfs

Author

Goldman, B., Afonso, C., Alard, C., J-N, Albert, Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Bauer, F., Jp. Beaulieu, Bouquet, A., Char, S., Couchot, F., Coutures, C., Derue, F., Ferlet, R., J-F, Glicenstein, Gould, A., Graff, D., Gros, M., Haissinski, J., J-C, Hamilton, Hardin, D., Kat, J., Kim, A., Lasserre, T., Lesquoy, E., Loup, C., Magneville, C., Mansoux, B., Jean-Baptiste Marquette, Maurice, E., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prevot, L., Rich, J., Spiro, M., Vidal-Madjar, A., Vigroux, L., Zylberajch, S., Lantz, Simone, Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), and EROS

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astrophysics::Galaxy Astrophysics
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.)., 5 pages, TeX, 3 Postscript figures, moriond2000.sty. To appear in the Proceedings of the XXth Moriond Astrophysics Meeting "Cosmological Physics with Gravitational Lensing", eds. J.-P. Kneib, Y. Mellier, M. Moniez and J. Tran Thanh Van

Published
2000

18. Observation of Microlensing towards the Galactic Spiral Arms. EROS II 3 year survey

Author

Derue, F., Afonso, C., Alard, C., J-N, Albert, Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Bauer, F., J-P, Beaulieu, Bouquet, A., Char, S., Charlot, X., François Couchot, Coutures, C., Ferlet, R., J-F, Glicenstein, Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., J-C, Hamilton, Hardin, D., Kat, J., Kim, A., Lasserre, L., Lesquoy, E., Loup, C., Magneville, C., Mansoux, B., J-B, Marquette, Maurice, E., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prevot, L., Regnault, N., Rich, J., Spiro, M., Vidal-Madjar, A., Vigrou, L., Zylberajch, S., Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), and EROS

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, High Energy Physics::Experiment, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astrophysics::Galaxy Astrophysics
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., Comment: 4 pages, 3 figures, submitted for publication in A&A Letters

Published
2000
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19. EROS 2 proper motion survey: a field brown dwarf and an L dwarf companion to LHS 102

Author

Goldman, B., Delfosse, X., Forveille, T., Afonso, C., Alard, C., Albert, J. N., Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Bauer, F., Beaulieu, J. P., Borsenberger, J., Bouquet, A., Char, S., Charlot, X., Couchot, F., Coutures, C., Derue, F., Ferlet, R., Fouqué, P., Glicenstein, J. F., Gould, A., Graff, D., Gros, M., Haissinski, J., Hamilton, J. C., Hardin, D., Kat, J., Kim, A., Lasserre, T., Lesquoy, E., Loup, C., Magneville, C., Mansoux, B., Jean-Baptiste Marquette, Martin, E. L., Maurice, E., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prévot, L., Regnault, N., Rich, J., Spiro, M., Vidal-Madjar, A., Vigroux, L., Zylberajch, S., The Eros Collaboration, Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée (DAPNIA), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Observatoire de Paris - Site de Meudon (OBSPM), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), EROS, Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Pierre et Marie Curie - Paris 6 (UPMC), and Lantz, Simone

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics
Abstract

We report the discovery of two L dwarfs (the new spectral class defined for dwarfs cooler than the M type) in a two-epoch CCD proper motion survey of 413 square degrees, complemented by infrared photometry from DENIS. One of them has a strong lithium line and is therefore a brown dwarf. The other is a common proper motion companion to the mid-M dwarf LHS 102 (GJ 1001), which has a well determined trigonometric parallax. LHS 102B is thus the coolest L dwarf of known distance and luminosity. Its infrared absolute photometry are very well reproduced by the Allard et al DUSTY models., Comment: 5 pages, LaTeX, 6 postscript figures, style correction, two spectra of the discovered objects added, coordinates of the LHS102 pair corrected

Published
1999

20. Microlensing towards the Small Magellanic Cloud --- EROS 2 two-year analysis

Author

Afonso, C., Alard, C., J-N, Albert, Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Bauer, F., Jp. Beaulieu, Bouquet, A., Char, S., Couchot, F., Coutures, C., Derue, F., Ferlet, R., J-F, Glicenstein, Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., J-C, Hamilton, Hardin, D., Kat, J., Kim, A., Lasserre, T., Lesquoy, E., Loup, C., Magneville, C., Mansoux, B., Jean-Baptiste Marquette, Maurice, E., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prevot, L., Rich, J., Spiro, M., Vidal-Madjar, A., Vigroux, L., Zylberajch, S., Lantz, Simone, Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), and EROS

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics
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., Comment: 4 pages, 2 figures, revised version accepted for publication in A&A Letters

Published
1998

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

Author

Bauer, F., Afonso, C., Albert, J. N., Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Jp. Beaulieu, Bouquet, A., Char, S., Charlot, X., François Couchot, Coutures, C., Derue, F., Ferlet, R., Kim, A., Gaucherel, C., Glicenstein, J. F., Goldman, B., Gould, A., Graff, D. S., Gros, M., Haissinski, J., Hamilton, J. C., Hardin, D., Lasserre, T., Lesquoy, E., Loup, C., Kat, J., Magneville, C., Mansoux, B., Jb. Marquette, Maurice, E., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prevot, L., Renault, C., Regnault, N., Rich, J., Spiro, M., Vidal-Madjar, A., Vigroux, L., Zylberajch, S., Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de l'Accélérateur Linéaire (LAL), Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), EROS, and Lantz, Simone

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics
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), Comment: 4 pages, 4 ps figures. Submitted to Astronomy & Astrophysics. Halo interpretation excluded at the 93% CL (instead of 89%)

Published
1998
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22. Microlensing towards the Small Magellanic Cloud - EROS 2 first year survey

Author

Palanque-Delabrouille, N., Afonso, C., J-N, Albert, Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Bauer, F., J-P, Beaulieu, Bouquet, A., Char, S., Charlot, X., Couchot, F., Coutures, C., Derue, F., Ferlet, R., J-F, Glicenstein, Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., J-C, Hamilton, Hardin, D., Kat, J., Lesquoy, E., Loup, C., Magneville, C., Mansoux, B., Jean-Baptiste Marquette, Maurice, E., Milsztajn, A., Moniez, M., Perdereau, O., Prevot, L., Renault, C., Rich, J., Spiro, M., Vidal-Madjar, A., Vigrou, L., Zylberajch, S., Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), and EROS

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics
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., Comment: 10 pages, 11 figures (9 included .eps and 2 separate .gif). Numerical value for constrain on mass and distance of deflector from parallax analysis less severe than previously. Minor changes otherwise. Accepted for publication in Astronomy & Astrophysics

Published
1998

23. The effect of metallicity on the Cepheid distance scale and its implications for the Hubble constant ($H_0$) determination

Author

Beaulieu, J. P., Sasselov, D. D., Renault, C., Grison, P., Ferlet, R., Vidal-Madjar, A., Maurice, E., Prévot, L., Aubourg, E., Bareyre, P., Brehin, S., Coutures, C., Delabrouille, N., de Kat, J., Gros, M., Laurent, B., Lachièze-Rey, M., Lesquoy, E., Magneville, C., Milsztajn, A., Moscoso, L., Queinnec, F., Rich, J., Spiro, M., Vigroux, L., Zylberajch, S., Ansari, R., Cavalier, F., Moniez, M., Gry, C., Guibert, J., Moreau, O., Tajhmady, F., Institut d'Astrophysique de Paris (IAP), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée (DAPNIA), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Laboratoire d'Astrophysique de Marseille (LAM), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Centre National d'Études Spatiales [Toulouse] (CNES), Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Centre d'Analyse des Images de l'INSU (CENTRE D'ANALYSE DES IMAGES DE L'INSU), Centre National de la Recherche Scientifique (CNRS), EROS, Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), and Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)

Subjects
galaxies : distances, [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Stars : fundamental parameters, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics, Stars : cepheids
Abstract

Recent HST determinations of the expansion's rate of the Universe (the Hubble constant, H_0) assumed that the Cepheid Period-Luminosity relation at V and I are independent of metallicity (Freedman, et al., 1996, Saha et al., 1996, Tanvir et al., 1995). The three groups obtain different vales for H_0. We note that most of this discrepancy stems from the asumption (by both groups) that the Period-Luminosity relation is independent of metallicity. We come to this conclusion as a result of our study of the Period-Luminosity relation of 481 Cepheids with 3 millions two colour measurements in the Large Magellanic Cloud and the Small Magellanic Cloud obtained as a by-product of the EROS microlensing survey. We find that the derived interstellar absorption corrections are particularly sensitive to the metallicity and when our result is applied to recent estimates based on HST Cepheids observations it makes the low-H_0 values higher and the high-H_0 value lower, bringing those discrepant estimates into agrement around $H_0 \approx 70 km/s Mpc^{-1}$., Comment: 4 pages, Latex, with 2 .ps accepted for publication astronomy and astrophysics Letters

Published
1997

24. AGAPEROS: Searches for microlensing in the LMC with the Pixel Method. I. Data treatment and pixel light curves production

Author

Melchior, A. -L, Afonso, C., Ansari, R., Aubourg, É, Baillon, P., Bareyre, P., Bauer, F., Beaulieu, J. -Ph, Bouquet, A., Brehin, S., Cavalier, F., Char, S., Couchot, F., Coutures, C., Ferlet, R., Fernandez, J., Gaucherel, C., Giraud-Héraud, Y., Glicenstein, J. -F, Goldman, B., Paolo Gondolo, Gros, M., Guibert, J., Hardin, D., Kaplan, J., Kat, J., Lachièze-Rey, M., Laurent, B., Lesquoy, É, Magneville, Ch, Mansoux, B., Marquette, J. -B, Maurice, E., Milsztajn, A., Moniez, M., Moreau, O., Moscoso, L., Palanque-Delabrouille, N., Perdereau, O., Prévôt, L., Renault, C., Queinnec, F., Rich, J., Spiro, M., Vidal-Madjar, A., Vigroux, L., and Zylberajch, S.

Subjects
Physics, Pixel, 010308 nuclear & particles physics, Bar (music), Astrophysics (astro-ph), General Physics and Astronomy, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Gravitational microlensing, Light curve, 01 natural sciences, Luminosity, Data set, Stars, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Variable star, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

Recent surveys monitoring millions of light curves of resolved stars in the LMC have discovered several microlensing events. Unresolved stars could however significantly contribute to the microlensing rate towards the LMC. Monitoring pixels, as opposed to individual stars, should be able to detect stellar variability as a variation of the pixel flux. We present a first application of this new type of analysis (Pixel Method) to the LMC Bar. We describe the complete procedure applied to the EROS 91-92 data (one tenth of the existing CCD data set) in order to monitor pixel fluxes. First, geometric and photometric alignments are applied to each images. Averaging the images of each night reduces significantly the noise level. Second, one light curve for each of the 2.1 10^6 pixels is built and pixels are lumped into 3.6"x3.6" super-pixels, one for each elementary pixel. An empirical correction is then applied to account for seeing variations. We find that the final super-pixel light curves fluctuate at a level of 1.8% of the flux in blue and 1.3% in red. We show that this noise level corresponds to about twice the expected photon noise and confirms previous assumptions used for the estimation of the contribution of unresolved stars. We also demonstrate our ability to correct very efficiently for seeing variations affecting each pixel flux. The technical results emphasised here show the efficacy of the Pixel Method and allow us to study luminosity variations due to possible microlensing events and variable stars in two companion papers., Comment: 15 pages, 26 figures -- accepted for publication in Astronomy and Astrophysics Supplement Series -- Changed contents + Corrected typos

Published
1997
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25. Eros Variable Stars: Discovery of Beat Cepheids in the Small Magellanic Cloud and the effect of metallicity on pulsation

Author

Beaulieu, J P., Krockenberger, M., Sasselov, D D., Renault, C., Ferlet, R., Vidal-Madjar, A., Maurice, E., Prvt, L., Aubourg, E., Bareyre, P., Brehin, S., Coutures, C., Delabrouille, N., De Kat, J., Gros, M., Laurent, B., Lachize-Rey, M., Lesquoy, E., Magneville, C., Milsztajn, A., Moscoso, L., Queinnec, F., Rich, J., Spiro, M., Vigroux, L., Zylberajch, S., Ansari, R., Cavalier, F., Moniez, M., Gry, C., Lantz, Simone, Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de l'Accélérateur Linéaire (LAL), and Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11)

Subjects
[SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Information need, Bibliographic database, Astrophysics (astro-ph), FOS: Physical sciences, Open access, Information market, Astrophysics, [SDU.ASTR] Sciences of the Universe [physics]/Astrophysics [astro-ph], Scientific research, Electronic document, [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Scientific technical information, Technological watch, [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Publication, Firm cooperation
Abstract

We report the discovery of eleven beat Cepheids in the Small Magellanic Cloud, using data obtained by the EROS microlensing survey. Four stars are beating in the fundamental and first overtone mode (F/1OT), seven are beating in the first and second overtone (1OT/2OT). The SMC F/1OT ratio is systematically higher than the LMC F/1OT, while the 1OT/2OT period ratio in the SMC Cepheids is the same as the LMC one., 4 pages, Latex file with 4 .ps figures. accepted for publication in A A Letters

Published
1997

26. Metallicity Effects on the Cepheid Extragalactic Distance Scale from EROS photometry in LMC and SMC

Author

Sasselov, D.D., Beaulieu, J.P., Renault, C., Grison, P., Ferlet, R., Vidal-Madjar, A., Maurice, E., Prévot, L., Aubourg, E., Bareyre, P., Brehin, S., Coutures, C., Delabrouille, N., De Kat, J., Gros, M., Laurent, B., Lachièze-Rey, M., Lesquoy, E., Magneville, C., Milsztajn, A., Moscoso, L., Queinnec, F., Rich, J., Spiro, M., Vigroux, L., Zylberajch, S., Ansari, R., Cavalier, F., Moniez, M., Gry, C., Guibert, J., Moreau, O., Tajhmady, F., Institut d'Astrophysique de Paris (IAP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée (DAPNIA), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de l'Accélérateur Linéaire (LAL), Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Centre d'Analyse des Images de l'INSU (CENTRE D'ANALYSE DES IMAGES DE L'INSU), Centre National de la Recherche Scientifique (CNRS), Girod, Dominique, Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Centre National d'Études Spatiales [Toulouse] (CNES), and Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11)

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Astrophysics (astro-ph), FOS: Physical sciences, [SDU.ASTR] Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics
Abstract

This is an investigation of the period-luminosity relation of classical Cepheids in samples of different metallicity. It is based on 481 Cepheids in the Large and Small Magellanic Clouds from the blue and red filter CCD observations (most similar to V_J & R_J) of the French EROS microlensing project. The data-set is complete and provides an excellent basis for a differential analysis between LMC and SMC. In comparison to previous studies of effects on the PL-relation, the EROS data-set offers extremely well-sampled light curves and well-filled instability strips. This allows reliable separation of Cepheids pulsating in the fundamental and the first overtone mode and derivation of differential reddening. Our main result concerns the determination of distances to galaxies which are inferred by using the LMC as a base and using two color photometry to establish the amount of reddening. We find a zero-point offset between SMC and LMC which amounts to a difference between inferred and true distance modulus of 0.14 \pm 0.06 mag in the VI_c system. The offset is exactly the same in both sets of PL-relations - of the fundamental and of the first overtone mode Cepheids. No effect is seen on the slopes of the PL-relations, although the fundamental and the first overtone mode Cepheids have different PL slopes. We attribute the color and the zero-point offset to the difference in metallicity between the SMC and LMC Cepheids. A metallicity effect of that small magnitude still has important consequencies for the inferred Cepheid distances and the determination of H_0. When applied to recent estimates based on HST Cepheid observations, our metallicity dependence makes the low-H_0 values (Sandage et al. 1994) higher and the high-H_0 values (Freedman et al. 1994b) lower, thus bringing those, 14 pages, Latex, with 8 .ps accepted for publication in astronomy and astrophysics

Published
1997

27. Observation of Microlensing towards the Galactic Spiral Arms. EROS II 2 year survey

Author

Derue, F., Afonso, C., Alard, C., J-N, Albert, Andersen, J., Ansari, R., Aubourg, E., Bareyre, P., Bauer, F., J-P, Beaulieu, Bouquet, A., Char, S., François Couchot, Coutures, C., Ferlet, R., J-F, Glicenstein, Goldman, B., Gould, A., Graff, D., Gros, M., Haissinski, J., J-C, Hamilton, Hardin, D., Kat, J., Kim, A., Lasserre, L., Lesquoy, E., Loup, C., Magneville, C., Mansoux, B., J-B, Marquette, Maurice, E., Milsztajn, A., Moniez, M., Palanque-Delabrouille, N., Perdereau, O., Prevot, L., Regnault, N., Rich, J., Spiro, M., Vidal-Madjar, A., Vigrou, L., Zylberajch, S., Charlot, X., Lantz, Simone, Laboratoire de l'Accélérateur Linéaire (LAL), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF (institution))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), and EROS

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

We present the analysis of the light curves of 8.5 million stars observed during two seasons by EROS (Experience de Recherche d'Objets Sombres), in the galactic plane away from the bulge. Three stars have been found that exhibit luminosity variations compatible with gravitational microlensing effects due to unseen objects. The corresponding optical depth, averaged over four directions, is 0.38 (+0.53, -0.15) 10^{-6}. All three candidates have long Einstein radius crossing times ($\sim$ 70 to 100 days). For one of them, the lack of evidence for a parallax or a source size effect enabled us to constrain the lens-source % geometric configuration. Another candidate displays a modulation of the magnification, which is compatible with the lensing of a binary source. The interpretation of the optical depths inferred from these observations is hindered by the imperfect knowledge of the distance to the target stars. Our measurements are compatible with expectations from simple galactic models under reasonable assumptions on the target distances., Comment: 11 pages, 13 figures, accepted by A&A in Aug 99

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